First off, thanks for the reply. I'll try and provide a brief (or maybe not so brief... sorry) lesson in eyeball spectroscopy as part of my reply. To really understand these sources, you have to do a deeper analysis of the spectrum, fitting the various lines and the continuum. But you can make some obvious comparisons between sources much more simply.
Also, a technical question about the board itself: when I click the "quote" button, it only quotes your reply, not my comments that you are replying to. Is there a way to get it to quote the entire conversation, so I don't have to go back and fill it in?
Lehnert et al. 1999, the redshift of 3c343 is actually 0.998, and they call it a Seyfert 2 galaxy. Though, that's a fine splitting of hairs, if you ask me.
By luminosity profiling, do you mean determining the light profile of the source? If so, then yes: the light profile tells you whether a source is a point source, or an extended source. But I don't think the DSS PSF is well enough determined to do PSF subtraction
I'm going to reorder things a bit in my reply.
BL Lacs are currently thought to be systems where we are looking directly into the "mouth of the beast," if you will. Direct line of sight into the central black hole with the relativistic jet pointed at us. There are less than a thousand known BL Lacs: a hundred or so with SDSS spectroscopy. So, according to the standard view, this is very similar to a quasar, but viewed at a particular angle. It has many of the same properties of other quasars: bright in X-ray and radio, high variability, and a bright point source in the core of a galaxy.
Blue, pure-blackbody continuum, some absorption, no emission? Star. Compare it with (1).
Also, the first is more than an order of magnitude brighter than the second, in this pair. Something is definitely going on in the nucleus of the first one (which is also a radio and X-ray source).
Keep these spectra in mind as we move on. I'm going to flip the order of the next two...
It is a spiral galaxy, but the nuclear spectrum is quite odd: notice how broad the H-alpha emission line is? That's a line-broadening of several thousand kilometers per second! The continuum is kinda funny as well. Definitely a disturbed system, and the galaxy that probably caused the mess is visible just north-west in the finding chart image. There aren't many ways to get an emission line that broad; the standard view is the accretion disk of the central black hole.
spectrum that was taken of a knot in the owl. Strong [OII], very weak H-alpha and H-beta, generally flat continuum. Also compare it to the not-quasar star-forming galaxy in interacting pair above.
Personally? I don't really know if Arp has an actual working definition of the term quasar, beyond what you said above about looking like a star but having high redshift. From what I've seen of Arp's work, his quasars are simply those objects that he has selected from other catalogs (SDSS, 2df, or even NED) for his own analysis, thus they are whatever the given catalog classified as a quasar.