Optical identification of the X-ray source E 1405-451 : a 101.5 minutebinary system with extremely rapid quasi-periodic variability.
Abstract
A 15th magnitude blue emission-line star is identified as the optical counterpart of the variable soft X-ray source El405-45l. The spectrum shows strong, asymmetric emission lines of H, He I, He II and Ca II which have a full width at base of 2000 km s-1. Optical photometry reveals that the light of the star is modulated with a period of 101.52±0.02 minutes. The morphology of the light curve is a function of color. A broad, asymmetric modulation of amplitude 1 mag is seen in white light, with a shallow secondary minimum occurring 0.4 of a cycle after the deep primary minimum. In the U band, however, the broad modulation is much less pronounced, and a narrow (FWHM ∼2.5 minutes) eclipse-like feature that is coincident with the broad minimum is prominent. In addition to the 101.5 minute modulation, the star flickers on time scales of order 1 minute with an amplitude as high as 0.3 mag at all phases of the light curve. Fourier analysis of the data shows a broad peak of power at frequencies between 0.4 and 0.8 Hz (∼1-3 s), corresponding to an rms variation of 1.2% of the stellar light. The peak remains broad when the data are analysed in intervals as short as ten minutes. The properties of E1405-451 suggest that it may be related to the magnetic cataclysmic variables of the AM Her type. We consider the probable geometry of the source and discuss various mechanisms that might produce the quasi periodicity, whose rapid time scale is thus far unique among cataclysmic variables.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1983
- DOI:
- 10.1086/160627
- Bibcode:
- 1983ApJ...264..575M
- Keywords:
-
- Binary Stars;
- Magnetic Stars;
- Stellar Spectrophotometry;
- Variable Stars;
- X Ray Sources;
- Emission Spectra;
- Line Spectra;
- Spectrum Analysis;
- Stellar Models;
- Stellar Spectra;
- Time Series Analysis;
- Astrophysics