61 research outputs found
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 뱉elements (Si, Ca, Ti) abundances are comparable to our estimated errors in all clusters
Geometry of the Draco C1 Symbiotic Binary
Draco C1 is a known symbiotic binary star system composed of a carbon red
giant and a hot, compact companion -- likely a white dwarf -- belonging to the
Draco dwarf spheroidal galaxy. From near-infrared spectroscopic observations
taken by the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2),
part of Sloan Digital Sky Survey IV, we provide updated stellar parameters for
the cool, giant component, and constrain the temperature and mass of the hot,
compact companion. Prior measurements of the periodicity of the system, based
on only a few epochs of radial velocity data or relatively short baseline
photometric observations, were sufficient only to place lower limits on the
orbital period ( days). For the first time, we report precise orbital
parameters for the binary system: With 43 radial velocity measurements from
APOGEE spanning an observational baseline of more than 3 years, we definitively
derive the period of the system to be days. Based on the
newly derived orbital period and separation of the system, together with
estimates of the radius of the red giant star, we find that the hot companion
must be accreting matter from the dense wind of its evolved companion.Comment: 8 pages, 4 figures, 1 table. Accepted for publication in ApJ
Stellar multiplicity and stellar rotation::Insights from APOGEE
We measure rotational broadening in spectra taken by the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) survey to characterise the
relationship between stellar multiplicity and rotation. We create a sample of
2786 giants and 24 496 dwarfs with stellar parameters and multiple radial
velocities from the APOGEE pipeline, projected rotation speeds \vsini\
determined from our own pipeline, and distances, masses, and ages measured by
Sanders \& Das. We use the statistical distribution of the maximum shift in the
radial velocities, \drvm, as a proxy for the close binary fraction to explore
the interplay between stellar evolution, rotation, and multiplicity. Assuming
that the minimum orbital period allowed is the critical period for Roche Lobe
overflow and rotational synchronization, we calculate theoretical upper limits
on expected \vsini\ and \drvm\ values. These expectations agree with the
positive correlation between the maximum \drvm\ and \vsini\ values observed in
our sample as a function of \logg. We find that the fast rotators in our sample
have a high occurrence of short-period ()
companions. We also find that old, rapidly-rotating main sequence stars have
larger completeness-corrected close binary fractions than their younger peers.
Furthermore, rapidly-rotating stars with large \drvm\ consistently show
differences of 1-10 Gyr between the predicted gyrochronological and measured
isochronal ages. These results point towards a link between rapid rotation and
close binarity through tidal interactions. We conclude that stellar rotation is
strongly correlated with stellar multiplicity in the field, and caution should
be taken in the application of gyrochronology relations to cool stars.Comment: 12 pages, 9 figures; accepted by MNRA
The Close Binary Fraction as a Function of Stellar Parameters in APOGEE:A Strong Anti-Correlation With α Abundances
We use observations from the APOGEE survey to explore the relationship
between stellar parameters and multiplicity. We combine high-resolution repeat
spectroscopy for 41,363 dwarf and subgiant stars with abundance measurements
from the APOGEE pipeline and distances and stellar parameters derived using
\textit{Gaia} DR2 parallaxes from \cite{Sanders2018} to identify and
characterise stellar multiples with periods below 30 years, corresponding to
\drvm 3 \kms, where \drvm\ is the maximum APOGEE-detected shift in the
radial velocities. Chemical composition is responsible for most of the
variation in the close binary fraction in our sample, with stellar parameters
like mass and age playing a secondary role. In addition to the previously
identified strong anti-correlation between the close binary fraction and \feh\,
we find that high abundances of elements also suppress multiplicity at
most values of \feh\ sampled by APOGEE. The anti-correlation between
abundances and multiplicity is substantially steeper than that observed for Fe,
suggesting C, O, and Si in the form of dust and ices dominate the opacity of
primordial protostellar disks and their propensity for fragmentation via
gravitational stability. Near \feh{} = 0 dex, the bias-corrected close binary
fraction ( au) decreases from 100 per cent at \alh{} = 0.2
dex to 15 per cent near \alh{} = 0.08 dex, with a suggestive turn-up
to 20 per cent near \alh{} = 0.2. We conclude that the relationship
between stellar multiplicity and chemical composition for sun-like dwarf stars
in the field of the Milky Way is complex, and that this complexity should be
accounted for in future studies of interacting binaries.Comment: 15 pages, 10 figures, plus appendices; accepted to MNRA
Exploring the brown dwarf desert : new substellar companions from the SDSS-III MARVELS survey
Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within âŒ5 au in the mass range of âŒ10â80 MJup. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help assess the reality of the desert and provide insight to the formation and evolution of these objects. Here, we present 10 new brown dwarf and 2 low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III. These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from âŒ13 to 76 MJup and have orbital radii of less than 1 au. The two stellar companions have minimum masses of âŒ98 and 100 MJup. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 ± 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than âŒ300 d to be âŒ0.56 per cent
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
ASPCAP: THE APOGEE STELLAR PARAMETER AND CHEMICAL ABUNDANCES PIPELINE
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has built the largest moderately high-resolution (R â 22,500) spectroscopic map of the stars across the Milky Way, and including dust-obscured areas. The APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) is the software developed for the automated analysis of these spectra. ASPCAP determines atmospheric parameters and chemical abundances from observed spectra by comparing observed spectra to libraries of theoretical spectra, using Ï2 minimization in a multidimensional parameter space. The package consists of a fortran90 code that does the actual minimization and a wrapper IDL code for book-keeping and data handling. This paper explains in detail the ASPCAP components and functionality, and presents results from a number of tests designed to check its performance. ASPCAP provides stellar effective temperatures, surface gravities, and metallicities precise to 2%, 0.1 dex, and 0.05 dex, respectively, for most APOGEE stars, which are predominantly giants. It also provides abundances for up to 15 chemical elements with various levels of precision, typically under 0.1 dex. The final data release (DR12) of the Sloan Digital Sky Survey III contains an APOGEE database of more than 150,000 stars. ASPCAP development continues in the SDSS-IV APOGEE-2 survey
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