Planet Host Research Articles

Constraining planetary formation models using conditional occurrences of various planet types

ABSTRACT We report the conditional occurrences between three planetary types: super-Earths (m sin i < 10 M⊕, P < 100 d), warm Jupiters (m sin i > 95 M⊕, 10 < P < 100 d), and cold Jupiters (m sin i > 95 M⊕, P > 400 d) for sun-like stars. We find that while the occurrence of cold Jupiters in systems with super-Earths is $22.2\substack{+8.3 \\ -5.4}$ per cent, compared to 10 per cent for the absolute occurrence rate of cold Jupiters, the occurrence of super-Earths in systems with cold Jupiters is $66.0\substack{+18.0 \\ -16.0}$ per cent, compared to 30 per cent for the absolute occurrence rate of super-Earths for Sun-like stars. We find that the enhancement of super-Earths in systems with cold Jupiters is evident for Sun-like stars, in agreement with several previous studies. We also conduct occurrence studies between warm Jupiters and super-Earths, and between warm Jupiters and cold Jupiters, to consolidate our methods. We conduct an independent observational test to study the effects of cold Jupiters against the inner multiplicity using the well-established giant planet host star metallicity correlation for all transiting planets found to date. The conditional occurrences we find here can be used to constrain the validity of various planetary formation models. The extremely interesting correlations between the super-Earths, cold Jupiters, and warm Jupiters can also be used to understand the formation histories of these planetary types.

Self-consistent modeling of metastable helium exoplanet transits

Absorption of stellar X-ray and extreme ultraviolet (EUV) radiation in the upper atmosphere of close-in exoplanets can give rise to hydrodynamic outflows, which may lead to the gradual shedding of their primordial light element envelopes. Excess absorption by neutral helium atoms in the metastable 2 3S state [He I(2 3S)], at ~10 830 Å, has recently emerged as a viable diagnostic of atmospheric escape. Here we present a public add-on module to the 1D photoionization hydrodynamic code ATES, designed to calculate the He I(2 3S) transmission probability for a broad range of planetary parameters. By relaxing the isothermal outflow assumption, the code enables a self-consistent assessment of the He I(2 3S) absorption depth along with the atmospheric mass-loss rate and the outflow temperature profile, which strongly affects the recombination rate of He II into He I(2 3S). We investigate how the transit signal can be expected to depend upon known system parameters, including host spectral type, orbital distance, and planet gravity. At variance with previous studies, which identified K-type stars as favorable hosts, we conclude that late M dwarfs with Neptune-sized planets orbiting at ~0.05–0.1 AU can be expected to yield the strongest transit signal, well in excess of 30% for near-cosmological He-to-H abundances. More generally, we show that the physics that regulates the population and depletion of the metastable state, combined with geometrical effects, can yield somewhat counterintuitive results, such as a nonmonotonic dependence of the transit depth on orbital distance. These are compounded by a strong degeneracy between the stellar EUV flux intensity and the atmospheric He-to-H abundance, both of which are highly uncertain. Compared with spectroscopy data, now available for over 40 systems, our modeling suggests either that a large fraction of the targets have helium-depleted envelopes or that the input stellar EUV spectra are systematically overestimated. The updated code and transmission probability module are available publicly as an online repository.

The GAPS Programme at TNG

Context. Stellar activity is the most relevant types of astrophysical noise that affect the discovery and characterization of extrasolar planets. On the other hand, the amplitude of stellar activity could hint at an interaction between the star and a close-in giant planet. Progress has been made in recent years in understanding how to deal with stellar activity and search for observational evidence of star-planet interactions. Aims. The aim of this work is to characterize the chromospheric activity of stars hosting short-period exoplanets by studying the correlations between the chromospheric emission (CE) in the Ca II H&K and the planetary parameters. Methods. We measured CE in the Ca II H&K lines using more than 1900 high-resolution spectra of a sample composed of 76 targets, observed with the HARPS-N spectrograph between 2012 and 2020. We transformed the fluxes into bolometric- and photospheric-corrected chromospheric emission ratios, R′HK. Furthermore, we completed the sample of hosts digging for data in previous works. Stellar parameters Teff, B–V, and V were retrieved homogeneously from the Gaia DR3. Then, M★, R★, and ages were determined from isochrone fitting. We retrieved planetary data from the literature and catalogs. The search for correlations between the log(R′HK) and planetary parameters have been performed through both Spearman’s rank and its statistics as well as the more sophisticated Gaussian mixture model method. Results. We found that the distribution of log(R′HK) for the transiting planet hosts is different from the distribution of field main-sequence and sub-giant stars. The log(R′HK) of planetary hosts is correlated with planetary parameters proportional to the planetary radius to the power of n (RPn, indicating a common origin for the correlations. The statistical analysis has also highlighted four clusters of host stars with different behavior in terms of their stellar activity with respect to the planetary surface gravity. Some of the host stars have a value of log(R′HK) that is lower than the basal level of activity for main sequence stars. The planets of these systems are very close to filling their Roche lobe, suggesting that they evaporate through hydrodynamic escape under the strong irradiation of the host star, creating shrouds that absorb the core of the chromospheric resonance lines.

The Strength and Variability of the Helium 10830 Å Triplet in Young Stars, with Implications for Exosphere Detection

Young exoplanets trace planetary evolution, in particular the atmospheric mass loss that is most dynamic in youth. However, the high activity level of young stars can mask or mimic the spectroscopic signals of atmospheric mass loss. This includes the activity-sensitive He 10830 Å triplet, which is an increasingly important exospheric probe. To characterize the He-10830 triplet at young ages, we present time-series NIR spectra for young transiting planet hosts taken with the Habitable-zone Planet Finder. The He-10830 absorption strength is similar across our sample, except at the fastest and slowest rotations, indicating that young chromospheres are dense and populate metastable helium via collisions. Photoionization and recombination by coronal radiation only dominates metastable helium population at the active and inactive extremes. Volatile stellar activity, such as flares and changing surface features, drives variability in the He-10830 triplet. Variability is largest at the youngest ages before decreasing to ≲5–10 mÅ (or 3%) at ages above 300 Myr, with six of eight stars in this age range agreeing with there being no intrinsic variability. He-10830 triplet variability is smallest and age-independent at the shortest timescales. Intrinsic stellar variability should not preclude detection of young exospheres, except at the youngest ages. We recommend out-of-transit comparison observations taken directly surrounding transit and observation of multiple transits to minimize activity’s effect. Regardless, caution is necessary when interpreting transit observations in the context of stellar activity, as many scenarios can lead to enhanced stellar variability even on timescales of an hour.

Exoplanet host star classification: multi-objective optimization of incomplete stellar abundance data

Abstract The presence of a planetary companion around its host star has been repeatedly linked with stellar properties, affecting the likelihood of substellar object formation and stability in the protoplanetary disc, thus presenting a key challenge in exoplanet science. Furthermore, abundance and stellar parameter data sets tend to be incomplete, which limits the ability to infer distributional characteristics harnessing the entire data set. This work aims to develop a methodology using machine learning (ML) and multi-objective optimization for reliable imputation for subsequent comparison tests and host star recommendation. It integrates fuzzy clustering for imputation and ML classification of hosts and comparison stars into an evolutionary multi-objective optimization algorithm. We test several candidates for the classification model, starting with a binary classification for giant planet hosts. Upon confirmation that the eXtreme Gradient Boosting algorithm provides the best performance, we interpret the performance of both the imputation and classification modules for binary classification. The model is extended to handle multilabel classification for low-mass planets and planet multiplicity. Constraints on the model’s use and feature/sample selection are given, outlining strengths and limitations. We conclude that the careful use of this technique for host star recommendation will be an asset to future missions and the compilation of necessary target lists.

Analytical Lightcurves for Transiting Exomoons

Transit photometry has remained the most effective technique to detect and characterize exoplanets. As thousands of exoplanets have been discovered in the last few decades, the possibility of the existence of exomoons in some of these systems can not be avoided. However, the detection of exomoons has still remained elusive, owing to their much smaller expected size compared to their planetary host. With the advent of next generation space telescopes and large ground based telescopes, the possibility to detect them is imminent in near future. In such scenario, a comprehensive analytical formalism to model the transit lightcurves of a transiting exomoon hosting system will be necessary to confirm their detection and study their physical and dynamical characteristics. Here, I present such an analytical formulation, that can be used to simulate the transit lightcurves for an exoplanetary system hosting transiting exomoons. This formalism uses the physical and orbital properties of the three-body star-planet-moon system, to solve their orbital dynamics, and model the transit lightcurves for every possible physical scenarios. In this report, various aspects of this analytical formalism has been discussed, and the model lightcurves for a few of the practical scenarios have been presented.

Measuring the stellar and planetary parameters of the 51 Eridani system

Abstract In order to study exoplanets, a comprehensive characterisation of the fundamental properties of the host stars – such as angular diameter, temperature, luminosity, and age, is essential, as the formation and evolution of exoplanets are directly influenced by the host stars at various points in time. In this paper, we present interferometric observations taken of directly imaged planet host 51 Eridani at the CHARA Array. We measure the limb-darkened angular diameter of 51 Eridani to be $\theta_\mathrm{LD} = 0.450\pm 0.006$ mas and combining with the Gaia zero-point corrected parallax, we get a stellar radius of $1.45 \pm 0.02$ R $_{\odot}$ . We use the PARSEC isochrones to estimate an age of $23.2^{+1.7}_{-2.0}$ Myr and a mass of $1.550^{+0.006}_{-0.005}$ M $_{\odot}$ . The age and mass agree well with values in the literature, determined through a variety of methods ranging from dynamical age trace-backs to lithium depletion boundary methods. We derive a mass of $4.1\pm0.4$ M $_\mathrm{Jup}$ for 51 Eri b using the Sonora Bobcat models, which further supports the possibility of 51 Eri b forming under either the hot-start formation model or the warm-start formation model.

The California-Kepler Survey. XI. A Survey of Chromospheric Activity through the Lens of Precise Stellar Properties

Surveys of exoplanet host stars are valuable tools for assessing population level trends in exoplanets, and their outputs can include stellar ages, activity, and rotation periods. We extracted chromospheric activity measurements from the California-Kepler Survey Gaia survey spectra in order to probe connections between stellar activity and fundamental stellar properties. Building on the California Kepler Survey's legacy of 1189 planet host star stellar properties including temperature, surface gravity metallicity, and isochronal age, we add measurements of the Ca ii H and K lines as a proxy for chromospheric activity for 879 planet hosting stars. We used these chromospheric activity measurements to derive stellar rotation periods. We find a discrepancy between photometrically derived and activity-derived rotation periods for stars on the Rossby Ridge. These results support the theory of weakened magnetic braking. We find no evidence for metallicity-dependent activity relations, within the metallicity range of −0.2 to +0.3 dex. With our single epoch spectra we identify stars that are potentially in Maunder minimum–like state using a combination of log( RHK′ ) and position below the main sequence. We do not yet have the multiyear time series needed to verify stars in Maunder minimum–like states. These results can help inform future theoretical studies that explore the relationship between stellar activity, stellar rotation, and magnetic dynamos.

The Potential of The Cataclysmic Variable DW UMa to Host Planets

Evrimleşmiş bir altcüce ya da beyaz cüce ile bir M cücesinden oluşan örten çiftler kısa yörünge dönemleri, hızlı geçilen, simetrik, V-şeklindeki minimum profilleri nedeniyle hassas tutulma zamanlarının belirlenmesi için ideal sistemlerdir. Tutulma zamanlarındaki değişimin incelenmesi sonucu sisteme kütle çekimle bağlı birinci nesil ya da sistemin evrimi sırasında bileşenlerden birinin kaybettiği materyalden kaynaklı birikim disklerinde oluşabilecek ikinci nesil ötegezegenlerin neden olabileceği ışık-zaman etkisi tespit edilebilir. Bugüne kadar bu yöntemle yapılan ötegezegen keşiflerinin çok büyük bir çoğunluğu evriminin ileri aşamalarındaki bu tür sistemlerde gerçekleştirilmiştir. Bu çalışmada nova benzeri kataklizmik çift sistem DW UMa’nın tutulma zamanları analiz edilerek sonuçlar kütle transferi, eksen dönmesi ve ışık zaman etkisi bağlamında yorumlanmış ve tartışılmıştır.

Not-so-fast Kepler-1513: a perturbing planetary interloper in the exomoon corridor

ABSTRACT Transit timing variations (TTVs) can be induced by a range of physical phenomena, including planet–planet interactions, planet–moon interactions, and stellar activity. Recent work has shown that roughly half of moons would induce fast TTVs with a short period in the range of 2–4 orbits of its host planet around the star. An investigation of the Kepler TTV data in this period range identified one primary target of interest, Kepler-1513 b. Kepler-1513 b is a $8.05^{+0.58}_{-0.40}$ R⊕ planet orbiting a late G-type dwarf at $0.53^{+0.04}_{-0.03}$ au. Using Kepler photometry, this initial analysis showed that Kepler-1513 b’s TTVs were consistent with a moon. Here, we report photometric observations of two additional transits nearly a decade after the last Kepler transit using both ground-based observations and space-based photometry with TESS. These new transit observations introduce a previously undetected long period TTV, in addition to the original short period TTV signal. Using the complete transit data set, we investigate whether a non-transiting planet, a moon, or stellar activity could induce the observed TTVs. We find that only a non-transiting perturbing planet can reproduce the observed TTVs. We additionally perform transit origami on the Kepler photometry, which independently applies pressure against a moon hypothesis. Specifically, we find that Kepler-1513 b’s TTVs are consistent with an exterior non-transiting ∼Saturn mass planet, Kepler-1513 c, on a wide orbit, $\sim 5~{{\ \rm per \, cent}}$ outside a 5:1 period ratio with Kepler-1513 b. This example introduces a previously unidentified cause for planetary interlopers in the exomoon corridor, namely an insufficient baseline of observations.

Monitoring the young planet host V1298 Tau with SPIRou: planetary system and evolving large-scale magnetic field

ABSTRACT We report results of a spectropolarimetric monitoring of the young Sun-like star V1298 Tau based on data collected with the near-infrared spectropolarimeter SPIRou at the Canada–France–Hawaii Telescope between late 2019 and early 2023. Using Zeeman–Doppler Imaging and the Time-dependent Imaging of Magnetic Stars methods on circularly polarized spectra, we reconstructed the large-scale magnetic topology of the star (and its temporal evolution), found to be mainly poloidal and axisymmetric with an average strength varying from 90 to 170 G over the ∼3.5 yr of monitoring. The magnetic field features a dipole whose strength evolves from 85 to 245 G, and whose inclination with respect to the stellar rotation axis remains stable until 2023 where we observe a sudden change, suggesting that the field may undergo a polarity reversal, potentially similar to those periodically experienced by the Sun. Our data suggest that the differential rotation shearing the surface of V1298 Tau is about 1.5 times stronger than that of the Sun. When coupling our data with previous photometric results from K2 and TESS and assuming circular orbits for all four planets, we report a 3.9σ detection of the radial velocity signature of the outermost planet (e), associated with a most probable mass, density, and orbital period of $M_\mathrm{e}=0.95^{+0.33}_{-0.24}$ MꝜ, $\rho _\mathrm{e}=1.66^{+0.61}_{-0.48}$$\rm g\, cm^{-3}$, and Pe = 53.0039 ± 0.0001 d, respectively. For the three inner planets, we only derive 99 per cent confidence upper limits on their mass of 0.44, 0.22, and 0.25 MꝜ, for b, c, and d, respectively.

Visual Orbits and Alignments of Planet-hosting Binary Systems

Roughly half of Solar-type planet hosts have stellar companions, so understanding how these binary companions affect the formation and evolution of planets is an important component to understanding planetary systems overall. Measuring the dynamical properties of planet host binaries enables a valuable test of planet formation in multistar systems and requires knowledge of the binary orbital parameters. Using high-resolution imaging, we have measured the relative astrometry and visual orbits of 13 binary systems where one of the stars is known to host a transiting exoplanet. Our results indicate that the mutual inclination between the orbits of the binary hosts and the transiting planets are well aligned. Our results for close binary systems (a < 100 au) complement past work for wide planet host binaries from Gaia.

The Physical Oceanography of Ice-Covered Moons.

In the outer solar system, a growing number of giant planet satellites are now known to be abodes for global oceans hidden below an outer layer of ice. These planetary oceans are a natural laboratory for studying physical oceanographic processes in settings that challenge traditional assumptions made for Earth's oceans. While some driving mechanisms are common to both systems, such as buoyancy-driven flows and tides, others, such as libration, precession, and electromagnetic pumping, are likely more significant for moons in orbit around a host planet. Here, we review these mechanisms and how they may operate across the solar system, including their implications for ice-ocean interactions. Future studies should continue to advance our understanding of each of these processes as well as how they may act together in concert. This interplay also has strong implications for habitability as well as testing oceanic hypotheses with future missions.

Do all gaps in protoplanetary discs host planets?

Following the assumption that the disc substructures observed in protoplanetary discs originate from the interaction between the disc and the forming planets embedded therein, we aim to test if these putative planets could represent the progenitors of the currently observed giant exoplanets. We performed N-body simulations initially assuming three, four, five, or seven planets. Our model includes pebble and gas accretion, migration, damping of eccentricities and inclinations, disc-planet interaction, and disc evolution. We located the planets in the positions where the gaps in protoplanetary discs have been observed and we evolved the systems for 100 Myr including a few million years of gas disc evolution, while also testing three values of α viscosity. For planetary systems with initially three and four planets, we find that most of the growing planets lie beyond the radial-velocity (RV) detection limit of 5AU and only a small fraction of them migrate into the inner region. We also find that these systems have final eccentricities that are too low to be in agreement with the observed giant planet population. Systems initially consisting of five or seven planets become unstable after ≈40 Kyr of integration time. This clearly shows that not every gap can host a planet. The general outcome of our simulations – eccentricities that are too low – is independent of the disc’s viscosity and surface density. Further observations could either confirm the existence of an undetected population of wide-orbit giants or exclude the presence of such an undetected population to constrain how many planets hide in gaps even further.

Physical and Kinematical Characteristics of Wolf–Rayet Central Stars and their Host Planetary Nebulae

We address the physical and kinematical properties of Wolf–Rayet [WR] central stars (CSs) and their host planetary nebulae (PNe). The studied sample comprises all [WR] CSs that are currently known. The analysis is based on recent observations of the parallax, proper motion, and color index of [WR] CSs from the Gaia space mission’s early third release (eDR3) catalog, as well as common nebular characteristics. The results revealed an evolutionary sequence, in terms of decreasing T eff, from the early hot [WO 1] to the late cold [WC 12] stars. This evolutionary sequence extends beyond [WR] CS temperature and luminosity to additional CS and nebular characteristics. The statistical analysis shows that the mean final stellar mass and evolutionary age of the [WR] CS sample are 0.595 ± 0.13 M ⊙ and 9449 ± 2437 yr, respectively, with a mean nebular dynamical age of 7270 ± 1380 yr. In addition, we recognize that the color of the majority (∼85%) of [WR] CSs tends to be red rather than their genuine blue color. The analysis indicates that two-thirds of the apparent red color of most [WR]s is attributed to the interstellar extinction whereas the other one-third is due to the PN self-extinction effect.

Pathways of survival for exomoons and inner exoplanets

Context. It is conceivable that a few thousand confirmed exoplanets initially harboured satellites similar to the moons of the Solar System or larger. We ask the question of whether some of them have survived over the æons of dynamical evolution to the present day. The dynamical conditions are harsh for exomoons in such systems because of the greater influence of the host star and of the tidal torque it exerts on the planet. Aims. We investigate the stability niches of exomoons around hundreds of innermost exoplanets for which the needed parameters are known today, and we determine the conditions of these moons’ long-term survival. General lower and upper bounds on the exomoon survival niches are derived for orbital separations, periods, and masses. Methods. The fate of an exomoon residing in a stability niche depends on the initial relative rate of the planet’s rotation and on the ability of the moon to synchronise the planet by overpowering the tidal action from the star. State-of-the-art models of tidal dissipation and secular orbital evolution are applied to a large sample of known exoplanet systems, which have the required estimated physical parameters. Results. We show that in some plausible scenarios, exomoons can prevent close exoplanets from spiralling into their host stars, thus extending these planets’ lifetimes. This is achieved when exomoons synchronise the rotation of their parent planets, overpowering the tidal action from the stars. Conclusions. Massive moons are more likely to survive and help their host planets maintain a high rotation rate (higher than these planets’ mean motion).

Elemental Abundances of Kepler Objects of Interest in APOGEE DR17

The elemental abundances of planet host stars can shed light on the conditions of planet forming environments. We test if individual abundances of 130 known/candidate planet hosts in APOGEE are statistically different from those of a reference doppelgänger sample. The reference set comprises objects selected with the same T eff, , [Fe/H], and [Mg/H] as each Kepler Object of Interest (KOI). We predict twelve individual abundances (X = C, N, O, Na, Al, Si, Ca, Ti, V, Cr, Mn, Ni) for the KOIs and their doppelgängers using a local linear model of these four parameters, training on ASPCAP abundance measurements for a sample of field stars with high-fidelity (signal-to-noise ratio > 200) APOGEE observations. We compare element prediction residuals (model–measurement) for the two samples and find them to be indistinguishable, given a high-quality sample selection. We report median intrinsic dispersions of ∼0.038 dex and ∼0.041 dex, for the KOI and doppelgänger samples, respectively, for these elements. We conclude that the individual abundances at fixed T eff, , [Fe/H], and [Mg/H] are unremarkable for known planet hosts. Our results establish an upper limit on the abundance precision required to uncover any chemical signatures of planet formation in planet host stars.

Revising Properties of Planet–Host Binary Systems. III. There Is No Observed Radius Gap for Kepler Planets in Binary Star Systems* * Based on observations obtained with the Hobby–Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Binary stars are ubiquitous; the majority of solar-type stars exist in binaries. Exoplanet occurrence rate is suppressed in binaries, but some multiples do still host planets. Binaries cause observational biases in planet parameters, with undetected multiplicity causing transiting planets to appear smaller than they truly are. We have analyzed the properties of a sample of 119 planet-host binary stars from the Kepler mission to study the underlying population of planets in binaries that fall in and around the radius valley, which is a demographic feature in period–radius space that marks the transition from predominantly rocky to predominantly gaseous planets. We found no statistically significant evidence for a radius gap for our sample of 122 planets in binaries when assuming that the primary stars are the planet hosts, with a low probability (p < 0.05) of the binary planet sample radius distribution being consistent with the single-star population of small planets via an Anderson–Darling test. These results reveal demographic differences in the planet size distribution between planets in binary and single stars for the first time, showing that stellar multiplicity may fundamentally alter the planet formation process. A larger sample and further assessment of circumprimary versus circumsecondary transits is needed to either validate this nondetection or explore other scenarios, such as a radius gap with a location that is dependent on binary separation.

Planet engulfment detections are rare according to observations and stellar modelling

ABSTRACTDynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere abundance pattern will reflect accretion of rocky material from planets. Multistar systems are excellent environments to search for such abundance trends because stellar companions form from the same natal gas cloud and are thus expected to share primordial chemical compositions to within 0.03–0.05 dex. Abundance measurements have occasionally yielded rocky enhancements, but a few observations targeted known planetary systems. To address this gap, we carried out a Keck-HIRES survey of 36 multistar systems, where at least one star is a known planet host. We found that only HAT-P-4 exhibits an abundance pattern suggestive of engulfment but is more likely primordial based on its large projected separation (30 000 ± 140 au) that exceeds typical turbulence scales in molecular clouds. To understand the lack of engulfment detections among our systems, we quantified the strength and duration of refractory enrichments in stellar photospheres using mesa stellar models. We found that observable signatures from 10 M⊕ engulfment events last for ∼90 Myr in 1 M⊙ stars. Signatures are largest and longest lived for 1.1–1.2 M⊙ stars, but are no longer observable ∼2 Gyr post-engulfment. This indicates that engulfment will rarely be detected in systems that are several Gyr old.

Marauding Moons Spell Disaster for Some Planets

In solar systems beyond our own, some moons might eventually collide with their host planets, new simulations suggest.