The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia ...Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS ( 200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature Teff, surface gravity log g, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.
We present results from a medium-resolution (R ∼ 2000) spectroscopic follow-up campaign of 1694 bright (V < 13.5), very metal-poor star candidates from the RAdial Velocity Experiment (RAVE). Initial ...selection of the low-metallicity targets was based on the stellar parameters published in RAVE Data Releases 4 and 5. Follow up was accomplished with the Gemini-N and Gemini-S, the ESO/NTT, the KPNO/Mayall, and the SOAR telescopes. The wavelength coverage for most of the observed spectra allows for the determination of carbon and -element abundances, which are crucial for considering the nature and frequency of the carbon-enhanced metal-poor (CEMP) stars in this sample. We find that 88% of the observed stars have ≤ −1.0, 61% have ≤ −2.0, and 3% have ≤ −3.0 (with four stars at ≤ −3.5). There are 306 CEMP star candidates in this sample, and we identify 169 CEMP Group I, 131 CEMP Group II, and 6 CEMP Group III stars from the A(C) versus Fe/H diagram. Inspection of the abundance ratios reveals that five of the CEMP Group II stars can be classified as "mono-enriched second-generation" stars. Gaia DR1 matches were found for 734 stars, and we show that transverse velocities can be used as a confirmatory selection criteria for low-metallicity candidates. Selected stars from our validated list are being followed-up with high-resolution spectroscopy to reveal their full chemical-abundance patterns for further studies.
Gaia Data Release 2 Andrae, René; Fouesneau, Morgan; Creevey, Orlagh ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
The second Gaia data release (Gaia DR2) contains, beyond the astrometry, three-band photometry for 1.38 billion sources. One band is the G band, the other two were obtained by integrating the Gaia ...prism spectra (BP and RP). We have used these three broad photometric bands to infer stellar effective temperatures, Teff, for all sources brighter than G = 17 mag with Teff in the range 3000–10 000 K (some 161 million sources). Using in addition the parallaxes, we infer the line-of-sight extinction, AG, and the reddening, E(BP − RP), for 88 million sources. Together with a bolometric correction we derive luminosity and radius for 77 million sources. These quantities as well as their estimated uncertainties are part of Gaia DR2. Here we describe the procedures by which these quantities were obtained, including the underlying assumptions, comparison with literature estimates, and the limitations of our results. Typical accuracies are of order 324 K (Teff), 0.46 mag (AG), 0.23 mag (E(BP − RP)), 15% (luminosity), and 10% (radius). Being based on only a small number of observable quantities and limited training data, our results are necessarily subject to some extreme assumptions that can lead to strong systematics in some cases (not included in the aforementioned accuracy estimates). One aspect is the non-negativity contraint of our estimates, in particular extinction, which we discuss. Yet in several regions of parameter space our results show very good performance, for example for red clump stars and solar analogues. Large uncertainties render the extinctions less useful at the individual star level, but they show good performance for ensemble estimates. We identify regimes in which our parameters should and should not be used and we define a “clean” sample. Despite the limitations, this is the largest catalogue of uniformly-inferred stellar parameters to date. More precise and detailed astrophysical parameters based on the full BP/RP spectrophotometry are planned as part of the third Gaia data release.
ABSTRACT We analyze the kinematics of ∼2000 giant stars in the direction of the Galactic bulge, extracted from the Gaia-ESO survey in the region − 10 ° 10 ° and − 11 ° b − 3 ° . We find distinct ...kinematic trends in the metal-rich ( M / H > 0 ) and metal-poor ( M / H < 0 ) stars in the data. The velocity dispersion of the metal-rich stars drops steeply with latitude, compared to a flat profile in the metal-poor stars, as has been seen previously. We argue that the metal-rich stars in this region are mostly on orbits that support the boxy-peanut shape of the bulge, which naturally explains the drop in their velocity dispersion profile with latitude. The metal-rich stars also exhibit peaky features in their line of sight velocity histograms, particularly along the minor axis of the bulge. We propose that these features are due to stars on resonant orbits supporting the boxy-peanut bulge. This conjecture is strengthened through the comparison of the minor axis data with the velocity histograms of resonant orbits generated in simulations of buckled bars. The "banana" or 2:1:2 orbits provide strongly bimodal histograms with narrow velocity peaks that resemble the Gaia-ESO metal-rich data.
Context.
Over the past few years, new multiplex spectrographs have emerged to observe several millions of stars. The optimisation of these instruments (w.r.t. their resolution or wavelength range), ...their associated surveys (choice of instrumental set-up), and their parameterisation pipelines require methods that estimate which wavelengths (or pixels) contain useful information.
Aims.
We propose a method that establishes the usefulness of an atomic spectral line, whereby usefulness is defined by the purity of the line and its detectability. We demonstrate two applications of our code: a) optimising an instrument by comparing the number of detected useful lines at a given wavelength range and resolution; and b) optimising the line list for a given set-up, in the sense of creating a golden subsample of the least-blended lines that are detectable at a range of signal-to-noise ratio values.
Methods.
The method compares pre-computed normalised synthetic stellar spectra containing all of the elements and molecules with spectra solely containing the lines of specific elements. Then, the flux ratios between the full spectrum and the element spectrum are computed to estimate the line purities. The method automatically identifies: (i) the line’s central wavelength, (ii) its detectability based on its depth and a given signal-to-noise threshold, and (iii) its usefulness based on the purity ratio defined above.
Results.
We applied this method to compare the three WEAVE high-resolution set-ups (blue: 404–465 nm, green: 473–545 nm, red: 595–685 nm) and find that the green+red set-up both allows us to measure more elements and contains more numerous useful lines. However, there is a disparity in terms of which elements are detected over each of the set-ups that we have characterised. We also studied the performances of high-resolution (
R ~
20 000) and low-resolution (
R ~
6000) spectra covering the entire optical wavelength range. Assuming a purity threshold of 60%, we find that the high-resolution set-up contains a much wealthier selection of lines, for any of the considered elements; whereas the low-resolution set-up displays a ‘loss’ of 50% to 90% of the lines (depending on the nucleosynthetic channel considered), even when the signal-to-noise ratio is increased.
Conclusions.
The method presented here provides a vital diagnostic of where to focus to get the most out of a spectrograph. It is easy to implement for future instruments that have not yet determined their final configuration, as well as for pipelines that require line masks.
Context.
The accretion history of the Milky Way is still unknown, despite the recent discovery of stellar systems that stand out in terms of their energy-angular momentum space, such as
Gaia
...-Enceladus-Sausage. In particular, it is still unclear how these groups are linked and to what extent they are well-mixed.
Aims.
We investigate the similarities and differences in the properties between the prograde and retrograde (counter-rotating) stars and set those results in context by using the properties of
Gaia
-Enceladus-Sausage, Thamnos/Sequoia, and other suggested accreted populations.
Methods.
We used the stellar metallicities of the major large spectroscopic surveys (APOGEE,
Gaia
-ESO, GALAH, LAMOST, RAVE, SEGUE) in combination with astrometric and photometric data from
Gaia’s
second data-release. We investigated the presence of radial and vertical metallicity gradients as well as the possible correlations between the azimuthal velocity,
v
ϕ
, and metallicity, M/H, as qualitative indicators of the presence of mixed populations.
Results.
We find that a handful of super metal-rich stars exist on retrograde orbits at various distances from the Galactic center and the Galactic plane. We also find that the counter-rotating stars appear to be a well-mixed population, exhibiting radial and vertical metallicity gradients on the order of ∼ − 0.04 dex kpc
−1
and −0.06 dex kpc
−1
, respectively, with little (if any) variation when different regions of the Galaxy are probed. The prograde stars show a
v
ϕ
− M/H relation that flattens – and, perhaps, even reverses as a function of distance from the plane. Retrograde samples selected to roughly probe Thamnos and
Gaia
-Enceladus-Sausage appear to be different populations yet they also appear to be quite linked, as they follow the same trend in terms of the eccentricity versus metallicity space.
Abstract Making use of the APOGEE DR17 catalogue with high quality data for 143,509 red giant branch stars we explore the strength of different mechanisms that causes a star to radially migrate in ...the Milky Way stellar disk. At any position in the disk we find stars that are more metal-rich than the local interstellar medium. This is surprising and normally attributed to the migration of these stars after their formation inside their current Galactocentric-radius. Such stars are prime candidates for studying the strength of different migratory processes. We specifically select two types of metal-rich stars: i) super metal-rich stars (Fe/H > 0.2) and ii) stars that are more metal-rich than their local environment. For both, we explore the distribution of orbital parameters and ages as evidence of their migration history. We find that most super metal-rich stars have experienced some amount of churning as they have orbits with Rg ≳ 5kpc. Furthermore, about half of the super metal-rich stars are on non-circular orbits (ecc > 0.15) and therefore also have experienced blurring. The metallicity of young stars in our sample is generally the same as the metallicity of the interstellar medium, suggesting they have not radially migrated yet. Stars with lower metallicity than the local environment have intermediate to old ages. We further find that super metal-rich stars have approximately the same age distribution at all Galactocentric-radii, which suggests that radial migration is a key mechanism responsible for the chemical compositions of stellar populations in the Milky Way.
First stellar parameters from Apsis Andrae, Rene; Fouesneau, Morgan; Creevey, Orlagh ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
The second Gaia data release (Gaia DR2) contains, beyond the astrometry, three-band photometry for 1.38 billion sources. One band is the G band, the other two were obtained by integrating the Gaia ...prism spectra (BP and RP). We have used these three broad photometric bands to infer stellar effective temperatures, T-eff, for all sources brighter than G = 17 mag with T-eff in the range 3000-10 000K (some 161 million sources). Using in addition the parallaxes, we infer the line-of-sight extinction, A(G), and the reddening, E(BP-RP), for 88 million sources. Together with a bolometric correction we derive luminosity and radius for 77 million sources. These quantities as well as their estimated uncertainties are part of Gaia DR2. Here we describe the procedures by which these quantities were obtained, including the underlying assumptions, comparison with literature estimates, and the limitations of our results. Typical accuracies are of order 324K (T-eff), 0.46 mag (A(G)), 0.23 mag (E(BP-RP)), 15% (luminosity), and 10% (radius). Being based on only a small number of observable quantities and limited training data, our results are necessarily subject to some extreme assumptions that can lead to strong systematics in some cases (not included in the aforementioned accuracy estimates). One aspect is the non-negativity contraint of our estimates, in particular extinction, which we discuss. Yet in several regions of parameter space our results show very good performance, for example for red clump stars and solar analogues. Large uncertainties render the extinctions less useful at the individual star level, but they show good performance for ensemble estimates. We identify regimes in which our parameters should and should not be used and we define a "clean" sample. Despite the limitations, this is the largest catalogue of uniformly-inferred stellar parameters to date. More precise and detailed astrophysical parameters based on the full BP/RP spectrophotometry are planned as part of the third Gaia data release.
Gaia Data Release 2 Andrae, René; Fouesneau, Morgan; Creevey, Orlagh ...
Astronomy and astrophysics (Berlin),
8/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
The second
Gaia
data release (
Gaia
DR2) contains, beyond the astrometry, three-band photometry for 1.38 billion sources. One band is the
G
band, the other two were obtained by integrating the
Gaia
...prism spectra (BP and RP). We have used these three broad photometric bands to infer stellar effective temperatures,
T
eff
, for all sources brighter than
G
= 17 mag with
T
eff
in the range 3000–10 000 K (some 161 million sources). Using in addition the parallaxes, we infer the line-of-sight extinction,
A
G
, and the reddening,
E
(BP − RP), for 88 million sources. Together with a bolometric correction we derive luminosity and radius for 77 million sources. These quantities as well as their estimated uncertainties are part of
Gaia
DR2. Here we describe the procedures by which these quantities were obtained, including the underlying assumptions, comparison with literature estimates, and the limitations of our results. Typical accuracies are of order 324 K (
T
eff
), 0.46 mag (
A
G
), 0.23 mag (
E
(BP − RP)), 15% (luminosity), and 10% (radius). Being based on only a small number of observable quantities and limited training data, our results are necessarily subject to some extreme assumptions that can lead to strong systematics in some cases (not included in the aforementioned accuracy estimates). One aspect is the non-negativity contraint of our estimates, in particular extinction, which we discuss. Yet in several regions of parameter space our results show very good performance, for example for red clump stars and solar analogues. Large uncertainties render the extinctions less useful at the individual star level, but they show good performance for ensemble estimates. We identify regimes in which our parameters should and should not be used and we define a “clean” sample. Despite the limitations, this is the largest catalogue of uniformly-inferred stellar parameters to date. More precise and detailed astrophysical parameters based on the full BP/RP spectrophotometry are planned as part of the third
Gaia
data release.
The metallicity distribution function (MDF) of the stellar components of the Milky Way hold valuable information regarding the processes that have taken place in the evolution of our Galaxy. In this ...proceeding, we investigate updates concerning the MDF now that the Tycho-Gaia Astrometric Solution (TGAS) catalogue has been released and that trigonometric distances are available. In particular, vertical changes and skewness of the MDF are investigated, together with the properties of the metal-rich stars in the sample, at different positions in the Galaxy.
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