The discovery of orbital dips in the soft X-ray emission of U GEM during an outburst.
Abstract
A series of Exosat and IUE observations of the dwarf nova U Geminorum have been made during the decline from an unusually long outburst that occurred in 1985 October and November. A strong soft X-ray flux was recorded which is modulated with the orbital period of the binary. The modulation takes the form of broad, deep dips whose morphology changes from cycle to cycle and which are reminiscent of the orbital dips seen in some low-mass X-ray binaries. The dips in U Gem last for up to half the orbital cycle and are centered either at phase 0.7 or phase 0.15 with respect to the time of optical eclipse. The relative importance of the dips at these two phases changes with time. At the beginning of one dip the soft X-ray flux was extinguished within 15 s. There is no evidence for dips in the medium energy X-rays, in the ultraviolet, or in the optical band. It is argued that the dips are caused by photoelectric absorption in material with a column density of about 3 x 10 to the 20th atoms/sq cm that is at a substantial distance from the X-ray source and high above the orbital plane.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 1988
- DOI:
- 10.1093/mnras/232.4.779
- Bibcode:
- 1988MNRAS.232..779M
- Keywords:
-
- Dwarf Novae;
- Emission Spectra;
- Stellar Motions;
- X Ray Astronomy;
- X Ray Spectra;
- Binary Stars;
- Exosat Satellite;
- Iue;
- Light Curve;
- Orbital Elements;
- Astrophysics