NOAO >   Observing Info >   Approved Programs >   2018A-0447

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Program Information for 2018A-0447


PI: Erika K Carlson, U. of Wisconsin, Madison, ecarlson@astro.wisc.edu
Address: Department of Astronomy, 475 N. Charter St., Madison, WI 53706 United States

CoI: Robert Mathieu, U. of Wisconsin, Madison
CoI: Benjamin Tofflemire, U. of Wisconsin, Madison
CoI: Emily Leiner, U. of Wisconsin, Madison
CoI: Maxwell Pollack, 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 (2.4 Gyr). Notably, NGC 6819 has 33 potential BSs, NGC 2506 has 10, while NGC 7789 has at least 27. We will also gather RV data for similar targets in the old open cluster NGC 6791 (8 Gyr). 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.

Program Type: WTAC

Scheduled Nights:
Run 1 (2018A):  WIYN/HYDR -- 4n on Mar 28 - Mar 29 2018, Apr 05 - Apr 06 2018
Run 2 (2018A):  WIYN/HYDR -- 5n on May 18 - May 22 2018


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