Search

Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with a 6 m class IR/O/UV space telescope, recently dubbed the Habitable Worlds Observatory, is a high-priority goal of the Astro2020 Decadal Survey. To prepare for future direct imaging (DI) surveys, the list of potential targets should be thoroughly vetted to maximize efficiency and scientific yield. We present an analysis of archival radial velocity data for southern stars from the NASA/NSF Extreme Precision Radial Velocity (EPRV) Working Group’s list of high-priority target stars for future DI missions (drawn from the HabEx, LUVOIR, and Starshade Rendezvous studies). For each star, we constrain the region of companion mass and period parameter space we are already sensitive to based on the observational baseline, sampling, and precision of the archival radial velocity (RV) data. Additionally, for some of the targets, we report new estimates of magnetic activity cycle periods, rotation periods, improved orbital parameters for previously known exoplanets, and new candidate planet signals that require further vetting or observations to confirm. Our results show that for many of these stars we are not yet sensitive to even Saturn-mass planets in the habitable zone, let alone smaller planets, highlighting the need for future EPRV vetting efforts before the launch of a DI mission. We present evidence that the candidate temperate super-Earth exoplanet HD 85512b is most likely due to the star’s rotation, and report an RV acceleration for δ Pav that supports the existence of a distant giant planet previously inferred from astrometry.

AU Microscopii (AU Mic) is the second closest pre-main-sequence star, at a distance of 9.79 parsecs and with an age of 22 million years1. AU Mic possesses a relatively rare2 and spatially resolved3 edge-on debris disk extending from about 35 to 210 astronomical units from the star4, and with clumps exhibiting non-Keplerian motion5-7. Detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic 'activity' on the star8,9. Here we report observations of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of 8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4 Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3σ confidence. Our observations of a planet co-existing with a debris disk offer the opportunity to test the predictions of current models of planet formation and evolution.

Based on two decades of radial velocity (RV) observations using Keck/HIRESand McDonald/Tull, and more recent observations using the Automated PlanetFinder, we found that the nearby star HR 5183 (HD 120066) hosts a 3$M_J$minimum mass planet with an orbital period of $74^{+43}_{-22}$ years. The orbitis highly eccentric (e$\simeq$0.84), shuttling the planet from within the orbitof Jupiter to beyond the orbit of Neptune. Our careful survey design enabledhigh cadence observations before, during, and after the planet's periastronpassage, yielding precise orbital parameter constraints. We searched forstellar or planetary companions that could have excited the planet'seccentricity, but found no candidates, potentially implying that the perturberwas ejected from the system. We did identify a bound stellar companion morethan 15,000 au from the primary, but reasoned that it is currently too widelyseparated to have an appreciable effect on HR 5183 b. Because HR 5183 b's wideorbit takes it more than 30 au (1") from its star, we also explored thepotential of complimentary studies with direct imaging or stellar astrometry.We found that a Gaia detection is very likely, and that imaging at 10 $\mu$m isa promising avenue. This discovery highlights the value of long-baseline RVsurveys for discovering and characterizing long-period, eccentric Jovianplanets. This population may offer important insights into the dynamicalevolution of planetary systems containing multiple massive planets.

© 2019. The American Astronomical Society. All rights reserved. Located at Dome A, the highest point of the Antarctic plateau, the Chinese Kunlun station is considered to be one of the best ground-based photometric sites because of its extremely cold, dry, and stable atmosphere. A target can be monitored from there for over 40 days without diurnal interruption during a polar winter. This makes Kunlun station a perfect site to search for short-period transiting exoplanets. Since 2008, an observatory has existed at Kunlun station, and three telescopes are working there. Using these telescopes, the AST3 project has been carried out over the last 6 yr with a search for transiting exoplanets as one of its key programs (CHESPA). In the austral winters of 2016 and 2017, a set of target fields in the southern continuous viewing zone (CVZ) of TESS were monitored by the AST3-II telescope. In this paper, we introduce the CHESPA and present the first data release containing photometry of 26,578 bright stars (). The best photometric precision at the optimum magnitude for the survey is around 2 mmag. To demonstrate the data quality, we also present a catalog of 221 variables with a brightness variation greater than 5 mmag from the 2016 data. Among these variables, 179 are newly identified periodic variables not listed in the AAVSO database (https://www.aavso.org/), and 67 are listed in the Candidate Target List. These variables will require careful attention to avoid false-positive signals when searching for transiting exoplanets. Dozens of new transiting exoplanet candidates will be released in a subsequent paper.

© 2019. The American Astronomical Society. All rights reserved. We report first results from the CHinese Exoplanet Searching Program from Antarctica (CHESPA) - a wide-field high-resolution photometric survey for transiting exoplanets carried out using telescopes of the AST3 (Antarctic Survey Telescopes times 3) project. There are now three telescopes (AST3-I, AST3-II, and CSTAR-II) operating at Dome A - the highest point on the Antarctic Plateau - in a fully automatic and remote mode to exploit the superb observing conditions of the site, and its long and uninterrupted polar nights. The search for transiting exoplanets is one of the key projects for AST3. During the austral winters of 2016 and 2017 we used the AST3-II telescope to survey a set of target fields near the southern ecliptic pole, falling within the continuous viewing zone of the TESS mission. The first data release of the 2016 data, including images, catalogs, and light curves of 26,578 bright stars (), was presented in Zhang et al. The best precision, as measured by the rms of the light curves at the optimum magnitude of the survey (), is around 2 mmag. We detect 222 objects with plausible transit signals from these data, 116 of which are plausible transiting exoplanet candidates according to their stellar properties as given by the TESS Input Catalog, Gaia DR2, and TESS-HERMES spectroscopy. With the first data release from TESS expected in late 2018, this candidate list will be timely for improving the rejection of potential false-positives.

Giant planets on long-period orbits around the nearest stars are among the easiest to directly image. Unfortunately these planets are difficult to fully constrain by indirect methods, e.g. transit and radial velocity (RV). In this study, we present the discovery of a super-Jupiter, HD 222237 b, orbiting a star located |$11.445\pm 0.002$|  pc away. By combining RV data, Hipparcos , and multi-epoch Gaia astrometry, we estimate the planetary mass to be |${5.19}_{-0.58}^{+0.58}\, M_{\rm Jup}$|⁠ , with an eccentricity of |${0.56}_{-0.03}^{+0.03}$| and a period of |${40.8}_{-4.5}^{+5.8}$|  yr, making HD 222237 b a promising target for imaging using the Mid-Infrared Instrument (MIRI) of JWST. A comparative analysis suggests that our method can break the inclination degeneracy and thus differentiate between prograde and retrograde orbits of a companion. We further find that the inferred contrast ratio between the planet and the host star in the F 1550 C filter (⁠|$15.50\, \mu \rm m$|⁠) is approximately |$1.9\times 10^{-4}$|⁠ , which is comparable with the measured limit of the MIRI coronagraphs. The relatively low metallicity of the host star (⁠|$\rm -0.32\, dex$|⁠) combined with the unique orbital architecture of this system presents an excellent opportunity to probe the planet–metallicity correlation and the formation scenarios of giant planets. [ABSTRACT FROM AUTHOR]

Most stars become white dwarfs after they have exhausted their nuclear fuel (the Sun will be one such). Between one-quarter and one-half of white dwarfs have elements heavier than helium [...]

Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation, which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here, we present the characterization of a new mini-Neptune planet orbiting the bright (V = 9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS  light curves from sectors 2, 3, 29, and 30, with an orbital period of 4.138 d. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.5 |$\pm$| 4.6  |$M_{\oplus }$|⁠. When we combine this with the measured radius from TESS  of 2.70 |$\pm$| 0.05  |$R_{\oplus }$|⁠ , we find a high planetary density of 7.1 |$\pm$| 1.4 g cm |$^{-3}$|⁠. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23 per cent H |$_2$| O and 77 per cent Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy. [ABSTRACT FROM AUTHOR]

Pioneering photometric, astrometric, and spectroscopic surveys is helping exoplanetary scientists better constrain the fundamental properties of stars within our galaxy and the planets these stars host. In this study, we use the third data release from the stellar spectroscopic GALAH Survey, coupled with astrometric data of eDR3 from the Gaia satellite, and other data from NASA's Exoplanet Archive, to refine our understanding of 279 confirmed and candidate exoplanet host stars and their exoplanets. This homogenously analysed data set comprises 105 confirmed exoplanets, along with 146 K2 candidates, 95 TESS Objects of Interest (TOIs), and 52 Community TOIs (CTOIs). Our analysis significantly shifts several previously (unknown) planet parameters while decreasing the uncertainties for others. Our radius estimates suggest that 35 planet candidates are more likely brown dwarfs or stellar companions due to their new radius values. We are able to refine the radii and masses of WASP-47 e, K2-106 b, and CoRoT-7 b to their most precise values yet to less than 2.3 per cent and 8.5 per cent, respectively. We also use stellar rotational values from GALAH to show that most planet candidates will have mass measurements that will be tough to obtain with current ground-based spectrographs. With GALAH's chemical abundances, we show through chemo-kinematics that there are five planet hosts that are associated with the galaxy's thick disc, including NGTS-4, K2-183, and K2-337. Finally, we show that there is no statistical difference between the chemical properties of hot Neptune and hot rocky exoplanet hosts, with the possibility that short-period rocky worlds might be the remnant cores of hotter, gaseous worlds. [ABSTRACT FROM AUTHOR]

We present the bright (V mag = 9.12), multiplanet system TOI-431, characterized with photometry and radial velocities (RVs). We estimate the stellar rotation period to be 30.5 ± 0.7 d using archival photometry and RVs. Transiting Exoplanet Survey Satellite (TESS) objects of Interest (TOI)-431 b is a super-Earth with a period of 0.49 d, a radius of 1.28 ± 0.04 R⊕, a mass of 3.07 ± 0.35 M⊕, and a density of 8.0 ± 1.0 g cm−3; TOI-431 d is a sub-Neptune with a period of 12.46 d, a radius of 3.29 ± 0.09 R⊕, a mass of |$9.90^{+1.53}_{-1.49}$|  M⊕, and a density of 1.36 ± 0.25 g cm−3. We find a third planet, TOI-431 c, in the High Accuracy Radial velocity Planet Searcher RV data, but it is not seen to transit in the TESS light curves. It has an M sin  i of |$2.83^{+0.41}_{-0.34}$|  M⊕, and a period of 4.85 d. TOI-431 d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterization, while the super-Earth TOI-431 b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431 b is a prime TESS discovery for the study of rocky planet phase curves. [ABSTRACT FROM AUTHOR]

In order to accurately determine stellar properties, knowledge of the effective temperature of stars is vital. We implement Gaia and 2MASS photometry in the InfraRed Flux Method and apply it to over 360 000 stars across different evolutionary stages in the GALAH DR3 survey. We derive colour-effective temperature relations that take into account the effect of metallicity and surface gravity over the range |$4000\, \rm {K}\lesssim T_{\rm {eff}}\lesssim 8000\, \rm {K}$|⁠ , from very metal-poor stars to supersolar metallicities. The internal uncertainty of these calibrations is of order 40–80 K depending on the colour combination used. Comparison against solar-twins, Gaia benchmark stars, and the latest interferometric measurements validates the precision and accuracy of these calibrations from F to early M spectral types. We assess the impact of various sources of uncertainties, including the assumed extinction law, and provide guidelines to use our relations. Robust solar colours are also derived. [ABSTRACT FROM AUTHOR]

We report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright (V  = 8.75 mag, K  = 7.15 mag) solar twin HD 183579, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located 56.8 ± 0.1 pc away with a radius of R * = 0.97 ± 0.02  R ⊙ and a mass of M * = 1.03 ± 0.05  M ⊙. We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of R p = 3.53 ± 0.13  R ⊕ on a 17.47 d orbit with a mass of M p = 11.2 ± 5.4  M ⊕ (3σ mass upper limit of 27.4  M ⊕). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high-resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion. [ABSTRACT FROM AUTHOR]

An unprecedented number of exoplanets are being discovered by the Transiting Exoplanet Survey Satellite (TESS). Determining the orbital parameters of these exoplanets, and especially their mass and radius, will depend heavily upon the measured physical characteristics of their host stars. We have cross-matched spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the TESS Input Catalog and Gaia Data Release 2, to create a curated, self-consistent catalogue of physical and chemical properties for 47 285 stars. Using these data, we have derived isochrone masses and radii that are precise to within 5 per cent. We have revised the parameters of three confirmed, and twelve candidate, TESS planetary systems. These results cast doubt on whether CTOI-20125677 is indeed a planetary system, since the revised planetary radii are now comparable to stellar sizes. Our GALAH– TESS catalogue contains abundances for up to 23 elements. We have specifically analysed the molar ratios for C/O, Mg/Si, Fe/Si, and Fe/Mg, to assist in determining the composition and structure of planets with Rp < 4R⊕. From these ratios, 36 per cent fall within 2 |$\sigma$| sigma of the Sun/Earth values, suggesting that these stars may host rocky exoplanets with geological compositions similar to planets found within our own Solar system. [ABSTRACT FROM AUTHOR]

We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva -Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP  = 0.138 ± 0.023  |$\rm {M_J}$| (43.9 ± 7.3  |$\, M_{\rm \oplus}$|⁠), a radius of RP  = 0.639 ± 0.013  |$\rm {R_J}$| (7.16 ± 0.15  |$\, \mathrm{ R}_{\rm \oplus}$|⁠), bulk density of |$0.65^{+0.12}_{-0.11}$| (cgs), and period |$18.38818^{+0.00085}_{-0.00084}$|   |$\rm {days}$|⁠. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M * = 1.390 ± 0.046  |$\rm {M_{sun}}$|⁠ , R * = 1.888 ± 0.033  |$\rm {R_{sun}}$|⁠ , T eff = 6075 ± 90  |$\rm {K}$|⁠ , and v sin  i  = 11.3 ± 0.5 km s−1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems. [ABSTRACT FROM AUTHOR]

Accurate and precise radius estimates of transiting exoplanets are critical for understanding their compositions and formation mechanisms. To know the planet, we must know the host star in as much detail as possible. We present complete results for planet-candidate hosts from the K2-HERMES survey, which uses the HERMES multi-object spectrograph on the Anglo-Australian Telescope to obtain |$R\sim 28\, 000$| spectra for more than 30 000 K2 stars. We present complete host-star parameters and planet-candidate radii for 224 K2 candidate planets from C1–C13. Our results cast severe doubt on 30 K2 candidates, as we derive unphysically large radii, larger than 2 R Jup. This work highlights the importance of obtaining accurate, precise, and self-consistent stellar parameters for ongoing large planet search programs – something that will only become more important in the coming years, as TESS begins to deliver its own harvest of exoplanets. [ABSTRACT FROM AUTHOR]

Our understanding of planetary systems different to our own has grown dramatically in the past 30 yr. 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 18-yr archive of data from the Anglo-Australian Planet Search to examine the abundance of 'cool Jupiters' – analogues to the Solar system's 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 |$6.73^{+2.09}_{-1.13}$|  per cent, almost an order of magnitude higher than the occurrence of hot Jupiters (at |$0.84^{+0.70}_{-0.20}$|  per cent). We also find that the occurrence rate of giant planets is essentially constant beyond orbital distances of ∼1 au. Our results reinforce the importance of legacy radial velocity surveys for the understanding of the Solar system's place in the cosmos. [ABSTRACT FROM AUTHOR]

Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here, we present the final data release of the Pan-Pacific Planet Search (PPPS), a 5 yr radial velocity survey using the 3.9 m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight 6 potential substellar-mass companions, which require additional observations to confirm. Correcting for the substantial incompleteness in the sample, we estimate the occurrence rate of giant planets orbiting low-luminosity giant stars to be approximately 7.8 |$^{+9.1}_{-3.3}$|  per cent. This result is consistent with the frequency of such planets found to orbit main-sequence A-type stars, from which the PPPS stars have evolved. [ABSTRACT FROM AUTHOR]

We examine eight known single-eccentric planetary systems in light of recently released large data archives and new analysis techniques. For four of these systems (HD 7449, HD 65216, HD 89744, HD 92788) we find evidence for additional long-period companions. HD 65216c is a Jupiter analogue, with a period of 14.7 yr, e  = 0.18, and m sin i of 2 M Jup, while the remaining candidate companions move on as-yet-incomplete orbits. Our results highlight the importance of revisiting the analysis of known exoplanetary systems when new data become available, particularly given the possibility that poorly sampled data might previously have led to the detection of a 'false-positive' single-eccentric planet, when the system in question actually contains two (or more) planets on near-circular orbits. [ABSTRACT FROM AUTHOR]

When, in the course of searching for exoplanets, sparse sampling and noisy data make it necessary to disentangle possible solutions to the observations, one must consider the possibility that what appears to be a single eccentric Keplerian signal may in reality be attributed to two planets in near-circular orbits. There is precedent in the literature for such outcomes, whereby further data or new analysis techniques reveal hitherto occulted signals. Here, we perform suites of simulations to explore the range of possible two-planet configurations that can result in such confusion. We find that a single Keplerian orbit with e ≳ 0.5 can virtually never be mimicked by such deceptive system architectures. This result adds credibility to the most eccentric planets that have been found to date, and suggests that it could well be worth revisiting the catalogue of moderately eccentric 'confirmed' exoplanets in the coming years, as more data become available, to determine whether any such deceptive couplets are hidden in the observational data. [ABSTRACT FROM AUTHOR]

We present an analysis of the relative throughputs of the 3.9-m Anglo-Australian Telescope's 2dF/HERMES (High Efficiency and Resolution Multi-Element Spectrograph) system, based upon spectra acquired during the first two years of the Galactic Archaeology with HERMES survey. Averaged spectral fluxes of stars were compared to their photometry to determine the relative throughputs of fibres for a range of fibre position and atmospheric conditions. We find that overall the throughputs of the 771 usable fibres have been stable over the first two years of its operation. About 2.5 per cent of fibres have throughputs much lower than the average. There are also a number of yet unexplained variations between the HERMES bandpasses, and mechanically and optically linked fibre groups known as retractors or slitlets related to regions of the focal plane. These findings do not impact the science that HERMES will produce. [ABSTRACT FROM AUTHOR]

Context. Recently, using the light-travel time effect, planets and substellar companions have been proposed to orbit around binary star systems (also known as circumbinary companions) as a result of variations in timing of the observed eclipses. For the majority of these systems the proposed orbital architecture features a crossing of the orbital configurations as a result of high eccentricities for one or both of the companions. For such systems, strong mutual gravitational interactions are expected, resulting in catastrophic orbital instabilities, or collisions between the proposed components, on very short timescales. Aims. We re-examine the primary and secondary eclipse timings of the short-period and semi-detached binary RZ Draconis (RZ Dra). The proposed companions were reported to have masses of around ≃0.07 and ≃0.18 M⊙ with the inner companion on an orbit with moderate eccentricity (0.46), whose apocenter distance crosses the orbit of the outer companion. We show that the companions proposed previously follow highly unstable orbits. In an attempt to find a stable system we searched the underlying χ2 parameter space for a best-fit model and carried out an orbit-stability study to test possible best-fit models. If the binary period changes are truly due to additional massive companions in a hierarchical configuration, they must follow stable orbits. Methods. For numerical orbital stability calculations we used well established orbit integration routines. Computations were carried out using a large-scale multi-CPU computing environment. Our data analysis of times of primary and secondary eclipse is based on the Levenberg-Marquardt least-squares minimization algorithm using the two-body Keplerian light-travel time effect model. Results. Despite the wide variety of potential models tested for the RZ Dra system in this work, we found very few models that were stable for even one million years, with the vast majority of systems tested falling apart on timescales of just hundreds of years. It seems therefore likely that the observed timing variations are not solely the result of massive, unseen companions. [ABSTRACT FROM AUTHOR]

We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical (interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40° and 60°, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90° provides the best combination of goodness-of-fit and long-term dynamical stability. [ABSTRACT FROM AUTHOR]

We present a detailed dynamical analysis of the orbital stability of the two circumbinary planets recently proposed to orbit the evolved eclipsing binary star system NSVS 14256825. As is the case for other recently proposed circumbinary planetary systems detected through the timing of mutual eclipses between the central binary stars, the proposed planets do not stand up to dynamical scrutiny. The proposed orbits for the two planets are extremely unstable on time-scales of less than a thousand years, regardless of the mutual inclination between the planetary orbits.For the scenario where the planetary orbits are coplanar, a small region of moderate stability was observed, featuring orbits that were somewhat protected from destabilization by the influence of mutual 2:1 mean-motion resonance between the orbits of the planets. Even in this stable region, however, the systems tested typically only survived on time-scales of the order of 1 Myr, far shorter than the age of the system.Our results suggest that if there are planets in the NSVS 14256825 system, they must move on orbits dramatically different to those proposed in the discovery work. More observations are clearly critically required in order to constrain the nature of the suggested orbital bodies. [ABSTRACT FROM AUTHOR]

We review the possible formation and orbital stability of Earth-mass or super Earth-mass planets around either of the stars Alpha Centauri A or B and describe a program at Mt John University Observatory using the Doppler method that aims to detect such planets. From New Zealand, we are able to observe the Alpha Centauri system year-round. This is critical in order to acquire data of sufficient quantity and phase coverage to detect the orbit of a terrestrial-mass planet in the habitable zone. Our observations are being made at high resolution (R = 70,000) and high signal-to-noise with the Hercules vacuum echelle spectrograph attached to the 1-m McLellan telescope by a 25-m long optical fibre and using an iodine cell. We discuss the velocity precision and instrumental stability required for success and outline the progress of the observations so far. At present we are collecting about 10,000 observations of each star, A and B, per year with a typical precision of 2.5 m/s per observation. [ABSTRACT FROM PUBLISHER]

We present high-precision radial velocity (RV) observations of four solar-type (F7-G5) stars--HD 79498, HD 155358, HD 197037, and HD 220773--taken as part of the McDonald Observatory Planet Search Program. For each of these stars, we see evidence of Keplerian motion caused by the presence of one or more gas giant planets in long-period orbits. We derive orbital parameters for each system and note the properties (composition, activity, etc.) of the host stars. While we have previously announced the two-gas-giant HD 155358 system, we now report a shorter period for planet c. This new period is consistent with the planets being trapped in mutual 2:1 mean-motion resonance. We therefore perform an in-depth stability analysis, placing additional constraints on the orbital parameters of the planets. These results demonstrate the excellent long-term RV stability of the spectrometers on both the Harlan J. Smith 2.7 m telescope and the Hobby-Eberly telescope. [ABSTRACT FROM AUTHOR]

ABSTRACT It has recently been proposed, on the basis of eclipse-timing data, that the eclipsing polar cataclysmic variable HU Aquarii is host to at least two giant planets. However, that result has been called into question based upon the dynamical stability of the proposed planets. In this work, we present a detailed re-analysis of all eclipse-timing data available for the HU Aquarii system, making use of standard techniques used to fit orbits to radial-velocity data. We find that the eclipse timings can be used to obtain a two-planet solution that does not require the presence of additional bodies within the system. We then perform a highly detailed dynamical analysis of the proposed planetary system. We show that the improved orbital parameters we have derived correspond to planets that are dynamically unstable on unfeasibly short time-scales (of the order of 104 yr or less). Given these results, we discuss briefly how the observed signal might in fact be the result of the intrinsic properties of the eclipsing polar, rather than being evidence of dynamically improbable planets. Taken in concert, our results highlight the need for caution in interpreting such timing variations as being planetary in nature. [ABSTRACT FROM AUTHOR]

We measure a tilt of 86° ± 6° between the sky projections of the rotation axis of the WASP-7 star and the orbital axis of its close-in giant planet. This measurement is based on observations of the Rossiter--McLaughlin (RM) effect with the Planet Finder Spectrograph on the Magellan II telescope. The result conforms with the previously noted pattern among hot-Jupiter hosts, namely, that the hosts lacking thick convective envelopes have high obliquities. Because the planet's trajectory crosses a wide range of stellar latitudes, observations of the RM effect can in principle reveal the stellar differential rotation profile; however, with the present data the signal of differential rotation could not be detected. The host star is found to exhibit radial-velocity noise ("stellar jitter") with an amplitude of ≈30 m s-1 over a timescale of days. [ABSTRACT FROM AUTHOR]

We introduce the Pan-Pacific Planet Search, a survey of 170 metal-rich Southern Hemisphere subgiants using the 3.9 m Anglo-Australian Telescope. We report the first discovery from this program, a giant planet orbiting 7 CMa (HD 47205) with a period of 763 ± 17 days, eccentricity e = 0.14 ± 0.06, and m sin i = 2.6 ± 0.6 Mjup. The host star is a K giant with a mass of 1.5 ± 0.3 M⊙ and metallicity [Fe/H] = 0.21 ± 0.10. The mass and period of 7 CMa b are typical of planets which have been found to orbit intermediate-mass stars (M* > 1.3 M⊙). Hipparcos photometry shows this star to be stable to 0.0004 mag on the radial-velocity period, giving confidence that this signal can be attributed to reflex motion caused by an orbiting planet. [ABSTRACT FROM AUTHOR]

Determining the occurrence rate of "super-Earth" planets (m sin i < 10 M⊕) is a critically important step on the path toward determining the frequency of Earth-like planets (η⊕), and hence the uniqueness of our solar system. Current radial-velocity surveys, achieving precisions of 1 m s-1, are now able to detect super-Earths and provide meaningful estimates of their occurrence rate. We present an analysis of 67 solar-type stars from the Anglo-Australian Planet Search specifically targeted for very high precision observations. When corrected for incompleteness, we find that the planet occurrence rate increases sharply with decreasing planetary mass. Our results are consistent with those from other surveys: in periods shorter than 50days, we find that 3.0% of stars host a giant (msin; > 100 M⊕) planet, and that 17.4% of stars host a planet with msin/ < 10 Me. The preponderance of low-mass planets in short-period orbits is in conflict with formation simulations in which the majority of super-Earths reside at larger orbital distances. This work gives a hint as to the size of η⊕, but to make meaningful predictions on the frequency of terrestrial planets in longer, potentially habitable orbits, low-mass terrestrial planet searches at periods of 100-200 days must be made an urgent priority for ground-based Doppler planet searches in the years ahead. [ABSTRACT FROM AUTHOR]

ABSTRACT It has recently been suggested that the eclipsing polar HU Aquarii is a host to at least two giant planets. We have performed highly detailed dynamical analyses of the orbits of those planets and showed that the proposed system is highly unstable on time-scales of <5 × 103 yr. For the coplanar orbits suggested in the discovery Letter, we find stable orbital solutions for the planetary system only if the outer body moves on an orbit that brings it no closer to the host star than ∼6 au. The required periastron distance for the outer planet lies approximately 5 Hill radii beyond the orbit of the inner planet, and well beyond the 1σ error bars placed on the orbit of the outer planet in the discovery Letter. If the orbits of the proposed planets are significantly inclined with respect to one another, the median stability increases slightly, but such systems still become destabilized on astronomically minute time-scales (typically within a few 104 yr). Only in the highly improbable scenario where the outer planet follows a retrograde but coplanar orbit (i.e. inclined by 180° to the orbit of the inner planet) is there any significant region of stability within the original 1σ orbital uncertainties. Our results suggest that, if there is a second (and potentially, a third planet) in the HU Aquarii system, its orbit is dramatically different from that suggested in the discovery Letter, and that more observations are critically required in order to constrain the nature of the suggested orbital bodies. [ABSTRACT FROM AUTHOR]