Enhanced effects of starlight on the interstellar medium

The photodesorption of molecules and atoms from the surfaces of interstellar grains can be an important source of heating for the interstellar medium and the origin of instabilities which may separate grains and gas. For low densities, the force exerted on the grains is proportional to the gas density and independent of the radiation intensity; for high densities, it is proportional to the radiative flux and independent of the gas density. This force may act differently on grains of different sizes. The photoelectric effect may also be an efficient mechanism for the separation of gas and dust in diffuse clouds

Theory of the continuous spectrum of gaseous nebula of pure hydrogen

It has been studied the formation of the continuum of nebular hydrogen when ionization is due to radiation and to collisions. Two photon emission and continuous emissivity in the reaction of formation of H- have been included. The continuum results extremely sensitive to the relative amount of the two types of thermal excitation.Asociación Argentina de Astronomí

Theory of the continuous spectrum of gaseous nebula of pure hydrogen

It has been studied the formation of the continuum of nebular hydrogen when ionization is due to radiation and to collisions. Two photon emission and continuous emissivity in the reaction of formation of H- have been included. The continuum results extremely sensitive to the relative amount of the two types of thermal excitation.Asociación Argentina de Astronomí

Statistical Time-Dependent Model for the Interstellar Gas

We present models for temperature and ionization structure of low, uniform-density (n ~ 0.3 cm^-3) interstellar gas in a galactic disk which is exposed to soft X-rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction x, temperature T, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas with structure in x, T that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (T ~ 30° K), ionized (x ~ 0.1) regions

Ionization of Carbon and Nitrogen in The Intercloud Medium

If the intercloud medium in the solar neighborhood was suddenly ionized less than 106 years ago, the subsequent relaxation of the gas can account for the very low observed column density of C III and N III yet still leave a significant fraction ( \u270.05) of ionized hydrogen and of C I in a cold (T ≈ 20° K) intercloud medium. The OAO-C Copernicus observations in the direction of X Sco are consistent with cosmic abundances and a uniform-density medium, except for C III whose predicted column density from the C m ionization zone surrounding the star is a factor ~1Q greater than the observed result

Collisional excitation in nebulae and symbiotic variables

It is proposed that the temperature simulation effect for the continuum of gaseous envelopes which are collisionally excited may explain the spectra of symbiotic objects such as Ag Pegasi. So it would not be necessary to postulate the binary structure for all the symbiotic objects. It has been found that in the case of AG Pegasi the binary hypothesis and the single object hypothesis are equivalent.Asociación Argentina de Astronomí

Ultraviolet excess in peculiar galaxies

The two colour diagram for the continuum of the Seyfert galaxies has been calculated with a two component model; a stellar component identical to that of the giant elliptical galaxies and the radiation of a gaseous component excited by thermal collisions. It is found that the continuum of several of the Seyfert galaxies (NGC 4151, 3C 120 and NGC 3516) fall in this region of the diagram. For NGC 4151 the observed continuum variations would indicate that the emission is purely thermal.Asociación Argentina de Astronomí

Ultraviolet excess in peculiar galaxies

The two colour diagram for the continuum of the Seyfert galaxies has been calculated with a two component model; a stellar component identical to that of the giant elliptical galaxies and the radiation of a gaseous component excited by thermal collisions. It is found that the continuum of several of the Seyfert galaxies (NGC 4151, 3C 120 and NGC 3516) fall in this region of the diagram. For NGC 4151 the observed continuum variations would indicate that the emission is purely thermal.Asociación Argentina de Astronomí

Ultraviolet excess in peculiar galaxies

The two colour diagram for the continuum of the Seyfert galaxies has been calculated with a two component model; a stellar component identical to that of the giant elliptical galaxies and the radiation of a gaseous component excited by thermal collisions. It is found that the continuum of several of the Seyfert galaxies (NGC 4151, 3C 120 and NGC 3516) fall in this region of the diagram. For NGC 4151 the observed continuum variations would indicate that the emission is purely thermal.Asociación Argentina de Astronomí

Collisional excitation in nebulae and symbiotic variables

It is proposed that the temperature simulation effect for the continuum of gaseous envelopes which are collisionally excited may explain the spectra of symbiotic objects such as Ag Pegasi. So it would not be necessary to postulate the binary structure for all the symbiotic objects. It has been found that in the case of AG Pegasi the binary hypothesis and the single object hypothesis are equivalent.Asociación Argentina de Astronomí