arXiv subjects

Timothy D. Morton

Publications and source records attributed to Timothy D. Morton.

58 records · Page 4Linked to original sources

arXiv2010

Orbital Orientations of Exoplanets: HAT-P-4b is Prograde and HAT-P-14b is Retrograde

We present observations of the Rossiter-McLaughlin effect for two exoplanetary systems, revealing the orientations of their orbits relative to the rotation axes of their parent stars. HAT-P-4b is prograde, with a sky-projected spin-orbit angle of lambda = -4.9 +/- 11.9 degrees. In contrast, HAT-P-14b is retrograde, with lambda = 189.1 +/- 5.1 degrees. These results conform with a previously noted pattern among the stellar hosts of close-in giant planets: hotter stars have a wide range of obliquities and cooler stars have low obliquities. This, in turn, suggests that three-body dynamics and tidal dissipation are responsible for the short-period orbits of many exoplanets. In addition, our data revealed a third body in the HAT-P-4 system, which could be a second planet or a companion star.

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arXiv2010

LHS6343C: A Transiting Field Brown Dwarf Discovered by the Kepler Mission

We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS6343AB every 12.71 days. The transits were discovered using photometric data from the Kelper public data release. The LHS6343 stellar system was previously identified as a single high-proper-motion M dwarf. We use high-contrast imaging to resolve the system into two low-mass stars with masses 0.45 Msun and 0.36 Msun, respectively, and a projected separation of 55 arcsec. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M_C = 62.8 +/- 2.3 Mjup. Based on an analysis of the Kepler light curve we estimate the radius of the companion to be R_C = 0.832 +/- 0.021 Rjup, which is consistent with theoretical predictions of the radius of a > 1 Gyr brown dwarf.

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arXiv2010

Discerning Exoplanet Migration Models Using Spin-Orbit Measurements

We investigate the current sample of exoplanet spin-orbit measurements to determine whether a dominant planet migration channel can be identified, and at what confidence. We use the predictions of Kozai migration plus tidal friction (Fabrycky and Tremaine 2007) and planet-planet scattering (Nagasawa et al. 2008) as our misalignment models, and we allow for a fraction of intrinsically aligned systems, explainable by disk migration. Bayesian model comparison demonstrates that the current sample of 32 spin-orbit measurements strongly favors a two-mode migration scenario combining planet-planet scattering and disk migration over a single-mode Kozai migration scenario. Our analysis indicates that between 34% and 76% of close-in planets (95% confidence) migrated via planet-planet scattering. Separately analyzing the subsample of 12 stars with T_eff > 6250 K---which Winn et al. (2010) predict to be the only type of stars to maintain their primordial misalignments---we find that the data favor a single-mode scattering model over Kozai with 81% confidence. We also assess the number of additional hot star spin-orbit measurements that will likely be necessary to provide a more confident model selection, finding that an additional 20-30 measurements has a >50% chance of resulting in a 95%-confident model selection, if the current model selection is correct. While we test only the predictions of particular Kozai and scattering migration models in this work, our methods may be used to test the predictions of any other spin-orbit misaligning mechanism.

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arXiv2010

A hot Jupiter orbiting the 1.7 Msun Subgiant HD102956

We report the detection of a giant planet in a 6.4950 day orbit around the 1.7 Msun subgiant HD102956. The planet has a semimajor axis a = 0.081 AU and minimum mass Msini = 0.96 Mjup. HD102956 is the most massive star known to harbor a hot Jupiter, and its planet is only the third known to orbit within 0.6 AU of a star more massive than 1.5 Msun. Based on our sample of 137 subgiants with M* > 1.45 Msun we find that 0.5-2.3% of A-type stars harbor a close-in planet (a < 0.1 AU) with Msini > 1 Mjup, consistent with hot-Jupiter occurrence for Sun-like stars. Thus, the paucity of planets with 0.1 < a/AU < 1.0 around intermediate-mass stars may be an exaggerated version of the "period valley" that is characteristic of planets around Sun-like stars.

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