Calan-Yale "Key Project" on the Local Group of Galaxies

PIs: Robert Zinn (Yale) and Eduardo Hardy (NRAO/Calan)

CoIs: E. Costa (Calan), P. Demarque (Yale), C. Gallart (IAC, former Andes Fellow), R. Larson (Yale), R. Mendez (Calan), M. Rubio (Calan), W. van Altena (Yale)

Students: S. Duffau (Calan/Yale)

I. Introduction

The approximately 40 galaxies making up the Local Group (LG) span large ranges in both luminosity and morphological type. The LG is dominated, of course, by its two large, luminous spiral galaxies, the Milky Way and M31, which are centers of rich systems of satellite galaxies. In addition, there are several other galaxies which are separate from these two major mass concentrations.

It is not an exaggeration to say that studies of LG galaxies, including the Milky Way, and their stars and star clusters have provided most of the tests of the theory of stellar evolution, and also a large fraction of what is known about the evolution of galaxies. The LG galaxies are our primary source of information on the stellar content, star formation history, and dynamics of spiral and dwarf galaxies. They are also of fundamental importance to the calibration of the cosmic distance scale.

It is the resolution of the LG galaxies into stars by ground-based telescopes that makes them so important to astronomy. The interpretive power of the theory of stellar evolution can be applied to sort out, for example, their histories of star formation. Stellar spectroscopy can reveal details of their chemical evolution. With very few exceptions, one cannot study the individual stars of more distant galaxies, which must be studied by the far more uncertain procedure of interpreting their integrated light. Here too the LG galaxies can help because they can be studied both by integrated light, and also star-by-star, and thus serve as a check on the integrated light methods.

II. Research Areas

This U. de Chile/Yale key project involves a number of separate, but closely related projects in the areas of the formation and evolution of dwarf galaxies and their relationships to large spiral galaxies, and the use of the LG as a test-bed for stellar evolution. The following is a list of the major projects and their publications:

A. The star formation histories of the dwarf spheroidal galaxies and the Magellanic Clouds.

Using color-magnitude diagrams and spectroscopy to derive star formation histories: VLT observations of Fornax. Gallart, C., Zinn, R., Pont, F., Hardy, E., Marconi, G., Buonanno, R. 2002, The ESO Messenger, 108, 16.

The Chemical Enrichment History of the Fornax Dwarf Spheroidal Galaxy from the Infrared Calcium Triplet. Pont, F., Zinn, R., Gallart, C., Hardy, E. and, Winnick, R.A. 2004, A.J. in press (Jan). Combining wide-field, old main-sequence turnoff color-magnitude diagrams and spectroscopy to derive accurate star formation histories: the LMC and Fornax. Gallart, Pont, F., Zinn, R. & Hardy, E. 2001. Proceedings of the conference ``Observed HR diagrams and stellar evolution models: the interplay between observational constraints and theoretical limitations'', Eds. T. Lejeune & J. Fernandes, ASP Conf. Ser., 274, 397.

Deriving star formation histories: evolutionary or population synthesis codes versus color-magnitude diagrams. Alloin, D., Gallart, C., Fleurence, E., Pompei, E., Raimann, D., Fritze-von Alvensleben, U. & Yi, S. 2002, Astrophysics and Space Science, 281, 109. (Proceedings of the Euroconference ``The Evolution of Galaxies: the basic building blocks'').

The Evolution of the Milky Way Satellites: The Early Universe through the Color-Magnitude Diagram. Gallart, C. 2001. Proceedings of the Euroconference "The evolution of galaxies. I- Observational Clues" in Astrophysics and Space Science, Eds. J.M. Vilchez, G. Stasinska, E. Perez.

SMC: Stellar Populations and their gradients through old main-sequence photometry. Noel, N., Gallart, C., Costa, E., & Mendez, R. 2003, Proceedings of the conference: "Stellar Populations 2003", Garching Germany.

B. Testing stellar evolution using the star clusters of the Magellanic Clouds

Testing intermediate-age stellar evolution with VLT photometry of LMC clusters: I.The data. Gallart, C., Zoccali, M., Bertelli, G., Chiosi, C., Demarque, P., Girardi, L., Nasi, E., Woo, J.-H. & Yi, S, 2003, A.J., 125, 742.

Testing intermediate-age stellar evolution with VLT photometry of LMC clusters: II. Analysis with the Yale models. Woo, J.-H., Gallart, C., Demarque, P. & Yi, S, Zoccali, M. 2003, A.J., 125, 754.

Testing Overshoot with intermediate-age Magellanic Cloud clusters. Woo, J.-H., Gallart, C., Demarque, P., Yi, S., & Zoccali, M. 2002. Proceedings of the conference ``Observed HR diagrams and stellar evolution models: the interplay between observational constraints and theoretical limitations'', Eds. T. Lejeune & J. Fernandes, ASP Conf. Ser., 274, 377.

Testing intermediate-age stellar evolution with Magellanic Clouds clusters. Gallart, C., Zoccali, M., Bertelli, G., Chiosi, C., Demarque, P., Girardi, L. & Yi, S. 2002. Proceedings of IAU Symposium 207 on ``Extragalactic star clusters'', Eds. E. Grebel, D. Geisler, D. Minitti, p. 713.

C. Substructure in the Milky Way's Halo: spectroscopy of the RR Lyrae variables in the QUEST survey.

Halo Substructure in the QUEST RR Lyrae Survey. R. Zinn, A. K. Vivas, C. Gallart, R. Winnick, 2003, Proceedings of the conference ``Satellites and Tidal Streams'', ASP Conf. Series in press.

Velocities of RR Lyrae Stars in the Sagittarius Tidal Stream. A. K. Vivas, R. Zinn, C. Gallart, 2003, Proceedings of the conference ``Satellites and Tidal Streams'', ASP Conf. Series in press.