Exploring the properties of exoplanets near or inside the radius valley provides insight on the transition from the rocky super-Earths to the larger, hydrogen-rich atmosphere mini-Neptunes. Here, we report the discovery of TOI-1452b, a transiting super-Earth (R_p = 1.67 ± 0.07 R_⊕) in an 11.1 day temperate orbit (T_eq = 326 ± 7 K) around the primary member (H = 10.0, T_eff = 3185 ± 50 K) of a nearby visual-binary M dwarf. The transits were first detected by the Transiting Exoplanet Survey Satellite, then successfully isolated between the two 32 companions with ground-based photometry from the Observatoire du Mont-Mégantic and MuSCAT3. The planetary nature of TOI-1452b was established through high-precision velocimetry with the near-infrared SPIRou spectropolarimeter as part of the ongoing SPIRou Legacy Survey. The measured planetary mass (4.8 ± 1.3 M_⊕) and inferred bulk density ( g cm⁻³) is suggestive of a rocky core surrounded by a volatile-rich envelope. More quantitatively, the mass and radius of TOI-1452b, combined with the stellar abundance of refractory elements (Fe, Mg, and Si) measured by SPIRou, is consistent with a core-mass fraction of 18% ± 6% and a water-mass fraction of %. The water world candidate TOI-1452b is a prime target for future atmospheric characterization with JWST, featuring a transmission spectroscopy metric similar to other well-known temperate small planets such as LHS 1140b and K2-18 b. The system is located near Webb's northern continuous viewing zone, implying that is can be followed at almost any moment of the year.

In the search for life beyond our solar system, attention should be focused on those planets that have the potential to maintain habitable conditions over the prolonged periods of time needed for the emergence and expansion of life as we know it. The observable planetary architecture is one of the determinants for long-term habitability as it controls the orbital evolution and ultimately the stellar fluxes received by the planet. With an ensemble of n-body simulations and obliquity models of hypothetical planetary systems, we demonstrate that the amplitude and period of the eccentricity, obliquity, and precession cycles of an Earth-like planet are sensitive to the orbital characteristics of a giant companion planet. A series of transient, ocean-coupled climate simulations show how these characteristics of astronomical cycles are decisive for the evolving surface conditions and long-term fractional habitability relative to the modern Earth. The habitability of Earth-like planets increases with the eccentricity of a Jupiter-like companion, provided that the mean obliquity is sufficiently low to maintain temperate temperatures over large parts of its surface throughout the orbital year. A giant companion closer in results in shorter eccentricity cycles of an Earth-like planet but longer, high-amplitude, obliquity cycles. The period and amplitude of obliquity cycles can be estimated to first order from the orbital pathways calculated by the n-body simulations. In the majority of simulations, the obliquity amplitude relates directly to the orbital inclination whereas the period of the obliquity cycle is a function of the nodal precession and the proximity of the giant companion.

We present 114 trigonometric parallaxes for 107 nearby white dwarf (WD) systems from both the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI) and the U. S. Naval Observatory Flagstaff Station (NOFS) parallax programs. Of these, 76 parallaxes for 69 systems were measured by the CTIOPI program and 38 parallaxes for as many systems were measured by the NOFS program. A total of 50 systems are confirmed to be within the 25-pc horizon of interest. Coupled with a spectroscopic confirmation of a common proper-motion companion to a Hipparcos star within 25 pc as well as confirmation parallax determinations for two WD systems included in the recently released Tycho Gaia Astrometric Solution catalog, we add 53 new systems to the 25-pc WD sample—a 42% increase. Our sample presented here includes four strong candidate halo systems, a new metal-rich DAZ WD, a confirmation of a recently discovered nearby short-period (P = 2.85 hr) double degenerate, a WD with a new astrometric perturbation (long period, unconstrained with our data), and a new triple system where the WD companion main-sequence star has an astrometric perturbation (P ∼ 1.6 year).

Because of the diversity of stellar masses and orbital sizes of binary systems and the complex interaction between star–star, star–planet, and planet–planet, it has been difficult to fully characterize the planetary systems associated with binary systems. Here, we report high-precision astrometric observations of the low-mass binary system GJ 896AB, revealing the presence of a Jupiter-like planetary companion (GJ 896Ab). The planetary companion is associated to the main star GJ 896A, with an estimated mass of 2.3 Jupiter masses and an orbit period of 284.4 days. A simultaneous analysis of the relative astrometric data obtained in the optical and infrared with several telescopes, and the absolute astrometric data obtained at radio wavelengths with the Very Long Baseline Array (VLBA), reveals, for the first time, the fully characterized three-dimensional (3D) orbital plane orientation of the binary system and the planetary companion. The planetary and binary orbits are found to be in a retrograde configuration and with a large mutual inclination angle (Φ = 148°) between both orbital planes. Characterizing the 3D orbital architecture of binary systems with planets is important in the context of planet formation, as it could reveal whether the systems were formed by disk fragmentation or turbulence fragmentation, as well as the origin of spin–orbit misalignment. Furthermore, as most stars are in binary or multiple systems, our understanding of systems such as this one will help to further understand the phenomenon of planetary formation in general.

Recent analyses have shown that distant orbits within the scattered disk population of the Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion. While several hypotheses have been put forward to explain this alignment, to date, a theoretical model that can successfully account for the observations remains elusive. In this work we show that the orbits of distant Kuiper Belt objects (KBOs) cluster not only in argument of perihelion, but also in physical space. We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin. We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass ≳10 m_⊕ whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180° away from the perihelia of the minor bodies. In addition to accounting for the observed orbital alignment, the existence of such a planet naturally explains the presence of high-perihelion Sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60° and 150° whose origin was previously unclear. Continued analysis of both distant and highly inclined outer solar system objects provides the opportunity for testing our hypothesis as well as further constraining the orbital elements and mass of the distant planet.

The planetary and lunar ephemerides called DE440 and DE441 have been generated by fitting numerically integrated orbits to ground-based and space-based observations. Compared to the previous general-purpose ephemerides DE430, seven years of new data have been added to compute DE440 and DE441, with improved dynamical models and data calibration. The orbit of Jupiter has improved substantially by fitting to the Juno radio range and Very Long Baseline Array (VLBA) data of the Juno spacecraft. The orbit of Saturn has been improved by radio range and VLBA data of the Cassini spacecraft, with improved estimation of the spacecraft orbit. The orbit of Pluto has been improved from use of stellar occultation data reduced against the Gaia star catalog. The ephemerides DE440 and DE441 are fit to the same data set, but DE441 assumes no damping between the lunar liquid core and the solid mantle, which avoids a divergence when integrated backward in time. Therefore, DE441 is less accurate than DE440 for the current century, but covers a much longer duration of years −13,200 to +17,191, compared to DE440 covering years 1550–2650.

We present the occurrence rates for rocky planets in the habitable zones (HZs) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. We define η_⊕ as the HZ occurrence of planets with radii between 0.5 and 1.5 R_⊕ orbiting stars with effective temperatures between 4800 and 6300 K. We find that η_⊕ for the conservative HZ is between (errors reflect 68% credible intervals) and planets per star, while the optimistic HZ occurrence is between and planets per star. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We find similar occurrence rates between using Poisson likelihood Bayesian analysis and using Approximate Bayesian Computation. Our results are corrected for catalog completeness and reliability. Both completeness and the planet occurrence rate are dependent on stellar effective temperature. We also present occurrence rates for various stellar populations and planet size ranges. We estimate with 95% confidence that, on average, the nearest HZ planet around G and K dwarfs is ∼6 pc away and there are ∼4 HZ rocky planets around G and K dwarfs within 10 pc of the Sun.

The radius valley, a bifurcation in the size distribution of small, close-in exoplanets, is hypothesized to be a signature of planetary atmospheric loss. Such an evolutionary phenomenon should depend on the age of the star–planet system. In this work, we study the temporal evolution of the radius valley using two independent determinations of host star ages among the California–Kepler Survey (CKS) sample. We find evidence for a wide and nearly empty void of planets in the period–radius diagram at the youngest system ages (≲2–3 Gyr) represented in the CKS sample. We show that the orbital period dependence of the radius valley among the younger CKS planets is consistent with that found among those planets with asteroseismically determined host star radii. Relative to previous studies of preferentially older planets, the radius valley determined among the younger planetary sample is shifted to smaller radii. This result is compatible with an atmospheric loss timescale on the order of gigayears for progenitors of the largest observed super-Earths. In support of this interpretation, we show that the planet sizes that appear to be unrepresented at ages ≲2–3 Gyr are likely to correspond to planets with rocky compositions. Our results suggest that the size distribution of close-in exoplanets and the precise location of the radius valley evolve over gigayears.

We investigate the origins of the photometrically very red (VR) and less red (LR) trans-Neptunian objects (TNOs). We first reanalyze the data set of Marsset et al. and find that in addition to the known color–inclination correlation in hot TNOs, a similar trend exists for color–eccentricity. We show that VR TNOs are sharply constrained to eccentricities <0.42 and inclinations <21°, leading to a paucity of VR scattered disk and distant mean motion resonance objects. We then interpret these findings using N-body simulations accounting for Neptune's outward migration into a massless particles disk and find that these observations are best reproduced with an LR-to-VR color transition line between ∼38 and 42 au in the primordial disk, separating the objects' formation locations. For an initial surface density profile (Σ ∝ 1/r²), a color transition around 38 au is needed to explain the high abundance of VR plutinos, but it creates too many VR scattered disk objects, while a transition line around 42 au seems to better reproduce the scattered disk colors but creates virtually no VR plutinos. Our simulations furthermore show that the rarity of VR particles at high eccentricity is possibly due to the absence of sweeping higher-order MMRs, and secular resonances, beyond 42 au. Inspecting individual populations, we show that the majority of VR SDOs originate as objects trapped in Neptune's second- and third-order MMRs. These then evolve due to diffusion, scattering, Kozai–Lidov cycles, and secular resonances into their current orbits. Future unbiased color surveys are crucial to better constrain the TNOs dynamical origins.

We present spectral and photometric observations of 10 Type Ia supernovae (SNe Ia) in the redshift range 0.16 ≤ z ≤ 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High-z Supernova Search Team and recent results by Riess et al., this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmological parameters: the Hubble constant (H₀), the mass density (Ω_M), the cosmological constant (i.e., the vacuum energy density, Ω_Λ), the deceleration parameter (q₀), and the dynamical age of the universe (t₀). The distances of the high-redshift SNe Ia are, on average, 10%–15% farther than expected in a low mass density (Ω_M = 0.2) universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., Ω_Λ > 0) and a current acceleration of the expansion (i.e., q₀ < 0). With no prior constraint on mass density other than Ω_M ≥ 0, the spectroscopically confirmed SNe Ia are statistically consistent with q₀ < 0 at the 2.8 σ and 3.9 σ confidence levels, and with Ω_Λ > 0 at the 3.0 σ and 4.0 σ confidence levels, for two different fitting methods, respectively. Fixing a "minimal" mass density, Ω_M = 0.2, results in the weakest detection, Ω_Λ > 0 at the 3.0 σ confidence level from one of the two methods. For a flat universe prior (Ω_M + Ω_Λ = 1), the spectroscopically confirmed SNe Ia require Ω_Λ > 0 at 7 σ and 9 σ formal statistical significance for the two different fitting methods. A universe closed by ordinary matter (i.e., Ω_M = 1) is formally ruled out at the 7 σ to 8 σ confidence level for the two different fitting methods. We estimate the dynamical age of the universe to be 14.2 ± 1.7 Gyr including systematic uncertainties in the current Cepheid distance scale. We estimate the likely effect of several sources of systematic error, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination. Presently, none of these effects appear to reconcile the data with Ω_Λ = 0 and q₀ ≥ 0.

We present a new pipeline developed to detect and characterize faint astronomical companions at small angular separation from the host star using sets of wide-field imaging observations not specifically designed for high-contrast imaging analysis. The core of the pipeline relies on Karhunen–Loéve truncated transformation of the reference point-spread function (PSF) library to perform PSF subtraction and identify candidates. Tests of reliability of detections and characterization of companions are made through simulation of binaries and generation of receiver operating characteristic curves for false-positive/true-positive analysis. The algorithm has been successfully tested on large HST/ACS and WFC3 data sets acquired for two HST Treasury Programs on the Orion Nebula Cluster. Based on these extensive numerical experiments we find that, despite being based on methods designed for observations of a single star at a time, our pipeline performs very well on mosaic space-based data. In fact, we are able to detect brown-dwarf-mass companions almost down to the planetary-mass limit. The pipeline is able to reliably detect signals at separations as close as ≳01 with a completeness of ≳10%, or ∼02 with a completeness of ∼30%. This approach can potentially be applied to a wide variety of space-based imaging surveys, from data in the existing HST archive to near-future JWST mosaics and future wide-field Roman images.

For a sample of 4378 nearby spiral and S0 galaxies, Yu & Ho used Fourier analysis of Sloan Digital Sky Survey images to show that the strengths of the spiral arms and the pitch angles of the arms are inversely correlated with central concentration. In the current study, we search for trends in the Yu & Ho spiral arm parameters with environment and specific star formation rate (sSFR). When comparing galaxies with similar concentrations, we do not find a significant difference in the arm strengths or pitch angles of spiral galaxies in clusters compared to field galaxies. When differences in concentration are taken into account, we also find no significant difference in the parameter f3 for cluster spirals compared to field spirals, where f3 is the normalized m = 3 Fourier amplitude. When concentration is held fixed, both arm strength and pitch angle are correlated with sSFR, but f3 is not. These relations support the suggestion by Davis et al. of a "fundamental plane" of spiral structure involving pitch angle, bulge stellar mass, and gas surface density. We discuss these results in terms of theories of spiral arm production and quenching in galaxies. To aid comparison with earlier studies based on Galaxy Zoo, we explore how the Yu & Ho parameters relate to similar parameters measured by Galaxy Zoo (i.e., f3 versus the number of arms, pitch angle versus winding parameter, and concentration versus bulge class).

Classical supersoft X-ray sources (SSSs) are understood as close binary systems in which a massive white dwarf accretes from its companion at rates sustaining steady hydrogen burning on its surface generating bolometric luminosities of 10³⁶–2 × 10³⁸ erg s⁻¹. Here, we perform for the first time the global supersoft X-rays to near-infrared (NIR) spectral energy distribution (SED) for the brightest SSSs in the Large Magellanic Cloud and Small Magellanic Cloud. We test a model in which the ultraviolet–NIR is dominated by emission from a compact (unresolved) circumstellar nebula represented by the ionized gas outflowing from the SSS. The SED models correspond to luminosities of SSSs of a few times 10³⁸–10³⁹ erg s⁻¹, radiating at blackbody temperatures of ≈3 × 10⁵ K, and indicate a nebular continuum, whose emission measure of ≳2 × 10⁶⁰ cm⁻³ corresponds to a wind mass loss at rates ≳2 × 10⁻⁶ M_⊙ yr⁻¹. Such extreme parameters suggest that the brightest SSSs could be unidentified optical novae in a post-nova SSS state sustained at a high long-lasting luminosity by resumed accretion, possibly at super-Eddington rates. New observations and theoretical multiwavelength modeling of the global SED of SSSs are needed to reliably determine their parameters, and thus understand their proper stage in stellar evolution.

Planetary systems with mean-motion resonances hold special value in terms of their dynamical complexity and their capacity to constrain planet formation and migration histories. The key toward making these connections, however, is to have a reliable characterization of the resonant dynamics, especially the so-called "libration amplitude," which qualitatively measures how deep the system is into the resonance. In this work, we identify an important complication with the interpretation of libration amplitude estimates from observational data of resonant systems. Specifically, we show that measurement noise causes inferences of the libration amplitude to be systematically biased to larger values, with noisier data yielding a larger bias. We demonstrated this through multiple approaches, including using dynamical fits of synthetic radial velocity data to explore how the libration amplitude distribution inferred from the posterior parameter distribution varies with the degree of measurement noise. We find that even modest levels of noise still result in a slight bias. The origin of the bias stems from the topology of the resonant phase space and the fact that the available phase-space volume increases nonuniformly with increasing libration amplitude. We highlight strategies for mitigating the bias through the usage of particular priors. Our results imply that many known resonant systems are likely deeper in resonance than previously appreciated.

The atmospheres of gas giant planets are thought to be inhomogeneous due to weather and patchy clouds. We present two full nights of coronagraphic observations of the HR 8799 planets using the CHARIS integral field spectrograph behind the SCExAO adaptive optics system on the Subaru Telescope to search for spectrophomometric variability. We did not detect significant variability signals, but placed the lowest variability upper limits for HR 8799c and d. Based on injection-recovery tests, we expected to have a 50% chance to detect signals down to 10% H-band photometric variability for HR 8799c and down to 30% H-band variability for HR 8799d. We also investigated spectral variability and expected a 50% chance to recover 20% variability in the H/K flux ratio for HR 8799c. We combined all the data from the two nights to obtain some of the most precise spectra obtained for HR 8799c, d, and e. Using a grid of cloudy radiative–convective–thermochemical equilibrium models, we found all three planets prefer supersolar metallicity with effective temperatures of ∼1100 K. However, our high signal-to-noise spectra show that HR 8799d has a distinct spectrum from HR 8799c, possibly preferring more vertically extended and uniform clouds and indicating that the planets are not identical.

We present a new pipeline developed to detect and characterize faint astronomical companions at small angular separation from the host star using sets of wide-field imaging observations not specifically designed for high-contrast imaging analysis. The core of the pipeline relies on Karhunen–Loéve truncated transformation of the reference point-spread function (PSF) library to perform PSF subtraction and identify candidates. Tests of reliability of detections and characterization of companions are made through simulation of binaries and generation of receiver operating characteristic curves for false-positive/true-positive analysis. The algorithm has been successfully tested on large HST/ACS and WFC3 data sets acquired for two HST Treasury Programs on the Orion Nebula Cluster. Based on these extensive numerical experiments we find that, despite being based on methods designed for observations of a single star at a time, our pipeline performs very well on mosaic space-based data. In fact, we are able to detect brown-dwarf-mass companions almost down to the planetary-mass limit. The pipeline is able to reliably detect signals at separations as close as ≳01 with a completeness of ≳10%, or ∼02 with a completeness of ∼30%. This approach can potentially be applied to a wide variety of space-based imaging surveys, from data in the existing HST archive to near-future JWST mosaics and future wide-field Roman images.

For a sample of 4378 nearby spiral and S0 galaxies, Yu & Ho used Fourier analysis of Sloan Digital Sky Survey images to show that the strengths of the spiral arms and the pitch angles of the arms are inversely correlated with central concentration. In the current study, we search for trends in the Yu & Ho spiral arm parameters with environment and specific star formation rate (sSFR). When comparing galaxies with similar concentrations, we do not find a significant difference in the arm strengths or pitch angles of spiral galaxies in clusters compared to field galaxies. When differences in concentration are taken into account, we also find no significant difference in the parameter f3 for cluster spirals compared to field spirals, where f3 is the normalized m = 3 Fourier amplitude. When concentration is held fixed, both arm strength and pitch angle are correlated with sSFR, but f3 is not. These relations support the suggestion by Davis et al. of a "fundamental plane" of spiral structure involving pitch angle, bulge stellar mass, and gas surface density. We discuss these results in terms of theories of spiral arm production and quenching in galaxies. To aid comparison with earlier studies based on Galaxy Zoo, we explore how the Yu & Ho parameters relate to similar parameters measured by Galaxy Zoo (i.e., f3 versus the number of arms, pitch angle versus winding parameter, and concentration versus bulge class).

Classical supersoft X-ray sources (SSSs) are understood as close binary systems in which a massive white dwarf accretes from its companion at rates sustaining steady hydrogen burning on its surface generating bolometric luminosities of 10³⁶–2 × 10³⁸ erg s⁻¹. Here, we perform for the first time the global supersoft X-rays to near-infrared (NIR) spectral energy distribution (SED) for the brightest SSSs in the Large Magellanic Cloud and Small Magellanic Cloud. We test a model in which the ultraviolet–NIR is dominated by emission from a compact (unresolved) circumstellar nebula represented by the ionized gas outflowing from the SSS. The SED models correspond to luminosities of SSSs of a few times 10³⁸–10³⁹ erg s⁻¹, radiating at blackbody temperatures of ≈3 × 10⁵ K, and indicate a nebular continuum, whose emission measure of ≳2 × 10⁶⁰ cm⁻³ corresponds to a wind mass loss at rates ≳2 × 10⁻⁶ M_⊙ yr⁻¹. Such extreme parameters suggest that the brightest SSSs could be unidentified optical novae in a post-nova SSS state sustained at a high long-lasting luminosity by resumed accretion, possibly at super-Eddington rates. New observations and theoretical multiwavelength modeling of the global SED of SSSs are needed to reliably determine their parameters, and thus understand their proper stage in stellar evolution.

Planetary systems with mean-motion resonances hold special value in terms of their dynamical complexity and their capacity to constrain planet formation and migration histories. The key toward making these connections, however, is to have a reliable characterization of the resonant dynamics, especially the so-called "libration amplitude," which qualitatively measures how deep the system is into the resonance. In this work, we identify an important complication with the interpretation of libration amplitude estimates from observational data of resonant systems. Specifically, we show that measurement noise causes inferences of the libration amplitude to be systematically biased to larger values, with noisier data yielding a larger bias. We demonstrated this through multiple approaches, including using dynamical fits of synthetic radial velocity data to explore how the libration amplitude distribution inferred from the posterior parameter distribution varies with the degree of measurement noise. We find that even modest levels of noise still result in a slight bias. The origin of the bias stems from the topology of the resonant phase space and the fact that the available phase-space volume increases nonuniformly with increasing libration amplitude. We highlight strategies for mitigating the bias through the usage of particular priors. Our results imply that many known resonant systems are likely deeper in resonance than previously appreciated.

The atmospheres of gas giant planets are thought to be inhomogeneous due to weather and patchy clouds. We present two full nights of coronagraphic observations of the HR 8799 planets using the CHARIS integral field spectrograph behind the SCExAO adaptive optics system on the Subaru Telescope to search for spectrophomometric variability. We did not detect significant variability signals, but placed the lowest variability upper limits for HR 8799c and d. Based on injection-recovery tests, we expected to have a 50% chance to detect signals down to 10% H-band photometric variability for HR 8799c and down to 30% H-band variability for HR 8799d. We also investigated spectral variability and expected a 50% chance to recover 20% variability in the H/K flux ratio for HR 8799c. We combined all the data from the two nights to obtain some of the most precise spectra obtained for HR 8799c, d, and e. Using a grid of cloudy radiative–convective–thermochemical equilibrium models, we found all three planets prefer supersolar metallicity with effective temperatures of ∼1100 K. However, our high signal-to-noise spectra show that HR 8799d has a distinct spectrum from HR 8799c, possibly preferring more vertically extended and uniform clouds and indicating that the planets are not identical.

Studies of resolved stellar populations in the Milky Way and nearby galaxies reveal an amazingly detailed and clear picture of galaxy evolution. Within the Local Group, the ability to probe the stellar populations of small and large galaxies opens up the possibility of exploring key questions such as the nature of dark matter, the detailed formation history of different galaxy components, and the role of accretion in galactic formation. Upcoming wide-field surveys promise to extend this ability to all galaxies within 10 Mpc, drastically increasing our capability to decipher galaxy evolution and enabling statistical studies of galaxies' stellar populations. To facilitate the optimum use of these upcoming capabilities, we develop a simple formalism to predict the density of resolved stars for an observation of a stellar population at fixed surface brightness and population parameters. We provide an interface to calculate all quantities of interest to this formalism via a public release of the code walter. This code enables calculation of (i) the expected number density of detected stars; (ii) the exposure time needed to reach certain population features, such as the horizontal branch; and (iii) an estimate of the crowding limit, among other features. We provide a limited test of the code and formalism of the paper against existing resolved star observations. These calculations will be very useful for planning surveys with NASA's upcoming Nancy Grace Roman Space Telescope (Roman, formerly WFIRST), which we use for example calculations throughout this work.

We give an overview and describe the rationale, methods, and testing of the Hubble Space Telescope (HST) Archival Legacy project "SKYSURF." SKYSURF uses HST's unique capability as an absolute photometer to measure the ∼0.2–1.7 μm sky-surface brightness (sky-SB) from 249,861 WFPC2, ACS, and WFC3 exposures in ∼1400 independent HST fields. SKYSURF's panchromatic data set is designed to constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light (ZL), Kuiper Belt Objects (KBOs), Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic Background Light (EBL). We outline SKYSURF's methods to: (1) measure sky-SB levels between detected objects; (2) measure the discrete EBL, most of which comes from AB≃17–22 mag galaxies; and (3) estimate how much truly diffuse light may exist. Simulations of HST WFC3/IR images with known sky values and gradients, realistic cosmic ray (CR) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the "Lowest Estimated Sky-SB" (LES) in each image between the discrete objects. The best algorithms recover the LES values within 0.2% when there are no image gradients, and within 0.2%–0.4% when there are 5%–10% gradients. We provide a proof of concept of our methods from the WFC3/IR F125W images, where any residual diffuse light that HST sees in excess of zodiacal model predictions does not depend on the total object flux that each image contains. This enables us to present our first SKYSURF results on diffuse light in Carleton et al.

Ultrahot Jupiters are ideal candidates to explore with high-resolution emission spectra. Detailed theoretical studies are necessary to investigate the range of spectra that we can expect to see from these objects throughout their orbit, because of the extreme temperature and chemical longitudinal gradients that exist across their dayside and nightside regions. Using previously published 3D general circulation models of WASP-76b with different treatments of magnetic drag, we postprocess the 3D atmospheres to generate high-resolution emission spectra for two wavelength ranges, throughout the planet's orbit. We find that the high-resolution emission spectra vary strongly as a function of phase, at times showing emission features, absorption features, or both, which are a direct result of the 3D structure of the planet. At phases exhibiting both emission and absorption features, the Doppler shift differs in direction between the two spectral features, making them differentiable, instead of canceling each other out. Through the use of cross correlation, we find different patterns in net Doppler shift for models with different treatments of drag: the nightside spectra show opposite signs in their Doppler shift, while the dayside phases display a reversal in the trend of net shift with phase. Finally, we caution researchers against using a single spectral template throughout the planet's orbit; this can bias the corresponding net Doppler shift returned, as it can pick up on a bright region on the edge of the planet disk that is highly redshifted or blueshifted.

Prospects for expanding the available mass measurements of the Kepler sample are limited. Planet masses have typically been inferred via radial velocity (RV) measurements of the host star or time-series modeling of transit timing variations (TTVs) in multiplanet systems; however, the majority of Kepler hosts are too dim for RV follow-up, and only a select number of systems have strong enough TTVs for time-series modeling. Here, we develop a method of constraining planet mass in multiplanet systems using low signal-to-noise ratio (S/N) TTVs. For a sample of 175 planets in 79 multiplanet systems from the California-Kepler Survey, we infer posteriors on planet mass using publicly available TTV time series from Kepler. For 53 planets (>30% of our sample), low-S/N TTVs yield informative upper bounds on planet mass, i.e., the mass constraint strongly deviates from the prior on mass and yields a physically reasonable bulk composition. For 25 small planets, low-S/N TTVs favor volatile-rich compositions. Where available, low-S/N TTV-based mass constraints are consistent with RV-derived masses. TTV time series are publicly available for each Kepler planet, and the compactness of Kepler systems makes TTV-based constraints informative for a substantial fraction of multiplanet systems. Leveraging low-S/N TTVs offers a valuable path toward increasing the available mass constraints of the Kepler sample.

Identifying rocky planets in or near the habitable zones of their stars (near-Earth analogs) is one of the key motivations of many past and present planet-search missions. The census of near-Earth analogs is important because it informs calculations of the occurrence rate of Earth-like planets, which in turn feed into calculations of the yield of future missions to directly image other Earths. Only a small number of potential near-Earth analogs have been identified, meaning that each planet should be vetted carefully and then incorporated into the occurrence rate calculation. A number of putative near-Earth analogs have been identified within binary-star systems. However, stellar multiplicity can bias measured planetary properties, meaning that apparent near-Earth analogs in close binaries may have different radii or instellations than initially measured. We simultaneously fit unresolved optical spectroscopy, optical speckle and near-IR adaptive optics contrasts, and unresolved photometry and retrieved revised stellar temperatures and radii for a sample of 11 binary Kepler targets that host at least one near-Earth-analog planet, for a total of 17 planet candidates. We found that 10 of the 17 planets in our sample had radii that fell in or above the radius gap, suggesting that they are not rocky planets. Only two planets retained super-Earth radii and stayed in the habitable zone, making them good candidates for inclusion in rocky-planet occurrence rate calculations.