Brown Dwarfs Research Articles

The Keck-HGCA Pilot Survey II: Direct imaging discovery of HD 63754 B, a ∼20 au massive companion near the hydrogen burning limit

Abstract We present the joint astrometric and direct imaging discovery, mass measurement, and orbital analysis of HD 63754 B (HIP 38216 B), a companion near the stellar-substellar boundary orbiting ∼20 AU from its Sun-like host. HD 63754 was observed in our ongoing high-contrast imaging survey targeting stars with significant proper-motion accelerations between Hipparcosand Gaia consistent with wide-separation substellar companions. We utilized archival HIRES and HARPS radial velocity (RV) data, together with the host star’s astrometric acceleration extracted from the Hipparcos–Gaia Catalog of Accelerations (HGCA), to predict the location of the candidate companion around HD 63754 A. We subsequently imaged HD 63754 B at its predicted location using the Near Infrared Camera 2 (NIRC2) in the L′ band at the W. M. Keck Observatory. We then jointly modeled the orbit of HD 63754 B with RVs, Hipparcos–Gaia accelerations, and our new relative astrometry, measuring a dynamical mass of ${81.9}_{-5.8}^{+6.4} \rm {M_{\rm Jup}}$, an eccentricity of ${0.260}_{-0.059}^{+0.065}$, and a nearly face-on inclination of $174.\!\!^\circ 81_{-0.50}^{+0.48}$. For HD 63754 B, we obtain an L′ band absolute magnitude of L′ = 11.39 ± 0.06 mag, from which we infer a bolometric luminosity of $\mathrm{log(L_{\rm bol}/\rm {\mathrm{L}_{\odot }})= -4.55 \pm 0.08}$ dex using a comparison sample of L and T dwarfs with measured luminosities. Although uncertainties linger in age and dynamical mass estimates, our analysis points toward HD 63754 B’s identity as a brown dwarf on the L/T transition rather than a low-mass star, indicated by its inferred bolometric luminosity and model-estimated effective temperature. Future RV, spectroscopic, and astrometric data such as those from JWST and Gaia DR4 will clarify HD 63754 B’s mass, and enable spectral typing and atmospheric characterization.

Primeval very low-mass stars and brown dwarfs – VIII. The first age benchmark L subdwarf, a wide companion to a halo white dwarf

Abstract We report the discovery of five white dwarf + ultracool dwarf systems identified as common proper motion wide binaries in the Gaia Catalogue of Nearby Stars. The discoveries include a white dwarf + L subdwarf binary, VVV 1256−62AB, a gravitationally-bound system located 75.6$^{+1.9}_{-1.8}$ pc away with a projected separation of 1375$^{+35}_{-33}$ au. The primary is a cool DC white dwarf with a hydrogen dominated atmosphere, and has a total age of $10.5^{+3.3}_{-2.1}$ Gyr, based on white dwarf model fitting. The secondary is an L subdwarf with a metallicity of [M/H] = $-0.72^{+0.08}_{-0.10}$ (i.e. [Fe/H] = −0.81 ± 0.10) and Teff = 2298$^{+45}_{-43}$ K based on atmospheric model fitting of its optical to near infrared spectrum, and likely has a mass just above the stellar/substellar boundary. The subsolar metallicity of the L subdwarf and the system’s total space velocity of 406 km/s indicates membership in the Galactic halo, and it has a flat eccentric Galactic orbit passing within 1 kpc of the centre of the Milky Way every ∼0.4 Gyr and extending to 15-31 kpc at apogal. VVV 1256−62B is the first L subdwarf to have a well-constrained age, making it an ideal benchmark of metal-poor ultracool dwarf atmospheres and evolution.

JWST Imaging of the Closest Globular Clusters. II. Discovery of Brown Dwarfs in NGC 6397 and Measurement of Age from the Brown Dwarf Cooling Sequence, Using SANDee—A New Grid of Model Isochrones across the Hydrogen-burning Limit

Globular clusters contain vast repositories of metal-poor stars that represent some of the oldest stellar generations in the Universe. The archaeological footprint of early Galactic evolution may be retained in the measurable properties of globular clusters, such as their ages, mass functions, and chemical abundances. Until recently, all photometric studies of globular clusters were restricted to stellar members. Now, the sensitivity of JWST can extend this analysis to the substellar regime. If detected in sufficient numbers, brown dwarf members can provide tight constraints on the properties of their parent population. We present SANDee—a new grid of stellar models that accurately represent the color–magnitude diagrams of globular clusters across the hydrogen-burning limit at a wide range of metallicities. Using JWST NIRCam photometry and the new models, we identify three brown dwarfs in the globular cluster NGC 6397 with T eff = 1300–1800 K, confirmed by both proper motion and model fitting. We use the observed luminosities of discovered brown dwarfs to obtain the first age estimate of a globular cluster from its substellar cooling sequence: 13.4 ± 3.3 Gyr. We also derive the local mass function of the cluster across the hydrogen-burning limit and find it to be top heavy, suggesting extensive dynamical evolution. We expect that the constraints on both age and mass function of NGC 6397 derived in this work can be greatly improved by a second epoch of NIRCam imaging in the same field.

TIC 165797593: A new slow pulsating HW Vir type sdB + Brown dwarf eclipsing binary

First photometric and spectroscopic results of sdB binary TIC 165797593 are presented. This object is a HW Vir type eclipsing binary system where primary is a sdB and secondary is a Brown dwarf. It is a short period binary with an orbital period of 0.3697 days which shows a prominent reflection effect in the light curve. The temperature T1 = 30000 K and log(g) = 6.0 were determined using STERNE atmospheric model by fitting the observed spectra. The photometric solutions were derived using Wilson–Devinney (WD) method where the best fit was achieved at q = 0.103. The mass of the secondary was determined to be 0.048 M⊙ using photometric solutions obtained from the WD method, assuming a canonical mass of 0.47 M⊙ for the primary. From the determined mass, we presume that the secondary component is a Brown dwarf. Asteroseismological analysis shows that the pulsation type corresponds to the g-mode, and the rotational period of the interior of sdB was determined and reported.

The ESO SupJup Survey

Context. It has been proposed that the distinct formation and evolutionary pathways of exoplanets and brown dwarfs may affect the chemical and isotopic content of their atmospheres. Recent work has indeed shown differences in the 12C/13C isotope ratio, which have provisionally been attributed to the top-down formation of brown dwarfs and the core accretion pathway of super-Jupiters. Aims. The ESO SupJup Survey is aimed at disentangling the formation pathways of isolated brown dwarfs and planetary-mass companions using chemical and isotopic tracers. The survey utilises high-resolution spectroscopy with the recently upgraded CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES+) at the Very Large Telescope, covering a total of 49 targets. Here, we present the first results of this survey: an atmospheric characterisation of DENIS J0255-4700, an isolated brown dwarf near the L-T transition. Methods. We analysed its observed CRIRES+ K-band spectrum using an atmospheric retrieval framework in which the radiative transfer code petitRADTRANS was coupled with the PyMultiNest sampling algorithm. Gaussian processes were employed to model inter-pixel correlations. In addition, we adopted an updated parameterisation of the pressure-temperature profile. Results. Abundances of CO, H2O, CH4, and NH3 were retrieved for this fast-rotating L-dwarf. The ExoMol H2O line list provides a significantly better fit than that of HITEMP. A free-chemistry retrieval is strongly favoured over equilibrium chemistry, caused by an under-abundance of CH4. The free-chemistry retrieval constrains a super-solar C/O-ratio of ~0.68 and a solar metallicity. We find tentative evidence (~3σ) for the presence of 13CO, with a constraint on the isotopologue ratio of 12CO/13CO = 184−40+61 and a lower limit of ≳97, which suggests a depletion of 13C compared to the local interstellar medium (12C/13C ~ 68). Conclusions. High-resolution, high signal-to-noise K-band spectra provide an excellent means of constraining the chemistry and isotopic content of sub-stellar objects, which is the main objective of the ESO SupJup Survey.

Probing the Heights and Depths of Y Dwarf Atmospheres: A Retrieval Analysis of the JWST Spectral Energy Distribution of WISE J035934.06–540154.6

We present an atmospheric retrieval analysis of the Y0 brown dwarf WISE J035934.06−540154.6 using the low-resolution 0.96–12 μm James Webb Space Telescope (JWST) spectrum presented in Beiler et al. We obtain volume number mixing ratios of the major gas-phase absorbers (H2O, CH4, CO, CO2, PH3, and H2S) that are three to five times more precise than previous work that used Hubble Space Telescope (HST) spectra. We also find an order-of-magnitude improvement in the precision of the retrieved thermal profile, a direct result of the broad wavelength coverage of the JWST data. We used the retrieved thermal profile and surface gravity to generate a grid of chemical forward models with varying metallicity, (C/O)atm, and strengths of vertical mixing as encapsulated by the eddy diffusion coefficient K zz. Comparison of the retrieved abundances with this grid of models suggests that the deep atmosphere of WISE 0359−54 shows signs of vigorous vertical mixing with K zz = 109 [cm2 s−1]. To test the sensitivity of these results to our five-knot spline thermal profile model, we performed a second retrieval using the Madhusudhan & Seager thermal profile model. While the results of the two retrievals generally agree well, we do find differences between the retrieved values of mass and volume number mixing ratio of H2S with fractional differences of the median values of −0.64 and −0.10, respectively. In addition, the five-knot thermal profile is consistently warmer at pressure between 1 and 70 bar. Nevertheless, our results underscore the power that the broad-wavelength infrared spectra obtainable with the JWST have to characterize the atmospheres of cool brown dwarfs.

RTModel: A platform for real-time modeling and massive analyses of microlensing events

Context. The microlensing of stars in our Galaxy has long been used to detect and characterize stellar populations, exoplanets, brown dwarfs, stellar remnants, and all other objects that may magnify the source stars with their gravitational fields. The interpretation of microlensing light curves is relatively simple for single lenses and single sources, but it becomes more and more complicated when we add more objects and take their relative motions into account. Aims. RTModel is a modeling platform that has been very active in the real-time investigations of microlensing events, providing preliminary models that have proven very useful for driving follow-up resources towards the most interesting events. The success of RTModel comes from its ability to carry out a thorough and focused exploration of the parameter space in a relatively short time. Methods. This modeling process is based on three key ideas. First, the initial conditions are chosen from a template library including all possible caustic crossing and approaches. The fits are then made using the Levenberg-Marquardt algorithm with the addition of a bumper mechanism to explore multiple minima. Finally, the basic computations of microlensing magnification are performed by the fast and robust VBBinaryLensing package. Results. In this paper, we illustrate all the algorithms of RTModel in detail with the intention to foster new approaches in view of future microlensing pipelines aimed at massive microlensing analyses.

Discovery of a Hypervelocity L Subdwarf at the Star/Brown Dwarf Mass Limit

We report the discovery of a high-velocity, very low-mass star or brown dwarf whose kinematics suggest it is unbound to the Milky Way. CWISE J124909.08+362116.0 was identified by citizen scientists in the Backyard Worlds: Planet 9 program as a high-proper-motion (μ = 0.″9 yr−1) faint red source. Moderate-resolution spectroscopy with Keck/NIRES reveals it to be a metal-poor early L subdwarf with a large radial velocity (−103 ± 10 km s−1), and its estimated distance of 125 ± 8 pc yields a speed of 456 ± 27 km s−1 in the Galactic rest frame, near the local escape velocity for the Milky Way. We explore several potential scenarios for the origin of this source, including ejection from the Galactic center ≳3 Gyr in the past, survival as the mass donor companion to an exploded white dwarf, acceleration through a three-body interaction with a black hole binary in a globular cluster, and accretion from a Milky Way satellite system. CWISE J1249+3621 is the first hypervelocity very low-mass star or brown dwarf to be found and the nearest of all such systems. It may represent a broader population of very high-velocity, low-mass objects that have undergone extreme accelerations.

Rotation and Abundances of the Benchmark Brown Dwarf HD 33632 Ab from Keck/KPIC High-resolution Spectroscopy

We present the projected rotational velocity and molecular abundances for HD 33632 Ab obtained via Keck Planet Imager and Characterizer (KPIC) high-resolution spectroscopy. HD 33632 Ab is a nearby benchmark brown dwarf companion at a separation of ∼20 au that straddles the L–T transition. Using a forward-modeling framework with on-axis host star spectra, which provides self-consistent substellar atmospheric and retrieval models for HD 33632 Ab, we derive a projected rotational velocity of 53 ± 3 km s−1 and carbon monoxide and water mass fractions of logCO = −2.3 ± 0.3 and logH2O = −2.7 ± 0.2, respectively. The inferred carbon-to-oxygen ratio (C/O = 0.58 ± 0.14), molecular abundances, and metallicity ([C/H] = 0.0 ± 0.2 dex) of HD 33632 Ab are consistent with its host star. Although detectable methane opacities are expected in L–T transition objects, we did not recover methane in our KPIC spectra, partly due to the high v sin i and to disequilibrium chemistry at the pressures to which we are sensitive. We parameterize the spin as the ratio of rotation to the breakup velocity, and compare HD 33632 Ab to a compilation of >200 very low-mass objects (M ≲ 0.1 M ⊙) that have spin measurements in the literature. There appears to be no clear trend for the isolated low-mass field objects versus mass, but a tentative trend is identified for low-mass companions and directly imaged exoplanets, similar to previous findings. A larger sample of close-in gas giant exoplanets and brown dwarfs will critically examine our understanding of their formation and evolution through rotation and chemical abundance measurements.

ASASSN-21js: A multi-year transit of a ringed disc

Aims. The early-type star ASASSN-21js started to fade in 2021, as was detected by the All Sky Automated Survey for Supernovae, undergoing a multi-year eclipse that is still underway. We interpret this event as being due to a structured disc of material transiting in front of the star. The disc is in orbit around a substellar object with the mass and luminosity of a brown dwarf or smaller. We want to determine the expected duration and ending date of the eclipse. Methods. We modelled a tilted and inclined azimuthally symmetric ring system around an unseen companion and calculated the resulting time-varying light curve as the object transited in front of the star. We made an initial estimate of the ring parameters and used these as inputs to an MCMC algorithm to determine the geometric properties of the rings with associated uncertainties. Results. The model most consistent with the light curve to date is a two-ring system at high inclination with respect to the line of sight that has a semi-major axis of 71.6 stellar radii. With an estimate of the stellar radius, the transverse velocity is around 0.7 km s−1, which if bound to the star is an orbit with a semi-major axis of around 13 000 au, placing it in the Oort cloud of the parent star. The transit is ongoing and will finish around MJD 61526 (May 1 2027). We encourage the community to continue observing this object in order to understand its properties.

Combining Gaia and GRAVITY: Characterising five new directly detected substellar companions

Precise mass constraints are vital for the characterisation of brown dwarfs and exoplanets. Here we present how the combination of data obtained by Gaia and GRAVITY can help enlarge the sample of substellar companions with measured dynamical masses. We show how the Non-Single-Star (NSS) two-body orbit catalogue contained in Gaia DR3 can be used to inform high-angular-resolution follow-up observations with GRAVITY. Applying the method presented in this work to eight Gaia candidate systems, we detect all eight predicted companions, seven of which were previously unknown and five are of a substellar nature. Among the sample is Gaia DR3 2728129004119806464 B, which – detected at an angular separation of (34.01 ± 0.15) mas from the host – is the closest substellar companion ever imaged. In combination with the system’s distance and the orbital elements, this translates to a semi-major axis of (0.938 ± 0.023) AU. WT 766 B, detected at a greater angular separation, was confirmed to be on an orbit exhibiting an even smaller semi-major axis of (0.676 ± 0.008) AU. The GRAVITY data were then used to break the host-companion mass degeneracy inherent to the Gaia NSS orbit solutions as well as to constrain the orbital solutions of the respective target systems. Knowledge of the companion masses enabled us to further characterise them in terms of their ages, effective temperatures, and radii via the application of evolutionary models. The inferred ages exhibit a distinct bias towards values younger than what is to be expected based on the literature. The results serve as an independent validation of the orbital solutions published in the NSS two-body orbit catalogue and show that the combination of astrometric survey missions and high-angular-resolution direct imaging holds great promise for efficiently increasing the sample of directly imaged companions in the future, especially in the light of Gaia’s upcoming DR4 and the advent of GRAVITY+.

Ion Precipitation Into Io's Poles Driven by a Strong Sub‐Alfvénic Interaction

AbstractJuno performed two close flybys of Io and found enhanced field‐aligned proton fluxes are absorbed by Io. These protons are absorbed at mass input rates comparable to previous estimates for hydrogen losses from Io, hence Jupiter is likely the source of hydrogen at Io. The conditions necessary for this to occur are: (a) formation of Alfvén waves at Io, (b) wave‐particle coupling to energize protons, (c) anti‐planetward transport of ions due to the magnetic mirror force and/or parallel acceleration, and (d) strong sub‐Alfvénic interaction slowing the flow connected to Io's fluxtube allowing for sufficient travel time for energized ions to transit to Io. The derived slowdown of ≤12% the upstream value is linked to filamentation within the Alfvén wing. This mechanism is likely operating at all strongly interacting satellites and provides an avenue to transfer material from a planetary body to its satellites, including exoplanets and brown dwarfs.

Potential coconut (Cocos nucifera L.) genotypes for farmers: Evaluation of agronomic traits in a lethal yellowing disease endemic zone in Ghana

A four-year study was conducted to evaluate selected vegetative and reproductive characteristics in four coconut genotypes namely: Niu Leka Dwarf (NLD), New Guinea Brown Dwarf (NGBD), Malayan Green Dwarf (MGD), Indonesian Brown Dwarf (IBD), and a hybrid between Sri Lankan Green Dwarf and Vanuatu Tall (SGDVTT), which was used as a control. The study was located at Anwea in the Western Region of Ghana, an endemic zone to the lethal yellowing disease. This experiment was laid out in a randomized complete block design (RCBD) in three replications. Results showed a significant higher growth for NGBD, IBD, and NLD in stem girth, leaf length, petiole length, and number of leaflets. NGBD, IBD, and SGDVTT also recorded significantly higher reproductive characteristics. Time taken for first flowering was noticed in IBD (41.30 months). NGBD recorded the highest number of female flowers (27.80), number of spikelets with female flowers (17.20), and total number of spadix (12.50) seasonally. Significant and positive correlations were observed between the number of leaves emitted, and the number of female flowers produced in the coconut genotypes except for MGD. The highest correlation between these vegetative and reproductive characteristics was expressed in IBD while the least was observed in the MGD genotype. MGD also recorded the least number of spikelets with female flowers, suggesting that this genotype is not likely to produce high number of fruits and should not be included in future breeding programs. Low and less robust characteristics were expressed in both SGDVTT, and MGD in the growing period, which could be ascribed to the rather low number of leaflets observed in these genotypes. Conclusions from this study suggest that NGBD, IBD, and NLD are potential genotypes to be integrated into further breeding programs across coconut-growing regions in Ghana.

The ESO SupJup Survey II. The 12C/13C isotope ratios of three young brown dwarfs with CRIRES+

Young brown dwarfs exhibit atmospheric characteristics similar to those of super-Jupiters, providing a unique opportunity to study planetary atmospheres. Atmospheric retrievals of high-resolution spectra reveal detailed properties of these objects, with elemental and isotopic ratios offering insights into their formation history. The ESO SupJup Survey, utilising CRIRES$^+$ on the Very Large Telescope, aims to assess the role of as a formation tracer. We present observations of three young brown dwarfs: 2MASS J12003792-7845082, TWA 28, and 2MASS J08561384-1342242. Our goal is to constrain their chemical compositions, thermal profiles, surface gravities, spin rotations, and Cratio. We conducted atmospheric retrievals of CRIRES$^+$ K-band spectra, coupling the radiative transfer code petitRADTRANS with the Bayesian inference algorithm MultiNest The retrievals provide a detailed characterisation of the atmospheres of the three objects. We report the volume mixing ratios of the main molecular and atomic species: HF, Na, Ca, and Ti, including the novel detection of hydrogen fluoride (HF) in the atmosphere of a brown dwarf. We determine values of $ and $79^ $ in the atmospheres of TWA 28 and J0856, respectively, with strong significance ($>3 We also report tentative evidence ($ of in J1200, at $. Additionally, we detect at moderate significance in J0856 (3.3sigma ) and TWA 28 (2.1sigma ). The retrieved thermal profiles are consistent with hot atmospheres ($2300-2600$ K) with low surface gravities and slow spins, as expected for young objects. The measured carbon isotope ratios are consistent among the three objects and show no significant deviation from that of the local interstellar medium, suggesting a fragmentation-based formation mechanism similar to star formation. The tentative detection of in two objects of our sample highlights the potential of high-resolution spectroscopy to probe additional isotope ratios, such as O in the atmospheres of brown dwarfs and super-Jupiters.

Low-mass Stellar and Substellar Content of the Young Cluster Berkeley 59

We present a multiwavelength analysis of the young star cluster Berkeley 59, based on Gaia data and deep IR observations with the 3.58 m Telescopio Nazionale Galileo and Spitzer space telescope. The mean proper motion of the cluster is found to be μ α cosδ ∼ −0.63 mas yr−1 and μ δ ∼ −1.83 mas yr−1, and the kinematic distance of the cluster, ∼1 kpc, is in agreement with previous photometric studies. The present data are the deepest available near-IR observations for the cluster so far and reach below 0.03 M ⊙. The mass function of the cluster region is calculated using the statistically cleaned color–magnitude diagram and is similar to the Salpeter value for the member stars above 0.4 M ⊙. In contrast, the slope becomes shallower (Γ ∼ 0.01 ± 0.18) in the mass range 0.04–0.4 M ⊙, comparable to other nearby clusters. The spatial distribution of young brown dwarfs (BDs) and stellar candidates shows a nonhomogeneous distribution. This suggests that the radiation feedback from massive stars may be a prominent factor contributing to the BD population in the cluster Berkeley 59. We also estimated the star-to-BD ratio for the cluster, which is found to be ∼3.6. The Kolmogorov–Smirnov test shows that the stellar and BD populations significantly differ, and stellar candidates are nearer the cluster center compared to the BDs, suggesting mass segregation in the cluster toward the substellar mass regime.

Vanadium oxide clusters in substellar atmospheres. A quantum chemical study

As a refractory material, vanadia (solid V$_2$O$_5$) is likely to be found as a condensate in the atmospheres of substellar objects such as exoplanets and brown dwarfs. However, the nature of the nanometer-sized vanadium oxide clusters that partake in the nucleation process is not well understood. We aim to understand the formation of cloud condensation nuclei in oxygen-rich substellar atmospheres by calculating the relevant fundamental properties of the energetically most favorable vanadium oxide molecules and clusters and, investigate how they contribute to the formation of condensation seeds. We applied a hierarchical optimization approach in order to find the most favourable structures for clusters of (VO) N and (VO$_2$) N for N=1-10, and of (V$_2$O$_5$) N for N=1-4, and to calculate their thermodynamical potentials. The candidate geometries are initially optimized by applying classical interatomic potentials; these are then refined at the B3LYP/cc-pVTZ level of theory to obtain accurate zero-point energies and thermochemical quantities. We present previously unreported vanadium oxide cluster structures as the lowest-energy isomers. Moreover, we report revised cluster energies and their thermochemical properties. Chemical equilibrium calculations are used to asses the impact of the updated and newly derived thermodynamic potentials on the gas-phase abundances of vanadium-bearing species. In chemical equilibrium, larger clusters from different stoichiometric families are found to be the most abundant vanadium-bearing species for temperatures below sim 1000 K, while molecular VO is the most abundant between sim 1000 K and sim 2000 K. We determine the nucleation rates of each stoichiometric family for a given (T$_ gas $, p$_ gas $) profile of a brown dwarf using both classical and non-classical nucleation theory. Small differences in the revised Gibbs free energies of the clusters have a large impact on the abundances of vanadium-bearing species in chemical equilibrium at temperatures below sim 1000 K. These abundance changes subsequently have an impact on the nucleation rates of each stoichiometric family. We find that with the revised and more accurate cluster data, non-classical nucleation rates are up to 15 orders of magnitude higher than classical nucleation rates.

Differential image motion in astrometric observations with very large seeing-limited telescopes

We investigate how to quantitatively model the observed differential image motion (DIM) in relative astrometric observations. As a test bed we used differential astrometric observations from the FORS2 camera of the Very Large Telescope (VLT) obtained during 2010--2019 under several programs of observations of southern brown dwarfs . The measured image motion was compared to models that decompose atmospheric turbulence in frequency space and translate the vertical turbulence profile into DIM amplitude. This approach accounts for the spatial filtering by the telescope's entrance pupil and the observation parameters (field size, zenith angle, reference star brightness and distribution, and exposure time), and it aggregates that information into a newly defined metric integral term. We demonstrate excellent agreement (within 1<!PCT!>) between the model parameters derived from the DIM variance and determined by the observations. For a 30 s exposure of a typical 1 field close to the Galactic plane, image motion limits astrometric precision to sim 60 mu as when sixth-order transformation polynomial is applicable. We confirm that the measured image motion variance is well described by Kolmogorov-type turbulence with exponent 11/3 dependence on the field size at effective altitudes of 16--18 km, where the best part of the DIM is generated. Extrapolation to observations with extremely large telescopes enables the estimation of the astrometric precision limit for seeing-limited observations of sim 5 mu as, which has a variety of exciting scientific applications.

A new atmospheric characterization of the sub-stellar companion HR 2562 B with JWST/MIRI observations

HR\,2562\,B is a planetary-mass companion at an angular separation of $0.56 ($19$\,au) from the host star, which is also a member of a select number of L/T transitional objects orbiting a young star. This companion gives us a great opportunity to contextualize and understand the evolution of young objects in the L/T transition. However, the main physical properties (e.g., $ T_ eff $ and mass) of this companion have not been well constrained (34<!PCT!> uncertainties on $ T_ eff $, 22<!PCT!> uncertainty for log(g)) using only near-infrared (NIR) observations. We aim to narrow down some of its physical parameters uncertainties (e.g., $ T_ eff $: 1200K-1700K, log(g): 4-5) incorporating new observations in the Rayleigh-Jeans tail with the JWST/MIRI filters at $10.65$, $11.40$, and $15.50\ m$, as well as to understand its context in terms of the L/T transition and chemical composition. We processed the MIRI observations with reference star differential imaging (RDI) and detect the companion at high S/N (around $16$) in the three filters, allowing us to measure its flux and astrometry. We used two atmospheric models ATMO and Exo-REM to fit the spectral energy distribution using different combinations of mid-IR and near-IR datasets. We also studied the color-magnitude diagram using the F1065C and F1140C filters combined with field brown dwarfs to investigate the chemical composition in the atmosphere of HR\,2562\,B, as well as a qualitative comparison with the younger L/T transitional companion VHS\,1256\,b. We improved the precision on the temperature of HR\,2562\,B ($ T_ eff $ = $1255$\,K) by a factor of $6 compared to previous estimates ($ vs $ using ATMO . The precision of its luminosity was also narrowed down to $-4.69 dex. The surface gravity still presents a wider range of values (4.4 to 4.8 dex). While its mass was not narrowed down, we find the most probable values between $8 M_ Jup $ ($3$-sigma lower limit from our atmospheric modeling) and $18.5 M_ Jup $ (from the upper limit provided by astrometric studies). We report a sensitivity to objects of mass ranging between $2-5 M_ Jup $ at $100$\,au, reaching the lower limit at F1550C . We also implemented a few improvements in the pipeline related to the background subtraction and stages 1 and 2. HR\,2562\,B has a mostly (or near) cloud-free atmosphere, with the ATMO model demonstrating a better fit to the observations. From the color-magnitude diagram, the most probable chemical species at MIR wavelengths are silicates (but with a weak absorption feature); however, follow-up spectroscopic observations are necessary to either confirm or reject this finding. The mass of HR\,2562\,B could be better constrained with new observations at $3-4 m$. Although HR\,2562\,B and VHS\,1256\,b have very similar physical properties, both are in different evolutionary states in the L/T transition, which makes HR\,2562\,B an excellent candidate to complement our knowledge of young objects in this transition. Considering the actual range of possible masses, HR\,2562\,B could be considered as a planetary-mass companion; hence, its name then ought to be rephrased as HR\,2562\,b.

Searching for Protoplanets around MWC 758 and MWC 480 in Br-γ Using Kernel Phase and SCExAO/CHARIS

Discovering new actively accreting protoplanets is crucial to answering open questions about planet formation. However, identifying such planets at orbital distances where they are expected to be abundant is extremely challenging, both due to the technical requirements and large distances to star-forming regions. Here we use the kernel phase interferometry (KPI) technique to search for companions around the ∼6 and ∼8 Myr old Herbig Ae stars MWC 758 and MWC 480. KPI is a data analysis technique that is sensitive to moderate asymmetries, arising from, e.g., a circumstellar disk or companions with contrasts of up to 6–8 mag, at separations down to and even below the classical Rayleigh diffraction limit (∼1.2λ/D). Using the high-spectral-resolution K-band mode of the SCExAO/CHARIS integral field spectrograph, we search for both excess Br-γ line emission and continuum emission from companions around MWC 480 and MWC 758. We are able to set limits on the presence of rapidly accreting protoplanets and brown dwarfs between 4 and 16 au, well interior to those of previous studies. In Br-γ, we set limits on excess line emission equivalent to accretion rates ranging from 10−5Mj2.yr−1 to 10−6Mj2.yr−1 . Our achievable contrasts demonstrate that KPI using SCExAO/CHARIS is a promising technique to search for giant accreting protoplanets at smaller separations compared to conventional imaging.

The JWST weather report from the nearest brown dwarfs I: multiperiod JWST NIRSpec + MIRI monitoring of the benchmark binary brown dwarf WISE 1049AB

ABSTRACT We report results from 8 h of JWST/MIRI low resolution spectroscopic (LRS) monitoring directly followed by 7 h of JWST/NIRSpec prism spectroscopic monitoring of the benchmark binary brown dwarf WISE 1049AB, the closest, brightest brown dwarfs known. We find water, methane, and CO absorption features in both components, including the 3.3 μm methane absorption feature and a tentative detection of small grain ($\lt $ 1μm) silicate absorption at $\gt $8.5 μm in WISE 1049A. Both components vary significantly ($\gt 1~{{\rm per\ cent}}$), with WISE 1049B displaying larger variations than WISE 1049A. Using K-means clustering, we find three main transition points in wavelength for both components of the binary: (1) change in behaviour at $\sim$2.3 μm coincident with a CO absorption bandhead, (2) change in behaviour at 4.2 μm, close to the CO fundamental band at $\lambda \gt $ 4.4 µm, and (3) change in behaviour at 8.3–8.5 µm, potentially corresponding to silicate absorption. We interpret the light curves observed with both NIRSpec and MIRI as likely stemming from (1) a deep pressure level driving the double-peaked variability seen in WISE 1049B at wavelengths $\lt $2.3 and $\gt $8.5 µm, (2) an intermediate pressure level shaping the light-curve morphology between 2.3 and 4.2 µm, and (3) a higher altitude pressure level producing single-peaked and plateaued light-curve behaviour between 4.2 and 8.5 µm.