AAVSO: American Association of Variable Star Observers

First Discovery of the Galactic Plane eXoplanet Survey: GPX-1b, a Transiting 15 MJup Companion to a Rapidly Rotating F-type Star (Abstract)

Volume 48 number 1 (2020)

Paul Benni
3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net
Artem Burdanov
address correspondence to Paul Benni, 3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net
Eugene Sokov
address correspondence to Paul Benni, 3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net
Khalid Barkaoui
address correspondence to Paul Benni, 3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net
GPX follow-up team
address correspondence to Paul Benni, 3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net
SOPHIE team
address correspondence to Paul Benni, 3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net
Vadim Krushinsky
address correspondence to Paul Benni, 3 Concetta Circle, Acton, MA 01720; pbenni@verizon.net

Abstract

(Abstract only) We announce the discovery of GPX-1b, a 15 MJup transiting hot Jupiter/brown dwarf companion to a rapidly rotating 12 V mag F-type star on a 1.7-day orbit. This object is scientifically interesting as its mass is close to the brown dwarf—gas giant planet mass transition, being close to the lower mass range of brown dwarfs (13–80 MJup ) where 13 MJup is the lower limiting mass for thermonuclear fusion of deuterium. The closest short period bright transiting brown dwarf systems that are < 13 V mag and are of similar mass as GPX-1b are WASP-18b and HATS-70b, which have a mass just below the 13 MJup limit. GPX-1b currently would be the brightest transiting brown dwarf system just above the 13 MJup limit and thus a favorable target for atmospheric characterization. From Gaia DR2, star Teff = 6420 K, and Rsol = 1.6. Preliminary planet/brown dwarf characteristics: RJup = 1.5, MJup = 15 (SOPHIE RV spectroscopy), 10 mmag transit depth, 2.1 hour transit duration, with an orbital period of 1.745 days. More data to follow pending publication. The GPX survey is designed to search high density star fields that other surveys, such as WASP, HATNet, XO, and KELT would find challenging due to blending of transit-like events. The GPX survey telescope is a wide-field telescope (Celestron RASA, 279 mm f/2.2, based in Acton, MA) on a Losmandy Titan mount, and configured with a FLI ML16200 camera. The resultant image resolution of GPX is about 2 arcsec/pixel compared to 13.7–23 arcsec/pixel of the aforementioned surveys and the TESS space telescope exoplanet survey. GPX evolved from the Kourovka Planet Search (KPS) prototype survey and consequent discovery of KPS-1b, a transiting hot-jupiter, using the same RASA survey telescope. While the Galactic Plane eXoplanet (GPX) Survey primary goal is to search for exoplanet transits, many unreported variable stars are also discovered. One very interesting 14.7 Vmag star (survey name GPX-TF16E-48), was previously reported to VSX as NEV239, a W Ursae Majoris-type eclipsing variable (EW) in Cassiopeia, with a period of 0.297545 d (7.141 hr). Follow-up with first a C14 telescope, then later with larger aperture telescopes, reveals a box-like transit ~ 10 minutes in duration, with sharp 50-sec ingress and egress. Spectroscopic follow-up revealed that the primary companion of the system is a K7 dwarf star, with no spectral features of the second companion. Interestingly, depths of eclipses show unusual spectral energy distribution: the deepest transit depth ~ 60 mmag occurs in red wavelength (SDSS r and Rc bands) filters. We assume that the eclipsing body is a white dwarf and its calculated magnitudes are 19.2, 17.3, and 18.3 for SDSS g, r, and I bands, respectively. Such SED cannot be described by a black body model of the white dwarf, but is in agreement under the assumption that the eclipsed body is red. Or more strictly, the eclipsed body is red on one side that we can see immediately before and after the eclipse. We assume that this increase of the flux in red bands corresponds to strong H-alpha emission, but suitable narrow spectral features are not seen in the spectrum. The primary variability of the tidally distorted primary K7 dwarf star is about 180 mmag, whereas the asymmetric primary and secondary peaks seem to be slowly changing in peak-to-peak magnitude and shape over a period of months, possibly due to hot or cold spots. The primary K star mass is estimated to be 0.63 Msol and radius 0.65 Rsol, with a Teff = 4070 K. The companion white dwarf mass is estimated to be 0.72 Msol, with a radius of 0.013 Rsol. There is some preliminary evidence suggesting that the white dwarf is a low accretion rate polar, which is being further explored at this time. Note: The authors for the first part of this presentation are Benni, Burdanov, Sokov, Barkaoui, GPX follow-up team, SOPHIE team. The authors for the second part of this presentation are Benni, Krushinsky, Burdanov, Barkaoui, GPX follow-up team.