Radial Velocity Observations Research Articles

Revisiting the Transit Timing Variations in the TrES-3 and Qatar-1 Systems with TESS Data

We present and analyze 58 transit light curves of TrES-3b and 98 transit light curves of Qatar-1b, observed by the Transiting Exoplanet Survey Satellite, plus two transit light curves of Qatar-1b, observed by us, using a ground-based 1.23 m telescope. These light curves are combined with the best-quality light curves taken from the Exoplanet Transit Database and the literature. The precisely determined midtransit times from these light curves enable us to obtain the refined orbital ephemerides, with improved precision, for both hot Jupiters. From the timing analysis, we find indications of the presence of transit timing variations (TTVs) in both systems. Since the observed TTVs are unlikely to be short-term and periodic, the possibility of additional planets in orbits close to TrES-3b and Qatar-1b is ruled out. The possible causes of long-term TTVs, such as orbital decay, apsidal precession, the Applegate mechanism, and line-of-sight acceleration, are also examined. However, none of these possibilities are found to explain the observed TTV of TrES-3b. In contrast to this, line-of-sight acceleration appears to be a plausible explanation for the observed TTV of Qatar-1b. In order to confirm these findings, further high-precision transit and radial velocity observations of both systems would be worthwhile.

Utilizing a Global Network of Telescopes to Update the Ephemeris for the Highly Eccentric Planet HD 80606 b and to Ensure the Efficient Scheduling of JWST

The transiting planet HD 80606 b undergoes a 1000 fold increase in insolation during its 111 days orbit due to it being highly eccentric (e = 0.93). The planet’s effective temperature increases from 400 to over 1400 K in a few hours as it makes a rapid passage to within 0.03 au of its host star during periapsis. Spectroscopic observations during the eclipse (which is conveniently oriented a few hours before periapsis) of HD 80606 b with the James Webb Space Telescope (JWST) are poised to exploit this highly variable environment to study a wide variety of atmospheric properties, including composition, chemical and dynamical timescales, and large scale atmospheric motions. Critical to planning and interpreting these observations is an accurate knowledge of the planet’s orbit. We report on observations of two full-transit events: 2020 February 7 as observed by the TESS spacecraft and 2021 December 7–8 as observed with a worldwide network of small telescopes. We also report new radial velocity observations which, when analyzed with a coupled model to the transits, greatly improves the planet’s orbital ephemeris. Our new orbit solution reduces the uncertainty in the transit and eclipse timing of the JWST era from tens of minutes to a few minutes. When combined with the planned JWST observations, this new precision may be adequate to look for non-Keplerian effects in the orbit of HD 80606 b.

Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40

Context. Despite being a prominent subset of the exoplanet population discovered in the past three decades, the nature and provenance of sub-Neptune-sized planets is still one of the open questions in exoplanet science. Aims. For planets orbiting bright stars, precisely measuring the orbital and planet parameters of the system is the best approach to distinguish between competing theories regarding their formation and evolution. Methods. We obtained 69 new radial velocity observations of the mid-M dwarf G 9–40 with the CARMENES instrument to measure for the first time the mass of its transiting sub-Neptune planet, G 9–40 b, discovered in data from the K2 mission. Results. Combined with new observations from the TESS mission during Sectors 44, 45, and 46, we are able to measure the radius of the planet to an uncertainty of 3.4% (Rb = 1.900 ± 0.065 R⊕) and determine its mass with a precision of 16% (Mb = 4.00 ± 0.63 M⊕). The resulting bulk density of the planet is inconsistent with a terrestrial composition and suggests the presence of either a water-rich core or a significant hydrogen-rich envelope. Conclusions. G 9–40 b is referred to as a keystone planet due to its location in period-radius space within the radius valley. Several theories offer explanations for the origin and properties of this population and this planet is a valuable target for testing the dependence of those models on stellar host mass. By virtue of its brightness and small size of the host, it joins L 98-59 d as one of the two best warm (Teq ~ 400 K) sub-Neptunes for atmospheric characterization with JWST, which will probe cloud formation in sub-Neptune-sized planets and break the degeneracies of internal composition models.

Towards a consistent model of the hot quadruple system HD 93206 = QZ Carinæ

Aims.HD 93206 is a massive early-type stellar system composed of components resolved by direct imaging (Ab, Ad, B, C, D) and a compact subsystem (Aa1, Aa2, Ac1, Ac2). Its geometry was already determined on the basis of extensive photometric, spectroscopic, and interferometric observations. However, the fundamental absolute parameters are still not known precisely enough.Methods.We use an advancedN-body model to account for all mutual gravitational perturbations among the four close components, and all observational data types, including astrometry, radial velocities, eclipse timing variations, squared visibilities, closure phases, triple products, normalized spectra, and spectral energy distribution (SED). The model has 38 free parameters, grouped into three sets of orbital elements, component masses, and their basic radiative properties (T, logg,vrot).Results.We revised the fundamental parameters of QZ Car as follows. For a model with the nominal extinction coefficientRV ≡ AV/E(B − V) = 3.1, the best-fit masses arem1 = 26.1 MS,m2 = 32.3 MS,m3 = 70.3 MS, andm4 = 8.8 MS, with uncertainties of the order of 2 MS, and the system distanced = (2800 ± 100) pc. In an alternative model, where we increased the weights of the radial velocity (RV) and transit timing variation (VTT) observations and relaxed the SED constraints, because extinction can be anomalous withRV ∼ 3.4, the distance is smaller:d = (2450 ± 100) pc. This corresponds to the distance of the Collinder 228 cluster. Independently, this is confirmed by dereddening the SED, which is only then consistent with the early-type classification (O9.7Ib for Aa1, O8III for Ac1). Future modelling should also account for an accretion disk around the Ac2 component.

New Dynamical State and Habitability of the HD 45364 Planetary System

Planetary systems with multiple giant planets provide important opportunities to study planetary formation and evolution. The HD 45364 system hosts two giant planets that reside within the habitable zone (HZ) of their host star and was the first system discovered with a 3:2 mean motion resonance (MMR). Several competing migration theories with different predictions have previously provided explanations regarding the observed resonance through dynamical simulations that utilized limited data. Here, over ten years since the original discovery, we revisit the system with a substantially increased radial velocity (RV) sample from High Accuracy Radial Velocity Planet Searcher spectrograph and High Resolution Echelle Spectrometer that significantly extends the observational baseline. We present the revised orbital solutions for the two planets using both Keplerian and dynamical models. Our RV models suggest orbits that are more circular and separated than those previously reported. As a result, the predicted strong planet–planet interactions were not detected. The system dynamics were reanalyzed, and the planet pair was found to exhibit apsidal behavior of both libration and circulation, indicating a quasi-resonance state rather than being truly in MMR. The new orbital solution and dynamical state of the system confirm migration models that predicted near-circular orbits as the preferred scenario. We also study the habitability prospects of this system and found that an additional Earth-mass planet and exomoons in the HZ are possible. This work showcases the importance of continued RV observations and its impact on our knowledge of the system’s dynamical history. HD 45364 continues to be an interesting target for both planetary formation and habitability studies.

On Variation Mechanisms in Recurrent Nova IM Normae

Light curves by Woudt and Warner (WW) of recurrent nova IM Nor show eclipse-like dips that they saw as too wide for eclipses alone, and interpreted as mainly a reflection effect due to irradiation of the companion (mass donor) star with some amplitude increase due to eclipse of IM Nor’s disk. A mainly reflection interpretation cannot be made to work because reflection does not produce dips over a restricted phase range but a somewhat distorted sinusoid that extends over the entire orbital cycle. Here, the dip features are interpreted in two ways, with testing via quantitative light curve modeling that includes an equipotential disk. One way is as alternating eclipses of and by the disk that surrounds this cataclysmic variable’s accreting white dwarf, rather than purely a succession of disk-by-star eclipses. WW’s estimated period of 0.d1026 was accordingly doubled to 0.d2052, with the observed dips now half of their previous width in phase, and with the modeled eclipses matching the observed dips in width and shape. In the 2nd interpretation, a toroidal disk’s capability to produce very wide eclipses is demonstrated computationally. Furthermore, much of the perceived eclipse width can be recognized as an apparent effect due to tidal stretching of the companion star and the disk. In overview, disk eclipses and tidal variation combine with reflection to produce a light curve waveform of approximately the observed shape and duration. Eclipses, tides, and reflection all have essential roles in the 2nd interpretation and no change from WW’s period is needed. Radial velocity observations will be crucial for identification of the correct resolution of the ”excessively wide eclipse” problem.

HD 23472: a multi-planetary system with three super-Earths and two potential super-Mercuries,

Context.Comparing the properties of planets orbiting the same host star, and thus formed from the same accretion disc, helps in constraining theories of exoplanet formation and evolution. As a result, the scientific interest in multi-planetary systems is growing with the increasing number of detections of planetary companions.Aims.We report the characterisation of a multi-planetary system composed of five exoplanets orbiting the K-dwarf HD 23472 (TOI-174).Methods.In addition to the two super-Earths that were previously confirmed, we confirm and characterise three Earth-size planets in the system using ESPRESSO radial velocity observations. The planets of this compact system have periods ofPd~3.98,Pe~7.90,Pf~12.16,Pb~ 17.67, andPc~ 29.80 days and radii ofRd~ 0.75 ,Re~ 0.82,,Rf~ 1.13 ,Rb~ 2.01, and,Rc~1.85R⊕.Because of its small size, its proximity to planet d’s transit, and close resonance with planet d, planet e was only recently found.Results.The planetary masses were estimated to beMd= 0.54 ± 0.22,Me= 0.76 ± 0.30,Mf= 0.64−0.39+0.46,Mb= 8.42−0.84+0.83, andMc= 3.37−0.87+0.92M⊕. These planets are among the lightest planets, with masses measured using the radial velocity method, demonstrating the very high precision of the ESPRESSO spectrograph. We estimated the composition of the system’s five planets and found that their gas and water mass fractions increase with stellar distance, suggesting that the system was shaped by irradiation. The high density of the two inner planets (ρd= 7.5−3.1+3.9andρe= 7.5−3.0+3.9g cm−3) indicates that they are likely to be super-Mercuries. This is supported by the modelling of the internal structures of the planets, which also suggests that the three outermost planets have significant water or gas content.Conclusions.If the existence of two super-Mercuries in the system is confirmed, this system will be the only one known to feature two super-Mercuries, making it an excellent testing bed for theories of super-Mercuries formation. Furthermore, the system is close to a Laplace resonance, and further monitoring could shed light on how it was formed. Its uniqueness and location in the continuous viewing zone of theJames Webbspace telescope will make it a cornerstone of future in-depth characterisations.

Accounting for stellar activity signals in radial-velocity data by using change point detection techniques

Context.Active regions on the photosphere of a star have been the major obstacle for detecting Earth-like exoplanets using the radial velocity (RV) method. A commonly employed solution for addressing stellar activity is to assume a linear relationship between the RV observations and the activity indicators along the entire time series, and then remove the estimated contribution of activity from the variation in RV data (overall correction method). However, since active regions evolve on the photosphere over time, correlations between the RV observations and the activity indicators will correspondingly be anisotropic.Aims.We present an approach that recognizes the RV locations where the correlations between the RV and the activity indicators significantly change in order to better account for variations in RV caused by stellar activity.Methods.The proposed approach uses a general family of statistical breakpoint methods, often referred to as change point detection (CPD) algorithms; several implementations of which are available in R and python. A thorough comparison is made between the breakpoint-based approach and the overall correction method. To ensure wide representativity, we use measurements from real stars that have different levels of stellar activity and whose spectra have different signal-to-noise ratios.Results.When the corrections for stellar activity are applied separately to each temporal segment identified by the breakpoint method, the corresponding residuals in the RV time series are typically much smaller than those obtained by the overall correction method. Consequently, the generalized Lomb–Scargle periodogram contains a smaller number of peaks caused by active regions. The CPD algorithm is particularly effective when focusing on active stars with long time series, such asαCen B. In that case, we demonstrate that the breakpoint method improves the detection limit of exoplanets by 74% on average with respect to the overall correction method.Conclusions.CPD algorithms provide a useful statistical framework for estimating the presence of change points in a time series. Since the process underlying the RV measurements generates anisotropic data by its intrinsic properties, it is natural to use CPD to obtain cleaner signals from RV data. We anticipate that the improved exoplanet detection limit may lead to a widespread adoption of such an approach. Our test on the HD 192310 planetary system is encouraging, as we confirm the presence of the two hosted exoplanets and we determine orbital parameters consistent with the literature, also providing much more precise estimates for HD 192310 c.

Identifying Exoplanets with Deep Learning. IV. Removing Stellar Activity Signals from Radial Velocity Measurements Using Neural Networks

Exoplanet detection with precise radial velocity (RV) observations is currently limited by spurious RV signals introduced by stellar activity. We show that machine-learning techniques such as linear regression and neural networks can effectively remove the activity signals (due to starspots/faculae) from RV observations. Previous efforts focused on carefully filtering out activity signals in time using modeling techniques like Gaussian process regression. Instead, we systematically remove activity signals using only changes to the average shape of spectral lines, and use no timing information. We trained our machine-learning models on both simulated data (generated with the SOAP 2.0 software) and observations of the Sun from the HARPS-N Solar Telescope. We find that these techniques can predict and remove stellar activity both from simulated data (improving RV scatter from 82 to 3 cm s−1) and from more than 600 real observations taken nearly daily over 3 yr with the HARPS-N Solar Telescope (improving the RV scatter from 1.753 to 1.039 m s−1, a factor of ∼1.7 improvement). In the future, these or similar techniques could remove activity signals from observations of stars outside our solar system and eventually help detect habitable-zone Earth-mass exoplanets around Sun-like stars.

Impacts of Assimilating Future Clear-Air Radial Velocity Observations from Phased Array Radar on Convection Initiation Forecasts: An Observing System Simulation Experiment Study

Abstract Phased-array radar (PAR) technology can potentially provide high-quality clear-air radial velocity observations at a high spatiotemporal resolution, usually ∼1 min or less. These observations are hypothesized to partially fill the gaps in current operational observing systems with relatively coarse-resolution surface mesonet observations and the lack of high-resolution upper-air observations especially in planetary boundary layer. In this study, observing system simulation experiments are conducted to investigate the potential value of assimilating PAR observations of clear-air radial velocity to improve the forecast of convection initiation (CI) along small-scale boundary layer convergence zones. Both surface-based and elevated CIs driven by meso-γ-scale boundary layer convergence are tested. An ensemble Kalman filter method is used to assimilate synthetic surface mesonet observations and PAR clear-air radial velocity observations. Results show that assimilating only surface mesonet observations fails to predict either surface-based or elevated CI processes. Assimilating clear-air radial velocity observations in addition to surface mesonet observations can capture both surface-based and elevated CI processes successfully. Such an improvement benefits from the better analyses of boundary layer convergence, resulting from the assimilation of clear-air radial velocity observations. Additional improvement is observed with more frequent assimilation. Assimilating clear-air radial velocity observations only from the one radar results in analysis biases of cross-beam winds and CI location biases, and assimilating additional radial velocity observations from the second radar at an appropriate position can reduce these biases while sacrificing the CI timing. These results suggest the potential of assimilating clear-air radial velocity observations from PAR to improve the forecast of CI processes along boundary layer convergence zones.

Detached eclipsing binaries from the Kepler field: radii and photometric masses of components in short-period systems

ABSTRACT The characterization of detached eclipsing binaries with low-mass components has become important when verifying the role of convection in stellar evolutionary models, which requires model-independent measurements of stellar parameters with great precision. However, spectroscopic characterization depends on single-target radial velocity observations and only a few tens of well-studied low-mass systems have been diagnosed in this way. We characterize eclipsing detached systems from the Kepler field with low-mass components by adopting a purely photometric method. Based on an extensive multicolour data set, we derive effective temperatures and photometric masses of individual components using clustering techniques. We also estimate the stellar radii from additional modelling of the available Kepler light curves. Our measurements confirm the presence of an inflation trend in the mass–radius diagram against theoretical stellar models in the low-mass regime.

Stability Constrained Characterization of the 23 Myr Old V1298 Tau System: Do Young Planets Form in Mean Motion Resonance Chains?

A leading theoretical expectation for the final stages of planet formation is that disk migration should naturally drive orbits into chains of mean motion resonances (MMRs). In order to explain the dearth of MMR chains observed at Gyr ages (<1%), this picture requires such configurations to destabilize and scramble period ratios following disk dispersal. Strikingly, the only two known stars with three or more planets younger than ≲100 Myr, HR 8799 and V1298 Tau, have been suggested to be in such MMR chains, given the orbits’ near-integer period ratios. We incorporate recent transit and radial velocity (RV) observations of the V1298 Tau system, and investigate constraints on the system’s orbital architecture imposed by requiring dynamical stability on timescales much shorter than the system’s age. We show that the recent RV mass measurement of V1298 Tau b places it within a factor of 2 of the instability limit, and that this allows us to set significantly lower limits on the eccentricity (e b ≤0.17 at 99.7% confidence). Additionally, we rule out a resonant chain configuration for V1298 Tau at ≳99% confidence. Thus, if the ∼23 Myr old V1298 Tau system did form as a resonant chain, it must have undergone instability and rearrangement shortly after disk dispersal. We expect that similar stability constrained characterization of future young multiplanet systems will be valuable in informing planet formation models.

Gaia May Detect Hundreds of Well-characterized Stellar Black Holes

Detection of black holes (BHs) with detached luminous companions (LCs) can be instrumental in connecting the BH properties with their progenitors since the latter can be inferred from the observable properties of the LC. Past studies showed the promise of Gaia astrometry in detecting BH–LC binaries. We build on these studies by (1) initializing the zero-age binary properties based on realistic, metallicity-dependent star formation history in the Milky Way (MW); (2) evolving these binaries to current epoch to generate realistic MW populations of BH–LC binaries; (3) distributing these binaries in the MW, preserving the complex age–metallicity-Galactic position correlations; (4) accounting for extinction and reddening using three-dimensional dust maps; and (5) examining the extended Gaia mission’s ability to resolve BH–LC binaries. We restrict ourselves to detached BH–LC binaries with orbital period P orb ≤ 10 yr such that Gaia can observe at least one full orbit. We find that (1) the extended Gaia mission can astrometrically resolve ∼30–300 detached BH–LC binaries depending on our assumptions of supernova physics and astrometric detection threshold; (2) Gaia’s astrometry alone can indicate BH candidates for ∼10–100 BH–LC binaries by constraining the dark primary mass ≥3 M ⊙; and (3) distributions of observables, including orbital periods, eccentricities, and component masses, are sensitive to the adopted binary evolution model and hence can directly inform binary evolution models. Finally, we comment on the potential to further characterize these BH binaries through radial velocity measurements and observation of X-ray counterparts.

The Warm Neptune GJ 3470b Has a Polar Orbit

The warm Neptune GJ 3470b transits a nearby (d = 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter–McLaughlin effect, yielding a sky-projected obliquity of and a . Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of , revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope of over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b’s mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ∼1.5–1.7, which could help account for its evaporating atmosphere.

The TESS-Keck Survey. XI. Mass Measurements for Four Transiting Sub-Neptunes Orbiting K Dwarf TOI–1246

Multiplanet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf (V = 11.6, K = 9.9) and four transiting sub-Neptunes identified by TESS with orbital periods of 4.31, 5.90, 18.66, and 37.92 days. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii (2.97 ± 0.06 R ⊕, 2.47 ± 0.08 R ⊕, 3.46 ± 0.09 R ⊕, and 3.72 ± 0.16 R ⊕) and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets (8.1 ± 1.1 M ⊕, 8.8 ± 1.2 M ⊕, 5.3 ± 1.7 M ⊕, and 14.8 ± 2.3 M ⊕). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance (P e/P d = 2.03) and exhibit transit-timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only five systems with measured masses and radii for all four transiting planets. The planet densities range from 0.70 ± 0.24 to 3.21 ± 0.44 g cm−3, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 ± 3.6 M ⊕. This planet candidate is exterior to TOI-1246 e, with a candidate period of 93.8 days, and we discuss the implications if it is confirmed to be planetary in nature.

TOI-1670 b and c: An Inner Sub-Neptune with an Outer Warm Jupiter Unlikely to Have Originated from High-eccentricity Migration

We report the discovery of two transiting planets around the bright (V = 9.9 mag) main-sequence F7 star TOI-1670 by the Transiting Exoplanet Survey Satellite. TOI-1670 b is a sub-Neptune ( R ⊕) on a 10.9 day orbit, and TOI-1670 c is a warm Jupiter ( R Jup) on a 40.7 day orbit. Using radial velocity observations gathered with the Tull Coudé Spectrograph on the Harlan J. Smith telescope and HARPS-N on the Telescopio Nazionale Galileo, we find a planet mass of M Jup for the outer warm Jupiter, implying a mean density of g cm−3. The inner sub-Neptune is undetected in our radial velocity data (M b < 0.13 M Jup at the 99% confidence level). Multiplanet systems like TOI-1670 hosting an outer warm Jupiter on a nearly circular orbit () and one or more inner coplanar planets are more consistent with “gentle” formation mechanisms such as disk migration or in situ formation rather than high-eccentricity migration. Of the 11 known systems with a warm Jupiter and a smaller inner companion, eight (73%) are near a low-order mean-motion resonance, which can be a signature of migration. TOI-1670 joins two other systems (27% of this subsample) with period commensurabilities greater than 3, a common feature of in situ formation or halted inward migration. TOI-1670 and the handful of similar systems support a diversity of formation pathways for warm Jupiters.

Apsidal motion in massive eccentric binaries in NGC 6231

Context. The measurement of the apsidal motion in close eccentric massive binary systems provides essential information to probe the internal structure of the stars that compose the system. Aims. Following the determination of the fundamental stellar and binary parameters, we make use of the tidally induced apsidal motion to infer constraints on the internal structure of the stars composing the binary system HD 152219. Methods. The extensive set of spectroscopic, photometric, and radial velocity observations allowed us to constrain the fundamental parameters of the stars together with the rate of apsidal motion of the system. Stellar structure and evolution models were further built with the Clés code testing different prescriptions for the internal mixing occurring inside the stars. The effect of stellar rotation axis misalignment with respect to the normal to the orbital plane on our interpretation of the apsidal motion in terms of internal structure constants is investigated. Results. Made of an O9.5 III primary star (M1 = 18.64 ± 0.47 M⊙, R1 = 9.40−0.15+0.14 R⊙, Teff,1 = 30 900 ± 1000 K, Lbol,1 = (7.26 ± 0.97)×104 L⊙) and a B1-2 V-III secondary star (M2 = 7.70 ± 0.12 M⊙, R2 = 3.69 ± 0.06 R⊙, Teff,2 = 21 697 ± 1000 K, Lbol,2 = (2.73 ± 0.51)×103 L⊙), the binary system HD 152219 displays apsidal motion at a rate of (1.198 ± 0.300)° yr−1. The weighted-average mean of the internal structure constant of the binary system is inferred: k̄2 = 0.00173 ± 0.00052. For the Clés models to reproduce the k2-value of the primary star, a significantly enhanced mixing is required, notably through the turbulent mixing, but at the cost that other stellar parameters cannot be reproduced simultaneously. Conclusions. The difficulty to reproduce the k2-value simultaneously with the stellar parameters as well as the incompatibility between the age estimates of the primary and secondary stars are indications that some physics of the stellar interior are still not completely understood.

Eclipse Timing the Milky Way’s Gravitational Potential

Abstract We show that a small but measurable shift in the eclipse midpoint time of eclipsing binary (EBs) stars of ∼0.1 s over a decade baseline can be used to directly measure the Galactic acceleration of stars in the Milky Way at ∼kiloparsec distances from the Sun. We consider contributions to the period drift rate from dynamical mechanisms other than the Galaxy’s gravitational field and show that the Galactic acceleration can be reliably measured using a sample of Kepler EBs with orbital and stellar parameters from the literature. The contribution from tidal decay we estimate here is an upper limit assuming the stars are not tidally synchronized. We find there are about 200 detached EBs that have estimated timing precision better than 0.5 s, and for which other dynamical effects are subdominant to the Galactic signal. We illustrate the method with a prototypical, precisely timed EB using an archival Kepler light curve and a modern synthetic HST light curve (which provides a decade baseline). This novel method establishes a realistic possibility to constrain dark matter substructure and the Galactic potential using eclipse timing to measure Galactic accelerations, along with other emerging new methods, including pulsar timing and extreme-precision radial velocity observations. This acceleration signal grows quadratically with time. Therefore, given baselines established in the near future for distant EBs, we can expect to measure the period drift in the future with space missions like JWST and the Roman Space Telescope.

Scheduling Direct Imaging Observations Based on Radial Velocity Orbital Fits: Best Practices for Translating Orbits and Failure Modes

Abstract Future direct imaging mission concepts are planning to observe planets discovered via Doppler spectroscopy, with observation scheduling decisions based on radial velocity (RV) fit orbits to increase the mission’s odds of making a detection. However, some orbital parameters, such as inclination and planet radius, that are necessary to determine when a planet is detectable via imaging cannot be resolved with only RV data. This work studies how to best use a RV fit to determine when a planet will be detectable with direct imaging and quantify the impacts of RV-measurement precision on direct imaging observations. Beginning by defining a “true” planet, we simulate RV observations, fit the RV observations via Bayesian orbit fitting, construct many Keplerian orbits based on the RV fit and priors on the unknown orbital parameters, and propagate the constructed orbits and the true orbit for 20 yr to determine when the constructed orbits deviate significantly. We identify four methods of constructing orbits, ultimately finding that creating and sampling high-likelihood orbital parameters from a multivariate Gaussian produces the best results for high RV error and that creating and sampling from a simple normal distribution for each orbital parameter independently performs the best for low RV error. Further, we establish two modes of failure: intermittent failure, which captures when the constructed orbits incorrectly indicate that a planet is detectable; and dispersion failure, when the constructed orbits have dispersed so much that they no longer provide useful information.

HD 207897 b: A dense sub-Neptune transiting a nearby and bright K-type star

We present the discovery and characterization of a transiting sub-Neptune that orbits the nearby (28 pc) and bright (V = 8.37) K0V star HD 207897 (TOI-1611) with a 16.20-day period. This discovery is based on photometric measurements from the Transiting Exoplanet Survey Satellite mission and radial velocity (RV) observations from the SOPHIE, Automated Planet Finder, and HIRES high-precision spectrographs. We used EXOFASTv2 to model the parameters of the planet and its host star simultaneously, combining photometric and RV data to determine the planetary system parameters. We show that the planet has a radius of 2.50 ± 0.08 RE and a mass of either 14.4 ± 1.6 ME or 15.9 ± 1.6 ME with nearly equal probability. The two solutions correspond to two possibilities for the stellar activity period. The density accordingly is either 5.1 ± 0.7 g cm−3 or 5.5−0.7+0.8 g cm−3, making it one of the relatively rare dense sub-Neptunes. The existence of this dense planet at only 0.12 AU from its host star is unusual in the currently observed sub-Neptune (2 &lt; RE &lt; 4) population. The most likely scenario is that this planet has migrated to its current position.