Journal articles: 'Stellar associations'

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Kalloghlian, A. T. "Stellar associations." Astrophysics 52, no. 2 (April 2009): 157–67. http://dx.doi.org/10.1007/s10511-009-9066-4.

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Quillen, Alice C., Alex R. Pettitt, Sukanya Chakrabarti, Yifan Zhang, Jonathan Gagné, and Ivan Minchev. "Birth sites of young stellar associations and recent star formation in a flocculent corrugated disc." Monthly Notices of the Royal Astronomical Society 499, no. 4 (October 15, 2020): 5623–40. http://dx.doi.org/10.1093/mnras/staa3189.

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ABSTRACT With backwards orbit integration, we estimate birth locations of young stellar associations and moving groups identified in the solar neighbourhood that are younger than 70 Myr. The birth locations of most of these stellar associations are at a smaller galactocentric radius than the Sun, implying that their stars moved radially outwards after birth. Exceptions to this rule are the Argus and Octans associations, which formed outside the Sun’s galactocentric radius. Variations in birth heights of the stellar associations suggest that they were born in a filamentary and corrugated disc of molecular clouds, similar to that inferred from the current filamentary molecular cloud distribution and dust extinction maps. Multiple spiral arm features with different but near corotation pattern speeds and at different heights could account for the stellar association birth sites. We find that the young stellar associations are located in between peaks in the radial/tangential (UV) stellar velocity distribution for stars in the solar neighbourhood. This would be expected if they were born in a spiral arm, which perturbs stellar orbits that cross it. In contrast, stellar associations seem to be located near peaks in the vertical phase-space distribution, suggesting that the gas in which stellar associations are born moves vertically together with the low-velocity dispersion disc stars.

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Ivanov, G. R. "Stellar associations in M81." Monthly Notices of the Royal Astronomical Society 257, no. 1 (July 1, 1992): 119–24. http://dx.doi.org/10.1093/mnras/257.1.119.

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Moskal, E. V., and V. G. Surdin. "Dynamical models of stellar associations." Astronomical & Astrophysical Transactions 15, no. 1-4 (April 1998): 37–43. http://dx.doi.org/10.1080/10556799808201748.

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Kontizas, E., M. Kontizas, D. Gouliermis, A. Dapergolas, R. Korakitis, and D. H. Morgan. "Stellar Associations in the LMC." Symposium - International Astronomical Union 190 (1999): 410–16. http://dx.doi.org/10.1017/s007418090011842x.

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The stellar associations are defined as loose unbound concentrations of young stars with a bright OB stellar component, mainly located at the most recent star forming regions, representing the smallest units in the hierarchy of stellar systems in galaxies. The definition of the associations is discussed and the main properties of their stellar content are summarized. Using plates taken with the 1.2m UK Schmidt Telescope a method is developed to detect all stellar associations in the LMC and to find their spatial distribution relative to the LMC's recent star formation history. In 40% of the LMC region, the number of “single peak” associations has increased considerably (~ 3x). A very interesting result is that the faint limit, where the identified associations are revealed, varies by about 3 mag. This indicates not only extinction differences but also the presence of pre-main sequence stars at a wide range of masses.

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Efremov, Yu N., G. R. Ivanov, and N. S. Nikolov. "New Stellar Associations in M31." Symposium - International Astronomical Union 116 (1986): 389–90. http://dx.doi.org/10.1017/s0074180900149216.

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About twenty years ago van den Bergh (1964) recognized 188 OB associations in the Andromeda Nebula. He used plates taken by the 52-inches Tautenburgh Schmidt telescope in GDR. Later on Richter (1971) added 7 new associations in the south-western periphery of M31. Now we have the opportunity to continue the search of stellar associations in M31 with the 2m Ritchey-Chrétien (RC) telescope of the Bulgarian National Astronomical Observatory. The limiting magnitude of this telescope is approximately the same as that of the Tautenburg 2m Schmidt telescope but it possesses somewhat smaller field (1°x1°) with plate-scale 12.8 mm−1. That is why a new search of stellar associations in M31 by means of the 2m RC telescope is very efficient. Indeed, some previous inspections of the RC plates (Efremov, 1982) indicated some new associations in M31.

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Hatzidimitriou, Despina, Charles J. Lada, Ata Sarajedini, Russell D. Cannon, Kyle McC Cudworth, Gary S. Da Costa, LiCai Deng, Young-Wook Lee, Ata Sarajedini, and Monica Tosi. "COMMISSION 37: STAR CLUSTERS AND ASSOCIATIONS." Proceedings of the International Astronomical Union 4, T27A (December 2008): 277–79. http://dx.doi.org/10.1017/s1743921308025684.

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Star clusters are valuable tools for theoretical and observational astronomy across a wide range of disciplines from cosmology to stellar spectroscopy. For example, properties of globular clusters are used to constrain stellar evolutionary models, nucleosynthesis and chemical evolution, as well as the star formation and assembly histories of galaxies and the distribution of dark matter in present-day galaxies. Open clusters are widely used as stellar laboratories for the study of specific stellar phenomena (e.g., various emission-line stars, pulsating pre-MS stars, magnetic massive stars, binarity, stellar rotation, etc.). They also provide observational constraints on models of massive star evolution and of Galactic disk formation and chemical evolution.

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Wood, Mackenna L., Andrew W. Mann, Madyson G. Barber, Jonathan L. Bush, Reilly P. Milburn, Pa Chia Thao, Stephen P. Schmidt, Benjamin M. Tofflemire, and Adam L. Kraus. "A Lithium Depletion Age for the Carina Association." Astronomical Journal 166, no. 6 (November 15, 2023): 247. http://dx.doi.org/10.3847/1538-3881/ad03f3.

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Abstract The dispersed remnants of stellar nurseries, stellar associations, provide unparalleled samples of coeval stars critical for studies of stellar and planetary formation and evolution. The Carina Stellar Association is one of the closest stellar associations to Earth, and yet measurements of its age have varied from 13 to 45 Myr. We aim to update the age of Carina using the lithium depletion boundary (LDB) method. We obtain new measurements of the Li 6708 Å absorption feature in likely members using optical spectra from the Goodman High Throughput Spectrograph on SOAR and NRES on LCO. We detect the depletion boundary at M K ≃ 6.8 (M5). This age is consistent within uncertainties across six different models, including those that account for magnetic fields and spots. We also estimate the age through analysis of the group’s overall variability, and by comparing the association members’ color–magnitude diagram to stellar evolutionary models using a Gaussian Mixture Model, recovering ages consistent with the LDB. Combining these age measures we obtain an age for the Carina association of 41 − 5 + 3 Myr. The resulting age agrees with the older end of previous age measurements and is consistent with the lithium depletion age for the neighboring Tucana-Horologium moving group.

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Hodge, Paul. "Systems of Stellar Associations in Galaxies." Symposium - International Astronomical Union 116 (1986): 369–79. http://dx.doi.org/10.1017/s0074180900149186.

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This paper begins with an attempt to examine the problem of identifying stellar associations in galaxies in a consistent way, so that meaningful physical comparisons can be made for the population of stellar associations of different galaxies. A compilation of the existing data on associations in other galaxies is given and their properties compared. Questions relating to star formation in stellar associations are discussed, and then the issue of the initial mass function of core clusters, especially those located in giant HII regions, is briefly examined.

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de Geus, Eugène, and Tim de Zeeuw. "The Stellar Content of SCO OB2." Symposium - International Astronomical Union 115 (1987): 205–6. http://dx.doi.org/10.1017/s0074180900095553.

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The study of the stellar content of nearby OB associations is important for understanding the Initial Mass Function, the study of differential age effects and for a better knowledge of the ambient radiation field, which plays an important role in the interpretation of measurements of gas and dust. Unfortunately, even for the nearest OB associations membership is known very poorly. In most cases no main sequence members of spectral type later than B5 are known. Membership determination using colour-magnitude diagrams suffers from the large intrinsic distance spread. The large angular extent on the sky of most associations makes proper motion measurements difficult to compare because of problems connecting photographic plates with different plate centers. In order to remedy this situation a consortium called SPECTER has been formed at Leiden Observatory. It has been granted observing time on the HIPPARCOS satellite for measuring proper motions of about 10000 candidate members of the OB associations within 600 pc of the Sun. Candidates were selected according to spectral type (not later than F8) apparent magnitude, and location. In anticipation of the HIPPARCOS results, SPECTER will gather a variety of other data. We have nearly completed a program aimed at obtaining VBLUW-photometry (Lub and Pel 1977) of all candidate stars visible from the Southern Hemisphere. Here we discuss the preliminary results for the association Sco OB2.

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Ivanov, G. R. "Stellar associations and complexes in M33." Astrophysics and Space Science 136, no. 1 (1987): 113–28. http://dx.doi.org/10.1007/bf00661259.

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Mdzinarishvili, T. G. "Relationship between pulsars and stellar associations." Astrophysics 40, no. 1 (January 1997): 36–38. http://dx.doi.org/10.1007/bf02877189.

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Tovmassian, H. M., Y. M. Khodjayants, M. N. Krmoyan, R. V. Isadjanian, O. N. Gasparian, A. Z. Zakharian, and D. Huguenin. "Glazar-2: A Wide-Field Camera Aboard the MIR Space Station." Symposium - International Astronomical Union 161 (1994): 55–56. http://dx.doi.org/10.1017/s0074180900047045.

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In 1987 the UV imaging telescope Glazar (Tovmassian et al. 1988) was launched to the Mir Space Station. Its sensitivity was lower than was expected. For this reason the UV survey of the sky was not done and only observations of OB stellar associations were made. The fields of about 15 stellar associations and of the Large Magellanic Cloud were observed. Only images of O, B or early A type stars were obtained on the Glazar photographs at 1640 å. The observations allowed the detection of an average ∼ 15 % new, unknown OB type stars in each of the observed fields, the discovery of hot unknown components of some late type stars and a detailed study of the distribution of stars in space. Some new, unknown OB stellar associations were discovered and more correct distances of stellar associations were determined. The distribution of the absorbing matter was also studied. New, B-type stellar associations, named B were discovered.

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Sullivan, Kendall, and Adam L. Kraus. "Starspots and Undetected Binary Stars Have Distinct Signatures in Young Stellar Associations." Astrophysical Journal 969, no. 2 (July 1, 2024): 117. http://dx.doi.org/10.3847/1538-4357/ad4998.

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Abstract Young stars form in associations, meaning that young stellar associations provide an ideal environment to measure the age of a nominally coeval population. Isochrone fitting, which is the typical method for measuring the age of a coeval population, can be impacted by observational biases that obscure the physical properties of a population. One feature in isochrone fits of star-forming regions is an apparent mass-dependent age gradient, where lower-mass stars appear systematically younger than higher-mass stars. Starspots and stellar multiplicity are proposed mechanisms for producing the mass-dependent age gradient, but the relative importance of starspots versus multiplicity remains unclear. We performed a synthetic red optical low-resolution spectroscopic survey of a simulated analog to a 10 Myr stellar association including mass-dependent multiplicity statistics and age-dependent starspot coverage fractions. We found that undetected starspots alone do not produce an apparent mass-dependent age gradient, but instead uniformly reduce the average measured age of the population. We also found that binaries continue to produce an apparent mass-dependent age gradient and introduce more scatter in the age measurement than spots, but are easily removed from the population as long as there are good distance measurements to each target. We conclude that it is crucial to incorporate treatments of both starspots and undetected stellar multiplicity into isochrone fits of young stellar associations to attain reliable ages.

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Lada, Charles J. "Star Formation: From OB Associations to Protostars." Symposium - International Astronomical Union 115 (1987): 1–18. http://dx.doi.org/10.1017/s0074180900094766.

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The study of star formation is a relatively young discipline of the field of astronomy. Up until the mid point of the twentieth century only a most rudimentary understanding of the subject was possible. This is because prior to that time there did not exist any substantive body of empirical data which could be used to critically test even the most basic hypotheses concerning stellar origins. However, as a result of impressive advances in observational technology and in our understanding of stellar evolution during the last forty years, the subject of star formation has developed into one of the most important branches of modern astrophysical research. A large body of observational data and a considerable literature pertaining to this subject now exist and a significant fraction of the international astronomical community devotes their efforts towards trying to comprehend the origins of stars and planets. Yet, despite these efforts we have yet to observationally identify, with any certainty, a single object in the process of stellar birth! Moreover, we have not yet produced a viable theory of star formation, one capable of being tested and refined by critical experiment. In many ways, stellar birth is as much a mystery today as it was forty years ago. However, there can be little doubt that during the last two decades truly revolutionary progress has been made in the quest to understand the star formation process in our galaxy. This apparent paradox in the state of our knowledge concerning stellar origins is resolved with the realization that the history of the study of star formation has been a history of the study of progressively earlier and earlier stages of stellar evolution. Indeed, it is in precisely this area of endeavor that we have learned so much.

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Mirzoyan, L. V. "Stellar Associations and Regions of Star Formation." Symposium - International Astronomical Union 115 (1987): 200–201. http://dx.doi.org/10.1017/s0074180900095528.

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The genetic nature of the OB and T-Tau stars connection with stellar associations is at present beyond any doubt. They present the characteristic population of the latter. From this important observational fact follows that all young objects connected with OB and T-Tau stars also originated in stellar associations, and hence, are genetically connected with them.

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Tovmasyan, G. M., R. Kh Oganesyan, R. A. Epremyan, and D. Huguenin. "New O-type stellar associations in Carina." Astronomical Journal 106 (August 1993): 627. http://dx.doi.org/10.1086/116667.

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Torres, Diego F., Eva Domingo-Santamara, and Gustavo E. Romero. "High-Energy Gamma Rays from Stellar Associations." Astrophysical Journal 601, no. 1 (January 16, 2004): L75—L78. http://dx.doi.org/10.1086/381803.

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Burbidge, G., A. Hewitt, J. V. Narlikar, and P. Das Gupta. "Associations between quasi-stellar objects and galaxies." Astrophysical Journal Supplement Series 74 (November 1990): 675. http://dx.doi.org/10.1086/191514.

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Hodge, P. "Stellar associations in the galaxy NGC 2403." Publications of the Astronomical Society of the Pacific 97 (November 1985): 1065. http://dx.doi.org/10.1086/131663.

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Brown, Anthony G. A. "Stellar Content and Evolution of OB Associations." Publications of the Astronomical Society of the Pacific 108 (May 1996): 459. http://dx.doi.org/10.1086/133748.

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Mentuch, Erin, Alexis Brandeker, Marten H. van Kerkwijk, Ray Jayawardhana, and Peter H. Hauschildt. "Lithium Depletion of Nearby Young Stellar Associations." Astrophysical Journal 689, no. 2 (December 20, 2008): 1127–40. http://dx.doi.org/10.1086/592764.

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Martins, B. L. Canto, S. Vieira, C. A. O. Torres, G. R. Quast, L. da Silva, R. de La Reza, C. H. F. de Melo, and J. R. de Medeiros. "Lithium survey in evolved stars observed in the sacy project." Proceedings of the International Astronomical Union 5, S266 (August 2009): 368. http://dx.doi.org/10.1017/s1743921309991335.

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AbstractThe primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.

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Zari, Eleonora, and Anthony G. A. Brown. "Mapping young stellar populations towards Orion with Gaia DR1." Proceedings of the International Astronomical Union 12, S330 (April 2017): 197–200. http://dx.doi.org/10.1017/s1743921317005622.

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AbstractOB associations are prime sites for the study of star formation processes and of the interaction between young massive stars with the interstellar medium. Furthermore, the kinematics and structure of the nearest OB associations provide detailed insight into the properties and origin of the Gould Belt. In this context, the Orion complex has been extensively studied. However, the spatial distribution of the stellar population is still uncertain: in particular, the distances and ages of the various sub-groups composing the Orion OB association, and their connection to the surrounding interstellar medium, are not well determined. We used the first Gaia data release to characterize the stellar population in Orion, with the goal to obtain new distance and age estimates of the numerous stellar groups composing the Orion OB association. We found evidence of the existence of a young and rich population spread over the entire region, loosely clustered around some known groups. This newly discovered population of young stars provides a fresh view of the star formation history of the Orion region.

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Gouliermis, D., M. Kontizas, E. Kontizas, and R. Korakitis. "OB stellar associations in the Large Magellanic Cloud: Survey of young stellar systems." Astronomy & Astrophysics 405, no. 1 (June 16, 2003): 111–24. http://dx.doi.org/10.1051/0004-6361:20030483.

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Stahl, Asa G., Christopher M. Johns-Krull, and L. Flagg. "Follow-up of Young Stars Identified with BANYAN Σ: New Low-mass Members of Nearby Moving Groups." Astrophysical Journal 941, no. 1 (December 1, 2022): 101. http://dx.doi.org/10.3847/1538-4357/ac8b78.

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Abstract The characterization of moving groups offers a powerful means to identify large populations of young stars. In this paper, we present a sample of follow-up observations for 56 systems that have previously been proposed as members of young stellar associations through the application of the BANYAN Σ kinematic classification tool. Our measurements, which probe seven different associations, provide a sample of 39 stellar systems that either are confirmed or appear consistent with being young members of their respective associations. Nineteen of these are single M dwarfs. This sample expands our knowledge of Upper Centaurus Lupus, Coma Berenices, and AB Doradus Major to cooler temperatures and also significantly increases the known population of the Carina-Near association. The young systems present excellent targets for future planet searches and would also be valuable for studies of star formation and evolution. Additionally, we find two stellar systems that show indications of being rare instances of late-stage circumstellar accretion. Lastly, our follow-up measurements serve as a test of BANYAN Σ, finding an overall contamination rate that is consistent with previous findings (29% for systems with RV measurements, 37% without).

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Melnik, Anna M., Andrei K. Dambis, Elena V. Glushkova, and Pertti Rautiainen. "Kinematics of OB-associations in the 3-kpc solar neighborhood." Proceedings of the International Astronomical Union 14, S345 (August 2018): 39–42. http://dx.doi.org/10.1017/s1743921318008335.

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AbstractWe use Gaia (DR1, DR2) stellar proper motions to study the kinematics of OB-associations. The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 Gaia DR1 stars is σv = 3.9 km s−1. The median virial and stellar masses of OB-associations are equal to 7×105 and 9 × 103 solar masses, respectively. The median star-formation efficiency is ε = 2.1%. We have found the expansion in several OB-associations. Models of the Galaxy with a two-component outer ring R1R2 can reproduce the average residual velocities of OB-associations in the Perseus, Sagittarius and Local System complexes.

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Kovlakas, Konstantinos, Andreas Zezas, Jeff J. Andrews, Antara Basu-Zych, Tassos Fragos, Ann Hornschemeier, Bret Lehmer, and Andrew Ptak. "Ultraluminous X-ray source populations in the Chandra Source Catalog 2.0." Proceedings of the International Astronomical Union 14, S346 (August 2018): 247–51. http://dx.doi.org/10.1017/s1743921318008086.

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Abstract. The nature and evolution of ultraluminous X-ray sources (ULXs) is an open problem in astrophysics. They challenge our current understanding of stellar compact objects and accretion physics. The recent discovery of pulsar ULXs further demonstrates the importance of this intriguing and rare class of objects.In order to overcome the difficulties of directly studying the optical associations of ULXs, we generally resort in statistical studies of the stellar properties of their host galaxies. We present the largest such study based on the combination of Chandra archival data with the most complete galaxy catalog of the Local Universe. Incorporating robust distances and stellar population parameters based on associated multi-wavelength information, and we explore the association of ULXs with galaxies in the (star formation rate, stellar mass, metallicity) space.We confirm the known correlation with morphology, star formation rate and stellar mass, while we find an excess of ULXs in dwarf galaxies, indicating dependence on age and metallicity.

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Grossi, M., E. Corbelli, C. Giovanardi, and L. Magrini. "Young stellar clusters and associations in M 33." Astronomy and Astrophysics 521 (October 2010): A41. http://dx.doi.org/10.1051/0004-6361/200913513.

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Hodge, P. "The stellar associations of the Small Magellanic Cloud." Publications of the Astronomical Society of the Pacific 97 (June 1985): 530. http://dx.doi.org/10.1086/131564.

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Saviane, I., J. E. Hibbard, and R. M. Rich. "Stellar Associations in the Tail of NGC 4038." Symposium - International Astronomical Union 217 (2004): 546–49. http://dx.doi.org/10.1017/s0074180900198353.

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We have used the Hubble Space Telescope and Wide Field Planetary Camera 2 to image the putative tidal dwarf galaxy located at the tip of the Southern tidal tail of NGC 4038/9, the Antennae. We resolve individual stars, and identify two stellar populations. Hundreds of massive stars are present, concentrated into tight OB associations on scales of 200 pc, with ages ranging from 2-100 Myr. An older stellar population is distributed roughly following the outer contours of the neutral hydrogen in the tidal tail; we associate these stars with material ejected from the outer disks of the two spirals. The older stellar population has a red giant branch tip at I = 26.5 ± 0.2 from which we derive a distance modulus (m - M)0 = 30.7 ± 0.25. The implied distance of 13.8 ± 1.7 Mpc is nearly a factor of two closer than commonly quoted distances for NGC 4038/9. In contrast to the previously studied core of the merger, we find no super star clusters. One might conclude that SSCs require the higher pressures found in the central regions in order to form, while spontaneous star formation in the tail produces the kind of O-B star associations seen in dwarf irregular galaxies.

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Mathieu, Robert D. "The Dynamical Evolution of Young Clusters and Associations." Highlights of Astronomy 7 (1986): 481–88. http://dx.doi.org/10.1017/s153929960000681x.

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A young cluster or association bears the imprint of the conditions at its birth for perhaps ten million years, after which the initial conditions are lost to either dilution in the galactic field or erasure by orbital mixing and stellar encounters. In its youngest years, however, the dynamical state of the system can provide valuable information concerning the structure and energetics of the parent gas, the star-formation efficiency and the star-formation process itself. This short review discusses recent theoretical and observational progress in the study of the very youngest of stellar systems.

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Grudić, Michael Y., J. M. Diederik Kruijssen, Claude-André Faucher-Giguère, Philip F. Hopkins, Xiangcheng Ma, Eliot Quataert, and Michael Boylan-Kolchin. "A model for the formation of stellar associations and clusters from giant molecular clouds." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 5, 2021): 3239–58. http://dx.doi.org/10.1093/mnras/stab1894.

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ABSTRACT We present a large suite of magnetohydrodynamic simulations of turbulent, star-forming giant molecular clouds (GMCs) with stellar feedback, extending previous work by simulating 10 different random realizations for each point in the parameter space of cloud mass and size. It is found that once the clouds disperse due to stellar feedback, both self-gravitating star clusters and unbound stars generally remain, which arise from the same underlying continuum of substructured stellar density, i.e. the hierarchical cluster formation scenario. The fraction of stars that are born within gravitationally bound star clusters is related to the overall cloud star formation efficiency set by stellar feedback, but has significant scatter due to stochastic variations in the small-scale details of the star-forming gas flow. We use our numerical results to calibrate a model for mapping the bulk properties (mass, size, and metallicity) of self-gravitating GMCs on to the star cluster populations they form, expressed statistically in terms of cloud-level distributions. Synthesizing cluster catalogues from an observed GMC catalogue in M83, we find that this model predicts initial star cluster masses and sizes that are in good agreement with observations, using only standard IMF and stellar evolution models as inputs for feedback. Within our model, the ratio of the strength of gravity to stellar feedback is the key parameter setting the masses of star clusters, and of the various feedback channels direct stellar radiation (photon momentum and photoionization) is the most important on GMC scales.

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Gagné, Jonathan. "A Quick Guide to Nearby Young Associations." Publications of the Astronomical Society of the Pacific 136, no. 6 (June 1, 2024): 063001. http://dx.doi.org/10.1088/1538-3873/ad4e6a.

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Abstract Nearby associations of stars which are coeval are important benchmark laboratories because they provide robust measurements of stellar ages. The study of such coeval groups makes it possible to better understand star formation by studying the initial mass function, the binary fraction or the circumstellar disks of stars, to determine how the initially dense populations of young stars gradually disperse to form the field population, and to shed light on how the properties of stars, exoplanets and substellar objects evolve with distinct snapshots along their lifetime. The advent of large-scale missions such as Gaia is reshaping our understanding or stellar kinematics in the Solar neighborhood and beyond, and offers the opportunity to detect a large number of loose, coeval stellar associations for the first time, which evaded prior detection because of their low density or the faintness of their members. In parallel, advances in detection and characterization of exoplanets and substellar objects are starting to unveil the detailed properties of extrasolar atmospheres, as well as population-level distributions in fundamental exoplanet properties such as radii, masses, and orbital parameters. Accurate ages are still sparsely available to interpret the evolution of both exoplanets and substellar objects, and both fields are now ripe for detailed age investigations because we are starting to uncover ever-closer low-density associations that previously escaped detection, as well as exoplanets and ever lower-mass members of more distant open clusters and star-forming regions. In this paper, we review some recent advances in the identification and characterization of nearby associations, the methods by which stellar ages are measured, and some of the direct applications of the study of young associations such as the emergent field of isolated planetary-mass objects.

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Aniol, R., H. W. Duerbeck, W. C. Seitter, and M. K. Tsvetkov. "An automatic search for flare stars in southern stellar aggregates of different ages." Symposium - International Astronomical Union 137 (1990): 85–94. http://dx.doi.org/10.1017/s0074180900187509.

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Statistically relevant samples of flare stars in stellar aggregates can be used to specify the stellar mass-age-activity-relation when the ages of the aggregates are known from independent investigations. Associations and clusters of the southern sky are currently surveyed with the GPO astrograph of the European Southern Observatory. The plates are digitized with the PDS 2020 GMplus microdensitometer and the data are reduced automatically at the Astronomical Institute of Muenster University. The programme package “FLARE” is described. First results from the Orion association are presented.

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Jugaku, J., G. Cayrel de Strobel, Y. Andrillat, W. K. Bonsack, P. S. Conti, C. R. Cowley, C. O. R. Jaschek, et al. "29. Stellar Spectra." Transactions of the International Astronomical Union 19, no. 1 (1985): 353–74. http://dx.doi.org/10.1017/s0251107x00006416.

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During the triennium under review, Commission 29 has sponsored or cosponsored the following IAU meetings: Symposium 102, “Solar and Stellar Magnetic Fields,” Zurich, Switzerland, August 1982; Symposium 108, “Structure and Evolution of the Magellanic Clouds,” Tübingen, FRG, September 1983; Symposium 111, “Calibration of Fundamental Stellar Quantities,” Como, Italy, May 1984; and Colloquium 82, “Cepheids: Observation and Theory,” Toronto, Canada, May-June 1984. Commission 29 has also supported or sponsored several IAU meetings proposed for 1985 and 1986. They include “Luminous Stars and Associations in Galaxies,” Porto Heli, Greece, May 1985; “Upper Main Sequence Stars with Anomalous Abundances,” Crimea, USSR, May 1985; “Astrochemistry,” Goa, India, December 1985; “Hydrogen Deficient Stars and Related Objects,” Bangalore, India, December 1985; “Circumstellar Matter,” Heidelberg, FRG, June 1986; and “Be Stars,” Boulder, USA, August 1986.

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37

Corral, Luis J., Miriam García, Silvana G. Navarro, and Artemio Herrero. "The massive stellar population of IC 10." Proceedings of the International Astronomical Union 14, S344 (August 2018): 57–61. http://dx.doi.org/10.1017/s1743921318006774.

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AbstractUsing photometric data available in the literature we want to identify the massive stars members of the metal-poor irregular galaxy IC 10 and the clusters and associations that they form. The census of the clusters and associations of these objects is needed to provide information about age and environment on this galaxy that is apparently going through a starburst phase.

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Sneden, Christopher, M. Parthasarathy, Fiorella Castelli, Katia Cunha, Philippe Eenens, Eileen Friel, Raffaele Gratton, et al. "Commission 29: Stellar Spectra." Proceedings of the International Astronomical Union 1, T26A (December 2005): 203–4. http://dx.doi.org/10.1017/s1743921306004558.

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Participants in Commission 29 study various aspects of stellar spectra and the information that can be extracted from spectra. The list of fields of interest of the Organizing Committee members suggest some major current research topics in this area are stellar chemical compositions and surface/envelope phenomena. Some of the topics of this commission have overlap with other commissions, such as Commission 14 (Atomic and Molecular Data), 26 (Double and Multiple Stars), 27 (Variable Stars), 30 (Radial Velocities), 36 (Theory of Stellar Atmospheres), and 37 (Star Clusters and Associations). Many Commission 29 members are also members of these other commissions.

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39

Mirzoyan, L. V. "Optical Flares: Observations and Interpretations." International Astronomical Union Colloquium 151 (1995): 47–54. http://dx.doi.org/10.1017/s0252921100034552.

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AbstractObservational results on flare stars in the Galaxy and their interpretation, based on the observational approach to early stages of stellar evolution at Byurakan, are considered. The evolutionary path of red flare stars is determined. Stellar flare activity is explained as an internal phenomenon of stars. The significance of photographic observations of stellar flares in star clusters and associations is emphasized.

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40

Glagolevskij, Yu V., V. G. Klochkova, and I. M. Kopylov. "Investigations of the Magnetic Fields of Chemically Peculiar Stars of Different Age." International Astronomical Union Colloquium 90 (1986): 29–32. http://dx.doi.org/10.1017/s0252921100091156.

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The program of comprehensive investigations of stellar magnetism in the Special Astrophysical Observatory of the USSR AS includes the study of origin and evolution of the stellar magnetic fields in open clusters and associations of different age. In the papers by Borra (1981), Brown et al. (1981) and North and Cramer (1984) have been found some indications on the evolutionary decay of the fossil stellar fields.

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41

Yep, Alexandra C., and Russel J. White. "Collision of two stellar associations in the nearby Gum Nebula." Monthly Notices of the Royal Astronomical Society 511, no. 3 (January 19, 2022): 4500–4510. http://dx.doi.org/10.1093/mnras/stab3725.

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ABSTRACT Based on Gaia DR2 data and new CHIRON radial velocities, we have discovered that two nearby stellar associations UPK 535 (318.08 ± 0.29 pc, $25^{+15}_{-10}$ Myr, 174 stars) and Yep 3 (339.54 ± 0.25 pc, $45^{+55}_{-20}$ Myr, 297 stars) in the Gum Nebula have recently collided. We project stars’ current positions, motions, and measurement uncertainties backward and forward through time in a 10 000-trial Monte Carlo simulation. On average, the associations’ centres of mass come within 18.89 ± 0.73 pc of each other 0.84 ± 0.03 Myr ago. A mode of 54 ± 7 close (<1 pc) stellar encounters occur during the collision. We cannot predict specific star–star close encounters with our current ∼7.6 pc distance precision and 21.5 per cent complete radial velocity sample. Never the less, we find that two stars in UPK 535 and two stars in Yep 3 undergo a nonspecific close encounter in >70 per cent of trials and multiple close encounters in ∼30 per cent. On average, the closest approach of any two stars is 0.13 ± 0.06 pc, or 27 000 ± 12 000 au. With impulse-tracing values up to $2.7^{+3.1}_{-1.1}$ M⊙ pc−2 km−1 s, such close encounters could perturb stars’ Oort cloud comets (if present), cause heavy bombardment events for exoplanets (if present), and reshape Solar system architectures. Finally, an expansion of our simulation suggests other associations in the region are also interacting. Association collisions may be commonplace, at least in the Gum Nebula straddling the Galactic plane, and may spur Solar system evolution more than previously recognized.

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42

Bik, A., Th Henning, S. W. Wu, M. Zhang, W. Brandner, A. Pasquali, and A. Stolte. "Near-infrared spectroscopy of the massive stellar population of W51: evidence for multi-seeded star formation." Astronomy & Astrophysics 624 (April 2019): A63. http://dx.doi.org/10.1051/0004-6361/201935061.

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Context. The interplay between the formation of stars, stellar feedback and cloud properties strongly influences the star formation history of giant molecular clouds. The formation of massive stars leads to a variety of stellar clusters, ranging from low stellar density OB associations to dense, gravitationally bound starburst clusters. Aims. We aimed at identifying the massive stellar content and reconstructing the star formation history of the W51 giant molecular cloud. Methods. We performed near-infrared imaging and K-band spectroscopy of the massive stars in W51. We analysed the stellar populations using colour-magnitude and colour-colour diagrams and compared the properties of the spectroscopically identified stars with stellar evolution models. Results. We derive the ages of the different sub-clusters in W51 and, based on our spectroscopy derive an age for W51 of 3 Myr or less. The age of the P Cygni star LS1 and the presence of two still forming proto-clusters suggests that the star formation history of W51 is more complex than a single burst. Conclusions. We did not find evidence for triggered star formation and we concluded that the star formation in W51 is multi seeded. We finally concluded that W51 is an OB association where different sub-clusters form over a time span of at least 3–5 Myr.

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Tovmassian, H. M., R. A. Epremian, Kh Hovhannessian, G. Cruz-Gonzalez, S. G. Navarro, and A. A. Karapetian. "OB Stellar Associations in the Direction of Centaurus OB2." Astronomical Journal 115, no. 3 (March 1998): 1083–95. http://dx.doi.org/10.1086/300237.

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Tovmassian, H. M., S. G. Navarro, and O. Cardona. "OB Stellar Associations in Crux. II. Analysis and Discussion." Astronomical Journal 111 (January 1996): 306. http://dx.doi.org/10.1086/117782.

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Hojaev, Alisher S. "Galaxy open clusters and associations: study of stellar population." Proceedings of the International Astronomical Union 2, S237 (August 2006): 428. http://dx.doi.org/10.1017/s1743921307002165.

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Hovhannessian, R. Kh, H. M. Tovmassian, and R. A. Epremian. "Observations of stellar associations on the space telescope Glazar." Astrophysics 38, no. 4 (October 1995): 291–93. http://dx.doi.org/10.1007/bf02044696.

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Liu, Jiaming, Min Fang, and Chao Liu. "Discovery of Two Nearby Post-T Tauri Stellar Associations." Astronomical Journal 159, no. 3 (February 13, 2020): 105. http://dx.doi.org/10.3847/1538-3881/ab6b22.

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Distefano, E., A. C. Lanzafame, A. F. Lanza, S. Messina, and F. Spada. "Activity cycles in members of young loose stellar associations." Astronomy & Astrophysics 606 (October 2017): A58. http://dx.doi.org/10.1051/0004-6361/201730967.

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Dale, Daniel A., Médéric Boquien, Ashley T. Barnes, Francesco Belfiore, Frank Bigiel, Yixian Cao, Rupali Chandar, et al. "PHANGS–JWST First Results: The Influence of Stellar Clusters on Polycyclic Aromatic Hydrocarbons in Nearby Galaxies." Astrophysical Journal Letters 944, no. 2 (February 1, 2023): L23. http://dx.doi.org/10.3847/2041-8213/aca769.

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Abstract We present a comparison of theoretical predictions of dust continuum and polycyclic aromatic hydrocarbon (PAH) emission with new JWST observations in three nearby galaxies: NGC 628, NGC 1365, and NGC 7496. Our analysis focuses on a total of 1063 compact stellar clusters and 2654 stellar associations previously characterized by the Hubble Space Telescope in the three galaxies. We find that the distributions and trends in the observed PAH-focused infrared colors generally agree with theoretical expectations, and that the bulk of the observations is more aligned with models of larger, ionized PAHs. These JWST data usher in a new era of probing interstellar dust and studying how the intense radiation fields near stellar clusters and associations play a role in shaping the physical properties of PAHs.

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Boily, Christian M. "The internal dynamics of stellar clusters." Proceedings of the International Astronomical Union 5, S266 (August 2009): 238–49. http://dx.doi.org/10.1017/s1743921309991104.

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AbstractIn this brief review I summarise recent progress in the area of stellar dynamics, focusing on the dynamics of bound, self-gravitating stellar associations in isolation and (approximate) equilibrium. The basics of stellar dynamics are first outlined and the importance of stellar evolution is stressed. Subsequently, I argue that the evolution of anisotropic clusters of stars still holds solutions to current outstanding problems, such as the dynamics of galactic nuclei. I take a more personal standpoint when discussing the role of stellar evolution in the dynamics on relaxation timescales and draw from several recent models to underscore that a major step forward has been made in coupling stellar evolution and dynamics. I then briefly visit the issue of multiple stars and highlight some as yet unsolved problems.

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Journal articles on the topic 'Stellar associations'

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