NOAO >   Observing Info >   Approved Programs >   2015A-0407

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Program Information for 2015A-0407


PI: Katelyn E Milliman, U. of Wisconsin, Madison, milliman@astro.wisc.edu
Address: Astronomy Department, 465 N. Charter Street, Madison, WI 53706 USA

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

Title: A Study of Anomalous Stars and Binary Populations Within Open Clusters

Abstract: ``Anomalous'' 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 anomalous 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 anomalous 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. 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 anomalous star production. These data will be the touchstones for detailed $N$-body open cluster simulations and 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 anomalous stellar systems.

Program Type: WTAC

Scheduled Nights:
Run 1 (2015A):  WIYN/HYDR -- 5n on Feb 04 2015, Feb 08 2015, Mar 04 - Mar 08 2015
Run 2 (2015A):  WIYN/HYDR -- 4n on May 24 - May 25 2015, Jul 02 - Jul 05 2015, Jul 30 - Jul 31 2015
Run 2 (2015B):  WIYN/HYDR -- 1n on Aug 01 - Aug 02 2015


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NOAO >   Observing Info >   Approved Programs >   2015A-0407

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