ULTRAVIOLET-BRIGHT STELLAR POPULATIONS AND THEIR EVOLUTIONARY IMPLICATIONS IN THE COLLAPSED-CORE CLUSTER M15

Journal Article · Sun Oct 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/158· OSTI ID:21464652

Haurberg, Nathalie C; Lubell, Gabriel M. G.; Cohn, Haldan N; Lugger, Phyllis M ^[1]; Anderson, Jay ^[2]; Cool, Adrienne M ^[3]

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1. Indiana University Department of Astronomy, Bloomington, IN 47405 (United States)
2. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
3. Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132 (United States)

We performed deep photometry of the central region of the Galactic globular cluster M15 from archival Hubble Space Telescope data taken on the High Resolution Channel and Solar Blind Channel of the Advanced Camera for Surveys. Our data set consists of images in far-UV (FUV{sub 140}; F140LP), near-UV (NUV{sub 220}; F220W), and blue (B{sub 435}; F435W) filters. The addition of an optical filter complements previous UV work on M15 by providing an additional constraint on the UV-bright stellar populations. Using color-magnitude diagrams (CMDs), we identified several populations that arise from non-canonical evolution including candidate blue stragglers, extreme horizontal branch (HB) stars, blue hook (BHk) stars, cataclysmic variables (CVs), and helium-core white dwarfs (He WDs). Due to preliminary identification of several He WD and BHk candidates, we add M15 as a cluster containing an He WD sequence and suggest it be included among clusters with a BHk population. We also investigated a subset of CV candidates that appear in the gap between the main sequence (MS) and WDs in FUV{sub 140}-NUV{sub 220} but lie securely on the MS in NUV{sub 220}-B{sub 435}. These stars may represent a magnetic CV or detached WD-MS binary population. Additionally, we analyze our candidate He WDs using model cooling sequences to estimate their masses and ages and investigate the plausibility of thin versus thick hydrogen envelopes. Finally, we identify a class of UV-bright stars that lie between the HB and WD cooling sequences, a location not usually populated on cluster CMDs. We conclude these stars may be young, low-mass He WDs.

• OSTI ID: 21464652
• Journal Information: Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/158; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COLOR
HELIUM
HYDROGEN
OPTICAL FILTERS
PHOTOMETRY
STAR EVOLUTION
TELESCOPES
ULTRAVIOLET RADIATION
WHITE DWARF STARS
DWARF STARS
ELECTROMAGNETIC RADIATION
ELEMENTS
EVOLUTION
FILTERS
FLUIDS
GASES
NONMETALS
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
RARE GASES
STARS