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The tip of the red giant branch (TRGB) based distance method in the I band is one of the most efficient and precise techniques for measuring distances to nearby galaxies (D ≲ 15 Mpc). The TRGB in the near-infrared (NIR) is 1–2 mag brighter relative to the I band, and has the potential to expand the range over which distance measurements to nearby galaxies are feasible. Using Hubble Space Telescope (HST) imaging of 12 fields in eight nearby galaxies, we determine color-based corrections and zero-points of the TRGB in the Wide Field Camera 3 IR (WFC3/IR) F110W and F160W filters. First, we measure TRGB distances in the I band equivalent Advanced Camera System (ACS) F814W filter from resolved stellar populations with the HST. The TRGB in the ACS F814W filter is used for our distance anchor and to place the WFC3/IR magnitudes on an absolute scale. We then determine the color dependence (a proxy for metallicity/age) and zero-point of the NIR TRGB from photometry of WFC3/IR fields that overlap with the ACS fields. The new calibration is accurate to ∼1% in distance relative to the F814W TRGB. Validating the accuracy of the calibrations, we find that the distance modulus for each field using the NIR TRGB calibration agrees with the distance modulus of the same field as determined from the F814W TRGB. This is a JWST preparatory program, and the work done here will directly inform our approach to calibrating the TRGB in JWST NIRCam and NIRISS photometric filters. [ABSTRACT FROM AUTHOR]

We present the first large‐scale statistical survey of the Jovian main emission (ME) to map auroral properties from their ionospheric locations out into the equatorial plane of the magnetosphere, where they are compared directly to in‐situ spacecraft measurements. We use magnetosphere‐ionosphere (MI) coupling theory to calculate currents from the auroral brightness as measured with the Hubble Space Telescope and from plasma flow speeds measured in‐situ with the Galileo spacecraft. The effective Pedersen conductance of the ionosphere ΣP∗ $\left({{\Sigma }}_{P}^{\ast }\right)$ remains a free parameter in this comparison. We calculate the Pedersen conductance from the combined data sets, and find it ranges from 0.03<ΣP∗<2.40 $0.03< {{\Sigma }}_{P}^{\ast }< 2.40$ mho overall with averages of 0.13−0.07+0.26 $0.1{3}_{-0.07}^{+0.26}$ mho in the north and 0.16−0.10+0.34 $0.1{6}_{-0.10}^{+0.34}$ mho in the south. Considering the HST‐derived field‐aligned currents per radian of azimuth only, we find values of I‖=9.34−3.54+5.72 ${I}_{\Vert }=9.3{4}_{-3.54}^{+5.72}$ MA rad−1 and I‖=8.61−3.05+6.77 ${I}_{\Vert }=8.6{1}_{-3.05}^{+6.77}$ MA rad−1 in the north and south, respectively, in general agreement with previous results. Taking the currents and effective Pedersen conductance together, we find that the average ME intensity and plasma flow speed in the middle magnetosphere (10–30 RJ) are broadly consistent with one another under MI coupling theory. We find evidence for peaks in the distribution of ΣP∗ ${{\Sigma }}_{P}^{\ast }$ near dawn, then again near 12 and 14 hr magnetic local time (MLT). This variation in Pedersen conductance with MLT may indicate the importance of conductance in modulating MLT‐ and local‐time‐asymmetries in the ME, including the apparent subcorotation of some auroral features within the ME. Plain Language Summary: The brightest part of Jupiter's aurorae– the main emission– forms arcs of sheet‐like lights surrounding both magnetic poles, similar to the Earth's aurorae. At both planets, these lights are caused by charged particles flowing into the planet's atmosphere, where they collide with gases and glow. According to one theory, at Jupiter these particles are electrons which flow in electrical currents connecting the planet to the charged‐particle‐filled space surrounding it. Here, we use Hubble Space Telescope images of Jupiter's aurorae spanning a decade to build up an average picture of the brightness and location of this main emission. The brightness is related to the energy of the electrons, which in turn is related to the strength of the electrical currents. We then use particle measurements made by the Galileo spacecraft in orbit around Jupiter to make an average picture of these particles as they move around Jupiter. These speeds are related to the same electrical currents, but include an electrical conductivity term describing how easily currents flow through Jupiter's auroral atmosphere. We combine all these measurements to calculate the conductivity, and present results which are consistent with expectations but which fluctuate more quickly than expected in parts of the main emission. Key Points: The effective ionospheric Pedersen conductance in Jupiter's main emission auroral region is derived from remote and in‐situ measurementsEffective Pedersen conductances of ∼0.14 mho and field‐aligned auroral currents near ∼10 MA/rad−1 are derived, consistent with past workThe effective Pedersen conductance varies significantly in magnetic local time, and may explain the enigmatic motions of some auroral forms [ABSTRACT FROM AUTHOR]

deepCR is a deep-learning-based cosmic-ray (CR) rejection framework originally presented by Zhang & Bloom. The original approach requires a dedicated training set that consists of multiple frames of the same fields, enabling automatic CR labeling through comparison with their median coadds. Here, we present a novel training approach that circumvents the need for a dedicated training set, but instead utilizes dark frames and the science images requiring CR removal themselves. During training, CRs present in dark frames are added to the science images, which the network is then trained to identify. In turn, the trained deepCR model can then be applied to identify CRs originally present in the science images. Using this approach, we present a new deepCR model trained on a diverse set of Hubble Space Telescope images taken from resolved galaxies in the Local Group, which is universally applicable across all WFC3/UVIS filters. We introduce a robust approach to determining the threshold for generating binary cosmic-ray masks from predictions from deepCR probability maps. When applied to the Panchromatic Hubble Andromeda Southern Treasury survey, our new deepCR model added ∼7% of good-quality stars that exhibit distinct features in their color–magnitude diagrams. [ABSTRACT FROM AUTHOR]

Far-ultraviolet (FUV) emission lines from dwarf stars are important driving sources of photochemistry in planetary atmospheres. Properly interpreting spectral features of planetary atmospheres critically depends on the emission of its host star. While the spectral energy distributions (SEDs) of K- and M-type stars have been extensively characterized by previous observational programs, the full X-ray to infrared SED of F-type stars has not been assembled to support atmospheric modeling. On the second flight of the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE-2) rocket-borne spectrograph, we successfully captured the FUV spectrum of Procyon A (F5 IV-V) and made the first simultaneous observation of several emission features across the FUV bandpass (1010–1270 and 1300–1565 Å) of any cool star. We combine flight data with stellar models and archival observations to develop the first SED of a mid-F star. We model the response of a modern Earth-like exoplanet's upper atmosphere to the heightened X-ray and extreme UV radiation within the habitable zone of Procyon A. These models indicate that this planet would not experience significant atmospheric escape. We simulate observations of the Ly α transit signal of this exoplanet with the Hubble Space Telescope (HST) and the Habitable Worlds Observatory (HWO). While marginally detectable with HST, we find that H i Ly α transits of potentially habitable exoplanets orbiting high radial velocity F-type stars could be observed with HWO for targets up to 150 pc away. [ABSTRACT FROM AUTHOR]

We present a comprehensive atmospheric retrieval study of the hot Jupiter WASP-77A b using eclipse observations from the Hubble Space Telescope (HST) and JWST. Using atmospheric retrievals, the spectral features of H _2 O, CO, and TiO are identified, with volume mixing ratios estimated at log _10 (VMR) = −4.40 ${}_{-0.11}^{+0.14}$ , −4.44 ${}_{-0.28}^{+0.34}$ , and −6.40 ${}_{-0.23}^{+0.22}$ , respectively. We derive the atmospheric C-to-O ratio—a key planetary formation tracer—to be C/O = 0.54 ± 0.12, which is consistent with both the stellar host value and previous studies of the planet’s atmosphere, suggesting a relatively close-in formation. Computing other elemental ratios (i.e., C/H, O/H, and Ti/H), we conclude that the general enrichment of the atmosphere (i.e., metallicity) is substellar, depleted in C and O, but that Ti appears slightly superstellar. A low C and O content could be obtained, in combination with a stellar C/O ratio if the planet formed outside of the CO _2 snow line before migrating inwards. Meanwhile, a superstellar Ti/H could be obtained by late contamination from refractory rich planetesimals. While broadly in agreement with previous works, we do find some differences and discuss these while also highlighting the need for homogeneous analyses when comparative exoplanetology is conducted.

Over the last decade, precise exoplanet transmission spectroscopy has revealed the atmospheres of dozens of exoplanets, driven largely by observatories like the Hubble Space Telescope. One major discovery has been the ubiquity of atmospheric aerosols, often blocking access to exoplanet chemical inventories. Tentative trends have been identified, showing that the clarity of planetary atmospheres may depend on equilibrium temperature. Previous work has often grouped dissimilar planets together in order to increase the statistical power of any trends, but it remains unclear from observed transmission spectra whether these planets exhibit the same atmospheric physics and chemistry. We present a reanalysis of a smaller, more physically similar sample of 15 exo-Neptune transmission spectra across a wide range of temperatures (200–1000 K). Using condensation cloud and hydrocarbon haze models, we find that the exo-Neptune population is best described by low cloud sedimentation efficiency ( f _sed ∼ 0.1) and high metallicity (100 × solar). There is an intrinsic scatter of ∼0.5 scale height, perhaps evidence of stochasticity in these planets’ formation processes. Observers should expect significant attenuation in transmission spectra of Neptune-size exoplanets, up to 6 scale heights for equilibrium temperatures between 500 and 800 K. With JWST's greater wavelength sensitivity, colder (

In this work, we build a satellite attitude Proportional-Integral-Derivative (PID) controlled system by using the Hubble Space Telescope (HST) parameters as a reference and tune its controller parameters using various tuning methods. First, we give the equations for the motion of a satellite. We elaborate the control structure as controller, actuator, dynamics, and kinematics subsystems and construct an external disturbance model. We use a reaction wheel assembly used in the HST with the same configuration as the actuator. We evaluate the performance of the linearization by comparing it with the nonlinear model output. By working on the linearized model, we tune the PID controller parameters using two different methods: “Model-Based Root Locus Tuning” and “Genetic Algorithm Based Tuning”. First, we obtain the controller parameters by manipulating the poles on the root locus plot of the linearized system. In addition, we use genetic algorithms to find the optimized controller values of the system. Finally, we compare the performances of the two methods based on their cost function values and find that the Genetic Algorithm-based tuned parameters are more fruitful in terms of the cost function value than the parameters obtained by the Root Locus-based tuning. However, it is found that the Root Locus-based tuning performs better in disturbance rejection.

Several observations using the Hubble Space Telescope reported that the brightness morphology of the oxygen OI] 135.6 nm emissions on Europa's atmosphere has a north‐south asymmetry which changes with the position of Europa with respect to the Jovian magnetospheric plasma sheet. Similar north‐south asymmetry of Io's auroral limb glow has been explained by higher electron flux into the atmosphere on the hemisphere that faces the plasma sheet center. This explanation, however, has not yet been evaluated for the case of Europa quantitatively. In this study, we used a test particle simulation for the Jovian magnetospheric electrons to estimate the brightness of the 135.6 nm aurora in Europa's atmosphere and evaluate the cause of the north‐south asymmetry with the previously suggested idea, in which the strong deceleration of the magnetospheric flux tube results in the inhomogeneous electron flux into Europa's atmosphere (the "slow‐down effect"). Our simulation successfully recreates the systematically changing north‐south asymmetry of Europa's oxygen aurora brightness using the "slow‐down effect." With deceleration into 10% of the background plasma flow, the maximum north‐to‐south brightness ratio is estimated at 2.17 and 2.56 on the trailing (plasma‐upstream) and leading (downstream) side, respectively. However, the previously observed brightness ratio is larger on the trailing side (up to ∼5). The results indicate that additional model scenarios are required to fully explain the north‐south asymmetry of Europa's oxygen aurora morphology. Plain Language Summary: Europa is one of Jupiter's icy moons and possesses a tenuous oxygen atmosphere. A ultraviolet oxygen aurora at 135.6 nm is generated due to the collision between atmospheric oxygen molecules and magnetospheric electrons in Europa's atmosphere, and the aurora has a time‐variable north‐south asymmetric structure. We simulated electron motion near Europa and calculated the aurora brightness to investigate how the spatial distribution of Europa's oxygen aurora becomes north‐south asymmetric. Previous studies qualitatively explain that the strong deceleration of the magnetospheric plasma flux tube results in the unequal electron flux into the atmosphere to generate the north‐south asymmetric aurora structure, but this explanation has never been quantitatively evaluated for the case of Europa. Based on this "slow‐down effect" scenario, we successfully reproduced the time‐variation of the north‐south asymmetry of Europa's oxygen aurora. However, our model estimates a larger north‐to‐south brightness ratio on the leading side, whereas previous auroral observations show that the trailing hemisphere has more pronounced north‐south asymmetry. This result indicates that the "slow‐down effect" cannot fully explain the structure of Europa's oxygen aurora and that additional model scenarios are required to understand the auroral north‐south asymmetry. Key Points: Morphology of Europa's oxygen 135.6 nm aurora was reproduced by test particle method to investigate the north‐south aurora asymmetryWe confirmed that a flux tube decelerated to 10% of the background plasma flow creates the periodic changes of the north‐south asymmetryBut the slow‐down scenario does not explain the larger north‐south asymmetry observed on the trailing hemisphere [ABSTRACT FROM AUTHOR]

The most luminous quasars at z > 6 are suspected to be both highly clustered and to reside in the most massive dark matter halos in the early universe, making them prime targets to search for galaxy overdensities and/or protoclusters. We search for Lyman-break dropout-selected galaxies using HST WFC3/ACS broadband imaging in the fields of three 6 < z < 7 quasars, as well as for their simultaneously observed coordinated parallel fields, and constrain their photometric redshifts using EAZY. One field, J0305-3150, shows a volume density 10× higher than the blank-field UV luminosity function (UVLF) at M UV < −20, with tentative evidence of a 3 σ overdensity in its parallel field located 15 cMpc away. Another field, J2054–0005, shows an angular overdensity within 500 ckpc from the quasar, but this is still consistent with UVLF predictions within 3 σ, while the last field, J2348–3054, shows no enhancement. We discuss methods for reducing uncertainty in overdensity measurements when using photometric selection and show that we can robustly select Lyman-break galaxies (LBGs) consistent with being physically associated with the quasar, corroborated by existing JWST/NIRCam WFSS data in the J0305 field. Even accounting for incompleteness, the overdensities in J0305 and J2054 are higher for brighter galaxies at short angular separations, suggesting preferential enhancement of more massive galaxies in the quasar's immediate vicinity. Finally, we compare the population of LBGs with previously identified [C ii ] and millimeter-continuum companions. The LBG overdensities are not accompanied by an enhanced number of dusty galaxies, suggesting that the overdense quasar fields are not in the bursty star-forming phase sometimes seen in high-redshift protoclusters. [ABSTRACT FROM AUTHOR]

The LHS 6343 system consists of a resolved M-dwarf binary with an evolved, negligibly irradiated brown dwarf (BD), LHS 6343 C, orbiting the primary star. Such BD eclipsing binaries present rare and unique opportunities to calibrate substellar evolutionary and atmosphere models since mass, radius, temperature, and luminosity can be directly measured. We update this BD’s mass (62.6 ± 2.2 M _Jup ) and radius (0.788 ± 0.043 R _Jup ) using empirical stellar relations and a Gaia Data Release 3 distance. We use Hubble Space Telescope/Wide Field Camera 3 (WFC3) observations of an LHS 6343 C secondary eclipse to obtain a near-IR emission spectrum, which matches to a spectral type of T1.5 ± 1. We combine this spectrum with existing Kepler and Spitzer/IRAC secondary-eclipse photometry to perform atmospheric characterization using the ATMO-2020, Sonora-Bobcat, and BT-Settl model grids. ATMO-2020 models with strong nonequilibrium chemistry yield the best fit to observations across all modeled bandpasses while predicting physical parameters consistent with Gaia-dependent analogs. BT-Settl predicts values slightly more consistent with such analogs but offers a significantly poorer fit to the WFC3 spectrum. Finally, we obtain a semi-empirical measurement of LHS 6343 C’s apparent luminosity by integrating its observed and modeled spectral energy distribution. Applying knowledge of the system’s distance yields a bolometric luminosity of log( L _bol / L _☉ ) = −4.77 ± 0.03 and, applying the Stefan–Boltzmann law for the known radius, an effective temperature of 1303 ± 29 K. We also use the ATMO-2020 and Sonora-Bobcat evolutionary model grids to infer an age for LHS 6343 C of $2.86\hspace{0.08cm}{}_{-0.33}^{+0.40}\,\mathrm{Gyr}$ and $3.11\hspace{0.08cm}{}_{-0.38}^{+0.50}\,\mathrm{Gyr}$ respectively.

We test the relationship between UV-derived star formation rates (SFRs) and the 7.7 μ m polycyclic aromatic hydrocarbon luminosities from the integrated emission of galaxies at z ∼ 0–2. We utilize multiband photometry covering 0.2–160 μ m from the Hubble Space Telescope, CFHT, JWST, Spitzer, and Herschel for galaxies in the Cosmic Evolution Early Release Science (CEERS) Survey. We perform spectral energy distribution (SED) modeling of these data to measure dust-corrected far-UV (FUV) luminosities, L _FUV , and UV-derived SFRs. We then fit SED models to the JWST/MIRI 7.7–21 μ m CEERS data to derive rest-frame 7.7 μ m luminosities, L _770 , using the average flux density in the rest-frame MIRI F770W bandpass. We observe a correlation between L _770 and L _FUV , where $\mathrm{log}{L}_{770}\propto (1.27\pm 0.04)\mathrm{log}{L}_{\mathrm{FUV}}$ . L _770 diverges from this relation for galaxies at lower metallicities, lower dust obscuration, and for galaxies dominated by evolved stellar populations. We derive a “single-wavelength” SFR calibration for L _770 that has a scatter from model estimated SFRs ( σ _ΔSFR ) of 0.24 dex. We derive a “multiwavelength” calibration for the linear combination of the observed FUV luminosity (uncorrected for dust) and the rest-frame 7.7 μ m luminosity, which has a scatter of σ _ΔSFR = 0.21 dex. The relatively small decrease in σ suggests this is near the systematic accuracy of the total SFRs using either calibration. These results demonstrate that the rest-frame 7.7 μ m emission constrained by JWST/MIRI is a tracer of the SFR for distant galaxies to this accuracy, provided the galaxies are dominated by star formation with moderate-to-high levels of attenuation and metallicity.

We present high angular resolution imaging that detects the MOA-2008-BLG-379L exoplanet host star using Keck adaptive optics and the Hubble Space Telescope. These observations reveal host star and planet masses of M _host = 0.434 ± 0.065 M _⊙ and m _p = 2.44 ± 0.49 M _Jupiter . They are located at a distance of D _L = 3.44 ± 0.53 kpc, with a projected separation of 2.70 ± 0.42 au. These results contribute to our determination of exoplanet host star masses for the Suzuki et al. statistical sample, which will determine the dependence of the planet occurrence rate on the mass and distance of the host stars. We also present a detailed discussion of the image-constrained modeling version of the eesunhong light-curve modeling code that applies high angular resolution image constraints to the light-curve modeling process. This code increases modeling efficiency by a large factor by excluding models that are inconsistent with the high angular resolution images. The analysis of this and other events from the Suzuki et al. statistical sample reveals the importance of including higher-order effects, such as microlensing parallax and planetary orbital motion, even when these features are not required to fit the light-curve data. The inclusion of these effects may be needed to obtain accurate estimates of the uncertainty of other microlensing parameters that affect the inferred properties of exoplanet microlens systems. This will be important for the exoplanet microlensing survey of the Roman Space Telescope, which will use both light-curve photometry and high angular resolution imaging to characterize planetary microlens systems.

The tip of the red giant branch (TRGB) based distance method in the I band is one of the most efficient and precise techniques for measuring distances to nearby galaxies ( D ≲ 15 Mpc). The TRGB in the near-infrared (NIR) is 1–2 mag brighter relative to the I band, and has the potential to expand the range over which distance measurements to nearby galaxies are feasible. Using Hubble Space Telescope (HST) imaging of 12 fields in eight nearby galaxies, we determine color-based corrections and zero-points of the TRGB in the Wide Field Camera 3 IR (WFC3/IR) F110W and F160W filters. First, we measure TRGB distances in the I band equivalent Advanced Camera System (ACS) F814W filter from resolved stellar populations with the HST. The TRGB in the ACS F814W filter is used for our distance anchor and to place the WFC3/IR magnitudes on an absolute scale. We then determine the color dependence (a proxy for metallicity/age) and zero-point of the NIR TRGB from photometry of WFC3/IR fields that overlap with the ACS fields. The new calibration is accurate to ∼1% in distance relative to the F814W TRGB. Validating the accuracy of the calibrations, we find that the distance modulus for each field using the NIR TRGB calibration agrees with the distance modulus of the same field as determined from the F814W TRGB. This is a JWST preparatory program, and the work done here will directly inform our approach to calibrating the TRGB in JWST NIRCam and NIRISS photometric filters.

Galaxy cluster mergers that exhibit clear dissociation between their dark matter, intracluster gas, and stellar components are great laboratories for probing dark matter properties. Mergers that are binary and in the plane of the sky have the additional advantage of being simpler to model, allowing for a better understanding of the merger dynamics. We report the discovery of a galaxy cluster merger with all these characteristics and present a multiwavelength analysis of the system, which was found via a search in the redMaPPer optical cluster catalog. We perform a galaxy redshift survey to confirm the two subclusters are at the same redshift (0.541, with 368 ± 519 km s ^−1 line-of-sight velocity difference between them). The X-ray morphology shows two surface brightness peaks between the brightest cluster galaxies (BCGs). We construct weak-lensing mass maps that reveal a mass peak associated with each subcluster. Fitting Navarro–Frenk–White profiles to the lensing data, we find masses of M _200c = 36 ± 11 × 10 ^13 and 38 ± 11 × 10 ^13 M _⊙ h ^−1 for the southern and northern subclusters, respectively. From the mass maps, we infer that the two mass peaks are separated by ${520}_{-125}^{+162}$ kpc along the merger axis, whereas the two BCGs are separated by 697 kpc. We also present deep GMRT 650 MHz data to search for a radio relic or halo and find none. Using the observed merger parameters, we find analog systems in cosmological n -body simulations and infer that this system is observed between 96 and 236 Myr after pericenter, with the merger axis within 28° of the plane of the sky.

Exoplanet transmission spectra provide rich information about the chemical composition, clouds, and temperature structure of exoplanet atmospheres. Most exoplanet transmission spectra only span infrared wavelengths (≳1 μ m), which can preclude crucial atmospheric information from shorter wavelengths. Here, we explore how retrieved atmospheric parameters from exoplanet transmission spectra change with the addition of optical data. From a sample of 14 giant planets with transit spectra from 0.3–4.5 μ m, primarily from the Hubble and Spitzer space telescopes, we apply a free chemistry retrieval to planetary spectra for wavelength ranges of 0.3–4.5 μ m, 0.6–4.5 μ m, and 1.1–4.5 μ m. We analyze the posterior distributions of these retrievals and perform an information content analysis, finding wavelengths below 0.6 μ m are necessary to constrain cloud scattering slope parameters ( $\mathrm{log}a$ and γ ) and alkali species Na and K. There is limited improvement in the constraints on the remaining atmospheric parameters. Across the population, we find that limb temperatures are retrieved colder than planetary equilibrium temperatures but have an overall good agreement with Global Circulation Models. As the JWST extends to a minimum wavelength of 0.6 μ m, we demonstrate that exploration into complementing JWST observations with optical HST data is important to further our understanding of aerosol properties and alkali abundances in exoplanet atmospheres.

TWA 27B (2M1207b) is the first directly imaged planetary-mass ( M _p ≈ 5 M _J ) companion and was observed at 0.9–5.3 μ m with ​​​JWST/NIRSpec. To understand the accretion properties of TWA 27B, we search for continuum-subtracted near-infrared helium and hydrogen emission lines and measure their widths and luminosities. We detect the He i triplet at 4.3 σ and all Paschen-series lines covered by NIRSpec (Pa α , Pa β , Pa γ , Pa δ ) at 4 σ –5 σ . The three brightest Brackett-series lines (Br α , Br β , Br γ ) as well as Pf γ and Pf δ are tentative detections at 2 σ –3 σ . We provide upper limits on the other hydrogen lines, including on H α through Hubble Space Telescope archival data. Three lines can be reliably deconvolved to reveal an intrinsic width Δ v _intrsc = (67 ± 9) km s ^−1 , which is 60% of the surface freefall velocity. The line luminosities seem significantly too high to be due to chromospheric activity. Converting line luminosities to an accretion rate yields $\dot{M}\approx 5\times {10}^{-9}\,{M}_{{\rm{J}}}\,{\mathrm{yr}}^{-1}$ when using scaling relationships for planetary masses, and $\dot{M}\approx 0.1\times {10}^{-9}\,{M}_{{\rm{J}}}\,{\mathrm{yr}}^{-1}$ with extrapolated stellar scalings. Several of these lines represent the first detections at an accretor of such low mass. The weak accretion rate implies that formation is likely over. This analysis shows that JWST can be used to measure low line-emitting mass accretion rates onto planetary-mass objects, motivates deeper searches for the mass reservoir feeding TWA 27B, and hints that other young directly imaged objects might—hitherto unbeknownst—also be accreting.

Resolving the environments of massive stars is crucial for understanding their formation mechanisms and their impact on galaxy evolution. An important open question is whether massive stars found in diffuse regions outside spiral arms formed in situ or migrated there after forming in denser environments. To address this question, we use multiresolution measurements of extinction in the Andromeda galaxy (M31) to probe the interstellar medium surrounding massive stars across galactic environments. We construct a catalog of 42,107 main-sequence massive star candidates ( M ≥ 8 M _⊙ ) using resolved stellar photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) program, plus stellar and dust model fits from the Bayesian Extinction and Stellar Tool (BEAST). We quantify galactic environments by computing surrounding stellar densities of massive stars using kernel density estimation. We then compare high-resolution line-of-sight extinction estimates from the BEAST with 25 pc resolution dust maps from PHAT, measuring the total column density distribution of extinction. Our key finding is that, although the average total column density of dust increases with the density of massive stars, the average line-of-sight extinction toward massive stars remains constant across all environments. This suggests that massive stars have a uniform amount of dust in their immediate environment, regardless of their location in the galaxy. One possible explanation for these findings is that small molecular clouds are still capable of forming massive stars, even if they are not resolvable at 25 pc. These results indicate that massive stars are forming in the sparse regions of M31, as opposed to migrating there.

We present results from the search for astrometric accelerations of stars in ω Centauri using 13 yr of regularly scheduled Hubble Space Telescope WFC3/UVIS calibration observations in the cluster core. The high-precision astrometry of ∼160,000 sources was searched for significant deviations from linear proper motion. This led to the discovery of four cluster members and one foreground field star with compelling acceleration patterns. We interpreted them as the result of the gravitational pull by an invisible companion and determined preliminary Keplerian orbit parameters, including the companion’s mass. For the cluster members, our analysis suggests periods ranging from 8.8 to 19+ yr and dark companions in the mass range of ∼0.7 to ∼1.4 M _☉ . At least one companion could exceed the upper mass boundary of white dwarfs and can be classified as a neutron star candidate.

We present the first results of the Hubble Deep Hydrogen Alpha (HDH α ) project, which analyzes the space-borne deep H α narrowband imaging data in the GOODS-S region. The HDH α data comprises 72 orbits’ images taken with the Hubble Space Telescope (HST) Advanced Camera for Surveys/Wide Field Channel F658N filter. The exposure time varies across a total area of ∼76.1 arcmin ^2 , adding up to a total exposure time of 195.7 ks, among which 68.8 ks are spent in the deepest region. These images are aligned, reprojected, and combined to have the same pixel grid as the Hubble Legacy Fields. The scientific goals of the HDH α include establishing a sample of emission-line galaxies (ELGs) including [O iii ] emitters at z ∼ 0.3, [O ii ] emitters at z ∼ 0.8, and Ly α emitters (LAEs) at z ∼ 4.4, studying the line morphology of ELGs with high resolution imaging data, and statistically analyzing the line luminosity functions and line equivalent-width distributions of ELGs selected with HST. Furthermore, the HDH α project enhances the legacy value of the GOODS-S field by contributing the first HST-based narrowband image to the existing data sets, which includes the HST broadband data and other ancillary data from X-ray to radio taken by other facilities. In this paper, we describe the data reduction process of the HDH α , select ELGs based on HST's F658N and broadband data, validate the redshifts of the selected candidates by crossmatching with the public spectroscopic catalogs in the GOODS-S, and present a final catalog of the confirmed [O iii ] emitters at z ∼ 0.3, [O ii ] emitters at z ∼ 0.8, and LAEs at z ∼ 4.4.

deepCR is a deep-learning-based cosmic-ray (CR) rejection framework originally presented by Zhang & Bloom. The original approach requires a dedicated training set that consists of multiple frames of the same fields, enabling automatic CR labeling through comparison with their median coadds. Here, we present a novel training approach that circumvents the need for a dedicated training set, but instead utilizes dark frames and the science images requiring CR removal themselves. During training, CRs present in dark frames are added to the science images, which the network is then trained to identify. In turn, the trained deepCR model can then be applied to identify CRs originally present in the science images. Using this approach, we present a new deepCR model trained on a diverse set of Hubble Space Telescope images taken from resolved galaxies in the Local Group, which is universally applicable across all WFC3/UVIS filters. We introduce a robust approach to determining the threshold for generating binary cosmic-ray masks from predictions from deepCR probability maps. When applied to the Panchromatic Hubble Andromeda Southern Treasury survey, our new deepCR model added ∼7% of good-quality stars that exhibit distinct features in their color–magnitude diagrams.

A recent ultraviolet luminosity function (UVLF) analysis in the Hubble Frontier Fields, behind foreground lensing clusters, has helped solidify estimates of the faint-end of the z ∼ 5–9 UVLF at up to 5 mag fainter than in the field. These measurements provide valuable information regarding the role of low-luminosity galaxies in reionizing the universe and can help in calibrating expectations for JWST observations. We fit a semiempirical model to the lensed and previous UVLF data from Hubble. This fit constrains the average star formation efficiency (SFE) during reionization, with the lensed UVLF measurements probing halo mass scales as small as M ∼ 2 × 10 ^9 M _⊙ . The implied trend of SFE with halo mass is broadly consistent with an extrapolation from previous inferences at M ≳ 10 ^10 M _⊙ , although the joint data prefer a shallower SFE. This preference, however, is partly subject to systematic uncertainties in the lensed measurements. Near z ∼ 6, we find that the SFE peaks at ∼20% between ∼10 ^11 and 10 ^12 M _⊙ . Our best-fit model is consistent with the Planck 2020 determinations of the electron scattering optical depth, and most current reionization history measurements, provided the escape fraction of ionizing photons is f _esc ∼ 10%–20%. The joint UVLF accounts for nearly 80% of the ionizing photon budget at z ∼ 8. Finally, we show that recent JWST UVLF estimates at z ≳ 11 require strong departures from the redshift evolution suggested by the Hubble data.

We present the first star formation history (SFH) and age–metallicity relation (AMR) derived from resolved stellar populations imaged with the JWST NIRCam instrument. The target is the Local Group star-forming galaxy WLM at 970 kpc. The depth of the color–magnitude diagram (CMD) reaches below the oldest main sequence turnoff with a signal-to-noise ratio = 10 at M _F090W = + 4.6 mag. This is the deepest CMD for any galaxy that is not a satellite of the Milky Way. We use Hubble Space Telescope (HST) optical imaging that overlaps with the NIRCam observations to directly evaluate the SFHs derived based on data from the two great observatories. The JWST and HST-based SFHs are in excellent agreement. We use the metallicity distribution function measured from stellar spectra to confirm the trends in the AMRs based on the JWST data. Together, these results confirm the efficacy of recovering an SFH and AMR with the NIRCam F090W−F150W filter combination, and validate the sensitivity and accuracy of stellar evolution libraries in the near-infrared relative to the optical for SFH recovery work. From the JWST data, WLM shows an early onset to star formation, followed by an extended pause post-reionization before star formation reignites, which is qualitatively similar to what has been observed in the isolated galaxies Leo A and Aquarius. Quantitatively, 15% of the stellar mass formed in the first Gyr, while only 10% formed over the next ∼5 Gyr. The stellar mass then rapidly doubled in ∼2.5 Gyr, followed by constant star formation over the last ∼5 Gyr.

A deep learning (DL) algorithm is built and tested for its ability to determine centers of star images in HST/WFPC2 exposures, in filters F555W and F814W. These archival observations hold great potential for proper-motion studies, but the undersampling in the camera's detectors presents challenges for conventional centering algorithms. Two exquisite data sets of over 600 exposures of the cluster NGC 104 in these filters are used as a testbed for training and evaluating the DL code. Results indicate a single-measurement standard error from 8.5 to 11 mpix, depending on the detector and filter. This compares favorably to the ∼20 mpix achieved with the customary "effective point spread function (PSF)" centering procedure for WFPC2 images. Importantly, the pixel-phase error is largely eliminated when using the DL method. The current tests are limited to the central portion of each detector; in future studies, the DL code will be modified to allow for the known variation of the PSF across the detectors. [ABSTRACT FROM AUTHOR]

Recent years have seen increasing interest in the characterization of sub-Neptune-sized planets because of their prevalence in the Galaxy, contrasted with their absence in our solar system. HD 97658 is one of the brightest stars hosting a planet of this kind, and we present the transmission spectrum of this planet by combining four Hubble Space Telescope transits, 12 Spitzer/IRAC transits, and eight MOST transits of this system. Our transmission spectrum has a higher signal-to-noise ratio than those from previous works, and the result suggests that the slight increase in transit depth from wavelength 1.1-1.7 μm reported in previous works on the transmission spectrum of this planet is likely systematic. Nonetheless, our atmospheric modeling results are inconclusive, as no model provides an excellent match to our data. Nonetheless, we find that atmospheres with high C/O ratios (C/O ≈ 0.8) and metallicities of ≈100× solar metallicity are favored. We combine the mid-transit times from all of the new Spitzer and MOST observations and obtain an updated orbital period of P = 9.489295 ± 0.000005, with a best-fit transit time center at T 0 = 2456361.80690 ± 0.00038 (BJD). No transit timing variations are found in this system. We also present new measurements of the stellar rotation period (34 ± 2 days) and stellar activity cycle (9.6 yr) of the host star HD 97658. Finally, we calculate and rank the Transmission Spectroscopy Metric of all confirmed planets cooler than 1000 K and with sizes between 1 R ⊕ and 4 R ⊕. We find that at least a third of small planets cooler than 1000 K can be well characterized using James Webb Space Telescope, and of those, HD 97658b is ranked fifth, meaning that it remains a high-priority target for atmospheric characterization.

Likelihood analysis is typically limited to normally distributed noise due to the difficulty of determining the probability density function of complex, high-dimensional, non-Gaussian, and anisotropic noise. This is a major limitation for precision measurements in many domains of science, including astrophysics, for example, for the analysis of the cosmic microwave background, gravitational waves, gravitational lensing, and exoplanets. This work presents Score-based LIkelihood Characterization, a framework that resolves this issue by building a data-driven noise model using a set of noise realizations from observations. We show that the approach produces unbiased and precise likelihoods even in the presence of highly non-Gaussian correlated and spatially varying noise. We use diffusion generative models to estimate the gradient of the probability density of noise with respect to data elements. In combination with the Jacobian of the physical model of the signal, we use Langevin sampling to produce independent samples from the unbiased likelihood. We demonstrate the effectiveness of the method using real data from the Hubble Space Telescope and James Webb Space Telescope.

We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius ( r _eff ∼ 5 pc) and ellipticity ( ϵ ∼ 0.05), while the Sérsic index ( n ) and position angle (PA) drop from n ∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared, r _eff ∼ 12 pc, ϵ ∼ 0.4, and n ∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of ${\mathrm{log}}_{10}\,({M}_{\star }^{\mathrm{nsc}}/{M}_{\odot })=7.06\pm 0.31$ , as derived through B − V , confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

We report results of Hubble Space Telescope observations from Ganymede's orbitally trailing side which were taken around the flyby of the Juno spacecraft on 7 June 2021. We find that Ganymede's northern and southern auroral ovals alternate in brightness such that the oval facing Jupiter's magnetospheric plasma sheet is brighter than the other one. This suggests that the generator that powers Ganymede's aurora is the momentum of the Jovian plasma sheet north and south of Ganymede's magnetosphere. Magnetic coupling of Ganymede to the plasma sheet above and below the moon causes asymmetric magnetic stresses and electromagnetic energy fluxes ultimately powering the auroral acceleration process. No clear statistically significant timevariability of the auroral emission on short time scales of 100s could be resolved. We show that electron energy fluxes of several tens of mW m−2 are required for its OI 1,356 Å emission making Ganymede a very poor auroral emitter. Plain Language Summary: Jupiter's moon Ganymede is the largest moon in the solar system and the only known moon with an intrinsic magnetic field and two auroral ovals around its north and south poles. Earth also possesses two auroral ovals, which are bands of emission around its poles. This emission is also referred to as northern and southern lights. We use the Hubble Space Telescope to observe Ganymede's aurora around the time when NASA's Juno spacecraft had a close flyby at Ganymede. We find that the brightness of the northern and southern ovals alternate in intensity with a period of 10 hr. Additionally, we derive that an energy flux of several tens of milli‐Watt per square meter is necessary to power the auroral emission. This energy flux comes from energetic electrons accelerated in the vicinity of Ganymede. Key Points: Hubble Space Telescope observations of Ganymede's orbitally trailing hemisphere on 7 June 2021 in support of Juno flybyBrightness ratio of northern and southern auroral ovals oscillates such that the oval facing the Jovian plasma sheet is brighterOscillation suggests the aurora is driven by magnetic stresses coupling the moon's magnetic field to the surrounding Jovian plasma sheet [ABSTRACT FROM AUTHOR]

The first non-Earth aerobraking experiment occurred in 1993 as part of the Magellan satellite's mission to Venus. Magellan reduced its orbit from elliptical to nearly circular over a span of 70 Earth days by leveraging the non-conservative force of aerodynamic drag to reduce its orbital energy via transiting the upper region of Venus' sensible atmosphere. First tested with the Hiten probe in the Earth-Moon system in 1991, the subsequent Magellan experiment helped prove the viability of aerobraking for planetary missions and paved the way for its implementation in Mars missions starting in the late 1990s and the 2014 Venus Express mission. This paper, for the first time in literature, investigates the Magellan aerobraking experiment from the perspective of both 3- and 6-degree-of-freedom analysis. Multiple atmospheric density models are considered, as well as J 4 gravitational perturbations in order to understand the complexity and sensitivity of numerous aerobraking maneuvers in the thick Venusian atmosphere. Alternative satellites are also studied to ascertain their capability of maintaining the Magellan aerobraking flight profile. So as to examine a wide range of vehicle mass and drag reference area, the Hubble Space Telescope (HST) and Hiten satellites are modeled and their aerobraking performance analyzed for the hypothetical case of Venus orbital operations. When reconstructing the historical Magellan aerobraking maneuvers, 3DOF and 6DOF analysis yielded minimal trajectory deviation with the Magellan and Hiten models, while more significant deviation was experienced with the larger HST model. Both 3DOF and 6DOF analyses also reveal the sensitivity of the atmospheric density model and indicate a higher fidelity gravity model is necessary for Venusian aerobraking modeling, planning, and analysis. • 6DOF modeling achieved improved agreement with the Magellan historical data than the 3DOF simulations. • A high-fidelity gravity model of at least J4 is necessary for Venusian aerobraking modeling, planning, and analysis. • The 1968 high-density and Venus GRAM models enabled the greatest agreement between the 3DOF model and historical data. • Satellites with small drag reference areas encounter lower aerodynamic torques during aerobraking. [ABSTRACT FROM AUTHOR]

The James Webb Space Telescope, or JWST, or simply Webb, is a large, space-based observatory, designed primarily to conduct infrared astronomy. The telescope is named after James Edwin Webb (1906–1992), who was the second administrator of NASA during 1961–1968. It is an advanced next-generation telescope that will complement and extend the discoveries of the Hubble Space Telescope. The JWST has been developed by the National Aeronautics and Space Administration (NASA) of the United States of America in collaboration with the European Space Agency (ESA) and the Canadian Space Agency (CSA). It took over 24 years to place the Webb on the launch pad. The Webb was launched on 25 December 2021 at 7:20 AM (12:20 UTC) onboard ESA's Ariane 5 rocket from Kourou, French Guiana. [ABSTRACT FROM AUTHOR]

We present 14 simultaneous Chandra X‐ray Observatory (CXO)‐Hubble Space Telescope (HST) observations of Jupiter's Northern X‐ray and ultraviolet (UV) aurorae from 2016 to 2019. Despite the variety of dynamic UV and X‐ray auroral structures, one region is conspicuous by its persistent absence of emission: the dark polar region (DPR). Previous HST observations have shown that very little UV emission is produced by the DPR. We find that the DPR also produces very few X‐ray photons. For all 14 observations, the low level of X‐ray emission from the DPR is consistent (within 2‐standard deviations) with scattered solar emission and/or photons spread by Chandra's Point Spread Function from known X‐ray‐bright regions. We therefore conclude that for these 14 observations the DPR produced no statistically significant detectable X‐ray signature. Plain Language Summary: Jupiter produces the most powerful ultraviolet (UV) and X‐ray aurorae in the solar system. While the UV and X‐ray aurora of the planet have each been explored independently, previous work exploring the spatial connection between Jupiter's X‐ray and UV aurorae was limited to a single simultaneous Chandra X‐ray Observatory (CXO) and Hubble Space Telescope (HST) observation from 2003. Since 2016, the arrival of the Juno spacecraft at Jupiter has led to extensive observing campaigns with CXO and HST, resulting in many new simultaneous X‐ray‐UV observations. Here, we present the analysis of 14 simultaneous CXO and HST observations of Jupiter's Northern aurorae from 2016 to 2019. While much of the emission from these bright aurorae is dynamic, there is one region that is dim for all 14 observations: Jupiter's dark polar region. Previous observations of this region have shown that it produces very little UV light. However, the extent to which X‐ray light is produced by the region remained unexplored and could provide the key to identifying why the region is so dark and what this tells us about the Jovian system. Across these 14 observations, we find that the region produces no significant X‐ray emission. Key Points: We compare 14 simultaneous Chandra X‐ray Observatory and Hubble Space Telescope UV observations of Jupiter's Northern AuroraeWe detect no statistically significant X‐ray emission from the UV dark polar region (DPR)The DPR expands and the X‐ray and UV emission on the swirl region boundary shifts when the aurora show solar wind compression morphology [ABSTRACT FROM AUTHOR]

In 2022 November, the James Webb Space Telescope (JWST) returned deep near-infrared images of A2744—a powerful lensing cluster capable of magnifying distant, incipient galaxies beyond it. Together with existing Hubble Space Telescope (HST) imaging, this publicly available data set opens a fundamentally new discovery space to understand the remaining mysteries of the formation and evolution of galaxies across cosmic time. In this work, we detect and measure some 60,000 objects across the 49 arcmin ^2 JWST footprint down to a 5 σ limiting magnitude of ∼30 mag in 0.″32 apertures. Photometry is performed using circular apertures on images matched to the point-spread function (PSF) of the reddest NIRCam broad band, F444W, and cleaned of bright cluster galaxies and the related intracluster light. To give an impression of the photometric performance, we measure photometric redshifts and achieve a σ _NMAD ≈ 0.03 based on known, but relatively small, spectroscopic samples. With this paper, we publicly release our HST and JWST PSF-matched photometric catalog with optimally assigned aperture sizes for easy use, along with single aperture catalogs, photometric redshifts, rest-frame colors, and individual magnification estimates. These catalogs will set the stage for efficient and deep spectroscopic follow up of some of the first JWST-selected samples in summer of 2023.

The recent UNCOVER survey with the James Webb Space Telescope (JWST) exploits the nearby cluster A2744 to create the deepest view of our Universe to date by leveraging strong gravitational lensing. In this work, we perform photometric fitting of more than 50,000 robustly detected sources out to z ∼ 15. We show the redshift evolution of stellar ages, star formation rates, and rest-frame colors across the full range of 0.2 ≲ z ≲ 15. The galaxy properties are inferred using the Prospector Bayesian inference framework using informative Prospector - β priors on the masses and star formation histories to produce joint redshift and stellar populations posteriors. Additionally, lensing magnification is performed on the fly to ensure consistency with the scale-dependent priors. We show that this approach produces excellent photometric redshifts with σ _NMAD ∼ 0.03, of a similar quality to the established photometric redshift code EAzY . In line with the open-source scientific objective of this Treasury survey, we publicly release the stellar population catalog with this paper, derived from our photometric catalog adapting aperture sizes based on source profiles. This release (the catalog and all related documentation are accessible via the UNCOVER survey web page: https://jwst-uncover.github.io/DR2.html#SPSCatalogs with a copy deposited to Zenodo at doi: https://doi.org/10.5281/zenodo.8401181 ) includes posterior moments, maximum likelihood spectra, star formation histories, and full posterior distributions, offering a rich data set to explore the processes governing galaxy formation and evolution over a parameter space now accessible by JWST.

We have undertaken a near-IR weak-lensing (NIRWL) analysis of the CANDELS HST/WFC3-IR F160W observations. With the Gaia proper motion–corrected catalog as an astrometric reference, we updated the astrometry of the five CANDELS mosaics and achieved an absolute alignment within 0.″02 ± 0.″02, on average, which is a factor of several superior to existing mosaics. These mosaics are available to download ( https://drive.google.com/drive/folders/1k9WEV3tBOuRKBlcaTJ0-wTZnUCisS__r ). We investigated the systematic effects that need to be corrected for weak-lensing measurements. We find that the largest contributing systematic effect is caused by undersampling. We find a subpixel centroid dependence on the PSF shape that causes the PSF ellipticity and size to vary by up to 0.02 and 3%, respectively. Using the UDS as an example field, we show that undersampling induces a multiplicative shear bias of −0.025. We find that the brighter-fatter effect causes a 2% increase in the size of the PSF and discover a brighter-rounder effect that changes the ellipticity by 0.006. Based on the small range of slopes in a galaxy’s spectral energy distribution (SED) within the WFC3-IR bandpasses, we suggest that the impact of the galaxy SED on the PSF is minor. Finally, we model the PSF of WFC3-IR F160W for weak lensing using a principal component analysis. The PSF models account for temporal and spatial variations of the PSF. The PSF corrections result in residual ellipticities and sizes, ∣ de _1 ∣ < 0.0005 ± 0.0003, ∣ de _2 ∣ < 0.0005 ± 0.0003, and ∣ dR ∣ < 0.0005 ± 0.0001, that are sufficient for the upcoming NIRWL search for massive overdensities in the five CANDELS fields.

We present analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with Hubble’s Wide Field Camera 3 (WFC3). For over half of these, we statistically detect spectral modulation that our retrievals attribute to molecular species. Among these, we use Bayesian hierarchical modeling to search for chemical trends with bulk parameters. We use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet’s mass. We also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. However, although previous studies have found evidence of a mass–metallicity trend, we find no such relation within our data. For the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the H ^− opacity. We suggest that the general lack of trends seen across this population study could be due to (i) the insufficient spectral coverage offered by the Hubble Space Telescope’s WFC3 G141 band, (ii) the lack of a simple trend across the whole population, (iii) the essentially random nature of the target selection for this study, or (iv) a combination of all the above. We set out how we can learn from this vast data set going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as the JWST, Twinkle, and Ariel. We conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection.

The proposed protoplanet AB Aur b is a spatially concentrated emission source imaged in the millimeter-wavelength disk gap of the Herbig Ae/Be star AB Aur. Its near-infrared spectrum and absence of strong polarized light have been interpreted as evidence supporting the protoplanet interpretation. However, the complex scattered-light structures in the AB Aur disk pose challenges in resolving the emission source and interpreting the true nature of AB Aur b. We present new images of the AB Aur system obtained using the Hubble Space Telescope Wide Field Camera 3 in the ultraviolet (UV) and optical bands. AB Aur b and the known disk spirals are recovered in the F336W, F410M, and F645N bands. The spectral energy distribution of AB Aur b shows absorption in the Balmer jump, mimicking that of early-type stars. By comparing the colors of AB Aur b to those of the host star, the disk spirals, and predictions from scattered light and self-luminous models, we find that the emission from AB Aur b is inconsistent with planetary photospheric or accretion shock models. Instead, it is consistent with those measured in the circumstellar disks that trace scattered light. We conclude that the UV and visible emission from AB Aur b does not necessitate the presence of a protoplanet. We synthesize observational constraints on AB Aur b and discuss inconsistent interpretations among different data sets. Considering the significance of the AB Aur b discovery, we advocate for further observational evidence to verify its planetary nature.

Far-ultraviolet (FUV) emission lines from dwarf stars are important driving sources of photochemistry in planetary atmospheres. Properly interpreting spectral features of planetary atmospheres critically depends on the emission of its host star. While the spectral energy distributions (SEDs) of K- and M-type stars have been extensively characterized by previous observational programs, the full X-ray to infrared SED of F-type stars has not been assembled to support atmospheric modeling. On the second flight of the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE-2) rocket-borne spectrograph, we successfully captured the FUV spectrum of Procyon A (F5 IV-V) and made the first simultaneous observation of several emission features across the FUV bandpass (1010–1270 and 1300–1565 Å) of any cool star. We combine flight data with stellar models and archival observations to develop the first SED of a mid-F star. We model the response of a modern Earth-like exoplanet’s upper atmosphere to the heightened X-ray and extreme UV radiation within the habitable zone of Procyon A. These models indicate that this planet would not experience significant atmospheric escape. We simulate observations of the Ly α transit signal of this exoplanet with the Hubble Space Telescope (HST) and the Habitable Worlds Observatory (HWO). While marginally detectable with HST, we find that H i Ly α transits of potentially habitable exoplanets orbiting high radial velocity F-type stars could be observed with HWO for targets up to 150 pc away.

Ly α line profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Ly α line profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Ly α emission profile in the bottom of a damped, Ly α absorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Ly α absorption and the Ly α emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Ly α exchange between high- N _H _i and low- N _H _i paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Ly α peak separation and the [O iii ]/[O ii ] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Ly α peak separation decreases. We combine measurements of Ly α peak separation and Ly α red peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Ly α trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Ly α peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Ly α photons outside the spectroscopic aperture reshapes Ly α profiles because the distances to these compact starbursts span a large range.

There are expected to be ∼10 ^8 isolated black holes (BHs) in the Milky Way. OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462) is the only such BH with a mass measurement to date. However, its mass is disputed: Lam et al. measured a lower mass of 1.6–4.4 M _⊙ , while Sahu et al. and Mróz et al. measured a higher mass of 5.8–8.7 M _⊙ . We reanalyze OB110462, including new data from the Hubble Space Telescope (HST) and rereduced Optical Gravitational Lensing Experiment (OGLE) photometry. We also rereduce and reanalyze the HST data set with newly available software. We find significantly different (∼1 mas) HST astrometry than Lam et al. in the unmagnified epochs due to the amount of positional bias induced by a bright star ∼0.″4 from OB110462. After modeling the updated photometric and astrometric data sets, we find the lens of OB110462 is a ${6.0}_{-1.0}^{+1.2}{M}_{\odot }$ BH. Future observations with the Nancy Grace Roman Space Telescope, which will have an astrometric precision comparable or better to HST but a field of view 100× larger, will be able to measure hundreds of isolated BH masses via microlensing. This will enable the measurement of the BH mass distribution and improve understanding of massive stellar evolution and BH formation channels.

The exact nature of the luminous fast blue optical transient AT 2018cow is still debated. In this first of a two-paper series, we present a detailed analysis of three Hubble Space Telescope (HST) observations of AT 2018cow covering ∼50–60 days post-discovery in combination with other observations throughout the first two months and derive significantly improved constraints of the late thermal properties. By modeling the spectral energy distributions (SEDs), we confirm that the UV–optical emission over 50–60 days was still a smooth blackbody (i.e., optically thick) with a high temperature ( T _BB ∼ 15,000 K) and small radius ( R _BB ≲ 1000 R _⊙ ). Additionally, we report for the first time a break in the bolometric light curve: the thermal luminosity initially declined at a rate of L _BB ∝ t ^−2.40 but faded much faster at t ^−3.06 after day 13. Reexamining possible late-time power sources, we disfavor significant contributions from radioactive decay based on the required ^56 Ni mass and lack of UV line blanketing in the HST SEDs. We argue that the commonly proposed interaction with circumstellar material may face significant challenges in explaining the late thermal properties, particularly the effects of the optical depth. Alternatively, we find that continuous outflow/wind driven by a central engine can still reasonably explain the combination of a receding photosphere, optically thick and rapidly fading emission, and intermediate-width lines. However, the rapid fading may have further implications on the power output and structure of the system. Our findings may support the hypothesis that AT 2018cow and other “Cow-like transients” are powered mainly by accretion onto a central engine.

In this second of a two-paper series, we present a detailed analysis of three Hubble Space Telescope observations taken ∼2–4 yr post-discovery, examining the evolution of a UV-bright underlying source at the precise position of AT 2018cow. While observations at ∼2–3 yr post-discovery revealed an exceptionally blue ( L _ν ∝ ν ^1.99 ) underlying source with relatively stable optical brightness, fading in the near-UV was observed at year 4, indicating flattening in the spectrum (to L _ν ∝ ν ^1.64 ). The resulting spectral energy distributions can be described by an extremely hot but small blackbody, and the fading may be intrinsic (cooling) or extrinsic (increased absorption). Considering possible scenarios and explanations, we disfavor significant contributions from stellar sources and dust formation, based on the observed color and brightness. By comparing the expected power and the observed luminosity, we rule out interaction with known radio-producing circumstellar material (CSM) as well as magnetar spin down with B ∼ 10 ^15 G as possible power sources, though we cannot rule out the possible existence of a denser CSM component (e.g., a previously ejected hydrogen envelope) or a magnetar with B ≲ 10 ^14 G. Finally, we find that a highly inclined precessing accretion disk can reasonably explain the color, brightness, and evolution of the underlying source. However, a major uncertainty in this scenario is the mass of the central black hole (BH), as both stellar-mass and intermediate-mass BHs face notable challenges that cannot be explained by our simple disk model, and further observations and theoretical works are needed to fully constrain the nature of this underlying source.

We present an atmospheric analysis of LTT 9779 b, a rare planet situated in the hot-Neptune desert, that has been observed with Hubble Space Telescope (HST)/WFC3 with G102 and G141. The combined transmission spectrum, which covers 0.8–1.6 μ m, shows a gradual increase in transit depth with wavelength. Our preferred atmospheric model shows evidence for H _2 O, CO _2 , and FeH with a significance of 3.1 σ , 2.4 σ , and 2.1 σ , respectively. In an attempt to constrain the rate of atmospheric escape for this planet, we search for the 1.083 μ m helium line in the G102 data but find no evidence of excess absorption that would indicate an escaping atmosphere using this tracer. We refine the orbital ephemerides of LTT 9779 b using our HST data and observations from TESS, searching for evidence of orbital decay or apsidal precession, which are not found. The phase-curve observation of LTT 9779 b with JWST NIRISS should provide deeper insights into the atmosphere of this planet and the expected atmospheric escape might be detected with further observations concentrated on other tracers such as Ly α .