63 research outputs found
The metallicity distribution of G dwarfs in the solar neighbourhood
We derive a new metallicity distribution of G dwarfs in the solar
neighbourhood, using uvby photometry and up-to-date parallaxes. Our
distribution comprises 287 G dwarfs within 25 pc from the Sun, and differs
considerably from the classic solar neighbourhood distribution of Pagel &
Patchett and Pagel by having a prominent single peak around [Fe/H] = -0.20 dex.
The raw data are corrected for observational errors and cosmic scatter assuming
a deviation of 0.1. In order to obtain the true abundance distribution, we use
the correction factors given by Sommer-Larsen, which take into account the
stellar scale heights. The distribution confirms the G dwarf problem, that is,
the paucity of metal-poor stars relative to the predictions of the simple model
of chemical evolution. Another feature of this distribution, which was already
apparent in previous ones, is the small number of metal-rich stars again in
comparison with the simple model. Our results indicate that it is very
difficult to fit the simple model to this distribution, even with the
definition of an `effective yield'. A comparison with several models from the
literature is made. We find that models with infall are the most appropriate to
explain the new metallicity distribution. We also show that the metallicity
distribution is compatible with a major era of star formation occurring 5 to 8
Gyr ago, similar to results found by several authors.Comment: Tex, uses mn.tex v1.6, 13 pages, 8 figures available upon request,
accepted for publication in Monthly Notices of Roy. Astr. So
Exploring Halo Substructure with Giant Stars: Spectroscopy of Stars in the Galactic Anticenter Stellar Structure
To determine the nature of the recently discovered, ring-like stellar
structure at the Galactic anticenter, we have collected spectra of a set of
presumed constituent M giants selected from the 2MASS point source catalog.
Radial velocities have been obtained for stars spanning ~100 degrees,
exhibiting a trend in velocity with Galactic longitude and an estimated
dispersion of 20 +/- 4 km/sec. A mean metallicity [Fe/H] = -0.4 +/- 0.3
measured for these stars combines with previous evidence from the literature to
suggest a population with a significant metallicity spread. In addition, a
curious alignment of at least four globular clusters of lower mean metallicity
is noted to be spatially and kinematically consistent with this stellar
distribution. We interpret the M giant sample position and velocity variation
with Galactic longitude as suggestive of a satellite galaxy currently
undergoing tidal disruption in a non-circular, prograde orbit about the Milky
Way.Comment: (1) University of Virginia, 4 pages, 3 figures, accepted for
publication in The Astrophysical Journal Letter
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