Sun, 06/12/2022 - 20:41
I see in the June newsletter about the SPP section: "Gathering observations in M13, as well as the “Legacy Stars,” so lots of data is expected to be collected over the next few months." I've not heard anything about this but might be interested in contributing. Are there more details to be had?
I'll have to check on the status of M13 observations, but I might mention that, together with several collaborators, I've been working on the long-term period changes of RR Lyrae stars and Cepheids in M13. Results for the Cepheids (all rather short period, and type II of course) have been published in Osborn et al. 2019 (Variable Stars in M13. III. The Cepheid Variables and their Relation to Evolutionary Changes in Metal-Poor BL Her Stars) available through the NASA ADS. Results for the RR Lyrae stars should be done soon. One of things we noticed is the need for observers to keep the variables under observation. Gaps in the observing record can create ambiguities in the period changes. Some of the M13 RR Lyrae stars also appear to have poorly understood multiple periods. More when I get further information.
The M13 period-change project I have been working on (others may have other projects) has decided to go ahead with the observations we've already obtained, rather than hold up results longer, so I don't have specific observing suggestions right now for M13 -- although I will think about what might be needed in the future. There are some stars in M13 that we are puzzling over. However, I've heard that a new campaign on an individual RR Lyrae star might be in the works. If the researchers decide to go ahead with the campaign, we may hear about it soon, but it is still tentative for now.
I'm curious to know what software you are using to get your M-13 photometry? Are you doing aperture photometry or PSF fitting? If PSF fitting what software are you using?
We used Peter Stetson's daophot/allstar for PSF fitting. However, image differencing methods helped with some of the most crowded stars. Some of the more isolated variables could perhaps have been measured with aperture photometry, but we treated them all with PSF fitting.