Open AccessA non‐main‐sequence secondary in SY Cancri
Author(s) -
Smith Robert Con,
Mehes Otto,
Vande Putte Dave,
Hawkins Nigel A.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09040.x
Subject(s) - physics , astrophysics , white dwarf , mass ratio , effective temperature , radial velocity , radius , star (game theory) , stellar mass , main sequence , roche limit , roche lobe , astronomy , calibration , binary star , stars , star formation , quantum mechanics , computer science , computer security
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.