Friends of Hot Jupiters. I. A Radial Velocity Search for Massive, Long-Period Companions to Close-in Gas Giant Planets

Abstract

In this paper we search for distant massive companions to known transiting gas giant planets that may have influenced the dynamical evolution of these systems. We present new radial velocity observations for a sample of 51 planets obtained using the Keck HIRES instrument, and find statistically significant accelerations in fifteen systems. Six of these systems have no previously reported accelerations in the published literature: HAT-P-10, HAT-P-22, HAT-P-29, HAT-P-32, WASP-10, and XO-2. We combine our radial velocity fits with Keck NIRC2 adaptive optics (AO) imaging data to place constraints on the allowed masses and orbital periods of the companions responsible for the detected accelerations. The estimated masses of the companions range between 1 − 500 M Jup , with orbital semi-major axes typically between 1 − 75 AU. A significant majority of the companions detected by our survey are constrained to have minimum masses comparable to or larger than those of the transiting planets in these systems, making them candidates for influencing the orbital evolution of the inner gas giant. We estimate a total occurrence rate of 51 ± 10% for companions with masses between 1 − 13 M Jup and orbital semi-major axes between 1 − 20 AU in our sample. We find no statistically significant difference between the frequency of companions to transiting planets with misaligned or eccentric orbits and those with well-aligned, circular orbits. We combine our expanded sample of radial velocity measurements with constraints from transit and secondary eclipse observations to provide improved measurements of the physical and orbital characteristics of all of the planets included in our survey.

Friends of Hot Jupiters. Iii. An Infrared Spectroscopic Search for Low-Mass Stellar Companions

“…We therefore consider whether or not any of the candidate spectroscopic stellar companions detected in this study might be responsible for the radial velocity accelerations reported in Knutson et al (2014).…”

“…Keck Observatory on Mauna Kea, which has a resolution R=30,000 in the K band (2.0-2.4 μm). See Knutson et al (2014) for details on the sample selection. We extract onedimensional spectra from the raw images using an IDL (Interactive Data Language) pipeline that flat fields and dark subtracts the images as well as removes any bad pixels following the methods described in Boogert et al (2002).…”

“…For the systems where the mass of NIRSPEC candidate companion is consistent with the measured radial velocity trend, we calculate the system's likely angle from face-on given by Winn et al (2009), whereġ is the RV trend measured by Knutson et al (2014), M c is the mass of the NIRSPEC candidate companion calculated from T eff according to Baraffe et al (1998), and a c is the candidate companion's semimajor axis. This latter value is the least well-known and only vaguely constrained by the size of the NIRSPEC slit.…”

“…In Knutson et al (2014) we searched for long-term radial velocity accelerations due to distant planetary or stellar companions in these systems, and found that 51±10% of the stars in our sample hosted planetary mass companions with orbits between 1 and 20 AU. In Bechter et al (2014) and Ngo et al (2015) we performed a complementary K band AO imaging search for stellar companions on relatively wide orbits, and found a binary rate of 48±9% for stellar companions with projected separations between 50 and 2000 AU.…”

Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b

“…It has a mass of M b = 1.39 ± 0.19 M Jup (Knutson et al 2014) and a radius R b = 1.90 ± 0.09 R Jup (Maciejewski et al 2013), which results in a mean density of Partly based on (1) data collected with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, (2) observations made at the Centro Astronómico Hispano Alemán (CAHA), operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), and (3) data collected with telescopes at the Rozhen National Astronomical Observatory.…”