[Message Prev][Message Next][Thread Prev][Thread Next][Message Index][Thread Index]

[vsnet 840] Comparison sequence for CI Cygni

     A long string of photometric nights has allowed me to do some additional
work on comparison sequences for variable stars.  I have managed to complete
several fields for which Charles Scovil, the AAVSO chartmaker, has supplied
preliminary charts to work from (as long as four years ago!).
     Although otherwise extremely well-studied, CI Cygni appears not have a
convincing sequence published for it.  I observed stars selected from the
preliminary AAVSO (e)-scale chart dated Decmeber 1973, which contains mainly
eyeball estimates for the comparison stars.  However, both the magnitude 
zero-point and scale appear to be as good as any AAVSO chart lacking proper
photometry, with the usual scatter of a few tenths of a magnitude.
     I observed the stars on two nights (11 July 1994 and 13 October 1996 UT)
using the Lowell 53cm photometric telescope, either a 19- or 29-arcsec
aperture, and Stromgren y and b filters.  The 1994 data was taken during a full
night of observing that included over 30 primary and secondary standards whose
rms residuals averaged about 0.007 mag. in both V and b-y; the short session
last night involved a dozen standards with similar scatter.
     The results are shown below in a form similar to those I've sent out
previously.  The positions are from the PPM or the GSC.  For the two faintest
stars, which are not in the GSC, the positions are from the USNO "UJ1.0"
CD-ROM; the names for these stars are simply the position rounded to 1s/0'.1
precision.  The second line of each entry shows the rms scatter of the pairs
of observations as appropriate; for the faintest star, the value in parentheses
is the scatter in the batch of integrations plus the error in the fit to the
standards taken in quadrature.
     Most of the spectral types are from a paper by Mikolajewska and
Mikolajewski (1980, Acta Astron. 30, 347), which gives photographic UBV
photometry and MK types for a couple hundred stars in the field of this
variable.  The photometry here unfortunately shows a lot of scatter (~0.2 mag),
so isn't useful for much.  However, the MK types for fainter stars appear to
be just fine, consistent with those given in the HDE catalogue.  The region
lies just outside the spectral surveys done at Case and Crimea.
     Photometry for many of these stars and others in the field was published
by Howarth & Bailey (1980, JBAA 90, 265).  In comparison to my results, their
V magnitudes range from 0.05 to 0.2 mag. too bright as a function of color
(redder stars are progressively brighter).
     Among the individual stars, I was surprised to find that the very red star
GSC 2677-1273 appears to be not variable:  it is evidently simply strongly
reddened.  In combination with the stars of more ordinary color in the field,
it can provide a check on color transformations with CCD systems.  Visual
observers should note, however, that the star will appear too faint relative
to other stars.  The apparent difference visually with nearby GSC 2677-0784 is
much smaller than the delta-V would suggest.



Photometry of stars in the field of CI Cygni

Name                RA  (2000)  Dec         V      b-y   n  spec  Remarks
HD226041         19 49 59.6  +35 40 14    8.588   0.236  2  F5      
                                           .022    .002
HD226107         19 50 38.8  +35 50 27    8.620  -0.029  2  B9V     (1)
                                           .001    .003
HD226117         19 50 49.5  +35 47 45    9.009   0.812  2  K2III
                                           .011    .005
HD225992         19 49 30.0  +35 50 01   10.487   0.188  2  F1V     (2)
                                           .004    .012
GSC 2677-1273    19 50 39.7  +35 33 42   10.673   1.344  2
                                           .010    .030
GSC 2677-0784    19 50 32.6  +35 32 52   11.170   0.783  2
                                           .009    .013
GSC 2861-0298    19 50 33.1  +35 42 42   11.56    0.28   1

GSC 2861-1332    19 50 24.6  +35 43 10   11.715   0.201  2  B6IV
                                           .015    .001
J195019+3539.5   19 50 19.0  +35 38 32   12.52    0.43   2
                                           .04     .02
J195022+3541.1   19 50 21.7  +35 41 05   13.42    0.36   1
                                          (.04)   (.04)


Remarks

1   V = 8.55 (Golay 1958, Publ. Obs. Geneve, fasc. 57).
2   V = 10.49 (SIMBAD:  can't find the source!).



\Brian Skiff  (bas@lowell.edu)

VSNET Home Page

Return to Daisaku Nogami

vsnet-adm@kusastro.kyoto-u.ac.jp