Journal Article

Two serendipitous low-mass LMC clusters discovered with <i>HST</i>

Basílio X. Santiago, Rebecca A. W. Elson, Steinn Sigurdsson and Gerard F. Gilmore

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 295, issue 4, pages 860-868
Published in print April 1998 | ISSN: 0035-8711
Published online April 1998 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-8711.1998.01339.x
Two serendipitous low-mass LMC clusters discovered with HST

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Abstract

We present V and I photometry of two open clusters in the LMC down to V∼26. The clusters were imaged with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST), as part of the Medium Deep Survey Key Project. Both are low-luminosity (MV∼−3.5), low-mass (M∼103 M) systems. The chance discovery of these two clusters in two parallel WFPC2 fields suggests a significant incompleteness in the LMC cluster census near the bar. One of the clusters is roughly elliptical and compact, with a steep light profile, a central surface brightness μV(0)∼20.2 mag arcsec−2, a half-light radius rhl∼0.9 pc (total visual major diameter D∼3 pc) and an estimated mass M∼1500 M. From the colour-magnitude diagram and isochrone fits we estimate its age as τ∼(2–5)×108 yr. Its mass function has a fitted slope of Γ=Δlogφ(M)/ΔlogM=−1.8±0.7 in the range probed (0.9≲M/M≲4.5). The other cluster is more irregular and sparse, having shallower density and surface brightness profiles. We obtain Γ=−1.2±0.4, and estimate its mass as M∼400 M. A derived upper limit for its age is τ≲5×108 yr. Both clusters have mass functions with slopes similar to that of R136, a massive LMC cluster, for which HST results indicate Γ∼−1.2. They also seem to be relaxed in their cores and well contained in their tidal radii.

Keywords: stars: luminosity function, mass function; stars: statistics; Magellanic Clouds; galaxies: star clusters

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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