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We report results from 8 hours of JWST/MIRI LRS spectroscopic monitoring directly followed by 7 hours of JWST/NIRSpec prism spectroscopic monitoring of the benchmark binary brown dwarf WISE 1049AB, the closest, brightest brown dwarfs known. We find water, methane, and CO absorption features in both components, including the 3.3 $\mu$m methane absorption feature and a tentative detection of small grain ($<$ 1$\mu$m) silicate absorption at $>$8.5 $\mu$m in WISE 1049A. Both components vary significantly ($>$1$\%$), with WISE 1049B displaying larger variations than WISE 1049A. Using K-means clustering, we find three main transition points in wavelength for both components of the binary: 1) change in behavior at $\sim$2.3 $\mu$m coincident with a CO absorption bandhead, 2) change in behavior at 4.2 $\mu$m, close to the CO fundamental band at $\lambda >$ 4.4 $\mu$m, and 3) change in behavior at 8.3-8.5 $\mu$m, potentially corresponding to silicate absorption. We interpret the lightcurves observed with both NIRSpec and MIRI as likely stemming from 1) a deep pressure level driving the double-peaked variability seen in WISE 1049B at wavelengths $<$2.3 $\mu$m and $>$8.5 $\mu$m, 2) an intermediate pressure level shaping the lightcurve morphology between 2.3 and 4.2 $\mu$m, and 3) a higher-altitude pressure level producing single-peaked and plateaued lightcurve behavior between 4.2 and 8.5 $\mu$m., Comment: 28 pages, 27 figures, accepted to MNRAS

We present two-dimensional near-infrared temperature maps of the canonical hot Jupiter WASP-43b using a phase-curve observation with JWST NIRSpec/G395H. From the white-light planetary transit, we improve constraints on the planet's orbital parameters and measure a planet-to-star radius ratio of $0.15883^{+0.00056}_{-0.00053}$. Using the white-light phase curve, we measure a longitude of maximum brightness of $6.9^{+0^\circ.5}_{-0^\circ.5}$ east of the substellar point and a phase-curve offset of $10.0^{+0^\circ.8}_{-0^\circ.8}$. We also find an $\approx4\sigma$ detection of a latitudinal hotspot offset of $-13.4^{+3^\circ.2}_{-1^\circ.7}$, the first significant detection of a non-equatorial hotspot in an exoplanet atmosphere. We show that this detection is robust to variations within planetary parameter uncertainties, but only if the transit is used to improve constraints, showing the importance of transit observations to eclipse mapping. Maps retrieved from the NRS1 and NRS2 detectors are similar, with hotspot locations consistent between the two detectors at the $1\sigma$ level. Our JWST data show brighter (hotter) nightsides and a dimmer (colder) dayside at the shorter wavelengths relative to fits to \textit{Spitzer} 3.6 and 4.5 \microns\ phase curves. Through comparison between our phase curves and a set of general circulation models, we find evidence for clouds on the nightside and atmospheric drag or high metallicity reducing the eastward hotspot offset., Comment: 15 pages, 8 figures. In review at ApJ Letters

Most brown dwarfs show some level of photometric or spectral variability. However, finding the most variable dwarfs more suited for a thorough variability monitoring campaign remained a challenge until a few years ago with the design of spectral indices to find the most likely L and T dwarfs using their near-infrared single-epoch spectrum. In this work, we designed and tested near-infrared spectral indices to pre-select the most likely variable L4-L8 dwarfs, complementing the indices presented by Ashraf et al. (2022) and Oliveros-Gomez et al. (2022). We used time-resolved near-infrared Hubble Space Telescope Wide Field Camera 3 spectra of an L6.0 dwarf, LP 261-75b, to design our novel spectral indices. We tested these spectral indices on 75 L4.0-L8.0 near-infrared SpeX/IRTF spectra, providing 27 new variable candidates. Our indices have a recovery rate of 80 percent and a false negative rate of 25 percent. All the known non-variable brown dwarfs were found to be non-variable by our indices. We estimated the variability fraction of our sample to be near 51 percent, which agrees with the variability fractions provided by Buenzli et al. (2014), Radigan et al. (2014), and Metchev et al. (2015) for L4-L8 dwarfs. These spectral indices may support in the future, the selection of the most likely variable directly-imaged exoplanets for studies with the James Webb Space Telescope and as well as the 30-m telescopes., Comment: Accepted for publication in ApJ. 22 pages, 13 figures, 3 tables. GitHub code: https://github.com/ntlucia/BrownDwarf-SpectralIndices

The majority of brown dwarfs show some level of photometric or spectro-photometric variability in different wavelength ranges. This variability allow us to trace the 3D atmospheric structures of variable brown dwarfs and directly-imaged exoplanets with radiative-transfer models and mapping codes. Nevertheless, to date, we do not have an informed method to pre-select the brown dwarfs that might show a higher variability amplitude for a thorough variability study. In this work, we designed and tested near-infrared spectral indices to pre-select the most likely variable mid- and late-T dwarfs, which overlap in effective temperatures with directly-imaged exoplanets. We used time-resolved near-infrared Hubble Space Telescope Wide Field Camera 3 spectra of a T6.5 dwarf, 2MASS J22282889--431026, to design our novel spectral indices. We tested these spectral indices on 26 T5.5--T7.5 near-infrared SpeX/IRTF spectra, and we provided eight new mid- and late-T variable candidates. We estimated the variability fraction of our sample in $38^{+4}_{-30}$%, which agrees with the variability fractions provided by Metchev, et. al, (2015) for mid-to late-T dwarfs. In addition, two of the three previously known variables in our SpeX spectra sample are flagged as variable candidates by our indices. Similarly, all seven known non-variable in our sample are flagged as non-variable objects by our indices. These results suggest that our spectral indices might be used to find variable mid- and late-T brown dwarf variables. These indices may be crucial in the future to select cool directly-imaged exoplanets for variability studies., Comment: Accepted for publication in AJ. 17 pages, 12 figures, 3 tables

Only a handful of late-T brown dwarfs have been monitored for spectro-photometric variability, leaving incomplete the study of the atmospheric cloud structures of the coldest brown dwarfs, that share temperatures with some cold, directly-imaged exoplanets. 2MASSJ00501994-332240 is a T7.0 rapidly rotating, field brown dwarf that showed low-level photometric variability in data obtained with the Spitzer Space telescope. We monitored 2MASSJ00501994-332240 during ~2.6 hr with MOSFIRE, installed at the Keck I telescope, with the aim of constraining its near-infrared spectro-photometric variability. We measured fluctuations with a peak-to-peak amplitude of 1.48+\-0.75% in the J-band photometric light curve, an amplitude of 0.62+/-0.18% in the J-band spectro-photometric light curve, and an amplitude of 1.26+/-0.93% in the H-band light curve, and an amplitude of 5.33+/-2.02% in the CH_4-H_2O band light curve. Nevertheless, the Bayesian Information Criterion does not detect significant variability in any of the light curves. Thus, given the detection limitations due to the MOSFIRE sensitivity, we can only claim tentative low-level variability for 2M0050-3322 in the best-case scenario. The amplitudes of the peak-to-peak fluctuations measured for 2MASSJ00501994-332240 agree with the variability amplitude predictions of General Circulation Models for a T7.0 brown dwarf for an edge on object. Radiative-transfer models predict that the Na_2S and KCl clouds condense at pressures lower than that traced by the CH_4-H_2O band, which might explain the higher peak-to-peak fluctuations measured for this light curve. Finally, we provide a visual recreation of the map provided by General Circulation Models and the vertical structure of 2MASSJ00501994-332240 provided by radiative-transfer models., Comment: Accepted at AJ June 13 2022