Unknown Variable at RA 272.589d, Dec +06.585d (Cepheid???)

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

Intranight variation is nil.


Four nights of observation show distinct internight variation.


Could be a Mira variable coincidentally caught just before maximum, and
then in decline, this maximal tip fitting fairly well over the sixty day
period in terms of scale for a Mira, but a 0.6 V range over this time
period seems a little small.  Would be better if semiregular.


HOWEVER, range in V data is about 0.5 and range in I data is about 0.4,
ie very close.  LPVs are usually fairly suppressed in Ic variation
relative to V.


So there is a possibility that this is a delta Cepheid or even W
Virginis star sampled at various points of a ~1 magnitude (V) or so
range.

The period of such an object would be several days to weeks, and the
mildest monitoring would sort the two possibilities as short term rise
and fall over small amplitude would confirm Cepheid nature, continued
decline would be confirmation of Mira, and an upturn that continues
without further decline for quite a few days and/or an irregular pattern
could be Semiregular.  Semiregulars rarely look sinusoidal though, so
that could be a distinguisher. Shorter periods fit Cepheids too.

B-V is about 2 or so from Tycho2 data which is possibly a bit too red
for a Cepheid, and possibly not quite red enough for an LPV.

Finally, three DSS red images gleaned via the USNO NOFS image server
shows no large variation of this object. If it was a Mira you usually
get at least one bright/faint image compared to two faint/bright images
out of a sample of three this way.  The N plates show no real sign of
far-red excess.  The possibly interfering nearby stars within the pixel
size range all appear to be mag 16 or less so shouldn't affect the
results for the star in question.

Any other viewpoints re this lightcurve?

NOTE RE OBSERVATIONS

If someone like Michael K. wanted to follow this star over the next few
days note that it would only need a short observation run of only a few
minutes (ie sufficient to be confident of good data) per clear night, so
it could be looked at just before or just after a data run on summat
else.

I reckon it's a must on the follow up front ;)

Cheers

John G.