The young star cluster NGC 2362: low-mass population and initial mass function from a Chandra X-ray observation

Details The young star cluster NGC 2362: low-mass population and initial mass function from a Chandra X-ray observation The young star cluster NGC 2362: low-mass population and initial mass function from a Chandra X-ray observation

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...460..133d&link_type=abstract

Astronomy and Astrophysics, Volume 460, Issue 1, December II 2006, pp.133-144

Astronomy and Astrophysics

Astrophysics

6

Open Clusters And Associations: Individual: Ngc 2362, Stars: Coronae, Stars: Pre-Main-Sequence, Stars: Luminosity Function, Mass Function, X-Rays: Stars

Scientific paper

Context: . We study the stellar population of the very young cluster NGC 2362, using a deep Chandra ACIS-I X-ray observation. This cluster, only 5 Myr old, has already cleared most of its inter- and circumstellar dust, and with its small and uniform reddening offers a unique opportunity of studying its pre-main-sequence stellar population with minimal disturbance from a dense interstellar medium. Aims: .Our main purposes are to select cluster members down to low masses and to study their properties as a population (spatial properties, initial mass function, and coronal properties). Methods: .We compare existing deep optical photometry and Hα data with new X-ray data. We use combined optical and X-ray criteria to select cluster members. Results: .We detect 387 X-ray sources down to log LX = 29.0 (erg/s), and identify most of them (308) with star-like objects. The majority (88%) of optically identified X-ray sources are found to be very good candidate low-mass pre-main-sequence stars, with minimal field-object contamination. This increases the known cluster census by a substantial amount at low masses, with respect to previous optical/IR studies. The fraction of stars with active accretion is found to be in the range 5-9%. We find a significantly wider spatial distribution for low-mass stars than for massive stars (mass segregation). We find only a small spread around the low-mass cluster sequence in the HR diagram, indicating that star formation lasted only about 1-2 Myr. We have derived the cluster initial mass function, which appears to flatten (on the low-mass side) at higher masses with respect to other very young clusters. The quiescent X-ray emission of low-mass cluster stars is found to be rather strictly correlated with the stellar bolometric luminosity: the small spread in this correlation puts an upper bound on the amplitude of X-ray variability on time scales longer than one day (e.g., activity cycles) in such young coronal sources. We find significant X-ray spectral differences between low-mass stars brighter and fainter than log LX ˜ 30.3 (erg/s), respectively, with X-ray brighter stars showing hotter components (kT ˜ 2 keV), absent in fainter stars.

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