PI: Robert Mathieu, U. of Wisconsin, Madison, firstname.lastname@example.org
Address: Department of Astronomy, 475 N. Charter St., Madison, WI 53703 United States
CoI: Andrew Nine, U. of Wisconsin, Madison
CoI: Benjamin Tofflemire, U. of Texas, Austin
CoI: Emily M Leiner, Northwestern U.
CoI: Meng Sun, U. of Wisconsin, Madison
Title: A Study of Binary Populations and Alternative Pathways of Stellar Evolution in Open Clusters
Abstract: Nonstandard stars, such as blue stragglers (BSs), sub-subgiants (SSGs), and yellow giants, have been an enduring challenge for stellar evolution theory. It is now clear that in star clusters these systems are closely linked to the binary star populations. Furthermore, sophisticated N-body models show that stellar dynamical processes, specifically binary encounters, play a central role in the formation of such nonstandard stars. These stars trace the interface between the classical fields of stellar evolution and stellar dynamics. We propose a study to directly probe this interface through high-precision radial- velocity measurements of the nonstandard stars and the binary populations in three intermediate-age open clusters of similar richness: NGC 7789 (1.8 Gyr), NGC 2506 (2.1 Gyr) and NGC 6819 (2.3 Gyr). Notably, NGC 2506 has 10 BSs, while NGC 7789 has at least 27. Our observations will provide cluster membership and binary orbital properties for these BSs, as well as identify possible SSG RV members. Our observations will also establish the hard-binary fraction and frequency distributions of orbital parameters (periods, eccentricities, secondary mass distributions, etc.) in these clusters, establishing the environmental factors that may influence nonstandard star production. These data will be the touchstones for detailed N-body open cluster simulations. Combining the observed populations and the theoretical models will shed light on the different BS production rates in these clusters, and ultimately the formation mechanisms of these nonstandard stellar systems. We have also expanded our published study of the very old cluster NGC 6791 to the cluster main sequence. NGC 6791, being in the Kepler field, it is a superb case to see if there are rapidly rotating "blue stragglers" on the main sequence, as found by Leiner et al. in M67 (Leiner, PhD dissertation; Leiner et al., in draft).
Program Type: WTAC
Run 1 (2019A): WIYN/HYDR -- 5n on Mar 19 - Mar 23 2019
Run 2 (2019A): WIYN/HYDR -- 5n on Jun 06 - Jun 10 2019
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360