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Талмач, Дмитро Павлович. "Детерміновані методи відображення повідомлення в точку еліптичної кривої, заданої у різних формах." Bachelor's thesis, КПІ ім. Ігоря Сікорського, 2021. https://ela.kpi.ua/handle/123456789/44276.
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Данна робота присвячена розробцi детермiнованих полiномiальних
алгоритмiв кодування бiтових векторiв в точки елiптичних кривих
представлених у рiзних формах. У роботi приводяться основнi необхiднi
для розумiння викладок вiдомостi про елiптичнi кривi, особливо кривi в
формi Едвардса. Далi детально розглядається проблема кодування
елементiв поля, над яким визначена крива, у множину точок кривої для
використання у криптографiчних протоколах, в основi яких лежить
хешування або задача iнкапсуляцiї ключа. У останньому роздiлi
презентуються новi алгоритми, наводиться їх порiвняльний аналiз.The work is devoted to constructing deterministic polynomial algorithm for encoding sequences of bits into points of Elliptic Curves represented in different forms. The work presents basic information related to the topic of Elliptic Curves, especially in the Edwards form, that is necessary for understanding further mathematical calculations. Next, the problem of encoding underlying field elements, over which the curve is defined, into points of the curve for using this encoding in cryptographic protocols, which are based on hashing or key encapsulation schemes, is considered in more detail. In the last section new algorithms are presented and compared.
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Voss, Björn. "White dwarfs in the SPY and HQS surveys an analysis of a large set of white dwarf spectra and a search for variable ZZ Ceti white dwarfs /." [S.l.] : [s.n.], 2006. http://e-diss.uni-kiel.de/diss_1796/d1796.pdf.
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Gomes, Joana. "Searching for benchmark systems containing ultra-cool dwarfs and white dwarfs." Thesis, University of Hertfordshire, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630036.
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I here present my search for benchmark systems with main sequence stars widely separated from ultracool dwarfs or white dwarfs. Different near-infrared and optical surveys have been used to create samples of L dwarf candidates from colour cuts and by exploring the faintest limits of available surveys. I started by using the Two Micron All Sky Survey, and then expanded my method in order to include sources from the UKIRT Infrared Deep Sky Survey, which has not yet been fully explored for L dwarfs. In order to search for wide main sequence star companions I have used stars from Hipparcos, Gliese and PPMXL. I then applied a set of selection rules based on photometry and proper motion to find these systems. This search led to the discovery of two new benchmark systems with genuine L dwarfs, that have been spectroscopically confirmed. A large sample of potentially new systems still awaits a complete analysis, and we thus expect more exciting discoveries to stem from the method utilized. A method to identify new late-T and Y dwarfs from the Wide-field Infrared Survey was also been developed, with the aim of using the surveys maximum sensitive limits. The technique relies on objects only detected in the W2-band and through a series of rejection methods 158 sources are retrieved with signal-to-noises ranging from 8-10. I have performed aperture photometry and measured proper motions for a set of candidates that were observed during the follow-up campaign. I then present a new sample of potentially white dwarfs with common proper motions main sequence star companions. The white dwarfs are retrieved from SuperCOSMOS whereas stellar companions are from Tycho. I present spectra for 39 WD candidates and for 6 stars. Temperatures and surface gravities are estimated for the white dwarf objects, whilst main sequence stars abundances are obtained from the fitting of synthetic spectra to the observations. Finally I discuss the implications of these findings and what future work can be done with these benchmark systems.
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Deshpande, Rohit. "Search for gas giants around late-M dwarfs." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4640.
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The absolute radial and rotational velocities of our targets were also calculated. Values of rotational velocities indicate that M dwarfs are, in general, slow rotators. Using our result and that from literature, we extended our study of rotational velocities to L dwarfs. Our observations show an increase in rotational velocities from late M to L dwarfs. We also find that the mean periods of M dwarfs are less than 10 hours. In order to improve our precision in measuring relative radial velocity (RV), we employed the use of deconvolution method. With this method we were able to ameliorate relative RV precision from 300 m/s to 200 m/s. This was a substantial improvement in our ability to detect gas-giant planets. However none of the 15 dwarfs we monitored indicate a presence of companions. This null result was then used to compute the upper limit to the binary frequency and close-in Jupiter mass planetary frequency. We find the binary frequency to be 11% while the planetary frequency was 1.20%.; We carried out a near-infrared radial velocity search for Jupiter-mass planets around 36 late M dwarfs. This survey was the first of its kind undertaken to monitor radial velocity variability of these faint dwarfs. For this unique survey we employed the 10-m Keck II on Mauna Kea in Hawaii. With a resolution of 20,000 on the near-infrared spectrograph, NIRSPEC, we monitored these stars over four epochs in 2007. In addition to the measurement of relative radial velocity we established physical properties of these stars. The physical properties of M dwarfs we determined included the identification of neutral atomic lines, the measurement of pseudo-equivalent widths, masses, surface gravity, effective temperature, absolute radial velocities, rotational velocities and rotation periods. The identification of neutral atomic lines was carried out using the Vienna Atomic line Database. We were able to confirm these lines that were previously identified. We also found that some of the lines observed in the K-type stars, such as Mg I though weak, still persist in late M dwarfs. Using the measurement of pseudo-equivalent widths (p-EW) of 13 neutral atomic lines, we have established relations between p-EW and spectral type. Such relations serve as a tool in determining the spectral type of an unknown dwarf star by means of measuring its p-EW. We employed the mass-luminosity relation to compute the masses of M dwarfs. Our calculations indicate these dwarfs to be in the range of 0.1 to 0.07 solar masses. This suggests that some of the late M dwarfs appear to be in the Brown dwarf regime. Assuming their radii of 0.1 solar radii, we calculated their surface gravity. The mean surface gravity is, log g = 5.38. Finally their effective temperature was determined by using the spectral-type temperature relationship. Our calculations show effective temperatures in the range of 3000 to 2300 K. Comparison of these values with models in literature show a good agreement.ID: 029094443; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 224-246).
Ph.D.
Doctorate
Department of Physics
Sciences
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Day-Jones, A. C. "Searching for brown dwarf companions." Thesis, University of Hertfordshire, 2009. http://hdl.handle.net/2299/3475.
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In this thesis I present the search for ultracool dwarf companions to main sequence stars, subgiants and white dwarfs. The ultracool dwarfs identified here are benchmark objects, with known ages and distances. The online data archives, the two micron all sky survey (2MASS) and SuperCOSMOS were searched for ultracool companions to white dwarfs, where one M9 1 companion to a DA white dwarf is spectroscopically confirmed as the widest separated system of its kind known to date. The age of the M9 1 is constrained to a minium age of 1.94Gyrs, based on the estimated age of the white dwarf from a spectroscopically derived Teff and log g and an initial-final mass relation. This search was extended using the next generation surveys, the sloan digital sky survey (SDSS) and the UK infrared deep sky survey (UKIDSS), where potential white dwarf + ultracool dwarf binary systems from this search are presented. A handful of these candidate systems were followed-up with second epoch near infrared (NIR) imaging. A new white dwarf with a spectroscopic M4 companion and a possible wide tertiary ultracool component is here confirmed. Also undertaken was a pilot imaging survey in the NIR, to search for ultracool companions to subgiants in the southern hemisphere using the Anglo-Australian telescope. The candidates from that search, as well as the subsequent follow-up of systems through second epoch NIR/optical imaging and methane imaging are presented. No systems are confirmed from the current data but a number of good candidates remain to be followed-up and look encouraging. A search for widely separated ultracool objects selected from 2MASS as companions to Hipparcos main-sequence stars was also undertaken. 16 candidate systems were revealed, five of which had been previously identified and two new L0 2 companions are here confirmed, as companions to the F5V spectroscopic system HD120005 and the M dwarf GD 605. The properties of HD120005C were calculated using the DUSTY and COND models from the Lyon group, and the age of the systems were inferred from the primary members. For GD 605B no age constraint could be placed due to the lack of information available about the primary, but HD120005C has an estimated age of 2-4Gyr. In the final part of this thesis I investigate correlations with NIR broadband colours (J - H, H - K and J - K) with respect to properties, Teff , log g and [Fe/H] for the benchmark ultracool dwarfs, both confirmed from the searches undertaken in this work and those available from the literature. This resulted in an observed correlation with NIR colour and Teff, which is presented here. I find no correlation however with NIR colours and log g or [Fe/H], due in part to a lack of suitable benchmarks. I show that despite the current lack of good benchmark objects, this work has the potential to allow UCD properties to be measured from observable characteristics, and suggest that expanding this study should reveal many more benchmarks where true correlation between properties and observables can be better investigated.
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Kuzmychov, Oleksii [Verfasser], and Svetlana [Akademischer Betreuer] Berdyugina. "Spectropolarimetric approach for measuring magnetic fields on brown dwarfs." Freiburg : Universität, 2015. http://d-nb.info/1122742681/34.
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Edstam, Louise. "Ranking line-depth ratios for determining relative star temperatures in dwarfs." Thesis, Uppsala universitet, Observationell astrofysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-202315.
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The central line-depths of absorption lines depend upon stellar temperature. By dividing the central line-depth of such a line with a central line-depth independent of temperature, a thermometer of relative star temperatures is obtained in the form of a line-depth ratio (LDR), once it is related to an effective temperature scale. Such thermometers are known to give precise results which is why the method is pursued. The purpose of this work is to rank LDRs according to a set of criteria to find the most suitable ratio to measure temperature. This is done based on a set of LDRs measured for a large sample of dwarf stars with known effective temperature, atmospheric pressure and chemical composition. Numerous LDRs are eliminated because their temperature dependence are limited to a short temperature interval. Further LDRs are eliminated due to dependence on the atmospheric pressure and chemical composition of the LDR. The remaining LDRs are ranked based on the strength of temperature dependence, the fit of the representative polynomial to the data points and the number of data points available. The best ranked LDR provides a temperature resolution smaller than 10 K over a temperature interval of 4500-6250 K, assuming an uncertainty in LDR of 0.01.
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Rowell, Nicholas. "The luminosity function for white dwarfs in the SuperCOSMOS Sky Survey." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/25139.
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I present a magnitude and proper motion limited catalogue of ~ 10,000 white dwarf candidates, obtained from the SuperCOSMOS Sky Survey by means of reduced proper motion selection. This catalogue extends to R ~ 19.75 and μ ~ 0".05 yr⁻¹, and covers more than three quarters of the sky. Spectroscopic follow-up observations have been obtained for a subsample of objects, and are used to assess the reliability of the selection procedure and contamination of the final catalogue. Photometric parallaxes provide distance estimates accurate to ~ 50%. This catalogue is used to measure the luminosity function (LF) for white dwarfs in the Solar neighbourhood over the range 4 ≤ Mbol ≤ 18. A new technique is devised to separate the LFs for disk and spheroid stars, which allows all stars to contribute to the LF even at tangential velocities where the populations overlap. The disk LF shows a sharp decline at Mbol = 15.75, in agreement with other studies, and extends over a magnitude fainter than previously determined. The spheroid LF has a sharp peak at Mbol = 15.75, then levels out and shows no sign of a drop off at faint magnitudes, as expected for a considerably older population. By simulating white dwarf LFs for stellar populations with a range of star formation histories, I measure the age of the local disk and spheroid. The disk age of 9.13⁺⁰ ⁶⁶₋₀.₆₇ Gyr agrees with that measured in similar studies, and with the basic picture of galaxy formation in a cosmological context. No reliable solution is found for the spheroid age. By integrating the LFs, I investigate the local mass density of spheroid white dwarfs, with particular reference to their contribution to the baryonic dark matter content of the Galaxy. I also place an upper limit on their contribution to the possible MACHO population and the microlensing events observed towards the LMC.
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Hendler, Nathanial P., Gijs D. Mulders, Ilaria Pascucci, Aaron Greenwood, Inga Kamp, Thomas Henning, Francois Menard, William R. F. Dent, and Neal J. II Evans. "Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624452.
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The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O I] 63 mu m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O I] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O I] 63 mu m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA-to establish if and how disk radii scale with stellar mass-should be pursued further.
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Hepburn, Ian David. "Development of linear InSb array instrumentation and the search for brown dwarfs." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46816.
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Hogan, Emma. "A direct imaging search for substellar and planetary mass companions around white dwarfs." Thesis, University of Leicester, 2008. http://hdl.handle.net/2381/3955.
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Even though the radial velocity technique has detected almost all of the 269 extrasolar planets discovered to date, this method does not directly observe the light from the planet. The ability to directly detect this light would allow spectra of extrasolar planets to be obtained, providing information about their information and evolution through the investigation of their composition and structure. To date, none of the extrasolar planets found using the radial velocity technique have been directly imaged, as these faint companions are too close to their bright parent stars. White dwarfs are intrinsically faint objects and can be upto 10,000 times less luminous than their main sequence progenitors, substantially increasing the probability of directly imaging an extrasolar planet in orbit around them. The Degenerate Objects around Degenerate Objects (DODO) survey aims to obtain a direct image of an extrasolar planet in a wide orbit around a white dwarf. By acquiring J band images of 26 equatorial and northern hemisphere white dwarfs a year or two apart, common proper motion companions to the white dwarfs can be identified. The discovery of such a system could supply new information on the frequency and mass distribution of extrasolar planets around intermediate mass main sequence starts and confirm whether these companions can survive the final stages of stellar evolution. In addition, the direct detection of an extrasolar planet in orbit around a white dwarf would allow the spectroscopic investigation of planets much older than any previously found. Using the 24 white dwarfs in the DODO survey within 20pc, the frequency of substellar companions with effective temperatures > 500K and projected physical separations from the white dwarf between 60-200AU is estimated to be <5%. For the same range of projected physical separations, the frequency of substellar companions with masses >10Mjup is estimated to be<9%.
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Knox, Richard Alan. "A survey for cool white dwarfs and the age of the galactic disc." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/30368.
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This thesis describes a survey specifically undertaken to obtain a sample of cool white dwarfs directly from original Schmidt plate material. Concerns regarding of the subjectivity of 'eye-blinked' proper motion measures are avoided by using digitised data obtained using the COSMOS and SuperCOSMOS microdensitometers. The observational material is restricted to a single 6 deg field in which an exceptionally large database of over 300 Schmidt plates exists. As a brief aside, the issue of stacking digitised plate data is examined. In particular, recommendations for the correct weighting algorithm and bad pixel rejection algorithm to adopt are made, following detailed experimentation, with a variety of techniques. The plate stacking technique is used for the white dwarf survey material to extend the photometric survey limits, while the optimum proper motion limit to adopt is investigated in detail, with the principal concern being elimination of contaminants while retaining as many genuine proper motion objects as possible. Application of the reduced proper motion population discrimination technique to the resultant proper motion catalogue results in final sample comprising 56 white dwarf candidates. Follow up spectroscopic observations show the survey has been successful in identifying cool white dwarfs, gives no indication of contamination in the white dwarf sample for other stellar types, and also provides two further cool white dwarfs to include in the sample which were marginally excluded by the reduced proper motion survey criteria. Comparison of photographic colours with model predictions allow effective temperatures and bolometric luminosities to be estimated for the sample members. The luminosity function constructed from the sample members is in good agreement with previous work, although the slightly higher space density found for the coolest white dwarfs leads to a modest increase in the age estimate for the Galactic Disc when the luminosity function is compared to theoretical models. The Disc age is found to be 10-1+3 Gyr.
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Schwartz, Michael J. "A deep infrared photometric survey for Pleiades brown dwarfs toward the deuterium burning limit." Diss., Restricted to subscribing institutions, 2004. http://proquest.umi.com/pqdweb?did=828432841&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Manseau, P. M., P. Bergeron, and E. M. Green. "A SPECTROSCOPIC SEARCH FOR CHEMICALLY STRATIFIED WHITE DWARFS IN THE SLOAN DIGITAL SKY SURVEY." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622679.
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We present a detailed search and analysis of chemically stratified hybrid (traces of helium and hydrogen) white dwarfs in the Sloan Digital Sky Survey (SDSS). Only one stratified white dwarf, PG 1305-017, was known prior to this analysis. The main objective is to confirm the existence of several new stratified objects. We first describe our new generation of stratified model atmospheres, where a thin hydrogen layer floats in diffusive equilibrium on top of a more massive helium layer. We then present the results of our search for hot (T-eff > 30,000 K) white dwarfs with a hybrid spectral type among the similar to 38,000 white dwarf spectra listed in the SDSS. A total of 51 spectra were retained in our final sample, which we analyze using spectroscopic fits to both chemically homogeneous and stratified model atmospheres. We identify 14 new stratified white dwarfs in the SDSS sample. From these results, we draw several conclusions regarding the physical processes that might explain the presence of helium in the atmospheres of all the stars in our sample.
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Faedi, Francesca. "Variable white dwarfs in the SuperWASP archive : a search for sub-stellar and planetary companions." Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/7944.
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This PhD thesis is an investigation of the characteristics and detection limits for transit signals due to sub-stellar and terrestrial companions to white dwarfs in the SuperWASP survey. The work is described as follow: there is an introductory chapter on the field of white dwarfs and exoplanets. In chapter 2 I describe the SuperWASP project, the two SuperWASP telescopes the problematics of data analysis and the results obtained so far. In chapter 3 I discuss the simulations I performed to investigate the characteristics of the transit signals due to sub-stellar and planetary companions to white dwarfs and the detection limits derived for SuperWASP light-curves by means of my optimised version of Box-Least Square (BLS) algorithm. In chapter 4 I present a study of 194 spectroscopically identified white dwarfs which are a cross-correlation of the McCook & Sion catalogue and the SuperWASP archive. In addition, I derive upper limits to the frequency of sub-stellar and planetary companions to white dwarfs using my sample and the results obtained from my simulations. In chapter 5 I present a variability study for the sample of 194 white dwarfs. I have investigated the light-curves of the 194 white dwarfs in the sample to search for photometric variability due to non-radial pulsations, the presence of star spots in magnetic white dwarfs, and to irradiation and reflection effects on low-mass close companions. Finally, in chapter 6 I conclude and present my project for future work.
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Hardegree-Ullman, Kevin Karlyle. "Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533214839813619.
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Cheng, Wing-hong, and 鄭穎康. "Tidal evolution of Pluto-Charon and the implications for the origin ofthe satellites Nix and Hydra." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B45846856.
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Schmidt, Sarah J., Erika L. Wagoner, Jennifer A. Johnson, James R. A. Davenport, Keivan G. Stassun, Diogo Souto, and Jian Ge. "Examining the relationships between colour, T eff , and [M/H] for APOGEE K and M dwarfs." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/621724.
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We present the effective temperatures (T-eff), metallicities, and colours in Sloan Digital Sky Survey (SDSS), Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer filters, of a sample of 3834 late-K and early-M dwarfs selected from the SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectroscopic survey ASPCAP (APOGEE Stellar Parameters and Chemical Abundances Pipeline) catalogue. We confirm that ASPCAP T-eff values between 3550 < T-eff < 4200 K are accurate to similar to 100 K compared to interferometric T-eff values. In that same T-eff range, ASPCAP metallicities are accurate to 0.18 dex between -1.0 <[M/H]< 0.2. For these cool dwarfs, nearly every colour is sensitive to both T-eff and metallicity. Notably, we find that g - r is not a good indicator of metallicity for near-solar metallicity early-M dwarfs. We confirm that J - K-S colour is strongly dependent on metallicity, and find that W1 - W2 colour is a promising metallicity indicator. Comparison of the late-K and early-M dwarf colours, metallicities, and T-eff to those from three different model grids shows reasonable agreement in r - z and J - K-S colours, but poor agreement in u - g, g - r, and W1 - W2. Comparison of the metallicities of the KM dwarf sample to those from previous colour-metallicity relations reveals a lack of consensus in photometric metallicity indicators for late-K and early-M dwarfs. We also present empirical relations for T-eff as a function of r - z colour combined with either [M/H] or W1 - W2 colour, and for [M/H] as a function of r - z and W1 - W2 colour. These relations yield T-eff to similar to 100 K and [M/H] to similar to 0.18 dex precision with colours alone, for T-eff in the range of 3550-4200 K and [M/H] in the range of -0.5-0.2.
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Borrell, James S. "Ecological genomics for the conservation of Dwarf Birch." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24556.
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The persistence of woody plant populations faces numerous environmental challenges, including climate change, hybridisation and population fragmentation. Here I explore the genomic signatures and relative importance of these pressures in Dwarf Birch (Betula nana), which has declined significantly over the last century across the Scottish Highlands. Firstly, I find that future climate is likely to result in a significant range reduction and that relict populations are likely to display reduced fitness. Secondly, I show that combining multiple mutation rate markers yields more accurate estimates of demographic history and the impact of fragmentation. I develop a novel method to derive high mutation rate markers from short sequencing reads, to facilitate more widespread application. Thirdly, I assess the degree of local adaptation, and explore potential for composite provenancing for the restoration of B. nana populations. Surprisingly, the data yields little evidence of adaptive introgression from the related tree B. pubescens, suggesting that this may not be an alternative route to climate tolerance. Finally, I review published literature on the population structure and genetic diversity of genus Betula in Europe and consider options for the conservation and management of B. nana, including assisted gene flow and prioritization of in situ genetic diversity.
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Zhou, Yifan, Dániel Apai, Ben W. P. Lew, and Glenn Schneider. "A Physical Model-based Correction for Charge Traps in the Hubble Space Telescope’s Wide Field Camera 3 Near-IR Detector and Its Applications to Transiting Exoplanets and Brown Dwarfs." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625388.
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The Hubble Space Telescope Wide Field Camera 3 (WFC3) near-IR channel is extensively used in time-resolved observations, especially for transiting exoplanet spectroscopy as well as. brown dwarf and directly imaged exoplanet rotational phase mapping. The ramp effect is the dominant source of systematics in the WFC3 for time-resolved observations, which limits its photometric precision. Current mitigation strategies are based on empirical fits and require additional orbits to help the telescope reach a thermal equilibrium. We show that the ramp-effect profiles can be explained and corrected with high fidelity using charge trapping theories. We also present a model for this process that can be used to predict and to correct charge trap systematics. Our model is based on a very small number of parameters that are intrinsic to the detector. We find that these parameters are very stable between the different data sets, and we provide best-fit values. Our model is tested with more than 120 orbits (similar to 40 visits) of WFC3 observations. and is proved to be able to provide near photon noise limited corrections for observations made with both staring and scanning modes of transiting exoplanets as well as for starting-mode observations of brown dwarfs. After our model correction, the light curve of the first orbit in each visit has the same photometric precision as subsequent orbits, so data from the first orbit no longer need. to. be discarded. Near-IR arrays with the same physical characteristics (e.g., JWST/NIRCam) may also benefit from the extension of this model if similar systematic profiles are observed.
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Sakaue, Takahito. "Nonlinear Alfvén Wave Model for Solar/Stellar Chromosphere, Corona and Wind from the Sun to M Dwarfs." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263472.
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Levenhagen, Ronaldo S., Marcos P. Diaz, Paula R. T. Coelho, and Ivan Hubeny. "A Grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624926.
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In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA white dwarfs (WDs). In addition to its usefulness for the determination of fundamental stellar parameters of isolated WDs and in binaries, this grid will be of interest for the construction of theoretical libraries for stellar studies from integrated light. The spectral grid covers both a wide temperature and gravity range, with 17,000 K <= T-eff <= 100,000 K and 7.0 <= log g <= 9.5. The stellar models are built for pure hydrogen and the spectra cover a wavelength range from 900 angstrom to 2.5 mu m. Additionally, we derive synthetic HST/ACS, HST/WFC3, Bessel UBVRI, and SDSS magnitudes. The grid was also used to model integrated spectral energy distributions of simple stellar populations and our modeling suggests that DAs might be detectable in ultraviolet bands for populations older than similar to 8 Gyr.
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Toloza, O., B. T. Gänsicke, J. J. Hermes, D. M. Townsley, M. R. Schreiber, P. Szkody, A. Pala, et al. "GW Librae: a unique laboratory for pulsations in an accreting white dwarf." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/621433.
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Non-radial pulsations have been identified in a number of accreting white dwarfs in cataclysmic variables. These stars offer insight into the excitation of pulsation modes in atmospheres with mixed compositions of hydrogen, helium, and metals, and the response of these modes to changes in the white dwarf temperature. Among all pulsating cataclysmic variable white dwarfs, GW Librae stands out by having a well-established observational record of three independent pulsation modes that disappeared when the white dwarf temperature rose dramatically following its 2007 accretion outburst. Our analysis of Hubble Space Telescope (HST) ultraviolet spectroscopy taken in 2002, 2010, and 2011, showed that pulsations produce variations in the white dwarf effective temperature as predicted by theory. Additionally in 2013 May, we obtained new HST/Cosmic Origin Spectrograph ultraviolet observations that displayed unexpected behaviour: besides showing variability at a parts per thousand integral 275 s, which is close to the post-outburst pulsations detected with HST in 2010 and 2011, the white dwarf exhibits high-amplitude variability on an a parts per thousand integral 4.4 h time-scale. We demonstrate that this variability is produced by an increase of the temperature of a region on white dwarf covering up to a parts per thousand integral 30 per cent of the visible white dwarf surface. We argue against a short-lived accretion episode as the explanation of such heating, and discuss this event in the context of non-radial pulsations on a rapidly rotating star.
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Willman, Beth. "A survey for resolved Milky Way dwarf galaxy satellites /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/5445.
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Draper, Christian D. "Search for Dwarf Emission Line Galaxies in Galaxy Voids." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7604.
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The population and formation of dwarf galaxies, Mr > −14, contain clues about the nature of dark matter. The best place to search for these dwarf galaxies without influence from nearby large galaxies is within galaxy voids, where no galaxies have yet been found. To search for this potential dwarf galaxy population we have developed and applied a new photometric technique. We use three redshifted Ha filters, designated Ha8, Ha12, and Ha16, along with the Sloan broadband filters, g', r', and i' to identify emission line galaxies. From the ratio of the object flux through the Ha filters, Ha12-Ha8 and Ha12-Ha16, we are able to determine the distance to these galaxies and the strength of the emission line captured in the filter set. One problem with using just the three Ha filters is that the system will be sensitive to any emission line which has been redshifted enough to fall within the set. Of particular concern are the [OII] and [OIII] lines which will contaminate the sample. To overcome this we use a color-color relation, g' - r' and r' - i', to help separate which type of emission has been detected. We have applied this method to search for galaxies within the void FN2 and FN8. From this we have found 23 candidate objects which could have Ha emission placing them inside of the void. To better understand the population density dwarf galaxies through voids we have also modeled the population of objects which we will detect having Ha emission compared to the contamination of back ground objects which we can then use to compare the density in the void with the mean galaxy density. We have also begun taking spectra of the emission objects, to ensure our method does detect emission line objects, to test how well the distance and emission strength determination is, and to begin identifying which type of emission we have detected. To date we have taken spectra on 6 objects. All 6 showed emission, 4 with [OII] and 2 with [OIII]. Though none was Ha we formed a “pseudo-redshift” to determine the accuracy of our measurements. This shows that our method is accurate to -127+-204 km/sec.
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Saffer, R. A., and J. Liebert. "Search for Close Binary Evolved Stars." Steward Observatory, The University of Arizona (Tucson, Arizona), 1988. http://hdl.handle.net/10150/623897.
Full textAbstract:
We report on a search for short -period binary systems composed of pairs of
evolved stars. The search is being carried out concurrently with a program to characterize
the kinematical properties of two different samples of stars. Each sample has produced one
close binary candidate for which further spectroscopic observations are planned. We also
recapitulate the discovery of a close detached binary system composed of two cool DA
white dwarfs, and we discuss the null results of Ha observations of the suspected white
dwarf /brown dwarf system G 29-38.
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Halm, Grant Bernard. "Domestic market opportunities for high yielding semi-dwarf wheat varieties." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61963.
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Sismanis, Yannis. "Dwarf a complete system for analyzing high-dimensional data sets /." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1876.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Computer Science. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Roberts, Sarah. "Search for low surface brightness dwarf galaxies in different environments." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56002/.
Full textAbstract:
Current theories of large scale structure and galaxy formation predict the existence of numerous low mass dark matter haloes in the Universe today. If these haloes contain sufficient stars they should be detectable as low luminosity stellar systems or dwarf galaxies. We have searched for these objects in four regions of increasing density - the general field, the area around a giant spiral galaxy, the low density Ursa Major cluster, and the high density Virgo cluster. Using identical deep optical data covering a total of 602 and probing fainter magnitudes than has been done previously, we used identical selection and detection methods to compare the dwarf galaxy populations in these different environments. We found substantially more dwarfs per giant galaxy in the Virgo cluster (20:1) compared to the field environment (6:1 max). A comparison of the HI properties and (B-I) colours for the objects for which we had additional data also showed that in general, the cluster objects are redder and gas poor compared to the objects in the field. We discuss the possible mechanisms which may have resulted in creating a population of cluster dwarf galaxies, which would explain the high number density which we found in our data. It is likely that a combination of tidal interactions and transformation of infalling dlrrs into dEs will result in the large population of cluster dwarfs. Conclusive evidence regarding their formation must now be obtained by a more detailed investigation of their stellar populations. The lack of dwarf galaxies in the field region is likely to be due to the effect of inefficient star formation in the field environment compared to the cluster. Thus the low mass dark matter haloes predicted by CDM models must still be 'dark' and can only be identified by further deep HI studies of the field environment, and future gravitational lensing studies of substructure.
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Kirkpatrick, Joseph Davy. "Spectroscopic and photometric studies of main sequence M stars and a search for late-type dwarfs in the solar vicinity." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185978.
Full textAbstract:
As any introductory astronomy student knows, M dwarfs are the most common stars in the Galaxy and are the faintest of the core hydrogen burners. A comprehensive study of these faint objects is crucial to our understanding of the stellar composition of the Galaxy and necessary for a more complete knowledge of the transition between main sequence M stars and their slightly less massive counterparts, the brown dwarfs, which never achieve hydrogen burning in their cores. In this thesis, a spectroscopic catalog of 125 K and M dwarfs is first presented. This catalog covers the wavelength range from 6300 to 9000 Å, near where these objects emit most of their light. Eight of these spectra, covering classes M2 through M9, are combined with infrared spectra from 0.9 to 1.5 μm to create a second catalog. The two sets of spectra are used to search for temperature-sensitive atomic lines and molecular bands, which are then used in fitting the observed spectra to a sequence of theoretical models. As a result, a new temperature scale for M dwarfs is determined, and this scale is more accurate than previous determinations which have depended on blackbody energy distributions. The sequence of spectra is also used to compare the spectrum of the brown dwarf candidate GD 165 B to known M dwarfs. Furthermore, the spectral catalog is used in an attempt to separate the spectra of faint companions from their M dwarf primaries in systems where the two objects are too close for conventional spectroscopy to resolve the individual components. A survey for faint M dwarfs is also launched using the data acquired through the CCD/Transit Instrument (CTI) on Kitt Peak, Arizona. Follow-up spectroscopy is presented for 133 of these objects, and several more very late M dwarfs are identified. This spectroscopy combined with photometric data from the CTI are used to construct a luminosity function for M dwarfs which is in excellent agreement with determinations from previous surveys. Finally, possible avenues for future work are discussed. These include spectroscopic follow-up of the reddest of Luyten's proper motion objects--the first results from which have uncovered, in just twelve observations, two objects of type M7 and one of type M8, among the coolest objects yet recognized. Future searches, such as an all-sky survey for objects of extremely high proper motion, are also outlined.
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Greco, Claudia <1979>. "Looking for the building blocks of the Galactic halo: variable stars in Fornax and bootes Dwarfs and in NGC 2419." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/362/.
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Ramos, Gabriel Lauffer. "Evolutionary sequences for H and He atmosphere massive white dwarf stars." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/181005.
Full textAbstract:
White dwarf stars are the most common final stage of stellar evolution, corresponding to 99% of all stars in the Galaxy. White dwarf models can be used to obtain the age of stellar populations, to build an initial to final mass relation to understand the connection between the properties of white dwarfs and their progenitors, determine the upper mass limit that separates white dwarfs progenitors from Type II supernovae, enhance the comprehension of the physical properties of high density matter and derive ages and masses for observed white dwarfs from the cooling tracks. The literature is populated with low mass and intermediate mass white dwarf models, however the massive white dwarfs are often forgotten and the evolutionary sequences are incomplete. In this dissertation, we compute full evolutionary sequences for massive white dwarfs, exploring the evolution of hydrogen-rich and hydrogen-deficient white dwarfs stars with masses between 1.012 and 1.307 M , and initial metallicity of Z = 0.02. These sequences are the result of main sequence stars with masses between 8.8 and 11.8 M . The simulations were performed with the Modules for Experiments in Stellar Astrophysics - MESA code, starting at the zero-age main sequence, through thermally pulsing and mass-loss phases, ending as the white dwarfs at the cooling sequence. Our simulations are full evolutionary, in which we consider the entire evolutionary history of the progenitors. We present reliable nuclear chemical profiles for the whole mass range considered, covering the different expected central compositions, i.e. C/O, O/Ne and Ne/O/Mg, and their dependence with the stellar mass. In addition, we present detailed chemical profiles of hybrid C/O-O/Ne core white dwarfs, found in the mass range between 1.024 and 1.150 M . We present the initial-to-final mass relation, mass-radius relation, and cooling times with improved crystallization limits, considering the effects of atmosphere and core composition.
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Henry, Todd Jackson. "A systematic search for low-mass companions orbiting nearby stars and the calibration of the end of the stellar main sequence." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185689.
Full textAbstract:
We have completed a search for low luminosity companions, including high mass brown dwarfs, to all M dwarfs known within eight parsecs of the sun, and north of -25°. We found six new companions orbiting the survey stars. The masses of the six new secondaries fall between 0.39 and 0.05 M(⊙). Three of the new companions, G208-44B, GL 623B and LHS 1047B, and one previously known secondary in the survey, Ross 614B, are brown dwarf candidates with masses ∼80 Jupiters (0.08 M(⊙)), the dividing line between stars and brown dwarfs. In addition, we provide infrared photometry at J, H and K for all 99 survey members, and spectral types on standard system for half. Analysis of the entire sample indicates that 50% of the stars in the more distant half of the survey volume remain undetected, as is supported by the steadily growing M dwarf census over the last 45 years. The binary fraction of M dwarfs, 30-40%, is lower than that of earlier type main sequence stars, and there are more companions to M dwarfs found between 1 and 10 AU than in any other decade interval. We find that the luminosity function of the lowest mass stars is flat or rising to the end of the main sequence, and that the mass function undoubtedly rises to the stellar/substellar break. We illustrate that the resolution of close binaries is crucial if accurate luminosity and mass functions are to be determined. Finally, we estimate 0.02 M(⊙)/pc³ to be the amount of mass contributed by M dwarfs to the galactic mass. Based upon new mass-luminosity relations developed at infrared wavelengths using a sample of stars with well-determined masses between 1.2 and 0.08 M(⊙), we are able to define empirically the end of the main sequence. We present absolute magnitudes, colors and spectral types for objects at the theoretical lowest stellar mass. Using these relations, we conclude that a few brown dwarfs may have already been discovered. (Abstract shortened with permission of author.)
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Paltridge, Nicholas G. "The development of molecular markers for barley Yd2, the barley yellow dwarf virus resistance gene /." Title page, contents and summary only, 1998. http://web4.library.adelaide.edu.au/theses/09APSP/09apspp183.pdf.
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Schimeczek, Christoph [Verfasser], and Günter [Akademischer Betreuer] Wunner. "2D calculations for atoms and ions in strong magnetic fields of white dwarfs and neutron stars / Christoph Schimeczek. Betreuer: Günter Wunner." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1047337266/34.
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Flateau, Davin C. "Weather on Other Worlds IV: In-Depth Study of Photometric Variability and Radiative Timescales for Atmospheric Evolution in Four L Dwarfs." Thesis, The University of Arizona, 2015. http://hdl.handle.net/10150/594630.
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Rotational phase mapping of brown dwarfs allows exploration of different cloud and photospheric properties within the same atmospheres, allowing a separation of these parameters from global parameters, such as composition, surface gravity, and age. This work presents an in-depth characterization of high SNR light curves from the Spitzer Space Telescope with up to 13 hours of continuous monitoring of four dwarfs spanning the L3 to L8 spectral type. An exhaustive exploration of currently available state-of-the-art models explains the observed color changes for two of these dwarfs with a linear combination of two model cloudy surfaces differing in effective temperature, cloud opacity and vertical mixing. Using state-of-the-art purely radiative convective atmospheric models, we calculate basic radiative timescales for temperature perturbations in the atmosphere, and consider the effects of dynamics on these timescales. Along with dynamical atmospheric advection timescales, we discuss the relationships between model timescales and the observed light curve evolution.
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Häuser, Marco Verfasser], and Ralf [Akademischer Betreuer] [Bender. "Radial velocity measurements for white-dwarf/brown-dwarf binarie candidates and development of an active mirror control for the 11 m Hobby-Eberly-Telescope / Marco Häuser ; Betreuer: Ralf Bender." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1196529205/34.
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Häuser, Marco [Verfasser], and Ralf [Akademischer Betreuer] Bender. "Radial velocity measurements for white-dwarf/brown-dwarf binarie candidates and development of an active mirror control for the 11 m Hobby-Eberly-Telescope / Marco Häuser ; Betreuer: Ralf Bender." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1196529205/34.
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Bigi, Patrick. "A search for radio signatures of Dark Matter particles in the Draco dwarf galaxy." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25345/.
Full textAbstract:
Dark Matter is a fundamental component of the Universe both on Galactic
and cosmological scales, albeit its intrinsic nature is still largely unknown. Weakly
interactive massive particles (WIMPs) have been a long standing Dark Matter
particle candidate from the theory stand point, although they have not received
observational confirmation so far. Theoretical models suggest that WIMPs can
annihilate/decay into electron/positron pairs and, in the presence of magnetic
fields, such relativistic electrons would generate an observable synchrotron radio
emission that would be the footprint of the WIMP particle and its cross section.
In this thesis we present a search for the radio signature of Dark Matter
particles in the Draco dwarf spheroidal galaxy with Giant Metrewave Radio
Telescope observations. We analyzed observations from the GMRT, taken with
a large bandwidth around 650 MHz and with full array configuration in order to
obtain the maximum sensitivity. We used long baselines to identify and remove
compact sources, leading to a final image with 20.5′′ angular resolution and a
230 μJy beam−1 rms noise. We modeled the DM-induced synchrotron emission
in Draco in order to place constraints to the annihilation cross section from our
observations.
We found marginal evidence (σ = 1.97) of a diffuse signal over the whole field of
view that is unlikely due to DM but to residual artifacts left in the image after source
subtraction. We still present best fits on the annihilation cross section of WIMPs
assuming that the signal was due to DM. A best fit cross section of ∼10−23 cm3 s−1
is obtained at 100 GeV for different annihilation channels. We estimate the best
noise rms image that we could achieve with improved calibration/subtraction and
we use it to place upper limits near 2 ·10−24 cm3 s−1 on the DM cross section for
100 GeV particle mass. We discuss our result in the light of the current literature
constraints and explore alternative models for the theoretical emission.
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Ottman, Michael, and Joy M. Hought. "Recommendations for Growing Standard-Height Wheat Varieties in Arizona." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2014. http://hdl.handle.net/10150/311218.
Full textAbstract:
2 pp.Until the introduction of semi-dwarf wheat in the late 1960s, wheat varieties were typically one and a half to two times their current height. Most heirloom, traditional, or landrace varieties are considered standard-height wheat (e.g. Sonoran white); in general they are adapted to lower-input conditions, and cannot tolerate high-fertility environments without lodging. Lodging reduces grain yield, delays harvest, and increases harvesting costs. Standard-height wheat needs to be grown at a lower plant density and with less nitrogen and irrigation water than semi-dwarfs in order to prevent lodging, optimize yield, and make the most efficient use of resources.
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Wang, Yu. "HPLC method development for the evaluation of pheromones from the dwarf African clawed frog Hymenochirus." Scholarly Commons, 2003. https://scholarlycommons.pacific.edu/uop_etds/587.
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Martinez, Arturo O., Ian J. M. Crossfield, Joshua E. Schlieder, Courtney D. Dressing, Christian Obermeier, John Livingston, Simona Ciceri, et al. "Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623204.
Full textAbstract:
The NASA K2 mission uses photometry to find planets transiting stars of various types. M dwarfs are of high interest since they host more short-period planets than any other type of main-sequence star and transiting planets around M dwarfs have deeper transits compared to other main-sequence stars. In this paper, we present stellar parameters from K and M dwarfs hosting transiting planet candidates discovered by our team. Using the SOFI spectrograph on the European Southern Observatory's New Technology Telescope, we obtained R approximate to 1000 J-, H-, and K-band (0.95-2.52 mu m) spectra of 34 late-type K2 planet and candidate planet host systems and 12 bright K4-M5 dwarfs with interferometrically measured radii and effective temperatures. Out of our 34 late-type K2 targets, we identify 27 of these stars as M dwarfs. We measure equivalent widths of spectral features, derive calibration relations using stars with interferometric measurements, and estimate stellar radii, effective temperatures, masses, and luminosities for the K2 planet hosts. Our calibrations provide radii and temperatures with median uncertainties of 0.059 R-circle dot (16.09%) and 160 K (4.33%), respectively. We then reassess the radii and equilibrium temperatures of known and candidate planets based on our spectroscopically derived stellar parameters. Since a planet's radius and equilibrium temperature depend on the parameters of its host star, our study provides more precise planetary parameters for planets and candidates orbiting late-type stars observed with K2. We find a median planet radius and an equilibrium temperature of approximately 3 R-circle plus and 500 K, respectively, with several systems (K2-18b and K2-72e) receiving near-Earth-like levels of incident irradiation.
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Trusler, Jonathan. "Searching for the role of ICTs in development : a case study of a rural multi-purpose community centre in the Dwars River Valley, South Africa." Master's thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/5654.
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Bibliography: leaves 94-99.This dissertation examines ICTs and their role in development. It explores a single case study of a rural Multi-Purpose Community Centre in South Africa in an attempt to gain a richer understanding of the issues surrounding the implementation of such centres. The study is socio-technical in nature and is based on a framework composed of interpretivism, hermeneutics and the actor-network theory. Key issues explored include: the affect of ICTs on the emergence of a local champion; the struggle of creating active participants in a project of this nature; and the usefulness of replication models in guiding implementations.
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Rackham, Benjamin V., Dániel Apai, and Mark S. Giampapa. "The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627040.
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Transmission spectra are differential measurements that utilize stellar illumination to probe transiting exoplanet atmospheres. Any spectral difference between the illuminating light source and the disk-integrated stellar spectrum due to starspots and faculae will be imprinted in the observed transmission spectrum. However,. few constraints exist for the extent of photospheric heterogeneities in M dwarfs. Here we model spot and faculae covering fractions consistent with observed photometric variabilities for M dwarfs and the associated 0.3-5.5. mu m stellar contamination spectra. We find that large ranges of spot and faculae covering fractions are consistent with observations and corrections assuming a linear relation between variability amplitude, and covering fractions generally underestimate the stellar contamination. Using realistic estimates for spot and faculae covering fractions, we find that stellar contamination can be more than 10x. larger than the transit depth changes expected for atmospheric features in rocky exoplanets. We also find that stellar spectral contamination can lead to systematic errors in radius and therefore the derived density of small planets. In the case of the TRAPPIST-1 system, we show that TRAPPIST-1 ' s rotational variability is consistent with spot covering fractions f(spot) = 8(7)(+18)% and faculae covering fractions f(fac) = 54(-46)(+16)%. The associated stellar contamination signals alter the transit depths of the TRAPPIST-1 planets at wavelengths of interest for planetary atmospheric species by roughly 1-15x. the strength of planetary features, significantly complicating JWST follow-up observations of this system. Similarly, we find that stellar contamination can lead to underestimates of the bulk densities of the TRAPPIST-1 planets of Delta(rho) = -8(-20)(+7)%, thus leading to overestimates of their volatile contents.
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Cashmore, Claire R. "The puzzling problems of the local group dwarf spheroidals : the fight for survival in the early universe." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/43053.
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The dwarf spheroidal galaxies (dSphs) of our Local Group pose challenges to our theories of galaxy formation and evolution in a ΛCDM Universe. Despite the wealth of information available from these systems provided by their close proximity, little is understood about their individual histories. The faintest dSphs host a single, ancient stellar population, the formation of stars in these galaxies ceased billions of years ago and they are devoid of gas. As these systems are so small, they are susceptible to gas loss, however this cannot be a simple process due to the diverse range of properties they exhibit, despite residing in haloes of the same mass. In this thesis I address two processes resulting in gas removal at early times and attempt to further our understanding of these systems by isolating each process. I use hydrodynamical simulations to explore the impact of each process to asses their significance and to identify the dominant influences on their evolution. Firstly I simulate the effect of SNe feedback on dSph progenitors undergoing an initial burst of star formation at high redshift (z~10) and the conditions under which they retain gas. In order to host an extended burst of star formation the number of supernovae must be lower than that expected if we assume star formation proceeds in a similar fashion to that in larger galaxies. The impact of an AGN outflow originating from the Milky Way on the surrounding dwarf galaxies is also simulated, which easily strips gas from these systems, leaving behind a halo with an ancient stellar population. The difficulty of retaining gas in the early Universe could be alleviated if they accreted gas during the period of extended star formation. I investigate these three process in the context of isolated dwarfs.
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Wang, Yu. "HPLC method development for the evaluation of pheromones from the dwarf African clawed frog Hymenochirus : a thesis." Scholarly Commons, 2001. https://scholarlycommons.pacific.edu/uop_etds/587.
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Walentosky, Matthew J. "ON THE NATURE OF RADIAL DISPERSION PROFILES FOR DWARF SPHEROIDAL GALAXIES IN THE LOCAL GROUP ACCORDING TO MOND." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1462970320.
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Collins, Michelle L. M., Erik J. Tollerud, David J. Sand, Ana Bonaca, Beth Willman, and Jay Strader. "Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623924.
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We present a chemodynamical analysis of the Leo V dwarf galaxy, based on the Keck II DEIMOS spectra of eight member stars. We find a systemic velocity for the system of nu(r) = 170.9(+2.1) (-1.9) km s(-1) and barely resolve a velocity dispersion for the system, with sigma nu(r) = 2.3(+3.2) (-1.6) km s(-1), consistent with previous studies of Leo V. The poorly resolved dispersion means we are unable to adequately constrain the dark-matter content of Leo V. We find an average metallicity for the dwarf of [ Fe/ H] =-2.48 +/- 0.21 and measure a significant spread in the iron abundance of its member stars, with -3.1 <= [ Fe/ H] <=-1.9 dex, which clearly identifies Leo V as a dwarf galaxy that has been able to self-enrich its stellar population through extended star formation. Owing to the tentative photometric evidence for the tidal substructure around Leo V, we also investigate whether there is any evidence for tidal stripping or shocking of the system within its dynamics. We measure a significant velocity gradient across the system, of dv d chi = -4.1(+2.8) (-2.6) km s(-1) arcmin(-1) ( or d nu/d chi=-71.9(vertical bar 50.8) (-45.6) km s(-1) kpc(-1)), which points almost directly towards the Galactic Centre. We argue that Leo V is likely a dwarf on the brink of dissolution, having just barely survived a past encounter with the centre of the Milky Way.
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Brüns, Renate Claudia [Verfasser]. "A Unified Formation Scenario for the Zoo of Extended Star Clusters and Ultra-Compact Dwarf Galaxies / Renate Claudia Brüns." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1238687687/34.
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Salihu, Sydha. "Basis for Selectivity of Isoxaben in Ajuga (Ajuga reptans), Wintercreeper (Euonymus fortunie), and Dwarf Burning Bush (Euonymus alatus 'Compacta')." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30285.
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Isoxaben is a preemergence herbicide used for broadleaf weed control in turf and ornamentals. Although isoxaben can be used on a number of ornamentals, certain species are injured by isoxaben applications. The objectives of this research were: a) to evaluate the tolerance of ajuga, wintercreeper and dwarf burning bush to isoxaben applications, b) to compare the absorption, translocation and metabolism of isoxaben following root and shoot application in these ornamentals, and c) to examine the effect of isoxaben on glucose incorporation in the roots of these species.
Greenhouse and lathhouse studies demonstrated that ajuga was the most sensitive species compared to wintercreeper and dwarf burning bush following root and shoot exposure to isoxaben at 0.84, 1.69 and 3.39 kg ai/ha. Following root and shoot application, isoxaben at 3.39 kg/ha caused approximately 50% shoot injury in ajuga at 2 months after treatment compared to approximately 30% in dwarf burning bush in sand culture. Wintercreeper was not visually injured by any isoxaben rate. Isoxaben at 3.39 kg/ha reduced wintercreeper root weight by 15% following root application and shoot weight by 10% following shoot application.
Field studies showed that isoxaben applications made one month after bud-break caused 30 to 45% injury to dwarf burning bush. However, the plants outgrew the injury in the following year. Dwarf burning bush was not injured from applications of isoxaben made at the dormant stage or two months after the bud-break stage.
Studies with root-applied radiolabeled isoxaben showed that ajuga and dwarf burning bush had absorbed 34 and 41% of the applied radioactivity, respectively, while wintercreeper had absorbed only 21% at 14 days after treatment (DAT). The percent of absorbed radioactivity which translocated was greater in ajuga (58%) and wintercreeper (50%) than in dwarf burning bush (28%). In the root extracts, metabolism of isoxaben was greater in ajuga than wintercreeper or dwarf burning bush at 3, 7 and 14 DAT. Most of the radioactivity recovered from the shoots of the three species appeared to be polar metabolites of isoxaben, possibly conjugates.
In studies with shoot-applied radiolabeled isoxaben, radioactivity recovered from the treated leaf of ajuga increased from 46% of applied at 3 days to 64% at 14 days after treatment. In wintercreeper, the most tolerant species, approximately 40% of the applied radioactivity was recovered in the treated leaf at each harvest date. Radioactivity recovered from the treated leaflet increased from 45 at 3 DAT to 70% at 14 DAT in both growth stages of dwarf burning bush. Ajuga and wintercreeper metabolized isoxaben faster than dwarf burning bush. There was no difference in the metabolism of isoxaben between the two growth stages of dwarf burning bush. Incorporation of glucose in the roots of wintercreeper and dwarf burning bush was not inhibited by isoxaben (1 mM). Approximately 10% inhibition of glucose incorporation by isoxaben was observed in the roots of the sensitive species ajuga.Ph. D.