Application of line transfer calculations to active nuclei and novae

Journal Article · Sun Apr 01 04:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156952· OSTI ID:6216510

Ferland, G; Netzer, H

We apply Monte Carlo calculations to realistic nebulae in order to study the effects of internal dust and level-2 population on the observed spectrum. We show that severe L..cap alpha.. trapping is obtained in all cases, and penetration of line photons to optical depths as large as 10/sup 7/ is common. We use photoionization calculations to mimic the photon generating function in quasars and other gaseous nebulae, and show that level-2 population is concentrated deep in the cloud, due to trappping and some collisional excitation of L..cap alpha... We calculate the Balmer optical depth and give simple formulae to deduce it in different situations. The optical depth tau/sub Halpha/ can reach a very large value, but an effective optical depth 8--15 times smaller must be used when calculating Balmer self-absorption. We use our results to study the collisional excitation of Balmer lines, the level-2 ionization by L..cap alpha.., and thermalization. The last cannot amount to more than approx.30% destruction of L..cap alpha.. under typical active nuclei conditions (N/sub e/<10/sup 10/ cm/sup -3/) and cannot therefore explain the anomalous observed L..cap alpha../H..beta... we study the destruction of L..cap alpha.. and some metallic lines like C IV lambda1549 in nebulae containing dust, and give their destruction as a function of both the dust and the line optical depths. Severe destruction of L..cap alpha.. can occur, but observed line ratios like He II lambda1640/L..cap alpha.. suggest that the amount of internal dust in QSOs is small; and if it is the only attenuation mechanism, then L..cap alpha../H..beta..> or approx. = 15. External dust may be more important. Synthetic QSO spectra are shown for cases of internal dust with different dust/gas ratios. In an appendix we apply some results to novae, and show that they can nicely explain the observed H..cap alpha../H..beta.. and O I lambda8446 in V1500 Cygni. The calculations demonstrate the importance of using realistic ionization structure and dust properties in investigating line trapping and destruction.

• Research Organization: McDonald Observatory and Department of Astronomy, University of Texas at Austin
• OSTI ID: 6216510
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 229:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BALMER LINES
COSMIC RADIO SOURCES
ELEMENTARY PARTICLES
ENERGY LEVELS
ENERGY SPECTRA
ERUPTIVE VARIABLE STARS
GALAXIES
IONIZATION
LYMAN LINES
MASSLESS PARTICLES
MONTE CARLO METHOD
NEBULAE
NOVAE
OPACITY
OPTICAL PROPERTIES
PHOTONS
PHYSICAL PROPERTIES
QUASARS
SPECTRA
STARS
VARIABLE STARS