Binary T/Y dwarfs: double brown dwarfs or BD-planet systems?

It could help starting a topic for other similar entries concerning T and Y dwarfs with planetary/substellar companions like these:

The latest ones:

An Improved Near-Infrared Spectrum of the Archetype Y Dwarf WISEP J182831.08+265037.8

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We present a Hubble Space Telescope/Wide-Field Camera 3 near infrared spectrum of the archetype Y dwarf WISEP 182831.08+265037.8. The spectrum covers the 0.9-1.7 um wavelength range at a resolving power of lambda/Delta lambda ~180 and is a significant improvement over the previously published spectrum because it covers a broader wavelength range and is uncontaminated by light from a background star. The spectrum is unique for a cool brown dwarf in that the flux peaks in the Y, J, and H band are of near equal intensity in units of f_lambda. We fail to detect any absorption bands of NH_3 in the spectrum, in contrast to the predictions of chemical equilibrium models, but tentatively identify CH_4 as the carrier of an unknown absorption feature centered at 1.015 um. Using previously published ground- and spaced-based photometry, and using a Rayleigh Jeans tail to account for flux emerging longward of 4.5 um, we compute a bolometric luminosity of log (L_bol/L_sun)=-6.50+-0.02 which is significantly lower than previously published results. Finally, we compare the spectrum and photometry to two sets of atmospheric models and find that best overall match to the observed properties of WISEP 182831.08+265037.8 is a ~1 Gyr old binary composed of two T_eff~325 K, ~5 M_Jup brown dwarfs with subsolar [C/O] ratios.

Hence the closest thing to a "binary planet". But the suggestion that WISE J1828+2650 might be "binary" dates back to 2012:

A Comparison of Near-Infrared Photometry and Spectra for Y Dwarfs with a New Generation of Cool Cloudy Models

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We present YJHK photometry, or a subset, for the six Y dwarfs discovered in WISE data by Cushing et al.. The data were obtained using NIRI on the Gemini North telescope. We also present a far-red spectrum obtained using GMOS-North for WISEPC J205628.90+145953.3. We compare the data to Morley et al. (2012) models, which include cloud decks of sulfide and chloride condensates. We find that the models with these previously neglected clouds can reproduce the energy distributions of T9 to Y0 dwarfs quite well, other than near 5um where the models are too bright. This is thought to be because the models do not include departures from chemical equilibrium caused by vertical mixing, which would enhance the abundance of CO, decreasing the flux at 5um. Vertical mixing also decreases the abundance of NH_3, which would otherwise have strong absorption features at 1.03um and 1.52um that are not seen in the Y0 WISEPC J205628.90+145953.3. We find that the five Y0 to Y0.5 dwarfs have 300 < T_eff K < 450, 4.0 < log g < 4.5 and f_sed ~ 3. These temperatures and gravities imply a mass range of 5 - 15 M_Jupiter and ages around 5 Gyr. We suggest that WISEP J182831.08+265037.8 is a binary system, as this better explains its luminosity and color. We find that the data can be made consistent with observed trends, and generally consistent with the models, if the system is composed of a T_eff = 325 K and log g <~ 4.5 primary, and a T_eff = 300 K and log g >~ 4.0 secondary, corresponding to masses of 10 and 7 M_Jupiter and an age around 2 Gyr. If our deconvolution is correct, then the T_eff = 300 K cloud-free model fluxes at K and W2 are too faint by 0.5 - 1.0 magnitudes. We will address this discrepancy in our next generation of models, which will incorporate water clouds and mixing.

Next comes a "Y subdwarf" and likely ejected rogue exoplanet:

The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (aka "The Accident")

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Continued follow-up of WISEA J153429.75-104303.3, announced in Meisner et al (2020), has proven it to have an unusual set of properties. New imaging data from Keck/MOSFIRE and HST/WFC3 show that this object is one of the few faint proper motion sources known with J-ch2 > 8 mag, indicating a very cold temperature consistent with the latest known Y dwarfs. Despite this, it has W1-W2 and ch1-ch2 colors ~1.6 mag bluer than a typical Y dwarf. A new trigonometric parallax measurement from a combination of WISE, Spitzer, and HST astrometry confirms a nearby distance of 16.3^+1.4_-1.2 pc and a large transverse velocity of 207.4±15.9 km/s. The absolute J, W2, and ch2 magnitudes are in line with the coldest known Y dwarfs, despite the highly discrepant W1-W2 and ch1-ch2 colors. We explore possible reasons for the unique traits of this object and conclude that it is most likely an old, metal-poor brown dwarf and possibly the first Y subdwarf. Given that the object has an HST F110W magnitude of 24.7 mag, broad-band spectroscopy and photometry from JWST are the best options for testing this hypothesis.

A similar (nearby) object, possibly linked to WISE J163940.83-684738.6 (a_A-B = 5.92'' = 29.6 AUs):

WISE J163940.83-684738.6: A Y Dwarf Identified by Methane Imaging

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We have used methane imaging techniques to identify the near-infrared counterpart of the bright Wide-field Infrared Survey Explorer (WISE) source WISE J163940.83-684738.6. The large proper motion of this source (~3".0/yr) has moved it, since its original WISE identification, very close to a much brighter background star–it currently lies within 1".5 of the J = 14.90 ±0.04 star 2MASS 16394085-6847446. Observations in good seeing conditions using methane-sensitive filters in the near-infrared J band with the FourStar instrument on the Magellan 6.5 m Baade telescope, however, have enabled us to detect a near-infrared counterpart. We have defined a photometric system for use with the FourStar J2 and J3 filters, and this photometry indicates strong methane absorption, which unequivocally identifies it as the source of the WISE flux. Using these imaging observations we were then able to steer this object down the slit of the Folded-port Infrared Echellette spectrograph on a night of 0".6 seeing, and so obtain near-infrared spectroscopy confirming a Y0-Y0.5 spectral type. This is in line with the object's near-infrared-to-WISE J3 - W2 color. Preliminary astrometry using both WISE and FourStar data indicates a distance of 5.0±0.5 pc and a substantial tangential velocity of 73 ± 8 km/s. WISE J163940.83-684738.6 is the brightest confirmed Y dwarf in the WISE W2 passband and its distance measurement places it among the lowest luminosity sources detected to date.

Finally a "revived" triple BD from the past (2013):

Discovery of a Visual T-Dwarf Triple System and Binarity at the L/T Transition

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We present new high contrast imaging of 8 L/T transition brown dwarfs using the NIRC2 camera on the Keck II telescope. One of our targets, the T3.5 dwarf 2MASS J08381155 + 1511155, was resolved into a hierarchal triple with projected separations of 2.5+/-0.5 AU and 27+/-5 AU for the BC and A(BC) components respectively. Resolved OSIRIS spectroscopy of the A(BC) components confirm that all system members are T dwarfs. The system therefore constitutes the first triple T-dwarf system ever reported. Using resolved photometry to model the integrated-light spectrum, we infer spectral types of T3, T3, and T4.5 for the A, B, and C components respectively. The uniformly brighter primary has a bluer J-Ks color than the next faintest component, which may reflect a sensitive dependence of the L/T transition temperature on gravity, or alternatively divergent cloud properties amongst components. Relying on empirical trends and evolutionary models we infer a total system mass of 0.034-0.104 Msun for the BC components at ages of 0.3-3 Gyr, which would imply a period of 12-21 yr assuming the system semi-major axis to be similar to its projection. We also infer differences in effective temperatures and surface gravities between components of no more than ~150 K and ~0.1 dex. Given the similar physical properties of the components, the 2M0838+15 system provides a controlled sample for constraining the relative roles of effective temperature, surface gravity, and dust clouds in the poorly understood L/T transition regime. Combining our imaging survey results with previous work we find an observed binary fraction of 4/18 or 22_{-8}^{+10}% for unresolved spectral types of L9-T4 at separations >~0.1 arcsec. This translates into a volume-corrected frequency of 13^{-6}_{+7}%, which is similar to values of ~9-12% reported outside the transition.

The thread should be updated periodically due to previously overlooked papers concerning these peculiar substellar objects.

And this could be a "brown dwarf emoticon" *lol*

Regarded as Beta Pic b's analogue, 2M2208+2921 has the features of a young rogue gas giant (9-11 M_J) planet

Revealing the Vertical Cloud Structure of a young low-mass Brown Dwarf, an analog to the beta-Pictoris b directly-imaged exoplanet, through Keck I/MOSFIRE spectro-photometric variability

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Young brown dwarfs are analogs to giant exoplanets, as they share effective temperatures, near-infrared colors, and surface gravities. Thus, the detailed characterization of young brown dwarfs might shed light on the study of giant exoplanets, that we are currently unable to observe with sufficient signal-to-noise to allow precise characterization of their atmospheres. 2MASS J22081363+2921215 is a young L3 brown dwarf, member of the beta-Pictoris young moving group (23 +/-3 Myr), that shares its effective temperature and mass with the beta Pictoris b giant exoplanet. We performed a ~2.5 hr spectro-photometric J-band monitoring of 2MASS J22081363+2921215 with the MOSFIRE multi-object spectrograph, installed at the Keck I telescope. We measured a minimum variability amplitude of 3.22 +/- 0.42 % for its J-band light curve. The ratio between the maximum and the minimum flux spectra of 2MASS J22081363+2921215 shows a weak wavelength dependence and a potential enhanced variability amplitude in the alkali lines. Further analysis suggests that the variability amplitude on the alkali lines is higher than the overall variability amplitude (4.5-11 %, depending on the lines). The variability amplitudes in these lines are lower if we degrade the resolution of the original MOSFIRE spectra to R~100, which explains why this potential enhanced variability in the alkali lines has not been found previously in HST/WFC3 light curves. Using radiative-transfer models, we obtained the different cloud layers that might be introducing the spectro-photometric variability we observe for 2MASS J22081363+2921215, that further support the measured enhanced variability amplitude in the alkali lines. We provide an artistic recreation of the vertical cloud structure of this beta-Pictoris b analog.

Young brown dwarf ITG 17 in Taurus is found to be surrounded by a disk and bound to a complex multiple system.

Near-Infrared Polarization from Unresolved Disks Around Brown Dwarfs and Young Stellar Objects

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Wide-field near-infrared (NIR) polarimetry was used to examine disk systems around two brown dwarfs (BD) and two young stellar objects (YSO) embedded in the Heiles Cloud 2 (HCl2) dark molecular cloud in Taurus as well as numerous stars located behind HCl2. Inclined disks exhibit intrinsic NIR polarization due to scattering of photospheric light which is detectable even for unresolved systems. After removing polarization contributions from magnetically aligned dust in HCl2 determined from the background star information, significant intrinsic polarization was detected from the disk systems of of one BD (ITG~17) and both YSOs (ITG~15, ITG~25), but not from the other BD (2M0444). The ITG~17 BD shows good agreement of the disk orientation inferred from the NIR and from published ALMA dust continuum imaging. ITG~17 was also found to reside in a 5,200~au wide binary (or hierarchical quad star system) with the ITG~15 YSO disk system. The inferred disk orientations from the NIR for ITG~15 and ITG~17 are parallel to each other and perpendicular to the local magnetic field direction. The multiplicity of the system and the large BD disk nature could have resulted from formation in an environment characterized by misalignment of the magnetic field and the protostellar disks.

ITG 17 A (aka CFHT Tau 4) has a companion "ITG 17 B" at 4.2'' (ca. 570 AUs) whose mass is uncertain, likely lower than primary, that is <<0.095 M_Sol. ITG 17 A lies 5,200 AUs away from another BD, ITG 15, in turn binary with "ITG 15 B" at 3'' arcsec (ca. 410 AUs) whose mass is better constrained and well within planetary domain (0.009 M_Sol = 9.4 M_Jup).

An overlooked M dwarf + BD pair: HIP 113201AB in Grus (aka Smethells 119 or GJ 4303).

Dynamical masses for two M1 + mid-M dwarf binaries monitored during the SPHERE-SHINE survey

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We present orbital fits and dynamical masses for HIP 113201AB and HIP 36985AB, two M1 + mid-M dwarf binary systems monitored as part of the SPHERE SHINE survey. To robustly determine ages via gyrochronology, we undertook a photometric monitoring campaign for HIP 113201 and for GJ 282AB, the two wide K star companions to HIP 36985, using the 40 cm Remote Observatory Atacama Desert (ROAD) telescope. We adopt ages of 1.2±0.1 Gyr for HIP 113201AB and 750±100 Myr for HIP 36985AB. To derive dynamical masses for all components of these systems, we used parallel-tempering Markov Chain Monte Carlo sampling to fit a combination of radial velocity, direct imaging, and Gaia and Hipparcos astrometry. Fitting the direct imaging and radial velocity data for HIP 113201 yields a primary mass of 0.54±0.03 M⊙, fully consistent with its M1 spectral type, and a secondary mass of 0.145± M⊙. The secondary masses derived with and without including Hipparcos/Gaia data are more massive than the 0.1 M⊙ estimated mass from the photometry of the companion. An undetected brown dwarf companion to HIP 113201B could be a natural explanation for this apparent discrepancy. At an age >1 Gyr, a 30 M_Jup companion to HIP 113201B would make a negligible (<1%) contribution to the system luminosity, but could have strong dynamical impacts. Fitting the direct imaging, radial velocity, and Hipparcos/Gaia proper motion anomaly for HIP 36985AB, we find a primary mass of 0.54±0.01 M⊙ and a secondary mass of 0.185±0.001 M⊙ which agree well with photometric estimates of component masses, the masses estimated from MK-- mass relationships for M dwarf stars, and previous dynamical masses in the literature.

And Merry Christmas to everybody in the Forum!

Some updates from Solar Neighbourhood

The Solar Neighborhood XLIX: New Discoveries and Orbits of M Dwarf Multiples with Speckle Interferometry at SOAR

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We present the first results of a multi-year program to map the orbits of M dwarf multiples within 25 parsecs. The observations were conducted primarily during 2019 - 2020 using speckle interferometry at the Southern Astrophysical Research (SOAR) Telescope in Chile, using the High-Resolution Camera mounted on the adaptive optics module (HRCam+SAM). The sample of nearby M dwarfs is drawn from three sources: multiples from the RECONS long-term astrometric monitoring program at the SMARTS 0.9m, known multiples for which these new observations will enable or improve orbit fits, and candidate multiples flagged by their astrometric fits in Gaia Data Release 2 (DR2). We surveyed 333 of our 338 M dwarfs via 830 speckle observations, detecting companions for 63% of the stars. Most notably, this includes new companions for 76% in the subset selected from Gaia DR2. In all, we report the first direct detections of 97 new stellar companions to the observed M dwarfs. Here we present the properties of those detections, the limits of each non-detection, and five orbits with periods 0.67 - 29 yr already observed as part of this program. Companions detected have projected separations of 0.024 - 2.0 arcsec (0.25 - 66 AU) from their primaries and have mag. This multi-year campaign will ultimately map complete orbits for nearby M dwarfs with periods up to 3 yr, and provide key epochs to stretch orbital determinations for binaries to 30 yr.

Among systems of interests LP 788-001 (or LP 788-1), for which a substellar secondary is considered but the orbit seems not to be constrained.

Overlooked paper: several new brown dwarf companions imaged to M dwarf

Discovery of 34 low-mass comoving systems using NOIRLab Source Catalog DR2

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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 ∼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 ∼2 and ∼56", parallactic distances between ∼43 and ∼261 pc and projected physical separations between ∼169 and ∼8487 AU. The lowest measured total proper motion is 97 mas yr−1, the highest 314 mas yr−1. Tangential velocities range from ∼23 to ∼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.

Here are M dwarf+BD systems with individual spectral types, constellations, separations and masses

NSC J004058.68-294212.37 (M7V+T5V) Scl 1095 AUs 36 Mj
NSC J014827.71-035716.63 (M4V+L4V) Cet 1395.73 AUs 58 Mj
NSC J020029.71-125451.00 (K7V+L9V) Cet 8486.73 AUs 48 Mj
NSC J020048.45-470755.84 (M2V+L4V) Phe 1691.2 AUs 58 Mj
NSC J020541.24+020249.66 (M7V+L8V) Cet/Psc 637.1 AUs 36 Mj
NSC J023113.30-031147.09 (M7V+L4V) Cet 423.6 AUs 58 Mj
NSC J043503.99-355911.42 (M4V+L5V) Eri 2555.9 AUs 58 Mj
NSC J045724.25-230012.74 (M4V+T3V) Lep 933 AUs 48 Mj
NSC J052307.20-565522.36 (M5V+T0V) Pic 706.5 AUs 48 Mj
NSC J123900.73-005433.72 (M4V+L4V) Vir 377 AUs  58 Mj

Radio Emission from Binary Ultracool Dwarf Systems

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Well-characterized binary systems will provide valuable opportunities to study the conditions that are necessary for the onset of both auroral and non-auroral magnetospheric radio emission in the ultracool dwarf regime. We present new detections of non-auroral "quiescent" radio emission at 4-8 GHz of the three ultracool dwarf binary systems GJ 564 BC, LP 415-20, and 2MASS J21402931+1625183. We also tentatively detect a highly circularly polarized pulse at 4-6 GHz that may indicate aurorae from GJ 564 BC. Finally, we show that the brightest binary ultracool dwarf systems may be more luminous than predictions from single-object systems.

I’m posting this here
Near-infrared Accretion Signatures from the Circumbinary Planetary Mass Companion Delorme 1 (AB)b

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Accretion signatures from bound brown dwarf and protoplanetary companions provide evidence for ongoing planet formation, and accreting substellar objects have enabled new avenues to study the astrophysical mechanisms controlling formation and accretion processes. Delorme 1 (AB)b, a ~30-45 Myr circumbinary planetary mass companion, was recently discovered to exhibit strong Hα emission. This suggests ongoing accretion from a circumplanetary disk, somewhat surprising given canonical gas disk dispersal timescales of 5-10 Myr. Here, we present the first NIR detection of accretion from the companion in Paβ, Paγ, and Brγ emission lines from SOAR/TripleSpec 4.1, confirming and further informing its accreting nature. The companion shows strong line emission, with Lline≈1−6×10^-8 L⊙ across lines and epochs, while the binary host system shows no NIR hydrogen line emission (Lline<0.32−11×10^-7 L⊙). Observed NIR hydrogen line ratios are more consistent with a planetary accretion shock than with local line excitation models commonly used to interpret stellar magnetospheric accretion. Using planetary accretion shock models, we derive mass accretion rate estimates of M˙pla∼3-4×10^-8 M_J yr^-1, somewhat higher than expected under the standard star formation paradigm. Delorme 1 (AB)b's high accretion rate is perhaps more consistent with formation via disk fragmentation. Delorme 1 (AB)b is the first protoplanet candidate with clear (S/N∼5) NIR hydrogen line emission.

Updated orbital monitoring and dynamical masses for nearby M-dwarf binaries
https://arxiv.org/abs/2208.09503

A binary system, 2MASS J04595855-0333123 (aka SCR J0459-0333 or JNN 29) with substellar companion is resolved but the mass straddles the H-D burning limit (0.07 M_Sol).

VVV J165507.19-421755.5: A Nearby T Dwarf Hidden in the Galactic Plane

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We present the discovery of VVV J165507.19−421755.5, a mid-T dwarf found through ongoing unWISE-based proper motion searches. A near-infrared spectrum of this object obtained with the NIRES instrument on the Keck II telescope indicates a spectral classification of T5. Using data from the VISTA Variables in the Via Lactea (VVV) catalog with a 9 year baseline, we measure a proper motion of (${\mu }_{\alpha }\cos (\delta )$, μδ) = (−631.0 ± 1.3, −315.0 ± 1.4) mas yr−1 and a trigonometric parallax of πabs = 66.0 ± 4.8 mas, corresponding to a distance of 15.2 ± 1.1 pc. The trigonometric parallax agrees well with our photometric distance estimate (16.1${}_{-3.9}^{+5.1}$ pc) assuming that VVV J165507.19−421755.5 is a single T5 dwarf. VVV J165507.19−421755.5 is a new member of the 20 parsec census.

Interesting update at EPE about a well-known young, low-mass nearby multiple system, Gliese 569 (aka CE Bootis):

http://exoplanet.eu/catalog/gl_569b_b/

Patchy Forsterite Clouds in the Atmospheres of Two Highly Variable Exoplanet Analogs

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We present an atmospheric retrieval analysis of a pair of highly variable, ∼200 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 μm 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 (Mg2SiO4) 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 H2O 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.

Polarised radio pulsations from a new T dwarf binary

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Brown dwarfs display Jupiter-like auroral phenomena such as magnetospheric Hα emission and coherent radio emission. Coherent radio emission is a probe of magnetospheric acceleration mechanisms and provides a direct measurement of the magnetic field strength at the emitter's location, both of which are difficult to access by other means. Observations of the coldest brown dwarfs (spectral types T and Y) are particularly interesting as their magnetospheric phenomena may be very similar to those in gas-giant exoplanets. Here we present 144 MHz radio and infrared adaptive optics observations of the brown dwarf WISEP J101905.63+652954.2 made using the LOFAR and Keck telescopes respectively. The radio data shows pulsed highly circularly polarised emission which yields a rotation rate of 0.32±0.03 hr−1. The infrared imaging reveals the source to be a binary with a projected separation of 423.0±1.6 mas between components of spectral type T5.5±0.5 and T7.0±0.5. With a simple "toy model" we show that the radio emission can in principle be powered by the interaction between the two dwarfs with a mass-loss rates of at least 25 times the Jovian value. WISEP J101905.63+652954.2 is interesting because it is the first pulsed methane dwarf detected in a low radio-frequency search. Unlike previous gigahertz-frequency searches that were only sensitive to objects with kiloGauss fields, our low-frequency search is sensitive to surface magnetic fields of ≈50 Gauss and above which might reveal the coldest radio-loud objects down to planetary mass-scales.

Discovery of a resolved white dwarf-brown dwarf binary with a small projected separation: SDSS J222551.65+001637.7AB

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We present the confirmation of SDSS J222551.65+001637.7AB as a closely separated, resolved, white dwarf-brown dwarf binary. We have obtained spectroscopy from GNIRS and seeing-limited Ks-band imaging from NIRI on Gemini North. The target is spatially resolved into its constituent components: a 10926± 246 K white dwarf, with log g=8.214±0.168 and a mass of 0.66+0.11−0.06 M⊙, and an L4 brown dwarf companion, which are separated by 0.9498±0.0022". We derive the fundamental properties of the companion from the Sonora-Bobcat evolutionary models, finding a mass of 25−53 MJup and a radius of 0.101−0.128 R⊙ for the brown dwarf, at a confidence level of 1σ. We use wdwarfdate to determine the age of the binary as 1.97+4.41−0.76 Gyr. A kinematic analysis shows that this binary is likely a member of the thick disc. The distance to the binary is 218+14−13 pc, and hence the projected separation of the binary is 207+13−12 AU. Whilst the white dwarf progenitor was on the main sequence the binary separation would have been 69±5 AU. SDSS J222551.65+001637.7AB is the third closest spatially resolved white dwarf-brown dwarf binary after GD 165AB and PHL 5038AB.

Rather strange system

Discovery of the Exceptionally Short Period Ultracool Dwarf Binary LP 413-53AB

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We report the detection of large-amplitude, rapid radial velocity (RV) variations and line-splitting in high-resolution Keck/NIRSPEC spectra of the M9 dwarf LP 413-53. We attribute these features to binary motion. Analyzing data spanning 9 months, we infer an orbital period of 0.852725^+0.000002_-0.000003 day, an eccentricity of 0.080^+0.020_-0.013, a primary RV semi-amplitude of 24.2^+1.8_-1.4 km s^-1, and a secondary RV semi-amplitude of 29.4^+2.2_-1.7 km~s^-1, implying a system mass ratio M_secondary/M_primary = 0.822^+0.009_-0.008. These measurements identify LP 413-53 as the shortest-period ultracool binary discovered to date, and one of the smallest separation main sequence binaries known. The position and velocity of the system rules out previously reported membership in the Hyades Moving Group, and indicate that this is likely a pair of evolved (age ≳ 1 Gyr), very-low-mass stars. Assuming masses consistent with evolved late-M and L dwarfs, we estimate an orbital separation of 0.0093-0.0095~au or 19-22 stellar radii, and an orbital inclination angle of 27±2 deg, making it unlikely that this system exhibits eclipse events. The larger radii of these stars at young ages would have put them in contact at the system's current separation, and we speculate that this system has undergone dynamical evolution, either through orbital angular momentum loss or ejection of a third component followed by tidal circularization.

M₁ = ca. 76 M_J, M₂ = ca. 62 M_J.

JWST unveils the brown dwarf sequence of 47 Tucanae

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We have developed a technique to restore scientific usage in compromised (publicly-available) images collected with the James Webb Space Telescope (JWST) of the Galactic globular cluster NGC 104 (47 Tucanae). In spite of the degradation and limited data, we were able to recover photometry and astrometry for the coolest stellar objects ever observed within a globular cluster, possibly unveiling the brightest part of the brown dwarf (BD) sequence. This is supported by: (i) proper motion membership, derived by the comparison with positions obtained from Hubble Space Telescope archival early epochs; (ii) the predicted location of the BD sequence; and (iii) the mass function for low-mass stars derived from models. Future JWST observations will provide the necessary deep and precise proper motions to confirm the nature of the here-identified BD candidates belonging to this globular cluster.

JWST/NIRCam discovery of the first Y+Y brown dwarf binary: WISE J033605.05-014350.4

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We report the discovery of the first brown dwarf binary system with a Y dwarf primary, WISE J033605.05−014350.4, observed with NIRCam on JWST with the F150W and F480M filters. We employed an empirical point spread function binary model to identify the companion, located at a projected separation of 84 milliarcseconds, position angle of 295 degrees, and with contrast of 2.8 and 1.8 magnitudes in F150W and F480M, respectively. At a distance of 10pc based on its Spitzer parallax, and assuming a random inclination distribution, the physical separation is approximately 1au. Evolutionary models predict for that an age of 1-5 Gyr, the companion mass is about 4-12.5 Jupiter masses around the 7.5-20 Jupiter mass primary, corresponding to a companion-to-host mass fraction of q=0.61±0.05. Under the assumption of a Keplerian orbit the period for this extreme binary is in the range of 5-9 years. The system joins a small but growing sample of ultracool dwarf binaries with effective temperatures of a few hundreds of Kelvin. Brown dwarf binaries lie at the nexus of importance for understanding the formation mechanisms of these elusive objects, as they allow us to investigate whether the companions formed as stars or as planets in a disk around the primary.

Investigating Possible Binarity for GJ 229B

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GJ 229B, the first type-T brown dwarf to be discovered, has presented a tension between comparisons with evolutionary models and the larger-than-expected mass and radius values derived from spectroscopic and astrometric observations. We examine the hypothesis that GJ 229B is actually a binary sub-stellar object by using two grid-based fits using evolutionary models to explore the range of mass ratios of the possible binary components. We find that the best-fit component values are most consistent with a roughly 2:1 binary mass ratio and an age range of 2-6 Gyr. The observed temperatures, masses, and apparent radii match expected values from evolutionary models for a binary much better than a single-object model, but more detailed observations and modeling are needed to definitively confirm the binary hypothesis.

The First JWST Spectral Energy Distribution of a Y dwarf

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We present the first JWST spectral energy distribution of a Y dwarf. This spectral energy distribution of the Y0 dwarf WISE J035934.06−540154.6 consists of low-resolution (λ/Δλ ∼ 100) spectroscopy from 1−12 μm and three photometric points at 15, 18, and 21 μm. The spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of H2O, CH4, CO, CO2, and NH3, including the previously unidentified ν3 band of NH3 at 3 μm. Using a Rayleigh-Jeans tail to account for the flux emerging at wavelengths greater than 21 μm, we measure a bolometric luminosity of 1.523±0.090×1020 W. We determine a semi-empirical effective temperature estimate of 467+16−18 K using the bolometric luminosity and evolutionary models to estimate a radius. Finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having Teff=450 K, log g=3.25 [cm s−2], [M/H]=−0.3. However, the low surface gravity implies an extremely low mass of 1 MJup and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.