arXiv subjects

Robert A. Wittenmyer

Publications and source records attributed to Robert A. Wittenmyer.

At least 19 recordsLinked to original sources

arXiv2026

HD 715 b, a Warm Jupiter Orbiting a Massive Subgiant Discovered from a Single TESS Transit

Transiting Warm Jupiters orbiting bright stars are scarcely known, but a substantial number of these planets have been uncovered by the TESS mission. In this work we report the discovery and confirmation of a transiting Warm Jupiter orbiting the bright ($V$ = 8.70) subgiant star HD 715 (TOI-6893). HD 715 b was originally identified from a single transit event in TESS Sector 70. We acquired two seasons of radial velocity follow-up using the PFS, TRES, and MINERVA-Australis spectrographs, which clearly detect the planetary orbit. At $M_*=1.60\pm0.04 M_\odot$, HD 715 thus becomes one of the most massive stars known to host a transiting Warm Jupiter. From a joint fit to the TESS transit and our RVs, we find that HD 715 b has a $56.40^{+0.19}_{-0.23}$ day orbital period and measure a precise mass and radius of $0.635\pm0.056 M_J$ and $1.07\pm0.04 R_J$, rendering it a relatively typical member of the Warm Jupiter population. The moderate orbital eccentricity of $0.21^{+0.07}_{-0.08}$ contrasts with the higher eccentricities of other similar Warm Jupiters orbiting evolved stars, indicating a greater diversity in orbital eccentricities than previously known. The absence of additional transits in preceding TESS observations in Sectors 42 and 43 allows us to further refine the range of possible orbital periods to $[56.01, 56.35]$ days. Though the ephemeris uncertainty remains substantial, future photometric observations may nonetheless allow for recovery of the transit of HD 715 b.

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arXiv2026

Joint RV-Astrometric Analysis of two-planet system HD 65216: Prospects for Gaia DR4

We provide updated mass and orbital constraints on the planetary system around HD 65216, consisting of at least two giant planets on eccentric orbits. We first analyse new RV data to constrain the periods and eccentricities of both planets, before applying the Hipparcos-Gaia proper motion anomaly to constrain the inclination of HD 65216 c. From this joint analysis, we find that HD 65216 c is most likely in an eccentric orbit ($e$ = 0.42$\pm$0.05) with a longer period (7007$^{+192}_{-161}$ days) than previously determined. The proper motion anomaly is consistent with a bimodal distribution of inclinations, with peaks at sin$i\sim$0.5, producing true masses of 2.23$^{+0.96}_{-0.77}$ M$_{\mathrm{J}}$ and 3.32$^{+1.40}_{-1.16}$ M$_{\mathrm{J}}$ for HD 65216 b and c respectively, assuming the planets are co-planar. Finally, we simulate Gaia DR4 epoch astrometry and the DR3-DR4 proper motion anomaly. We find that these methods will be sensitive enough to further constrain orbital parameters and true mass.

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arXiv2026

Transit Timing Variations in TESS: A Catalog from the First Five Years

We present the first catalog of transit timing variations (TTVs) in TESS systems with multiple TESS Objects of Interest (TOIs) using data from Sector 1 to Sector 69, spanning the first five years of mission operations. With an initial sample of 175 multi-TOI systems, we find significant TTVs in 20 systems, 13 of which had not been previously detected. Our results are generally consistent with the findings of previous Kepler TTV catalogs, with compact systems more likely to have detectable TTVs. However, the TTV systems in TESS exhibit a pile-up at the 2:1 orbital period resonance, in contrast to the pile-up near the 3:2 resonance from previous Kepler catalogs. This provides a tentative indicator that there may be different disk migration recipes that Kepler systems favor versus TESS systems. This catalog is a vital first step in determining which orbital resonances migrating planets tend to occupy at the end of formation, and aims to provide a list of high-impact targets for future in-depth follow up.

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arXiv2026

The Pan-Pacific Planet Search -- IX. A menagerie of companions orbiting evolved stars

We present resolutions as to the nature of six speculative candidate companions proposed in the final data release of the Pan-Pacific Planet Search, a 6-year radial-velocity survey of 164 southern evolved stars using the now-decommissioned UCLES spectrograph on the 3.9m Anglo-Australian Telescope. New radial-velocity observations, TESS asteroseismology, and Hipparcos-Gaia astrometry are incorporated to refine the companion and host-star parameters. We confirm that HD 126105b is a giant planet ($P=524.0\pm$2.9 d, $m$ sin $i=1.67^{+0.19}_{-0.17}M_{Jup}$), and that HD 205577B is a massive, eccentric brown dwarf ($P\sim$11.2 yr, $m=77^{+11}_{-9}M_{Jup}$, $e=0.68$). HD 115066B and HD 121156B are low-mass stellar companions, while HD 114899 and HD 159743 are shown to be unadorned by any detectable companions whatsoever. This demonstrates the utility of astrometric information to help overcome the temporal limitations of incomplete radial-velocity data sets and elucidate the true nature of suspected companion bodies.

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arXiv2026

HD 38973 b -- a cold Saturn orbiting a Sun-like star

We report the detection of a long-period companion to the nearby solar-type star HD\,38973 using precision radial-velocity measurements. The radial-velocity data reveal a coherent Keplerian signal with a period of $\sim$3000~days and moderate eccentricity, yielding a minimum mass in the sub-Jovian regime. We complement the radial-velocity analysis with astrometric constraints from the \emph{Hipparcos--Gaia} Catalog of Accelerations (HGCA). Although no significant proper-motion anomaly is detected for HD\,38973, the absence of an astrometric signal provides an informative upper limit on the companion mass. By combining the radial-velocity posterior with the HGCA likelihood, we rule out high-mass solutions at low inclinations and derive a robust upper bound on the true companion mass. We find the best-fitting true mass to be $0.240_{-0.040}^{+0.102}\,M_{\rm Jup}$, on an orbit with period $2733^{+210}_{-190}$ days, making HD\,38973b a likely cold Saturn. This study highlights the diagnostic power of astrometric non-detections when combined with precision radial velocities, demonstrating that meaningful constraints on companion masses can be obtained even in the absence of a detected astrometric signal.

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arXiv2026

Finding Alien Worlds in Queensland -- A Decade of MINERVA-Australis

Three decades ago, humanity entered the Exoplanet Era, with the discovery of the first planets orbiting other stars. Today, more than 6000 exoplanets are known - a tally recently bolstered by NASA's TESS spacecraft. Whilst TESS is an exceptional planet finding machine, dedicated follow-up observations from the ground are required to confirm the existence of the planets it discovers. To achieve this, we constructed the southern hemisphere's only dedicated exoplanet detection and characterisation facility, MINERVA-Australis, at the University of Southern Queensland's Mt Kent Observatory. Funded in 2015, MINERVA-Australis saw first light in 2018, in time for the launch of TESS. MINERVA-Australis has since been scouring the skies, working to confirm and characterise the incredible harvest of planets detected by TESS. To date, the facility has contributed to the discovery of 40 new exoplanets, and continued the legacy of radial velocity data from the Anglo-Australian Planet Search program.

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arXiv2026

A Planetary Illusion's Funeral: Non-detection of a Gaia DR3 Exoplanet Candidate, and the Role of Intermediate-precision Radial Velocities in Gaia Exoplanet Follow-up

The detection of exoplanets using astrometry has long been an area of interest, but is fraught with challenges. The Gaia mission is fundamentally reshaping this field thanks to its unprecedentedly precise all-sky astrometric observations. The 2022 release of Gaia DR3 brought the first exoplanets discovered from the Gaia astrometry, including a new candidate around the bright ($V=6.6$) solar-type star HD 12800. However, two years after announcement, the Gaia exoplanet candidate was retracted. In this work we report radial velocity observations of HD 12800 acquired with the TRES spectrograph, which we began immediately after the release of Gaia DR3. Our observations failed to detect the planet candidate; nonetheless, we emphasise that the originally proposed companion would have been easily detected in our radial velocity observations. We conclude with a discussion on the role of intermediate-precision ($\approx$10 m s$^{-1}$) RV spectrographs in the follow-up of Gaia astrometric exoplanet candidates, relevant to the forthcoming release of Gaia DR4. We argue that such observations may play an important role in planet confirmation for stars between approximately $8<G<12$, likely to represent a significant fraction of Gaia exoplanet discoveries.

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arXiv2026

Hot Jupiter - Cold Jupiter: A complex sibling relation

A handful of planetary systems hosting a Hot Jupiter have been subsequently found to also host long-period giant planets. These ``cold Jupiters,'' giant planets residing beyond the snow line ($\sim$3\,au), play an important role in the dynamical evolution of the system as a whole. In this work, we investigate the detectability of cold Jupiters around a sample of 28 well-studied Hot Jupiter host stars to estimate the occurrence rate of this distinctive system architecture. We perform extensive simulations using the combination of all publicly available radial velocity (RV) data for those stars with synthetic RV data. The synthetic data test observing strategies along three axes: cadence, duration, and measurement precision. For each scenario, we determine detection limits based on the semi-major axis at which a 1 Jupiter mass planet would be recovered 50\% of the time. We find the following: 1) the existing RV data are remarkably insensitive to these Hot Jupiter/Cold Jupiter pairs; 2) the total baseline over which an observational campaign is carried out is the dominant factor in our ability to detect cold Jupiters; and 3) the results are relatively insensitive to the individual RV measurement precision. We conclude that metre-class telescopes with lower RV precision are ideally suited to surveying Hot Jupiter-cold Jupiter systems.

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arXiv2026

A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2

The transit method is currently one of our best means for the detection of potentially habitable "Earth-like" exoplanets. In principle, given sufficiently high photometric precision, cool Earth-sized exoplanets orbiting Sun-like stars could be discovered via single transit detections; however, this has not previously been achieved. In this work, we report a 10-hour long single transit event which occurred on the $V=10.1$ K-dwarf HD 137010 during K2 Campaign 15 in 2017. The transit is comparatively shallow ($225\pm10$ ppm), but is detected at high signal-to-noise thanks to the exceptionally high photometric precision achieved for the target. Our analysis of the K2 photometry, historical and new imaging observations, and archival radial velocities and astrometry strongly indicate that the event was astrophysical, occurred on-target, and can be best explained by a transiting planet candidate, which we designate HD 137010 b. The single observed transit implies a radius of $1.06^{+0.06}_{-0.05}$ $R_\oplus$, and assuming negligible orbital eccentricity we estimate an orbital period of $355^{+200}_{-59}$ days ($a=0.88^{+0.32}_{-0.10}$ AU), properties comparable to Earth. We project an incident flux of $0.29^{+0.11}_{-0.13}$ $I_\oplus$, which would place HD 137010 b near the outer edge of the habitable zone. This is the first planet candidate with Earth-like radius and orbital properties that transits a Sun-like star bright enough for substantial follow-up observations.

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arXiv2025

SPORES-HWO. II. Companion Mass Limits and Updated Planet Properties for 120 Future Exoplanet Imaging Targets from 35 yr of Precise Doppler Monitoring

A goal of the future Habitable Worlds Observatory (HWO) is to directly image and spectroscopically characterize true Earth-analogs. However, if a large fraction of HWO target stars host unknown dynamically disruptive giant planets in their habitable zones (HZs), then additional targets that are farther away will need to be surveyed, potentially requiring a larger-aperture telescope and a coronagraph with a smaller inner working angle. Therefore, the sooner we constrain the presence of massive planets orbiting potential HWO target stars, the easier and less costly it will be to adjust key aspects of HWO's architecture. In this work, we uniformly analyze over 153,000 public radial velocity (RV) observations of 120 potential HWO target stars to derive mass limits on planetary companions. The RVs were measured by 23 spectrographs located at 15 observatories around the world, with the first observations going back to 1987. Based on empirical search completeness tests, we determine that undetected Jupiter-mass (Saturn-mass) planets may be hiding in up to 38% (53%) of the HZs of targets in the ExEP Mission Star List. The median mass sensitivity limit in the middle of the conservative HZ is approximately 48 $\rm M_\oplus$. We also provide updated parameters for 53 known companions, and we detect at least 26 additional RV signals corresponding to stellar activity and 4 signals that are planet candidates. We note that 44 of the ExEP stars lack substantial RV monitoring history, and we advocate for community-coordinated observing campaigns of these stars using moderate-precision RV facilities.

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arXiv2025

Exploring Warm Jupiter Migration Pathways with Eccentricities. I. Catalog of Uniform Keplerian Fits to Radial Velocities of 200 Warm Jupiters

Giant planets are expected to predominantly form beyond the water ice line and occasionally undergo inward migration. Unlike hot Jupiters, which can result from high-eccentricity tidal migration, warm Jupiters between 0.1-1 AU ($\approx$10--365 d) are in many ways more challenging to explain because they reside outside the tidal influence of their host stars. Warm Jupiters should therefore preserve traces of their origins as their eccentricities are directly related to their past interactions. We analyze the eccentricities of 200 warm Jupiters orbiting 194 Sun-like host stars (with FGKM spectral types) using 18,587 RV measurements across 40 high-resolution spectrographs. RVs are compiled from the literature and are supplemented with 540 new observations from MINERVA-Australis at Mt. Kent Observatory and the Habitable-zone Planet Finder spectrograph at McDonald Observatory's Hobby-Eberly Telescope, which are timed to improve eccentricity constraints by sampling orbits near periastron passage. The overarching goal of this program is to establish the relative importance of giant planet migration channels through the largest homogeneous analysis of warm Jupiter orbital properties to date. In particular, we evaluate and compare the impact of different system architectures and host star characteristics on the population-level eccentricity distributions of warm Jupiters. Here, we present the target sample, observations, orbit fitting procedure, and parameter summary statistics of our survey. All orbit fit solutions, parameter posterior chains, and merged RV tables for each system are made publicly available.

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arXiv2025

The NEID Earth Twin Survey. II. Dynamical Masses in Seven High-acceleration Star Systems

We present a set of companion dynamical masses and orbital parameters of seven star systems from the NEID Earth Twin Survey with significant absolute astrometric accelerations between the epochs of Hipparcos and Gaia. These include four binary star systems (HD 68017 AB, 61 Cygni AB, HD 24496 AB, and HD 4614 AB) and three planetary systems (HD 217107, HD 190360, and HD 154345). Our analyses incorporate a long baseline of RVs that includes over 1100 previously unpublished measurements from NEID and MINERVA, extending the overall RV baseline for each system by $\approx$2.5 years, as well as relative astrometry for the stellar binary systems where the positions of both stars are well-measured. In each case, the combination of astrometry and RVs constrains the three-dimensional acceleration of the host star and enables precise dynamical masses. We publish true masses for three planets whose measurements were previously entangled with their inclinations, four stellar masses with $\lesssim$1% relative precision, and improved orbital solutions for all seven systems, including the first for HD 24496 AB. These solutions not only agree with previous estimates, but also improve their fidelity. We also explore each system for evidence of periodic signals in the residuals around our best-fit models, and discuss the potential that the three planetary systems have for being directly imaged. With dynamical mass estimates and reliable orbit ephemerides, these seven star systems represent promising benchmarks for future stellar and planetary characterization efforts, and are amenable for further improvement with the upcoming release of Gaia epoch astrometry.

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arXiv2025

Three-dimensional Orbit and Dynamical Masses of GJ 105 AC

The precision of stellar models is higher than the precision at which we are able to measure the masses of most stars, with the notable exception of binaries where we can determine dynamical masses of the component stars. In addition to well-measured stellar properties, the ideal benchmark star is far enough from its companion that its properties are indistinguishable from an otherwise identical single star. Currently, there are a handful of stars with precise ($\pm$3 %), model-independent mass measurements that are "effectively single" and for which we can obtain clean spectra (i.e. spectra that are not blended with a close companion). In this paper, we introduce GJ 105 AC as the newest members of this exclusive population. We present an updated orbital analysis for the long-period K3+M7 binary GJ 105 AC. We jointly analyze radial velocity (RV) and relative astrometry data, including new RVs from the Miniature Exoplanet Radial Velocity Array (MINERVA) that capture the full periapsis passage and the RV minimum of the $76.0 \pm 1.3$ yr orbit for the first time. We derive precise dynamical masses of $M_1 = 0.78 \pm 0.02\, \mathrm{M}_\odot$ and $M_2 = 0.098 \pm 0.002\, \mathrm{M}_\odot$. We find that of all stars with similarly precise masses (~2%), GJ 105 AC stands out as having the widest on-sky separation after $α$ Centauri AB, making it one of the most easily accessible to spectroscopy, as well as the the second-widest true separation, ensuring that its members are truly "effectively single" in terms of their evolution.

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arXiv2025

Optimising Radial Velocity Detection Limits for Southern Habitable Worlds Observatory Targets

The planned NASA Habitable Worlds Observatory (HWO) flagship mission aims to image and spectroscopically characterise 25 Earth-size planets in the habitable zones of their stars. However, one giant planet in the habitable zone can ruin your whole day. Recent work has examined the current state of our knowledge on the presence or absence of such objects in samples of likely HWO targets, and that knowledge has been found wanting; even Saturn-mass planets remain undetectable in many of these systems. In this work, we present simulations assessing the degree to which new campaigns of high-cadence radial velocity observations can ameliorate this woeful state of affairs. In particular, we highlight the value of moderate-precision but highly flexibly-scheduled RV facilities in aiding this necessary HWO precursor science. We find that for a subset of Southern HWO stars, 6 years of new RVs from the Minerva-Australis telescope array in Australia can improve the median detection sensitivity in the habitable zones of 13 likely HWO targets to $\sim$50 Earth masses, an improvement of $\sim$44%.

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arXiv2024

Two Earth-size Planets and an Earth-size Candidate Transiting the Nearby Star HD 101581

We report the validation of multiple planets transiting the nearby ($d = 12.8$ pc) K5V dwarf HD 101581 (GJ 435, TOI-6276, TIC 397362481). The system consists of at least two Earth-size planets whose orbits are near a mutual 4:3 mean-motion resonance, HD 101581 b ($R_{p} = 0.956_{-0.061}^{+0.063}~R_{\oplus}$, $P = 4.47$ days) and HD 101581 c ($R_{p} = 0.990_{-0.070}^{+0.070}~R_{\oplus}$, $P = 6.21$ days). Both planets were discovered in Sectors 63 and 64 TESS observations and statistically validated with supporting ground-based follow-up. We also identify a signal that probably originates from a third transiting planet, TOI-6276.03 ($R_{p} = 0.982_{-0.098}^{+0.114}~R_{\oplus}$, $P = 7.87$ days). These planets are remarkably uniform in size and their orbits are evenly spaced, representing a prime example of the "peas-in-a-pod" architecture seen in other compact multi-planet systems. At $V = 7.77$, HD 101581 is the brightest star known to host multiple transiting planets smaller than $1.5~R_{\oplus}$. HD 101581 is a promising system for atmospheric characterization and comparative planetology of small planets.

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arXiv2024

The Search for the Inbetweeners: How packed are TESS planetary systems?

In this work, we examine seven systems discovered by TESS, to see whether there is any room in those systems for an additional planet (or several) to lurk unseen between the two planets already confirmed therein. In five of those systems (namely HD 15337; HD 21749; HD 63433; HD 73583 and LTT 3780) we find that there is ample room for an undiscovered planet to move between those that have already been discovered. In other words, as they currently stand, those systems are not tightly packed. In stark contrast, the perturbative influence of the two known TOI-1670 planets is such that additional planets in between are ruled out. The final system, TOI 421, is more challenging. In the vast majority of cases, adding an Earth-mass planet to that system between the orbits of the known planets caused catastrophic instability. Just ~1.1% of our simulations of the modified system proved dynamically stable on a timescale of one million years. As a result, it seems that there is very little room between the two known planets in the TOI 421 system for an addition unseen world to exist, but the existence of such a planet can not be definitely ruled out on dynamical grounds alone.

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arXiv2024

HD 28185 Revisited: An Outer Planet, Instead of a Brown Dwarf, On a Saturn-like Orbit

As exoplanet surveys reach ever-higher sensitivities and durations, planets analogous to the solar system giant planets are increasingly within reach. HD 28185 is a Sun-like star known to host a $m\sin i=6 M_J$ planet on an Earth-like orbit; more recently, a brown dwarf with a more distant orbit has been claimed. In this work we present a comprehensive reanalysis of the HD 28185 system, based on 22 years of radial velocity observations and precision Hipparcos-Gaia astrometry. We confirm the previous characterisation of HD 28185 b as a temperate giant planet, with its $385.92^{+0.06}_{-0.07}$ day orbital period giving it an Earth-like incident flux. In contrast, we substantially revise the parameters of HD 28185 c; with a new mass of $m=6.0\pm0.6 M_J$ we reclassify this companion as a super-jovian planet. HD 28185 c has an orbital period of $24.9^{+1.3}_{-1.1}$ years, a semi-major axis of $8.50^{+0.29}_{-0.26}$ AU, and a modest eccentricity of $0.15\pm0.04$, resulting in one of the most Saturn-like orbits of any known exoplanet. HD 28185 c lies at the current intersection of detection limits for RVs and direct imaging, and highlights how the discovery of giant planets at $\approx$10 AU separations is becoming increasingly routine.

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arXiv2024

HD 222237 b: a long period super-Jupiter around a nearby star revealed by radial-velocity and Hipparcos-Gaia astrometry

Giant planets on long period orbits around the nearest stars are among the easiest to directly image. Unfortunately these planets are difficult to fully constrain by indirect methods, e.g., transit and radial velocity (RV). In this study, we present the discovery of a super-Jupiter, HD 222237 b, orbiting a star located $11.445\pm0.002$ pc away. By combining RV data, Hipparcos and multi-epoch Gaia astrometry, we estimate the planetary mass to be ${5.19}_{-0.58}^{+0.58}\,M_{\rm Jup}$, with an eccentricity of ${0.56}_{-0.03}^{+0.03}$ and a period of ${40.8}_{-4.5}^{+5.8}$ yr, making HD 222237 b a promising target for imaging using the Mid-Infrared Instrument (MIRI) of JWST. A comparative analysis suggests that our method can break the inclination degeneracy and thus differentiate between prograde and retrograde orbits of a companion. We further find that the inferred contrast ratio between the planet and the host star in the F1550C filter ($15.50\,μ\rm m$) is approximately $1.9\times10^{-4}$, which is comparable with the measured limit of the MIRI coronagraphs. The relatively low metallicity of the host star ($\rm-0.32\,dex$) combined with the unique orbital architecture of this system presents an excellent opportunity to probe the planet-metallicity correlation and the formation scenarios of giant planets.

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