1,302 research outputs found
High-precision photometry of WASP-12 b transits
The transiting extrasolar planet WASP-12 b was found to be one of the most
intensely irradiated exoplanets. It is unexpectedly bloated and is losing mass
that may accrete into the host star. Our aim was to refine the parameters of
this intriguing system and search for signs of transit timing variations. We
gathered high-precision light curves for two transits of WASP-12 b. Assuming
various limb-darkening laws, we generated best-fitting models and redetermined
parameters of the system. Error estimates were derived by the prayer bead
method and Monte Carlo simulations. System parameters obtained by us are found
to agree with previous studies within one sigma. Use of the non-linear
limb-darkening laws results in the best-fitting models. With two new
mid-transit times, the ephemeris was refined to BJD(TDB)=(2454508.97682 +/-
0.00020) + (1.09142245 +/- 0.00000033) E. Interestingly, indications of transit
timing variation are detected at the level of 3.4 sigma. This signal can be
induced by an additional planet in the system. Simplified numerical simulations
shows that a perturber could be a terrestrial-type planet if both planets are
in a low-order orbital resonance. However, we emphasise that further
observations are needed to confirm variation and to constrain properties of the
perturber.Comment: 5 pages, 3 figures, accepted for publication in A&
High-precision photometry by telescope defocussing. III. The transiting planetary system WASP-2
We present high-precision photometry of three transits of the extrasolar
planetary system WASP-2, obtained by defocussing the telescope, and achieving
point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled
using the JKTEBOP code, and taking into account the light from the
recently-discovered faint star close to the system. The physical properties of
the WASP-2 system are derived using tabulated predictions from five different
sets of stellar evolutionary models, allowing both statistical and systematic
errorbars to be specified. We find the mass and radius of the planet to be M_b
= 0.847 +/- 0.038 +/- 0.024 Mjup and R_b = 1.044 +/- 0.029 +/- 0.015 Rjup. It
has a low equilibrium temperature of 1280 +/- 21 K, in agreement with a recent
finding that it does not have an atmospheric temperature inversion. The first
of our transit datasets has a scatter of only 0.42 mmag with respect to the
best-fitting light curve model, which to our knowledge is a record for
ground-based observations of a transiting extrasolar planet.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 10 table
Analysis of new high-precision transit light curves of WASP-10 b: starspot occultations, small planetary radius, and high metallicity
The WASP-10 planetary system is intriguing because different values of radius
have been reported for its transiting exoplanet. The host star exhibits
activity in terms of photometric variability, which is caused by the rotational
modulation of the spots. Moreover, a periodic modulation has been discovered in
transit timing of WASP-10 b, which could be a sign of an additional body
perturbing the orbital motion of the transiting planet. We attempt to refine
the physical parameters of the system, in particular the planetary radius,
which is crucial for studying the internal structure of the transiting planet.
We also determine new mid-transit times to confirm or refute observed anomalies
in transit timing. We acquired high-precision light curves for four transits of
WASP-10 b in 2010. Assuming various limb-darkening laws, we generated best-fit
models and redetermined parameters of the system. The prayer-bead method and
Monte Carlo simulations were used to derive error estimates. Three transit
light curves exhibit signatures of the occultations of dark spots by the planet
during its passage across the stellar disk. The influence of stellar activity
on transit depth is taken into account while determining system parameters. The
radius of WASP-10 b is found to be no greater than 1.03 Jupiter radii, a value
significantly smaller than most previous studies indicate. We calculate
interior structure models of the planet, assuming a two-layer structure with
one homogeneous envelope atop a rock core. The high value of the WASP-10 b's
mean density allows one to consider the planet's internal structure including
270 to 450 Earth masses of heavy elements. Our new mid-transit times confirm
that transit timing cannot be explained by a constant period if all literature
data points are considered. They are consistent with the ephemeris assuming a
periodic variation of transit timing...Comment: Accepted for publication in A&
Refined physical properties and g',r',i',z',J,H,K transmission spectrum of WASP-23b from the ground
Multi-band observations of planetary transits using the telescope defocus
technique may yield high-quality light curves suitable for refining the
physical properties of exoplanets even with small or medium size telescopes.
Such observations can be used to construct a broad-band transmission spectrum
of transiting planets and search for the presence of strong absorbers. We have
thoroughly characterised the orbital ephemeris and physical properties of the
transiting planet and host star in the WASP-23b system, constructed a
broad-band transmission spectrum of WASP-23b and performed a comparative
analysis with theoretical models of hot Jupiters. We observed a complete
transit of WASP-23b in seven bands simultaneously, using the GROND instrument
on the MPG/ESO 2.2m telescope at La Silla Observatory and telescope
defocussing. The optical data were taken in the Sloan g',r',i' and z' bands.
The resulting light curves are of high quality, with a root-mean-square scatter
of the residual as low as 330ppm in the z'-band, with a cadence of 90s.
Near-infrared data were obtained in the JHK bands. We performed MCMC analysis
of our photometry plus existing radial velocity data to refine measurements of
the ephemeris and physical properties of the WASP-23. We constructed a
broad-band transmission spectrum of WASP-23b and compared it with a theoretical
transmission spectrum of a Hot Jupiter. We measured the central transit time
with a precision about 8s. From this and earlier observations we obtain an
orbital period of P=2.9444300+/-0.0000011d. Our analysis also yielded a larger
radius and mass for the planet (Rp=1.067+0.045-0.038 RJup and,
Mp=0.917+0.040-0.039MJup). The transmission spectrum is marginally flat, given
the limited precision of the measurements for the planet radius and poor
spectral resolution of the data.Comment: 8 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Combined observations of meteors by image-orthicon television camera and multi-station radar
Observations from multiple sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the relation for the radar magnitude to the panchromatic absolute magnitude was found in terms of velocity of the meteor. A very tentative fit to the data on the duration of long enduring echoes versus visual absolute magnitude is made. The exponential decay characteristics of the later parts of several of the light curves are pointed out as possible evidence of mutual coalescence of droplets into which the meteoroid has completely broken
Simultaneous follow-up of planetary transits: revised physical properties for the planetary systems HAT-P-16 and WASP-21
Context. By now more than 300 planets transiting their host star have been
found, and much effort is being put into measuring the properties of each
system. Light curves of planetary transits often contain deviations from a
simple transit shape, and it is generally difficult to differentiate between
anomalies of astrophysical nature (e.g. starspots) and correlated noise due to
instrumental or atmospheric effects. Our solution is to observe transit events
simultaneously with two telescopes located at different observatories. Aims.
Using this observational strategy, we look for anomalies in the light curves of
two transiting planetary systems and accurately estimate their physical
parameters. Methods. We present the first photometric follow-up of the
transiting planet HAT-P-16 b, and new photometric observations of WASP-21 b,
obtained simultaneously with two medium-class telescopes located in different
countries, using the telescope defocussing technique. We modeled these and
other published data in order to estimate the physical parameters of the two
planetary systems. Results. The simultaneous observations did not highlight
particular features in the light curves, which is consistent with the low
activity levels of the two stars. For HAT-P-16, we calculated a new ephemeris
and found that the planet is 1.3 \sigma colder and smaller (Rb = 1.190 \pm
0.037 RJup) than the initial estimates, suggesting the presence of a massive
core. Our physical parameters for this system point towards a younger age than
previously thought. The results obtained for WASP-21 reveal lower values for
the mass and the density of the planet (by 1.0 \sigma and 1.4 \sigma
respectively) with respect to those found in the discovery paper, in agreement
with a subsequent study. We found no evidence of any transit timing variations
in either system.Comment: 8 pages, 6 figures, accepted for publication in A&
Physical properties of the WASP-44 planetary system from simultaneous multi-colour photometry
We present ground-based broad-band photometry of two transits in the WASP-44
planetary system obtained simultaneously through four optical (Sloan g', r',
i', z') and three near-infrared (NIR; J, H, K) filters. We achieved low
scatters of 1-2 mmag per observation in the optical bands with a cadence of 48
s, but the NIR-band light curves present much greater scatter. We also observed
another transit of WASP-44 b by using a Gunn-r filter and telescope
defocussing, with a scatter of 0.37 mmag per point and an observing cadence
around 135 s. We used these data to improve measurements of the time of
mid-transit and the physical properties of the system. In particular, we
improved the radius measurements of the star and planet by factors of 3 and 4,
respectively. We find that the radius of WASP-44 b is 1.002 R_Jup, which is
slightly smaller than previously thought and differs from that expected for a
core-free planet. In addition, with the help of a synthetic spectrum, we
investigated the theoretically-predicted variation of the planetary radius as a
function of wavelength, covering the range 370-2440 nm. We can rule out extreme
variations at optical wavelengths, but unfortunately our data are not precise
enough (especially in the NIR bands) to differentiate between the theoretical
spectrum and a radius which does not change with wavelength.Comment: 13 pages, 6 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
- …