Tom Droege pointed his Mark IV at globular cluster M5 on the night of April 24, 2000. He took pictures in the V and I bands as a check on the quality of the Mark IV optics.
(unfortunately, I don't have the exposure time of the images, nor do I know where the cluster fell in the field of view)
Tom performed minimal cleaning on these images: he wrote
I have done minimal processing. I just made a median flat from 8 images and divided the M5 frame with it. Note there was no dark subtraction anywhere. This works, I think, if the dark is small and constant and there is not very much flat to be corrected. In any case, the result looks pretty good as you can see.
You may download the FITS images Tom provided:
I have made a set of sample "pretty pictures" from the images, for those who don't want to get into the FITS image display business.
First, a picture of M5 from the Digitized Sky Survey. North is up, East to the left, and the field of view is about 1 degree across:
Now, the subsections of the Mark IV images Tom took. They are oriented with North up, East to the left. Each is about one degree high by a bit less wide.
Click on this V-band image to see a larger version.
Here's a closeup of the cluster itself, at a harder stretch:
Now, the I-band images (which aren't as sharp). The I-band "cleaning" wasn't nearly as good as that of the V-band, as this stretch of the I-band image shows. There's a satellite trail faintly visible along right edge of image.
Here's the I-band subsection at a harder stretch, which doesn't show residuals of the cleaning as much. Again, click on the image for a bigger version:
And now, a closeup of the cluster itself in I-band:
The FWHM of stars in the V-band image is about 1.8 pixels. The FWHM of stars in the I-band image is larger, about 2.6 pixels. The I-band PSF shows a little coma, I think.
One can find photometry of stars around M5 in a paper by Halton Arp, ApJ 135, 311 (1962). I've done a quick match of a few of the brightest stars in the Arp's list and stars in the Mark IV V-band image.
The identified stars have the following magnitudes (I used aperture photometry with a radius of 3 pixels, probably a poor way to measure
Letter Arp number Arp V instr. mag delta mag
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B B 11.52 14.75 3.23
D D 12.35 15.69 3.34
E E 12.38 15.70 3.32
Y 318 13.17 16.42 3.25
Z 378 13.83 17.40 3.57
W 469 14.60 17.75??? 3.15???
The star marked "X" is actually a close double, with components of mag V = 13.11 and 14.36. The star marked "W" was barely detected on the TASS image, so its magnitude isn't measured well at all.
This quick look shows that the Mark IV in V-band can detect stars down to V > 14 in a crowded field; I don't know what the exposure time was. It also shows, of course, that we do NOT want to use the Mark IV to study globular clusters ....