We present results from a quantitative spectroscopic analysis conducted on archival Keck/HIRES high-resolution spectra from the California-Kepler Survey (CKS) sample of transiting planetary host ...stars identified from the Kepler mission. The spectroscopic analysis was based on a carefully selected set of Fe i and Fe ii lines, resulting in precise values for the stellar parameters of effective temperature (Teff) and surface gravity (log g). Combining the stellar parameters with Gaia DR2 parallaxes and precise distances, we derived both stellar and planetary radii for our sample, with a median internal uncertainty of 2.8% in the stellar radii and 3.7% in the planetary radii. An investigation into the distribution of planetary radii confirmed the bimodal nature of this distribution for the small-radius planets found in previous studies, with peaks at ∼1.47 0.05 and ∼2.72 0.10 R⊕ with a gap at ∼1.9 R⊕. Previous studies that modeled planetary formation that is dominated by photoevaporation predicted this bimodal radii distribution and the presence of a radius gap, or photoevaporation valley. Our results are in overall agreement with these models, as well as core powered mass-loss models. The high internal precision achieved here in the derived planetary radii clearly reveal the presence of a slope in the photoevaporation valley for the CKS sample, indicating that the position of the radius gap decreases with orbital period; this decrease was fit by a power law of the form Rpl ∝ P−0.11, which is consistent with both photoevaporation and core powered mass-loss models of planet formation, with Earth-like core compositions.
The data and analysis methodology used for the SDSS/APOGEE Data Releases 13 and 14 are described, highlighting differences from the DR12 analysis presented in Holtzman et al. Some improvement in the ...handling of telluric absorption and persistence is demonstrated. The derivation and calibration of stellar parameters, chemical abundances, and respective uncertainties are described, along with the ranges over which calibration was performed. Some known issues with the public data related to the calibration of the effective temperatures (DR13), surface gravity (DR13 and DR14), and C and N abundances for dwarfs (DR13 and DR14) are highlighted. We discuss how results from a data-driven technique, The Cannon, are included in DR14 and compare those with results from the APOGEE Stellar Parameters and Chemical Abundances Pipeline. We describe how using The Cannon in a mode that restricts the abundance analysis of each element to regions of the spectrum with known features from that element leads to Cannon abundances can lead to significantly different results for some elements than when all regions of the spectrum are used to derive abundances.
Abstract
We present a study of metallicities in a sample of main-sequence stars with spectral types
M
,
K
,
G
, and
F
(
T
eff
∼3200–6500K and log
g
∼ 4.3–5.0 dex) belonging to the solar neighborhood ...young open cluster Coma Berenices. Metallicities were determined using the high-resolution (
R
=
λ
/Δ
λ
∼ 22,500) NIR spectra (
λ
1.51–
λ
1.69
μ
m) of the Sloan Digital Sky Survey IV APOGEE survey. Membership to the cluster was confirmed using previous studies in the literature along with APOGEE radial velocities and Gaia DR2. An LTE analysis using plane-parallel MARCS model atmospheres and the APOGEE DR16 line list was adopted to compute synthetic spectra and derive atmospheric parameters (
T
eff
and log
g
) for the
M
dwarfs and metallicities for the sample. The derived metallicities are near-solar and are homogeneous at the level of the expected uncertainties, in particular when considering stars from a given stellar class. The mean metallicity computed for the sample of
G, K
, and
M
dwarfs is 〈Fe/H〉 = +0.04 ± 0.02 dex; however, the metallicities of the
F
-type stars are slightly lower, by about 0.04 dex, when compared to cooler and less massive members. Models of atomic diffusion can explain this modest abundance dip for the
F
dwarfs, indicating that atomic diffusion operates in Coma Berenices stars. The Fe/H dip occurs in nearly the same effective temperature range as that found in previous analyses of the lithium and beryllium abundances in Coma Berenices.
We report the first APOGEE metallicities and -element abundances measured for 3600 red giant stars spanning a large radial range of both the Large (LMC) and Small Magellanic Clouds, the largest Milky ...Way (MW) dwarf galaxies. Our sample is an order of magnitude larger than that of previous studies and extends to much larger radial distances. These are the first results presented that make use of the newly installed southern APOGEE instrument on the du Pont telescope at Las Campanas Observatory. Our unbiased sample of the LMC spans a large range in metallicity, from Fe/H = −0.2 to very metal-poor stars with Fe/H −2.5, the most metal-poor Magellanic Cloud (MC) stars detected to date. The LMC /Fe-Fe/H distribution is very flat over a large metallicity range but rises by ∼0.1 dex at −1.0 < Fe/H −0.5. We interpret this as a sign of the known recent increase in MC star formation activity and are able to reproduce the pattern with a chemical evolution model that includes a recent "starburst." At the metal-poor end, we capture the increase of /Fe with decreasing Fe/H and constrain the " -knee" to Fe/H −2.2 in both MCs, implying a low star formation efficiency of ∼0.01 Gyr−1. The MC knees are more metal-poor than those of less massive MW dwarf galaxies such as Fornax, Sculptor, or Sagittarius. One possible interpretation is that the MCs formed in a lower-density environment than the MW, a hypothesis that is consistent with the paradigm that the MCs fell into the MW's gravitational potential only recently.
ABSTRACT
We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within ∼4 kpc of the Galactic Centre. Characterized by a chemical composition resembling those ...of low-mass satellites of the Milky Way, this new inner Galaxy structure (IGS) seems to be chemically and dynamically detached from more metal-rich populations in the inner Galaxy. We conjecture that this structure is associated with an accretion event that likely occurred in the early life of the Milky Way. Comparing the mean elemental abundances of this structure with predictions from cosmological numerical simulations, we estimate that the progenitor system had a stellar mass of ∼5 × 108 M⊙, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:in situ ratio within our metal-poor (Fe/H < –0.8) bulge sample is somewhere between 1:3 and 1:2, confirming predictions of cosmological numerical simulations by various groups.
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
We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce, and Nd abundances of 2283 red giant stars in 31 globular clusters from high-resolution spectra observed in both the Northern and ...Southern hemisphere by the SDSS-IV APOGEE-2 survey. This unprecedented homogeneous data set, largest to date, allows us to discuss the intrinsic Fe spread, the shape, and statistics of Al-Mg and N-C anti-correlations as a function of cluster mass, luminosity, age, and metallicity for all 31 clusters. We find that the Fe spread does not depend on these parameters within our uncertainties including cluster metallicity, contradicting earlier observations. We do not confirm the metallicity variations previously observed in M22 and NGC 1851. Some clusters show a bimodal Al distribution, while others exhibit a continuous distribution as has been previously reported in the literature. We confirm more than two populations in ω Cen and NGC 6752, and find new ones in M79. We discuss the scatter of Al by implementing a correction to the standard chemical evolution of Al in the Milky Way. After correction, its dependence on cluster mass is increased suggesting that the extent of Al enrichment as a function of mass was suppressed before the correction. We observe a turnover in the Mg-Al anticorrelation at very low Mg in ω Cen, similar to the pattern previously reported in M15 and M92. ω Cen may also have a weak K-Mg anticorrelation, and if confirmed, it would be only the third cluster known to show such a pattern.
We analyze chemical abundances of stars in the Sagittarius (Sgr) tidal stream using high-resolution Gemini+GRACES spectra of 42 members of the highest surface-brightness portions of both the trailing ...and leading arms. Targets were chosen using a 2MASS+WISE color-color selection, combined with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) radial velocities. In this Letter, we analyze Fe/H and -elements produced by both hydrostatic (O, Mg) and explosive (Si, Ca, Ti) nucleosynthetic processes. The average Fe/H for our Sgr stream stars is lower than that for stars in the Sgr core, and stars in the trailing and leading arms show systematic differences in Fe/H. Both hydrostatic and explosive elements are depleted relative to Milky Way (MW) disk and halo stars, with a larger gap between the MW trend and Sgr stars for the hydrostatic elements. Chemical abundances of Sgr stream stars show similar patterns to those measured in the core of the Sgr dSph. We explore the ratio of hydrostatic to explosive -elements h/ex (which we refer to as the "HEx ratio"). Our observed HEx ratio trends for Sgr debris are deficient relative to MW stars. Via simple chemical evolution modeling, we show that these HEx ratio patterns are consistent with a Sgr IMF that lacks the most massive stars. This study provides a link between the chemical properties in the intact Sgr core and the significant portion of the Sgr system's luminosity that is estimated to currently reside in the streams.
Abstract
The updated
H
-band spectral-line list (from
λ
15000–17000) adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) for the SDSS-IV Data Release 16 (DR16) is presented ...in this work. The APOGEE line list is a combination of atomic and molecular lines, with data drawn from laboratory, theoretical, and astrophysical sources. Oscillator strengths and damping constants are adjusted using high signal-to-noise, high-resolution spectra of the Sun, and
α
Boo (Arcturus), as “standard stars.” Updates to the DR16 line list, as compared to the previous DR14 version, include the addition of molecular H
2
O and FeH lines, as well as a much larger (by a factor of ∼4) atomic line list, including a significantly greater number of transitions with hyperfine splitting. More recent references and line lists for the crucial molecules, CO and OH, as well as for C
2
and SiH, are also included. In contrast to DR14, DR16 contains measurable lines from the heavy neutron-capture elements cerium (as Ce
ii
), neodymium (as Nd
ii
), and ytterbium (as Yb
ii
), as well as one line from rubidium (as Rb
i
), which may be detectable in a small fraction of APOGEE red giants.
Abstract
Abundances of fluorine (
19
F), as well as isotopic ratios of
16
O/
17
O, are derived in a sample of luminous young (∼10
7
–10
8
yr) red giants in the Galactic center (with galactocentric ...distances ranging from 0.6–30 pc), using high-resolution infrared spectra and vibration-rotation lines of H
19
F near
λ
2.3
μ
m. Five of the six red giants are members of the Nuclear star cluster that orbits the central supermassive black hole. Previous investigations of the chemical evolution of
19
F in Galactic thin and thick-disk stars have revealed that the nucleosynthetic origins of
19
F may be rather complex, resulting from two, or more, astrophysical sites; fluorine abundances behave as a primary element with respect to Fe abundances for thick-disk stars and as a secondary element in thin-disk stars. The Galactic center red giants analyzed fall within the thin-disk relation of F with Fe, having near-solar, to slightly larger, abundances of Fe (〈Fe/H〉 = +0.08 ± 0.04), with a slight enhancement of the F/Fe abundance ratio (〈F/Fe〉 = +0.28 ± 0.17). In terms of their F and Fe abundances, the Galactic center stars follow the thin-disk population, which requires an efficient source of
19
F that could be the winds from core-He burning Wolf–Rayet stars, or thermally pulsing AGB stars, or a combination of both. The observed increase of F/Fe with increasing Fe/H found in thin-disk and Galactic center stars is not predicted by any published chemical evolution models that are discussed, thus a quantitative understanding of yields from the various possible sources of
19
F remains unknown.
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