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1. WTP 21aaeuqd: NEOWISE Discovery and Keck Confirmation of a Heavily Reddened, Optically Missed Galactic Nova

   https://doi.org/10.3847/2515-5172/adcea6  

   Ramesh, Padmalakshmi; De, Kishalay; Frostig, Danielle (April 2025, Research Notes of the AAS)

   Abstract Despite their long history, a complete inventory of Galactic novae has remained incomplete due to severe dust extinction. Recent ground-based near-infrared (NIR) as well as space-based mid-infrared (MIR) searches are providing a new window into discovering heavily obscured Galactic novae. Even with its slow cadence, archival photometric searches for large-amplitude, fast fading outbursts in the NEOWISE survey were previously used to identify Galactic nova candidates between 2014 and 2020. In this paper, we demonstrate the efficacy of the method with the discovery and NIR spectroscopy of WTP 21aaeuqd—a bright (peak W2 AB flux ≈10.5 mag), rapidly evolving (t₂ ≈ 120 days) MIR Galactic outburst (at $\mid b\mid \approx 1\stackrel{°}{.}3$). The reduced spectrum exhibits broad (≈800 km s⁻¹) emission lines of H iand C i, confirming its classification as a missed Fe iinova. This result confirms that archival infrared photometric searches are an effective way to identify nova candidates missed in optical searches. 

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2. JWST Observations of Starbursts: Massive Star Clusters in the Central Starburst of M82

   https://doi.org/10.3847/2041-8213/ad7af3  

   Levy, Rebecca C; Bolatto, Alberto D; Mayya, Divakara; Cuevas-Otahola, Bolivia; Tarantino, Elizabeth; Boyer, Martha L; Boogaard, Leindert A; Böker, Torsten; Cronin, Serena A; Dale, Daniel A; et al (September 2024, The Astrophysical Journal Letters)

   Abstract We present a near-infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses >10⁴M_⊙. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of ≈1 pc and stellar masses up to 10⁶M_⊙. By comparing the color–color diagram to dust-freeyggdrasilstellar population models, we estimate that the star cluster candidates haveA_V∼ 3−24 mag, corresponding toA_2.5μm∼ 0.3−2.1 mag. There is still appreciable dust extinction toward these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function isβ= 1.9 ± 0.2, in excellent agreement with studies of star clusters in other galaxies. 

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3. Evidence for an Instability-induced Binary Merger in the Double-peaked, Helium-rich Type IIn Supernova 2023zkd

   https://doi.org/10.3847/1538-4357/adea38  

   Gagliano, A; Villar, V A; Matsumoto, T; Jones, D O; Ransome, C L; Nugent, A E; Hiramatsu, D; Auchettl, K; Tsuna, D; Dong, Y; et al (August 2025, The Astrophysical Journal)

   Abstract We present ultraviolet to infrared observations of the extraordinary Type IIn supernova 2023zkd (SN 2023zkd). Photometrically, it exhibits persistent and luminous precursor emission spanning ∼4 yr preceding discovery (M_r ≈ −15 mag, 1500 days in the observer frame), followed by a secondary stage of gradual brightening in its final year. Post-discovery, it exhibits two photometric peaks of comparable brightness (M_r ≲ −18.7 mag andM_r ≈ −18.4 mag, respectively) separated by 240 days. Spectroscopically, SN 2023zkd exhibits highly asymmetric and multicomponent Balmer and HeIprofiles that we attribute to ejecta interaction with fast-moving (1000–2000 km s⁻¹) He-rich polar material and slow-moving (∼400 km s⁻¹) equatorially distributed H-rich material. HeIIfeatures also appear during the second light curve peak and evolve rapidly. Shock-driven models fit to the multiband photometry suggest that the event is powered by interaction with ∼5–6M_⊙of CSM, with 2–3M_⊙associated with each light curve peak, expelled during mass-loss episodes ∼3–4 yr and ∼1–2 yr prior to explosion. The observed precursor emission, combined with the extreme mass-loss rates required to power each light curve peak, favors either super-Eddington accretion onto a black hole or multiple long-lived eruptions from a massive star to luminosities that have not been previously observed. We consider multiple progenitor scenarios for SN 2023zkd, and find that the brightening optical precursor and inferred explosion properties are most consistent with a massive (M_ZAMS≥ 30M_⊙) and partially stripped He star undergoing an instability-induced merger with a black hole companion. 

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4. BUFFALO/Flashlights: Constraints on the abundance of lensed supergiant stars in the Spock galaxy at redshift 1

   https://doi.org/10.1051/0004-6361/202346761  

   Diego, Jose M.; Li, Sung Kei; Meena, Ashish K.; Niemiec, Anna; Acebron, Ana; Jauzac, Mathilde; Struble, Mitchell F.; Amruth, Alfred; Broadhurst, Tom J.; Cerny, Catherine; et al (January 2024, Astronomy & Astrophysics)

   In this work, we present a constraint on the abundance of supergiant (SG) stars at redshiftz ≈ 1, based on recent observations of a strongly lensed arc at this redshift. First we derived a free-form model of MACS J0416.1-2403 using data from the Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) program. The new lens model is based on 72 multiply lensed galaxies that produce 214 multiple images, making it the largest sample of spectroscopically confirmed lensed galaxies on this cluster. The larger coverage in BUFFALO allowed us to measure the shear up to the outskirts of the cluster, and extend the range of lensing constraints up to ∼1 Mpc from the central region, providing a mass estimate up to this radius. As an application, we make predictions for the number of high-redshift multiply lensed galaxies detected in future observations with theJames WebbSpace Telescope (JWST). Then we focus on a previously known lensed galaxy atz = 1.0054, nicknamed Spock, which contains four previously reported transients. We interpret these transients as microcaustic crossings of SG stars and explain how we computed the probability of such events. Based on simplifications regarding the stellar evolution, we find that microlensing (by stars in the intracluster medium) of SG stars atz = 1.0054 can fully explain these events. The inferred abundance of SG stars is consistent with either (1) a number density of stars with bolometric luminosities beyond the Humphreys-Davidson (HD) limit (L_max ≈ 6 × 10⁵ L_⊙for red stars), which is below ∼400 stars kpc⁻², or (2) the absence of stars beyond the HD limit but with a SG number density of ∼9000 kpc⁻²for stars with luminosities between 10⁵ L_⊙and 6 × 10⁵ L_⊙. This is equivalent to one SG star per 10 × 10 pc². Finally, we make predictions for future observations with JWST’s NIRcam. We find that in observations made with theF200Wfilter that reach 29 mag AB, if cool red SG stars exist atz ≈ 1 beyond the HD limit, they should be easily detected in this arc. 

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5. James Webb Space Telescope Observations of the Nearby and Precisely Localized FRB 20250316A: A Potential Near-IR Counterpart and Implications for the Progenitors of Fast Radio Bursts

   https://doi.org/10.3847/2041-8213/adf29f  

   Blanchard, Peter K; Berger, Edo; Andrew, Shion E; Suresh, Aswin; Uno, Kohki; Kilpatrick, Charles D; Metzger, Brian D; Kumar, Harsh; Sridhar, Navin; Cook, Amanda M; et al (August 2025, The Astrophysical Journal Letters)

   Abstract We present deep James Webb Space Telescope near-infrared imaging to search for a quiescent or transient counterpart to FRB 20250316A, which was precisely localized with the CHIME Outriggers array to an area of 11 × 13 pc in the outer regions of NGC 4141 atd≈ 40 Mpc. Our F150W2 image reveals a faint source near the center of the fast radio burst (FRB) localization region (“NIR-1”;M_F150W2≈ −2.5 mag; probability of chance coincidence ≈0.36), the only source within ≈2.7σ. We find that it is too faint to be a globular cluster, a young star cluster, a red supergiant star, or a giant star near the tip of the red giant branch (RGB). It is instead consistent with a red giant near the RGB “clump” or a massive (≳20M_⊙) main-sequence star, although the latter explanation is less likely. The source is too bright to be a supernova (SN) remnant, Crab-like pulsar wind nebula, or isolated magnetar. Alternatively, NIR-1 may represent transient emission, namely a dust echo from an energetic outburst associated with the FRB, in which case we would expect it to fade in future observations. We explore the stellar population near the FRB and find that it is composed of a mix of young massive stars (∼10–100 Myr) in a nearby Hiiregion that extends to the location of FRB 20250316A and old evolved stars (≳Gyr). The overlap with a young stellar population, containing stars of up to ≈20M_⊙, may implicate a neutron star/magnetar produced in the core collapse of a massive star as the source of FRB 20250316A. 

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