Frequency of planets orbiting M dwarfs in the Solar neighbourhood
M. Tuomi, H. R. A. Jones, R. P. Butler, P. Arriagada, S. S. Vogt, J. Burt, G. Laughlin, B. Holden, S. A. Shectman, J. D. Crane, I. Thompson, S. Keiser, J. S. Je… 展开作者
M. Tuomi, H. R. A. Jones, R. P. Butler, P. Arriagada, S. S. Vogt, J. Burt, G. Laughlin, B. Holden, S. A. Shectman, J. D. Crane, I. Thompson, S. Keiser, J. S. Jenkins, Z. Berdiñas, M. Diaz, M. Kiraga, J. R. Barnes
备注：
Manuscript submitted to AAS journals. 338 pages, including 66 pages of tables summarising data properties, target properties, and selected parameter estimates
The most abundant stars in the Galaxy, M dwarfs, are very commonly hosts to diverse systems of low-mass planets. Their abundancy implies that the general occurrence rate of planets is dominated by their occurrence rate around such M dwarfs. In this article, we combine the M dwarf surveys conducted with the HIRES/Keck, PFS/Magellan, HARPS/ESO, and UVES/VLT instruments supported with data from several other instruments. We analyse the radial velocities of an approximately volume- and brightness-limited sample of 426 nearby M dwarfs in order to search for Doppler signals of cadidate planets. In addition, we analyse spectroscopic activity indicators and ASAS photometry to rule out radial velocity signals corresponding to stellar activity as Doppler signals of planets. We calculate estimates for the occurrence rate of planets around the sample stars and study the properties of this occurrence rate as a function of stellar properties. Our analyses reveal a total of 118 candidate planets orbiting nearby M dwarfs. Based on our results accounting for selection effects and sample detection threshold, we estimate that M dwarfs have on average at least 2.39$^{+4.58}_{-1.36}$ planets per star orbiting them. Accounting for the different sensitivities of radial velocity surveys and Kepler transit photometry implies that there are at least 3.0 planets per star orbiting M dwarfs. We also present evidence for a population of cool mini-Neptunes and Neptunes with indications that they are found an order of magnitude more frequently orbiting the least massive M dwarfs in our sample.
We report the discovery of planets orbiting two bright, nearby early K dwarf stars, HD 97658 and Gl 785. These planets were detected by Keplerian modelling of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth with minimum mass Msini = 8.2 +/- 1.2 M_Earth, orbital period P = 9.494 +/- 0.005 d, and an orbit that is consistent with circular. Gl 785 b is a Neptune-mass planet with Msini = 21.6 +/- 2.0 M_Earth, P = 74.39 +/- 0.12 d, and orbital eccentricity 0.30 +/- 0.09. Photometric observations with the T12 0.8 m automatic photometri…
We introduce the Pan-Pacific Planet Search, a survey of 170 metal-rich Southern hemisphere subgiants using the 3.9m 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 M_jup. The host star is a K giant with a mass of 1.5+/-0.3 M_sun 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_sun). Hipparcos photometry shows this star to be stable to 0.000…
Gas giants orbiting interior to the ice line are thought to have been displaced from their formation locations by processes that remain debated. Here we uncover several new metallicity trends, which together may indicate that two competing mechanisms deliver close-in giant planets: gentle disk migration, operating in environments with a range of metallicities, and violent planet-planet gravitational interactions, primarily triggered in metal-rich systems in which multiple giant planets can form. First, we show with 99.1% confidence that giant planets with semi-major axes between 0.1 and 1 AU o…
An Earth-like exoplanet orbiting a white dwarf would be exposed to different UV environments than Earth, influencing both its atmospheric photochemistry and UV surface environment. Using a coupled 1D climate-photochemistry code we model atmospheres of Earth-like planets in the habitable zone of white dwarfs for surface temperatures between 6000 K and 4000 K, corresponding to about 7 billion years of white dwarf evolution, as well as discuss the evolution of planetary models in the habitable zone during that evolution.
Debris discs are commonly detected orbiting main-sequence stars, yet little is known regarding their fate as the star evolves to become a giant. Recent observations of radial velocity detected planets orbiting giant stars highlight this population and its importance for probing, for example, the population of planetary systems orbiting intermediate mass stars. Our Herschel survey observed a subset of the Johnson et al program subgiants, finding that 4/36 exhibit excess emission thought to indicate debris, of which 3/19 are planet-hosting stars and 1/17 are stars with no current planet detectio…
Initially designed to discover short-period planets, the N2K campaign has since evolved to discover new worlds at large separations from their host stars. Detecting such worlds will help determine the giant planet occurrence at semi-major axes beyond the ice line, where gas giants are thought to mostly form. Here we report four newly-discovered gas giant planets (with minimum masses ranging from 0.4 to 2.1 MJup) orbiting stars monitored as part of the N2K program. Two of these planets orbit stars already known to host planets: HD 5319 and HD 11506. The remaining discoveries reside in previousl…
Tidal force plays an important role in the evolution of the planet-moon system. The tidal force of a moon can excite seismic waves in the planet it is orbiting. A tidal-seismic resonance is expected when a tidal force frequency matches a free-oscillation frequency of the planet. Here we show that when the moon is close to the planet, the tidal-seismic resonance can cause large-amplitude seismic waves, which can change the shape of the planet and in turn exert a negative torque on the moon to cause it to fall rapidly toward the planet. We postulate that the tidal-seismic resonance may be an imp…
Radial velocity observations from three instruments reveal the presence of a 4 M_jup planet candidate orbiting the K giant HD 76920. HD 76920b has an orbital eccentricity of 0.856$\pm$0.009, making it the most eccentric planet known to orbit an evolved star. There is no indication that HD 76920 has an unseen binary companion, suggesting a scattering event rather than Kozai oscillations as a probable culprit for the observed eccentricity. The candidate planet currently approaches to about four stellar radii from its host star, and is predicted to be engulfed on a $\sim$100 Myr timescale due to …
In current theories of planet formation, close-orbiting planets as massive as Neptune are expected to be very rare around low-mass stars. We report the discovery of a Neptune-mass planet orbiting the `ultracool' star LHS 3154, which is nine times less massive than the Sun. The planet's orbital period is 3.7 days and its minimum mass is 13.2 Earth masses, giving it the largest known planet-to-star mass ratio among short-period planets ($<$\,100 days) orbiting ultracool stars. Both the core accretion and gravitational instability theories for planet formation struggle to account for this system.…
We report the detection of two new planets orbiting the K giants HD 86950 and HD 222076, based on precise radial velocities obtained with three instruments: AAT/UCLES, FEROS, and CHIRON. HD 86950b has a period of 1270$\pm$57 days at $a=2.72\pm$0.08 AU, and m sin $i=3.6\pm$0.7 Mjup. HD 222076b has $P=871\pm$19 days at $a=1.83\pm$0.03 AU, and m sin $i=1.56\pm$0.11 Mjup. These two giant planets are typical of the population of planets known to orbit evolved stars. In addition, we find a high-amplitude periodic velocity signal ($K\sim$50 m/s) in HD 29399, and show that it is due to stellar variabi…
Planets are known to orbit giant stars, yet there is a shortage of planets orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded enough to engulf such planets, but tidal forces can bring planets to the surface of the star far beyond the stellar radius. So the question remains: are tidal forces strong enough in these stars to engulf all the missing planets? We describe a high-cadence observational program to obtain precise radial velocities of bright giants from Weihai Observatory of Shandong University. We present data on the planet host Beta Gem (HD 62509), confirming ou…
We report a new giant planet orbiting the K giant HD 155233, as well as four stellar-mass companions from the Pan-Pacific Planet Search, a southern hemisphere radial velocity survey for planets orbiting nearby giants and subgiants. We also present updated velocities and a refined orbit for HD 47205b (7 CMa b), the first planet discovered by this survey. HD 155233b has a period of 885$\pm$63 days, eccentricity e=0.03$\pm$0.20, and m sin i=2.0$\pm$0.5 M_jup. The stellar-mass companions range in m sin i from 0.066 M_sun to 0.33 M_sun. Whilst HD 104358B falls slightly below the traditional 0.08 M_…
The First Dedicated Survey of Atmospheric Escape from Planets Orbiting F Stars
California Institute of Technology（加州理工学院）；Carnegie Science Observatories（卡内基科学天文台）；University of California, Santa Cruz（加州大学圣克鲁斯分校）；Earth and Planets Laboratory, Carnegie Institution for Science（卡内基科学研究所地球与行星实验室）；University of California, Los Angeles（加州大学洛杉矶分校）；Yale University（耶鲁大学）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究所）
In this paper, we report the evidence for a planetary mass body orbiting the close binary star KIC 5095269. This detection arose from a search for eclipse timing variations among the more than 2,000 eclipsing binaries observed by Kepler. Light curve and periodic eclipse time variations have been analysed using Systemic and a custom Binary Eclipse Timings code based on the Transit Analysis Package which indicates a $7.70\pm0.08M_{Jup}$ object orbiting every $237.7\pm0.1d$ around a $1.2M_\odot$ primary and $0.51M_\odot$ secondary in an 18.6d orbit. A dynamical integration over $10^7$ years sugge…
The recent detections of temperate terrestrial planets orbiting nearby stars and the promise of characterizing their atmospheres motivates a need to understand how the diversity of possible planetary parameters affects the climate of terrestrial planets. In this work, we investigate the atmospheric circulation and climate of terrestrial exoplanets orbiting both Sun-like and M-dwarf stars over a wide swath of possible planetary parameters, including the planetary rotation period, surface pressure, incident stellar flux, surface gravity, planetary radius, and cloud particle size. We do so using …
Several planets have been found that orbit their host star on retrograde orbits (spin-orbit angle ϕ > 90°). Currently, the largest measured projected angle between the orbital angular momentum axis of a planet and the rotation axis of its host star has been found for HAT-P-14b to be $\approx$ 171°. One possible mechanism for the formation of such misalignments is through long-term interactions between the planet and other planetary or stellar companions. However, with this process, it has been found to be difficult to achieve retrogradely orbiting planets, especially planets that almost exactl…
The photometric and spectroscopic signatures of habitable planets orbiting FGK stars may be modulated by surface ice coverage. To estimate its frequency and locations, we simulated the climates of hypothetical planets with a 1D energy balance model and assumed that the planets possess properties similar to modern Earth (mass, geography, atmosphere). We first simulated planets with fixed rotational axes and circular orbits, finding that the vast majority (>90%) of planets with habitable surfaces are free of ice. For planets with partial ice coverage, the parameter space for ice caps (interannua…
Exoplanet surveys around M dwarfs have detected a growing number of exoplanets with Earth-like insolation. It is expected that some of those planets are rocky planets with the potential for temperate climates favourable to surface liquid water. However, various models predict that terrestrial planets orbiting in the classical habitable zone around M dwarfs have no water or too much water, suggesting that habitable planets around M dwarfs might be rare. Here we present the results of an updated planetary population synthesis model, which includes the effects of water enrichment in the primordia…
Among a hundred transiting planets with a measured projected spin-orbit angle λ, several systems are suggested to be counter-orbiting. While they may be due to the projection effect, the mechanism to produce a counter-orbiting planet is not established. A promising scenario for the counter-orbiting planets is the extreme eccentricity evolution in near-coplanar hierarchical triple systems with eccentric inner and outer or- bits. We examine this scenario in detail by performing a series of systematic numerical simulations, and consider the possibility of forming hot Jupiters, especially counter-…
We use archival HARPS spectra to detect three planets orbiting the M3 dwarf Wolf1061 (GJ 628). We detect a 1.36 Mearth minimum-mass planet with an orbital period P = 4.888d (Wolf1061b), a 4.25 Mearth minimum-mass planet with orbital period P = 17.867d (Wolf1061c), and a likely 5.21 Mearth minimum-mass planet with orbital period P = 67.274d (Wolf1061d). All of the planets are of sufficiently low mass that they may be rocky in nature. The 17.867d planet falls within the habitable zone for Wolf 1061 and the 67.274d planet falls just outside the outer boundary of the habitable zone. There are no s…
The co-planarity of solar-system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the Kepler satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. We report here the discovery of an intermediate system OGLE-2013-BLG-0723LB/Bb composed of a Venus-mass planet orbiting a brown dwarf, which may…
We report the discovery of two giant planets orbiting the K giant HD 33844 based on radial velocity data from three independent campaigns. The planets move on nearly circular orbits with semimajor axes $a_b=1.60\pm$0.02 AU and $a_c=2.24\pm$0.05 AU, and have minimum masses (m sin $i$) of $M_b=1.96\pm$0.12 Mjup and $M_c=1.76\pm$0.18 Mjup. Detailed N-body dynamical simulations show that the two planets remain on stable orbits for more than $10^6$ years for low eccentricities, and are most likely trapped in a mutual 3:5 mean-motion resonance.
We report the discovery of an extrasolar planet, KMT-2015-1b, that was detected using the microlensing technique. The planetary lensing event was observed by KMTNet survey that has commenced in 2015. With dense coverage by using network of globally distributed telescopes equipped with very wide-field cameras, the short planetary signal is clearly detected and precisely characterized. We find that KMT-2015-1b is a giant planet orbiting a low-mass M-dwarf host star. The planet has a mass about twice that of Jupiter and it is located beyond the snow line of the host star. With the improvement of …
CONTEXT: The recent discovery of three giant planets orbiting the extremely metal-poor stars HIP11952 and HIP13044 have challenged theoretical predictions of the core-accretion model. According to this, the metal content of the protoplanetary disk from which giant planets are formed is a key ingredient for the early formation of planetesimals prior to the runaway accretion of the surrounding gas. AIMS: We reanalyzed the original FEROS data that were used to detect the planets to prove or refute their existence, employing our new reduction and analysis methods. METHOD: We applied the cross-corr…
The UV environment of a host star affects the photochemistry in the atmosphere, and ultimately the surface UV environment for terrestrial planets and therefore the conditions for the origin and evolution of life. We model the surface UV radiation environment for Earth-sized planets orbiting FGKM stars at the 1AU equivalent distance for Earth through its geological evolution. We explore four different types of atmospheres corresponding to an early Earth atmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to present day levels at 2.0 Gyr ago, 0.8 Gyr ago and modern Earth …
The phenomenon of microlensing has successfully been used to detect extrasolar planets. By observing characteristic, rare deviations in the gravitational microlensing light curve one can discover that a lens is a star--planet system. In this paper we consider an opposite case where the lens is a single star and the source has a transiting planetary companion. We have studied the light curve of a source star with transiting companion magnified during microlensing event. Our model shows that in dense stellar fields, in which blending is significant, the light drop generated by transits is greate…
We present precision radial velocity (RV) data sets from Keck-HIRES and from Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby, slightly evolved, K-type star HD 141399. Our 91 observations over 10.5 years suggest the presence of four planets with orbital periods of 94.35, 202.08, 1070.35, and 3717.35 days and minimum masses of 0.46, 1.36, 1.22, and 0.69 Jupiter masses respectively. The orbital eccentricities of the three inner planets are small, and the phase curves are well sampled. The inner…
We re-analyse the recently published HARPS and PFS velocities of the nearby K dwarf GJ 221 that have been reported to contain the signatures of two planets orbiting the star. Our goal is to see whether the earlier studies discussing the system fell victims of false negative detections. We perform the analyses by using an independent statistical method based on posterior samplings and model comparisons in the Bayesian framework that is known to be more sensitive to weak signals of low-mass planets. According to our analyses, we find strong evidence in favour of a third candidate planet in the s…
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 orb…
We present a systematic search for transiting giant planets ($0.6 R_{\rm J} \leq R_{\rm P} \leq 2.0 R_{\rm J}$) orbiting nearby low-mass stars ($M_{*} \leq 0.71 M_{\odot}$). The formation of giant planets around low-mass stars is predicted to be rare by the core-accretion planet formation theory. We search 91,306 low-mass stars in the TESS 30 minute cadence photometry detecting fifteen giant planet candidates, including seven new planet candidates which were not known planets or identified as TOIs prior to our search. Our candidates present an exciting opportunity to improve our knowledge of t…
Most of the known transiting exoplanets are in short-period orbits, largely due to the bias inherent in detecting planets through the transit technique. However, the eccentricity distribution of the known radial velocity planets results in many of those planets having a non-negligible transit probability. One such case is the massive planet orbiting the giant star iota Draconis, a situation where both the orientation of the planet's eccentric orbit and the size of the host star inflate the transit probability to a much higher value than for a typical hot Jupiter. Here we present a revised fit …
The requirement that a planet must orbit outside of its Roche limit gives a lower limit on the planet's mean density. The minimum density depends almost entirely on the orbital period and is immune to systematic errors in the stellar properties. We consider the implications of this density constraint for the newly-identified class of small planets with periods shorter than half a day. When the planet's radius is known accurately, this lower limit to the density can be used to restrict the possible combinations of iron and rock within the planet. Applied to KOI 1843.03, with a radius of 0.6 Ear…
Precision radial velocities from the Automated Planet Finder and Keck/HIRES reveal an M*sin(i) =18 +/- 2 Earth mass planet orbiting the nearby M3V star GJ 687. This planet has an orbital period, P = 38.14 days, and a low orbital eccentricity. Our Stromgren b and y photometry of the host star suggests a stellar rotation signature with a period of P = 60 days. The star is somewhat chromospherically active, with a spot filling factor estimated to be several percent. The rotationally{induced 60-day signal, however, is well-separated from the period of the radial velocity variations, instilling co…
Terrestrial planets are more likely to be detected if they orbit M dwarfs due to the favorable planet/star size and mass ratios. However, M dwarf habitable zones are significantly closer to the star than the one around our Sun, which leads to different requirements for planetary habitability and its detection. We review 1) the current limits to detection, 2) the role of M dwarf spectral energy distributions on atmospheric chemistry, 3) tidal effects, stressing that tidal locking is not synonymous with synchronous rotation, 4) the role of atmospheric mass loss and propose that some habitable wo…
Potentially-habitable planets orbiting M-dwarfs are of intense astrobiological interest because they are the only rocky worlds accessible to biosignature search over the next 10+ years due to a confluence of observational effects. Simultaneously, recent experimental and theoretical work suggests that UV light may have played a key role in the origin of life on Earth, and especially the origin of RNA. Characterizing the UV environment on M-dwarfs planets is important to understanding whether life as we know it could emerge on such worlds. In this work, we couple radiative transfer models to obs…
The vast majority of known extrasolar planets orbit stars with a narrow range of masses (0.7-1.3 M_sun). Recent years have seen rapid growth in our knowledge about the properties of planetary systems with host stars significantly more massive than the Sun. Planet formation models predict that giant planets are more common around higher-mass stars (M>1.5M_sun). However, these types of stars pose severe observational challenges while on the main sequence, resulting in a strong bias against them in current planet searches. Fortunately, it is possible to obtain high-precision Doppler velocities fo…
High-contrast near-infrared imaging of the nearby star HR 8799 has shown three giant planets. Such images were possible due to the wide orbits (> 25 AU) and youth (< 100 Myr) of the imaged planets, which are still hot and bright as they radiate away gravitational energy acquired during their formation. A major area of contention in the extrasolar planet community is whether outer planets (> 10 AU) more massive than Jupiter form via one-step gravitational instabilities or, rather, via a two-step process involving accretion of a core followed by accumulation of a massive outer envelope composed …
The NASA Kepler and K2 Missions have recently revealed a population of transiting giant planets orbiting moderately evolved, low-luminosity red giant branch stars. Here, we present radial velocity measurements of three of these systems, revealing significantly non-zero orbital eccentricities in each case. Comparing these systems with the known planet population suggests that close-in giant planets around evolved stars tend to have more eccentric orbits than those around main-sequence stars. We interpret this as tentative evidence that the orbits of these planets pass through a transient, moder…
We aim to detect and characterize substellar companions to K giant stars, to further our knowledge of planet formation and stellar evolution of intermediate-mass stars. For more than a decade we have used Doppler spectroscopy to acquire high precision radial velocity measurements of K giant stars. All data for this survey have been taken at Lick Observatory. Our survey includes 373 G and K giants. Radial velocity data showing periodic variations are fitted with Keplerian orbits using a chi^2 minimization technique. We report the presence of two substellar companions to the K giant stars tau Ge…
We report on the validation of two planets orbiting the nearby (36pc) M2 dwarf TOI-1266 observed by the TESS mission. The inner planet is sub-Neptune-sized ($R=2.46 \pm 0.08 R_\oplus$) with an orbital period of 10.9 days. The outer planet has a radius of $1.67_{-0.11}^{+0.09} R_\oplus$ and resides in the exoplanet Radius Valley---the transition region between rocky and gaseous planets. With an orbital period of 18.8 days, the outer planet receives an insolation flux of 2.4 times that of Earth, similar to the insolation of Venus. Using precision near-infrared radial velocities with the Habitabl…
We investigate the formation of close-in planets in near-coplanar eccentric hierarchical triple systems via the secular interaction between an inner planet and an outer perturber (Coplanar High-eccentricity Migration, CHEM). We generalize the previous work on the analytical condition for successful CHEM for point masses interacting only through gravity by taking into account the finite mass effect of the inner planet. We find that efficient CHEM requires that the systems should have m_1<<m_0 and m_1<<m_2. In addition to the gravity for point masses, we examine the importance of the short-range…
The habitable zone is the region around a star where standing bodies of liquid water can be stable on a planetary surface. Its width is often assumed to be dictated by the efficiency of the carbonate-silicate cycle, which has maintained habitable surface conditions on our planet for billions of years. This cycle may be inhibited by surface condensation of significant amounts of $CO_{\mathrm{2}}$ ice, which is likely to occur on distant planets containing high enough levels of atmospheric $CO_{\mathrm{2}}$. Such a process could permanently trap $CO_{\mathrm{2}}$ ice within the planet, threateni…
The N2K planet search program was designed to exploit the planet-metallicity correlation by searching for gas giant planets orbiting metal-rich stars. Here, we present the radial velocity measurements for 378 N2K target stars that were observed with the HIRES spectrograph at Keck Observatory between 2004 and 2017. With this data set, we announce the discovery of six new gas giant exoplanets: a double-planet system orbiting HD 148164 ($M \sin i$ of 1.23 and 5.16 M$_{\rm JUP}$) and single planet detections around HD 55696 ($M \sin i$ = 3.87 M$_{\rm JUP}$), HD 98736 ($M \sin i$ = 2.33 M$_{\rm JUP…
A scatter plot of exoplanet mass against red giant host star radius demonstrates an interesting positive trend: larger stars have more massive planets. This implies that the evolution of a star towards a red giant affects the masses of planets in the system.
Doppler observations from Keck Observatory have revealed a triple planet system orbiting the nearby mid-type K dwarf, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with \msini\ = 11.6 \mearth (0.036 \mjup), an orbital period of 8.135 $\pm$ 0.004 d, and slightly eccentric orbit $e=0.19 \pm 0.1$. We calculate a transit probability of 6.5% for the inner planet. The second planet has \msini\ = 0.4 \mjup\ with an orbital period of 32.0 $\pm 0.02$ d in a nearly circular orbit, and $e = 0.05 \pm 0.03$. The third planet has \msini\ = 0.53 \mjup\ with an orbital period of 432 $\pm 8$ d (1.1…
The Large Synoptic Survey Telescope (LSST) will photometrically monitor approximately 1 billion stars for ten years. The resulting light curves can be used to detect transiting exoplanets. In particular, as demonstrated by Lund et al. (2015), LSST will probe stellar populations currently undersampled in most exoplanet transit surveys, including out to extragalactic distances. In this paper we test the efficiency of the box-fitting least-squares (BLS) algorithm for accurately recovering the periods of transiting exoplanets using simulated LSST data. We model planets with a range of radii orbiti…
We report the discovery of an extrasolar planet detected from the combined data of a microlensing event OGLE-2015-BLG-0051/KMT-2015-BLG-0048 acquired by two microlensing surveys. Despite that the short planetary signal occurred in the very early Bulge season during which the lensing event could be seen for just about an hour, the signal was continuously and densely covered. From the Bayesian analysis using models of the mass function, matter and velocity distributions combined with the information of the angular Einstein radius, it is found that the host of the planet is located in the Galacti…
We present the discovery of three modestly-irradiated, roughly Neptune-mass planets orbiting three nearby Solar-type stars. HD 42618 b has a minimum mass of $15.4 \pm 2.4$ M$_{\oplus}$, a semi-major axis of 0.55 AU, an equilibrium temperature of 337 K, and is the first planet discovered to orbit the solar analogue host star, HD 42618. We also discover new planets orbiting the known exoplanet host stars HD 164922 and HD 143761 ($ρ$ CrB). The new planet orbiting HD 164922 has a minimum mass of $12.9 \pm 1.6$ M$_{\oplus}$ and orbits interior to the previously known Jovian mass planet orbiting at …
A free-floating planet is a planetary-mass object that orbits around a non-stellar massive object (e.g. a brown dwarf) or around the Galactic Center. The presence of exomoons orbiting free-floating planets has been theoretically predicted by several models. Under specific conditions, these moons are able to retain an atmosphere capable of ensuring the long-term thermal stability of liquid water on their surface. We model this environment with a one-dimensional radiative-convective code coupled to a gas-phase chemical network including cosmic rays and ion-neutral reactions. We find that, under …
Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed. The precise ages of meteorites indicate that planetesimals - the building blocks of planets - are produced within the first million years of a star's life. A prominent question is: how early can one find fully formed planets like those frequently detected on short orbital periods around mature stars? Some theories suggest the in situ formation of planets close to thei…
We characterize the occurrence rate of planets, ranging in size from 0.5-16 R$_\oplus$, orbiting FGK stars with orbital periods from 0.5-500 days. Our analysis is based on results from the "DR25" catalog of planet candidates produced by NASA's Kepler mission and stellar radii from Gaia "DR2". We incorporate additional Kepler data products to accurately characterize the efficiency of planets being recognized as a "threshold crossing events" (TCE) by Kepler's Transiting Planet Search pipeline and labeled as a planet candidate by the robovetter. Using a hierarchical Bayesian model, we derive plan…
Exoplanets smaller than Neptune are common around red dwarf stars (M dwarfs), with those that transit their host star constituting the bulk of known temperate worlds amenable for atmospheric characterization. We analyze the masses and radii of all known small transiting planets around M dwarfs, identifying three populations: rocky, water-rich, and gas-rich. Our results are inconsistent with the previously known bimodal radius distribution arising from atmospheric loss of a hydrogen/helium envelope. Instead, we propose that a density gap separates rocky from water-rich exoplanets. Formation mod…
In the near future we will have ground- and space-based telescopes that are designed to observe and characterize Earth-like planets. While attention is focused on exoplanets orbiting main sequence stars, more than 150 exoplanets have already been detected orbiting red giants, opening the intriguing question of what rocky worlds orbiting in the habitable zone of red giants would be like and how to characterize them. We model reflection and emission spectra of Earth-like planets orbiting in the habitable zone of red giant hosts with surface temperatures between 5200 and 3900 K at the Earth-equiv…
Kepler-91b is a rare example of a transiting hot Jupiter around a red giant star, providing the possibility to study the formation and composition of hot Jupiters under different conditions compared to main-sequence stars. However, the planetary nature of Kepler-91b, which was confirmed using phase-curve variations by Lillo-Box et al., was recently called into question based on a re-analysis of Kepler data. We have obtained ground-based radial velocity observations from the Hobby-Eberly Telescope and unambiguously confirm the planetary nature of Kepler-91b by simultaneously modeling the Kepler…
Temperate terrestrial planets orbiting low-mass stars are subject to strong tidal forces. The effects of gravitational tides on the solid planet and that of atmospheric thermal tides have been studied, but the direct impact of gravitational tides on the atmosphere itself has so far been ignored. We first develop a simplified analytic theory of tides acting on the atmosphere of a planet. We then implement gravitational tides into a general circulation model of a static-ocean planet in a short-period orbit around a low-mass star -- the results agree with our analytic theory. Because atmospheric …
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=9.7\pm$0.5 Mjup). HD 30177c can be regarded as a massive Saturn analog in this system, with a=9.9$\pm$1.0 au and m sin $i=7.6\pm$3.1 Mjup. The formal best fit solution slightly favours a closer-in planet at $a\sim$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 ad…
We report the discovery of the first low-mass planet to emerge from the NASA-UC Eta-Earth Program, a super-Earth orbiting the K0 dwarf HD 7924. Keplerian modeling of precise Doppler radial velocities reveals a planet with minimum mass M_P sin i = 9.26 M_Earth in a P = 5.398 d orbit. Based on Keck-HIRES measurements from 2001 to 2008, the planet is robustly detected with an estimated false alarm probability of less than 0.001. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 7924 is photometrically constant over the radial velocity period …
We report the detection of a giant planet orbiting a G-type giant star HD 167768 from radial velocity measurements using HIgh Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory (OAO). HD 167768 has a mass of $1.08_{-0.12}^{+0.14} M_{\odot}$, a radius of $9.70_{-0.25}^{+0.25} R_{\odot}$, a metallicity of $\rm{[Fe/H]}=-0.67_{-0.08}^{+0.09}$, and a surface gravity of $\log g = 2.50_{-0.06}^{+0.06}$. The planet orbiting the star is a warm Jupiter, having a period of $20.6532_{-0.0032}^{+0.0032}\ \rm{d}$, a minimum mass of $0.85_{-0.11}^{+0.12}\ M_{\rm{J}}$, and an orbital…
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 timescales of less than a thousand years, regardless of the mutual inclination between the planetary orbits. For the scenario where the pl…
We present high-precision relative radial velocities of the very low-mass star VB10 that were obtained over a time span of 0.61 yr as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the VLT with an ammonia gas cell. The typical internal precision of the measurements is 10 m/s. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect th…
