From march 4th to may 3th of 2025 I have been recording M3 globular cluster for its RR Lyrae stars in V and I-band. I have managed to record 77 of those over 21 nights.
1 of those is the RRab/bl star IY CVn. And indeed when combined with my run in V from march 2023 it shows some amplitude modulation in the peak in the phase plot.
However, I also see hints of period and/or amplitude modulation in 3 strars which are labeled as RRab type in VSX. Can someone help me interpret this and confirm or debunk that they could have blazko effect? These 3 are:
KN CVn, which seems to show period modulation in both V and Ic.
Unfortunately these 3 stars where not earlier in the AAVSO database. So I could only find my own datapoints from 2025, which are in the phase plots above.
Probably another one for Sebastian or someone from the short-period pulsator group to comment on.
However, I’m interested to know where you are observing from? Your weather is many orders of “magnitude” better than central Virginia over your observing time!
I am observing from Woerden, in the middle of the Netherlands. Here is also notoriously cloudy, except in spring. This year we had a lucky run in spring. This month the clouds are still good but nights are very short due to 52 degree latitude. so mostly these kind of projects I plan om springtime
These are very interesting plots! As regards the variations from cycle-to-cycle, one might have look at work led by Merieme Chadid, based on long runs of data taken from Dome C in Antarctica plus hi-res specdtroscopy, such as:
…among her other work related to this. These seem to put the various problems in interpreting RR Lyrae pulsations on a whole new footing.
It is hard for me to see differences with both filters on the same plot, could you make separate plots for the V and I bands for each star?
But I looked these variables up in the GCVS and they have all 3 marked as having a Blazhko effect, here are links to their entries: KN CVn, NP CVn, and IZ CVn.
Here is a somewhat recent paper about M3 RR Lyrae and the Blazhko effect: Jurcsik. 2019, MNRAS, 490, 80
There is a newer paper by Kumar et al that uses archival data, but in both cases the observations seem to be at least more than 5 years ago.
At this magnitude and with this much crowding, TESS probably isn’t much help. So maybe it is worthwhile to consider publishing this in some way? And depending on your images, you may be able to say something about some of the questionable variables in the Jurcsik paper with your newer data.
I am currently writing a article about it (first of all for my own fun). The main goal of this project was with comparing the distance to M3 with the PL relation from Catelan et al (2004) to the Gaia distance. In that sense I am 11% of with about 3.1 sigma significance. See the bottom panel of the plot below for my Relation and the Catelan relation imposed on it.
Next step is to get my own PL relation based on Gaia distance.
On the 3 mentioned stars, I will run those through phase04 to see if something shows up in an O-C diagram.
I will have a look at the images again to asses if they suffer from crowding. Some might but I also filtered outliers from the relation in the plot below. Which should also adress crowding I guess.
Indeed I could. When I plotted V seperately in Vstar the modulation in amplitude/period is clearer then in the double plot. All my data points of this project are in the AAVSO database under observers code KREA,
