178 research outputs found
A ground-based NUV secondary eclipse observation of KELT-9b
KELT-9b is a recently discovered exoplanet with a 1.49 d orbit around a
B9.5/A0-type star. The unparalleled levels of UV irradiation it receives from
its host star put KELT-9b in its own unique class of ultra-hot Jupiters, with
an equilibrium temperature > 4000 K. The high quantities of dissociated
hydrogen and atomic metals present in the dayside atmosphere of KELT-9b bear
more resemblance to a K-type star than a gas giant. We present a single
observation of KELT-9b during its secondary eclipse, taken with the Wide Field
Camera on the Isaac Newton Telescope (INT). This observation was taken in the
U-band, a window particularly sensitive to Rayleigh scattering. We do not
detect a secondary eclipse signal, but our 3 upper limit of 181 ppm on
the depth allows us to constrain the dayside temperature of KELT-9b at
pressures of ~30 mbar to 4995 K (3). Although we can place an
observational constraint of 0.14, our models suggest that the actual
value is considerably lower than this due to H opacity. This places KELT-9b
squarely in the albedo regime populated by its cooler cousins, almost all of
which reflect very small components of the light incident on their daysides.
This work demonstrates the ability of ground-based 2m-class telescopes like the
INT to perform secondary eclipse studies in the NUV, which have previously only
been conducted from space-based facilities.Comment: Accepted in ApJL. 7 pages, 3 figure
Molecular ruby: exploring the excited state landscape
The discovery of the highly NIR-luminescent molecular ruby [Cr(ddpd)2]3+ (ddpd = N,N′-dimethyl-N,N′-dipyridin-2-ylpyridine-2,6-diamine) has been a milestone in the development of earth-abundant luminophors and has led to important new impulses in the field of spin-flip emitters. Its favourable optical properties such as a high photoluminescence quantum yield and long excited state lifetime are traced back to a remarkable excited state landscape which has been investigated in great detail. This article summarises the results of these studies with the aim to create a coherent picture of the excited state ordering and the ultrafast as well as long-timescale dynamics. Additional experimental data is provided to fill in gaps left by previous reports
FastChem Cond: Equilibrium chemistry with condensation and rainout for cool planetary and stellar environments
Cool astrophysical objects, such as (exo)planets, brown dwarfs, or asymptotic
giant branch stars, can be strongly affected by condensation. Condensation does
not only directly affect the chemical composition of the gas phase by removing
elements but the condensed material also influences other chemical and physical
processes in these object. This includes, for example, the formation of clouds
in planetary atmospheres and brown dwarfs or the dust-driven winds of evolved
stars. In this study we introduce FastChem Cond, a new version of the FastChem
equilibrium chemistry code that adds a treatment of equilibrium condensation.
Determining the equilibrium composition under the impact of condensation is
complicated by the fact that the number of condensates that can exist in
equilibrium with the gas phase is limited by a phase rule. However, this phase
rule does not directly provide information on which condensates are stable. As
a major advantage of FastChem Cond is able to automatically select the set
stable condensates satisfying the phase rule. Besides the normal equilibrium
condensation, FastChem Cond can also be used with the rainout approximation
that is commonly employed in atmospheres of brown dwarfs or (exo)planets.
FastChem Cond is available as open-source code, released under the GPLv3
licence. In addition to the C++ code, FastChem Cond also offers a Python
interface. Together with the code update we also add about 290 liquid and solid
condensate species to FastChem.Comment: submitted to MNRAS, code available at
https://github.com/exoclime/FastChe
The Mantis Network III: Expanding the limits of chemical searches within ultra hot-Jupiters. New detections of Ca I, V I, Ti I, Cr I, Ni I, Sr II, Ba II, and Tb II in KELT-9 b
Cross-correlation spectroscopy is an invaluable tool in the study of
exoplanets. However, aliasing between spectral lines makes it vulnerable to
systematic biases. This work strives to constrain the aliases of the
cross-correlation function to provide increased confidence in the detections of
elements in the atmospheres of ultra-hot Jupiters (UHJs) observed with
high-resolution spectrographs. We use a combination of archival transit
observations of the UHJ KELT-9 b obtained with the HARPS-N and CARMENES
spectrographs and show that it is possible to leverage each instrument's
strengths to produce robust detections at substantially reduced
signal-to-noise. Aliases that become present at low signal-to-noise regimes are
constrained through a linear regression model. We confirm previous detections
of H I, Na I, Mg I, Ca II, Sc II, Ti II, Cr II, Fe I, and Fe II, and detect
eight new species Ca I, Cr I, Ni I, Sr II, Tb II at the 5 level and Ti
I, V I, Ba II above the 3 level. Ionised terbium (Tb II) has never
before been seen in an exoplanet atmosphere. We further conclude that a
5 threshold may not provide a reliable measure of confidence when used
to claim detections, unless the systematics in the cross-correlation function
caused by aliases are taken into account.Comment: Accepted for publication on the 1st of April 202
Phase curve and geometric albedo of WASP-43b measured with CHEOPS, TESS, and HST WFC3/UVIS
Context. Observations of the phase curves and secondary eclipses of extrasolar planets provide a window onto the composition and thermal structure of the planetary atmospheres. For example, the photometric observations of secondary eclipses lead to the measurement of the planetary geometric albedo, Ag, which is an indicator of the presence of clouds in the atmosphere.
Aims. In this work, we aim to measure the Ag in the optical domain of WASP-43b, a moderately irradiated giant planet with an equilibrium temperature of ~1400 K.
Methods. For this purpose, we analyzed the secondary eclipse light curves collected by CHEOPS together with TESS along with observations of the system and the publicly available photometry obtained with HST WFC3/UVIS. We also analyzed the archival infrared observations of the eclipses and retrieve the thermal emission spectrum of the planet. By extrapolating the thermal spectrum to the optical bands, we corrected for the optical eclipses for thermal emission and derived the optical Ag.
Results. The fit of the optical data leads to a marginal detection of the phase-curve signal, characterized by an amplitude of 160 ± 60 ppm and 80−50+60 ppm in the CHEOPS and TESS passbands, respectively, with an eastward phase shift of ~50° (1.5σ detection). The analysis of the infrared data suggests a non-inverted thermal profile and solar-like metallicity. The combination of the optical and infrared analyses allows us to derive an upper limit for the optical albedo of Ag< 0.087, with a confidence of 99.9%.
Conclusions. Our analysis of the atmosphere of WASP-43b places this planet in the sample of irradiated hot Jupiters, with monotonic temperature-pressure profile and no indication of condensation of reflective clouds on the planetary dayside
Discrepancy between the CHEOPS and TESS eclipse depths
Recent studies based on photometry from the Transiting Exoplanet Survey Satellite (TESS) have suggested that the dayside of KELT-1b, a strongly irradiated brown dwarf, is significantly brighter in visible light than what would be expected based on Spitzer observations in the infrared. We observed eight eclipses of KELT-1b with CHaracterising ExOPlanet Satellite (CHEOPS) to measure its dayside brightness temperature in the bluest passband observed so far, and we jointly modelled the CHEOPS photometry with the existing optical and near-infrared photometry from TESS, LBT, CFHT, and Spitzer. Our modelling has led to a self-consistent dayside spectrum for KELT-1b covering the CHEOPS, TESS, H, Ks, and Spitzer IRAC 3.6 and 4.5 µm bands, where our TESS, H, Ks, and Spitzer band estimates largely agree with the previous studies. However, we discovered a strong discrepancy between the CHEOPS and TESS bands. The CHEOPS observations yield a higher photometric precision than the TESS observations, but they do not show a significant eclipse signal, while a deep eclipse is detected in the TESS band. The derived TESS geometric albedo of 0.36−0.13+0.12 is difficult to reconcile with a CHEOPS geometric albedo that is consistent with zero because the two passbands have considerable overlap. Variability in cloud cover caused by the transport of transient nightside clouds to the dayside could provide an explanation for reconciling the TESS and CHEOPS geometric albedos, but this hypothesis needs to be tested by future observations
A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
Context: KELT-9 b exemplifies a newly emerging class of short-period gaseous
exoplanets that tend to orbit hot, early type stars - termed ultra-hot
Jupiters. The severe stellar irradiation heats their atmospheres to
temperatures of K, similar to the photospheres of dwarf stars. Due
to the absence of aerosols and complex molecular chemistry at such
temperatures, these planets offer the potential of detailed chemical
characterisation through transit and day-side spectroscopy. Studies of their
chemical inventories may provide crucial constraints on their formation process
and evolution history.
Aims: To search the optical transmission spectrum of KELT-9 b for absorption
lines by metals using the cross-correlation technique.
Methods: We analyse 2 transits observed with the HARPS-N spectrograph. We use
an isothermal equilibrium chemistry model to predict the transmission spectrum
for each of the neutral and singly-ionized atoms with atomic numbers between 3
and 78. Of these, we identify the elements that are expected to have spectral
lines in the visible wavelength range and use those as cross-correlation
templates.
Results: We detect absorption of Na I, Cr II, Sc II and Y II, and confirm
previous detections of Mg I, Fe I, Fe II and Ti II. In addition, we find
evidence of Ca I, Cr I, Co I, and Sr II that will require further observations
to verify. The detected absorption lines are significantly deeper than model
predictions, suggesting that material is transported to higher altitudes where
the density is enhanced compared to a hydrostatic profile. There appears to be
no significant blue-shift of the absorption spectrum due to a net day-to-night
side wind. In particular, the strong Fe II feature is shifted by km~s, consistent with zero. Using the orbital velocity of the
planet we revise the steller and planetary masses and radii.Comment: Submitted to Astronomy and Astrophysics on January 18, 2019. Accepted
on May 3, 2019. 26 pages, 11 figure
Retrieval study of cool, directly imaged exoplanet 51 Eri b
Retrieval methods are a powerful analysis technique for modelling
exoplanetary atmospheres by estimating the bulk physical and chemical
properties that combine in a forward model to best-fit an observed spectrum,
and they are increasingly being applied to observations of directly-imaged
exoplanets. We have adapted TauREx3, the Bayesian retrieval suite, for the
analysis of near-infrared spectrophotometry from directly-imaged gas giant
exoplanets and brown dwarfs. We demonstrate TauREx3's applicability to
sub-stellar atmospheres by presenting results for brown dwarf benchmark GJ 570D
which are consistent with previous retrieval studies, whilst also exhibiting
systematic biases associated with the presence of alkali lines. We also present
results for the cool exoplanet 51 Eri b, the first application of a free
chemistry retrieval analysis to this object, using spectroscopic observations
from GPI and SPHERE. While our retrieval analysis is able to explain
spectroscopic and photometric observations without employing cloud extinction,
we conclude this may be a result of employing a flexible temperature-pressure
profile which is able to mimic the presence of clouds. We present Bayesian
evidence for an ammonia detection with a 2.7 confidence, the first
indication of ammonia in an exoplanetary atmosphere. This is consistent with
this molecule being present in brown dwarfs of a similar spectral type. We
demonstrate the chemical similarities between 51 Eri b and GJ 570D in relation
to their retrieved molecular abundances. Finally, we show that overall
retrieval conclusions for 51 Eri b can vary when employing different spectral
data and modelling components, such as temperature-pressure and cloud
structures
Small but mighty : high-resolution spectroscopy of ultra-hot Jupiter atmospheres with compact telescopes
When observing transmission spectra produced by the atmospheres of ultra-hot Jupiters (UHJs), large telescopes are typically the instrument of choice given the very weak signal of the planet’s atmopshere. The aim of the present study is to demonstrate that, for favourable targets, smaller telescopes are fully capable of conducting high-resolution cross-correlation spectroscopy. We apply the cross-correlation technique to data from the 2.1 m telescope at the Wendelstein Observatory, using its high-resolution spectrograph FOCES, in order to demonstrate its efficacy in resolving the atmosphere of the UHJ KELT-9 b. Using three nights of observations with the FOCES spectrograph and one with the HARPS-N spectrograph, we conduct a performance comparison between FOCES and HARPS-N. This comparison considers both single-transit and combined observations over the three nights. We then consider the potential of 2 m class telescopes by generalising our results to create a transit emulator capable of evaluating the potential of telescopes of this size. With FOCES, we detected seven species in the atmosphere of KELT-9b: Ti II, Fe I, Fe II, Na I, Mg I, Na II, Cr II, and Sc II. Although HARPS-N surpasses FOCES in performance thanks to the mirror of the TNG, our results reveal that smaller telescope classes are capable of resolving the atmospheres of UHJs given sufficient observing time. This broadens the potential scope of such studies, demonstrating that smaller telescopes can be used to investigate phenomena such as temporal variations in atmospheric signals and the atmospheric loss characteristics of these close-in planets
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