CNO abundances in Bulge giants

Coordinator: B. Gustaffson (Uppsala, Sweden)

Co-Is: B. Edvardsson, N. Ryde


We propose to study CNO abundances in a sample of bulge giants. This proposal is intended to test the possibility to use Crires to acquire stellar spectra and sky spectra in crowded fields with high insterstellar extinction. We will be able to present scientifically interesting results within a few months.

Targets list

NameRA(2000)DEC(2000)Spectral rangeWavelength IDF_nu or F_lineExp.Time - DIT(s),NDIT
ARP 101218 03 35.8-29 58 351537-1560nm36/-1/iH=11.8300, 4
ARP 114118 03 41.9-30 00 041537-1560nm36/-1/iH=12300, 5
ARP 119418 03 48.6-29 59 311537-1560nm36/-1/iH=12300, 4
ARP 120218 03 49.9-30 00 081537-1560nm36/-1/iH=11.8300, 4
ARP 132218 03 49.4-30 01 541537-1560nm36/-1/iH=10.3150, 2
ARP 315218 03 28.3-30 04 111537-1560nm36/-1/iH=11.9300, 4
ARP 400318 03 33.4-29 58 121537-1560nm36/-1/iH=11.4300, 3
ARP 407218 03 28.4-29 59 581537-1560nm36/-1/iH=12.4300, 5
ARP 420318 03 23.6-30 01 591537-1560nm36/-1/iH=9.250, 2
ARP 432918 03 28.4-29 58 421537-1560nm36/-1/iH=11.1300, 3

Allocated Time: 3 hours (to observe in one slit direction)

Project description/scientific objective:

The chemical properties of the Bulge are poorly understood. These are critical for our understanding of the formation and evolution of the Milky Way, but also of galaxies in general. A study of abundance ratios of Bulge giants can constrain models of the formation and evolution of the Bulge. Due to the dust obscuration very few abundance analyses have been performed and the existing ones show a large spread. The infrared, with lower extinction and predominantly molecular rather than atomic abundance indicators, is a preferred wavelength region to study elemental abundances in bulge stars.

We concentrate here on the important CNO abundances. Carbon abundances yield information on C yields in a rapidly star-forming region such as the Bulge. Nitrogen abundances probe mixing processes with C+N being conserved, and oxygen abundance ratios set strong constraints on the star formation history, ages and chemical evolution of the Bulge. In particular, we shall investigate the oxygen abundance trends found from *optical* spectra of K giants in the Bulge by McWilliam & Rich (2004), which indicate a surprising interruption of oxygen production in the Bulge for metallicities larger than -0.5. There are several reasons to believe that oxygen abundance determinations based on OH lines in the IR are more trustworthy than those based on optical measurements. A determination of an oxygen abundance can only be carried out with confidence if the carbon abundance is precisely known since the CO molecule holds most of the C and O in cool star atmospheres.

In the band 6378-6470 cm-1, Crires (at R=50,000, 0.4" slit) will be able to retrieve numerous individual vib-rot lines of CO, OH, and CN of different strengths and excitation, as well as lines from Fe, Ni, Si, S and V. The ten target stars, with well-determined stellar parameters, lie in Baade's Window. Ten stars will be sufficient to map the metallicity range needed. Since the stellar parameters are well determined and we have all infrastructure necessary in Uppsala (reduction package, REDUCE, advanced model atmospheres, and synthesis etc), we will be able to analyse these data and present them within a few months.

Observing strategy

We need a SNR/(resolution element) of 120. According to ETC we then need a SNR/pixel of 70, since we have 4.2 pixels per resolution element. PA in the table above is given in degrees, defined here as counter-clockwise from the North direction.

We have proposed 2*2.8 hours=5.6 hours of observations. Only observing in one of the direction (wavelength IDs) would give useful results (2.8 hours observing time). All data will be scientifically useful, but the more the larger the relevance. We have judged that ten stars will give solid and fully conclusive scientific results.

The stars 1012 and 4003 could perhaps be taken in the same shot. Please, check whether this would be possible or not. Maybe they would lie too close to the slit edges. I don't know whether this procedure would save much time if skys are needed too.

In order to avoid overlapping spectra in the crowded stellar fields of the Bulge, good seeing is desirable.


McWilliam & Rich, 2004, COAS vol. 4, Eds. McWilliam & Rausch