504 research outputs found
Standard Giant Branches in the Washington Photometric System
We have obtained CCD photometry in the Washington system C,T1 filters for
some 850,000 objects associated with 10 Galactic globular clusters and 2 old
open clusters. These clusters have well-known metal abundances, spanning a
metallicity range of 2.5 dex from [Fe/H]~-2.25 to +0.25 at a spacing of ~0.2
dex. Analogous to the method employed by Da Costa and Armandroff (1990, AJ,
100, 162) for V,I photometry, we then proceed to construct standard giant
branches for these clusters. The Washington system technique is found to have
three times the metallicity sensitivity of the V,I technique. Thus, for a given
photometric accuracy, metallicities can be determined three times more
precisely with the Washington technique. We find a linear relationship between
(C-T1)o (at M(T1)=-2) and metallicity (on the Zinn 1985, ApJ, 293, 424 scale)
exists over the full metallicity range, with an rms of only 0.04 dex. We also
derive methods to determine distance, reddening and metallicity simultaneously,
and note that the Washington system holds great potential for deriving accurate
ages as well.Comment: To be published in the 1999 AJ January issu
Ca II triplet spectroscopy of small magellanic cloud red giants. II. abundances for a sample of field stars
We have obtained metallicities of ∼360 red giant stars distributed in 15 Small Magellanic Cloud (SMC) fields from near-infrared spectra covering the Ca II triplet lines using the VLT + FORS2. The errors of the derived [Fe/H] values range from 0.09 to 0.35 dex per star, with a mean of 0.17 dex. The metallicity distribution (MD) of the whole sample shows a mean value of [Fe/H] = -1.00 ± 0.02, with a dispersion of 0.32 0.01, in agreement with global mean [Fe/H] values found in previous studies. We find no evidence of a metallicity gradient in the SMC. In fact, on analyzing the MD of each field, we derived mean values of [Fe/H] = -0.99 ± 0.08 and [Fe/H] = -1.02 ± 0.07 for fields located closer and farther than 4° from the center of the galaxy, respectively. In addition, there is a clear tendency for the field stars to be more metal-poor than the corresponding cluster they surround, independent of their positions in the galaxy and of the clusters' age. We argue that this most likely stems from the field stars being somewhat older and therefore somewhat more metal-poor than most of our clusters. © 2010. The American Astronomical Society.Fil: Parisi, Maria Celeste. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Geisler, Doug. Universidad de Concepción; ChileFil: Grocholski, A. J.. University of Florida; Estados Unidos. Space Telescope Science Institute; Estados UnidosFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Sarajedini, A.. University of Florida; Estados Unido
Newly Identified Star Clusters in M33. II. Radial HST/ACS Fields
We present integrated photometry and color-magnitude diagrams for 161 star
clusters in M33, of which 115 were previously uncataloged, using the Advanced
Camera For Surveys Wide Field Channel onboard the Hubble Space Telescope. The
integrated V-band magnitudes of these clusters range from Mv~-9 to as faint as
Mv~-4, extending the depth of the existing M33 cluster catalogs by ~1 mag.
Comparisons of theoretical isochrones to the color-magnitude diagrams using the
Padova models yield ages for 148 of these star clusters. The ages range from
Log (t)~7.0 to Log (t)~9.0. Our color-magnitude diagrams are not sensitive to
clusters older than ~1 Gyr. We find that the variation of the clusters'
integrated colors and absolute magnitudes with age is consistent with the
predictions of simple stellar population models. These same models suggest that
the masses of the clusters in our sample range from 5x10^3 to 5x10^4 *Msun.Comment: 28 pages, 12 figures, accepted for publication in The Astrophysical
Journa
Resolved Stellar Populations of Super-Metal-Rich Star Clusters in the Bulge of M31
We have applied the MCS image deconvolution algorithm (Magain, Courbin & Sohy
1998) to HST/WFPC2 V, I data of three M31 bulge globular clusters (G170, G177,
and G198) and control fields near each cluster. All three clusters are clearly
detected, with an increase in stellar density with decreasing radius from the
cluster centers; this is the first time that stars have been resolved in bulge
clusters in the inner regions of another galaxy. From the RGB slopes of the
clusters and the difference in I magnitude between the HB and the top of the
RGB, we conclude that these three clusters all have roughly solar metallicity,
in agreement with earlier integrated-light spectroscopic measurements. Our data
support a picture whereby the M31 bulge clusters and field stars were born from
the same metal-rich gas, early in the galaxy formation.Comment: 7 pages, 4 Postscript figures, accepted for publication in A&
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