scholarly journals Determination of the spectroscopic stellar parameters for 257 field giant stars★

2015 ◽  
Vol 448 (3) ◽  
pp. 2749-2765 ◽  
Author(s):  
S. Alves ◽  
L. Benamati ◽  
N. C. Santos ◽  
V. Zh. Adibekyan ◽  
S. G. Sousa ◽  
...  
Keyword(s):  
Giant Stars

The determination of carbon and oxygen abundances in very metal-poor globular cluster giant stars

1992 ◽  
Vol 104 ◽  
pp. 1127 ◽  
Author(s):  
R. A. Bell ◽  
M. M. Briley ◽  
John E. Norris
Keyword(s):  
Globular Cluster ◽  
Giant Stars

scholarly journals Asteroseismology of red giants to constrain angular momentum transport

2014 ◽  
Vol 9 (S307) ◽  
pp. 165-170
Author(s):  
P. Eggenberger
Keyword(s):  
Angular Momentum ◽  
Rotational Frequency ◽  
Momentum Transport ◽  
Red Giants ◽  
Angular Momentum Transport ◽  
Rotation Rates ◽  
Giant Stars ◽  
Red Giant ◽  
Core Rotation

AbstractAsteroseismic data obtained by theKeplerspacecraft have led to the recent detection and characterization of rotational frequency splittings of mixed modes in red-giant stars. This has opened the way to the determination of the core rotation rates for these stars, which is of prime importance to progress in our understanding of internal angular momentum transport. In this contribution, we discuss which constraints can be brought by these asteroseismic measurements on the modelling of angular momentum transport in stellar radiative zones.

scholarly journals Abundances of C, N and O in Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 218-218 ◽  
Author(s):  
A. A. Nikitin ◽  
A. F. Kholtygin ◽  
A. A. Sapar ◽  
T. H. Feklistova
Keyword(s):  
Planetary Nebulae ◽  
Abundance Ratio ◽  
Evolutionary Status ◽  
Spectral Features ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Abundance Determination

The abundances of C, N and O in planetary nebulae must correspond to the evolutionary status of their progenitor red giant stars. The best spectral features for abundance determination of these elements are the recombination lines, which depend weakly on the variations of Te and ne. The abundance ratio of the ions A+ and H+ can be given by [1–3].

Determination of fundamental properties of giant stars by means of the Geneva photometric system

Astrophysics ◽  
1989 ◽  
Vol 31 (3) ◽  
pp. 735-742
Author(s):  
L. V. Korotina ◽  
A. V. Dragunova ◽  
N. S. Komarov
Keyword(s):  
Photometric System ◽  
Giant Stars ◽  
Fundamental Properties

scholarly journals The Gaia-ESO Survey: Spectroscopic-asteroseismic analysis of K2 stars in Gaia-ESO

2020 ◽  
Vol 643 ◽  
pp. A83
Author(s):  
C. C. Worley ◽  
P. Jofré ◽  
B. Rendle ◽  
A. Miglio ◽  
L. Magrini ◽  
...  
Keyword(s):  
Seismic Analysis ◽  
High Resolution Spectroscopy ◽  
Red Giants ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Iterative Analysis ◽  
Special Project ◽  
Red Giant ◽  
Good Agreement

Context. The extensive stellar spectroscopic datasets that are available for studies in Galactic Archeaology thanks to, for example, the Gaia-ESO Survey, now benefit from having a significant number of targets that overlap with asteroseismology projects such as Kepler, K2, and CoRoT. Combining the measurements from spectroscopy and asteroseismology allows us to attain greater accuracy with regard to the stellar parameters needed to characterise the stellar populations of the Milky Way. Aims. The aim of this Gaia-ESO Survey special project is to produce a catalogue of self-consistent stellar parameters by combining measurements from high-resolution spectroscopy and precision asteroseismology. Methods. We carried out an iterative analysis of 90 K2@Gaia-ESO red giants. The spectroscopic values of Teff were used as input in the seismic analysis to obtain log g values. The seismic estimates of log g were then used to re-determine the spectroscopic values of Teff and [Fe/H]. Only one iteration was required to obtain parameters that are in good agreement for both methods and, thus, to obtain the final stellar parameters. A detailed analysis of outliers was carried out to ensure a robust determination of the parameters. The results were then combined with Gaia DR2 data to compare the seismic log g with a parallax-based log g and to investigate instances of variations in the velocity and possible binaries within the dataset. Results. This analysis produced a high-quality catalogue of stellar parameters for 90 red giant stars from K2@Gaia-ESO that were determined through iterations between spectroscopy and asteroseismology. We compared the seismic gravities with those based on Gaia parallaxes to find an offset which is similar to other studies that have used asteroseismology. Our catalogue also includes spectroscopic chemical abundances and radial velocities, as well as indicators for possible binary detections.

scholarly journals A new method for the asteroseismic determination of the evolutionary state of red-giant stars

2016 ◽  
Vol 466 (3) ◽  
pp. 3344-3352 ◽  
Author(s):  
Yvonne Elsworth ◽  
Saskia Hekker ◽  
Sarbani Basu ◽  
Guy R. Davies
Keyword(s):  
New Method ◽  
Giant Stars ◽  
Evolutionary State ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals Precise radial velocities of giant stars

2018 ◽  
Vol 616 ◽  
pp. A33 ◽  
Author(s):  
Stephan Stock ◽  
Sabine Reffert ◽  
Andreas Quirrenbach
Keyword(s):  
Test Sample ◽  
Evolutionary Stage ◽  
Evolutionary Models ◽  
Planetary Evolution ◽  
Giant Stars ◽  
Small Test ◽  
Red Giant ◽  
Stellar Masses ◽  
Host Stars

Context. The determination of accurate stellar parameters of giant stars is essential for our understanding of such stars in general and as exoplanet host stars in particular. Precise stellar masses are vital for determining the lower mass limit of potential substellar companions with the radial velocity method, but also for dynamical modeling of multiplanetary systems and the analysis of planetary evolution. Aims. Our goal is to determine stellar parameters, including mass, radius, age, surface gravity, effective temperature and luminosity, for the sample of giants observed by the Lick planet search. Furthermore, we want to derive the probability of these stars being on the horizontal branch (HB) or red giant branch (RGB), respectively. Methods. We compare spectroscopic, photometric and astrometric observables to grids of stellar evolutionary models using Bayesian inference. Results. We provide tables of stellar parameters, probabilities for the current post-main sequence evolutionary stage, and probability density functions for 372 giants from the Lick planet search. We find that 81% of the stars in our sample are more probably on the HB. In particular, this is the case for 15 of the 16 planet host stars in the sample. We tested the reliability of our methodology by comparing our stellar parameters to literature values and find very good agreement. Furthermore, we created a small test sample of 26 giants with available asteroseismic masses and evolutionary stages and compared these to our estimates. The mean difference of the stellar masses for the 24 stars with the same evolutionary stages by both methods is only ΔM = 〈Mtrk. − MAst.〉 = 0.01 ± 0.20 M⊙. Conclusions. We do not find any evidence for large systematic differences between our results and estimates of stellar parameters based on other methods. In particular we find no significant systematic offset between stellar masses provided by asteroseismology to our Bayesian estimates based on evolutionary models.

scholarly journals A New Program to Determine K(z) from Main Sequence Stars

1977 ◽  
Vol 4 (2) ◽  
pp. 75-76
Author(s):  
A. R. Upgren
Keyword(s):  
Velocity Distribution ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Gaussian Distributions ◽  
Giant Stars ◽  
The North ◽  
The Stability ◽  
North Galactic ◽  
Stability Of The Solution

Recently Dessureau and Upgren (1975) redetermined the velocity distribution of giant stars in the north galactic pole direction using Upgren’s (1962) catalogue and Oort’s (1960) determination of K(z). The velocities were assumed to be represented by n Gaussian distributions with no further constraints imposed. The velocities are well represented by three such distributions whose properties disagree with those found by Oort. A larger number did not improve the stability of the solution. Without radial velocities, however, they could not redetermine the K(z) force itself.

New calibration of the Vilnius photometric system

2018 ◽  
Vol 14 (A30) ◽  
pp. 486-486
Author(s):  
M. Maskoliunas ◽  
J. Zdanavičius ◽  
V. Čepas ◽  
A. Kazlauskas ◽  
R. P. Boyle ◽  
...  
Keyword(s):  
Photometric Determination ◽  
High Dispersion ◽  
Physical Parameters ◽  
Photometric System ◽  
Homogeneous Sample ◽  
Giant Stars ◽  
Stellar Temperatures ◽  
Absolute Magnitudes ◽  
Gaia Dr2

AbstractThe medium-band Vilnius photometric system with the mean wavelengths at 345 (U), 374 (P), 405 (X), 466 (Y), 516 (Z), 544 (V), and 656 (S) nm for many years was an important tool to determine interstellar reddenings and distances of single stars due to its ability to classify stars of all temperatures in spectral classes and luminosity classes in the presence of different interstellar reddenings. At present, Gaia DR2 presents distances to stars with an unprecedented accuracy at least up to 3 kpc. However, multicolor photometry, which allows the classification of stars as well as the preliminary determination of stellar temperatures, gravities, metallicities and interstellar reddenings, remains an important method for distant stars. Here we present an empirical calibration of the intrinsic color indices of the Vilnius system in terms of physical parameters of stars for dwarf and giant stars of spectral classes F-G-K-M. In any attempted photometric determination of physical parameters of stars it is important to have an extensive and homogeneous sample of spectroscopically determined parameters for stars for which there are also accurate photometric data. As a source catalogue for the Vilnius photometry the latest updated version of the Catalogue of Photoelectric Observations in the Vilnius System was used, which contains compilations from the published photometry for about 11 000 stars. The stars which had both the Gaia DR2 parallaxes and the determinations of stellar parameters from high-dispersion spectra were extracted from this catalogue. The final sample contains more than 1500 stars of spectral classes F-M. The majority of these stars (ca 70%) are not reddened, for others the values of interstellar reddening AV were determined using the regular techniques of photometric classification in the Vilnius system. The absolute magnitudes MV and consequently the luminosity classes were determined using Gaia DR2 parallaxes. We present the analytical expressions for the effective temperature Teff and surface gravity logg and evaluate the errors of solutions for dwarf and giant stars. To test the accuracy of the proposed method, we have compared our results with the stars observed by Gaia and with the stellar parameters available from the large spectroscopic surveys: APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE and SEGUE. The results of comparison contain 5-6 % outliers.The proposed method allows the fast and straightforward evaluation of stellar physical parameters for the stars observed in the Vilnius photometric system. Despite the fact, that the accuracy of determination is significantly lower than in the case of spectroscopic methods, the method described may be useful for distant faint stars, which are still inaccessible for spectroscopic observations.

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