Evidence of disequilibrium chemistry due to vertical mixing in the atmospheres of many T and Y-dwarfs has been inferred due to enhanced mixing ratios of CO and reduced NH\(_3\). Atmospheric models of ...planets and brown dwarfs typically parameterize this vertical mixing phenomenon with the vertical eddy diffusion coefficient, \(K_{\rm zz}\). While \(K_{\rm zz}\) can perhaps be approximated in the convective regions in the atmosphere with mixing length theory, in radiative regions the strength of vertical mixing is uncertain by many orders of magnitude. With a new grid of self-consistent 1D model atmospheres from \(T_{\rm eff}\) of 400 - 1000 K, computed with a new radiative-convective equilibrium python code PICASO 3.0, we aim to assess how molecular abundances and corresponding spectra can be used as a probe of depth-dependent \(K_{\rm zz}\). At a given surface gravity, we find non-monotonic behavior in the CO abundance as a function of \(T_{\rm eff}\), as chemical abundances are sometimes quenched in either of two potential atmospheric convective zones, or quenched in either of two possible radiative zones. The temperature structure and chemical quenching behavior also changes with gravity. We compare our models with available near-infrared and M-band spectroscopy of several T and Y-dwarfs and assess their atmospheric vertical mixing profiles. We also compare to color-magnitude diagrams and make predictions for JWST spectra. This work yields new constraints, and points the way to significant future gains, in determining \(K_{\rm zz}\), a fundamental atmospheric parameter in substellar atmospheres, with significant implications for chemistry and cloud modeling.
We observed HD 19467 B with JWST's NIRCam in six filters spanning 2.5-4.6 \(\mu m\) with the Long Wavelength Bar coronagraph. The brown dwarf HD 19467 B was initially identified through a long-period ...trend in the radial velocity of G3V star HD 19467. HD 19467 B was subsequently detected via coronagraphic imaging and spectroscopy, and characterized as a late-T type brown dwarf with approximate temperature \(\sim1000\)K. We observed HD 19467 B as a part of the NIRCam GTO science program, demonstrating the first use of the NIRCam Long Wavelength Bar coronagraphic mask. The object was detected in all 6 filters (contrast levels of \(2\times10^{-4}\) to \(2\times10^{-5}\)) at a separation of 1.6 arcsec using Angular Differential Imaging (ADI) and Synthetic Reference Differential Imaging (SynRDI). Due to a guidestar failure during acquisition of a pre-selected reference star, no reference star data was available for post-processing. However, RDI was successfully applied using synthetic Point Spread Functions (PSFs) developed from contemporaneous maps of the telescope's optical configuration. Additional radial velocity data (from Keck/HIRES) are used to constrain the orbit of HD 19467 B. Photometric data from TESS are used to constrain the properties of the host star, particularly its age. NIRCam photometry, spectra and photometry from literature, and improved stellar parameters are used in conjunction with recent spectral and evolutionary substellar models to derive physical properties for HD 19467 B. Using an age of 9.4\(\pm\)0.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS asteroseismology, we obtain a model-derived mass of 62\(\pm 1M_{J}\), which is consistent within 2-\(\sigma\) with the dynamically derived mass of 81\(^{+14}_{-12}M_{J}\).
The future is now - after its long-awaited launch in December 2021, JWST began science operations in July 2022 and is already revolutionizing exoplanet astronomy. The Early Release Observations (ERO) ...program was designed to provide the first images and spectra from JWST, covering a multitude of science cases and using multiple modes of each on-board instrument. Here, we present transmission spectroscopy observations of the hot-Saturn WASP-96b with the Single Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph, observed as part of the ERO program. As the SOSS mode presents some unique data reduction challenges, we provide an in-depth walk-through of the major steps necessary for the reduction of SOSS data: including background subtraction, correction of 1/f noise, and treatment of the trace order overlap. We furthermore offer potential routes to correct for field star contamination, which can occur due to the SOSS mode's slitless nature. By comparing our extracted transmission spectrum with grids of atmosphere models, we find an atmosphere metallicity between 1x and 5x solar, and a solar carbon-to-oxygen ratio. Moreover, our models indicate that no grey cloud deck is required to fit WASP-96b's transmission spectrum, but find evidence for a slope shortward of 0.9\(\mu\)m, which could either be caused by enhanced Rayleigh scattering or the red wing of a pressure-broadened Na feature. Our work demonstrates the unique capabilities of the SOSS mode for exoplanet transmission spectroscopy and presents a step-by-step reduction guide for this new and exciting instrument.
We use data from the All Wavelength Extended Groth Strip International Survey to construct stacked X-ray maps of optically bright active galaxies (AGN) and an associated control sample of galaxies at ...high redshift (z less than 0.6). From our analysis of the surface brightness profiles obtained from these X-ray maps, we find evidence of feedback from the active nuclei. We find that excluding galaxies and AGN, residing in group environments, from our samples enhances the significance of our detection. Our results support the tentative findings of Chatterjee et al. who use X-ray selected AGN for their analysis. We discuss the implications of these results in the context of quantifying AGN feedback and show that the current method can be used to extract X-ray source population in high redshift galaxies.
We present a sample of 88 candidate z~8.5-14.5 galaxies selected from the completed NIRCam imaging from the Cosmic Evolution Early Release Science (CEERS) survey. These data cover ~90 arcmin^2 (10 ...NIRCam pointings) in six broad-band and one medium-band imaging filter. With this sample we confirm at higher confidence early JWST conclusions that bright galaxies in this epoch are more abundant than predicted by most theoretical models. We construct the rest-frame ultraviolet luminosity functions at z~9, 11 and 14, and show that the space density of bright (M_UV=-20) galaxies changes only modestly from z~14 to z~9, compared to a steeper increase from z~8 to z~4. While our candidates are photometrically selected, spectroscopic followup has now confirmed 13 of them, with only one significant interloper, implying that the fidelity of this sample is high. Successfully explaining the evidence for a flatter evolution in the number densities of UV-bright z>10 galaxies may thus require changes to the dominant physical processes regulating star formation. While our results indicate that significant variations of dust attenuation with redshift are unlikely to be the dominant factor at these high redshifts, they are consistent with predictions from models which naturally have enhanced star-formation efficiency and/or stochasticity. An evolving stellar initial mass function could also bring model predictions into better agreement with our results. Deep spectroscopic followup of a large sample of early galaxies can distinguish between these competing scenarios.
Direct imaging studies have mainly used low-resolution spectroscopy (\(R\sim20-100\)) to study the atmospheres of giant exoplanets and brown dwarf companions, but the presence of clouds has often led ...to degeneracies in the retrieved atmospheric abundances (e.g. C/O, metallicity). This precludes clear insights into the formation mechanisms of these companions. The Keck Planet Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to transport light into NIRSPEC (\(R\sim35,000\) in \(K\) band), and aims to address these challenges with high-resolution spectroscopy. Using an atmospheric retrieval framework based on petitRADTRANS, we analyze KPIC high-resolution spectrum (\(2.29-2.49~\mu\)m) and archival low-resolution spectrum (\(1-2.2~\mu\)m) of the benchmark brown dwarf HD 4747 B (\(m=67.2\pm1.8~M_{\rm{Jup}}\), \(a=10.0\pm0.2\) au, \(T_{\rm eff}\approx1400\) K). We find that our measured C/O and metallicity for the companion from the KPIC high-resolution spectrum agree with that of its host star within \(1-2\sigma\). The retrieved parameters from the \(K\) band high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO, H\(_2\)O, and CH\(_4\) (volume mixing ratio of log(CH\(_4\))=\(-4.82\pm0.23\)) in this L/T transition companion with the KPIC data. The relative molecular abundances allow us to constrain the degree of chemical disequilibrium in the atmosphere of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper limit predicted from mixing length theory.
Photochemistry is a fundamental process of planetary atmospheres that
regulates the atmospheric composition and stability. However, no unambiguous
photochemical products have been detected in ...exoplanet atmospheres to date.
Recent observations from the JWST Transiting Exoplanet Early Release Science
Program found a spectral absorption feature at 4.05 $\mu$m arising from SO$_2$
in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass
(0.28 M$_J$) gas giant exoplanet orbiting a Sun-like star with an equilibrium
temperature of $\sim$1100 K. The most plausible way of generating SO$_2$ in
such an atmosphere is through photochemical processes. Here we show that the
SO$_2$ distribution computed by a suite of photochemical models robustly
explains the 4.05 $\mu$m spectral feature identified by JWST transmission
observations with NIRSpec PRISM (2.7$\sigma$) and G395H (4.5$\sigma$). SO$_2$
is produced by successive oxidation of sulphur radicals freed when hydrogen
sulphide (H$_2$S) is destroyed. The sensitivity of the SO$_2$ feature to the
enrichment of the atmosphere by heavy elements (metallicity) suggests that it
can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an
inferred metallicity of $\sim$10$\times$ solar. We further point out that
SO$_2$ also shows observable features at ultraviolet and thermal infrared
wavelengths not available from the existing observations.
The presence of AGB stars in clusters provides key constraints for stellar models, as has been demonstrated with historical data from the Magellanic Clouds. In this work, we look for candidate AGB ...stars in M31 star clusters from the Panchromatic Hubble Andromeda Treasury (PHAT) survey. Our photometric criteria selects stars brighter than the tip of the red giant branch, which includes the bulk of the thermally-pulsing AGB stars as well as early-AGB stars and other luminous cool giants expected in young stellar populations (e.g. massive red supergiants, and intermediate-mass red helium-burning stars). The AGB stars can be differentiated, a posteriori, using the ages already estimated for our cluster sample. 937 candidates are found within the cluster aperture radii, half (450) of which are very likely cluster members. Cross-matching with additional databases reveals two carbon stars and ten secure variables among them. The field-corrected age distribution reveals the presence of young supergiants peaking at ages smaller than 100 Myr, followed by a long tail of AGB stars extending up to the oldest possible ages. This long tail reveals the general decrease in the numbers of AGB stars from initial values of 50e-6/Msun at 100 Myr down to 5e-6/Msun at 10 Gyr. Theoretical models of near-solar metallicity reproduce this general trend, although with localized discrepancies over some age intervals, whose origin is not yet identified. The entire catalogue is released together with finding charts to facilitate follow-up studies.
With a dynamical mass of \(3 \, M_\mathrm{Jup}\), the recently discovered giant planet AF Lep b is the lowest-mass imaged planet with a direct mass measurement. Its youth and spectral type near the ...L/T transition make it a promising target to study the impact of clouds and atmospheric chemistry at low surface gravities. In this work, we present JWST/NIRCam imaging of AF Lep b. Across two epochs, we detect AF Lep b in F444W (\(4.4 \, \mathrm{\mu m}\)) with S/N ratios of 9.6 and 8.7, respectively. At the planet's separation of \(320 \, \mathrm{mas}\) during the observations, the coronagraphic throughput is \({\approx}7\%\), demonstrating that NIRCam's excellent sensitivity persists down to small separations. The F444W photometry of AF Lep b affirms the presence of disequilibrium carbon chemistry and enhanced atmospheric metallicity. These observations also place deep limits on wider-separation planets in the system, ruling out \(1.1 \, M_\mathrm{Jup}\) planets beyond \(15.6 \, \mathrm{au}\) (0.58 arcsec), \(1.1 \, M_\mathrm{Sat}\) planets beyond \(27 \, \mathrm{au}\) (1 arcsec), and \(2.8 \, M_\mathrm{Nep}\) planets beyond \(67 \, \mathrm{au}\) (2.5 arcsec). We also present new Keck/NIRC2 \(L'\) imaging of AF Lep b; combining this with the two epochs of F444W photometry and previous Keck \(L'\) photometry provides limits on the long-term 3-\(5 \, \mathrm{\mu m}\) variability of AF Lep b on months-to-years timescales. AF Lep b is the closest-separation planet imaged with JWST to date, demonstrating that planets can be recovered well inside the nominal (50% throughput) NIRCam coronagraph inner working angle.
Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability. However, no unambiguous photochemical products have been detected in ...exoplanet atmospheres to date. Recent observations from the JWST Transiting Exoplanet Early Release Science Program found a spectral absorption feature at 4.05 \(\mu\)m arising from SO\(_2\) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 M\(_J\)) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of \(\sim\)1100 K. The most plausible way of generating SO\(_2\) in such an atmosphere is through photochemical processes. Here we show that the SO\(_2\) distribution computed by a suite of photochemical models robustly explains the 4.05 \(\mu\)m spectral feature identified by JWST transmission observations with NIRSpec PRISM (2.7\(\sigma\)) and G395H (4.5\(\sigma\)). SO\(_2\) is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H\(_2\)S) is destroyed. The sensitivity of the SO\(_2\) feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of \(\sim\)10\(\times\) solar. We further point out that SO\(_2\) also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.
