Is this enough info to construct a binary?

[ajtribick]

Who is Grant and how do I get my hands on his spreadsheet? (I love spreadsheets).

Grant is Grant Hutchison. He maintains various catalogue files included with Celestia but is no longer so active on the forums

The relevant spreadsheet is here.

How/where did you find this? I couldn't find Star B.. but I'm ignorant in the ways of SIMBAD.

It's at the bottom of the page in the External Archives section, the link that says CCDM J14038-6022AB, gives position angle and separation.

ACTUALLY it strikes me that I have almost certainly calculated the position of BET Cen B (and hence the barycenter) incorrectly by making a woefully stupid error during an approximation. The Aa/Ab subsystem should be correct though.

I got these numbers from Jim Kaler's website

Unfortunately Jim Kaler does not cite his source for those numbers (I took the numbers from the Davis article which he cites for the orbit diagram, but he doesn't appear to be using it for the masses, which is odd - the orbit and the masses are not independent, so this kind of mixing and matching is not a good idea!)

[ajtribick]

New version without stupid maths errors (I hope).

Code: Select all

Barycenter 68702 # position assuming mass ratio 18.18:~4
{
   RA 210.955835572
   Dec -60.373041266
   Distance 333.84
}

Barycenter "Agena A:Hadar A:BET Cen A"
{
   RA 210.955852083 # from SIMBAD
   Dec -60.373039444 # from SIMBAD
   Distance 333.84 # from Davis et al. paper
}

"Agena Aa:Hadar Aa:BET Cen Aa"
{
   OrbitBarycenter "BET Cen A"

   AbsMag -3.85 # given in paper
   SpectralType "B1III"

   EllipticalOrbit {
      Period 0.978528771
      SemiMajorAxis 1.285 # mass ratio 9.09:9.09
      Eccentricity 0.821
      Inclination 112.35
      AscendingNode 133.95
      ArgOfPericenter 233.15
      MeanAnomaly 304.23
   }
}

"Agena Ab:Hadar Ab:BET Cen Ab"
{
   OrbitBarycenter "BET Cen A"

   AbsMag -3.70 # given in paper
   SpectralType "B1III" # guess - it has the same mass as Aa.

   EllipticalOrbit {
      Period 0.978528771
      SemiMajorAxis 1.285 # mass ratio 9.09:9.09
      Eccentricity 0.821
      Inclination 112.35
      AscendingNode 133.95
      ArgOfPericenter 53.15
      MeanAnomaly 304.23
   }
}

"Agena B:Hadar B:BET Cen B"
{
   RA 210.955161403
   Dec -60.373157008
   Distance 333.84
   AppMag 4.1
   SpectralType "B8" # from Kaler
}

[Slartibartfast]

ajtribick, let's assume for the sake of argument that Hadar B is part of the system and orbits a common barycenter with Aa and Ab. How would that look in the STC?

[ajtribick]

ajtribick, let's assume for the sake of argument that Hadar B is part of the system and orbits a common barycenter with Aa and Ab. How would that look in the STC?

There isn't enough information to implement the orbit. All we've got is a separation and the angle it appears at with respect to Beta Centauri A.

Even the separation isn't particularly helpful as it is only the minimum separation, because it is calculated assuming it lies at the same distance from us as the A star. The accuracy of measurements to determine star distances is not good enough to tell whether Beta Centauri B is hundreds (or even thousands) of AU nearer or further from us than Beta Centauri A, so the actual separation could be much larger than the ~100 AU which is quoted.

Add to that the fact we don't know the eccentricity or the orientation of the orbit, and you've basically got the situation where any orbit you put into the .stc file is pretty much total fantasy.

[Slartibartfast]

I'm cool with fantasy. =) I am doing this all for the sci-fi book I'm writing after all.... to help me visualize everything... that and it's fun to see my creations in Celestia. =) Is there a fantastic way to show B orbiting the A pair that would put B at the same starting point that it is seen in the sky (ala the measurements we have from SIMBAD)??

[Hungry4info]

Is there a fantastic way to show B orbiting the A pair that would put B at the same starting point that it is seen in the sky (ala the measurements we have from SIMBAD)??

Of course it's possible, but I wouldn't know what to do to get it like that, other that constantly playing with the orbit until the star is in the right place. That would be rather strenuous, though.

[Slartibartfast]

Of course it's possible, but I wouldn't know what to do to get it like that, other that constantly playing with the orbit until the star is in the right place. That would be rather strenuous, though.

Yeah, I was afraid of that. Thanks for all the help everyone!

[Slartibartfast]

So, I asked Jim Kaler about Hadar B, and he said there was little info on the star. He pointed me to the WDS:

http://ad.usno.navy.mil/wds/wdsnewframe3.html

If you do a search/find for 14038-6022VOU 31Aa-B it'll bring you right to the star. Is any of this useful?

[Hungry4info]

If you do a search/find for 14038-6022VOU 31Aa-B it'll bring you right to the star. Is any of this useful?

Correction:

Code: Select all

14038-6022VOU  31Aa-B

I think when you posted your last post, the forum removed the second empty space between ...VOU and 31A...

Very nice link, too! Thank-you!

[Slartibartfast]

Hey, ajtribick, looking back, I got to wondering...

Barycenter 68702 # position assuming mass ratio 18.18:~4
{
RA 210.955835572
Dec -60.373041266
Distance 333.84
}

Barycenter "Agena A:Hadar A:BET Cen A"
{
RA 210.955852083 # from SIMBAD
Dec -60.373039444 # from SIMBAD
Distance 333.84 # from Davis et al. paper
}

Why the two barycenters, when your systems only use one? At first I assumed one was the barycenter for star B, but now I don't think that's what you meant.

[ajtribick]

Code: Select all

Barycenter 68702 # position assuming mass ratio 18.18:~4
{
RA 210.955835572
Dec -60.373041266
Distance 333.84
}

This one is the AB barycentre. I haven't put a name on it because the names are already defined in starnames.dat, but since Celestia automatically transfers the names across in this situation, it is the one which has the name "Agena:Hadar:BET Cen".

Since we know the positions and have an estimate of the masses, it is possible to calculate where the barycentre would be.

Thus I can put in the AB barycentre despite not knowing the orbit, which is what I did. It's just there to mark the position in space. Celestia is perfectly happy if you set up a barycentre without putting anything in orbit around it. Some of the binary stars implemented in Celestia use the same trick - the barycentre is in place but nothing is orbiting it.

Of course, this neglects differences in distance along the line of sight to the system, which are unknown.

The other barycentre is obviously the barycentre of the Aa/Ab subsystem.

[Slartibartfast]

Just my luck. I found the two papers, the abstracts of which I posted at the beginning of this thread. They both share many of the same authors. It turns out the stats we've been using are from the first paper. The second paper explains why they are wrong and gives new stats. I am combing the second one now for what is needed. If you're interested, the papers (and many, many more) can be found here:

http://front.math.ucdavis.edu/author/J.Davis

Search for Beta Centauri to find the papers.

[Hungry4info]

I do not get the numbers you do for the orbit of the Aa/Ab pair of BET Cen.

Ajtribick, a quick check on my part reveals that the SIMBAD data I used is nearly a decade older than the data from the paper you used. As we were using different parallaxes (Grammar?), we both got different distance and thus the seperation was different. That was the source of the discontinuity. I apologize, and recognize that your STC is more accurate than mine.

[ajtribick]

Problem with the second paper is that it does not give the full orbital parameters: the method is spectroscopic and thus only gives components of the motion along the line of sight.

I don't know how much this would affect the non-spectroscopic parameters: it does change the dynamical parallax and masses after all.

[Hungry4info]

Um... okay. I've finally gotten around to making that spreadsheat avalible. As far as I know, the only section that doesn't work well enough to be taken half seriously is the Dec to Deg converter.

http://www.mediafire.com/?9jjjmp2cpoz

[Slartibartfast]

Info I culled from the second paper:


Parameter Value
Porb (days) 356.92 ?± 0.03
v?? (kms??’1) 9.3 ?± 0.3
K1 (kms??’1) 63.2 ?± 0.6
K2 (kms??’1) 72.1 ?± 0.6
e 0.825 ?± 0.002
E0 (HJD) 2451600.03 ?± 0.08
longof periastron (degrees) 60.8 ?± 0.6

(in Porb, vy, K1, K2 and E0, the orb, y, 1, 2 and 0 should be subscripts)

M1 =10.7 +/- 0.1 (Sun)
M2 = 10.3 +/- 0.1 (Sun)
Orbital inclination 67.4 degrees
angular semi-major axis = 0,0253 degrees
orbital period 356.92 days
eccentricity = 0.81
distance = 108.4pc

[Slartibartfast]

Great spreadsheet Hungry! Thanks!
I'm trying to plug in the latest acquired data. How did you determine the separation between Aa and Ab in AU from the data we started with?

[t00fri]

Sorry to pester you with so many questions, but I can't learn if I don't ask, eh?

Well.. you might consider to READ instead...

F.

[Slartibartfast]

Well.. you might consider to READ instead...

Thanks for the constructive criticism! As a former teacher, I've told my students that many times. The problem for me is that much of what I read is greek to me. It has been very helpful to have people hold my hand and walk me through things, and I am very appreciative.

As far as the AU question above, the STC script guide says that a semi-major axis is measured in AU. The cause for my question is that the spreadsheet implies something else to my ignorant self.

[Hungry4info]

I used Grant Hutchison's spreadsheat.

The relevant spreadsheet is here.

Please just ignore t00fri's "constructive criticism". He's very knowledgable, and in my honest opinion, a great guy, but he sometimes is a bit... blunt.