A Search for Candidate Light Echoes: Photometry of Supernova Environments

Supernova (SN) light echoes could be a powerful tool for determining distances to galaxies geometrically, Sparks 1994. In this paper we present CCD photometry of the environments of 64 historical supernovae, the first results of a program designed to search for light echoes from these SNe. We commonly find patches of optical emission at, or close to, the sites of the supernovae. The color distribution of these patches is broad, and generally consistent with stellar population colors, possibly with some reddening. However there are in addition patches with both unusually red and unusually blue colors. We expect light echoes to be blue, and while none of the objects are quite as blue in V-R as the known light echo of SN1991T, there are features that are unusually blue and we identify these as candidate light echoes for follow-on observations.Comment: 13 pages, Latex, 5 Postscript Tables, 42 Postscript figures, accepted for publication in the A&AS. Figures 1 through 36 are available at the web address: http://www.stsci.edu/~boffi

Cryogenic thermocouple calibration tables

Thermocouple calibration standards are developed for low-temperature thermocouple materials. Thermovoltage, thermopower, and the thermopower derivative are presented in tabular and graphical form

A stress-controlled mechanism for the intensity of very large magnitude explosive eruptions

Large magnitude explosive eruptions are the result of the rapid and large-scale transport of silicic magma stored in the Earth's crust, but the mechanics of erupting teratonnes of silicic magma remain poorly understood. Here, we demonstrate that the combined effect of local crustal extension and magma chamber overpressure can sustain linear dyke-fed explosive eruptions with mass fluxes in excess of 10^10 kg/s from shallow-seated (4–6 km depth) chambers during moderate extensional stresses. Early eruption column collapse is facilitated with eruption duration of the order of few days with an intensity of at least one order of magnitude greater than the largest eruptions in the 20th century. The conditions explored in this study are one way in which high mass eruption rates can be achieved to feed large explosive eruptions. Our results corroborate geological and volcanological evidences from volcano-tectonic complexes such as the Sierra Madre Occidental (Mexico) and the Taupo Volcanic Zone (New Zealand)

Low radiative efficiency accretion at work in active galactic nuclei: the nuclear spectral energy distribution of NGC4565

We derive the spectral energy distribution (SED) of the nucleus of the Seyfert galaxy NGC4565. Despite its classification as a Seyfert2, the nuclear source is substantially unabsorbed. The absorption we find from Chandra data (N_H=2.5 X 10^21 cm^-2) is consistent with that produced by material in the galactic disk of the host galaxy. HST images show a nuclear unresolved source in all of the available observations, from the near-IR H band to the optical U band. The SED is completely different from that of Seyfert galaxies and QSO, as it appears basically ``flat'' in the IR-optical region, with a small drop-off in the U-band. The location of the object in diagnostic planes for low luminosity AGNs excludes a jet origin for the optical nucleus, and its extremely low Eddington ratio L_o/L_Edd indicates that the radiation we observe is most likely produced in a radiatively inefficient accretion flow (RIAF). This would make NGC4565 the first AGN in which an ADAF-like process is identified in the optical. We find that the relatively high [OIII] flux observed from the ground cannot be all produced in the nucleus. Therefore, an extended NLR must exist in this object. This may be interpreted in the framework of two different scenarios: i) the radiation from ADAFs is sufficient to give rise to high ionization emission-line regions through photoionization, or ii) the nuclear source has recently ``turned-off'', switching from a high-efficiency accretion regime to the present low-efficiency state.Comment: 7 pages, 6 figures, accepted for publication in the Astrophysical Journa

Polarization Diagnostics for Cool Core Cluster Emission Lines

The nature of the interaction between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields, and suprathermal particles. Under certain physical conditions, theoretical calculations predict of the order of 10% polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits ( 0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfacesPeer reviewe

The Effects of Changes in Reaction Rates on Simulations of Nova Explosions

Classical novae participate in the cycle of Galactic chemical evolution in which grains and metal enriched gas in their ejecta, supplementing those of supernovae, AGB stars, and Wolf-Rayet stars, are a source of heavy elements for the ISM. Once in the diffuse gas, this material is mixed with the existing gases and then incorporated into young stars and planetary systems during star formation. Infrared observations have confirmed the presence of carbon, SiC, hydrocarbons, and oxygen-rich silicate grains in nova ejecta, suggesting that some fraction of the pre-solar grains identified in meteoritic material come from novae. The mean mass returned by a nova outburst to the ISM probably exceeds ~2 x 10^{-4} Solar Masses. Using the observed nova rate of 35 per year in our Galaxy, it follows that novae introduce more than ~7 x 10^{-3} Solar Masses per year of processed matter into the ISM. Novae are expected to be the major source of 15N and 17O in the Galaxy and to contribute to the abundances of other isotopes in this atomic mass range. Here, we report on how changes in the nuclear reaction rates affect the properties of the outburst and alter the predictions of the contributions of novae to Galactic chemical evolution. We also discuss the necessity of including the pep reaction in studies of thermonuclear runaways in material accreted onto white dwarfs.Comment: 9 pages, 2 figures, as it appeared in the Proceedings of the Tours 2006 Symposium on Nuclear Physic

Available low temperature thermocouple information and services

Voltage vs temperature data for thermocouple pairs at low temperatures - cryogenic temperatur

Battery workshop

The workshop was attended by representatives from industry and government. The requirements for energy storage and the plans for battery development were reviewed. The workshop followed a debate format, with the objective of recommending improvements to the development plans presented by NASA and the Air Force. The issues addressed were: (1) significant technology deficiencies which can be identified; (2) adequacy of current and proposed programs to resolve the technology deficiencies identified; (3) additional tasks which should be undertaken, including benefits and timing; and (4) lowest priority items in the presently planned program, both in content and in timing

Carbon thin film thermometry

The work concerning carbon thin film thermometry is reported. Optimum film deposition parameters were sought on an empirical basis for maximum stability of the films. One hundred films were fabricated for use at the Marshall Space Flight Center; 10 of these films were given a precise quasi-continuous calibration of temperature vs. resistance with 22 intervals between 5 and 80 K using primary platinum and germanium thermometers. Sensitivity curves were established and the remaining 90 films were given a three point calibration and fitted to the established sensitivity curves. Hydrogen gas-liquid discrimination set points are given for each film