[en] Results are reported of an IR photometry study of 18 Parkes flat spectrum radio sources, which was undertaken without regard to optical morphology to test the recent suggestion of the existence of a new class of quasars with IR excess more extreme than that of any extragalactic object. It was found that the red sources are just the tail of the normal distribution of quasar colours and the results imply that a considerable fraction of flat spectrum sources from complete samples may have properties similar to the BL Lac objects. (U.K.)

[en] Optical polarimetry is presented for 163 radio-selected quasars, including a complete sample of 90 sources stronger than 2 Jy at 5 GHz. Synchrotron components are detected in over 30 percent of these flat spectrum quasars, with an optical polarization threshold of p greater than 3 percent. The fraction of polarized quasars is a strong function of the compactness of the radio emission, as measured on VLBI scales. Including the duty cycle correction, essentially every quasar with S(core) greater than S(ext) at radio wavelengths has a prominent blazar component at optical wavelengths. Virtually all of the radio sources with weak emission lines (or BL Lac objects) are highly polarized. Optical and radio polarization are not correlated, and there is no difference in the alpha(ro) distributions of high- and low-polarization quasars, or sources with strong and weak emission lines. Redshift information is incomplete, but BL Lac objects appear to have lower redshifts than strong-lined quasars. 76 refs

[en] Near-infrared photometry in several apertures has been obtained for eight low redshift extragalactic radio sources. The measurements in the J, H and K bands isolate the central regions of the galaxies identified with these sources, covering a range of -0.17 < log A/D(0) <-1.42. Four of these objects are strong extended sources from the 3CR sample, and three are BL Lac objects with compact radio structure. These seven sources are all identified with E or SO systems. The final object is 3C 305, the only double-lobed 3C radio source to be identified with a spiral galaxy. For the 3C sources, there is no indication of a non-thermal component even through the smallest apertures. However, two of them show central 2.2 μm fluxes in excess of those predicted from the radial flux gradient (curve-of-growth) for normal ellipticals. The BL Lac objects show a range in the relative proportions of non-thermal and galaxian flux, from power law to normal elliptical spectrum. In one object where the non-thermal component is resolved, the annular flux has the colours of a normal elliptical galaxy. There is no evidence in any of these objects that the violent nuclear activity affects the colours of the surrounding galaxy. (author)

[en] Optical polarimetry of a complete sample of radio sources has led to the discovery of 31 blazars and the confirmation of five others. Some of the new blazars are shown to have large redshifts and to be optically faint. It is found that there are equal numbers of objects with strong and weak emission lines, with the weak-lined objects having the largest ratios of optical to radio power. Evidence is provided for an unprecedented pair of polarized objects, only one of which is a radio source. 28 references

[en] This paper presents observations of 162 blazars, over one-half of which were detected with data from the IRAS satellite using a coadded survey and pointed observations. The far-IR data were combined with published data at other wavelengths to complete 93 energy distributions from 10 to the 8th to 10 to the 18th Hz. The IRAS data were used to search for variability on time scales of 3-9 months in 24 objects. The detection rate of variability found for blazars was nearly 40 percent, as compared with a complete absence of detected variability in data sets for quasars and Seyfert galaxies. The range of variability in both spectral index and flux density increases with decreasing wavelength. Half of the blazars with total luminosities less than 10 to the 12th solar luminosity show evidence for thermal IR component. The global energy budget of blazars is dominated by IR emission from 1 to 100 microns. 56 references

[en] An IR survey of radio galaxies in the Bologna B2 catalog is reported. It is found that 40 percent of the sample has IR luminosities of at least one billion solar luminosities, as opposed to about 8 pecent of normal ellipticals. The galaxies are inhomogeneous in their IR properties. The most IR-luminous galaxies are those listed as peculiar by Zwicky. Statistically, these galaxies are strikingly different from Seyfert galaxies in their IR properties in that they show much more radio emission in comparison with their IR emission than do Seyferts, even when the emission from the extended radio lobes has been discounted. 51 refs

[en] Simultaneous infrared and optical polarimetry and photometry have been obtained for AO 0235 + 164 covering a five night period. The object underwent a polarization burst during which the 2.2 μm polarization rose from 17.5 to 28.7 per cent and fell again to 14.9 per cent. At its peak the degree of optical polarization was 43.9 per cent, the highest linear polarization observed in a BL Lac object. The data show the degree of polarization to increase towards shorter wavelengths, and the effect is inconsistent with either dilution by a galactic component or simple one-component synchrotron models. The large changes in polarization are not accompanied by large changes in flux, a result which is difficult to explain using conventional models of these objects. Other implications of the luminosity, polarization and variability are discussed. (author)

[en] Infrared polarimetry and photometry have been obtained for a sample of 18 BL Lac objects. The data covers a period of one year and is part of a continuing monitoring programme; all observations were in the J,H and K wavebands. Large and variable degrees of polarization are a common property of the sample. Two BL Lac objects show wavelength-dependent polarization, with the polarization increasing towards shorter wavelengths, and two objects show evidence for position angle rotations over a five-day period. The relationship between changes in polarized and total flux is also discussed. The BL Lac objects cover an enormous range of infrared luminosity; the three most luminous having Lsub(IR) > 10⁴⁶ erg s^-1 and the other end of the range having infrared luminosities similar to normal elliptical galaxies. These are the first published infrared polarimetric observations for eight of the sample. (author)

[en] The compact core of 3C 273 has been studied for over two years using optical photometry and accurate polarimetry. A wealth of polarization behavior, including variable polarization, observed at a level of under 1 percent is described. The results indicate that 3C 273 harbors a weak continuum component having all the characteristic properties of blazars. It is predicted that other compact radio sources with low optical polarization will also be found to harbor miniblazars. The detection of variable polarization in 3C 273 strengthens the link between superluminal motion at radio wavelengths and blazar activity at optical wavelengths. 76 refs

[en] Observations of the BL Lac object OJ287 were made simultaneously at infrared JHK wavelengths and in optical and near infrared wavelengths at UBVRI in 1983 January. These observations, of total flux reaching a peak and then decaying, and of complex polarization changes, are explained in terms of a model of a jet emanating from an accretion disc. (author)