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1. The MOSFIRE Deep Evolution Field Survey: Implications of the Lack of Evolution in the Dust Attenuation–Mass Relation to z ∼ 2*

   https://doi.org/10.3847/1538-4357/ac4742  

   Shapley, Alice E. ; Sanders, Ryan L. ; Salim, Samir ; Reddy, Naveen A. ; Kriek, Mariska ; Mobasher, Bahram ; Coil, Alison L. ; Siana, Brian ; Price, Sedona H. ; Shivaei, Irene ; et al ( February 2022 , The Astrophysical Journal)

   We investigate the relationship between dust attenuation and stellar mass (M_*) in star-forming galaxies over cosmic time. For this analysis, we compare measurements from the MOSFIRE Deep Evolution Field survey atz∼ 2.3 and the Sloan Digital Sky Survey (SDSS) atz∼ 0, augmenting the latter optical data set with both UV Galaxy Evolution Explorer (GALEX) and mid-infrared Wide-field Infrared Survey Explorer (WISE) photometry from the GALEX-SDSS-WISE Catalog. We quantify dust attenuation using both spectroscopic measurements of Hαand Hβemission lines, and photometric measurements of the rest-UV stellar continuum. The Hα/Hβratio is used to determine the magnitude of attenuation at the wavelength of Hα,A_Hα. Rest-UV colors and spectral energy distribution fitting are used to estimateA₁₆₀₀, the magnitude of attenuation at a rest wavelength of 1600 Å. As in previous work, we find a lack of significant evolution in the relation between dust attenuation andM_*over the redshift rangez∼ 0 toz∼ 2.3. Folding in the latest estimates of the evolution ofM_dust, (M_dust/M_gas), and gas surface density at fixedM_*, we find that the expectedM_dustand dust mass surface density are both significantly higher atz∼ 2.3 than atz∼ 0. These differences appear at odds with the lack of evolution in dust attenuation. To explain the striking constancy in attenuation versusM_*, it is essential to determine the relationship between metallicity and (M_dust/M_gas), the dust mass absorption coefficient and dust geometry, and the evolution of these relations and quantities fromz∼ 0 toz∼ 2.3.

    

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2. TESS Asteroseismic Analysis of HD 76920: The Giant Star Hosting an Extremely Eccentric Exoplanet

   https://doi.org/10.3847/1538-4357/acb8ac  

   Jiang 姜, Chen 晨. ; Wu 吴涛, Tao ; Feinstein, Adina D. ; Stassun, Keivan G. ; Bedding, Timothy R. ; Veras, Dimitri ; Corsaro, Enrico ; Buzasi, Derek L. ; Stello, Dennis ; Li 李亚光, Yaguang ; et al ( March 2023 , The Astrophysical Journal)

   The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing for detailed asteroseismic studies of individual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet (e= 0.878) with an orbital period of 415 days, using five sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around 52μHz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass (1.22 ± 0.11M_⊙), radius (8.68 ± 0.34R_☉), and age (5.2 ± 1.4 Gyr). With the updated parameters of the host star, we update the semimajor axis and mass of the planet asa= 1.165 ± 0.035 au and$M_{\mathrm{p}}\sin i=3.57\pm 0.22M_{\mathrm{Jup}}$. With an orbital pericenter of 0.142 ± 0.005 au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100 Myr, depending on the stellar model used.

    

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3. Forbidden hugs in pandemic times: II. The luminous red nova variety: AT 2020hat and AT 2020kog

   https://doi.org/10.1051/0004-6361/202039953  

   Pastorello, A. ; Valerin, G. ; Fraser, M. ; Elias-Rosa, N. ; Valenti, S. ; Reguitti, A. ; Mazzali, P. A. ; Amaro, R. C. ; Andrews, J. E. ; Dong, Y. ; et al ( March 2021 , Astronomy & Astrophysics)

   null (Ed.)

   We present the results of our monitoring campaigns of the luminous red novae (LRNe) AT 2020hat in NGC 5068 and AT 2020kog in NGC 6106. The two objects were imaged (and detected) before their discovery by routine survey operations. They show a general trend of slow luminosity rise, lasting at least a few months. The subsequent major LRN outbursts were extensively followed in photometry and spectroscopy. The light curves present an initial short-duration peak, followed by a redder plateau phase. AT 2020kog is a moderately luminous event peaking at ∼7 × 10 40 erg s −1 , while AT 2020hat is almost one order of magnitude fainter than AT 2020kog, although it is still more luminous than V838 Mon. In analogy with other LRNe, the spectra of AT 2020kog change significantly with time. They resemble those of type IIn supernovae at early phases, then they become similar to those of K-type stars during the plateau, and to M-type stars at very late phases. In contrast, AT 2020hat already shows a redder continuum at early epochs, and its spectrum shows the late appearance of molecular bands. A moderate-resolution spectrum of AT 2020hat taken at +37 d after maximum shows a forest of narrow P Cygni lines of metals with velocities of 180 km s −1 , along with an H α emission with a full-width at half-maximum velocity of 250 km s −1 . For AT 2020hat, a robust constraint on its quiescent progenitor is provided by archival images of the Hubble Space Telescope. The progenitor is clearly detected as a mid-K type star, with an absolute magnitude of M F 606 W  = −3.33 ± 0.09 mag and a colour of F 606 W  −  F 814 W  = 1.14 ± 0.05 mag, which are inconsistent with the expectations from a massive star that could later produce a core-collapse supernova. Although quite peculiar, the two objects nicely match the progenitor versus light curve absolute magnitude correlations discussed in the literature. 

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4. Extreme variability in an active galactic nucleus: Gaia16aax

   https://doi.org/10.1093/mnras/staa186  

   Cannizzaro, G ; Fraser, M ; Jonker, P G ; Pringle, J E ; Mattila, S ; Hewett, P C ; Wevers, T ; Kankare, E ; Kostrzewa-Rutkowska, Z ; Wyrzykowski, Ł ; et al ( March 2020 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present the results of a multiwavelength follow-up campaign for the luminous nuclear transient Gaia16aax, which was first identified in 2016 January. The transient is spatially consistent with the nucleus of an active galaxy at z = 0.25, hosting a black hole of mass ${\sim }6\times 10^8\, \mathrm{M}_\odot$. The nucleus brightened by more than 1 mag in the Gaia G band over a time-scale of less than 1 yr, before fading back to its pre-outburst state over the following 3 yr. The optical spectra of the source show broad Balmer lines similar to the ones present in a pre-outburst spectrum. During the outburst, the H α and H β emission lines develop a secondary peak. We also report on the discovery of two transients with similar light-curve evolution and spectra: Gaia16aka and Gaia16ajq. We consider possible scenarios to explain the observed outbursts. We exclude that the transient event could be caused by a microlensing event, variable dust absorption or a tidal encounter between a neutron star and a stellar mass black hole in the accretion disc. We consider variability in the accretion flow in the inner part of the disc, or a tidal disruption event of a star ${\ge } 1 \, \mathrm{M}_{\odot }$ by a rapidly spinning supermassive black hole as the most plausible scenarios. We note that the similarity between the light curves of the three Gaia transients may be a function of the Gaia alerts selection criteria. 

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5. First Observations of the Brown Dwarf HD 19467 B with JWST

   https://doi.org/10.3847/1538-4357/acb68b  

   Greenbaum, Alexandra Z. ; Llop-Sayson, Jorge ; Lew, Ben W. P. ; Bryden, Geoffrey ; Roellig, Thomas L. ; Ygouf, Marie ; Fulton, B. J. ; Hey, Daniel R. ; Huber, Daniel ; Mukherjee, Sagnick ; et al ( March 2023 , The Astrophysical Journal)

   We observed HD 19467 B with JWST’s NIRCam in six filters spanning 2.5–4.6μm with the long-wavelength bar coronagraph. The brown dwarf HD 19467 B was initially identified through a long-period trend in the radial velocity of the G3V star HD 19467. HD 19467 B was subsequently detected via coronagraphic imaging and spectroscopy, and characterized as a late-T type brown dwarf with an approximate temperature ∼1000 K. We observed HD 19467 B as a part of the NIRCam GTO science program, demonstrating the first use of the NIRCam Long Wavelength Bar coronagraphic mask. The object was detected in all six filters (contrast levels of 2 × 10⁻⁴to 2 × 10⁻⁵) at a separation of 1.″6 using angular differential imaging and synthetic reference differential imaging. Due to a guide star failure during the acquisition of a preselected reference star, no reference star data were available for post-processing. However, reference differential imaging was successfully applied using synthetic point-spread functions developed from contemporaneous maps of the telescope’s optical configuration. Additional radial velocity data (from Keck/HIRES) are used to constrain the orbit of HD 19467 B. Photometric data from TESS are used to constrain the properties of the host star, particularly its age. NIRCam photometry, spectra, and photometry from the literature, and improved stellar parameters are used in conjunction with recent spectral and evolutionary substellar models to derive the physical properties of HD 19467 B. Using an age of 9.4 ± 0.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS asteroseismology, we obtain a model-derived mass of 62 ± 1M_J, which is consistent within 2σwith the dynamically derived mass of${81}_{-12}^{+14}$M_J.

    

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