Wednesday, January 14, 2015

checked Diadem

Tried to answer Sally-Anne's questions in her comment on my alpha Com article.

Q: Is it possible that the exact dates of periastron can be known?

A: Yes, I believe so. SkyTools 3 Professional shows that the orbit is "definitive." This suggests the orbital data is known with some confidence. I'm not an expert on these matters but I think there are 6 (?) parameters used to calculate an orbit, like eccentricity, argument of pericentre, etc.

Q: [Can periastron be determined] by counting forward from previous PA and comparing?

A: Yes, that should be quick and give a crude answer. But, again, if the orbit data are known, it should be possible to compute with some accuracy. According to the SkyTools Stellar Orbital Companion motion trails plot, the next periastron should occur late 2025 or early 2026.

Q: Do [you] have an idea when in spring '15 it will occur?

A: I did a plot and it actually looks like the close approach happened in November or December of 2014. And now, the B star, is moving to the north.
Q: "U said but rt now AB are separate... i guess that is to be expected since it's winter, or shd they not need to have so far to travel?"

A: I'm not sure I fully understand the question. In my 19 Jan 2014 post, I shared that the software predicted the stars to be 0.21 seconds-of-arc apart. This seems to correspond to the plot, i.e. about 1/3 of the maximum elongation. But they were moving closer. Now, a year later, they should be virtually on top of one another, so difficult or impossible to split. That is supported by the current report from SkyTools: "not splittable currently." In the summer of 2017, for two years, the stars should be far apart, almost at their maximum.

See the Journal of Double Star Observations for more information.

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