240 research outputs found
Lithium-rich stars in the Sloan Digital Sky Survey
We report the discovery of 23 lithium-rich post-main-sequence stars,
identified from moderate-resolution SDSS spectroscopy and confirmed with
high-resolution spectra taken at the Hobby-Eberly Telescope. These new Li-rich
stars cover a broad range in mass and evolutionary phase, including bright
giants and post-AGB stars. The process responsible for preserving or producing
excess lithium in a small fraction of evolved stars remains unclear.Comment: 5 pages, XII International Symposium on Nuclei in the Cosmos, August
5-12, 2012, Cairns, Australia. To appear in Proceedings of Scienc
Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo build-up with SDSS-IV
There is ample evidence in the Milky Way for globular cluster (GC)
disruption. Hence one may expect that also part of the Galactic halo field
stars may once have formed in GCs. We quantify the fraction of halo stars
donated by GCs by searching for stars that bear the unique chemical
fingerprints typical for a subset of GC stars often dubbed `second-generation
stars'. These are stars showing light element abundance anomalies such as a
pronounced CN-band strength accompanied by weak CH-bands. Based on this
indicator, past studies have placed the fraction of halo stars with a GC origin
between a few to up to 50%. Using low-resolution spectra from the most recent
data release of the latest extension of the Sloan Digital Sky Survey (SDSS-IV),
we were able to identify 118 metal-poor ([Fe/H]) CN-strong
stars in a sample of 4470 halo giant stars out to 50 kpc. This results in an
observed fraction of these stars of 2.60.2%. Using an updated formalism to
account for the fraction of stars lost early on in the GCs' evolution we
estimate the fraction of the halo that stems from disrupted clusters to be
111%. This number represents the case that stars lost from GCs were
entirely from the first generation and is thus merely an upper limit. Our
conclusions are sensitive to our assumptions of the mass lost early on from the
first generation formed in the GCs, the ratio of first-to-second generation
stars, and other GC parameters. We carefully test the influence of varying
these parameters on the final result and find that, under realistic scenarios,
the above fraction depends on the main assumptions at less than 10%. We further
recover a flat trend in this fraction with Galactocentric radius, with a
marginal indication of a rise beyond 30 kpc that could reflect the ex-situ
origin of the outer halo. (abridged)Comment: 13 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
New halo stars of the Galactic globular clusters M3 and M13 in the LAMOST DR1 Catalog
M3 and M13 are Galactic globular clusters with previous reports of
surrounding stellar halos. We present the results of a search for members and
extratidal cluster halo stars within and outside of the tidal radius of these
clusters in the LAMOST Data Release 1. We find seven candidate cluster members
(inside the tidal radius) of both M3 and M13 respectively. In M3 we also
identify eight candidate extratidal cluster halo stars at distances up to ~9.8
times the tidal radius, and in M13 we identify 12 candidate extratidal cluster
halo stars at distances up to ~13.8 times the tidal radius. These results
support previous indications that both M3 and M13 are surrounded by extended
stellar halos, and we find that the GC destruction rates corresponding to the
observed mass loss are generally significantly higher than theoretical studies
predict.Comment: 21 pages, 10 figures. Accepted for publication in Ap
New cluster members and halo stars of the Galactic globular cluster NGC 1851
NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar
evolutionary sequences, light and heavy element abundance variations and
indications of a surrounding stellar halo. We present the first results of a
spectroscopic study of red giant stars within and outside of the tidal radius
of this cluster. Our results identify nine probable new cluster members (inside
the tidal radius) with heliocentric radial velocities consistent with that of
NGC 1851. We also identify, based on their radial velocities, four probable
extratidal cluster halo stars at distances up to ~3.1 times the tidal radius,
which are supportive of previous findings that NGC 1851 is surrounded by an
extended stellar halo. Proper motions were available for 12 of these 13 stars
and all are consistent with that of NGC 1851. Apart from the cluster members
and cluster halo stars, our observed radial velocity distribution agrees with
the expected distribution from a Besancon disk/N-body stellar halo Milky Way
model generated by the Galaxia code, suggesting that no other structures at
different radial velocities are present in our field. The metallicities of
these stars are estimated using equivalent width measurements of the near
infrared calcium triplet absorption lines and are found, within the limitations
of this method, to be consistent with that of NGC 1851. In addition we recover
110 red giant cluster members from previous studies based on their radial
velocities and identify three stars with unusually high radial velocities.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
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