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  • On the Information Content of Ariel Transmission Spectra: Reassessing the Tier System
    The European Space Agency’s Ariel mission will conduct a survey of the atmospheric properties of exoplanets around bright stars. The mission is nominally divided into three tiers. The Tier 1 survey will consist of low-precision observations of ∼1000 planets, with a subset of these included in the higher-precision Tier 2 survey expected to be necessary for atmospheric characterization. Tier 3 will be repeated observations of a small number of benchmark planets. Though previous studies have assessed the ability of Ariel to uncover population-level trends, they have generally presupposed a given tier. Here we interrogate this assumption and assess the information content of Ariel transmission spectra as a function of tier for three benchmark planets: a hot-Saturn, warm-Neptune, and temperate sub-Neptune. We simulate a grid of Ariel transit spectra at different Tiers for each target and use retrievals to assess which chemical species are well constrained. We find that for giant planets like a hot-Saturn or warm-Neptune, Tier 1 quality observations are sufficient for ≲1.5 dex constraints on H2O and CO2, even in the presence of grey clouds—meaning important chemical insights are already obtainable in the Tier 1 survey. Moving to Tiers 2 and 3 results in an incremental increase in precision as well as other molecules becoming constrainable in certain scenarios (e.g., H2S, CO). Tier 1 observations are also sufficient to identify CH4 in a temperate sub-Neptune, whereas observations with at least Tier 2 precision are necessary for CO2. The number of transits necessary to reach this observational S/N, however, may be prohibitive for the inclusion of temperate sub-Neptunes in even the Tier 1 survey.

  • BS Cassiopeiae: A Contact Binary with Starspot-driven Variability and Evidence for Additional Components
    We present a comprehensive photometric and spectroscopic analysis of the contact eclipsing binary BS Cas, based on 22 yr multisite light curves and 2 yr high-resolution spectra. The long-term photometry shows pronounced year-to-year changes in the light-curve shape, including eclipse-depth reversals between the primary and secondary minima and variations in the O’Connell effect. The first double-lined radial-velocity (RV) curves of BS Cas are derived from the spectra using broadening-function (BF) profiles. Sharp peaks absent from the 2018 BFs appear in the 2020 BFs, suggesting an additional component along the same line of sight as BS Cas. Simultaneous modeling of the BVR light curves and the RVs shows that BS Cas is a contact binary in which the more massive component is cooler than its less massive companion, with a mass ratio of 2.515 and a fill-out factor of 32.3%. Multiepoch modeling suggests that the long-term photometric variations arise from evolving starspots and changes in the third-light contribution. The eclipse-timing variation diagram confirms a secular orbital period decrease at a rate of −2.305 × 10−7 days yr−1 consistent with angular momentum loss and mass transfer, along with an 18.376 yr modulation interpreted as a light-travel-time effect from a third body. The TESS timings reveal anticorrelated variations between the primary and secondary minima that appear to result from differential rotation of high-latitude starspots. These results suggest that BS Cas is a physically complex contact binary in which long-term photometric and eclipse-timing variations reflect multiple processes, including magnetic activity and the influence of a third body.

  • Increasing Sensitivity to Trailed Solar System Objects in Archival JWST NIRCam Imaging with Group Differencing
    The JWST archive contains thousands of NIRCam exposures distributed across the sky. Small solar system bodies (SSSBs) are present in many of these fields, but are often trailed and more difficult to detect. The standard pipeline produces a single image by fitting a slope to a sequence of N cumulative “up-the-ramp” groups of the detector. Thus, each JWST image comprises a time series of cumulative reads. We demonstrate that transforming the ramp into a series of group difference images reduces the per-image trail length of moving sources, producing an (N − 1)-group photometrically calibrated time series from an N-group integration. This enables higher-cadence trajectory-based searches using as few as a single JWST exposure. A generalized least-squares fit of the group difference images along the trajectory of a moving source recovers the source flux at higher signal-to-noise ratio (SNR) when compared to the ramp fit, with the improvement scaling with the reduction in trailing. We validate our procedure on 13 moving objects detected in archival JWST NIRCam images. To estimate our increase in sensitivity, we perform an injection/recovery simulation on the JWST imagery. Trailed moving objects recovered via group differencing show higher SNRs, improving completeness to moving sources compared to standard calibrations. For typical integration lengths of N = 4 or 6 for archival JWST/NIRCam exposures in the ecliptic, group differencing yields gains in sensitivity between ∼1.1 and 1.4 mag, based on simulation results. This method significantly increases the sensitivity of archival JWST surveys to trailed SSSBs.

  • Shortest Period for Outer Orbit in Compact Hierarchical Triple? Discovery of SB1 Around V 885 Per
    I present a discovery of SB1 in the LAMOST-MRS spectra of eclipsing contact binary V 885 Per. Spectroscopic orbit has period only P = 21.8 days, which will make it shortest known outer period in compact hierarchical triple system, if this SB1 is indeed bound to the inner system. Unfortunately quality of available spectra do not allow to give definitive answer to this question, with other orbital hierarchy like 2+2 is also possible. Analysis of the eclipse timing variations showed a gradual increase in the orbital period of the inner eclipsing pair, as well as long-term changes that can be explained either by the light time travel effect due to an additional component or by magnetic activity.

  • JWST Observations of Starbursts: The Motion of Dust—PAH Kinematics of M82 and NGC 253 with JWST/MIRI Spectroscopy
    We present an analysis of dust kinematics in the local starburst galaxies M82 (NGC 3034) and NGC 253 using polycyclic aromatic hydrocarbon (PAH) features observed with JWST/MIRI spectroscopy. We are able to produce high-quality velocity maps of the 5.2, 6.2, and 11.3 μm PAH features, as well as numerous lines of molecular gas via H2 rotational transitions and ionized gas from [Ne ii] and H recombination lines. Given the field of view and inclination, we trace a rotating disk in M82 where we observe a steep rise in the velocities followed by flattening, typical of galaxy rotation curves. In NGC 253, however, the 6.2 and 11.3 μm PAH features trace the launching region of the outflow, firmly within the starburst region. We find the ionized gas also shows outflow contributions in NGC 253 while the warm molecular gas is dominated by rotation. Additionally, the molecular gas outflow velocities are lower than the ionized gas, with the 11.3 μm PAH feature consistent with the ionized gas rather than the molecular gas. We therefore suggest that PAHs are more closely associated with the ionized gas rather than the molecular at the base of the galaxy outflow, whereas larger-scale imaging shows comparable morphology between PAHs and H I. The 6.2 μm PAH feature has an even higher outflow velocity for both galaxies, possibly suggesting preferential ionization of the PAHs within the faster-moving hot phase of the base of the outflow.