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Evidence for a 6 Year Periodicity in X Persei

Published online by Cambridge University Press:  14 August 2015

J. D. Dorren  and
E. F. Guinan
J. D. Dorren
Affiliation:
Biruni Observatory, Shiraz University, Shiraz, Iran
E. F. Guinan
Affiliation:
Villanova University, Villanova, Pennsylvania, 19085, USA

Extract

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Intermediate and narrow-band photoelectric observations obtained at Biruni and Villanova Observatories from 1977 to the present, when combined with previous data, strongly suggest that light increases of about 0.5 mag occur at 6 year intervals. Possible explanations are considered.

The X-ray pulsator X Persei (4U 0352+30) is an intriguing object at both X-ray and optical wavelengths. From the X-ray data a period of 13.9 minutes now appears well-established, but early suggestions of a 22.4 hour periodicity remain unconfirmed (White et al.,1976, Becker et al., 1979). The nature of the X-ray emission is unusual; the source is about 3 orders of magnitude weaker than other X-ray binary pulsars, and the spectrum contains a strong high-energy X-ray component (Mushotzky et al., 1977). Long known as an irregular variable, X Per has been classified as a Be star with an 09.5 (III-IV)e spectral type and showing broad hydrogen emission and absorption features (Brucato and Kristian 1972, Hutchings et al., 1975). A 581-day period is indicated by the radial velocity study of Hutchings et al., (1975). This has been variously interpreted as an orbital period (about a black hole) or an apsidal period, the models having in common accretion on to a neutron star as the source of the pulsed X-rays. In 1977 an increase in brightness of the star was observed by Kalv (1977) and Guinan et al., (1978), and by April 1979 we had accumulated sufficient evidence to suggest that X Per undergoes periodic (≃ 6-year) outbursts (Dorren et al., 1979a).

Type
VI. X-Ray Binaries
Information
Symposium - International Astronomical Union , Volume 88: Close Binary Stars: Observations and Interpretation , 1980 , pp. 361 - 365
Copyright
Copyright © Reidel 1980 

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