基于 LAMOST 巡天数据的大样本 M 巨星搜寻和分类

基于LAMOST巡天数据的大样本M巨星搜寻和分类 钟靖中国科学院上海天文台

M giants Red： surface temperature lower than 4000K Luminous: MJ from -3.49 to -7.04 mag (Covey et al.2007) Red Giant: luminous giant star of low or intermediate mass ( 0.3~8 solar masses), including the K and M spectral type. RGB ( red giant branch) RC (red clump) AGB ( asymptotic giant branch)

The distance we can detected Magnitude Limit： 16 mag M0V: 1.1 kpc K0V: 2.4 kpc G0V: 3.8 kpc F0V: 5.2 kpc A0V: 13 kpc Diameter of MW: 25 kpc M giants are luminous and allow us to probe the Galactic halo, so they are good tracers to study the substructures and the accretion history of the MW. M0III : 80 kpc Absolute magnitudes are calculated by Covey et al.2007

The problem of the M giants study Stellar library (observation) Fulks et al. 1994 (97) Danks et al. 1994 (8) Allen et al. 1995 (16) Serote et al. 1996 (4) Montes et al. 1999 (16) Lancon et al. 2000 (34) … Less than200giant spectra have been presented The number of M giants spectra

Separation method Giant contamination [Mg2, g-r] covey et al. 2008 DR6 1 square degree 8750 M dwarfs ~1% (104) SDSS H2O absorption in M dwarf/giant atmospheres are different West et al. 2011 DR7 70841 M dwarfs ~0.5% (354) [J-H,H-K] Bessell & Brett (1988) Yi et al. 2014 Pilot 58360 M dwarfs ~4% (2334) LAMOST [CaH2+CaH3, TiO5] Zhong et al. 2014 (in preparation) DR1 132748 M dwarfs 7377 M giants ~5% (7377) Lepine et al.2011

M dwarf/giant Separation Mann et al. 2012 M dwarfs : 135865 M giants : 8276

Classify M giants along the temperature sequence r-i color is a good criterion to classify the temperature sequence of M giants Covey et al. 2007

Color Selection Data selection 8276 Cross-match with SDSS 3588 err(r) < 0.05, extic(r) < 0.2 1880 Covey et al. 2007 r-i > 0.5, 1.2 < g-r < 1.4 647 Manual inspection 184

M giant Classification r-i SpTy 0.5---0.65 M0.0 0.6---0.8 M1.0 0.75---0.95 M2.0 0.9---1.15 M3.0 M4.0 1.0---1.3 Covey’s relationship between MK spectral type and r-icolor M5.0 1.3---1.7 M6.0 1.6---2.0

Radial velocity calibration 184 LAMOST Standard spectra CaII triplet Correct RV for each spectrum IRAF rv.rvidlines package The accuracy for each spectrum is less than 10 km/s

Spectra for temperature subset M0 III M5 III

Template spectra The mean standard deviation for each spectra is about 5%

Spectral indices

Spectral indices CaH2 CaH3 TiO5 VO1 TiO6 VO2

M giants identified from the LAMOST DR1 DR1 2204696 spectra Template fitting method 7378 M giants Radial Velocity Calculation • Template spectra in rest frame • Interpolate both template spectra and LAMOST spectrum (39000 pixel) • Shift LAMOST spectrum towards the blue or red by a number of pixel (±50 pixels) • For each pixel shifting, recalculate the chi-square value against template spectrum around the CaII triplet region from 8400 to 8800 Å • The pixel shifting which has the minimum chi-square value is selected as the best fit • Using the best fit pixel shifting value to calculate the RV

Comparison with Apogee data cross-match LAMOST M giant candidates 7378 Apogee catalog 59607 41 common star Spectral name Plateid Ra Dec CaH2 CaH3 TiO5 Rv Sn SpTy Teff Teff_err Logg Logg_err FeH Feh_err RV Rv_err

Radial velocity comparison Average residual : -1.5 km/s Residual standard error : 15 km/s

Teff Vs. SpTy Logg Vs. SpTy Early type high temperature, high surface gravity low brightness, small radius Late type low temperature, low surface gravity high brightness, large radius

Possible contamination • Late K type • Early type dwarf • Binary • Low S/N spectra Li et al.2014

Summary • Using on the molecular spectral indices, we found that M giants are well separate from the M dwarfs sample. • Basing on the r-i color criteria from Covey et al. 2007, we used the LAMOST DR1 data to composite template of M giants spanning types M0 – M6. • We identified 7378 M giants from the LAMOST DR1 data.

基于 LAMOST 巡天数据的大样本 M 巨星搜寻和分类