The Calcium Triplet in the Near Infrared: Its Calibration and Use in Determining the Evolution of the Large Magellanic Cloud

University Of California-Irvine, Irvine CA

Investigators

Abstract

AST-0070985 Tammy Smecker-Hane The goals of this proposal are to: a) Obtain spectra (in the wavelength region of the 8000-Angstrom calcium triplet) of 10 to 20 red giant stars in 11 Galactic clusters and determine (using stellar atmospheres ) the calibration of the CaII triplet as a metallicity indicator. b) Obtain spectra of ~110 Red Giants in each of 3 regions in LMC and apply the calibration from the Galactic cluster giants to determine the LMC giant's metallicity and thus determine the star formation history in the LMC . The LMC observations will aid in understanding how local variations in star-formation history are distributed. This, in turn, will help us to understand star-formation in intermediate redshift galaxies. One of the fundamental goals of modern astrophysics is to understand how galaxies have evolved. A galaxy's evolution can be determined by measuring the chemical compositions and ages of its stars. In this project, Professor Smecker-Hane and collaborators will accomplish two goals. First, they will calibrate the depth of calcium absorption lines in the near-infrared spectra of stars as a function of age and chemical composition. They will extend the current calibration to younger and more metal-rich stars so the calcium lines can be used to investigate other galaxies which have stars with ages from 2 to 15 billion years and chemical compositions from one to one-thousandth of the Sun. Second, these investigators will use this new calibration to determine the chemical composition of stars as a function of radius in the Large Magellanic Cloud (LMC) using Cerro Tololo InterAmerican 4 meter Telescope in Chile. The LMC is a gas-rich, intermediate-mass galaxy with a distance of only 160,000 light years, which makes it one of the Milky Way's nearest neighbors. They will combine the chemical compositions with data from the Hubble Space Telescope in order to accurately measure the LMC's star-formation history. Existing data hints that the LMC experienced a significant burst of star formation approximately 3 to 5 billion years ago, and understanding the details of the burst -- its strength, duration, and cause - can give us valuable clues about the nature of star bursts frequently seen in faint blue galaxies at intermediate redshifts. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC). ***