J. D. Finke, J. C. Shields, M. Böttcher, and S. Basu
Astronomy & Astrophysics, 447, 513 (2007)
Context. BL Lacertae objects have been the targets for numerous
recent multiwavelength campaigns, continuum spectral variability studies,
and theoretical spectral and variability modeling. A meaningful interpretation
of the results of such studies requires a reliable knowledge o the objects'
redshifts; however, the redshifts for many are still unknown or uncertain.
Aims. Therefore, we hope to determine or constrain the redshifts of
six BL Lac objects with unknown or poorly known redshifts.
Methods. Observations were made of these objects with the MDM 2.4 m
Hiltner telescope. Although no spectral features were detected, and thus no
redshifts could be measured, lower redshift limits were assigned to the objects
based on the expected equivalent width of absorption features in their host
galaxies. Redshifts were also estimated for some objects by assuming the host
galaxies are standard candles and using host galaxy apparent magnitudes taken
from the literature.
Results. The commonly used redshift of z = 0.102 for 1219+285
is almost certainly wrong, and the questionable redshift of z = 0.129
for 1426+428 has been verified photometrically. The redshifts of the other
objects studied remain undetermined.