Important phases

We are adopting the following ephemeris equation:

(1)
\begin{align} {\rm JD} = {\rm JD_0} + 2022.7\,(\Phi - 11), \end{align}

where ${\rm JD_0}=2452819.2$ and $\Phi$ is the cycle+phase count (current cycle is 12). Below you can see the light curve obtained from the equivalent width of the He II $\lambda$4686 line (Teodoro et al. 2012), as well as the crucial dates around periastron.

• Phase zero is expected to occur on JD=2456864.599, which corresponds to 2014 July 26 02:23:00UT (this date is not absolute and should be taken as a reference only). Regarding the He II $\lambda$4686 line, it is expected to reach zero intensity on 2014 August 1st.
• Phases of large variations (May/1 through July/10). This time frame marks the rising to the high luminosity in He II $\lambda$4686 spectral line, and encompasses the P1 and P2 peaks, which epoch and intensity are not firmly known. For this time frame, 1 spectrum every 3 days is necessary. Number of spectra for this phase: 17.
• Critical phases (July/11 through August/10). This encompasses the He II $\lambda$4686 peak before minimum (P2), the phases of fast drop in all emission lines, plus the short minimum in He II $\lambda$4686. For that time-frame at least 1 spectrum per night is necessary. The ideal situation would be to record 2 spectra per day, to improve the period length. Number of spectra for this phase: 30.
• Periastron passage (July/23 through August/02). A specially dense monitoring should be organized for this 10 days time interval. Combining telescopes in New Zealand, Australia, South Africa, Brazil, Argentina and Chile, we should be able to cover enough time zones so as to improve the accuracy in the period (currently 1.3 days) by a factor greater than 5. A similar improvement would demand >25 years, if we were to cover just a few time zones, as we have done in the past periastron passages.
• Collapse phase (August/11 through September/30). The He II $\lambda$4686 P3 peak - corresponding to the collapse of the secondary’s wind - is expected to occur around September/13. These phases are very challenging to observe, since the star crosses the meridian at noon on September/01. Only a few observatories in the world would be able to make it. Spectra 1x/week are necessary. Number of spectra for this phase: 13.