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Title: BARIUM SURFACE ABUNDANCES OF BLUE STRAGGLERS IN THE OPEN CLUSTER NGC 6819

We present a barium surface abundance of 12 blue stragglers (BSs) and 18 main-sequence (MS) stars in the intermediate-age open cluster NGC 6819 (2.5 Gyr) based on spectra obtained from the Hydra Multi-object Spectrograph on the WIYN 3.5 m telescope. For the MS stars we find [Fe/H] = +0.05 ± 0.04 and [Ba/Fe] = −0.01 ± 0.10. The majority of the BS stars are consistent with these values. We identify five BSs with significant barium enhancement. These stars most likely formed through mass transfer from an asymptotic giant branch star that polluted the surface of the BS with the nucleosynthesis products generated during thermal pulsations. This conclusion aligns with the results from the substantial work done on the BSs in old open cluster NGC 188 that identifies mass transfer as the dominant mechanism for BS formation in that open cluster. However, four of the BSs with enhanced barium show no radial-velocity evidence for a companion. The one star that is in a binary is a double-lined system, meaning the companion is not a white dwarf and not the remnant of a prior AGB star. In this paper we attempt to develop a consistent scenario to explain the origin of thesemore » five BSs.« less
Authors:
;  [1] ;  [2]
  1. Department of Astronomy, University of Wisconsin-Madison, 475 North Charter St, Madison, WI 53706 (United States)
  2. University of Tampa, 401 West Kennedy Boulevard, Tampa, FL 33606 (United States)
Publication Date:
OSTI Identifier:
22520155
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 150; Journal Issue: 3; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASYMPTOTIC SOLUTIONS; BARIUM; BINARY STARS; ELEMENT ABUNDANCE; GIANT STARS; IRON; MAIN SEQUENCE STARS; MASS TRANSFER; NUCLEOSYNTHESIS; RADIAL VELOCITY; STAR CLUSTERS; SURFACES; TELESCOPES; WHITE DWARF STARS