183 research outputs found
Specific heat of the ideal gas obeying the generalized exclusion statistics
We calculate the specific heat of the ideal gas obeying the generalized
exclusion statistics (GES) in the continuum model and the tight binding model
numerically. In the continuum model of 3-d space, the specific heat increases
with statistical parameter at low temperature whereas it decreases with
statistical parameter at high temperature. We find that the critical
temperature normalized by (Fermi energy) is 0.290. The specific heat of
2-d space was known to be independent of in the continuum model, but it
varies with drastically in the tight-binding model. From its unique
behavior, identification of GES particles will be possible from the specific
heat.Comment: 14 pages, 9 figures, to be published in Eur. Phys. J. B, References
and figures added, typos corrected, one section removed and two sections
merge
The ORFEUS II Echelle Spectrum of HD 93521: A reference for interstellar molecular hydrogen
During the second flight of the ORFEUS-SPAS mission in November/December
1996, the Echelle spectrometer was used extensively by the Principal and Guest
Investigator teams as one of the two focal plane instruments of the ORFEUS
telescope. The spectrum of HD 93521 was obtained during this mission with a
total integration time of 1740 s. This spectrum shows numerous sharp
interstellar absorption lines. We identified 198 lines of molecular hydrogen
including at least 7 lines with a high velocity component. Also most of the 67
identified interstellar metal lines are visible with a high velocity component.
We present plots of the complete ORFEUS Echelle spectrum together with tables
of all identified interstellar absorption lines including all 14 detectable HI
lines. In addition several identified stellar lines, partially with narrow
absorption components, and stellar wind lines are given in a separate table.Comment: 18 pages, 33 figure
Millimetre-VLBI Monitoring of AGN with Sub-milliarcsecond Resolution
Global millimetre VLBI allows detailed studies of the most central jet
regions of AGN with unprecedent spatial resolution of a few 100-1000
Schwartzschild radii to be made. Study of these regions will help to answer the
question how the highly relativistic AGN jets are launched and collimated.
Since the early 1990s, bright mm-sources have been observed with global 3 mm
VLBI. Here we present new images from an ongoing systematic analysis of the
available observations. In particular, we focus on the structure and structural
evolution of the best observed AGN jets, taking 3C 454.3 as a characteristic
example. This core-dominated and highly variable quasar shows a complex
morphology with individual jet components accelerating superluminally towards
the outer structure. We briefly discuss the X-ray properties of 3C 454.3 and
present its radio- to X-ray large-scale brightness distribution.Comment: 4 pages, 4 figures, Proceedings of the 7th EVN Symposium held in
Toledo, Spain in October 2004, needs evn2004.cl
SUMER: Solar Ultraviolet Measurements of Emitted Radiation
The SUMER (solar ultraviolet measurements of emitted radiation) experiment is described. It will study flows, turbulent motions, waves, temperatures and densities of the plasma in the upper atmosphere of the Sun. Structures and events associated with solar magnetic activity will be observed on various spatial and temporal scales. This will contribute to the understanding of coronal heating processes and the solar wind expansion. The instrument will take images of the Sun in EUV (extreme ultra violet) light with high resolution in space, wavelength and time. The spatial resolution and spectral resolving power of the instrument are described. Spectral shifts can be determined with subpixel accuracy. The wavelength range extends from 500 to 1600 angstroms. The integration time can be as short as one second. Line profiles, shifts and broadenings are studied. Ratios of temperature and density sensitive EUV emission lines are established
ORFEUS-II Far-Ultraviolet Observations of 3C273: 1. Interstellar and Intergalactic Absorption Lines
We present the first intermediate-resolution (lambda / 3000) spectrum of the
bright quasi-stellar object 3C273 at wavelengths between 900 and 1200 A.
Observations were performed with the Berkeley spectrograph aboard the
ORFEUS-SPAS II mission. We detect Lyman beta counterparts to
previously-identified intergalactic Lyman-alpha features at cz = 19900, 1600,
and 1000 km/s; counterparts to other putative Lyman-alpha clouds along the
sight line are below our detection limit. The strengths of the two very low
redshift Lyman-beta features, which are believed to arise in Virgo intracluster
gas, exceed preflight expectations, suggesting that the previous determination
of the cloud parameters may underestimate the true column densities. A
curve-of-growth analysis sets a minimum H I column density of 4 E14/cm^2 for
the 1600 km/s cloud. We find marginally significant evidence for Galactic H_2
along the sight line, with a total column density of about 1 E15/cm^2. We
detect the stronger interstellar O VI doublet member unambiguously; the weaker
member is blended with other features. If the Doppler b value for O VI is
comparable to that determined for N V then the O VI column density is 7 +/- 2
E14/cm^2, significantly above the only previous estimate. The O VI / N V ratio
is about 10, consistent with the low end of the range observed in the disk.
Additional interstellar species detected for the first time toward 3C273 (at
modest statistical significance) include P II, Fe III, Ar I, and S III.Comment: LaTeX file, 11 pages, 4 encapsulated PostScript figures. Uses
aaspp4.sty and astrobib.sty. (Astrobib is available from
http://www.stsci.edu/software/TeX.html .) The ORFEUS telescope is described
at http://sag-www.ssl.berkeley.edu/orfeus/ . To appear in ApJ (Letters
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