THE DISTANCE TO THE MASSIVE GALACTIC CLUSTER WESTERLUND 2 FROM A SPECTROSCOPIC AND HST PHOTOMETRIC STUDY

被引：36

作者：

Alvarez, Carlos A. Vargas ^{[1
]}

Kobulnicky, Henry A. ^{[1
]}

Bradley, David R. ^{[2
]}

Kannappan, Sheila J. ^{[2
]}

Norris, Mark A. ^{[2
]}

Cool, Richard J. ^{[3
]}

Miller, Brendan P. ^{[4
]}

机构：

[1] Univ Wyoming, Dept Phys & Astron, Dept 3905, Laramie, WY 82071 USA

[2] Univ N Carolina, Dept Phys & Astron, Chapel Hill, NC 27599 USA

[3] Observ Carnegie Inst Washington, Pasadena, CA 91101 USA

[4] Univ Michigan, Dept Astron, Ann Arbor, MI 48109 USA

来源：

ASTRONOMICAL JOURNAL | 2013年 / 145卷 / 05期

基金：

美国国家航空航天局; 美国国家科学基金会;

关键词：

open clusters and associations: individual (Westerlund 2); stars: early-type; stars: fundamental parameters; NEAREST STARBURST CLUSTER; EARLY-TYPE STARS; SPECTRAL CLASSIFICATION; FUNDAMENTAL PARAMETERS; CYGNUS OB2; O-STARS; WR; 20A; GLIMPSE; EXTINCTION; SYSTEM;

D O I：

10.1088/0004-6256/145/5/125

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

We present a spectroscopic and photometric determination of the distance to the young Galactic open cluster Westerlund 2 using WFPC2 imaging from the Hubble Space Telescope (HST) and ground-based optical spectroscopy. HST imaging in the F336W, F439W, F555W, and F814W filters resolved many sources previously undetected in ground-based observations and yielded photometry for 1136 stars. We identified 15 new O-type stars, along with two probable binary systems, including MSP 188 (O3 + O5.5). We fit reddened spectral energy distributions based on the Padova isochrones to the photometric data to determine individual reddening parameters R-V and A(V) for O-type stars in Wd2. We find average values < R-V > = 3.77 +/- 0.09 and < A(V)> = 6.51 +/- 0.38 mag, which result in a smaller distance than most other spectroscopic and photometric studies. After a statistical distance correction accounting for close unresolved binaries (factor of 1.08), our spectroscopic and photometric data on 29 O-type stars yield that Westerlund 2 has a distance < d > = 4.16 +/- 0.07 (random) +0.26 (systematic) kpc. The cluster's age remains poorly constrained, with an upper limit of 3Myr. Finally, we report evidence of a faint mid-IR polycyclic aromatic hydrocarbon ring surrounding the well-known binary candidate MSP 18, which appears to lie at the center of a secondary stellar grouping within Westerlund 2.

引用

页数：24

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