Advanced

Gaia-ESO Survey: Empirical classification of VLT/Giraffe stellar spectra in the wavelength range 6440-6810 angstrom in the gamma Velorum cluster, and calibration of spectral indices

Damiani, F.; Prisinzano, L.; Micela, G.; Randich, S.; Gilmore, G.; Drew, J. E.; Jeffries, R. D.; Fremat, Y.; Alfaro, E. J. and Bensby, Thomas LU , et al. (2014) In Astronomy & Astrophysics 566.
Abstract
We present a study of spectral diagnostics available from optical spectra with R = 17 000 obtained with the VLT/Giraffe HR15n setup, using observations from the Gaia-ESO Survey, on the gamma Vel young cluster, with the purpose of classifying these stars and finding their fundamental parameters. We define several spectroscopic indices, sampling the amplitude of TiO bands, the H alpha line core and wings, and temperature- and gravity-sensitive sets of lines, each useful as a T-eff or log g indicator over a limited range of stellar spectral types. H alpha line indices are also useful as chromospheric activity or accretion indicators. Furthermore, we use all indices to define additional global T-eff - and logg-sensitive indices tau and gamma,... (More)
We present a study of spectral diagnostics available from optical spectra with R = 17 000 obtained with the VLT/Giraffe HR15n setup, using observations from the Gaia-ESO Survey, on the gamma Vel young cluster, with the purpose of classifying these stars and finding their fundamental parameters. We define several spectroscopic indices, sampling the amplitude of TiO bands, the H alpha line core and wings, and temperature- and gravity-sensitive sets of lines, each useful as a T-eff or log g indicator over a limited range of stellar spectral types. H alpha line indices are also useful as chromospheric activity or accretion indicators. Furthermore, we use all indices to define additional global T-eff - and logg-sensitive indices tau and gamma, valid for the entire range of types in the observed sample. We find a clear difference between gravity indices of main-sequence and pre-main-sequence stars, as well as a much larger difference between these and giant stars. The potentially great usefulness of the (gamma, t) diagram as a distance-independent age measurement tool for young clusters is discussed. We discuss the effect on the defined indices of classical T Tauri star veiling, which is however detected in only a few stars in the present sample. Then, we present tests and calibrations of these indices, on the basis of both photometry and literature reference spectra, from the UVES Paranal Observatory Project and the ELODIE 3.1 Library. The known properties of these stars, spanning a wide range of stellar parameters, enable us to obtain a good understanding of the performances of our new spectral indices. For non-peculiar stars with known temperature, gravity, and metallicity, we are able to calibrate quantitatively our indices, and derive stellar parameters for a wide range of stellar types. To this aim, a new composite index is defined, providing a good metallicity indicator. The ability of our indices to select peculiar, or otherwise rare classes of stars is also established. For pre-main-sequence stars outside the parameter range of the ELODIE dataset, index calibration relies on model isochrones. We check our calibrations against current Gaia-ESO UVES results, plus a number of Survey benchmark stars, and also against Gaia-ESO observations of young clusters, which contribute to establishing the good performance of our method across a wide range of stellar parameters. Our gravity determination for late-type PMS stars is found to be accurate enough to let us obtain gravity-based age estimates for PMS clusters. Finally, our gravity determinations support the existence of an older pre-main-sequence population in the gamma Vel sky region, in agreement with evidence obtained from the lithium depletion pattern of the same stars. (Less)
Please use this url to cite or link to this publication:
author
, et al. (More)
(Less)
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars: fundamental parameters, stars: pre-main sequence, open clusters, and associations: individual: gamma2 Velorum
in
Astronomy & Astrophysics
volume
566
publisher
EDP Sciences
external identifiers
  • wos:000338681500080
  • scopus:84902247562
ISSN
0004-6361
DOI
10.1051/0004-6361/201323306
language
English
LU publication?
yes
id
5673d50e-4f2a-47c7-94d0-5afca50cae75 (old id 4602414)
date added to LUP
2014-09-05 08:39:50
date last changed
2017-08-20 03:55:58
@article{5673d50e-4f2a-47c7-94d0-5afca50cae75,
  abstract     = {We present a study of spectral diagnostics available from optical spectra with R = 17 000 obtained with the VLT/Giraffe HR15n setup, using observations from the Gaia-ESO Survey, on the gamma Vel young cluster, with the purpose of classifying these stars and finding their fundamental parameters. We define several spectroscopic indices, sampling the amplitude of TiO bands, the H alpha line core and wings, and temperature- and gravity-sensitive sets of lines, each useful as a T-eff or log g indicator over a limited range of stellar spectral types. H alpha line indices are also useful as chromospheric activity or accretion indicators. Furthermore, we use all indices to define additional global T-eff - and logg-sensitive indices tau and gamma, valid for the entire range of types in the observed sample. We find a clear difference between gravity indices of main-sequence and pre-main-sequence stars, as well as a much larger difference between these and giant stars. The potentially great usefulness of the (gamma, t) diagram as a distance-independent age measurement tool for young clusters is discussed. We discuss the effect on the defined indices of classical T Tauri star veiling, which is however detected in only a few stars in the present sample. Then, we present tests and calibrations of these indices, on the basis of both photometry and literature reference spectra, from the UVES Paranal Observatory Project and the ELODIE 3.1 Library. The known properties of these stars, spanning a wide range of stellar parameters, enable us to obtain a good understanding of the performances of our new spectral indices. For non-peculiar stars with known temperature, gravity, and metallicity, we are able to calibrate quantitatively our indices, and derive stellar parameters for a wide range of stellar types. To this aim, a new composite index is defined, providing a good metallicity indicator. The ability of our indices to select peculiar, or otherwise rare classes of stars is also established. For pre-main-sequence stars outside the parameter range of the ELODIE dataset, index calibration relies on model isochrones. We check our calibrations against current Gaia-ESO UVES results, plus a number of Survey benchmark stars, and also against Gaia-ESO observations of young clusters, which contribute to establishing the good performance of our method across a wide range of stellar parameters. Our gravity determination for late-type PMS stars is found to be accurate enough to let us obtain gravity-based age estimates for PMS clusters. Finally, our gravity determinations support the existence of an older pre-main-sequence population in the gamma Vel sky region, in agreement with evidence obtained from the lithium depletion pattern of the same stars.},
  articleno    = {A50},
  author       = {Damiani, F. and Prisinzano, L. and Micela, G. and Randich, S. and Gilmore, G. and Drew, J. E. and Jeffries, R. D. and Fremat, Y. and Alfaro, E. J. and Bensby, Thomas and Bragaglia, A. and Flaccomio, E. and Lanzafame, A. C. and Pancino, E. and Recio-Blanco, A. and Sacco, G. G. and Smiljanic, R. and Jackson, R. J. and de Laverny, P. and Morbidelli, L. and Worley, C. C. and Hourihane, A. and Costado, M. T. and Jofre, P. and Lind, K. and Maiorca, E.},
  issn         = {0004-6361},
  keyword      = {stars: fundamental parameters,stars: pre-main sequence,open clusters,and associations: individual: gamma2 Velorum},
  language     = {eng},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Gaia-ESO Survey: Empirical classification of VLT/Giraffe stellar spectra in the wavelength range 6440-6810 angstrom in the gamma Velorum cluster, and calibration of spectral indices},
  url          = {http://dx.doi.org/10.1051/0004-6361/201323306},
  volume       = {566},
  year         = {2014},
}