A non-main-sequence secondary in SY Cancri |
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| Authors: | Robert Connon Smith Otto Mehes Dave Vande Putte Nigel A Hawkins |
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| Institution: | Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9QH |
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| Abstract: | Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Na i doublet, yielded a semi-amplitude of K 2= 127 ± 23 km s?1 . Taking the published value of 86 ± 9 km s?1 for K 1 gives a mass ratio of q = M 2/ M 1= 0.68 ± 0.14 ; this is very different from the value of 1.13 ± 0.35 quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass–radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star. |
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| Keywords: | stars: dwarf novae stars: individual: SY Cnc novae cataclysmic variables |
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