1,093 research outputs found
The chemical composition of normal stellar atmospheres
Spectroscopic analysis of stellar atmosphere chemical compositio
Planetary nebulae and the interstellar medium
In addition to available published data on planetary nebulae (PN), some 40 objects largely concentrated towards the galactic center and anticenter regions were included. All were observed with the Lick 3(sup m) telescope and image tube scanner. Abundances of C, N, O, Ne, Cl, and Ar were determined by a procedure in which theoretical models were used to obtain ionization correction factors (ICF). Of the 106 PN, 66 are N-rich and 40 are N-poor. There appear to be no significant differences between the average compositions in the solar neighborhood and the average taken over the entire observable portion of the galaxy
Analysis of high excitation planetary nebulae
Combination of extensive ground-based spectroscopic observation of high excitation planetary with IUE data permit determination not only of improved diagnostics but also better abundances for elements such as C and N that are well represented in the ultraviolet spectra and also C, Ar and metals Na, Ca and K whose lines appear in the wavelength 3200-8100 A region
Studies of the Solar System and Probable Lunar Abundances of Elements of Geochemical and Metallurgical Significance Status Report
Lunar abundances of elements of geochemical and metallurgical significanc
Dual-Frequency VSOP Observations of AO 0235+164
AO 0235+164 is a very compact, flat spectrum radio source identified as a BL
Lac object at a redshift of z=0.94. It is one of the most violently variable
extragalactic objects at both optical and radio wavelengths. The radio
structure of the source revealed by various ground-based VLBI observations is
dominated by a nearly unresolved compact component at almost all available
frequencies.
Dual-frequency space VLBI observations of AO 0235+164 were made with the VSOP
mission in January-February 1999. The array of the Japanese HALCA satellite and
co-observing ground radio telescopes in Australia, Japan, China and South
Africa allowed us to study AO 0235+164 with an unprecedented angular resolution
at frequencies of 1.6 and 5 GHz. We report on the sub-milliarcsecond structural
properties of the source. The 5-GHz observations led to an estimate of T_B >
5.8 x 10^{13} K for the rest-frame brightness temperature of the core, which is
the highest value measured with VSOP to date.Comment: 8 pages, 8 figures, to appear in Publ. Astron. Soc. Japa
Doppler Boosting, Superluminal Motion, and the Kinematics of AGN Jets
We discuss results from a decade long program to study the fine-scale
structure and the kinematics of relativistic AGN jets with the aim of better
understanding the acceleration and collimation of the relativistic plasma
forming AGN jets. From the observed distribution of brightness temperature,
apparent velocity, flux density, time variability, and apparent luminosity, the
intrinsic properties of the jets including Lorentz factor, luminosity,
orientation, and brightness temperature are discussed. Special attention is
given to the jet in M87, which has been studied over a wide range of
wavelengths and which, due to its proximity, is observed with excellent spatial
resolution.
Most radio jets appear quite linear, but we also observe curved non-linear
jets and non-radial motions. Sometimes, different features in a given jet
appear to follow the same curved path but there is evidence for ballistic
trajectories as well. The data are best fit with a distribution of Lorentz
factors extending up to gamma ~30 and intrinsic luminosity up to ~10^26 W/Hz.
In general, gamma-ray quasars may have somewhat larger Lorentz factors than non
gamma-ray quasars. Initially the observed brightness temperature near the base
of the jet extend up to ~5x10^13 K which is well in excess of the inverse
Compton limit and corresponds to a large excess of particle energy over
magnetic energy. However, more typically, the observed brightness temperatures
are ~2x10^11 K, i.e., closer to equipartition.Comment: 10 pages, 12 color figures; proceedings of the 5th Stromlo Symposium:
Disks, Winds, and Jets - from Planets to Quasars; accepted in Astrophysics &
Space Scienc
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