List of Past LMA/CARMA Seminars : 01-Sep-1999 to 31-Dec-1999

Date:   Thu 09-Sep-1999
Speaker:   Xiaolei Zhang
Title:   "The Role of Spiral Density Wave to the Secular Evolution of Disk Galaxies and the Galactic Interstellar Medium"

Date:   Thu 23-Sep-1999
Speaker:   Kip Kuntz (Goddard)
Title:  "Deconstructing the Spectrum of the Soft X-ray Background"

Abstract: The soft X-ray background in the 0.1-1.0 keV band is known to be produced by at least three sources; the Local Hot Bubble, the extragalactic power law, and a seemingly galactic component that lies outside the bulk of the absorption that is due to the ISM of the galactic disk. This last component, which we call the Trans-Absorption Emission (TAE), has been modeled by a number of groups who have derived disparate measures of its temperature. The differences have arisen from differing assumptions about the structure of the emitting gas and unrecognized methodological difficulties. In particular, spectral fitting methods do not uniquely separate the TAE from the foreground emission that is due the Local Hot Bubble. This ``degeneracy'' can be resolved using the spatial variation of the absorption of the TAE.

We show that the TAE cannot be characterized by a single thermal component; no single-component model can be consistent with both the spectral energy distribution of the TAE emission {\it and} the spatial variation due to absorption by the galactic disk. We use the spatial anticorrelation of the \rosat\ All-Sky Survey with the galactic absorption to separate local from distant emission components, and to fit the spectral energy distribution of the resulting distant emission. We find that the emission is best described by a two-thermal -component model with $\log T_S = 6.08^{+0.11}_{-0.17}$ and $\log T_H = 6.47^{+0.14}_{-0.13}$. This two-thermal-component TAE fits the \rosat\ spectral energy distribution significantly better than single-component models, and is consistent with {\it both} spatial variation and spectral constraints.

Date:   Tue 12-Oct-1999
Speaker:   Tony Wong (Berkeley)
Title:   "Gas Flows and Star Formation in NGC 4736: A Case Study for BIMA SONG"

Date:   Thu 18-Nov-1999
Speaker:   Floris van der Tak (Leiden)
Title:   "The physical structure of YSO envelopes"

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