Target Stars Research Articles

Stability analysis of three exoplanet systems

ABSTRACT The orbital solutions of published multiplanet systems are not necessarily dynamically stable on time-scales comparable to the lifetime of the system as a whole. For this reason, dynamical tests of the architectures of proposed exoplanetary systems are a critical tool to probe the stability and feasibility of the candidate planetary systems, with the potential to point the way towards refined orbital parameters of those planets. Such studies can even help in the identification of additional companions in such systems. Here, we examine the dynamical stability of three planetary systems, orbiting HD 67087, HD 110014, and HD 133131A. We use the published radial velocity measurements of the target stars to determine the best-fitting orbital solutions for these planetary systems using the systemic console. We then employ the N-body integrator mercury to test the stability of a range of orbital solutions lying within 3σ of the nominal best fit for a duration of 100 Myr. From the results of the N-body integrations, we infer the best-fitting orbital parameters using the Bayesian package astroemperor. We find that both HD 110014 and HD 133131A have long-term stable architectures that lie within the 1σ uncertainties of the nominal best fit to their previously determined orbital solutions. However, the HD 67087 system exhibits a strong tendency towards instability on short time-scales. We compare these results to the predictions made from consideration of the angular momentum deficit criterion, and find that its predictions are consistent with our findings.

Starshade formation flying II: formation control

Several starshade concepts for imaging exo-Earths would operate at the second Earth–Sun Lagrange point (L2) and consist of a starshade flying in formation tens to hundreds of thousands of kilometers from a telescope. The starshade would need to maintain meter-level lateral alignment with the line of sight from telescope to target star. A companion paper describes an optical sensing scheme using a pupil imaging camera in the telescope that can sense the relative lateral position to a few centimeters. A full flight-traceable formation flying framework that leverages this sensor is presented. In particular, a two-dimensional “disk deadbanding” algorithm is introduced for lateral control. The framework also maximizes the drift time between thruster burns to reduce interruption to scientific observations. The main sources of uncertainty affecting the control performance are compared, and it is found that spacecraft mass uncertainty is a driving factor. The formation flying environment is also analyzed to identify conditions that lead to worst-case differential gravity and solar radiation pressure disturbances. Finally, for a representative observation scenario with the Wide Field Infrared Space Telescope, this control system is tested through Monte Carlo simulations. The results show robust meter-level control with essentially optimal drift time between thruster burns.

Diffuse Interstellar Bands (DIBs) on the spectra of GALAH data: Correlation study between DIBs and DIBs with color excess

Diffuse interstellar bands (DIBs) are a collection of weak interstellar absorptions in the spectra of reddened objects. We have successfully measured three strong DIBs (i.e., λ 5780, 5797, and 6614 Å) on the spectra of 125 Galactic Archaeology with HERMES (GALAH) target stars. The fitting uses a template spectrum in order to extract and measure individual DIB. We applied a correlation study between DIBs and confirmed that DIBs are positively correlated with each other, meaning that their carrier(s) are co-existing in the interstellar medium. Also, DIBs are well-correlated with color excess E(B-V). From this result, which is in a good agreement with earlier studies, conclude that DIBs can be used as a tracer of the interstellar medium.

Toward Extremely Precise Radial Velocities. I. Simulated Solar Spectra for Testing Exoplanet Detection Algorithms

Recent and upcoming stabilized spectrographs are pushing the frontier for Doppler spectroscopy to detect and characterize low-mass planets. Specifications for these instruments are so impressive that intrinsic stellar variability is expected to limit their Doppler precision for most target stars (Fischer et al. 2016). To realize their full potential, astronomers must develop new strategies for distinguishing true Doppler shifts from intrinsic stellar variability. Stellar variability due to star spots, faculae and other rotationally-linked variability are particularly concerning, as the stellar rotation period is often included in the range of potential planet orbital periods. To robustly detect and accurately characterize low-mass planets via Doppler planet surveys, the exoplanet community must develop statistical models capable of jointly modeling planetary perturbations and intrinsic stellar variability. Towards this effort, this note presents simulations of extremely high resolution, solar-like spectra created with SOAP 2.0 (arXiv:1409.3594) that includes multiple evolving star spots. We anticipate this data set will contribute to future studies developing, testing, and comparing statistical methods for measuring physical radial velocities amid contamination by stellar variability.

ISPY-NACO Imaging Survey for Planets around Young stars

Context.The occurrence rate of long-period (a≳ 50 au) giant planets around young stars is highly uncertain since it is not only governed by the protoplanetary disc structure and planet formation process, but also reflects both dynamical re-structuring processes after planet formation as well as possible capture of planets not formed in situ. Direct imaging is currently the only feasible method to detect such wide-orbit planets and constrain their occurrence rate.Aims.We aim to detect and characterise wide-orbit giant planets during and shortly after their formation phase within protoplanetary and debris discs around nearby young stars.Methods.We carry out a largeL′-band high-contrast direct imaging survey for giant planets around 200 young stars with protoplanetary or debris discs using the NACO instrument at the ESO Very Large Telescope on Cerro Paranal in Chile. We use very deep angular differential imaging observations with typically >60° field rotation, and employ a vector vortex coronagraph where feasible to achieve the best possible point source sensitivity down to an inner working angle of about 100 mas. This paper introduces the NACO Imaging Survey for Planets around Young stars (NACO-ISPY), its goals and strategy, the target list, and data reduction scheme, and presents preliminary results from the first 2.5 survey years.Results.We achieve a mean 5σcontrast of ΔL′ = 6.4 ± 0.1 mag at 150 mas and a background limit ofL′bg= 16.5±0.2 mag at >1.′′5. Our detection probability is >50% for companions with ≳8MJupat semi-major axes of 80–200 au and >13MJupat 30–250 au. It thus compares well to the detection space of other state-of-the-art high-contrast imaging surveys. We have already contributed to the characterisation of two new planets originally discovered by VLT/SPHERE, but we have not yet independently discovered new planets around any of our target stars. We have discovered two new close-in low-mass stellar companions around R CrA and HD 193571 and report in this paper the discovery of close co-moving low-mass stellar companions around HD 72660 and HD 92536. Furthermore, we reportL′-band scattered light images of the discs around eleven stars, six of which have never been imaged atL′-band before.Conclusions.The first 2.5 yr of the NACO-ISPY survey have already demonstrated that VLT/NACO combined with our survey strategy can achieve the anticipated sensitivity to detect giant planets and reveal new close stellar companions around our target stars.

Searching for exoplanets by HEPS II. detecting earth-like planets in habitable zone around planet hosts within 30 pc

HEPS (Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone (HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.

Interstellar Extinction in the Direction of the Young Open Cluster NGC 6530

We present UBVRI polarization observations of 12 B-type stars in the direction of the young open cluster NGC 6530, nine of them confirmed as probable members. The maximum degree of polarization for our target stars ranges from 0.16% to 2.84%, with an average value of 1.1%. We note variations of the polarization vector orientations across the cluster field. We use the polarization data to infer the wavelength of maximum polarization and obtain the total-to-selective extinction ratio for each star. Based on all 12 observed stars, the weighted average wavelength of the maximum degree of polarization is 0.563 ± 0.001 μm. This yields an average value of R = 3.15 ± 0.06 for the total-to-selective extinction associated with this field. Despite slight variations, RV is not abnormal. Using UBV photometry combined with recent photometric calibrations yields average E(B − V) = 0.38 ± 0.07 (s.d.) mag and average AV = 1.20 ± 0.24 (s.d.) mag. Both RV and E(B − V) show star-to-star variations. Our study yields a photometry-based distance of 1.6 kpc. For more precise distance estimates, especially when seeking agreement with the Gaia parallaxes, better evaluation of peculiarity and duplicity of these stars is needed. We studied comparisons between the photometric UBV absolute magnitudes, Gaia-based absolute magnitudes and magnitudes obtained from direct measurements of the Balmer discontinuity and discuss the presently existing disagreements for the cluster field.

A compact multi-planet system around a bright nearby star from the Dispersed Matter Planet Project

The Dispersed Matter Planet Project targets stars with anomalously low Ca II H&K chromospheric emission. High precision, high cadence radial velocity measurements of the F8V star HD 38677 / DMPP-1 reveal four short period planets. DMPP-1 has log(R'HK) = -5.16 which probably indicates the presence of circumstellar absorbing gas arising from an ablating hot planet. The planets have P$_{\rm orb}$ ~ 2.9 - 19 d, i.e., a compact planetary system with super-Earth (~3 M$_\oplus$) to Neptune-mass (~24 M$_\oplus$) planets. These irradiated planets may be chthonian: remnant cores of giant planets after mass-loss while crossing the Neptune desert. Modelling the possible long-term activity indicators while searching for Keplerian signals modifies the recovered planetary signals. A priori inferences about the presence of short period planets allowed the efficient discovery of the DMPP-1 planets. They have great potential for novel and informative follow-up characterisation studies.

MOPSS. II. Extreme Optical Scattering Slope for the Inflated Super-Neptune HATS-8b

Abstract We present results for the inflated super-Neptune HATS-8b from the Michigan Optical Planetary Spectra Survey (MOPSS). This program is aimed at creating a database of optical planetary transmission spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. HATS-8b orbits a G dwarf and is a low-density super-Neptune with a radius of 0.873 R Jup, a mass of 0.138 M Jup, and a density of 0.259 g cm−3. Two transits of HATS-8b were observed in 2017 July and August with the Inamori-Magellan Areal Camera and Spectrograph (IMACS) instrument on the Magellan Baade 6.5 m telescope. We find an enhanced scattering slope on each night that agree within 2.3σ. This slope is stronger than one due only to Rayleigh scattering and cannot be fully explained by unocculted starspots. We explore the impact of condensates on the scattering slope and determine that MnS particulates smaller than 10−2 μm can explain up to 80% of our measured slope if the planet is warmer than equilibrium, or 50% of the slope at the equilibrium temperature of the planet for a low mean molecular weight atmosphere. The scattering slope that we observe is thus beyond even the most extreme haze case we consider. We suggest further follow up on this target and host star to determine if the temporal variation of the slope is primarily due to stellar or planetary effects, and to better understand what these effects may be.

Asteroseismological analysis of the ultra-massive ZZ Ceti stars BPM 37093, GD 518, and SDSS J0840+5222

Context. Ultra-massive (≳1 M⊙) hydrogen-rich (DA) white dwarfs are expected to have a substantial portion of their cores in a crystalline state at the effective temperatures characterising the ZZ Ceti instability strip (Teff ∼ 12 500 K) as a result of Coulomb interactions in very dense plasmas. Asteroseismological analyses of these white dwarfs can provide valuable information related to the crystallisation process, the core chemical composition, and the evolutionary origin of these stars. Aims. We present a thorough asteroseismological analysis of the ultra-massive ZZ Ceti star BPM 37093, which exhibits a rich period spectrum, on the basis of a complete set of fully evolutionary models that represent ultra-massive oxygen/neon (ONe) core DA white dwarf stars harbouring a range of hydrogen (H) envelope thicknesses. We also carry out preliminary asteroseismological inferences on two other ultra-massive ZZ Ceti stars that exhibit fewer periods, GD 518, and SDSS J0840+5222. Methods. We considered g-mode adiabatic pulsation periods for ultra-massive ONe-core DA white dwarf models with stellar masses in the range 1.10 ≲ M⋆/M⊙ ≲ 1.29, effective temperatures in the range 10 000 ≲ Teff ≲ 15 000 K, and H-envelope thicknesses in the interval −10 ≲ log(MH/M⋆)≲ − 6. We explored the effects of employing different H-envelope thicknesses on the mode-trapping properties of our ultra-massive ONe-core DA white dwarf models and performed period-to-period fits to ultra-massive ZZ Ceti stars with the aim of finding an asteroseismological model for each target star. Results. We find that the trapping cycle and trapping amplitude are larger for thinner H envelopes, and that the asymptotic period spacing is longer for thinner H envelopes. We find a mean period spacing of ΔΠ ∼ 17 s in the data of BPM 37093, which is likely to be associated with ℓ = 2 modes. However, we are not able to put constraints on the stellar mass of BPM 37093 using this mean period spacing due to the simultaneous sensitivity of ΔΠ with M⋆, Teff, and MH, which is an intrinsic property of DAV stars. We find asteroseismological models for the three objects under analysis, two of them (BPM 37093 and GD 518) characterised by canonical (thick) H envelopes, and the third one (SDSS J0840+5222) with a thinner H envelope. The effective temperature and stellar mass of these models are in agreement with the spectroscopic determinations. The percentage of crystallised mass for these asteroseismological models is 92%, 97%, and 81% for BPM 37093, GD 518, and SDSS J0840+5222, respectively. We also derive asteroseismological distances which differ somewhat from the astrometric measurements of Gaia for these stars. Conclusions. Asteroseismological analyses like the one presented in this paper could lead to a more complete understanding of the processes occurring during crystallisation inside white dwarfs. Also, such analyses could make it possible to deduce the core chemical composition of ultra-massive white dwarfs and, in this way, to infer their evolutionary origin, such as the correlation between a star’s ONe core and its having originated through single-star evolution or a carbon/oxygen (CO) core indicating the star is the product of a merger of the two components of a binary system. However, in order to achieve these objectives, it is necessary to find a greater number of pulsating ultra-massive WDs and to carry out additional observations of known pulsating stars to detect more pulsation periods. Space missions such as TESS can provide a great boost towards achieving these aims.

Carbon depletion observed inside T Tauri inner rims

Context. The carbon content of protoplanetary disks is an important parameter to characterize planets formed at different disk radii. There is some evidence from far-infrared and submillimeter observations that gas in the outer disk is depleted in carbon, with a corresponding enhancement of carbon-rich ices at the disk midplane. Observations of the carbon content inside of the inner sublimation rim could confirm how much carbon remains locked in kilometer size bodies in the disk. Aims. I aim to determine the density, temperature, and carbon abundance inside the disk dust sublimation rim in a set of T Tauri stars with full protoplanetary disks. Methods. Using medium-resolution, near-infrared (0.8–2.5 μm) spectra and the new Gaia DR2 distances, I self-consistently determine the stellar, extinction, veiling, and accretion properties of the 26 stars in my sample. From these values, and non-accreting T Tauri spectral templates, I extract the inner disk excess of the target stars from their observed spectra. Then I identify a series of C0 recombination lines in 18 of these disks and use the CHIANTI atomic line database with an optically thin slab model to constrain the average ne, Te, and nc for these lines in the five disks with a complete set of lines. By comparing these values with other slab models of the inner disk using the Cloudy photoionization code, I also constrain nH and the carbon abundance, XC, and hence the amount of carbon “missing” from the slab. For one disk, DR Tau, I use relative abundances for the accretion stream from the literature to also determine XSi and XN. Results. The inner disks modeled here are extremely dense (nH ~ 1016 cm−3), warm (Te ~ 4500 K), and moderately ionized (log Xe ~ 3.3). Three of the five modeled disks show robust carbon depletion up to a factor of 42 relative to the solar value. I discuss multiple ways in which the “missing” carbon could be locked out of the accreting gas. Given the high-density inner disk gas, evidence for radial drift, and lack of obvious gaps in these three systems, their carbon depletion is most consistent with the “missing” carbon being sequestered in kilometer size bodies. For DR Tau, nitrogen and silicon are also depleted by factors of 45 and 4, respectively, suggesting that the kilometer size bodies into which the grains are locked were formed beyond the N2 snowline. I explore briefly what improvements in the models and observations are needed to better address this topic in the future.

Model of the Search for Extraterrestrial Intelligence with Coronagraphic Imaging

Abstract We present modeled detection limits of the Gemini Planet Imager (GPI) and the Wide-Field Infrared Space Telescope (WFIRST) to an optical and infrared laser which could be used by an extraterrestrial civilization to signal their presence. GPI and WFIRST could utilize a coronagraph to search for extraterrestrial intelligence in the present and future. We use archival data for GPI stars and simulated WFIRST observations to find the detectable flux ratio of a laser signal to residual scattered starlight around the target star. This flux ratio is then converted to detectable power as a function of distance from the parent star. For GPI, we assume a monochromatic laser wavelength of 1.55 μm and a wavelength of 575 nm for WFIRST. We assume that the lasers are projected through a 10 m aperture, and that the intensity of the laser beam follows a Gaussian profile. Our analysis is performed on six stars with spectral types later than F within 20 pc (with an emphasis on solar analogs at different distances). The most notable result is the detection limit for τ Ceti, a G5V star with four known exoplanets, two of those within the habitable zone (HZ). The result shows that a 24 kW laser is detectable from τ Ceti from outside of the HZ with GPI and a 7.3 W laser is detectable from within τ Ceti’s HZ by WFIRST.

A Host-star Calibration Based Polarimeter for Earth-like Exoplanet Imaging

We propose a polarimeter, which is dedicated to Earth-like exoplanet imaging for future space missions. We adopt a minimum-polarization-component design philosophy, which makes a compact and robust system as well as high-performance achievable in the real world. Our polarimeter consists of two polarization components of a liquid crystal variable retarders (LCVR) and a Wollaston prism. The polarimeter can deliver an extra contrast better than 10−4.5. Combined with one of the currently available coronagraphs that are delivering a contrast on the order of 10−6.5, the coronagraph and polarimeter system can deliver a contrast better than 10−11 at a small inner working angle in the visible over the entire imaging plane. We discuss the polarimeter design concept and dedicated data-reduction technique. Our unique host-star calibration algorithm allows the starlight to be totally removed, regardless of whether the host-star image is intrinsically polarized or whether the light is polarized by preoptics, such as the telescope that is located before the polarimeter, which makes exoplanet polarization imaging feasible with any telescope, optical system, and target star. Using minimum-polarization components with a solid-state image LCVR as the key polarization component, our polarimeter is less sensitive to the wavefront phase and amplitude errors than other exoplanet imaging techniques. Based on commercial-grade optical components, we demonstrated for the first time that by combining our polarimeter with a currently available coronagraph, the polarimeter and coronagraph system can deliver a contrast better than 10−11 at a small inner working angle in the visible wavelengths, which paves the way for Earth-like exoplanet imaging for a future space mission.

A Recipe for Finding Stellar Radii, Temperatures, Surface Gravities, Metallicities, and Masses Using Spectral Lines

Abstract A recipe based on physical principles employs the observed equivalent widths of 10 spectral lines to model the photosphere of a target star. Coupled with the visual magnitude and an absolute flux calibration, the recipe yields the angular radius, effective temperature, surface gravity, and metallicity. With the addition of a parallax, a linear radius and a mass estimate are added to the results. The method is applied to a sample of 26 G and K stars that span luminosity classes V to IIIa. The recipe-determined angular radii agree with the interferometer radii and have comparable errors. But unlike interferometers, the recipe is not limited to sizes ≳1 mas. The veracity of the other recipe-derived parameters is supported by numerous comparisons with previously published values.

Catalog for the ESPRESSO blind radial velocity exoplanet survey

Aims.One of the main scientific drivers for ESPRESSO, Échelle SPectrograph, is the detection and characterization of Earth-class exoplanets. With this goal in mind, the ESPRESSO guaranteed time observations (GTO) Catalog identifies the best target stars for a blind search for the radial velocity (RV) signals caused by Earth-class exoplanets.Methods.Using the most complete stellar catalogs available, we screened for the most suitable G, K, and M dwarf stars for the detection of Earth-class exoplanets with ESPRESSO. For most of the stars, we then gathered high-resolution spectra from new observations or from archival data. We used these spectra to spectroscopically investigate the existence of any stellar binaries, both bound or background stars. We derived the activity level using chromospheric activity indexes using log (R′HK), as well as the projected rotational velocityvsini. For the cases where planet companions are already known, we also looked at the possibility that additional planets may exist in the host’s habitable zone using dynamical arguments.Results.We estimated the spectroscopic contamination level,vsini, activity, stellar parameters and chemical abundances for 249 of the most promising targets. Using these data, we selected 45 stars that match our criteria for detectability of a planet like Earth. The stars presented and discussed in this paper constitute the ESPRESSO GTO catalog for the RV blind search for Earth-class planets. They can also be used for any other work requiring a detailed spectroscopic characterization of stars in the solar neighborhood.

Detection of Hundreds of New Planet Candidates and Eclipsing Binaries in K2 Campaigns 0–8

Abstract We implement a search for exoplanets in campaigns zero through eight (C0–8) of the K2 extension of the Kepler spacecraft. We apply a modified version of the QATS planet search algorithm to K2 light curves produced by the EVEREST pipeline, carrying out the C0–8 search on 1.5 × 105 target stars with magnitudes in the range of Kp = 9−15. We detect 818 transiting planet candidates, of which 374 were undiscovered by prior searches, with {64, 15, 5, 2, 1} in {2, 3, 4, 5, 6}-planet multiplanet candidate systems, respectively. Of the new planets detected, 100 orbit M dwarfs, including one that is potentially rocky and in the habitable zone. A total of 154 of our candidates reciprocally transit with our solar system: they are geometrically aligned to see at least one solar system planet transit. We find candidates that display transit timing variations and dozens of candidates on both period extremes with single transits or ultrashort periods. We point to evidence that our candidates display similar patterns in frequency and size–period relation to confirmed planets, such as tentative evidence for the radius gap. Confirmation of these planet candidates with follow-up studies will increase the number of K2 planets by up to 50%, and characterization of their host stars will improve statistical studies of planet properties. Our sample includes many planets orbiting bright stars amenable for radial velocity follow-up and future characterization with JWST. We also list the 579 eclipsing binary systems detected as part of this search.

Photometric Observation of WASP-52b and TrES-3b

We present the photometric observation of transiting exoplanets WASP-52 b and TrES-3 b using Bosscha Robotic Telescope. The transit method relies on measuring the flux drops of the target star when the planet is transiting in front of it. We have derived physical parameters of these planets using single transit light curve and the results are consistent with the discovery paper which used more observation data.

Tracing Galactic Arm with 6614 Å Diffuse Interstellar Band and Gaia DR2 Distances

Enigmatic problem in astronomical spectroscopy is diffuse interstellar bands (DIBs). DIBs are ∼ 500 weak and broad absorption features seen in the spectra of stars or other astronomical objects located behind interstellar materials. Despite the unknown ions or molecules that caused the absorptions, except for two near infrared DIBs, DIBs can be used as a potential interstellar medium (ISM) tracer to map Galactic structure. Gaia is a mission of the European Space Agency (ESA) which was launched on 2013. It provides precise distances which greatly improve our knowledge of the structure and history of our Galaxy. In this work, we used previously determined DIB equivalent width (EW) measurements by means of DIB fitting that is a combination of a synthetic stellar spectrum, a synthetic telluric transmission, and empirical DIB profile to the Gaia–ESO Large Public Spectroscopic Survey data. From DIB measurements from stellar spectra of distributed target stars and together with Gaia DR2 distances, we investigated the ISM distribution along particular line of sight, i.e., (l,b)∼(213°, -2°) which probes Local and Perseus Arm.

Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars IV: Updated Properties for 86 Cool Dwarfs Observed During Campaigns 1-17.

We present revised stellar properties for 172 K2 target stars that were identified as possible hosts of transiting planets during Campaigns 1-17. Using medium-resolution near-infrared spectra acquired with the NASA Infrared Telescope Facility/SpeX and Palomar/TripleSpec, we found that 86 of our targets were bona fide cool dwarfs, 74 were hotter dwarfs, and 12 were giants. Combining our spectroscopic metallicities with Gaia parallaxes and archival photometry, we derived photometric stellar parameters and compared them to our spectroscopic estimates. Although our spectroscopic and photometric radius and temperature estimates are consistent, our photometric mass estimates are systematically ΔM * = 0.11 M⊙ (34%) higher than our spectroscopic mass estimates for the least massive stars (M *,phoi < 0.4 M⊙). Adopting the photometric parameters and comparing our results to parameters reported in the Ecliptic Plane Input Catalog, our revised stellar radii are ΔR * = 0.15R⊙ (40%) larger and our revised stellar effective temperatures are roughly ΔT eff = 65K cooler. Correctly determining the properties of K2 target stars is essential for characterizing any associated planet candidates, estimating the planet search sensitivity, and calculating planet occurrence rates. Even though Gaia parallaxes have increased the power of photometric surveys, spectroscopic characterization remains essential for determining stellar metallicities and investigating correlations between stellar metallicity and planetary properties.

Testing Seismic Models of Hot B Subdwarfs with Gaia Data

Abstract We report the results of a study designed to test further the basic validity of the seismic models of hot pulsating B subdwarfs that have been developed over the last two decades. Given estimates of the effective temperature, surface gravity, and mass as obtained from a seismic analysis, and given an estimate of the He/H ratio as available from independent spectroscopy, it is possible to compute a “seismic distance” that is suitably corrected for interstellar reddening from a model atmosphere calculation in conjunction with two-band photometry. The test consists of comparing such a distance with that obtained directly from the high-accuracy Gaia parallax measurements that have become available through Data Release 2. Using observed magnitudes in the Gaia G BP, G RP bandpasses as well as ground-based photometry in the Johnson B, V, Strömgren b, y, and SDSS g, r filters, we find that all of our seismic estimates fall within 1σ of their parallax counterparts. In addition, the derived reddening for our target stars is shown to be generally consistent with Galactic dust reddening and extinction maps. These results apply to a sample of 14 pulsating hot B subdwarfs for which seismic models were published in the past. We also derive useful constraints on the distances to two more pulsators that belong to unresolved binary systems. The excellent agreement found between seismic and parallax distances for the bulk of the sample adds further credibility to the seismic models that have been calculated for pulsators of this type.