Abstract
We present second observations by K2 of OJ 287 and seven other
γ
-ray active galactic nuclei (AGNs) obtained in 2017–2018, second and third observations of the lobe-dominated, steep-spectrum ...quasar 3C 207, and observations of nine additional blazars not previously observed with K2. The AGNs were observed simultaneously with K2 and the Fermi Large Area Telescope for 51–81 days. Our full sample, observed in 2014–2018, contained 16 BL Lacertae objects (BL Lacs), nine flat-spectrum radio quasars (FSRQs), and four other
γ
-ray AGNs. Twelve BL Lacs and seven FSRQs exhibited fast, jagged light curves, while four BL Lacs and two FSRQs had slow, smooth light curves. Some objects changed their red-noise character significantly between repeated K2 observations. The optical characteristics of OJ 287 derived from the short-cadence K2 light curves changed between observations made before and after the predicted passage of the suspected secondary supermassive black hole through the accretion disk of the primary supermassive black hole. The average slopes of the periodogram power spectral densities of the BL Lacs’ and FSRQs’ light curves differed significantly, by ≈12%, with the BL Lac slopes being steeper, and a Kolmogorov–Smirnov test with a
p
-value of 0.039 indicates that these samples probably come from different populations; however, this result is not as strongly supported by power spectral response (PSRESP) analyses. Differences in the origin of the jets from the ergosphere or accretion disk in these two classes could produce such a disparity, as could different sizes or locations of emission regions within the jets.
Abstract NASA’s Transiting Exoplanet Survey Satellite (TESS) has identified over 7000 candidate exoplanets via the transit method, with gas giants among the most readily detected due to their large ...radii. Even so, long intervals between TESS observations for much of the sky lead to candidates for which only a single transit is detected in one TESS sector, leaving those candidate exoplanets with unconstrained orbital periods. Here, we confirm the planetary nature of TIC 393818343 b, originally identified via a single TESS transit, using radial velocity data and ground-based photometric observations from citizen scientists with the Unistellar Network and Exoplanet Watch. We determine a period of P = 16.24921 − 0.00011 + 0.00010 days, a mass M P = 4.34 ± 0.15 M J , and semimajor axis a = 0.1291 − 0.0022 + 0.0021 au, placing TIC 393818343 b in the “warm Jupiter” population of exoplanets. With an eccentricity e = 0.6058 ± 0.0023, TIC 393818343 b is the most eccentric warm Jupiter to be discovered by TESS orbiting less than 0.15 au from its host star and therefore an excellent candidate for follow-up, as it may inform our future understanding of how hot and warm Jupiter populations are linked.
Abstract
We present 2241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its 2 yr Prime Mission. We list these candidates in the TESS Objects of ...Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously known planets recovered by TESS observations. We describe the process used to identify TOIs, investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well suited for detailed follow-up observations. The TESS data products for the Prime Mission (sectors 1–26), including the TOI catalog, light curves, full-frame images, and target pixel files, are publicly available at the Mikulski Archive for Space Telescopes.
Exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. Young planets (<1 Gyr) offer an opportunity to probe the ...critical early stages of this evolution, where planets evolve the fastest. However, most of the known young planets orbit prohibitively faint stars. We present the discovery of two planets transiting HD 63433 (TOI 1726, TIC 130181866), a young Sun-like ( ) star. Through kinematics, lithium abundance, and rotation, we confirm that HD 63433 is a member of the Ursa Major moving group (τ = 414 23 Myr). Based on the TESS light curve and updated stellar parameters, we estimate that the planet radii are 2.15 0.10 R⊕ and 2.67 0.12 R⊕, the orbital periods are 7.11 and 20.55 days, and the orbital eccentricities are lower than about 0.2. Using High Accuracy Radial velocity Planet Searcher for the Northern hemisphere velocities, we measure the Rossiter-McLaughlin signal of the inner planet, demonstrating that the orbit is prograde. Since the host star is bright (V = 6.9), both planets are amenable to transmission spectroscopy, radial velocity measurements of their masses, and more precise determination of the stellar obliquity. This system is therefore poised to play an important role in our understanding of planetary system evolution in the first billion years after formation.
Much of the science from the exoplanets detected by the Transiting Exoplanet Survey Satellite (TESS) mission relies on precisely predicted transit times that are needed for many follow-up ...characterization studies. We investigate ephemeris deterioration for simulated TESS planets and find that the ephemerides of 81% of those will have expired (i.e., 1 mid-transit time uncertainties greater than 30 minutes) 1 yr after their TESS observations. We verify these results using a sample of TESS planet candidates as well. In particular, of the simulated planets that would be recommended as James Webb Space Telescope (JWST) targets by Kempton et al., ∼80% will have mid-transit time uncertainties >30 minutes by the earliest time JWST would observe them. This rapid deterioration is driven primarily by the relatively short time baseline of TESS observations. We describe strategies for maintaining TESS ephemerides fresh through follow-up transit observations. We find that the longer the baseline between the TESS and the follow-up observations, the longer the ephemerides stay fresh, and that 51% of simulated primary mission TESS planets will require space-based observations. The recently approved extension to the TESS mission will rescue the ephemerides of most (though not all) primary mission planets, but the benefits of these new observations can only be reaped 2 yr after the primary mission observations. Moreover, the ephemerides of most primary mission TESS planets (as well as those newly discovered during the extended mission) will again have expired by the time future facilities such as the ELTs, Ariel, and the possible LUVOIR/Origins Space Telescope missions come online, unless maintenance follow-up observations are obtained.
We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD 332231—an F8 dwarf star with a V-band ...magnitude of 8.56—was observed by TESS in Sectors 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder, Keck I, and SONG telescopes. The orbital period we infer from radial velocity (RV) observations leads to the discovery of another transit in Sector 14 that was masked by PDC due to scattered light contamination. A joint analysis of the transit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size (0.867 (+0.027,-0.025 R(J)), sub-Saturn-mass (0.244 ± 0.021M(J)) exoplanet on a 18.71 day circular orbit. The low surface gravity of HD 332231 b and the relatively low stellar flux it receives make it a compelling target for transmission spectroscopy. Also, the stellar obliquity is likely measurable via the Rossiter–McLaughlin effect, an exciting prospect given the 0.14 au orbital separation of HD 332231 b. The spectroscopic observations do not provide substantial evidence for any additional planets in the HD 332231 system, but continued RV monitoring is needed to further characterize this system. We also predict that the frequency and duration of masked data in the PDC light curves for TESS Sectors 14–16 could hide transits of some exoplanets with orbital periods between 10.5 and 17.5 days.
We report the discovery of TOI-4127 b, which is a transiting, Jupiter-sized exoplanet on a long period (P=56.39879 +0.00010-0.00010days) and a high-eccentricity orbit around a late F-type dwarf star. ...This warm Jupiter was first detected and identified as a promising candidate from a search for single-transit signals in TESS Sector 20 data and was later characterized as a planet following two subsequent transits (TESS Sectors 26 and 53) and follow-up ground-based RV observations with the NEID and SOPHIE spectrographs. We jointly fit the transit and RV data to constrain the physical (Rp=1.096+0.039-0.032RJ, Mp=2.30+0.11-0.11MJ) and orbital parameters of the exoplanet. Given its high orbital eccentricity (𝓮=0.7471+0.0078-0.0086), TOI-4127 b is a compelling candidate for studies of warm Jupiter populations and of hot Jupiter formation pathways. We show that the present periastron separation of TOI-4127 b is too large for high-eccentricity tidal migration to circularize its orbit, and that TOI-4127 b is unlikely to be a hot Jupiter progenitor unless it is undergoing angular momentum exchange with an undetected outer companion. Although we find no evidence for an external companion, the available observational data are insufficient to rule out the presence of a perturber that can excite eccentricity oscillations and facilitate tidal migration.
ABSTRACT
We analyse high-cadence data from the Transiting Exoplanet Survey Satellite (TESS) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical changing-look phenomenon in ASASSN-18el ...has been argued to be due to either a drastic change in the accretion rate of the existing active galactic nucleus (AGN) or the result of a tidal disruption event (TDE). Throughout the TESS observations, short-time-scale stochastic variability is seen, consistent with an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW) model and recover a rest-frame variability amplitude of $\hat{\sigma } = 0.93 \pm 0.02$ mJy and a rest-frame time-scale of $\tau _{DRW} = 20^{+15}_{-6}$ d. We find that the estimated τDRW for ASASSN-18el is broadly consistent with an apparent relationship between the DRW time-scale and central supermassive black hole mass. The large-amplitude stochastic variability of ASASSN-18el, particularly during late stages of the flare, suggests that the origin of this ANT is likely due to extreme AGN activity rather than a TDE.
Abstract We report the discovery and confirmation of the Transiting Exoplanet Survey Satellite (TESS) single-transit, warm and dense sub-Saturn, TIC 139270665 b. This planet is unusually dense for ...its size: with a bulk density of 2.13 g cm −3 (0.645 R J , 0.463 M J ), it is the densest warm sub-Saturn of the TESS family. It orbits a metal-rich G2 star. We also found evidence of a second planet, TIC 139270665 c, with a longer period of 1010 − 220 + 780 days and minimum mass M P sin i of 4.89 − 0.37 + 0.66 M J . First clues of TIC 139270665 b’s existence were found by citizen scientists inspecting TESS photometric data from sector 47 in 2022 January. Radial velocity measurements from the Automated Planet Finder combined with TESS photometry and spectral energy distributions via EXOFASTv2 system modeling suggested a 23.624 − 0.031 + 0.030 day orbital period for TIC 139270665 b and also showed evidence for the second planet. Based on this estimated period, we mobilized the Unistellar citizen science network for photometric follow-up, capitalizing on their global distribution to capture a second transit of TIC 139270665 b. This citizen science effort also served as a test bed for an education initiative that integrates young students into modern astrophysics data collection. The Unistellar photometry did not definitively detect a second transit, but did enable us to further constrain the planet’s period. As a transiting, warm, and dense sub-Saturn, TIC 139270665 b represents an interesting laboratory for further study to enhance our models of planetary formation and evolution.
Abstract Discovering and characterizing exoplanets at the outer edge of the transit method’s sensitivity has proven challenging owing to geometric biases and the practical difficulties associated ...with acquiring long observational baselines. Nonetheless, a sample of giant exoplanets on orbits longer than 100 days has been identified by transit hunting missions. We present long-term Doppler spectroscopy for 11 such systems with observation baselines spanning a few years to a decade. We model these radial velocity observations jointly with transit photometry to provide initial characterizations of these objects and the systems in which they exist. Specifically, we make new precise mass measurements for four long-period giant exoplanets (Kepler-111 c, Kepler-553 c, Kepler-849 b, and PH-2 b), we place new upper limits on mass for four others (Kepler-421 b, KOI-1431.01, Kepler-1513 b, and Kepler-952 b), and we show that several confirmed planets are in fact not planetary at all. We present these findings to complement similar efforts focused on closer-in short-period giant planets, and with the hope of inspiring future dedicated studies of cool giant exoplanets.
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