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: M J from to 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)

Magnitude Limit ： 16 mag Diameter of MW: 25 kpc The distance we can detected M0V: 1.1 kpc K0V: 2.4 kpc G0V: 3.8 kpc F0V: 5.2 kpc A0V: 13 kpc M0III : 80 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. Absolute magnitudes are calculated by Covey et al.2007

The problem of the M giants study The number of M giants spectra Fulks et al (97) Danks et al (8) Allen et al (16) Serote et al (4) Montes et al (16) Lancon et al (34) … Less than 200 giant spectra have been presented Stellar library (observation)

SDSS LAMOST West et al DR M dwarfs covey et al DR6 1 square degree 8750 M dwarfs ~1% (104) ~0.5% (354) Giant contamination Bessell & Brett (1988) H 2 O absorption in M dwarf/giant atmospheres are different Yi et al Pilot M dwarfs Zhong et al (in preparation) DR M dwarfs 7377 M giants ~4% (2334) ~5% (7377) [Mg 2, g-r] [CaH2+CaH3, TiO5] [J-H,H-K] Separation method Lepine et al.2011

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

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

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

M giant Classification r- i M0.0 SpTy M2.0 M3.0 M4.0 M5.0 M6.0 M1.0 Covey’s relationship between MK spectral type and r-i color

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

M0 III Spectra for temperature subset M5 III

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

Spectral indices

CaH2 CaH3 TiO5 VO1 TiO6 VO2

M giants identified from the LAMOST DR1 Template fitting method 7378 M giants DR spectra 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 LAMOST M giant candidates 7378 Apogee catalog cross-match 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. SpTyLogg 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 Li et al.2014 Late K type Early type dwarf Binary Low S/N spectra

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.