Sivan Ginzburg

SUPERLUMINOUS LIGHT CURVES FROM SUPERNOVAE EXPLODING IN A DENSE WIND

Observations from the last decade have indicated the existence of a general class of superluminous supernovae (SLSNe), in which the peak luminosity exceeds 1044 erg s–1. Here we focus on a subclass of these events, where the light curve is also tens of days wide, so the total radiated energy is of order 1051 erg. If the origin of these SLSNe is a core-collapse-driven explosion of a massive star, then the mechanism that converts the explosion energy into radiation must be very efficient (much more than in typical core-collapse SNe, where this efficiency is of order 1%). We examine the scenario where the radiated luminosity is due to efficient conversion of kinetic energy of the ejected stellar envelope into radiation by interaction with an optically thick, pre-existing circumstellar material, presumably the product of a steady wind from the progenitor. We base the analysis on analytical derivations of various limits, and on a simple, numerically solved, hydrodynamic diffusion model, which allows us to explore the regime of interest, which does not correspond to the analytical limits. In our results, we identify the qualitative behavior of the observable light curves, and relate them to the parameters of the wind. We specifically show that a wide and superluminous supernova requires the mass of the relevant wind material to be comparable to that of the ejected material from the exploding progenitor. We find the wind parameters that explain the peak luminosity and width of the bolometric light curves of three particular SLSNe, namely, SN 2005ap, SN 2006gy, and SN 2010gx, and show that they are best fitted with a wind that extends to a radius of order 1015 cm. These results serve as an additional indication that at least some SLSNe may be powered by interaction of the ejected material with a steady wind of similar mass.

SUPER-EARTH ATMOSPHERES: SELF-CONSISTENT GAS ACCRETION AND RETENTION

Some recently discovered short-period Earth to Neptune sized exoplanets (super Earths) have low observed mean densities which can only be explained by voluminous gaseous atmospheres. Here, we study the conditions allowing the accretion and retention of such atmospheres. We self-consistently couple the nebular gas accretion onto rocky cores and the subsequent evolution of gas envelopes following the dispersal of the protoplanetary disk. Specifically, we address mass-loss due to both photo-evaporation and cooling of the planet. We find that planets shed their outer layers (dozens of percents in mass) following the disks dispersal (even without photo-evaporation), and their atmospheres shrink in a few Myr to a thickness comparable to the radius of the underlying rocky core. At this stage, atmospheres containing less particles than the core (equivalently, lighter than a few % of the planets mass) can be blown away by heat coming from the cooling core, while heavier atmospheres cool and contract on a timescale of Gyr at most. By relating the mass-loss timescale to the accretion time, we analytically identify a Goldilocks region in the mass-temperature plane in which low-density super Earths can be found: planets have to be massive and cold enough to accrete and retain their atmospheres, while not too massive or cold, such that they do not enter runaway accretion and become gas giants (Jupiters). We compare our results to the observed super-Earth population and find that low-density planets are indeed concentrated in the theoretically allowed region. Our analytical and intuitive model can be used to investigate possible super-Earth formation scenarios.

Core-powered mass-loss and the radius distribution of small exoplanets

Recent observations identify a valley in the radius distribution of small exoplanets, with planets in the range

Tidal heating of young super-Earth atmospheres

1.5-2.0\,{\rm R}_\oplus

Hot-Jupiter core mass from Roche lobe overflow

significantly less common than somewhat smaller or larger planets. This valley may suggest a bimodal population of rocky planets that are either engulfed by massive gas envelopes that significantly enlarge their radius, or do not have detectable atmospheres at all. One explanation of such a bimodal distribution is atmospheric erosion by high-energy stellar photons. We investigate an alternative mechanism: the luminosity of the cooling rocky core, which can completely erode light envelopes while preserving heavy ones, produces a deficit of intermediate sized planets. We evolve planetary populations that are derived from observations using a simple analytical prescription, accounting self-consistently for envelope accretion, cooling and mass loss, and demonstrate that core-powered mass loss naturally reproduces the observed radius distribution, regardless of the high-energy incident flux. Observations of planets around different stellar types may distinguish between photoevaporation, which is powered by the high-energy tail of the stellar radiation, and core-powered mass loss, which depends on the bolometric flux through the planets equilibrium temperature that sets both its cooling and mass-loss rates.

Deep and wide gaps by super Earths in low-viscosity discs

Short-period Earth to Neptune size exoplanets (super-Earths) with voluminous gas envelopes seem to be very common. These gas atmospheres are thought to have originated from the protoplanetary disk in which the planets were embedded during their first few Myr. The accretion rate of gas from the surrounding nebula is determined by the ability of the gas to cool and radiate away its gravitational energy. Here we demonstrate that heat from the tidal interaction between the star and the young (and therefore inflated) planet can inhibit the gas cooling and accretion. Quantitatively, we find that the growth of super-Earth atmospheres halts for planets with periods of about 10 days, provided that their initial eccentricities are of the order of 0.2. Thus, tidal heating provides a robust and simple mechanism that can simultaneously explain why these planets did not become gas giants and account for the deficit of low-density planets closer to the star, where the tides are even stronger. We suggest that tidal heating may be as important as other factors (such as the nebulas lifetime and atmosphere evaporation) in shaping the observed super-Earth population.

Super-Earths: Atmospheric Accretion, Thermal Evolution and Envelope Loss

The orbits of many observed hot Jupiters are decaying rapidly due to tidal interaction, eventually reaching the Roche limit. We analytically study the ensuing coupled mass loss and orbital evolution during the Roche-lobe overflow and find two possible scenarios. Planets with light cores

HOT-JUPITER INFLATION DUE TO DEEP ENERGY DEPOSITION

M_c\lesssim 6M_\oplus

LIGHT CURVES FROM SUPERNOVA SHOCK BREAKOUT THROUGH AN EXTENDED WIND

(assuming a nominal tidal dissipation factor

BLACKBODY RADIATION FROM ISOLATED NEPTUNES

Q\sim 10^6