A HIGH-RESOLUTION MULTIBAND SURVEY OF WESTERLUND 2 WITH THE HUBBLE SPACE TELESCOPE. II. MASS ACCRETION IN THE PRE-MAIN-SEQUENCE POPULATION

作者：Zeidler Peter^*; Grebel Eva K; Nota Antonella; Sabbi Elena; Pasquali Anna; Tosi Monica; Bonanos Alceste Z; Christian Carol

来源：Astronomical Journal, 2016, 152(4): 84.

DOI：10.3847/0004-6256/152/4/84

• accretion, accretion disks
• H II regions
• infrared: stars
• open clusters and associations: individual (Westerlund 2)
• stars: pre-main sequence
• techniques: photometric

We present a detailed analysis of the pre-main-sequence (PMS) population of the young star cluster Westerlund 2 (Wd2), the central ionizing cluster of the H II region RCW 49, using data from a high-resolution multiband survey with the Hubble Space Telescope. The data were acquired with the Advanced Camera for Surveys in the F555W, F814W, and F658N filters and with the Wide Field Camera 3 in the F125W, F160W, and F128N filters. We find a mean age of the region of 1.04 +/- 0.72 Myr. The combination of dereddened F555W and F814W photometry in combination with F658N photometry allows us to study and identify stars with Ha excess emission. With a careful selection of 240 bona-fide PMS Ha excess emitters we were able to determine their Ha luminosity, which has a mean value L(H alpha) = 1.67 x 10(-31) erg s(-1). Using the PARSEC 1.2S isochrones to obtain the stellar parameters of the PMS stars, we determined a mean mass accretion rate (M)over dot(acc) = 4.43 x 10(-8) M-circle dot yr(-1) per star. A careful analysis of the spatial dependence of the mass accretion rate suggests that this rate is similar to 25% lower in the center of the two density peaks of Wd2 in close proximity to the luminous OB stars, compared to the Wd2 average. This rate is higher with increasing distance from the OB stars, indicating that the PMS accretion disks are being rapidly destroyed by the far-ultraviolet radiation emitted by the OB population.

• 出版日期2016-10