Abstract
Open clusters are key chemical and age tracers of Milky Way evolution. While open clusters provide significant constraints on galaxy evolution, their use has been limited due to ...discrepancies in measuring abundances from different studies. We analyze medium-resolution (
R
∼ 19,000) Cerro Tololo Inter-American Observatory/Hydra spectra of giant stars in 58 open clusters using The Cannon to determine Fe/H, Mg/Fe, Si/Fe, Al/Fe, and O/Fe. This work adds an additional 55 primarily southern hemisphere open clusters calibrated to the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment DR16 metallicity system. This uniform analysis is compared to previous studies Fe/H measurements for 23 clusters and we present spectroscopic metallicities for the first time for 35 open clusters.
APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing ∼3 × 105 stars across the entire sky. It is the successor to APOGEE and is part of the Sloan Digital Sky Survey IV ...(SDSS-IV). APOGEE-2 is expanding on APOGEE's goals of addressing critical questions of stellar astrophysics, stellar populations, and Galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at Las Campanas Observatory in Chile. APOGEE-2 is targeting red giant branch and red clump stars, RR Lyrae, low-mass dwarf stars, young stellar objects, and numerous other Milky Way and Local Group sources across the entire sky from both hemispheres. In this paper, we describe the APOGEE-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the SDSS data releases.
Context . In chemically peculiar Ap/Bp stars with large-scale organised magnetic fields of simple centred dipole configuration, the ratio between the maximum and the minimum of the mean magnetic ...field modulus is on the order of 1.25. Values of two or more are observed only for very few Ap/Bp stars and are indicative of a very unusual magnetic field geometry. Aims . Determining the magnetic field structure of Ap/Bp stars is bound to provide a different insight into the physics and the origin of the magnetic fields in early-type stars. In this respect, the Bp star HD 57372 is of particular interest because strongly variable magnetically split lines have been observed in HARPS and APOGEE spectra. Methods . We obtained and analysed measurements of the mean magnetic field modulus and of the mean longitudinal magnetic field using near-infrared spectra and optical polarimetric spectra distributed over the stellar rotation period. Results . The mean magnetic field modulus 〈 B 〉 of HD 57372, as estimated from absorption lines that are split via the Zeeman effect and resolved in both optical and near-infrared spectra, is found to vary by an extraordinary amount: about 10 kG. The exceptional value of three for the ratio between the maximum and the minimum of the field modulus is indicative of a very unusual geometry for HD 57372’s magnetic field. All observable quantities were found to vary in phase with the photometric period of 7.889 days. This includes the longitudinal magnetic field 〈 B z 〉, which varies from −6 kG up to 1.7 kG in FORS2 spectra, as well as the metal line strengths, whose equivalent widths change by up to 50% of their mean values over the course of the rotation period. The B8 temperature class of HD 57372 also places it among the hottest stars known to exhibit resolved, magnetically split lines.
APOGEE DR14/DR15 Abundances in the Inner Milky Way Zasowski, G.; Schultheis, M.; Hasselquist, S. ...
Astrophysical journal/The Astrophysical journal,
01/2019, Letnik:
870, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present an overview of the distributions of 11 elemental abundances in the Milky Way's (MW) inner regions, as traced by APOGEE stars released as part of the Sloan Digital Sky Survey Data Release ...14/15 (DR14/DR15), including O, Mg, Si, Ca, Cr, Mn, Co, Ni, Na, Al, and K. This sample spans ∼4000 stars with RGC ≤ 4.0 kpc, enabling the most comprehensive study to date of these abundances and their variations within the innermost few kiloparsecs of the MW. We describe the observed abundance patterns (X/Fe-Fe/H), compare to previous literature results and to patterns in stars at the solar Galactocentric radius (RGC), and discuss possible trends with DR14/DR15 effective temperatures. We find that the position of the Mg/Fe-Fe/H "knee" is nearly constant with RGC, indicating a well-mixed star-forming medium or high levels of radial migration in the early inner Galaxy. We quantify the linear correlation between pairs of elements in different subsamples of stars and find that these relationships vary; some abundance correlations are very similar between the -rich and -poor stars, but others differ significantly, suggesting variations in the metallicity dependencies of certain supernova yields. These empirical trends will form the basis for more detailed future explorations and for the refinement of model comparison metrics. That the inner MW abundances appear dominated by a single chemical evolutionary track and that they extend to such high metallicities underscore the unique importance of this part of the Galaxy for constraining the ingredients of chemical evolution modeling and for improving our understanding of the evolution of the Galaxy as a whole.
Abstract
APOGEE is a high-resolution (
R
∼ 22,000), near-infrared, multi-epoch, spectroscopic survey of the Milky Way. The second generation of the APOGEE project, APOGEE-2, includes an expansion of ...the survey to the Southern Hemisphere called APOGEE-2S. This expansion enabled APOGEE to perform a fully panoramic mapping of all of the main regions of the Milky Way; in particular, by operating in the
H
band, APOGEE is uniquely able to probe the dust-hidden inner regions of the Milky Way that are best accessed from the Southern Hemisphere. In this paper we present the targeting strategy of APOGEE-2S, with special attention to documenting modifications to the original, previously published plan. The motivation for these changes is explained as well as an assessment of their effectiveness in achieving their intended scientific objective. In anticipation of this being the last paper detailing APOGEE targeting, we present an accounting of all such information complete through the end of the APOGEE-2S project; this includes several main survey programs dedicated to exploration of major stellar populations and regions of the Milky Way, as well as a full list of programs contributing to the APOGEE database through allocations of observing time by the Chilean National Time Allocation Committee and the Carnegie Institution for Science. This work was presented along with a companion article, Beaton et al. (2021), presenting the final target selection strategy adopted for APOGEE-2 in the Northern Hemisphere.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the ...principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of ~10 super(5) red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.
The Sloan Digital Sky Survey III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a three-year survey that is collecting 10 super(5) high-resolution spectra in the ...near-IR across multiple Galactic populations. To derive stellar parameters and chemical compositions from this massive data set, the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP) has been developed. Here, we describe empirical calibrations of stellar parameters presented in the first SDSS-III APOGEE data release (DR10). These calibrations were enabled by observations of 559 stars in 20 globular and open clusters. The cluster observations were supplemented by observations of stars in NASA's Kepler field that have well determined surface gravities from asteroseismic analysis. We discuss the accuracy and precision of the derived stellar parameters, considering especially effective temperature, surface gravity, and metallicity; we also briefly discuss the derived results for the abundances of the alpha -elements, carbon, and nitrogen. Overall, we find that ASPCAP achieves reasonably accurate results for temperature and metallicity, but suffers from systematic errors in surface gravity. We derive calibration relations that bring the raw ASPCAP results into better agreement with independently determined stellar parameters. The internal scatter of ASPCAP parameters within clusters suggests that metallicities are measured with a precision better than 0.1 dex, effective temperatures better than 150 K, and surface gravities better than 0.2 dex. The understanding provided by the clusters and Kepler giants on the current accuracy and precision will be invaluable for future improvements of the pipeline.
ABSTRACT
The main-sequence mercury–manganese (HgMn) stars are known to exhibit large overabundances of exotic elements and, similar to magnetic Ap/Bp stars, are spectrum variables, implying the ...presence of an inhomogeneous element distribution over the stellar surface. A number of magnetic field studies have been attempted in the last decades, indicating that magnetic fields in HgMn stars, if they exist, should be rather weak. The presence of tangled magnetic fields was suggested by several authors who detected quadratic magnetic fields using the moment technique. We employ the least-squares deconvolution technique to carry out a sensitive search for weak magnetic fields in spectropolarimetric observations of three HgMn stars, HD 221507, HD 65949, and HD 101189, which have different fundamental parameters and spectral characteristics. A definite weak longitudinal field is discovered in HD 221507 and HD 65949 on single epochs, while only marginal field detections were achieved for HD 101189. The new measurements indicate that the structure of the magnetic fields is probably rather complex: our analysis reveals the presence of reversed Stokes V profiles at the same observational epoch if individual elements are used in the measurements. This is the first observational evidence that individual elements sample distinct local magnetic fields of different polarity across the stellar surface.
ABSTRACT
NGC 1624-2 is an O7f?p star with a reported probable polar magnetic field strength ≥20 kG, which is the strongest magnetic field ever measured in an O-type star. We study the variability of ...the mean longitudinal magnetic field 〈Bz〉 and the mean field modulus 〈B〉 to obtain constraints on its field geometry. Only one magnetic pole is observable over the rotation cycle. The approximately sinusoidal variation of 〈Bz〉 and the ratio of the values of the extrema of 〈B〉 indicate that there is an important component of the field that is dipolar. The 〈Bz〉 values measured over the rotation cycle are in the range from −0.2 to 4.5 kG, whereas the values for 〈B〉 vary between 9 and 12 kG. The 〈Bz〉 values obtained using the O iii λ7455 emission line are in the range from 0.4 to 2.3 kG and show a variability pattern similar to that detected for the absorption lines. The fact that the phase of the 〈Bz〉 minimum coincides with the phase of the 〈B〉 maximum, indicates that the field structure must significantly depart from a centred dipole. Further, we discuss the nature of the observed variable Stokes V profiles corresponding to a longitudinal field of negative polarity detected in the emission He i lines and present the first magnetohydrodynamical numerical simulations of the gas flow in the magnetosphere of this star.
We report the results of spectroscopic and photometric observations of the emission-line object AS 386. For the first time we found that it exhibits the Be phenomenon and fits the definition of an FS ...CMa type object. The optical spectrum shows the presence of a B-type star with the following properties: Teff = 11,000 500 K, log L/L = 3.7 0.3, a mass of 7 1 M , and a distance D = 2.4 0.3 kpc from the Sun. We detected regular radial velocity variations of both absorption and emission lines with the following orbital parameters: Porb =131.27 0.09 days, semiamplitude K1 = 51.7 3.0 km s−1, systemic radial velocity γ = −31.8 2.6 km s−1, and a mass function of f(m) = 1.9 0.3 M . AS 386 exhibits irregular variations of the optical brightness (V = 10.92 0.05 mag), while the near-IR brightness varies up to ∼0.3 mag following the spectroscopic period. We explain this behavior by a variable illumination of the dusty disk inner rim by the B-type component. Doppler tomography based on the orbital variations of emission-line profiles shows that the material is distributed near the B-type component and in a circumbinary disk. We conclude that the system has undergone a strong mass transfer that created the circumstellar material and increased the B-type component mass. The absence of any traces of a secondary component, whose mass should be ≥7 M , suggests that it is most likely a black hole.
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