Radial Velocity Exoplanet Research Articles

Radial velocity analysis of stars with debris discs

ABSTRACT This study aims to identify potential exoplanet signals from nearby stars with resolved debris discs. However, the high activity of many stars with debris discs limits the detection of periodic signals. Our study is constrained to a sample of 29 stars that have appropriate radial velocity data and debris disc measurements sufficient to resolve their inclination. Our results confirm and update previous findings for exoplanets around HD 10647, HD 115617, HD 69830, GJ 581, HD 22049, and HD 142091, and we identify long-term activity signals around HD 207129 and HD 202628. We utilize the inclination angles of the debris discs, assuming co-planarity between debris disc and exoplanet orbit, to determine the ‘disc-aligned’ masses of radial velocity exoplanets in this study. The ‘disc-aligned’ masses of HD 69830 b, HD 69830 c, and 61 Vir b suggests that they may be classified as ‘hot’ or ‘warm’ Jupiters and so might be nearby examples of planets that have undergone recent type-II disc migration.

Trials and Tribulations in the Reanalysis of KELT-24 b: A Case Study for the Importance of Stellar Modeling

We present a new analysis of the KELT-24 system, comprising a well-aligned hot Jupiter, KELT-24 b, and a bright (V = 8.3), nearby (d = 96.9 pc) F-type host star. KELT-24 b was independently discovered by two groups in 2019, with each reporting best-fit stellar parameters that were notably inconsistent. Here, we present three independent analyses of the KELT-24 system, each incorporating a broad range of photometric and spectroscopic data, including eight sectors of Transiting Exoplanet Survey Satellite (TESS) photometry and more than 200 new radial velocities (RVs) from the MINiature Exoplanet Radial Velocity Array. Two of these analyses use KELT-24's observed spectral energy distribution (SED) through a direct comparison to stellar evolutionary models, while our third analysis assumes an unknown additional body contributing to the observed broadband photometry and excludes the SED. Ultimately, we find that the models that include the SED are a poor fit to the available data, so we adopt the system parameters derived without it. We also highlight a single transit-like event observed by TESS, deemed likely to be an eclipsing binary bound to KELT-24, that will require follow-up observations to confirm. We discuss the potential of these additional bodies in the KELT-24 system as a possible explanation for the discrepancies between the results of the different modeling approaches, and explore the system for longer-period planets that may be weakly evident in the RV observations. The comprehensive investigations that we present not only increase the fidelity of our understanding of the KELT-24 system but also serve as a blueprint for future stellar modeling in global analyses of exoplanet systems.

Analysis of the public HARPS/ESO spectroscopic archive

Context. Magnetic activity is currently the primary limiting factor in radial velocity (RV) exoplanet searches. Even inactive stars, such as the Sun, exhibit RV jitter of the order of a few m s−1 due to active regions on their surfaces. Time series of chromospheric activity indicators, such as the Ca II H&K lines, can be utilized to reduce the impact of such activity phenomena on exoplanet search programmes. In addition, the identification and correction of instrumental effects can improve the precision of RV exoplanet surveys. Aims. We aim to update the HARPS -RVBANK RV database and include an additional 3.5 yr of time series and Ca II H&K lines (R′HK) chromospheric activity indicators. This additional data will aid in the analysis of the impact of stellar magnetic activity on the RV time series obtained with the HARPS instrument. Our updated database aims to provide a valuable resource for the exoplanet community in understanding and mitigating the effects of such stellar magnetic activity on RV measurements. Methods. The new HARPS-RVBANK database includes all stellar spectra obtained with the HARPS instrument prior to January 2022. The RVs corrected for small but significant nightly zero-point variations were calculated using an established method. The R′HK estimates were determined from both individual spectra and co-added template spectra with the use of model atmospheres. As input for our derivation of R′HK, we derived stellar parameters from co-added, high signal-to-noise ratio templates for a total of 3230 stars using the stellar parameter code SPECIES. Results. The new version of the HARPS RV database has a total of 252 615 RVs of 5239 stars. Of these, 195 387 have R′HK values, which corresponds to 77% of all publicly available HARPS spectra. Currently, this is the largest public database of high-precision (down to ~1 m s−1) RVs, and the largest compilation of R′HK measurements. We also derived lower limits for the RV jitter of F-, G-, and K-type stars as a function of R′HK.

Inferring Stellar Parameters from Iodine-imprinted Keck/HIRES Spectra with Machine Learning

The properties of exoplanet host stars are traditionally characterized through a detailed forward-modeling analysis of high-resolution spectra. However, many exoplanet radial velocity surveys employ iodine-cell-calibrated spectrographs, such that the vast majority of spectra obtained include an imprinted forest of iodine absorption lines. For surveys that use iodine cells, iodine-free “template” spectra must be separately obtained for precise stellar characterization. These template spectra often require extensive additional observing time to obtain, and they are not always feasible to obtain for faint stars. In this paper, we demonstrate that machine-learning methods can be applied to infer stellar parameters and chemical abundances from iodine-imprinted spectra with high accuracy and precision. The methods presented in this work are broadly applicable to any iodine-cell-calibrated spectrograph. We make publicly available our spectroscopic pipeline, the Cannon HIRES Iodine Pipeline, which derives stellar parameters and 15 chemical abundances from iodine-imprinted spectra of FGK stars and which has been set up for ease of use with Keck/HIRES spectra. Our proof of concept offers an efficient new avenue to rapidly estimate a large number of stellar parameters even in the absence of an iodine-free template spectrum.

A review of planetary systems around HD 99492, HD 147379, and HD 190007 with HARPS-N

Context. The Rocky Planet Search (RPS) program is dedicated to a blind radial velocity (RV) search of planets around bright stars in the northern hemisphere, using the high-resolution echelle spectrograph HARPS-N installed on the Telescopio Nazionale Galileo (TNG). Aims. The goal of this work is to revise and update the properties of three planetary systems by analysing the HARPS-N data with state-of-the-art stellar activity mitigation tools. The stars considered are HD 99492 (83Leo B), HD 147379 (Gl617 A), and HD 190007. Methods. We employ a systematic process of data modelling, which we selected from the comparison of different approaches. We use YARARA to remove instrumental systematics from the RV, and then use SPLEAF to further mitigate the stellar noise with a multidimensional correlated noise model. We also search for transit features in the Transiting Exoplanets Survey Satellite (TESS) data of these stars. Results. We report on the discovery of a new planet around HD 99492, namely HD 99492 c, with an orbital period of 95.2 days and a minimum mass of m sin i = 17.9 M⊕, and refine the parameters of HD 99492 b. We also update and refine the Keplerian solutions for the planets around HD 147379 and HD 190007, but do not detect additional planetary signals. We discard the transiting geometry for the planets, but stress that TESS did not exhaustively cover all the orbital phases. Conclusions. The addition of the HARPS-N data, and the use of advanced data analysis tools, has allowed us to present a more precise view of these three planetary systems. It demonstrates once again the importance of long observational efforts such as the RPS program. Added to the RV exoplanet sample, these planets populate two apparently distinct populations revealed by a bimodality in the planets’ minimum mass distribution. The separation is located between 30 and 50 M⊕.

Dynamics of Photospheric Magnetic Flux Distribution and Variations in Solar RVs: A Study Using HARPS-N Solar and SDO Observations

The distribution and evolution of photospheric magnetic fields in sunspots, plages, and network, and variations in their relative flux content, play key roles in radial velocity (RV) fluctuations observed in Sun-as-a-star spectra. Differentiating and disentangling such magnetic contributions to RVs help in building models to account for stellar activity signals in high-precision RV exoplanet searches. In this work, as earlier authors, we employ high-resolution images of the solar magnetic field and continuum intensities from SDO/HMI to understand the activity contributions to RVs from HARPS-N solar observations. Using well-observed physical relationships between strengths and fluxes of photospheric magnetic fields, we show that the strong fields (spots, plages, and network) and the weak inter-network fields leave distinguishing features in their contributions to the RV variability. We also find that the fill factors and average unsigned magnetic fluxes of different features correlate differently with the RVs and hence warrant care in employing either of them as a proxy for RV variations. In addition, we examine disk-averaged UV intensities at 1600 and 1700 Å wavelength bands imaged by SDO/AIA and their performances as proxies for variations in different magnetic features. We find that the UV intensities provide a better measure of contributions of plage fields to RVs than the Ca ii H-K emission indices, especially during high activity levels when the latter tend to saturate.

The Masses of a Sample of Radial-velocity Exoplanets with Astrometric Measurements

Being one of the most fundamental physical parameter of astronomical objects, mass plays a vital role in the study of exoplanets, including their temperature structure, chemical composition, formation, and evolution. However, nearly a quarter of the known confirmed exoplanets lack measurements of their masses. This is particularly severe for those discovered via the radial velocity (RV) technique, which alone could only yield the minimum mass of planets. In this study, we use published RV data combined with astrometric data from a cross-calibrated Hipparcos-Gaia Catalog of Accelerations to jointly constrain the masses of 115 RV-detected substellar companions, by conducting full orbital fits using the public tool orvara. Among them, 9 exoplanets with are reclassified to the brown dwarf (BD) regime, and 16 BD candidates () turn out to be low-mass M dwarfs. We point out the presence of a transition in the BD regime as seen in the distributions of host star metallicity and orbital eccentricity with respect to planet masses. We confirm the previous findings that companions with masses below 42.5 M Jup might primarily form in the protoplanetary disk through core accretion or disk gravitational instability, while those with masses above 42.5 M Jup formed through the gravitational instability of a molecular cloud like stars. Selection effects and detection biases, which may affect our analysis to some extent, are discussed.

Null transit detections of 68 radial-velocity exoplanets observed by TESS

In recent years, the number of exoplanets has grown considerably. The most successful techniques in these detections are the radial velocity (RV) and planetary transits techniques, the latter of which has been significantly advanced by the Kepler, K2 and, more recently, the Transiting Exoplanet Survey Satellite (TESS) missions. The detection of exoplanets by means of both transits and RVs is of importance because this allows the characterization of their bulk densities and internal compositions. The TESS survey offers a unique possibility to search for transits of extrasolar planets detected using RVs. In this work, we present the results of our search for transits of RV-detected planets using the photometry of the TESS space mission. We focus on systems with super-Earth- and Neptune-sized planets on orbits with periods of shorter than 30 days. This cut is intended to keep objects with a relatively high transit probability, and is also consistent with the duration of TESS observations on a single sector. Given the summed geometric transit probabilities, the expected number of transiting planets is 3.4 ± 1.8. The sample contains two known transiting planets. We report null results for the remaining 66 out of 68 planets studied, and we exclude in all cases planets larger than 2.4 R⊕ under the assumption of central transits. The remaining two planets orbit HD 136352 and were recently announced.

The need for a public forecast of stellar activity to optimize exoplanet radial velocity detections and transmission spectroscopy

ABSTRACT Advances in high-precision spectrographs have paved the way for the search for an Earth analogue orbiting a Sun-like star within its habitable zone. However, the research community remains limited by the presence of stellar noise produced by stellar magnetic activity. These activity phenomena can obscure the detection of Earth-mass exoplanets and can create parasitic signals in transmission spectra. In this paper, we outline the need for a public forecast of stellar activity and produce a proof of principle. Using publicly available spectra we are able to forecast stellar minima several years ahead and reach a typical uncertainty on the timing of these minima of $\pm 0.5~\rm yr$, similar to the precision reached on our own Sun’s magnetic cycle. Furthermore, we use our toy model to show that knowing when to observe can improve the sensitivity of HARPS-North’s Solar telescope to low-mass planets by up to an order of magnitude, and we show that the majority of exoplanets selected for Early Release Science and Guaranteed Time Observations on the James Webb will be observed close or during stellar maxima, incurring a higher risk of stellar contamination. We finish our paper by outlining a number of next steps to create a public forecast usable by teams around the globe, by telescope time allocation committees, and in preparation for spacecraft such as Ariel.

Multi-mask least-squares deconvolution: extracting RVs using tailored masks

ABSTRACT To push the radial velocity (RV) exoplanet detection threshold, it is crucial to find more reliable RV extraction methods. The least-squares deconvolution (LSD) technique has been used to infer the stellar magnetic flux from spectropolarimetric data for the past two decades. It relies on the assumption that stellar absorption lines are similar in shape. Although this assumption is simplistic, LSD provides a good model for intensity spectra and likewise an estimate for their Doppler shift. We present the multi-mask least-squares deconvolution (MM-LSD) RV extraction pipeline that extracts the RV from two-dimensional echelle-order spectra using LSD with multiple tailored masks after continuum normalization and telluric absorption line correction. The flexibility of LSD allows to exclude spectral lines or pixels at will, providing a means to exclude variable lines or pixels affected by instrumental problems. The MM-LSD pipeline was tested on HARPS-N data for the Sun and selected well-observed stars with 5.7 < Vmag < 12.6. For FGK-type stars with median signal-to-noise ratio above 100, the pipeline delivered RV time series with on average 12 per cent lower scatter as compared to the HARPS-N RV extraction pipeline based on the cross-correlation function technique. The MM-LSD pipeline may be used as a standalone RV code, or modified and extended to extract a proxy for the magnetic field strength.

The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities

Abstract Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV rms than classic linear decorrelation, but no method is yet consistently reducing the RV rms to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data sets—such as solar data or data with known injected planetary and/or stellar signals—to better understand method performance and whether planetary signals are preserved.

Precise Masses and Orbits for Nine Radial-velocity Exoplanets

Abstract Radial-velocity (RV) surveys have discovered hundreds of exoplanetary systems but suffer from a fundamental degeneracy between planet mass M p and orbital inclination i. In this paper, we resolve this degeneracy by combining RVs with complementary absolute astrometry taken from the Gaia EDR3 version of the cross calibrated Hipparcos–Gaia Catalog of Accelerations (HGCA). We use the Markov Chain Monte Carlo orbit code orvara to simultaneously fit literature RVs and absolute astrometry from the HGCA. We constrain the orbits, masses, and inclinations of nine single and massive RV companions orbiting nearby G and K stars. We confirm the planetary nature of six companions: HD 29021 b ( 4.47 − 0.65 + 0.67 M Jup ), HD 81040 b ( 7.24 − 0.37 + 1.0 M Jup ), HD 87883 b ( 6.31 − 0.32 + 0.31 M Jup ), HD 98649 b ( 9.7 − 1.9 + 2.3 M Jup ), HD 106252 b ( 10.00 − 0.73 + 0.78 M Jup ), and HD 171238 b ( 8.8 − 1.3 + 3.6 M Jup ). We place one companion, HD 196067 b ( 12.5 − 1.8 + 2.5 M Jup ) on the planet–brown dwarf boundary and two companions in the low-mass brown dwarf regime: HD 106515 Ab ( 18.9 − 1.4 + 1.5 M Jup ), and HD 221420 b ( 20.6 − 1.6 + 2.0 M Jup ). The brown dwarf HD 221420 b, with a semimajor axis of 9.99 − 0.70 + 0.74 au, a period of 27.7 − 2.5 + 3.0 yr, and an eccentricity of 0.162 − 0.030 + 0.035 represents a promising target for high-contrast imaging. The RV orbits of HD 87883 b, HD 98649 b, HD 171238 b, and HD 196067 b are not fully constrained yet because of insufficient RV data. We find two possible inclinations for each of these orbits due to difficulty in separating prograde from retrograde orbits, but we expect this will change decisively with future Gaia data releases.

Estimating Magnetic Filling Factors from Simultaneous Spectroscopy and Photometry: Disentangling Spots, Plage, and Network

Abstract State-of-the-art radial velocity (RV) exoplanet searches are limited by the effects of stellar magnetic activity. Magnetically active spots, plage, and network regions each have different impacts on the observed spectral lines and therefore on the apparent stellar RV. Differentiating the relative coverage, or filling factors, of these active regions is thus necessary to differentiate between activity-driven RV signatures and Doppler shifts due to planetary orbits. In this work, we develop a technique to estimate feature-specific magnetic filling factors on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our technique using observations from the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE. We then compare the results of each technique to direct observations by the Solar Dynamics Observatory. Both implementations yield filling factor estimates that are highly correlated with the observed values. Modeling the solar RVs using these filling factors reproduces the expected contributions of the suppression of convective blueshift and rotational imbalance due to brightness inhomogeneities. Both implementations of this technique reduce the overall activity-driven rms RVs from 1.64 to 1.02 m s−1, corresponding to a 1.28 m s−1 reduction in the rms variation. The technique provides an additional 0.41 m s−1 reduction in the rms variation compared to traditional activity indicators.

The Mass Budgets and Spatial Scales of Exoplanet Systems and Protoplanetary Disks

Abstract Planets are born from disks of gas and dust, and observations of protoplanetary disks are used to constrain the initial conditions of planet formation. However, dust mass measurements of Class II disks with ALMA have called into question whether they contain enough solids to build the exoplanets that have been detected to date. In this paper, we calculate the mass and spatial scale of solid material around Sun-like stars probed by transit and radial velocity exoplanet surveys and compare those to the observed dust masses and sizes of Class II disks in the same stellar-mass regime. We show that the apparent mass discrepancy disappears when accounting for observational selection and detection biases. We find a discrepancy only when the planet formation efficiency is below 100%, or if there is a population of undetected exoplanets that significantly contributes to the mass in solids. We identify a positive correlation between the masses of planetary systems and their respective orbital periods, which is consistent with the trend between the masses and the outer radii of Class II dust disks. This implies that, despite a factor 100 difference in spatial scale, the properties of protoplanetary disks seem to be imprinted on the exoplanet population.

A Hermite–Gaussian based exoplanet radial velocity estimation method

As the first successful technique used to detect exoplanets orbiting distant stars, the radial velocity method aims to detect a periodic Doppler shift in a stellar spectrum due to the star’s motion along the line sight. We introduce a new, mathematically rigorous approach to detect such a signal that accounts for the smooth functional relationship of neighboring wavelengths in the spectrum, minimizes the role of wavelength interpolation, accounts for heteroskedastic noise and easily allows for accurate calculation of the estimated radial velocity standard error. Using Hermite–Gaussian functions, we show that the problem of detecting a Doppler shift in the spectrum can be reduced to linear regression in many settings. A simulation study demonstrates that the proposed method is able to accurately estimate an individual spectrum’s radial velocity with precision below 0.3 m s−1, corresponding to a Doppler shift much smaller than the size of a spectral pixel. Furthermore, the new method outperforms the traditional cross-correlation function approach for estimating the radial velocity by reducing the root mean squared error up to 15 cm s−1. The proposed method is also demonstrated on a new set of observations from the EXtreme PREcision Spectrometer (EXPRES) for the host star 51 Pegasi, and successfully recovers estimates of the planetary companion’s parameters that agree well with previous studies. The method is implemented in the R package rvmethod, and supplemental Python code is also available.

Speckle Imaging Characterization of Radial Velocity Exoplanet Systems

Abstract We conducted speckle imaging observations of 53 stellar systems that were members of long-term radial velocity (RV) monitoring campaigns and exhibited substantial accelerations indicative of planetary or stellar companions in wide orbits. Our observations were made with blue and red filters using the Differential Speckle Survey Instrument at Gemini-South and the NN-Explore Exoplanet Stellar Speckle Imager at the WIYN telescope. The speckle imaging identifies eight luminous companions within 2″ of the primary stars. In three of these systems—HD 1388, HD 87359, and HD 104304—the properties of the imaged companion are consistent with the RV measurements, suggesting that these companions may be associated with the primary and the cause of the RV variation. For all 53 stellar systems, we derive differential magnitude limits (i.e., contrast curves) from the imaging. We extend this analysis to include upper limits on companion mass in systems without imaging detections. In 25 systems, we rule out companions with masses greater than 0.2 M ⊙, suggesting that the observed RV signals are caused by late-M dwarfs or substellar (potentially planetary) objects. On the other hand, the joint RV and imaging analysis almost entirely rules out planetary explanations of the RV signal for HD 19522 and suggests that the companion must have an angular separation below a few tenths of an arcsecond. This work highlights the importance of combined RV and imaging observations for characterizing the outer regions of nearby planetary systems.

A Full Implementation of Spectro-perfectionism for Precise Radial Velocity Exoplanet Detection: A Test Case With the MINERVA Reduction Pipeline

We present a computationally tractable implementation of spectro-perfectionism, a method which minimizes error imparted by spectral extraction. We develop our method in conjunction with a full raw reduction pipeline for the MINiature Exoplanet Radial Velocity Array (MINERVA), capable of performing both optimal extraction and spectro-perfectionism. Although spectro-perfectionism remains computationally expensive, our implementation can extract a MINERVA exposure in approximately 30 minutes. We describe our localized extraction procedure and our approach to point-spread function (PSF) fitting. We compare the performance of both extraction methods on a set of 119 exposures on HD 122064, an RV standard star. Both the optimal extraction and spectro-perfectionism pipelines achieve nearly identical RV precision under a six-exposure chronological binning. We discuss the importance of reliable calibration data for PSF fitting and the potential of spectro-perfectionism for future precise radial velocity exoplanet studies.

First Radial Velocity Results From the MINiature Exoplanet Radial Velocity Array (MINERVA)

The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated observatory of four 0.7 m robotic telescopes fiber-fed to a KiwiSpec spectrograph. The MINERVA mission is to discover super-Earths in the habitable zones of nearby stars. This can be accomplished with MINERVA’s unique combination of high precision and high cadence over long time periods. In this work, we detail changes to the MINERVA facility that have occurred since our previous paper. We then describe MINERVA’s robotic control software, the process by which we perform 1D spectral extraction, and our forward modeling Doppler pipeline. In the process of improving our forward modeling procedure, we found that our spectrograph’s intrinsic instrumental profile is stable for at least nine months. Because of that, we characterized our instrumental profile with a time-independent, cubic spline function based on the profile in the cross dispersion direction, with which we achieved a radial velocity precision similar to using a conventional “sum-of-Gaussians” instrumental profile: 1.8 m s−1 over 1.5 months on the RV standard star HD 122064. Therefore, we conclude that the instrumental profile need not be perfectly accurate as long as it is stable. In addition, we observed 51 Peg and our results are consistent with the literature, confirming our spectrograph and Doppler pipeline are producing accurate and precise radial velocities.

HARPS-N Solar RVs Are Dominated by Large, Bright Magnetic Regions

Abstract State-of-the-art radial-velocity (RV) exoplanet searches are currently limited by RV signals arising from stellar magnetic activity. We analyze solar observations acquired over a 3 yr period during the decline of Carrington Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built solar telescope at the High Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) provides disk-integrated solar spectra, from which we extract RVs and log R HK ′ . The Solar Dynamics Observatory (SDO) provides disk-resolved images of magnetic activity. The Solar Radiation and Climate Experiment (SORCE) provides near-continuous solar photometry, analogous to a Kepler light curve. We verify that the SORCE photometry and HARPS-N log R HK ′ correlate strongly with the SDO-derived magnetic filling factor, while the HARPS-N RV variations do not. To explain this discrepancy, we test existing models of RV variations. We estimate the contributions of the suppression of convective blueshift and the rotational imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We investigate the time variation of these contributions over several rotation periods, and how these contributions depend on the area of active regions. We find that magnetic active regions smaller than 60 Mm2 do not significantly suppress convective blueshift. Our area-dependent model reduces the amplitude of activity-induced RV variations by a factor of two. The present study highlights the need to identify a proxy that correlates specifically with large, bright magnetic regions on the surfaces of exoplanet-hosting stars.

Predicted Yield of Transits of Known Radial Velocity Exoplanets from the TESS Primary and Extended Missions

Radial velocity (RV) surveys have detected hundreds of exoplanets through their gravitational interactions with their host stars. Some will be transiting, but most lack sufficient follow-up observations to confidently detect (or rule out) transits. We use published stellar, orbital, and planetary parameters to estimate the transit probabilities for nearly all exoplanets that have been discovered via the RV method. From these probabilities, we predict that of the known RV exoplanets should transit their host stars. This prediction is more than double the amount of RV exoplanets that are currently known to transit. The Transiting Exoplanet Survey Satellite (TESS) presents a valuable opportunity to explore the transiting nature of many of the known RV exoplanet systems. Based on the anticipated pointing of TESS during its two-year primary mission, we identify the known RV exoplanets that it will observe and predict that of them will have transits detected by TESS. However, we only expect the discovery of transits for ∼3 of these exoplanets to be novel (i.e., not previously known). We predict that the TESS photometry will yield dispositive null results for the transits of ∼125 RV exoplanets. This will represent a substantial increase in the effort to refine ephemerides of known RV exoplanets. We demonstrate that these results are robust to changes in the ecliptic longitudes of future TESS observing sectors. Finally, we consider how several potential TESS extended mission scenarios affect the number of transiting RV exoplanets we expect TESS to observe.