RW Cephei 9th January 2023

On Monday, in the early evening, we had some clear dark skies before the moon came up and so I was able to make a couple of variable star observations. The moon was 3 days past full and wasn't due to rise until 18:32 UT. Twilight ended at 18:10.

I started off with another observation of RW Cephei. The constellation of Cepheus at this time is still relatively high in the sky. At 18:24 UT I noted that RW was fainter than star E (=7.3 mag.) on BAA chart 312.02 but not by much. At 18:27 I confirmed that RW was brighter than star H (=7.8 mag.) and so my estimate was it was 1 "point" from E and two "points from H (or E(1)V(2)H). This made it magnitude 7.5 to 1 d.p.

This means that, in my estimation, the star hasn't shifted in brightness since Christmas Eve 16 days ago. However, my estimate seems slightly at odds with what other members of the BAA are seeing.

The above light curve courtesy of the BAAVSS shows all the data between the 01/01/2022 and the 09/01/2023. The last data point to the extreme right is the observation I have made here. It seems my magnitude 7.5 values are probably 0.2 magnitudes from the mean and on the upper edge of the spread of values. I find it hard to understand how the estimates could be as faint as magnitude 7.9 as this would mean that it was fainter than star H which I am pretty sure it wasn't.

Here is the light curve for this star from the AAVSO:-

What is interesting here is that AAVSO shows a similar spread in values between about 7.4 and 8.0 magnitudes but curiously CCD measurements (shown in green squares) can't quite agree either even though these should be much more accurate than visual observations. Note that there is a marked increase in the number of observations around JD 2459929 (16 December 2022) as this was when an alert from the AAVSO went out asking for more data. Prior to this date one observer (VOL) had a nice sequence of DSLR observations (in green squares) with very little scatter. Here is his data shown on its own:-

This observer seems to be seeing what I see in that dimming of RW is flattening out and tending to magnitude 7.5 (however, there may be a 0.2 magnitude systematic difference between visual and DSLR observers).

All text and images © Duncan Hale-Sutton 2023 except those by the BAAVSS and AAVSO.