[vsnet 272] Preliminary revised comparison sequence for BF Cygni

[bas@lowell.edu (Brian Skiff)]

     At the request of Gary Poyner, I have begun revising the comparison
sequence around the symbiotic star BF Cygni.  The BAA sequence (using results
from the GEOS group) extends to only mag. 11.5, whereas the star is presently
near mag. 12.5.  The AAVSO sequence goes fainter, but is based on photographic
photometry and clearly has a zero-point error.
     Because I may not be able to get to it again soon, I present the first
night's results below.  I worked from the AAVSO preliminary (d)-scale chart
last revised Sep 1988.  For stars fainter than AAVSO "125" (which has V=12.2),
I chose stars closer to the variable than the ones labelled on the chart.
     Note that AAVSO stars "144" and "145" just west of the variable are both
wide, roughly equal pairs on the digitized POSS-I E images (obtained via
SkyView) and thus should be avoided.  I tried to carefully select isolated
stars at the telescope, but was not completely successful, as the notes
indicate.  I do not think the companions noted are serious problems for visual
observers.
     The AAVSO magnitudes in common are consistently a few tenths too faint.
The two BAA/GEOS stars in common agree fairly well, although for the fainter
star the difference is perhaps significant.  Considering how crowded the
field is, it may merely be that a larger photometer aperture in the GEOS 
observations resulted in the stars being found brighter---rather than some
observational error in either set of photometry.  (On the Lowell 53cm
telescope, I almost always use a 29-arcsec diaphragm.)
     I include the precise GSC position for BF Cygni in the list below since
it is given slightly inaccurately on both the BAA and AAVSO charts.  Finally,
note that some additional fainter stars about one-half degree west (around 
AV and DV Cygni) already have published photometry (IBVS 3968).  A few of
these fall on the west edge of AAVSO chart for BF Cygni.
\Brian


Preliminary photometry for stars in the field of BF Cygni


Name               RA  (2000)  Dec        V     b-y   spec   remarks
BF Cygni        19 23 53.5  +29 40 29                        (1)

BD+29 3579      19 23 11.3  +29 30 10    9.76   1.20  K2     (2)

BD+29 3586      19 24 37.4  +29 34 17   10.51   0.26         (3)

GSC 2137-1762   19 24 12.7  +29 35 04   10.97   0.77         (4)

GSC 2136-0649   19 23 35.5  +29 39 19   11.29   0.83

GSC 2136-0027   19 23 27.7  +29 41 28   12.02   0.70         (5)

GSC 2136-0778   19 23 41.1  +29 37 05   12.90   0.78

GSC 2137-1408   19 23 52.4  +29 43 57   13.43   0.50         (6)


Remarks:
(1)   GSC 2137-0234 = LS II +29 05
(2)   GSC 2136-0601 = BAA/GEOS "B":  V = 9.73
(3)   GSC 2137-0298
(4)   BAA/GEOS "D":  V = 10.83
(5)   star ~20" N excluded, but two very faint merged companions included
(6)   SkyView image shows merged companion on NE side; appeared single 
      visually in 53cm telscope photometer post-viewer (~500x).

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