846 research outputs found
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%
A Third Exoplanetary System with Misaligned Orbital and Stellar Spin Axes
We present evidence that the WASP-14 exoplanetary system has misaligned
orbital and stellar-rotational axes, with an angle lambda = 33.1 +/- 7.4 deg
between their sky projections. The evidence is based on spectroscopic
observations of the Rossiter-McLaughlin effect as well as new photometric
observations. WASP-14 is now the third system known to have a significant
spin-orbit misalignment, and all three systems have "super-Jupiter" planets
(M_P > 3 Mjup) and eccentric orbits. This finding suggests that the migration
and subsequent orbital evolution of massive, eccentric exoplanets is somehow
different from that of less massive close-in Jupiters, the majority of which
have well-aligned orbits.Comment: 8 pages, 5 figures, 3 tables, PASP accepte
A Prograde, Low-Inclination Orbit for the Very Hot Jupiter WASP-3b
We present new spectroscopic and photometric observations of the transiting
exoplanetary system WASP-3. Spectra obtained during two separate transits
exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the
sky-projected angle between the planetary orbital axis and the stellar rotation
axis, lambda = 3.3^{+2.5}_{-4.4} degrees. This alignment between the axes
suggests that WASP-3b has a low orbital inclination relative to the equatorial
plane of its parent star. During our first night of spectroscopic measurements,
we observed an unexpected redshift briefly exceeding the expected sum of the
orbital and RM velocities by 140 m/s. This anomaly could represent the
occultation of material erupting from the stellar photosphere, although it is
more likely to be an artifact caused by moonlight scattered into the
spectrograph.Comment: 23 pages, 4 figures, Accepted for publication in The Astrophysical
Journal, Replacement includes revised citation
HAT-P-7: A Retrograde or Polar Orbit, and a Third Body
We show that the exoplanet HAT-P-7b has an extremely tilted orbit, with a
true angle of at least 86 degrees with respect to its parent star's equatorial
plane, and a strong possibility of retrograde motion. We also report evidence
for an additional planet or companion star. The evidence for the unparalleled
orbit and the third body is based on precise observations of the star's
apparent radial velocity. The anomalous radial velocity due to rotation (the
Rossiter-McLaughlin effect) was found to be a blueshift during the first half
of the transit and a redshift during the second half, an inversion of the usual
pattern, implying that the angle between the sky-projected orbital and stellar
angular momentum vectors is 182.5 +/- 9.4 degreees. The third body is
implicated by excess radial-velocity variation of the host star over 2 yr. Some
possible explanations for the tilted orbit are a close encounter with another
planet, the Kozai effect, and resonant capture by an inward-migrating outer
planet.Comment: ApJ Letters, in press [7 pages
Relative photometry of HAT-P-1b occultations
We present HST STIS observations of two occultations of the transiting
exoplanet HAT-P-1b. By measuring the planet to star flux ratio near opposition,
we constrain the geometric albedo of the planet, which is strongly linked to
its atmospheric temperature gradient. An advantage of HAT-P-1 as a target is
its binary companion ADS 16402 A, which provides an excellent photometric
reference, simplifying the usual steps in removing instrumental artifacts from
HST time-series photometry. We find that without this reference star, we would
need to detrend the lightcurve with the time of the exposures as well as the
first three powers of HST orbital phase, and this would introduce a strong bias
in the results for the albedo. However, with this reference star, we only need
to detrend the data with the time of the exposures to achieve the same
per-point scatter, therefore we can avoid most of the bias associated with
detrending. Our final result is a 2 sigma upper limit of 0.64 for the geometric
albedo of HAT-P-1b between 577 and 947 nm.Comment: 8 pages, 2 figures, 3 table
Transits and Occultations of an Earth-Sized Planet in an 8.5-Hour Orbit
We report the discovery of an Earth-sized planet () in
an 8.5-hour orbit around a late G-type star (KIC 8435766, Kepler-78). The
object was identified in a search for short-period planets in the {\it Kepler}
database and confirmed to be a transiting planet (as opposed to an eclipsing
stellar system) through the absence of ellipsoidal light variations or
substantial radial-velocity variations. The unusually short orbital period and
the relative brightness of the host star ( = 11.5) enable robust
detections of the changing illumination of the visible hemisphere of the
planet, as well as the occultations of the planet by the star. We interpret
these signals as representing a combination of reflected and reprocessed light,
with the highest planet dayside temperature in the range of 2300 K to 3100 K.
Follow-up spectroscopy combined with finer sampling photometric observations
will further pin down the system parameters and may even yield the mass of the
planet.Comment: Accepted for publication, ApJ, 10 pages and 6 figure
Absence of a metallicity effect for ultra-short-period planets
Ultra-short-period (USP) planets are a newly recognized class of planets with
periods shorter than one day and radii smaller than about 2 Earth radii. It has
been proposed that USP planets are the solid cores of hot Jupiters that lost
their gaseous envelopes due to photo-evaporation or Roche lobe overflow. We
test this hypothesis by asking whether USP planets are associated with
metal-rich stars, as has long been observed for hot Jupiters. We find the
metallicity distributions of USP-planet and hot-Jupiter hosts to be
significantly different (), based on Keck spectroscopy of
Kepler stars. Evidently, the sample of USP planets is not dominated by the
evaporated cores of hot Jupiters. The metallicity distribution of stars with
USP planets is indistinguishable from that of stars with short-period planets
with sizes between 2--4~. Thus it remains possible that the USP
planets are the solid cores of formerly gaseous planets smaller than Neptune.Comment: AJ, in pres
The Rotation Period of the Planet-Hosting Star HD 189733
We present synoptic optical photometry of HD 189733, the chromospherically
active parent star of one of the most intensively studied exoplanets. We have
significantly extended the timespan of our previously reported observations and
refined the estimate of the stellar rotation period by more than an order of
magnitude: days. We derive a lower limit on the
inclination of the stellar rotation axis of 56\arcdeg (with 95% confidence),
corroborating earlier evidence that the stellar spin axis and planetary orbital
axis are well aligned.Comment: To appear in A
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