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Post Info TOPIC: The Large Magellanic Cloud
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RE: The Large Magellanic Cloud
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Dusty Space Cloud

614848main_pia15254-43_946-710.jpg

This new image shows the Large Magellanic Cloud galaxy in infrared light as seen by the Herschel Space Observatory, a European Space Agency-led mission with important NASA contributions, and NASA's Spitzer Space Telescope. In the instruments' combined data, this nearby dwarf galaxy looks like a fiery, circular explosion.

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Large Magellanic Cloud Cepheids
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Title: Large Magellanic Cloud Cepheids in the ASAS data
Authors: P. Karczmarek, W. A. Dziembowski, P. Lenz, P. Pietrukowicz, G. Pojmanski

A catalogue of Cepheids in the Large Magellanic Cloud (LMC) from the ASAS project is presented. It contains data on 65 fundamental mode pulsators with periods longer than about 8 days. The period-luminosity (PL) relation in the V-band does not significantly differ from the relation determined by Soszynski et al. (2008) from the OGLE data extended toward longer periods but with much larger spread. For objects with periods longer than 40 days there is an evidence for a shallower PL relation. The rates of long-term period variations significant at 3 sigma level are found only for 7 objects. The rates for 25 objects determined with the 1 sigma significance are confronted with the values derived from stellar evolution models. The models from various sources yield discrepant predictions. Over the whole data range, a good agreement with measurements is found for certain models but not from the same source.

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Blobrana


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RE: The Large Magellanic Cloud
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Title: H.E.S.S. observations of the Large Magellanic Cloud
Authors: Nu. Komin, A. Djannati-Ataï, Y. Gallant, V. Marandon, C.C. Lu, S. Ohm, E. de Oña Wilhelmi, for the H.E.S.S. collaboration

The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way at a distance of approximately 48 kpc. Despite its distance it harbours several interesting targets for TeV gamma-ray observations. The composite supernova remnant N 157B/PSR J05367-6910 was discovered by H.E.S.S. being an emitter of very high energy (VHE) gamma-rays. It is the most distant pulsar wind nebula ever detected in VHE gamma-rays. Another very exciting target is SN 1987A, the remnant of the most recent supernova explosion that occurred in the neighbourhood of the Milky Way. Models for Cosmic Ray acceleration in this remnant predict gamma-ray emission at a level detectable by H.E.S.S. but this has not been detected so far. Fermi/LAT discovered diffuse high energy (HE) gamma-ray emission from the general direction of the massive star forming region 30 Doradus but no clear evidence for emission from either N 157B or SN 1987A has been published. The part of the LMC containing these objects has been observed regularly with the H.E.S.S. telescopes since 2003. With deep observations carried out in 2010 a very good exposure of this part of the sky has been obtained. The current status of the H.E.S.S. LMC observations is reported along with new results on N 157B and SN 1987A.

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NEIGHBOUR GALAXY CAUGHT STEALING STARS

Astronomers from the National Optical Astronomy Observatory (NOAO) and their collaborators have found that hundreds of the stars found in the Large Magellanic Cloud (LMC) were stolen from another nearby galaxy - the Small Magellanic Cloud (SMC). The Large and Small Magellanic Clouds are both neighbour galaxies to our Milky Way Galaxy and easily visible to the unaided eye from the southern hemisphere.
By analysing the spectra of 5900 giant and supergiant stars in the Large Magellanic Cloud galaxy, NOAO astronomers Knut Olsen and Bob Blum, and their collaborators Dennis Zaritsky (University of Arizona), and Martha Boyer and Karl Gordon (Space Telescope Science Institute) found that over 5% of the stars they observed in the LMC are rotating counter to the direction of the majority of LMC stars, or perhaps in a plane that is greatly inclined to the rotation of the LMC. An ambiguity remains in the result, because the astronomers were only able to measure the projection of the stellar velocities into the line of sight, and not their full velocity vectors. In either case, these peculiar orbits indicate that these stars probably did not form from the rotating and collapsing cloud of gas that formed the LMC, a galaxy located about 160,000 light years away.

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Title: A Population of Accreted SMC Stars in the LMC
Authors: Knut A.G. Olsen, Dennis Zaritsky, Robert D. Blum, Martha L. Boyer, Karl D. Gordon

We present an analysis of the stellar kinematics of the Large Magellanic Cloud based on ~5900 new and existing velocities of massive red supergiants, oxygen-rich and carbon-rich AGB stars, and other giants. After correcting the line-of-sight velocities for the LMC's space motion and accounting for asymmetric drift in the AGB population, we derive a rotation curve that is consistent with all of the tracers used, as well as that of published HI data. The amplitude of the rotation curve is v_0=87±5 km s^-1 beyond a radius R_0=2.4±0.1 kpc, and has a position angle of the kinematic line of nodes of theta=142 degrees ±5 degrees. By examining the outliers from our fits, we identify a population of 376 stars, or >~5% of our sample, that have line-of-sight velocities that apparently oppose the sense of rotation of the LMC disk. We find that these kinematically distinct stars are either counter-rotating in a plane closely aligned with the LMC disk, or rotating in the same sense as the LMC disk, but in a plane that is inclined by 54 degrees ±2 degrees to the LMC. Their kinematics clearly link them to two known HI arms, which have previously been interpreted as being pulled out from the LMC. We measure metallicities from the Ca triplet lines of ~1000 LMC field stars and 30 stars in the kinematically distinct population. For the LMC field, we find a median [Fe/H]=-0.56 ±0.02 with dispersion of 0.5 dex, while for the kinematically distinct stars the median [Fe/H] is -1.25 ±0.13 with a dispersion of 0.7 dex. The metallicity differences provide strong evidence that the kinematically distinct population originated in the SMC. This interpretation has the consequence that the HI arms kinematically associated with the stars are likely falling into the LMC, instead of being pulled out.

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Astronomers scanning the skies as part of ESO's VISTA Magellanic Cloud survey have now obtained a spectacular picture of the Tarantula Nebula in our neighbouring galaxy, the Large Magellanic Cloud. This panoramic near-infrared view captures the nebula itself in great detail as well as the rich surrounding area of sky. The image was obtained at the start of a very ambitious survey of our neighbouring galaxies, the Magellanic Clouds, and their environment.
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LHA 120-N 11
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Hubble captures gas clouds and star clusters in Large Magellanic Cloud.

The NASA/ESA Hubble Space Telescope captures a complex network of gas clouds and star clusters within our neighbouring galaxy, the Large Magellanic Cloud. This region of energetic star birth is one of the most active in the nearby Universe.
The Large Magellanic Cloud contains many bright bubbles of glowing gas. One of the largest and most spectacular is LHA 120-N 11, from the catalogue compiled in 1956 by the late astronomer and astronaut Karl Henize. It is informally known as N11.
Close up, N11's billowing pink clouds of glowing gas resemble a puffy swirl of fairground candyfloss. From further away, its distinctive overall shape led some observers to nickname it the Bean Nebula. The dramatic and colourful features in the nebula are the telltale signs of star birth.
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Title: Structure of the Large Magellanic Cloud using red clump stars
Authors: Smitha Subramanian, Annapurni Subramaniam

The structural parameters of the disk of the Large Magellanic Cloud (LMC) are estimated. We used the red clump stars from the VI photometric data of the Optical Gravitational Lensing Experiment (OGLE III) survey and from the Magellanic Cloud Photometric Survey (MCPS) for the estimation of inclination and position angle of line of nodes of the LMC disk. The dereddened peak I magnitude of the red clump stars in each subregion is used to obtain the relative distances and hence the z coordinate. The RA and Dec of each sub-region is converted into x & y cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. We find an inclination of i =23.0 ±0.8 and PAlon = 163.7 ±1.5 for the LMC disk using the OGLE III data and an inclination of i=37.4 ±2.3 and PAlon= 141.2 ±3.7 for the LMC disk using the MCPS data. Extra-planar features which are in front as well as behind the fitted plane are seen in both the data sets. The effect of choice of centre, reddening and area covered on the estimated parameters are discussed. Regions in the north west, south west and south east of the LMC disk are warped with respect to the fitted plane. We also identify a symmetric but off-centred warp in the inner LMC. We identify that the structure of the LMC disk inside the 3 degree radius is different from the outside disk such that the inner LMC has relatively less inclination and relatively large PAlon. The 3D plot of the LMC disk suggests an off-centred increase in the inclination for the north-eastern regions which might be due to tidal effects. We suggest that the variation in the planar parameters estimated by various authors as well as in this study is because of the difference in coverage and the complicated inner structure of the LMC disk. In the inner LMC, the stellar and HI disk are found to have similar properties.

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BI 237
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Title: Massive runaway stars in the Large Magellanic Cloud
Authors: V.V. Gvaramadze, P. Kroupa, J. Pflamm-Altenburg
(Version v2)

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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Astronomers spy the trail carved through interstellar gas by a massive runaway.

They are more than a 100 times the mass of the Sun, glow more than 10 million times as brightly, and, over the course of their lives, spew out more than half their mass in the form of a relentless stellar wind. Yet the origin of the young massive stars in the Large Magellanic Cloud (LMC) galaxy has been a mystery for astronomers for decades.
Vasilii Gvaramadze, an astronomer at the Sternberg Astronomical Institute at Moscow State University, and his colleagues have now located the birthplace of one of the group, and have shown that it is a 'runaway star', bolting across the LMC at more than 130 kilometres per second after being ejected from its home cluster. The discovery implies that other young massive stars in the LMC might also be runaways, and casts light on the violent processes that can cause giant stars to be ejected from the stellar clusters in which they first form.
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