Reddening, distance, and stellar content of the young open cluster Westerlund 2
Abstract
We present deep UBVIC photometric data of the young open cluster Westerlund 2. An abnormal reddening law of RV, cl = 4.14 ± 0.08 was found for the highly reddened early-type members (E(B-V)≥q 1.45), whereas a fairly normal reddening law of RV, fg = 3.33 ± 0.03 was confirmed for the foreground early-type stars (E(B - V)fg < 1.05). The distance modulus was determined from zero-age main-sequence fitting to the reddening-corrected colour-magnitude diagram of the early-type members to be V0 - MV = 13.9 ± 0.14 (random error) _{-0.1}^{+0.4} (the upper limit of systematic error) mag (d = 6.0 ± 0.4 _{-0.3}^{+1.2} kpc). To obtain the initial mass function, pre-main-sequence (PMS) stars were selected by identifying the optical counterparts of Chandra X-ray sources and mid-infrared emission stars from the Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) source catalogue. The initial mass function shows a shallow slope of Γ = -1.1 ± 0.1 down to log m = 0.7. The total mass of Westerlund 2 is estimated to be at least 7 400 M⊙. The age of Westerlund 2 from the main-sequence turn-on and PMS stars is estimated to be ≲ 1.5 Myr. We confirmed the existence of a clump of PMS stars located ∼1 arcmin north of the core of Westerlund 2, but we could not find any clear evidence for an age difference between the core and the northern clump.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2015
- DOI:
- 10.1093/mnras/stu2329
- arXiv:
- arXiv:1411.0879
- Bibcode:
- 2015MNRAS.446.3797H
- Keywords:
-
- stars: luminosity function;
- mass function;
- stars: pre-main-sequence;
- open clusters and associations: individual: Westerlund 2;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 25 pages, 22 figures, 6 tables, accepted for publication in MNRAS