An evolved donor star in the long-period cataclysmic variable HS 0218+3229

Abstract

Context. We present time-resolved spectroscopy and photometry of HS 0218+3229, a new long-period cataclysmic variable discovered within the Hamburg Quasar Survey. It is one of the few systems that allow a dynamical measurement of the masses of the stellar components. Aims. We combine the analysis of time-resolved optical spectroscopy and R-band photometry with the aim of measuring the mass of the white dwarf and the donor star and the orbital inclination. Methods. Cross-correlation of the spectra with K-type dwarf templates is used to derive the radial velocity curve of the donor star. An optimal subtraction of the broadened templates is performed to measure the rotational broadening and constrain the spectral type of the donor. Finally, an ellipsoidal model is fitted to the R-band light curve to obtain constraints upon the orbital inclination of the binary system. Results. The orbital period of HS 0218+3229 is found to be 0.297229661 ± 0.000000001 d (7.13351186 ± 0.00000002 h), and the amplitude of the donor's radial velocity curve is K 2 = 162.4 ± 1.4 km s −1 . Modelling the ellipsoidal light curves gives an orbital inclination in the range i = 59 • ± 3 • . A rotational broadening between 82.4 ± 1.2 km s −1 and 89.4 ± 1.3 km s −1 is found when assuming zero and continuum limb darkening, respectively. The secondary star has most likely a spectral type K5 and contributes ∼80-85% to the R-band light. Our analysis yields a mass ratio of 0.52 < q < 0.65, a white dwarf mass of 0.44 < M 1 (M ) < 0.65, and a donor star mass of 0.23 < M 2 (M ) < 0.44. Conclusions. We find that the donor star in HS 0218+3229 is significantly undermassive for its spectral type. It is therefore very likely that it has undergone nuclear evolution prior to the onset of mass transfer.

Multicolor photometry of the dwarf nova HS 0218 + 3229

“…8). A similar variation in the amplitude of the system brightness has also been observed by Rodriguez-Gil, et al [2]. It should be noted that they made their observations without a filter.…”

“…8) and in all the other calculations. RodriguezGil, et al [2], found a somewhat different value for the orbital period, 0 d .29722966. Note that this value of the period does not match all the observations.…”

“…interstellar reddening. The interstellar reddening is estimated to be E(B -V ) = 0 m .07 [2]. Thus, in most cases (except Section 6) we have neglected the interstellar reddening in interpreting the data.…”

“…The double wave is caused by the elliptical shape of the red component, since it contributes 80-85% of the overall R band brightness of the system in the quiescent state [2] and dominates the combined emission from the system.…”

“…From 2000 through 2005, Rodriguez-Gil, et al [2], made photometric and spectral observations of the variable with various telescopes. A study of the photometric series for this system did not reveal any outbursts, and they classified HS 0218+3229 as a cataclysmic variable without establishing a precise type.…”