Celestia Forums

In Celestia 1.6.1 Alcor has a companion star, listed as TYC 4242-6717-0 almost but not quite identical to Alcor, yet I can find no reference to this star anywhere, in fact Alcor does have a companion, but it's a red dwarf, so where did this A type twin pop up from, is it an error in the Tycho catalogue?

Thanks for your reply Argelesmer, I think the point I was making was that TYC 4242-6717-0 seems to be a spurious star, as if it existed, though it may not be a true companion to Alcor, it would at least be classed as a double star and would be visible in a telescope, unless the distance between the stars is to great to show that, in which case it is likely it would then be a spectroscopic double, but Alcor is not listed as a double star and all the times I have seen it in the scope it is alone, so where does the above star come from?

Did you mean then that it is an error in the hipparcos cat, or that we do no have the M class companion in celestia as it is using data from pre 2009?

Thanks again for taking time to reply, much appreciated!

That is wonderful argelesmer , thank you kindly for taking the time and effort to produce that, Alcor now has the correct Red Companion!


This does of course still leave the puzzle as to what exactly TYC 4242-6717-0 is doing in Celestia, it does not exist in SIMBAD, It does not exist in my eyepiece,

I suspect it does not exist at all, most strange!

Again, thank you for taking time to reply.

TYC 4242-6717-0 doesn't exist in a clean installation of Celestia 1.6.1.
Do you both have Pascal Hartmann's Tycho catalogue add-on installed, by any chance?

Grant

Yes I do have that as well Grant, thanks for spotting it! I am guessing that this is a small error then? Mystery solved, though I still wonder how it came to be.

Many thanks Grant, I have been pretty puzzled by this additional star.

Ah, I thought so.
For some reason, Pascal's data extraction generated some strange, long Hipparcos codes for multiple stars. These are interpreted by Celestia as being short Tycho codes. Hence the terminal "0", which isn't standard for Tycho.
Although I converted Pascal's original stars.dat files when Celestia changed its data format (you'll see my name on the Motherlode download link), I made no effort to correct this problem, because I didn't know exactly how it happened, and I was afraid I would break something else.
In this case, I'm guessing this is an artefactual "echo" of Mizar or Alcor.

Grant

Well I am wondering now if it is a mix up in some way with Mizar's B component (by that I mean the star you see in a scope, not the very close star that is less than 1AU from Mizar, no way could we see that!) which at a separation of 14" would make them 500 AU apart. Although I have the close star, the wide star forming the double is actually absent, truly it is most odd.

Although it seems unlikely to be a mix up, nevertheless, the Mizar star TYC 3850-1386-1 is missing, although entering either TYC 3850-1385-1 or TYC 3850-1386-1 brings you in both instances to Mizar A.

http://en.wikipedia.org/wiki/Mizar_and_Alcor

Mizar => HIP 65378

Alcor => HIP 65477

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http://en.wikipedia.org/wiki/Alcor_B

alcor B => red dwarf

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http://arxiv.org/abs/0911.5028

http://simbad.u-strasbg.fr/simbad/sim-i ... =ALCOR%20B

http://arxiv.org/pdf/0911.5028v2.pdf

Alcor A
Spectral type: A5V
magnitude: 3.99 mag
masse: 1.8 Msol


Alcor B
Spectral type: M3-4V C
magnitude: 8.82 mag
masse: ~0.3 Msol

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page 20 - 21

the semi-major axis (27.8 AU), then A (with mass 1.8 M?) and B (with mass 0.3 M?)
period of ?100 yr

====================
http://iopscience.iop.org/0004-637X/709 ... _2_733.pdf

page 6

Assuming a mass of 0.25M for the companion, a circular orbit of the projected radius 26 AU (1.05 at 24.9 pc) would have a period of roughly 93 years


ok