413 research outputs found
- 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
Instrumentation, Field Network And Process Automation for the LHC Cryogenic Line Tests
This paper describes the cryogenic control system and associated instrumentation of the test facility for 3 pre-series units of the LHC Cryogenic Distribution Line. For each unit, the process automation is based on a Programmable Logic Con-troller implementing more than 30 closed control loops and handling alarms, in-terlocks and overall process management. More than 160 sensors and actuators are distributed over 150 m on a Profibus DP/PA network. Parameterization, cali-bration and diagnosis are remotely available through the bus. Considering the diversity, amount and geographical distribution of the instru-mentation involved, this is a representative approach to the cryogenic control system for CERN's next accelerator
The Hubble/STIS Near-ultraviolet Transmission Spectrum of HD 189733b
The benchmark hot Jupiter HD 189733b has been a key target to lay out the
foundations of comparative planetology for giant exoplanets. As such, HD
189733b has been extensively studied across the electromagnetic spectrum. Here,
we report the observation and analysis of three transit light curves of HD
189733b obtained with {\Hubble}/STIS in the near ultraviolet, the last
remaining unexplored spectral window to be probed with present-day
instrumentation for this planet. The NUV is a unique window for atmospheric
mass-loss studies owing to the strong resonance lines and large photospheric
flux. Overall, from a low-resolution analysis () we found that the
planet's near-ultraviolet spectrum is well characterized by a relatively flat
baseline, consistent with the optical-infrared transmission, plus two regions
at 2350 and 2600 {\AA} that exhibit a broad and significant excess
absorption above the continuum. From an analysis at a higher resolution
(), we found that the transit depths at the core of the magnesium
resonance lines are consistent with the surrounding continuum. We discarded the
presence of \ion{Mg}{ii} absorption in the upper atmosphere at a
2--4 confidence level, whereas we could place no significant
constraint for \ion{Mg}{i} absorption. These broad absorption features coincide
with the expected location of \ion{Fe}{ii} bands; however, solar-abundance
hydrodynamic models of the upper atmosphere are not able to reproduce the
amplitude of these features with iron absorption. Such scenario would require a
combination of little to no iron condensation in the lower-atmosphere,
super-solar metallicities, and a mechanism to enhance the absorption features
(such as zonal wind broadening). The true nature of this feature remains to be
confirmed.Comment: Accepted for publication at Astronomy and Astrophysic
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
First Experience with the LHC Cryogenic Instrumentation
The LHC under commissioning at CERN will be the world's largest superconducting accelerator and therefore makes extensive use of cryogenic instruments. These instruments are installed in the tunnel and therefore have to withstand the LHC environment that imposes radiation-tolerant design and construction. Most of the instruments require individual calibration; some of them exhibit several variants as concerns measuring span; all relevant data are therefore stored in an Oracle® database. Those data are used for the various quality assurance procedures defined for installation and commissioning, as well as for generating tables used by the control system to configure automatically the input/output channels. This paper describes the commissioning of the sensors and the corresponding electronics, the first measurement results during the cool-down of one machine sector; it discusses the different encountered problems and their corresponding solutions
Instrumentation amplifiers and voltage controlled current sources for LHC cryogenic instrumentation
The Kepler-11 system: evolution of the stellar high-energy emission and {initial planetary} atmospheric mass fractions
The atmospheres of close-in planets are strongly influenced by mass loss
driven by the high-energy (X-ray and extreme ultraviolet, EUV) irradiation of
the host star, particularly during the early stages of evolution. We recently
developed a framework to exploit this connection and enable us to recover the
past evolution of the stellar high-energy emission from the present-day
properties of its planets, if the latter retains some remnants of their
primordial hydrogen-dominated atmospheres. Furthermore, the framework can also
provide constraints on planetary initial atmospheric mass fractions. The
constraints on the output parameters improve when more planets can be
simultaneously analysed. This makes the Kepler-11 system, which hosts six
planets with bulk densities between 0.66 and 2.45g cm^{-3}, an ideal target.
Our results indicate that the star has likely evolved as a slow rotator (slower
than 85\% of the stars with similar masses), corresponding to a high-energy
emission at 150 Myr of between 1-10 times that of the current Sun. We also
constrain the initial atmospheric mass fractions for the planets, obtaining a
lower limit of 4.1% for planet c, a range of 3.7-5.3% for planet d, a range of
11.1-14% for planet e, a range of 1-15.6% for planet f, and a range of 4.7-8.7%
for planet g assuming a disc dispersal time of 1 Myr. For planet b, the range
remains poorly constrained. Our framework also suggests slightly higher masses
for planets b, c, and f than have been suggested based on transit timing
variation measurements. We coupled our results with published planet atmosphere
accretion models to obtain a temperature (at 0.25 AU, the location of planet f)
and dispersal time of the protoplanetary disc of 550 K and 1 Myr, although
these results may be affected by inconsistencies in the adopted system
parameters.Comment: 8 pages, 3 figure
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