Shell model on a random gaussian basis

Pauli-projected random gaussians are used as a representation to solve the shell model equations. The elements of the representation are chosen by a variational procedure. This scheme is particularly suited to describe cluster formation and cluster decay in nuclei. It overcomes the basis-size problem of the ordinary shell model and the technical difficulties of the cluster-configuration shell model. The model reproduces the $\alpha$-decay width of $^{212}$Po satisfactorily.Comment: Latex, Submitted to Phys. Lett. B, 7 pages, 2 figures available upon request, ATOMKI-1994-

SN 2017ein and the Possible First Identification of a Type Ic Supernova Progenitor

We have identified a progenitor candidate in archival Hubble Space Telescope (HST) images for the Type Ic SN 2017ein in NGC 3938, pinpointing the candidate's location via HST Target-of-Opportunity imaging of the SN itself. This would be the first identification of a stellar-like object as a progenitor candidate for any Type Ic supernova to date. We also present observations of SN 2017ein during the first ~49 days since explosion. We find that SN 2017ein most resembles the well-studied Type Ic SN 2007gr. We infer that SN 2017ein experienced a total visual extinction of A_V~1.0--1.9 mag, predominantly because of dust within the host galaxy. Although the distance is not well known, if this object is the progenitor, it was likely of high initial mass, ~47--48 M_sun if a single star, or ~60--80 M_sun if in a binary system. However, we also find that the progenitor candidate could be a very blue and young compact cluster, further implying a very massive (>65 M_sun) progenitor. Furthermore, the actual progenitor might not be associated with the candidate at all and could be far less massive. From the immediate stellar environment, we find possible evidence for three different populations; if the SN progenitor was a member of the youngest population, this would be consistent with an initial mass of ~57 M_sun. After it has faded, the SN should be reobserved at high spatial resolution and sensitivity, to determine whether the candidate is indeed the progenitor.Comment: Revised, following referee's comments, and accepted to ApJ; 21 pages, 10 figure

SN~2015da: Late-time observations of a persistent superluminous Type~IIn supernova with post-shock dust formation

We present photometry and spectroscopy of the slowly evolving superluminous Type IIn SN2015da. SN2015da is extraordinary for its very high peak luminosity, and also for sustaining a high luminosity for several years. Even at 8\,yr after explosion, SN2015da remains as luminous as the peak of a normal SNII-P. The total radiated energy integrated over this time period (with no bolometric correction) is at least 1.6 FOE. Including a mild bolometric correction, adding kinetic energy of the expanding cold dense shell of swept-up circumstellar material (CSM), and accounting for asymmetry, the total explosion kinetic energy was likely 5-10 FOE. Powering the light curve with CSM interaction requires an energetic explosion and 20 Msun of H-rich CSM, which in turn implies a massive progenitor system above 30 Msun. Narrow P Cyg features show steady CSM expansion at 90 km/s, requiring a high average mass-loss rate of roughly 0.1 Msun/yr sustained for 2 centuries before explosion (although ramping up toward explosion time). No current theoretical model for single-star pre-SN mass loss can account for this. The slow CSM, combined with broad wings of H$\alpha$ indicating H-rich material in the unshocked ejecta, disfavor a pulsational pair instability model for the pre-SN mass loss. Instead, violent pre-SN binary interaction is a likely cuprit. Finally, SN2015da exhibits the characteristic asymmetric blueshift in its emission lines from shortly after peak until the present epoch, adding another well-studied superluminous SNeIIn with unambiguous evidence of post-shock dust formation.Comment: 18 pages, 11 figs. submitte

Early-Time Ultraviolet and Optical Hubble Space Telescope Spectroscopy of the Type II Supernova 2022wsp

We report early-time ultraviolet (UV) and optical spectroscopy of the young, nearby Type II supernova (SN) 2022wsp obtained by the Hubble Space Telescope (HST)/STIS at about 10 and 20 days after the explosion. The SN 2022wsp UV spectra are compared to those of other well-observed Type II/IIP SNe, including the recently studied Type IIP SN 2021yja. Both SNe exhibit rapid cooling and similar evolution during early phases, indicating a common behavior among SNe II. Radiative-transfer modeling of the spectra of SN 2022wsp with the TARDIS code indicates a steep radial density profile in the outer layer of the ejecta, a supersolar metallicity, and a relatively high total extinction of E(B-V) = 0.35 mag. The early-time evolution of the photospheric velocity and temperature derived from the modeling agree with the behavior observed from other previously studied cases. The strong suppression of hydrogen Balmer lines in the spectra suggests interaction with a pre-existing circumstellar environment could be occurring at early times. In the SN 2022wsp spectra, the absorption component of the Mg II P Cygni profile displays a double-trough feature on day +10 that disappears by day +20. The shape is well reproduced by the model without fine-tuning the parameters, suggesting that the secondary blueward dip is a metal transition that originates in the SN ejecta.Comment: Submitted to ApJ Letters on 4/11/202