Astronomy and Astrophysics, volume 566A, 50-50 (2014/6-1)
Gaia-ESO Survey: Empirical classification of VLT/Giraffe stellar spectra in the wavelength range 6440-6810 Å in the γ 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., BENSBY T., BRAGAGLIA A., FLACCOMIO E., LANZAFAME A.C., PANCINO E., RECIO-BLANCO A., SACCO G.G., SMILJANIC R., JACKSON R.J., DE LAVERNY P., MORBIDELLI L., WORLEY C.C., HOURIHANE A., COSTADO M.T., JOFRE P., LIND K. and MAIORCA E.
Abstract (from CDS):
We present a study of spectral diagnostics available from optical spectra with R=17000 obtained with the VLT/Giraffe HR15n setup, using observations from the Gaia-ESO Survey, on the γ 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 Hα line core and wings, and temperature- and gravity-sensitive sets of lines, each useful as a Teff
or logg indicator over a limited range of stellar spectral types. Hα line indices are also useful as chromospheric activity or accretion indicators. Furthermore, we use all indices to define additional global Teff
- and logg-sensitive indices τ and γ, 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 (γ,τ) 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 γ Vel sky region, in agreement with evidence obtained from the lithium depletion pattern of the same stars.
stars: fundamental parameters - stars: pre-main sequence - open clusters and associations: individual: gamma2 Velorum
VizieR on-line data:
<Available at CDS (J/A+A/566/A50): table1.dat table3.dat>
Status at CDS:
could be processed
Fig.3 objects MNNNNN ([JNW2009] FF NNNN) not in SIMBAD.
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