scholarly journals Local Stellar Kinematics from RAVE Data: IV. Solar Neighbourhood Age–Metallicity Relation

2013 ◽  
Vol 30 ◽  
Author(s):  
Ş. Duran ◽  
S. Ak ◽  
S. Bilir ◽  
S. Karaali ◽  
T. Ak ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Spectral Type ◽  
Stellar Kinematics ◽  
Bayesian Procedure ◽  
Experiment Data ◽  
Data Release ◽  
Galactic Population ◽  
Effective Temperatures ◽  
Metallicity Distribution ◽  
Total Velocity

AbstractWe investigated the age–metallicity relation using a sample of 5691 F- and G-type dwarfs from RAdial Velocity Experiment Data Release 3 (RAVE DR3) by applying several constraints. (i) We selected stars with surface gravities log g(cm s−2) ≥ 3.8 and effective temperatures in the $5310\le T_{\text{eff}}\text{(K)}\le 7300$ range and obtained a dwarf sample. (ii) We plotted the dwarfs in metallicity sub-samples in the $T_{\text{eff}}\text{--}(J-K_s)_0$ plane to compare with the corresponding data of González Hernández & Bonifacio (2009) and identified the ones in agreement. (iii) We fitted the reduced dwarf sample obtained from constraints (i) and (ii) to the Padova isochrones and re-identified those which occupy the plane defined by isochrones with ages t ≤ 13 Gyr. (iv) Finally, we omitted dwarfs with total velocity errors larger than 10.63 km s−1. We estimated the ages using the Bayesian procedure of Jørgensen & Lindegren (2005). The largest age–metallicity slope was found for early F-type dwarfs. We found steeper slopes when we plotted the data as a function of spectral type rather than Galactic population. We noticed a substantial scatter in metallicity distribution at all ages. The metal-rich old dwarfs turned out to be G-type stars which can be interpreted as they migrated from the inner disc or bulge.

scholarly journals Local Stellar Kinematics from RAVE data—VII. Metallicity Gradients from Red Clump Stars

2016 ◽  
Vol 33 ◽  
Author(s):  
Ö. Önal Taş ◽  
S. Bilir ◽  
G. M. Seabroke ◽  
S. Karaali ◽  
S. Ak ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Selection Effects ◽  
Stellar Kinematics ◽  
Experiment Data ◽  
Radial Gradient ◽  
Data Release ◽  
The Difference ◽  
Red Clump

AbstractWe investigate the Milky Way Galaxy’s radial and vertical metallicity gradients using a sample of 47 406 red clump stars from the RAdial Velocity Experiment Data Release 4. Distances are calculated by adopting Ks-band absolute magnitude as −1.54±0.04 mag for the sample. The metallicity gradients are calculated with their current orbital positions (Rgc and Z) and with their orbital properties (Rm and zmax): d[Fe/H]/dRgc = −0.047±0.003 dex kpc−1 for |Z| ≤ 0.5 kpc and d[Fe/H]/dRm = −0.025±0.002 dex kpc−1 for zmax ≤ 0.5 kpc. This reaffirms the radial metallicity gradient in the thin disc but highlights that gradients are sensitive to the selection effects caused by the difference between Rgc and Rm. The radial gradient is flat in the distance interval 0.5-1 kpc from the plane and then becomes positive greater than 1 kpc from the plane. The radial metallicity gradients are also eccentricity dependent. We showed that d[Fe/H]/dRm = −0.089±0.010, −0.073±0.007, −0.053±0.004 and −0.044±0.002 dex kpc−1 for ep ≤ 0.05, ep ≤ 0.07, ep ≤ 0.10 and ep ≤ 0.20 sub-samples, respectively, in the distance interval zmax ≤ 0.5 kpc. Similar trend is found for vertical metallicity gradients. Both the radial and vertical metallicity gradients are found to become shallower as the eccentricity of the sample increases. These findings can be used to constrain different formation scenarios of the thick and thin discs.

scholarly journals Identification of field dwarfs and giants in the second Radial Velocity Experiment Data Release

2011 ◽  
Vol 418 (1) ◽  
pp. 444-455 ◽  
Author(s):  
S. Bilir ◽  
S. Karaali ◽  
S. Ak ◽  
Ö. Önal ◽  
B. Coşkunoğlu ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Experiment Data ◽  
Data Release

scholarly journals The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14

2019 ◽  
Vol 626 ◽  
pp. A16 ◽  
Author(s):  
A. Rojas-Arriagada ◽  
M. Zoccali ◽  
M. Schultheis ◽  
A. Recio-Blanco ◽  
G. Zasowski ◽  
...  
Keyword(s):  
Fundamental Parameters ◽  
Elemental Abundances ◽  
Data Release ◽  
Bulge Region ◽  
Solar Metallicity ◽  
Inner Region ◽  
Clean Sample ◽  
Metallicity Distribution ◽  
Single Sequence

Context. The Galactic bulge has a bimodal metallicity distribution function: different kinematic, spatial, and, potentially, age distributions characterize the metal-poor and metal-rich components. Despite this observed dichotomy, which argues for different formation channels for those stars, the distribution of bulge stars in the α-abundance versus metallicity plane has been found so far to be a rather smooth single sequence. Aims. We use data from the fourteenth data release of the APOGEE spectroscopic survey (DR14) to investigate the distribution in the Mg abundance (as tracer of the α-elements)-versus-metallicity plane of a sample of stars selected to be in the inner region of the bulge. Methods. A clean sample has been selected from the DR14 using a set of data- and pipeline-flags to ensure the quality of their fundamental parameters and elemental abundances. An additional selection made use of computed spectro-photometric distances to select a sample of likely bulge stars as those with RGC ≤ 3.5 kpc. We adopt magnesium abundance as an α-abundance proxy for our clean sample as it has been proven to be the most accurate α-element as determined by ASPCAP, the pipeline for data products from APOGEE spectra. Results. From the distribution of our bulge sample in the [Mg/Fe]-versus-[Fe/H] plane, we found that the sequence is bimodal. This bimodality is given by the presence of a low-Mg sequence of stars parallel to the main high-Mg sequence over a range of ∼0.5 dex around solar metallicity. The two sequences merge above [Fe/H] ∼ 0.15 dex into a single sequence whose dispersion in [Mg/Fe] is larger than either of the two sequences visible at lower metallicity. This result is confirmed when we consider stars in our sample that are inside the bulge region according to trustworthy Gaia DR2 distances.

scholarly journals The SAMI Galaxy Survey: the third and final data release

2021 ◽  
Author(s):  
Scott M Croom ◽  
Matt S Owers ◽  
Nicholas Scott ◽  
Henry Poetrodjojo ◽  
Brent Groves ◽  
...  
Keyword(s):  
Large Scale ◽  
Resolving Power ◽  
Stellar Kinematics ◽  
New Era ◽  
Optical Wavelength ◽  
Astronomical Optics ◽  
Data Release ◽  
Gas Ionization ◽  
Release Data ◽  
First Time

Abstract We have entered a new era where integral-field spectroscopic surveys of galaxies are sufficiently large to adequately sample large-scale structure over a cosmologically significant volume. This was the primary design goal of the SAMI Galaxy Survey. Here, in Data Release 3 (DR3), we release data for the full sample of 3068 unique galaxies observed. This includes the SAMI cluster sample of 888 unique galaxies for the first time. For each galaxy, there are two primary spectral cubes covering the blue (370–570 nm) and red (630–740 nm) optical wavelength ranges at spectral resolving power of R = 1808 and 4304 respectively. For each primary cube, we also provide three spatially binned spectral cubes and a set of standardized aperture spectra. For each galaxy, we include complete 2D maps from parameterized fitting to the emission-line and absorption-line spectral data. These maps provide information on the gas ionization and kinematics, stellar kinematics and populations, and more. All data are available online through Australian Astronomical Optics (AAO) Data Central.

scholarly journals The first data release of LAMOST low-resolution single-epoch spectra

2021 ◽  
Vol 21 (10) ◽  
pp. 249
Author(s):  
Zhong-Rui Bai ◽  
Hao-Tong Zhang ◽  
Hai-Long Yuan ◽  
Dong-Wei Fan ◽  
Bo-Liang He ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Signal To Noise Ratio ◽  
Time Lag ◽  
Spectral Lines ◽  
Low Resolution ◽  
Signal To Noise ◽  
Data Release ◽  
Repeat Exposure ◽  
Noise Ratio ◽  
Single Epoch

Abstract LAMOST Data Release 5, covering ∼17 000 deg2 from –10° to 80° in declination, contains 9 million co-added low-resolution spectra of celestial objects, each spectrum combined from repeat exposure of two to tens of times during Oct 2011 to Jun 2017. In this paper, we present the spectra of individual exposures for all the objects in LAMOST Data Release 5. For each spectrum, the equivalent width of 60 lines from 11 different elements are calculated with a new method combining the actual line core and fitted line wings. For stars earlier than F type, the Balmer lines are fitted with both emission and absorption profiles once two components are detected. Radial velocity of each individual exposure is measured by minimizing χ 2 between the spectrum and its best template. The database for equivalent widths of spectral lines and radial velocities of individual spectra are available online. Radial velocity uncertainties with different stellar type and signal-to-noise ratio are quantified by comparing different exposure of the same objects. We notice that the radial velocity uncertainty depends on the time lag between observations. For stars observed in the same day and with signal-to-noise ratio higher than 20, the radial velocity uncertainty is below 5km s−1, and increases to 10 km s−1 for stars observed in different nights.

scholarly journals The Absolute Calibration of the HR Diagram: Fundamental Effective Temperatures and Bolometric Corrections

1978 ◽  
Vol 80 ◽  
pp. 65-76 ◽  
Author(s):  
D. S. Hayes
Keyword(s):  
Spectral Type ◽  
Absolute Calibration ◽  
Effective Temperatures ◽  
The Absolute ◽  
Hr Diagram

Scales of fundamental bolometric connections (B.C.) and effective temperatures (Teff) as a function of spectral type or color are necessary for the comparison of observations and theory in the HR diagram.

scholarly journals Problems with the Baade Wesselink Method

1989 ◽  
Vol 111 ◽  
pp. 250-250
Author(s):  
E. Böhm-Vitense ◽  
P. Garnavich ◽  
M. Lawler ◽  
J. Mena-Werth ◽  
S. Morgan ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Radial Velocities ◽  
Phase Relations ◽  
Expansion Velocity ◽  
Effective Temperatures ◽  
The Difference

AbstractIt is well known that the Baade-Wesselink method leads to different radii for Cepheids depending on which colors are used to determine the effective temperatures. We try to find the reasons for this discrepancy. We employ yet another version of this method using only maximum and minimum radii, thereby circumventing uncertainties in the phase relations between radial velocities and colors. This has essentially no influence on the derived radii. One major uncertainty is the relation between the photospheric expansion velocity and the measured radial velocity. The main reason for the discrepant results obtained by using different colors appears to be an inconsistency in the difference in the applied temperature-color calibrations. Small changes in the d(log Teff)/d(color) can cause major changes in the derived radii.

scholarly journals The effective temperatures of the O stars

1970 ◽  
Vol 36 ◽  
pp. 59-63
Author(s):  
Donald C. Morton
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Theoretical Relation ◽  
Accurate Model ◽  
Average Temperature ◽  
Lyman Continuum ◽  
Effective Temperatures

Effective temperatures of O-type stars imbedded in diffuse nebulae are derived from measurements of Hα and radio fluxes from the nebulae and the apparent magnitudes of the stars. Accurate model atmospheres, with ultraviolet line blanketing where appropriate, are used for the theoretical relation between effective temperature and the ratio of Lyman continuum to visual stellar fluxes. Although there is considerable scatter in the results, an average temperature of 48000 K is found for spectral type O5, 40000 K for O6, and 35000 K for O7.

scholarly journals The GALAH survey: unresolved triple Sun-like stars discovered by the Gaia mission

2019 ◽  
Vol 487 (2) ◽  
pp. 2474-2490 ◽  
Author(s):  
Klemen Čotar ◽  
Tomaž Zwitter ◽  
Gregor Traven ◽  
Janez Kos ◽  
Martin Asplund ◽  
...  
Keyword(s):  
Correction Factor ◽  
Spectral Type ◽  
Triple System ◽  
Stellar System ◽  
Solar Spectrum ◽  
Data Driven ◽  
Single Star ◽  
Photometric And Spectroscopic Observations ◽  
Data Release ◽  
Orbital Periods

Abstract The latest Gaia data release enables us to accurately identify stars that are more luminous than would be expected on the basis of their spectral type and distance. During an investigation of the 329 best solar twin candidates uncovered among the spectra acquired by the GALAH survey, we identified 64 such overluminous stars. In order to investigate their exact composition, we developed a data-driven methodology that can generate a synthetic photometric signature and spectrum of a single star. By combining multiple such synthetic stars into an unresolved binary or triple system and comparing the results to the actual photometric and spectroscopic observations, we uncovered 6 definitive triple stellar system candidates and an additional 14 potential candidates whose combined spectrum mimics the solar spectrum. Considering the volume correction factor for a magnitude-limited survey, the fraction of probable unresolved triple stars with long orbital periods is ∼2 per cent. Possible orbital configurations of the candidates were investigated using the selection and observational limits. To validate the discovered multiplicity fraction, the same procedure was used to evaluate the multiplicity fraction of other stellar types.

scholarly journals Hypervelocity star candidates in Gaia DR1/TGAS

2017 ◽  
Vol 12 (S330) ◽  
pp. 181-184
Author(s):  
T. Marchetti ◽  
E. M. Rossi ◽  
G. Kordopatis ◽  
A. G. A. Brown ◽  
A. Rimoldi ◽  
...  
Keyword(s):  
Neural Network ◽  
Data Mining ◽  
Rest Frame ◽  
Milky Way ◽  
Galactic Centre ◽  
Predicted Probability ◽  
Data Release ◽  
Galactic Potentials ◽  
Escape Speed ◽  
Total Velocity

AbstractHypervelocity stars (HVSs) are characterized by a total velocity in excess of the Galactic escape speed, and with trajectories consistent with coming from the Galactic Centre. We apply a novel data mining routine, an artificial neural network, to discover HVSs in the TGAS subset of the first data release of the Gaia satellite, using only the astrometry of the stars. We find 80 stars with a predicted probability >90% of being HVSs, and we retrieved radial velocities for 47 of those. We discover 14 objects with a total velocity in the Galactic rest frame >400 km s−1, and 5 of these have a probability >50% of being unbound from the Milky Way. Tracing back orbits in different Galactic potentials, we discover 1 HVS candidate, 5 bound HVS candidates, and 5 runaway star candidates with remarkably high velocities, between 400 and 780 km s−1. We wait for future Gaia releases to confirm the goodness of our sample and to increase the number of HVS candidates.

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