312 research outputs found
EChO spectra and stellar activity II. The case of dM stars
EChO is a dedicated mission to investigate exoplanetary atmospheres. When
extracting the planetary signal, one has to take care of the variability of the
hosting star, which introduces spectral distortion that can be mistaken as
planetary signal. Magnetic variability is a major deal in particular for M
stars. To this purpose, assuming a one spot dominant model for the stellar
photosphere, we develop a mixed observational-theoretical tool to extract the
spot's parameters from the observed optical spectrum. This method relies on a
robust library of spectral M templates, which we derive using the observed
spectra of quiet M dwarfs in the SDSS database. Our procedure allows to correct
the observed spectra for photospheric activity in most of the analyzed cases,
reducing the spectral distortion down to the noise levels. Ongoing refinements
of the template library and the algorithm will improve the efficiency of our
algorithm.Comment: Submitted to Experimental Astronom
The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry
GJ3470b is a rare example of a "hot Uranus" transiting exoplanet orbiting a
nearby M1.5 dwarf. It is of crucial interest for atmospheric studies because it
is one of the most inflated low-mass planets known, bridging the boundary
between "super-Earths" and Neptunian planets. We present two new ground-based
light curves of GJ3470b gathered by the LBC camera at the Large Binocular
Telescope. Simultaneous photometry in the ultraviolet (lambda_c = 357.5 nm) and
optical infrared (lambda_c = 963.5 nm) allowed us to detect a significant
change of the effective radius of GJ3470b as a function of wavelength. This can
be interpreted as a signature of scattering processes occurring in the
planetary atmosphere, which should be cloud-free and with a low mean molecular
weight. The unprecedented accuracy of our measurements demonstrates that the
photometric detection of Earth-sized planets around M dwarfs is achievable
using 8-10m size ground-based telescopes. We provide updated planetary
parameters, and a greatly improved orbital ephemeris for any forthcoming study
of this planet.Comment: 8 pages, 6 figures, 1 table; accepted for publication in A&
Synergies between space telescopes in the photometric characterization of the atmospheres of Hot Jupiters
Previous generation of instruments have the opportunity to discover thousands
of extra-solar planets and more will come with the current and future
planet-search missions. In order to go one step further in the characterization
of exoplanets, in this paper we describe a way to compare the photometric
observation of Hot Jupiters done with space telescopes such as HST, CHEOPS,
TESS, PLATO, and JWST and give the first-hand characterization on their
atmospheres. We analyze a set of planetary systems hosting a Hot Jupiter for
which an atmospheric template is available in the literature. For each system,
we simulate the transit light curves observed by different instruments,
convolving the incoming spectrum with the corresponding instrumental
throughput. For each instrument, we thus measure the expected transit depth and
estimate the associated uncertainty. Finally, we compare the transit depths as
seen by the selected instruments and we quantify the effect of the planetary
atmosphere on multi-band transit photometry. We also analyze a set of simulated
scenarios with different stellar magnitudes, activity levels, transit durations
and atmospheric templates to find the best cases for this kind of observational
approach. We find in general that current and especially future space
telescopes provide enough photometric precision to detect significant
differences between the transit depths at different wavelengths. In particular,
we find that the chromatic effect due to the atmosphere of the Hot Jupiters is
maximized at later spectral types and that the effect of stellar activity is
smaller than the measurement uncertainties.Comment: 14 pages, 17 figures, Published in MNRA
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
Coordinated X-ray and Optical observations of Star-Planet Interaction in HD 17156
The large number of close-in Jupiter-size exoplanets prompts the question
whether star-planet interaction (SPI) effects can be detected. We focused our
attention on the system HD 17156, having a Jupiter-mass planet in a very
eccentric orbit. Here we present results of the XMM-Newton observations and of
a five months coordinated optical campaign with the HARPS-N spectrograph. We
observed HD 17156 with XMM-Newton when the planet was approaching the apoastron
and then at the following periastron passage, quasi simultaneously with
HARPS-N. We obtained a clear () X-ray detection only at the
periastron visit, accompanied by a significant increase of the
chromospheric index. We discuss two possible scenarios for the activity
enhancement: magnetic reconnection and flaring or accretion onto the star of
material tidally stripped from the planet. In any case, this is possibly the
first evidence of a magnetic SPI effect caught in action
Broad-band spectrophotometry of the hot Jupiter HAT-P-12b from the near-UV to the near-IR
The detection of trends or gradients in the transmission spectrum of
extrasolar planets is possible with observations at very low spectral
resolution. Transit measurements of sufficient accuracy using selected
broad-band filters allow for an initial characterization of the atmosphere of
the planet. We obtained time series photometry of 20 transit events and
analyzed them homogeneously, along with eight light curves obtained from the
literature. In total, the light curves span a range from 0.35 to 1.25 microns.
During two observing seasons over four months each, we monitored the host star
to constrain the potential influence of starspots on the derived transit
parameters. We rule out the presence of a Rayleigh slope extending over the
entire optical wavelength range, a flat spectrum is favored for HAT-P-12b with
respect to a cloud-free atmosphere model spectrum. A potential cause of such
gray absorption is the presence of a cloud layer at the probed latitudes.
Furthermore, in this work we refine the transit parameters, the ephemeris and
perform a TTV analysis in which we found no indication for an unseen companion.
The host star showed a mild non-periodic variability of up to 1%. However, no
stellar rotation period could be detected to high confidence.Comment: 13 pages, 6 figures, Accepted for publication in A&
A coordinated optical and X-ray spectroscopic campaign on HD179949: searching for planet-induced chromospheric and coronal activity
HD179949 is an F8V star, orbited by a close-in giant planet with a period of
~3 days. Previous studies suggested that the planet enhances the magnetic
activity of the parent star, producing a chromospheric hot spot which rotates
in phase with the planet orbit. However, this phenomenon is intermittent since
it was observed in several but not all seasons. A long-term monitoring of the
magnetic activity of HD179949 is required to study the amplitude and time
scales of star-planet interactions. In 2009 we performed a simultaneous optical
and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949
during ~5 orbital periods and ~2 stellar rotations. We analyzed the CaII H&K
lines as a proxy for chromospheric activity, and we studied the X-ray emission
in search of flux modulations and to determine basic properties of the coronal
plasma. A detailed analysis of the flux in the cores of the CaII H&K lines and
a similar study of the X-ray photometry shows evidence of source variability,
including one flare. The analysis of the the time series of chromospheric data
indicates a modulation with a ~11 days period, compatible with the stellar
rotation period at high latitudes. Instead, the X-ray light curve suggests a
signal with a period of ~4 days, consistent with the presence of two active
regions on opposite hemispheres. The observed variability can be explained,
most likely, as due to rotational modulation and to intrinsic evolution of
chromospheric and coronal activity. There is no clear signature related to the
orbital motion of the planet, but the possibility that just a fraction of the
chromospheric and coronal variability is modulated with the orbital period of
the planet, or the stellar-planet beat period, cannot be excluded. We conclude
that any effect due to the presence of the planet is difficult to disentangle
Phase curve and geometric albedo of WASP-43b measured with CHEOPS, TESS, and HST WFC3/UVIS
Context. Observations of the phase curves and secondary eclipses of extrasolar planets provide a window onto the composition and thermal structure of the planetary atmospheres. For example, the photometric observations of secondary eclipses lead to the measurement of the planetary geometric albedo, Ag, which is an indicator of the presence of clouds in the atmosphere.
Aims. In this work, we aim to measure the Ag in the optical domain of WASP-43b, a moderately irradiated giant planet with an equilibrium temperature of ~1400 K.
Methods. For this purpose, we analyzed the secondary eclipse light curves collected by CHEOPS together with TESS along with observations of the system and the publicly available photometry obtained with HST WFC3/UVIS. We also analyzed the archival infrared observations of the eclipses and retrieve the thermal emission spectrum of the planet. By extrapolating the thermal spectrum to the optical bands, we corrected for the optical eclipses for thermal emission and derived the optical Ag.
Results. The fit of the optical data leads to a marginal detection of the phase-curve signal, characterized by an amplitude of 160 ± 60 ppm and 80−50+60 ppm in the CHEOPS and TESS passbands, respectively, with an eastward phase shift of ~50° (1.5σ detection). The analysis of the infrared data suggests a non-inverted thermal profile and solar-like metallicity. The combination of the optical and infrared analyses allows us to derive an upper limit for the optical albedo of Ag< 0.087, with a confidence of 99.9%.
Conclusions. Our analysis of the atmosphere of WASP-43b places this planet in the sample of irradiated hot Jupiters, with monotonic temperature-pressure profile and no indication of condensation of reflective clouds on the planetary dayside
The GAPS programme at TNG XXVI. Magnetic activity in M stars: spectroscopic monitoring of AD Leonis
Understanding stellar activity in M dwarfs is fundamental to improving our
knowledge of the physics of stellar atmospheres and for planet search
programmes. High levels of stellar activity (also with flare events) can cause
additional variations in the stellar emission that contaminate the signal
induced by a planet and that need to be corrected. The study of activity
indicators in active stars can improve our capability of modelling this signal.
Our aim is to understand the behaviour of stellar chromospheres of M stars,
studying the more sensitive chromospheric activity indicators, characterising
their variability and on finding the correlations among these indicators to
obtain information on the origin of the magnetic activity in low-mass stars. We
studied the main optical activity indicators (Ca II H&K, Balmer lines, Na I
D doublet, He I D and other helium lines) measured for AD Leonis
using the data provided by HARPS-N in 2018 and by HARPS in 2006. We measured
excess flux of the selected activity indicators and analysed the correlation
between the different indicators as well as the temporal evolution of fluxes. A
stellar flare was identified during the 2018 observing run and the H,
H, He I 4471 A and He I 5876 A lines were analysed in detail by fitting
the line profiles with two Gaussian components. We found that the Ca II H&K
flux excesses are strongly correlated with each other, but the Ca II H&K
doublet is generally less correlated with the other indicators. Moreover,
H is correlated with Na I doublet and helium lines. Analysing the time
variability of flux of the studied lines, we found a higher level of activity
of the star during the observations in 2018 than in 2006, while Ca II H&K
showed more intense emission on spectra obtained during the observations in
2006. We investigated the flare evaluating the mass motion during the event.Comment: 18 pages, 6 figures, 12 tables. Accepted for publication in Section
8. Stellar atmospheres of Astronomy and Astrophysics. The official date of
acceptance is 31/07/2020. Abstract shortened for the arXiv listin
- …