Re: The reddest stars

[jg <jg@jgws.freeisp.co.uk>]

aah@nofs.navy.mil wrote:
> 
> Good, someone took me up on my suggestion to look for
> the reddest stars.  Now do the other half (the bluest
> stars).  They are equally interesting since most CV and
> Be stars are blue.

;)

Not many papers are entitled "We did an n year study of such and such
region looking for thingamibobs and found bugger all, please can we have
more funding?" (although there are ones nowadays that more or less say
"we think we may have a hint of something, can we have a bigger
telescope/satellite and a new project please?"

So, I'm pretty sure Patrick, and others, have looked at lots of stuff
only to find little to say.

There's not a tendency to report negative results.  I'll mention a few
negative results, but this shouldn't put other people off their
attempts, as my selection assumptions could be quite wrong, or just too
stringent.

(Of course others may be beavering away quietly biding their time
getting a nice set of results together before saying anything).

I'm looking for indications of variability, which is my first selection
effect.  Next there need to be enough observations to say something
about one particular object, and this is actually by far the minority
data subset on CD 23.  And if you do find them, often not much happens.

66170 in collected.big, quite "blue", average V-Ic -0.05, Welch-Stetson
index about 4 or 5, 336 observations.  That means there're observations
for six separate nights, and each nights' run is of a reasonable
length.  Intranight variation barely +/-0.05 V peak to peak when at most
extreme, internight variation very barely 0.2 V.  A good example at the
blue end. This is more or less within the scatter.


Red stars.  There's a strong bias towards these being LPVs.  I did a
search a
week or so ago on all those with more than 180 observations (at least 3
nights, maybe more), Welch-Stetson index 1><13 (I'd already looked at
all index>=13 objects) and V-Ic about 2 upwards.  Still quite a few
objects, but not lots.

Few have internight range in V of greater than 0.2 over 100 days.  Ic is
of course less, as it would be even if they were long period variables.

Tom's circumstantial strip which avoided bright stars also avoids 2MASS
2nd incremental release data, there is barely any at all around this
declination.  No circumstantial evidence help there.

It is also a poorly covered piece of sky survey plate wise.  Usually
I've only been able to find just one O plate, one J plate and a
singleton each of E and F plates.  So, only these latter two plates to
independently check by usually.  Anyway, I've examined NOFS plate
archive images for about a coupla dozen of these red objects that also
have a reasonable number of TASS observations, and there is invariably
no hint of variability.  Sometimes there's more F plates, and
occasionally a pair of NIV plates (but these latter are usually
overexposed for these red objects anyway) still usually no hint. With so
few plates though, pretty equivocal.

All in all a good stretch of sky to look for new stuff, because it
doesn't seem to have been that well surveyed before ;)


There's 31 objects with 180+ observations that are bluer than V-Ic 0.1
and have Welch-Stetson index greater than 1 (you don't have to rely on
that index, but it certainly cuts down the workload, and it seems mostly
of practical use).  There's a project for someone ;) These objects need
their graphs checked, and the likeliest handful attacked with a
periodogram. I persoanlly would want peak to peak variation of at least
0.05 V intranight, probably more, before examining any further.


I'll have a quick look at _all_ objects with V-Ic<=0.1 and V>=13 for
objects cataclysmic (GZ Cnc was V 13.5 and V-Ic 0.05 for example).  I'm
welcome to any suggestions re better cut off points for this particular
arbitrarily decided selection effect.  Current thinking is only 1
observation is meaningless, 2 observations is possibly coincidental, 3
observations is barest minimum to be sure of reality.

Though Patrick's assessment of GSC discrepant objects will probably have
already covered this ground via a different route.


Cheers

John G.