Bibcode
Recio-Blanco, A.; Piotto, G.; Aparicio, A.; Renzini, A.
Bibliographical reference
New Horizons in Globular Cluster Astronomy, ASP Conference Proceedings, Vol. 296, held 24-28 June 2002 at Dipartimento di Astronomia, Universita' di Padova, Padova, Italy. Edited by Giampaolo Piotto, Georges Meylan, S. George Djorgovski and Marco Riello. ISBN: 1-58381-143-5, 2003, p.305
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2003
Citations
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Description
We present high resolution UVES+VLT spectroscopic observations of 61
stars in the extended blue horizontal branches of the Galactic globular
clusters NGC 1904 (M79), NGC 2808, NGC 6093 (M80), and NGC 7078 M15).
Our data reveal for the first time the presence in NGC 1904 of a sizable
population of fast (v sin(i) >= 20 km/s) horizontal branch (HB)
rotators, confined to the cool end of the EHB, similar to that found in
M13. We also confirm the fast rotators already observed in NGC 7078. The
cooler stars (T_eff < 11,500 K) in these three clusters show a range
of rotation rates, with a group of stars rotating at ~ 15 km/s or less,
and a fast rotating group at ~ 30 km/s. Apparently, the fast rotators
are relatively more abundant in NGC 1904 and M13, than in NGC 7078. No
fast rotators have been identified in NGC 2808 and NGC 6093. All the
stars hotter than T_eff ~ 11,500 K have projected rotational velocities
vsini< 12 km/s. The connection between photometric gaps in the HB and
the change in the projected rotational velocities is not confirmed by
the new data. However, our data are consistent with a relation between
this discontinuity and the HB jump.