90 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
Light-Element Abundance Variations at Low Metallicity: the Globular Cluster NGC 5466
We present low-resolution (R~850) spectra for 67 asymptotic giant branch
(AGB), horizontal branch and red giant branch (RGB) stars in the
low-metallicity globular cluster NGC 5466, taken with the VIRUS-P
integral-field spectrograph at the 2.7-m Harlan J. Smith telescope at McDonald
Observatory. Sixty-six stars are confirmed, and one rejected, as cluster
members based on radial velocity, which we measure to an accuracy of 16 km s-1
via template-matching techniques. CN and CH band strengths have been measured
for 29 RGB and AGB stars in NGC 5466, and the band strength indices measured
from VIRUS-P data show close agreement with those measured from Keck/LRIS
spectra previously taken of five of our target stars. We also determine carbon
abundances from comparisons with synthetic spectra. The RGB stars in our data
set cover a range in absolute V magnitude from +2 to -3, which permits us to
study the rate of carbon depletion on the giant branch as well as the point of
its onset. The data show a clear decline in carbon abundance with rising
luminosity above the luminosity function "bump" on the giant branch, and also a
subdued range in CN band strength, suggesting ongoing internal mixing in
individual stars but minor or no primordial star-to-star variation in
light-element abundances.Comment: 10 pages, emulateapj format, AJ accepte
Street View Data Collection Design for Disaster Reconnaissance
Over the last decade, street-view type images have been used across
disciplines to generate and understand various place-based metrics. However
efforts to collect this data were often meant to support investigator-driven
research without regard to the utility of the data for other researchers. To
address this, we describe our methods for collecting and publishing
longitudinal data of this type in the wake of the COVID-19 pandemic and discuss
some of the challenges we encountered along the way. Our process included
designing a route taking into account both broad area canvassing and community
capitals transects. We also implemented procedures for uploading and publishing
data from each survey. Our methods successfully generated the kind of
longitudinal data that can be beneficial to a variety of research disciplines.
However, there were some challenges with data collection consistency and the
sheer magnitude of data produced. Overall, our approach demonstrates the
feasibility of generating longitudinal street-view data in the wake of a
disaster event. Based on our experience, we provide recommendations for future
researchers attempting to create a similar data set.Comment: 11 pages, 2 figures, 1 tabl
Chemical tagging can work: Identification of stellar phase-space structures purely by chemical-abundance similarity
Chemical tagging promises to use detailed abundance measurements to identify
spatially separated stars that were in fact born together (in the same
molecular cloud), long ago. This idea has not yielded much practical success,
presumably because of the noise and incompleteness in chemical-abundance
measurements. We have succeeded in substantially improving spectroscopic
measurements with The Cannon, which has now delivered 15 individual abundances
for ~100,000 stars observed as part of the APOGEE spectroscopic survey, with
precisions around 0.04 dex. We test the chemical-tagging hypothesis by looking
at clusters in abundance space and confirming that they are clustered in phase
space. We identify (by the k-means algorithm) overdensities of stars in the
15-dimensional chemical-abundance space delivered by The Cannon, and plot the
associated stars in phase space. We use only abundance-space information (no
positional information) to identify stellar groups. We find that clusters in
abundance space are indeed clusters in phase space. We recover some known
phase-space clusters and find other interesting structures. This is the
first-ever project to identify phase-space structures at survey-scale by blind
search purely in abundance space; it verifies the precision of the abundance
measurements delivered by The Cannon; the prospects for future data sets appear
very good.Comment: accepted for publication in the Ap
Exploring Anticorrelations and Light Element Variations in Northern Globular Clusters Observed by the APOGEE Survey
We investigate the light-element behavior of red giant stars in Northern globular clusters (GCs) observed by the SDSS-III Apache Point Observatory Galactic Evolution Experiment (APOGEE). We derive abundances of nine elements (Fe, C, N, O, Mg, Al, Si, Ca, and Ti) for 428 red giant stars in 10 globular clusters. The intrinsic abundance range relative to measurement errors is examined, and the well-known C-N and Mg-Al anticorrelations are explored using an extreme-deconvolution code for the first time in a consistent way. We find that Mg and Al drive the population membership in most clusters, except in M107 and M71, the two most metal-rich clusters in our study, where the grouping is most sensitive to N. We also find a diversity in the abundance distributions, with some clusters exhibiting clear abundance bimodalities (for example M3 and M53) while others show extended distributions. The spread of Al abundances increases significantly as cluster average metallicity decreases as previously found by other works, which we take as evidence that low metallicity, intermediate mass AGB polluters were more common in the more metal poor clusters. The statistically significant correlation of [Al/Fe] with [Si/Fe] in M15 suggests that 28Si leakage has occurred in this cluster. We also present C, N and O abundances for stars cooler than 4500 K and examine the behavior of A(C+N+O) in each cluster as a function of temperature and [Al/Fe]. The scatter of A(C+N+O) is close to its estimated uncertainty in all clusters and independent on stellar temperature. A(C+N+O) exhibits small correlations and anticorrelations with [Al/Fe] in M3 and M13, but we cannot be certain about these relations given the size of our abundance uncertainties. Star-to-star variations of α−elements (Si, Ca, Ti) abundances are comparable to our estimated errors in all clusters
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
Chemical Tagging in the Sdss-Iii/Apogee Survey: New Identifications of Halo Stars with Globular Cluster Origins
We present new identifications of five red giant stars in the Galactic halo with chemical abundance patterns that indicate they originally formed in globular clusters. Using data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey (SDSS) Data Release 12, we first identify likely halo giants, and then search those for the well-known chemical tags associated with globular clusters, specifically enrichment in nitrogen and aluminum. We find that 2% of the halo giants in our sample have this chemical signature, in agreement with previous results. Following the interpretation in our previous work on this topic, this would imply that at least 13% of halo stars originally formed in globular clusters. Recent developments in the theoretical understanding of globular cluster formation raise questions about that interpretation, and we concede the possibility that these migrants represent a small fraction of the halo field. There are roughly as many stars with the chemical tags of globular clusters in the halo field as there are in globular clusters, whether or not they are accompanied by a much larger chemically untaggable population of former globular cluster stars
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