Distribution of Lick Indices in the Globular Cluster NGC 2808

Details Distribution of Lick Indices in the Globular Cluster NGC 2808 Distribution of Lick Indices in the Globular Cluster NGC 2808

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21915118o&link_type=abstract

American Astronomical Society, AAS Meeting #219, #151.18

Astronomy and Astrophysics

Astronomy

Scientific paper

We have analyzed low resolution spectra for a large sample ( 200) of red giant branch (RGB) stars in the Galactic globular cluster NGC 2808 for indications of bimodality with respect to Lick indices and radial dispersion. Target stars were observed in nine fields over 5 nights in March 2010 with the Blanco 4m telescope and Hydra multi--object positioner and bench spectrograph located at Cerro Tololo Inter--American Observatory. The full wavelength coverage spans from 3900--8200 A; for nights 1 and 2, and from 4500--6950 A; for nights 3, 4, and 5. The low resolution data ( 500 for nights 1 and 2, 1200 for nights 3, 4, and 5; 70) were used to measure radial velocities (RVs) and to determine cluster membership. RVs were measured with the IRAF task xcsao using stars with known radial RVs included in our observed fields as templates. Template candidates were taken from Cacciari et al. (2004) and Carretta et al. (2006), and cross--matched by RA and Dec to stars in our sample. A conservative approach was adopted when including stars as cluster members, with RV= 101.9 ± 7.17 km s-1 (σ=2.83). Indexf was employed to measure 12 Lick indices, with particular attention to CN1, CN2 and Na. The peak distribution of these indices appears to be correlated in stars 2.5--3.5 arc minutes from the cluster center. The correlation becomes less apparent in stars outside this radius.