P Cygni stars

The characteristic star of this group is P Cygni, a nova which flared up in 1600. P Cygni is now a variable B1 supergiant of 5.0 mean magnitude. P Cygni stars lines shows a profile type called "P Cyg": an emission component to the red side of an aborption line. There are blue super-giant stars. They have larges masses and high intrinsic luminosities.

Numerous stars can present some lines with a "P Cyg" profile, but the only true candidate P-Cyg stars are P Cyg itself and AG Car (= Eta Carina) and R 81 (S Dor)  in the Large Magellanic Cloud. Other possible members in outer galaxies: SN1961V in NGC 1058 and SN1954J (V12) in NGC 2403.

The spectral profiles can evolve according to the time (these stars are often named LBV for Luminous Blue Variable). P Cygni features is indicative of energetic mass outflows. Some time, LBV shows giant eruptions. For example, Eta Carina became the brightest star in the sky between the years 1837 and 1860! For these events the star ejected at least one solar mass of material. It is estimated that LBV are possible progenitors for Wolf-Rayet stars.

P Cyg localisation:

P Cyg = 34 Cyg     R.A.(2000) = 20 h 17 m 47 s    Dec.(2000) = +38° 01' 59''

Observations of P Cygni

The observations have been made with the middle resolution (R=3000) spectrograph mounted at the focus of 190 mm flat-field telescope and an Audine camera.

Typical aspect of P-Cygni spectrum (the bright line is H-alpha).

Wide spectral range. Note the charateristic P Cygni profile.

Zoom on the H-alpha line.

Background around H-alpha and He I lines.

Comparison of profiles spectra for 29/08/1999 and 10/09/1999. Fine modifications are noted for the background (to be confirmed...).

Spectr'Aude - Dispersion of 4 A/pixel. Click on the image to enlarge.