| 1. |
- Donor, John, et al.
(författare)
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The Open Cluster Chemical Abundances and Mapping Survey. IV. Abundances for 128 Open Clusters Using SDSS/APOGEE DR16
- 2020
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Ingår i: Astronomical Journal. - : Institute of Physics (IOP). - 0004-6256 .- 1538-3881. ; 159:5
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Tidskriftsartikel (refereegranskat)abstract
- The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to constrain key Galactic dynamical and chemical evolution parameters by the construction of a large, comprehensive, uniform, infrared-based spectroscopic data set of hundreds of open clusters. This fourth contribution from the OCCAM survey presents analysis using Sloan Digital Sky Survey/APOGEE DR16 of a sample of 128 open clusters, 71 of which we designate to be "high quality" based on the appearance of their color-magnitude diagram. We find the APOGEE DR16 derived [Fe/H] abundances to be in good agreement with previous high-resolution spectroscopic open cluster abundance studies. Using the high-quality sample, we measure Galactic abundance gradients in 16 elements, and find evolution of some of the [X/Fe] gradients as a function of age. We find an overall Galactic [Fe/H] versus R-GC gradient of -0.068 0.001 dex kpc(-1) over the range of 6 R-GC < 13.9 kpc; however, we note that this result is sensitive to the distance catalog used, varying as much as 15%. We formally derive the location of a break in the [Fe/H] abundance gradient as a free parameter in the gradient fit for the first time. We also measure significant Galactic gradients in O, Mg, S, Ca, Mn, Cr, Cu, Na, Al, and K, some of which are measured for the first time. Our large sample allows us to examine four well-populated age bins in order to explore the time evolution of gradients for a large number of elements and comment on possible implications for Galactic chemical evolution and radial migration.
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| 2. |
- Hasselquist, Sten, et al.
(författare)
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Exploring the stellar age distribution of the milky way bulge using APOGEE
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 901:2
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Tidskriftsartikel (refereegranskat)abstract
- We present stellar age distributions of the Milky Way bulge region using ages for ∼6000 high-luminosity (log(g)< 2.0), metal-rich ([Fe/H] ≥ -0.5) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment. Ages are derived using The Cannon label-transfer method, trained on a sample of nearby luminous giants with precise parallaxes for which we obtain ages using a Bayesian isochrone-matching technique. We find that the metal-rich bulge is predominantly composed of old stars (>8 Gyr). We find evidence that the planar region of the bulge (ZGC| 0.25 kpc) is enriched in metallicity, Z, at a faster rate (dZ/dt ∼ 0.0034 Gyr-1) than regions farther from the plane (dZ/dt ∼ 0.0013 Gyr-1 at | ZGC| > 1.00 kpc). We identify a nonnegligible fraction of younger stars (age ∼2-5 Gyr) at metallicities of +0.2 < [Fe/H] < +0.4. These stars are preferentially found in the plane (ZGC| ≤ 0.25 kpc) and at R cy ≈ 2-3 kpc, with kinematics that are more consistent with rotation than are the kinematics of older stars at the same metallicities. We do not measure a significant age difference between stars found inside and outside the bar. These findings show that the bulge experienced an initial starburst that was more intense close to the plane than far from the plane. Then, star formation continued at supersolar metallicities in a thin disk at 2 kpc ≲ R cy ≲ 3 kpc until ∼2 Gyr ago.
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| 3. |
- Jönsson, Henrik, et al.
(författare)
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APOGEE Data and Spectral Analysis from SDSS Data Release 16 : Seven Years of Observations Including First Results from APOGEE-South
- 2020
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Ingår i: Astronomical Journal. - : Institute of Physics Publishing (IOPP). - 0004-6256 .- 1538-3881. ; 160:3
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Tidskriftsartikel (refereegranskat)abstract
- The spectral analysis and data products in Data Release 16 (DR16; 2019 December) from the high-resolution near-infrared Apache Point Observatory Galactic Evolution Experiment (APOGEE)-2/Sloan Digital Sky Survey (SDSS)-IV survey are described. Compared to the previous APOGEE data release (DR14; 2017 July), APOGEE DR16 includes about 200,000 new stellar spectra, of which 100,000 are from a new southern APOGEE instrument mounted on the 2.5 m du Pont telescope at Las Campanas Observatory in Chile. DR16 includes all data taken up to 2018 August, including data released in previous data releases. All of the data have been re-reduced and re-analyzed using the latest pipelines, resulting in a total of 473,307 spectra of 437,445 stars. Changes to the analysis methods for this release include, but are not limited to, the use of MARCS model atmospheres for calculation of the entire main grid of synthetic spectra used in the analysis, a new method for filling "holes" in the grids due to unconverged model atmospheres, and a new scheme for continuum normalization. Abundances of the neutron-capture element Ce are included for the first time. A new scheme for estimating uncertainties of the derived quantities using stars with multiple observations has been applied, and calibrated values of surface gravities for dwarf stars are now supplied. Compared to DR14, the radial velocities derived for this release more closely match those in the Gaia DR2 database, and a clear improvement in the spectral analysis of the coolest giants can be seen. The reduced spectra as well as the result of the analysis can be downloaded using links provided on the SDSS DR16 web page.
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| 4. |
- Lorenzetti, Angelica, et al.
(författare)
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Low purity enzymes and ultrasound pretreatment applied to partially hydrolyze whey protein
- 2020
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Ingår i: Food Bioscience. - : ELSEVIER. - 2212-4292 .- 2212-4306. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- The hydrolysis of whey protein isolate with low purity enzymes was studied with application of ultrasound pretreatment. The aim was to increase the degree of hydrolysis and produce new biologically active peptides. The experiments were carried out with hydrolysis times up to 24 h. The influence of temperature, pH, enzymes (pepsin and papain), substrate concentration, and use or not of the ultrasonic probe was investigated. The peptide’s structure and profile were examined after exposure to ultrasound. The highest degree of hydrolysis occurred with the use of pepsin for 10 h, 37 degrees C, and pH 2.5. The ultrasound pre-treatment allowed a reduction of 6 h in the process. After partial enzymatic hydrolysis and ultrasound pretreatment a higher proportion of low molar mass peptides were observed at 1000-2000 g.mol(-1). In vitro simulated digestion showed slight differences in peptide profile indicating that active compounds were preserved intact with a slight impact on bioactivity.
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| 5. |
- Nidever, David L., et al.
(författare)
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The Lazy Giants : APOGEE Abundances Reveal Low Star Formation Efficiencies in the Magellanic Clouds
- 2020
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Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 895:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the first APOGEE metallicities and alpha-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 [alpha/Fe]-[Fe/H] distribution is very flat over a large metallicity range but rises by similar to 0.1 dex at -1.0 < [Fe/H] less than or similar to -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 [alpha/Fe] with decreasing [Fe/H] and constrain the "alpha-knee" to [Fe/H] less than or similar to -2.2 in both MCs, implying a low star formation efficiency of similar to 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.
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| 6. |
- Ryde, Nils, et al.
(författare)
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Fluorine in the Solar Neighborhood : The Need for Several Cosmic Sources
- 2020
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Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 893:1
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Tidskriftsartikel (refereegranskat)abstract
- The cosmic origin of fluorine is still not well constrained. Several nucleosynthetic channels at different phases of stellar evolution have been suggested, but these must be constrained by observations. For this, the fluorine abundance trend with metallicity spanning a wide range is required. Our aim is to determine stellar abundances of fluorine for -1.1 < [Fe H] < +0.4. We determine the abundances from HF lines in infrared K-band spectra ( 2.3 mm) of cool giants, observed with the IGRINS and Phoenix high-resolution spectrographs. We derive accurate stellar parameters for all our observed K giants, which is important as the HF lines are very temperaturesensitive. We find that [F/Fe] is flat as a function of metallicity at [ F/Fe]0, but increases as the metallicity increases. The fluorine slope shows a clear secondary behavior in this metallicity range. We also find that the [F/ Ce] ratio is relatively flat for -0.6 < [Fe H] < 0, and that for two metal-poor ([Fe H] < - 0.8), s-process element-enhanced giants, we do not detect an elevated fluorine abundance. We interpret all of these observational constraints as indications that several major processes are at play for the cosmic budget of fluorine over time: from those in massive stars at low metallicities, through the asymptotic giant branch star contribution at -0.6 < [Fe H] < 0, to processes with increasing yields with metallicity at supersolar metallicities. The origins of the latter, and whether or not Wolf-Rayet stars and/or novae could contribute at supersolar metallicities, is currently not known. To quantify these observational results, theoretical modeling is required. More observations in the metal-poor region are required to clarify the processes there.
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| 7. |
- Souto, Diogo, et al.
(författare)
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Stellar Characterization of M Dwarfs from the APOGEE Survey : A Calibrator Sample for M-dwarf Metallicities
- 2020
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Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 890:2
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Tidskriftsartikel (refereegranskat)abstract
- We present spectroscopic determinations of the effective temperatures, surface gravities, and metallicities for 21 M dwarfs observed at high resolution (R similar to 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 H2O and FeH molecular line lists. Our sample range in T-eff from similar to 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 M-KS-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 Delta= -0.01 +/- 0.02 R star/R-circle dot. In addition, the derived M-dwarf masses based upon the radii and surface gravities tend to be slightly smaller (by similar to 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.
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