Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-12-21
Astronomy and Astrophysics
Astrophysics
To appear in Baltic Astronomy. Proceedings of the 2nd meeting on Hot Subdwarf Stars, La Palma, June 2005. 4 pages, 2 figures
Scientific paper
We performed a spectroscopic search for binaries among hot Horizontal Branch stars in globular clusters. We present final results for a sample of 51 stars in NGC6752, and preliminary results for the first 15 stars analyzed in M80. The observed stars are distributed along all the HBs in the range 8000 < Teff < 32000 K, and have been observed during four nights. Radial velocity variations have been measured with the cross-correlation technique. We carefully analyzed the statistical and systematic errors associated with the measurements in order to evaluate the statistical significance of the observed variations. No close binary system has been detected, neither among cooler stars nor among the sample of hot EHB stars (18 stars with Teff > 22000 K in NGC6752). The data corrected for instrumental effects indicate that the radial velocity variations are always below the 3sigma level of ~15 km/s. These results are in sharp contrast with those found for field hot subdwarfs, and open new questions about the formation of EHB stars in globular clusters, and possibly of the field subdwarfs.
Bidin Christian Moni
Mendez Rafael A.
Moehler Sabine
Momany Yazan
Piotto Giampaolo
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