Philip A. Pinto

Albedo and Reflection Spectra of Extrasolar Giant Planets

We generate theoretical albedo and reflection spectra for a full range of extrasolar giant planet (EGP) models, from Jovian to 51 Pegasi class objects. Our albedo modeling utilizes the latest atomic and molecular cross sections, Mie theory treatment of scattering and absorption by condensates, a variety of particle size distributions, and an extension of the Feautrier technique, which allows for a general treatment of the scattering phase function. We find that, because of qualitative similarities in the compositions and spectra of objects within each of five broad effective temperature ranges, it is natural to establish five representative EGP albedo classes. At low effective temperatures (Teff 150 K) is a class of Jovian objects (class I) with tropospheric ammonia clouds. Somewhat warmer class II, or water cloud, EGPs are primarily affected by condensed H2O. Gaseous methane absorption features are prevalent in both classes. In the absence of nonequilibrium condensates in the upper atmosphere, and with sufficient H2O condensation, class II objects are expected to have the highest visible albedos of any class. When the upper atmosphere of an EGP is too hot for H2O to condense, radiation generally penetrates more deeply. In these objects, designated class III or clear because of a lack of condensation in the upper atmosphere, absorption lines of the alkali metals, sodium and potassium, lower the albedo significantly throughout the visible. Furthermore, the near-infrared albedo is negligible, primarily because of strong CH4 and H2O molecular absorption and collision-induced absorption (CIA) by H2 molecules. In those EGPs with exceedingly small orbital distance (roasters) and 900 K Teff 1500 K (class IV), a tropospheric silicate layer is expected to exist. In all but the hottest (Teff 1500 K) or lowest gravity roasters, the effect of this silicate layer is likely to be insignificant because of the very strong absorption by sodium and potassium atoms above the layer. The resonance lines of sodium and potassium are expected to be salient features in the reflection spectra of these EGPs. In the absence of nonequilibrium condensates, we find, in contrast to previous studies, that these class IV roasters likely have the lowest visible and Bond albedos of any class, rivaling the lowest albedos of our solar system. For the small fraction of roasters with Teff 1500 K and/or low surface gravity (103 cm s-2; class V), the silicate layer is located very high in the atmosphere, reflecting much of the incident radiation before it can reach the absorbing alkali metals and molecular species. Hence, the class V roasters have much higher albedos than those of class IV. In addition, for class V objects, UV irradiation may result in significant alkali metal ionization, thereby further weakening the alkali metal absorption lines. We derive Bond albedos (AB) and Teff estimates for the full set of known EGPs. A broad range in both values is found, with Teff ranging from ~150 to nearly 1600 K, and AB from ~0.02 to 0.8. We find that variations in particle size distributions and condensation fraction can have large quantitative, or even qualitative, effects on albedo spectra. In general, less condensation, larger particle sizes, and wider size distributions result in lower albedos. We explore the effects of nonequilibrium condensed products of photolysis above or within principal cloud decks. As in Jupiter, such species can lower the UV/blue albedo substantially, even if present in relatively small mixing ratios.

Shock breakout in core-collapse supernovae and its neutrino signature

We present results from dynamical models of core-collapse supernovae in one spatial dimension, employing a newly developed Boltzmann neutrino radiation transport algorithm, coupled to Newtonian Lagrangian hydrodynamics and a consistent high-density nuclear equation of state. The transport method is multigroup, employs the Feautrier technique, uses the tangent-ray approach to resolve angles, is implicit in time, and is second-order accurate in space. We focus on shock breakout and follow the dynamical evolution of the cores of 11, 15, and 20 M☉ progenitors through collapse and the first 250 ms after bounce. The shock breakout burst is the signal event in core-collapse evolution, is the brightest phenomenon in astrophysics, and is largely responsible for the initial debilitation and stagnation of the bounce shock. As such, its detection and characterization could test fundamental aspects of the current collapse/supernova paradigm. We examine the effects on the emergent neutrino spectra, light curves, and mix of species (particularly in the early postbounce epoch) of artificial opacity changes, the number of energy groups, the weak magnetism/recoil corrections, nucleon-nucleon bremsstrahlung, neutrino-electron scattering, and the compressibility of nuclear matter. Furthermore, we present the first high-resolution look at the angular distribution of the neutrino radiation field both in the semitransparent regime and at large radii and explore the accuracy with which our tangent-ray method tracks the free propagation of a pulse of radiation in a near vacuum. Finally, we fold the emergent neutrino spectra with the efficiencies and detection processes for a selection of modern underground neutrino observatories and argue that the prompt electron-neutrino breakout burst from the next galactic supernova is in principle observable and usefully diagnostic of fundamental collapse/supernova behavior. Although we are not in this study focusing on the supernova mechanism per se, our simulations support the theoretical conclusion (already reached by others) that spherical (one-dimensional) supernovae do not explode when good physics and transport methods are employed.

The Carnegie Supernova Project: The Low-Redshift Survey

Supernovae are essential to understanding the chemical evolution of the universe. Type Ia supernovae also provide the most powerful observational tool currently available for studying the expansion history of the universe and the nature of dark energy. Our basic knowledge of supernovae comes from the study of their photometric and spectroscopic properties. However, the presently available data sets of optical and near- infrared light curves of supernovae are rather small and/or heterogeneous, and employ photometric systems that are poorly characterized. Similarly, there are relatively few supernovae whose spectral evolution has been well sampled, both in wavelength and phase, with precise spectrophotometric observations. The low-redshift portion of the Carnegie Supernova Project (CSP) seeks to remedy this situation by providing photometry and spectrophotometry of a large sample of supernovae taken on telescope/filter/detector systems that are well understood and well characterized. During a 5 year program that began in 2004 September, we expect to obtain high-precision ugriBVYJHKs light curves and optical spectrophotometry for about 250 supernovae of all types. In this paper we provide a detailed description of the CSP survey observing and data reduction methodology. In addition, we present preliminary photometry and spectra obtained for a few representative supernovae during the first observing campaign.

The Physics of Type Ia Supernova Light Curves. II. Opacity and Diffusion

We examine the nature of the opacity and radiation transport in Type Ia supernovae. The dominant opacity arises from line transitions. We discuss the nature of line opacities and diffusion in expanding media and the appropriateness of various mean and expansion opacities used in light-curve calculations. Fluorescence is shown to be the dominant physical process governing the rate at which energy escapes the supernova. We present a sample light curve that was obtained using a time-dependent solution of the radiative transport equation with a spectral resolution of 80 km s-1 and employing an LTE equation of state. The result compares favorably with light curves and spectra of typical supernovae and is used to illustrate the physics controlling the evolution of the light curve and especially the secondary maxima seen in infrared photometry.

Theory of Extrasolar Giant Planet Transits

We present a synthesis of physical effects influencing the observed light curve of an extrasolar giant planet (EGP) transiting its host star. The synthesis includes a treatment of Rayleigh scattering, cloud scattering, refraction, and molecular absorption of starlight in the EGP atmosphere. Of these effects, molecular absorption dominates in determining the transit-derived radius R for planetary orbital radii less than a few AU. Using a generic model for the atmosphere of EGP HD 209458b, we perform a fit to the best available transit light-curve data and infer that this planet has a radius at a pressure of 1 bar, R1, equal to 94,430 km, with an uncertainty of ~500 km arising from plausible uncertainties in the atmospheric temperature profile. We predict that R will be a function of wavelength of observation, with a robust prediction of at least ±1% variations at infrared wavelengths where H2O opacity in the high EGP atmosphere dominates.

Airborne spectrophotometry of SN 1987A from 1.7 to 12.6 microns: time history of the dust continuum and line emission

Spectrophotometric observations (1.7-12.6 μm) of SN 1987A from the Kuiper Airborne Observatory are presented for five epochs at 60, 260, 415, 615, and 775 days after the explosion. A variety of emission lines is seen, including members of the hydrogen Humphreys, Pfund, Brackett, and Paschen series, fine-structure lines of metals (including (Ni II] 6.634 μm, (Ni I] 7.507 μm, (Ar II] 6.985 μm, and [Co II] 10.521 μm), and CO and SiO molecular bands. The temporal evolution of the seven strongest H lines follows case C recombination theory and yields large values of τ(Hα) at 260 and 415 days. A mass of ∼ 2 × 10 −3 M ○. is derived for stable nickel, and the ratio of the [Ni I] 7.507 μm and [Ni II] 6.634 μm line intensities yields a high ionization fraction of 0.9 in the nickel zone

The Physics of Type Ia Supernova Light Curves. I. Analytic Results and Time Dependence

We develop an analytic solution of the radiation transport problem for Type Ia supernovae (SNe Ia) and show that it reproduces bolometric light curves produced by more detailed calculations under the assumption of a constant-extinction coefficient. This model is used to derive the thermal conditions in the interior of SNe Ia and to study the sensitivity of light curves to various properties of the underlying supernova explosions. Although the model is limited by simplifying assumptions, it is adequate for demonstrating that the relationship between SNe Ia maximum-light luminosity and rate of decline is most easily explained if SNe Ia span a range in mass. The analytic model is also used to examine the size of various terms in the transport equation under conditions appropriate to maximum light. For instance, the Eulerian and advective time derivatives are each shown to be of the same order of magnitude as other order v/c terms in the transport equation. We conclude that a fully time-dependent solution to the transport problem is needed in order to compute SNe Ia light curves and spectra accurate enough to distinguish subtle differences of various explosion models.

Optical and Infrared Spectroscopy of SN 1999ee and SN 1999ex

We report optical and infrared spectroscopic observations of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both of which were hosted by the galaxy IC 5179. For SN 1999ee we obtained a continuous sequence with an unprecedented wavelength and temporal coverage beginning 9 days before maximum light and extending through day 42. Before maximum light SN 1999ee displayed a normal spectrum with a strong Si II λ6355 absorption, thus showing that not all slow-declining supernovae (SNe) are spectroscopically peculiar at these evolutionary phases. A comparative study of the infrared spectra of SN 1999ee and other Type Ia SNe shows that there is a remarkable homogeneity among the Branch-normal SNe Ia during their first 60 days of evolution. SN 1991bg–like objects, on the other hand, display spectroscopic peculiarities at infrared wavelengths. SN 1999ex was characterized by the lack of hydrogen lines, weak optical He I lines, and strong He I λλ10830, 20581, thus providing an example of an intermediate case between pure Ib and Ic supernovae. We conclude, therefore, that SN 1999ex provides the first clear evidence for a link between the Ib and Ic classes and that there is a continuous spectroscopic sequence ranging from the He-deficient SNe Ic to the SNe Ib, which are characterized by strong optical He I lines.

A New Algorithm for Supernova Neutrino Transport and Some Applications

We have developed an implicit, multigroup, time-dependent, spherical neutrino transport code based on the Feautrier variables, the tangent-ray method, and accelerated ? iteration. The code achieves high angular resolution, is good to O(v/c), is equivalent to a Boltzmann solver (without gravitational redshifts), and solves the transport equation at all optical depths with precision. In this paper, we present our formulation of the relevant numerics and microphysics and explore protoneutron star atmospheres for snapshot postbounce models. Our major focus is on spectra, neutrino-matter heating rates, Eddington factors, angular distributions, and phase-space occupancies. In addition, we investigate the influence on neutrino spectra and heating of final-state electron blocking, stimulated absorption, velocity terms in the transport equation, neutrino-nucleon scattering asymmetry, and weak magnetism and recoil effects. Furthermore, we compare the emergent spectra and heating rates obtained using full transport with those obtained using representative flux-limited transport formulations to gauge their accuracy and viability. Finally, we derive useful formulae for the neutrino source strength due to nucleon-nucleon bremsstrahlung and determine bremsstrahlungs influence on the emergent ?? and ?? neutrino spectra. These studies are in preparation for new calculations of spherically symmetric core-collapse supernovae, proto-neutron star winds, and neutrino signals.

Hard emission at late times from SN 1987A

A model for the explosion that has been successful in predicting and explaining the evolution of SN 1987A during its first one and one-half years is used to calculate the future photometric evolution of the supernova in the UV-optical-IR, X-ray, and gamma-ray bands using Monte Carlo techniques. Special attention is given to the contribution from radioactive isotopes other than Co-56, notably Co-57, Ti-44, and Na-22, and to the possible appearance, probably within the next year, of X-rays from an accreting magnetic neutron star at the center of the supernova. The signature of a radio pulsar like the Crab is also considered. In both cases the time history of the bolometric light curve may be a more sensitive diagnostic than the existence of either pulses or hard emission, but will become confused in the near future by contributions from the rare radioactivities. A source as faint as the pulsed emission of the Crab pulsar will never be discernable in the bolometric light curve. Pulsed hard emission is best sought near 30 keV near the end of 1989 (and thereafter), although more sensitive instrumentation than hitherto employed may be necessary. 75 refs.