Broad Emission Lines From the Mass-Loss Envelopes of Giant Stars in Active Galactic Nuclei
Abstract
The X-ray and UV luminosity of an active galactic nucleus will irradiate and ionize the mass-loss envelopes of giant stars in the central star cluster of the host galaxy. For a star with mass loss at 10^-5^ M_sun_ yr^-1^ situated 10^18^ cm from the AGN, the inverted Stromgren sphere in the mass-loss envelope will extend down to a radius of 10^14^ cm at which point the density is 10^9^ cm^-3^. We propose that the broad emission-line clouds in active galaxies are the ionized mass-loss envelopes of giant stars with the line widths due to orbital motion in the massive central star cluster. Previous objections to a stellar origin for the broad line regions based on collisional destruction are circumvented by noting that although the giants do collide and their envelopes are removed, the envelopes are replenished within a few years. The required numbers of red giants could be a natural consequence of massive starbursts in the cores of galaxies (Norman and Scoville). Stellar density distributions yielding logarithmic line profiles are explored. The favored model has n_*_ is proportional to d^-3/2^, v_*_ is proportional to r^-1/2^, and M^dot^ is proportional to d^-1^ where d is the distance from the cluster center. These relations should be taken only as best estimates since the observed profiles are only approximately logarithmic. Since the stars which are closer to the central luminosity source are ionized to a greater depth and have high orbital velocities, the model predicts correlations of the line width and time scale for flux variations with the critical density of the observed transition {DELTA}v is proportional to n^0.1^ and τ is proportional to n^-2/3^).
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1988
- DOI:
- 10.1086/166641
- Bibcode:
- 1988ApJ...332..163S
- Keywords:
-
- Active Galactic Nuclei;
- Emission Spectra;
- Red Giant Stars;
- Star Formation;
- Stellar Envelopes;
- Stellar Mass Ejection;
- Density Distribution;
- Late Stars;
- Star Clusters;
- Stellar Luminosity;
- Astrophysics;
- GALAXIES: NUCLEI;
- STARS: FORMATION;
- STARS: LATE-TYPE;
- STARS: MASS LOSS