Re: Atypical variable stars...

[Michael Sallman <msallman@pro-ns.net>]

Robert and all,

As to whether something like this could be detected (as things are
currently done), I would say "it depends".

As has been already mentioned, if it were too dim to be detected in V,
it would be rejected in the pipeline, before ever reaching my database.

If I have the data, such a decline would be detected. As Tom said, there
are many stars that show this trend. See, for example:
http://sallman.tass-survey.org/servlet/markiv/template/TassPlot.vm?object_id=7320192
http://sallman.tass-survey.org/servlet/markiv/template/TassPlot.vm?object_id=3093828
(though this one appears to have "come back")
Both of these show a greater decrease in V than I. But I think this is a
common effect in pulsating variables.

I would think that you would want to start with stars whose IRAS or
2MASS data fit a certain profile, and then check TASS/ASAS/whatever for
the type of variability you are looking for.

I think it would be a lot of work to determine whether a star had
disappeared or not. There are so many vagaries to deal with (bad region
on CCD, star just off the edge of the CCD, clouds, etc.). Not to say
that it couldn't be done. :-)

Mike


Robert J. Bradbury wrote:
> On Tue, 24 Aug 2004, Thomas Droege wrote:
> 
> 
>>This brings up an interesting problem with the TASS data.  The present
>>software requires simultaneous hits in V and I to keep an measurement.
>>This throws out about 80% of the data.  OK, I have set the cut low because
>>of this, but still we probably only put half the possible data in the data
>>base.
> 
> 
> In particular it would seem to remove the type of trend that MBrain
> development would represent.  In that case V would diminish quite
> a bit faster than I.  (This is because as MBrain development takes
> place the star still radiates the energy but it gets shifted further
> and further from the visible into the infrared region (even far
> beyond I into J, K, L, etc.).
> 
> So one would want to identify cases where V is going down at some
> rate where I is decreasing at a slower rate.
> 
> As mentioned -- these trends may vary from rates that involve days
> to years (ultimately millions of years -- but this involves very
> old/cold MBrains that are probably invisible in both the V/I regions).
> 
> 
>>Long period stars tend to be red.  This means the V component is typically
>>2-4 mags less than the I component.  As the star dims, when the V component
>>drops below 13 or so we begin to have losses, and most data is lost by V of
>>15.   But the I component is still quite bright for a typical red long
>>period star.  Too bad, it is lost by our present analysis.
> 
> 
> Understood.  But the question is whether the *rate* of decline in V
> is significantly different from the rate of decline in I.
> 
> If one is shifting the blackbody radiation curve of a star you
> can have a decline in V but it has to be compensated for by
> a maintenance or increase in I.  So those stars that TASS
> "drops" because they decrease in V should be sub-selected for
> those that "never" come back.  If these still have a detectable
> I component they may be significant.  Ultimately one would like
> to match this with the Hipparcos, 2MASS or IRAS data to determine
> if the star is excessively bright (or brighter) in with respect to
> IR wavelengths.
> 
> 
>>...but I don't think there are any stars where V is many mags
>>brighter than I???
> 
> 
> Not normally as far as I know *but* there are scenarios I can
> imagine where one would attempt to heat up a star for various
> energy production purposes (if you can surround a star with
> solar collectors you can obviously reflect all the energy
> back onto the star with some interesting effects most likely).
> There are MBrain applications where one might want to produce
> the greatest amount of energy in the shortest period of time
> in which case stellar super-heating may be a reasonable engineering
> strategy.  There are also strategies along this line that I
> could envision might be used for shifting the nucleosynthesis
> reactions in the surface of the star to produce heavier elements
> (which get blown off into space and subsequently collected).
> 
> So I would suggest that there is merit in noticing any data
> that varies from the "norm" to any significant degree.
> 
> Robert
> 
> 
> 
>