We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates. [S0034-6861(98)00704-1]

We examine radiatively driven mass loss from stars near and above the Eddington limit. Building on the standard CAK theory of driving by scattering in an ensemble of lines with a power-law distribution of opacity, we first show that the formal divergence of such line-driven mass loss as a star approaches the Eddington limit is actually limited by the ''photon tiring'' associated with the work needed to lift material out of the star's gravitational potential. We also examine such tiring in simple continuum-driven models in which a specified outward increase in opacity causes a net outward acceleration above the radius where the generalized Eddington parameter exceeds unity. When the density at this radius implies a mass loss too close to the tiring limit, the overall result is flow stagnation at a finite radius. Since escape of a net steady wind is precluded, such circumstances are expected to lead to extensive variability and spatial structure. After briefly reviewing convective and other instabilities that also can be expected to lead to extensive structure in the envelope and atmosphere of a star near or above the Eddington limit, we investigate how the porosity of such a structured medium can reduce the effective coupling between the matter and radiation. Introducing a new ''porosity-length'' formalism, we derive a simple scaling for the reduced effective opacity and use this to derive an associated scaling for the porosity-moderated, continuumdriven mass-loss rate from stars that formally exceed the Eddington limit. For a simple super-Eddington model with a single porosity length that is assumed to be on the order of the gravitational scale height, the overall mass loss is similar to that derived in previous porosity models, given roughly by L à =a à c (where L * is the stellar luminosity and c and a * are the speed of light and the atmospheric sound speed). This is much higher than is typical of line-driven winds but is still only a few percent of the tiring limit. To obtain still stronger mass loss that approaches observationally inferred values near this limit, we draw on an analogy with the power-law distribution of line-opacity in the standard CAK model of line-driven winds and thereby introduce a ''power-law-porosity'' model in which the associated structure has a broad range of scales. We show that for power indices p < 1, the mass-loss rate can be enhanced over the single-scale model by a factor that increases with the Eddington parameter as À À1þ1= p . For lower p (%0.5-0.6) and/or moderately large À (>3-4), such models lead to mass-loss rates that approach the photon-tiring limit. Together with the ability to drive quite fast outflow speeds (of order the surface escape speed), the derived, near-tiring-limited mass loss offers a potential dynamical basis to explain the observationally inferred large mass loss and flow speeds of giant outbursts in Carinae and other luminous blue variable stars.

There is a growing number of Type IIn supernovae (SNe) which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to poorly charted phenomena in the final stages of stellar evolution. By coadding Palomar Transient Factory (PTF) images taken prior to the explosion, here we present a search for precursors in a sample of 16 Type IIn SNe. We find five SNe IIn that likely have at least one possible precursor event (PTF 10bjb, SN 2010mc, PTF 10weh, SN 2011ht, and PTF 12cxj), three of which are reported here for the first time. For each SN we calculate the control time. We find that precursor events among SNe IIn are common: at the one-sided 99% confidence level, >50% of SNe IIn have at least one pre-explosion outburst that is brighter than 3 × 10 7 L taking place up to 1/3 yr prior to the SN explosion. The average rate of such precursor events during the year prior to the SN explosion is likely 1 yr −1 , and fainter precursors are possibly even more common. Ignoring the two weakest precursors in our sample, the precursors rate we find is still on the order of one per year. We also find possible correlations between the integrated luminosity of the precursor and the SN total radiated energy, peak luminosity, and rise time. These correlations are expected if the precursors are mass-ejection events, and the early-time light curve of these SNe is powered by interaction of the SN shock and ejecta with optically thick circumstellar material.

Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as a supernova.[1−4] Interestingly, several models predict such pre-explosion outbursts. [5−7] Establishing a causal connection between these mass-loss episodes and the final supernova explosion will provide a novel way to study pre-supernova massive-star evolution. Here we report on observations of a remarkable mass-loss event detected 40 days prior to the explosion of the Type IIn supernova SN 2010mc (PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 × 10 47 erg of energy, and releasing about 2 Ofek et al. 10−2 M ⊙ at typical velocities of 2000 km s −1 . We show that the temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model [6] , and disfavour alternative suggestions [7] . An outburst from a SN progenitor 3 Spectra of the supernova, showing a blue continuum with Balmer emission lines, are presented in Figure 2. The continuum becomes redder with time, and its slope corresponds to an effective temperature of over 16,000 K at day five and drops to about 8,000 K at day 27. The Hα line has an initial width of ∼ 3×10 3 km s −1 at day 6, decreasing to ∼ 10 3 km s −1 at day 14. A broad (10 4 km s −1 ) P-Cygni profile emerges by day 27. The spectra also show He I lines with decreasing strength, presumably due to the drop in temperature.The nature of the precursor bump is very intriguing and can potentially tell us a great deal about the SN explosion and the progenitor. The only interpretation that is fully consistent with the photometric and spectroscopic evidence is that the first bump represents an outburst from the SN progenitor about one month prior to explosion, while the brighter bump is initiated by a full explosion of the star a few weeks later. Below we analyse this model in the context of the photometric and spectroscopic data. In SI §6 we discuss some alternative models and conclude that they are unlikely.The mass ejected by the precursor burst can be estimated in various independent ways.By requiring that the precursor integrated bolometric luminosity, E bol,prec , is lower than the kinetic energy of the precursor outburst (moving at velocity v prec ) which powers it, we can set a lower limit on the mass ejected in the precursor outburstThe outburst velocity is estimated from the line widths of 1000-3000 km s −1 , seen in the early-time spectra of the SN. As this mass was presumably ejected over a period of about one month (i.e., the outburst duration), the annual mass-loss rate is about 10 times higher. A similar order of magnitude argument can be used to put an upper limit on the mass in the precursor outburst. If some of the SN bolometric energy, E bol,SN , is due to interaction between the SN ejecta, moving a...

No abstract

Striking similarities exist between high energy gamma ray emission from active galactic nuclei (AGN) and gamma ray bursts (GRBs). They suggest that GRBs are generated by inverse Compton scattering from highly relativistic electrons in transient jets. Such jets may be produced along the axis of an accretion disk formed around stellar black holes (BH) or neutron stars (NS) in BH-NS and NS-NS mergers and in accretion induced collapse of magnetized white dwarfs (WD) or neutron stars in close binary systems. Such events may produce the cosmological GRBs. Transient jets formed by single old magnetized neutron stars in an extended Galactic halo may produce a local population of GRBs. Here we show that jet production of GRBs by inverse Compton scattering can explain quite simply the striking correlations that exist between various temporal features of GRBs, their duration histogram, the power spectrum of their complex multipeak light curves, their power-law high energy spectra and other features of GRBs. Some additional predictions are made including the expected polarization of gamma-rays in the bursts.

No abstract

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.