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Re: flares in Mira stars The following information is from John Greaves: Date: Tue, 3 Jun 2003 16:35:42 +0000 Subject: preliminary flaring mira shortlist Okay, thanks to Ondrej's post especially, there can a very short short list put forward for this. I consider Ondrej's post interesting because it is instrument based, and thereby free from Purkinje Effect. Of course, instrumentation is not totally free of problems. The inclusion of V Cyg is very interesting in light of the de Laverny/Hipparcos Venice Symposium conjecture that a bias existed towards late type M stars (ie relatively 'oxygen rich' red giants with higher than average concentrations of Vanadium Oxide, VO, in their outer atmospheres). V Cyg is a carbon star (CGCS 4939), objects usually deemed oxygen poor. Yet on the other hand, the MSX5C experiment logs it as being variable in band A, and band A only, said band encompassing the 9.8 micron emission region for silicates. Maybe the professionals can comment on this apparent contradiction? X Dra and RU Lyr seem to fit the bill better in terms of the VO hypothesis expectations. T UMi may flare or not, but it is not a normal Mira, and I would not include it in any first instance. SUGGESTED OBSERVING SHORTLIST I would suggest that people already observing R Aur and X Dra and in their sessions would put in the extra effort to observe each of them several times during the nights they observe them, rather than just the usual once as they probably do at present. If they would care to observe them more regularly on a night by night basis, too, it would also be useful. These two stars should be reasonably circumpolar for most Northern Hemisphere observers As to whether archiving bodies readily accept multiple observations of Miras for a single date, I do not know, but obviously this is what is needed in this case. I intend to read through and check the few papers on this topic, note the dozen or two Miras mentioned in them, and check their lightcurves from several organisations, also checking any interesting datapoints on an observer identity level, when possible. This will take time. Also, I may not have access to much data for all of them (eg X Dra seems not to be well covered), and I have very little data altogether for Southern Hemisphere objects. Anyway, a couple of people have expressed interest, so this is a short list to be going on with, hopefully the sequences aren't too bad. Mira itself can be added to the list if people wish. T UMi may well be under regular observation at the moment due to its declining period, so that too could be a target, but the amount of coverage these objects need probably means it is best to select as short a short list as possible, whilst not trying to put all your eggs in one basket. The first step is to observe enough objects frequently enough such that if no flares are seen within a year or two, the phenomenon can be fairly safely dismissed, or alternatively to catch better evidence of flaring actually occuring than exists at present. I'll try and find a couple more candidates to make this list slightly larger. The current hypotheses suggest it should be fairly common for certain types of stars, so if it's there, it should be seen soon enough, maybes... If flares are detected/confirmed, matters like frequency, duration, phenomenology and host star characterization can follow naturally as more data is accrued. Cheers John John Greaves
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