F. Dai

TESTS OF THE PLANETARY HYPOTHESIS FOR PTFO 8-8695b

The T Tauri star PTFO 8-8695 exhibits periodic fading events that have been interpreted as the transits of a giant planet on a precessing orbit. Here we present three tests of the planet hypothesis. First, we sought evidence for the secular changes in light-curve morphology that are predicted to be a consequence of orbital precession. We observed 28 fading events spread over several years, and did not see the expected changes. Instead we found that the fading events are not strictly periodic. Second, we attempted to detect the planets radiation, based on infrared observations spanning the predicted times of occultations. We ruled out a signal of the expected amplitude. Third, we attempted to detect the Rossiter-McLaughlin effect by performing high-resolution spectroscopy throughout a fading event. No effect was seen at the expected level, ruling out most (but not all) possible orientations for the hypothetical planetary orbit. Our spectroscopy also revealed strong, time-variable, high-velocity H{\alpha} and Ca H & K emission features. All these observations cast doubt on the planetary hypothesis, and suggest instead that the fading events represent starspots, eclipses by circumstellar dust, or occultations of an accretion hotspot.

Doppler monitoring of five k2 transiting planetary systems

In an effort to measure the masses of planets discovered by the NASA K2 mission, we have conducted precise Doppler observations of five stars with transiting planets. We present the results of a joint analysis of these new data and previously published Doppler data. The first star, an M dwarf known as K2-3 or EPIC 201367065, has three transiting planets (“b,” with radius 2.1 R⊕; “c,” 1.7 R⊕; and “d,” 1.5 R⊕). Our analysis leads to the mass constraints: Mb = 8.1 -1.9 to +2.0 M⊕ and Mc < 4.2 M⊕ (95% confidence). The mass of planet d is poorly constrained because its orbital period is close to the stellar rotation period, making it difficult to disentangle the planetary signal from spurious Doppler shifts due to stellar activity. The second star, a G dwarf known as K2-19 or EPIC 201505350, has two planets (“b,” 7.7 R⊕; and “c,” 4.9 R⊕) in a 3:2 mean-motion resonance, as well as a shorter period planet (“d,” 1.1 R⊕). We find Mb = 28.5 -5.0 to +5.4 M⊕, Mc = 25.6 -7.1 to + 7.1 M⊕ and Md < 14.0M⊕ (95% conf.). The third star, a G dwarf known as K2-24 or EPIC 203771098, hosts two transiting planets (“b,” 5.7 R⊕; and “c,” 7.8 R⊕) with orbital periods in a nearly 2:1 ratio. We find Mb = 19.8 -4.4 to +4.5 M⊕ and Mc = 26.0 -6.1 to +5.8 M⊕. The fourth star, a G dwarf known as EPIC 204129699, hosts a hot Jupiter for which we measured the mass to be 1.857 +0.081 to -0.081 MJup. The fifth star, a G dwarf known as EPIC 205071984, contains three transiting planets (“b,” 5.4 R⊕; “c,” 3.5 R⊕; and “d,” 3.8 R⊕), the outer two of which have a nearly 2:1 period ratio. We find Mb = 21.1 -5.9 to +5.9 M⊕, Mc < 8.1 M⊕ (95% conf.) and Md < 35M⊕ (95% conf.).

K2-106, a system containing a metal-rich planet and a planet of lower density

Planets in the mass range from 2 to 15 M_Earth are very diverse. Some of them have low densities, while others are very dense. By measuring the masses and radii, the mean densities, structure, and composition of the planets are constrained. These parameters also give us important information about their formation and evolution, and about possible processes for atmospheric loss.We determined the masses, radii, and mean densities for the two transiting planets orbiting K2-106. The inner planet has an ultra-short period of 0.57 days. The period of the outer planet is 13.3 days. Although the two planets have similar masses, their densities are very different. For K2-106b we derive Mb=8.36-0.94+0.96 M_Earh, Rb=1.52+/-0.16 R_Earth, and a high density of 13.1-3.6+5.4 g/cm^3. For K2-106c, we find Mc=5.8-3.0+3.3 M_Earth, Rc=2.50-0.26+0.27 R_Earth and a relatively low density of 2.0-1.1+1.6 g/cm^3.Since the system contains two planets of almost the same mass, but different distances from the host star, it is an excellent laboratory to study atmospheric escape. In agreement with the theory of atmospheric-loss processes, it is likely that the outer planet has a hydrogen-dominated atmosphere. The mass and radius of the inner planet is in agreement with theoretical models predicting an iron core containing 80+20-30% of its mass. Such a high metal content is surprising, particularly given that the star has an ordinary (solar) metal abundance. We discuss various possible formation scenarios for this unusual planet.

DOPPLER MONITORING OF THE WASP-47 MULTIPLANET SYSTEM

We present precise Doppler observations of WASP-47, a transiting planetary system featuring a hot Jupiter with both inner and outer planetary companions. This system has an unusual architecture and also provides a rare opportunity to measure planet masses in two different ways: the Doppler method, and the analysis of transit-timing variations (TTV). Based on the new Doppler data, obtained with the Planet Finder Spectrograph on the Magellan/Clay 6.5m telescope, the mass of the hot Jupiter is

The K2-ESPRINT Project II: Spectroscopic follow-up of three exoplanet systems from Campaign 1 of K2

370 \pm 29~M_{\oplus}

A LOW STELLAR OBLIQUITY FOR WASP-47, A COMPACT MULTIPLANET SYSTEM WITH A HOT JUPITER AND AN ULTRA-SHORT PERIOD PLANET

. This is consistent with the previous Doppler determination as well as the TTV determination. For the inner planet WASP-47e, the Doppler data lead to a mass of

THE K2-ESPRINT PROJECT. V. A SHORT-PERIOD GIANT PLANET ORBITING A SUBGIANT STAR

12.2\pm 3.7~ M_{\oplus}

K2-137 b: an Earth-sized planet in a 4.3-h orbit around an M-dwarf

, in agreement with the TTV-based upper limit of

EPIC 219388192b—An Inhabitant of the Brown Dwarf Desert in the Ruprecht 147 Open Cluster

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K2-141 b. A 5-M_oplus super-Earth transiting a K7 V star every 6.7 hours

22~