18 research outputs found
Non-detection of He I in the atmosphere of GJ1214b with Keck/NIRSPEC, at a time of minimal telluric contamination
Observations of helium in exoplanet atmospheres may reveal the presence of
large gaseous envelopes, and indicate ongoing atmospheric escape. Orell-Miquel
et al. (2022) used CARMENES to measure a tentative detection of helium for the
sub-Neptune GJ 1214b, with a peak excess absorption reaching over 2% in transit
depth at 10830 Angstroms. However, several non-detections of helium had
previously been reported for GJ 1214b. One explanation for the discrepancy was
contamination of the planetary signal by overlapping telluric absorption- and
emission lines. We used Keck/NIRSPEC to observe another transit of GJ 1214b at
10830 Angstroms, at a time of minimal contamination by telluric lines, and did
not observe planetary helium absorption. Accounting for correlated noise in our
measurement, we place an upper limit on the excess absorption size of 1.22%
(95% confidence). We find that the discrepancy between the CARMENES and NIRSPEC
observations is unlikely to be caused by using different instruments or stellar
activity. It is currently unclear whether the difference is due to correlated
noise in the observations, or variability in the planetary atmosphere.Comment: Accepted for publication in ApJ
Single transit candidates from K2 : detection and period estimation
Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool (‘Namaste: An Mcmc Analysis of Single Transit Exoplanets’) to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of 540+410 −230 d and a radius of 0.51 ± 0.05RJup. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia
One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c
The K2 mission has recently begun to discover new and diverse planetary
systems. In December 2014 Campaign 1 data from the mission was released,
providing high-precision photometry for ~22000 objects over an 80 day timespan.
We searched these data with the aim of detecting further important new objects.
Our search through two separate pipelines led to the independent discovery of
K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2
), orbiting a K dwarf extremely close to the 3:2 mean motion
resonance. The two planets each show transits, sometimes simultaneously due to
their proximity to resonance and alignment of conjunctions. We obtain further
ground based photometry of the larger planet with the NITES telescope,
demonstrating the presence of large transit timing variations (TTVs), and use
the observed TTVs to place mass constraints on the transiting objects under the
hypothesis that the objects are near but not in resonance. We then
statistically validate the planets through the \texttt{PASTIS} tool,
independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published
versio
Abundance measurements of H<sub>2</sub>O and carbon-bearing species in the atmosphere of WASP-127b confirm its super-solar metallicity
The chemical abundances of exoplanet atmospheres may provide valuable information about the bulk compositions, formation pathways, and evolutionary histories of planets. Exoplanets with large, relatively cloud-free atmospheres, and which orbit bright stars provide the best opportunities for accurate abundance measurements. For this reason, we measured the transmission spectrum of the bright (V∼10.2), large (), sub-Saturn mass () exoplanet WASP-127b across the near-UV to near-infrared wavelength range (0.3–5 μm), using the Hubble and Spitzer Space Telescopes. Our results show a feature-rich transmission spectrum, with absorption from Na, , and , and wavelength-dependent scattering from small-particle condensates. We ran two types of atmospheric retrieval models: one enforcing chemical equilibrium, and the other which fit the abundances freely. Our retrieved abundances at chemical equilibrium for Na, O and C are all super-solar, with abundances relative to solar values of , , and respectively. Despite giving conflicting C/O ratios, both retrievals gave super-solar volume mixing ratios, which adds to the likelihood that WASP-127b’s bulk metallicity is super-solar, since abundance is highly sensitive to atmospheric metallicity. We detect water at a significance of 13.7 σ. Our detection of Na is in agreement with previous ground-based detections, though we find a much lower abundance, and we also do not find evidence for Li or K despite increased sensitivity. In the future, spectroscopy with JWST will be able to constrain WASP-127b’s C/O ratio, and may reveal the formation history of this metal-enriched, highly observable exoplanet
Diurnal variations in the stratosphere of the ultrahot giant exoplanet WASP-121b
The temperature profile of a planetary atmosphere is a key diagnostic of radiative and dynamical processes governing the absorption, redistribution and emission of energy. Observations have revealed dayside stratospheres that either cool1,2 or warm3,4 with altitude for a small number of gas giant exoplanets, whereas other dayside stratospheres are consistent with constant temperatures5,6,7. Here we report spectroscopic phase curve measurements for the gas giant WASP-121b (ref.8) that constrain stratospheric temperatures throughout the diurnal cycle. Variations measured for a water vapour spectral feature reveal a temperature profile that transitions from warming with altitude on the dayside hemisphere to cooling with altitude on the nightside hemisphere. The data are well explained by models assuming chemical equilibrium, with water molecules thermally dissociating at low pressures on the dayside and recombining on the nightside9,10. Nightside temperatures are low enough for perovskite (CaTiO3) to condense, which could deplete titanium from the gas phase11,12 and explain recent non-detections at the day–night terminator13,14,15,16. Nightside temperatures are also consistent with the condensation of refractory species such as magnesium, iron and vanadium. Detections15,16,17,18 of these metals at the day–night terminator suggest, however, that if they do form nightside clouds, cold trapping does not efficiently remove them from the upper atmosphere. Horizontal winds and vertical mixing could keep these refractory condensates aloft in the upper atmosphere of the nightside hemisphere until they are recirculated to the hotter dayside hemisphere and vaporized
Identification of carbon dioxide in an exoplanet atmosphere
Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called ‘metallicity’), and thus the formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme. The data used in this study span 3.0–5.5 micrometres in wavelength and show a prominent CO2 absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative–convective–thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models
WASP-135b : a highly irradiated, inflated hot Jupiter orbiting a G5V star
We report the discovery of a new transiting planet from the WASP survey. WASP-135b is a hot Jupiter with a radius of 1.30 pm 0.09 Rjup, a mass of 1.90 pm 0.08 Mjup and an orbital period of 1.401 days. Its host is a Sun-like star, with a G5 spectral type and a mass and radius of 0.98 pm 0.06 Msun and 0.96 pm 0.05 Rsun respectively. The proximity of the planet to its host means that WASP-135b receives high levels of insolation, which may be the cause of its inflated radius. Additionally, we find weak evidence of a transfer of angular momentum from the planet to its star.PostprintPeer reviewe
Solar-to-supersolar sodium and oxygen absolute abundances for a "hot Saturn" orbiting a metal-rich star
We present new analysis of infrared transmission spectroscopy of the
cloud-free hot-Saturn WASP-96b performed with the Hubble and Spitzer Space
Telescopes (HST and Spitzer). The WASP-96b spectrum exhibits the absorption
feature from water in excellent agreement with synthetic spectra computed
assuming a cloud-free atmosphere. The HST-Spitzer spectrum is coupled with Very
Large Telescope (VLT) optical transmission spectroscopy which reveals the full
pressure-broadened profile of the sodium absorption feature and enables the
derivation of absolute abundances. We confirm and correct for a spectral offset
of of the
VLT data relative to the HST-Spitzer spectrum. This offset can be explained by
the assumed radius for the common-mode correction of the VLT spectra, which is
a well-known feature of ground-based transmission spectroscopy. We find
evidence for a lack of chromospheric and photometric activity of the host star
which, therefore, make a negligible contribution to the offset. We measure
abundances for Na and O that are consistent with solar to supersolar, with
abundances relative to solar values of and ,
respectively. We complement the transmission spectrum with new thermal emission
constraints from Spitzer observations at 3.6 and m, which are best
explained by the spectrum of an atmosphere with a temperature decreasing with
altitude. A fit to the spectrum assuming an isothermal blackbody atmosphere
constrains the dayside temperature to be =K.Comment: Accepted for publication in MNRA