Spectra of the stellar population in three objects related to BL Lacertae.

Results are reported for observations with an intensified image dissector scanner of the nebulosities surrounding the BL Lac objects B2 1101+38 and Markarian 180 as well as of the central region of the galaxy Markarian 11, which is a flat-spectrum radio source. For B2 1101+38 a measurement of the redshift based on spectral scans of the nebulosity confirms the previously obtained value of 0.03. Five galaxies within 15 arcmin of B2 1101+38 are found to have redshifts of approximately 0.03, which adds support to the above value and shows that this BL Lac object belongs to a cluster of galaxies. In the case of Markarian 180, the spectral scans of the nebulosity reveal several absorption lines usually seen in the spectra of elliptical galaxies and yield a redshift of 0.046. These results are entirely consistent with the nebulosities being elliptical galaxies which have BL Lac object in their nuclei. The scans of Markarian 11 show a number of absorption features, including the Ca II H and K lines and the Balmer lines from H10 to H-beta.