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1. Identification of a White Dwarf Companion in the V* HP Dra System

   https://doi.org/10.3847/2515-5172/ac151f  

   Jalowiczor, Peter A.; Casewell, Sarah; Schneider, Adam C.; Faherty, Jacqueline K.; Kuchner, Marc J. (July 2021, Research Notes of the AAS)

   Abstract We present Gaia DR2 2144465183642117888, a previously unknown, wide white dwarf companion to the HP Dra eclipsing binary system. This companion was discovered through the Backyard Worlds: Planet 9 citizen science collaboration. It has separation of 14.″4 on the sky from the central eclipsing pair, translating to a projected separation of ∼1140 au. We present a review of the orbit and physical parameters of all the components in this now triple system. 

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2. ZTFJ0038+2030: a long period eclipsing white dwarf and a substellar companion

   van Roestel, Jan; Kupfer, Thomas; Bell, Keaton J; Burdge, Kevin; Mroz, Przemek; Prince, Thomas A; Bellm, Eric C; Drake, Andrew; Dekany, Richard; Mahabal, Ashish A; et al (May 2021, ArXivorg)

   In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with a dark, substellar companion. The lack of an infrared excess and an orbital period of 10 hours made this a potential exoplanet candidate. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of 0.50±0.02M⊙ and a temperature of 10900±200K. The companion has a mass of 0.059±0.004M⊙ and a small radius of 0.0783±0.0013R⊙. It is one of the smallest transiting brown dwarfs known and likely old, ≳8Gyr. The ZTF discovery efficiency of substellar objects transiting white dwarfs is limited by the number of epochs and as ZTF continues to collect data we expect to find more of these systems. This will allow us to measure period and mass distributions and allows us to understand the formation channels of white dwarfs with substellar companions. 

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3. A Close-in Puffy Neptune with Hidden Friends: The Enigma of TOI 620

   https://doi.org/10.3847/1538-3881/ac658b  

   Reefe, Michael A.; Luque, Rafael; Gaidos, Eric; Beard, Corey; Plavchan, Peter P.; Cointepas, Marion; Cale, Bryson L.; Palle, Enric; Parviainen, Hannu; Feliz, Dax L.; et al (May 2022, The Astronomical Journal)

   Abstract We present the validation of a transiting low-density exoplanet orbiting the M2.5 dwarf TOI 620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations ≳0.″2. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple precision radial velocity (PRV) spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5 σ upper limit of M P < 7.1 M ⊕ and ρ P < 0.74 g cm −3 , and we identify a nontransiting 17.7 day candidate. We also find evidence for a substellar (1–20 M J ) companion with a projected separation ≲20 au from a combined analysis of Gaia, adaptive optics imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multiwavelength transit photometry, thus validating TOI 620 b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with the James Webb Space Telescope and Ariel, validated or confirmed by the TESS mission to date. 

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4. Unique Stellar Dynamics of ES1144

   Marrero_Diaz, Y S; Soto_Nieves, A; Bernal, J_P; Conaway-Hernandez, P L; Pantoja_Pantoja, C A; Lebron_Santos, M E; Storrie-Lombardi, L; Gomez, E; Hopkinson, A; Freed, R; et al (July 2024, Journal of double star observations)

   Freed, R; Harshaw, R; Genet, Russell M (Ed.)

   This investigation selected a double star system: ES1144 (also known as HD67007A and HD67007B), which is an eclipsing binary and member of a quadruple star system. We report on our observations and measurements of position angle and separation using images taken with Las Cumbres Observatory telescopes. We found a separation of 6.7 arcsec and a position angle of 337°. We conclude that more observations will be required to establish the orbit of the system. 

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5. A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate

   https://doi.org/10.1093/mnras/stab907  

   Jayasinghe, T; Stanek, K Z; Thompson, Todd A; Kochanek, C S; Rowan, D M; Vallely, P J; Strassmeier, K G; Weber, M; Hinkle, J T; Hambsch, F-J; et al (May 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby ($$d\sim 460\, \rm pc$$), bright (V ≃ 8.3 mag), evolved (Teff, giant ≃ 4440 K, and Lgiant ≃ 173 L⊙) red giant in a high mass function, f(M) = 1.72 ± 0.01 M⊙, nearly circular binary (P = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of $$87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$$, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of Mcomp = 3.04 ± 0.06 M⊙, a stellar radius of Rgiant = 24.9 ± 0.7 R⊙, and a giant mass of Mgiant = 1.00 ± 0.07 M⊙. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of $${\sim }63{{\ \rm per\ cent}}$$ and $${\sim }24{{\ \rm per\ cent}}$$, respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion discs. The X-ray luminosity of the system is $$L_{\rm X}\simeq 7.6\times 10^{29}~\rm ergs~s^{-1}$$, corresponding to L/Ledd ∼ 10−9. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the ‘mass gap’. 

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