We present a transmission spectrum for the Neptune-sized exoplanet HD 106315c from optical to infrared wavelengths based on transit observations from the Hubble Space Telescope/Wide Field Camera 3, ...K2, and Spitzer. The spectrum shows tentative evidence for a water absorption feature in the 1.1–1.7 μm wavelength range with a small amplitude of 30 ppm (corresponding to just 0.8 ± 0.04 atmospheric scale heights). Based on an atmospheric retrieval analysis, the presence of water vapor is tentatively favored with a Bayes factor of 1.7–2.6 (depending on prior assumptions). The spectrum is most consistent with either an enhanced metallicity or high-altitude condensates, or both. Cloud-free solar composition atmospheres are ruled out at >5σ confidence. We compare the spectrum to grids of cloudy and hazy forward models and find that the spectrum is fit well by models with moderate cloud lofting or haze formation efficiency over a wide range of metallicities (1–100× solar). We combine the constraints on the envelope composition with an interior structure model and estimate that the core mass fraction is ≳0.3. With a bulk composition reminiscent of that of Neptune and an orbital distance of 0.15 au, HD 106315c hints that planets may form out of broadly similar material and arrive at vastly different orbits later in their evolution.
We describe a joint high-contrast imaging survey for planets at the Keck and Very Large Telescope of the last large sample of debris disks identified by the Spitzer Space Telescope. No new substellar ...companions were discovered in our survey of 30 Spitzer-selected targets. We combine our observations with data from four published surveys to place constraints on the frequency of planets around 130 debris disk single stars, the largest sample to date. For a control sample, we assembled contrast curves from several published surveys targeting 277 stars that do not show infrared excesses. We assumed a double power-law distribution in mass and semimajor axis (SMA) of the form , where we adopted power-law values and logarithmically flat values for the mass and SMA of planets. We find that the frequency of giant planets with masses 5-20 MJup and separations 10-1000 au around stars with debris disks is 6.27% (68% confidence interval 3.68%-9.76%), compared to 0.73% (68% confidence interval 0.20%-1.80%) for the control sample of stars without disks. These distributions differ at the 88% confidence level, tentatively suggesting distinctness of these samples.
Using the Spitzer/Infrared Spectrograph (IRS) low-resolution modules covering wavelengths from 5 to 35 {mu}m, we observed 52 main-sequence A and late B type stars previously seen using ...Spitzer/Multiband Imaging Photometer (MIPS) to have excess infrared emission at 24 {mu}m above that expected from the stellar photosphere. The mid-IR excess is confirmed in all cases but two. While prominent spectral features are not evident in any of the spectra, we observed a striking diversity in the overall shape of the spectral energy distributions. Most of the IRS excess spectra are consistent with single-temperature blackbody emission, suggestive of dust located at a single orbital radius-a narrow ring. Assuming the excess emission originates from a population of large blackbody grains, dust temperatures range from 70 to 324 K, with a median of 190 K corresponding to a distance of 10 AU. Thirteen stars however, have dust emission that follows a power-law distribution, F {sub {nu}} = F {sub 0}{lambda}{sup {alpha}}, with exponent {alpha} ranging from 1.0 to 2.9. The warm dust in these systems must span a greater range of orbital locations-an extended disk. All of the stars have also been observed with Spitzer/MIPS at 70 {mu}m, with 27 of the 50 excess sources detected (signal-to-noise ratio > 3). Most 70 {mu}m fluxes are suggestive of a cooler, Kuiper Belt-like component that may be completely independent of the asteroid belt-like warm emission detected at the IRS wavelengths. Fourteen of 37 sources with blackbody-like fits are detected at 70 {mu}m. The 13 objects with IRS excess emission fit by a power-law disk model, however, are all detected at 70 {mu}m (four above, three on, and six below the extrapolated power law), suggesting that the mid-IR IRS emission and far-IR 70 {mu}m emission may be related for these sources. Overall, the observed blackbody and power-law thermal profiles reveal debris distributed in a wide variety of radial structures that do not appear to be correlated with spectral type or stellar age. An additional 43 fainter A and late B type stars without 70 {mu}m photometry were also observed with Spitzer/IRS; results are summarized in Appendix B.
As an inflated Hot Jupiter orbiting an early-type primary star in the evolved
binary HD 202772 system, HD 202772 A b's presence invites a study of how such a
planet forms and evolves. As a prelude to ...potential atmospheric
characterization with the latest generation of observatories, we present a
reduction and analysis of eclipse light curve observations of HD 202772 A b
acquired with the Spitzer Space Telescope using the 3.6 and 4.5 $\mu$m
channels. We find eclipse depths of $680\pm68$ and $1081^{+54}_{-53}$ ppm,
respectively, corresponding to day-side effective temperatures of
$2130^{+102}_{-91}$ and $2611^{+46}_{-49}$ K. The corresponding Bond albedos
are consistent with the distribution of albedos for Hot Jupiters observed with
both Spitzer and TESS. The heat redistribution efficiencies consistent with the
Bond albedo range predicted by 1-D atmospheric models in radiative-convective
equilibrium are $0.71\pm0.10$ and $0.03^{+0.03}_{-0.02}$, respectively,
indicating a weak day-night contrast for the former and a strong contrast for
the latter. Given this, and the unique environment in which this planet
resides, we recommend follow-up observations with JWST to more precisely
constrain its atmospheric composition and structure, as well as its host
stellar environment, to elucidate if and how the atmospheres of these close-in
giants evolve with host stars in binaries past the main sequence.
The Kepler and TESS missions revealed a remarkable abundance of sub-Neptune exoplanets. Despite this abundance, our understanding of the nature and compositional diversity of sub-Neptunes remains ...limited, to a large part because atmospheric studies via transmission spectroscopy almost exclusively aimed for low-density sub-Neptunes and even those were often affected by high-altitude clouds. The recent TESS discovery of the hot, dense TOI-824b (\(2.93\,R_\oplus\) and \(18.47\,M_\oplus\)) opens a new window into sub-Neptune science by enabling the study of a dense sub-Neptune via secondary eclipses. Here, we present the detection of TOI-824b's hot day side via Spitzer secondary eclipse observations in the \(3.6\) and \(4.5\,\mathrm{\mu m}\) channels, combined with a reanalysis of its interior composition. The measured eclipse depths (142\(^{+57}_{-52}\) and 245\(^{+75}_{-77}\) ppm) and brightness temperatures (1463\(^{+183}_{-196}\) and 1484\(^{+180}_{-202}\) K) indicate a poor heat redistribution (\(f>\) 0.49) and a low Bond albedo (A\(_{B}<\) 0.26). We conclude that TOI-824b could be an "exposed Neptune mantle": a planet with a Neptune-like water-rich interior that never accreted a hydrogen envelope or that subsequently lost it. The hot day-side temperature is then naturally explained by a high-metallicity envelope re-emitting the bulk of the incoming radiation from the day side. TOI-824b's density is also consistent with a massive rocky core that accreted up to 1% of hydrogen, but the observed eclipse depths favor our high-metallicity GCM simulation to a solar-metallicity GCM simulation with a likelihood ratio of 7:1. The new insights into TOI-824b's nature suggest that the sub-Neptune population may be more diverse than previously thought, with some of the dense hot sub-Neptunes potentially not hosting a hydrogen-rich envelope as generally assumed for sub-Neptunes.
The increasing numbers of rocky, terrestrial exoplanets known to orbit nearby stars (especially M dwarfs) has drawn increased attention to the possibility of studying these planets' surface ...properties, and atmospheric compositions & escape histories. Here we report the detection of the secondary eclipse of the terrestrial exoplanet GJ1252b using the Spitzer Space Telescope's IRAC2 4.5 micron channel. We measure an eclipse depth of 149(+25/-32) ppm, corresponding to a day-side brightness temperature of 1410(+91/-125) K and consistent with the prediction for no atmosphere. Comparing our measurement to atmospheric models indicates that GJ1252b has a surface pressure of <10 bar, substantially less than Venus. Assuming energy-limited escape, even a 100 bar atmosphere would be lost in <1 Myr, far shorter than estimated age of 3.9+/-0.4 Gyr. The expected mass loss could be overcome by mantle outgassing, but only if the mantle's carbon content were >7% by mass - over two orders of magnitude greater than that found in Earth. We therefore conclude that GJ1252b has no significant atmosphere. Model spectra with granitoid or feldspathic surface composition, but with no atmosphere, are disfavored at >2 sigma. The eclipse occurs just +1.4(+2.8/-1.0) min after orbital phase 0.5, indicating e cos omega=+0.0025(+0.0049/-0.0018), consistent with a circular orbit. Tidal heating is therefore likely to be negligible to GJ1252b's global energy budget. Finally, we also analyze additional, unpublished TESS transit photometry of GJ1252b which improves the precision of the transit ephemeris by a factor of ten, provides a more precise planetary radius of 1.180+/-0.078 R_E, and rules out any transit timing variations with amplitudes <1 min.
We present ground and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a ...bright (K-mag=8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1), and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using 8 different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of \(\sim\)10 minutes and a super-period of \(\sim\)3 years, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modeling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of \(M_{\mathrm{b}}=1.48\pm0.18\,M_\oplus\), \(M_{c}=6.20\pm0.31\,M_\oplus\) and \(M_{\mathrm{d}}=4.20\pm0.16\,M_\oplus\) for planets b, c and d, respectively. We also detect small, but significant eccentricities for all three planets : \(e_\mathrm{b} =0.0167\pm0.0084\), \(e_{c} =0.0044\pm0.0006\) and \(e_{d} = 0.0066\pm0.0020\). Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H\(_2\)O atmosphere for the outer two. TOI-270 is now one of the best-constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization.
As an inflated Hot Jupiter orbiting an early-type primary star in the evolved binary HD 202772 system, HD 202772 A b's presence invites a study of how such a planet forms and evolves. As a prelude to ...potential atmospheric characterization with the latest generation of observatories, we present a reduction and analysis of eclipse light curve observations of HD 202772 A b acquired with the Spitzer Space Telescope using the 3.6 and 4.5 \(\mu\)m channels. We find eclipse depths of \(680\pm68\) and \(1081^{+54}_{-53}\) ppm, respectively, corresponding to day-side effective temperatures of \(2130^{+102}_{-91}\) and \(2611^{+46}_{-49}\) K. The corresponding Bond albedos are consistent with the distribution of albedos for Hot Jupiters observed with both Spitzer and TESS. The heat redistribution efficiencies consistent with the Bond albedo range predicted by 1-D atmospheric models in radiative-convective equilibrium are \(0.71\pm0.10\) and \(0.03^{+0.03}_{-0.02}\), respectively, indicating a weak day-night contrast for the former and a strong contrast for the latter. Given this, and the unique environment in which this planet resides, we recommend follow-up observations with JWST to more precisely constrain its atmospheric composition and structure, as well as its host stellar environment, to elucidate if and how the atmospheres of these close-in giants evolve with host stars in binaries past the main sequence.
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