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Post Info TOPIC: The Large Magellanic Cloud


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RE: The Large Magellanic Cloud
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Title: Extinction in the Large Magellanic Cloud
Authors: Nia Imara, Leo Blitz

We present an extinction map of the Large Magellanic Cloud (LMC), using 204,502 stars from the Two Micron All Sky Survey point source catalogue. We first use the NICE method to determine the reddening distribution, \ehk and \ejh, which we compare to the HI distribution to find a near-infrared reddening law of \ejh/\ehk=1.200.04. A visual extinction map (~6^\circ x 6^\circ) of the LMC is created using the NICER method; at 4 arcmin resolution, a mean value of \av=0.38 mag is found. We derive the LMC CO-to-H_2 conversion factor, \x{LMC}, independent of assumptions about the virialisation of giant molecular clouds, by comparing the NICER extinction map with NANTEN ^{12}CO observations. In regions where \av>1 mag and ^{12}CO emission is \ge 2 \counits, we measure \x{LMC}=9.30.4 x 10^{20} \xunits. In the same regions, the LMC contains a total molecular mass of (4.50.2) x 10^7 \msun.

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Title: A delta Scuti distance to the Large Magellanic Cloud
Authors: D. H. McNamara, G. Clementini, M. Marconi

We present results from a well studied delta Scuti star discovered in the LMC. The absolute magnitude of the variable was determined from the PL relation for Galactic delta Scuti stars and from the theoretical modelling of the observed B,V,I light curves. The two methods give distance moduli for the LMC of 18.460.19 and 18.480.15, respectively, for a consistent value of the stellar reddening of E(B-V)=0.080.02. We have also analysed 24 delta Scuti candidates discovered in the OGLE II survey of the LMC, and 7 variables identified in the open cluster LW 55 and in the galaxy disk by Kaluzny et al. (2003, 2006). We find that the LMC delta Scuti stars define a PL relation whose slope is very similar to that defined by the Galactic delta Scuti variables, and yield a distance modulus for the LMC of 18.500.22 mag. We compare the results obtained from the delta Scuti variables with those derived from the LMC RR Lyrae stars and Cepheids. Within the observational uncertainties, the three groups of pulsating stars yield very similar distance moduli. These moduli are all consistent with the "long" astronomical distance scale for the Large Magellanic Cloud.

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NGC1978
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Title: The globular cluster NGC 1978 in the Large Magellanic Cloud
Authors: Alessio Mucciarelli (Bologna Univ.), Francesco R. Ferraro (Bologna Univ.), Livia Origlia (INAF - OA Bologna), Flavio Fusi Pecci (INAF - OA Bologna)

We have used deep high-resolution Hubble Space Telescope ACS observations to image the cluster NGC 1978 in the Large Magellanic Cloud. This high-quality photometric data set allowed us to confirm the high ellipticity (~0.300.02) of this stellar system. The derived Colour Magnitude Diagram allowed a detailed study of the main evolutionary sequences: in particular we have detected the so called Bump along the Red Giant Branch (at V_{555}=19.100.10). This is the first detection of this feature in an intermediate-age cluster. Moreover the morphology of the evolutionary sequence and their population ratios have been compared with the expectations of different theoretical models (namely BaSTI, PEL and Padua) in order to quantify the effect of convective overshooting. The best agreement (both in terms of morphology and star counts) has been found the PEL (Pisa Evolutionary Library) isochrone with Z=0.008 (consistently with the most recent determination of the cluster metallicity, [M/H]=-0.37 dex) and a mild overshooting efficiency (Lambda_{os}=0.1). By adopting this theoretical set an age of 1.90.1 Gyr has been obtained.

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LH 95 Star-Forming Region
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Swirls of gas and dust reside in this ethereal-looking region of star formation imaged by NASA's Hubble Space Telescope. This majestic view of LH 95, located in the Large Magellanic Cloud, reveals a region where low-mass, infant stars and their much more massive stellar neighbours reside. A shroud of blue haze gently lingers amid the stars. The image was taken in March 2006 with Hubble's Advanced Camera for Surveys.

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RE: The Large Magellanic Cloud
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Title: Eclipsing binaries in the LMC: a wealth of data for astrophysical tests
Authors: A. Derekas, L. L. Kiss, T. R. Bedding

We have analysed publicly available MACHO observations of 6833 variable stars in the Large Magellanic Cloud, classified as eclipsing binaries. After finding that a significant fraction of the sample was misclassified, we redetermined periods and variability class for all stars, producing a clean sample of 3031 eclipsing binaries. We have investigated their distribution in the period-colour-luminosity space, which was used, for example, to assign a foreground probability to every object and establish new period-luminosity relations to selected types of eclipsing stars. We found that the orbital period distribution of LMC binaries is very similar to those of the SMC and the Milky Way. We have also determined the rate of period change for every star using the O-C method, discovering about 40 eclipsing binaries with apsidal motion, 45 systems with cyclic period changes and about 80 stars with parabolic O-C diagrams. In a few objects we discovered gradual amplitude variation, which can be explained by changes in the orbital inclination caused by a perturbing third body in the system.

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MACHO-LMC-20
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Title: Identification of the Microlens in Event MACHO-LMC-20
Authors: Nitya Kallivayalil (1), Brian M. Patten (1), Massimo Marengo (1), Charles Al**** (1), Michael W. Werner (2), Giovanni G. Fazio (1); (1)CfA (2)JPL

We report on the identification of the lens responsible for microlensing event MACHO-LMC-20. As part of a Spitzer/IRAC program conducting mid-infrared follow-up of the MACHO Large Magellanic Cloud microlensing fields, we discovered a significant flux excess at the position of the source star for this event. These data, in combination with high resolution near-infrared Magellan/PANIC data has allowed us to classify the lens as an early M dwarf in the thick disk of the Milky Way, at a distance of ~2 kpc. This is only the second microlens to have been identified, the first also being a M dwarf star in the disk. Together, these two events are still consistent with the expected frequency of nearby stars in the Milky Way thin and thick disks acting as lenses.

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RE: The Large Magellanic Cloud
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The scientists wove together information from thousands of infrared images captured by the Infrared Array Camera and the Multiband Imaging Photometer of NASA's Spitzer Space Telescope, an orbiting telescope managed by NASA's Jet Propulsion Laboratory in Pasadena, California.

Launched on a six-year mission in 2003, the Spitzer has been collecting snapshots of the universe at infrared wavelengths of light, a form of light that is invisible to the human eye. Examining the universe at such wavelengths is crucial because it allows astronomers to see objects in outer space that would otherwise be impossible to detect. At visible wavelengths, for example, many stars are completely shrouded in swirls of galactic dust. But when viewed with infrared light, the same stars become conspicuous.

www.news.wisc.edu

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A new image from NASA's Spitzer Space Telescope is helping astronomers understand how stardust is recycled in galaxies.

ssc2006LMC
Expand (336kb, 720x900)
Position (J2000): RA: 05h18m48.00s Dec: 68d34m12.00s
Credit: NASA/JPL-Caltech/M. Meixner (STScI) & the SAGE Legacy Team

The cosmic portrait shows the Large Magellanic Cloud, a nearby dwarf galaxy named after Ferdinand Magellan, the seafaring explorer who observed the murky object at night during his fleet's historic journey around Earth. Now, nearly 500 years after Magellan's voyage, astronomers are studying Spitzer's view of this galaxy to learn more about the circular journey of stardust, from stars to space and back again.

"The Large Magellanic Cloud is like an open book. We can see the entire lifecycle of matter in a galaxy in this one snapshot" - Dr. Margaret Meixner of the Space Telescope Science Institute, Baltimore

Meixner is lead author of a paper on the findings to appear in the November 2006 issue of the Astronomical Journal.
The vibrant false-colour image, a mosaic of approximately 300,000 individual frames, shows a central blue sea of stars amidst lots of colourful, choppy waves of dust.

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-- Edited by Blobrana at 23:36, 2006-08-31

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N180B
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This active region of star formation in the Large Magellanic Cloud (LMC), as photographed by NASA's Hubble Space Telescope, unveils wispy clouds of hydrogen and oxygen that swirl and mix with dust on a canvas of astronomical size. The LMC is a satellite galaxy of the Milky Way.

N 180B
Expand (1.13mb, 1280 x 1266)
Position (2000): R.A. 05h 48m 48s.65 Dec. -70 04' 27 ".36

This particular region within the LMC, referred to as N 180B, contains some of the brightest known star clusters. This image was taken with Hubble's Wide Field Planetary Camera 2 in 1998 using filters that isolate light emitted by hydrogen and oxygen gas.

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Magellanic Planetary Nebulae
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Title: Hubble Space Telescope Images of Magellanic Cloud Planetary Nebulae
Authors: Richard A. Shaw (NOAO), Letizia Stanghellini (NOAO), Eva Villaver (STScI/ESA), Max Mutchler (STScI)

We present images and slitless spectra which were obtained in HST surveys of Planetary Nebulae (PNe) in both the Large and Small Magellanic Clouds, using the Space Telescope Imaging Spectrograph. These new data on 59 PNe (54 in the LMC and five in the SMC) permit us to determine the nebular dimensions and morphology in the monochromatic light of several emission lines: Halpha, (N II) lambda 6583 and (O III) lambda 5007, plus others of varying ionisation, including (O I), He I, and (S II). We describe the nebular morphology and related features in detail. This survey, when combined with similar data from our prior HST programs and other archived PN images, brings the total of nebulae imaged with HST to 114 in the LMC and 35 in the SMC. We describe various basic properties for the sample, including sizes, morphologies, densities, and completeness. Trends in (O III) lambda 5007 flux, surface brightness, and electron density with physical radius suggest that many nebulae, particularly those with bipolar morphology, may be optically thick even at large size. Bipolars also show the most extreme values of (N II)/Halpha flux ratios, which is a rough indicator N enrichment.

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