Just to refresh your memory, double dipping is taking in a few deep sky objects while still making variable star observations. Now that winter has arrived, we have a whole new set of deep sky wonders to distract us from our variables. Fortunately, there are plenty of variables within a short star hop of many of your favorite nebulae and clusters. So if you have visitors braving the cold who want to see faint fuzzies, you can still sneak in some variable star observing.
In the last 'double dipping' blog we left off at M33 in Triangulum. Picking up where we left off, we can jump easily from M33 to three of my favorite cataclysmic variables. First, about 2.5 degrees NW of M33 is TY Psc. TY is a UGSU that can get as bright as 11.7V during a superoutburst, but most CV enthusiasts know the field for the distinctive little four-star asterism due south. This grouping provides a convenient mix of magnitudes to use when the star in outburst.
TW Tri is closer to M33, about 1.4 degrees NE of the galaxy. This CV lies in a rather barren part of the sky. It erupts about once a month, making it rewarding to follow its activity. TW is suspected of being a Z Cam type CV, but standstills will have to be verified by CCD observers, since they will probably occur around 15th magnitude or fainter.
While you pretend to hunt for M33 you can zoom over about 1 degree SE of the galaxy and land on the field of TX Tri. Not a particularly active star, I can�t tell you why I still enjoy chasing after it. Maybe it�s because not many of us do. Now scoot back over to M33 and let your guests pretend they can actually see spiral structure in the eyepiece.
Then grab a pair of binoculars and show them the Double Cluster (NGC 869 and 884) in Perseus. RS Per is a red semi-regular variable right smack in the middle of the eastern cluster NGC 884. It varies from about 7.8-10V, so most of the time it can be seen in binoculars. You don�t have to let anyone know you are making a variable star observation while taking in the beauty of the Double Cluster.
Almost 1 degree due west is UV Per. This UGSU gets to 11th magnitude in outburst, but outbursts are few and far between. You may have to wait a year or two for the next one. Fortunately, UV lies in an interesting double string of stars, making this field a pleasure to take in while hunting for an outburst.
TZ Per, an active UGZ, 1.3 degrees NW of the double cluster is another fun, active star you might want to sneak in before the guests get antsy. With outbursts every other week or so, it�s bright more often than not, so it�s often visible in an eight or ten-inch telescope.
M76 is known as the Little Dumbbell Nebula because of its resemblance to M27 in Vulpecula. It also makes a fine place to star hop from to get to KT Per. Slew one degree SW of the faintest Messier object until you find an almost perfect little baseball diamond of 12th and 13th magnitude stars. KT Per is another fine, active CV that gets as bright as 11th magnitude in outburst.
While we�re in Taurus, slide further south to the Hyades. Just west of Aldebaran is a bright double star consisting of theta 1 and theta 2 Tau. In the same medium power field of view is W Tau, a semi-regular variable that ranges from 8.2-13.0V with a period of approximately 165 days.
The Eskimo Nebula (NGC 2392), in Gemini, is a bright, round planetary nebula that has a fairly remarkable green color to it. Not many deep sky objects exhibit any color at all through modest scopes, but this one always looks green to me. The central star is fairly easy to see, compared to many planetary nebulae. I�ve seen some rings, dark lanes and other features in this planetary on very good nights in the 12-inch, but it takes averted vision and lots of patience to eek out any detail at all. I�d rather be hunting down a few more variables! R, S, T, and U Gem are all within a few degrees of this deep sky favorite. S and T Gem form an equilateral triangle about 1.5 degrees on a side with kappa Gem. Kappa Gem, NGC 2392 form a triangle with U Gem., kappa being about 3.2 degrees north and the Eskimo being about 6 degrees to the west. You can probably get all of them in the FOV of your finder scope. R Gem is a little harder to find, lying a little less than half way from NGC 2392 to epsilon Gem. 6th magnitude 44 Gem is a good sign post for finding R Gem, which lies about 28 arc minutes east.
If your guests have endured the cold night air up to now with you wandering off and doing variable star estimates in between, you can reward them with the �Piesta Resistance� of the winter sky, the Orion Nebula, M42. By all means, do take in this glorious sight. I don�t think anyone ever really gets tired of looking at it. Be happy in the knowledge that a mere 1.6 degrees NW of the center of this mammoth nebula, S Orionis, a very interesting Mira that often exhibits a hump in the ascending branch of its light curve, is waiting for you to stop by for a visit. Varying from 7th to 14th magnitude with a longish period of 415 days, this variable can supply you with a lot of entertaining observing sessions. Plotting the strange behavior of this star on the light curve generator can be fun too. What�s up with the hump? I don�t know, and I don�t think anyone else does either. Imagine that, a mystery that could potentially be solved utilizing amateur data!
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