Context. The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the Very Large Telescope (VLT) enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, an untargeted and spectroscopically complete transient survey, has enabled us to perform a minimally biased statistical analysis of CCSN environments. Aims. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe – 78 II, nine IIn, seven IIb, four Ic, seven Ib, three Ibn, two Ic-BL, one ambiguous Ibc, and one superluminous SN – detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves. Methods. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all H II regions detected within each galaxy, including the star formation rate (SFR), H α equivalent width (EW), oxygen abundance, and extinction. Results. We found that stripped-envelope supernovae (SESNe) occur in environments with a higher median SFR, H α EW, and oxygen abundances than SNe II and SNe IIn/Ibn. Most of the distributions have no statistically significant differences, except between oxygen abundance distributions of SESNe and SNe II, and between H α EW distributions of SESNe and SNe II. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, H α EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and H α EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, s , of SNe II correlates with the H α EW, and that the luminosity and the Δ m 15 parameter of SESNe correlate with the oxygen abundance, H α EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.

The ASAS-SN Low Surface Brightness Survey utilizes the ∼7 years of g-band CCD data from ASAS-SN (The All-Sky Automated Survey for Supernovae) to create stacked images of the entire sky. It is significantly deeper than previous photographic surveys. Our median/95th percentile cumulative exposure time per field is 58.1/86.8 hours, and our median 3σ g-band surface brightness limit off the Galactic plane (|b| > 20°) is 26.1 mag arcsec^-2. We image large-scale diffuse structures within the Milky Way, such as multiple degree-spanning supernova remnants and star-forming nebulae, and tidal features of nearby galaxies. To quantify how effective our deep images are, we compare with a catalog of known ultra-diffuse galaxies and find a recovery rate of 82%. In the future, we intend to use this data set to perform an all-sky search for new nearby dwarf galaxies, create an all-sky Galactic cirrus map, create an all-sky low surface brightness mosaic for public use, and more.

We present the class of extreme nuclear transients (ENTs), including the most energetic single transient yet found, Gaia18cdj. Each ENT is coincident with its host-galaxy nucleus and exhibits a smooth (<10% excess variability), luminous (2 × 1045 to 7 × 1045 erg per second), and long-lived (>150 days) flare. ENTs are extremely rare (≥1 × 10-3 cubic gigaparsec per year) compared to any other known class of transients. They are at least twice as energetic (0.5 × 1053 to 2.5 × 1053 erg) as any other known transient, ruling out supernova origins. Instead, the high peak luminosities, long flare timescales, and immense radiated energies of the ENTs are most consistent with the tidal disruption of high-mass ( [Formula: see text] ) stars by massive ( [Formula: see text] ) supermassive black holes (SMBHs). ENTs will be visible to high redshifts (z ~ 4 to 6) in upcoming surveys, providing an avenue to study the high-mass end of the SMBH mass distribution, complementing recent studies of actively accreting SMBHs at high redshifts with the James Webb Space Telescope.

We present an analysis of three near-infrared (NIR; 1.0–2.4 μ m) spectra of the SN 2003fg–like/“super-Chandrasekhar” Type Ia supernovae (SNe Ia) SN 2009dc, SN 2020hvf, and SN 2022pul at respective phases of +372, +296, and +294 days relative to the epoch of B -band maximum. We find that all objects in our sample have asymmetric, or “tilted,” [Fe ii ] 1.257 and 1.644 μ m profiles. We quantify the asymmetry of these features using five methods: velocity at peak flux, profile tilts, residual testing, velocity fitting, and comparison to deflagration–detonation transition models. Our results demonstrate that, while the profiles of the [Fe ii ] 1.257 and 1.644 μ m features are widely varied between 2003fg-likes, these features are correlated in shape within the same SNe. This implies that line blending is most likely not the dominant cause of the asymmetries inferred from these profiles. Instead, it is more plausible that 2003fg-like SNe have aspherical chemical distributions in their inner regions. These distributions may come from aspherical progenitor systems, such as double white dwarf mergers, or off-center delayed-detonation explosions of near-Chandrasekhar mass carbon–oxygen white dwarfs. Additional late-phase NIR observation of 2003fg-like SNe and detailed 3D non-LTE modeling of these two explosion scenarios are encouraged.

Novae are thermonuclear eruptions on accreting white dwarfs in interacting binaries. Although most of the accreted envelope is expelled, the mechanism-impulsive ejection, multiple outflows or prolonged winds, or a common-envelope interaction-remains uncertain. Gigaelectronvolt γ-ray detections from >20 Galactic novae establish these eruptions as nearby laboratories for shock physics and particle acceleration, underscoring the need to determine how novae eject their envelopes. Here we report on near-infrared interferometry, supported by multiwavelength observations, of two γ-ray-detected novae. The images of the very fast 2021 nova V1674 Her, taken just 2-3 days after discovery, reveal the presence of two perpendicular outflows. The interaction between these outflows probably drives the observed γ-ray emission. Conversely, the images of the very slow 2021 nova V1405 Cas suggest that the bulk of the accreted envelope was ejected more than 50 days after the eruption began, as the nova slowly rose to its visible peak, during which the envelope engulfed the system in a common-envelope phase. These images offer direct observational evidence that the mechanisms driving mass ejection from the surfaces of accreting white dwarfs are not as simple as previously thought, revealing multiple outflows and delayed ejections.

In November 2020, the Swift team announced a major update to the calibration of the UltraViolet and Optical Telescope (UVOT) data to correct for the gradual loss of sensitivity over time. Beginning in roughly 2015, the correction affected observations in the three near ultraviolet (UV) filters, reaching levels of up to 0.3 mag immediately prior to the correction. Over the same time period, an increasing number of Type I superluminous supernovae (SLSNe-I) were discovered and studied. Many SLSNe-I are hot (T$_\textrm{eff}$ $\approx 10,000$ K) near peak, and therefore accurate UV data are imperative towards properly understanding their physical properties and energetics. We re-compute Swift UVOT photometry for SLSNe-I discovered between 2014 and 2021 with at least 5 Swift observations in 2015 or later. We calculate host-subtracted magnitudes for each SLSN and fit their spectral energy distributions with modified blackbodies to obtain the radius and temperature evolution. We also fit multi-band photometry using the Modular Open Source Fitter for Transients (MOSFiT) to obtain key parameters such as the spin period (P), magnetic field strength (B), ejecta mass (M$_\textrm{ej}$), and kinetic energy (E$_\textrm{kin}$). From our MOSFiT modeling, we also estimate the peak UV/optical luminosity (L$_\textrm{peak}$) and total radiative energy (E$_\textrm{rad}$). Under the assumption of magnetar-powered SLSNe we find several strong trends, including anti-correlations between P and both L$_\textrm{peak}$ and E$_\textrm{rad}$, a correlation between E$_\textrm{kin}$ and E$_\textrm{rad}$, and an anti-correlation between B and E$_\textrm{rad}$.

We present optical photometric and spectroscopic observations of the peculiar Type Ia supernovae (SNe Ia) ASASSN-20jq/SN 2020qxp. It is a low-luminosity object, with a peak absolute magnitude of M-B = -17.1 +/- 0.5 mag, while its post-peak light-curve decline rate of Delta m(15)(B) = 1.35 +/- 0.09 mag and color-stretch parameter of s(BV) & gap; 0.82 is similar to that of normal luminosity SNe Ia. That makes it a prevalent outlier in both the SN Ia luminosity-width and the luminosity-color-stretch relations. The analysis of the early light curves indicates a possible "bump" during the first approximate to 1.4 days of explosion. ASASSN-20jq synthesized a low radioactive Ni-56 mass of 0.09 +/- 0.01 M-circle dot. The near-maximum light spectra of the supernova show strong Si II absorption lines, indicating a cooler photosphere than normal SNe Ia; however, it lacks Ti II absorption lines. Additionally, it shows unusually strong absorption features of O I lambda 7773 and the Ca II near-infrared triplet. The nebular spectra of ASASSN-20jq show a remarkably strong but narrow forbidden [Ca II] lambda lambda 7291, 7324 doublet emission that has not been seen in SNe Ia except for a handful of Type Iax events. There is also a marginal detection of the [O I] lambda lambda 6300, 6364 doublet emission in nebular spectra, which is extremely rare. Both the [Ca II] and [O I] lines are redshifted by roughly 2000 km s(-1). ASASSN-20jq also exhibits a strong [Fe II] lambda 7155 emission line with a tilted-top line profile, which is identical to the [Fe II] lambda 16433 line profile. The asymmetric [Fe II] line profiles, along with the redshifted [Ca II] and emission lines, suggest a high central density white dwarf progenitor that underwent an off-center delayed-detonation explosion mechanism, synthesizing roughly equal amounts of Ni-56 during the deflagration and detonation burning phases. The equal production of Ni-56 in both burning phases distinguishes ASASSN-20jq from normal bright and subluminous SNe Ia. Assuming this scenario, we simultaneously modeled the optical and near-infrared nebular spectra, achieving a good agreement with the observations. The light curve and spectroscopic features of ASASSN-20jq do not align with any single sub-class of SNe Ia. However, the significant deviation from the luminosity versus light-curve shape relations (along with several light-curve and spectroscopic features) exhibits similarities to some 2002es-like objects. Therefore, we have identified ASASSN-20jq as an extreme candidate within the broad and heterogeneous parameter space of 2002es-like SNe Ia.

Period-luminosity relations of long period variables (LPVs) are a powerful tool to map the distances of stars in our galaxy, and are typically calibrated using stars in the Large Magellanic Cloud (LMC). Recent results demonstrated that these relations show a strong dependence on the amplitude of the variability, which can be used to greatly improve distance estimates. However, one of the only highly sampled catalogs of such variables in the LMC is based on OGLE photometry, which does not provide all-sky coverage. Here, we provide the first measurement of the period-luminosity relation of long-period variables in the LMC using photometry from the Asteroid Terrestrial-impact Last Alert System (ATLAS). We derive conversions between ugriz, Gaia, and ATLAS c and o passbands with a precision of approximately 0.02 mag, which enable the measurement of reliable amplitudes with ATLAS for crowded fields. We successfully reproduce the known PL sequences A through E, and show evidence for sequence F using the ratios of amplitudes observed in both ATLAS pass-bands. Our work demonstrates that the ATLAS survey can recover variability in evolved red giants and lays the foundation for an all-sky distance map of the Milky Way using long-period variables.

Transient events associated with supermassive black holes provide rare opportunities to study accretion and the environments of supermassive black holes. We present a multiwavelength study of AT2020adpi (ZTF20acvfraq), a luminous optical/UV transient in the nucleus of the galaxy WISEA J231853.77-103505.6 (z=0.26) that exhibits the properties of an ambiguous nuclear transient. Near peak, its spectral energy distribution is well described by a power law ( λ L λ ∝ λ − α , α = 0.44 ± 0.04 ), with a maximum g -band luminosity of ( 3.6 ± 0.6 ) × 10 44 erg s, which is consistent with luminous AGN flares. We detect a strong mid-infrared flare ( L p e a k M I R = ( 2.3 ± 0.05 ) × 10 44 erg s) delayed by ∼ 210 rest-frame days, indicating a hot dust echo from material at ∼ 0.2 pc. The optical and near-infrared spectra show broad H, He I, [OIII] lines, as well as narrow Fe II, and prominent Mg II, which is a combination not typical of TDEs. Taken together, these features suggest AT2020adpi is an ambiguous nuclear transient, where an accretion episode was triggered by stellar disruption of an accretion disk or instabilities within an active nucleus. This source demonstrates the need for careful multiwavelength analysis to distinguish between extreme AGN variability and TDEs.

We present an optical variability analysis and comparison of the samples of Seyfert 1 (Sy1) and Seyfert 2 (Sy2) galaxies, selected from the Swift 9 month BAT catalog, using the light curves from Transiting Exoplanet Survey Satellite (TESS) and All-Sky Automated Survey for SuperNovae (ASAS-SN). We measured the normalized excess variance of TESS and ASAS-SN light curves for each target and performed a Kolmogorov–Smirnov test between the two samples, where our results showed significant differences. This is consistent with predictions from the unification model, where Seyfert 2s are obscured by the larger scale dust torus and their variability is suppressed. This variability difference is independent of the luminosity, Eddington ratio, or black hole mass, further supporting geometrical unification models. We searched the dependence of the normalized excess variance of Sy1s on absolute magnitudes, Eddington ratio, and black hole mass, where our results are consistent with relations found in the literature. Finally, a small subsample of changing-look (CL) active galactic nuclei (AGNs) that transitioned during the time frame of the ASAS-SN light curves, with their variability amplitudes changing according to the classification, have larger variability as type 1s and smaller as 2s. The change of variability amplitudes can be used to better pinpoint when the type transition occurred. The consistency trend of the variability amplitude differences between Sy1s and Sy2s and between CL AGNs in 1 or 2 stages suggests that variability can be a key factor in shedding light on the CL AGN or the dichotomy between Sy1 or Sy2 populations.

Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 ± 0.8 mm s ^–1 yr ^–1 , which deviates from the acceleration predicted by equilibrium Milky Way (MW) models at a 4 σ level. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the MW interacting with orbiting dwarf galaxies (∼1 mm s ^–1 yr ^–1 ), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in Gaia DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 60 kyr, a companion mass of 0.3 M _⊙ (indicative of a white dwarf or low-mass star), and a semimajor axis of 1900 au. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios.

We investigate the relationship between AGN optical variability timescales, amplitudes, and supermassive black hole (SMBH) masses using homogeneous light curves from the All-Sky Automated Survey for SuperNovae (ASAS-SN). We fit a damped random walk (DRW) model to high-cadence, long-baseline ASAS-SN light curves to estimate the characteristic variability timescale (τ_DRW) and amplitude (σ) for 57 AGN with precise SMBH mass measurements from reverberation mapping and dynamical methods. We confirm a significant correlation between τ_DRW and SMBH mass, and find: log_10(M_BH/ M_⊙) = (1.85±0.20)×log_10 (τ_DRW/200 days)+7.59±0.08. Incorporating σ̂^2 = 2σ^2/τ_DRW in a plane model significantly improves residuals, and we find: log_10(M_BH/ M_⊙) = (2.27±0.20)×log_10 (τ_DRW/200 days)+(1.20±0.20)×log_10(σ̂/1 mJy/days^1/2)+7.68±0.08 with a scatter of 0.39 dex. We calculate τ_DRW, σ̂, and estimate SMBH masses for 203 bright (V<16 mag) AGN from the Milliquas catalog and compare these estimates with measurements from the BAT AGN Spectroscopic Survey for 42 overlapping AGN. In 10 years, LSST could extend this method to survey 7≲log_10(M_BH/M_⊙)≲9 SMBHs out to z∼1 and log_10(M_BH/M_⊙)∼8.0 out to z∼4, and ASAS-SN could probe 5≲log_10(M_BH/M_⊙)≲10.5 SMBHs in the local universe and log_10(M_BH/M_⊙)∼9.0 out to z∼2. Measuring AGN variability with these datasets will provide a unique probe of SMBH evolution by making estimates of M_BH spanning several orders of magnitude with photometric observations alone.

We search a sample of 5,685,060 isolated sources in the All Sky Automated Survey for SuperNovae (ASAS-SN) with 14.5

The light curves of radioactive transients, such as supernovae and kilonovae, are powered by the decay of radioisotopes, which release high-energy leptons through $\beta^+$ and $\beta^-$ decays. These leptons deposit energy into the expanding ejecta. As the ejecta density decreases during expansion, the plasma becomes collisionless, with particle motion governed by electromagnetic forces. In such environments, strong or turbulent magnetic fields are thought to confine particles, though the origin of these fields and the confinement mechanism have remained unclear. Using fully kinetic particle-in-cell (PIC) simulations, we demonstrate that plasma instabilities can naturally confine high-energy leptons. These leptons generate magnetic fields through plasma streaming instabilities, even in the absence of pre-existing fields. The self-generated magnetic fields slow lepton diffusion, enabling confinement and transferring energy to thermal electrons and ions. Our results naturally explain the positron trapping inferred from late-time observations of thermonuclear and core-collapse supernovae. Furthermore, they suggest potential implications for electron dynamics in the ejecta of kilonovae. We also estimate synchrotron radio luminosities from positrons for Type Ia supernovae and find that such emission could only be detectable with next-generation radio observatories from a Galactic or local-group supernova in an environment without any circumstellar material.

We present the second and final release of optical spectroscopy of Type Ia Supernovae (SNe Ia) obtained during the first and second phases of the Carnegie Supernova Project (CSP-I and CSP-II). The newly released data consist of 148 spectra of 30 SNe Ia observed in the course of the CSP-I, and 234 spectra of 127 SNe Ia obtained during the CSP-II. We also present 216 optical spectra of 46 historical SNe Ia, including 53 spectra of 30 SNe Ia observed by the Calán/Tololo Supernova Survey. We combine these observations with previously published CSP data and publicly-available spectra to compile a large sample of measurements of spectroscopic parameters at maximum light, consisting of pseudo-equivalent widths and expansion velocities of selected features, for 232 CSP and historical SNe Ia (including more than 1000 spectra). Finally, we review some of the strongest correlations between spectroscopic and photometric properties of SNe Ia. Specifically, we define two samples: one consisting of SNe Ia discovered by targeted searches (most of them CSP-I objects) and the other composed of SNe Ia discovered by untargeted searches, which includes most of the CSP-II objects. The analysed correlations are similar for both samples. We find a larger incidence of SNe Ia belonging to the Cool (CL)and Broad Line (BL) Branch subtypes among the events discovered by targeted searches, Shallow Silicon (SS) SNe Ia are present with similar frequencies in both samples, while Core Normal (CN) SNe Ia are more frequent in untargeted searches.

We present a detailed analysis of nearly two decades of optical/UV and X-ray data to study the multi-wavelength pre-explosion properties and post-explosion X-ray properties of nearby SN2023ixf located in M101. We find no evidence of precursor activity in the optical to UV down to a luminosity of less than or similar to 1.0 x 10(5)L(circle dot), while X-ray observations covering nearly 18 yr prior to explosion show no evidence of luminous precursor X-ray emission down to an absorbed 0.3-10.0 keV X-ray luminosity of similar to 6 x 10(36) erg s(-1). Extensive Swift observations taken post-explosion did not detect soft X-ray emission from SN2023ixf within the first similar to 3.3 days after first light, which suggests a mass-loss rate for the progenitor of less than or similar to 5 x 10(-4 )M(circle dot) yr(-1) or a radius of less than or similar to 4 x 10(15) cm for the circumstellar material. Our analysis also suggests that if the progenitor underwent a mass-loss episode, this had to occur > 0.5-1.5 yr prior to explosion, consistent with previous estimates. Swift detected soft X-rays from SN2023ixf similar to 4.25$ days after first light, and it rose to a peak luminosity of similar to 10(39) erg s(-1) after 10 days and has maintained this luminosity for nearly 50 days post first light. This peak luminosity is lower than expected, given the evidence that SN2023ixf is interacting with dense material. However, this might be a natural consequence of an asymmetric circumstellar medium. X-ray spectra derived from merging all Swift observations over the first 50 days are best described by a two-component bremsstrahlung model consisting of a heavily absorbed and hotter component similar to that found using NuSTAR, and a less-absorbed, cooler component. We suggest that this soft component arises from cooling of the forward shock similar to that found in Type IIn SN2010jl.

We present JWST spectral and photometric observations of the Type IIP supernova (SN) 2022acko at  50 days past explosion. These data are the first JWST spectral observations of a core-collapse SN. We identify  30 different H I features, other features associated with products produced from the CNO cycle, and s-process elements such as Sc II and Ba II. By combining the JWST spectra with ground-based optical and NIR spectra, we construct a full Spectral Energy Distribution from 0.4 to 25 microns and find that the JWST spectra are fully consistent with the simultaneous JWST photometry. The data lack signatures of CO formation and we estimate a limit on the CO mass of < 10^-8 solar mass. We demonstrate how the CO fundamental band limits can be used to probe underlying physics during stellar evolution, explosion, and the environment. The observations indicate little mixing between the H envelope and C/O core in the ejecta and show no evidence of dust. The data presented here set a critical baseline for future JWST observations, where possible molecular and dust formation may be seen.

We report the discovery and characterisation of TIC 350842552 ("Zvrk"), an apparently isolated, rapidly-rotating ($P_\text{rot} \sim 99\ \mathrm{d}$) red giant observed by TESS in its Southern Continuous Viewing Zone. The star's fast surface rotation is independently verified by the use of p-mode asteroseismology, strong periodicity in TESS and ASAS-SN photometry, and measurements of spectroscopic rotational broadening. A two-component fit to APOGEE spectra indicates a coverage fraction of its surface features consistent with the amplitude of the photometric rotational signal. Variations in the amplitude of its photometric modulations over time suggest the evolution of its surface morphology, and therefore enhanced magnetic activity. We further develop and deploy new asteroseismic techniques to characterise radial differential rotation, and find weak evidence for rotational shear within Zvrk's convective envelope. This feature, in combination with such a high surface rotation rate, is incompatible with models of angular-momentum transport in single-star evolution. Spectroscopic abundance estimates also indicate a high lithium abundance, among other chemical anomalies. Taken together, all of these suggest a planet-ingestion scenario for the formation of this rotational configuration, various models for which we examine in detail.

ABSTRACT We identify 182 flares on 158 stars within 100 pc of the Sun in both the near-ultraviolet (NUV; $1750\!-\!2750$ Å) and far-ultraviolet (FUV; $1350\!-\!1750$ Å) using high-cadence light curves from the Galaxy Evolution Explorer. Ultraviolet (UV) emission from stellar flares plays a crucial role in determining the habitability of exoplanetary systems. However, whether such UV emission promotes or threatens such life depends strongly on the energetics of these flares. Most studies assessing the effect of flares on planetary habitability assume a 9000 K blackbody spectral energy distribution that produces more NUV flux than FUV flux ($\mathcal {R} \equiv F_{\rm FUV} / F_{\rm NUV} \approx \frac{1}{6}$). Instead, we observe the opposite with the excess FUV reaching $\mathcal {R} \approx \frac{1}{2}\!-\!2$, roughly $3\!-\!12$ times the expectation of a 9000 K blackbody. The ratio of FUV to NUV time-integrated flare energies is 3.0 times higher on average than would be predicted by a constant 9000 K blackbody during the flare. Finally, we find that the FUV/NUV ratio at peak tentatively correlates (${\sim} 2 \sigma$ significance) both with total UV flare energy and with the G − RP colour of the host star. On average, we observe higher FUV/NUV ratios at peak in $E_{\text{UV}}\gt 10^{32}$ erg flares and in flares on fully convective stars.

The optical spectra of novae are characterized by emission lines from the hydrogen Balmer series and either Fe II or He/N, leading to their traditional classification into two spectral classes: 'Fe II' and 'He/N'. For decades, the origins of these spectral features were discussed in the literature in the contexts of different bodies of gas or changes in the opacity of the ejecta, particularly associated with studies by R. E. Williams and S. N. Shore. Here, we revisit these major studies with dedicated, modern data sets, covering the evolution of several novae from early rise to peak all the way to the nebular phase. Our data confirm previous suggestions in the literature that the 'Fe ii' and 'He/N' spectral classes are phases in the spectroscopic evolution of novae driven primarily by changes in the opacity, ionization, and density of the ejecta, and most if not all novae go through at least three spectroscopic phases as their eruptions evolve: an early He/N (phase 1; observed during the early rise to visible peak and characterized by P Cygni lines of He I and N II/III), then an Fe ii (phase 2; observed near visible peak and characterized by P Cygni lines of Fe II and O I), and then a later He/N (phase 3; observed during the decline and characterized by emission lines of He I/II, N II/III), before entering the nebular phase. This spectral evolution seems to be ubiquitous across novae, regardless of their speed class; however the duration of each of these phases differs based on the speed class of the nova.