It has been a while but at the end of March we had a clear evening when I could get back to do some variable star observing. I haven't looked at these stars since the end of last year and so I was keen to get some new estimates. Unfortunately, the moon was in the sky and it was 2 days before first quarter. Also, the evenings are getting lighter and astronomical twilight didn't end until about 20:20 UT (21:20 BST).
I began with my current favourite Z UMa. Using chart 217.02 from the BAA and my Nikon 7x50 binoculars, I was able to see star H on the chart near to Z and this was a good sign as it meant my limiting magnitude was fainter than H which is 8.7. I could see that Z was brighter than star D (=7.9) and C(=7.5) and at 20:19 UT I estimated that Z was between stars A (=6.3) and B (=7.3). I found that Z was 2 points from A and 1 point from B, namely A(2)V(1)B which made it magnitude 7.0 (to 1d.p.). This is in good agreement with estimates from other BAA observers.
So this indicates that this star is approaching its peak luminosity. I have written a thread about this star on the BAA Forum. What makes this star interesting at the moment is that the recent rises in luminosity have been double peaked and it may be this is due to the two pulsation periods that contribute to the brightness changes of this star. In my latest post I considered whether this was a reasonable explanation.
Using the same chart I then went on to look at RY. I saw that this variable was fainter than comparison star 1 (=6.7). In fact, I thought it was roughly equal in brightness at 20:33 UT to star 2 which is magnitude 7.4. Other observers in the BAA had this star at magnitude 7.6 and 7.7 on this night, so perhaps I was slightly on the bright side with my recording.
I then went onto chart 106.4 to have a look at TX Draconis. This star was lower in the sky than the previous two and rising in the East. At 21:34 UT TX was fainter than star K (=7.0) but marginally brighter than star N (=7.7). I estimated it to be 3 points from K and 1 from N, that is K(3)V(1)N. This made magnitude 7.5 (to 1d.p.). I think this estimate was fine.
Finally, from the same chart I had a look at another semi-regular variable AH Dra. At 21:44 I noted that this star was fainter than star 1 (=7.0) on the chart. At 21:49 I thought it was between star 2 (=7.3) and star 6 (=7.8) in brightness, namely 2(1)V(1)6, which made it magnitude 7.6 (to 1 d.p.). Other observations of this star are a bit sparse at the moment so I am not sure if I was on the ball with this one.
All text and images © Duncan Hale-Sutton 2023
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