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)

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. 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 than 200 giant spectra have been presented

Stellar library (observation)

SDSS

LAMOST

West et al. 2011

DR7 70841 M dwarfs

covey et al. 2008DR6 1 square degree 8750 M dwarfs ~1% (104)

~0.5% (354)

Giant contamination

Bessell & Brett (1988)

H2O absorption in M dwarf/giant atmospheres are different

Yi et al. 2014

Pilot 58360 M dwarfs

Zhong et al. 2014 (in preparation)DR1 132748 M dwarfs 7377 M giants

~4% (2334)

~5% (7377)

[Mg2, g-r]

[CaH2+CaH3, TiO5]

[J-H,H-K]

Separation method

Lepine et al.2011

M dwarf/giant Separation

Mann et al. 2012

M dwarfs : 135865M giants : 8276

Covey et al. 2007

Classify M giants along the temperature sequence

r-i color is a good criterion to classify the temperature sequence of M giants

Color Selection

8276

3588

647

1880

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. 2007

Data selection

184

Manual inspection

M giant Classification

0.5---0.65

0.6---0.8

0.75---0.95

0.9---1.15

1.0---1.3

1.3---1.7

1.6---2.0

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

Spectral indices

CaH2

CaH3

TiO5

VO1

TiO6

VO2

M giants identified from the LAMOST DR1

Template fitting method 7378 M giantsDR1

2204696 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 candidates7378

Apogee catalog 59607

cross-match

41 common star Spectral

namePlateid

RaDec

CaH2CaH3TiO5RvSn

SpTy

TeffTeff_err

LoggLogg_err

FeHFeh_err

RVRv_err

Radial velocity comparison

Average residual : -1.5 km/sResidual 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

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.