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DOE OSTI2020

Nearby Quintuple Systems κ Tucanae and ξ Scorpii

Architecture and parameters of two wide, nearby hierarchical systems containing five solar-type stars each, κ Tuc and ξ Sco, are studied. Using Gaia astrometry and photometry, masses are determined from visual orbits and isochrones, and effective temperatures from spectra or colors. Both systems are ∼2 Gyr old. Their spatial motion corresponds to a young disk but does not match any known kinematic group. Internal proper motions relative to the center of mass and radial velocities show that wide ∼8 kau outer pairs are bound. No correlation between orbit orientations in the inner subsystems is observed. All masses except one are confined to the narrow range from 0.8 to 1.5 solar. Strongly correlated masses and wide orbits can be explained if those systems formed by fragmentation in relative isolation and their components accreted gas from a common source, as expected in a hierarchical collapse. Young moving groups could be formed in similar environments, and many of them contain high-order hierarchies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Visual Orbits of Spectroscopic Binaries with the CHARA Array. III. HD 8374 and HD 24546

We present the visual orbits of two long-period spectroscopic binary stars, HD 8374 and HD 24546, using interferometric observations acquired with the CHARA Array and the Palomar Testbed Interferometer. We also obtained new radial velocities from echelle spectra using the APO 3.5 m and Fairborn 2.0 m telescopes. By combining the visual and spectroscopic observations, we solve for the full, three-dimensional orbits and determine the stellar masses and distances to within 3% uncertainty. We then estimate the effective temperature and radius of each component star through Doppler tomography and spectral energy distribution analyses, in order to compare the observed stellar parameters to the predictions of stellar evolution models. For HD 8374, we find masses of M {sub 1} = 1.636 ± 0.050M {sub ⊙} and M {sub 2} = 1.587 ± 0.049M {sub ⊙}, radii of R {sub 1} = 1.84 ± 0.05R {sub ⊙} and R {sub 2} = 1.66 ± 0.12R {sub ⊙}, temperatures of T{sub eff1}=7280±110 K and T{sub eff2}=7280±120 K, and an estimated age of 1.0 Gyr. For HD 24546, we find masses of M {sub 1} = 1.434 ± 0.014M {sub ⊙} and M {sub 2} = 1.409 ± 0.014M {sub ⊙}, radii of R {sub 1} = 1.67 ± 0.06R {sub ⊙} and R {sub 2} = 1.60 ± 0.10R {sub ⊙}, temperatures of T{sub eff1}=6790±120 K and T{sub eff2}=6770±90 K, and an estimated age of 1.4 Gyr. HD 24546 is therefore too old to be a member of the Hyades cluster, despite its physical proximity to the group.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

KELT-9 b’s Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment

KELT-9 b is an ultra-hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b’s transit light curve using photometry from the Transiting Exoplanet Survey Satellite to constrain the planet’s true spin–orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star’s equatorial radius to be 1.089 ± 0.017 times as large as its polar radius and its local surface brightness to vary by ∼38% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light-curve asymmetry to constrain KELT-9 b’s true spin–orbit angle (87{sup ∘}{sub −11{sup ∘+10{sup {sup ∘}}}}), agreeing with Gaudi et al. that KELT-9 b is in a nearly polar orbit. We also apply a gravity-darkening correction to the spectral energy distribution model from Gaudi et al. and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star’s polar effective temperature.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

The Pre-He White Dwarfs in Eclipsing Binaries. I. WASP 0131+28

We report the first BV light curves and high-resolution spectra of the post-mass transfer binary star WASP 0131+28 to study the absolute properties of extremely low-mass white dwarfs. From the observed spectra, the double-lined radial velocities were derived, and the effective temperature and rotational velocity of the brighter, more massive primary were found to be T{sub eff,1}=10,000±200 K and v{sub 1}sin i = 55 ± 10 km s{sup −1}, respectively. The combined analysis of the Transiting Exoplanet Survey Satellite (TESS) archive data and ours yielded the accurate fundamental parameters of the program target. The masses were derived to about 1.0% accuracy and the radii to 0.6%, or better. The secondary component's parameters of M{sub 2}=0.200±0.002 M{sub ⊙}, R{sub 2}=0.528±0.003 R{sub ⊙}, T{sub eff,2} = 11,186 ± 235 K, and L{sub 2}=3.9±0.3 L{sub ⊙} are in excellent agreement with the evolutionary sequence for a helium-core white dwarf of mass 0.203 M{sub ⊙}, and indicates that this star is halfway through the constant luminosity phase. The results presented in this article demonstrate that WASP 0131+28 is an EL CVn eclipsing binary in a thin disk, which is formed from the stable Roche-lobe overflow channel and composed of a main-sequence dwarf with a spectral type A0 and a pre-He white dwarf.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

The Sixth Data Release of the Radial Velocity Experiment (Rave). II. Stellar Atmospheric Parameters, Chemical Abundances, and Distances

We present part 2 of the sixth and final Data Release (DR6) of the Radial Velocity Experiment (Rave), a magnitude-limited (9<I<12) spectroscopic survey of Galactic stars randomly selected in Earth’s southern hemisphere. The Rave medium-resolution spectra (R ∼ 7500) cover the Ca triplet region (8410–8795 Å) and span the complete time frame from the start of Rave observations on 2003 April 12 to their completion on 2013 April 4. In the second of two publications, we present the data products derived from 518,387 observations of 451,783 unique stars using a suite of advanced reduction pipelines focusing on stellar atmospheric parameters, in particular purely spectroscopically derived stellar atmospheric parameters (T{sub eff}, logg, and the overall metallicity), enhanced stellar atmospheric parameters inferred via a Bayesian pipeline using Gaia DR2 astrometric priors, and asteroseismically calibrated stellar atmospheric parameters for giant stars based on asteroseismic observations for 699 K2 stars. In addition, we provide abundances of the elements Fe, Al, and Ni, as well as an overall [α/Fe] ratio obtained using a new pipeline based on the GAUGUIN optimization method that is able to deal with variable signal-to-noise ratios. The Rave DR6 catalogs are cross-matched with relevant astrometric and photometric catalogs, and are complemented by orbital parameters and effective temperatures based on the infrared flux method. The data can be accessed via the Rave website (http://rave-survey.org) or the Vizier database.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Moderate-resolution K-band Spectroscopy of Substellar Companion κ Andromedae b

We present moderate-resolution (R ∼ 4000) K-band spectra of the “super-Jupiter,” κ Andromedae b. The data were taken with the OSIRIS integral field spectrograph at Keck Observatory. The spectra reveal resolved molecular lines from H{sub 2}O and CO, and are compared to a custom PHOENIX atmosphere model grid appropriate for young planetary-mass objects. We fit the data using a Markov chain Monte Carlo forward-modeling method. Using a combination of our moderate-resolution spectrum and low-resolution, broadband data from the literature, we derive an effective temperature of T {sub eff} = 1950–2150 K, a surface gravity of logg=3.5--4.5, and a metallicity of [M/H] = −0.2–0.0. These values are consistent with previous estimates from atmospheric modeling and the currently favored young age of the system (<50 Myr). We derive a C/O ratio of 0.70{sub −0.24}{sup +0.09} for the source, broadly consistent with the solar C/O ratio. This, coupled with the slightly subsolar metallicity, implies a composition consistent with that of the host star, and is suggestive of formation by a rapid process. The subsolar metallicity of κ Andromedae b is also consistent with predictions of formation via gravitational instability. Further constraints on formation of the companion will require measurement of the C/O ratio of κ Andromedae A. We also measure the radial velocity of κ Andromedae b for the first time, with a value of −1.4 ± 0.9 km s{sup −1} relative to the host star. We find that the derived radial velocity is consistent with the estimated high eccentricity of κ Andromedae b.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Physical Nature of the Eclipsing δ Scuti Star AO Serpentis

We present the absolute properties of the eclipsing binary AO Ser with a pulsating component from our BV photometric and high-resolution spectroscopic observations, which were performed between 2017 April and May. The radial velocities (RVs) for both components were measured, and the effective temperature and projected rotational velocity of the primary star were determined to be T eff,1 = 8,820 ± 62 K and v 1 sini 1 = 90 ± 18 km s -1 , respectively, by comparing the observed spectrum with the Kurucz models. The accurate fundamental parameters of AO Ser were determined by a simultaneous analysis of the light and RV curves. The masses and radii of the primary and secondary components are M 1 = 2.55 ± 0.09 M ⊙ and R 1 = 1.64 ± 0.02 R ⊙ and M 2 = 0.49 ± 0.02 M ⊙ and R 2 = 1.38 ± 0.02 R ⊙ , respectively. Multiple frequency analyses for the eclipse-subtracted light residuals were conducted. As a result, we detected two frequencies of f 1 = 21.852 days -1 and f 2 = 23.484 days -1 . The evolutionary position on the HR diagram and the pulsational characteristics indicate that the primary star is a δ Sct pulsator with a radial fundamental mode. On the other hand, the relatively evolved secondary is oversized for its own mass.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Hot Stars with Kepler Planets Have High Obliquities

It has been known for a decade that hot stars with hot Jupiters tend to have high obliquities. Less is known about the degree of spin–orbit alignment for hot stars with other kinds of planets. Here, we reassess the obliquities of hot Kepler stars with transiting planets smaller than Neptune, based on spectroscopic measurements of their projected rotation velocities (vsin i). The basis of the method is that a lower obliquity—all other things being equal—causes sin i to be closer to unity and increases the value of vsin i. We sought evidence for this effect using a sample of 150 Kepler stars with effective temperatures between 5950 and 6550 K and a control sample of 101 stars with matching spectroscopic properties and random orientations. The planet hosts have systematically higher values of vsin i than the control stars, but not by enough to be compatible with perfect spin–orbit alignment. The mean value of sin i is 0.856 ± 0.036, which is 4σ away from unity (perfect alignment), and 2σ away from π/4 (random orientations). There is also evidence that the hottest stars have a broader obliquity distribution: when modeled separately, the stars cooler than 6250 K have 〈sin i〉=0.928±0.042 while the hotter stars are consistent with random orientations. This is similar to the pattern previously noted for stars with hot Jupiters. Based on these results, obliquity excitation for early-G and late-F stars appears to be a general outcome of star and planet formation, rather than being exclusively linked to hot Jupiter formation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

The Red Supergiant Content of M31 and M33

We identify red supergiants (RSGs) in our spiral neighbors M31 and M33 using near-IR (NIR) photometry complete to a luminosity limit of logL/L{sub ⊙}=4.0. Our archival survey data cover 5 deg{sup 2} of M31, and 3 deg{sup 2} for M33, and are likely spatially complete for these massive stars. Gaia is used to remove foreground stars, after which the RSGs can be separated from asymptotic giant branch (AGB) stars in the color–magnitude diagram. The photometry is used to derive effective temperatures and bolometric luminosities via MARCS stellar atmosphere models. The resulting H-R diagrams show superb agreement with the evolutionary tracks of the Geneva evolutionary group. Our census includes 6400 RSGs in M31 and 2850 RSGs in M33 within their Holmberg radii; by contrast, only a few hundred RSGs are known so far in the Milky Way. Our catalog serves as the basis for a study of the RSG binary frequency being published separately, as well as future studies relating to the evolution of massive stars. Here we use the matches between the NIR-selected RSGs and their optical counterparts to show that the apparent similarity in the reddening of OB stars in M31 and M33 is the result of Malmquist bias; the average extinction in M31 is likely higher than that of M33. As expected, the distribution of RSGs follows that of the spiral arms, while the much older AGB population is more uniformly spread across each galaxy’s disk.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

TOI-811b and TOI-852b: New Transiting Brown Dwarfs with Similar Masses and Very Different Radii and Ages from the TESS Mission

We report the discovery of two transiting brown dwarfs (BDs), TOI-811b and TOI-852b, from NASA’s Transiting Exoplanet Survey Satellite mission. These two transiting BDs have similar masses but very different radii and ages. Their host stars have similar masses, effective temperatures, and metallicities. The younger and larger transiting BD is TOI-811b at a mass of M {sub b} = 59.9 ± 13.0M {sub J} and radius of R {sub b} = 1.26 ± 0.06R {sub J}, and it orbits its host star in a period of P = 25.16551 ± 0.00004 days. We derive the host star’s age of 93{sub −29}{sup +61} Myr from an application of gyrochronology. The youth of this system, rather than external heating from its host star, is why this BD’s radius is relatively large. This constraint on the youth of TOI-811b allows us to test substellar mass–radius evolutionary models at young ages where the radius of BDs changes rapidly. TOI-852b has a similar mass at M {sub b} = 53.7 ± 1.4M {sub J} but is much older (4 or 8 Gyr, based on bimodal isochrone results of the host star) and is also smaller with a radius of R {sub b} = 0.83 ± 0.04R {sub J}. TOI-852b’s orbital period is P = 4.94561 ± 0.00008 days. TOI-852b joins the likes of other old transiting BDs that trace out the oldest substellar mass–radius evolutionary models where contraction of the BD’s radius slows and approaches a constant value. Both host stars have a mass of M {sub ⋆} = 1.32M {sub ⊙} ± 0.05 and differ in their radii, T {sub eff}, and [Fe/H], with TOI-811 having R {sub ⋆} = 1.27 ± 0.09R {sub ⊙}, T {sub eff} = 6107 ± 77 K, and [Fe/H] = + 0.40 ± 0.09 and TOI-852 having R {sub ⋆} = 1.71 ± 0.04R {sub ⊙}, T {sub eff} = 5768 ± 84 K, and [Fe/H] = + 0.33 ± 0.09. We take this opportunity to examine how TOI-811b and TOI-852b serve as test points for young and old substellar isochrones, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

Analysis of Spectral Lines in Large Databases of Synthetic Spectra for Massive Stars

In this paper, we describe a program that identifies in the optical spectrum the main parameters of a spectral line, namely the initial and final wavelengths, and the line depth. Moreover, using numerical calculations, it identifies and removes adjacent lines. Next, the program calculates the equivalent width and the FWHM. The software was tested in a sample of 300 lines in two databases of synthetic spectra generated by the CMFGEN and PoWR codes, and 300 lines in observed spectra from the IACOB database, showing a Gaussian distribution of relative errors, from which it is inferred that 80% of the measured lines have errors less than 17% and only 5% of the lines have errors greater than 26%. The program was also run on the entire database of 45,000 CMFGEN and 202 POWR synthetic spectra, generating a library of H i, He i, and He ii lines necessary to feed the FITspec code for the derivation of stellar parameters: effective temperature, surface gravity, and luminosity.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Searching for Low-mass Population III Stars Disguised as White Dwarfs

It is uncertain whether or not low-mass Population III stars ever existed. While limits on the number density of Population III stars with M {sub *} ≈ 0.8 M {sub ⊙} have been derived, using Sloan Digital Sky Survey (SDSS) data, little is known about the occurrence of Population III stars at lower masses. In the absence of reliable parallaxes, the spectra of metal-poor main-sequence (MPMS) stars with M {sub *} ≲ 0.8 M {sub ⊙} can easily be confused with those of cool white dwarfs. To resolve this ambiguity, in this paper we present a classifier that differentiates between MPMS stars and white dwarfs, based on photometry and/or spectroscopy without the use of parallax information. We build and train our classifier using state-of-the-art theoretical spectra, and evaluate it on existing SDSS-based classifications for objects with reliable Gaia DR2 parallaxes. We then apply our classifier to a large catalog of objects with SDSS photometry and spectroscopy to search for MPMS candidates. We discover several previously unknown, extremely metal-poor (EMP) candidate stars, and recover numerous confirmed EMP stars already noted in the literature. We conclude that archival SDSS spectroscopy has already been exhaustively searched for EMP stars. We predict that the lowest-mass stars of primordial composition will have redder optical-to-infrared colors than cool white dwarfs at constant effective temperature, due to surface gravity-dependent collision-induced absorption from molecular hydrogen. We suggest that the application of our classifier to data produced by next-generation spectroscopic surveys will set stronger constraints on the number density of low-mass Population III stars in the Milky Way.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Revisiting Newly Large Magellanic Cloud Age-gap Star Clusters

Recently, a noticeable number of new star clusters was identified in the outskirts of the Large Magellanic Cloud (LMC) populating the so-called star-cluster age gap, a space of time (∼4–12 Gyr) where the only known star cluster is up-to-date ESO 121-SC 03. We used Survey of the Magellanic Stellar History DR2 data sets, as well as those employed to identify these star-cluster candidates, to produce relatively deep color–magnitude diagrams (CMDs) of 17 out of 20 discovered age-gap star clusters with the aim of investigating them in detail. Our analysis relies on a thorough CMD cleaning procedure of the field-star contamination, which presents variations in its stellar density and astrophysical properties, such as luminosity and effective temperature, around the star-cluster fields. We built star-cluster CMDs from stars with membership probabilities assigned from the cleaning procedure. These CMDs and their respective spatial distribution maps favor the existence of LMC star field density fluctuations rather than age-gap star clusters, although a definitive assessment on them will be possible from further deeper photometry.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

The High-energy Spectrum of the Nearby Planet-hosting Inactive Mid-M Dwarf LHS 3844

To fully characterize the atmospheres, or lack thereof, of terrestrial exoplanets, we must include the high-energy environments provided by their host stars. The nearby mid-M dwarf LHS 3844 hosts a terrestrial world that lacks a substantial atmosphere. We present a time-series UV spectrum of LHS 3844 from 1131 to 3215 Å captured by HST/COS. We detect one flare in the FUV that has an absolute energy of 8.96 ± 0.77 × 10{sup 28} erg and an equivalent duration of 355 ± 31 s. We extract the flare and quiescent UV spectra separately. For each spectrum, we estimate the Lyα flux using correlations between UV line strengths. We use Swift-XRT to place an upper limit on the soft X-ray flux and construct a differential emission model to estimate flux that is obscured by the interstellar medium. We compare the differential emission model flux estimates in the XUV to other methods that rely on scaling from the Lyα, Si iv, and N v lines in the UV. The XUV, FUV, and NUV flux of LHS 3844 relative to its bolometric luminosity is log{sub 10}(L {sub band}/L {sub Bol}) =−3.65, −4.16, and −4.48, respectively, for the quiescent state. These values agree with trends in high-energy flux as a function of stellar effective temperature found by the MUSCLES survey for a sample of early-M dwarfs. Many of the most spectroscopically accessible terrestrial exoplanets orbit inactive mid-to-late M dwarfs like LHS 3844. Measurements of M dwarf high-energy spectra are preferable for exoplanet characterization but are not always possible. The spectrum of LHS 3844 is a useful proxy for the current radiation environment for these worlds.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Stellar and Accretion Disk Parameters of the Close Binary HD 50526

We present a photometric and spectroscopic study of HD 50526, an ellipsoidal binary member of the group Double Periodic Variable stars. Performing data mining in photometric surveys and conducting new spectroscopic observations with several spectrographs during 2008–2015, we obtained orbital and stellar parameters of the system. The radial velocities were analyzed with the genetic PIKAIA algorithm, whereas Doppler tomography maps for the Hα and Hβ lines were constructed with the Total Variation Minimization code. An optimized simplex algorithm was used to solve the inverse problem adjusting the light curve with the best stellar parameters for the system. We find an orbital period of 6.ͩ701 ± 0.ͩ001 and a long photometric cycle of 191 ± 2 days. We detected the spectral features of the coldest star and modeled it with a logg=2.79±0.02 dex giant of mass 1.13 ± 0.02 M {sub ⊙} and effective temperature 10500 ± 125 K. In addition, we determine a mass ratio q = 0.206 ± 0.033 and that the hot star is a B-type dwarf of mass 5.48 ± 0.02 M {sub ⊙}. The V-band orbital light curve can be modeled including the presence of an accretion disk around the hotter star. This fills the Roche lobe of the hotter star and has a radius 14.74 ± 0.02 R {sub ⊙} and the temperature at the outer edge is 9400 K. Two bright spots located in the disk account for the global morphology of the light curve. The Doppler tomography maps of Hα and Hβ reveal complex structures of mass fluxes in the system.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

SCExAO/MEC and CHARIS Discovery of a Low-mass, 6 au Separation Companion to HIP 109427 Using Stochastic Speckle Discrimination and High-contrast Spectroscopy

We report the direct imaging discovery of a low-mass companion to the nearby accelerating A star, HIP 109427, with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument coupled with the Microwave Kinetic Inductance Detector Exoplanet Camera (MEC) and CHARIS integral field spectrograph. CHARIS data reduced with reference star point spread function (PSF) subtraction yield 1.1–2.4 μm spectra. MEC reveals the companion in Y and J band at a comparable signal-to-noise ratio using stochastic speckle discrimination, with no PSF subtraction techniques. Combined with complementary follow-up L {sub p} photometry from Keck/NIRC2, the SCExAO data favors a spectral type, effective temperature, and luminosity of M4–M5.5, 3000–3200 K, and log{sub 10}(L/L{sub ⊙})=−2.28{sub −0.04}{sup +0.04}, respectively. Relative astrometry of HIP 109427 B from SCExAO/CHARIS and Keck/NIRC2, and complementary Gaia–Hipparcos absolute astrometry of the primary favor a semimajor axis of 6.55{sup +3.0} {sub −0.48} au, an eccentricity of 0.54{sub −0.15}{sup +0.28}, an inclination of 66.7{sub −14}{sup +8.5} degrees, and a dynamical mass of 0.280{sub −0.059}{sup +0.18} M {sub ⊙}. This work shows the potential for extreme AO systems to utilize speckle statistics in addition to widely used postprocessing methods to directly image faint companions to nearby stars near the telescope diffraction limit.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2021

Detection and Bulk Properties of the HR 8799 Planets with High-resolution Spectroscopy

Using the Keck Planet Imager and Characterizer, we obtained high-resolution (R ~ 35,000) K-band spectra of the four planets orbiting HR 8799. We clearly detected H{sub 2}O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H{sub 2}O in b. These are the most challenging directly imaged exoplanets that have been observed at high spectral resolution to date when considering both their angular separations and flux ratios. We developed a forward-modeling framework that allows us to jointly fit the spectra of the planets and the diffracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their effective temperatures, surface gravities, radial velocities, and spins. We measured vsin (i) values of 10.1{sub -2.7}{sup +2.8} km s{sup -1} for HR 8799 d and 15.0{sub -2.6}{sup +2.3} km s{sup -1} for HR 8799 e, and placed an upper limit of <14 km s{sup -1} of HR 8799 c. Under two different assumptions of their obliquities, we found tentative evidence that rotation velocity is anticorrelated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less efficient at spinning down lower-mass planets.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Directly Determined Properties of HD 97658 from Interferometric Observations

We conducted interferometric observations with the CHARA Array of transiting super-Earth host HD 97658 and measured its limb-darkened angular diameter to be θ {sub LD} = 0.314 ± 0.004 mas. The combination of the angular diameter with the Gaia EDR3 parallax value with zero-point correction (π = 46.412 ± 0.022 mas, d =21.546 ± 0.011 pc) yields a physical radius of R {sub ·} = 0.728 ± 0.008 R {sub ⊙}. We also measured the bolometric flux of the star to be F {sub bol} = 2.42 ± 0.05 × 10{sup -8} erg s{sup -1} cm{sup -2}, which, together with angular size, allows a measurement of the effective temperature T {sub eƒƒ} = 5212 ± 43 K. Our directly determined physical stellar properties are in good agreement with previous estimates derived from spectroscopy. We used our measurements in combination with stellar evolutionary models and properties of the transit of HD 97658 b to determine the mass and age of HD 97658 as well as constrain the properties of the planet. Our results and our analysis of the TESS light curve on the planet (TOI-1821) corroborate previous studies of this system with tighter uncertainties.

47 OTHER INSTRUMENTATION↗