Brown Dwarfs Research Articles

Destined to Change: Shifting Roles of Film and TV Stars in Shaping Canadian Mass Perception Amidst New Media Dominance

The transformative impact of new media and multiple media platforms on Canada's communication landscape has redefined how film and television stars shape and influence the mass population's thinking and behavior, in contrast to the traditional media era. This research explores these changes by examining the interplay between celebrity influence, media consumption, and societal dynamics. The mediatization theory serves as a theoretical framework to understand the relationship between media and society, particularly in the context of Canada. The study focuses on the shifting roles of film and television stars within this dynamic media landscape, and highlighting their evolving influence on public perceptions and behaviors. Qualitative content analysis, grounded in mediatization theory and guided by a comparative lens, has been employed as the research methodology. This method allows for a meticulous examination of diverse media sources, encompassing traditional and new media platforms, to unveil the multifaceted ways celebrities shape mass population thinking and behavior. The advent of new media platforms has facilitated direct and interactive communication between stars and their audiences, fostering personalized engagement and dismantling hierarchical barriers. The influence of film and television stars extends beyond entertainment, interacting with Canadian cultural narratives and societal issues. As celebrities leverage new media platforms to champion social causes, they contribute to reshaping cultural norms and values. The findings contribute to a deeper understanding of the dynamics of media influence in the digital age, showcasing the sophisticated bond between media, celebrities, and societal evolution within the Canadian narrative.

Rotational Variability and Detection of Superflares in a Young Brown Dwarf by TESS

We present a comprehensive analysis of a Transiting Exoplanet Survey Satellite (TESS) high-quality light curve for a young brown dwarf, MHO 4 having spectral type M7.0, in the Taurus star-forming region. We investigate the rotation periods and characterize the brown dwarf’s dynamic atmosphere and surface features. Our light curve analysis of MHO 4 reveals a rotation period of approximately 2.224 days. Remarkably, MHO 4 exhibits two significant flaring events. Furthermore, we estimate the bolometric flare energies to be within the energy range of 1034 to 1035 erg, classifying them as superflares.

Spherical Harmonics for the 1D Radiative Transfer Equation. II. Thermal Emission

Approximate methods for radiative transfer equations that are fast, reliable, and accurate are essential for the understanding of atmospheres of exoplanets and brown dwarfs. The simplest and most popular choice is the “two-stream method,” which is often used to produce simple yet effective models for radiative transfer in scattering and absorbing media. Toon et al. (hereafter, Toon89) outlined a two-stream method for computing reflected light and thermal spectra that was later implemented in the open-source radiative transfer model PICASO. In Part I of this series, we developed an analytical spherical harmonics method for solving the radiative transfer equation for reflected solar radiation that was implemented in PICASO to increase the accuracy of the code by offering a higher-order approximation. This work is an extension of this spherical harmonics derivation, to study thermal emission spectroscopy. We highlight the model differences in the approach for thermal emission and benchmark the four-term method (SH4) against Toon89 and a high-stream discrete-ordinates method, CDISORT. By comparing the spectra produced by each model, we demonstrate that the SH4 method provides a significant increase in accuracy, compared to Toon89, which can be attributed to the increased order of approximation and to the choice of phase function. We also explore the trade-off between computational time and model accuracy. We find that our four-term method is twice as slow as our two-term method, but is up to five times more accurate, when compared with CDISORT. Therefore, SH4 provides excellent improvement in model accuracy with minimal sacrifice in numerical expense.

HST astrometry of the closest brown dwarfs‐II. Improved parameters and constraints on a third body

AbstractLocated at less than two pc away, Luhman 16 AB (WISE J104915.57‐531906.1) is the closest pair of brown dwarfs and the third closest “stellar” system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re‐analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune‐mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses 1.5 M♆ (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses 3 M♆ and periods between 2 and 400 days (1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this sub‐stellar binary, including its mass‐ratio 0.8305 , individual component masses 35.40.2 MꝜ and 29.40.2 MꝜ (Jupiter masses), and parallax distance 1.9960 pc 50 AU. Comparison of the masses and luminosities of Luhman 16 AB to several evolutionary models shows persistent discrepancies in the ages of the two components, but strengthens the case that this system is a member of the 51095 Myr Oceanus Moving Group.

Orbital Eccentricity of Celestial Motion—from Stars to Planets

The orbital eccentricity is one of the key parameters to describe the orbit of celestial bodies, which can provide important clues to reveal their dynamical evolution, and thus help to understand their formation and evolution processes along with the physical mechanisms behind them. The continuous improvement of observational technologies, enable us to explore the orbit of celestial bodies beyond the solar system, i.e., from stellar systems to planetary systems. Focusing on the orbital eccentricity of celestial bodies, this paper reviews the progress in stellar systems (including the main sequence stars, brown dwarfs, and compact stars) and planetary systems (including gas-giants, low-mass exoplanets such as “super-Earth” and “sub-Neptune”), and summarizes several similarities and issues among the investigations of orbital eccentricity under different scales. Finally, based on the ongoing and future astronomical facilities and missions, we discuss the future prospect on eccentricity studies of stellar systems, extra-solar planetary systems, and even extra-solar satellite systems.

FlopPITy: Enabling self-consistent exoplanet atmospheric retrievals with machine learning

Context. Interpreting the observations of exoplanet atmospheres to constrain physical and chemical properties is typically done using Bayesian retrieval techniques. Since these methods require many model computations, a compromise must be made between the model’s complexity and its run time. Achieving this compromise leads to a simplification of many physical and chemical processes (e.g. parameterised temperature structure). Aims. Here, we implement and test sequential neural posterior estimation (SNPE), a machine learning inference algorithm for atmospheric retrievals for exoplanets. The goal is to speed up retrievals so they can be run with more computationally expensive atmospheric models, such as those computing the temperature structure using radiative transfer. Methods. We generated 100 synthetic observations using ARtful Modeling Code for exoplanet Science (ARCiS), which is an atmospheric modelling code with the flexibility to compute models across varying degrees of complexity and to perform retrievals on them to test the faithfulness of the SNPE posteriors. The faithfulness quantifies whether the posteriors contain the ground truth as often as we expect. We also generated a synthetic observation of a cool brown dwarf using the self-consistent capabilities of ARCiS and ran a retrieval with self-consistent models to showcase the possibilities opened up by SNPE. Results. We find that SNPE provides faithful posteriors and is therefore a reliable tool for exoplanet atmospheric retrievals. We are able to run a self-consistent retrieval of a synthetic brown dwarf spectrum using only 50 000 forward model evaluations. We find that SNPE can speed up retrievals between ∼2× and ≥10× depending on the computational load of the forward model, the dimensionality of the observation, and its signal-to-noise ratio (S/N). We have made the code publicly available for the community on Github.

Theoretical study of the spin-orbit coupled molecular states of the Mg-He dimer.

The primary objective of this study is to conduct precise ab initio calculations of the spin-orbit interaction between Mg and He atoms. Our investigation centers on identifying the first low-lying electronic states of the Mg-He molecule through high-level theoretical methods such as CCSD(T) and RCCSD(T) and SA-CASSCF/MRCI, while also integrating Davidson and BSSE corrections to refine our findings further. Additionally, we employ the state-interacting method to comprehensively account for the influence of spin-orbit coupling (SO) on molecular states. We carefully characterize the potential energy curves (PECs) of these molecular states by deriving crucial spectroscopic parameters including Re, De, Be and Te, which are then compared against data from prior studies. Moreover, our analysis extends to evaluating vibrational levels, radiative lifetimes, and transition dipole moments (TDMs), offering a comprehensive understanding of the system's dynamics. Notably, we locate the positions of satellite features within the absorption spectra of brown and white dwarfs. To validate the precision and reliability of our findings, extensive comparisons are made with both theoretical predictions and experimental observations, ensuring robustness and accuracy in our conclusions.

Photometric Variability of Low Mass Stars and Brown Dwarfs in IC 348 and Taurus Star-Forming Regions

Low-mass stars belonging to the M spectral type are the most numerous stars in our Galaxy, amounting to about two-thirds in number, and are found at the bottom of the main sequence in the H-R diagram. Photometric studies of low-mass stars, including brown dwarfs (Bds), provide several important evolutions of their atmosphere, magnetic flares and chromospheric activity. This paper highlights a few interesting results from our optical I-band observations of 2MASS J03435638+3209591 in the young star-forming IC 348 region and three BDs in Taurus star-forming regions using ground-based telescopes as well as a space-based telescope. We estimated the fast periodicities in the range of 1.5 to 3 hours in Taurus BDs. Furthermore, using the long-term photometry from the Transiting Exoplanet Survey Satellite (TESS), we have conducted a time-resolved variability analysis of CFHT-BD-Tau 4. The periodogram analysis of TESS data reveals an orbital period of ∼ 3 days. We found two flare events in TESS sector 43 data for this BD and estimated the flared energies as 4.59×1035 erg and 2.64×1036 erg, which sit in the superflare range.

Cover Picture: Astron. Nachr. 1/2024

Motion on the sky of the brown dwarf binary system Luhman 16 AB. At a distance of less than 2 pc, it is known as the nearest pair of this type to Earth. (Top:) The entire 4.7ʹ × 4ʹ region surrounding Luhman 16 AB, as monitored by HST. (Bottom:) Zoom‐in of the 25ʺ × 7ʺ rectangular region indicated in red in the top panel, showing the complete trajectory in the sky of Luhman 16 A and B during the period of 7.4 years monitored by recent HST observations. The astrometric solution for the Luhman AB barycenter, with and without parallax is indicated by blue and magenta curves, respectively. For details about the search for a suspected exoplanet orbiting one of the brown dwarf components see Bedin et al., this issue, e230158.image

Exploring the Chemistry and Mass Function of the Globular Cluster 47 Tucanae with New Theoretical Color–Magnitude Diagrams

Despite their shared origin, members of globular clusters display star-to-star variations in composition. The observed pattern of element abundances is unique to these stellar environments and cannot be fully explained by any proposed mechanism. It remains unclear whether stars form with chemical heterogeneity or inherit it from interactions with other members. These scenarios may be differentiated by the dependence of chemical spread on stellar mass; however, obtaining a sufficiently large mass baseline requires abundance measurements on the lower main sequence, which is too faint for spectroscopy even in the nearest globular clusters. We developed a stellar modeling method to obtain precise chemical abundances for stars near the end of the main sequence from multiband photometry, and we applied it to the globular cluster 47 Tucanae. The computational efficiency is attained by matching chemical elements to the model components that are most sensitive to their abundance. We determined [O/Fe] for ∼5000 members below the main-sequence knee at the level of accuracy, comparable to the spectroscopic measurements of evolved members in the literature. The inferred distribution disfavors stellar interactions as the origin of chemical spread; however, an accurate theory of accretion is required to draw a more definitive conclusion. We anticipate that future observations of 47 Tucanae with the James Webb Space Telescope will extend the mass baseline of our analysis into the substellar regime. Therefore, we present predicted color–magnitude diagrams and mass–magnitude relations for the brown dwarf members of 47 Tucanae.

Uniform Forward-modeling Analysis of Ultracool Dwarfs. III. Late-M and L Dwarfs in Young Moving Groups, the Pleiades, and the Hyades

We present a uniform forward-modeling analysis of 90 late-M and L dwarfs in nearby young (∼10–200 Myr) moving groups, the Pleiades, and the Hyades using low-resolution (R ≈ 150) near-infrared (0.9–2.4 μm) spectra and the BT-Settl model atmospheres. We derive the objects’ effective temperatures, surface gravities, radii, and masses by comparing our spectra to the models using a Bayesian framework with nested sampling and calculate the same parameters using evolutionary models. Assuming the evolutionary-based parameters are more robust, our spectroscopically inferred parameters from BT-Settl exhibit two types of systematic behavior for objects near the M-L spectral type boundary. Several objects are clustered around T eff ≈ 1800 K and logg≈5.5 dex, implying impossibly large masses (150–1400 M Jup), while others are clustered around T eff ≳ 3000 K and logg≲3.0 dex, implying unphysically low masses and unreasonably young ages. We find the fitted BT-Settl model spectra tend to overpredict the peak J- and H-band flux for objects located near the M-L boundary, suggesting the dust content included in the model atmospheres is insufficient to match the observations. By adding an interstellar medium–like reddening law to the BT-Settl model spectra, we find the fits between models and observed spectra are greatly improved, with the largest reddening coefficients occurring at the M-L transition. This work delivers a systematic examination of the BT-Settl model atmospheres and constitutes the largest spectral analysis of benchmark late-M- and L-type brown dwarfs to date.

A search for auroral radio emission from β Pictoris b

Abstract Magnetized exoplanets can serve as the source of auroral radio emissions, allowing us to characterize the magnetospheric properties of these planets. Successful detections of auroral radio emissions from brown dwarfs, as well as from Jupiter, suggest that Jupiter-like planets in distant orbits may also generate radio emissions through a similar mechanism. In this study, we present our search for 250-500 MHz emissions from β Pictoris b, one of the most extensively studied young Jupiter-like planets. We conducted the search using the upgraded Giant Metrewave Radio Telescope (uGMRT). Despite the favourable orbital inclination, no signal was detected, putting 3σ upper limits on the radiation at 0.18 mJy. We translate this limit into constraints on the ionospheric and magnetospheric parameters, assuming that the emission is powered by the Hill current system. While the upper limit is larger by a factor of a few than the nominal estimate of radio intensity, we put constraints on the magnetospheric and ionospheric parameters.

The impact of spectral line wing cut-off: recommended standard method with application to MAESTRO opacity data base

Abstract When computing cross-sections from a line list, the result depends not only on the line strength, but also the line shape, pressure-broadening parameters, and line wing cut-off (i.e. the maximum distance calculated from each line centre). Pressure-broadening can be described using the Lorentz line shape, but it is known to not represent the true absorption in the far wings. Both theory and experiment have shown that far from the line centre, non-Lorentzian behaviour controls the shape of the wings and the Lorentz line shape fails to accurately characterize the absorption, leading to an underestimation or overestimation of the opacity continuum depending on the molecular species involved. The line wing cut-off is an often overlooked parameter when calculating absorption cross-sections, but can have a significant effect on the appearance of the spectrum since it dictates the extent of the line wing that contributes to the calculation either side of every line centre. Therefore, when used to analyse exoplanet and brown dwarf spectra, an inaccurate choice for the line wing cut-off can result in errors in the opacity continuum, which propagate into the modelled transit spectra, and ultimately impact/bias the interpretation of observational spectra, and the derived composition and thermal structure. Here, we examine the different methods commonly utilized to calculate the wing cut-off and propose a standard practice procedure (i.e. absolute value of 25 cm−1 for P ≤ 200 bar and 100 cm−1 for P > 200 bar) to generate molecular opacities which will be used by the open-access MAESTRO (Molecules and Atoms in Exoplanet Science: Tools and Resources for Opacities) data base. The pressing need for new measurements and theoretical studies of the far-wings is highlighted.

Searching for Planets Orbiting Fomalhaut with JWST/NIRCam

We report observations with the JWST/NIRCam coronagraph of the Fomalhaut (α PsA) system. This nearby A star hosts a complex debris disk system discovered by the IRAS satellite. Observations in F444W and F356W filters using the round 430R mask achieve a contrast ratio of ∼4 × 10−7 at 1″ and ∼4 × 10−8 outside of 3″. These observations reach a sensitivity limit of <1 M Jup across most of the disk region. Consistent with the hypothesis that Fomalhaut b is not a massive planet but is a dust cloud from a planetesimal collision, we do not detect it in either F356W or F444W (the latter band where a Jovian-sized planet should be bright). We have reliably detected 10 sources in and around Fomalhaut and its debris disk, all but one of which are coincident with Keck or Hubble Space Telescope sources seen in earlier coronagraphic imaging; we show them to be background objects, including the “Great Dust Cloud” identified in Mid-Infrared Instrument (MIRI) data. However, one of the objects, located at the edge of the inner dust disk seen in the MIRI images, has no obvious counterpart in imaging at earlier epochs and has a relatively red [F356W]–[F444W] > 0.7 mag (Vega) color. Whether this object is a background galaxy, brown dwarf, or a Jovian-mass planet in the Fomalhaut system will be determined by an approved Cycle 2 follow-up program. Finally, we set upper limits to any scattered light from the outer ring, placing a weak limit on the dust albedo at F356W and F444W.

A JWST Survey for Planetary Mass Brown Dwarfs in IC 348* *Based on observations made with the NASA/ESA/CSA James Webb Space Telescope and the Gaia mission.

We have obtained images of the center of the star-forming cluster IC 348 with the James Webb Space Telescope and have identified brown dwarf candidates based on their photometry and point-like flux profiles. Low-resolution spectroscopy has been performed on four promising candidates, three of which have molecular absorption bands that indicate late spectral types. Among those late-type objects, the brightest is similar to known young L dwarfs while the other two show the so-called 3.4 μm feature that has been previously observed in the diffuse interstellar medium and in the atmospheres of Saturn and Titan, which has been attributed to an unidentified aliphatic hydrocarbon. Those two objects also exhibit features between 1.1 and 2.6 μm that we identify as the overtone and combination bands for that hydrocarbon. After accounting for the hydrocarbon bands, the remaining spectral features are consistent with youth and inconsistent with field dwarfs. Based on the low extinctions of those objects and the strengths of the overtone and combination bands, we conclude that the hydrocarbon resides in their atmospheres rather than in foreground material. Thus, our detections of the 3.4 μm feature are the first in atmospheres outside of the solar system. The presence of this hydrocarbon is not predicted by any atmospheric models of young brown dwarfs. Based on its luminosity and evolutionary models, the faintest new member of IC 348 has an estimated mass of 3–4 M Jup, making it a strong contender for the least massive free-floating brown dwarf that has been directly imaged to date.

Elemental abundance differences in the massive planet-hosting wide binary HD 196067−68

ABSTRACT It has been suggested that small chemical anomalies observed in planet-hosting wide binary systems could be due to planet signatures, where the role of the planetary mass is still unknown. We search for a possible planet signature by analysing the TC trends in the remarkable binary system HD 196067–HD 196068. At the moment, only HD 196067 is known to host a planet that is near the brown dwarf regime. We take advantage of the strong physical similarity between both stars, which is crucial to achieving the highest possible precision in stellar parameters and elemental chemical abundances. This system gives us a unique opportunity to explore whether a possible depletion of refractories in a binary system could be inhibited by the presence of a massive planet. We performed a line-by-line chemical differential study, employing the non-solar-scaled opacities, in order to reach the highest precision in the calculations. After differentially comparing both stars, HD 196067 displays a clear deficiency in refractory elements in the TC plane, a lower iron content (0.051 dex), and also a lower Li i content (0.14 dex) than its companion. In addition, the differential abundances reveal a TC trend. These targets represent the first cases of an abundance difference around a binary system hosting a super-Jupiter. Although we explored several scenarios to explain the chemical anomalies, none of them can be entirely ruled out. Additional monitoring of the system as well as studies of larger sample of wide binary systems hosting massive planets are needed to better understand the chemical abundance trend observed in HD 196067−68.

JWST/NIRSpec Observations of the Coldest Known Brown Dwarf* *Based on observations made with the NASA/ESA/CSA James Webb Space Telescope.

We present 1–5 μm spectroscopy of the coldest known brown dwarf, WISE J085510.83−071442.5 (WISE 0855), performed with the Near-Infrared Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST). NIRSpec has dramatically improved the measurement of the spectral energy distribution (SED) of WISE 0855 in terms of wavelength coverage, signal-to-noise ratios, and spectral resolution. We have performed preliminary modeling of the NIRSpec data using the ATMO 2020 models of cloudless atmospheres, arriving at a best-fitting model that has T eff = 285 K. That temperature is ∼20 K higher than the value derived by combining our luminosity estimate with evolutionary models (i.e., the radius in the model fit to the SED is somewhat smaller than expected from evolutionary models). Through comparisons to the model spectra, we detect absorption in the fundamental band of CO, which is consistent with an earlier detection in a ground-based spectrum and indicates the presence of vertical mixing. Although PH3 is expected in Y dwarfs that experience vertical mixing, it is not detected in WISE 0855. Previous ground-based M-band spectroscopy of WISE 0855 has been cited for evidence of H2O ice clouds, but we find that the NIRSpec data in that wavelength range are matched well by our cloudless model. Thus, clear evidence of H2O ice clouds in WISE 0855 has not been identified yet, but it may still be present in the NIRSpec data. The physical properties of WISE 0855, including the presence of H2O clouds, can be better constrained by more detailed fitting with both cloudless and cloudy models and the incorporation of unpublished 5–28 μm data from the Mid-infrared Instrument on JWST.

Evidence of a sub-solar star in a microlensing event toward the LMC

Gravitational microlensing is known to be an impressive tool for searching dark, small, and compact objects that are missed by the usual astronomical observations. In this paper, by analysing multiple images acquired by DECam, we present the detection and a complete description of the microlensing event LMC J05074558-65574990 which is most likely due to a sub-solar object with mass (0.16±0.10) M⊙, hence in the mass range between a massive brown dwarf and a red dwarf, whose distance is estimated to be 7.8−3.4+4.1×102 pc thanks to the Gaia observation of the source, leading us to consider this lens as one the closest ever detected.

Aerosols are not spherical cows: using discrete dipole approximation to model the properties of fractal particles

ABSTRACT The optical properties of particulate-matter aerosols, within the context of exoplanet and brown dwarf atmospheres, are compared using three different models: Mie theory, modified mean field (MMF) theory, and discrete dipole approximation (DDA). Previous results have demonstrated that fractal haze particles (MMF and DDA) absorb much less long-wavelength radiation than their spherical counterparts (Mie), however it is shown here that the opposite can also be true if a more varying refractive index profile is used. Additionally, it is demonstrated that absorption/scattering cross-sections, and the asymmetry parameter, are underestimated if Mie theory is used. Although DDA can be used to obtain more accurate results, it is known to be much more computationally intensive; to avoid this, the use of low-resolution aerosol models is explored, which could dramatically speed up the process of obtaining accurate computations of optical cross-sections within a certain parameter space. The validity of DDA is probed for wavelengths of interest for observations of aerosols within exoplanet and brown dwarf atmospheres ($0.2-15~\mu$m). Finally, novel code is presented to compare the results of Mie, MMF, and DDA theories (coral: Comparison Of Radiative AnaLyses), as well as to increase and decrease the resolution of DDA shape files accordingly (spherify). Both codes can be applied to a range of other interesting astrophysical environments in addition to exoplanet atmospheres, for example dust grains within protoplanetary discs.

The First Y Dwarf Data from JWST Show that Dynamic and Diabatic Processes Regulate Cold Brown Dwarf Atmospheres

The James Webb Space Telescope (JWST) is now observing Y dwarfs, the coldest known brown dwarfs, with effective temperatures T eff ≲ 475 K. The first published observations provide important information: not only is the atmospheric chemistry out of equilibrium, as previously known, but the pressure–temperature profile is not in the standard adiabatic form. The rapid rotation of these Jupiter-size, isolated, brown dwarfs dominates the atmospheric dynamics, and thermal and compositional changes disrupt convection. These processes produce a colder lower atmosphere, and a warmer upper atmosphere, compared to a standard adiabatic profile. Leggett et al. presented empirical models where the pressure–temperature profile was adjusted so that synthetic spectra reproduced the 1 ≲ λ (μm) ≲ 20 spectral energy distributions of brown dwarfs with 260 ≤ T eff (K) ≤ 540. We show that spectra generated by these models fit the first JWST Y dwarf spectrum better than standard-adiabat models. Unexpectedly, there is no 4.3 μm PH3 feature in the JWST spectrum and atmospheres without phosphorus better reproduce the 4 μm flux peak. Our analysis of new JWST photometry indicates that the recently discovered faint secondary of the WISE J033605.05-014350AB system has T eff ≈ 295 K, making it the first dwarf in the significant luminosity gap between the 260 K WISE J085510.83-071442.5, and all other known Y dwarfs. The adiabat-adjusted disequilibrium-chemistry models are recommended for analyses of all brown dwarfs cooler than 600 K, and a grid is publicly available. Photometric color transformations are provided in an appendix.