A Hubble View of Star Forming Regions in the Magellanic Clouds

Gouliermis, D. A.; Henning, Thomas; Brandner, W.; Rosa, M. R.; Dolphin, Andrew E.; Schmalzl, M.; Hennekemper, Eva; Zinnecker, H.; Panagia, N.; Chu, Y. H.; Brandl, Bernhard R.; Quanz, Sascha P.; Robberto, M.; Marchi, Guido De; Gruendl, R. A.; Romaniello, M.

doi:10.1007/978-90-481-3400-7_14

The Impact of HST on European Astronomy

2009

DOI: 10.1007/978-90-481-3400-7_14

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A Hubble View of Star Forming Regions in the Magellanic Clouds

D. A. Gouliermis¹,

Thomas Henning²,

W. Brandner³

et al.

Abstract: The Magellanic Clouds (MCs) offer an outstanding variety of young stellar associations, in which large samples of low-mass stars (with M ∼ < 1 M ⊙ ) currently in the act of formation can be resolved and explored sufficiently with the Hubble Space Telescope. These premain sequence (PMS) stars provide a unique snapshot of the star formation process, as it is being recorded for the last 20 Myr, and they give important information on the low-mass Initial Mass Function (IMF) of their host environments. We present t… Show more

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Cited by 4 publications

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Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

Gouliermis

2012

Space Sci Rev

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The stellar Initial Mass Function (IMF) suggests that stars with sub-solar mass form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre-main-sequence (PMS) evolutionary phase, i.e., they have not started their lives on the main-sequence yet. The peculiar nature of these objects and the contamination of their samples by the fore-and background evolved populations of the Galactic disk impose demanding observational techniques, such as X-ray surveying and optical spectroscopy of large samples for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the metal-poor companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of the above techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope within the last five years yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of star-forming regions in these galaxies, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of the PMS stellar content of the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the Magellanic Clouds allowed thus a more comprehensive understanding of the star formation process in our neighboring galaxies.

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Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

Gouliermis

2012

Space Sci Rev

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A NEW METHOD FOR THE ASSESSMENT OF AGE AND AGE SPREAD OF PRE-MAIN-SEQUENCE STARS IN YOUNG STELLAR ASSOCIATIONS OF THE MAGELLANIC CLOUDS^,

Rio¹,

Gouliermis²,

Gennaro³

2010

ApJ

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We present a new method for the evaluation of the age and age-spread among pre-main-sequence (PMS) stars in star-forming regions in the Magellanic Clouds, accounting simultaneously for photometric errors, unresolved binarity, differential extinction, stellar variability, accretion and crowding. The application of the method is performed with the statistical construction of synthetic color-magnitude diagrams using isochrones from two families of PMS evolutionary models. We convert each isochrone into 2D probability distributions of artificial PMS stars in the CMD by applying the aforementioned biases that dislocate these stars from their original CMD positions. A maximum-likelihood technique is then applied to derive the probability for each observed star to have a certain age, as well as the best age for the entire cluster. We apply our method to the photometric catalog of ∼ 2 000 PMS stars in the young association LH 95 in the Large Magellanic Cloud, based on the deepest HST/ACS imaging ever performed toward this galaxy, with a detection limit of V ∼ 28, corresponding to M ∼ 0.2 M . We assume the Initial Mass Function and reddening distribution for the system, as they are previously derived by us. Our treatment shows that the age determination is very sensitive to the considered grid of evolutionary models and the assumed binary fraction. The age of LH 95 is found to vary from 2.8 Myr to 4.4 Myr, depending on these factors. We evaluate the accuracy of our age estimation and we find that the method is fairly accurate in the PMS regime, while the precision of the measurement of the age is lower at higher luminosities. Our analysis allows us to disentangle a real age-spread from the apparent CMD-broadening caused by the physical and observational biases. We find that LH 95 hosts an age-spread well represented by a gaussian distribution with a FWHM of the order of 2.8 Myr to 4.2 Myr depending on the model and binary fraction. We detect a dependence of the average age of the system with stellar mass. This dependence does not appear to have any physical meaning, being rather due to imperfections of the PMS evolutionary models, which tend to predict lower ages for the intermediate masses, and higher ages for low-mass stars. Subject headings: stars: formation -stars: pre-main sequence -Hertzsprung-Russell and C-M diagrams -open clusters and associations: individual (LH 95) -methods: statistical

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Pre-Main-Sequence Stellar Populations Across Shapley Constellation Iii. I. Photometric Analysis and Identification,

Gouliermis

Dolphin

Robberto

et al. 2011

ApJ

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We present our investigation of pre-main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope WFPC2 camera. Our targets of interest are four starforming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed colormagnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross-sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63 and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.

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A Hubble View of Star Forming Regions in the Magellanic Clouds

Cited by 4 publications

References 27 publications

Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

A NEW METHOD FOR THE ASSESSMENT OF AGE AND AGE SPREAD OF PRE-MAIN-SEQUENCE STARS IN YOUNG STELLAR ASSOCIATIONS OF THE MAGELLANIC CLOUDS^,

Pre-Main-Sequence Stellar Populations Across Shapley Constellation Iii. I. Photometric Analysis and Identification,

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A Hubble View of Star Forming Regions in the Magellanic Clouds

Cited by 4 publications

References 27 publications

Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

A NEW METHOD FOR THE ASSESSMENT OF AGE AND AGE SPREAD OF PRE-MAIN-SEQUENCE STARS IN YOUNG STELLAR ASSOCIATIONS OF THE MAGELLANIC CLOUDS,

Pre-Main-Sequence Stellar Populations Across Shapley Constellation Iii. I. Photometric Analysis and Identification,

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Product

Resources

About

A NEW METHOD FOR THE ASSESSMENT OF AGE AND AGE SPREAD OF PRE-MAIN-SEQUENCE STARS IN YOUNG STELLAR ASSOCIATIONS OF THE MAGELLANIC CLOUDS^,