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1
Revelle, Melissa C. "OBSERVATIONS OF STAR FORMING REGION NGC 1333." Thesis, The University of Arizona, 2009. http://hdl.handle.net/10150/192971.
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Rane, Akshaya. "Physical Conditions in a Galactic Star forming region W22." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_theses/158.
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This document describes study of an active star forming region in our galaxy (the Milky Way) known as W22. Physical conditions in these regions can help us in understanding star formation processes in the universe and hence the structure and evolution of the universe. Zeeman effect measurements in 18 cm OH absorption line were carried out in order to estimate the line of sight magnetic field strength in the molecular cloud associated with this star forming region. Other physical parameters such as hydrogen column density, optical depth, critical magnetic field were also determined from these measurements. The region was mapped at 18 cm and the distribution of molecular gas within this star forming complex was described.
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Verdirame, Chiara. "The core mass function in star-forming region NGC6357." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/6581/.
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The aim of this work was to study the dense cloud structures and to obtain the mass distribution of the dense cores (CMF) within the NGC6357 complex, from observations of the dust continuum at 450 and 850~$\mu$m of a 30 $\times$ 30 arcmin$^2$ region containing the H\textsc{ii} regions, G353.2+0.9 and G353.1+0.6.
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Buenzli, Esther. "Observation, modeling and interpretation of the star forming region S140." Zürich : ETH, Eidgenössische Technische Hochschule Zürich, Institute of Astronomy, 2007. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=298.
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Garden, Rognvald Peebles. "An infrared and millimeter-wave spectroscopic study of the DR21 outflow." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/28084.
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In this thesis, new high-angular resolution infrared and millimeter-wave spectroscopic observations of the enigmatic outflow activity associated with the luminous DR21 star-form ing region are presented and discussed. The intent is to use these observations to undertake a detailed investigation of the physical nature of the central driving engine and the related dynamical processes involved in collimating the hypersonic outflow gas. In the infrared, large-scale mapping and high-spectral resolution profile measurements of the vibrational H2 v = l-0 S(l) line are used to investigate the morphology and kinematic structure of the hot, dense gas that is collisionally excited behind fast shocks. The H2 emission delineates a highly-collimated pair of bipolar jets that extend over a projected distance of ~ 5 pc, centred on the DR21 molecular cloud core; this is undoubtedly the most luminous (in H2 line emission) and extended galactic outflow source yet discovered. Furthermore, the H2 line profiles at certain locations within the jets possess high-velocity wings that extend to beyond 100 km s-1 from the DR21 rest velocity. These observations pose interesting dynamical consequencies as at such high velocities H 2 should be entirely dissociated. In an attempt to derive the mass distribution and velocity structure of the molecular gas participating in the outflow, and hence the driving force and associated mechanical luminosity, detailed observations were also undertaken at millimeter-wavelengths in the CO J= 1 -0 and CS J = l-0 , J= 2-l lines. It is found that the DR21 outflow is considerably more massive and energetic than any other outflow source studied to date. Another feature unique to the DR21 region is the discovery of extended high-velocity CS emission that is dynamically associated with the outflow lobes and extends to a distance of ~ 3 pc from the cloud core; this component presumably originates from am bient gas that has been swept up and compressed by the outflow. The high-velocity CS may be overabundant by 2 orders of magnitude, in good agreement with current numerical models of post-shock chemistry. The CS observations further reveal the existence of an extremely massive, slowly rotating disc of high-density neutral gas that surrounds the central outflow source. It is most probable that the large momentum flux in outflow material derives from efficient mass-loss from the surface of this disc, mediated via a centrifugally propelled, magneto-hydrodynamic wind. An additional confinment mechanism is required to collimate the outflow at large distances from the flow origin. If this confinment is primarily pressure driven, then sudden changes in the ambient cloud pressure could induce a succession of oblique shocks within the outflow that may give rise to the periodic clumpy structure that characterizes the H2 emission-line jets. Other consequencies of the pressure-confinment mechanism are discussed and a broad resemblance to extragalactic radio jets is remarked upon.
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Dobson, Amy. "Kinematics and age spreads of the young star-forming region NGC 2264." Thesis, Keele University, 2016. http://eprints.keele.ac.uk/2413/.
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While stars are relatively well understood, the timescales on which they form are still debated. The young cluster NGC 2264 is an ideal region in which to test hypotheses about the timescale of star and cluster formation. Co-eval stars at any given e�ective temperature are expected to have similar luminosities and radii, but previous research on clusters, including NGC 2264, has found that this may not be the case. In this thesis, �bre spectroscopy from the FLAMES spectrograph is used to �nd radial and projected equatorial velocities for many low-mass pre-main sequence stars in NGC 2264. Projected radii are estimated by combining these data with published rotation periods. The projected radius distribution is compared with models incorporating radius and age dispersions. These methods circumvent many uncertainties that arise when using luminosities to infer ages from the Hertzsprung-Russell diagram (HRD). Comparisons of models and data favour a spread of radii that is inconsistent with a coeval population but consistent with the spread of ages seen in the HRD. Modeldependent, but distance-independent, ages of 1 - 2.6 Myrs are found, and agreement with ages determined from the HRD is found for a cluster distance of 770� 46 pc. The cluster velocity dispersion is well resolved, and a connection between spatial and kinematic substructure is established. The substructure is unlikely to be responsible for the observed age dispersion. A catalogue of 547 spectroscopic observations of stars in NGC 2264 is presented, with measurements of radial and projected equatorial velocities.
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Kovács, Gábor. "Infrared variability studies of low-mass stars in the field and in the Carina Nebula star forming region." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709097.
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Czanik, Robert Johann. "An optical study of the high mass star forming region RCW 34 / Robert Johann Czanik." Thesis, North-West University, 2013. http://hdl.handle.net/10394/9102.
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This study consisted of an optical photometric and spectroscopic analysis on a 7′ 7′ field around
the Southern high mass star forming region RCW 34. A previous study on RCW 34 in the NIR discov-
ered many deeply embedded young stellar objects which were suspected to be T Tauri stars and which
justified further investigation. The data used in this study consisted of three sets, the first two are
photometric and spectroscopic data sets which were obtained during the first two weeks of February
2002. A third data set of spectroscopic observations was obtained by the author during the second week
of 2011 of selected candidates using results from the NIR study and from the photometric data sets.
All of the spectroscopy was conducted with the long slit spectrograph on the 1.9-m telescope and the
photometry with DANDICAM on the 1.0-m telescope at the South African Astronomical Observatory
(SAAO) in Sutherland. Objectives accomplished in the course of this study were to understand, ob-
tain, reduce and interpret photometric and long slit spectroscopic CCD images. From the photometric
results 57 stars showed excess blue emission on a colour-colour diagram which could be generated by
circumstellar matter. The spectroscopic study showed 5 stars that showed H emission and 2 with
strong Li absorption lines which confirm the suspicions of the NIR study about T Tauri stars in the
region. All of the stars from the spectroscopic study in 2011 were identified as low-mass K or M type
stars. Using colour-magnitude diagrams it was possible to see that the majority of the stars in the
cluster are low-mass pre-main sequence stars. The stars matching between the optical and NIR filters
were plotted on NIR colour-colour diagrams showing that the 5 stars that had H emission lines also
had NIR colours characteristic to T Tauri stars. Out of the 5 stars that showed H emission, 2 were
found to be classical T Tauris and three were found to be weak line T Tauris.Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013
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Oskinova, L., R. Gruendl, Richard Ignace, Y. H. Chu, W. R. Hamann, and A. Feldmeier. "Hard X-ray Emission from the Massive Star-Forming Region ON 2: Discovery with XMM-Newton." Digital Commons @ East Tennessee State University, 2010. https://dc.etsu.edu/etsu-works/6259.
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We obtained X-ray XMM-Newton observations of the open cluster Berkeley 87 and the massive star-forming region (SFR) ON 2. In addition, archival infrared Spitzer Space Telescope observations were used to study the morphology of ON 2, to uncover young stellar objects, and to investigate their relationship with the X-ray sources. It is likely that the SFR ON 2 and Berkeley 87 are at the same distance, 1.23 kpc, and hence are associated. The XMM-Newton observations detected X-rays from massive stars in Berkeley 87 as well as diffuse emission from the SFR ON 2. The two patches of diffuse X-ray emission are encompassed in the shell-like H II region GAL 75.84+0.40 in the northern part of ON 2 and in the ON 2S region in the southern part of ON 2. The diffuse emission from GAL 75.84+0.40 suffers an absorption column equivalent to AV ≈ 28 mag. Its spectrum can be fitted either with a thermal plasma model at T ≳ 30 MK or by an absorbed power-law model with γ ≈ −2.6. The X-ray luminosity of GAL 75.84+0.40 is LX ≈ 6 × 1031 erg s−1. The diffuse emission from ON 2S is adjacent to the ultra-compact H II (UCH II) region Cygnus 2N, but does not coincide with it or with any other known UCH II region. It has a luminosity of LX ≈ 4 × 1031 erg s−1. The spectrum can be fitted with an absorbed power-law model with γ ≈ −1.4. We adopt the view of Turner & Forbes that the SFR ON 2 is physically associated with the massive star cluster Berkeley 87 hosting the WO-type star WR 142. We discuss different explanations for the apparently diffuse X-ray emission in these SFRs. These include synchrotron radiation, invoked by the co-existence of strongly shocked stellar winds and turbulent magnetic fields in the star-forming complex, cluster wind emission, or an unresolved population of discrete sources.
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Harayama, Yohei. "The IMF of the massive star-forming region NGC 3603 from NIR adaptive optics observations." Diss., [S.l.] : [s.n.], 2007. http://edoc.ub.uni-muenchen.de/archive/00007108.
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Imara, Nia, Charles Lada, John Lewis, John H. Bieging, Shuo Kong, Marco Lombardi, and Joao Alves. "X Marks the Spot: Nexus of Filaments, Cores, and Outflows in a Young Star-forming Region." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624336.
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We present a multiwavelength investigation of a region of a nearby giant molecular cloud that is distinguished by a minimal level of star formation activity. With our new (CO)-C-12(J = 2-1) and (CO)-C-13(J = 2-1) observations of a remote region within the middle of the California molecular cloud, we aim to investigate the relationship between filaments, cores, and a molecular outflow in a relatively pristine environment. An extinction map of the region from Herschel Space Observatory observations reveals the presence of two 2 pc long filaments radiating from a highextinction clump. Using the (CO)-C-13 observations, we show that the filaments have coherent velocity gradients and that their mass-per-unit-lengths may exceed the critical value above which filaments are gravitationally unstable. The region exhibits structure with eight cores, at least one of which is a starless, prestellar core. We identify a low-velocity, low-mass molecular outflow that may be driven by a flat spectrum protostar. The outflow does not appear to be responsible for driving the turbulence in the core with which it is associated, nor does it provide significant support against gravitational collapse.
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Carlhoff, Philipp Christoph [Verfasser], Peter [Akademischer Betreuer] Schilke, and Jürgen [Akademischer Betreuer] Stutzki. "Molecular cloud structure in the star-forming region W43 / Philipp Christoph Carlhoff. Gutachter: Peter Schilke ; Jürgen Stutzki." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1048676994/34.
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Leeks, Sarah Jane. "The long wavelength spectrometer : reduction and interpretation of data on W28 A2, a high-mass star-forming region." Thesis, Queen Mary, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341928.
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Imanishi, Kensuke. "X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi Star-forming Region with Chandra." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149052.
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Langa, Mihloti Christina. "An investigation into the variability of methanol and hydroxyl masers in the star-forming region G12.89+0.49 / Mihloti Christina Langa." Thesis, North-West University, 2006. http://hdl.handle.net/10394/1700.
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Frink, Sabine. "Kinematics of T Tauri stars in nearby star forming regions." [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=961689390.
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Lee, Pawel. "Structure in star forming regions." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/12395/.
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Stars form in clumpy, highly substructured environments. In this thesis I set up N-body simulations of substructured star forming regions and investigate the impact that the substructure has on the survival of the star forming regions. I also present a broad range of methods used in other fields to quantify and identify structure. I discuss their strengths and shortcomings and assess their suitability for use in astronomical contexts. I use the Q and Λ methods to compare the distributions of class I and class II sources in observed star forming regions to learn more about the dynamical evolution of systems and infer whether they are bound or unbound.
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Gledhill, Timothy Michael. "Optical polarimetry of star forming regions." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6757/.
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Contreras, Peña Carlos Eduardo. "Exteme variables in star forming regions." Thesis, University of Hertfordshire, 2015. http://hdl.handle.net/2299/15590.
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The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution. The original classification of eruptive variables divides them in two separate subclasses known as FU Orionis stars (FUors) and EX Lupi stars (EXors). In this classical view FUors are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths. Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables, show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables. However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to farinfrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV. We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data releases of the UKIDSS Galactic Plane Survey. We find 71 stars with _K > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded from the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| < 1◦ yields 816 high amplitude variables, which include known variables of different classes such as high mass X-ray binaries, Novae and eclipsing binaries among others. Remarkably, 65% of the sample are found concentrated towards areas of star formation, similar to the results from GPS. In both surveys, sources in SFRs show spectral energy distributions (SEDs) that support classification as YSOs. This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow-up allows us to confirm the pre-main sequence nature of several GPS and VVV Objects. Most objects in both samples show spectroscopic signatures that can be attributed to YSOs undergoing high states of accretion, such as veiling of photospheric features and CO emission, or show FUor-like spectra. We also find a large fraction of objects with 2.12 μm H2 emission that can be explained as arising from shock-excited emission caused by molecular outflows. Whether these molecular outflows are related to outbursts events cannot be confirmed from our data. Adding the GPS and VVV spectroscopic results, we find that between 6 and 14 objects are new additions to the FUor class from their close resemblance to the near-infrared spectra of FUors, and at least 23 more objects are new additions to the eruptive variable class. For most of these we are unable to classify them into any of the original definitions for this variable class. In any case, we are adding up to 37 new stars to the eruptive variable class which would double the current number of known objects. We note that most objects are found to be deeply embedded optically invisible stars, thus increasing the number of objects belonging to this subclass by a much larger factor. In general, objects in our samples which are found to be likely eruptive variable stars show a mixture of characteristics that can be attributed to both of the optically-defined classes. This agrees well with the recent discoveries in the literature. Finally, we are able to derive a first rough estimate on the incidence of episodic accretion among class I YSOs in the star-forming complex G305. We find that _ 9% of such objects are in a state of high accretion. This number is in agreement with previous theoretical and observational estimates among class I YSOs.
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Kalari, Venu Madhav. "Disc-accretion in star-forming regions." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.695381.
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In this thesis, I present new ultraviolet/optical/infrared photometric and spectroscopic observations of pre-main sequence stars (PMS) that have formed either in metal-poor conditions, or in the vicinity of strong ionising radiation. This includes observations of 235 Classical T Tauri stars in the Lagoon Nebula; 63 Classical T Tauril Herbig Ae stars in the Carina Nebula open cluster Trumpler 14; 24 intermediate mass T Tauri stars in the low-Z Sh 2-284 star-forming region; and one Herbig 8[e] PMS candidate in the metal-poor 30 Doradus region. I measure the accretion rates of these PMS stars using the intensities of the U/Halpha band excess measured through either optical spectra of imaging. Where possible, I use archive infrared photometry in the 1.2-8 micron wavelength range to estimate the PMS disc evolutionary stage. The influence of the surrounding environment on the accretion rate evolution of pre-main sequence stars in these regions is explored using the spatial, and temporal distributions of accretion rate, mass, age and disc stage of PMS stars. In the wide-field photometric data of the Lagoon Nebula, I find that the spatial distributions of PMS stars is a continuum, ranging from dense clustering to relative isolation. Strongly accretion PMS stars are generally clumped together, in close proximity to their natal molecular cloud, whereas weaker, older accretors are relatively space apart. Ionising radiation from early-type stars appears to positively affect accretion rates on scales of 2-3 pc, but no evidence for triggered star formation is found. In addition, the accretion rates measured from Halpha imaging correlate well to those estimated from U-band photometry. In wide-field photometric data of Trumpler 14, I discover a population of PMS candidates nearly 25 Myrs old. I argue that these PMS candidates are a foreground population, approximately 5 Myr old that belong to the Carina Nebula cluster Trumpler 16. Using Halpha spectra of 24 intermediate mass T Tauri stars in Sh 2-284 (Z-0.004), I demonstrate that there is little evidence for a systematic change in accretion rates with metallicity, contrary to previous literature results at Z-0.006-0.002 in the Magellanic Clouds. I suggest that previous studies are likely affected by detection limits and biases. I also present ultraviolet/optical spectra of the Herbig 8[e] PMS candidate VFTS 822 located in the 30 Doradus region of the Large Magellanic Cloud. I discuss the impact of the discovery of VFTS 822 for star formation studies in the Magellanic Clouds, external Galaxies .
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Juárez, Rodríguez Carmen. "Collapse scenarios in magnetized star-forming regions." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/459253.
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Turbulence, magnetic fields and gravity driven flows are important for the formation of new stars. Although magnetic fields have been proven to be important in the formation of stars, only a few works have been done combining magnetic field and kinematic information. Such studies are important to analyze both gravity and gas dynamics and be able to compare them with the magnetic field. In this thesis we will combine dust polarization studies with kinematic analysis towards different star-forming regions. We aim to study the physical properties at core scales (<0.1 pc) from molecular line and dust emission, and study the role of the magnetic field in their dynamic evolution. For this, we will use millimeter and submillimeter observational data taken towards low- and high- mass star-forming regions in different environments and evolutionary states.
The first project is the study of the physical, chemical and magnetic properties of the pre-stellar core FeSt1-457 in the Pipe nebula. We studied the emission of the molecular line N2H+(1-0) which is a good tracer of dense gas and therefore describes well the structure of the core. In addition, we detected more than 15 molecular lines and found a clear chemical spatial differentiation for molecules with nitrogen, oxygen and sulfur. Using the ARTIST radiative transfer code (Brinch & Hogerheijde 2010, Padovani et al., 2011, 2012, Jørgensen et al., 2014), we simulated the emission of the different molecules detected and estimated their abundance. In addition, we estimated the magnetic field properties of the core (using the Chandrasekhar-Fermi approximation) from polarization data previously obtained by Alves et al., (2014). Finally, we found interesting correlations between the polarization properties and the chemistry in the region.
The second project is the study of a high-mass star-forming region called NGC6334V. NGC6334V is in a more advanced evolutionary state and in an environment surrounded by other massive star-forming regions. During the project we studied the magnetic field from the polarized emission of the dust and also the kinematics of the gas from the molecular line emission of the different tracers of dense gas. From the molecular emission of the gas tracing the envelope of the dense core, we see two different velocity structures separated by 2 km/s and converging towards the potential well in the region. In addition, the magnetic field also presents a bimodal pattern following the distribution of the two velocity structures. Finally, we compared the observational results with 3D magnetohydrodynamic simulations of star-forming regions dominated by gravity.
The last project is the study of a lower-mass star-forming region, L1287. From the data obtained with the SMA, the dust continuum structure shows six main dense cores with masses between ~0.4 and 4 solar masses. The dense gas tracer DCN(3-2) shows two velocity structures separated by 2-3 km/s, converging towards the highest-density region, the young stellar object IRAS00338+6312, in a similar scenario to the one observed in the higher-mass case of NGC6334V.
Finally, the studies of the pre-stellar core FeSt1-457 and the massive region NGC6334V, show how the magnetic field has been overcome by gravity and is not enough to avoid the gravitational collapse. In addition, NGC6334V and the lower- mass region L1287 present very similar scenarios with the material converging from large scales (~0.1 pc) to the potential wells of both regions at smaller scales (~0.02 pc) through two dense gas flows separated by 2-3 km/s. In a similar scenario, FeSt1-457 is located just in the region where two dense gas structures separated by 3 km/s appear to converge.La turbulencia, el campo magnético y la gravedad juegan un papel importante en la formación estelar. Aunque se ha mostrado que el campo magnético es importante, sólo se han llevado a cabo un número limitado de trabajos combinando el estudio del campo magnético y la cinemática del gas. Este tipo de trabajos son esenciales para estudiar la gravedad y la dinámica del gas y poder compararlas con el campo magnético a las mismas escalas espaciales. En este trabajo combinamos estudios de polarización a partir de la emisión del polvo, con el análisis de la cinemática del gas en diferentes regiones de formación estelar. El objetivo es estudiar las propiedades físicas a escalas de núcleos densos (<0.1 pc) a partir de la emisión molecular y del polvo, y estudiar el papel del campo magnético en la evolución dinámica de las regiones. Para ello hemos utilizado datos observacionales milimétricos y submilimétricos. Los estudios se han realizado en 3 regiones de formación estelar. El núcleo pre- estelar FeSt 1-457 localizado en un entorno aislado y muy magnetizado en la nebulosa de la Pipa. NGC 6334 V, una región de mayor masa, en un estado evolutivo más avanzado y en un entorno rodeado de otras regiones de formación estelar masiva. Y L1287, una región menos masiva pero con características similares a NGC 6334 V, con presencia de gas de alta velocidad y fuentes centimétricas e infrarrojas. Los estudios del núcleo pre-estelar FeSt 1-457 y la región de formación estelar de alta masa NGC 6334 V, muestran como el campo magnético ha sido superado por la gravedad y no es suficiente para evitar el colapso gravitatorio. Además NGC 6334 V y la región de menor masa L1287 presentan escenarios muy similares, con el material convergiendo desde escalas grandes hacia los pozos de potencial de ambas regiones a escalas más pequeñas a través de flujos de gas denso separados por 2-3 km/s. En un escenario parecido, FeSt 1-457 se encuentra justo en la zona donde parecen converger dos flujos de gas denso separados por 3 km/s.
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Simon, Robert. "Multiline CN observations of star forming regions." [S.l. : s.n.], 1997. http://deposit.ddb.de/cgi-bin/dokserv?idn=955972264.
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Maskoliūnas, Marius. "Investigation of star forming regions in Cepheus." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140203_133341-51153.
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The interstellar matter in the Galaxy is concentrated in a thin layer close to the galactic plane, mostly in spiral arms. Most of the interstellar matter is in a form of atomic and molecular gas and only 1% of its mass is in a form of small (0.01 – 0.1 µm) dust grains which absorb and scatter the light of stars and cause the interstellar extinction. A part of interstellar gas and dust are in a diffuse form and fill the space with density which exponentially decreases with the distance from the galactic plane. However, in the spiral arms gigantic molecular clouds are present which play an outstanding role in the evolution of the Galaxy, since in them star forming processes take place. Molecular and dust clouds, young star clusters and associations and other star forming regions are concentrated in the Milky Way plane.
However, due to gravitational and radiation interactions between the molecular clouds and the young massive stars, some fragments of spiral arms deviate from the galactic plane. One of such deviating branches from the Local (Orion) spiral arm is a huge elongated system of molecular and dust clouds located in the Cepheus constellation which is known as the Cepheus Flare. Most of the objects investigated in this dissertation belong to this branch of the Local spiral arm.
The objects selected for the investigation are star forming regions in the vicinity of the reflection nebula NGC 7023, a group of dark clouds TGU 619, the young open cluster NGC 7129 and the... [to full text]Paukščių tako Galaktikoje didžioji dalis tarpžvaigždinės medžiagos yra susitelkusi į ploną sluoksnį Galaktikos plokštumoje, daugiausiai spiralinėse vijose. Didžiąją dalį tarpžvaigždinės medžiagos sudaro atominės ir molekulinės dujos ir tik maždaug 1% masės yra mažos (0.01 – 0.1 µm) dydžio dulkelės, kurios sugeria ir išsklaido šviesą ir sukelia tarpžvaigždinės ekstinkcijos reiškinį. Spiralinėse vijose esantys molekuliniai debesys yra svarbūs Galaktikos evoliucijos procese, nes juose vyksta aktyvūs žvaigždžių formavimosi procesai. Molekuliniai ir dulkių debesys, jaunų žvaigždžių spiečiai ir asociacijos bei kitos žvaigždžių susidarymo sritys dažniausiai yra Galaktikos plokštumoje. Tačiau dėl gravitacinės ir radiacinės sąveikos tarp jaunų didelės masės žvaigždžių ir molekulinių debesų kai kuriose Paukščių Tako srityse žvaigždėdaros rajonai nukrypsta nuo Galaktikos plokštumos. Viename iš tokių rajonų Cefėjo žvaigždyno kryptimi dalis tarpžvaigždinių debesų ir žvaigždėdaros rajonų yra nukrypę nuo Galaktikos plokštumos link šiaurinio dangaus poliaus ir sudaro Paukščių Tako atšaką, literatūroje žinomą kaip Cepheus Flare. Dauguma šioje disertacijoje tyrinėjamų objektų priklauso šiai Cefėjo atšakai. Šio darbo tikslas yra Cefėjo žvaigždėdaros rajonų, žinomų kaip atspindžio ūkas NGC 7023, tamsiųjų debesų kompleksas TGU 619 ir jaunas spiečius NGC 7129 fotometrinis tyrimas, siekiant nustatyti šių objektų nuotolį ir tarpžvaigždinę ekstinkciją, jauno spiečiaus NGC 7129 ir... [toliau žr. visą tekstą]
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Tideswell, David Mark. "Chemical modelling of extragalactic star forming regions." Thesis, University of Manchester, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529246.
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Abel, Nicholas Paul. "DETERMINING PHYSICAL CONDITIONS IN STAR FORMING REGIONS." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_diss/428.
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This dissertation is a study of the physical conditions in star-forming regions, and combines observational data and theoretical calculations. We studied the physical conditions of Orions Veil, which is an absorbing screen that lies along the line of sight to the Orion H II region. We computed photoionization models of the Veil. We combined calculations with UV, radio, and optical spectra that resolve the Veil into two velocity components. We derive many physical parameters for each component seen in 21 cm absorption. We find the magnetic field energy dominates turbulent and thermal energies in one component while the other component is close to equipartition between turbulent and magnetic energies. We observe H2 absorption for highly excited levels. We find that the low ratio of H2/H0 in the Veil is due to the high UV flux incident upon the Veil. We detect blueshifted S+2 and P+2 ions which must arise from ionized gas between the neutral portions of the Veil and the Trapezium and shields the Veil from ionizing radiation. We determine the ionized and neutral layers of the Veil will collide in less than 85,000 years. The second part of this dissertation involved self-consistently calculating the thermal and chemical structure of an H II region and photodissociation region (PDR) that are in pressure equilibrium. This differs from previous work, which used separate calculations for each gas phase. Our calculations span a wide range of initial conditions. We describe improvements made to the spectral synthesis code Cloudy which made these calculations possible. These include the addition of a molecular network with ~1000 reactions involving 68 molecules and improved treatment of the grain physics. Archival data are used to derive important physical characteristics of observed H II regions and PDRs. These include stellar temperatures, electron densities, ionization parameters, UV flux, and PDR density. The contribution of the H II region to PDR emission line diagnostics is also calculated. Finally, these calculations are used to derive emission line ratios than can tell us the equation of state in star-forming regions.
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Pattison, Ian. "High-mass star-forming regions in M33." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422023.
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Barsony, Mary Anne Scoville Nicholas Zabriskie Scoville Nicholas Zabriskie. "Outflows in high mass star-forming regions /." Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-09102008-084535.
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Cunningham, Nichol. "Molecular outflows in massive star forming regions." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/11180/.
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This thesis presents millimetre continuum and molecular line observations exploring the properties of molecular outflows towards massive star forming regions. Massive stars produce some of the most energetic phenomena in the Galaxy, yet we still do not have a comprehensive understanding of how they actually form. Outflows are known to play a key role in this formation process and their properties, particularly how they change depending on the mass, luminosity and evolution of the driving source can shed light on how massive stars actually form. This thesis presents observations at both high (SMA 3 arcsecond) and low (JCMT 15 arcsecond) spatial resolution of the known jet/outflow tracers, SiO and 12CO, towards a sample massive star forming region drawn from the RMS survey. Furthermore, the presence of infall signatures is explored through observations of HCO+ and H13CO+, and the hot core nature of the regions is probed using tracers such as CH3CN, HC3N and CH3OH. SiO is detected towards approximately 50% of the massive young stellar objects and HII regions in the JCMT sample. The detection of SiO appears to be linked to the age of the RMS source, with the likely younger sources showing a stronger dependence with SiO. The presence of SiO also appears to be linked to the CO velocity, with SiO more efficiently tracing sources with higher velocity dispersions. In the MOPRA observations towards a sample of 33 RMS sources, CH3CN is detected towards 66% of the sources, with the redder likely younger sources having the largest rotational temperatures. This thesis presents the first interferometric SiO (5-4) and 12CO (2-1) observations, taken with the SMA, towards the massive star forming region G203.3166/NGC 2264-C. In this intermediate/massive star forming cluster, SiO is again tracing the youngest sources. Both the SiO and 12CO emission trace two bipolar, high velocity outflows towards the mm brightest, IR-dark, likely youngest sources in this region. In contrast the IR-bright RMS source, AFGL 989-IRS1, in NGC 2264-C displays no associated molecular outflow emission. Furthermore, the high resolution follow-up SMA observations towards G192.6005/S255IR and the first interferometric 12CO and SiO observations towards G194.9349 show a high velocity outflow traced by 12CO in each region. In both regions the outflow appears to be driven by the IR-bright RMS source. However, no high velocity SiO counterpart is observed in either region. Thus, the lack of associated SiO emission may be a sign of age in these regions.
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Fukue, Tsubasa. "Polarimetric Study of Star/Planet-Forming Regions." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124422.
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Groppi, Christopher Emil. "Submillimeter heterodyne spectroscopy of star forming regions." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280414.
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The sub-mm wave portion of the electromagnetic spectrum is on the frontier of both scientific and technical research in astrophysics. Being a relatively young field, scientific advancement is driven by advancements in detector technology. In this thesis, I discuss the design, construction, testing and deployment of two sub-mm wave heterodyne array receivers. Polestar is a 4 pixel (2 x 2) heterodyne array built for operation in the 810 GHz atmospheric window. It is in operation at the AST/RO telescope at the South Pole. This receiver has increased imaging speed in this band at AST/RO by a factor of ∼20 compared to previous receiver systems. DesertStar is a 7 pixel, hexagonally close packed heterodyne array receiver built to operate in the 345 GHz atmospheric window at the Heinrich Hertz Telescope in Arizona. This system will be a facility instrument at the telescope, and will increase mapping speed over the existing dual polarization single beam receiver at the telescope now by a factor of ∼16. Both these receiver systems enable scientific projects requiring large area imaging that were previously impossible. I also discuss two scientific applications of sub-mm wave receiver systems. We have used multiple telescopes to observe several mm, sub-mm transitions and continuum emission towards the R CrA molecular cloud core. Originally thought to be associated with high mass star formation, we find that the driving source behind the mm-wave emission is a low mass protostar. The close proximity of R CrA allows us to achieve high spatial resolution even with single dish mm-wave and sub-mm wave telescopes. With this resolution, we are able to disentangle the effects of infall, rotation and outflow motions. We also use vibrationally excited HCN emission to probe the protostellar accretion disk in a sample of nearby high and low mass protostars of varying ages. While these observations are difficult with single dish telescopes, we show the promise of the technique, and report results on 4 sources.
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Slesnick, Catherine Louise Brown Michael E. "1-10 Myr-old low mass stars and brown dwarfs in nearby star forming regions /." Diss., Pasadena, Calif. : Caltech, 2008. http://resolver.caltech.edu/CaltechETD:etd-08102007-161741.
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Telleschi, Alessandra Silvia. "Coronal evolution of solar-like stars : X-ray spectroscopy of stars in star-forming regions and the solar neighborhood /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17018.
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Rundle, David. "Molecular line transfer calculations in star forming regions." Thesis, University of Exeter, 2010. http://hdl.handle.net/10036/111934.
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This thesis describes the development, benchmarking and application of a non-LTE, co-moving frame Monte Carlo molecular line radiative transfer module for TORUS. Careful attention has been paid to the convergence, acceleration and optimisation of the code. I present the results of the application of the code to various benchmarking scenarios, including a collapsing cloud, a circumstellar disc and a very optically thick cloud of interstellar water. Benchmarking is an essential step in verifying the accuracy and efficiency of the code which is vital if it is to be used to analyse real data. In all cases, the code was able to accurately reproduce either the expected analytical solution or (in the absence of such a solution) was able to produce results commensurate with the results of other codes. In order to facilitate the motivating radiative transfer calculations of a star-forming cluster simulated using smoothed particle hydrodynamics (SPH) performed in this thesis, it was first necessary to devise and test an algorithm that efficiently maps an irregular distribution of smoothed particle hydrodynamics (SPH) particles onto a regular adaptive mesh. Whilst the algorithm was designed with this in mind it has also been used to study the effects of radiative feedback in circumstellar discs as well create a synthetic survey of a simulated galaxy. Bate et al.'s particle representation was resampled onto an adaptive mesh to enable me to use TORUS to obtain non-LTE level populations of multiple molecular species throughout the cluster and create velocity-resolved datacubes by calculating the emergent intensity using raytracing. I compared line profiles of cores traced by N2H+ (1-0) to probes of low density gas (13CO and C18O (1-0)) surrounding the cores along the line-of-sight. The relative differences of the line-centre velocities were found to be small compared to the velocity dispersion, matching recent observations. The conclusion is that one cannot reject competitive accretion as a viable theory of star formation based on observed velocity profiles.
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Furness, James. "Observations of young high mass star forming regions." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515251.
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Hermanowicz, Maciej Tomasz. "Populations of star forming regions in nearby galaxies." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648576.
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Craigon, Alison M. "The morphology and kinematics of star forming regions." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27550.
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To develop a complete picture of the early stages of star and planet formation, it is necessary to understand the molecular clouds from which they form. The physical properties of these clouds and the interactions between their gas and solid constituents are not well known. This thesis presents an observational study of the morphology and kinematics of carbon monoxide(CO) gas in molecular clouds. It forms part of a wider project to produce the first coupled gas-solid maps of a broad sample of starless and star forming clouds. Nine molecular clouds were observed with the James Clerk Maxwell Telescope, the Institut de Radio Astronomie Millimétrique 30 m Telescope and the Nobeyama 45 m Radio Telescope to produce large scale(14.6 × 14.6 arcmin), high resolution (15.3 arcsec) maps of CO emission. The COROLINE software was developed to derive maps from the observations which show how the CO gas is distributed; the temperature and density structures of the clouds; and how the morphology and kinematics of CO gas is influenced by embedded and nearby stars. A comprehensive analysis is made of Barnard 35A: a cloud heavily processed both internally by a young stellar object and externally by massive stars. The temperature, density and velocity structures of this cloud are explored in detail. Observational evidence is proposed for photoelectric heating through a correlation between the gas temperature and emission from PolyAromatic Hydrocarbons. A clump of enhanced emission ahead of a Herbig–Haro object is thought to be due to photodesorption of CO ice from the surface of dust grains. A chain of similar clumps, following an arc equidistant from the YSO, suggest that the outflow is precessing. This work concludes with the first coupled gas-solid maps. This thesis demonstrates the importance of understanding the often complex morphology and kinematics of a star forming region prior to considering the interactions between its gas and solid-phase species.
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Martin, Clare E. "Alfvén waves in low-mass star-forming regions." Thesis, University of St Andrews, 1999. http://hdl.handle.net/10023/14190.
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Low-mass star-forming regions have a lifetime which is greater than their dynamical time and must therefore be, in an average sense, in mechanical equilibrium. The work presented here proposes that an equilibrium exists between the self-gravity, gas pressure, and the magnetic field and the waves it supports. Specifically the equilibrium in the direction perpendicular to the ordered magnetic field is given by the Lorentz force, while that parallel to the field is given by an Alfvén wave pressure force. The work detailed in this thesis models a low-mass star-forming region as a one-dimensional gas slab with a magnetic field lying perpendicular to the layer. Analytical, self-consistent models are formulated to study the equilibrium parallel to the background magnetic field. It is found that both short-wavelength (modelled using the WKB approximation) and large-amplitude, long-wavelength Alfvén waves can provide the necessary support parallel to the magnetic field, generating model cloud thicknesses that are consistent with the observations. The effect of damping by the linear process of ion-neutral friction is considered. It is found that the damping of the waves is not a necessary condition for the support of the cloud although it is an advantage. The possible sources of these waves are discussed. The Alfvén waves are also found to make an important contribution to the heating of a low-mass star-forming region. By modelling the dominant heating and cooling mechanisms in a molecular cloud, it is discovered that a cloud supported against its self-gravity by short-wavelength Alfvén waves will be hotter at its outer edge than in the central regions. These models successfully describe a low-mass star-forming region in equilibrium between its self-gravity, the gas pressure and an Alfvén wave pressure force. The question of the stability of such an equilibrium is considered, specifically that of an isothermal gas slab supported by short-wavelength Alfvén waves. The initial results suggest that the presence of a magnetic field and its associated Alfvén waves have a stabilising effect on the layer, and encourage further consideration of the role of Alfvén waves in low-mass star-forming regions.
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FAUSTINI, FABIANA. "Multiwave analysis of high-mass star forming regions." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1198.
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Ci sono stati notevoli sforzi per capire come si formano le stelle, sia da un punto di vista teorico che osservativo. Abbiamo raggiunto una buona comprensione di come si formano le stelle di bassa massa isolate (Klein et al. 2006). Lo scenario attualmente accettato è che le stelle di bassa massa si formano attraverso il collasso gravitazionale di un core prestellare; in seguito la formazione della sorgente prosegue con un accrescimanto dal disco che la circonda.
Estendere questa teoria ad stelle di alta massa non è banale. Le protostelle di alta massa raggiungono la sequenza principale mentre sono ancora nella fase di accrescimento principale. Quando la protostella centrale raggiunge una massa di circa 10 masse solari si innesca la fusione dell'idrogeno nel nucleo della stella e la pressione di radiazione e il vento dovrebbero impedire un'ulteriore accrescimento. Diverse teorie sono oggi proposte per permettere la formazione di oggetti di alta massa, che vengono presentate nel capitolo introduttivo, e noi cerchiamo di discriminare tra questi modelli teorici attraverso la ricostruzione della Star-Formation Hystori di ammassi stellari che si formano in regioni di formazione di alta massa. La presentazione di questo lavoro è divisa in tre sezioni.
• La prima parte presenta l'analisi del nostro campione di sorgenti e la discussione dei risultati scientifici. Questa è a sua volta divisa in tre capitoli. Nel capitolo 2 presentiamo i risultati della nostra analisi nelle bande del Vicino-InfraRosso caratterizzando le proprietà dei clusters di bassa massa; mentre nel capitolo 3, abbiamo mostriamo come ottenere le SEDS per gli oggetti di massa intermedia ed alta e come queste si confrontano con i modelli teorici. Nel Capitolo4 mettiamo insieme i risultati su tutte le lunghezze d'onda prese in esame per estrapolare le informazioni sulla storia dei clusters in fase di formazione.
• Nella seconda sezione presentiamo la struttura e le prestazioni dell' algoritmo di analisi dati da noi sviluppato.
• L'ultima sezione riassume i risultati ottenuti in questo lavoro di ricerca.There have been considerable efforts to understand how stars form from both a theoretical and an observational point of view. We have reached a good understanding of how isolated lowmass stars form (Klein et al. 2006). The widely accepted scenario is that low-mass stars form by the gravitational collapse of a prestellar core followed at later stages by disk accretion. Extending this theory to high-mass stars is not trivial. Highmass (proto-)stars reach the zero age main sequence while still accreting. When the central protostar reaches a mass of about 10 Msun hydrogen fusion ignites in the core and the star’s radiation pressure and wind should prevent further accretion. Several theories are today proposed, we discuss about them in the introduction, and we try to discriminate between these theoretical models through the re-building of the Star-Formation Hystori of clusters formed in high-mass star formation regions. The presentation of this work is divided into three section. • The first part presents the analysis of our sample and the discussion of our scientific results, it is divided in three chapter. In the chapter 2 we presents the results of our analysis in the Near-IR banbs to characterized the properties of low mass cluster in our sample, while in the chapter 3 we shown the SEDs building for intermediate and high-mass objects and the fits with theoretical models. In the chapter4 we take again our results on all the examinated wavelengths to extrapolate the information about the clusters star formation history. • In the second section the structure and the performances of our data analysis algorithm is presented. • The last section recapitulates the results obtain in all this work
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Draper, Peter Walter. "CCD polarimetry as a probe of regions of recent star-formation." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6597/.
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Chapter 1 of this thesis details the incorporation of a Charged Coupled Device (CCD) detector system with the Durham Imaging Polarimeter. The details include the physical characteristics of the device and the electronics and software associated with the device control and data storage. The introduction of the CCD detector system haa made necessary the inclusion of a super-achromatic half-wave plate in the polarimeter which has an inherent variability in its optic axis. Chapter 2of this work describes fully how suitable corrections for this effect can be made, and derives "first order" results. The CCD performance is examined in comparison with the detector used previously and hence the veracity of the new results is established. Chapter 3 is a relevant summary of the status of the astronomy of the immediate regions of recent star-formation. Chapter 4 describes multicolour polarimetry of NGC2261/R Mon covering the period 1979 to 1986. The data conclusively proves that the polarisation of R Mon must be due to effects close to R Mon (~ 14 astronomical units). This is evident because of the dynamic timescale of the variations of the polarisation of R Mon and the anomalous band of polarisations seen across the head of the nebula. The interpretation presented is an extension of the Elsasser and Staude (1978) method of polarising objects embedded within the confines of a nearly edge-on disk. Detailed polarisations within the main nebula body provide evidence for this extended interpretation and also for an extensive helical magnetic field which may extend into the disk. Also it is seen that R Mon must still be "shrouded" in material preventing light from directly reflecting in the main nebula body. It is not thought that the variations in the region close to R Mon are due to planetary bodies but to accretion from the disk. The results of this re-interpretation of the polarising mechanism are tentatively applied to other similar objects.
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Gómez, Ruiz Arturo [Verfasser]. "Molecular Outflows in Star Forming Regions / Arturo Gómez Ruiz." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1052582044/34.
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Ruffle, Deborah Patricia. "The physical and chemical evolution of star forming regions." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300792.
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Russell, Adrian Paul Grenville. "Studies in out-flowing material in star-forming regions." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330314.
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Al-Edhari, Ali Jaber. "Complex organic molecules in solar-type star forming regions." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY048/document.
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Le but de la présente thèse est l'étude de la compléxité moléculaire dans les régions de formation stellaires. Cette thèse s'axe sur deux classes de molécule aux caractéristiques prébiotiques : les molécules organiques complexes et les cyanopolyynes.Dans ce contexte, j'ai analysé des données d'un seul échantillon de relevés spec- traux en exploitant des codes de transfert radiatif à l'équilibre thermodynamique local (LTE) et/ou non-LTE pour deux sources : une proto-étoile de type solaire dans un environnement calme (IRAS 16293-2422) et un proto-ama constitué de proto-étoile de type solaire (OMC2-FIR4).L'objectif est de trouver des similar- ités et des différences entre ces deux cas.J'ai utilisé des données issu de deux relevés spectraux : TIMASSS (The IRAS16293-2422 Millimeter And Submilimeter Spectral Survey) réalisés en 2011 (Caux et al. 2011), et ASAI(Astrochemical Surveys At IRAM) réalisés pen- dant la période 2013-2015 (eg Lopez-Sepulcre et al.2015). J'ai extrais les lignes (identification et intensité intégrée) en utilisant le paquet disponible publique- ment : CASSIS (Centre d'Analyse Scientifique de Spectres Infrarouges et Sub- millimetrique). Pour finir, j'ai utilisé le paquet GRAPES (GRenoble Analysis of Protostellar Envelope Spectral) afin de modéliser la distribution spectrale énergétique de ligne (SLED) des molécules détectées, mais aussi afin d'estimer leurs abondances à travers l'envelope de IRAS16293 et du coeur chaud OMC2- FIR4.Les principaux résultats de la thèse sont :1. Le premier recensement complet des molecules organiques complexes (COMs) dans IRAS162932. La première détéction de COMs dans l'enveloppe froide d'une proto-étoile de type solaire (IRAS16293-2422) supportant l'idée qu'un méchanisme de formation, relativement efficace pour les COMs détectées, doit exister en phase gazeuse froide.3. La découverte d'une fine corrélation entre le diméthyle-éther (DME) et le méthyle-formate (MF) suggère une relation mère fille entre ces deux espèces.4. La detection de formamide, espèce avec un très fort potentiel prébiotique, dans plusieurs protoétoiles incluant IRAS16293-2422 et OMC2-FIR4.5. Le recensement complet des cyanopolyynes dans IRAS16293 et OMC2- FIR4 avec la détection de HC3N, HC5N, DC3N et pour OMC2-FIR4: le C13 isotopologue du HC3N cyanopolyynes.Ces résultats sont le sujet principal de deux publications (Jaber et al.2014, ApJ; Lopez-Sepulcre, Jaber et al.2015,MNRAS), un article accepté (Jaber et al., A & A) et un article à soumettre (Jaber et al. A & A)The present PhD thesis goal is the study of the molecular complexity in solar type star forming regions. It specifically focuses on two classes of molecules with a pre-biotic value, the complex organic molecules and the cyanopolyynes.At this scope, I analyzed data from single-dish spectral surveys by means of non-LTE or/and non-LTE radiative transfer codes in two sources, a solar type protostar in an isolated and quiet environment (IRAS16293-2422) and a proto-cluster of solar type protostars (OMC2-FIR4). The goal is to find similarities and differences between these two cases.I used data from two spectra surveys: TIMASSS (The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey), which has been carried out in 2011 (Caux et al. 2011), and ASAI (Astrochemical Surveys At IRAM), which has been carried out in 2013-2015 (e.g. Lopez-Sepulcre et al. 2015).I extracted the lines (identification and integrated intensity) by means of the publicly available package CASSIS (Centre dAnalyse Scientifique de Spectres Infrarouges et Submillimtriques).Finally, I used the package GRAPES (GRenoble Analysis of Protostellar Envelope Spectra) to model the Spectral Line Energy Distribution (SLED) of the detected molecules, and to estimate their abundance across the envelope and hot corino of IRAS16293-2422 and OMC2-FIR4, respectively.The major results of the thesis are:1) The first full census of complex organic molecules (COMs) in IRAS16293-2422;2) The first detection of COMs in the cold envelope of a solar type protostar (IRAS16293-2422), supporting the idea that a relatively efficient formation mechanism for the detected COMs must exist in the cold gas phase;3) The discovery of a tight correlation between the dimethyl ether (DME) and methyl format (MF), suggesting a mother-daughter relationship;4) The detection of formamide, a species with a very high pre-biotic value, in several protostars, included IRAS16293-2422 and OMC2-FIR4;5) The full census of the cyanopolyynes in IRAS16293-2422 and OMC2-FIR4, with the detection of HC3N and HC5N, DC3N and, for OMC2-FIR4, the 13C isotopologue of HC3N cyanopolyynes.These results are the focus of two published articles (Jaber et al. 2014, ApJ; Lopez-Sepulcre, Jaber et al. 2015, MNRAS), one accepted article (Jaber et al., A&A) and a final article to be submitted (Jaber et al., A&A)
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Machado, Ana Cristina Moreira. "Optical and near-infrared surveys in star forming regions." Universidade Federal de Minas Gerais, 2005. http://hdl.handle.net/1843/ESCZ-6L6H6C.
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We have observed several different star formation regions, in top quality observatories: two missions at the Kitt Peak National Observatory, in Arizona, using the 4m and the 0.9m telescopes and two other missions at the Mauna Kea observatory in Hawaii, using the 2.2m optical telescope and the 4m infrared telescope (UKIRT). We have obtained very good quality data, high resolution deep images with seeing of the order of 1 or less, combined with large field of view, with the objective to obtain as much information on each region as possible.In order to probe the more evolved optically visible young stars, we have analyzed surveys to detect H_ emission stars in two very well known star forming regions: NGC 2264 and M 42. They where obtained with a wide field Schmidt telescope associated with the best quality photographic films, providing a survey of an area of 5×5 in the sky and enough sensitivity to reach red photographic magnitudes up to 19 mag, yielding a detection of a much larger number of young stars than previously known. We provide tables with coordinates, finding charts, cross identification with other surveys and magnitudes in public catalogs. Optical narrow-band surveys to detect Herbig-Haro objects are presented as well, for the star forming regions S140 and L1551. In the latter, previous images allowed the determination of proper motion using a cross correlation technique. A modern wide
field MOSAIC CCD was used, providing a large scale view of the entire region, as well as high enough resolution (0.26/pix) to detect structure details of the knots inside the shock regions. New Herbig-Haro objects were detected. A possible alignment of the main flow axis with the magnetic field in the cloud is discussed. The same correlation technique was used to measure proper motions in the well known HH 47 jet, using even higher resolution Hubble Space Telescope images (0.1/pix) taken in two epochs. Some other known star forming regions were surveyed at optical and near-infrared wavelengths for a study of both the young sources and the Herbig-Haro objects, in an attempt to relate them and to shed more light into the understanding of the star formation processes in those areas. Two of those regions are presented in this work: the IC 1396N globule and a region called by us the Gulf of Mexico, because of its location in the dark cloud southwest of the North America Nebula. The optical images were obtained in perfect conditions in one of the best observing sites in the world (the Mauna Kea observatory in Hawaii). The surveyed regions were only a few arcminutes wide, but the resolution was good and the areas cover the main region where the star formation processes are occurring. Several new Herbig-Haro objects were found, as well as new H_ emission line stars. The near-infrared observations allowed a view of the interior of the molecular clouds, probing embedded young stars and outflows. In some cases the near-infrared observations lacked the quality necessary for building a comprehensive view of the young sources, and we could not infer physical properties for those stars. But we were able to detect some previously unknown young stars, some of them powering outflows of various types. So far we have seven different star forming regions studied using various techniques, for which we discuss differences and similarities. A few other regions were also observed and their study is planned in the near future. We conclude that the star formation process is much more complex than it was thought a few years ago, and only with the simultaneous use of different techniques applied to several star forming regions will we be able to answer the numerous questions about this process (and probably create many more questions. . . ).Algumas regiões de formação estelar com características bem diferentes foram medidas em observatórios localizados em alguns dos melhores sítios do mundo: duas missões no Kitt Peak National Observatory no Arizona, Estados Unidos, usando os telescópios de 4m e de 0,9m, e outras duas missões no observatório de Mauna Kea no Havaí, com o telescópio óptico de 2.2m e o telescópio infravermelho de 4m (UKIRT). Obtivemos dados de ótima qualidade, imagens com alta resolução, longo tempo de exposição, com seeing da ordem de 1 ou menos, aliados a grandes campos de visão, com objetivo de obter o maior número possível de informações para cada região. Para procurar por estrelas jovens, porém já mais evoluídas (opticamente visíveis), analisamos buscas feitas por estrelas com emissão em H_ em duas regiões de formação estelar bem conhecidas: NGC 2264 e M 42. As buscas foram feitas usando-se um telescópio Schmidt, com grande campo de visão, associado a filmes fotográficos da melhor qualidade, fornecendo uma pesquisa que cobre uma área de 5×5 no céu e sensibilidade suficiente para alcançar limites de magnitudes no vermelho de até 19 mag, resultando na detecção de um número superior de estrelas do que previamente conhecido. Apresentamos tabelas, cartas de identificação, correlação com levantamentos prévios e magnitudes obtidas em catálogos públicos. Apresentamos também buscas por objetos Herbig-Haro usando imagens ópticas de banda estreita, nas regiões de S140 e L1551. Nesta última, imagens obtidas anteriormente permitiram a determinação de movimentos próprios usando uma técnica de correlação cruzada. Um moderno CCD MOSAIC forneceu uma visão em grande escala de toda a região, bem como resolução (0.26/pix) para se detectar detalhes na estrutura dos nós dentro das regiões de choque. Novos objetos Herbig-Haro foram detectados. Discutimos um possível alinhamento do eixo principal dos jatos com o campo magnético da nuvem. A mesma técnica de correlação foi usada para se medir movimentos próprios no bastante conhecido HH 47, com imagens de resolução ainda maior (0.1/pix) obtidas pelo Hubble Space Telescope em duas épocas distintas. Algumas outras regiões de formação estelar foram pesquisadas em comprimentos de onda no visível e no infravermelho próximo, para um estudo tanto das fontes jovens quanto dos objetos Herbig-Haro, numa tentativa de relacioná-los e melhorar o entendimento dos processos de formação estelar nessas áreas. Duas das regiões observadas são apresentadas neste trabalho: a nuvem globular IC 1396N e uma região chamada por nós de Golfo do México, por sua localização na nuvem escura a sudoeste da Nebulosa América do Norte. As imagens ópticas foram obtidas em condições perfeitas em um dos melhores sítios de observação no mundo (o observatório de Mauna Kea, no Havaí). A região pesquisada tinha tamanho de apenas alguns minutos de arco, mas a resolução foi ótima e as áreas cobrem a região principal onde os processos de formação estão acontecendo. Muitos objetos Herbig-Haro novos foram descobertos, bem como novas estrelas com linhas de emissão em H_ As observações no infravermelho permitem uma visão do interior da nuvem molecular, detectando estrelas jovens embebidas, bem como ejeções de matéria. Em alguns casos, as observações no infravermelho não possuem a mesma qualidade, necessária para se construir uma visão compreensível das fontes jovens, e não pudemos determinar propriedades físicas para estas estrelas. Mas fomos capazes de detectar estrelas até então desconhecidas, algumas delas criando jatos de vários tipos. Até agora sete regiões diferentes foram estudadas com uso de técnicas variadas, para as quais discutimos as diferenças e similaridades. Algumas outras regiões também foram observadas e seu estudo está planejado para breve. Concluímos, através de nosso estudo, que o processo de formação estelar é bem mais complexo do que se acreditava há poucos anos, e que somente o uso de várias técnicas aplicadas a diversas regiões de formação estelar poderá responder às inúmeras questões ainda sem resposta sobre este processo (e provavelmente colocar muitas outras questões . . . ).
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Giannetti, Andrea <1986>. "The evolution of massive clumps in star forming regions." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6216/1/giannetti_andrea_tesi.pdf.
Full textAbstract:
In this thesis two related arguments are investigated:
- The first stages of the process of massive star formation, investigating the physical conditions and -properties of massive clumps in different evolutionary stages, and their CO depletion;
- The influence that high-mass stars have on the nearby material and on the activity of star formation.
I characterise the gas and dust temperature, mass and density of a sample of massive clumps, and analyse the variation of these properties from quiescent clumps, without any sign of active star formation, to clumps likely hosting a zero-age main sequence star. I briefly discuss CO depletion and recent observations of several molecular species, tracers of Hot Cores and/or shocked gas, of a subsample of these clumps.
The issue of CO depletion is addressed in more detail in a larger sample consisting of the brightest sources in the ATLASGAL survey: using a radiative tranfer code I investigate how the depletion changes from dark clouds to more evolved objects, and compare its evolution to what happens in the low-mass regime.
Finally, I derive the physical properties of the molecular gas in the photon-dominated region adjacent to the HII region G353.2+0.9 in the vicinity of Pismis 24, a young, massive cluster, containing some of the most massive and hottest stars known in our Galaxy. I derive the IMF of the cluster and study the star formation activity in its surroundings.
Much of the data analysis is done with a Bayesian approach. Therefore, a separate chapter is dedicated to the concepts of Bayesian statistics.
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Giannetti, Andrea <1986>. "The evolution of massive clumps in star forming regions." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6216/.
Full textAbstract:
In this thesis two related arguments are investigated:
- The first stages of the process of massive star formation, investigating the physical conditions and -properties of massive clumps in different evolutionary stages, and their CO depletion;
- The influence that high-mass stars have on the nearby material and on the activity of star formation.
I characterise the gas and dust temperature, mass and density of a sample of massive clumps, and analyse the variation of these properties from quiescent clumps, without any sign of active star formation, to clumps likely hosting a zero-age main sequence star. I briefly discuss CO depletion and recent observations of several molecular species, tracers of Hot Cores and/or shocked gas, of a subsample of these clumps.
The issue of CO depletion is addressed in more detail in a larger sample consisting of the brightest sources in the ATLASGAL survey: using a radiative tranfer code I investigate how the depletion changes from dark clouds to more evolved objects, and compare its evolution to what happens in the low-mass regime.
Finally, I derive the physical properties of the molecular gas in the photon-dominated region adjacent to the HII region G353.2+0.9 in the vicinity of Pismis 24, a young, massive cluster, containing some of the most massive and hottest stars known in our Galaxy. I derive the IMF of the cluster and study the star formation activity in its surroundings.
Much of the data analysis is done with a Bayesian approach. Therefore, a separate chapter is dedicated to the concepts of Bayesian statistics.
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Randriamanakoto, Rojovola Zara-Nomena. "Super star cluster candidates in the star-forming regions of luminous infrared galaxies." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11807.
Full textAbstract:
Includes abstract.Includes bibliographical references (leaves 86-90).
We report on a study of super star cluster (SSC) candidates in the star-forming regions of a representative sample of local luminous infrared galaxies (LIRGs) using KS-band near-infrared (NIR) adaptive optics imaging with GEMINI/ALTAIR and VLT/NACO instruments. The evolution of the cosmic star formation rate (CSFR) indicates its rapid decline in the local Universe.
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Wampfler, Susanne Franziska. "The cosmic ray ionization rate in solarlike star forming regions." Zürich : ETH, Eidgenössische Technische Hochschule Zürich, Institute of Astronomy, Department of Physics, 2007. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=302.
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Cox, M. J. "Observations of star-forming regions with a computer-controlled receiver." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384426.
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Miret, Roig Núria. "COSMIC-DANCE : A comprehensive census of nearby star forming regions." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0327.
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Comprendre comment se forment les étoiles est l’une des questions fondamentales auxquelles l’astronomie entend répondre. Malheureusement, nous ne pouvons pas étudier la formation stellaire en temps réel et différentes méthodes indirectes doivent être utilisées pour faire la lumière sur ce sujet. L’objectif principal de cette thèse est de déterminer la fonction de masse initiale, la distribution de masse des étoiles à leur naissance, dans différentes associations et régions de formation d’étoiles. La fonction de masse est le produit direct de la formation stellaire et constitue donc un paramètre d’observation fondamental pour contraindre les théories de formation stellaire et sous-estellaire. Nous nous sommes concentrés sur l’amas ouvert de 30 Ma IC 4665 et la région de formation d’étoiles de 1 - 10 Ma de Upper Scorpius (USC) et r Ophiuchi (r Oph). Nous avons combiné l’astrométrie et la photométrie de Gaia Data Release 2 avec nos observations au sol pour préparer un catalogue profond et étendu de chaque région. Ensuite, nous avons calculé les probabilités d’appartenance en utilisanttoute l’astrométrie et la photométrie disponibles et identifié les membres à haute probabilité. Nous avons utilisé la liste finale des membres pour estimer la distribution de magnitude, et les fonctions de luminosité et masse de ces associations. Alors que la première a l’avantage d’être indépendante des modèles d’évolution, tandis que les fonctions de luminosité et de masse peuvent être utilisées pour contraindre les mécanismes de formation d’étoiles. L’étude d’IC 4556 nous a permis d’identifier des objets sous-stellaires, sans pour autant pouvoir fournir un recensement complet dans ce domaine de masse. Dans USC et r Oph, nous avons identifié une population très riche d’objets sous-stellaires, significativement plus nombreux que les prédictions des modèles de formation par effondrement de coeurs moléculaires, suggérant que la formation de naines brunes et d’objets de masses planétaires isolés par des phénomènes d’éjection dans des systèmes planétaires a une contribution importante et du même ordre que l’effondrement des coeurs moléculaires à la population finale d’objets dans un amas. L’âge est un paramètre fondamental pour étudier la formation et l’évolution des étoiles pour plusieurs raisons: premièrement puisqu’il établit une échelle de temps sur laquelle placer les observations. Deuxièmement car il est essentiel pour convertir les luminosités en masses, avec l’aide de modèles d’évolution stellaire. Les incertitudes sur l’age de USC et r Oph se traduisant en erreurs importantes dans notre estimation de la fonction de masse, j’ai développé une stratégie d’étude de "l’âge dynamique" au moyen d’une analyse orbitale de traçage des mouvements des membres d’associations jeunes. J’ai ainsi mis au point une stratégie incluant i) les observations et la recherche de données dans les archives publiques, ii) la réduction et l’analyse des spectres échelles obtenus; iii) et l’analyse dynamique, pour déterminer l’âge d’une association. La méthodologie, développée avec l’association b Pictoris (b Pic), est prête à être appliquée à d’autres régions et en particulier à USC et r Oph. Les membres que nous avons identifiés sont par ailleurs d’excellentes cibles pour des études complémentaires telles que la recherche de disques (produit également fondamental de la formation stellaire), d’exoplanètes, de système multiples, mais aussi pour la caractérisation des atmosphères et propriétés physiques des naines brunes et des planètes errantes. [...]Understanding how stars form is one of the fundamental questions which astronomy aims to answer. Currently, it is well accepted that the majority of stars form in groups and that their predominant mechanism of formation is the core-collapse. However, several mechanisms have been suggested to explain the formation of substellar objects, and their contribution is still under debate. The main goal of this thesis is to determine the initial mass function, the mass distribution of stars at birth time, in different associations and star-forming regions. The mass function constitutes a fundamental observational parameter to constrain stellar and substellar formation theories since different formation mechanisms predict different fraction of stellar and substellar objects. We used the Gaia Data Release 2 catalogue together with ground-based observations from the COSMIC-DANCe project to look for high probability members via a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. We applied this method to the 30 Myr open cluster IC 4665 and the 1 - 10 Myr star-forming region Upper Scorpius (USC) and r Ophiuchi (r Oph). We found very rich populations of substellar objects which largely exceed the numbers predicted by core-collapse models. In USC, where our sensitivity is best, we found a large number of free-floating planets and we suggest that ejection from planetary systems must have a similar contribution than core-collapse in their formation. The age is a fundamental parameter to study the formation and evolution of stars and is essential to accurately convert luminosities to masses. For that, we also presented a strategy to study the dynamical traceback age of young local associations through an orbital traceback analysis. We applied this method to determine the age of the b Pictoris moving group and in the future, we plan to apply it to other regions such as USC. The members we identified with the membership analysis are excellent targets for follow-up studies such as a search for discs, exoplanets, characterisation of brown dwarfs and free-floating planets. I this thesis, we presented a search for discs hosted by members of IC 4665 and we found six excellent candidates to be imaged with ALMA or the JWST. The tools we developed, are ready to be used in other regions such as USC and r Oph, where we expect to find a larger number of disc-host stars