2012/11/26 by Beomdu Lim, Moo-Young Chun, Moo‐Young Chun +9 · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1088/0004-6256/145/2/46
67 pages, 15 figures, 4 tables Accepted for publication in the Astronomical Journal
arxiv created 2012/11/26 · openalex publication_date 2013/01/15 · arxiv updated 2015/06/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Westerlund 1 is the most important starburst cluster in the Galaxy due to its massive star content. We have performed BVI C and JK S photometry to investigate the initial mass function (IMF). By comparing the observed color with the spectral-type–intrinsic-color relation, we obtain the mean interstellar reddening of 〈 E ( B − V )〉 = 4.19 ± 0.23 and 〈 E ( J − K S )〉 = 1.70 ± 0.21. Due to the heavy extinction toward the cluster, the zero-age main sequence fitting method based on optical photometry proved to be inappropriate for the distance determination, while the near-infrared photometry gave a reliable distance to the cluster—3.8 kpc from the empirical relation. Using the recent theoretical stellar evolution models with rotation, the age of the cluster is estimated to be 5.0 ± 1.0 Myr. We derived the IMF in the massive part and obtained a fairly shallow slope of Γ = −0.8 ± 0.1. The integration of the IMF gave a total mass for the cluster in excess of 5.0 × 10 4 M ☉ . The IMF shows a clear radial variation indicating the presence of mass segregation. We also discuss the possible star formation history of Westerlund 1 from the presence of red supergiants and relatively low luminosity yellow hypergiants.