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1
Gładkowski, Marcin, Marcin Hajduk, and Igor Soszyński. "Search for binary central stars of the Magellanic Clouds PNe." Proceedings of the International Astronomical Union 12, S323 (October 2016): 384–85. http://dx.doi.org/10.1017/s1743921317001892.
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AbstractThe Optical Gravitational Experiment (OGLE) was effectively used in discovering binary central stars of planetary nebulae (CSPNe). About 50 binary CSPNe have been hitherto identified in the Galaxy, almost half of them were detected in the OGLE database. We used the OGLE data to search for binary CSPNe in the Magellanic Clouds. We also searched for PNe mimics and removed them from the PNe sample. Here, we present results of the photometric analysis for Small Magellanic Cloud (SMC) and our progress on search of binary central stars in the Large Magellanic Cloud (LMC). So far, we have discovered one binary central star of the PN beyond the Milky Way, which is located in the Small Magellanic Cloud.
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Mahy, L., L. A. Almeida, H. Sana, J. S. Clark, A. de Koter, S. E. de Mink, C. J. Evans, et al. "The Tarantula Massive Binary Monitoring." Astronomy & Astrophysics 634 (February 2020): A119. http://dx.doi.org/10.1051/0004-6361/201936152.
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Context. A high fraction of massive stars are found to be binaries but only a few of them are reported as photometrically variable. By studying the populations of double-lined spectroscopic binaries in the 30 Doradus region, we found a subset of them that have photometry from the OGLE project and that display variations in their light curves related to orbital motions. Aims. The goal of this study is to determine the dynamical masses and radii of the 26 binary components in order to investigate the mass-discrepancy problem and to provide an empirical mass-luminosity relation for the Large Magellanic Cloud (LMC). Methods. We use the PHOEBE programme to perform a systematic analysis of the OGLE V and I light curves obtained for 13 binary systems in the 30 Doradus region. We adopt the effective temperatures, and orbital parameters derived previously to obtain the inclinations of the systems and the parameters of the individual components. Results. Three systems display eclipses in their light curves, while the others only display ellipsoidal variations. We classify two systems as over-contact, five as semi-detached, and four as detached. The two remaining systems have uncertain configurations due to large uncertainties on their inclinations. The fact that systems display ellipsoidal variations has a significant impact on the inclination errors. From the dynamical masses, luminosities, and radii, we provide LMC-based empirical mass-luminosity and mass-radius relations, and we compare them to other relations given for the Galaxy, the LMC, and the Small Magellanic Cloud. These relations differ for different mass ranges, but do not seem to depend on the metallicity regimes. We also compare the dynamical, spectroscopic, and evolutionary masses of the stars in our sample. While the dynamical and spectroscopic masses agree with each other, the evolutionary masses are systematically higher, at least for stars in semi-detached systems. This suggests that the mass discrepancy can be partly explained by past or ongoing interactions between the stars.
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Shenar, T., A. Gilkis, J. S. Vink, H. Sana, and A. A. C. Sander. "Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity." Astronomy & Astrophysics 634 (February 2020): A79. http://dx.doi.org/10.1051/0004-6361/201936948.
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Context. Classical Wolf-Rayet (WR) stars are massive, hydrogen-depleted, post main-sequence stars that exhibit emission-line dominated spectra. For a given metallicity Z, stars exceeding a certain initial mass MsingleWR(Z) can reach the WR phase through intrinsic mass-loss or eruptions (single-star channel). In principle, stars of lower masses can reach the WR phase via stripping through binary interactions (binary channel). Because winds become weaker at low Z, it is commonly assumed that the binary channel dominates the formation of WR stars in environments with low metallicity such as the Small and Large Magellanic Clouds (SMC, LMC). However, the reported WR binary fractions of 30−40% in the SMC (Z = 0.002) and LMC (Z = 0.006) are comparable to that of the Galaxy (Z = 0.014), and no evidence for the dominance of the binary channel at low Z could be identified observationally. Here, we explain this apparent contradiction by considering the minimum initial mass MspecWR(Z) needed for the stripped product to appear as a WR star. Aims. By constraining MspecWR(Z) and MsingleWR(Z), we estimate the importance of binaries in forming WR stars as a function of Z. Methods. We calibrated MspecWR using the lowest-luminosity WR stars in the Magellanic Clouds and the Galaxy. A range of MsingleWR values were explored using various evolution codes. We estimated the additional contribution of the binary channel by considering the interval [MspecWR(Z), MsingleWR(Z)], which characterizes the initial-mass range in which the binary channel can form additional WR stars. Results. The WR-phenomenon ceases below luminosities of log L ≈ 4.9, 5.25, and 5.6 [L⊙] in the Galaxy, the LMC, and the SMC, respectively, which translates to minimum He-star masses of 7.5, 11, 17 M⊙ and minimum initial masses of MspecWR = 18, 23, 37 M⊙. Stripped stars with lower initial masses in the respective galaxies would tend not to appear as WR stars. The minimum mass necessary for self-stripping, MsingleWR(Z), is strongly model-dependent, but it lies in the range 20−30, 30−60, and ≳40 M⊙ for the Galaxy, LMC, and SMC, respectively. We find that that the additional contribution of the binary channel is a non-trivial and model-dependent function of Z that cannot be conclusively claimed to be monotonically increasing with decreasing Z. Conclusions. The WR spectral appearance arises from the presence of strong winds. Therefore, both MspecWR and MsingleWR increase with decreasing metallicity. Considering this, we show that one should not a-priori expect that binary interactions become increasingly important in forming WR stars at low Z, or that the WR binary fraction grows with decreasing Z.
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Hamann, Wolf-Rainer, Lidia Oskinova, Helge Todt, Andreas Sander, Rainer Hainich, Tomer Shenar, and Varsha Ramachandran. "Massive stars in advanced evolutionary stages, and the progenitor of GW150914." Proceedings of the International Astronomical Union 12, S329 (November 2016): 223–27. http://dx.doi.org/10.1017/s1743921317002563.
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AbstractThe recent discovery of a gravitational wave from the merging of two black holes of about 30 solar masses each challenges our incomplete understanding of massive stars and their evolution. Critical ingredients comprise mass-loss, rotation, magnetic fields, internal mixing, and mass transfer in close binary systems. The imperfect knowledge of these factors implies large uncertainties for models of stellar populations and their feedback. In this contribution we summarize our empirical studies of Wolf-Rayet populations at different metallicities by means of modern non-LTE stellar atmosphere models, and confront these results with the predictions of stellar evolution models. At the metallicity of our Galaxy, stellar winds are probably too strong to leave remnant masses as high as ~30 M⊙, but given the still poor agreement between evolutionary tracks and observation even this conclusion is debatable. At the low metallicity of the Small Magellanic Cloud, all WN stars which are (at least now) single are consistent with evolving quasi-homogeneously. O and B-type stars, in contrast, seem to comply with standard evolutionary models without strong internal mixing. Close binaries which avoided early merging could evolve quasi-homogeneously and lead to close compact remnants of relatively high masses that merge within a Hubble time.
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Irrgang, A., S. Kreuzer, and U. Heber. "Hypervelocity stars in the Gaia era." Astronomy & Astrophysics 620 (December 2018): A48. http://dx.doi.org/10.1051/0004-6361/201833874.
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Context. Young massive stars in the halo are assumed to be runaway stars from the Galactic disk. Possible ejection scenarios are binary supernova ejections (BSE) or dynamical ejections from star clusters (DE). Hypervelocity stars (HVSs) are extreme runaway stars that are potentially unbound from the Galaxy. Powerful acceleration mechanisms such as the tidal disruption of a binary system by a supermassive black hole (SMBH) are required to produce them. Therefore, HVSs are believed to originate in the Galactic center (GC), the only place known to host an SMBH. Aims. The second Gaia data release (DR2) offers the opportunity of studying HVSs in an unprecedented manner. We revisit some of the most interesting high-velocity stars, that is, 15 stars (11 candidate HVSs and 4 radial velocity outliers) for which proper motions with the Hubble Space Telescope. were obtained in the pre-Gaia era, to unravel their origin. Methods. By carrying out kinematic analyses based on revised spectrophotometric distances and proper motions from Gaia DR2, kinematic properties were obtained that help constrain the spatial origins of these stars. Results. Stars that were previously considered (un)bound remain (un)bound in Galactic potentials favored by Gaia DR2 astrometry. For nine stars (five candidate HVSs plus all four radial velocity outliers), the GC can be ruled out as spatial origin at least at 2σ confidence level, suggesting that a large portion of the known HVSs are disk runaway stars launched close to or beyond Galactic escape velocities. The fastest star in the sample, HVS 3, is confirmed to originate in the Large Magellanic Cloud. Conclusions. Because the ejection velocities of five of our non-GC stars are close to or above the upper limits predicted for BSE and DE, another powerful dynamical ejection mechanism (e.g., involving massive perturbers such as intermediate-mass black holes) is likely to operate in addition to the three classical scenarios mentioned above.
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Villaseñor, J. I., W. D. Taylor, C. J. Evans, O. H. Ramírez-Agudelo, H. Sana, L. A. Almeida, S. E. de Mink, P. L. Dufton, and N. Langer. "The B-type binaries characterization programme I. Orbital solutions for the 30 Doradus population." Monthly Notices of the Royal Astronomical Society 507, no. 4 (July 31, 2021): 5348–75. http://dx.doi.org/10.1093/mnras/stab2197.
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ABSTRACT We present results from the B-type binaries characterization (BBC) programme, a multi-epoch spectroscopic study of 88 early B-type binary candidates in the 30 Doradus region of the Large Magellanic Cloud (LMC). From radial-velocity analysis of 29 observational epochs, we confirm the binary status of 64 of our targets, comprising 50 SB1 and 14 SB2 B-type binaries. A further 20 systems (classified as SB1*) show clear signs of periodicity but with more tentative periods. Orbital solutions are presented for these 84 systems, providing the largest homogeneous sample to date of the binary properties of early B-type stars. Our derived orbital-period distribution is generally similar to those for samples of more massive (O-type) binaries in both the LMC and the Galaxy. This similarity with the properties of the more massive O-type binaries is important as early B-type stars are expected to account for the majority of core-collapse supernovae. Differences in the period distributions of the different samples start to increase above 4 d, and are also present between the earliest (B0-0.7) and later-type (B1-2.5) systems within the BBC sample, although further study is required to understand if this is an observational bias or a real physical effect. We have examined the semi-amplitude velocities and orbital periods of our sample to identify potential candidates that could hide compact companions. Comparing with probability distributions of finding black hole companions to OB-type stars from a recent theoretical study, we have found 16 binaries in the higher probability region that warrant further study.
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Juryšek, J., P. Zasche, M. Wolf, J. Vraštil, D. Vokrouhlický, M. Skarka, J. Liška, et al. "New inclination changing eclipsing binaries in the Magellanic Clouds." Astronomy & Astrophysics 609 (January 2018): A46. http://dx.doi.org/10.1051/0004-6361/201730655.
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Context. Multiple stellar systems are unique laboratories for astrophysics. Analysis of their orbital dynamics, if well characterized from their observations, may reveal invaluable information about the physical properties of the participating stars. Unfortunately, there are only a few known and well described multiple systems, this is even more so for systems located outside the Milky Way galaxy. A particularly interesting situation occurs when the inner binary in a compact triple system is eclipsing. This is because the stellar interaction, typically resulting in precession of orbital planes, may be observable as a variation of depth of the eclipses on a long timescale. Aims. We aim to present a novel method to determine compact triples using publicly available photometric data from large surveys. Here we apply it to eclipsing binaries (EBs) in Magellanic Clouds from OGLE III database. Our tool consists of identifying the cases where the orbital plane of EB evolves in accord with expectations from the interaction with a third star. Methods. We analyzed light curves (LCs) of 26121 LMC and 6138 SMC EBs with the goal to identify those for which the orbital inclination varies in time. Archival LCs of the selected systems, when complemented by our own observations with Danish 1.54-m telescope, were thoroughly analyzed using the PHOEBE program. This provided physical parameters of components of each system. Time dependence of the EB’s inclination was described using the theory of orbital-plane precession. By observing the parameter-dependence of the precession rate, we were able to constrain the third companion mass and its orbital period around EB. Results. We identified 58 candidates of new compact triples in Magellanic Clouds. This is the largest published sample of such systems so far. Eight of them were analyzed thoroughly and physical parameters of inner binary were determined together with an estimation of basic characteristics of the third star. Prior to our work, only one such system was well characterized outside the Milky Way galaxy. Therefore, we increased this sample in a significant way. These data may provide important clues about stellar formation mechanisms for objects with different metalicity than found in our galactic neighborhood.
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Vink, Jorick S. "Constraining the progenitor evolution of GW 150914." Proceedings of the International Astronomical Union 14, S346 (August 2018): 444–48. http://dx.doi.org/10.1017/s1743921318007731.
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AbstractOne of the largest surprises from the LIGO results regarding the first gravitational wave detection (GW 150914) was the fact the black holes (BHs) were “heavy”, of order 30 - 40 Mȯ. The most promising explanation for this obesity is that the BH-BH merger occurred at low metallicity (Z): when the iron (Fe) contents is lower this is expected to result in weaker mass loss during the Wolf-Rayet (WR) phase. We therefore critically evaluate the claims for the reasons of heavy BHs as a function of Z in the literature. Furthermore, weaker stellar winds might lead to more rapid stellar rotation, allowing WR and BH progenitor evolution in a chemically homogeneous manner. However, there is as yet no empirical evidence for more rapid rotation amongst WR stars in the low Z environment of the Magellanic Clouds. Due to the intrinsic challenge of determining WR rotation rates from emission lines, the most promising avenue to constrain rotation-rate distributions amongst various WR subgroups is through the utilisation of their emission lines in polarised light. We thus provide an overview of linear spectro-polarimetry observations of both single and binary WRs in the Galaxy, as well as the Large and Small Magellanic Clouds, at 50% and 20% of solar Z, respectively. Initial results suggest that the route of chemically homogeneous evolution (CHE) through stellar rotation is challenging, whilst the alternative of a post-LBV or common envelope evolution is more likely.
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Kołaczkowski, Z., A. Pigulski, I. Soszyński, A. Udalski, M. Szymański, M. Kubiak, K. Żebruń, et al. "β Cephei and SPB stars in the Large Magellanic Cloud." International Astronomical Union Colloquium 193 (2004): 225–29. http://dx.doi.org/10.1017/s0252921100010666.
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AbstractThis is a progress report of the study of pulsating main-sequence stars in the LMC. Using the OGLE-II photometry supplemented by the MACHO photometry, we find 64 β Cephei stars in the LMC. Their periods are generally much longer than observed in stars of this type in the Galaxy (the median value is 0.27 d compared with 0.17 d in the Galaxy). In 20 stars with short periods attributable to the β Cephei-type instability, we also find modes with periods longer than ~0.4d. They are likely low-order g modes, which means that in these stars both kinds of variability, β Cephei and SPB, are observed. We also show examples of the multiperiodic SPB stars in the LMC, the first beyond our Galaxy.
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Hatzidimitriou, D., and R. K. Bhatia. "Do Binary Clusters Exist in the Large Magellanic Cloud?" Symposium - International Astronomical Union 126 (1988): 567–68. http://dx.doi.org/10.1017/s0074180900043102.
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The possible existence of binary clusters in our Galaxy (h and x Persei, Ocl 556) has been argued in the past, but it has never been a well established fact either in our Galaxy, or in external systems. An early speculation on the problem by Innanen et al (1972) has predicted a considerable degree of stability for binary clusters in low nuclear density galaxies, like the LMC.
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Niemela, Virpi S. "Two New Massive Binary Stars in the Magellanic Clouds." Symposium - International Astronomical Union 207 (2002): 202–4. http://dx.doi.org/10.1017/s0074180900223759.
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The discovery and preliminary spectroscopic orbits of two early O type binaries in very young open clusters in the Magellanic Clouds is reported. The binaries are NGC 346–1 in the Small Magellanic Cloud, and HDE 270145 in NGC 2122 in the Large Magellanic Cloud.
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Shore, Steven N. "GHRS Observations of Massive Stars in the Large Magellanic Cloud." Highlights of Astronomy 9 (1992): 475–76. http://dx.doi.org/10.1017/s1539299600009588.
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Hot stars are the natural targets for ultraviolet space observations. The bulk of their energy emerges shortward of the atmospheric cutoff and nearly all of the important atomic transitions required for their analysis are located in the region shortward of λ3000Å. However, since they are intrinsically rare, reddening and distance conspire to make the job of studying these important members of the stellar population of a galaxy a very difficulty task. The Goddard High Resolution Spectrograph (GHRS) adds the new dimension of photon counting to high sensitivity and resolution. This means that the massive stars can be more easily observed within our Galaxy, and also in other galaxies.
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Feitzinger, J. V. "Star Formation in the Large Magellanic Cloud." Symposium - International Astronomical Union 115 (1987): 521–33. http://dx.doi.org/10.1017/s0074180900096315.
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Methods used in pattern recognition and cluster analysis are applied to investigate the spatial distribution of the star forming regions. The fractal dimension of these structures is deduced. The new 21 cm, radio continuum (1.4 GHz) and IRAS surveys reveal scale structures of 700 pc to 1500 pc being identical with the optically identified star forming sites. The morphological structures delineated by young stars reflect physical parameters which determine the star formation in this galaxy. The formation of spiral arm filaments is understandable by stochastic selfpropagating star formation processes.
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Popowski, Piotr. "The Distance to the Large Magellanic Cloud." International Astronomical Union Colloquium 176 (2000): 203–7. http://dx.doi.org/10.1017/s0252921100057547.
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AbstractI demonstrate that the two unexpected results in the local Universe: anomalous intrinsic (V – I)0 colors of RR Lyrae stars and clump giants in the Galactic center, and very short distances to Magellanic Clouds inferred from clump giants, can be at least partially resolved with a modified coefficient of selective extinction AV/E(V – I). With this modification, I find a new clump-giant distance modulus to the Large Magellanic Cloud, μLMC = 18.27 ± 0.07, which is 0.09 larger than the Udalski (1998b) result. When distance estimates from the red clump, RR Lyrae stars and the eclipsing binary HV2274 are combined, one obtains μLMC = 18.31 ± 0.04 (internal).
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Bohannan, Bruce. "A Large Sample of Emission-Line Stars in the Large Magellanic Cloud: Their Location in the Hertzsprung-Russell Diagram." Symposium - International Astronomical Union 116 (1986): 227–28. http://dx.doi.org/10.1017/s0074180900148922.
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The paths that massive stars follow in their evolution can potentially be determined by studying a homogeneous collection of luminous stars. In this investigation, mass-losing stars in a galaxy are studied through a sample of 59 H alpha emission-line stars in the Large Magellanic Cloud (LMC). The most luminous, most massive stars in the LMC, like their counterparts in the Galaxy, are losing mass at a rate that significantly alters their spectroscopic appearance and that affects their evolution.
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Feast, M. W., and P. A. Whitelock. "CH stars in the Large Magellanic Cloud and in our Galaxy." Monthly Notices of the Royal Astronomical Society 259, no. 1 (November 1, 1992): 6–16. http://dx.doi.org/10.1093/mnras/259.1.6.
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Minelli, Alice, and Alessio Mucciarelli. "Chemical and kinematic study of Large Magellanic Cloud RGB stars." Proceedings of the International Astronomical Union 14, S351 (May 2019): 126–30. http://dx.doi.org/10.1017/s1743921319007178.
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AbstractThe Large Magellanic Cloud (LMC) is the closest massive satellite of the Milky Way (MW), and its proximity allows us to study its stellar populations with great detail, both with resolved photometry and spectroscopy. In turn, this is crucial to unveil its star formation and chemical enrichment histories, and also to investigate the effects that gravitational interactions with other systems (as the Small Magellanic Cloud (SMC) and the MW) may induce on an irregular galaxy. The LMC is characterized by a still on-going star formation activity, as traced by the wide range of ages and metallicities of its stellar populations. However, most of the information about the chemistry and the kinematics of this galaxy has been obtained from low-resolution spectra, which do not allow to draw firm conclusions on many crucial open questions. In particular, (1) we still miss a homogeneous determination of the LMC metallicity distribution; (2) the metal-poor component is still poorly known and described; and (3) we have no conclusive information on the existence of metallicity gradients, which would suggest to spatially inhomegeneous star formation events. To properly address these issues, we analysed nearly 500 high-resolution FLAMES spectra of red giant stars belonging to the LMC field, the largest set of high- resolution spectra of LMC stars analysed so far in a homogeneous way.
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Fujimoto, M., T. Sawa, and Y. Kumai. "The Magellanic Stream and the Magellanic Cloud System." Symposium - International Astronomical Union 186 (1999): 31–38. http://dx.doi.org/10.1017/s0074180900112161.
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A tidal model has been introduced to the triple system of the Galaxy, Large and Small Magellanic Clouds (the LMC and SMC hereafter) and successfully reproduced the Magellanic Stream (Murai and Fujimoto 1980; Lin and Lynden-Bell 1982; Gardiner et al. 1994; Gardiner and Noguchi 1995; Lin et al. 1995), a narrow band of diffuse atomic hydrogen gas emerging from the SMC region, passing by the South Galactic Pole along an overhead great circle spanning over 100° (Wannier and Wrixon 1972; Mathewson et al. 1974). The LMC and SMC have a hydrogen bridge and common envelope (Hindman 1964; McGee and Milton 1966) and, therefore, we can consider that they have been in a binary state for the Hubble time, revolving together around the Galaxy with a halo whose mass is larger than 1012M⊙ if the flat rotation curve extends up to more than 100 kpc. The strong gravitational force due to this heavy halo attracts the Magellanic Stream and produces the high negative radial velocities (Murai and Fujimoto 1980).
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Ramamani, N., T. Meinya Singh, and Saleh Mohammed Alladin. "Tidal interactions between the Galaxy and the Magellanic Clouds." Symposium - International Astronomical Union 106 (1985): 477–78. http://dx.doi.org/10.1017/s0074180900242964.
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The merging time and the disruption time in a binary galaxy system are analytically obtained under the Adiabatic Approximation (AA). Applications are made to the Galaxy-LMC (Large Magellanic Cloud) pair.
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Niemela, Virpi S. "Massive Binaries in the Magellanic Clouds." Highlights of Astronomy 13 (2005): 463. http://dx.doi.org/10.1017/s1539299600016270.
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We present results of our ongoing observing program on search and studies of massive stars (O and WR type) in binary systems in our neighbor galaxies, the Magellanic Clouds. Radial velocity orbits are presented for two new binaries, one in the Small Magellanic Cloud and another in the Large Magellanic Cloud, and improved orbits for previously known systems. We compare orbital parameters of selected binaries containing O and WR type components. We also discuss the present status of knowledge for massive binary stars in the Magellanic Clouds and the problems encountered in their orbital studies such as stellar winds the ubiquitous tendency to be born in multiple systems.
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Shenar, T., D. P. Sablowski, R. Hainich, H. Todt, A. F. J. Moffat, L. M. Oskinova, V. Ramachandran, et al. "The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud." Astronomy & Astrophysics 627 (July 2019): A151. http://dx.doi.org/10.1051/0004-6361/201935684.
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Context. Massive Wolf–Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z ≈ 0.5 Z⊙), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf–Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45 ± 30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only ≈12 ± 7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises ≈4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L ≈ 5.2 [L⊙], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (veq ≲ 250 km s−1) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.
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Schmidt, Thomas, Maria-Rosa L. Cioni, Florian Niederhofer, Jonathan Diaz, Anna B. A. Queiroz, Gal Matijevic, and Cristina Chiappini. "Proper motion of the Magellanic Bridge: Removal of foreground stars." Proceedings of the International Astronomical Union 14, S353 (June 2019): 128–29. http://dx.doi.org/10.1017/s1743921319008135.
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AbstractThe Large and Small Magellanic Cloud (LMC and SMC) are the most luminous dwarf galaxy satellites of the Milky Way. Thanks to their close proximity (50-60 kpc), they provide one of the best opportunities to study in detail the kinematics of resolved stellar populations in an interacting pair of galaxies. Large photometric surveys like the ongoing Gaia mission and the near-infrared VISTA survey of the Magellanic Cloud system (VMC) will have a significant impact on our insight into the Magellanic system. We have combined the individual strengths of VMC and Gaia DR2 data to improve our understanding of the internal kinematics of the galaxies. In this study, we present results from our ongoing project dedicated to measure and analyse the proper motions of large samples of stars across the Magellanic Clouds, efficiently removing Milk Way foreground stars utilising distances derived with the StarHorse code.
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Niemela, Virpi S., Roberto Gamen, Nidia I. Morrell, and Sixto Giménez Benítez. "Wolf-Rayet binaries: old friends and new acquaintances." Symposium - International Astronomical Union 193 (1999): 26–37. http://dx.doi.org/10.1017/s0074180900204890.
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Observations of WR stars in binary systems are discussed, emphasizing constraints on our knowledge of the binary frequency of WR stars, and of WR stars as a distinctive class of objects. Radial velocity orbits of newly discovered binaries, e.g., WR 29, a short period WN7+OB binary in our Galaxy, and SMC/AB 7, a massive WN+O7 binary in the Small Magellanic Cloud, are presented. New spectroscopic observations of binary systems with previously known orbits are also reported, showing in the case of WR 21 evidence of change of the orbital elements as derived from different spectral lines. An elliptic orbit for CV Ser is also illustrated.
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Smith, Lindsey F. "Wolf-Rayet stars in the Magellanic Clouds." Symposium - International Astronomical Union 148 (1991): 267–72. http://dx.doi.org/10.1017/s0074180900200570.
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The most striking feature of the Wolf-Rayet stars in the Magellanic Clouds is their subtype distribution. The range of WC subtypes found in the Large and Small Cloud agrees with evolutionary model predictions at the corresponding metallicities. It follows that the WR subtype distribution in any external galaxy is a clear indicator of the metallicity in that galaxy.The fluxes in the emission lines of WC stars appear to be consistent within the LMC. This can be used (with some precautions) in the Milky Way and other galaxies to determine reddening, distance and the numbers of WR stars in compact regions.
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Bekki, Kenji. "Triggered star formation in the Magellanic Clouds." Proceedings of the International Astronomical Union 2, S237 (August 2006): 373–77. http://dx.doi.org/10.1017/s1743921307001755.
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AbstractWe discuss how tidal interaction between the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), and the Galaxy triggers galaxy-wide star formation in the Clouds for the last ~0.2 Gyr based on our chemodynamical simulations on the Clouds. Our simulations demonstrate that the tidal interaction induces the formation of asymmetric spiral arms with high gas densities and consequently triggers star formation within the arms in the LMC. Star formation rate in the present LMC is significantly enhanced just above the eastern edge of the LMC's stellar bar owing to the tidal interaction. The location of the enhanced star formation is very similar to the observed location of 30 Doradus, which suggests that the formation of 30 Doradus is closely associated with the last Magellanic collision about 0.2 Gyr ago. The tidal interaction can dramatically compress gas initially within the outer part of the SMC so that new stars can be formed from the gas to become intergalactic young stars in the inter-Cloud region (e.g., the Magellanic Bridge). The metallicity distribution function of the newly formed stars in the Magellanic Bridge has a peak of [Fe/H] ~−0.8, which is significantly lower than the stellar metallicity of the SMC.
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Lozinskaya, Tatiana A. "Interstellar gas around WO stars in the Galaxy and the Magellanic Clouds." Symposium - International Astronomical Union 148 (1991): 438–39. http://dx.doi.org/10.1017/s0074180900201113.
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The four oxygen-sequence WR stars, Sand 1 in the Small Magellanic Cloud (SMC), Sand 2 in the Large Magellanic Cloud (LMC), and WR 102 and WR 142 in the Galaxy represent the latest stage of the evolution of massive stars (Sanduleak 1971, Barlow and Hummer 1982, Moffatet al.1985). We have shown WR 102 to be a stripped CO core of a supermassive star (Dopitaet al.1990), probably seen only several thousand years before a SN explosion. The four stars are characterized by extremely energetic stellar winds –Vw from 4500 to 7400 km/s (Barlow and Hummer 1982, Dopitaet al.1990, Torreset al.1986). Examination of the environments of WO stars leads to the conclusion that the four objects appear to be associated with optical and/or IR shell-like structures, although the short WO-superwind does not prevail in the shell's formation.
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Niemela, V. S., M. A. Cerruti, N. I. Morrell, and H. G. Luna. "Observations of Two Binary Systems with 04f Type Components." Symposium - International Astronomical Union 151 (1992): 505–8. http://dx.doi.org/10.1017/s0074180900122831.
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We present linear polarization observations of two binary systems with early Of type components, namely Sk-67°105 in the Large Magellanic Cloud, and LSS 3074 in our Galaxy. Both binaries show phase-locked polarization variations, from which we determined orbital inclinations for the systems.
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Graham, J. A. "Old Globular Clusters in the Magellanic Clouds." Symposium - International Astronomical Union 126 (1988): 151–58. http://dx.doi.org/10.1017/s0074180900042455.
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The old globular clusters in the Magellanic Clouds are important links between our understanding of globular clusters in our own galaxy and similar unresolved objects in more distant galaxies. The Cloud clusters spread over a large range in age. Several contain RR Lyrae variable stars. High weight abundance data are needed for individual cluster members as well as deeper color-magnitude diagrams.
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Bartzakos, P., A. F. J. Moffat, and V. S. Niemela. "A spectroscopic search for colliding winds in a complete sample of WC/WO stars in the Magellanic Clouds." Symposium - International Astronomical Union 163 (1995): 406–10. http://dx.doi.org/10.1017/s0074180900202374.
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The Magellanic Clouds provide an ideal laboratory to study the properties of Wolf-Rayet stars. In particular, the 25 WC/WO stars that they contain are nearly all of the same sub-class (21 WC4, one WC5, one WC6 and one WO in the Large Magellanic Cloud; one WO in the Small Magellanic Cloud). This, along with their formation in the same isolated environment, suggests that the wind structure is similar in each star. Thus, a study of other characteristics, such as the effects of binary separation and period on binary wind collisions, can be undertaken with little concern for differing winds. Some 30 high-quality CCD spectra for each of the 25 stars were obtained during three observing missions in the past decade. Although the analysis is not yet complete, the sample clearly contains four large-amplitude WR+O binaries with periods ranging from two to seventeen days and possibly other long-period systems. This paper deals with the wind interaction of the star B22.
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Bekki, Kenji, and Masashi Chiba. "Origin of Structural and Kinematic Properties of the Small Magellanic Cloud." Publications of the Astronomical Society of Australia 26, no. 1 (2009): 37–57. http://dx.doi.org/10.1071/as08020.
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AbstractWe investigate structural, kinematic and chemical properties of stars and gas in the Small Magellanic Cloud (SMC) interacting with the Large Magellanic Cloud (LMC) and the Galaxy based on a series of self-consistent chemodynamical simulations. We adopt a new ‘dwarf spheroidal model’ in which the SMC initially has both old stars with a spherical spatial distribution and an extended Hi gas disk. We mainly investigate the evolution of the SMC for the last ∼3 Gyr, during which the Magellanic Stream (MS) and the Magellanic Bridge (MB) could have formed as a result of the LMC–SMC–Galaxy interaction. Our principal results, which can be tested against observations, are as follows: The final spatial distribution of the old stars projected onto the sky is spherical, even after strong LMC–SMC–Galaxy interaction, whereas that of the new ones is significantly flattened and appears to form a bar structure. Old stars have a line-of-sight velocity dispersion σ ≃ 30 km s−1 and slow rotation, with a maximum rotational velocity, V < 20 km s−1 and show asymmetry in the radial profiles. New stars have a smaller Σ than old ones and a significant amount of rotation (V/σ > 1). Hi gas shows velocity dispersions of σ = 10–40 km s−1, a high maximum rotational velocity (V ∼ 50 km s−1) and a spatial distribution similar to that of new stars. New stars with ages younger than 3 Gyr show a negative metallicity gradient in the sense that more metal-rich stars are located in the inner regions of the SMC. The MB inevitably contains old stars with surface mass densities of 6−300 × 104 M⊙ deg−2 depending on initial stellar distributions of the modeled SMC. We find that the dwarf spheroidal model can explain more self-consistently the observed kinematic properties of stars and gas, compared with another type of the model (‘the disk model’) in which the SMC initially consists of stellar and gas disks. We suggest that, to better understand its evolution, the SMC needs to be modeled as having a spheroidal component, rather than being a pure disk.
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Gouliermis, Dimitrios A. "The sub-solar initial mass function in the Large Magellanic Cloud." Proceedings of the International Astronomical Union 4, S256 (July 2008): 250–55. http://dx.doi.org/10.1017/s1743921308028524.
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AbstractThe Magellanic Clouds offer a unique variety of star forming regions seen as bright nebulae of ionized gas, related to bright young stellar associations. Nowadays, observations with the high resolving efficiency of the Hubble Space Telescope allow the detection of the faintest infant stars, and a more complete picture of clustered star formation in our dwarf neighbors has emerged. I present results from our studies of the Magellanic Clouds, with emphasis in the young low-mass pre-main sequence populations. Our data include imaging with the Advanced Camera for Surveys of the association LH 95 in the Large Magellanic Cloud, the deepest observations ever taken with HST of this galaxy. I discuss our findings in terms of the initial mass function, which we constructed with an unprecedented completeness down to the sub-solar regime, as the outcome of star formation in the low-metallicity environment of the LMC.
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Clementini, G., L. Baldacci, A. Bragaglia, E. Carretta, L. Di Fabrizio, R. G. Gratton, C. Greco, et al. "Distance scale, variable stars and stellar populations in Local Group galaxies." International Astronomical Union Colloquium 193 (2004): 60–64. http://dx.doi.org/10.1017/s0252921100010344.
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AbstractWe present an overview of our study of the short period variable stars in the Large Magellanic Cloud, and in the dwarf galaxies Fornax, Leo I, and NGC 6822. Light curves are presented for RR Lyrae stars, Anomalous Cepheids and, for the first time, for Dwarf Cepheids in the field and in the globular cluster #3 of the Fornax galaxy.
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Schmidt, Thomas, Maria-Rosa Cioni, Florian Niederhofer, Jonathan Diaz, and Gal Matijevic. "VMC proper motions of the Magellanic Bridge." Proceedings of the International Astronomical Union 14, S344 (August 2018): 130–33. http://dx.doi.org/10.1017/s1743921318006762.
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AbstractDwarf galaxies enable us to study early phases of galaxy evolution and are key to many open questions about the hierarchical structure of the Universe. The Large and Small Magellanic Cloud (LMC and SMC) are the most luminous dwarf galaxy satellites of the Milky Way (MW). They are most likely gravitationally bound to each other, and their last interaction occurred about 200 Myr ago. Also, they are in an early phase of minor merging with the MW and will impact the Galactic structure in the future because of their relatively large mass. However, there are still major uncertainties regarding their origin and their interactions with one another and with the Milky Way. We cross-correlated the VMC and Gaia DR2 data to select a sample of stars that likely belong to the Magellanic Bridge, a feature formed of gas and stars which is connecting the LMC and the SMC. We removed potential MW foregound stars using a combination of parallax and colour-magnitude criteria and calculated the proper motions of the Bridge member stars. Our analysis supports a motion of star towards the LMC, which was found to be in good agreement with a dynamical simulation, of the SMC being stripped by the LMC.
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Udalski, Andrzej. "Eclipsing Binaries in the Magellanic Clouds." Highlights of Astronomy 13 (2005): 451. http://dx.doi.org/10.1017/s153929960001618x.
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We present results of a search for eclipsing binaries in the Magellanic Cloud fields covering central parts of these galaxies. The data were collected during the second phase of the Optical Gravitational Lensing Experiment survey (OGLE-II) in 1997-2000. In total, about 1500 and 3000 eclipsing stars were found in the Small and Large Magellanic Cloud, respectively (Udalski et al. 1998, Wyrzykowski et al. 2003). The photometric data of all objects are available to the astronomical community from the OGLE Internet archive (http://sirius.astrouw.edu.pl/~ogle/). OGLE-II data contain a full variety of classical eclipsing objects of all types: Algol EA-type, β-Lyr EB-type and W UMA EW-type stars. Large samples of stars allow to study in detail statistical properties of eclipsing objects. OGLE data also contain many very unusual eclipsing stars. Examples include eclipsing variable B-type stars (Mennickent et al. 2003), many spotted stars or eclipsing stars with a Cepheid as a component (Udalski et al. 1999). Recently three objects from the LMC revealing simultaneously RR Lyr and eclipsing binary type variability were discovered (Soszyński et al 2003). If the follow-up observations confirm that both components are physically bound and not optical blends these stars will provide a unique opportunity of direct determination of physical parameters of RR Lyr pulsating stars.
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Meixner, Margaret, Jean-Philippe Bernard, Robert D. Blum, Remy Indebetouw, William Reach, Sundar Srinivasan, Marta Sewilo, and Barbara A. Whitney. "Measuring the lifecycle of baryonic matter in the Large Magellanic Cloud with the Spitzer SAGE-LMC survey." Proceedings of the International Astronomical Union 4, S256 (July 2008): 3–8. http://dx.doi.org/10.1017/s1743921308028172.
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AbstractThe recycling of matter between the interstellar medium (ISM) and stars are key evolutionary drivers of a galaxy's baryonic matter. The Spitzer wavelengths provide a sensitive probe of circumstellar and interstellar dust and hence, allow us to study the physical processes of the ISM, the formation of new stars and the injection of mass by evolved stars and their relationships on the galaxy-wide scale of the LMC. Due to its proximity, favorable viewing angle, multi-wavelength information, and measured tidal interactions with the Small Magellanic Cloud (SMC), the LMC is uniquely suited for surveying the agents of a galaxy's evolution (SAGE), the ISM and stars. The SAGE-LMC project is measuring these key transition points in the life cycle of baryonic matter in the LMC. Here we present a connective view of the preliminary quantities estimated from SAGE-LMC for the total mass of the ISM, the galaxy wide star formation rate and the current stellar mass loss return. For context, we compare these numbers to the LMC's stellar mass.
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Lennon, Daniel J. "Massive star evolution in the Small Magellanic Cloud." Symposium - International Astronomical Union 212 (2003): 308–15. http://dx.doi.org/10.1017/s0074180900212370.
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We discuss abundances for eight early B-type giant/supergiant stars in the SMC cluster NGC 330. All are nitrogen rich with an abundance approximately 1.3 dex higher than an SMC main-sequence field. Given the number of B-type stars with low rotational projected velocities in NGC 330 (all our targets have v sin i < 50 kms–1), we suggest that it is unlikely that the stars in our sample are seen almost pole-on, but rather that they are intrinsically slow rotators. Comparing these results with the predictions of stellar evolution models including the effects of rotationally induced mixing, we conclude that while the abundance patterns may indeed be reproduced, those models with initially large rotational velocities do not reproduce the observed range of effective temperatures of our sample, nor the currently observed rotational velocities. Binary models may be able to produce stars in the observed temperature range and provide a promising alternative to single star models for explaining the observations. We also discuss the clear need for stellar evolution calculations employing the correct chemical mix of carbon, nitrogen and oxygen for the SMC.
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Zivkov, Viktor, Joana M. Oliveira, Monika G. Petr-Gotzens, Stefano Rubele, Maria-Rosa L. Cioni, Jacco Th van Loon, Richard de Grijs, et al. "The VMC survey – XXXVI. Young stellar variability in the Large Magellanic Cloud." Monthly Notices of the Royal Astronomical Society 494, no. 1 (March 4, 2020): 458–86. http://dx.doi.org/10.1093/mnras/staa626.
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ABSTRACT Studies of young stellar objects (YSOs) in the Galaxy have found that a significant fraction exhibits photometric variability. However, no systematic investigation has been conducted on the variability of extragalactic YSOs. Here we present the first variability study of massive YSOs in an $\sim 1.5\, \mathrm{deg^2}$ region of the Large Magellanic Cloud (LMC). The aim is to investigate whether the different environmental conditions in the metal-poor LMC ($\sim 0.4\!-\!0.5\, \mathrm{Z_{\odot }}$) have an impact on the variability characteristics. Multi-epoch near-infrared (NIR) photometry was obtained from the VISTA Survey of the Magellanic Clouds (VMC) and our own monitoring campaign using the VISTA telescope. By applying a reduced χ2-analysis, stellar variability was identified. We found 3062 candidate variable stars from a population of 362 425 stars detected. Based on several Spitzer studies, we compiled a sample of high-reliability massive YSOs: a total of 173 massive YSOs have NIR counterparts (down to $K_s\sim 18.5\,$mag) in the VMC catalogue, of which 39 display significant (>3σ) variability. They have been classified as eruptive, fader, dipper, short-term variable, and long-period variable YSOs based mostly on the appearance of their Ks-band light curves. The majority of YSOs are aperiodic; only five YSOs exhibit periodic light curves. The observed amplitudes are comparable or smaller than those for Galactic YSOs (only two Magellanic YSOs exhibit $\Delta K_s\gt 1\,$mag), not what would have been expected from the typically larger mass accretion rates observed in the Magellanic Clouds.
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Niemela, Virpi S. "Spectroscopic Binaries in the LMC." Symposium - International Astronomical Union 116 (1986): 85–86. http://dx.doi.org/10.1017/s007418090014865x.
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Preliminary results are presented of an observing programme aimed to obtain estimates of the stellar masses from studies of spectroscopic binary systems in the Large Magellanic Cloud. These are the first steps with the final purpose to determine an empirical mass-luminosity relation in a galaxy other than our own.
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Muraveva, T., G. Clementini, C. Maceroni, and M. I. Moretti. "The structure of the Large Magellanic Cloud from hot binary stars and Classical Cepheids." EAS Publications Series 64 (2013): 409–10. http://dx.doi.org/10.1051/eas/1364069.
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Schmidt, Thomas, Maria-Rosa L. Cioni, Florian Niederhofer, Kenji Bekki, Cameron P. M. Bell, Richard de Grijs, Jonathan Diaz, et al. "The VMC survey." Astronomy & Astrophysics 641 (September 2020): A134. http://dx.doi.org/10.1051/0004-6361/202037478.
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Context. The Magellanic Clouds are a nearby pair of interacting dwarf galaxies and satellites of the Milky Way. Studying their kinematic properties is essential to understanding their origin and dynamical evolution. They have prominent tidal features and the kinematics of these features can give hints about the formation of tidal dwarfs, galaxy merging and the stripping of gas. In addition they are an example of dwarf galaxies that are in the process of merging with a massive galaxy. Aims. The goal of this study is to investigate the kinematics of the Magellanic Bridge, a tidal feature connecting the Magellanic Clouds, using stellar proper motions to understand their most recent interaction. Methods. We calculated proper motions based on multi-epoch Ks-band aperture photometry, which were obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA), spanning a time of 1−3 yr, and we compared them with Gaia Data Release 2 (DR2) proper motions. We tested two methods for removing Milky Way foreground stars using Gaia DR2 parallaxes in combination with VISTA photometry or using distances based on Bayesian inference. Results. We obtained proper motions for a total of 576 411 unique sources over an area of 23 deg2 covering the Magellanic Bridge including mainly Milky Way foreground stars, background galaxies, and a small population of possible Magellanic Bridge stars (< 15 000), which mostly consist of giant stars with 11.0 < Ks < 19.5 mag. The first proper motion measurement of the Magellanic Bridge centre is 1.80 ± 0.25 mas yr−1 in right ascension and −0.72 ± 0.13 mas yr−1 in declination. The proper motion measurements of stars along the Magellanic Bridge from the VISTA survey of the Magellanic Cloud system (VMC) and Gaia DR2 data confirm a flow motion from the Small to the Large Magellanic Cloud. This flow can now be measured all across the entire length of the Magellanic Bridge. Conclusions. Our measurements indicate that the Magellanic Bridge is stretching. By converting the proper motions to tangential velocities, we obtain ∼110 km s−1 in the plane of the sky. Therefore it would take a star roughly 177 Myr to cross the Magellanic Bridge.
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Zinn, R., X. Chen, A. C. Layden, and D. I. Casetti-Dinescu. "Local RR Lyrae stars: native and alien." Monthly Notices of the Royal Astronomical Society 492, no. 2 (December 23, 2019): 2161–76. http://dx.doi.org/10.1093/mnras/stz3580.
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ABSTRACT Measurements of [Fe/H] and radial velocity are presented for 89 RR Lyrae (RRL) candidates within 6 kpc of the Sun. After the removal of two suspected non-RRLs, these stars were added to an existing data base, which yielded 464 RRLs with [Fe/H] on a homogeneous scale. Using data from the Gaia satellite (Data Release 2), we calculated the positions and space velocities for this sample. These data confirm the existence of a thin disc of RRL with [α/Fe] ∼ solar. The majority of the halo RRLs with large total energies have near-zero angular momenta about the Z-axis. Kinematically, these stars closely resemble the Gaia-Sausage/Gaia-Enceladus stars that others have proposed are debris from the merger of a large galaxy with the Milky Way. The metallicity and period distributions of the RRLs and their positions in the period–amplitude diagram suggest that this disrupted galaxy was as massive as the Large Magellanic Cloud and possibly greater.
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Mastropietro, Chiara. "Modeling a high velocity LMC: The formation of the Magellanic Stream." Proceedings of the International Astronomical Union 4, S256 (July 2008): 117–21. http://dx.doi.org/10.1017/s1743921308028330.
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AbstractI use high resolution N-body/SPH simulations to model the new proper motion of the Large Magellanic Cloud (LMC) within the Milky Way (MW) halo and investigate the effects of gravitational and hydrodynamical forces on the formation of the Magellanic Stream (MS). Both the LMC and the MW are fully self consistent galaxy models embedded in extended cuspy ΛCDM dark matter halos. I find that ram-pressure from a low density ionized halo is sufficient to remove a large amount of gas from the LMC's disk forming a trailing Stream that extends more than 120 degrees from the Cloud. Tidal forces elongate the satellite's disk but do not affect its vertical structure. No stars become unbound showing that tidal stripping is almost effectless.
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El Youssoufi, Dalal, Maria-Rosa L. Cioni, Cameron P. M. Bell, Stefano Rubele, Kenji Bekki, Richard de Grijs, Léo Girardi, et al. "The VMC survey – XXXIV. Morphology of stellar populations in the Magellanic Clouds." Monthly Notices of the Royal Astronomical Society 490, no. 1 (September 3, 2019): 1076–93. http://dx.doi.org/10.1093/mnras/stz2400.
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ABSTRACT The Magellanic Clouds are nearby dwarf irregular galaxies whose morphologies show different properties when traced by different stellar populations, making them an important laboratory for studying galaxy morphologies. We study the morphology of the Magellanic Clouds using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds system. We used about 10 and 2.5 million sources across an area of ∼105 and ∼42 deg2 towards the Large and Small Magellanic Cloud (LMC and SMC), respectively. We estimated median ages of stellar populations occupying different regions of the near-infrared (J − Ks, Ks) colour–magnitude diagram. Morphological maps were produced and detailed features in the central regions were characterized for the first time with bins corresponding to a spatial resolution of 0.13 kpc (LMC) and 0.16 kpc (SMC). In the LMC, we find that main-sequence stars show coherent structures that grow with age and trace the multiple spiral arms of the galaxy, star-forming regions become dimmer as we progress in age, while supergiant stars are centrally concentrated. Intermediate-age stars, despite tracing a regular and symmetrical morphology, show central clumps and hints of spiral arms. In the SMC, young main-sequence stars depict a broken bar. Intermediate-age populations show signatures of elongation towards the Magellanic Bridge that can be attributed to the LMC–SMC interaction ∼200 Myr ago. They also show irregular central features suggesting that the inner SMC has also been influenced by tidal interactions.
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Miszalski, Brent, Ralph Napiwotzki, Maria-Rosa L. Cioni, Martin A. T. Groenewegen, Jose M. Oliveira, Andrzej Udalski, and Jia-Cai Nie. "Planetary nebulae in the VISTA Magellanic Cloud (VMC) Survey." Proceedings of the International Astronomical Union 7, S283 (July 2011): 444–45. http://dx.doi.org/10.1017/s1743921312011842.
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AbstractThe multi-epoch YJKs sub-arcsecond photometry of the VMC survey provides a long anticipated deep near-infrared (NIR) window into further understanding the stellar populations of the Magellanic Clouds. The first year of observations consisted of six tiles covering ~9% of the Large Magellanic Cloud (LMC) survey region and contains 102 objects previously classified as planetary nebulae (PNe). A large proportion of the sample were found to be contaminated by non-PNe. These initial results underline the importance of establishing a clean catalogue of LMC PNe before they are applied in areas such as the planetary nebula luminosity function (PNLF) and searches for binary central stars. As the VMC survey progresses it will play a fundamental role in cleaning extant PN catalogues and a complementary role in the discovery of new PNe.
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Shara, Michael M., Steven M. Crawford, Dany Vanbeveren, Anthony F. J. Moffat, David Zurek, and Lisa Crause. "The spin rates of O stars in WR+O Magellanic Cloud binaries." Monthly Notices of the Royal Astronomical Society 492, no. 3 (January 8, 2020): 4430–36. http://dx.doi.org/10.1093/mnras/staa038.
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ABSTRACT Some massive, merging black holes (BHs) may be descendants of binary O stars. The evolution and mass transfer between these O stars determine the spins of their progeny BH. These will be measurable with future gravitational wave detectors, incentivizing the measurement of the spins of O stars in binaries. We previously measured the spins of O stars in Galactic Wolf–Rayet (WR)+O binaries. Here we measure the ve sin i of four Large Magellanic Cloud (LMC) and two Small Magellanic Cloud (SMC) O stars in WR+O binaries to determine whether lower metallicity might affect the spin rates. We find that the O stars in Galactic and Magellanic WR+O binaries display average ve sin i = 258 ± 18 and 270 ± 15 km s−1, respectively. Two LMC O stars measured on successive nights show significant line width variability, possibly due to differing orbital phases exhibiting different parts of the O stars illuminated differently by their WR companions. Despite this variability, the ve sin i are highly supersynchronous but distinctly subcritical for the O stars in all these binaries; thus we conclude that an efficient mechanism for shedding angular momentum from O stars in WR+O binaries must exist. This mechanism, probably related to Roche lobe overflow (RLOF)-created dynamo magnetic fields, prevents nearly 100 per cent breakup spin rates, as expected when RLOF operates, as it must, in these stars. A Spruit–Tayler dynamo and O star wind might be that mechanism.
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Condori, C. A. H., M. Borges Fernandes, M. Kraus, D. Panoglou, and C. A. Guerrero. "The study of unclassified B[e] stars and candidates in the Galaxy and Magellanic Clouds†." Monthly Notices of the Royal Astronomical Society 488, no. 1 (June 6, 2019): 1090–110. http://dx.doi.org/10.1093/mnras/stz1540.
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ABSTRACT We investigated 12 unclassified B[e] stars or candidates, 8 from the Galaxy, 2 from the Large Magellanic Cloud (LMC), and 2 from the Small Magellanic Cloud (SMC). Based on the analysis of high-resolution spectroscopic (FEROS) and photometric data, we confirmed the presence of the B[e] phenomenon for all objects of our sample, except for one (IRAS 07455-3143). We derived their effective temperature, spectral type, luminosity class, interstellar extinction and, using the distances from Gaia DR2, we obtained their bolometric magnitude, luminosity, and radius. Modelling of the forbidden lines present in the FEROS spectra revealed information about the kinematics and geometry of the circumstellar medium of these objects. In addition, we analysed the light curves of four stars, finding their most probable periods. The evolutionary stage of 11 stars of our sample is suggested from their position on the HR diagram, taking into account evolutionary tracks of stars with solar, LMC, and SMC metallicities. As results, we identified B and B[e] supergiants, B[e] stars probably at the main sequence or close to its end, post-AGB and HAeB[e] candidates, and A[e] stars in the main sequence or in the pre-main sequence. However, our most remarkable results are the identification of the third A[e] supergiant (ARDB 54, the first one in the LMC), and of an ‘LBV impostor’ in the SMC (LHA 115-N82).
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Majewski, S. R., J. C. Ostheimer, W. E. Kunkel, K. V. Johnston, R. J. Patterson, and C. Palma. "A Search for Tidal Stellar Debris from the Magellanic Clouds: Survey Results from the First Two Years." Symposium - International Astronomical Union 190 (1999): 508–10. http://dx.doi.org/10.1017/s007418090011873x.
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An important discriminant between leading models for the origin of the Magellanic Stream is the presence of a stellar counterpart to the HI gas stream: ram pressure stripping of gas by a putative hot Galactic halo would act only on Magellanic gas while gravitational tidal stripping would act on both gas and stars. Several previous attempts to find tidal stellar debris have failed to find carbon stars, A stars, or other main sequence stars in the Magellanic Stream (Mathewson et al. 1979; Recillas-Cruz 1982; Brück & Hawkins 1983; Guhathakurta & Lin 1999). However, there has long been a suggestion (Kunkel 1979; Lynden-Bell 1982) of a possible Magellanic association of satellite galaxies and globular clusters that have similar orbits and may derive from the break up of a greater Magellanic galaxy (Lynden-Bell & Lynden-Bell 1995; Majewski et al. 1997). Recent models (Moore & Davis 1994; Johnston 1998) of the tidal disruption of Large Magellanic Cloud (LMC)-like systems indicate a wide dispersal of debris, much wider than the rather confined HI stream, so that the contrast of tidal debris against the Galactic fore/background would be low. If true, this could explain some of the previous negative results for tidal debris searches.
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Ostrov, P. G., V. S. Niemela, and N. I. Morrell. "Discovery of a Stellar Association Surrounding the Massive Binary Sk–67°105 in the Large Magellanic Cloud." Symposium - International Astronomical Union 190 (1999): 235–36. http://dx.doi.org/10.1017/s0074180900117905.
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Sk–67°105, a luminous O4f type stars in the Large Magellanic Cloud, is the exiting star of the H II region N 50 (DEM 193). Niemela & Morrell (1986) found this hot star to be a massive short period double lined spectroscopic binary. Because luminous OB stars are usually found in young stellar groups, we have searched for such an aggregate in the vicinity of Sk–67°105.Here we report, as a result of our search, the discovery of a new OB association in the LMC. We also find that Sk–67°105 is the most luminous star of a small compact cluster inside this OB association.
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Pritchard, J. D., W. Tobin, M. Clark, and E. F. Guinan. "CCD photometry of variable stars in the Magellanic Clouds -- VI. The eclipsing binary HV 982 in the Large Magellanic Cloud." Monthly Notices of the Royal Astronomical Society 299, no. 4 (October 1, 1998): 1087–96. http://dx.doi.org/10.1046/j.1365-8711.1998.01849.x.
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Antoniou, Vallia, Andreas Zezas, and Despina Hatzidimitriou. "A comprehensive study of the link between star-formation history and X-ray source populations in the SMC." Proceedings of the International Astronomical Union 4, S256 (July 2008): 355–60. http://dx.doi.org/10.1017/s1743921308028706.
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AbstractUsing Chandra, XMM-Newton and optical photometric catalogs we study the young X-ray binary (XRB) populations of the Small Magellanic Cloud (SMC). We find that the Be/X-ray binaries (Be-XRBs) are observed in regions with star-formation (SF) rate bursts ~30–70 Myr ago, which coincides with the age of maximum Be-star formation, while regions with strong but more recent SF (e.g., the Wing) are deficient in Be-XRBs. Using the 2dF spectrograph of the Anglo-Australian Telescope (AAT) we have obtained optical spectra of 20 High-Mass X-ray Binaries (HMXBs) in the SMC. All of these sources were proved to be Be-XRBs. Similar spectral-type distributions of Be-XRBs and Be field stars in the SMC have been found. On the other hand, the Be-XRBs in the Galaxy follow a different distribution than the isolated Be stars in the Galaxy, in agreement with previous studies.