2. Observational data
We have used a spectrum of Cnc obtained with the ESO New Technology Telescope (NTT) at La Silla, Chile, provided by G. Mathys (ESO). The material consists of a continuous spectrum between 4100 and 6700 Å acquired with a resolving power of R = = 60000. Spectra for the HgMn star HR 7775 and a second set of observation material for Cnc were obtained with the Nordic Optical Telescope (NOT) at La Palma, Canary Islands, using the SOviet FINnish (SOFIN) high resolution spectrograph (Tuominen et al., 1999) at a resolving power of 60 000. The data obtained with the two telescopes are considered to be comparable in quality.
The Bright Star Catalogue (Hoffleit & Jascheck, 1982) lists Cnc as a multi-star system, consisting of three objects. A recent study (Ryabchikova et al., 1998) shows the flux ratio between the primary and secondary components to be approximately 11.5 in the V band, while the faint third component is assumed to make an insignificant contribution to the spectrum. The bright companion seems to be a relatively fast rotator and spectral lines from it are smeared out in the spectrum and show only features from the very strong lines CaII H & K and MgII 4481 in addition to the spectral lines of hydrogen and helium. The MgII line from the secondary component is observable in our spectrum and is used to determine the components relative velocity and the corresponding wavelength shift.
HR 7775 is also known to be a multiple star system. A fainter close companion was detected by the Hipparcos satellite at a distance of 0.68 arcsec. Our high resolution SOFIN spectrum was obtained using a slit width of 0.7 arcsec (Wahlgren et al., 2000). We have chosen to treat the spectrum of HR 7775 as originating from a single star due to the unknown nature of the binary orbit and the high likelihood that the close companion lies outside the aperture.
© European Southern Observatory (ESO) 2000
Online publication: December 11, 2000