Wayne A. Stein

0.35-3.5 MICRON PHOTOMETRY OF POLARIZED QSOS.

Visual and infrared photometry of strongly polarized QSOs (BL Lacertae objects) is reported. Spectral flux distributions of these objects are discussed in combination with results from earlier studies. With the exception of the well-resolved galaxies Mkn 421 and Mkn 501 only one object (1218 + 304) has a change in spectral index easily explained by the presence of an underlying galaxy. Six other sources appear to have either a break in their spectra near about 1 micron or a smoother general steepening of their spectra at shorter wavelengths. A spectral break at this wavelength may be attributed to a low flux of nonthermal radiation superimposed on a stellar energy distribution or by nonthermal electron energy losses.

Dust in the nuclei of the Seyfert galaxies Markarian 231 and NGC 4151

Observations carried out with a 8-13 micron grating-spectrometer of Mrk 231 and NGC 4151 are reported. The Mrk 231 data can be fitted to various thermal dust emission models or a single power law, with dust extinction. In all the model fits, except for that of graphite and silicon carbide grain emission, a component of silicate absorption of optical depth of not more than 0.7 is required. Confirming published work, the absorption being at the redshift of the low-redshift absorption-line system is ruled out. The high values of silicate optical depth absorption do not give ratios to the galaxys visual extinction which are comparable to those of galactic H II regions. Weak evidence for a 10-micron absorption feature in NGC 4151 is also reported. This is somewhat contrary to expectation, since the visual extinction of NGC 4151 is lower than that of Mrk 231, and since there is evidence to support a nonthermal rather than thermal dust origin for the infrared continuum emission.

V482 Cygni: an R Coronae Borealis star in a quadruple system

Observations of the R CrB variable star V482 Cyg, obtained with the University of Rochester 32 x 32 InSb array camera at the NASA IR Telescope Facility on Mauna Kea on August 20, 1984, are reported. The data-reduction and analysis procedures are described in detail, and the results are presented in tables and maps. V482 Cyg is shown to be a member of a quadruple system or perhaps a small obscured cluster. Parameters determined include distance 1.7 kpc, circumstellar-shell temperature 800 K, and absolute magnitude MV = -2.8.

The problem of extinction and thermal reradiation by dust in active galactic nuclei and quasi-stellar objects

Published Hα/HΒ ratios and infrared to visual flux ratios are examined as potential diagnostics for dust in Seyfert 1 galaxies, Seyfert 2 galaxies, and QSOs. Hα/β ratio distributions are very broad although some subtle distinctions may be evident among the various classes of objects. The distributions of the ratio of λ ~ 10-micron luminosity to that at visual-ultraviolet wavelengths are more narrow, and clear distinctions are evident among the various types of object. Clearly both Hα/Hβ and infrared emission together help determine the obscuring effects of dust. More homogeneous data are desirable but will require considerably large telescope observing time in order to pursue these results further.

Infrared angular size and the supermassive black hole hypothesis in AGN

Various methods of calculating the angular size of a dust cloud heated by a single central source are reviewed and compared with the observed λ∼10 μm angular size. Seyfert nuclei of NGC1068 and NGC4151 are consistent with this interpretation. However, a number of other central regions of galaxies NGC253, M82,MK171 are observed to be much larger than that expected for a centrally heated cloud implying that the source of heating luminosity is distributed within the volume. Thus, these are examples of regions of enhanced star formation activity. Another object of considerable importance, MK231, has been suggested to be an imbedded QSO. Published limits do not resolve the core of this object. Further work on resolving nuclei of galaxies at infrared wavelengths will be of significance, especially with the new generation of 10m class telescopes.

Accretion disk coronas in QSOs

Radiation pressure on gas in the hypothesized accretion disks of QSOs will result in a corona. Electrons of 340 kev, equivalent to Te∼3×108 K, may result in a significant. Compton optical depth for the implied mass loss rate. Comptonization of ultraviolet to 30 kev may result in contradiction to observations.

The theoretical gamma‐ray spectrum of quasars

Preliminary results of calculations concerning the theoretical γ‐ray spectrum of quasi‐stellar objects is presented with special application to 3C 273. The calculated spectra extent (in γ‐ray energy) from approximately 0.1 to 1000 MeV. In this simple model numerous γ‐ray producing mechanisms resulting from inelastic pp interactions are included to contribute to the total output. These include the decay of neutral pions, electron and positron bremsstrahlung, positron annihilation and the Compton scattering of synchrotron photons. Although very preliminary, the resulting model spectrum seems able to account for the observed spectrum. The emission may arise in various regions in which relativistic protons encounter sufficient quantities of target nuclei in the ambient gas.

Accretion-disk coronae in QSOs

Radiation pressure on gas in the hypothesized accretion disks of QSOs will result in a corona. The coronal temperature will be very high -T > 108^ K. The implied mass loss rate suggests that the Compton optical depth may be large unless some physical process disrupts the mass loss. As a result there may be a problem for observation of the ultraviolet photoionizing continuum since it would be Compton scattered to X-ray energies in contradiction to observations. Accretion disk models should include schemes to disrupt the mass loss if they are to be consistent with observations.

THE OPTICAL ABSORPTION OF SOLID GRAINS IN ASTROPHYSICAL ENVIRONMENTS

The optical absorptivity of grains of solid material in infrared sources is investigated by the comparison of calculated and observed temperatures and distances of the grains from the source of illumination. It is found that for the few sources for which appropriate measurements have been made the calculated distances of blackbody particles agree well with the measured values - a result which could lead to misleading conclusions about grain properties. The ratio of optical absorptivity to infrared emissivity is calculated for several sources taking into account expected effects of real grain materials. The measured angular size of dust shells surrounding stars can lead to information about the optical properties of grains under astrophysical conditions. Key words: interstellar matter - infrared sources