Baade’s window and APOGEE (original) (raw)
Related papers
The Astronomical Journal, 2018
Data from the SDSS-IV / Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have been released as part of SDSS Data Releases 13 (DR13) and 14 (DR14). These include high resolution H-band spectra, radial velocities, and derived stellar parameters and abundances. DR13, released in August 2016, contained APOGEE data for roughly 150,000 stars, and DR14, released in August 2017, added about 110,000 more. Stellar parameters and abundances have been derived with an automated pipeline, the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). We evaluate the performance of this pipeline by comparing the derived stellar parameters and abundances to those inferred from optical spectra and analysis for several hundred stars. For most elements-C, Na, Mg, Al, Si, S, Ca, Cr, Mn, Ni-the DR14 ASPCAP analysis have systematic differences with the comparisons samples of less than 0.05 dex (median), and random differences of less than 0.15 dex (standard deviation). These differences are a combination of the uncertainties in both the comparison samples as well as the ASPCAP-analysis. Compared to
Chemodynamics of the Milky Way - I. The first year of APOGEE data
2014
Context. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) features the first multi-object high-resolution fiber spectrograph in the Near-infrared (NIR) ever built, thus making the survey unique in its capabilities: APOGEE is able to peer through the dust that obscures stars in the Galactic disc and bulge in the optical wavelength range. Here we explore the APOGEE data included as part of the Sloan Digital Sky Survey's 10th data release (SDSS DR10). Aims. The goal of this paper is to a) investigate the chemo-kinematic properties of the Milky Way disc by exploring the first year of APOGEE data, and b) to compare our results to smaller optical high-resolution samples in the literature, as well as results from lower resolution surveys such as the Geneva-Copenhagen Survey (GCS) and the RAdial Velocity Experiment (RAVE). Methods. We select a high-quality (HQ) sample in terms of chemistry (amounting to around 20.000 stars) and, after computing distances and orbital parameters for this sample, we employ a number of useful subsets to formulate constraints on Galactic chemical and chemodynamical evolution processes in the Solar neighbourhood and beyond (e.g., metallicity distributions-MDFs, [α/Fe] vs. [Fe/H] diagrams, and abundance gradients). Results. Our red giant sample spans distances as large as 10 kpc from the Sun. Given our chemical quality requirements, most of the stars are located between 1 and 6 kpc from the Sun, increasing by at least a factor of eight the studied volume with respect to the most recent chemodynamical studies based on the two largest samples obtained from RAVE and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We find remarkable agreement between the MDF of the recently published local (d < 100 pc) high-resolution high-S/N HARPS sample and our local HQ sample (d < 1 kpc). The local MDF peaks slightly below solar metallicity, and exhibits an extended tail towards [Fe/H] = −1, whereas a sharper cutoff is seen at larger metallicities (the APOGEE sample shows a slight overabundance of stars with metallicities larger than +0.3 w.r.t. the HARPS sample). Both samples also compare extremely well in an [α/Fe] vs. [Fe/H] diagram. The APOGEE data also confirm the existence of a gap in the abundance diagram. When expanding our sample to cover three different Galactocentric distance bins (inner disc, solar vicinity and outer disc), we find the high-[α/Fe] stars to be rare towards the outer zones (implying a shorter scale-length of the thick disc with respect to the thin disc) as previously suggested in the literature. Finally, we measure the gradients in [Fe/H] and [α/Fe], and their respective MDFs, over a range of 6 < R < 11 kpc in Galactocentric distance, and a 0 < z < 3 kpc range of distance from the Galactic plane. We find a good agreement with the gradients traced by the GCS and RAVE dwarf samples. For stars with 1.5 < z < 3 kpc (not present in the previous samples), we find a positive metallicity gradient and a negative gradient in [α/Fe].
APOGEE Chemical Abundance Patterns of the Massive Milky Way Satellites
2021
The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has obtained high-resolution spectra for thousands of red giant stars distributed among the massive satellite galaxies of the Milky Way (MW): the Large and Small Magellanic Clouds (LMC/SMC), the Sagittarius Dwarf (Sgr), Fornax (Fnx), and the now fully disrupted Gaia Sausage/Enceladus (GSE) system. We present and analyze the APOGEE chemical abundance patterns of each galaxy to draw robust conclusions about their star formation histories, by quantifying the relative abundance trends of multiple elements (C, N, O, Mg, Al, Si, Ca, Fe, Ni, and Ce), as well as by fitting chemical evolution models to the [α/Fe]-[Fe/H] abundance plane for each galaxy. Results show that the chemical signatures of the starburst in the MCs observed by Nidever et al. in the α-element abundances extend to C+N, Al, and Ni, with the major burst in the SMC occurring some 3-4 Gyr before the burst in the LMC. We find that Sgr and Fnx a...
Chemical Abundances and Ages of the Bulge Stars in APOGEE High-velocity Peaks
The Astrophysical Journal, 2017
A cold, high-velocity (HV, ∼ 200 km s −1) peak was first reported in several Galactic bulge fields based on the Apache Point Observatory Galaxy Evolution Experiment (APOGEE) commissioning observations. Both the existence and the nature of the HV peak are still under debate. Here we revisit this feature with the latest APOGEE DR13 data. We find that most of the low latitude bulge fields display a skewed Gaussian distribution with an HV shoulder. However, only 3 out of 53 fields show distinct HV peaks around 200 km s −1. The velocity distribution can be well described by Gauss−Hermite polynomials, except for the three fields showing clear HV peaks. We find that the correlation between the skewness parameter (h 3) and the mean velocity (v), instead of a distinctive HV peak, is a strong indicator of the bar. It was recently suggested that the HV peak is composed of preferentially young stars. We choose three fields showing clear HV peaks to test this hypothesis using the metallicity, [α/M] and [C/N] as age proxies. We find that both young and old stars show HV features. The similarity between the chemical abundances of stars in the HV peaks and the main component indicates that they are not systematically different in terms of chemical abundance or age. In contrast, there are clear differences in chemical space between stars in the Sagittarius dwarf and the bulge stars. The strong HV peaks off-plane are still to be explained properly and could be different in nature.
Homogeneous photometry and metal abundances for a large sample of Hipparcos metal-poor stars
Monthly Notices of the Royal Astronomical Society, 1999
Homogeneous photometric data (Johnson V , B − V , V − K, Cousins V − I and Strömgren b − y), radial velocities, and abundances of Fe, O, Mg, Si, Ca, Ti, Cr and Ni are presented for 99 stars with high precision parallaxes measured by the HIPPARCOS satellite. These data have been previously used to assist the derivation of accurate distances and ages of galactic globular clusters. Magnitudes and colours for the programme stars were obtained combining and standardizing carefully selected literature data available in the Simbad data-base and V and B − V values measured by the Hipparcos/Tycho mission. Comparison of colours for our targets suggests: (i) ground-based and Tycho B − V 's agree well for colours bluer than 0.75 mag, but have a lot of scatter for redder colours; (ii) the Hipparcos V − I colours have a very large scatter and a zero point offset of +0.02 mag compared to the literature values. The programme stars have metal abundances in the range −2.5 <[Fe/H]< 0.2. The spectroscopic observational data set consists of high dispersion (15 000 < R < 60 000), high S/N (> 200) spectra obtained at the Asiago and McDonald Observatories for 66 stars. The analysis is carried out following the same precepts used in previous papers of this series and includes corrections for departures from LTE in the formation of the O lines. The main results are: (i) the equilibrium of ionization of Fe is well satisfied in late F-early K-dwarfs; (ii) Oxygen and α−elements are overabundant by ∼ 0.3 dex.
Astronomy & Astrophysics, 2012
Sm in a sample of 25 solar-type stars of the solar neighbourhood, correlating the abundances with the stellar ages, kinematics, and orbital parameters. Methods. The spectroscopic analysis, based on data of high resolution and high signal-to-noise ratio, was differential to the Sun and applied to atomic line equivalent widths supplemented by the spectral synthesis of C and C 2 features. We also performed a statistical study by using the method of tree clustering analysis, searching for groups of stars sharing similar elemental abundance patterns. We derived the stellar parameters from various criteria, with average errors of 30 K, 0.13 dex, and 0.05 dex, respectively, for T eff , log g, and [Fe/H]. The average error of the [X/Fe] abundance ratios is 0.06 dex. Ages were derived from theoretical HR diagrams and membership of the stars in known kinematical moving groups. Results. We identified four stellar groups: one having, on average, over-solar abundances ([X/H] = +0.26 dex), another with undersolar abundances ([X/H] = −0.24 dex), and two with intermediate values ([X/H] = −0.06 and +0.06 dex) but with distinct chemical patterns. Stars sharing solar metallicity, age, and Galactic orbit possibly have non-solar abundance ratios, a possible effect either of chemical heterogeneity in their natal clouds or migration. A trend of [Cu/Fe] with [Ba/Fe] seems to exist, in agreement with previous claims in the literature, and maybe also of [Sm/Fe] with [Ba/Fe]. No such correlation involving C, Na, Mn, and Zn is observed. The [X/Fe] ratios of various elements show significant correlations with age. [Mg/Fe], [Sc/Fe], and [Ti/Fe] increase with age. [Mn/Fe] and [Cu/Fe] display a more complex behaviour, first increasing towards younger stars up to the solar age, and then decreasing, a result we interpret as possibly related to time-varying yields of SN Ia and the weak s-process in massive stars. The steepest negative age relation is due to [Ba/Fe], but only for stars younger than the Sun, and a similar though less significant behaviour is seen for Zr, Ce, and Nd. [Sr/Fe] and [Y/Fe] show a linearly increasing trend towards younger stars. The [Cu/Ba] and [Sm/Ba] therefore decrease for younger stars. We found that [Ba/Mg], [Ba/Zn], and [Sr,Y,Ba/Sm] increase but only for stars younger than the Sun, whereas the [Sr/Mg], [Y/Mg], [Sr/Zn], and [Y/Zn] ratios increase linearly towards younger stars over the whole age range.
Aspcap: The Apogee Stellar Parameter and Chemical Abundances Pipeline
The Astronomical Journal, 2016
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has built the largest moderately high-resolution (R ≈ 22, 500) spectroscopic map of the stars across the Milky Way, and including dust-obscured areas. The APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) is the software developed for the automated analysis of these spectra. ASPCAP determines atmospheric parameters and chemical abundances from observed spectra by comparing observed spectra to libraries of theoretical spectra, using χ 2 minimization in a multidimensional parameter space. The package consists of a fortran90 code that does the actual minimization and a wrapper IDL code for book-keeping and data handling. This paper explains in detail the ASPCAP components and functionality, and presents results from a number of tests designed to check its performance. ASPCAP provides stellar effective temperatures, surface gravities, and metallicities precise to 2%, 0.1 dex, and 0.05 dex, respectively, for most APOGEE stars, which are predominantly giants. It also provides abundances for up to 15 chemical elements with various levels of precision, typically under 0.1 dex. The final data release (DR12) of the Sloan Digital Sky Survey III contains an APOGEE database of more than 150,000 stars. ASPCAP development continues in the SDSS-IV APOGEE-2 survey.
Mg, Ba and Eu abundances in thick disk and halo stars
Astronomy and Astrophysics, 2002
Our sample of cool dwarf stars from previous papers (Mashonkina & Gehren 2000, 2001) is extended in this study including 15 moderately metal-deficient stars. The samples of halo and thick disk stars have overlapping metallicities with [Fe/H] in the region from −0.9 to −1.5, and we compare chemical properties of these two kinematically different stellar populations independent of their metallicity. We present barium, europium and magnesium abundances for the new sample of stars. The results are based on NLTE line formation obtained in differential model atmosphere analyses of high resolution spectra observed mainly using the UVES spectrograph at the VLT of the European Southern Observatory. We confirm the overabundance of Eu relative to Mg in halo stars as reported in our previous papers. Eight halo stars show [Eu/Mg] values between 0.23 and 0.41, whereas stars in the thick and thin disk display a solar europium to magnesium ratio. The [Eu/Ba] values found in the thick disk stars to lie between 0.35 and 0.57 suggest that during thick disk formation evolved low-mass stars started to enrich the interstellar gas by s-nuclei of Ba, and the s-process contribution to barium thus varies from 30% to 50%. Based on these results, and using the chemical evolution calculations by Travaglio et al. (1999), we estimate that the thick disk stellar population formed on a timescale between 1.1 to 1.6 Gyr from the beginning of the protogalactic collapse. In the halo stars the [Eu/Ba] values are found mostly between 0.40 and 0.67, which suggests a duration of the halo formation of about 1.5 Gyr. For the whole sample of stars we present the even-to-odd Ba isotope ratios as determined from hyperfine structure seen in the Ba resonance line λ 4554. As expected, the solar ratio 82:18 (Cameron 1982) adjusts to observations of the Ba lines in the thin disk stars. In our halo stars the even-to-odd Ba isotope ratios are close to the pure r-process ratio 54:46 (Arlandini et al. 1999), and in the thick disk stars the isotope ratio is around 65:35 (±10%). Based on these data we deduce for thick disk stars the ratio of the s/r-process contribution to barium as 30:70 (±30%), in agreement with the results obtained from the [Eu/Ba] values.
Ba and Eu abundances in M 15 giant stars
Astronomy & Astrophysics, 2013
Aims. We investigate the Ba and Eu abundances for a sample of 63 giant stars in the globular cluster M 15. This is the largest sample of M 15 giant stars for which Ba abundances have been determined and, due to the target selection of the original research programme, the Ba abundances are complete along the red giant branch. Methods. Stellar parameters were taken from the previous key study and a microturbulence-surface gravity relation was determined for precise measurement of the Ba line at 6496.898 Å, which has a high sensitivity to microturbulence. Element abundances for Ba, La, Eu, Ca, Ni and Fe were calculated using spectrum synthesis and equivalent widths techniques. Results. A bimodal distribution in Ba, Eu and La abundances was found within the sample. The low Ba, Eu, La mode had mean abundances of [Ba/H] = −2.41 ± 0.16, [Eu/H] = −1.80 ± 0.08 and [La/H] = −2.19 ± 0.13 while the high Ba, Eu, La mode had mean abundances of [Ba/H] = −2.00 ± 0.16, [Eu/H] = −1.65 ± 0.13 and [La/H] = −1.95 ± 0.11. Conclusions. Both modes are indicative of a pollution scenario dominated by the r-process, hence contributions from explosive nucleosynthesis of massive stars. There may be evidence of further enhancement by another heavy element process and of potential anticorrelations in Na-O for both modes indicating a complex formation and evolution history for M 15.
Metallicities and ages of stellar populations at a high Galactic latitude field
Monthly Notices of the Royal Astronomical Society, 2009
We present an analysis of U BV RI data from the Selected Area SA 141. By applying recalibrated methods of measuring ultraviolet excess (UVX), we approximate abundances and absolute magnitudes for 368 stars over 1.3 square degrees out to distances over 10 kpc. With the density distribution constrained from our previous photometric parallax investigations and with sufficient accounting for the metallicity bias in the UVX method, we are able to compare the vertical abundance distribution to those measured in previous studies. We find that the abundance distribution has an underlying uniform component consistent with previous spectroscopic results that posit a monometallic thick disk and halo with abundances of [F e/H] = −0.8 and −1.4, respectively. However, there are a number of outlying data points that may indicate contamination by more metal-rich halo streams. The absence of vertical abundance gradients in the Galactic stellar populations and the possible presence of interloping halo streams would be consistent with expectations from merger models of Galaxy formation. We find that our UVX method has limited sensitivity in exploring the metallicity distribution of the distant Galactic halo, owing to the poor constraint on the U BV properties of very metal-poor stars. The derivation of metallicities from broadband U BV photometry remains fundamentally sound for the exploration of the halo but is in need of both improved calibration and superior data.