Photometric analysis of three totally eclipsing W UMa stars with increasing periods: TYC 3700-1384-1, V1511 Her, and V1179 Her

Abstract

ABSTRACT The first multicolour light-curve models and period studies for the totally eclipsing W UMa stars TYC 3700-1384-1, V1511 Her, and V1179 Her are presented. All three stars are A-subtype W UMa stars of spectral type F. The light-curve solutions show that TYC 3700-1384-1 has a moderately low mass ratio of q = 0.182 ± 0.001 and a degree of overcontact of $f = 49 {{\ \rm per\ cent}}$. For V1179 Her a mass ratio q = 0.153 ± 0.001 and a degree of overcontact of $f = 48 {{\ \rm per\ cent}}$ is derived. The solution for V1511 Her is inconclusive, however the mass ratio is expected to be between 0.13 < q < 0.15. The evolutionary status is compared with zero-age main sequence stars taking into account energy transfer from the primary to the secondary component. The primary component of TYC 3700-1384-1 fits well in the main-sequence, while V1179 Her is more evolved. The period study reveals for all three stars a continuously increasing period at a rate of ${{\mathrm{d}}P/{\mathrm{d}}t} = 6.1\times 10^{-7}\, \mathrm{d\, yr}^{-1}$, ${{\mathrm{d}}P/{\mathrm{d}}t} = 5.0\times 10^{-7}\, \mathrm{d\, yr}^{-1}$, and ${{\mathrm{d}}P/{\mathrm{d}}t} = 9.6\times 10^{-7}\, \mathrm{d\, yr}^{-1}$ for TYC 3700-1384-1, V1511 Her, and V1179 Her, respectively. The estimated mass transfer rates derived from these period changes are $\dot{M}=1.6 \times 10^{-7} {\, {\rm M}_\odot } \, \mathrm{yr}^{-1}$ for TYC 3700-1384-1 and $\dot{M}= 1.9 \times 10^{-7} {\, {\rm M}_\odot } \, \mathrm{yr}^{-1}$ for V1179 Her.