120 research outputs found
Regaining the FORS: optical ground-based transmission spectroscopy of the exoplanet WASP-19b with VLT+FORS2
In the past few years, the study of exoplanets has evolved from being pure
discovery, then being more exploratory in nature and finally becoming very
quantitative. In particular, transmission spectroscopy now allows the study of
exoplanetary atmospheres. Such studies rely heavily on space-based or large
ground-based facilities, because one needs to perform time-resolved, high
signal-to-noise spectroscopy. The very recent exchange of the prisms of the
FORS2 atmospheric diffraction corrector on ESO's Very Large Telescope should
allow us to reach higher data quality than was ever possible before. With
FORS2, we have obtained the first optical ground-based transmission spectrum of
WASP-19b, with 20 nm resolution in the 550--830 nm range. For this planet, the
data set represents the highest resolution transmission spectrum obtained to
date. We detect large deviations from planetary atmospheric models in the
transmission spectrum redwards of 790 nm, indicating either additional sources
of opacity not included in the current atmospheric models for WASP-19b or
additional, unexplored sources of systematics. Nonetheless, this work shows the
new potential of FORS2 for studying the atmospheres of exoplanets in greater
detail than has been possible so far.Comment: 7 pages, 9 figures, 3 tables. Accepted for publication in A&
TESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star
We present the detection and characterization of the full-orbit phase curve
and secondary eclipse of the ultra-hot Jupiter WASP-33b at optical wavelengths,
along with the pulsation spectrum of the host star. We analyzed data collected
by the Transiting Exoplanet Survey Satellite (TESS) in sector 18. WASP-33b
belongs to a very short list of highly irradiated exoplanets that were
discovered from the ground and were later visited by TESS. The host star of
WASP-33b is of delta Scuti-type and shows nonradial pulsations in the
millimagnitude regime, with periods comparable to the period of the primary
transit. These completely deform the photometric light curve, which hinders our
interpretations. By carrying out a detailed determination of the pulsation
spectrum of the host star, we find 29 pulsation frequencies with a
signal-to-noise ratio higher than 4. After cleaning the light curve from the
stellar pulsations, we confidently report a secondary eclipse depth of 305.8
+/- 35.5 parts-per-million (ppm), along with an amplitude of the phase curve of
100.4 +/- 13.1 ppm and a corresponding westward offset between the region of
maximum brightness and the substellar point of 28.7 +/- 7.1 degrees, making
WASP-33b one of the few planets with such an offset found so far. Our derived
Bond albedo, A_B = 0.369 +/- 0.050, and heat recirculation efficiency, epsilon
= 0.189 +/- 0.014, confirm again that he behavior of WASP-33b is similar to
that of other hot Jupiters, despite the high irradiation received from its host
star. By connecting the amplitude of the phase curve to the primary transit and
depths of the secondary eclipse, we determine that the day- and nightside
brightness temperatures of WASP-33b are 3014 +/- 60 K and 1605 +/- 45 K,
respectively. From the detection of photometric variations due to gravitational
interactions, we estimate a planet mass of M_P = 2.81 +/- 0.53 M$_J.Comment: 19 pages, 15 figure
Low albedos of hot to ultra-hot Jupiters in the optical to near-infrared transition regime
The depth of a secondary eclipse contains information of both the thermally
emitted light component of a hot Jupiter and the reflected light component. If
the dayside atmosphere of the planet is assumed to be isothermal, it is
possible to disentangle both. In this work, we analyze 11 eclipse light curves
of the hot Jupiter HAT-P-32b obtained at 0.89 m in the z' band. We obtain
a null detection for the eclipse depth with state-of-the-art precision, -0.01
+- 0.10 ppt. We confirm previous studies showing that a non-inverted atmosphere
model is in disagreement to the measured emission spectrum of HAT-P-32b. We
derive an upper limit on the reflected light component, and thus, on the
planetary geometric albedo . The 97.5%-confidence upper limit is <
0.2. This is the first albedo constraint for HAT-P-32b, and the first z' band
albedo value for any exoplanet. It disfavors the influence of large-sized
silicate condensates on the planetary day side. We inferred z' band geometric
albedo limits from published eclipse measurements also for the ultra-hot
Jupiters WASP-12b, WASP-19b, WASP-103b, and WASP-121b, applying the same
method. These values consistently point to a low reflectivity in the optical to
near-infrared transition regime for hot to ultra-hot Jupiters.Comment: accepted for publication in A&
First Light of Engineered Diffusers at the Nordic Optical Telescope Reveal Time Variability in the Optical Eclipse Depth of WASP-12b
We present the characterization of two engineered diffusers mounted on the
2.5 meter Nordic Optical Telescope, located at Roque de Los Muchachos, Spain.
To assess the reliability and the efficiency of the diffusers, we carried out
several test observations of two photometric standard stars, along with
observations of one primary transit observation of TrES-3b in the red (R-band),
one of CoRoT-1b in the blue (B-band), and three secondary eclipses of WASP-12b
in V-band. The achieved photometric precision is in all cases within the
sub-millimagnitude level for exposures between 25 and 180 seconds. Along a
detailed analysis of the functionality of the diffusers, we add a new transit
depth measurement in the blue (B-band) to the already observed transmission
spectrum of CoRoT-1b, disfavouring a Rayleigh slope. We also report variability
of the eclipse depth of WASP-12b in the V-band. For the WASP-12b secondary
eclipses, we observe a secondary-depth deviation of about 5-sigma, and a
difference of 6-sigma and 2.5-sigma when compared to the values reported by
other authors in similar wavelength range determined from Hubble Space
Telescope data. We further speculate about the potential physical processes or
causes responsible for this observed variabilityComment: 11 pages, 9 figure
Transmission spectroscopy of the inflated exo-Saturn HAT-P-19b
We observed the Saturn-mass and Jupiter-sized exoplanet HAT-P-19b to refine
its transit parameters and ephemeris as well as to shed first light on its
transmission spectrum. We monitored the host star over one year to quantify its
flux variability and to correct the transmission spectrum for a slope caused by
starspots. A transit of HAT-P-19b was observed spectroscopically with OSIRIS at
the Gran Telescopio Canarias in January 2012. The spectra of the target and the
comparison star covered the wavelength range from 5600 to 7600 AA. One
high-precision differential light curve was created by integrating the entire
spectral flux. This white-light curve was used to derive absolute transit
parameters. Furthermore, a set of light curves over wavelength was formed by a
flux integration in 41 wavelength channels of 50 AA width. We analyzed these
spectral light curves for chromatic variations of transit depth. The transit
fit of the combined white-light curve yields a refined value of the
planet-to-star radius ratio of 0.1390 pm 0.0012 and an inclination of 88.89 pm
0.32 degrees. After a re-analysis of published data, we refine the orbital
period to 4.0087844 pm 0.0000015 days. We obtain a flat transmission spectrum
without significant additional absorption at any wavelength or any slope.
However, our accuracy is not sufficient to significantly rule out the presence
of a pressure-broadened sodium feature. Our photometric monitoring campaign
allowed for an estimate of the stellar rotation period of 35.5 pm 2.5 days and
an improved age estimate of 5.5^+1.8_-1.3 Gyr by gyrochronology.Comment: 14 pages, 9 figures, Accepted for publication in A&
Role of the impact parameter in exoplanet transmission spectroscopy
Transmission spectroscopy is a promising tool for the atmospheric
characterization of transiting exoplanets. Because the planetary signal is
faint, discrepancies have been reported regarding individual targets. We
investigate the dependence of the estimated transmission spectrum on deviations
of the orbital parameters of the star-planet system that are due to the
limb-darkening effects of the host star. We describe how the uncertainty on the
orbital parameters translates into an uncertainty on the planetary spectral
slope. We created synthetic transit light curves in seven different wavelength
bands, from the near-ultraviolet to the near-infrared, and fit them with
transit models parameterized by fixed deviating values of the impact parameter
. Our simulations show a wavelength-dependent offset that is more pronounced
at the blue wavelengths where the limb-darkening effect is stronger. This
offset introduces a slope in the planetary transmission spectrum that becomes
steeper with increasing values. Variations of by positive or negative
values within its uncertainty interval introduce positive or negative slopes,
thus the formation of an error envelope. The amplitude from blue optical to
near-infrared wavelength for a typical uncertainty on corresponds to one
atmospheric pressure scale height and more. This impact parameter degeneracy is
confirmed for different host types; K stars present prominently steeper slopes,
while M stars indicate features at the blue wavelengths. We demonstrate that
transmission spectra can be hard to interpret, basically because of the
limitations in defining a precise impact parameter value for a transiting
exoplanet. This consequently limits a characterization of its atmosphere
Large Binocular Telescope view of the atmosphere of GJ1214b
The atmospheric composition and vertical structure of the super-Earth GJ1214b
has been a subject of debate since its discovery in 2009. Recent studies have
indicated that high-altitude clouds might mask the lower layers. However, some
data points that were gathered at different times and facilities do not fit
this picture, probably because of a combination of stellar activity and
systematic errors. We observed two transits of GJ1214b with the Large Binocular
Camera, the dual-channel camera at the Large Binocular Telescope. For the first
time, we simultaneously measured the relative planetary radius
at blue and red optical wavelengths (), thus
constraining the Rayleigh scattering on GJ1214b after correcting for stellar
activity effects. To the same purpose, a long-term photometric follow-up of the
host star was carried out with WiFSIP at STELLA, revealing a rotational period
that is significantly longer than previously reported. Our new unbiased
estimates of yield a flat transmission spectrum extending to shorter
wavelengths, thus confirming the cloudy atmosphere scenario for GJ1214b.Comment: 11 pages, 5 figures, 3 tables. Published in A&A. Minor changes to
reflect the published versio
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