UV-(2000 A) imaging of globular clusters. 2: The blue straggler stars of M3

Details UV-(2000 A) imaging of globular clusters. 2: The blue straggler stars of M3 UV-(2000 A) imaging of globular clusters. 2: The blue straggler stars of M3

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...282...37l&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 282, no. 1, p. 37-44

Physics

Optics

5

Blue Stars, Globular Clusters, Imagery, Ultraviolet Astronomy, Ultraviolet Radiation, Balloon-Borne Instruments, Cassegrain Optics, Color-Color Diagram, Color-Magnitude Diagram, Light (Visible Radiation)

Scientific paper

UV-(2000 A) observation of M3 with a 40-cm balloon-borne imaging telescope is used to investigate the nature of the blue straggler stars outside the central region. Identifications of the ultraviolet sources by their position in a B, V catalog provide a list of 25 stars which occupy the blue stragglers region of the visible color-magnitude diagram. In the color-color (B - V, m2000 - V)-plot, the blue stragglers are found on or above the horizontal branch, at roughly a constant ultraviolet color, extending to a region which is marginally populated by the colors of single, normal stars. The luminous blue stragglers in the visible and some of the bluest have ultraviolet colors compatible with that expected for cluster main-sequence stars. Half the blue stragglers however, including those at a low-luminosity in the visible, are in a region of the color-color diagram which is not accounted for by the usual metallicity or gravity effects on the colors of stars. The data suggest a difference in nature among blue stragglers. Simulation of their position in the color-color plot by unresolved binary stars indicates, at a first order, that the blue stragglers with a large ultraviolet color excess can be reproduced by a low-luminosity hot secondary orbiting a turnoff or a subgiant star; the composite V-mag and B - V fit in the color-magnitude diagram and, the required hot secondaries are similar to observed O- and B-type disk subdwarfs in the (MV, B - V)-plane. At least for some blue stragglers of the outer part of M3, the present ultraviolet colors could support the existence of a hot, low-luminosity, unseen secondary star, possible remnant of binary evolution with mass exchange.

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