Model-Independent Stellar and Planetary Masses from Multi-Transiting Exoplanetary Systems

Precise exoplanet characterization requires precise classification of exoplanet host stars. The masses of host stars are commonly estimated by comparing their spectra to those predicted by stellar evolution models. However, spectroscopically determined properties are difficult to measure accurately for stars that are substantially different from the Sun, such as M-dwarfs and evolved stars. Here, we propose a new method to dynamically measure the masses of transiting planets near mean-motion resonances and their host stars by combining observations of transit timing variations with radial velocity measurements. We derive expressions to analytically determine the mass of each member of the system and demonstrate the technique on the Kepler-18 system. We compare these analytic results to numerical simulations and find the two are consistent. We identify eight systems for which our technique could be applied if follow-up radial velocity measurements are collected. We conclude this analysis would be optimal for systems discovered by next generation missions similar to TESS or PLATO, which will target bright stars that are amenable to efficient RV follow-up.Comment: 9 pages, 1 figure, submitted to Ap

Estimates of the Planet Yield from Ground-based High-contrast Imaging Observations as a Function of Stellar Mass

We use Monte Carlo simulations to estimate the number of extrasolar planets that are directly detectable in the solar neighborhood using current and forthcoming high-contrast imaging instruments. Our calculations take into consideration the important factors that govern the likelihood for imaging a planet, including the statistical properties of stars in the solar neighborhood, correlations between star and planet properties, observational effects, and selection criteria. We consider several different ground-based surveys, both biased and unbiased, and express the resulting planet yields as a function of stellar mass. Selecting targets based on their youth and visual brightness, we find that strong correlations between star mass and planet properties are required to reproduce high-contrast imaging results to date (i.e., HR 8799, β Pic). Using the most recent empirical findings for the occurrence rate of gas-giant planets from radial velocity (RV) surveys, our simulations indicate that naive extrapolation of the Doppler planet population to semimajor axes accessible to high-contrast instruments provides an excellent agreement between simulations and observations using present-day contrast levels. In addition to being intrinsically young and sufficiently bright to serve as their own beacon for adaptive optics correction, A-stars have a high planet occurrence rate and propensity to form massive planets in wide orbits, making them ideal targets. The same effects responsible for creating a multitude of detectable planets around massive stars conspire to reduce the number orbiting low-mass stars. However, in the case of a young stellar cluster, where targets are approximately the same age and situated at roughly the same distance, MK-stars can easily dominate the number of detections because of an observational bias related to small number statistics. The degree to which low-mass stars produce the most planet detections in this special case depends upon whether multiple formation mechanisms are at work. Upon relaxing our assumption that planets in ultra-wide (a > 100 AU) orbits resemble the RV sample, our simulations suggest that the companions found orbiting late-type stars (AB Pic, 1RXSJ1609, GSC 06214, etc.) are consistent with a formation channel distinct from that of RV planets. These calculations explain why planets have thus far been imaged preferentially around A-stars and K-, M-stars, but no spectral types in between, despite concerted efforts targeting F-, G-stars

Spin-Orbit Alignment for the Circumbinary Planet Host Kepler-16 A

Kepler-16 is an eccentric low-mass eclipsing binary with a circumbinary transiting planet. Here, we investigate the angular momentum of the primary star, based on Kepler photometry and Keck spectroscopy. The primary star’s rotation period is 35.1 ± 1.0 days, and its projected obliquity with respect to the stellar binary orbit is 1°.6 ± 2°.4. Therefore, the three largest sources of angular momentum—the stellar orbit, the planetary orbit, and the primary’s rotation—are all closely aligned. This finding supports a formation scenario involving accretion from a single disk. Alternatively, tides may have realigned the stars despite their relatively wide separation (0.2 AU), a hypothesis that is supported by the agreement between the measured rotation period and the “pseudosynchronous” period of tidal evolution theory. The rotation period, chromospheric activity level, and fractional light variations suggest a main-sequence age of 2–4 Gyr. Evolutionary models of low-mass stars can match the observed masses and radii of the primary and secondary stars to within about 3%

HAT-P-30b: A Transiting Hot Jupiter on a Highly Oblique Orbit

We report the discovery of HAT-P-30b, a transiting exoplanet orbiting the V = 10.419 dwarf star GSC 0208-00722. The planet has a period P = 2.810595 ± 0.000005 days, transit epoch Tc = 2455456.46561 ± 0.00037 (BJD), and transit duration 0.0887 ± 0.0015 days. The host star has a mass of 1.24 ± 0.04 M_⊙, radius of 1.21 ± 0.05 R_⊙, effective temperature of 6304 ± 88 K, and metallicity [Fe/H] = +0.13 ± 0.08. The planetary companion has a mass of 0.711 ± 0.028 M J and radius of 1.340 ± 0.065 R J yielding a mean density of 0.37 ± 0.05 g cm^(–3). We also present radial velocity measurements that were obtained throughout a transit that exhibit the Rossiter-McLaughlin effect. By modeling this effect, we measure an angle of λ = 73.°5 ± 9.°0 between the sky projections of the planet's orbit normal and the star's spin axis. HAT-P-30b represents another example of a close-in planet on a highly tilted orbit, and conforms to the previously noted pattern that tilted orbits are more common around stars with T_(eff*) ≳ 6250 K

On the Metal Richness of M Dwarfs with Planets

Knowledge of the metallicities of M dwarfs rests predominantly on the photometric calibration of Bonfils and collaborators, which predicts that M dwarfs in the solar neighborhood, including those with known planets, are systematically metal poor compared to their higher-mass counterparts. We test this prediction using a volume-limited sample of low-mass stars, together with a subset of M dwarfs with high-metallicity, F, G, and K wide binary companions. We find that the Bonfils et al. photometric calibration systematically underestimates the metallicities of our high-metallicity M dwarfs by an average of 0.32 dex. We derive a new photometric metallicity calibration and show that M dwarfs with planets appear to be systematically metal rich, a result that is consistent with the metallicity distribution of FGK dwarfs with planets

The History of the Mysterious Eclipses of KH 15D: Asiago Observatory, 1967-1982

We are gathering archival observations to determine the photometric history of the unique and unexplained eclipses of the pre-main-sequence star KH 15D. Here we present a light curve from 1967-1982, based on photographic plates from Asiago Observatory. During this time, the system alternated periodically between bright and faint states, as observed today. However, the bright state was 0.9 mag brighter than the modern value, and the fractional variation between bright and faint states (Delta I = 0.7 mag) was smaller than observed today (3.5 mag). A possible explanation for these findings is that the system contains a second star that was previously blended with the eclipsing star, but is now completely obscured.Comment: Accepted to AJ. 24 pages, 10 figures, 2 tables. v2: Phase error corrected in figures 8 and 1