THE STARBURST CLUSTER WESTERLUND 1: THE INITIAL MASS FUNCTION AND MASS SEGREGATION

Journal Article · Fri Feb 01 04:00:00 EST 2013 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/145/2/46· OSTI ID:22089684

Lim, Beomdu; Sung, Hwankyung; Hur, Hyeonoh ^[1]; Chun, Moo-Young; Park, Byeong-Gon; Lee, Jae-Joon ^[2]; Sohn, Sangmo T. ^[3]

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1. Department of Astronomy and Space Science, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747 (Korea, Republic of)
2. Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yusung-gu, Daejeon (Korea, Republic of)
3. Space Telescope Science Institute, Baltimore, MD 21218 (United States)

Westerlund 1 is the most important starburst cluster in the Galaxy due to its massive star content. We have performed BVI{sub C} and JK{sub 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{sub 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 {Gamma} = -0.8 {+-} 0.1. The integration of the IMF gave a total mass for the cluster in excess of 5.0 Multiplication-Sign 10{sup 4} M{sub Sun }. 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.

• OSTI ID: 22089684
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 2 Vol. 145; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
COLOR
DISTANCE
GALAXIES
GIANT STARS
INFRARED SPECTRA
LUMINOSITY
MAIN SEQUENCE STARS
MASS
NEAR INFRARED RADIATION
PHOTOMETRY
ROTATION
STAR CLUSTERS
STAR EVOLUTION
VARIATIONS