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Near- and mid-infrared imaging polarimetry of NGC 1068
We present the results of a series of observations of the near- andmid-infrared polarization properties of the type 2 Seyfert galaxy NGC1068. Our data agree well with previously published results in showingthe need for a separate polarization mechanism in the near-infraredapart from scattering. We find that the predictions of a simple model inwhich this component arises through absorptive dichroism caused byaligned grains within the extended warm (~ 400 K) dust fit the datareasonably if the obscured background source is itself the result ofdust emission (at temperature >1000 K). By considering the change ofpolarization with wavelength we show that the extinction to this hotdust region is in the range A_V=20-40. Consideration of the observeddata then leads us to the conclusion that, if viewed face-on, NGC 1068would have a strong near-infrared excess similar to type 1 Seyfertgalaxies. Comparison with other independent measures of the extinctionto the active nucleus itself leads us to the conclusion that the hotdust must provide screening equivalent to at least A_V=40, and possiblymuch higher. We speculate that this component alone may be the`classical' torus discussed in terms of the unified model, and the moreextensive mid-infrared emission may arise from circumnuclear molecularcloud material, and dust in the ionization cones.
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| Fainter Southern JHK Standards Suitable for Infrared Arrays
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995MNRAS.276..734C&db_key=AST
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