Please find below the articles related to the oral presentations
sent to us as of August 16, 1999. We still expect the submission of
a number of contributions.
The proceedings will be printed and circulated as soon as all
contributions are received.
R.J. Laureijs and R. Siebenmorgen, Editors
OPTICAL TO MID-INFRARED POLARISATION OF SEYFERT 2 GALAXIES:
A BRIEF REVIEW
D.M. Alexander (1), M. Ruiz (2), J.H. Hough (2)
(1) SISSA, via Beirut 2-4, 34014 Trieste, Italy
(2) Department of Physical Sciences, University of Hertfordshire, Hatfield, Hertfordshire, AL10 9AB, UK
Abstract. We present a brief review of the optical to mid-infrared polarisation characteristics of Seyfert 2 galaxies. We briefly review the unification model for Seyfert galaxies and interpret polarisation observations under this scheme. We discuss the potential importance of our ISOCAM mid-infrared polarisation observations of a selected sample of Seyfert 2 galaxies. We focus on the detailed modelling and observations of NGC1068 and the Circinus galaxy and develop a simple model to predict the mid-infrared polarisation characteristics of our sample of galaxies.
ISO was used to perform far-infrared polarimetry of the thermal dust
emission from the filamentary dark cloud GF9 using the PHT instrument
and C_160 filter. Embedded magnetic fields within the GF9 cloud
were sought using linear polarization probes of a dense core region, a
diffuse filamentary region, and two reference regions. The observations
utilized the ISOPHT C200 2x2 pixel camera and took the form of small,
overlapping raster maps with each central sky position being viewed by
each of the camera pixels.
The magnetic fields contained within this dark cloud were directly detected -- the first such detections using space-based techniques. Polarized dust emission was detected from the dense core, the filament, and one reference region. The average degree of polarization found was about 5%. The polarization properties of the two regions within the GF9 cloud are completely different, however. The star-forming dense core (containing the Class 0 source IRAS PSC 20503+6006) shows exceedingly parallel polarization vectors, revealing a highly uniform embedded magnetic field. The non-star forming filament shows very disordered magnetic field directions, possibly indicating that magnetic turbulence may be important in supporting some dense cores against collapse.
Abstract. M4 is a Small Explorer (SMEX) concept for a dedicated space-borne far-infrared imaging polarimeter satellite, which was proposed to NASA in 1997 and which will be proposed again in the upcoming SMEX competition planned for the end of this year. When flown, M4 will be the first mission to conduct large-area surveys of the magnetic field directions and structures in the dense interstellar medium of the Milky Way, nearby star-forming and quiescent dark molecular clouds, and the infrared cirrus. M4 consists of a superfluid helium cooled 20 cm telescope, polarization light analysis optics, and two 32x32 Ge:Ga array detectors operating broadband at 95 microns wavelength. With no moving parts, M4 achieves high photometric and polarimetric sensitivity (S/N=150-600:1) via a novel mix of stepped spacecraft roll maneuvers and frequent recalibration using an internal light source. In its 4 to 6 month lifetime, M4 will map the magnetic field directions of over 1200 square degrees of the Milky Way with 0.8-2 arcmin resolution. The M4 flight plan also calls for a strong Guest Investigator Program of magnetic field mapping of nearby galaxies and Galactic targets.
Abstract ISOPHOT provided unique polarization capabilities in the MIR and FIR. We give an overview of the ISOPHOT polarimetric modes. This includes characteristics of the polarizer hardware, the observation modes, the on-ground and in-orbit calibration, the basic steps in data reduction and the assessment of achievable accuracies. The 1 sigma accuracy of linear polarization is 1 per cent for sources with total fluxes of few Jy. The polarization processes in the IR and targets observed with ISOPHOT are summarized.
Abstract. These proceedings summarize our results obtained from ISOPHOT 170 micron polarization measurements which we published in Klaas et al. (1999), but they also provide a wider overview of the physical context. The OVV quasar 3C 279 is a strong synchrotron source with a one-sided superluminal jet. After a gamma-ray burst in January 1996 we could successfully measure for the first time polarization of this source in the FIR wavelength regime at two epochs, in July 1996 and in June 1997. We found a strong polarization degree of 23% in July 1996, well aligned with the radio jet. Nearly one year later the measured FIR polarization degree had decreased to 6.5% with a less well alignment. We discuss the origin of this polarization and put these findings in the context of the current emission models for 3C 279.
The asteroids (6)Hebe and (9)Metis were observed at 25 micron with
ISOPHOT onboard the Infrared Space Observatory (ISO). The on- and off-source
measurements have been analysed with a special data reduction method to
achieve reliable photometric and polarimetric results. In parallel a
previously established thermophysical model has been extended to cover also
The model absolute fluxes are in good agreement with the photometric results. Although no linear polarization was detected, the upper limits together with the extended model enable us to put useful constraints on the regolith properties of the target asteroids. The derived detection limits are compared to model polarization, by spanning a range in surface roughness, refractive index, and thermal inertia parameter space. The Metis observations favor a low refractive index and high surface roughness, but the Hebe observations are inconclusive since they coincided with a minimum in the polarization curve.
Abstract. Aspherical dust grains in an anisotropic radiation field have different temperatures depending on the cross-sections projected to the radiation. The temperature difference produces polarized thermal emission even without alignment, if the observer looks at the grains from a direction different from the anisotropic radiation. When the dust grains are aligned, the anisotropic radiation makes various affects on the polarization of the thermal emission, depending on the relative angle between the anisotropy and alignment directions. This paper presents examples of the effects and demonstrates the importance of anisotropic radiation field on the polarized thermal emission.
Abstract An overview is given of the ISOCAM polarisation capabilities. The different polarisation modes, necessary steps in the data reduction and the calibration strategy are described. Deep raster observations in various optical configurations on the zodiacal light are presented. By assuming that the zodiacal light is unpolarised we derive the instrumental polarisation and find a mean fractional polarisation of p ~ 1.0+/-0.3%. Measurements of unpolarised standard stars have been performed and here we find for the lw2, 3" lens configuration an instrumental polarisation of p = 1.5+/-0.3%, consistent with the zodiacal light observations. With present processing techniques we achieve for moderately bright targets a 1 sigma = 0.5% accuracy limit of linear polarisation.
Abstract No abstract included in paper.