Physics
Scientific paper
Mar 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982phdt........27l&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SAN DIEGO, 1982.Source: Dissertation Abstracts International, Volume: 43-03, Section:
Physics
4
Scientific paper
Infrared spectrophotometry in the wavelength region from 0.85 to 1.4 (mu)m of ten planetary nebulae is presented. Line strengths were measured for the Paschen lines P(beta) and P(gamma), the {SIII} lines (lamda)9069 and (lamda)9532, and HeI (lamda)10830. In agreement with previous studies, a discrepancy is found between the measured ratio of the (lamda)10830 to (lamda)5876 helium triplet line fluxes and the theoretically predicted values. The discrepancy does not appear to result from photoionization of 2('3)S by the diffuse Ly(alpha) flux, but can be explained with a model in which the dust optical depth in the nebula, and resulting attenuation of resonantly-scattered (lamda)10830 photons, decreases with nebular expansion. Helium (lamda)10830 triplet line fluxes were measured in eight Sy1 galaxies, 3 QSO's, and two Sy2 galaxies. The (lamda)10830 fluxes are compared with published triplet (lamda)5876 line fluxes. The ratio of (lamda)10830 to (lamda)5876 is calculated for the physical conditions expected in the individual objects, and found compatible with the ratios measured in the Sy2 galaxies, but incompatible with those measured in Sy1 galaxies and QSO's. Because the observed (lamda)10830 strengths relative to (lamda)5876 are considerably smaller in Sy1 galaxies and QSO's than the expected values, significant reddening of the broad line ratios is probably not present. The possibility of absorption of resonantly scattered (lamda)10830 photons by dust internal to the emission line region leading to a reduction of the (lamda)10830/(lamda)5876 ratios in Sy1 galaxies and QSO's is shown unlikely. However, (lamda)10830 emission under optically thick conditions is found able to reproduce the (lamda)10830/(lamda)5876 ratios observed in Sy1 galaxies and QSO's, for "typical" electron densities (n(,e(, ))>(, )10('7) cm('-3)), and large (lamda)10830 optical depths ((tau) > 1200). Ratios of (lamda)5876/H(beta) larger than the recombination value are compatible with the measured (lamda)10830/(lamda)5876 interpreted with optically thick (lamda)10830 emission, with a normal helium abundance. A possible evolutionary relationship between Sy1 and Sy2 galaxies is suggested by a comparison of (lamda)10830 line luminosities with integrated non-thermal continuum luminosities. Optically thick radiative transfer calculations for a hydrogen and helium model atmosphere are presented to consider the possibility of reproducing both the observed Ly(alpha)/H(alpha) and (lamda)10830/(lamda)5876 ratios. The measured ratios may be simultaneously produced at n(,e) = 2.5 x 10('9) cm('-3) and T = 15,000 K, for Lyman continuum optical depths near 10('3). However, the strengths of the helium lines relative to the hydrogen lines suggest densities higher than 2.5 x 10('9) cm('-3).
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