With the current outburst of this object I have a new comp 135 which bridges the gap beytween stars 131 and 141 (this last one poor as it is a fairly close double with another comp, 149). Comp not yet uploaded (1631 UK time) but it should be by tonight! Minichart attached (OK, not attached as it seems there is no way to attach files). Source is APASS DR9. 135 is the star in line with comps 131 and 147, on the S side of 131.
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I made it 12.9 tonight by the way. Hopefully be using 135 soon!
Thanks for every additional comp star!
A remaining question in my mind is why AAVSO is usually giving quite red comp stars (B-V 0.6-1.2), while many of these outbursting targets and HADS stars are remarkably blue (B-V 0.0-0.4). Doesnât that make color transformation less precise? Iâm often searching for a few additional APASS DR10 comp stars in the blue range.
Regards,
Tom
Cheers Tom, in fact a B-V of 1.2 is right at the âdonât use if you can help itâ end. Ideally I go for a B-V between about 0.35 and 1.15 but this canât always be done of course. We can only use what the sky provides! A comp with a B-V of near zero could in fact be one of those very DSCT or RR Lyr objects itself. Since the app we use (seqplot or a dedicated team spreadsheet) outputs colour information and errors in several wavebands we trust that covers transformation issues.
Bear in mind also that APASS DR10 often carries errors that are too high for CCD observersâ desires, sometimes>0.1m; and there can be the occasional data holes. It is strongly recommended that requests for new sequences are made through the sequence team rather than âdo it yourselfâ because someone somewhere else may also be making a sequence for the same object but use different comparison stars (and may not necessarily be aware of some of the issues behind making a sequence)
Mike, sequence team