Giant Planet Companion Research Articles

Population of giant planets around B stars from the first part of the BEAST survey

Exoplanets form from circumstellar protoplanetary disks whose fundamental properties (notably their extent, composition, mass, temperature, and lifetime) depend on the host star properties, such as their mass and luminosity. B stars are among the most massive stars and their protoplanetary disks test extreme conditions for exoplanet formation. This paper investigates the frequency of giant planet companions around young B stars (median age of 16 Myr) in the Scorpius-Centaurus (Sco-Cen) association, the closest association containing a large population of B stars. We systematically searched for massive exoplanets with the high-contrast direct imaging instrument SPHERE using the data from the BEAST survey, which targets a homogeneous sample of young B stars from the wide Sco-Cen association. We derived accurate detection limits in the case of non-detections. We found evidence in previous papers for two substellar companions around 42 stars. The masses of these companions are straddling the sim 13 Jupiter mass deuterium burning limit, but their mass ratio with respect to their host star is close to that of Jupiter. We derived a frequency of such massive planetary-mass companions around B stars of $11_ $<!PCT!>, accounting for the survey sensitivity. The discoveries of substellar companions b and B happened after only a few stars in the survey had been observed, raising the possibility that massive Jovian planets might be common around B stars. However, our statistical analysis shows that the occurrence rate of such planets is similar around B stars and around solar-type stars of a similar age, while B-star companions exhibit low mass ratios and a larger semi-major axis.

The tidal excitation of r modes in a solar-type star orbited by a giant planet companion and the effect on orbital evolution – II. The effect of tides in the misaligned case

ABSTRACT We extend the study of Papaloizou and Savonije of the tidal interactions of close orbiting giant planets with a central solar-type star to the situation where the spin axis of the central star and the orbital angular momentum are misaligned. We determine the tidal response taking into account the possibility of the excitation of r modes and the effect of tidal forcing due to potential perturbations that have zero frequency in a non-rotating frame. Although there is near resonance with r modes with degree l′ = 1 and orders m = ±1, half widths turn out to be sufficiently narrow so that in practice dissipation rates are found to be similar to those produced by non-resonant potential perturbations. We use our results to determine the evolution of the misalignment for the full range of initial inclination angles taking account of the spin-down of the central star due to magnetic braking. Overall we find the rate of tidal evolution to be unimportant for a one Jupiter mass planet with orbital period ∼3.7 d over a main-sequence lifetime. However, it becomes significant for higher mass planets and shorter orbital periods, approximately scaling as the square of the planet mass and the inverse fourth power of the orbital period.

Hot Jupiters Have Giant Companions: Evidence for Coplanar High-eccentricity Migration

This study considers the characteristics of planetary systems with giant planets based on a population-level analysis of the California Legacy Survey planet catalog. We identified three characteristics common to hot Jupiters (HJs). First, while not all HJs have a detected outer giant planet companion (), such companions are ubiquitous when survey completeness corrections are applied for orbital periods out to 40,000 days. Giant-harboring systems without an HJ also host at least one outer giant planet companion per system. Second, the mass distributions of HJs and other giant planets are indistinguishable. However, within a planetary system that includes an HJ, the outer giant planet companions are at least 3× more massive than the inner HJs. Third, the eccentricity distribution of the outer companions in HJ systems (with an average model eccentricity of 〈e〉 = 0.34 ± 0.05) is different from the corresponding outer planets in planetary systems without HJs (〈e〉 = 0.19 ± 0.02). We conclude that the existence of two gas giants, where the outermost planet has an eccentricity ≥0.2 and is 3× more massive, are key factors in the production of an HJ. Our simple model based on these factors predicts that ∼10% of warm and cold Jupiter systems will by chance meet these assembly criteria, which is consistent with our measurement of a 16% ± 6% relative occurrence of HJ systems to all giant-harboring systems. We find that these three features favor coplanar high-eccentricity migration as the dominant mechanism for HJ formation.

The tidal excitation ofrmodes in a solar-type star orbited by a giant planet companion and the effect on orbital evolution I: the aligned case

ABSTRACTIt has been suggested that tidal interaction is important for shaping the orbital configurations of close orbiting giant planets. The excitation of propagating waves and normal modes (dynamical tide) will be important for estimating time-scales for orbital evolution. We consider the tidal interaction of a Jupiter mass planet orbiting a solar-type primary. Tidal and rotational frequencies are assumed comparable making the effect of rotation important. Although centrifugal distortion is neglected, Coriolis forces are fully taken into account. We focus in detail on the potentially resonant excitation of r modes associated with spherical harmonics of degrees three and five. These are mostly sited in the radiative core but with a significant response in the convective envelope where dissipation occurs. Away from resonance significant orbital evolution over the system lifetime is unlikely. However, tidal interaction is enhanced near resonances and the orbital evolution accelerated as they are passed through. This speed up may be sustained if near resonance can be maintained. For close orbits with primaries rotating sufficiently rapidly, this could arise from angular momentum loss and stellar spin-down through a stellar wind bringing about significant orbital evolution over the system lifetime.

A Jupiter Analog Orbiting The Nearby M Dwarf GJ 463

We report the detection of a long-period giant planetary companion to the nearby M3V star GJ 463 (=Ross 690). The detection is based on over ten years of highly-precise radial velocity measurements with the High Resolution Spectrograph at the Hobby–Eberly Telescope and the HIRES spectrograph at Keck. With an orbital period of 10 yr and a minimum mass of 1.55 ± 0.15 M Jup, GJ 463 b has a comparable orbital period to Jupiter and hence qualifies as a Jupiter analog around a low-mass star. We demonstrate that the radial velocity signal is not produced by a magnetic activity cycle of the host star. GJ 463 was observed with TESS, and we searched the light curve for any possible signals of stellar or planetary origin, but detected none. This planet is a candidate for possible direct detection with the coronagraph of the upcoming Nancy Grace Roman Space Telescope. We compared Gaia EDR3 with Hipparcos astrometry and detected a significant acceleration, which is likely caused by this long-period planetary companion at a = 3.53 ± 0.07 au.

Radial velocity survey for planets around young stars (RVSPY)

Aims. We aim to detect planetary companions to young stars with debris disks via the radial velocity method. Methods. We observed HD 114082 during April 2018–August 2022 as one of the targets of our RVSPY program (Radial Velocity Survey for Planets around Young stars). We use the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs). Additionally, we analyze archival HARPS spectra and TESS photometric data. We use the CERES, CERES++ and SERVAL pipelines to derive RVs and activity indicators and ExoStriker for the independent and combined analysis of the RVs and TESS photometry. Results. We report the discovery of a warm super-Jovian companion around HD 114082 based on a 109.8±0.4 day signal in the combined RV data from FEROS and HARPS, and on one transit event in the TESS photometry. The best-fit model indicates a 8.0±1.0 MJup companion with a radius of 1.00±0.03 RJup in an orbit with a semi-major axis of 0.51±0.01 au and an eccentricity of 0.4±0.04. The companions orbit is in agreement with the known near edge-on debris disk located at ∼28 au. HD 114082 b is possibly the youngest (15±6 Myr), and one of only three young (< 100 Myr) giant planetary companions for which both their mass and radius have been determined observationally. It is probably the first properly model-constraining giant planet that allows distinguishing between hot and cold-start models. It is significantly more compatible with the cold-start model.

Variation of the stellar color in high-magnification and caustic-crossing microlensing events

Context. To a first approximation, the microlensing phenomenon is achromatic and great advancements have been achieved with regard to the interpretation of the achromatic signals, leading to the discovery and characterization of well above 100 new exoplanets. At a higher order accuracy in the observations, microlensing has a chromatic component (a color term) that has thus far been explored to a much lesser extent. Aims. Here, we analyze the chromatic microlensing effect of four different physical phenomena, which have the potential to contribute key knowledge of the stellar properties that is not easily achievable with other methods of observation. Our simulation is limited to the case of main-sequence source stars. Methods. Microlensing is particularly sensitive to giant and sub-giant stars near the Galactic center. While this population can be studied in short snapshots by the largest telescopes in the world, a general monitoring and characterization of the population can be achieved by use of more accessible medium-sized telescopes with specialized equipment via dual-color monitoring from observatories at sites with excellent seeing. We limit the results of this study to what will be achievable from the Danish 1.54 m telescope at La Silla observatory based on the use of the existing dual-color lucky imaging camera. Such potential monitoring programs of the bulge population from medium-sized telescopes include the characterization of starspots, limb-darkening, the frequency of close-in giant planet companions, and gravity darkening for blended source stars. Results. We conclude our simulations with quantifying the likelihood of detecting these different phenomena per object where they are present to be ~60 and ~30% for the above-mentioned phenomena when monitored during both high-magnification and caustic crossings, respectively.

Strong scatterings of cold Jupiters and their influence on inner low-mass planet systems: theory and simulations

ABSTRACT Recent observations have indicated a strong connection between compact (a ≲ 0.5 au) super-Earth and mini-Neptune systems and their outer (a ≳ a few au) giant planet companions. We study the dynamical evolution of such inner systems subject to the gravitational effect of an unstable system of outer giant planets, focusing on systems whose end configurations feature only a single remaining outer giant. In contrast to similar studies which used on N-body simulations with specific (and limited) parameters or scenarios, we implement a novel hybrid algorithm which combines N-body simulations with secular dynamics with aims of obtaining analytical understanding and scaling relations. We find that the dynamical evolution of the inner planet system depends crucially on Nej, the number of mutual close encounters between the outer planets prior to eventual ejection/merger. When Nej is small, the eventual evolution of the inner planets can be well described by secular dynamics. For larger values of Nej, the inner planets gain orbital inclination and eccentricity in a stochastic fashion analogous to Brownian motion. We develop a theoretical model, and compute scaling laws for the final orbital parameters of the inner system. We show that our model can account for the observed eccentric super-Earths/mini-Neptunes with inclined cold Jupiter companions, such as HAT-P-11, Gliese 777, and π Men.

A SOPHIE RV search for giant planets around young nearby stars (YNS)

Context.The search of close (a≲ 5 au) giant planet (GP) companions with radial velocity (RV) around young stars and the estimate of their occurrence rates is important to constrain the migration timescales. Furthermore, this search will allow the giant planet occurrence rates to be computed at all separations via the combination with direct imaging techniques. The RV search around young stars is a challenge as they are generally faster rotators than older stars of similar spectral types and they exhibit signatures of magnetic activity (spots) or pulsation in their RV time series. Specific analyses are necessary to characterize, and possibly correct for, this activity.Aims.Our aim is to search for planets around young nearby stars and to estimate the GP occurrence rates for periods up to 1000 days.Methods.We used the SOPHIEspectrograph on the 1.93 m telescope at the Haute-Provence Observatory to observe 63 A−Myoung (<400 Myr) stars. We used our Spectroscopic data via Analysis of the Fourier Interspectrum Radial velocities software to compute the RVs and other spectroscopic observables. We then combined this survey with the HARPSYNS survey to compute the companion occurrence rates on a total of 120 youngA−Mstars.Results.We report one new trend compatible with a planetary companion on HD 109647. We also report HD 105693 and HD 112097 as binaries, and we confirm the binarity of HD 2454, HD 13531, HD 17250 A, HD 28945, HD 39587, HD 131156, HD 142229, HD 186704 A, and HD 195943. We constrained for the first time the orbital parameters of HD 195943 B. We refute the HD 13507 single brown dwarf (BD) companion solution and propose a double BD companion solution. Two GPs were previously reported from this survey in the HD 113337 system. Based on our sample of 120 young stars, we obtain a GP occurrence rate of 1−0.3+2.2% for periods lower than 1000 days, and we obtain an upper limit on BD occurrence rate of 0.9−0.9+2% in the same period range. We report a possible lack of close (P∈ [1;1000] days) GPs around young FK stars compared to their older counterparts, with a confidence level of 90%.

Inclination dynamics of resonant planets under the influence of an inclined external companion

ABSTRACT Recent observations suggest that a large fraction of Kepler super-Earth systems have external giant planet companions (cold Jupiters), which can shape the architecture of the inner planets, in particular their mutual inclinations. The dynamical perturbation from cold Jupiters may account for the population of misaligned planets in the Kepler data. The effectiveness of this mechanism can be hindered by a strong planet–planet coupling in the inner system. In this paper, we study how mean-motion resonances (MMRs) affect this coupling and the expected misalignment. We derive approximate analytical expressions for the mutual inclination excitations in the inner planet system induced by an inclined companion, for various period ratios and perturber properties. In most cases, the mutual inclination is proportional to a dimensionless parameter that characterizes the strength of the perturber relative to the coupling in the inner system. We show that the MMR strengthens the inner coupling, reducing the mutual inclination induced by the perturber by a factor of a few. We find that the resonance is resilient to the perturbation, and derive a criterion for the libration of the resonant angle. Our results have applications for constraining unseen planetary perturbers, and for understanding the architecture of multiplanet systems.

Single magnetic white dwarfs with Balmer emission lines: a small class with consistent physical characteristics as possible signposts for close-in planetary companions

ABSTRACT We report the identification of SDSS J121929.45+471522.8 as the third apparently isolated magnetic (B ≃ 18.5 ± 1.0 MG) white dwarf exhibiting Zeeman-split Balmer emission lines. The star shows coherent variability at optical wavelengths with an amplitude of ≃0.03 mag and a period of 15.26 h, which we interpret as the spin period of the white dwarf. Modelling the spectral energy distribution and Gaia parallax, we derive a white dwarf temperature of 7500 ± 148 K, a mass of 0.649 ± 0.022 M⊙, and a cooling age of 1.5 ± 0.1 Gyr, as well as an upper limit on the temperature of a sub-stellar or giant planet companion of ≃250 K. The physical properties of this white dwarf match very closely those of the other two magnetic white dwarfs showing Balmer emission lines: GD356 and SDSS J125230.93−023417.7. We argue that, considering the growing evidence for planets and planetesimals on close orbits around white dwarfs, the unipolar inductor model provides a plausible scenario to explain the characteristics of this small class of stars. The tight clustering of the three stars in cooling age suggests a common mechanism switching the unipolar inductor on and off. Whereas Lorentz drift naturally limits the lifetime of the inductor phase, the relatively late onset of the line emission along the white dwarf cooling sequence remains unexplained.

No Massive Companion to the Coherent Radio-emitting M Dwarf GJ 1151

Abstract The recent detection of circularly polarized, long-duration (>8 hr), low-frequency (∼150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star–planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at . With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151 (https://github.com/benjaminpope/video).

In situ scattering of warm Jupiters and implications for dynamical histories

ABSTRACT Many warm Jupiters (WJs) have substantial eccentricities, which are linked to their formation and migration histories. This paper explores eccentricity excitation of WJs due to planet–planet scattering, beginning with three to four planets in unstable orbits, with the innermost planet placed in the range (0.1−1) au. Such a setup is consistent with either in situ formation or arrival at sub-au orbits due to disc migration. Most previous N-body experiments have focused on ‘cold’ Jupiters at several au, where scattering results in planet ejections, efficiently exciting the eccentricities of surviving planets. In contrast, scattering at sub-au distances results in a mixture of collisions and ejections, and the final eccentricities of surviving planets are unclear. We conduct scattering experiments for a range of planet masses and initial spacings, including the effect of general relativistic apsidal precession, and systematically catalogue the scattering outcomes and properties of surviving planets. A comparable number of one-planet and two-planet systems are produced. Two-planet systems arise exclusively through planet–planet collisions, and tend to have low eccentricities/mutual inclinations and compact configurations. One-planet systems arise through a combination of ejections and collisions, resulting in higher eccentricities. The observed eccentricity distribution of solitary WJs (lacking detection of a giant planet companion) is consistent with roughly $60 {{\ \rm per\ cent}}$ of the systems having undergone in situ scattering, and the remaining experiencing a quiescent history.

A Recommendation Algorithm to Predict Giant Exoplanet Host Stars Using Stellar Elemental Abundances

The presence of certain elements within a star, and by extension its planet, strongly impacts the formation and evolution of the planetary system. The positive correlation between a host star's iron-content and the presence of an orbiting giant exoplanet has been confirmed; however, the importance of other elements in predicting giant planet occurrence is less certain despite their central role in shaping internal planetary structure. We designed and applied a machine learning algorithm to the Hypatia Catalog (Hinkel et a. 2014) to analyze the stellar abundance patterns of known host stars to determine those elements important in identifying potential giant exoplanet host stars. We analyzed a variety of different elements ensembles, namely volatiles, lithophiles, siderophiles, and Fe. We show that the relative abundances of oxygen, carbon, and sodium, in addition to iron, are influential indicators of the presence of a giant planet. We demonstrate the predictive power of our algorithm by analyzing stars with known giant planets and found that they had median 75% prediction score. We present a list of ~350 stars with no currently discovered planets that have a $\geq$90% prediction probability likelihood of hosting a giant exoplanet. We investigated archival HARPS data and found significant trends that HIP62345, HIP71803, and HIP10278 host long-period giant planet companions with estimated minimum $M_p\sin(i)$ values of 3.7, 6.8, and 8.5 M$_{J}$, respectively. We anticipate that our findings will revolutionize future target selection, the role that elements play in giant planet formation, and the determination of giant planet interior structure models.

Long-period Giant Companions to Three Compact, Multiplanet Systems

Abstract Understanding the relationship between long-period giant planets and multiple smaller short-period planets is critical for formulating a complete picture of planet formation. This work characterizes three such systems. We present Kepler-65, a system with an eccentric (e = 0.28 ± 0.07) giant planet companion discovered via radial velocities (RVs) exterior to a compact, multiply transiting system of sub-Neptune planets. We also use precision RVs to improve mass and radius constraints on two other systems with similar architectures, Kepler-25 and Kepler-68. In Kepler-68 we propose a second exterior giant planet candidate. Finally, we consider the implications of these systems for planet formation models, particularly that the moderate eccentricity in Kepler-65's exterior giant planet did not disrupt its inner system.

Giant planet effects on terrestrial planet formation and system architecture

The giant planets of the solar system likely played a large role in shaping the architecture of the terrestrial planets. Using an updated collision model, we conduct a suite of high resolution N-body integrations to probe the relationship between giant planet mass, and terrestrial planet formation and system architecture. We vary the mass of the planets that reside at Jupiter's and Saturn's orbit and examine the effects on the interior terrestrial system. We find a correlation between the mass of the exterior giant planets and the collision history of the resulting planets, which holds implications for the planet's properties. More massive giants also produce terrestrial planets that are on smaller, more circular orbits. We do not find a strong correlation between exterior giant planet mass and the number of Earth-analogs (analogous in mass and semi-major axis) produced in the system. These results allow us to make predictions on the nature of terrestrial planets orbiting distant Sun-like star systems that harbor giant planet companions on long orbits---systems which will be a priority for NASA's upcoming Wide-Field Infrared Space Telescope (WFIRST) mission.

Aldebaran b’s Temperate Past Uncovered in Planet Search Data

Abstract The nearby red giant Aldebaran is known to host a gas giant planetary companion from decades of ground-based spectroscopic radial velocity measurements. Using Gaussian Process-based Continuous Auto-Regressive Moving Average models, we show that these historic data also contain evidence of acoustic oscillations in the star itself, and verify this result with further dedicated ground-based spectroscopy using the SONG telescope and space-based photometry with the Kepler Space Telescope. From the frequency of these oscillations we determine the mass of Aldebaran to be 1.16 ± 0.07 , and note that this implies its planet will have been subject to insolation comparable to the Earth for some of the star’s main sequence lifetime. Our approach to sparse, irregularly sampled time series astronomical observations has the potential to unlock asteroseismic measurements for thousands of stars in archival data, and push to lower-mass planets around red giant stars.

Spiral Arms in Disks: Planets or Gravitational Instability?

Abstract Spiral arm structures seen in scattered-light observations of protoplanetary disks can potentially serve as signposts of planetary companions. They can also lend unique insights into disk masses, which are critical in setting the mass budget for planet formation but are difficult to determine directly. A surprisingly high fraction of disks that have been well studied in scattered light have spiral arms of some kind (8/29), as do a high fraction (6/11) of well-studied Herbig intermediate-mass stars (i.e., Herbig stars >1.5 M ⊙). Here we explore the origin of spiral arms in Herbig systems by studying their occurrence rates, disk properties, and stellar accretion rates. We find that two-arm spirals are more common in disks surrounding Herbig intermediate-mass stars than are directly imaged giant planet companions to mature A and B stars. If two-arm spirals are produced by such giant planets, this discrepancy suggests that giant planets are much fainter than predicted by hot-start models. In addition, the high stellar accretion rates of Herbig stars, if sustained over a reasonable fraction of their lifetimes, suggest that disk masses are much larger than inferred from their submillimeter continuum emission. As a result, gravitational instability is a possible explanation for multiarm spirals. Future observations can lend insights into the issues raised here.

Teetering stars: resonant excitation of stellar obliquities by hot and warm Jupiters with external companions

Stellar spin-orbit misalignments (obliquities) in hot Jupiter systems have been extensively probed. Such obliquities may reveal clues about hot Jupiter dynamical histories. Common explanations for generating obliquities include high-eccentricity migration and primordial disk misalignment. This paper investigates another mechanism for producing stellar spin-orbit misalignments in systems hosting a close-in planet with an external, modestly inclined companion. Spin-orbit misalignment may be excited due to a secular resonance, occurring when the precession rate of the stellar spin axis (driven by the inner planet) becomes comparable to the nodal precession rate of the inner planet (driven by the companion). Due to the spin-down of the host star via magnetic braking, this resonance may be achieved during the star's main-sequence lifetime for a wide range of planet masses and orbital architectures. Obliquity excitation is accompanied by a decrease in mutual inclination between the inner planet and perturber, and can thus erase high inclinations. For hot Jupiters, the stellar spin axis is strongly coupled to the orbital axis, and obliquity excitation by a giant planet companion requires a strong perturber, usually located within 1-2 AU. For warm Jupiters, the spin and orbital axes are more weakly coupled, and the resonance may be achieved for distant giant planet perturbers (at several to tens of AU). Since warm Jupiters have a high occurrence rate of distant planetary companions with appropriate properties for resonant obliquity excitation, stellar obliquities in warm Jupiter systems may be common, particularly for warm Jupiters orbiting cool stars that have undergone significant spin-down.

Moderately eccentric warm Jupiters from secular interactions with exterior companions

Recent studies have proposed that most warm Jupiters (WJs, giant planets with semi-major axes in the range of 0.1-1 AU) probably form in-situ, or arrive in their observed orbits through disk migration. However, both in-situ formation and disk migration, in their simplest flavors, predict WJs to be in low-eccentricity orbits, in contradiction with many observed WJs that are moderately eccentric (e=0.2-0.7). This paper examines the possibility that the WJ eccentricities are raised by secular interactions with exterior giant planet companions, following in-situ formation or migration on a circular orbit. Eccentricity growth may arise from an inclined companion (through Lidov-Kozai cycles), or from an eccentric, nearly coplanar companion (through apsidal precession resonances). We quantify the necessary conditions (in terms of the eccentricity, semi-major axis and inclination) for external perturbers of various masses to raise the WJ eccentricity. We also consider the sample of eccentric WJs with detected outer companions, and for each system, identify the range of mutual inclinations needed to generate the observed eccentricity. For most systems, we find that relatively high inclinations (at least $\sim 40^\circ$) are needed so that Lidov-Kozai cycles are induced; the observed outer companions are typically not sufficiently eccentric to generate the observed WJ eccentricity in a low-inclination configuration. The results of this paper place constraints on possibly unseen external companions to eccentric WJs. Observations that probe mutual inclinations of giant planet systems will help clarify the origin of eccentric WJs and the role of external companions.