7 Variation in the orbital period of VV Vul

VV Vul is also an EA-type eclipsing binary with orbital period $3\hbox{$.\!\!^{\rm d}$ }411361$ (GCVS, 1985). Halbedel (1984) determined its spectral type to be A2/3V. Up to now, the system is neglected for photometric and spectroscopic studies and no absolute parameter has been published. Whitney (1959) gave 5 visual minima and obtained an ephemeris:

$${\rm Min I}=2433266.356+3.41131\times{E}.$$ (20)

After Whitney's (1959) work, 9 times of light minimum published in BBSAG Bulletin have been collected at Eclipsing Minimum Database. With the ephemeris given in the fourth edition of the GCVS,

$${\rm Min I}=2445151.570+3.411361\times{E}.$$ (21)

The O-C values of the 14 timings are calculated and are listed in the fourth column of Table 7. The corresponding O-C diagram is plotted in Fig. 10.

Figure 10: O-C curve of VV Vul and its description by a quadratic ephemeris

As shown in Fig. 10, the orbital period of this star is variable. Since no observatins is between E=-2533 and E=-90, the character of the variation is not clear. Considering a continuous variation in the change of the orbital period, a least square solution leads to the following quadratic ephemeris:

$$% {\rm Min I}\!=\! 2445151.5619\! +\! 3.41142458 \! \times\! {E} \!+\!1.601\ {10^{-8}}\!\times\!{E^{2}}$$ (22)

$\pm{3}$ $\pm{18}$ $\pm{7}$

and to a continuous period increase rate: ${\rm d}P/{\rm d}E=+3.202\ {10^{-8}}$days/cycle $=+3.43\ {10^{-6}}$ days/year which is equivalent to a period increase of 29.6 s/century. This ephemeris can be used for the estimation of future times of light minimum.