Bernd Brinkmann wrote (of the trail of spurious "non-stars"):

"...first I thought it could be a diffraction spike from a bright star.
But there is none near that position."

Also, these tend not to cover an entire plate.

"...So it can be a scratch on the scanned photo plate, or a hair, or or or ..."

It looks to me to be a linear trail of points separated by about five
arcminutes each, covering the entire plate. Most likely, it's an
artificial satellite. I saw this streak some years ago, back before
I had a way to remove it. But it is now quite possible to remove
spurious objects from Guide. See

http://www.projectpluto.com/update8b.htm#err_suppress

I went ahead and added the seventy-odd objects in this streak (as
well as a few other spurious objects nearby). If you download

http://www.projectpluto.com/errata.txt

(about 4 KBytes) to your Guide directory, these objects will go
away.

-- Bill