250 results on '"Matthew Shetrone"'
Search Results
202. The DART imaging and CaT survey of the Fornax dwarf spheroidal galaxy
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Andreas Kaufer, Vanessa Hill, Nobuo Arimoto, Thomas Szeifert, Kozo Sadakane, Kim Venn, Matthew Shetrone, Eline Tolstoy, Pascale Jablonka, Tom Abel, Amina Helmi, Mike Irwin, Patrick Francois, Giuseppina Battaglia, Francesca Primas, B. Letarte, and Astronomy
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Stellar population ,EXPLORING HALO SUBSTRUCTURE ,Metallicity ,Population ,II TRIPLET ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,galaxies : kinematics and dynamics ,01 natural sciences ,galaxies : stellar content ,STELLAR POPULATIONS ,BRIGHTNESS PROFILES ,GLOBULAR-CLUSTERS ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,STAR-CLUSTERS ,10. No inequality ,education ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,galaxies : dwarf ,Physics ,education.field_of_study ,Y-2 ISOCHRONES ,010308 nuclear & particles physics ,Astrophysics (astro-ph) ,2ND-PARAMETER PROBLEM ,Astronomy and Astrophysics ,galaxies : individual : Fornax ,galaxies : Local Group ,GIANT STARS ,Accretion (astrophysics) ,Galaxy ,Dwarf spheroidal galaxy ,Red-giant branch ,Stars ,stars : abundances ,Space and Planetary Science ,Astrophysics::Earth and Planetary Astrophysics ,CLUSTER METALLICITY SCALE - Abstract
As part of the DART project we have used the ESO/2.2m Wide Field Imager in conjunction with the VLT/FLAMES GIRAFFE spectrograph to study the detailed properties of the resolved stellar population of the Fornax dwarf spheroidal galaxy out to and beyond its tidal radius. We re-derived the structural parameters of the Fornax dwarf spheroidal using our wide field imaging covering the galaxy out to its tidal radius, and analysed the spatial distribution of the Fornax stars of different ages as selected from Colour-Magnitude Diagram analysis. We have obtained accurate velocities and metallicities from spectra in the CaII triplet wavelength region for 562 Red Giant Branch stars which have velocities consistent with membership in Fornax dwarf spheroidal. We have found evidence for the presence of at least three distinct stellar components: a young population (few 100 Myr old) concentrated in the centre of the galaxy, visible as a Main Sequence in the Colour-Magnitude Diagram; an intermediate age population (2-8 Gyr old); and an ancient population (> 10Gyr),which are distinguishable from each other kinematically, from the metallicity distribution and in the spatial distribution of stars found in the Colour-Magnitude Diagram. From our spectroscopic analysis we find that the ``metal rich'' stars ([Fe/H]> -1.3) show a less extended and more concentrated spatial distribution, and display a colder kinematics than the ``metal poor'' stars ([Fe/H, Comment: 32 pages, 23 figures. Accepted for publication in A&A. The data table (Table 4) will be available in electronic form after publication. The full resolution version can be downloaded from http://www.astro.rug.nl/~gbattagl/battaglia_fullres.ps
- Published
- 2006
203. The Evolution of the Lithium Abundances of Solar-Type Stars.VII.M34 (NGC 1039) and the Role of Rotation in Lithium Depletion
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Matthew Shetrone, Burton F. Jones, David R. Soderblom, and Debra A. Fischer
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Physics ,Stars ,chemistry ,Space and Planetary Science ,chemistry.chemical_element ,Astronomy and Astrophysics ,Lithium ,Astrophysics ,Rotation - Published
- 1997
204. CNO Abundances of Bright Giants in the Globular Cluster M5
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Christopher W. Churchill, Matthew Shetrone, Graeme H. Smith, Roger A. Bell, and Michael M. Briley
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Physics ,Red giant ,Bright giant ,chemistry.chemical_element ,Astronomy and Astrophysics ,Astrophysics ,Nitrogen ,Spectral line ,Stars ,chemistry ,Space and Planetary Science ,Abundance (ecology) ,Globular cluster ,Carbon - Abstract
Spectra obtained with the Lick 3-m telescope show that a CN-CH band strength anticorrelation exists among a sample of six red giant members of the globular cluster M5 having absolute magnitudes in the range -2.0 < MV < -1.3. By contrast, a seventh giant (star IV-59 in the color-magnitude survey of Arp [1955]) is found to have both strong CN and strong CH bands. Carbon and nitrogen abundances determined for five of the observed stars reveal that for the giants exhibiting the CN-CH anticorrelation (i) carbon is depleted ([C/Fe] < -0.5) by comparison with the [C/Fe] abundances of typical halo subdwarfs, (ii) nitrogen is greatly enhanced (+0.5 < [N/Fe] < +1.2) relative to the [N/Fe] abundances of typical subdwarfs, and (iii) the nitrogen and carbon abundances are anticorrelated and correlated respectively with the [O/Fe] abundances determined by Sneden et~al. (1992). These properties are similar to the pattern of CNO abundances reported in the literature for upper-giant-branch stars in other globular clusters such as M92, M3, and M13. By contrast, star M5 IV-59 has [C/Fe] and [N/Fe] abundance ratios that are near the upper limits for red giants in M5. This star also appears to have an undepleted [O/Fe] abundance, despite a greatly enhanced nitrogen abundance.
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- 1997
205. Proton Capture Chains in Globular Cluster Stars.II.Oxygen, Sodium, Magnesium, and Aluminum Abundances in M13 Giants Brighter Than the Horizontal Branch
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Christopher Sneden, G. E. Langer, Robert P. Kraft, Matthew Shetrone, Graeme H. Smith, and Catherine A. Pilachowski
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Physics ,Proton ,Magnesium ,Sodium ,chemistry.chemical_element ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Horizontal branch ,Oxygen ,Stars ,chemistry ,Space and Planetary Science ,Aluminium ,Globular cluster - Published
- 1997
206. Magnesium and Carbon isotopes in Globular Cluster Giants. Test of Deep Mixing.II
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Matthew Shetrone
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Physics ,chemistry ,Space and Planetary Science ,Magnesium ,Isotopes of carbon ,Globular cluster ,Astronomy ,chemistry.chemical_element ,Astronomy and Astrophysics ,Astrophysics ,Mixing (physics) - Published
- 1996
207. AL, MG and EU Abundances in Globular Cluster Giants. I. Tests of Deep Mixing
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Matthew Shetrone
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Physics ,Space and Planetary Science ,Globular cluster ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Mixing (physics) - Published
- 1996
208. CNO Abundances of Bright Giants in the Globular Clusters M3 and M13
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Michael M. Briley, Roger A. Bell, Graeme H. Smith, Matthew Shetrone, and Christopher W. Churchill
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Physics ,Space and Planetary Science ,Bright giant ,Globular cluster ,Astronomy and Astrophysics ,Astrophysics ,Horizontal branch - Published
- 1996
209. The Evolution of the Lithium Abundances of Solar-Type Stars. VI. The End of Lithium in the Pleiades
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David R. Soderblom, Matthew Shetrone, Debra A. Fischer, and Burton F. Jones
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Physics ,Stars ,T Tauri star ,chemistry ,Space and Planetary Science ,K-type main-sequence star ,Astronomy ,chemistry.chemical_element ,Astronomy and Astrophysics ,Lithium ,Astrophysics ,Pleiades - Published
- 1996
210. Oxygen Abundances in Halo Giants. VI. M10, A Globular Cluster with Metallicity Similar to M3 and M13
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Matthew Shetrone, G. E. Langer, Christopher Sneden, Robert P. Kraft, and Michael Bolte
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Physics ,Galactic halo ,chemistry ,Space and Planetary Science ,Globular cluster ,Metallicity ,chemistry.chemical_element ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Halo ,Horizontal branch ,Oxygen - Published
- 1995
211. Rotation periods of open-cluster stars, 3
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Bentley D. Laaksonen, Laurence A. Marschall, Matthew Shetrone, Scott D. Williams, E. Marilli, S. Catalano, Dana E. Backman, John R. Stauffer, Charles F. Prosser, and Vikram Adige
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Physics ,Stars ,T Tauri star ,Star cluster ,Space and Planetary Science ,Stellar rotation ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Pleiades ,Monitoring program ,Main sequence ,Open cluster - Abstract
We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several show rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleiades stars with photometric periods together with current X-ray flux measurements, we illustrate the X-ray activity/rotation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P approximately 6-7 days -- in general accordance with previous results using more heterogeneous samples of G/K stars.
- Published
- 1995
212. Oxygen abundances in halo giants. 5: Giants in the fairly metal-rich globular cluster M71
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Matthew Shetrone, Christopher Sneden, G. E. Langer, Robert P. Kraft, and Charles F. Prosser
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Physics ,Metallicity ,Astronomy ,chemistry.chemical_element ,Astronomy and Astrophysics ,Astrophysics ,Giant star ,Oxygen ,Astronomical spectroscopy ,Metal ,chemistry ,Space and Planetary Science ,Abundance (ecology) ,visual_art ,Globular cluster ,visual_art.visual_art_medium ,Halo - Published
- 1994
213. Radial velocities and line cores of halo giants: M13 (NGC 6205)
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Matthew Shetrone
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Physics ,Radial velocity ,Stars ,Space and Planetary Science ,Globular cluster ,Binary star ,Astronomy ,Astronomy and Astrophysics ,Halo ,Astrophysics ,Variable star ,Astronomical spectroscopy ,Luminosity - Abstract
Archived data for 23 M13 giants, from the extensive series of Lick Hamilton Echelle studies of globular giants by Kraft, Sneden, Langer, et al., are analyzed for radial velocities and strong line core displacements. Of several giants in this program which were observed more than once, only III-73 was found to have significant radial velocity variations. However, when the Lick velocities are combined with the extensive set of velocities determined a decade earlier by Lupton et al. (1987), the stars L598, IV-25, III-56, II-90, III-73, and I-48 show differences > 4.0 km/sec which may reflect long-term variability or binary reflex motions. Displaced cores are found with increasing frequency as stars approach the tip of the giant branch. This suggests that mass outflow increases with increasing luminosity along the giant branch. Time variations are seen in core displacements of IV-25 and III-56.
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- 1994
214. Oxygen abundaces in Halo giants. IV - The oxygen-sodium anticorrelation in a sample of 22 bright giants in M13
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Robert P. Kraft, Matthew Shetrone, Christopher Sneden, and G. E. Langer
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Physics ,Stars ,Star cluster ,Space and Planetary Science ,Red giant ,Metallicity ,Bright giant ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,Giant star ,Stellar evolution ,Astronomical spectroscopy - Abstract
We have analyzed high resolution echelle spectra of nine bright M13 giants which, when added to those we have analyzed previously by similar techniques, bring our M13 sample size to 22. The sample is 88% complete from the red giant tip (at M bol 0 =−3.6) to a point one bolometric magnitude fainter, and is presumably representative down to M bol 0 =−2.1. We find that the brightest M13 giants are predominantly super oxygen poor ([O/Fe]∼−0.4 to −0. 8) and correspondingly sodium rich ([Na/Fe]∼+0.2 to +0.4). We argue that these super O-poor stars are first ascent giants. The most straightforward way to understand (1) the decline in the average oxygen abundance as M13 stars approach the tip of the giant branch and (2) their anticorrelated oxygen and sodium abundances, is that they are the results of very deep mixing
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- 1993
215. Carbon isotope ratios and lithium abundances in old disk giants
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Matthew Shetrone, Catherine A. Pilachowski, and Christopher Sneden
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Physics ,education.field_of_study ,Metallicity ,Population ,Astronomy and Astrophysics ,Astrophysics ,Giant star ,Astronomical spectroscopy ,Luminosity ,Stars ,Apparent magnitude ,Space and Planetary Science ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,education ,Stellar evolution ,Astrophysics::Galaxy Astrophysics - Abstract
New very high resolution, low noise CCD spectra at 8000 A and 6700 A have been obtained for stars of a previously studied sample of old disk giants. Carbon isotope ratios have been derived from CN red system features appearing on the 8000 A spectra, and lithium abundances have been derived from the Li I resonance doublet at 6708 A. The lithium abundances have been used to assist in the discrimination of true old disk giants from those that may belong to the young disk population. The carbon isotope ratios of the old disk stars exhibit a pronounced dependence on stellar luminosity, from 12C/13C >/= 40 in stars with MV >/= +1.8, to 12C/13C ~/= 13 in stars with MV < 1.8. Comparisons with cluster color-magnitude diagrams suggest that most of the sample stars are on their first ascent of the giant branch. The lower luminosity giants with high carbon isotope ratios have not experienced significant convective envelope mixing of CN-cycle fusion products to their surfaces; this agrees qualitatively and quantitatively with standard stellar evolution theory. The large change in 12C/13C ratios that sets in abruptly at MV ~ +1.8 appears to be due mainly to the first dredge-up. The observed absolute magnitude of this event is in reasonable accord with standard theory, but the amount of decrease in the isotope ratio is far more than predicted by first dredge-up computations.
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- 1993
216. New eclipse timings and an upper limit to the rate of mass transfer in the novalike variable RW Tri
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Edward L. Robinson, J. L. Africano, and Matthew Shetrone
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Physics ,Space and Planetary Science ,Mass transfer ,Astronomy and Astrophysics ,Astrophysics ,Limit (mathematics) ,Light curve ,Stellar evolution ,Variable (mathematics) ,Ephemeris time ,Eclipse - Published
- 1991
217. Stellar Characterization of M Dwarfs from the APOGEE Survey: A Calibrator Sample for M-dwarf Metallicities.
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Diogo Souto, Katia Cunha, Verne V. Smith, C. Allende Prieto, Adam Burgasser, Kevin Covey, D. A. García-Hernández, Jon A. Holtzman, Jennifer A. Johnson, Henrik Jönsson, Suvrath Mahadevan, Steven R. Majewski, Thomas Masseron, Matthew Shetrone, Bárbara Rojas-Ayala, Jennifer Sobeck, Keivan G. Stassun, Ryan Terrien, Johanna Teske, and Fábio Wanderley
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DWARF stars ,GALACTIC evolution ,MAIN sequence (Astronomy) ,ECLIPSING binaries ,ASTRONOMICAL surveys ,BINARY stars - Abstract
We present spectroscopic determinations of the effective temperatures, surface gravities, and metallicities for 21 M dwarfs observed at high resolution (R ∼ 22,500) in the H band as part of the Sloan Digital Sky Survey (SDSS)-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The atmospheric parameters and metallicities are derived from spectral syntheses with 1D LTE plane-parallel MARCS models and the APOGEE atomic/molecular line list, together with up-to-date H
2 O and FeH molecular line lists. Our sample range in Teff from ∼3200 to 3800 K, where 11 stars are in binary systems with a warmer (FGK) primary, while the other 10 M dwarfs have interferometric radii in the literature. We define an –radius calibration based on our M-dwarf radii derived from the detailed analysis of APOGEE spectra and Gaia DR2 distances, as well as a mass–radius relation using the spectroscopically derived surface gravities. A comparison of the derived radii with interferometric values from the literature finds that the spectroscopic radii are slightly offset toward smaller values, with Δ = −0.01 ± 0.02 R⋆/R⊙ . In addition, the derived M-dwarf masses based upon the radii and surface gravities tend to be slightly smaller (by ∼5%–10%) than masses derived for M-dwarf members of eclipsing binary systems for a given stellar radius. The metallicities derived for the 11 M dwarfs in binary systems, compared to metallicities obtained for their hotter FGK main-sequence primary stars from the literature, show excellent agreement, with a mean difference of [Fe/H](M dwarf – FGK primary) = +0.04 ± 0.18 dex, confirming the APOGEE metallicity scale derived here for M dwarfs. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
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218. Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. II. Atomic Diffusion in M67 Stars.
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Diogo Souto, C. Allende Prieto, Katia Cunha, Marc Pinsonneault, Verne V. Smith, R. Garcia-Dias, Jo Bovy, D. A. García-Hernández, Jon Holtzman, J. A. Johnson, Henrik Jönsson, Steve R. Majewski, Matthew Shetrone, Jennifer Sobeck, Olga Zamora, Kaike Pan, and Christian Nitschelm
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RED giants ,GLOBULAR clusters ,LOCAL thermodynamic equilibrium ,MAIN sequence (Astronomy) ,DIFFUSION ,GALACTIC evolution ,HR diagrams - Abstract
Chemical abundances for 15 elements (C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni) are presented for 83 stellar members of the 4 Gyr old solar-metallicity open cluster M67. The sample contains stars spanning a wide range of evolutionary phases, from G dwarfs to red clump stars. The abundances were derived from near-IR (λ1.5–1.7 μm) high-resolution spectra (R = 22,500) from the SDSS-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. A 1D local thermodynamic equilibrium abundance analysis was carried out using the APOGEE synthetic spectral libraries, via χ
2 minimization of the synthetic and observed spectra with the qASPCAP code. We found significant abundance differences (∼0.05–0.30 dex) between the M67 member stars as a function of the stellar mass (or position on the Hertzsprung–Russell diagram), where the abundance patterns exhibit a general depletion (in [X/H]) in stars at the main-sequence turnoff. The amount of the depletion is different for different elements. We find that atomic diffusion models provide, in general, good agreement with the abundance trends for most chemical species, supporting recent studies indicating that measurable atomic diffusion operates in M67 stars. [ABSTRACT FROM AUTHOR]- Published
- 2019
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219. Chemical Cartography with APOGEE: Multi-element Abundance Ratios.
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David H. Weinberg, Jon A. Holtzman, Sten Hasselquist, Jonathan C. Bird, Jennifer A. Johnson, Matthew Shetrone, Jennifer Sobeck, Carlos Allende Prieto, Dmitry Bizyaev, Ricardo Carrera, Roger E. Cohen, Katia Cunha, Garrett Ebelke, J. G. Fernandez-Trincado, D. A. García-Hernández, Christian R. Hayes, Henrik Jönsson, Richard R. Lane, Steven R. Majewski, and Viktor Malanushenko
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TYPE I supernovae ,CARTOGRAPHY ,STELLAR populations ,TRACE elements ,MILKY Way ,DISTRIBUTION (Probability theory) - Abstract
We map the trends of elemental abundance ratios across the Galactic disk, spanning and midplane distance , for 15 elements in a sample of 20,485 stars measured by the SDSS/APOGEE survey (O, Na, Mg, Al, Si, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni). Adopting Mg rather than Fe as our reference element, and separating stars into two populations based on [Fe/Mg], we find that the median trends of [X/Mg] versus [Mg/H] in each population are nearly independent of location in the Galaxy. The full multi-element cartography can be summarized by combining these nearly universal median sequences with our measured metallicity distribution functions and the relative proportions of the low-[Fe/Mg] (high-α) and high-[Fe/Mg] (low-α) populations, which depend strongly on R and . We interpret the median sequences with a semi-empirical “two-process” model that describes both the ratio of core collapse and Type Ia supernova (SN Ia) contributions to each element and the metallicity dependence of the supernova yields. These observationally inferred trends can provide strong tests of supernova nucleosynthesis calculations. Our results lead to a relatively simple picture of abundance ratio variations in the Milky Way, in which the trends at any location can be described as the sum of two components with relative contributions that change systematically and smoothly across the Galaxy. Deviations from this picture and future extensions to other elements can provide further insights into the physics of stellar nucleosynthesis and unusual events in the Galaxy’s history. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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220. Constraining Metallicity-dependent Mixing and Extra Mixing Using [C/N] in Alpha-rich Field Giants.
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Matthew Shetrone, Jamie Tayar, Jennifer A. Johnson, Garrett Somers, Marc H. Pinsonneault, Jon A. Holtzman, Sten Hasselquist, Thomas Masseron, Szabolcs Mészáros, Henrik Jönsson, Keith Hawkins, Jennifer Sobeck, Olga Zamora, and D. A. García-Hernández
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RED giants , *ALPHA rays , *STELLAR evolution , *GALACTIC evolution , *STELLAR luminosity function - Abstract
Internal mixing on the giant branch is an important process which affects the evolution of stars and the chemical evolution of the galaxy. While several mechanisms have been proposed to explain this mixing, better empirical constraints are necessary. Here, we use [C/N] abundances in 26,097 evolved stars from the SDSS-IV/APOGEE-2 Data Release 14 to trace mixing and extra mixing in old field giants with −1.7 < [Fe/H] < 0.1. We show that the APOGEE [C/N] ratios before any dredge-up occurs are metallicity dependent, but that the change in [C/N] at the first dredge-up is metallicity independent for stars above [Fe/H] ∼ −1. We identify the position of the red giant branch (RGB) bump as a function of metallicity, note that a metallicity-dependent extra mixing episode takes place for low-metallicity stars ([Fe/H] < −0.4) 0.14 dex in log g above the bump, and confirm that this extra mixing is stronger at low metallicity, reaching Δ[C/N] = 0.58 dex at [Fe/H] = −1.4. We show evidence for further extra mixing on the upper giant branch, well above the bump, among the stars with [Fe/H] < −1.0. This upper giant branch mixing is stronger in the more metal-poor stars, reaching 0.38 dex in [C/N] for each 1.0 dex in log g. The APOGEE [C/N] ratios for red clump (RC) stars are significantly higher than for stars at the tip of the RGB, suggesting additional mixing processes occur during the helium flash or that unknown abundance zero points for C and N may exist among the RC sample. Finally, because of extra mixing, we note that current empirical calibrations between [C/N] ratios and ages cannot be naively extrapolated for use in low-metallicity stars specifically for those above the bump in the luminosity function. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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221. Identifying Sagittarius Stream Stars by Their APOGEE Chemical Abundance Signatures.
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Sten Hasselquist, Jeffrey L. Carlin, Jon A. Holtzman, Matthew Shetrone, Christian R. Hayes, Katia Cunha, Verne Smith, Rachael L. Beaton, Jennifer Sobeck, Carlos Allende Prieto, Steven R. Majewski, Borja Anguiano, Dmitry Bizyaev, D. A. García-Hernández, Richard R. Lane, Kaike Pan, David L. Nidever, José. G. Fernández-Trincado, John C. Wilson, and Olga Zamora
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GALACTIC evolution ,GALAXIES ,SAGITTARIUS dwarf spheroidal galaxy ,N-body simulations (Astronomy) ,MILKY Way - Abstract
The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey provides precise chemical abundances of 18 chemical elements for ∼176,000 red giant stars distributed over much of the Milky Way Galaxy (MW), and includes observations of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). The APOGEE chemical abundance patterns of Sgr have revealed that it is chemically distinct from the MW in most chemical elements. We employ a k-means clustering algorithm to six-dimensional chemical space defined by [(C+N)/Fe], [O/Fe], [Mg/Fe], [Al/Fe], [Mn/Fe], and [Ni/Fe] to identify 62 MW stars in the APOGEE sample that have Sgr-like chemical abundances. Of the 62 stars, 35 have Gaia kinematics and positions consistent with those predicted by N-body simulations of the Sgr stream, and are likely stars that have been stripped from Sgr during the last two pericenter passages (<2 Gyr ago). Another 20 of the 62 stars exhibit chemical abundances indistinguishable from the Sgr stream stars, but are on highly eccentric orbits with median r
apo ∼ 25 kpc. These stars are likely the “accreted” halo population thought to be the result of a separate merger with the MW 8–11 Gyr ago. We also find one hypervelocity star candidate. We conclude that Sgr was enriched to [Fe/H] ∼ −0.2 before its most recent pericenter passage. If the “accreted halo” population is from one major accretion event, then this progenitor galaxy was enriched to at least [Fe/H] ∼ −0.6, and had a similar star formation history to Sgr before merging. [ABSTRACT FROM AUTHOR]- Published
- 2019
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222. APOGEE [C/N] Abundances across the Galaxy: Migration and Infall from Red Giant Ages.
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Sten Hasselquist, Jon A. Holtzman, Matthew Shetrone, Jamie Tayar, David H. Weinberg, Diane Feuillet, Katia Cunha, Marc H. Pinsonneault, Jennifer A. Johnson, Jonathan Bird, Timothy C. Beers, Ricardo Schiavon, Ivan Minchev, J. G. Fernández-Trincado, D. A. García-Hernández, Christian Nitschelm, and Olga Zamora
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GALAXIES ,MILKY Way ,CARBON ,DISPERSION (Chemistry) ,RED giants - Abstract
We present [C/N]–[Fe/H] abundance trends from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment survey, Data Release 14 (DR14), for red giant branch stars across the Milky Way (3 kpc < R < 15 kpc). The carbon-to-nitrogen ratio (often expressed as [C/N]) can indicate the mass of a red giant star, from which an age can be inferred. Using masses and ages derived by Martig et al., we demonstrate that we are able to interpret the DR14 [C/N]–[Fe/H] abundance distributions as trends in age–[Fe/H] space. Our results show that an anticorrelation between age and metallicity, which is predicted by simple chemical evolution models, is not present at any Galactic zone. Stars far from the plane ( kpc) exhibit a radial gradient in [C/N] (∼−0.04 dex kpc
−1 ). The [C/N] dispersion increases toward the plane (σ[C/N] = 0.13 at kpc to σ[C/N] = 0.18 dex at ∣Z∣ < 0.5 kpc). We measure a disk metallicity gradient for the youngest stars (age < 2.5 Gyr) of −0.060 dex kpc−1 from 6 to 12 kpc, which is in agreement with the gradient found using young CoRoGEE stars by Anders et al. Older stars exhibit a flatter gradient (−0.016 dex kpc−1 ), which is predicted by simulations in which stars migrate from their birth radii. We also find that radial migration is a plausible explanation for the observed upturn of the [C/N]–[Fe/H] abundance trends in the outer Galaxy, where the metal-rich stars are relatively enhanced in [C/N]. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
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223. Chemical composition of extremely metal-poor stars in the Sextans dwarf spheroidal galaxy
- Author
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Nobuo Arimoto, Thomas Szeifert, P. François, Francesca Primas, Matthew Shetrone, Giuseppina Battaglia, Eline Tolstoy, Kim Venn, Amina Helmi, Mike Irwin, Kozo Sadakane, Wako Aoki, M. Tafelmeyer, B. Letarte, Andreas Kaufer, Carine Babusiaux, Pascale Jablonka, Vanessa Hill, and Astronomy
- Subjects
Abundance Patterns ,stars: abundances ,Metallicity ,FOS: Physical sciences ,Sodium Abundance ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,High-Dispersion-Spectrograph ,01 natural sciences ,Spectral line ,Globular-Cluster Giants ,Galactic halo ,Neutron-Capture Elements ,nuclear reactions, nucleosynthesis, abundances ,0103 physical sciences ,Solar Neighborhood ,Astrophysics::Solar and Stellar Astrophysics ,Spectroscopy ,010303 astronomy & astrophysics ,Chemical composition ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,nuclear reactions ,Physics ,Oscillator-Strengths ,010308 nuclear & particles physics ,abundances ,nucleosynthesis ,Astronomy and Astrophysics ,galaxies: dwarf ,Astrophysics - Astrophysics of Galaxies ,Milky-Way ,Galaxy ,1St Stars ,Dwarf spheroidal galaxy ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Observational Data ,13. Climate action ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,galaxies: individual: Sextans ,galaxies: abundances ,Astrophysics::Earth and Planetary Astrophysics - Abstract
Chemical abundances of six extremely metal-poor ([Fe/H], Comment: 15 pages, 6 figures, 6 tables, A&A, in press
224. Li survey in giant stars : probing non-standard stellar physics
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Pierre North, Nadège Lagarde, Verne V. Smith, Julie K. Hollek, C. Charbonnel, Matthew Shetrone, and Gérard Jasniewicz
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Physics ,Stellar collision ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Rotation ,Giant star ,Stars ,T Tauri star ,Space and Planetary Science ,Abundance (ecology) ,Stellar mass loss ,Stellar physics ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
National Optical Astronomy Observatory, Tucson, USAAbstract.Lithium has long been known to be a good tracer of non-standard mixing processesoccurring in stellar interiors. Here we present the results of a large survey aimed at determiningthe surface Li abundance in a sample of about 800 giant (RGB and AGB) stars with accurateHipparcos parallaxes. We compare the observed Li behaviour with that predicted by stellarmodels including rotation and thermohaline mixing.Keywords.Hydrodynamics, instabilities, Stars: abundances, evolution, rotation
225. Cosmic variance in [O/Fe] in the Galactic disk
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Jian Ge, Jon A. Holtzman, Matthew Shetrone, Ricardo Carrera, David L. Nidever, Frederick R. Hearty, Steve Majewski, A. E. Garcia Perez, C. Allende Prieto, S. Bertran de Lis, Sz. Meszaros, Gail Zasowski, Peter M. Frinchaboy, and Ricardo P. Schiavon
- Subjects
010504 meteorology & atmospheric sciences ,Metallicity ,media_common.quotation_subject ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Spectral line ,0103 physical sciences ,Thick disk ,Astrophysics::Solar and Stellar Astrophysics ,Disc ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,QC ,0105 earth and related environmental sciences ,media_common ,QB ,Physics ,Astronomy and Astrophysics ,Cosmic variance ,Effective temperature ,Astrophysics - Astrophysics of Galaxies ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Sky ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics::Earth and Planetary Astrophysics - Abstract
We examine the distribution of the [O/Fe] abundance ratio in stars across the Galactic disk using H-band spectra from the Apache Point Galactic Evolution Experiment (APOGEE). We minimize systematic errors by considering groups of stars with similar atmospheric parameters. The APOGEE measurements in the Sloan Digital Sky Survey Data Release 12 reveal that the square root of the star-to-star cosmic variance in the oxygen-to-iron ratio at a given metallicity is about 0.03-0.04 dex in both the thin and thick disk. This is about twice as high as the spread found for solar twins in the immediate solar neighborhood and the difference is probably associated to the wider range of galactocentric distances spanned by APOGEE stars. We quantify the uncertainties by examining the spread among stars with the same parameters in clusters; these errors are a function of effective temperature and metallicity, ranging between 0.005 dex at 4000 K and solar metallicity, to about 0.03 dex at 4500 K and [Fe/H]= -0.6. We argue that measuring the spread in [O/Fe] and other abundance ratios provides strong constraints for models of Galactic chemical evolution., Comment: 6 pages, 4 figures; A&A, accepted
226. The age-metallicity structure of the Milky Way disc using APOGEE
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Peter M. Frinchaboy, Marc H. Pinsonneault, Jon A. Holtzman, Steven R. Majewski, Jo Bovy, David L. Nidever, Szabolcs Mészáros, Matthew Shetrone, Ana E. García Pérez, Michael R. Hayden, Ricardo P. Schiavon, Gail Zasowski, Katia Cunha, and J. Ted Mackereth
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Physics ,education.field_of_study ,010308 nuclear & particles physics ,Metallicity ,Milky Way ,Population ,Astronomy and Astrophysics ,Astrophysics ,Radius ,01 natural sciences ,Red-giant branch ,Stars ,Space and Planetary Science ,0103 physical sciences ,Galaxy formation and evolution ,education ,010303 astronomy & astrophysics ,QB - Abstract
The measurement of the structure of stellar populations in the Milky Way disc places fundamental constraints on models of galaxy formation and evolution. Previously, the disc's structure has been studied in terms of populations defined geometrically and/or chemically, but a decomposition based on stellar ages provides a more direct connection to the history of the disc, and stronger constraint on theory. Here, we use positions, abundances and ages for 31 244 red giant branch stars from the Sloan Digital Sky Survey (SDSS)-APOGEE survey, spanning 3 < R-gc < 15 kpc, to dissect the disc into mono-age and mono-[Fe/H] populations at low and high [alpha/Fe]. For each population, with Delta age < 2 Gyr and Delta [Fe/H] < 0.1 dex, we measure the structure and surface-mass density contribution. We find that low [alpha/Fe] mono-age populations are fit well by a broken exponential, which increases to a peak radius and decreases thereafter. We show that this profile becomes broader with age, interpreted here as a new signal of disc heating and radial migration. High [alpha/Fe] populations are well fit as single exponentials within the radial range considered, with an average scalelength of 1.9 +/- 0.1 kpc. We find that the relative contribution of high to low [alpha/Fe] populations at R-0 is f(Sigma) = 18 per cent +/- 5 per cent; high [alpha/Fe] contributes most of the mass at old ages, and low [alpha/Fe] at young ages. The low and high [alpha/Fe] populations overlap in age at intermediate [Fe/H], although both contribute mass at R-0 across the full range of [Fe/H]. The mass-weighted scaleheight h(Z) distribution is a smoothly declining exponential function. High [alpha a/Fe] populations are thicker than low [alpha/Fe], and the average h(Z) increases steadily with age, between 200 and 600 pc.
227. What is the Milky Way outer halo made of? High resolution spectroscopy of distant red giants
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E. Starkenburg, Pierre North, M. Savoy, Matthew Shetrone, Dante Minniti, Matías R. Díaz, Pascale Jablonka, Giuseppina Battaglia, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
stars: abundances ,Metallicity ,Milky Way ,interaction [Galaxies] ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Galactic halo ,0103 physical sciences ,galaxies: interactions ,Asymptotic giant branch ,halo [Galaxy] ,Astrophysics::Solar and Stellar Astrophysics ,010303 astronomy & astrophysics ,Galaxy: structure ,Astrophysics::Galaxy Astrophysics ,Dwarf galaxy ,Physics ,010308 nuclear & particles physics ,Star formation ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Galaxy: halo ,Red-giant branch ,formation [Galaxy] ,13. Climate action ,Space and Planetary Science ,Galaxy: formation ,Astrophysics of Galaxies (astro-ph.GA) ,abundances [Stars] ,Astrophysics::Earth and Planetary Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,structure [Galaxy] - Abstract
In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in-situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this work we focus on the outer regions of the Milky Way stellar halo, by determining chemical abundances of halo stars with large present-day Galactocentric distances, $>$15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, $-3.1 \lesssim$[Fe/H]$\lesssim -0.6$. We show that the ratio of $\alpha$-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H]$\gtrsim -1.5$ when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples., Comment: Accepted for publication in A&A
228. The Bulge Metallicity Distribution from the APOGEE Survey
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Mathias Schultheis, Léo Girardi, Ricardo P. Schiavon, Steven R. Majewski, Melissa Ness, Inmaculada Martinez-Valpuesta, Matthew Shetrone, Katia Cunha, Jo Bovy, Ana G. Pérez, Jennifer Sobeck, Carlos Allende Prieto, Szabolcs Mészáros, Gail Zasowski, David L. Nidever, Annie C. Robin, Verne V. Smith, Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Red giant ,Milky Way ,Metallicity ,Astrophysics::High Energy Astrophysical Phenomena ,Population ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Bulge ,0103 physical sciences ,Thick disk ,Astrophysics::Solar and Stellar Astrophysics ,education ,010303 astronomy & astrophysics ,ComputingMilieux_MISCELLANEOUS ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,QC ,QB ,Physics ,education.field_of_study ,010308 nuclear & particles physics ,Galactic Center ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Astrophysics - Solar and Stellar Astrophysics ,Thin disk ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics::Earth and Planetary Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on homogeneous measurements from the SDSS Data Release 12 for 7545 red giant stars within 4.5 kpc of the Galactic center, with the goal to shed light on the structure and origin of the Galactic bulge. Stellar metallicities are found, through multiple-Gaussian decompositions, to be distributed in several components indicative of the presence of various stellar populations such as the bar, or the thin and the thick disk. A super-solar ([Fe/H]=+0.32) and a solar ([Fe/H]=+0.00) metallicity components, tentatively associated with the thin disk and the Galactic bar, respectively, seem to be the major contributors near the midplane. The solar-metallicity component extends outwards in the midplane but is not observed in the innermost regions. The central regions (within 3 kpc of the Galactic center) reveal, on the other hand, the presence of a significant metal-poor population ([Fe/H] =-0.46), tentatively associated with the thick disk, and which becomes the dominant component far from the midplane ($|Z| > +0.75 kpc). Varying contributions from these different components produce a transition region at +0.5 kpc < |Z| < +1.0 kpc characterized by a significant vertical metallicity gradient., 15 pages, 11 figures
229. Galactic Doppelganger: The chemical similarity among field stars and among stars with a common birth origin
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Dante Minniti, Doug Geisler, Matthew Shetrone, H. W. Rix, Morgan Fouesneau, Gail Zasowski, Alexandre Roman-Lopes, Peter M. Frinchaboy, Melissa Ness, Jon A. Holtzman, Andrew R. Casey, and David W. Hogg
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Physics ,Field (physics) ,010308 nuclear & particles physics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Chemical similarity ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Methods statistical ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Galaxy formation and evolution ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Disc ,10. No inequality ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics - Abstract
We explore to which extent stars within Galactic disk open clusters resemble each other in the high-dimensional space of their photospheric element abundances, and contrast this with pairs of field stars. Our analysis is based on abundances for 20 elements, homogeneously derived from APOGEE spectra (with carefully quantified uncertainties, with a median value of $\sim 0.03$ dex). We consider 90 red giant stars in seven open clusters and find that most stars within a cluster have abundances in most elements that are indistinguishable (in a $��^2$-sense) from those of the other members, as expected for stellar birth siblings. An analogous analysis among pairs of $>1000$ field stars shows that highly significant abundance differences in the 20-dimensional space can be established for the vast majority of these pairs, and that the APOGEE-based abundance measurements have high discriminating power. However, pairs of field stars whose abundances are indistinguishable even at 0.03~dex precision exist: $\sim 0.3$ percent of all field star pairs, and $\sim 1.0$ percent of field star pairs at the same (solar) metallicity [Fe/H] = $0 \pm 0.02$. Most of these pairs are presumably not birth siblings from the same cluster, but rather doppelganger. Our analysis implies that 'chemical tagging' in the strict sense, identifying birth siblings for typical disk stars through their abundance similarity alone, will not work with such data. However, our approach shows that abundances have extremely valuable information for probabilistic chemo-orbital modeling and combined with velocities, we have identified new cluster members from the field., submitted to ApJ
230. Adding the s-Process Element Cerium to the APOGEE Survey: Identification and Characterization of Ce II Lines in the H-band Spectral Window
- Author
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D. Anibal García-Hernández, Peter M. Frinchaboy, Verne V. Smith, Matthew Shetrone, Jon A. Holtzman, Steven R. Majewski, Sten Hasselquist, Katia Cunha, Gail Zasowski, David L. Nidever, Dmitry Bizyaev, Mark Pinsonneault, Szabolcs Mészáros, Jennifer A. Johnson, Henrik Jőnsson, Olga Zamora, Diogo Souto, Jennifer Sobeck, Carlos Allende Prieto, José G. Fernández-Trincado, Ricardo P. Schiavon, and Michael F. Skrutskie
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Physics ,010308 nuclear & particles physics ,Spectral window ,Library science ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Space and Planetary Science ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Christian ministry ,010303 astronomy & astrophysics ,Administration (government) ,Astrophysics::Galaxy Astrophysics ,QB - Abstract
Nine Ce ii lines have been identified and characterized within the spectral window observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey (between λ1.51 and 1.69 μm). At solar metallicities, cerium is an element that is produced predominantly as a result of the slow capture of neutrons (the s-process) during asymptotic giant branch stellar evolution. The Ce ii lines were identified using a combination of a high-resolution ($R=\lambda /\delta \lambda ={\rm{100,000}}$) Fourier Transform Spectrometer (FTS) spectrum of α Boo and an APOGEE spectrum (R = 22,400) of a metal-poor, but s-process enriched, red giant (2M16011638-1201525). Laboratory oscillator strengths are not available for these lines. Astrophysical gf-values were derived using α Boo as a standard star, with the absolute cerium abundance in α Boo set by using optical Ce ii lines that have precise published laboratory gf-values. The near-infrared Ce ii lines identified here are also analyzed, as consistency checks, in a small number of bright red giants using archival FTS spectra, as well as a small sample of APOGEE red giants, including two members of the open cluster NGC 6819, two field stars, and seven metal-poor N- and Al-rich stars. The conclusion is that this set of Ce ii lines can be detected and analyzed in a large fraction of the APOGEE red giant sample and will be useful for probing chemical evolution of the s-process products in various populations of the Milky Way.
231. The Origin of the 300 km s−1 Stream near Segue 1.
- Author
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Sal Wanying Fu, Joshua D. Simon, Matthew Shetrone, Jo Bovy, Timothy C. Beers, J. G. Fernández-Trincado, Vinicius M. Placco, Olga Zamora, Carlos Allende Prieto, D. A. García-Hernández, Paul Harding, Inese Ivans, Richard Lane, Christian Nitschelm, Alexandre Roman-Lopes, and Jennifer Sobeck
- Subjects
SPATIAL distribution (Quantum optics) ,METAPHYSICAL cosmology ,PHOTOMETRIC stereo ,HELIOCENTRIC astrology ,COMPACT objects (Astronomy) - Abstract
We present a search for new members of the 300 km s
−1 stream (300S) near the dwarf galaxy Segue 1 using wide-field survey data. We identify 11 previously unknown bright stream members in the APOGEE-2 and SEGUE-1 and 2 spectroscopic surveys. Based on the spatial distribution of the high-velocity stars, we confirm for the first time that this kinematic structure is associated with a 24°-long stream seen in SDSS and Pan-STARRS imaging data. The 300S stars display a metallicity range of −2.17 < [Fe/H] < −1.24, with an intrinsic dispersion of dex. They also have chemical abundance patterns similar to those of Local Group dwarf galaxies, as well as that of the Milky Way halo. Using the open-source code galpy to model the orbit of the stream, we find that the progenitor of the stream passed perigalacticon about 70 Myr ago, with a closest approach to the Galactic center of about 4.1 kpc. Using Pan-STARRS DR1 data, we obtain an integrated stream luminosity of 4 × 103 L⊙ . We conclude that the progenitor of the stream was a dwarf galaxy that is probably similar to the satellites that were accreted to build the present-day Milky Way halo. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
232. APOGEE Data Releases 13 and 14: Stellar Parameter and Abundance Comparisons with Independent Analyses.
- Author
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Henrik Jönsson, Carlos Allende Prieto, Jon A. Holtzman, Diane K. Feuillet, Keith Hawkins, Katia Cunha, Szabolcs Mészáros, Sten Hasselquist, J. G. Fernández-Trincado, D. A. García-Hernández, Dmitry Bizyaev, Ricardo Carrera, Steven R. Majewski, Marc H. Pinsonneault, Matthew Shetrone, Verne Smith, Jennifer Sobeck, Diogo Souto, Guy S. Stringfellow, and Johanna Teske
- Published
- 2018
- Full Text
- View/download PDF
233. APOGEE Data Releases 13 and 14: Data and Analysis.
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Jon A. Holtzman, Sten Hasselquist, Matthew Shetrone, Katia Cunha, Carlos Allende Prieto, Borja Anguiano, Dmitry Bizyaev, Jo Bovy, Andrew Casey, Bengt Edvardsson, Jennifer A. Johnson, Henrik Jönsson, Szabolcs Meszaros, Verne V. Smith, Jennifer Sobeck, Olga Zamora, S. Drew Chojnowski, Jose Fernandez-Trincado, Anibal Garcia Hernandez, and Steven R. Majewski
- Published
- 2018
- Full Text
- View/download PDF
234. Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67.
- Author
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Diogo Souto, Katia Cunha, Henrik Jönsson, Steven R. Majewski, Jennifer Sobeck, Matthew Shetrone, Guy Stringfellow, Johanna Teske, Ricardo Carrera, Keivan Stassun, Sandro Villanova, J. G. Fernandez-Trincado, Dante Minniti, Felipe Santana, Verne V. Smith, C. Allende Prieto, D. A. García-Hernández, Olga Zamora, Marc Pinsonneault, and J. A. Johnson
- Subjects
STARS ,STAR formation ,GALACTIC nuclei ,STAR clusters ,INFRARED astronomy ,STELLAR mass - Abstract
Detailed chemical abundance distributions for 14 elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of ∼4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G dwarfs, two turnoff stars, two G subgiants, and two red clump (RC) K giants. The abundance analysis uses near-IR high-resolution spectra (λ1.5–1.7 μm) from the Apache Point Observatory Galactic Evolution Experiment survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+1153115 suggest that this star is a solar twin, exhibiting abundance differences relative to the Sun of ≤0.04 dex for all elements. Chemical homogeneity is found within each class of stars (∼0.02 dex), while significant abundance variations (∼0.05–0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the RCs tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
235. The Bulge Metallicity Distribution from the APOGEE Survey.
- Author
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Ana E. García Pérez, Melissa Ness, Annie C. Robin, Inma Martinez-Valpuesta, Jennifer Sobeck, Gail Zasowski, Steven R. Majewski, Jo Bovy, Carlos Allende Prieto, Katia Cunha, Léo Girardi, Szabolcs Mészáros, David Nidever, Ricardo P. Schiavon, Mathias Schultheis, Matthew Shetrone, and Verne V. Smith
- Subjects
GALACTIC evolution ,MILKY Way ,GALACTIC bulges ,ASTROPHYSICS ,MATHEMATICAL decomposition - Abstract
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way, which are inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on high-quality measurements for 7545 red giant stars within 4.5 kpc of the Galactic center, with the goal to shed light on the structure and origin of the Galactic bulge. Stellar metallicities are found, through multiple Gaussian decompositions, to be distributed in several components, which is indicative of the presence of various stellar populations such as the bar or the thin and the thick disks. Super-solar ([Fe/H] = +0.32) and solar ([Fe/H] = +0.00) metallicity components, tentatively associated with the thin disk and the Galactic bar, respectively, seem to be major contributors near the midplane. A solar-metallicity component extends outwards in the midplane but is not observed in the innermost regions. The central regions (within 3 kpc of the Galactic center) reveal, on the other hand, the presence of a significant metal-poor population ([Fe/H] = −0.46), tentatively associated with the thick disk, which becomes the dominant component far from the midplane ( kpc). Varying contributions from these different components produce a transition region at +0.5 kpc , characterized by a significant vertical metallicity gradient. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
236. Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations.
- Author
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Christian R. Hayes, Steven R. Majewski, Matthew Shetrone, Emma Fernández-Alvar, Carlos Allende Prieto, William J. Schuster, Leticia Carigi, Katia Cunha, Verne V. Smith, Jennifer Sobeck, Andres Almeida, Timothy C. Beers, Ricardo Carrera, J. G. Fernández-Trincado, D. A. García-Hernández, Doug Geisler, Richard R. Lane, Sara Lucatello, Allison M. Matthews, and Dante Minniti
- Subjects
GALACTIC halos ,GALACTIC evolution ,ASTRONOMICAL surveys ,STELLAR populations ,GALAXY formation - Abstract
We find two chemically distinct populations separated relatively cleanly in the [Fe/H]–[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities ) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the Sloan Digital Sky Survey. These two stellar populations show the most significant differences in their [X/Fe] ratios for the α-elements, C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote “the HMg population”) exhibits a significant net Galactic rotation, whereas the low-Mg population (or “the LMg population”) has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low- and high-α halo stars found in previous studies, suggesting that these are samples of the same two populations. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
237. APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy.
- Author
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Sten Hasselquist, Matthew Shetrone, Verne Smith, Jon Holtzman, Andrew McWilliam, J. G. Fernández-Trincado, Timothy C. Beers, Steven R. Majewski, David L. Nidever, Baitian Tang, Patricia B. Tissera, Emma Fernández Alvar, Carlos Allende Prieto, Andres Almeida, Borja Anguiano, Giuseppina Battaglia, Leticia Carigi, Gloria Delgado Inglada, Peter Frinchaboy, and D. A. García-Hernández
- Subjects
- *
COSMIC abundances , *DWARF galaxies , *GALACTIC evolution , *HYDROSTATICS , *INTERSTELLAR medium , *MILKY Way - Abstract
The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] ≳ −0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
238. Robert Paul Kraft (1927–2015).
- Author
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Catherine A. Pilachowski, Duane F. Carbon, Eileen Friel, Christian I. Johnson, and Matthew Shetrone
- Subjects
ASTRONOMERS - Published
- 2017
- Full Text
- View/download PDF
239. CHEMICAL TAGGING CAN WORK: IDENTIFICATION OF STELLAR PHASE-SPACE STRUCTURES PURELY BY CHEMICAL-ABUNDANCE SIMILARITY.
- Author
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David W. Hogg, Andrew R. Casey, Melissa Ness, Hans-Walter Rix, Daniel Foreman-Mackey, Sten Hasselquist, Anna Y. Q. Ho, Jon A. Holtzman, Steven R. Majewski, Sarah L. Martell, Szabolcs Mészáros, David L. Nidever, and Matthew Shetrone
- Subjects
STELLAR structure ,PHASE space ,OPEN clusters of stars ,GLOBULAR clusters ,COSMIC abundances ,STELLAR spectrophotometry - Abstract
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 TheCannon, which has now delivered 15 individual abundances for 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 TheCannon, 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, and we recover some known phase-space clusters and find other interesting structures. This is the first-ever project to identify phase-space structures at the survey-scale by blind search purely in abundance space; it verifies the precision of the abundance measurements delivered by TheCannon; the prospects for future data sets appear very good. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
240. IDENTIFICATION OF NEODYMIUM IN THE APOGEE H-BAND SPECTRA.
- Author
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Sten Hasselquist, Matthew Shetrone, Katia Cunha, Verne V. Smith, Jon Holtzman, J. E. Lawler, Carlos Allende Prieto, Timothy C. Beers, Drew Chojnowski, J. G. Fernández-Trincado, D. A. García-Hernández, Fred R. Hearty, Steven R. Majewski, C. B. Pereira, Vinicius M. Placco, Sandro Villanova, and Olga Zamora
- Subjects
- *
NEODYMIUM , *SPECTRAL lines , *BAND spectra , *CERIUM group , *MILKY Way , *IONIZATION (Atomic physics) - Abstract
We present the detection of 10 lines of singly ionized neodymium (Nd ii, Z = 60) in H-band spectra using observations from the SDSS-III Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. These lines were detected in a metal-poor ([Fe/H] ∼ −1.5), neutron-capture element-enhanced star recently discovered in the APOGEE sample. Using an optical high-resolution spectrum, we derive a Nd abundance for this star using Nd ii lines with precise, laboratory-derived gf values. This optical abundance is used to derive log(gf) values for the H-band lines. We use these lines to rederive Nd ii abundances for two more metal-rich, s-process enhanced stars observed by APOGEE and find that these lines yield consistent Nd ii abundances, confirming the Nd enhancement of these stars. We explore the region of parameter space in the APOGEE sample over which these lines can be used to measure Nd ii abundances. We find that Nd abundances can be reliably derived for ∼18% of the red giants observed by APOGEE. This will result in ∼50,000 Milky Way stars with Nd ii abundances following the conclusion of APOGEE-2, allowing for studies of neutron-capture element abundance distributions across the entire Milky Way. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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241. ASPCAP: THE APOGEE STELLAR PARAMETER AND CHEMICAL ABUNDANCES PIPELINE.
- Author
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Ana E. García Pérez, Carlos Allende Prieto, Jon A. Holtzman, Matthew Shetrone, Szabolcs Mészáros, Dmitry Bizyaev, Ricardo Carrera, Katia Cunha, D. A. García-Hernández, Jennifer A. Johnson, Steven R. Majewski, David L. Nidever, Ricardo P. Schiavon, Neville Shane, Verne V. Smith, Jennifer Sobeck, Nicholas Troup, Olga Zamora, David H. Weinberg, and Jo Bovy
- Published
- 2016
- Full Text
- View/download PDF
242. THE STELLAR POPULATION STRUCTURE OF THE GALACTIC DISK.
- Author
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Jo Bovy, Hans-Walter Rix, Edward F. Schlafly, David L. Nidever, Jon A. Holtzman, Matthew Shetrone, and Timothy C. Beers
- Subjects
GALACTIC evolution ,DISKS (Astrophysics) ,MILKY Way ,EVOLUTIONARY theories ,STELLAR structure - Abstract
The spatial structure of stellar populations with different chemical abundances in the Milky Way (MW) contains a wealth of information on Galactic evolution over cosmic time. We use data on 14,699 red-clump stars from the APOGEE survey, covering , to determine the structure of mono-abundance populations (MAPs)—stars in narrow bins in and —accounting for the complex effects of the APOGEE selection function and the spatially variable dust obscuration. We determine that all MAPs with enhanced are centrally concentrated and are well-described as exponentials with a scale length of over the whole radial range of the disk. We discover that the surface-density profiles of low- MAPs are complex: they do not monotonically decrease outwards, but rather display a peak radius ranging from to at low . The extensive radial coverage of the data allows us to measure radial trends in the thickness of each MAP. While high- MAPs have constant scale heights, low- MAPs flare. We confirm, now with high-precision abundances, previous results that each MAP contains only a single vertical scale height and that low-, low- and high-, high- MAPs have intermediate () scale heights that smoothly bridge the traditional thin- and thick-disk divide. That the high-, thick disk components do not flare is strong evidence against their thickness being caused by radial migration. The correspondence between the radial structure and chemical-enrichment age of stellar populations is clear confirmation of the inside-out growth of galactic disks. The details of these relations will constrain the variety of physical conditions under which stars form throughout the MW disk. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
243. TWO NEW LONG-PERIOD GIANT PLANETS FROM THE MCDONALD OBSERVATORY PLANET SEARCH AND TWO STARS WITH LONG-PERIOD RADIAL VELOCITY SIGNALS RELATED TO STELLAR ACTIVITY CYCLES.
- Author
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Michael Endl, Erik J. Brugamyer, William D. Cochran, Phillip J. MacQueen, Paul Robertson, Stefano Meschiari, Ivan Ramirez, Matthew Shetrone, Kevin Gullikson, Marshall C. Johnson, Robert Wittenmyer, Jonathan Horner, David R. Ciardi, Elliott Horch, Attila E. Simon, Steve B. Howell, Mark Everett, Caroline Caldwell, and Barbara G. Castanheira
- Subjects
GAS giants ,STELLAR activity ,RADIAL velocity of stars ,PLANETARY observations - Abstract
We report the detection of two new long-period giant planets orbiting the stars HD 95872 and HD 162004 ( Dra B) by the McDonald Observatory planet search. The planet HD 95872b has a minimum mass of 4.6 and an orbital semimajor axis of 5.2 AU. The giant planet Dra Bb has a minimum mass of 1.5 and an orbital semimajor axis of 4.4 AU. Both of these planets qualify as Jupiter analogs. These results are based on over one and a half decades of precise radial velocity (RV) measurements collected by our program using the McDonald Observatory Tull Coude spectrograph at the 2.7 m Harlan J. Smith Telescope. In the case of Dra B we also detect a long-term nonlinear trend in our data that indicates the presence of an additional giant planet, similar to the Jupiter–Saturn pair. The primary of the binary star system, Dra A, exhibits a very large amplitude RV variation due to another stellar companion. We detect this additional member using speckle imaging. We also report two cases—HD 10086 and HD 102870 (β Virginis)—of significant RV variation consistent with the presence of a planet, but that are probably caused by stellar activity, rather than reflexive Keplerian motion. These two cases stress the importance of monitoring the magnetic activity level of a target star, as long-term activity cycles can mimic the presence of a Jupiter-analog planet. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
244. THE DATA REDUCTION PIPELINE FOR THE APACHE POINT OBSERVATORY GALACTIC EVOLUTION EXPERIMENT.
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David L. Nidever, Jon A. Holtzman, Carlos Allende Prieto, Stephane Beland, Chad Bender, Dmitry Bizyaev, Adam Burton, Rohit Desphande, Scott W. Fleming, Ana E. García Pérez, Fred R. Hearty, Steven R. Majewski, Szabolcs Mészáros, Demitri Muna, Duy Nguyen, Ricardo P. Schiavon, Matthew Shetrone, Michael F. Skrutskie, Jennifer S. Sobeck, and John C. Wilson
- Published
- 2015
- Full Text
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245. THE CHEMICAL ABUNDANCES OF STARS IN THE HALO (CASH) PROJECT. III. A NEW CLASSIFICATION SCHEME FOR CARBON-ENHANCED METAL-POOR STARS WITH s-PROCESS ELEMENT ENHANCEMENT.
- Author
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Julie K. Hollek, Anna Frebel, Vinicius M. Placco, Amanda I. Karakas, Matthew Shetrone, Christopher Sneden, and Norbert Christlieb
- Subjects
RADIAL velocity of stars ,ASYMPTOTIC giant branch stars ,STELLAR atmospheres ,STELLAR populations ,POPULATION I (Astronomy) - Abstract
We present a detailed abundance analysis of 23 elements for a newly discovered carbon-enhanced metal-poor (CEMP) star, HE 0414−0343, from the Chemical Abundances of Stars in the Halo Project. Its spectroscopic stellar parameters are T
eff = 4863 K, ξ = 2.20 km s−1 , and [Fe/H] = −2.24. Radial velocity measurements covering seven years indicate HE 0414−0343 to be a binary. HE 0414−0343 has and is strongly enhanced in neutron-capture elements but its abundances cannot be reproduced by a solar-type s-process pattern alone. Traditionally, it could be classified as a “CEMP-r/s” star. Based on abundance comparisons with asymptotic giant branch (AGB) star nucleosynthesis models, we suggest a new physically motivated origin and classification scheme for CEMP-s stars and the still poorly understood CEMP-r/s. The new scheme describes a continuous transition between these two so-far distinctly treated subgroups: CEMP-sA, CEMP-sB, and CEMP-sC. Possible causes for a continuous transition include the number of thermal pulses the AGB companion underwent, the effect of different AGB star masses on their nucleosynthetic yields, and physics that is not well approximated in 1D stellar models such as proton ingestion episodes and rotation. Based on a set of detailed AGB models, we suggest the abundance signature of HE 0414−0343 to have arisen from a >1.3 M⊙ mass AGB star and a late-time mass transfer that transformed HE 0414−0343 into a CEMP-sC star. We also find that the [Y/Ba] ratio well parametrizes the classification and can thus be used to easily classify any future such stars. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
246. ABUNDANCES, STELLAR PARAMETERS, AND SPECTRA FROM THE SDSS-III/APOGEE SURVEY.
- Author
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Jon A. Holtzman, Matthew Shetrone, Jennifer A. Johnson, Carlos Allende Prieto, Friedrich Anders, Brett Andrews, Timothy C. Beers, Dmitry Bizyaev, Michael R. Blanton, Jo Bovy, Ricardo Carrera, S. Drew Chojnowski, Katia Cunha, Daniel J. Eisenstein, Diane Feuillet, Peter M. Frinchaboy, Jessica Galbraith-Frew, Ana E. García Pérez, D. A. García-Hernández, and Sten Hasselquist
- Published
- 2015
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- View/download PDF
247. RAPID ROTATION OF LOW-MASS RED GIANTS USING APOKASC: A MEASURE OF INTERACTION RATES ON THE POST-MAIN-SEQUENCE.
- Author
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Jamie Tayar, Tugdual Ceillier, D. A. García-Hernández, Nicholas W. Troup, Savita Mathur, Rafael A. García, O. Zamora, Jennifer A. Johnson, Marc H. Pinsonneault, Szabolcs Mészáros, Carlos Allende Prieto, William J. Chaplin, Yvonne Elsworth, Saskia Hekker, David L. Nidever, David Salabert, Donald P. Schneider, Aldo Serenelli, Matthew Shetrone, and Dennis Stello
- Subjects
GIANT stars ,STELLAR rotation ,STELLAR gravitation ,STELLAR mass ,RED giants - Abstract
We investigate the occurrence rate of rapidly rotating ( >10 km s
−1 ), low-mass giant stars in the Apache Point Observatory Galaxy Evolution Experiment-Kepler (APOKASC) fields with asteroseismic mass and surface gravity measurements. Such stars are likely merger products and their frequency places interesting constraints on stellar population models. We also identify anomalous rotators, i.e., stars with 5 km s−1 < < 10 km s−1 that are rotating significantly faster than both angular momentum evolution predictions and the measured rates of similar stars. Our data set contains fewer rapid rotators than one would expect given measurements of the Galactic field star population, which likely indicates that asteroseismic detections are less common in rapidly rotating red giants. The number of low-mass moderate (5–10 km s−1 ) rotators in our sample gives a lower limit of 7% for the rate at which low-mass stars interact on the upper red giant branch because single stars in this mass range are expected to rotate slowly. Finally, we classify the likely origin of the rapid or anomalous rotation where possible. KIC 10293335 is identified as a merger product and KIC 6501237 is a possible binary system of two oscillating red giants. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
248. EXPLORING ANTICORRELATIONS AND LIGHT ELEMENT VARIATIONS IN NORTHERN GLOBULAR CLUSTERS OBSERVED BY THE APOGEE SURVEY.
- Author
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Szabolcs Mészáros, Sarah L. Martell, Matthew Shetrone, Sara Lucatello, Nicholas W. Troup, Jo Bovy, Katia Cunha, Domingo A. García-Hernández, Jamie C. Overbeek, Carlos Allende Prieto, Timothy C. Beers, Peter M. Frinchaboy, Ana E. García Pérez, Fred R. Hearty, Jon Holtzman, Steven R. Majewski, David L. Nidever, Ricardo P. Schiavon, Donald P. Schneider, and Jennifer S. Sobeck
- Published
- 2015
- Full Text
- View/download PDF
249. THE PUZZLING Li-RICH RED GIANT ASSOCIATED WITH NGC 6819.
- Author
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Joleen K. Carlberg, Verne V. Smith, Katia Cunha, Steven R. Majewski, Szabolcs Mészáros, Matthew Shetrone, Carlos Allende Prieto, Dmitry Bizyaev, Keivan G. Stassun, Scott W. Fleming, Gail Zasowski, Fred Hearty, David L. Nidever, Donald P. Schneider, Jon A. Holtzman, and Peter M. Frinchaboy
- Subjects
LITHIUM ,ALKALI metals ,RED giants ,STARS ,ASYMPTOTIC giant branch stars - Abstract
A Li-rich red giant (RG) star (2M19411367+4003382) recently discovered in the direction of NGC 6819 belongs to the rare subset of Li-rich stars that have not yet evolved to the luminosity bump, an evolutionary stage where models predict Li can be replenished. The currently favored model to explain Li enhancement in first-ascent RGs like 2M19411367+4003382 requires deep mixing into the stellar interior. Testing this model requires a measurement of
12 C/13 C, which is possible to obtain from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. However, the Li-rich star also has abnormal asteroseismic properties that call into question its membership in the cluster, even though its radial velocity and location on color–magnitude diagrams are consistent with membership. To address these puzzles, we have measured a wide array of abundances in the Li-rich star and three comparison stars using spectra taken as part of the APOGEE survey to determine the degree of stellar mixing, address the question of membership, and measure the surface gravity. We confirm that the Li-rich star is a RG with the same overall chemistry as the other cluster giants. However, its is significantly lower, consistent with the asteroseismology results and suggestive of a very low mass if the star is indeed a cluster member. Regardless of the cluster membership, the12 C/13 C and C/N ratios of the Li-rich star are consistent with standard first dredge-up, indicating that Li dilution has already occurred, and inconsistent with internal Li enrichment scenarios that require deep mixing. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
250. HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES.
- Author
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S. Drew Chojnowski, David G. Whelan, John P. Wisniewski, Steven R. Majewski, Matthew Hall, Matthew Shetrone, Rachael Beaton, Adam Burton, Guillermo Damke, Steve Eikenberry, Sten Hasselquist, Jon A. Holtzman, Szabolcs Mészáros, David Nidever, Donald P. Schneider, John Wilson, Gail Zasowski, Dmitry Bizyaev, Howard Brewington, and J. Brinkmann
- Published
- 2015
- Full Text
- View/download PDF
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