We present an optical-to-infrared transmission spectrum of the inflated sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope (HST) Wide Field ...Camera 3 G141 spectroscopic grism, and the Spitzer Space Telescope (Spitzer) at 3.6 m, in addition to a Spitzer 4.5 m secondary eclipse. The precise HST transmission spectrum notably reveals a low-amplitude water feature with an unusual shape. Based on free-retrieval analyses with varying molecular abundances, we find strong evidence for water absorption. Depending on model assumptions, we also find tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water abundance is generally 0.1× solar (0.001-0.7× solar over a range of model assumptions), several orders of magnitude lower than expected from planet formation models based on the solar system metallicity trend. We also consider chemical-equilibrium and self-consistent 1D radiative-convective equilibrium model fits and find that they, too, prefer low metallicities (M/H −2, consistent with the free-retrieval results). However, all of the retrievals should be interpreted with some caution because they either require additional absorbers that are far out of chemical equilibrium to explain the shape of the spectrum or are simply poor fits to the data. Finally, we find that the Spitzer secondary eclipse is indicative of full heat redistribution from KELT-11b's dayside to nightside, assuming a clear dayside. These potentially unusual results for KELT-11b's composition are suggestive of new challenges on the horizon for atmosphere and formation models in the face of increasingly precise measurements of exoplanet spectra.
Abstract
We present a new transit of TRAPPIST-1 d from 2021 August 25. The measured mid-point of this transit agrees with the prediction from a recently published dynamical model for the TRAPPIST-1 ...system and differs significantly from a naive prediction from a simple linear ephemeris. This difference underlines the importance for using dynamical models to predict future transit times in the TRAPPIST-1 system.
We simulate the yield of small (0.5-4.0 R\(_\oplus\)) transiting exoplanets around single mid-M and ultra-cool dwarfs (UCDs) in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain ...Survey. We consider multiple approaches for simulating M3-T9 sources within the survey fields, including scaling local space densities and using Galactic stellar population synthesis models. These approaches independently predict \(\sim\)100,000 single mid-M dwarfs and UCDs brighter than a Roman F146 magnitude of 21 that are within the survey fields. Assuming planet occurrence statistics previously measured for early-to-mid M dwarfs, we predict that the survey will discover 1347\(^{+208}_{-124}\) small transiting planets around these sources, each to a significance of 7.1\(\sigma\) or greater. Significant departures from this prediction would test whether the occurrence rates of small planets increase or decrease around mid-M dwarfs and UCDs compared to early-M dwarfs. We predict the detection of 13\(^{+4}_{-3}\) habitable, terrestrial planets (\(R_p<\)1.23 R\(_\oplus\)) in the survey. However, atmospheric characterization of these planets will be challenging with current or near-future space telescope facilities due to the faintness of the host stars. Nevertheless, accurate statistics for the occurrence of small planets around mid-M dwarfs and UCDs will enable direct tests of predictions from planet formation theories and will determine our understanding of planet demographics around the objects at the bottom of the main sequence. This understanding is critical given the prevalence of such objects in our Galaxy, whose planets may therefore comprise the bulk of the galactic census of exoplanets.
We present design considerations for a ground-based survey for transiting exoplanets around L and T dwarfs, spectral classes that have yet to be thoroughly probed for planets. We simulate photometry ...for L and T targets with a variety of red-optical and near-infrared detectors, and compare the scatter in the photometry to anticipated transit depths. Based on these results, we recommend the use of a low-dark-current detector with H-band NIR photometric capabilities. We then investigate the potential for performing a survey for Earth-sized planets for a variety of telescope sizes. We simulate planetary systems around a set of spectroscopically confirmed L and T dwarfs using measured M dwarf planet occurrence rates from \(\textit{Kepler}\), and simulate their observation in surveys ranging in duration from 120 to 600 nights, randomly discarding 30% of nights to simulate weather losses. We find that an efficient survey design uses a 2-meter-class telescope with a NIR instrument and 360-480 observing nights, observing multiple L and T targets each night with a dithering strategy. Surveys conducted in such a manner have over an 80% chance of detecting at least one planet, and detect around 2 planets, on average. The number of expected detections depends on the true planet occurrence rate, however, which may in fact be higher for L and T dwarfs than for M dwarfs.
We acquired observations of a partial transit of Kepler-167e, a Jupiter-analog exoplanet on a 1,071-day orbit, well beyond its water ice line, with the Spitzer Space Telescope. The timing of the ...Spitzer transit is consistent with the ephemeris measured from the two transits observed previously by the Kepler Space Telescope. The Spitzer observation rules out the existence of transit timing variations (TTVs) of order hours to days that are known to exist for other long-period exoplanets. Such TTVs render transit follow-up efforts intractable due to the substantial observing time required and the high risk of non-detection. For Kepler-167e, however, we are now able to predict future transit times through the anticipated era of the James Webb Space Telescope with uncertainties of less than six minutes. We interpret the lack of TTVs as an indication that Kepler-167e either does not have an exterior massive companion or that the gravitational interactions with any companions are below our detection threshold. We also measure Kepler-167e's 3.6-\(\mu\)m transit depth and use exoplanet and solar system models to make predictions about its transmission spectrum. The transiting nature of Kepler-167e and its similarity to Jupiter make it a unique and exceptional target for follow-up atmospheric characterization. Kepler-167e falls into a truly rare category among transiting exoplanets, and with a precisely constrained transit ephemeris, it is poised to serve as a benchmark in comparative investigations between exoplanets and the solar system.
Multi-wavelength photometry of brown dwarfs and planetary-mass objects provides insight into their atmospheres and cloud layers. We present near-simultaneous \(J-\) and \(K_s-\)band multi-wavelength ...observations of the highly variable T2.5 planetary-mass object, SIMP J013656.5+093347. We reanalyze observations acquired over a single night in 2015 using a recently developed data reduction pipeline. For the first time, we detect a phase shift between \(J-\) and \(K_s-\)band light curves, which we measure to be \(39.9^{\circ +3.6}_{ -1.1}\). Previously, phase shifts between near-infrared and mid-infrared observations of this object were detected and attributed to probing different depths of the atmosphere, and thus different cloud layers. Using the Sonora Bobcat models, we expand on this idea to show that at least two different patchy cloud layers must be present to explain the measured phase shift. Our results are generally consistent with recent atmospheric retrievals of this object and other similar L/T transition objects.
The first JWST observations of TRAPPIST-1 c showed a secondary eclipse depth
of 421+/-94 ppm at 15 um, which is consistent with a bare rock surface or a
thin, O2-dominated, low CO2 atmosphere (Zieba ...et al. 2023). Here, we further
explore potential atmospheres for TRAPPIST-1 c by comparing the observed
secondary eclipse depth to synthetic spectra of a broader range of plausible
environments. To self-consistently incorporate the impact of photochemistry and
atmospheric composition on atmospheric thermal structure and predicted eclipse
depth, we use a two-column climate model coupled to a photochemical model, and
simulate O2-dominated, Venus-like, and steam atmospheres. We find that a
broader suite of plausible atmospheric compositions are also consistent with
the data. For lower pressure atmospheres (0.1 bar), our O2-CO2 atmospheres
produce eclipse depths within 1$\sigma$ of the data, consistent with the
modeling results of Zieba et al. (2023). However, for higher-pressure
atmospheres, our models produce different temperature-pressure profiles and are
less pessimistic, with 1-10 bar O2, 100 ppm CO2 models within 2.0-2.2$\sigma$
of the measured secondary eclipse depth, and up to 0.5% CO2 within 2.9$\sigma$.
Venus-like atmospheres are still unlikely. For thin O2 atmospheres of 0.1 bar
with a low abundance of CO2 ($\sim$100 ppm), up to 10% water vapor can be
present and still provide an eclipse depth within 1$\sigma$ of the data. We
compared the TRAPPIST-1 c data to modeled steam atmospheres of $\leq$ 3 bar,
which are 1.7-1.8$\sigma$ from the data and not conclusively ruled out. More
data will be required to discriminate between possible atmospheres, or to more
definitively support the bare rock hypothesis.
We describe a new transit detection algorithm designed to detect single transit events in discontinuous Perkins INfrared Exosatellite Survey (PINES) observations of L and T dwarfs. We use this ...algorithm to search for transits in 131 PINES light curves and identify two transit candidates: 2MASS J18212815+1414010 (2MASS J1821+1414) and 2MASS J08350622+1953050 (2MASS J0835+1953). We disfavor 2MASS J1821+1414 as a genuine transit candidate due to the known variability properties of the source. We cannot rule out the planetary nature of 2MASS J0835+1953's candidate event and perform follow-up observations in an attempt to recover a second transit. A repeat event has yet to be observed, but these observations suggest that target variability is an unlikely cause of the candidate transit. We perform a Markov chain Monte Carlo simulation of the light curve and estimate a planet radius ranging from \(4.2^{+3.5}_{-1.6}R_\oplus\) to \(5.8^{+4.8}_{-2.1}R_\oplus\), depending on the host's age. Finally, we perform an injection and recovery simulation on our light curve sample. We inject planets into our data using measured M dwarf planet occurrence rates and attempt to recover them using our transit search algorithm. Our detection rates suggest that, assuming M dwarf planet occurrence rates, we should have roughly a 1\(\%\) chance of detecting a candidate that could cause the transit depth we observe for 2MASS J0835+1953. If 2MASS J0835+1953 b is confirmed, it would suggest an enhancement in the occurrence of short-period planets around L and T dwarfs in comparison to M dwarfs, which would challenge predictions from planet formation models.
We present a reanalysis of five transit and eight eclipse observations of the ultra-short period super-Earth 55 Cancri e observed using the Spitzer Space Telescope during 2011-2013. We use ...pixel-level decorrelation to derive accurate transit and eclipse depths from the Spitzer data, and we perform an extensive error analysis. We focus on determining possible variability in the eclipse data, as was reported in Demory et al. 2016a. From the transit data, we determine updated orbital parameters, yielding T0 = 2455733.0037 \(\pm\) 0.0002, P = 0.7365454 \(\pm\) 0.0000003 days, i = 83.5 \(\pm\) 1.3 degrees, and \(R_p\) = 1.89 \(\pm\) 0.05 \(R_\oplus\). Our transit results are consistent with a constant depth, and we conclude that they are not variable. We find a significant amount of variability between the eight eclipse observations, and confirm agreement with Demory et al. 2016a through a correlation analysis. We convert the eclipse measurements to brightness temperatures, and generate and discuss several heuristic models that explain the evolution of the planet's eclipse depth versus time. The eclipses are best modeled by a year-to-year variability model, but variability on shorter timescales cannot be ruled out. The derived range of brightness temperatures can be achieved by a dark planet with inefficient heat redistribution intermittently covered over a large fraction of the sub-stellar hemisphere by reflective grains, possibly indicating volcanic activity or cloud variability. This time-variable system should be observable with future space missions, both planned (JWST) and proposed (i.e. ARIEL).
Seven rocky planets orbit the nearby dwarf star TRAPPIST-1, providing a unique opportunity to search for atmospheres on small planets outside the Solar System (Gillon et al., 2017). Thanks to the ...recent launch of JWST, possible atmospheric constituents such as carbon dioxide (CO2) are now detectable (Morley et al., 2017, Lincowski et al., 2018}. Recent JWST observations of the innermost planet TRAPPIST-1 b showed that it is most probably a bare rock without any CO2 in its atmosphere (Greene et al., 2023). Here we report the detection of thermal emission from the dayside of TRAPPIST-1 c with the Mid-Infrared Instrument (MIRI) on JWST at 15 micron. We measure a planet-to-star flux ratio of fp/fs = 421 +/- 94 parts per million (ppm) which corresponds to an inferred dayside brightness temperature of 380 +/- 31 K. This high dayside temperature disfavours a thick, CO2-rich atmosphere on the planet. The data rule out cloud-free O2/CO2 mixtures with surface pressures ranging from 10 bar (with 10 ppm CO2) to 0.1 bar (pure CO2). A Venus-analogue atmosphere with sulfuric acid clouds is also disfavoured at 2.6 sigma confidence. Thinner atmospheres or bare-rock surfaces are consistent with our measured planet-to-star flux ratio. The absence of a thick, CO2-rich atmosphere on TRAPPIST-1 c suggests a relatively volatile-poor formation history, with less than 9.5 +7.5 -2.3 Earth oceans of water. If all planets in the system formed in the same way, this would indicate a limited reservoir of volatiles for the potentially habitable planets in the system.
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