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The alkali metal sodium (Na) is one of the most commonly detected chemical species in the upper atmospheres of giant exoplanets. In this work we conducted a homogeneous survey of Na in a diverse sample of ten highly irradiated giant exoplanets using high-resolution transmission spectroscopy. Our sample includes nine planets with previous Na detections and one new detection. We confirm previous detections and assess multiple approaches for deriving Na line properties from high-resolution transmission spectra. The homogeneously measured sodium line depths were used to constrain the atmospheric heights ($H_{\text{Na}}$) with respect to the planetary radii ($R_{\text{p}}$). We assess an empirical trend describing the relative atmospheric height ($H_{\text{Na}}/R_{\text{p}}$) as a function of planetary equilibrium temperature ($T_{\text{eq}}$) and surface gravity ($g$), in which $H_{\text{Na}}/R_{\text{p}}$ decreases exponentially with $\xi \propto gT_{\text{eq}}$, approaching a constant at large $\xi$. We also report the sodium D2/D1 line ratios across our sample and find that seven targets have line ratios that are consistent with unity. Finally, we measured net blueshifted offsets of the sodium absorption lines from their rest frame wavelengths for all ten planets, corresponding to day-night wind velocities of a few km s$^{-1}$. This suggests that the broad sample of exoplanets share common underlying processes that govern atmospheric dynamics. Our study highlights a promising avenue for using high-resolution transmission spectroscopy to further our understanding of how atmospheric characteristics vary over a diverse sample of exoplanets.

Irradiated Jovian atmospheres are complex, dynamic, and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been catalogued to date, KELT-9b is the hottest Gas Giant known, with an equilibrium temperature of 4050 K. We probe the temporal variability of transmission spectroscopic signatures from KELT-9b via a set of archival multi-year ground-based transit observations, performed with the TRES facility on the 1.5 m reflector at the Fred Lawrence Whipple Observatory. Our observations confirm past detections of Fe I, Fe II and Mg I over multiple epochs, in addition to excess absorption at H-alpha, which is an indicator for ongoing mass-loss. From our multi-year dataset, the H-alpha light curve consistently deviates from a standard transit, and follows a 'W' shape that is deeper near ingress and egress, and shallower mid-transit. To search for and quantify any seasonal variations that may be present, we parameterise a 'cometary tail' model to fit for the H-alpha transit. We find no detectable variations between the different observed epochs. Though a 'cometary tail' describes the H-alpha flux variations well, we note that such a scenario requires a high density of neutral hydrogen in the n = 2 excited state far beyond the planetary atmosphere. Other scenarios, such as centre-to-limb variations larger than that expected from 1-D atmosphere models, may also contribute to the observed H-alpha transit shape. These multi-epoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres., 19 pages, 11 figures, accepted for publication in AJ

A planet's orbital alignment places important constraints on how a planet formed and consequently evolved. The dominant formation pathway of ultra-short period planets ($P, Comment: 12 pages, 4 figures, published in Nature Astronomy

The discoveries of two Interstellar Objects (ISOs) in recent years has generated significant interest in constraining their physical properties and the mechanisms behind their formation. However, their ephemeral passages through our Solar System permitted only incomplete characterization. We investigate avenues for identifying craters that may have been produced by ISOs impacting terrestrial Solar System bodies, with particular attention towards the Moon. A distinctive feature of ISOs is their relatively high encounter velocity compared to asteroids and comets. Local stellar kinematics indicate that terrestrial Solar System bodies should have experienced of order unity ISO impacts exceeding 100 km/s. By running hydrodynamical simulations for projectiles of different masses and impact velocities, up to 100 km/s, we show how late-stage equivalence dictates that transient crater dimensions are alone insufficient for inferring the projectile's velocity. On the other hand, the melt volume within craters of a fixed diameter may be a potential route for identifying ISO craters, as faster impacts produce more melt. This method requires that the melt volume scales with the energy of the projectile, while crater diameter scales with the point-source limit (sub-energy). Given that there are probably only a few ISO craters in the Solar System at best, and that transient crater dimensions are not a distinguishing feature for impact velocities at least up to 100 km/s, identification of an ISO crater proves a challenging task. Melt volume and high-pressure petrology may be diagnostic features once large volumes of material can be analyzed in situ., Comment: 23 Pages, 7 Figures, Published in PSJ

Ongoing, extreme-precision Doppler radial velocity surveys seek planets with masses less than several M$_\oplus$; population-level studies to determine the distribution of planetary masses, however, remain difficult due to the required observational time investment, as well as challenges associated with robustly detecting the lowest mass planets. We outline a novel approach that leverages extensive, existing RV datasets to constrain masses of exoplanet populations: stacking periodograms of RV timeseries across many targets. We show that an exoplanet population may be statistically identifiable in the stacked periodogram, even when individual planets do not pass the threshold of detection. We discuss analytical, statistical properties of the stacked periodogram, perform simulations to demonstrate the efficacy of the method, and investigate the influence of semi-structured window functions and stellar activity. Analysis of the Lick-Carnegie Exoplanet Survey data set reveals a marginally significant ($1.6\sigma$) signal consistent with a population of exoplanets occupying $3-7$ day periods with typical $K$ between $1.6-5.1$ m s$^{-1}$. More detailed investigation of signals associated with stellar activity and yearly systematics may be necessary to confirm this result or detect other underlying Keplerian contributions., Comment: 13 pages, 6 figures, accepted to AJ

The distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes $\lesssim 10$ cm s$^{-1}$, but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host $\epsilon$ Eridani, we separately use ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produce an activity model, which reduces the rms scatter in RVs obtained with EXPRES from 4.72 m s$^{-1}$ to 1.98 m s$^{-1}$. We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as the stellar inclination and orientation with respect to its debris disk to be definitely determined. This work shows that stellar surface maps obtained with high cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter., Comment: 24 pages, 12 figures, 5 tables, accepted for publication in AJ