Airborne 20-65 micron spectrophotometry of Comet Halley

Observations of Comet Halley with a grating spectrometer on board the Kuiper Airborne Observatory on four nights in Dec. 1985 to Apr. 1986 are reported. Low resolution 20 to 65 micrometer spectra of the nucleus with a 40 arcsec FWHM beam was obtained on 17 Dec. 1985, and on 15 and 17 Apr. 1986. On 20 Dec. 1985, only a 20 to 35 micrometer spectrum was obtained. Most of the data have been discussed in a paper where the continuum was dealt with. In that paper, models were fit to the continuum that showed that more micron sized particles of grain similar to amorphous carbon were needed to fit the spectrum than were allowed by the Vega SP-2 mass distribution, or that a fraction of the grains had to be made out of a material whose absorption efficiency fell steeper than lambda sup -1 for lambda greater than 20 micrometers. Spectra was also presented taken at several points on the coma on 15 Apr. which showed that the overall shape to the spectrum is the same in the coma. Tabulated values of the data and calibration curves are available. The spectral features are discussed

X-ray Evidence for Spectroscopic Diversity of Type Ia Supernovae: XMM observation of the elemental abundance pattern in M87

We present the results of a detailed element abundance study of hot gas in M87, observed by XMM-Newton. We choose two radial bins, 1'-3' and 8'-16' (8'-14' for EMOS; hereafter the central and the outer zones), where the temperature is almost constant, to carry out the detailed abundance measurements of O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni using EPIC-PN (EPN) and -MOS (EMOS) data. First, we find that the element abundance pattern in the central compared to the outer zone in M87 is characterized by SN Ia enrichment of a high (roughly solar) ratio of Si-group elements (Si, S, Ar, Ca) to Fe, implying that Si burning in SN Ia is highly incomplete. In nucleosynthesis modeling this is associated with either a lower density of the deflagration-detonation transition and/or lower C/O and/or lower central ignition density and observationally detected as optically subluminous SNe Ia in early-type galaxies. Second, we find that SN Ia enrichment has a systematically lower ratio of the Si-group elements to Fe by 0.2 dex in the outer zone associated with the ICM of the Virgo cluster. We find that such a ratio and even lower values by another 0.1 dex are a characteristic of the ICM in many clusters using observed Si:S:Fe ratios as found with ASCA. Third, the Ni/Fe ratio in the central zone of M87 is 1.5+/-0.3 solar (meteoritic), while values around 3 times solar are reported for other clusters. In modeling of SN Ia, this implies a reduced influence of fast deflagration SN Ia models in the chemical enrichment of M87's ISM. Thus, to describe the SN Ia metal enrichment in clusters, both deflagration as well as delayed detonation scenarios are required, supporting a similar conclusion, derived from optical studies on SNe Ia. Abridged.Comment: 11 pages, A&A, in pres

On the Phase Structure of the Schwinger Model with Wilson Fermions

We study the phase structure of the massive one flavour lattice Schwinger model on the basis of the finite size scaling behaviour of the partition function zeroes. At $\beta = 0$ we observe and discuss a possible discrepancy with results obtained by a different method.Comment: 3 pages (2 figures), POSTSCRIPT-file (174 KB), Contribution to Lattice 93, preprint UNIGRAZ-UTP 19-11-9

The energetics and mass structure of regions of star formation: S201

Theoretical predictions about dust and gas in star forming regions are tested by observing a 4 arcmin region surrounding the radio continuum source in 5201. The object was mapped in two far infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in 5201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far infrared emitting grains, equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources

Far infrared and submillimeter brightness temperatures of the giant planets

The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely

Convection and AGN Feedback in Clusters of Galaxies

A number of studies have shown that the convective stability criterion for the intracluster medium (ICM) is very different from the Schwarzchild criterion due to the effects of anisotropic thermal conduction and cosmic rays. Building on these studies, we develop a model of the ICM in which a central active galactic nucleus (AGN) accretes hot intracluster plasma at the Bondi rate and produces cosmic rays that cause the ICM to become convectively unstable. The resulting convection heats the intracluster plasma and regulates its temperature and density profiles. By adjusting a single parameter in the model (the size of the cosmic-ray acceleration region), we are able to achieve a good match to the observed density and temperature profiles in a sample of eight clusters. Our results suggest that convection is an important process in cluster cores. An interesting feature of our solutions is that the cooling rate is more sharply peaked about the cluster center than is the convective heating rate. As a result, in several of the clusters in our sample, a compact cooling flow arises in the central region with a size R that is typically a few kpc. The cooling flow matches onto a Bondi flow at smaller radii. The mass accretion rate in the Bondi flow is equal to, and controlled by, the rate at which mass flows in through the cooling flow. Our solutions suggest that the AGN regulates the mass accretion rate in these clusters by controlling R: if the AGN power rises above the equilibrium level, R decreases, the mass accretion rate drops, and the AGN power drops back down to the equilibrium level.Comment: 41 pages, 7 figures, accepted for publication in ApJ. Changes in this version: extended discussion of Bondi accretion in clusters, better mass model, new numerical solution

NGC 2024: Far-infrared and radio molecular observations

Far infrared continuum and millimeter wave molecular observations are presented for the infrared and radio source NGC 2024. The measurements are obtained at relatively high angular resolution, enabling a description of the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north/south direction and centered on the dark lane that is seen in visual photographs. Maps of the source using the high density molecules CS and HCN confirm this picture and allow a description of the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1' south of the bright mid infrared source IRS 2. The data presented here allows a presentation of a model for the source

Correlation of N2O and ozone in the Southern Polar vortex during the airborne Antarctic ozone experiment

In situ N20 mixing ratios, measured by an airborne laser spectrometer (ATLAS), have been used along with in situ ozone measurements to determine the correlation of N2O and ozone in the Antarctic stratosphere during the late austral winter. During the 1987 Airborne Antarctic Ozone Experiment (AAOE), N2O data were collected by a laser absorption spectrometer on board the ER-2 on five ferry flights between Ames Research Center (37 deg N) and Punta Arenas, Chile (53 deg S), and on twelve flights over Antarctica (53 S to 72 S). Of all the trace gas species measured by instruments on board the ER-2, only one showed a relationship to the N2O/O3 correlations in the vortex. With few exceptions, positive N20/O3 correlations coincided with total water mixing ratios of greater than 2.9 ppmv, and total water mixing ratios of less than 2.9 ppmv corresponded to negative correlations. The lower water mixing ratios, or dehydrated regions, are colocated with the negative correlations within the vortex, while the wetter regions always occur near the vortex edge