Carbon Enhanced Stars in the

Sloan Digital Sky Survey ( SDSS )

T. Sivarani, Young Sun Lee, B. Marsteller & T. C. Beers

Michigan State University &

Joint Institute for Nuclear Astrophysics

Carbon Stars

Carbon stars are objects with prominent C2 molecular bands They are known since 1884 (Duner 1884)

Carbon star:

Star with C/O > 1

Carbon stars

The observed Galactic and extra galactic carbon stars are ==> low mass stars on the AGB phase which has gone through the 3rd dredge up of He burned products.

==> CH stars, Ba Stars from binary AGB companion

==> Dwarf carbon stars – possibly AGB mass transfer

An increasing interest in this class of objects has arisen from

HK survey of metal-deficient stars conducted by

Beers, Preston, & Shectman.

Hamburg/ESO survey by Christlieb and Co.

revealed for the first time an unexpectedly large number

of very metal-poor stars with anomalously strong CH and CN bands

(~25% in the metallicity range [Fe/H] < -2.5 compared to few percent

among stars of higher metal abundances).

I

Large frequency of carbon enhanced stars at low metallicities

Implications

1. Is the intial mass function of the early galaxy was very different from the present day. Lucatello et al. (2004)

2. Pre Galactic metal enrichment.

3. The evolution at low metallcities are very different.

4. These stars are been accreted from metal poor local satellite galaxies

Carbon Enhanced Metal Poor (CEMP) stars

Carbon rich [C/Fe] > 1.0 (Though the classical carbon star at solar metallicity is about 2 times solar).

All of them are nitrogen rich (not all the carbon stars are nitrogen rich)

Carbon stars in our Galaxy are different from the C-stars in LMC and other local groups. Does metallicity play an important role ?.

Chemical composition of CEMP stars

s-process rich

r-process rich

with no n-capture enrichment. Alpha enhanced

mild CEMP stars.

N-capture in CEMP stars

Figure from Ryan et al. (2002)

S-process rich AGB mass transferOne with normal Li : LP706-7

CS22892-052The only r-process rich carbon starr-only pattern (Sneden et al. 2003)

No n-capture elementsHE 0107-5240 Christlieb et al 2002CS 22957-027 Aoki et al 2002HE 0007-1832 Cohen et al 200412C/13C ~ 6 – 9 (CNO equilibrium)Also have slightly higher nitrogen abundance compared to s-process rich stars.

n-Capture Processes in CEMP stars

[C/Fe]=0.88, [N/Fe]=1.01, [O/Fe]=0.72

[Mg,Si/Fe] ~ 0.3 [Ba/Fe] = 0.99[Eu/Fe] = 1.64[Tb,Dy,Er…./Fe] ~ 1.6

[Ba/Fe] ~ 2.0[Eu/Fe] ~ 1.5

[Ba/Eu] ~ -0.9 ~ pure r-process value at [Fe/H] ~ -3.0

r-process rich carbon star The only known CS 22892-052 r-only pattern (Sneden et al. 2003)

s and r-process 15 objects are known. High [Eu/Ba] compared to pure s-process

No n-capture elementsHE0107-5240 Christlieb et al 2002CS 22957-027 Aoki et al 2002HE 0007-1832 Cohen et al 200412C/13C ~ 6 – 9 (CNO equilibrium)s-only stars?

To have a better understanding

relative frequency among the various types and origin.

Increasing the no. of similar objects.

High resolution follow up. radial velocity monitoring.

SDSS DR4 100,000 + SEGUE +SDSS II .....

SDSS DR4 has about 102,714 stars at a resolution R= 1800 from 3800Å to 9000Å Already about 500 Faint high latitute carbon stars have been identified by Morgan et al. 2002 and Downes et al. 2004. from SDSS DR1The propermotions indicate that most of them are near by dwarfs. ==> Young population which had gone through binary mass transfer from an AGB star ==> the AGB star will now be seen as a white dwarf.There have been efforts in search for white dwarfs around these stars.

SDSS DR4

Most of the key problems in astrophysics rely on the determination of accurate stellar fundamental parameters

1. Grid of synthetic spectra

wavelength range 3000-10000A and 0.01Ang spacing

==> smoothed to SDSS resolution 2.5

2. Grid of synthetic colors and lineindices

3. Empirical grid.

High resolution spectra with well estimated parameters

smoothed to SDSS resolution

==> ELODIE, VLT UVES archive, Cflib, S4N

Analysis

Automated methods to estimate stellar parameters

Teff, logg, [Fe/H], [C/Fe] …

Validation of the estimation with real spectra.

Clusters, Standard stars .

Synthetic grid

Carbon Enhanced grid.

[C/Fe]=0.5,1.0,1.5,2.0,2.5,3.0

At low temperature the stellar atmospheric structure itself changes due to high carbon abundance. ==> Solar scaled models are not appropriate.

Teff = 3500K – 10000K , logg = 0.00-5.0 [Fe/H] = -5.00 – 0.00 Masseron et al. 2005

Synthetic spectra

Results from Artificial neural networks

[Fe/H] logg Teff---------------------------------------- ----------------------------------------- -------------------------------------------------

Com_cls True Diff IntErr Com_cls True Diff IntErr Com_cls True Diff IntErr

---------------------------------------- ----------------------------------------- -------------------------------------------------

-0.0524 -0.0000 -0.0524 0.0976 2.9984 3.0000 -0.0016 0.0054 4997.8731 5000.0000 -2.1269 11.4377

0.2335 0.2500 -0.0165 0.1056 2.9678 3.0000 -0.0322 0.0123 5000.5895 5000.0000 0.5895 8.7776

-0.3378 -0.2500 -0.0878 0.0758 3.0561 3.0000 0.0561 0.0203 4998.8447 5000.0000 -1.1553 10.4254

0.5235 0.5000 0.0235 0.0539 3.9910 4.0000 -0.0090 0.0039 5239.0910 5250.0000 -10.9090 5.4740

-0.5048 -0.5000 -0.0048 0.0573 4.0301 4.0000 0.0301 0.0229 5242.5087 5250.0000 -7.4913 3.2398

0.7738 0.7500 0.0238 0.0534 3.9812 4.0000 -0.0188 0.0116 5239.0285 5250.0000 -10.9715 6.4912

0.9883 1.0000 -0.0117 0.0594 4.0040 4.0000 0.0040 0.0236 5238.7821 5250.0000 -11.2179 4.3407

-0.9611 -1.0000 0.0389 0.0325 3.9825 4.0000 -0.0175 0.0449 5241.2428 5250.0000 -8.7572 4.3664

0.2654 0.2500 0.0154 0.0824 3.9911 4.0000 -0.0089 0.0086 5501.4074 5500.0000 1.4074 1.8401

-0.2632 -0.2500 -0.0132 0.0776 4.0072 4.0000 0.0072 0.0115 5504.5832 5500.0000 4.5832 3.8452

0.5351 0.5000 0.0351 0.0816 3.9833 4.0000 -0.0167 0.0189 5500.9626 5500.0000 0.9626 6.4307

-0.5114 -0.5000 -0.0114 0.0690 4.0111 4.0000 0.0111 0.0135 5504.9800 5500.0000 4.9800 5.3205

-1.4869 -1.5000 0.0131 0.0446 4.5127 4.5000 0.0127 0.0193 5985.8269 6000.0000 -14.1731 7.4680

-1.9174 -2.0000 0.0826 0.0849 4.4932 4.5000 -0.0068 0.0196 5987.6177 6000.0000 -12.3823 2.6852

-3.0891 -3.0000 -0.0891 0.0777 4.4984 4.5000 -0.0016 0.0275 5987.3293 6000.0000 -12.6707 4.6541

Now we are ready for the science

From the SDSS spectra 1. [C/Fe] versus [Fe/H]2. [alpha/Fe] versus [Fe/H]3. s-process and C abundance4. relative frequency of s-process rich and no n- enrichment How they are distributed in metallicity

High resolution follow up

C,N and isotopic abundance ==> hydrogen and helium burning

s-process abundance (light and heavy) ==> metal poor AGB evolution and nucleosynthesis.

r-process abundance ==> SN neucleosynthesis.

S-process among the C-enhanced stars

In the figure the straight lines

indicate the equivalent width

for solar composition of Ba

in

The metallicity range.

The symbols corresponds to

Ba equivalent width for the

SDSS-DR3 C-enhanced stars

Conclusions

● From SDSS data we can get [C/Fe], [alpha/Fe], [Sr/Fe] and [Ba/Fe] can be obtained.

● Relative frequency of various types of CEMP stars can be found from the Sr and Ba abundances.

● Several hundreds will be suitable for follow up high resolution studies.

● Radial velocity monitoring.