The First Detection of Blue Straggler Stars in the Milky Way Bulge

• Published in: The Astrophysical journal Vol. 735; no. 1; pp. 37 - jQuery1323907004848='48'
• Main Authors: Clarkson, W. I, Sahu, Kailash C, Anderson, Jay, Rich, R. Michael, Smith, T. Ed, Brown, Thomas M, Bond, Howard E, Livio, Mario, Minniti, Dante, Renzini, Alvio, Zoccali, Manuela
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.07.2011; IOP
• Subjects: Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DETECTION; Earth, ocean, space; Exact sciences and technology; GALAXIES; MILKY WAY; MOTION; PROPER MOTION; STARS; Blue stragglers; Galaxies; Galaxy: structure; Stellar content; Galaxy: kinematics and dynamics; Horizontal-branch stars; Variability; binaries: close; Galaxy bulge; Milky Way; Galaxy: stellar content; Anticorrelation; Galaxy structure; Dynamics; Galactic bulge; Kinematics; Color-magnitude diagrams; Close binary stars; Galaxy: bulge; Proper motion; Stellar systems
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/735/1/37

We report the first detections of Blue Straggler Stars (BSS) in the bulge of the Milky Way. Proper motions from extensive space-based observations along a single sight line allow us to separate a sufficiently clean and well-characterized bulge sample such that we are able to detect a small population of bulge objects in the region of the color-magnitude diagram commonly occupied by young objects and blue stragglers. Variability measurements of these objects clearly establish that a fraction of them are blue stragglers. Out of the 42 objects found in this region of the color-magnitude diagram, we estimate that at least 18 are genuine BSS. We normalize the BSS population by our estimate of the number of horizontal branch stars in the bulge in order to compare the bulge to other stellar systems. The BSS fraction is clearly discrepant from that found in stellar clusters. The blue straggler population of dwarf spheroidals remains a subject of debate; some authors claim an anticorrelation between the normalized blue straggler fraction and integrated light. If this trend is real, then the bulge may extend it by three orders of magnitude in mass. Conversely, we find that the genuinely young (<5 Gyr) population in the bulge, must be at most 3.4% under the most conservative scenario for the BSS population.