Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.5207t&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #52.07; Bulletin of the American Astronomical Society, Vol. 24, p.1209
Astronomy and Astrophysics
Astronomy
Scientific paper
The nuclear spectrum of the broad-line Seyfert galaxy Mrk 993 was observed to display strong variations in the strengths of the broad Hβ and Hα emission lines, changing its classification from a Seyfert 1 to a Seyfert 1.9. Moderate to high resolution spectra were obtained with the IDS and CCD spectrograph on the 3 m Shane telescope at Lick Observatory in four different epochs spanning a period of approximately eight years. Using a spectral decomposition method which isolates the pure emission component of the active nucleus from the contaminating underlying host galaxy, our analysis indicates that the broad-line fluxes varied such that the Balmer decrement steepens whenever broad Hα and Hβ decrease in strength, and that the ionizing continuum correspondingly reddens in slope. These direct observational evidences suggest that variation in extinction along the line of sight to the broad-line region of Mrk 993 provides a simple explanation to the behavior of its spectrum, although a combination of possibilities may also be possible.
Martel Andre
Osterbrock Donald E.
Tran Hien D.
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