8 research outputs found
A Survey of CN and CH Variations in Galactic Globular Clusters from SDSS Spectroscopy
We present a homogeneous survey of the CN and CH bandstrengths in eight
Galactic globular clusters observed during the course of the Sloan Extension
for Galactic Understanding and Exploration (SEGUE) sub-survey of the SDSS. We
confirm the existence of a bimodal CN distribution among RGB stars in all of
the clusters with metallicity greater than [Fe/H] = -1.7; the lowest
metallicity cluster with an observed CN bimodality is M53, with [Fe/H] ~ -2.1.
There is also some evidence for individual CN groups on the subgiant branches
of M92, M2, and M13, and on the red giant branches of M92 and NGC 5053.
Finally, we quantify the correlation between overall cluster metallicity and
the slope of the CN bandstrength-luminosity plot as a means of further
demonstrating the level of CN-enrichment in cluster giants. Our results agree
well with previous studies reported in the literature.Comment: AJ submitted; 80 pages, 22 figure
Light Curves and Period Changes of Type II Cepheids in the Globular Clusters M3 and M5
Light curves in the B, V, and I_c passbands have been obtained for the type
II Cepheids V154 in M3 and V42 and V84 in M5. Alternating cycle behavior,
similar to that seen among RV Tauri variables, is confirmed for V84. Old and
new observations, spanning more than a century, show that V154 has increased in
period while V42 has decreased in period. V84, on the other hand, has shown
large, erratic changes in period that do not appear to reflect the long term
evolution of V84 through the HR diagram.Comment: 28 pages, 12 figure
The SEGUE Stellar Parameter Pipeline. IV. Validation with an Extended Sample of Galactic Globular and Open Clusters
Spectroscopic and photometric data for likely member stars of five Galactic
globular clusters (M3, M53, M71, M92, and NGC 5053) and three open clusters
(M35, NGC 2158, and NGC 6791) are processed by the current version of the SEGUE
Stellar Parameter Pipeline (SSPP), in order to determine estimates of
metallicities and radial velocities for the clusters. These results are then
compared to values from the literature. We find that the mean metallicity
() and mean radial velocity () estimates for each cluster are
almost all within 2{\sigma} of the adopted literature values; most are within
1{\sigma}. We also demonstrate that the new version of the SSPP achieves small,
but noteworthy, improvements in estimates at the extrema of the
cluster metallicity range, as compared to a previous version of the pipeline
software. These results provide additional confidence in the application of the
SSPP for studies of the abundances and kinematics of stellar populations in the
Galaxy.Comment: 98 pages, 31 figures; accepted for publication in A