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Register a new userThe California Planet Survey III. A Possible 2:1 Resonance in the Exoplanetary Triple System HD 37124
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We present new radial velocities from Keck Observatory and both Newtonian and Keplerian solutions for the triple-planet system orbiting HD 37124. The orbital solution for this system has improved dramatically since the third planet was first reported in Vogt et al. 2005 with an ambiguous orbital period. We have resolved this ambiguity, and the outer two planets have an apparent period commensurability of 2:1. A dynamical analysis finds both resonant and non-resonant configurations consistent with the radial velocity data, and constrains the mutual inclinations of the planets to be less than about 30 degrees. We discuss HD 37124 in the context of the other 19 exoplanetary systems with apparent period commenserabilities, which we summarize in a table. We show that roughly one in three well-characterized multiplanet systems has a apparent low-order period commensuribility, which is more than would naively be expected if the periods of exoplanets in known multiplanet systems were drawn randomly from the observed distribution of planetary orbital periods.
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We present an update to seven stars with long-period planets or planetary candidates using new and archival radial velocities from Keck-HIRES and literature velocities from other telescopes. Our updated analysis better constrains orbital parameters for these planets, four of which are known multi-planet systems. HD 24040 b and HD 183263 c are super-Jupiters with circular orbits and periods longer than 8 yr. We present a previously unseen linear trend in the residuals of HD 66428 indicative on an additional planetary companion. We confirm that GJ 849 is a multi-planet system and find a good orbital solution for the c component: it is a $1 M_{rm Jup}$ planet in a 15 yr orbit (the longest known for a planet orbiting an M dwarf). We update the HD 74156 double-planet system. We also announce the detection of HD 145934 b, a $2 M_{rm Jup}$ planet in a 7.5 yr orbit around a giant star. Two of our stars, HD 187123 and HD 217107, at present host the only known examples of systems comprising a hot Jupiter and a planet with a well constrained period $> 5$ yr, and with no evidence of giant planets in between. Our enlargement and improvement of long-period planet parameters will aid future analysis of origins, diversity, and evolution of planetary systems.
The size of a planet is an observable property directly connected to the physics of its formation and evolution. We used precise radius measurements from the California-Kepler Survey (CKS) to study the size distribution of 2025 $textit{Kepler}$ planets in fine detail. We detect a factor of $geq$2 deficit in the occurrence rate distribution at 1.5-2.0 R$_{oplus}$. This gap splits the population of close-in ($P$ < 100 d) small planets into two size regimes: R$_P$ < 1.5 R$_{oplus}$ and R$_P$ = 2.0-3.0 R$_{oplus}$, with few planets in between. Planets in these two regimes have nearly the same intrinsic frequency based on occurrence measurements that account for planet detection efficiencies. The paucity of planets between 1.5 and 2.0 R$_{oplus}$ supports the emerging picture that close-in planets smaller than Neptune are composed of rocky cores measuring 1.5 R$_{oplus}$ or smaller with varying amounts of low-density gas that determine their total sizes.
Keck/HIRES precision radial velocities of HD 207832 indicate the presence of two Jovian-type planetary companions in Keplerian orbits around this G star. The planets have minimum masses of 0.56 and 0.73 Jupiter-masses with orbital periods of ~162 and ~1156 days, and eccentricities of 0.13 and 0.27, respectively. Stromgren b and y photometry reveals a clear stellar rotation signature of the host star with a period of 17.8 days, well separated from the period of the radial velocity variations, reinforcing their Keplerian origin. The values of the semimajor axes of the planets suggest that these objects have migrated from the region of giant planet formation to closer orbits. In order to examine the possibility of the existence of additional (small) planets in the system, we studied the orbital stability of hypothetical terrestrial-sized objects in the region between the two planets and interior to the orbit of the inner body. Results indicated that stable orbits exist only in a small region interior to planet b. However, the current observational data offer no evidence for the existence of additional objects in this system.
We apply, for the first time, the Transit Least Squares (TLS) algorithm to search for new transiting exoplanets. TLS is a successor to the Box Least Squares (BLS) algorithm, which has served as a standard tool for the detection of periodic transits. In this proof-of-concept paper, we demonstrate how TLS finds small planets that have previously been missed. We showcase TLS capabilities using the K2 EVEREST-detrended light curve of the star K2-32 (EPIC205071984) that was known to have three transiting planets. TLS detects these known Neptune-sized planets K2-32b, d, and c in an iterative search and finds an additional transit signal with a high signal detection efficiency (SDE_TLS) of 26.1 at a period of 4.34882 (-0.00075, +0.00069) d. We show that this signal remains detectable (SDE_TLS = 13.2) with TLS in the K2SFF light curve of K2-32, which includes a less optimal detrending of the systematic trends. The signal is below common detection thresholds, however, if searched with BLS in the K2SFF light curve (SDE_BLS = 8.9) as in previous searches. Markov Chain Monte Carlo sampling shows that the radius of this candidate is 1.01 (-0.09, +0.10) Earth radii. We analyze its phase-folded transit light curve using the vespa software and calculate a false positive probability FPP = 3.1e-3, formally validating K2-32e as a planet. Taking into account the multiplicity boost of the system, FPP < 3.1e-4. K2-32 now hosts at least four planets that are very close to a 1:2:5:7 mean motion resonance chain. The offset of the orbital periods of K2-32e and b from a 1:2 mean motion resonance is in very good agreement with the sample of transiting multi-planet systems from Kepler, lending further credence to the planetary nature of K2-32e. We expect that TLS can find many more transits of Earth-sized and smaller planets in the Kepler data that have hitherto remained undetected with BLS and similar algorithms.
We report the detection of three new exoplanets from Keck Observatory. HD 163607 is a metal-rich G5IV star with two planets. The inner planet has an observed orbital period of 75.29 $pm$ 0.02 days, a semi-amplitude of 51.1 $pm$ 1.4 ms, an eccentricity of 0.73 $pm$ 0.02 and a derived minimum mass of msini = 0.77 $pm$ 0.02 mjup. This is the largest eccentricity of any known planet in a multi-planet system. The argument of periastron passage is 78.7 $pm$ 2.0$^{circ}$; consequently, the planets closest approach to its parent star is very near the line of sight, leading to a relatively high transit probability of 8%. The outer planet has an orbital period of 3.60 $pm$ 0.02 years, an orbital eccentricity of 0.12 $pm$ 0.06 and a semi-amplitude of 40.4 $pm$ 1.3 ms. The minimum mass is msini = 2.29 $pm$ 0.16 mjup. HD 164509 is a metal-rich G5V star with a planet in an orbital period of 282.4 $pm$ 3.8 days and an eccentricity of 0.26 $pm$ 0.14. The semi-amplitude of 14.2 $pm$ 2.7 ms implies a minimum mass of 0.48 $pm$ 0.09 mjup. The radial velocities of HD 164509 also exhibit a residual linear trend of -5.1 $pm$ 0.7 ms per year, indicating the presence of an additional longer period companion in the system. Photometric observations demonstrate that HD 163607 and HD 164509 are constant in brightness to sub-millimag levels on their radial velocity periods. This provides strong support for planetary reflex motion as the cause of the radial velocity variations.
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