We present an atmospheric retrieval analysis on a set of young, cloudy, red L-dwarfs -- CWISER J124332.12+600126.2 and WISEP J004701.06+680352.1 -- using the \textit{Brewster} retrieval framework. We ...also present the first elemental abundance measurements of the young K-dwarf (K0) host star, BD+60 1417 using high resolution~(R = 50,000) spectra taken with PEPSI/LBT. In the complex cloudy L-dwarf regime the emergence of condensate cloud species complicates retrieval analysis when only near-infrared data is available. We find that for both L dwarfs in this work, despite testing three different thermal profile parameterizations we are unable to constrain reliable abundance measurements and thus the C/O ratio. While we can not conclude what the abundances are, we can conclude that the data strongly favor a cloud model over a cloudless model. We note that the difficulty in retrieval constraints persists regardless of the signal to noise of the data examined (S/N \(\sim\) 10 for CWISER J124332.12+600126.2 and~40 for WISEP J004701.06+680352.1). The results presented in this work provide valuable lessons about retrieving young, low-surface gravity, cloudy L-dwarfs. This work provides continued evidence of missing information in models and the crucial need for JWST to guide and inform retrieval analysis in this regime.
At the lowest masses, the distinction between brown dwarfs and giant exoplanets is often blurred and literature classifications rarely reflect the deuterium burning boundary. Atmospheric ...characterisation may reveal the extent to which planetary formation pathways contribute to the population of very-low mass brown dwarfs, by revealing if their abundance distributions differ from those of the local field population or, in the case of companions, their primary stars. The T8 dwarf Ross 458c is a possible planetary mass companion to a pair of M dwarfs, and previous work suggests that it is cloudy. We here present the results of the retrieval analysis of Ross 458c, using archival spectroscopic data in the 1.0 to 2.4 micron range. We test a cloud free model as well as a variety of cloudy models and find that the atmosphere of Ross 458c is best described by a cloudy model (strongly preferred). The CH4/H2O is higher than expected at 1.97 +0.13 -0.14. This value is challenging to understand in terms of equilibrium chemistry and plausible C/O ratios. Comparisons to thermochemical grid models suggest a C/O of ~ 1.35, if CH4 and H2O are quenched at 2000 K, requiring vigorous mixing. We find a C/H ratio of +0.18, which matches the metallicity of the primary system, suggesting that oxygen is missing from the atmosphere. Even with extreme mixing, the implied C/O is well beyond the typical stellar regime, suggesting a either non-stellar formation pathway, or the sequestration of substantial quantities of oxygen via hitherto unmodeled chemistry or condensation processes.
We present results from an atmospheric retrieval analysis of Gl 229B using the BREWSTER retrieval code. We find the best fit model to be cloud-free, consistent with the T dwarf retrieval work of Line ...et al. 2017, Zalesky et al. 2022 and Gonzales et al. 2020. Fundamental parameters (mass, radius, log(L_{Bol}/L_{Sun}), log(g)) determined from our model agree within 1\sigma to SED-derived values except for T_{eff} where our retrieved T_{eff} is approximately 100 K cooler than the evolutionary model-based SED value. We find a retrieved mass of 50^{+12}_{-9} M_{Jup}, however, we also find that the observables of Gl 229B can be explained by a cloud-free model with a prior on mass at the dynamical value, 70 M_{Jup}. We are able to constrain abundances for H_2O, CO, CH_4, NH_3, Na and K and find a supersolar C/O ratio as compared to its primary, Gl 229A. We report an overall subsolar metallicity due to atmospheric oxygen depletion but find a solar C/H, which matches that of the primary. We find that this work contributes to a growing trend in retrieval-based studies, particularly for brown dwarfs, toward supersolar C/O ratios and discuss the implications of this result on formation mechanisms, internal physical processes as well as model biases.
We have used the UKIRT Hemisphere Survey (UHS) combined with the UKIDSS Galactic Cluster Survey (GCS), the UKIDSS Galactic Plane Survey (GPS), and the CatWISE2020 catalog to search for new substellar ...members of the nearest open cluster to the Sun, the Hyades. Eight new substellar Hyades candidate members were identified and observed with the Gemini/GNIRS near-infrared spectrograph. All eight objects are confirmed as brown dwarfs with spectral types ranging from L6 to T5, with two objects showing signs of spectral binarity and/or variability. A kinematic analysis demonstrates that all eight new discoveries likely belong to the Hyades cluster, with future radial velocity and parallax measurements needed to confirm their membership. CWISE J042356.23\(+\)130414.3, with a spectral type of T5, would be the coldest ($T_{\rm eff}$$\approx\(1100 K) and lowest-mass (\)M$$\approx\(30 \)M_{\rm Jup}$) free-floating member of the Hyades yet discovered. We further find that high-probability substellar Hyades members from this work and previous studies have redder near-infrared colors than field-age brown dwarfs, potentially due to lower surface gravities and super-solar metallicities.
We present an atmospheric retrieval analysis of a pair of highly variable, \(\sim200~\)Myr old, early-T type planetary-mass exoplanet analogs SIMP J01365662+0933473 and 2MASS J21392676+0220226 using ...the Brewster retrieval framework. Our analysis, which makes use of archival \(1-15~\mu\)m spectra, finds almost identical atmospheres for both objects. For both targets, we find that the data is best described by a patchy, high-altitude forsterite (Mg\(_2\)SiO\(_4\)) cloud above a deeper, optically thick iron (Fe) cloud. Our model constrains the cloud properties well, including the cloud locations and cloud particle sizes. We find that the patchy forsterite slab cloud inferred from our retrieval may be responsible for the spectral behavior of the observed variability. Our retrieved cloud structure is consistent with the atmospheric structure previously inferred from spectroscopic variability measurements, but clarifies this picture significantly. We find consistent C/O ratios for both objects which supports their formation within the same molecular cloud in the Carina-Near Moving Group. Finally, we note some differences in the constrained abundances of H\(_2\)O and CO which may be caused by data quality and/or astrophysical processes such as auroral activity and their differing rotation rates. The results presented in this work provide a promising preview of the detail with which we will characterize extrasolar atmospheres with JWST, which will yield higher quality spectra across a wider wavelength range.
We report the identification of 89 new systems containing ultracool dwarf companions to main sequence stars and white dwarfs, using the citizen science project Backyard Worlds: Planet 9 and ...cross-reference between Gaia and CatWISE2020. Thirty-two of these companions and thirty-three host stars were followed up with spectroscopic observations, with companion spectral types ranging from M7-T9 and host spectral types ranging from G2-M9. These systems exhibit diverse characteristics, from young to old ages, blue to very red spectral morphologies, potential membership to known young moving groups, and evidence of spectral binarity in 9 companions. Twenty of the host stars in our sample show evidence for higher order multiplicity, with an additional 11 host stars being resolved binaries themselves. We compare this sample's characteristics with those of the known stellar binary and exoplanet populations, and find our sample begins to fill in the gap between directly imaged exoplanets and stellary binaries on mass ratio-binding energy plots. With this study, we increase the population of ultracool dwarf companions to FGK stars by \(\sim\)42\%, and more than triple the known population of ultracool dwarf companions with separations larger than 1,000 au, providing excellent targets for future atmospheric retrievals.
A complete accounting of nearby objects -- from the highest-mass white dwarf
progenitors down to low-mass brown dwarfs -- is now possible, thanks to an
almost complete set of trigonometric parallax ...determinations from Gaia,
ground-based surveys, and Spitzer follow-up. We create a census of objects
within a Sun-centered sphere of 20-pc radius and check published literature to
decompose each binary or higher-order system into its separate components. The
result is a volume-limited census of $\sim$3,600 individual star formation
products useful in measuring the initial mass function across the stellar ($<8
M_\odot$) and substellar ($\gtrsim 5 M_{Jup}$) regimes. Comparing our resulting
initial mass function to previous measurements shows good agreement above
0.8$M_\odot$ and a divergence at lower masses. Our 20-pc space densities are
best fit with a quadripartite power law, $\xi(M) = dN/dM \propto M^{-\alpha}$
with long-established values of $\alpha = 2.3$ at high masses ($0.55 < M < 8.00
M_\odot$) and $\alpha = 1.3$ at intermediate masses ($0.22 < M < 0.55
M_\odot$), but at lower masses we find $\alpha = 0.25$ for $0.05 < M <0.22
M_\odot$ and $\alpha = 0.6$ for $0.01 < M < 0.05 M_\odot$. This implies that
the rate of production as a function of decreasing mass diminishes in the
low-mass star/high-mass brown dwarf regime before increasing again in the
low-mass brown dwarf regime. Correcting for completeness, we find a star to
brown dwarf number ratio of, currently, 4:1, and an average mass per object of
0.41 $M_\odot$.
High-energy neutrinos are a promising tool for identifying astrophysical sources of high and ultra-high energy cosmic rays (UHECR). Prospects of detecting neutrinos at high energies (\(\gtrsim\)TeV) ...from blazars have been boosted after the recent association of IceCube-170922A and TXS 0506+056. We investigate the high-energy neutrino, IceCube-190331A, a high-energy starting event (HESE) with a high likelihood of being astrophysical in origin. We initiated a Swift/XRT and UVOT tiling mosaic of the neutrino localisation, and followed up with ATCA radio observations, compiling a multiwavelength SED for the most likely source of origin. NuSTAR observations of the neutrino location and a nearby X-ray source were also performed. We find two promising counterpart in the 90% confidence localisation region and identify the brightest as the most likely counterpart. However, no Fermi/LAT \(\gamma\)-ray source and no prompt Swift/BAT source is consistent with the neutrino event. At this point it is unclear whether any of the counterparts produced IceCube-190331A. We note that the Helix Nebula is also consistent with the position of the neutrino event, and we calculate that associated particle acceleration processes cannot produce the required energies to generate a high-energy HESE neutrino.
We present the discovery of 34 comoving systems containing an ultra-cool dwarf found by means of the NOIRLab Source Catalog (NSC) DR2. NSC's angular resolution of \(\sim\)1" allows for the detection ...of small separation binaries with significant proper motions. We used the catalog's accurate proper motion measurements to identify the companions by cross-matching a previously compiled list of brown dwarf candidates with NSC DR2. The comoving pairs consist of either a very low-mass star and an ultra-cool companion, or a white dwarf and an ultra-cool companion. The estimated spectral types of the primaries are in the K and M dwarf regimes, those of the secondaries in the M, L and T dwarf regimes. We calculated angular separations between \(\sim\)2 and \(\sim\)56", parallactic distances between \(\sim\)43 and \(\sim\)261 pc and projected physical separations between \(\sim\)169 and \(\sim\)8487 AU. The lowest measured total proper motion is 97 mas yr\(^{-1}\), the highest 314 mas yr\(^{-1}\). Tangential velocities range from \(\sim\)23 to \(\sim\)187 km s\(^{-1}\). We also determined comoving probabilities, estimated mass ratios and calculated binding energies for each system. We found no indication of possible binarity for any component of the 34 systems in the published literature. The discovered systems can contribute to the further study of the formation and evolution of low-mass systems as well as to the characterization of cool substellar objects.
We have used data from the UKIRT Hemisphere Survey (UHS) to search for substellar members of the Hyades cluster. Our search recovered several known substellar Hyades members, and two known brown ...dwarfs that we suggest may be members based on a new kinematic analysis. We uncovered thirteen new substellar Hyades candidates, and obtained near-infrared follow-up spectroscopy of each with IRTF/SpeX. Six candidates with spectral types between M7 and L0 are ruled out as potential members based on their photometric distances (\(\gtrsim\)100 pc). The remaining seven candidates, with spectral types between L5 and T4, are all potential Hyades members, with five showing strong membership probabilities based on BANYAN \(\Sigma\) and a convergent point analysis. Distances and radial velocities are still needed to confirm Hyades membership. If confirmed, these would be some of the lowest mass free-floating members of the Hyades yet known, with masses as low as \(\sim\)30 \(M_{\rm Jup}\). An analysis of all known substellar Hyades candidates shows evidence that the full extent of the Hyades has yet to be probed for low-mass members, and more would likely be recovered with deeper photometric and astrometric investigations.
