Exoplanet Host Research Articles

The GAPS Programme at TNG

Context. Exoplanetary properties strongly depend on stellar properties: to know the planet with accuracy and precision it is necessary to know the star as accurately and precisely as possible. Aims. Our immediate aim is to characterize in a homogeneous and accurate way a sample of 27 transiting planet-hosting stars observed within the Global Architecture of Planetary System program. For the wide visual binary XO-2, we considered both components (N: hosting a transiting planet; S: without a known transiting planet). Our final goal is to widely analyze the sample by deriving several stellar properties, abundances of many elements, kinematic parameters, and discuss them in the context of planetary formation. Methods. We determined the stellar parameters (effective temperature, surface gravity, rotational velocity) and abundances of 26 elements (Li, C, N, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Fe, Mn, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Nd, Eu). Our study is based on high-resolution HARPS-N at TNG and FEROS at ESO spectra and uniform techniques. Depending on stellar parameters and chemical elements, we used line equivalent widths or spectral synthesis methods. We derived kinematic properties taking advantage of Gaia data and for the first time in exoplanet host stars we estimated ages using elemental ratios as chemical clocks. Results. The effective temperature of our stars is ~4400–6700 K, while the iron abundance [Fe/H] is within −0.3 and 0.4 dex. Lithium is present in seven stars. The [X/H] and [X/Fe] abundances versus [Fe/H] are consistent with the Galactic chemical evolution. The dependence of [X/Fe] with the condensation temperature is critically analyzed with respect to stellar and kinematic properties. All targets with measured C and O abundances show C/O < 0.8, compatible with Si present in rock-forming minerals. Mean C/O and [C/O] values are slightly lower than for the Sun. Most of targets show 1.0 < Mg/Si < 1.5, compatible with Mg distributed between olivine and pyroxene, and mean Mg/Si lower than for the Sun. HAT-P-26, the target hosting the lowest-mass planet, shows the highest Mg/Si ratio. From our chemodynamical analysis we find agreement between ages and position within the Galactic disk. Finally, we note a tendency for higher-density planets to be around metal-rich stars and hints of higher stellar abundances of some volatiles (e.g., O) for lower-mass planets. We cannot exclude that part of our results could be also related to the location of the stars within the Galactic disk. Conclusions. We try to trace the planetary migration scenario from the composition of the planets related to the chemical composition of the hosting stars. This kind of study will be useful for upcoming space mission data to get more insights into the formation-migration mechanisms.

Dynamical fates of S-type planetary systems in embedded cluster environments

ABSTRACT The majority of binary star systems that host exoplanets will spend the first portion of their lives within a star-forming cluster that may drive dynamical evolution of the binary-planet system. We perform numerical simulations of S-type planets, with masses and orbital architecture analogous to the Solar system’s four gas giants, orbiting within the influence of a $0.5\, \mathrm{M}_{\odot }$ binary companion. The binary-planet system is integrated simultaneously with an embedded stellar cluster environment. ∼10 per cent of our planetary systems are destabilized when perturbations from our cluster environment drive the binary periastron towards the planets. This destabilization occurs despite all of our systems being initialized with binary orbits that would allow stable planets in the absence of the cluster. The planet–planet scattering triggered in our systems typically results in the loss of lower mass planets and the excitement of the eccentricities of surviving higher mass planets. Many of our planetary systems that go unstable also lose their binary companions prior to cluster dispersal and can therefore masquerade as hosts of eccentric exoplanets that have spent their entire histories as isolated stars. The cluster-driven binary orbital evolution in our simulations can also generate planetary systems with misaligned spin–orbit angles. This is typically done as the planetary system precesses as a rigid disc under the influence of an inclined binary, and those systems with the highest spin–orbit angles should often retain their binary companion and possess multiple surviving planets.

Determining Which Binary Component Hosts the TESS Transiting Planet

The NASA TESS mission has discovered many transiting planets orbiting bright nearby stars, and high-resolution imaging studies have revealed that a number of these exoplanet hosts reside in binary or multiple star systems. In such systems, transit observations alone cannot determine which star in the binary system actually hosts the orbiting planet. The knowledge of which star the planet orbits is necessary for determining accurate physical properties for the planet, especially its true radius and mean bulk density. We derived the mean stellar densities for the components of 23 binary systems using the light curve transit shape and the binary flux ratio from speckle imaging, then tested the consistency with stellar models to determine which component is the host star. We found that 70% of the TESS transiting planets in our sample orbit the primary star.

Exoplanet X-ray irradiation and evaporation rates with eROSITA

High-energy irradiation is a driver for atmospheric evaporation and mass loss in exoplanets. This work is based on data from eROSITA, the soft X-ray instrument on board the Spectrum Roentgen Gamma mission, as well as on archival data from other missions. We aim to characterise the high-energy environment of known exoplanets and estimate their mass-loss rates. We use X-ray source catalogues from eROSITA, XMM-Newton, Chandra, and ROSAT to derive X-ray luminosities of exoplanet host stars in the 0.2–2 keV energy band with an underlying coronal, that is, optically thin thermal spectrum. We present a catalogue of stellar X-ray and EUV luminosities, exoplanetary X-ray and EUV irradiation fluxes, and estimated mass-loss rates for a total of 287 exoplanets, 96 of which are characterised for the first time based on new eROSITA detections. We identify 14 first-time X-ray detections of transiting exoplanets that are subject to irradiation levels known to cause observable evaporation signatures in other exoplanets. This makes them suitable targets for follow-up observations.

Asteroseismology Across the Hertzsprung–Russell Diagram

Asteroseismology has grown from its beginnings three decades ago to a mature field teeming with discoveries and applications. This phenomenal growth has been enabled by space photometry with precision 10–100 times better than ground-based observations, with nearly continuous light curves for durations of weeks to years, and by large-scale ground-based surveys spanning years designed to detect all time-variable phenomena. The new high-precision data are full of surprises, deepening our understanding of the physics of stars. ▪ This review explores asteroseismic developments from the past decade primarily as a result of light curves from the Kepler and Transiting Exoplanet Survey Satellite space missions for massive upper main sequence OBAF stars, pre-main-sequence stars, peculiar stars, classical pulsators, white dwarfs and subdwarfs, and tidally interacting close binaries. ▪ The space missions have increased the numbers of pulsators in many classes by an order of magnitude. ▪ Asteroseismology measures fundamental stellar parameters and stellar interior physics—mass, radius, age, metallicity, luminosity, distance, magnetic fields, interior rotation, angular momentum transfer, convective overshoot, core-burning stage—supporting disparate fields such as galactic archeology, exoplanet host stars, supernovae progenitors, gamma-ray and gravitational wave precursors, close binary star origins and evolution, and standard candles. ▪ Stars are the luminous tracers of the Universe. Asteroseismology significantly improves models of stellar structure and evolution on which all inference from stars depends.

Follow‐up observations of the binary system γ Cep

AbstractWe present follow‐up imaging and spectroscopic observations of the exoplanet host star γ Cep A, and of its low‐mass stellar companion γ Cep B. We used the lucky‐imager AstraLux at the Calar Alto observatory to follow the orbital motion of the companion around its primary, whose radial velocity (RV) was determined with spectra of the star, taken with the Échelle spectrograph FLECHAS at the University Observatory Jena. We measured the astrometry of the companion relative to the exoplanet host star in all AstraLux images and determined its apparent SDSS i′‐band photometry, for which we obtained mag. Using stellar evolutionary models and the Gaia parallax of the exoplanet host star, we derived the mass of γ Cep B to be 0.39 ± 0.03 M⊙. This is in good agreement with the mass of the companion that we derived from its near‐infrared photometry given in the literature. With the detection limit reached in our AstraLux images, we explored the detection space of potential additional companions in the γ Cep binary system. In the background limited region at angular separations larger than 5 arcsec (or 69 au of projected separation) companions down to 0.11 M⊙ are detectable around the bright exoplanet host star. The radial field of view, fully covered by our AstraLux observations, exhibits a radius of 11.2 arcsec. This allows the detection of companions with projected separations up to 155 au. However, except for γ Cep B, no additional companions could be imaged with AstraLux around the exoplanet host star. We redetermined the orbital solution of the γ Cep binary system with the new AstraLux astrometry of γ Cep B and the additional radial velocities of γ Cep A, obtained from our FLECHAS spectroscopy of the star, combined with astrometric and RV data from the literature. The determined Keplerian orbital elements were used to derive the system parameters and to calculate specific future ephemeris for this intriguing exoplanet host binary star system.

A Guide to Realistic Uncertainties on the Fundamental Properties of Solar-type Exoplanet Host Stars

Abstract Our understanding of the properties and demographics of exoplanets critically relies on our ability to determine the fundamental properties of their host stars. The advent of Gaia and large spectroscopic surveys has now made it possible, in principle, to infer the properties of individual stars, including most exoplanet hosts, to very high precision. However, we show that, in practice, such analyses are limited by uncertainties in both the fundamental scale and our models of stellar evolution, even for stars similar to the Sun. For example, we show that current uncertainties on measured interferometric angular diameters and bolometric fluxes set a systematic uncertainty floor of ≈2.4% in temperature, ≈2.0% in luminosity, and ≈4.2% in radius. Comparisons between widely available model grids suggest uncertainties of order ≈5% in mass and ≈20% in age for main-sequence and subgiant stars. While the radius uncertainties are roughly constant over this range of stars, the model-dependent uncertainties are a complex function of luminosity, temperature, and metallicity. We provide open-source software for approximating these uncertainties for individual targets and discuss strategies for reducing these uncertainties in the future.

Effects of UV Stellar Spectral Uncertainty on the Chemistry of Terrestrial Atmospheres

Abstract The upcoming deployment of the James Webb Space Telescope will dramatically advance our ability to characterize exoplanet atmospheres, both in terms of precision and sensitivity to smaller and cooler planets. Disequilibrium chemical processes dominate these cooler atmospheres, requiring accurate photochemical modeling of such environments. The host star’s UV spectrum is a critical input to these models, but most exoplanet hosts lack UV observations. For cases in which the host UV spectrum is unavailable, a reconstructed or proxy spectrum will need to be used in its place. In this study, we use the MUSCLES catalog and UV line scaling relations to understand how well reconstructed host star spectra reproduce photochemically modeled atmospheres using real UV observations. We focus on two cases: a modern Earth-like atmosphere and an Archean Earth-like atmosphere that forms copious hydrocarbon hazes. We find that modern Earth-like environments are well-reproduced with UV reconstructions, whereas hazy (Archean Earth) atmospheres suffer from changes at the observable level. Specifically, both the stellar UV emission lines and the UV continuum significantly influence the chemical state and haze production in our modeled Archean atmospheres, resulting in observable differences in their transmission spectra. Our modeling results indicate that UV observations of individual exoplanet host stars are needed to accurately characterize and predict the transmission spectra of hazy terrestrial atmospheres. In the absence of UV data, reconstructed spectra that account for both UV emission lines and continuum are the next best option, albeit at the cost of modeling accuracy.

Kepler-93: A testbed for detailed seismic modelling and orbital evolution of super-Earths around solar-like stars

Context. The advent of space-based photometry missions such as CoRoT, Kepler and TESS has sparkled the rapid development of asteroseismology and its synergies with exoplanetology. In the near future, the advent of PLATO will further strengthen such multi-disciplinary studies. In that respect, testing asteroseismic modelling strategies and their importance for our understanding of planetary systems is crucial. Aims. We carried out a detailed modelling of Kepler-93, an exoplanet host star observed by the Kepler satellite for which high-quality seismic data are available. This star is particularly interesting because it is a solar-like star very similar to the PLATO benchmark target (G spectral type, ∼6000 K, ∼1 M⊙ and ∼1 R⊙) and provides a real-life testbed for potential procedures to be used in the PLATO mission. Methods. We used global and local minimisation techniques to carry out the seismic modelling of Kepler-93, for which we varied the physical ingredients of the given theoretical stellar models. We supplemented this step by seismic inversion techniques of the mean density. We then used these revised stellar parameters to provide new planetary parameters and to simulate the orbital evolution of the system under the effects of tides and atmospheric evaporation. Results. We provide the following fundamental parameters for Kepler-93: ρ̄⋆ = 1.654 ± 0.004 g cm−3, M⋆ = 0.907 ± 0.023 M⊙, R⋆ = 0.918 ± 0.008 R⊙, and Age = 6.78 ± 0.32 Gyr. The uncertainties we report for this benchmark star are well within the requirements of the PLATO mission and give confidence in the ability of providing precise and accurate stellar parameters for solar-like exoplanet-host stars. For the exoplanet Kepler-93b, we find Mp = 4.01 ± 0.67 M⊕, Rp = 1.478 ± 0.014 R⊕, and a semi-major axis a = 0.0533 ± 0.0005 AU. According to our simulations of the orbital evolution of the system, it seems unlikely that Kepler-93b formed with a mass high enough (Mp, initial > 100 M⊕) to be impacted on its orbit by stellar tides. Conclusions. For the benchmark case of a solar twin of the PLATO mission, detailed asteroseismic modelling procedures will be able to provide fundamental stellar parameters within the requirements of the PLATO mission. We also illustrate the synergies that can be achieved regarding the orbital evolution and atmospheric evaporation of exoplanets when these parameters are obtained. We also note the importance of the high-quality radial velocity follow-up, which here is a limiting factor, for providing precise planetary masses and mean densities to constrain the formation scenarii of exoplanets.

A 38 Million Year Old Neptune-sized Planet in the Kepler Field

Abstract Kepler 1627A is a G8V star previously known to host a 3.8 R ⊕ planet on a 7.2 day orbit. The star was observed by the Kepler space telescope because it is nearby (d = 329 pc) and it resembles the Sun. Here, we show using Gaia kinematics, TESS stellar rotation periods, and spectroscopic lithium abundances that Kepler 1627 is a member of the 38 − 5 + 6 Myr old δ Lyr cluster. To our knowledge, this makes Kepler 1627Ab the youngest planet with a precise age yet found by the prime Kepler mission. The Kepler photometry shows two peculiarities: the average transit profile is asymmetric, and the individual transit times might be correlated with the local light-curve slope. We discuss possible explanations for each anomaly. More importantly, the δ Lyr cluster is one of ∼103 coeval groups whose properties have been clarified by Gaia. Many other exoplanet hosts are candidate members of these clusters; their ages can be verified with the trifecta of Gaia, TESS, and ground-based spectroscopy.

Identifying interesting planetary systems for future X‐ray observations

AbstractX‐ray observations of star–planet systems are important to grow our understanding of exoplanets; these observations allow for studies of photoevaporation of the exoplanetary atmosphere, and in some cases even estimations of the size of the outer planetary atmosphere. The German–Russian eROSITA instrument onboard the SRG (Spectrum Roentgen Gamma) mission is performing the first all‐sky X‐ray survey since the 1990s, and provides X‐ray fluxes and spectra of exoplanet host stars over a much larger volume than was accessible before. Using new eROSITA data as well as archival data from XMM‐Newton, Chandra, and ROSAT, we estimate mass‐loss rates of exoplanets under an energy‐limited escape scenario and identify several exoplanets with strong X‐ray irradiation and expected mass loss that are amenable to follow‐up observations at other wavelengths. We model sample spectra using a toy model of an exoplanetary atmosphere to predict what exoplanet transit observations with future X‐ray missions such as Athena will look like and estimate the observable X‐ray transmission spectrum for a typical hot Jupiter‐type exoplanet.

X‐exoplanets coronal models and planet photoevaporation

AbstractHigh‐energy emission photons in the X‐ray and EUV bands ionize H and other atoms, posing a threat to the stability of the atmospheres of short‐period exoplanets orbiting late‐type stars. Effects such as planet atmospheric evaporation are being attributed in the last years to XUV stellar irradiation on the planets. Early theoretical works tried to model how the XUV emission would affect the planetary atmospheres, mainly by using the solar emission as a template. In X‐exoplanets, we reported for the first time coronal models based on actual data from the exoplanet host stars. The use of coronal models allows us to model the SED of the XUV emission of these stars, otherwise inaccessible to current telescopes. In this manuscript, I present the use of these models with datasets of different data quality, depending on the availability of low or high spectral resolution spectra in both X‐rays and UV. Comparison with actual data is shown for the exoplanet host star Proxima Cen and the Sun. The challenges for the future use of coronal models in exoplanet atmospheres are discussed, involving mainly the use of new EUV and X‐ray spectrographs, better atomic models, and more accurate planet atmosphere evolution models.

Resolving the Multiplicity of Exoplanet Host Stars in Gemini/NIRI Data

Abstract The majority of stars have one or more stellar companions. As exoplanets continue to be discovered, it is crucial to examine planetary systems to identify their stellar companions. By observing a change in proper motion, companions can be detected by the acceleration they induce on their host stars. We selected 701 stars from the Hipparcos–Gaia Catalog of Accelerations (HGCA) that have existing adaptive optics imaging data gathered with Gemini/Near InfraRed Imager (NIRI). Of these, we examined 21 stars known to host planet candidates and reduced their archival NIRI data with Gemini’s DRAGONS software. We assessed these systems for companions using the NIRI images as well as Renormalized Unit Weight Error values in Gaia and accelerations in the HGCA. We detected three known visible companions and found two more systems with no visible companions but astrometric measurements indicating likely unresolved companions.

EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of ϵ Eridani with Photometry and Interferometry

Abstract The distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes ≲ 10 cm s−1, but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host ϵ Eridani, we separately used ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produced an activity model that reduced the rms scatter in RVs obtained with EXPRES from 4.72 to 1.98 m s−1. We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as allow the stellar inclination and orientation with respect to the debris disk to be definitively determined. This work shows that stellar surface maps obtained with high-cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter.

The GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys

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

TOI-1431b/MASCARA-5b: A Highly Irradiated Ultrahot Jupiter Orbiting One of the Hottest and Brightest Known Exoplanet Host Stars

Abstract We present the discovery of a highly irradiated and moderately inflated ultrahot Jupiter, TOI-1431b/MASCARA-5 b (HD 201033b), first detected by NASA’s Transiting Exoplanet Survey Satellite mission (TESS) and the Multi-site All-Sky Camera (MASCARA). The signal was established to be of planetary origin through radial velocity measurements obtained using SONG, SOPHIE, FIES, NRES, and EXPRES, which show a reflex motion of K = 294.1 ± 1.1 m s−1. A joint analysis of the TESS and ground-based photometry and radial velocity measurements reveals that TOI-1431b has a mass of M p = 3.12 ± 0.18 M J (990 ± 60 M ⊕), an inflated radius of R p = 1.49 ± 0.05 R J (16.7 ± 0.6 R ⊕), and an orbital period of P = 2.650237 ± 0.000003 days. Analysis of the spectral energy distribution of the host star reveals that the planet orbits a bright (V = 8.049 mag) and young ( 0.29 − 0.19 + 0.32 Gyr) Am type star with T eff = 7690 − 250 + 400 K, resulting in a highly irradiated planet with an incident flux of 〈 F 〉 = 7.24 − 0.64 + 0.68 × 109 erg s−1 cm−2 ( 5300 − 470 + 500 S ⊕ ) and an equilibrium temperature of T eq = 2370 ± 70 K. TESS photometry also reveals a secondary eclipse with a depth of 127 − 5 + 4 ppm as well as the full phase curve of the planet’s thermal emission in the red-optical. This has allowed us to measure the dayside and nightside temperature of its atmosphere as T day = 3004 ± 64 K and T night = 2583 ± 63 K, the second hottest measured nightside temperature. The planet’s low day/night temperature contrast (∼420 K) suggests very efficient heat transport between the dayside and nightside hemispheres. Given the host star brightness and estimated secondary eclipse depth of ∼1000 ppm in the K band, the secondary eclipse is potentially detectable at near-IR wavelengths with ground-based facilities, and the planet is ideal for intensive atmospheric characterization through transmission and emission spectroscopy from space missions such as the James Webb Space Telescope and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey.

Asteroseismology of iota Draconis and Discovery of an Additional Long-period Companion

Abstract Giant stars as known exoplanet hosts are relatively rare due to the potential challenges in acquiring precision radial velocities and the small predicted transit depths. However, these giant host stars are also some of the brightest in the sky and so enable high signal-to-noise ratio follow-up measurements. Here, we report on new observations of the bright (V ∼ 3.3) giant star ι Draconis (ι Dra), known to host a planet in a highly eccentric ∼511 day period orbit. TESS observations of the star over 137 days reveal asteroseismic signatures, allowing us to constrain the stellar radius, mass, and age to ∼2%, ∼6%, and ∼28%, respectively. We present the results of continued radial-velocity monitoring of the star using the Automated Planet Finder over several orbits of the planet. We provide more precise planet parameters of the known planet and, through the combination of our radial-velocity measurements with Hipparcos and Gaia astrometry, we discover an additional long-period companion with an orbital period of ∼ 68 − 36 + 60 yr. Mass predictions from our analysis place this substellar companion on the border of the planet and brown dwarf regimes. The bright nature of the star combined with the revised orbital architecture of the system provides an opportunity to study planetary orbital dynamics that evolve as the star moves into the giant phase of its evolution.

On the Demographics of Exoplanet Host Stars

Abstract The NASA TESS mission has provided the community with a plethora of new exoplanet host stars. These bright, nearby stars have been examined in detail in a number of studies and it has been determined that nearly one-half of the solar-like stars are binary. Two recent papers which examined 700 TESS exoplanet hosts have provided stellar properties for the stars, both single and binary. Herein, we provide a quantitative look at some properties of the stars, particularly searching for differences between the single versus binary (primary) host stars. We also compare the properties of the binary (primary) host stars themselves.

Solar Neighborhood Exoplanet Host Stars within a Galactic Context

Abstract Ages, metallicities, and Galactic orbit parameters are considered for those stars with Henry Draper catalog designations that have been discovered to host planetary systems. There are quite a few such stars with above-solar metallicity and ages up to 4 Gyr older than the Sun. Some planet-hosting stars have Galactic orbits that take them within 4 kpc of the Galactic Center, while a substantial fraction attain displacements from the Galactic mid-plane consistent with the thick disk.

The M-dwarf Ultraviolet Spectroscopic Sample. I. Determining Stellar Parameters for Field Stars

Abstract Accurate stellar properties are essential for precise stellar astrophysics and exoplanetary science. In the M-dwarf regime, much effort has gone into defining empirical relations that can use readily accessible observables to assess physical stellar properties. Often, these relations for the quantity of interest are cast as a nonlinear function of available data; in Bayesian modeling, however, the reverse is needed. In this article, we introduce a new Bayesian framework to self-consistently and simultaneously apply multiple empirical calibrations to fully characterize the mass, luminosity, radius, and effective temperature of a field age M dwarf. This framework includes a new M-dwarf mass–radius relation with a scatter of 3.1% at fixed mass. We further introduce the M-dwarf Ultraviolet Spectroscopic Sample (MUSS), and apply our methodology to provide consistent stellar parameters for these nearby low-mass stars, selected as having available spectroscopic data in the ultraviolet. These targets are of interest largely as either exoplanet hosts or benchmarks in multiwavelength stellar activity. We use the field MUSS stars to define a low-mass main sequence in the solar neighborhood through Gaussian Process (GP) regression. These results enable us to empirically measure a feature in the GP derivative at  b = 0.337 ± 0.026 0.013 M ⊙ that indicates where the MUSS transitions from fully to partly convective interiors.