AAVSO Special Notice #131: Long-term photometric campaign on the luminous blue variable P Cygni

Bernd Hanisch and Ernst Pollman of the BAV (Germany) request
high-precision photometry of the bright luminous blue variable P Cygni
beginning now, and continuing through at least the end of Cygnus'
current season of visibility. High precision (<< 0.05 mag) instrumental
V-band photometry is requested to correlate with spectroscopic
measurements of the equivalent width of the hydrogen (H-alpha) spectral
line.  It is suspected that the photometric brightness and H-alpha line
equivalent width might be correlated and variable on similar timescales. 

Long-term photometry of P Cygni will be compared with spectroscopic
measurements by the VdS (Vereinigung der Sternfreunde e.V.) spectroscopy
section.  This project may continue indefinitely; we ask that the star
be added to the observing queues of as many observers as want to
participate.  Rapid time-series are not required; intra-day variability
does occur, but large variations are expected to occur with timescales
of weeks or longer.

This project is ideal for photoelectric observers, but may also be done
by CCD observers able to observe bright stars.  Please use at least a
Johnson V filter; other filters may be used in addition to V, but V is
the primary filter for this study.  Observers are also strongly
encouraged to transform their data if at all possible.  PEP data
processed through the WebObs/PEPObs system are transformed
automatically.  CCD observers: please be very clear as to the comparison
star used to perform differential photometry, and be careful to avoid
saturating the variable.


P Cygni is located at the following (J2000) coordinates:

RA: 20 17 47.202 , Dec: +38 01 58.55


This star is a part of the AAVSO Photoelectric Photometry program, and
has the following comparison and check stars:


Comp: SAO 69101 (= 22 Cyg, HD 188892) 
        RA: 19 55 51.762 , Dec: +38 29 12.14
        V = 4.936 , B-V = -0.086

Chk:  SAO 69803 (= 36 Cyg, HD 193369)
        RA: 20 18 28.656 , Dec: +36 59 59.29
        V = 5.573 , B-V = +0.056



Charts of the field may be plotted using VSP:

http://www.aavso.org/observing/charts/vsp/index.html?pickname=P%20Cyg


Please report all observations to the AAVSO with the name "P CYG".


This AAVSO Special Notice was prepared by M. Templeton.

Editor's Note: The SAO number listed for P Cygni on the archival
PEP chart is incorrect.  The correct SAO number is SAO 69773.
 -M. Templeton, November 8, 2008

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