We describe the Perkins INfrared Exosatellite Survey (PINES), a near-infrared photometric search for short-period transiting planets and moons around a sample of 393 spectroscopically confirmed L- ...and T-type dwarfs. PINES is performed with Boston University's 1.8 m Perkins Telescope Observatory, located on Anderson Mesa, Arizona. We discuss the observational strategy of the survey, which was designed to optimize the number of expected transit detections, and describe custom automated observing procedures for performing PINES observations. We detail the steps of the \(\texttt{PINES Analysis Toolkit}\) (\(\texttt{PAT}\)), software that is used to create light curves from PINES images. We assess the impact of second-order extinction due to changing precipitable water vapor on our observations and find that the magnitude of this effect is minimized in Mauna Kea Observatories \(\textit{J}\)-band. We demonstrate the validity of \(\texttt{PAT}\) through the recovery of a transit of WASP-2 b and known variable brown dwarfs, and use it to identify a new variable L/T transition object: the T2 dwarf WISE J045746.08-020719.2. We report on the measured photometric precision of the survey and use it to estimate our transit detection sensitivity. We find that for our median brightness targets, assuming contributions from white noise only, we are sensitive to the detection of 2.5 \(R_\oplus\) planets and larger. PINES will test whether the increase in sub-Neptune-sized planet occurrence with decreasing host mass continues into the L and T dwarf regime.
L-type and T-type dwarfs span the boundaries between main-sequence stars,
brown dwarfs, and planetary-mass objects. For these reasons, L and T dwarfs are
the perfect laboratories for exploring the ...relationship between planet
formation and moon formation, and evidence suggests they may be swarming with
close-in rocky satellites, though none have been found to date. The discovery
of satellites orbiting L or T dwarfs will have transformative implications for
the nature of planets, moons and even life in the Universe. These transiting
satellites will be prime targets for characterization with NASA's James Webb
Space Telescope. In this white paper, we discuss the scientific motivations
behind searching for transiting satellites orbiting L and T dwarfs and argue
that robotizing current 1-to-2-meter US optical/infrared (O/IR) facilities and
equipping them with recently developed low-cost infrared imagers will enable
these discoveries in the next decade. Furthermore, robotizing the 1-to-2-meter
O/IR fleet is highly synergistic with rapid follow-up of transient and
multi-messenger events.
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 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 \(\mu\)m, in addition to a Spitzer 4.5 \(\mu\)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 \(\lesssim 0.1\times\) solar (0.001--0.7\(\times\) 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 they too prefer low metallicities (\(M/H \lesssim -2\), consistent with the free retrieval results). However, all the retrievals should be interpreted with some caution since 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 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.
We find evidence for a strong thermal inversion in the dayside atmosphere of the highly irradiated hot Jupiter WASP-18b (T\(_{eq}=2411K\), \(M=10.3M_{J}\)) based on emission spectroscopy from Hubble ...Space Telescope secondary eclipse observations and Spitzer eclipse photometry. We demonstrate a lack of water vapor in either absorption or emission at 1.4\(\mu\)m. However, we infer emission at 4.5\(\mu\)m and absorption at 1.6\(\mu\)m that we attribute to CO, as well as a non-detection of all other relevant species (e.g., TiO, VO). The most probable atmospheric retrieval solution indicates a C/O ratio of 1 and a high metallicity (C/H=\(283^{+395}_{-138}\times\) solar). The derived composition and T/P profile suggest that WASP-18b is the first example of both a planet with a non-oxide driven thermal inversion and a planet with an atmospheric metallicity inconsistent with that predicted for Jupiter-mass planets at \(>2\sigma\). Future observations are necessary to confirm the unusual planetary properties implied by these results.
