Duncan Hale-Sutton

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  • in reply to: What’s happening to Z Ursae Majoris? #611242
    Duncan Hale-Sutton
    Participant

    Another aspect of the light curve of this star that interested me was that from time-to-time the maxima appear to be double peaked. This has been shown nicely by some recent observations using CMOS detectors (see the attached file which has been produced from the BAA database). If you look at the light curve after the 1st Jan 2022 you can see (green data points) that Z UMa reached a maximum of about magnitude 6.6 around the 14th March, then it faded a bit to about 7.7 around the 21st April before brightening again to about magnitude 6.8 around the 22nd May (roughly 69 days from peak-to-peak). The same double peak is seen in the visual data (black circles) but the scatter in the CMOS data is much tighter. Looking back at the four maxima prior to this the visual data (black circles) hint that this double peaked behaviour has been been developing as time progresses.

    If you go back further in time other reasonably clear examples of a double peak can be seen in August 2016, January 2008 to July 2009, January 1999, July 1999 and July 1995 (I haven’t gone back further than this). So what is causing this? One suggestion has been that this is due to the interaction of different pulsation cycles within the star but this is not so easy to understand if, as John Greaves says (see my first post), after 1995 there is virtually only one pulsation period of 189 days. With more people carrying out observations using more accurate electronic detectors it will be interesting to see how often this double peaked behaviour appears.

    in reply to: What’s happening to Z Ursae Majoris? #611094
    Duncan Hale-Sutton
    Participant

    Thanks Jeremy for all these useful links. I have had a brief look at the T UMi paper and scanned the June edition of the AGB Newsletter. People who are modelling the evolution of stars on the AGB seem very keen that we keep monitoring stars whose periods are changing over time.

    in reply to: Two Large Sunspots Groups #609954
    Duncan Hale-Sutton
    Participant

    Hi Lyn, this is embarrassing. I forgot to subtract an hour from my timing of my solar image I took on the 21st April. So this should read 11:07 UT not 12:07 UT. Sorry about this.

    in reply to: Two Large Sunspots Groups #609924
    Duncan Hale-Sutton
    Participant

    Hi Lyn, I am a new member of the BAA and thought I would try and contribute to this thread (my first post on the forum). I took this image on the 21st April at 12:07 UT using a Celestron NexStar 102SLT. I used a 25mm eyepiece and a star diagonal to project the image onto white paper. I have rotated it as best I could to give the correct orientation. There are two versions of the same image. One has the sunspot groups annotated. I hope that this is useful to you.

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