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

November 7, 2008
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:

obsolete link [obsolete:]

2016 link:  Plot using VSP at


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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