An official website of the United States government
ABSTRACT We present early spectral observations of the very slow Galactic nova Gaia22alz, over its gradual rise to peak brightness that lasted 180 d. During the first 50 d, when the nova was only 3–4 mag above its normal brightness, the spectra showed narrow (FWHM ≈ 400 km s−1) emission lines of H Balmer, He i, He ii, and C iv but no P Cygni absorption. A few weeks later, the high-excitation He ii and C iv lines disappeared, and P Cygni profiles of Balmer, He i, and eventually Fe ii lines emerged, yielding a spectrum typical of classical novae before peak. We propose that the early (first 50 d) spectra of Gaia22alz, particularly the emission lines with no P Cygni profiles, are produced in the white dwarf’s optically thin envelope or accretion disc, reprocessing ultraviolet and potentially X-ray emission from the white dwarf after a dramatic increase in the rate of thermonuclear reactions, during a phase known as the ‘early X-ray/UV flash’. If true, this would be one of the rare times that the optical signature of the early X-ray/UV flash has been detected. While this phase might last only a few hours in other novae and thus be easily missed, it was possible to detect in Gaia22alz due to its very slow and gradual rise and thanks to the efficiency of new all-sky surveys in detecting transients on their rise. We also consider alternative scenarios that could explain the early spectral features of Gaia22alz and its gradual rise.
more »
« less
Revisiting the classics: on the evolutionary origin of the ‘Fe ii ’ and ‘He/N’ spectral classes of novae
ABSTRACT 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.
more »
« less
- PAR ID:
- 10536266
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- ADS
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 527
- Issue:
- 3
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 9303 to 9321
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract SN 2018aoz is a Type Ia SN with aB-band plateau and excess emission in infant-phase light curves ≲1 day after the first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN 2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show that the SN is intermediate between two subtypes of normal Type Ia: core normal and broad line. The excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on Hαand Heifavor a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [Oi] and Heidisfavors a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN 2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Feii] and [Niii]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1D models are incompatible with the infant-phase excess emission, color, and weak strength of nebular-phase [Caii]. Although the explosion processes of SN 2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear to be normal after ∼1 day.more » « less
-
null (Ed.)ABSTRACT AT 2016dah and AT 2017fyp are fairly typical Andromeda galaxy (M 31) classical novae. AT 2016dah is an almost text book example of a ‘very fast’ declining, yet uncommon, Fe ii‘b’ (broad-lined) nova, discovered during the rise to peak optical luminosity, and decaying with a smooth broken power-law light curve. AT 2017fyp is classed as a ‘fast’ nova, unusually for M 31, its early decline spectrum simultaneously shows properties of both Fe ii and He/N spectral types – a ‘hybrid’. Similarly, the light curve of AT 2017fyp has a broken power-law decline but exhibits an extended flat-topped maximum. Both novae were followed in the UV and X-ray by the Neil Gehrels Swift Observatory, but no X-ray source was detected for either nova. The pair were followed photometrically and spectroscopically into their nebular phases. The progenitor systems were not visible in archival optical data, implying that the mass donors are main-sequence stars. What makes AT 2016dah and AT 2017fyp particularly interesting is their position with respect to M 31. The pair are close on the sky but are located far from the centre of M 31, lying almost along the semiminor axis of their host. Radial velocity measurements and simulations of the M 31 nova population leads to the conclusion that both novae are members of the Andromeda Giant Stellar Stream (GSS). We find the probability of at least two M 31 novae appearing coincident with the GSS by chance is $$\sim \!1{{\ \rm per\ cent}}$$. Therefore, we claim that these novae arose from the GSS progenitor, not M 31 – the first confirmed novae discovered in a tidal steam.more » « less
-
Abstract We present three new spectra of the nearby Type Ia supernova (SN Ia) 2011fe covering ≈480–850 days after maximum light and show that the ejecta undergoes a rapid ionization shift at ∼500 days after explosion. The prominent Feiiiemission lines at ≈4600 Å are replaced with Fei+Feiiblends at ∼4400 Å and ∼5400 Å. The ≈7300 Å feature, which is produced by [Feii]+[Niii] at ≲400 days after explosion, is replaced by broad (≈±15,000 km s−1) symmetric [Caii] emission. Models predict this ionization transition occurring ∼100 days later than what is observed, which we attribute to clumping in the ejecta. Finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for SN 2011fe. Nondetections of H and He exclude nearby nondegenerate companions, [Oi] nondetections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion.more » « less
-
Abstract Multipeaked supernovae with precursors, dramatic light-curve rebrightenings, and spectral transformation are rare, but are being discovered in increasing numbers by modern night-sky transient surveys like the Zwicky Transient Facility. Here, we present the observations and analysis of SN 2023aew, which showed a dramatic increase in brightness following an initial luminous (−17.4 mag) and long (∼100 days) unusual first peak (possibly precursor). SN 2023aew was classified as a Type IIb supernova during the first peak but changed its type to resemble a stripped-envelope supernova (SESN) after the marked rebrightening. We present comparisons of SN 2023aew’s spectral evolution with SESN subtypes and argue that it is similar to SNe Ibc during its main peak. P-Cygni Balmer lines are present during the first peak, but vanish during the second peak’s photospheric phase, before Hαresurfaces again during the nebular phase. The nebular lines ([Oi], [Caii], Mgi], Hα) exhibit a double-peaked structure that hints toward a clumpy or nonspherical ejecta. We analyze the second peak in the light curve of SN 2023aew and find it to be broader than that of normal SESNe as well as requiring a very high56Ni mass to power the peak luminosity. We discuss the possible origins of SN 2023aew including an eruption scenario where a part of the envelope is ejected during the first peak and also powers the second peak of the light curve through interaction of the SN with the circumstellar medium.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stad3342
