Recently I have been getting multi-color photometry of RR Lyraes and Cepheids. One of these is the well-known bright southern long-period Cepheid RS Puppis. The star culminates at airmass ~3.0 from Arizona, so the data are a bit of a challenge to get. The two attached plots show the phased lightcurves from data starting 2019 Jan up to last night (UT 2020 Feb 24). The first is from using a narrowband filter centered at 8900A, which I am adjusting to Sloan z; the second is Johnson B (I also have V-band data). The rms scatter is about 0.025 mag for each. Of interest to me is the change in the morphology of the lightcurve between the two wavelengths, having to do with the changing effective temperature of the star and the pulsation shocks emerging from the interior.
Some technical details: CCD data from the Lowell 0.7-m robotic telescope. Three (fairly blue) comparison stars are available in the 15'x15' field from a UBV sequence by Lars Loden (1969ArA.....5..149L); the Sloan z photometry is from the southern SkyMapper survey (VizieR item ii/358).
\Brian
Hi Brian,
nice phased light curves, especially considering the airmass you imaged through. RS Pup was one of my first targets when starting DSLR phtometry back in 2011. At the time I was observing from Sydney where RS Pup culminated at airmass 1.
Your B band light curves show much larger magnitude range than the z band. Its been years since I looked at the phased light curves I made but I vaguely recall the three DSLR filters (RGB) showed different magnitude ranges too. These ranges were somewhat smaller than yours because DSLR RGB filter wavelengths are much closer together than B and z.
Your comparison stars must be much fainter than RS Pup given that the field of view was only 15x15 arcmins. I presume you used multiple short exposures to avoid saturating RS Pup then stacked them to improve SNR of the comp stars. With my DSLR the FoV was 7x4.7 degrees so many bright comparisons were available. Cheers,
Mark
Thanks for your comments, Mark. The three comp stars lie about 12' southeast of RS Pup, specifically HD 69042, CD-34 4498, and CD-34 4503, for which I've adopted V = 8.13, 10.25, and 9.19, resp. They are in one corner of the 15' field, and RS Pup in the opposite one. The filters involved are all narrow, about 60A wide, so although the exposures are short, they are not very short. Multiple exposures are nevertheless necessary to beat down the scintillation noise, and just being at sec 3.0 - 3.5. I generally script the telescope to visit such fields twice per night since there are transparency 'funnies' that come into play that seem not to be amenable to root-n kinds of averaging. It's got to be pretty stably clear for this sort of thing to work, so not all the data are good.
\Brian