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RE: The Large Magellanic Cloud
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Title: Massive runaway stars in the Large Magellanic Cloud
Authors: V.V. Gvaramadze, P. Kroupa, J. Pflamm-Altenburg

The origin of massive field stars in the Large Magellanic Cloud (LMC) has long been an enigma. The recent measurements of large offsets (~100 km/s) between the heliocentric radial velocities of some very massive (O2-type) field stars and the systemic LMC velocity provides a possible explanation of this enigma and suggests that the field stars are runaway stars ejected from their birth places at the very beginning of their parent cluster's dynamical evolution. A straightforward way to prove this explanation is to measure the proper motions of the field stars and to show that they are moving away from one of the nearby star clusters or OB associations. This approach however is complicated by the large distance to the LMC, which makes accurate proper motion measurements difficult. We use an alternative approach for solving the problem, based on the search for bow shocks produced by runaway stars. The geometry of detected bow shocks would allow us to infer the direction of stellar motion and thereby to determine their possible parent clusters. In this paper we present the results of a search for bow shocks around six massive field stars which were suggested in the literature as candidate runaway stars. Using archival (Spitzer Space Telescope) data, we found a bow shock associated with one of our program stars, the O2 V((f*)) star BI 237, which is the first-ever detection of bow shocks in the LMC. Orientation of the bow shock suggests that BI 237 was ejected from the OB association LH 82 (located at ~120 pc in projection from the star). A by-product of our search is the detection of bow shocks generated by four OB stars in the field of the LMC and an arc-like structure attached to the candidate luminous blue variable R81 (HD 269128). The geometry of two of these bow shocks is consistent with the possibility that their associated stars were ejected from the 30 Doradus star forming complex.

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A Cosmic Zoo in the Large Magellanic Cloud

Astronomers often turn their telescopes to the Large Magellanic Cloud (LMC), one of the closest galaxies to our own Milky Way, in their quest to understand the Universe. In this spectacular new image from the Wide Field Imager (WFI) at ESO's La Silla Observatory in Chile, a celestial menagerie of different objects and phenomena in part of the LMC is on display, ranging from vast globular clusters to the remains left by brilliant supernovae explosions. This fascinating observation provides data for a wide variety of research projects unravelling the life and death of stars and the evolution of galaxies.
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Posts: 128681
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Large Magellanic Cloud
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Title: Spitzer SAGE Infrared Photometry of Massive Stars in the Large Magellanic Cloud
Authors: A. Z. Bonanos, D. Massa, M. Sewilo, D. J. Lennon, N. Panagia, L. J. Smith, M. Meixner, B. Babler, S. Bracker, M. Meade, K.D. Gordon, J. L. Hora, R. Indebetouw, B. Whitney

We present a catalogue of 1750 massive stars in the Large Magellanic Cloud, with accurate spectral types compiled from the literature, and a photometric catalogue for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalogue consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3-24 microns in the UBVIJHKs+IRAC+MIPS24 bands. The resulting infrared colour-magnitude diagrams illustrate that the supergiant B[e], red supergiant and luminous blue variable (LBV) stars are among the brightest infrared point sources in the Large Magellanic Cloud, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ~900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/Lo>=4) and the rare, dusty progenitors of the new class of optical transients (e.g. SN 2008S and NGC 300 OT), plus the fact that cold dust is present in both types of objects, suggests a common origin for them. We find the infrared colours for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

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Posts: 128681
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LMC Point Radio Sources
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Title: The Strongest 100 Point Radio Sources in the LMC at 1.4 GHz
Authors: J. L. Payne, L. A. Tauber, M. D. Filipovic, E. J. Crawford, A. Y. De Horta
(Version v2)

We present the 100 strongest 1.4 GHz point sources from a new mosaic image in the direction of the Large Magellanic Cloud (LMC). The observations making up the mosaic were made over a ten year period and were combined with Parkes single dish data at 1.4 GHz to complete the image for short spacing. An initial list of co-identifications within 10" at 0.843, 4.8 and 8.6 GHz consisted of 2682 sources. Elimination of extended objects and artefact noise allowed the creation of a refined list containing 1988 point sources. Most of these are presumed to be background objects seen through the LMC; a small portion may represent compact H II regions, young SNRs and radio planetary nebulae. We find an average spectral index of -0.53 and present a 1.4 GHz image showing source location in the direction of the LMC.

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Posts: 128681
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Large Magellanic Cloud
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Title: Star Formation Around Supergiant Shells in the LMC
Authors: Laura G. Book (1,2), You-Hua Chu (1), Robert A. Gruendl (1), Yasuo Fukui (3) ((1) University of Illinois at Urbana-Champaign, (2) California Institute of Technology, (3) Nagoya University)
(Version v2)

We examine the recent star formation associated with four supergiant shells (SGSs) in the Large Magellanic Cloud (LMC): LMC 1, 4, 5, and 6, which have been shown to have simple expanding-shell structures. H II regions and OB associations are used to infer star formation in the last few Myr, while massive young stellar objects (YSOs) reveal the current ongoing star formation. Distributions of ionised, H I, and molecular components of the interstellar gas are compared with the sites of recent and current star formation to determine whether triggering has taken place. We find that a great majority of the current star formation has occurred in gravitationally unstable regions, and that evidence of triggered star formation is prevalent at both large and local scales.

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RE: The Large Magellanic Cloud
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Title: The LMC's Top 250: Classification of the Most Luminous Compact 8 micron Sources in the Large Magellanic Cloud
Authors: Joel H. Kastner (Rochester Institute of Technology), Stephen L. Thorndike (University of Rochester), Paul A. Romanczyk (Rochester Institute of Technology), Catherine Buchanan (University of Melbourne), Bruce J. Hrivnak (Valparaiso University), Raghvendra Sahai (NASA/JPL), Michael Egan (National Geospatial-Intelligence Agency)
(Version v4)

To ascertain the nature of the brightest compact mid-infrared sources in the Large Magellanic Cloud (LMC), we have applied an updated version of the Buchanan et al. (2006) 2MASS-MSX colour classification system, which is based on the results of Spitzer Space Telescope spectroscopy, to a mid-infrared (8 micron) flux-limited sample of 250 LMC objects for which 2MASS and MSX photometry is available. The resulting 2MASS-MSX ("JHK8") colour-based classifications of these sources, which constitute the most mid-IR-luminous objects in the LMC, were augmented, cross-checked, and corrected where necessary via a variety of independent means, such that only 47 sources retain tentative classifications and only 10 sources cannot be classified at all. The sample is found to consist primarily of carbon-rich AGB stars (~35%), red supergiants (~18%), and compact H II regions (~30%), with additional, small populations of oxygen-rich AGB stars (~4%), dusty, early-type emission-line stars (~3%), and foreground, O-rich AGB stars in the Milky Way (~3%). The very large ratio of C-rich to O-rich objects among the luminous and heavily dust-enshrouded AGB stars in our LMC IR source sample is consistent with the hypothesis that carbon stars form easily in lower metallicity environments. We demonstrate that very luminous C-rich and O-rich AGB stars and red supergiants, identified here primarily on the basis of their JHK8 colours, also appear as distinct clusters in Spitzer IRAC/MIPS colour-colour diagrams. Thus, in principle, the IRS-based IR photometric classification techniques applied here to the LMC can be applied to any external galaxy whose most luminous IR point sources are detectable and resolvable by 2MASS and Spitzer.

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Title: CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters
Authors: B. Kumar, R. Sagar, J. Melnick

We present CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters namely NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2006, SL 538, NGC 2011, NGC 2098 and NGC 2136. The BVRI data reaching down to V ~ 21 mag, are collected from 3.5-meter NTT/EFOSC2 in sub-arcsec seeing conditions. For NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2011 and NGC 2136, broad band photometric CCD data are presented for the first time. Seven of the 9 clusters have ages between 16 to 25 Myr while remaining two clusters have ages 32 4 Myr (NGC 2098) and 90 10 Myr (NGC 2136). For 7 younger clusters, the age estimates based on a recent model and the integrated spectra are found to be systematically lower (~ 10 Myr) from the present estimate. In the mass range of ~ 2 - 12 solar masses, the MF slopes for 8 out of nine clusters were found to be similar with the value of \gamma ranging from -1.90 0.16 to -2.28 0.21. For NGC 1767 it is flatter with \gamma = -1.23 0.27. Mass segregation effects are observed for NGC 2002, NGC 2006, NGC 2136 and NGC 2098. This is consistent with the findings of Kontizas et al. for NGC 2098. Presence of mass segregation in these clusters could be an imprint of star formation process as their ages are significantly smaller than their dynamical evolution time. Mean MF slope of \gamma = -2.22 0.16 derived for a sample of 25 young ( 100 Myr) dynamically unevolved LMC stellar systems provide support for the universality of IMF in the intermediate mass range ~ 2-12 solar masses.

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Posts: 128681
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LMC X-3
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Title: LMC X-3 May Be a Relic of a GRB Similar to Cosmological GRBs
Authors: G.E. Brown, C.-H. Lee, E. Moreno Mendez

The present scenario for high-luminosity long gamma-ray bursts is strongly influenced by the paper of Fruchter et al. (2006). Whereas the main contention of this paper that these GRBs occur in low-metallicity irregular galaxies is based on a considerable collection of observational results and although the main thesis is doubtless correct, the paper does not explain the dynamics that produces such GRBs and much of the discussion not directly concerning the main thesis is wrong. We propose a dynamics and elucidate how the Fruchter et al. (2006) results may be tested, in our neighbourhood in the LMC, suggesting that LMC X-3 is a relic of a high luminosity explosion, probably accompanied by a GRB and hypernova explosion. The way to test our suggestion is to measure the system velocity of the present black hole. We correct errors of the Fruchter et al. paper in stellar evolution, so that the study of GRBs is consistent with it. We show that the subluminous GRB 060218 had a low-mass black hole as central engine.

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Posts: 128681
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RE: The Large Magellanic Cloud
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Title: Proper Motions of the LMC and SMC: Reanalysis of Hubble Space Telescope Data
Authors: S. Piatek, C. Pryor, E. W. Olszewski

Kallivayalil et al. have used the Hubble Space Telescope to measure proper motions of the LMC and SMC using images in 21 and five fields, respectively, all centred on known QSOs. These results are more precise than previous measurements, but have surprising and important physical implications: for example, the LMC and SMC may be approaching the Milky Way for the first time; they might not have been in a binary system; and the origin of the Magellanic Stream needs to be re-examined. Motivated by these implications, we have reanalysed the original data in order to check the validity of these measurements. Our work has produced a proper motion for the LMC that is in excellent agreement with that of Kallivayalil et al., and for the SMC that is in acceptable agreement.
We have detected a dependence between the brightness of stars and their mean measured motion in a majority of the fields in both our reduction and that of Kallivayalil et al. Correcting for this systematic error and for the errors caused by the decreasing charge transfer efficiency of the detector produces better agreement between the measurements from different fields. With our improved reduction, we do not need to exclude any fields from the final averages and, for the first time using proper motions, we are able to detect the rotation of the LMC. The best-fit amplitude of the rotation curve at a radius of 275 arcmin in the disk plane is 120 15 km s^-1. This value is larger than the 60--70 km s^-1 derived from the radial velocities of HI and carbon stars, but in agreement with the value of 107 km s^-1 derived from the radial velocities of red supergiants.

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Title: SPITZER SAGE Observations of Large Magellanic Cloud Planetary Nebulae
Authors: J. L. Hora, M. Cohen, R. G. Ellis, M. Meixner, R. D. Blum, W. B. Latter, B. A. Whitney, M. R. Meade, R. Indebetouw, K. Gordon, B.-Q. For, M. Block, K. Misselt, U. Vijh, C. Leitherer

We present IRAC and MIPS images and photometry of a sample of previously known planetary nebulae (PNe) from the SAGE survey of the Large Magellanic Cloud (LMC) performed with the Spitzer Space Telescope. Of the 233 known PNe in the survey field, 185 objects were detected in at least two of the IRAC bands, and 161 detected in the MIPS 24 micron images. Colour-colour and colour-magnitude diagrams are presented using several combinations of IRAC, MIPS, and 2MASS magnitudes. The location of an individual PN in the colour-colour diagrams is seen to depend on the relative contributions of the spectral components which include molecular hydrogen, polycyclic aromatic hydrocarbons (PAHs), infrared forbidden line emission from the ionised gas, warm dust continuum, and emission directly from the central star. The sample of LMC PNe is compared to a number of Galactic PNe and found to not significantly differ in their position in colour-colour space. We also explore the potential value of IR PNe luminosity functions (LFs) in the LMC. IRAC LFs appear to follow the same functional form as the well-established [O III] LFs although there are several PNe with observed IR magnitudes brighter than the cut-offs in these LFs.

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