784 research outputs found
Exoplanets in Open Clusters and Binaries: New Constraints on Planetary Migration
In this dissertation, we present three complementary studies of the processes that drive planetary migration. The first is a radial-velocity survey in search of giant planets in adolescent (\u3c1 \u3eGyr) open clusters. While several different mechanisms may act to drive giant planets inward, only some mechanisms will excite high eccentricities while doing so. Measuring the eccentricities of young hot Jupiters in these clusters (at a time before the orbits have had a chance to circularize due to tidal friction with their host stars) will allow us to identify which mechanisms are most important. Through this survey, we detect the first 3 hot Jupiters in open clusters (and at least 4 long-period planets), and we measure the occurrence rate of hot Jupiters in clusters to be similar to that of the field (~1%). We determine via analyses of hot Jupiter eccentricities and outer companions in these systems that high eccentricity migration mechanisms (those requiring the presence of a third body) are important for migration. The second project, an adaptive optics imaging survey for stellar companions to known hot Jupiter hosts, aims to determine the role that stellar companions in particular play in giant planet migration. Through a preliminary analysis, we derive a lower limit on the binary frequency of 45% (greater than that of the typical field star), and we find that the presence of a companion is correlated with misalignment of the spin-orbit angle of the planetary system, as would be expected for stellar Kozai-Lidov migration: at least 74% of misaligned systems reside in binaries. We thus conclude that among high eccentricity migration mechanisms, those requiring a stellar companion play a significant role. Finally, we describe simulations of measurements of the planet population expected to be discovered by TESS, and use these to demonstrate that a strong constraint on the obliquity distribution of small planets can be derived using only TESS photometry, Gaia astrometry, and vsin(i) measurements of the host stars. This obliquity distribution will be a key piece of evidence to help detemine the likely formation and migration histories of small planets, and can contribute to the assessment of the potential for Earth-like planets to harbor life
Kepler-432: A Red Giant Interacting with One of its Two Long-period Giant Planets
We report the discovery of Kepler-432b, a giant planet (M_b = 5.41^(+0.32)_(-0.18)M_Jup, R_b = 1.145^(+0.036)_(-0.039)R_Jup) transiting an evolved star (M_* = 1.32^(+0.10)_(-0.07)M_⊙, R_* = 4.06^(+0.12)_(-0.08)R_⊙) with an orbital period of P_b = 52.501129^(+0.000067)_(-0.000053) days. Radial velocities (RVs) reveal that Kepler-432b orbits its parent star with an eccentricity of e=0.5134^(+0.0098)_(-0.0089), which we also measure independently with asterodensity profiling (AP; e=0.507^(+0.039)_(-0.114)), thereby confirming the validity of AP on this particular evolved star. The well-determined planetary properties and unusually large mass also make this planet an important benchmark for theoretical models of super-Jupiter formation. Long-term RV monitoring detected the presence of a non-transiting outer planet (Kepler-432c; M_c sin i_c = 2.43^(+0.22)_(-0.24) M_Jup, P_c = 406.2^(+3.9)_(-2.5) days), and adaptive optics imaging revealed a nearby (0".87), faint companion (Kepler-432B) that is a physically bound M dwarf. The host star exhibits high signal-to-noise ratio asteroseismic oscillations, which enable precise measurements of the stellar mass, radius, and age. Analysis of the rotational splitting of the oscillation modes additionally reveals the stellar spin axis to be nearly edge-on, which suggests that the stellar spin is likely well aligned with the orbit of the transiting planet. Despite its long period, the obliquity of the 52.5 day orbit may have been shaped by star–planet interaction in a manner similar to hot Jupiter systems, and we present observational and theoretical evidence to support this scenario. Finally, as a short-period outlier among giant planets orbiting giant stars, study of Kepler-432b may help explain the distribution of massive planets orbiting giant stars interior to 1 AU
Stellar rotational periods in the planet hosting open cluster Praesepe
By using the dense coverage of the extrasolar planet survey project HATNet,
we Fourier analyze 381 high-probability members of the nearby open cluster
Praesepe (Beehive/M44/NGC 2632). In addition to the detection of 10 variables
(of \delta Scuti and other types), we identify 180 rotational variables
(including the two known planet hosts). This sample increases the number of
known rotational variables in this cluster for spectral classes earlier than M
by more than a factor of three. These stars closely follow a color/magnitude --
period relation from early F to late K stars. We approximate this relation by
polynomials for an easier reference to the rotational characteristics in
different colors. The total (peak-to-peak) amplitudes of the large majority
(94%) of these variables span the range of 0.005 to 0.04 mag. The periods cover
a range from 2.5 to 15 days. These data strongly confirm that Praesepe and the
Hyades have the same gyrochronological ages. Regarding the two planet hosts,
Pr0211 (the one with the shorter orbital period) has a rotational period that
is ~2 days shorter than the one expected from the main rotational pattern in
this cluster. This, together with other examples discussed in the paper, may
hint that star-planet interaction via tidal dissipation can be significant in
some cases in the rotational evolution of stars hosting Hot Jupiters.Comment: 17 pages, 13 figures, 5 tables; accepted for publication in MNRA
The Solar Neighborhood. XXXIV. A Search for Planets Orbiting Nearby M Dwarfs using Astrometry
Astrometric measurements are presented for seven nearby stars with previously
detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ
1214) and one K dwarf (BD 10 3166). Measurements are also presented for six
additional nearby M dwarfs without known planets, but which are more favorable
to astrometric detections of low mass companions, as well as three binary
systems for which we provide astrometric orbit solutions. Observations have
baselines of three to thirteen years, and were made as part of the RECONS
long-term astrometry and photometry program at the CTIO/SMARTS 0.9m telescope.
We provide trigonometric parallaxes and proper motions for all 16 systems, and
perform an extensive analysis of the astrometric residuals to determine the
minimum detectable companion mass for the 12 M dwarfs not having close stellar
secondaries. For the six M dwarfs with known planets, we are not sensitive to
planets, but can rule out the presence of all but the least massive brown
dwarfs at periods of 2 - 12 years. For the six more astrometrically favorable M
dwarfs, we conclude that none have brown dwarf companions, and are sensitive to
companions with masses as low as 1 for periods longer than two years.
In particular, we conclude that Proxima Centauri has no Jovian companions at
orbital periods of 2 - 12 years. These results complement previously published
M dwarf planet occurrence rates by providing astrometrically determined upper
mass limits on potential super-Jupiter companions at orbits of two years and
longer. As part of a continuing survey, these results are consistent with the
paucity of super-Jupiter and brown dwarf companions we find among the over 250
red dwarfs within 25 pc observed longer than five years in our astrometric
program.Comment: 18 pages, 5 figures, 4 tables, accepted for publication in A
Characterizing the Orbital Eccentricities of Transiting Extrasolar Planets with Photometric Observations
The discovery of over 200 extrasolar planets with the radial velocity (RV)
technique has revealed that many giant planets have large eccentricities, in
striking contrast with most of the planets in the solar system and prior
theories of planet formation. The realization that many giant planets have
large eccentricities raises a fundamental question: ``Do terrestrial-size
planets of other stars typically have significantly eccentric orbits or nearly
circular orbits like the Earth?'' Here, we demonstrate that photometric
observations of transiting planets could be used to characterize the orbital
eccentricities for individual transiting planets, as well the eccentricity
distribution for various populations of transiting planets (e.g., those with a
certain range of orbital periods or physical sizes). Such characterizations can
provide valuable constraints on theories for the excitation of eccentricities
and tidal dissipation. We outline the future prospects of the technique given
the exciting prospects for future transit searches, such as those to be carried
out by the CoRoT and Kepler missions.Comment: 32 pages, 10 figures, accepted to Ap
The Mass of the White Dwarf Companion in the Self-Lensing Binary KOI-3278: Einstein vs. Newton
KOI-3278 is a self-lensing stellar binary consisting of a white-dwarf
secondary orbiting a Sun-like primary star. Kruse and Agol (2014) noticed small
periodic brightenings every 88.18 days in the Kepler photometry and interpreted
these as the result of microlensing by a white dwarf with about 63 of the
mass of the Sun. We obtained two sets of spectra for the primary that allowed
us to derive three sets of spectroscopic estimates for its effective
temperature, surface gravity, and metallicity for the first time. We used these
values to update the Kruse and Agol (2014) Einsteinian microlensing model,
resulting in a revised mass for the white dwarf of . The spectra also allowed us to determine radial velocities and
derive orbital solutions, with good agreement between the two independent data
sets. An independent Newtonian dynamical MCMC model of the combined velocities
yielded a mass for the white dwarf of . The nominal uncertainty for the Newtonian mass is about four times
better than for the Einsteinian, vs. and the difference
between the two mass determinations is . We then present a joint
Einsteinian microlensing and Newtonian radial velocity model for KOI-3278,
which yielded a mass for the white dwarf of . This joint model does not rely on any white dwarf evolutionary
models or assumptions on the white dwarf mass-radius relation. We discuss the
benefits of a joint model of self-lensing binaries, and how future studies of
these systems can provide insight into the mass-radius relation of white
dwarfs.Comment: ApJ Accepted; 22 Pages, 8 Figures, 6 Tables and 4 Supplementary
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