31 research outputs found
The CHEOPS mission
The CHaracterising ExOPlanet Satellite (CHEOPS) was selected in 2012, as the
first small mission in the ESA Science Programme and successfully launched in
December 2019. CHEOPS is a partnership between ESA and Switzerland with
important contributions by ten additional ESA Member States. CHEOPS is the
first mission dedicated to search for transits of exoplanets using ultrahigh
precision photometry on bright stars already known to host planets. As a
follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible,
existing radii measurements or provide first accurate measurements for a subset
of those planets for which the mass has already been estimated from
ground-based spectroscopic surveys and to following phase curves. CHEOPS will
provide prime targets for future spectroscopic atmospheric characterisation.
Requirements on the photometric precision and stability have been derived for
stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS
shall be able to detect Earth-size planets transiting G5 dwarf stars in the
magnitude range between 6 and 9 by achieving a photometric precision of 20 ppm
in 6 hours of integration. For K stars in the magnitude range between 9 and 12,
CHEOPS shall be able to detect transiting Neptune-size planets achieving a
photometric precision of 85 ppm in 3 hours of integration. This is achieved by
using a single, frame-transfer, back-illuminated CCD detector at the focal
plane assembly of a 33.5 cm diameter telescope. The 280 kg spacecraft has a
pointing accuracy of about 1 arcsec rms and orbits on a sun-synchronous
dusk-dawn orbit at 700 km altitude.
The nominal mission lifetime is 3.5 years. During this period, 20% of the
observing time is available to the community through a yearly call and a
discretionary time programme managed by ESA.Comment: Submitted to Experimental Astronom
Nightside condensation of iron in an ultra-hot giant exoplanet
Ultra-hot giant exoplanets receive thousands of times Earth's insolation.
Their high-temperature atmospheres (>2,000 K) are ideal laboratories for
studying extreme planetary climates and chemistry. Daysides are predicted to be
cloud-free, dominated by atomic species and substantially hotter than
nightsides. Atoms are expected to recombine into molecules over the nightside,
resulting in different day-night chemistry. While metallic elements and a large
temperature contrast have been observed, no chemical gradient has been measured
across the surface of such an exoplanet. Different atmospheric chemistry
between the day-to-night ("evening") and night-to-day ("morning") terminators
could, however, be revealed as an asymmetric absorption signature during
transit. Here, we report the detection of an asymmetric atmospheric signature
in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this
signature thanks to the combination of high-dispersion spectroscopy with a
large photon-collecting area. The absorption signal, attributed to neutral
iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be
explained by a combination of planetary rotation and wind blowing from the hot
dayside. In contrast, no signal arises from the nightside close to the morning
terminator, showing that atomic iron is not absorbing starlight there. Iron
must thus condense during its journey across the nightside.Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11
figures, 3 table
THE SPECTROSCOPY AND PHOTOPHYSICS OF 2-, 4- AND 5-METHYLPYRIMIDINE.
Author Institution: Department of Chemistry, Purdue UniversityA spectroscopic study of the effect of the position of methyl substitution on the photophysics of methylpyrimidines has been carried out. Of particular interest is the effect the substitution position has on the barrier to internal rotation. Laser-induced fluorescence excitation was used to probe the states of jet-cooled 4-, 5- and 2-methylpyrimidine. The state was probed using dispersed fluorescence. In the case of 5-m-p, assignments could readily be made via comparison with the spectroscopy of unsubstituted pyrimidine. Furthermore, a nearly free rotor is seen in both and . With the reduction in symmetry in 4-m-p, we see a 100 barrier in with a 7-fold increase upon going to . In addition, the spectroscopic influence of the methyl group is more prevalent in 4-m-p than in 5-m-p. It appears at the present time that 2-m-p exhibits much the same spectroscopy as seen in 5-m-p, particularly with respect to internal rotation
Measurement and stability of the pointing of the BepiColombo Laser Altimeter under thermal load
The BepiColombo Laser Altimeter (BELA) has been selected to fly on ESA׳s BepiColombo mission to Mercury. The instrument will be the first European laser altimeter designed for interplanetary flight. This paper describes the setup used to characterize the angular movements of BELA under the simulated environmental conditions that the instrument will encounter when orbiting Mercury. The system comprises a laser transmitter and a receiving telescope, which can move with respect to each other under thermal load. Tests performed using the Engineering Qualification Model show that the setup is accurate enough to characterize angular movements of the instrument components to an accuracy of ≈10 μrad. The qualification instrument is thermally stable to operate during all mission phases around Mercury proving that the transmitter and receiver sections will remain within the alignment requirements during its mission