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Register a new userThe Observed Distribution of Spectroscopic Binaries from the Anglo-Australian Planet Search
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We report the detection of sixteen binary systems from the Anglo-Australian Planet Search. Solutions to the radial velocity data indicate that the stars have companions orbiting with a wide range of masses, eccentricities and periods. Three of the systems potentially contain brown-dwarf companions while another two have eccentricities that place them in the extreme upper tail of the eccentricity distribution for binaries with periods less than 1000 d. For periods up to 12 years, the distribution of our stellar companion masses is fairly flat, mirroring that seen in other radial velocity surveys, and contrasts sharply with the current distribution of candidate planetary masses, which rises strongly below 10MJ. When looking at a larger sample of binaries that have FGK star primaries as a function of the primary star metallicity, we find that the distribution maintains a binary fraction of ~43$pm$4% between -1.0 to +0.6 dex in metallicity. This is in stark contrast to the giant exoplanet distribution. This result is in good agreement with binary formation models that invoke fragmentation of a collapsing giant molecular cloud, suggesting this is the dominant formation mechanism for close binaries and not fragmentation of the primary stars remnant proto-planetary disk.
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We report the detection of two new planets from the Anglo-Australian Planet Search. These planets orbit two stars each previously known to host one planet. The new planet orbiting HD 142 has a period of 6005pm427 days, and a minimum mass of 5.3M_Jup. HD142c is thus a new Jupiter analog: a gas-giant planet with a long period and low eccentricity (e = 0.21 pm 0.07). The second planet in the HD 159868 system has a period of 352.3pm1.3 days, and m sin i=0.73pm0.05 M_Jup. In both of these systems, including the additional planets in the fitting process significantly reduced the eccentricity of the original planet. These systems are thus examples of how multiple-planet systems can masquerade as moderately eccentric single-planet systems.
We present updated simulations of the detectability of Jupiter analogs by the 17-year Anglo-Australian Planet Search. The occurrence rate of Jupiter-like planets that have remained near their formation locations beyond the ice line is a critical datum necessary to constrain the details of planet formation. It is also vital in our quest to fully understand how common (or rare) planetary systems like our own are in the Galaxy. From a sample of 202 solar-type stars, and correcting for imperfect detectability on a star-by-star basis, we derive a frequency of $6.2^{+2.8}_{-1.6}$% for giant planets in orbits from 3-7 AU. When a consistent definition of Jupiter analog is used, our results are in agreement with those from other legacy radial velocity surveys.
We report the discovery of two long-period giant planets from the Anglo-Australian Planet Search. HD 154857c is in a multiple-planet system, while HD 114613b appears to be solitary. HD 114613b has an orbital period P=10.5 years, and a minimum mass m sin i of 0.48 Jupiter masses; HD 154857c has P=9.5 years and m sin i=2.6 Jupiter masses. These new data confirm the planetary nature of the previously unconstrained long-period object in the HD 154857 system. We have performed detailed dynamical stability simulations which show that the HD 154857 two-planet system is stable on timescales of at least 100 million years. These results highlight the continued importance of legacy surveys with long observational baselines; these ongoing campaigns are critical for determining the population of Jupiter analogs, and hence of those planetary systems with architectures most like our own Solar system.
Our understanding of planetary systems different to our own has grown dramatically in the past 30 years. However, our efforts to ascertain the degree to which the Solar system is abnormal or unique have been hindered by the observational biases inherent to the methods that have yielded the greatest exoplanet hauls. On the basis of such surveys, one might consider our planetary system highly unusual - but the reality is that we are only now beginning to uncover the true picture. In this work, we use the full eighteen-year archive of data from the Anglo-Australian Planet Search to examine the abundance of Cool Jupiters - analogs to the Solar systems giant planets, Jupiter and Saturn. We find that such planets are intrinsically far more common through the cosmos than their siblings, the hot Jupiters. We find that the occurrence rate of such Cool Jupiters is $6.73^{+2.09}_{-1.13}$%, almost an order of magnitude higher than the occurrence of hot Jupiters (at $0.84^{+0.70}_{-0.20}$%). We also find that the occurrence rate of giant planets is essentially constant beyond orbital distances of $sim$1,au. Our results reinforce the importance of legacy radial velocity surveys for the understanding of the Solar systems place in the cosmos.
We report the discovery of a second long-period giant planet orbiting HD 30177, a star previously known to host a massive Jupiter analog (HD 30177b: a=3.8$pm$0.1 au, m sin $i=9.7pm$0.5 Mjup). HD 30177c can be regarded as a massive Saturn analog in this system, with a=9.9$pm$1.0 au and m sin $i=7.6pm$3.1 Mjup. The formal best fit solution slightly favours a closer-in planet at $asim$7 au, but detailed n-body dynamical simulations show that configuration to be unstable. A shallow local minimum of longer-period, lower-eccentricity solutions was found to be dynamically stable, and hence we adopt the longer period in this work. The proposed $sim$32 year orbit remains incomplete; further monitoring of this and other stars is necessary to reveal the population of distant gas giant planets with orbital separations $asim$10 au, analogous to that of Saturn.
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