[en] We present a dust spectral energy distribution (SED) and binary stellar population analysis revisiting the dust production rates (DPRs) in the winds of carbon-rich Wolf–Rayet (WC) binaries and their impact on galactic dust budgets. DustEM SED models of 19 Galactic WC “dustars” reveal DPRs of ${\stackrel{\dot{}<!--\; ??\; -->}{M}}_d\sim <!--\; ???\; -->{10}^{-<!--\; ???\; -->10}\text{--}{10}^{-<!--\; ???\; -->6}$ M _⊙ yr⁻¹ and carbon dust condensation fractions, χ _C, between 0.002% and 40%. A large (0.1–1.0 μm) dust grain size composition is favored for efficient dustars where χ _C ≳ 1%. Results for dustars with known orbital periods verify a power-law relation between χ _C, orbital period, WC mass-loss rate, and wind velocity consistent with predictions from theoretical models of dust formation in colliding-wind binaries. We incorporated dust production into Binary Population and Spectral Synthesis (BPASS) models to analyze dust production rates from WC dustars, asymptotic giant branch stars (AGBs), red supergiants (RSGs), and core-collapse supernovae (SNe). BPASS models assuming constant star formation (SF) and a coeval 10⁶ M _⊙ stellar population were performed at low, Large Magellanic Cloud (LMC)–like, and solar metallicities (Z = 0.001, 0.008, and 0.020). Both constant SF and coeval models indicate that SNe are net dust destroyers at all metallicities. Constant SF models at LMC-like metallicities show that AGB stars slightly outproduce WC binaries and RSGs by factors of 2–3, whereas at solar metallicities WC binaries are the dominant source of dust for ∼60 Myr until the onset of AGBs, which match the dust input of WC binaries. Coeval population models show that, for “bursty” SF, AGB stars dominate dust production at late times (t ≳  70 Myr).

[en] We present Spitzer/InfraRed Array Camera observations of dust formation from six extragalactic carbon-rich Wolf-Rayet (WC) binary candidates in low-metallicity (Z ≲ 0.65 Z _⊙) environments using multiepoch mid-infrared (IR) imaging data from the SPitzer InfraRed Intensive Transients Survey (SPIRITS). Optical follow-up spectroscopy of SPIRITS 16ln, 19q, 16df, 18hb, and 14apu reveals emission features from C iv λ5801−12 and/or the C iii–iv λ4650/He ii λ4686 blend that are consistent with early-type WC stars. We identify SPIRITS 16ln as the variable mid-IR counterpart of the recently discovered colliding-wind WC4 + O binary candidate, N604-WRXc, located in the subsolar metallicity NGC 604 H ii region in M33. We interpret the mid-IR variability from SPIRITS 16ln as a dust-formation episode in an eccentric colliding-wind WC binary. SPIRITS 19q, 16df, 14apu, and 18hb exhibit absolute [3.6] magnitudes exceeding that of one of the most IR-luminous dust-forming WC systems known, WR 104 (M _[3.6] ≲ −12.3). An analysis of dust formation in the mid-IR outburst from SPIRITS 19q reveals a high dust production rate of ${\stackrel{\dot{}<!--\; ??\; -->}{M}}_d\gtrsim <!--\; ???\; -->2\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->6}$ M _⊙ yr⁻¹, which may therefore exceed that of the most efficient dust-forming WC systems known. We demonstrate that efficient dust formation is feasible from early-type WC binaries in the theoretical framework of colliding-wind binary dust formation if the systems host an O-type companion with high mass-loss rates ($\stackrel{\dot{}<!--\; ??\; -->}{M}\gtrsim <!--\; ???\; -->1.6\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->6}$ M _⊙ yr⁻¹). This efficient dust formation from early-type WC binaries highlights their potential role as significant sources of dust in low-metallicity environments.

[en] The Galactic magnetar SGR 1935+2154 has been reported to produce the first example of a bright millisecond-duration radio burst (FRB 200428) similar to the cosmological population of fast radio bursts (FRBs). The detection of a coincident bright X-ray burst represents the first observed multiwavelength counterpart of an FRB. However, the search for similar emission at optical wavelengths has been hampered by the high inferred extinction on the line of sight. Here, we present results from the first search for second-timescale emission from the source at near-infrared (NIR) wavelengths using the Palomar Gattini-IR observing system in the J band, enabled by a novel detector readout mode that allows short exposure times of ≈0.84 s with 99.9% observing efficiency. With a total observing time of ≈12 hr (≈47,728 images) during its 2020 outburst, we place median 3σ limits on the second-timescale NIR fluence of ≲18 Jy ms (13.1 AB mag). The corresponding extinction-corrected limit is ≲125 Jy ms for an estimated extinction of A _J = 2.0 mag. Our observations were sensitive enough to easily detect an NIR counterpart of FRB 200428 if the NIR emission falls on the same power law as observed across its radio to X-ray spectrum. We report nondetection limits from epochs of four simultaneous X-ray bursts detected by the Insight-HXMT and NuSTAR telescopes during our observations. These limits provide the most stringent constraints to date on fluence of flares at ∼10¹⁴ Hz, and constrain the fluence ratio of the NIR emission to coincident X-ray bursts to R _NIR ≲ 0.025 (fluence index ≳0.35).

[en] We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) at ultraviolet and visible light wavelengths. We use this survey to constrain the geometry of the circumstellar material (CSM) surrounding SN IIn explosions, which may shed light on their progenitor diversity. In order to distinguish between aspherical and spherical CSM, we estimate the blackbody radius temporal evolution of the SNe IIn of our sample, following the method introduced by Soumagnac et al. We find that higher-luminosity objects tend to show evidence for aspherical CSM. Depending on whether this correlation is due to physical reasons or to some selection bias, we derive a lower limit between 35% and 66% for the fraction of SNe IIn showing evidence for aspherical CSM. This result suggests that asphericity of the CSM surrounding SNe IIn is common—consistent with data from resolved images of stars undergoing considerable mass loss. It should be taken into account for more realistic modeling of these events.

[en] The nova rate in the Milky Way remains largely uncertain, despite its vital importance in constraining models of Galactic chemical evolution as well as understanding progenitor channels for Type Ia supernovae. The rate has been previously estimated to be in the range of ≈10–300 yr⁻¹, either based on extrapolations from a handful of very bright optical novae or the nova rates in nearby galaxies; both methods are subject to debatable assumptions. The total discovery rate of optical novae remains much smaller (≈5–10 yr⁻¹) than these estimates, even with the advent of all-sky optical time-domain surveys. Here, we present a systematic sample of 12 spectroscopically confirmed Galactic novae detected in the first 17 months of Palomar Gattini-IR (PGIR), a wide-field near-infrared time-domain survey. Operating in the J band (≈1.2 μm), which is significantly less affected by dust extinction compared to optical bands, the extinction distribution of the PGIR sample is highly skewed to a large extinction values (>50% of events obscured by A _V ≳ 5 mag). Using recent estimates for the distribution of Galactic mass and dust, we show that the extinction distribution of the PGIR sample is commensurate with dust models. The PGIR extinction distribution is inconsistent with that reported in previous optical searches (null-hypothesis probability <0.01%), suggesting that a large population of highly obscured novae have been systematically missed in previous optical searches. We perform the first quantitative simulation of a 3π time-domain survey to estimate the Galactic nova rate using PGIR, and derive a rate of $\approx <!--\; ???\; -->{43.7}_{-<!--\; ???\; -->8.7}^{+19.5}$ yr⁻¹. Our results suggest that all-sky near-infrared time-domain surveys are well poised to uncover the Galactic nova population.

[en] We present time-resolved visible spectrophotometry of 2020 CD₃, the second known minimoon. The spectrophotometry was taken with the Keck I/Low Resolution Imaging Spectrometer between wavelengths 434 and 912 nm in the B, g, V, R, I, and RG850 filters as it was leaving the Earth–Moon system on 2020 March 23 UTC. The spectrum of 2020 CD₃ resembles V-type asteroids and some lunar rock samples with a 434–761 nm reddish slope of ∼18%/100 nm (g–r = 0.62 ± 0.08 and r–i = 0.21 ± 0.06) with an absorption band at ∼900 nm corresponding to i–z = −0.54 ± 0.10. Combining our measured H of 31.9 ± 0.1 with an albedo of 0.35 typical for V-type asteroids, we determine 2020 CD₃'s diameter to be ∼0.9 ± 0.1 m, making it the first minimoon and one of the smallest asteroids to be spectrally studied. We use our time-series photometry to detect significant periodic light-curve variations with a period of ∼573 s and amplitude of ∼1. In addition, we extend the observational arc of 2020 CD₃ to 37 days, to 2020 March 23 UTC. From the improved orbital solution for 2020 CD₃, we estimate the likely duration of its capture to be ∼2 yr and the nongravitational perturbation on its orbit due to radiation pressure with an area-to-mass ratio of (6.9 ± 2.4) × 10⁻⁴ m² kg⁻¹ implying a density of 2.3 ± 0.8 g cm⁻³, broadly compatible with other meter-scale asteroids and lunar rock. We searched for prediscovery detections of 2020 CD₃ in the Zwicky Transient Facility archive as far back as 2018 October but were unable to locate any positive detections.

[en] The Galactic Center contains some of the most extreme conditions for star formation in our Galaxy, as well as many other phenomena that are unique to this region. Given our relative proximity to the Galactic Center, we are able to study details of physical processes to a level that is simply not yet possible for more distant galaxies, yielding an otherwise inaccessible view of the nuclear region of a galaxy. We recently carried out a targeted imaging survey of mid-infrared bright portions of the Galactic Center at 25 and 37 μm using the FORCAST instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA). This survey was one of the inaugural Legacy Programs from SOFIA cycle 7, observing a total area of 403 arcmin² (2180 pc²), including the Sgr A, B, and C complexes. Here we present an overview of the survey strategy, observations, and data reduction as an accompaniment to the initial public release of the survey data. We discuss interesting regions and features within the data, including extended features near the circumnuclear disk, structures in the Arched Filaments and Sickle H ii regions, and signs of embedded star formation in Sgr B2 and Sgr C. We also feature a handful of less well studied mid-infrared sources located between Sgr A and Sgr C that could be sites of relatively isolated star formation activity. Last, we discuss plans for subsequent publications and future data releases from the survey.