1996A&A...314..754N

We present the results of deep broadband imaging and spectroscopy of the BL Lac object AO 0235+164 taken during 1994 when the object was in an exceptionally faint state. In addition to the well known southern companion, our images show an elongated galaxy ∼1.3arcsec to the East of AO 0235+164 in agreement with Yanny et al. (1989ApJ...338..735Y) and qualitatively similar to the galaxy detected by Stickel et al. (1988A&A...198L..13S). Our data do not show signs of the bright cD galaxy proposed to be responsible for the z=0.524 absorption by Abraham et al. (1993ApJ...415..101A). The spectrum of AO 0235+164 shows prominent hydrogen lines H_δ and H_γ at the object redshift of 0.94 in addition to the narrow λ3727 [OII] line and possibly λλ3346,3426 [NeV] at the same redshift. The equivalent width of the H_γ line is 7.2 A in the rest frame of AO 0235+164 exceeding the 5A limit set by Stickel et al. for an object to be included in their 1Jy BL Lac sample. At least when at minimum light AO 0235+164 shows spectral characteristics of a high polarization quasar (HPQ). The z=0.524 H_β emission line in the southern galaxy has a broad component with a width of 2500km/s, suggesting that it is an intermediate case between Seyfert 1 and 2 galaxies.