How could I determine semiamplitude from these data for NGC300 X-1 without fitting, only with data of phase and JD? This is a common problem for exoplanets, X-ray binaries and other general binary sistems. So, I am interested in general techniques (if any) beyond fitting (a list of software for data fitting for RV plots would be also welcome in the answer) enter image description here

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  • $\begingroup$ What do you mean by "without fitting"? Surely finding the semi-amplitude is fitting a sine curve to the graph. Least Squares has a good tradition (I get a least squares fit with an amplitude of 256.6. $\endgroup$
    – James K
    Feb 19 at 22:32
  • $\begingroup$ I was tempted to guess an approximation to K making K=(v_r(max)-(v_r(min))/2. Indeed, ... k(guess)=(456.6-(-68.3)(/2=262.5km/s, not far from the given value. I presume the issue is the phase and a trigonometric condition. $\endgroup$
    – riemannium
    Feb 19 at 23:31


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