Fri, 10/15/2021 - 14:14
Hi,
I'm observing (DSLR) AK Peg for a while. When I use my 80mm refraktor, also IW Peg is in the FOV. Due to VSX this should be a mira type star (mag range 10.9 - 15.5 CV) with period 505d.
In the last 750 days no sign of IW Peg appeared in the range from 14 to 16 mag. Also, when I look at the ASAS light curve (see http://www.astrouw.edu.pl/cgi-asas/asas_variable/230208+1035.4,asas3,505,5498.0000,500,0,0) nothing appears. I don't think this is a mira star with the mag range and period in VSX.
clear skies
Hans-Georg
Hi Hans-Georg,
The range in VSX is given as CV. If you check the revision history and the phase plot, you will see that it comes from CSS data.
Catalina Real-time Transient Survey observes unfiltered and they calibrate their magnitudes using V values for their comparison stars. However, for red stars, the difference between their "CV" and Johnson's V will be large. The redder the star, the larger the difference.
If you take a look at the star information, you will find that it is a very cool star of spectral type M9.5-M10. And its colours are very red, J-K is 3.17 and the SDSS magnitudes show g= 22.9, r= 19.5. We can get an approximate V from g and r, and we end up with V= 20.9.
From Pan-STARRS1 data we get V= 16.9. We get V= 16.7 from UCAC3 data. There are two maxima around V= 17 too in the ASAS-SN light curve.
So you were expecting to find a 11-16 mag. star when the object is actually a ~17-21 mag. star in V.
Thus it is very far from reach for ASAS-3 and barely detectable by ASAS-SN.
The CRTS light curve clearly shows mira-type variations.
Cheers,
Sebastian
Hi Sebastian
Thanks for explication. I didn't expect a difference of 5 mags between CV and V data.
Hans-Georg