I am working on finding spectroscopic elements of a single lined spectroscopic binary. All I have is irregularly spaced radial velocity data which needs to be phase folded to plot a velocity curve (RV vs Time from T). For phase folding I need orbital period P and time of periastron passage T. I have determined the period by plotting a Lomb-Scargle periodogram but I'm unable to find a method to determine T. I can use already published value of T for that spectroscopic binary, but I want to learn how to determine T myself. Is there any method to determine T from RV data?

  • 2
    $\begingroup$ You need to fit the RV curve. One of the free parameters can be time of periastron. NB. You can only get this if there's significant eccentricity! $\endgroup$
    – ProfRob
    Mar 20, 2022 at 23:18
  • 1
    $\begingroup$ @ProfRob Thanks for the help! This was very easy but I completely missed it 🥲. Basically one can fit the equation $$V = V_{com} + K\left[e \cos(\omega) \pm \sin\left(2\pi\frac{(t - T)}{P}\right)\right]$$ to the RV data, where the $\pm$ sign refers to the primary or secondary component and $t$ is the time of observation. Since $P$ is known, the parameters $V_{com}$, $K$, $e$, $\omega$ and $T$ can be determined via the fit. $\endgroup$
    – ShaunakP
    Mar 21, 2022 at 18:05
  • $\begingroup$ Yes, that is how it is done AFAIK. $\endgroup$
    – ProfRob
    Mar 21, 2022 at 19:05


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