[vsnet-chat 7582] FWD : CBA NEWS 764 (XMMUJ115113.3-623730 (Cen slow nova) - Stockdale lightcurve)

[substellar at Safe-mail.net]

Some bits and pieces extra leaking out on this object.

First, evidently from the below there's some quality optical spectrum floating around that hasn't been forwarded to ATel or CBAT as yet, ie unpublished.  Maybe high excitation means lots of emission lines in Balmer and He I and maybe He II??

Certainly further time can be seen to have been used on SWIFT for new observations of the object via examining quicklook, but whether UVM2 is being used deliberately as the passband or just happenstance is not clear, and if deliberately why it would be preferred (it's one of three UV passbands the UVOT 'scope uses).

More important to CCD observers are Joe Patterson's notes re needing more observations.

I've been favouring the 0.26 or even (though not well liked) the 0.36 day period from Chris Stockdale's lightcurve when the data are folded, still a bit gapped, and still lots of aliasing, Joe P. evidently prefers the fold based on 0.21 ish days.  None fold perfectly, akin to the V723 Cas situation, but I seem to remember the 0.21 ish one at least isn't gapped, but of course all this depends on whether all phases have been caught as of yet, and longitude restriction can be a problem when it comes to such things.  Notice, in terms of aliasing, that these periods are near big fractions of a day too (1/5, 1/4, 1/3), ie one day later and nearly 5, 4 or 3 whole cycles have repeated and we've returned to a very similar point in phase, as well as the one day between observing sessions repeating.  This is what Joe P. is meaning about hopes of another longitude breaking that pattern up.

Importantly though might be colour, especially as the minimum at least seems to vary giving a 'fuzzy' minima in phaseplots no matter what solution is preferred..  It's not clear if Berto M.'s data donated to CBASTRO are V filtered or not, but a single measure in the AAVSO International Database posted by Steve O'Connor of Bermuda shows V-Rc at least is significant, and if accretion disc and/or circumstellar matter are part of the variation cause, then colour might even be phase dependent, so the plain vertical traditional shifting of unfiltered data to fit filtered data might not be overly safe in this instance, so V filtered stuff might be safer.  Merely a thought, but the thing ain't strictly periodic, ie it ain't exactly repeating, as these objects do not do as such.  Unfortunately Steve O'C's data are not coincident with any of Chris S'.  Any sort of colour time series (V-Ic or whatever) might help out in that regard.

Anyway, here's what Joe P. says, and of course by extrapolation, and again in parallel to V723 Cas, the object should still be varying and likely exhibiting a hint of orbital signature (possibly even one that has evolved to a slightly different value) when it comes out of Eastern Twilight next observing season.

http://cbastro.org/communications/news/messages/0764.html

The main point is, Chris S. has put some serious useful effort into following this object, and none of any of the points others are making would mean anything if it wasn't for that, certainly there'd be no chance of digging out anything about orbital period (at least photometrically), so congrats to him!

Cheers

John

PS this one sneaked out, btw, this star.  If Jules Halpern hadn't made some offhand comment to Joe P., and Joe P. hadn't mentioned it in his publicly archive CBA maillist, there might well've never been anything noticed about past outburst at all, let alone any time series photometry taken.  It'd've been just another polar candidate likely not getting followed this time around due to being unseasonable, with nothing further probably but just the usual eventual atel claiming some tentative WD rotation period of a few hundred seconds based merely on some very, very sparse swift xray data (and I'm still expecting something like that to be claimed).

The transient interpratation and follow up field is still very, very hit and miss and dominated by personal selection effect biases which can actually hide the serendipitous at times.