Each Arp will be shown on a separate page. If the Arp also has a Messier, NGC, or IC number, those numbers will be shown in parentheses as part of the title for that page. UGC, MGC, PGC, VV, etc., catalog listings will not be shown as part of the title and but will usually be mentioned in the text.
The images are presented approximately North up, East
left. I have not done any
rotating or cropping to align them, so
some may be 5¡ã or so off relative to the
circles of R.A. and declination. Dr.
Arp¡¯s images were in just about all possible orientations and I have not tried to match
The individual pages show a positive image processed to emphasize structure in the brighter areas of the galaxy and a negative image processed to highlight the faint jets, loops, and bridges. For a few of the galaxies, a false color or high-contrast negative image is included to show details too faint to be seen with normal processing. Occasionally, an enlargement of part of the image is included to show interesting details. And, finally, as I have started to add color images, they may be either additions, or replacements for one of the other images.
The telescope, camera, and exposure time are shown on each image page. The raw images
acquired with either the Cookbook 245 or StarlightXpress MX716 cameras and either
of the larger telescopes (see Equipment) range from 14.8' to 15.8' on the long axis and 10.9' to
11.8' on the short axis. The raw images are generally cropped slightly to get rid of edge effects and tracking drift. I
consider all of these images to be a nominal 11' x 15' and don't list the size on the
individual pages. The apparent size of objects in these images is proportional
to the actual size. Obviously, true sizes are a function of distance.
Now that I've started imaging with an SBIG ST2000XM, the images with either of
the primary telescopes are roughly 21' x 28', almost twice as large. The
size will not be listed for ST2000 images unless it is substantially different.
images taken with a different telescope setup or camera, or severely cropped for any reason, will show the approximate image dimensions in
arc minutes along with the other information.
While many of the Arps are centered in the field, others are not. Occasionally, this is due to laziness on my part, or a catalog error. Most often, it is done to fit as many galaxies as possible, or a particularly bright or interesting one, into the field. The fields containing two, three, or four Arps tend to have the galaxies near the edges to fit them in. The Arp galaxy or group is always identified in the text unless it is the clearly the dominant feature of the image. At my whim, other galaxies in the field are identified, along with general comments about the Arp or the imaging experience. Precise positions, sizes, magnitudes, and a complete identification of other field galaxies are not included. For that detail, I suggest you refer to Kanipe and Webb, The Arp Atlas of Peculiar Galaxies, A Chronicle and Observer's Guide.
I have tried to make my fields large enough to completely include Dr. Arp's original field, but a few of them are a little undersized. The image pages will indicate if any of the field is cut off. If you are using a chart-generating program to plan your own images, be aware that they often assign the Arp number to only one galaxy. Some of the galaxy groups and clusters are large and centering on the primary galaxy may result in other significant members being outside your field -- the extreme case is Arp 317 which requires a field over 1 degree in the N-S direction.
Each page will indicate Dr. Arp's classification of the object. This is not the standard Hubble classification scheme but is a specific scheme designed for these peculiar galaxies. Also, if the Atlas notes are interesting or enlightening, they will be included. I've changed the beginning capital letter to lower-case so that the notes fit into a sentence. Many of the objects have no notes.
Each image page includes a link to the original Atlas image on the Cal Tech web site. Remember that the scale will be different, and the orientation may be. When you are ready to return to this site, just close or minimize the Atlas window.