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1. A giant planet candidate transiting a white dwarf

   https://doi.org/10.1038/s41586-020-2713-y  

   Vanderburg, Andrew; Rappaport, Saul A.; Xu, Siyi; Crossfield, Ian J.; Becker, Juliette C.; Gary, Bruce; Murgas, Felipe; Blouin, Simon; Kaye, Thomas G.; Palle, Enric; et al (September 2020, Nature)

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2. An Eccentric Brown Dwarf Eclipsing an M dwarf

   https://doi.org/10.3847/1538-3881/ac415f  

   Cañas, Caleb I.; Mahadevan, Suvrath; Bender, Chad F.; Salazar Rivera, Noah Isaac; Monson, Andrew; Beard, Corey; Lubin, Jack; Robertson, Paul; Gupta, Arvind F.; Cochran, William D.; et al (January 2022, The Astronomical Journal)

   Abstract We report the discovery of an M = 67 ± 2 M J brown dwarf transiting the early M dwarf TOI-2119 on an eccentric orbit ( e = 0.3362 ± 0.0005) at an orbital period of 7.200861 ± 0.000005 days. We confirm the brown dwarf nature of the transiting companion using a combination of ground-based and space-based photometry and high-precision velocimetry from the Habitable-zone Planet Finder. Detection of the secondary eclipse with TESS photometry enables a precise determination of the eccentricity and reveals the brown dwarf has a brightness temperature of 2100 ± 80 K, a value which is consistent with an early L dwarf. TOI-2119 is one of the most eccentric known brown dwarfs with P < 10 days, possibly due to the long circularization timescales for an object orbiting an M dwarf. We assess the prospects for determining the obliquity of the host star to probe formation scenarios and the possibility of additional companions in the system using Gaia EDR3 and our radial velocities. 

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3. WD1032 + 011, an inflated brown dwarf in an old eclipsing binary with a white dwarf

   https://doi.org/10.1093/mnras/staa1608  

   Casewell, S L; Belardi, C; Parsons, S G; Littlefair, S P; Braker, I P; Hermes, J J; Debes, J; Vanderbosch, Z; Burleigh, M R; Gänsicke, B T; et al (September 2020, Monthly Notices of the Royal Astronomical Society)

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   ABSTRACT We present the discovery of only the third brown dwarf known to eclipse a non-accreting white dwarf. Gaia parallax information and multicolour photometry confirm that the white dwarf is cool (9950 ± 150 K) and has a low mass (0.45 ± 0.05 M⊙), and spectra and light curves suggest the brown dwarf has a mass of 0.067 ± 0.006 M⊙ (70MJup) and a spectral type of L5 ± 1. The kinematics of the system show that the binary is likely to be a member of the thick disc and therefore at least 5-Gyr old. The high-cadence light curves show that the brown dwarf is inflated, making it the first brown dwarf in an eclipsing white dwarf-brown dwarf binary to be so. 

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4. A Luminous X-Ray Active Galactic Nucleus in the Dwarf–Dwarf Galaxy Merger RGG 66

   https://doi.org/10.3847/1538-4357/ad712d  

   Kimbrell, Seth_J; Reines, Amy_E (October 2024, The Astrophysical Journal)

   Abstract We present the discovery of a luminous X-ray active galactic nucleus (AGN) in the dwarf galaxy merger RGG 66. The black hole is predicted to have a mass ofM_BH∼ 10^5.4M_⊙and to be radiating close to its Eddington limit (L_bol/L_Edd∼ 0.75). The AGN in RGG 66 is notable both for its presence in a late-stage dwarf–dwarf merger and for its luminosity ofL_{2–10 keV}= 10^42.2erg s⁻¹, which is among the most powerful AGNs known in nearby dwarf galaxies. The X-ray spectrum has a best-fit photon index of Γ = 2.4 and an intrinsic absorption ofN_H∼ 10²¹cm⁻². These results come from a follow-up Chandra X-ray Observatory study of four irregular/disturbed dwarf galaxies with evidence for hosting AGNs based on optical spectroscopy. The remaining three dwarf galaxies do not have detectable X-ray sources with upper limits ofL_{2–10 keV}≲ 10⁴⁰erg s⁻¹. Taken at face value, our results on RGG 66 suggest that mergers may trigger the most luminous of AGNs in the dwarf galaxy regime, just as they are suspected to do in more massive galaxy mergers. 

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5. Methane emission from a cool brown dwarf

   https://doi.org/10.1038/s41586-024-07190-w  

   Faherty, Jacqueline K; Burningham, Ben; Gagné, Jonathan; Suárez, Genaro; Vos, Johanna M; Alejandro_Merchan, Sherelyn; Morley, Caroline V; Rowland, Melanie; Lacy, Brianna; Kiman, Rocio; et al (April 2024, Nature)

   Abstract Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs^1,2. Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H₃⁺and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported³. CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482 K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326 μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300 K centred at 1–10 mbar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H₃⁺emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H₃⁺at the higher pressure where the W1935 emission originates⁴. 

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