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1. Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf

   https://doi.org/10.3847/2041-8213/acb0cd  

   Schneider, Adam C. ; Burgasser, Adam J. ; Bruursema, Justice ; Munn, Jeffrey A. ; Vrba, Frederick J. ; Caselden, Dan ; Kabatnik, Martin ; Rothermich, Austin ; Sainio, Arttu ; Bickle, Thomas P. ; et al ( January 2023 , The Astrophysical Journal Letters)

   We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J−K)_MKOcolor of 2.97 ± 0.03 mag and aJ_MKO− W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH₄absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ–T0γ. We tentatively find that CWISE J0506+0738 is variable at 3–5μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in theβPic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.

    

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2. Mid-infrared dusty torus sizes in active galactic nuclei with Hβ reverberation mapping

   https://doi.org/10.1093/mnras/stad1136  

   Chen, Yong-Jie ; Liu, Jun-Rong ; Zhai, Shuo ; Yao, Zhu-Heng ; Li, Yan-Rong ; Du, Pu ; Hu, Chen ; Guo, Wei-Jian ; Xiao, Ming ; Songsheng, Yu-Yang ; et al ( April 2023 , Monthly Notices of the Royal Astronomical Society)

   We compile optical and mid-infrared light curves from the time-domain surveys (i.e. CRTS, PTF, ZTF, and ASAS-SN) and Wide-field Infrared Survey Explorer (WISE) archive for a selected sample of active galactic nuclei (AGNs) with Hβ reverberation mapping (RM) measurements. We measure the time lags (and thus torus sizes) of W1 (∼3.4 $\mu$ m) and W2 (∼4.6 $\mu$ m) band light curves relative to the optical one using the MICA method. Through Hβ RM, the sample has well-measured AGN properties, therefore allowing us to reliably constrain the relations between torus sizes and AGN properties. We perform linear regressions for the relations between torus sizes and 5100 Å luminosities ($R\propto L_{5100}^{\beta }$ ) in two cases: β = 0.5 and β set free. The latter case yields β ≈ 0.37 ± 0.028 for both W1 and W2 bands, shallower than the expected value of 0.5, possibly due to the dependence of torus size on accretion rate. For β = 0.5, by combining with the previous K band RM measurements, we obtain the characteristic broad-line region (BLR) and tours sizes following RBLR:RK :RW1:RW2 = 1.0:6.2:9.2:11.2. We investigate the deviations of the W1 and W2 band observed torus sizes from the corresponding best-fitting relations (with β = 0.5) and find that they both are correlated with accretion rate. As the accretion rate increases, the torus sizes tend to be shortened compared to the anticipated sizes from the best-fitting relations, similar to the behaviour found in BLRs. Such behaviours can be explained by the self-shadowing effect of slim discs. This is further supported by ratios of the W1 and W2 band torus sizes to BLR sizes, which do not show significant correlations with AGN properties.

    

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3. Spatially resolved study of the SS 433/W 50 west region with Chandra: X-ray structure and spectral variation of non-thermal emission

   https://doi.org/10.1093/pasj/psac060  

   Kayama, Kazuho ; Tanaka, Takaaki ; Uchida, Hiroyuki ; Tsuru, Takeshi Go ; Sudoh, Takahiro ; Inoue, Yoshiyuki ; Khangulyan, Dmitry ; Tsuji, Naomi ; Yamamoto, Hiroaki ( August 2022 , Publications of the Astronomical Society of Japan)

   The X-ray binary SS 433, embedded in the W 50 nebula (or supernova remnant W 50), shows bipolar jets that are ejected with mildly relativistic velocities and which extend toward the east and west out to scales of tens of parsecs. Previous X-ray observations revealed twin lobes along the jet precession axis that contain compact bright knots dominated by synchrotron radiation, which provide evidence of electron acceleration in this system. Particle acceleration in this system is substantiated by the recently detected gamma rays with energies up to at least 25 TeV. To elucidate the origin of the knots and particle acceleration sites in SS 433/W 50 further, we report here on detailed, spatially resolved X-ray spectroscopy of its western lobe with Chandra. We detect synchrotron emission along the jet precession axis, as well as optically thin thermal emission that is more spatially extended. Between the two previously known knots, w1 and w2, we discover another synchrotron knot, which we call w1.5. We find no significant synchrotron emission between SS 433 and the innermost X-ray knot (w1), suggesting that electrons only begin to be accelerated at w1. The X-ray spectra become gradually steeper from w1 to w2, and then rapidly so immediately outside of w2. Through comparison with a model taking into account electron transport and cooling along the jet, this result indicates that the magnetic field in w2 is substantially enhanced, which also explains its brightness. We discuss possible origins of the enhanced magnetic field of w2 as well as scenarios to explain the other two knots.

    

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4. RR Lyrae Mid-infrared Period–Luminosity–Metallicity and Period–Wesenheit–Metallicity Relations Based on Gaia DR3 Parallaxes

   https://doi.org/10.3847/1538-4357/acb20a  

   Mullen, Joseph P. ; Marengo, Massimo ; Martínez-Vázquez, Clara E. ; Chaboyer, Brian ; Bono, Giuseppe ; Braga, Vittorio F. ; Dall’Ora, Massimo ; D’Orazi, Valentina ; Fabrizio, Michele ; Monelli, Matteo ; et al ( March 2023 , The Astrophysical Journal)

   We present new empirical infrared period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyae based on the latest Gaia Early Data Release 3 (EDR3) parallaxes. The relations are provided in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands, as well as in the W(W1,V− W1) and W(W2,V− W2) Wesenheit magnitudes. The relations are calibrated using a very large sample of Galactic halo field RR Lyrae stars with homogeneous spectroscopic [Fe/H] abundances (over 1000 stars in the W1 band), covering a broad range of metallicities (−2.5 ≲ [Fe/H] ≲ 0.0). We test the performance of our PLZ and PWZ relations by determining the distance moduli of both galactic and extragalactic stellar associations: the Sculptor dwarf spheroidal galaxy in the Local Group (finding${\overline{\mu }}_0=19.47\pm 0.06$), the Galactic globular clusters M4 (${\overline{\mu }}_0=11.16\pm 0.05$), and the Reticulum globular cluster in the Large Magellanic Cloud (${\overline{\mu }}_0=18.23\pm 0.06$). The distance moduli determined through all our relations are internally self-consistent (within ≲0.05 mag) but are systematically smaller (by ∼2–3σ) than previous literature measurements taken from a variety of methods/anchors. However, a comparison with similar recent RR Lyrae empirical relations anchored with EDR3 likewise shows, to varying extents, a systematically smaller distance modulus for PLZ/PWZ RR Lyrae relations.

    

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5. Metallicities from high-resolution spectra of 49 RR Lyrae variables

   https://doi.org/10.1093/mnras/stab857  

   Gilligan, Christina K ; Chaboyer, Brian ; Marengo, Massimo ; Mullen, Joseph P ; Bono, Giuseppe ; Braga, Vittorio F ; Crestani, Juliana ; Dall’Ora, Massimo ; Fiorentino, Giuliana ; Monelli, Matteo ; et al ( April 2021 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Accurate metallicities of RR Lyrae are extremely important in constraining period–luminosity–metallicity (PLZ) relationships, particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope. We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.15 dex. All but one RR Lyrae in this sample has accurate ($\sigma _{\varpi }\lesssim 10{{\ \rm per\ cent}}$) parallax from Gaia. Combining these new high-resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ relationships in WISE W1 and W2 magnitudes, and the Wesenheit magnitudes W(W1, V − W1) and W(W2, V − W2). 

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