Publications of the MPIfR
Optical & Infrared
Interferometry Group
D. Burgarella, F. Paresce, G. Meylan,
I.R. King, P. Greenfield, D. Baxter, R. Jedrzejewski, A. Nota, R.
Albrecht, C. Barbieri, J.C. Blades, A. Boksenberg, P. Crane, J.M.
Deharveng, M.J. Disney, P. Jakobson, T.M. Kamperman, F. Macchetto, C.D.
Mackay, G. Weigelt
HST Observations of the Core of Globular
Cluster NGC 6397
Astronomy and Astrophysics, v.287, p.769-781 (1994)
Abstract
The core of the nearby and very concentrated globular cluster NGC 6397
has been imaged through the f/96-F140W, f/48-F140W, f/96-F210M, and
f/48-F220W ultraviolet filters of the Faint Object Camera on board the
Hubble Space Telescope down to an ultraviolet limiting magnitude of
~19.
The most interesting objects in the field of view are six very bright,
centrally concentrated, blue stragglers observed for the first time in
the UV. Using these and other data from ground-based observations, we
have been able to deduce from a comparison with Kurucz's atmosphere
models, temperatures of ~10000 K and masses of ~1.6Msun_ for
the four brightest ones, which is remarkably close to twice the
turn-off
mass of NGC 6397. This finding supports the idea that two-star
mechanisms (collisions, mergers) are at the origin of the blue
stragglers in the core of NGC 6397. Since the central density is very
high, collisions between main sequence stars are frequent, therefore
providing the best formation mechanism. We have computed the number of
such collisions in the core of NGC 6397 and found it to be of the same
order as the number of bright blue stragglers observed there. Thanks to
the HST resolution, we have also been able to resolve one object,
previously classified as a yellow straggler, into a blend of a blue
straggler and three redder stars.
You can get this publication ...