Dust in PG quasars as seen by ISO

Infrared to millimeter spectral energy distributions (SEDs) have been obtai ned for a random sample of 17 Palomar Green quasars. The observations were carried out between 4.8 and 200 mu m with ISO and supplemented for ten sour ces with IRAM at 1.3 mm. Eight sources were detected in the far infrared fo r the first time. The SEDs provide evidence for considerable dust emission and do not support the existence of dust-free, naked quasars. The SEDs rese mble those of warm ultraluminous infrared galaxies (ULIRGs). The SEDs show a variety of shapes (power-law, mid-infrared dominated, and far-infrared do minated), suggesting the influence of different heating mechanisms. The mid - and far-infrared luminosities are correlated, suggesting a dependence bet ween the heating mechanisms. The role of AGNs and starbursts for the dust h eating is discussed, as well as the link between general ULIRGs and dust-en shrouded quasars.