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2022 ◽  
Vol 6 (1) ◽  
pp. 8
Author(s):  
Kim Miskovetz ◽  
Trent J. Dupuy ◽  
Jessica Schonhut-Stasik ◽  
Keivan G. Stassun

Abstract The majority of stars have one or more stellar companions. As exoplanets continue to be discovered, it is crucial to examine planetary systems to identify their stellar companions. By observing a change in proper motion, companions can be detected by the acceleration they induce on their host stars. We selected 701 stars from the Hipparcos–Gaia Catalog of Accelerations (HGCA) that have existing adaptive optics imaging data gathered with Gemini/Near InfraRed Imager (NIRI). Of these, we examined 21 stars known to host planet candidates and reduced their archival NIRI data with Gemini’s DRAGONS software. We assessed these systems for companions using the NIRI images as well as Renormalized Unit Weight Error values in Gaia and accelerations in the HGCA. We detected three known visible companions and found two more systems with no visible companions but astrometric measurements indicating likely unresolved companions.


2022 ◽  
Vol 163 (2) ◽  
pp. 44
Author(s):  
Bradley M. S. Hansen

Abstract We present a catalog of unbound stellar pairs, within 100 pc of the Sun, that are undergoing close, hyperbolic, encounters. The data are drawn from the GAIA EDR3 catalog, and the limiting factors are errors in the radial distance and unknown velocities along the line of sight. Such stellar pairs have been suggested to be possible events associated with the migration of technological civilizations between stars. As such, this sample may represent a finite set of targets for a SETI search based on this hypothesis. Our catalog contains a total of 132 close passage events, featuring stars from across the entire main sequence, with 16 pairs featuring at least one main-sequence star of spectral type between K1 and F3. Many of these stars are also in binaries, so that we isolate eight single stars as the most likely candidates to search for an ongoing migration event—HD 87978, HD 92577, HD 50669, HD 44006, HD 80790, LSPM J2126+5338, LSPM J0646+1829 and HD 192486. Among host stars of known planets, the stars GJ 433 and HR 858 are the best candidates.


2021 ◽  
Vol 163 (1) ◽  
pp. 15
Author(s):  
Y. Cendes ◽  
P. K. G. Williams ◽  
E. Berger

Abstract We present the first systematic search for GHz frequency radio emission from directly imaged exoplanets using Very Large Array observations of sufficient angular resolution to separate the planets from their host stars. We obtained results for five systems and eight exoplanets located at ≲50 pc through new observations (Ross 458, GU Psc, and 51 Eri) and archival data (GJ 504 and HR 8799). We do not detect radio emission from any of the exoplanets, with 3σ luminosity upper limits of (0.9–23) × 1021 erg s−1. These limits are comparable to the level of radio emission detected in several ultracool dwarfs, including T dwarfs, whose masses are only a factor of two times higher than those of the directly imaged exoplanets. Despite the lack of detections in this pilot study, we highlight the need for continued GHz frequency radio observations of nearby exoplanets at μJy-level sensitivity.


2021 ◽  
Vol 162 (6) ◽  
pp. 301
Author(s):  
G. Mirek Brandt ◽  
Trent J. Dupuy ◽  
Yiting Li ◽  
Minghan Chen ◽  
Timothy D. Brandt ◽  
...  

Abstract We present comprehensive orbital analyses and dynamical masses for the substellar companions Gl 229 B, Gl 758 B, HD 13724 B, HD 19467 B, HD 33632 Ab, and HD 72946 B. Our dynamical fits incorporate radial velocities, relative astrometry, and, most importantly, calibrated Hipparcos-Gaia EDR3 accelerations. For HD 33632 A and HD 72946 we perform three-body fits that account for their outer stellar companions. We present new relative astrometry of Gl 229 B with Keck/NIRC2, extending its observed baseline to 25 yr. We obtain a <1% mass measurement of 71.4 ± 0.6 M Jup for the first T dwarf Gl 229 B and a 1.2% mass measurement of its host star (0.579 ± 0.007 M ⊙) that agrees with the high-mass end of the M-dwarf mass–luminosity relation. We perform a homogeneous analysis of the host stars’ ages and use them, along with the companions’ measured masses and luminosities, to test substellar evolutionary models. Gl 229 B is the most discrepant, as models predict that an object this massive cannot cool to such a low luminosity within a Hubble time, implying that it may be an unresolved binary. The other companions are generally consistent with models, except for HD 13724 B, which has a host star activity age 3.8σ older than its substellar cooling age. Examining our results in context with other mass–age–luminosity benchmarks, we find no trend with spectral type but instead note that younger or lower-mass brown dwarfs are overluminous compared to models, while older or higher-mass brown dwarfs are underluminous. The presented mass measurements for some companions are so precise that the stellar host ages, not the masses, limit the analysis.


2021 ◽  
Vol 162 (6) ◽  
pp. 273
Author(s):  
Melinda Soares-Furtado ◽  
Matteo Cantiello ◽  
Morgan MacLeod ◽  
Melissa K. Ness

Abstract Planetary engulfment events have long been proposed as a lithium (Li) enrichment mechanism contributing to the population of Li-rich giants (A(Li) ≥ 1.5 dex). Using MESA stellar models and A(Li) abundance measurements obtained by the GALAH survey, we calculate the strength and observability of the surface Li enrichment signature produced by the engulfment of a hot Jupiter (HJ). We consider solar-metallicity stars in the mass range of 1–2 M ⊙ and the Li supplied by a HJ of 1.0 M J. We explore engulfment events that occur near the main-sequence turn-off (MSTO) and out to orbital separations of R ⋆ ∼ 0.1 au = 22 R ⊙. We map our results onto the Hertzsprung–Russell Diagram, revealing the statistical significance and survival time of Li enrichment. We identify the parameter space of masses and evolutionary phases where the engulfment of a HJ can lead to Li enrichment signatures at a 5σ confidence level and with meteoritic abundance strengths. The most compelling strengths and survival times of engulfment-derived Li enrichment are found among host stars of 1.4 M ⊙ near the MSTO. Our calculations indicate that planetary engulfment is not a viable enrichment pathway for stars that have evolved beyond the subgiant branch. For these sources, observed Li enhancements are likely to be produced by other mechanisms, such as the Cameron–Fowler process or the accretion of material from an asymptotic giant branch companion. Our results do not account for second-order effects, such as extra mixing processes, which can further dilute Li enrichment signatures.


2021 ◽  
Vol 162 (6) ◽  
pp. 242
Author(s):  
L. Brefka ◽  
J. C. Becker

Abstract Ultra-short-period (USP) planets are exoplanets that have orbital periods of less than one day and are unique because they orbit inside the nominal magnetic truncation gap of their host stars. In some cases, USP planets have also been observed to exhibit unique dynamical parameters such as significant misalignments in inclination angle with respect to nearby planets. In this paper, we explore how the geometry of a multiplanet system hosting a USP planet can be expected to evolve as a star ages. In particular, we explore the relationship between the mutual inclination of the USP planet and the quadrupole moment (J 2) of the host star. We use secular perturbation theory to predict the past evolution of the example TOI-125 system, and then confirm the validity of our results using long-term N-body simulations. Through investigating how the misalignment between the candidate USP planet and the three other short-period planets in the TOI-125 system arose, we intend to derive a better understanding of the population of systems with misaligned USP planets and how their observed parameters can be explained in the context of their dynamical histories.


2021 ◽  
Vol 162 (6) ◽  
pp. 240
Author(s):  
Samuel W. Yee ◽  
Joshua N. Winn ◽  
Joel D. Hartman

Abstract Hot Jupiters are a rare and interesting outcome of planet formation. Although more than 500 hot Jupiters (HJs) are known, most of them were discovered by a heterogeneous collection of surveys with selection biases that are difficult to quantify. Currently, our best knowledge of HJ demographics around FGK stars comes from the sample of ≈40 objects detected by the Kepler mission, which have a well-quantified selection function. Using the Kepler results, we simulate the characteristics of the population of nearby transiting HJs. A comparison between the known sample of nearby HJs and simulated magnitude-limited samples leads to four conclusions. (1) The known sample of HJs appears to be ≈75% complete for stars brighter than Gaia G ≤ 10.5, falling to ≲50% for G ≤ 12. (2) There are probably a few undiscovered HJs with host stars brighter than G ≈ 10 located within 10° of the Galactic plane. (3) The period and radius distributions of HJs may differ for F-type hosts (which dominate the nearby sample) and G-type hosts (which dominate the Kepler sample). (4) To obtain a magnitude-limited sample of HJs that is larger than the Kepler sample by an order of magnitude, the limiting magnitude should be approximately G ≈ 12.5. This magnitude limit is within the range for which NASA’s Transiting Exoplanet Survey Satellite can easily detect HJs, presenting the opportunity to greatly expand our knowledge of hot-Jupiter demographics.


2021 ◽  
Vol 922 (1) ◽  
pp. 44
Author(s):  
Sean Jordan ◽  
Paul B. Rimmer ◽  
Oliver Shorttle ◽  
Tereza Constantinou

Abstract Compared to the diversity seen in exoplanets, Venus is a veritable astrophysical twin of the Earth; however, its global cloud layer truncates features in transmission spectroscopy, masking its non-Earth-like nature. Observational indicators that can distinguish an exo-Venus from an exo-Earth must therefore survive above the cloud layer. The above-cloud atmosphere is dominated by photochemistry, which depends on the spectrum of the host star and therefore changes between stellar systems. We explore the systematic changes in photochemistry above the clouds of Venus-like exoplanets orbiting K-dwarf or M-dwarf host stars, using a recently validated model of the full Venus atmosphere (0–115 km) and stellar spectra from the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury survey. SO2, OCS, and H2S are key gas species in Venus-like planets that are not present in Earth-like planets, and could therefore act as observational discriminants if their atmospheric abundances are high enough to be detected. We find that SO2, OCS, and H2S all survive above the cloud layer when irradiated by the coolest K dwarf and all seven M dwarfs, whereas these species are heavily photochemically depleted above the clouds of Venus. The production of sulfuric acid molecules that form the cloud layer decreases for decreasing stellar effective temperature. Less steady-state photochemical oxygen and ozone forms with decreasing stellar effective temperature, and the effect of chlorine-catalyzed reaction cycles diminish in favor of HO x and SO x catalyzed cycles. We conclude that trace sulfur gases will be prime observational indicators of Venus-like exoplanets around M-dwarf host stars, potentially capable of distinguishing an exo-Venus from an exo-Earth.


2021 ◽  
Vol 922 (1) ◽  
pp. 4
Author(s):  
Alexander P. Stephan ◽  
Smadar Naoz ◽  
B. Scott Gaudi

Abstract The recent discoveries of WD J091405.30+191412.25 (WD J0914 hereafter), a white dwarf (WD) likely accreting material from an ice-giant planet, and WD 1856+534 b (WD 1856 b hereafter), a Jupiter-sized planet transiting a WD, are the first direct evidence of giant planets orbiting WDs. However, for both systems, the observations indicate that the planets’ current orbital distances would have put them inside the stellar envelope during the red-giant phase, implying that the planets must have migrated to their current orbits after their host stars became WDs. Furthermore, WD J0914 is a very hot WD with a short cooling time that indicates a fast migration mechanism. Here, we demonstrate that the Eccentric Kozai–Lidov Mechanism, combined with stellar evolution and tidal effects, can naturally produce the observed orbital configurations, assuming that the WDs have distant stellar companions. Indeed, WD 1856 is part of a stellar triple system, being a distant companion to a stellar binary. We provide constraints for the orbital and physical characteristics for the potential stellar companion of WD J0914 and determine the initial orbital parameters of the WD 1856 system.


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