We update the capabilities of the software instrument Modules for Experiments in Stellar Astrophysics (MESA) and enhance its ease of use and availability. Our new approach to locating convective boundaries is consistent with the physics of convection, and yields reliable values of the convective core mass during both hydrogen and helium burning phases. Stars with M < 8 M become white dwarfs and cool to the point where the electrons are degenerate and the ions are strongly coupled, a realm now available to study with MESA due to improved treatments of element diffusion, latent heat release, and blending of equations of state. Studies of the final fates of massive stars are extended in MESA by our addition of an approximate Riemann solver that captures shocks and conserves energy to high accuracy during dynamic epochs. We also introduce a 1D capability for modeling the effects of Rayleigh-Taylor instabilities that, in combination with the coupling to a public version of the STELLA radiation transfer instrument, creates new avenues for exploring Type II supernovae properties. These capabilities are exhibited with exploratory models of pair-instability supernova, pulsational pair-instability supernova, and the formation of stellar mass black holes. The applicability of MESA is now widened by the capability of importing multi-dimensional hydrodynamic models into MESA. We close by introducing software modules for handling floating point exceptions and stellar model optimization, and four new software tools − MESA-Web, MESA-Docker, pyMESA, and mesastar.org − to enhance MESA's education and research impact.

The extremely luminous supernova SN 2006gy (ref. 1) challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too luminous by more than a factor of ten. Here we report that the brightest supernovae in the modern Universe arise from collisions between shells of matter ejected by massive stars that undergo an interior instability arising from the production of electron-positron pairs. This 'pair instability' leads to explosive burning that is insufficient to unbind the star, but ejects many solar masses of the envelope. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 10(50) erg of light, about a factor of ten more than an ordinary supernova. Our model is in good agreement with the observed light curve for SN 2006gy and also shows that some massive stars can produce more than one supernova-like outburst.

The optical/UV light curves of SN 1987A are analyzed with the multienergy group radiation hydrodynamics code STELLA. The calculated monochromatic and bolometric light curves are compared with observations shortly after shock breakout, during the early plateau, through the broad second maximum, and during the earliest phase of the radioactive tail. We have concentrated on a progenitor model calculated by Nomoto & Hashimoto and Saio, Nomoto, & Kato, which assumes that 14 of the stellar M _ mass is ejected. Using this model, we have updated constraints on the explosion energy and the extent of mixing in the ejecta. In particular, we determine the most likely range of E/M (explosion energy over ejecta mass) and (radius of the progenitor). In general, our best models have energies in the range R 0 E \ (1.1^0.3) ] 1051 ergs, and the agreement is better than in earlier, Ñux-limited di †usion calculations for the same explosion energy. Our modeled B and V Ñuxes compare well with observations, while the Ñux in U undershoots after D10 days by a factor of a few, presumably owing to NLTE and line transfer e †ects. We also compare our results with IUE observations, and a very good quantitative agreement is found for the Ðrst days, and for one IUE band (2500È3000 as long as for 3 months. We point out A ) that the V Ñux estimated by McNaught & Zoltowski should probably be revised to a lower value.

The light curve of supernova (SN) 1993J is calculated using two approaches to radiation transport as exempliÐed by the two computer codes, STELLA and EDDINGTON. Particular attention is paid to shock breakout and the photometry in the U, B, and V bands during the Ðrst 120 days. The hydrodynamical model, the explosion of a 13 star that has lost most of its hydrogenic envelope to a com-M _ panion, is the same in each calculation. The comparison elucidates di †erences between the approaches and also serves to validate the results of both. STELLA includes implicit hydrodynamics and is able to model supernova evolution at early times, before the expansion is homologous. STELLA also employs multigroup photonics and is able to follow the radiation as it decouples from the matter. EDDINGTON uses a di †erent algorithm for integrating the transport equation, assumes homologous expansion, and uses a Ðner frequency resolution. Good agreement is achieved between the two codes only when compatible physical assumptions are made about the opacity. In particular, the line opacity near the principal (second) peak of the light curve must be treated primarily as absorptive, even though the electron density is too small for collisional deexcitation to be a dominant photon destruction mechanism. JustiÐcation is given for this assumption and involves the degradation of photon energy by "" line splitting,ÏÏ i.e., Ñuores-cence. The fact that absorption versus scattering matters to the light curve is indicative of the fact that departures from equilibrium radiative di †usion are important. A new result for SN 1993J is a prediction of the continuum spectrum near the shock breakout (calculated by STELLA), which is superior to the results of other standard single energy group hydrocodes such as VISPHOT or TITAN. Based on the results of our independent codes, we discuss the uncertainties involved in the current time-dependent models of supernova light curves.

Recent discoveries of weak and fast optical transients raise the question of their origin. We investigate the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic. We show that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In this Letter, a detailed example is presented in which the pre-SN stellar mass is barely above the Chandrasekhar limit, resulting in the ejection of only ∼ 0.05 − 0.20 M ⊙ of material and the formation of a low-mass neutron star (NS). We compute synthetic light curves of this case and demonstrate that SN 2005ek could be explained by our model. We estimate that the fraction of such ultra-stripped to all SNe could be as high as 10 −3 − 10 −2 . Finally, we argue that the second explosion in some double NS systems (for example, the double pulsar PSR J0737−3039B) was likely associated with an ultra-stripped SN Ic.

Aims. We present synthetic bolometric and broad-band UBVRI light curves of SNe Ia for four selected 3D deflagration models of thermonuclear supernovae.Methods. The light curves are computed with the 1D hydro code stella, which models (multi-group time-dependent) nonequilibrium radiative transfer inside SN ejecta. Angle-averaged results from 3D hydrodynamical explosion simulations with the composition determined in a nucleosynthetic postprocessing step served as the input to the radiative transfer model. Results. The predicted model UBV light curves do agree reasonably well with the observed ones for SNe Ia in the range of low to normal luminosities, although the underlying hydrodynamical explosion models produced only a modest amount of radioactive 56 Ni (i.e. ∼0.24-0.42 M ) and relatively low kinetic energy in the explosion (less than 0.7 × 10 51 erg). The evolution of predicted B and V fluxes in the model with a 56 Ni mass of 0.42 M follows the observed decline rate after the maximum very well, although the behavior of fluxes in other filters deviates somewhat from observations, and the bolometric decline rate is a bit slow. The material velocity at the photospheric level is on the order of 10 4 km s −1 for all models. Using our models, we check the validity of Arnett's rule, relating the peak luminosity to the power of the deposited radioactive heating, and we also check the accuracy of the procedure for extracting the 56 Ni mass from the observed light curves. Conclusions. We find that the comparison between theoretical light curves and observations provides a useful tool to validate SN Ia models. The steps necessary for improving the agreement between theory and observations are set out.

We present and analyse spectra of the Type IIn supernova (SN) 1994W obtained between 18 and 203 d after explosion. During the luminous phase (first 100 d) the line profiles are composed of three major components: (i) narrow P‐Cygni lines with the absorption minima at −700 km s−1; (ii) broad emission lines with blue velocity at zero intensity ∼4000 km  s−1; and (iii) broad, smooth wings extending out to at least ∼5000 km s−1, most apparent in Hα. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post‐shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P‐Cygni lines from the SN is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the density (n≈ 109 cm−3), radial extent [∼(4–5) × 1015 cm] and Thomson optical depth (τT≳ 2.5) of the CS envelope during the first month. The plateau‐like SN light curve is reproduced by a hydrodynamical model and is found to be powered by a combination of internal energy leakage after the explosion of an extended pre‐SN (∼1015 cm) and subsequent luminosity from CS interaction. The pre‐explosion kinematics of the CS envelope is recovered, and is close to homologous expansion with outer velocity ∼1100 km s−1 and a kinematic age of ∼1.5 yr. The high mass (∼0.4 M⊙) and kinetic energy (∼2 × 1048 erg) of the CS envelope, combined with low age, strongly suggest that the CS envelope was explosively ejected ∼1.5 yr prior to the SN explosion.

We present an analytic model for bolometric light curves which are powered by the interaction between supernova ejecta and a dense circumstellar medium. This model is aimed at modeling Type IIn supernovae to determine the properties of their supernova ejecta and circumstellar medium. Our model is not restricted to the case of steady mass loss and can be applied broadly. We only consider the case in which the optical depth of the unshocked circumstellar medium is not high enough to affect the light curves. We derive the luminosity evolution based on an analytic solution for the evolution of a dense shell created by the interaction. We compare our model bolometric light curves to observed bolometric light curves of three Type IIn supernovae (2005ip, 2006jd, 2010jl) and show that our model can constrain their supernova ejecta and circumstellar medium properties. Our analytic model is supported by numerical light curves from the same initial conditions. c 2013 RAS 2 T. J. Moriya et al.