Fundamental Stellar Parameters from Spectroscopic Surveys off the MW plane*: Role of Insterstellar Reddening and Stellar Activity

Transcription

1 Fundamental Stellar Parameters from Spectroscopic Surveys off the MW plane*: * mostly RAVE: 574,630 spectra of 483,330 individual stars Role of Insterstellar Reddening and Stellar Activity Tomaž Zwitter Faculty of Mathematics and Physics, University of Ljubljana, Slovenia + the RAVE collaboration ( A very short summary: IS reddening & stellar activity does happen everywhere, can jeopardize derived parameters, spectroscopic surveys present a unique opportunity to study both phenomena.

2 Photometric temperatures: example of 2MASS No reddening assumed Difference to asymptotic reddening

3 Derived magnitudes: example of 2MASS No reddening assumed Difference to asymptotic reddening

4 Spectroscopic temperature and photometric colours at high Galactic latitudes Dwarfs from the RAVE survey.

5 A wider span of photometric colours is not an easy solution for reddening Reddening vector and stellar main sequence are almost parallel. Easy to find a solution for special objects (e.g. red clump stars) but not for field stars. Dwarfs from the RAVE survey.

6 A wider span of photometric colours is not an easy solution for reddening Reddening vector and stellar main sequence are almost parallel. Easy to find a solution for special objects (e.g. red clump stars) but not for field stars. Dwarfs from the RAVE survey.

7 Spectroscopic parameters + photometric colours + some priors on the MW = distance & reddening Binney et al. (2013, in preparation) Colour coding: logarithm of number of stars in a cell. Bayesian fitting of distances and reddening in the RAVE survey.

8 Alternatives for asymptotic reddening: FIR emission Kohyama et al. (2012) Comparison to Schlegel et al. (1998). β > 30o A better spatial resolution (6' vs. ~1o in Schlegel et al. 1998) and a better calibration. An alternative is colour variation & star counts from 2MASS (Dobashi 2011).

9 Comparison of optical and UV asymptotic extinction: evidence for different extinction laws Peek & Schiminovich (2013)

10 Strength of some Diffuse Interstellar Bands correlates with reddening A classical approach: Some DIBs (e.g. 5780, 6284 Å) have a moderately good correlation with reddening, analysis of hot stars with a significant reddening. Raimond et al. (2012)

11 Strength of some Diffuse Interstellar Bands correlates with reddening Kos et al. (2013), in preparation. a better correlation with reddening, all spectral types are analyzed, at high b and at large distances RAVE survey: a pseudo-3d map of DIB strength.

12 Strength of 8620Å in the Galaxy Kos et al. (2013), in preparation.

13 All stars are not 'normal', their spectra are different from those in grids of stellar atmospheres A morphological classification scheme using locally linear embedding (LLE). Matijevič et al. (2012) RAVE sample Normal: Normal: 90-95% 90-95% Binary: 1% Binary: 1% Ca II em.: 3% Ca II em.: 3% TiO band: 1% TiO band: 1% Pec. giant: 0.03% Pec. giant: 0.03% Carbon: 0.03% Carbon: 0.03% Obs.problem Obs.problem <1% <1%

14 Detection of candidates for chromospheric emission A scheme using observed non-active RAVE spectra as templates. Žerjal et al. (2013) Additional flux in strong resonance lines: Hα Hβ, Ca II H&K (3969, 3934 Å), Ca II IRT triplet.

15 Detection of candidates for chromospheric emission (and so of a young star population) 2σ Žerjal et al. (2013) candidates for chromospheric emission non-active stars pre main-sequence stars RAVE: ~ candidates, ~ have emission detected at a 2σ level.

16 Cromospheric activity can influence the values of derived stellar parameters Žerjal et al. (2013), in preparation.

17 Conclusions No spectroscopic survey can avoid reddening, diffuse interstellar bands and stellar activity. Bayesian fitting can yield also the extinction and distance as a survey result. Use of synthetic stellar templates can be largely replaced by using observed spectra without DIBs or stellar activity. Large scale spatial mapping of the ISM and population studies of stellar activity seem within reach for the first time. RAVE results are important by themselves. They also pave way to ESO-Gaia, Gaia, and Hermes/Galah.