Star Counts and The Galactic Structure

Xu Yan

Supervisor: Deng Li Cai

Introduction

Sloan digital sky survey Synthetic star counts model Future plan

Sloan Digital Sky Survey

Five broad band filters,u’,g’,r’,i’,z’

effective wavelengths, 3450Å, 4760Å, 6280Å, 7690Å,9250Å

point-source magnitude limit, 22.3, 23.3, 23.1, 22.3, 20.8 (s/n=5)

Pixels subtend 0”.4, PSF width1.4" median in r Exposure time in each band is 54.1s ‘run’, six 13’.5 wide strips, ‘rerun’, 12’.5

2o.5 wide stripe (Chen et. al. 2001)

45 survey stripes

DR2 Sky Coverage 3324 sq deg Equatorial

http://www.sdss.org/dr2/coverage/index.html

DR2 Sky Coverage Galactic

http://www.sdss.org/dr2/coverage/index.html

Synthetic model

ρ(R,Z), Φ(Mass) → surface number density of some direction of some population

each population → [Fe/H], Mass, Age From Isochrone → [Fe/H], Teff, g Color of each star

Robin(2003)group

Age(Gyr) [Fe/H](dex) IMF ρ0(MΘPC-3)

1 0 – 0.15 0.010.12 dn/dm=m-1.6

(M<1MΘ)

dn/dm=m-3

(M≥1MΘ)

4*10-3

2 0.15 - 1 0.030.12 7.9*10-3

3 1 - 2 0.030.1 6.2*10-3

4 2 - 3 0.010.11 4*10-3

5 3 - 5 -0.070.18 5.8*10-3

6 5 - 7 -0.140.17 4.9*10-3

7 7 - 10 -0.370.2 6.6*10-3

8 11 -0.780.3 dn/dm=m-0.5 1.34*10-3

9 14 -1.780.5 9.32*10-3

91

22

1

)()(

)(,

AAA

dRRdMassRdMassA

MassPMFZRdAMass

Mass R

i

i

]/||exp[]/)(exp[),( 2100 hzhrxMrd

87

4/1

0

])/(exp[

e

es

rr

rrbCsr

)()( massIMFmass

Chen (2001)

Bahcall(1980)

5.02

36.11

)(

)()(

mcM

mmcMRobin(2003)

PMF ~ IMF Mass density convert to number density

is normalized IMF

Logz=1.03[Fe/H]-1.689 (Carraro et. al. 1994) z, Age, Mass

dm

dn

dmdm

dnmcymassdenist dm

dm

dncnumdensity

Pseudo-random in age and metalicity

Group1,Mass: 0.1505000D+00 0.1515000D+00 (M☉)

The tables of bolometric corrections have been applied to Padova database of stellar evolutionary tracks and isochrones. http://pleiadi.pd.astro.it.

Interpolate in SDSS Isochrone of Giradi(2004) and Ma(2001)

0

02

1

2

1log5.2

Ss m

dSf

dSf

m

SbolS MMBC

0

0

4.0

2,

2

1

2

1

10

log5.2

]/)10(4log[5.2

S

A

bolbolS

m

dSf

dSF

LFpcMBC

Stellar spectra Fλ , spectral library

'1'0 2/sinhlog5.2 bfabmf

ea log5.2

'0 log5.20 bm

Lupton et al (1999)

fmfm log5.2)( 0

AB magnitude scale

00, ABm

121200, 10631.3 Hzcmsergf AB

u-g g-r r-I i-z

107 , 10 8,109,1010 yr (Giradi 2004)

12Gyr, z=0.0001,0.0004,0.001,0.004,0.008,0.019,0.03 (Giradi2004)

isoc_sloan/isoc_z0.dat.gz Metal-free models from Ma01.

isoc_sloan/isoc_z0001.dat.gz isoc_sloan/isoc_z0004.dat.gz isoc_sloan/isoc_z001.dat.gz isoc_sloan/isoc_z004.dat.gz isoc_sloan/isoc_z008.dat.gz isoc_sloan/isoc_z019.dat.gz

isoc_sloan/isoc_z030.dat.gz

Basic set obtained by combining Gi00+Gi01 (low- and intermediate-mass stars) with Be94+Gi96 (high masses) isochrones. With overshooting

R=50PC z=41.44PC

Ra=180 dec=60 skycoverage=1srL=134.4 b=55.97

R=150PC z=124.31PC

R=250PC z=207.186PC

R=350PC z=290.06PC

Mass(M ) Log(age) group z logT logg☉ u g r u-g g-r 0.200000 9.76540 61 0.0233971 3.62080 2.98324 6.95622 4.73258 3.71290 2.22364 1.01968. 0.200000 9.83367 61 0.0131369 3.61070 3.21589 7.97221 5.66942 4.60236 2.30279 1.06706.

R=450PC z=372.94PC

Mass(M☉) Log(age) group z logT logg u g r u-g g-r0.200000 9.19340 31 0.0124033 3.63555 3.41523 7.13436 4.98482 4.02208 2.14954 0.962740 0.200000 9.75101 61 0.0118220 3.63816 3.01763 6.46198 4.38647 3.44567 2.07551 0.940800 0.200000 9.71720 61 0.0124870 3.62821 3.20643 7.34673 5.19215 4.20510 2.15458 0.987050

R=550PC z=455.81PC

R=650PC z=538.68

R=750PC z=621.56PC

R=850PC z=704.43PC

R=950PC z=787.37PC

Classify metallicity z>0.019 0.019>z>0.004 z<0.004

Classify age

Age<12Gyr 5Gyr<Age<12Gyr Age<5Gyr

RA=180 DEC=60 33289

Compare result of model with observation

4422

Future plan

Constrain model with observation Do further deducing for physical parameter

of observational data to obtain distance Pick up stars that have special meaning to

the structure of the Galaxy

Thank you!