An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4 M giant star HIP 67537

Jones, M. I. and Brahm, R. and Wittenmyer, R. A. and Drass, H. and Jenkins, J. S. and Melo, C. H. F. and Vos, J. and Rojo, P. (2017) An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4 M giant star HIP 67537. Astronomy and Astrophysics, 602. ISSN 0004-6361

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Abstract

We report the discovery of a substellar companion around the giant star HIP 67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP 67537 b: mb sin i = 11.1+0.4-1.1Mjup, a =4.9+0.14-0.13 AU and e = 0.59+0.05-0.02 . Considering random inclination angles, this object has ≳65% probability to be above the theoretical deuterium-burning limit, thus it is one of the few known objects in the planet to brown-dwarf (BD) transition region. In addition, we analyzed the Hipparcos astrometric data of this star, from which we derived a minimum inclination angle for the companion of ~2 deg. This value corresponds to an upper mass limit of ~0.3 M⊙, therefore the probability that HIP 67537 b is stellar in nature is ≲7%. The large mass of the host star and the high orbital eccentricity makes HIP 67537 b a very interesting and rare substellar object. This is the second candidate companion in the brown dwarf desert detected in the sample of intermediate-mass stars targeted by the EXoPlanets aRound Evolved StarS (EXPRESS) radial velocity program, which corresponds to a detection fraction of f = +2.0-0.5 %. This value is larger than the fraction observed in solar-type stars, providing new observational evidence of an enhanced formation efficiency of massive substellar companions in massive disks. Finally, we speculate about different formation channels for this object.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to published version in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 20 Nov 2017 01:28
Last Modified: 20 Nov 2017 01:28
Uncontrolled Keywords: planetary systems; astrometry; techniques; radial velocities; techniques: spectroscopic
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1051/0004-6361/201630278
URI: http://eprints.usq.edu.au/id/eprint/32750

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