41 research outputs found
Gasplanetenentstehung und der Corot-Planetenzensus
Das Ziel dieser Arbeit war die Erarbeitung einer Vorhersage möglicher Planetenpopulationen um andere Sterne. Mittel der Wahl ist die so genannte Mannigfaltigkeit: die Menge aller möglichen Gleichgewichte im Sinne des Sternaufbaus, die ein fester Gesteinskern mit verschiedenen ihn umgebenden Nebeln einnehmen kann. Die Gleichgewichte werden hierfĂŒr in-situ, im Rahmen der Kerninduzierten GasinstabilitĂ€tshypothese, berechnet. Der Fokus liegt dabei auf engen Planeten mit Umlaufzeiten von weniger als 64 Tagen. Aber auch Jupiters Position wird mit der gleichen Methode untersucht. Hierbei gibt es eine Ăberraschung: Offenbar unterscheidet sich die Entstehung der sehr engen, nach ihrem ersten Vertreter oft Pegasi-Planeten genannten Planeten, grundlegend von der Entstehung von Jupiter. Es gibt keine dynamische Gasakkretionsphase, vielmehr lĂ€uft die gesamte Entwicklung quasistatisch ab. FĂŒr HD149026 b - den bis dato unerklĂ€rlichen Transitplaneten mit extrem groĂem Kern - wird die statische Entwicklung dann auch mit numerischen, strahlungshydrodynamischen Rechnungen ĂŒberprĂŒft. Die berechnete Mannigfaltigkeit erlaubt die Bestimmung der genauen Anfangsbedingungen, um diesen Planeten zu formen. Damit ist es uns erstmals gelungen, eine mögliche Entstehung von HD149026 b zu prĂ€sentieren. Den Höhepunkt dieser Arbeit stellt schlieĂżlich der Corot-Survey Mark 1 dar: Es handelt sich um die Vorhersage der relativen HĂ€ufigkeiten von Planetenmassen fĂŒr verschiedene Umlaufzeiten und Zentralgestirne. Insgesamt wurden fĂŒr den Survey 48 verschiedene Mannigfaltigkeiten mit jeweils mehr als 10000 Planetenmodellen berechnet. Das Ergebnis zeigt sehr vielfĂ€ltige Massenverteilungen, die bei verschiedenen Umlaufzeiten stark variieren. Dies lĂ€sst auf eine groĂe Vorhersagekraft der Theorie schlieĂen. Weiterhin fĂŒhren die Ergebnisse zu einer Einteilung der Gasplaneten in drei Klassen: Die Klasse G der ganz heiĂen, die Klasse H der heiĂen und die Klasse J der jupiterĂ€hnlichen Gasplaneten. Die Abstandsgrenzen sind ParameterabhĂ€ngig und mĂŒssen noch genau bestimmt werden. Eine mögliche Wahl fĂŒr Bedingungen um unsere Sonne ist die Trennung bei etwa 2 (Grenze G/H) sowie 28 (Grenze H/J) Tagen Umlaufzeit. Diese FĂŒlle an Information wird prĂ€gnant in 7 Thesen zusammengefasst, die schon bald mit Hilfe von Beobachtungen ĂŒberprĂŒft werden können
On the low-mass planethood criterion
We propose a quantitative concept for the lower planetary boundary, requiring
that a planet must keep its atmosphere in vacuum. The solution-set framework of
Pecnik and Wuchterl (2005) enabled a clear and quantitative criterion for the
discrimination of a planet and a minor body. Using a simple isothermal
core-envelope model, we apply the proposed planetary criterion to the large
bodies in the Solar System.Comment: 13 pages, 1 table, submitted to journal of Planetary and Space
Scienc
CHEOPS launch in 2019! â Payload Capabilities and In-Orbit Commissioning Preview
ESA Science Programme Committee (SPC) selected CHEOPS as the first small class science mission in 2012. CHEOPS is considered as a pilot case for the implementation of âsmall science missionsâ and its success is key for the continuation of fast-paced, small missions. The mission has been developed and brought into a flight readiness state within 5-6 years from selection, which is about half the time of other ESA missions. This paper focuses on the CHEOPS payload and its predicted capabilities. The 300mm effective aperture Ritchey-Chretien telescope provided by the CHEOPS consortium has been tested and characterized on ground in a 2 months calibration campaign after the qualification for flight. The results have led to performance estimations, which are discussed here. We show that the performance requirements in flight are expected to be met by the instrument. A preview is given towards the 2 months lasting In Orbit Commissioning (IOC) phase of the CHEOPS payload after LEOP and platform check-out. The activities in orbit range from dark current measurements, PSF characterization and parasitic stray light determination to AOCS and instrument performance verifications to science validation using reference transits
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planetâs birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25â7.8 ÎŒm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10â100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed â using conservative estimates of mission performance and a full model of all significant noise sources in the measurement â using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL â in line with the stated mission objectives â will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
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
A pair of Sub-Neptunes transiting the bright K-dwarf TOI-1064 characterised with CHEOPS
Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine Teff,â=4734±67Kâ , Râ=0.726±0.007Rââ , and Mâ=0.748±0.032Mââ . We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 Râ, and a mass of Mb=13.5+1.7â1.8 Mâ, whilst TOI-1064 c has an orbital period of Pc=12.22657+0.00005â0.00004 d, a radius of Rc = 2.65 ± 0.04 Râ, and a 3Ï upper mass limit of 8.5 Mâ. From the high-precision photometry we obtain radius uncertainties of âŒ1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of massâradius space, and it allow us to identify a trend in bulk densityâstellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.Publisher PDFPeer reviewe
TOI-836 : a super-Earth and mini-Neptune transiting a nearby K-dwarf
Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (T = 8.5 mag), high proper motion (âŒ200 mas yrâ1), low metallicity ([Fe/H]ââ0.28) K-dwarf with a mass of 0.68 ± 0.05 Mâ and a radius of 0.67 ± 0.01 Râ. We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a 1.70 ± 0.07 Râ super-Earth in a 3.82 day orbit, placing it directly within the so-called âradius valleyâ. The outer planet, TOI-836 c, is a 2.59 ± 0.09 Râ mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of 4.5 ± 0.9 Mâ, while TOI-836 c has a mass of 9.6 ± 2.6 Mâ. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.Publisher PDFPeer reviewe
TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf
We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364)
using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (
mag), high proper motion ( mas yr), low metallicity
([Fe/H]) K-dwarf with a mass of M and a
radius of R. We obtain photometric follow-up
observations with a variety of facilities, and we use these data-sets to
determine that the inner planet, TOI-836 b, is a R
super-Earth in a 3.82 day orbit, placing it directly within the so-called
'radius valley'. The outer planet, TOI-836 c, is a R
mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that
TOI-836 b has a mass of M , while TOI-836 c has a mass
of M. Photometric observations show Transit Timing
Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are
no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by
an undetected exterior planet
Two warm Neptunes transiting HIP 9618 revealed by TESS and Cheops
peer reviewedHIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of 3.9 ± 0.044 R (HIP 9618 b) and 3.343 ± 0.039 R (HIP 9618 c). While the 20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 ± 3.1M for HIP 9618 b, which, according to our interior structure models, corresponds to a 6.8 ± 1.4 per cent gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of 50 d, opening the door for the atmospheric characterization of warm (Teq < 750 K) sub-Neptunes