397 research outputs found
Signs of strong Na and K absorption in the transmission spectrum of WASP-103b
Context: Transmission spectroscopy has become a prominent tool for
characterizing the atmospheric properties on close-in transiting planets.
Recent observations have revealed a remarkable diversity in exoplanet spectra,
which show absorption signatures of Na, K and , in some cases
partially or fully attenuated by atmospheric aerosols. Aerosols (clouds and
hazes) themselves have been detected in the transmission spectra of several
planets thanks to wavelength-dependent slopes caused by the particles'
scattering properties. Aims: We present an optical 550 - 960 nm transmission
spectrum of the extremely irradiated hot Jupiter WASP-103b, one of the hottest
(2500 K) and most massive (1.5 ) planets yet to be studied with this
technique. WASP-103b orbits its star at a separation of less than 1.2 times the
Roche limit and is predicted to be strongly tidally distorted. Methods: We have
used Gemini/GMOS to obtain multi-object spectroscopy hroughout three transits
of WASP-103b. We used relative spectrophotometry and bin sizes between 20 and 2
nm to infer the planet's transmission spectrum. Results: We find that WASP-103b
shows increased absorption in the cores of the alkali (Na, K) line features. We
do not confirm the presence of any strong scattering slope as previously
suggested, pointing towards a clear atmosphere for the highly irradiated,
massive exoplanet WASP-103b. We constrain the upper boundary of any potential
cloud deck to reside at pressure levels above 0.01 bar. This finding is in line
with previous studies on cloud occurrence on exoplanets which find that clouds
dominate the transmission spectra of cool, low surface gravity planets while
hot, high surface gravity planets are either cloud-free, or possess clouds
located below the altitudes probed by transmission spectra.Comment: Accepted for publication in A&
Young planets under extreme UV irradiation. I. Upper atmosphere modelling of the young exoplanet K2-33b
The K2-33 planetary system hosts one transiting ~5 R_E planet orbiting the
young M-type host star. The planet's mass is still unknown, with an estimated
upper limit of 5.4 M_J. The extreme youth of the system (<20 Myr) gives the
unprecedented opportunity to study the earliest phases of planetary evolution,
at a stage when the planet is exposed to an extremely high level of high-energy
radiation emitted by the host star. We perform a series of 1D hydrodynamic
simulations of the planet's upper atmosphere considering a range of possible
planetary masses, from 2 to 40 M_E, and equilibrium temperatures, from 850 to
1300 K, to account for internal heating as a result of contraction. We obtain
temperature profiles mostly controlled by the planet's mass, while the
equilibrium temperature has a secondary effect. For planetary masses below 7-10
M_E, the atmosphere is subject to extremely high escape rates, driven by the
planet's weak gravity and high thermal energy, which increase with decreasing
mass and/or increasing temperature. For higher masses, the escape is instead
driven by the absorption of the high-energy stellar radiation. A rough
comparison of the timescales for complete atmospheric escape and age of the
system indicates that the planet is more massive than 10 M_E.Comment: 11 pages, 7 figure
A grid of upper atmosphere models for 1--40 MEARTH planets: application to CoRoT-7 b and HD219134 b,c
There is growing observational and theoretical evidence suggesting that
atmospheric escape is a key driver of planetary evolution. Commonly, planetary
evolution models employ simple analytic formulae (e.g., energy limited escape)
that are often inaccurate, and more detailed physical models of atmospheric
loss usually only give snapshots of an atmosphere's structure and are difficult
to use for evolutionary studies. To overcome this problem, we upgrade and
employ an already existing upper atmosphere hydrodynamic code to produce a
large grid of about 7000 models covering planets with masses 1 - 39 Earth mass
with hydrogen-dominated atmospheres and orbiting late-type stars. The modeled
planets have equilibrium temperatures ranging between 300 and 2000 K. For each
considered stellar mass, we account for three different values of the
high-energy stellar flux (i.e., low, moderate, and high activity). For each
computed model, we derive the atmospheric temperature, number density, bulk
velocity, X-ray and EUV (XUV) volume heating rates, and abundance of the
considered species as a function of distance from the planetary center. From
these quantities, we estimate the positions of the maximum dissociation and
ionisation, the mass-loss rate, and the effective radius of the XUV absorption.
We show that our results are in good agreement with previously published
studies employing similar codes. We further present an interpolation routine
capable to extract the modelling output parameters for any planet lying within
the grid boundaries. We use the grid to identify the connection between the
system parameters and the resulting atmospheric properties. We finally apply
the grid and the interpolation routine to estimate atmospheric evolutionary
tracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c...Comment: 21 pages, 4 Tables, 15 Figure
- A tool for multiband light curve modeling of planetary transits and stellar spots
Several studies have shown that stellar activity features, such as occulted
and non-occulted starspots, can affect the measurement of transit parameters
biasing studies of transit timing variations and transmission spectra. We
present , which we designed to model multiband transit
light curves showing starspot anomalies, inferring both transit and spot
parameters. The code follows a pixellation approach to model the star with its
corresponding limb darkening, spots, and transiting planet on a two dimensional
Cartesian coordinate grid. We combine with an MCMC
framework to study and derive exoplanet transmission spectra, which provides
statistically robust values for the physical properties and uncertainties of a
transiting star-planet system. We validate 's performance
by analyzing eleven synthetic light curves of four different star-planet
systems and 20 transit light curves of the well-studied WASP-41b system. We
also investigate the impact of starspots on transit parameters and derive
wavelength dependent transit depth values for WASP-41b covering a range of
6200-9200 , indicating a flat transmission spectrum.Comment: 17 pages, 22 figures; accepted for publication in Astronomy &
Astrophysic
Impact of MgII interstellar medium absorption on near-ultraviolet exoplanet transit measurements
Ultraviolet (UV) transmission spectroscopy probes atmospheric escape, which
has a significant impact on planetary atmospheric evolution. If unaccounted
for, interstellar medium absorption (ISM) at the position of specific UV lines
might bias transit depth measurements, and thus potentially affect the
(non-)detection of features in transmission spectra. Ultimately, this is
connected to the so called ``resolution-linked bias'' (RLB) effect. We present
a parametric study quantifying the impact of unresolved or unconsidered ISM
absorption in transit depth measurements at the position of the MgII h&k
resonance lines (i.e. 2802.705 {\AA} and 2795.528 {\AA} respectively) in the
near-ultraviolet spectral range. We consider main-sequence stars of different
spectral types and vary the shape and amount of chromospheric emission, ISM
absorption, and planetary absorption, as well as their relative velocities. We
also evaluate the role played by integration bin and spectral resolution. We
present an open-source tool enabling one to quantify the impact of unresolved
or unconsidered MgII ISM absorption in transit depth measurements. We further
apply this tool to a few already or soon to be observed systems. On average, we
find that ignoring ISM absorption leads to biases in the MgII transit depth
measurements comparable to the uncertainties obtained from the observations
published to date. However, considering the bias induced by ISM absorption
might become necessary when analysing observations obtained with the next
generation space telescopes with UV coverage (e.g. LUVOIR, HABEX), which will
provide transmission spectra with significantly smaller uncertainties compared
to what obtained with current facilities (e.g. HST).Comment: Accepted for publication in MNRA
Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b
Several results indicate that the atmospheric temperature of the ultra-hot
Jupiter KELT-9b in the main line formation region is a few thousand degrees
higher than predicted by self-consistent models. We test whether non-local
thermodynamic equilibrium (NLTE) effects are responsible for the presumably
higher temperature. We employ the Cloudy NLTE radiative transfer code to
self-consistently compute the upper atmospheric temperature-pressure (TP)
profile of KELT-9b, assuming solar metallicity. The Cloudy NLTE TP profile is
2000 K hotter than that obtained with previous models assuming local
thermodynamic equilibrium (LTE). In particular, in the 1-10 bar range
the temperature increases from 4000 K to 8500 K, remaining
roughly constant at lower pressures. We find that the high temperature in the
upper atmosphere of KELT-9b is driven principally by NLTE effects modifying the
Fe and Mg level populations, which strongly influence the atmospheric thermal
balance. We employ Cloudy to compute LTE and NLTE synthetic transmission
spectra on the basis of the TP profiles computed in LTE and NLTE, respectively,
finding that the NLTE model generally produces stronger absorption lines than
the LTE model (up to 30%), which is largest in the ultraviolet. We compare the
NLTE synthetic transmission spectrum with the observed H and H
line profiles obtaining an excellent match, thus supporting our results. The
NLTE synthetic transmission spectrum can be used to guide future observations
aiming at detecting features in the planet's transmission spectrum. Metals,
such as Mg and Fe, and NLTE effects shape the upper atmospheric temperature
structure of KELT-9b and thus affect the mass-loss rates derived from it.
Finally, our results call for checking whether this is the case also of cooler
planets.Comment: Accepted for publication on A&A. The abstract has been shortened to
fit the available spac
Instrumentation, Field Network and Process Automation for the Cryogenic System of the LHC Test String
CERN is now setting up String 2, a full-size prototype of a regular cell of the LHC arc. It is composed of two quadrupole, six dipole magnets, and a separate cryogenic distribution line (QRL) for the supply and recovery of the cryogen. An electrical feed box (DFB), with up to 38 High Temperature Superconducting (HTS) leads, powers the magnets. About 700 sensors and actuators are distributed along four Profibus DP and two Profibus PA field buses. The process automation is handled by two controllers, running 126 Closed Control Loops (CCL). This paper describes the cryogenic control system, associated instrumentation, and their commissioning
The Cryogenic System for the LHC Test String 2: Design, Commissioning and Operation
A 107-m long superconducting magnet string representing a full-cell of the LHC machine was designed for assembly and commissioning at CERN in order to validate the final design choices. This new facility, thereafter called Test String 2, and its cryogenic infrastructure cons ist of feed and return boxes coupled via transfer lines to a 6 kW @ 4.5 K refrigerator and to a low pressure pumping group, a separate cryogenic distribution line, an electrical feed box with HTS current leads, 2 quadrupole and 6 dipole prototype and pre-series superconducting magnets
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