Spectroscopy of Blue Horizontal Branch Stars in the Globular Cluster NGC 6752
Session 74 -- Globular Clusters
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[74.14] Spectroscopy of Blue Horizontal Branch Stars in the Globular Cluster NGC 6752

P. C\^ot\'e (McMaster), M. Bolte (UCO/Lick Obs.), C.D. Wilson, K. Patel (McMaster)

Optical spectra (at 0.9 \AA /pixel dispersion) for 24 candidate blue horizontal branch stars in the globular cluster NGC 6752 have been obtained with ARGUS, the multi-object spectrograph on the CTIO 4.0m telescope. In addition to strong hydrogen lines, ten of the stars exhibit the 4471 \AA\ line of neutral helium. The equivalent widths of this line, the full widths of H$_{\gamma}$ and H$_{\delta}$ at the 20\% absorption level and $BV$ CCD photometry have been used to derive effective temperatures, surface gravities and surface helium abundances for our program objects. With the exception of one star which has an exceptionally strong 4471 \AA\ line, all of the objects with detected helium are consistent with the rather low value of N(He)/N(H) $\simeq$ 0.008, suggesting that neither enhanced atmospheric helium nor increased stellar rotation is responsible for the extremely blue horizontal branch observed in this intermediate metallicity cluster.