arXiv subjects

Benjamin J. Shappee

Publications and source records attributed to Benjamin J. Shappee.

At least 19 recordsLinked to original sources

arXiv2026

Nebular Spectra of the Extremely Metal-Poor SN II 2023ufx Over a Year After Explosion: A Massive Progenitor and Unique Circumstellar Environment

We present new observations of the metal-poor ($< 0.1$ $\rm Z_\odot$) Type II supernova 2023ufx and its host galaxy. The deep nebular spectrum, obtained roughly a year after explosion, has a triple-peaked [O I] emission profile suggesting an asymmetric explosion. Comparison to nebular spectra models suggests a zero-age main sequence mass of $ M_{\rm ZAMS} \sim 25-35$ $\rm M_\odot$, which is supported by the low [Ca II]/[O I] emission-line ratio of $\approx0.4$. The diminishing, broad, boxy H$\alpha$ emission and flattening of the light curve in the late ($\sim2$ yr) photometry suggest a complex mass-loss history in the centuries to millennia before explosion. New optical and near-infrared imaging of the host galaxy confirms that it is a dwarf, with a stellar mass of $10^{6.6\pm0.1}$ $\rm M_\odot$ and a SFR of $10^{-2.5\pm0.1}$ $\rm M_\odot$/yr. Results from both SED fitting and galaxy stellar mass-metallicity scaling relations all lead to an environmental metallicity estimate of $0.02-0.07$ $\rm Z_\odot$. Taken together, these observations confirm that SN 2023ufx is the explosion of a very metal-poor, heavily stripped red supergiant.

astro-ph.HE↗

arXiv2026

The host galaxies of 2003fg-like type Ia supernovae

SN~2003fg-like events are a peculiar type Ia supernova (SN~Ia) subtype characterized by broader light curves, higher near-infrared luminosities, and stronger carbon absorptions at early times. Here we present observations of the largest compilation of 2003fg-like SN Ia host galaxies to date, obtained with Integral Field Spectroscopy (IFS). For 20 objects, we study both the global host-galaxy properties and, for the first time for a sizeable sample, the local environment at the SN position. Globally, 2003fg-like SNe~Ia occur in galaxies with lower stellar mass, lower oxygen abundance, and marginally higher specific star-formation rate (sSFR) than those of normal SNe~Ia, although their hosts are not as extreme in such properties as superluminous SNe, nor representative of metal-poor dwarf-galaxy samples. Locally, the SN positions show lower star-formation-rate, stellar-mass surface densities, and lower sSFR, than normal SN~Ia environments, consistent with a significant preference for the outskirts of their hosts, while their stellar age indicators are typical. The most distinctive local property is metallicity, with 2003fg-like SNe~Ia occupying the most metal-poor environments among SNe~Ia. We also find a tentative positive correlation between the light-curve width and the oxygen abundance for 2003fg-like events. Our results imply that 2003fg-like SNe~Ia arise from the merger of two white dwarfs (WDs) or the core-degenerate scenario, but disfavor the single, rapidly rotating super-M$_{ch}$ C-O WD progenitor, as this channel requires a young stellar population that we do not observe at the SN positions. The preference of 2003fg-like SNe~Ia for low-metallicity environments suggests that they may have been more common in the early Universe. (abridged)

astro-ph.CO↗

arXiv2026

JWST Spectroscopy of Type Ia Supernova 2025rbs from Maximum Light to the Nebular Phase

We present JWST observations of the Type Ia supernova (SN Ia) 2025rbs ($D=$14.5 Mpc) at +1, +23, and +84 days after B-band maximum, spanning peak light through a wavelength-dependent transition toward the nebular phase. Combined with ground-based optical and near-infrared (NIR) data, our panchromatic spectra (0.4-14 $\mu$m) include the first maximum-light mid-infrared (MIR) spectrum and the earliest MIR spectroscopic sequence of an SN Ia to date. At peak light, the MIR spectrum exhibits a continuum with permitted and forbidden features, including Si II, Ni II, and early-emerging [Ni III-IV] and [Ar II-III]. By +23 days the MIR is dominated by forbidden lines with a weak continuum, and by +84 days it is fully nebular, whereas the optical/NIR spectra remain transitional. The nebular spectrum reveals strongly stratified ejecta, with stable Ni concentrated at the lowest velocities, radioactive Co at intermediate velocities but absent within ~2000 km s$^{-1}$, and Ar occupying an outer shell. We detect small-scale substructure in [Ca IV] 3.21 $\mu$m with fractional amplitudes of a few percent and a characteristic velocity scale of ~800 km s$^{-1}$, which may reflect compositional structure, ionization variations, or both. Radiative-transfer calculations substantially underpredict these MIR Mg II features despite approximately reproducing the NIR Mg II 1.0927 $\mu$m line, suggesting that the relative strengths of these transitions are sensitive to the treatment of Mg ionization and excitation. These observations demonstrate that MIR spectroscopy beginning near maximum light simultaneously probes the emerging inner ejecta and rapidly fading outer burning products, providing new constraints for explosion and radiative-transfer models.

astro-ph.HE↗

arXiv2026

ATLAS22kjn (AT 2022fpx): A Coronal Line Emitter with an Early Light Curve Bump and Mid-Infrared Dust Echo

We present an analysis of ATLAS22kjn (AT 2022fpx), whose high-ionisation coronal lines (CLs) and pre-peak light curve bump provide distinctive opportunities to investigate the physical mechanisms powering tidal disruption events (TDEs). In addition to CLs, the optical spectra show common TDE features, including a strong, blue continuum and broad Balmer and He II lines. The CLs appear before UV/optical light curve peak, preceding the detection of X-rays by $\sim 300$ days and persisting after X-rays are no longer detected, suggesting the X-ray emission is obscured at both early and late times. Using the CL luminosities, we constrain the temperature evolution of the ionising source, finding a decrease of $\lesssim 10 \%$ over 500 days. In the UV/optical light curve, we observe a $9 \substack{+4 \\ -2}$ day bump that peaks $125 \substack{+5 \\ -3}$ rest-frame days before the peak of the main flare. Although we cannot definitively determine the origins of the bump, we find that its timescale and luminosity are most consistent with theoretical predictions for a precursor feature produced by a stream-stream collision or a wind-stream collision. ATLAS22kjn also shows a prominent dust echo in its mid-infrared (MIR) light curves, indicating a high dust covering fraction $f_c \simeq 0.40 \pm 0.03$, similar to the covering fractions of other CL-emitting TDEs. From the multi-wavelength observations of ATLAS22kjn, we estimate the size and relative radii of the emission regions in its nuclear environment and determine that the CL region lies between the broad line region and the MIR-emitting dust. ATLAS22kjn demonstrates the importance of multi-wavelength and early-time observations, and the utility of CLEs in characterising the otherwise unobservable EUV/ultrasoft X-ray emission of TDEs.

astro-ph.HE↗

arXiv2026

AT2021yky: A Fast-Rising Optical Transient with Evolving Broad Hydrogen Emission Consistent with an Ambiguous Nuclear Transient

Nuclear transients are powerful probes of supermassive black hole properties, offering insight into black hole mass, accretion physics, and the structure of galactic nuclei. Among these, a growing class of events cannot be classified as either tidal disruption events (TDEs) or active galactic nuclei (AGN) flares, and their physical origins remain poorly understood. We present a multi-wavelength photometric and spectroscopic analysis of AT2021yky (ZTF21abzciqh), an ambiguous nuclear transient (ANT) at a redshift of $z = 0.076$. AT2021yky reached a peak bolometric luminosity of $L_{\rm peak} = (4.1 \pm 1.1) \times 10^{43}~\mathrm{erg~s^{-1}}$, with a rise-time of $18.2 \pm 0.7$ days. The early-time UV/optical emission is well described by a blackbody with a temperature of $T \simeq 1.4 \times 10^{4}$ K, cooler than most optically selected TDEs. No X-ray emission from the transient is detected, with a $3\sigma$ limit of $L_X \lesssim 3.4 \times 10^{41}$ erg s$^{-1}$ near peak. Spectroscopic observations reveal a largely featureless blue continuum with broad (FWHM$\sim 11,000$ km s$^{-1}$) H$\alpha$ emission line that appears around 20$-$40 days post-peak. The host-galaxy emission-line ratios indicate the presence of an AGN, though the absence of optical or mid-IR variability and a non-AGN mid-IR color suggest it is weak. AT2021yky exhibits a rapid rise time comparable to that of luminous fast blue optical transients (LFBOTs), while its decay timescale and late-time broad H$\alpha$ emission resemble those observed in TDEs. However, its cooler blackbody temperature and the absence of He II and Balmer emission lines other than H$\alpha$ instead favour its classification as an ANT.

astro-ph.HE↗

arXiv2026

Detection of Variability in Seyfert 2 Galaxies and Measurement of the Optical Scattering Region Size

One main theme of the Unification Model of active galactic nuclei is that there is an obscuring torus structure blocking the direct view of the central engine for Seyfert 2 galaxies. Here, we present the detection of long-term optical variability for a sample of nearby Seyfert 2s. We found that Seyfert 2s exhibit a relatively low but significant level of variability beyond the constant fluxes established by galaxies over month to year time scales. The variability is also detected in the structure functions of Seyfert 2s. Assuming a simple variability suppression model by the scattering region and dilution due to host starlight, where the region smooths the unobscured photon packets from the central engine as the light scatters over the torus, we estimate AGN scattering region sizes by matching the variability amplitudes of Seyfert 1s to 2s. Our measured scattering sizes are largely consistent with the torus size measured using their emission properties, suggesting that the scattering region is of a similar size as the torus. Our results pave the way towards variability as a powerful and independent test for AGN unification models.

astro-ph.GA↗

arXiv2026

Hawai`i Supernova Flows: Bulk Flow Measurements using SNe Ia in the Optical and NIR

The present day peculiar velocity-field was sourced by primordial density fluctuations and sculpted over the lifespan of the Universe. Cosmological models such as $\Lambda$CDM make predictions for various statistical properties of peculiar velocities. Bulk flow, the average velocity within a given volume, has an expectation value of $\vec{0}$ due to isotropy, and a variance directly tied to the Hubble constant, the growth-rate of structure, and the matter power spectrum. In this paper, we use the redshifts and optical and near-infrared distance estimates to Type Ia Supernovae (SNe Ia) within subsets of the Hawai`i Supernova Flows dataset to infer the bulk flow within $z \lesssim 0.1$. The inferred speeds vary between ~100 to 400 km/s but are all consistent with the predictions of $\Lambda$CDM. As a secondary focus, we discuss the systematic uncertainty introduced by the discrete choice of methodology using two bulk flow estimators, two types of SN Ia distance estimators, and data covering two distinct regimes in wavelength space.

astro-ph.CO↗

arXiv2026

A Disappearing Act: Constraints From "Missing" Flares of Repeating Partial TDE Candidates

Recurrent tidal disruption events (rTDEs) are sources that exhibit multiple TDE-like flares; many are likely powered by the recurring partial disruption of a bound star, in a repeating partial TDE (rpTDE). Two such sources, TDE 2022dbl (ASASSN-22ci) and TDE 2020vdq (ZTF20acaazkt), each exhibited two UV/optical flares and, under the assumption of periodicity, both were expected to exhibit a third flare in early 2026. Neither exhibited such a flare, to limits of $L_{\textrm{UV/optical}} \lesssim 10^{42}$ erg s$^{-1}$, $\sim$30$\times$ fainter than the previous flares. Here, we examine several possible explanations. Observing two independent TDEs from the same galaxy within $\sim$2 yr has a probability of $\lesssim$0.5% for measured average TDE rates and currently expected rate enhancements, unless there is extreme intrinsic dispersion in the rates. Theoretical predictions for a double TDE of both stars in a binary are inconsistent with the observed flares. We therefore conclude that TDE 2022dbl and TDE 2020vdq are rpTDEs. To produce only two observable flares with similar energetics, our semi-analytical modeling strongly favors a main-sequence star promptly placed on a bound orbit with a deep initial tidal encounter at pericenter. These results suggest that the majority of rTDEs with multiple flares over a few-year baseline are likely to be rpTDEs, and that a significant fraction of systems may produce only two observable flares. This has important implications for the use of r(p)TDEs as probes of TDE physics and dynamical processes in the nuclei of other galaxies, in addition to the expected yield from upcoming surveys.

astro-ph.HE↗

arXiv2026

SCAT Data Release 1: 1812 optical spectra of 1331 transients

We present the first data release (DR1) of the Spectroscopic Classification of Astronomical Transients (SCAT) survey, covering the first $\approx 5$ years of observations (March 2018 - January 2023). DR1 includes 1812 spectra of 1331 transients, which we sort into broad spectroscopic classes including supernovae (SNe), transients originating in galactic nuclei, and stellar variability. We collect multi-filter light curves from imaging surveys and fit them with phenomenological models to estimate peak brightnesses and the time of explosion/first-light. Extragalactic transients are matched to candidate host galaxies, and we compare host-galaxy luminosities and projected offsets by SN type. SNe appear to be a reliable way to augment the redshift coverage of nearby ($z\lesssim 0.1$) galaxies in tandem with dedicated redshift surveys. We present new redshifts for roughly half of the SN host galaxies, most of which are low-luminosity dwarfs similar to the Magellanic Clouds ($M_r \gtrsim -18$ mag). This set of transient spectra, light curves, luminosities, redshifts, and host galaxies offers an excellent testbed for real-time photometric/light curve classification pipelines in the modern era of deep and large-area surveys. We conclude with a brief discussion of the provided data products and status of the SCAT survey.

astro-ph.HE↗

arXiv2026

A Natural $\gtrsim 100\times$ Telescope: Discovery of the Strongly Lensed Type II SN 2025mkn at $z=1.37$

We present the discovery of SN 2025mkn, a gravitationally lensed Type II supernova. First detected as a blue transient in ZTF, 0.83$^{\prime\prime}$ from a $z=0.42$ elliptical galaxy, follow-up SNIFS/UH2.2m and LRIS/Keck spectra revealed absorption lines at $z=1.371$. Later JWST NIRCam imaging shows that the bright transient is a close pair of point sources separated by $\sim 0.07^{\prime\prime}$, and a 30 times fainter counterimage opposite the lens, for which NIRSpec reveals strong H$\alpha$ emission also at $z=1.371$. The light curves and spectra are consistent with the Type II supernova source being magnified $\gtrsim 100$ times, with $\sim 250$ required to reconcile its luminosity with that of nearby events such as SN 2023ixf. Lens models are consistent with such high magnifications, and always show that the faint image arrived first (undetected in earlier ZTF imaging), consistent with the later spectral phase of this fainter image. A fourth image is also predicted and possibly detected in the NIRSpec data. Light-curve-based time-delay measurements are not possible due to the first image being the faintest; however, the resolved NIRSpec spectra offer a future opportunity for time-delay cosmography through supernova phase measurements.

astro-ph.CO↗

arXiv2026

Supernova 2025wny: High-angular resolution Keck/NIRC2 observations and preliminary lens modeling

Multiply imaged, gravitationally lensed supernovae are rare but powerful tools for providing independent measurements on cosmological parameters. Supernova (SN) 2025wny ("SN Winny") is the first gravitationally-lensed Type I superluminous supernova and the first lensed supernova in a galaxy-scale system that is suitable for time-delay cosmography studies. In this work, we present high-resolution $K_p$-band adaptive optics imaging of SN Winny obtained with the near-infrared camera (NIRC2) on the W. M. Keck II telescope. With exquisite image quality (FWHM$\approx0.^{\prime\prime}065$) we determine and make use of the precise astrometric positions of the five multiple images as constraints for our lens mass models. With lenstronomy and Glee, we parameterize the total mass of the system with a singular isothermal ellipsoid, a singular isothermal sphere, and external shear. The two independent models are in excellent agreement and reproduce the observed image positions with sub-milli-arcsecond residuals. The inferred projected total masses enclosed within the Einstein radii of the primary and secondary lens galaxies are M$_1$ = 4.44$^{+0.06}_{-0.05}\times10^{11} M_\odot$ and M$_2$ = 0.96$^{+0.02}_{-0.02}\times10^{11} M_\odot$, respectively. Likewise, the inferred effective velocity dispersion of the primary lens is $\sigma_{1} = $ 277.4$^{+0.9}_{-0.7}$ km/s, consistent with the independent spectroscopic measurement made by DESI of $\sigma_{\star,1} = $ 298$\,\pm\,37$ km/s. Our modeling results are also consistent with previous results for the same system with data from the Large Binocular Telescope (LBT), using the same lens modeling codes. We also corroborate their finding that the SN multiple image A has an anomalous excess of flux by a factor of ~2-3 beyond what our smooth mass models predict.

astro-ph.GA↗

arXiv2026

ASAS-SN Rates IV: Constraints on the Kilonova Rate

Kilonovae (KNe) are the electromagnetic signatures of neutron star mergers and are likely the dominant site of cosmic $r$-process nucleosynthesis. However, their intrinsic rate remains poorly constrained due to a paucity of confirmed events. We use the All-Sky Automated Survey for Supernovae (ASAS-SN) to place limits on the rate of bright, nearby KNe over an 11-year baseline ranging from 2014 to 2024. To evaluate the survey's completeness for KNe, we employ an injection-recovery simulation using a shock-cooling cocoon model calibrated to the early blue emission of the only well-sampled KN, SSS17a (AT 2017gfo). Finding no KNe within the survey, we calculate a $2\sigma$ ($\sim95\%$) upper limit on the local volumetric KN rate of $R_{\mathrm{KN}} < 4400\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}$. Despite ASAS-SN's shallower limiting magnitude compared to other time-domain searches, its continuous, high-cadence, all-sky monitoring yields a constraint that is competitive with the strongest results from electromagnetic surveys but remains a factor of 18 higher than the LIGO-Virgo-KAGRA GWTC-4 estimate of the binary neutron star merger rate.

astro-ph.HE↗

arXiv2026

Contemporaneous Optical and Near-Infrared Observations of the Interstellar Comet 3I/ATLAS Pre- and Post-Perihelion

Interstellar objects provide a unique view into the formation of other star systems. Here we present spectroscopic observations of the recently discovered interstellar object 3I/ATLAS between a heliocentric distance of $3.7$ to $1.8$~au on either side of its travels through perihelion. We obtained several observations with the Keck-I/LRIS, Keck-II/NIRES, Gemini/GMOS, and UH88/SNIFS spectrographs, covering a wavelength range of $0.3 - 2.5~\mathrm{\mu m}$. We report the continued emission of both Ni and CN, along with post-perihelion detections of Fe and a weak detection of $\mathrm{C_3}$. We determine the spectral slope across optical and NIR wavelengths and find a positive spectral slope in the optical, with values ranging from $\sim 21 - 27\%$ in the blue regions ($0.4 - 0.55~\mathrm{\mu m}$) to $\sim 6 - 10\%$ in the red ($0.65 - 0.9~\mathrm{\mu m}$) regions. In contrast, the NIR showed a negative spectral slope of $\sim -0.9 \%$ between $0.9 - 1.5~\mathrm{\mu m}$ and $\sim -2.3\%$ between $1.9 - 2.5~\mathrm{\mu m}$. 3I/ATLAS shows a clear turnover in its spectral shape at $\sim 1.1~\mathrm{\mu m}$, corresponding to scattered light from the dusty coma. Finally, in the NIR, we do not find an increase in the depth of the water features identified in an earlier NIR observation of 3I/ATLAS. Our observations of 3I/ATLAS in the NIR show a similar shape to the NIR spectrum of 2I/Borisov as it approached perihelion.

astro-ph.EP↗

arXiv2026

Supernova Rates and Luminosity Functions from ASAS-SN III: Over a Decade of Type Ia SNe and Their Subtypes

We present volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the All-Sky Automated Survey for Supernovae (ASAS-SN), covering the 11-year period from 2014 to 2024. By combining the 2014--2017 $V$-band sample with the 2018--2024 $g$-band sample, we construct a large statistical dataset of $1776$ SNe Ia. We compute completeness corrections based on injection-recovery simulations of the ASAS-SN light curves, taking into account the variations in light curve shapes. For our standard sample ($M_{g,\mathrm{peak}}<-16.0$ mag), we extract a total volumetric SN Ia rate of $R_{\mathrm{tot}} = (2.55 \pm 0.12) \times 10^4\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h_{70}^3$ at a median redshift of $z=0.029$. With a statistical uncertainty of $4.7\%$, this is the most precise local measurement to date. While the "normal" SNe Ia account for $(92.7 \pm 1.9)\%$ of this rate, the total LF reveals immense diversity, with $M_{g,\mathrm{peak}}$ spanning over five magnitudes. The LF of SNe Iax is also broad and rises toward lower luminosities, resulting in a likely lower limit of $(4.3 \pm 1.8)\%$ of the total rate. We place strong constraints on the rate of SNe Ia-CSM, finding they account for only $(0.036 \pm 0.017)\%$ of the total local rate. Finally, we find that the low-luminosity 02es-like SNe are $7 \pm 5$ times more common than the luminous 03fg-like SNe. This places demographic constraints on models proposing a physical continuum for these two subtypes, implying that any common channel for the two classes must strongly favor lower-luminosity explosions.

astro-ph.HE↗

arXiv2026

Post-Perihelion Integral Field Spectroscopy of the Interstellar Comet 3I/ATLAS

The environs of other stellar systems may be directly probed by analyzing the cometary activity of interstellar objects. The recently discovered interstellar object 3I/ATLAS was the subject of an intensive worldwide follow-up campaign in its pre-perihelion approach. Now, 3I/ATLAS has begun its post-perihelion departure from the Solar System. In this letter, we report the first post-perihelion blue-sensitive integral-field unit spectroscopy of 3I/ATLAS using the Keck Cosmic Web Imager on November 16, 2025. We confirm previously reported CN, Fe, and Ni outgassing along with detections of carbon chain molecules $\mathrm{C}_2$ and $\mathrm{C}_3$. We calculate production rates for each species. We find Fe and Ni production rates of $\mathrm{Q_{Fe}} = (9.55\pm3.96)\times10^{25}$ atoms s$^{-1}$, and $\mathrm{Q_{Ni}} = (6.61\pm2.74)\times10^{25}$ atoms s$^{-1}$, resulting in a ratio of $\log(\mathrm{Q_{Ni}} / \mathrm{Q_{Fe}}) = -0.16\pm0.03$, which matches Solar System comets well and continues the pre-perihelion trend of declining $\log(\mathrm{Q_{Ni}} / \mathrm{Q_{Fe}})$ with $r_h$. We investigate the radial distributions of these elemental species and find characteristic $e$-folding radii of 3880$\pm$39 km for Ni, 6053$\pm$68 km for CN, 4194$\pm$45 km for $\mathrm{C}_2$, and 3833$\pm$45 km for $\mathrm{C}_3$. Compared to pre-perihelion measurements, these radii have increased by a factor of $\sim$6.5--7. Our post-perihelion observations reveal that 3I/ATLAS continues to exhibit cometary behavior broadly consistent with Solar System comets.

astro-ph.EP↗

arXiv2025

JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS

Interstellar objects (ISOs), particularly those with cometary activity, provide unique insight into the primordial physical and chemical conditions present during the formation of the planetary system in which they originated. Observations in the sub-mm regime allow for direct measurements of several parent molecules released from the comet nucleus into the coma. Here we present observations of the third ISO, 3I/ATLAS, with the `\=U`\=u heterodyne receiver on the James Clerk Maxwell Telescope (JCMT), which targeted emission from HCN($J = 3 - 2$) and CO($J = 2 - 1$). Our observations, taken between 16 July 2025 and 21 July 2025 (UT), when 3I/ATLAS was at a heliocentric distance between 4.01 and 3.84 au, provide the earliest sub-mm constraints on its activity. We do not detect HCN or CO in these epochs, with 3$\sigma$ upper-limits on the production rates of $Q(HCN) < 1.7 \times 10^{24}$ s$^{-1}$ at $r_h = 4.01 - 3.97$ au and $Q(CO) < 1.1 \times 10^{27}$ s$^{-1}$ at $r_h = 3.94 - 3.84$ au, respectively. We combine this HCN limit with later JCMT observations of HCN to constrain its temporal evolution. Fitting the HCN detections with a $Q(HCN) \propto r_h^{-n}$ model and accounting for the upper-limits yields $n = 12.7^{+6.9}_{-2.5}$. This slope is steeper than those of typical Solar System comets, but consistent with the production rate slopes measured for other species in the coma of 3I/ATLAS.

astro-ph.EP↗

arXiv2025

The Unhurried Universe: A Continued Search for Long Term Variability in ASAS-SN

We search a sample of 5,685,060 isolated sources in the All Sky Automated Survey for SuperNovae (ASAS-SN) with 14.5<g<15 mag for slowly varying sources with brightness changes larger than ~0.03 mag/year over 10 years. We find 426 slowly-varying systems. Of these systems, 200 are identified as variables for the first time, 226 are previously classified as variables, and we find equal numbers of sources becoming brighter and fainter. Previously classified systems were mostly identified as semi-regular variables (SR), slow irregular variables (L), or unknown (MISC or VAR), as long time scale variability does not fit into a standard class. Much like Petz & Kochanek 2025, the sources are scattered across the color magnitude diagram and can be placed into 5 groups that exhibit distinct behaviors. There are also six AGN. There are 262 candidates (~62 percent) that also show shorter time scale periodic variability, mostly with periods longer than 10 days. The variability of 66 of these candidates may be related to dust. Combining the new slow variable candidates with the candidates from Petz & Kochanek 2025, we have found a total of 1208 slow variables.

astro-ph.SR↗

arXiv2025

Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS

We report initial observations aimed at the characterization of a third interstellar object. This object, 3I/ATLAS or C/2025 N1 (ATLAS), was discovered on 2025 July 1 UT and has an orbital eccentricity of $e\sim6.1$, perihelion of $q\sim 1.36$ au, inclination of $\sim175^\circ$, and hyperbolic velocity of $V_\infty\sim 58$ km s$^{-1}$. We report deep stacked images obtained using the Canada-France-Hawaii Telescope and the Very Large Telescope that resolve a compact coma. Using images obtained from several smaller ground-based telescopes, we find minimal light curve variation for the object over a $\sim4$ day time span. The visible/near-infrared spectral slope of the object is 17.1$\pm$0.2 %/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids). 3I/ATLAS will be observable through early September 2025, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late November 2025. Although this limitation unfortunately prohibits detailed Earth-based observations at perihelion when the activity of 3I/ATLAS is likely to peak, spacecraft at Mars could be used to make valuable observations at this time.

astro-ph.EP↗