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  1. Abstract We present the discovery of 34 comoving systems containing an ultracool 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 ultracool companion, or a white dwarf and an ultracool 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 , with 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 systemsmore »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.« less
    Free, publicly-accessible full text available June 6, 2023
  2. Abstract While stars are often found in binary systems, brown dwarf binaries are much rarer. Brown dwarf–brown dwarf pairs are typically difficult to resolve because they often have very small separations. Using brown dwarfs discovered with data from the Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, we inspected other, higher-resolution, sky surveys for overlooked cold companions. During this process, we discovered the brown dwarf binary system CWISE J0146−0508AB, which we find has a very small chance alignment probability based on the similar proper motions of the components of the system. Using follow-up near-infrared spectroscopy with Keck/NIRES, we determined component spectral types of L4 and L8 (blue), making CWISE J0146−0508AB one of only a few benchmark systems with a blue L dwarf. At an estimated distance of ∼40 pc, CWISE J0146−0508AB has a projected separation of ∼129 au, making it the widest-separation brown dwarf pair found to date. We find that such a wide separation for a brown dwarf binary may imply formation in a low-density star-forming region.
    Free, publicly-accessible full text available February 1, 2023
  3. Abstract Through the Backyard Worlds: Planet 9 citizen science project we discovered a late-type L dwarf co-moving with the young K0 star BD+60 1417 at a projected separation of 37″ or 1662 au. The secondary—CWISER J124332.12+600126.2 (W1243)—is detected in both the CatWISE2020 and 2MASS reject tables. The photometric distance and CatWISE proper motion both match that of the primary within ∼1 σ and our estimates for a chance alignment yield a zero probability. Follow-up near-infrared spectroscopy reveals W1243 to be a very red 2MASS ( J – K s = 2.72), low surface gravity source that we classify as L6–L8 γ . Its spectral morphology strongly resembles that of confirmed late-type L dwarfs in 10–150 Myr moving groups as well as that of planetary mass companions. The position on near- and mid-infrared color–magnitude diagrams indicates the source is redder and fainter than the field sequence, a telltale sign of an object with thick clouds and a complex atmosphere. For the primary we obtained new optical spectroscopy and analyzed all available literature information for youth indicators. We conclude that the Li i abundance, its loci on color–magnitude and color–color diagrams, and the rotation rate revealed in multiple TESS sectors are allmore »consistent with an age of 50–150 Myr. Using our re-evaluated age of the primary and the Gaia parallax, along with the photometry and spectrum for W1243, we find T eff = 1303 ± 31 K, log g = 4.3 ± 0.17 cm s −2 , and a mass of 15 ± 5 M Jup . We find a physical separation of ∼1662 au and a mass ratio of ∼0.01 for this system. Placing it in the context of the diverse collection of binary stars, brown dwarfs, and planetary companions, the BD+60 1417 system falls in a sparsely sampled area where the formation pathway is difficult to assess.« less
  4. Abstract We present photometric and spectroscopic observations of Supernova 2020oi (SN 2020oi), a nearby (∼17 Mpc) type-Ic supernova (SN Ic) within the grand-design spiral M100. We undertake a comprehensive analysis to characterize the evolution of SN 2020oi and constrain its progenitor system. We detect flux in excess of the fireball rise model δ t ≈ 2.5 days from the date of explosion in multiband optical and UV photometry from the Las Cumbres Observatory and the Neil Gehrels Swift Observatory, respectively. The derived SN bolometric luminosity is consistent with an explosion with M ej = 0.81 ± 0.03 M ⊙ , E k = 0.79 ± 0.09 × 10 51 erg s −1 , and M Ni56 = 0.08 ± 0.02 M ⊙ . Inspection of the event’s decline reveals the highest Δ m 15,bol reported for a stripped-envelope event to date. Modeling of optical spectra near event peak indicates a partially mixed ejecta comparable in composition to the ejecta observed in SN 1994I, while the earliest spectrum shows signatures of a possible interaction with material of a distinct composition surrounding the SN progenitor. Further, Hubble Space Telescope pre-explosion imaging reveals a stellar cluster coincident with the event. From the clustermore »photometry, we derive the mass and age of the SN progenitor using stellar evolution models implemented in the BPASS library. Our results indicate that SN 2020oi occurred in a binary system from a progenitor of mass M ZAMS ≈ 9.5 ± 1.0 M ⊙ , corresponding to an age of 27 ± 7 Myr. SN 2020oi is the dimmest SN Ic event to date for which an early-time flux excess has been observed, and the first in which an early excess is unlikely to be associated with shock cooling.« less
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  6. ABSTRACT

    We present the discovery of TOI-2136 b, a sub-Neptune planet transiting a nearby M4.5V-type star every 7.85 d, identified through photometric measurements from the Transiting Exoplanet Survey Satellite (TESS) mission. The host star is located 33 pc away with a radius of R* = 0.34 ± 0.02 R⊙, a mass of $0.34\pm 0.02 \, \mathrm{M}_{\odot }$, and an effective temperature of 3342 ± 100 K. We estimate its stellar rotation period to be 75 ± 5 d based on archival long-term photometry. We confirm and characterize the planet based on a series of ground-based multiwavelength photometry, high-angular-resolution imaging observations, and precise radial velocities from Canada–France–Hawaii Telescope (CFHT)/SpectroPolarimètre InfraROUge (SPIRou). Our joint analysis reveals that the planet has a radius of 2.20 ± 0.17 R⊕ and a mass of 6.4 ± 2.4 M⊕. The mass and radius of TOI-2136 b are consistent with a broad range of compositions, from water-ice to gas-dominated worlds. TOI-2136 b falls close to the radius valley for M dwarfs predicted by thermally driven atmospheric mass-loss models, making it an interesting target for future studies of its interior structure and atmospheric properties.