Velocity, redshift and pressure shift of van Maanen 2

The perspective acceleration of the cool white dwarf van Maanen 2 has been measured by van de Kamp. He predicts a radial velocity of +160 km . Vith probable Einstein shift, the expected Doppler shift of +200 km s-l contrasts sharply with the newly measured velocity of Ca ii, +39 + 4 km 1 from 15 spectra. The H-line shows a velocity +29 + 7 km s ' larger than the K-line. A tentative explanation suggested is extreme pressure broadening and the violet shift found in the laboratory for resonance lines of the alkalis with helium perturhers. The relative density, estimated from analogous transitions in the laboratory, is about 50, i.e., a pressure near 1000 atmospheres, in agreement with Weidemann's hydrogenand metal-poor model. There is an apparent additional negative shift of the blended Fe I lines in the ultraviolet.