Rotation Periods of TESS Objects of Interest from the Magellan-TESS Survey with Multiband Photometry from Evryscope and TESS

Stellar radial-velocity (RV) jitter due to surface activity may bias the RV semiamplitude and mass of rocky planets. The amplitude of the jitter may be estimated from the uncertainty in the rotation period, allowing the mass to be more accurately obtained. We find candidate rotation periods for 17 out of 35 TESS Objects of Interest (TOI) hosting <3 R ⊕ planets as part of the Magellan-TESS survey, which is the first-ever statistically robust study of exoplanet masses and radii across the photoevaporation gap. Seven periods are ≥3σ detections, two are ≥1.5σ, and eight show plausible variability, but the periods remain unconfirmed. The other 18 TOIs are nondetections. Candidate rotators include the host stars of the confirmed planets L 168-9 b, the HD 21749 system, LTT 1445 A b, TOI 1062 b, and the L 98-59 system. Thirteen candidates have no counterpart in the 1000 TOI rotation catalog of Canto Martins et al. We find periods for G3-M3 dwarfs using combined light curves from TESS and the Evryscope all-sky array of small telescopes, sometimes with longer periods than would be possible with TESS alone. Secure periods range from 1.4 to 26 days with Evryscope-measured photometric amplitudes as small as 2.1 mmag in g′. We also apply Monte Carlo sampling and a Gaussian process stellar activity model from exoplanet to the TESS light curves of six TOIs to confirm the Evryscope periods

TOI-942b: A Prograde Neptune in a ∼ 60 Myr Old Multi-transiting System

Mapping the orbital obliquity distribution of young planets is one avenue toward understanding mechanisms that sculpt the architectures of planetary systems. TOI-942 is a young field star, with an age of ∼60 Myr, hosting a planetary system consisting of two transiting Neptune-sized planets in 4.3 and 10.1 day period orbits. We observed the spectroscopic transits of the inner Neptune TOI-942b to determine its projected orbital obliquity angle. Through two partial transits, we find the planet to be in a prograde orbit, with a projected obliquity angle of |λ| = 1-33+41 deg. In addition, incorporating the light curve and the stellar rotation period, we find the true 3D obliquity to be 2-23+27 deg. We explored various sources of uncertainties specific to the spectroscopic transits of planets around young active stars, and showed that our reported obliquity uncertainty fully encompassed these effects. TOI-942b is one of the youngest planets to have its obliquity characterized, and one of even fewer residing in a multi-planet system. The prograde orbital geometry of TOI-942b is in line with systems of similar ages, none of which have yet been identified to be in strongly misaligned orbits

Revisiting the HD 21749 planetary system with stellar activity modelling

HD 21749 is a bright (V = 8.1 mag) K dwarf at 16 pc known to host an inner terrestrial planet HD 21749c as well as an outer sub-Neptune HD 21749b, both delivered by Transiting Exoplanet Survey Satellite (TESS). Follow-up spectroscopic observations measured the mass of HD 21749b to be 22.7 ± 2.2 M with a density of 7.0^{+1.6}_{-1.3} g cm-3, making it one of the densest sub-Neptunes. However, the mass measurement was suspected to be influenced by stellar rotation. Here, we present new high-cadence PFS RV data to disentangle the stellar activity signal from the planetary signal. We find that HD 21749 has a similar rotational time-scale as the planet's orbital period, and the amplitude of the planetary orbital RV signal is estimated to be similar to that of the stellar activity signal. We perform Gaussian process regression on the photometry and RVs from HARPS and PFS to model the stellar activity signal. Our new models reveal that HD 21749b has a radius of 2.86 ± 0.20 R, an orbital period of 35.6133 ± 0.0005 d with a mass of Mb = 20.0 ± 2.7 M and a density of 4.8^{+2.0}_{-1.4} g cm-3 on an eccentric orbit with e = 0.16 ± 0.06, which is consistent with the most recent values published for this system. HD 21749c has an orbital period of 7.7902 ± 0.0006 d, a radius of 1.13 ± 0.10 R, and a 3σ mass upper limit of 3.5 M. Our Monte Carlo simulations confirm that without properly taking stellar activity signals into account, the mass measurement of HD 21749b is likely to arrive at a significantly underestimated error bar

Follow-up Imaging of Disk Candidates from the Disk Detective Citizen Science Project: New Discoveries and False Positives in WISE Circumstellar Disk Surveys

The Disk Detective citizen science project aims to find new stars with excess 22 μm emission from circumstellar dust in the AllWISE data release from the Wide-field Infrared Survey Explorer. We evaluated 261 Disk Detective objects of interest with imaging with the Robo-AO adaptive optics instrument on the 1.5 m telescope at Palomar Observatory and with RetroCam on the 2.5 m du Pont Telescope at Las Campanas Observatory to search for background objects at 0.″15-12″ separations from each target. Our analysis of these data leads us to reject 7% of targets. Combining this result with statistics from our online image classification efforts implies that at most 7.9% ± 0.2% of AllWISE-selected infrared excesses are good disk candidates. Applying our false-positive rates to other surveys, we find that the infrared excess searches of McDonald et al. and Marton et al. all have false-positive rates >70%. Moreover, we find that all 13 disk candidates in Theissen & West with W4 signal-to-noise ratio >3 are false positives. We present 244 disk candidates that have survived vetting by follow-up imaging. Of these, 213 are newly identified disk systems. Twelve of these are candidate members of comoving pairs based on Gaia astrometry, supporting the hypothesis that warm dust is associated with binary systems. We also note the discovery of 22 μm excess around two known members of the Scorpius-Centaurus association, and we identify known disk host WISEA J164540.79-310226.6 as a likely Sco-Cen member. Thirty of these disk candidates are closer than ∼125 pc (including 26 debris disks), making them good targets for both direct-imaging exoplanet searches

The Discovery and Mass Measurement of a New Ultra-Short-Period Planet: K2-131b

FWN – Publicaties zonder aanstelling Universiteit LeidenStars and planetary system

TESS discovery of a super-earth and three sub-neptunes hosted by the bright, sunlike star HD 108236

We report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD 108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance, and precise Doppler spectroscopy, as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD 108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly rocky super-Earth with a period of 3.79523+0.00047-0.00044 days and has a radius of 1.586 ± 0.098 R⊗.The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of 2.068+0.10-0.091 R⊗, 2.72 ± 0.11 R⊗, and 3.12+0.13-0.12 R⊗ and periods of 6.20370+0.00064-0.00052 days, 14.17555+0.00099-0.0011 days, and 19.5917+0.0022-0.0020 days, respectively. With V and Ks magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD 108236 is the brightest Sun-like star in the visual (V ) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures and share a common history of insolation from a Sun-like star (R∗ = 0.888 ± 0.017 R⊙, Teff = 5730 ± 50 K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution

TOI-1231 b: A Temperate, Neptune-sized Planet Transiting the Nearby M3 Dwarf NLTT 24399

We report the discovery of a transiting, temperate, Neptune-sized exoplanet orbiting the nearby (d = 27.5 pc), M3V star TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program. Combining the photometric data sets, we find that the newly discovered planet has a radius of {3.65}_{-0.15}^{+0.16}\,{R}_{\oplus } and an orbital period of 24.246 days. Radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5 3.3 M ⊕. With an equilibrium temperature of just 330 K, TOI-1231 b is one of the coolest small planets accessible for atmospheric studies thus far, and its host star's bright near-infrared brightness (J = 8.88, Ks = 8.07) makes it an exciting target for the Hubble Space Telescope and the James Webb Space Telescope. Future atmospheric observations would enable the first comparative planetology efforts in the 250-350 K temperature regime via comparisons with K2-18 b. Furthermore, TOI-1231's high systemic radial velocity (70.5 km s-1) may allow for the detection of low-velocity hydrogen atoms escaping the planet by Doppler, shifting the H i Lyα stellar emission away from the geocoronal and interstellar medium absorption features

The Discovery and Mass Measurement of a New Ultra-short-period Planet: K2-131

We report the discovery of a new ultra-short-period planet and summarize the properties of all such planets for which the mass and radius have been measured. The new planet, EPIC 228732031b, was discovered in K2 Campaign 10. It has a radius of 1.81-0.12+0.16 R_Earth and orbits a G dwarf with a period of 8.9 hr. Radial velocities obtained with Magellan/PFS and TNG/HARPS-N show evidence for stellar activity along with orbital motion. We determined the planetary mass using two different methods: (1) the “floating chunk offset” method, based only on changes in velocity observed on the same night; and (2) a Gaussian process regression based on both the radial velocity and photometric time series. The results are consistent and lead to a mass measurement of 6.5+/- 1.6 M_Earth and a mean density of 6.0-2.7+3.0 g cm‑3