PV Cephei and Gyulbudaghian’s Variable Nebula

PV Cephei is a young Herbig Ae type variable star located in the constellation of Cepheus at RA 20:45:54 Dec +67:57:39. It is embedded in a dense molecular cloud from which it formed. Young stars like this are accreting material from a rotating disc surrounding the star. The accretion process often creates a strong magnetic field in the star which in turn causes bipolar outflows and jets along the magnetic axes of the star. In the case of PV Cephei, one of these outflows from the star has cleared a conical cavity out through the edge of the molecular cloud and light from the star is illuminating the inside of this cavity creating a fan-shaped reflection nebula adjacent to the star. The accretion process from the disc onto the star varies randomly causing the star to brighten and fade on a timescale of months. This in turn changes the illumination of the nebula which we see as changes in its apparent size, shape and brightness. The nebula was first catalogued by Armen Gyulbudaghian, an Armenian astronomer, and as a result it is known as Gyulbudaghian’s Variable Nebula.

PV Cephei is conveniently placed almost overhead during the autumn. Although it is faint, currently around magnitude 15, a CCD image through a telescope will show both the star and the variable nebula as a fan-shaped glow to the north-west of the star.

David Boyd