[vsnet-newvar 1684] CMC12 190725.0-013825 is a Mira variable

[jg@jgws.freeisp.co.uk]

CMC12 190725.0-013825   -   Mira variable

RA 19 07 25.0810 sd 0.213"  Dec -01 38 25.323 sd 0.142"  (ICRS)  [REF1]

has r'_CMT_ mag 15.631 with standard deviation (sd) 1.125 from 8
photometric observatoins [see note2]

(see REF1 for details of r'_CMT_ magnitudes, which are meant to be
similar to SDSS r', itself a modification/extension/rederivation of the
'red' passband gunn r)

Examination of archival survey plate images of 1' square [REF2] confirms
this to be a large amplitude object on four red plates dated 1950.5448,
1951.6427, 1988.4668, 1995.5797. It also appears on blue plates of 
1950.5448, 1951.6427, 1984.4175, 1988.6119, being almost invisible on
the first plate, relatively bright compared to adjacent stars on the
second, and very faint on the latter two. Marked variation of the object
relative to adjacent stars is evident on the red plates.

The large difference in relative brightness of the object between the
contemporaneous 1950s' red and blue plates suggests that it is quite
red, both relative to the adjacent stars, and inherently.

Also, despite being apparently quite faint visually (it is not in the
GSC, but that is not conclusive), the object is overexposed on a
1992.4011 'far red' IVN plate and has 2MASS photometry of:-

J  9.171 +/- 0.033 ;  H  8.191 +/- 0.015  ;  Ks  7.676 +/- 0.018

showing the object to be quite bright in the near infrared.

It is solely detected at and shows a point source function in Band A of
the MSX5C infrared catalogue, suggestive of silicate emission from a
late type star.  (It lies comfortably within the 3" error margin of the
MSX5C position, with no other prospective candidates evident within an
arcminute).

Marked variation randomly sampled over several survey plates is usually
consistant with a large amplitude regularly varying object (an erratic
object is likely to be at non-active brightness most of the time).

Red stars undergoing large amplitude change over time are invariably
Mira variables.


IDENTIFICATIONS :

USNOB1.0 0833-0471917 19 07 25.06 err .14" -01 38 24.8 err .24"
[REF2] [note1]

GSC2.2 S300232233058 19 07 25.06 err .26" -01 38 25.2 err .25"

2MASS 1907250-013825

MSX5C_G033.2938-04.3040

---------------------------------------------------------



John Greaves



Acknowledgements: This research made strong use of Guide 8 by Bill J
Gray; the CDS online services of SIMBAD, VizieR and Aladin; and NOFS
archive server [REF2].  The CMC12 V1.0 (Carlsberg Meridian Catalogue 12
Version 1.0) was sourced via CDS ftp services from subdirectory
.../I/282, where an explanatory readme file and copy of [REF1] can also
be found.


[REF1] Evans D.W., Irwin M.J., Helmer L.  Astron. Astrophys. 395, 347
(2002)

[REF2] This examination made use of the USNOFS Image and Catalogue
server at www.nofs.navy.mil/data/FchPix


[note1] (USNOB1.0 identifiers' reality/meaning unsure at this time)

[note2]
A guesstimatory feel for the meaning of the r'_CMT_ standard deviations
was made by comparison of handfuls common objects from the CMC12 and
MISAO variables, and also of FASTT variables thought to be LPVs.  The
latter was also useful in having an instrumental magnitude passband not
too dissimilar to CMC12, indeed mean magnitudes from CMC12 and FASTT
often compared well to within a tenth or two of a magnitude.  From this
a cut off standard deviation on r'_CMT_ was guesstimated to give an
extremely small subset of the whole that possibility contained long
period variables.

Each is examined individually through many catalogue searches, which
often revealed that variability of the object was already known in the
GCVS, NSV, MISAO project, ASAS survey or FASTT.

Objects without a known and/or suspect variable star catalogue entry
were then examined via the NOFS archive images.  In some cases these
images revealed that the standard deviation values were the result of
duplicity induced variability (two or more _very_ close similar stars),
or revealed that the object just wasn't variable, at least to a large
enough amplitude to be noted on the images, such that the standard
deviation was likely to be caused by unknown experiment specific
factors.

The remaining, smallest number, of objects show evidence of being
unknown Miras.

This is from a subset of roughly 4100 objects in CMC12 with standard
deviation greater than 0.75 (out of 6.3 million objects, but single
observations perforce have no standard deviation) preliminary results
suggest somewhere between 1 to 5 percent will be unknown Miras).

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