6,868 research outputs found
HATS-1b: The First Transiting Planet Discovered by the HATSouth Survey
We report the discovery of HATS-1b, a transiting extrasolar planet orbiting
the moderately bright V=12.05 G dwarf star GSC 6652-00186, and the first planet
discovered by HATSouth, a global network of autonomous wide-field telescopes.
HATS-1b has a period P~3.4465 d, mass Mp~1.86MJ, and radius Rp~1.30RJ. The host
star has a mass of 0.99Msun, and radius of 1.04Rsun. The discovery light curve
of HATS-1b has near continuous coverage over several multi-day periods,
demonstrating the power of using a global network of telescopes to discover
transiting planets.Comment: Submitted to AJ 10 pages, 5 figures, 6 table
Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope
Doppler and transit surveys are finding extrasolar planets of ever smaller
mass and radius, and are now sampling the domain of superEarths (1-3 Earth
radii). Recent results from the Doppler surveys suggest that discovery of a
transiting superEarth in the habitable zone of a lower main sequence star may
be possible. We evaluate the prospects for an all-sky transit survey targeted
to the brightest stars, that would find the most favorable cases for
photometric and spectroscopic characterization using the James Webb Space
Telescope (JWST). We use the proposed Transiting Exoplanet Survey Satellite
(TESS) as representative of an all-sky survey. We couple the simulated TESS
yield to a sensitivity model for the MIRI and NIRSpec instruments on JWST. We
focus on the TESS planets with radii between Earth and Neptune. Our simulations
consider secondary eclipse filter photometry using JWST/MIRI, comparing the 11-
and 15-micron bands to measure CO2 absorption in superEarths, as well as
JWST/NIRSpec spectroscopy of water absorption from 1.7-3.0 microns, and CO2
absorption at 4.3-microns. We project that TESS will discover about eight
nearby habitable transiting superEarths. The principal sources of uncertainty
in the prospects for JWST characterization of habitable superEarths are
superEarth frequency and the nature of superEarth atmospheres. Based on our
estimates of these uncertainties, we project that JWST will be able to measure
the temperature, and identify molecular absorptions (water, CO2) in one to four
nearby habitable TESS superEarths.Comment: accepted for PASP; added discussion and figure for habitable planets;
abridged Abstrac
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
We present a direct method for isolating the component of the starlight
blocked by a planet as it transits its host star, and apply it to spectra of
the bright transiting planet HD 189733b. We model the global shape of the
stellar cross-correlation function as the convolution of a limb-darkened
rotation profile and a gaussian representing the Doppler core of the average
photospheric line profile. The light blocked by the planet during the transit
is a gaussian of the same intrinsic width, whose trajectory across the line
profile yields a precise measure of the misalignment angle and an independent
measure of v sin I. We show that even when v sin I is less than the width of
the intrinsic line profile, the travelling Doppler "shadow" cast by the planet
creates an identifiable distortion in the line profiles which is amenable to
direct modelling. Direct measurement of the trajectory of the missing starlight
yields self-consistent measures of the projected stellar rotation rate, the
intrinsic width of the mean local photospheric line profile, the projected
spin-orbit misalignment angle, and the system's centre-of-mass velocity.
Combined with the photometric rotation period, the results give a geometrical
measure of the stellar radius which agrees closely with values obtained from
high-precision transit photometry if a small amount of differential rotation is
present in the stellar photosphere.Comment: 8 pages, 5 figures, 2 tables; accepted by MNRA
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
HAT-P-24b: An inflated hot-Jupiter on a 3.36d period transiting a hot, metal-poor star
We report the discovery of HAT-P-24b, a transiting extrasolar planet orbiting
the moderately bright V=11.818 F8 dwarf star GSC 0774-01441, with a period P =
3.3552464 +/- 0.0000071 d, transit epoch Tc = 2455216.97669 +/- 0.00024
(BJD_UTC), and transit duration 3.653 +/- 0.025 hours. The host star has a mass
of 1.191 +/- 0.042 Msun, radius of 1.317 +/- 0.068 Rsun, effective temperature
6373 +/- 80 K, and a low metallicity of [Fe/H] = -0.16 +/- 0.08. The planetary
companion has a mass of 0.681 +/- 0.031 MJ, and radius of 1.243 +/- 0.072 RJ
yielding a mean density of 0.439 +/- 0.069 g cm-3 . By repeating our global
fits with different parameter sets, we have performed a critical investigation
of the fitting techniques used for previous HAT planetary discoveries. We find
that the system properties are robust against the choice of priors. The effects
of fixed versus fitted limb darkening are also examined. HAT-P-24b probably
maintains a small eccentricity of e = 0.052 +0.022 -0.017, which is accepted
over the circular orbit model with false alarm probability 5.8%. In the absence
of eccentricity pumping, this result suggests HAT-P-24b experiences less tidal
dissipation than Jupiter. Due to relatively rapid stellar rotation, we estimate
that HAT-P-24b should exhibit one of the largest known Rossiter-McLaughlin
effect amplitudes for an exoplanet (deltaVRM ~ 95 m/s) and thus a precise
measurement of the sky-projected spin-orbit alignment should be possible.Comment: 13 pages with 4 figures and 8 tables in emulateapj format. Minor
changes. Accepted in The Astrophysical Journa
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
Neutron scattering study of spin ordering and stripe pinning in superconducting LaSrCuO
The relationships among charge order, spin fluctuations, and
superconductivity in underdoped cuprates remain controversial. We use neutron
scattering techniques to study these phenomena in
LaSrCuO, a superconductor with a transition temperature
of ~K. At , we find incommensurate spin fluctuations with a
quasielastic energy spectrum and no sign of a gap within the energy range from
0.2 to 15 meV. A weak elastic magnetic component grows below ~K,
consistent with results from local probes. Regarding the atomic lattice, we
have discovered unexpectedly strong fluctuations of the CuO octahedra about
Cu-O bonds, which are associated with inequivalent O sites within the CuO
planes. Furthermore, we observed a weak elastic superlattice peak
that implies a reduced lattice symmetry. The presence of inequivalent O sites
rationalizes various pieces of evidence for charge stripe order in underdoped
\lsco. The coexistence of superconductivity with quasi-static spin-stripe order
suggests the presence of intertwined orders; however, the rotation of the
stripe orientation away from the Cu-O bonds might be connected with evidence
for a finite gap at the nodal points of the superconducting gap function.Comment: 13 pages, 11 figures; accepted versio
The central image of a gravitationally lensed quasar
A galaxy can act as a gravitational lens, producing multiple images of a
background object. Theory predicts there should be an odd number of images but,
paradoxically, almost all observed lenses have 2 or 4 images. The missing image
should be faint and appear near the galaxy's center. These ``central images''
have long been sought as probes of galactic cores too distant to resolve with
ordinary observations. There are five candidates, but in one case the third
image is not necessarily a central image, and in the others, the central
component might be a foreground source rather than a lensed image. Here we
report the most secure identification of a central image, based on radio
observations of PMN J1632-0033, one of the latter candidates. Lens models
incorporating the central image show that the mass of the lens galaxy's central
black hole is less than 2 x 10^8 M_sun, and the galaxy's surface density at the
location of the central image is more than 20,000 M_sun per square parsec, in
agreement with expectations based on observations of galaxies hundreds of times
closer to the Earth.Comment: Nature, in press [7 pp, 2 figs]. Standard media embargo applies
before publicatio
Improved parameters for extrasolar transiting planets
We present refined values for the physical parameters of transiting
exoplanets, based on a self-consistent and uniform analysis of transit light
curves and the observable properties of the host stars. Previously it has been
difficult to interpret the ensemble properties of transiting exoplanets,
because of the widely different methodologies that have been applied in
individual cases. Furthermore, previous studies often ignored an important
constraint on the mean stellar density that can be derived directly from the
light curve. The main contributions of this work are 1) a critical compilation
and error assessment of all reported values for the effective temperature and
metallicity of the host stars; 2) the application of a consistent methodology
and treatment of errors in modeling the transit light curves; and 3) more
accurate estimates of the stellar mass and radius based on stellar evolution
models, incorporating the photometric constraint on the stellar density. We use
our results to revisit some previously proposed patterns and correlations
within the ensemble. We confirm the mass-period correlation, and we find
evidence for a new pattern within the scatter about this correlation: planets
around metal-poor stars are more massive than those around metal-rich stars at
a given orbital period. Likewise, we confirm the proposed dichotomy of planets
according to their Safronov number, and we find evidence that the systems with
small Safronov numbers are more metal-rich on average. Finally, we confirm the
trend that led to the suggestion that higher-metallicity stars harbor planets
with a greater heavy-element content.Comment: To appear in The Astrophysical Journal. 23 pages in emulateapj
format, including figures and tables. Figures 7, 8, and 9 are low resolution;
higher resolution versions will be available from the journal when published.
Acknowledgement added, and minor changes made to TrES-3 and TrES-4 in the
Appendi
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