NOAO >   Observing Info >   Approved Programs >   2015B-0804

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Program Information for 2015B-0804


PI: Katelyn E Milliman, U. of Wisconsin, Madison, milliman@astro.wisc.edu
Address: Astronomy Department, 475 N. Charter St., Madison, Wisconsin 53706 United States

CoI: Robert D Mathieu, U. of Wisconsin, Madison
CoI: Emily Leiner, U. of Wisconsin, Madison
CoI: Benjamin M Tofflemire, U. of Wisconsin, Madison
CoI: Maxwell Pollack, U. of Wisconsin, Madison

Title: A Study of the Nonstandard Stellar Populations and Binary Populations of Open Clusters

Abstract: Nonstandard stars, such as blue stragglers (BSs) and sub-subgiants (SSGs), 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 (2.5 Gyr). Notably, NGC 6819 has 33 potential BSs, NGC 2506 has 10, 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 and complete the PIs thesis work. 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 blue stragglers, sub-subgiants, and other nonstandard stellar systems.

Program Type: WTAC

Scheduled Nights:
Run 1 (2015B):  WIYN/HYDR -- 3n on Sep 05 - Sep 07 2015
Run 2 (2015B):  WIYN/HYDR -- 2.5n on Dec 21 - Dec 23 2015
Run 3 (2015B):  WIYN/HYDR -- 3n on Jan 17 - Jan 18 2016, Jan 20 2016


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