Celestia Forums

I'm looking for a list of doubles/multiple star systems where the orbits of the companions are known - speciifcally I need to know the semimajor axis distances and eccentricities of the orbits.

The only catalogue I've found is at
http://ad.usno.navy.mil/wds/orb6.html

But the units it provides the numbers in are meaningless to me (theta? rho? milliarcseconds?) - to be useful for me, I need the distance info in AU or km (or need to know a way to convert to km or AU from those). I imagine one needs the distances from Earth to those stars... but they don't provide that!

Can anyone help, please?!
Cheers,
Consty

The 6th Binary Catalog you reference gives Hipparcos numbers, which allows parallaxes to be pulled out of the Hip catalogue, and from that a little trig gives you the semimajor axis in distance, rather than angular separation. Fridger would no doubt have knocked together a Perl script in a spare moment , but I took a slightly more brute-force approach, using the Hip catalogue as a look-up table in a spreadsheet.
So I've now generated Celestia (ecliptic-based) orbital elements for all entries in the 6th Binary Catalog that have a sensible parallax entry in Hipparcos.
I'm away for a few days now, but when I get back I can trim the data down into a simple text file (rather than a monster speadsheet) and send it to you, if you like.

Grant

Ooh, that'd be great - thanks! Much appreciated! I did notice that they had the orbital periods there, which gives some idea of the separation, but really I'm wanting to know what the spread of orbital distances is for a large sample of binary systems.

I also noticed on that catalogue that some stars are listed more than once, with different periods. Is that showing the orbital periods of both stars in the system around the centre of mass?

I do find it rather annoying that these star catalogues don't give you *all* the data to extract the information one needs. Maybe arcseconds are useful from an practial purposes, but it doesn't tell you a thing about how far the stars really are from eachother without having the distance to the star there... and they don't give that. And then you get star lists that show what magnitude the stars are, and neglect to mention spectral types or actual luminosities. Drives me nuts as a planet builder .

It seems that most of the time people just put up the basic observational data and don't process it into more refined forms... very frustrating!

Evil Dr Ganymede wrote:Ooh, that'd be great - thanks!

OK. Should get on to it tonight.

Evil Dr Ganymede wrote:... I'm wanting to know what the spread of orbital distances is for a large sample of binary systems.

Because the 6th Catalog is an astrometric catalogue, you're going to be missing data at both ends of the distance scale - companions that are so distant their orbits are undefined (like Proxima), and close spectroscopic companions that don't show up astrometrically.

Evil Dr Ganymede wrote:I also noticed on that catalogue that some stars are listed more than once, with different periods. Is that showing the orbital periods of both stars in the system around the centre of mass?

No - they're different published solutions to the same orbit. For your purposes I guess meaning the semimajor axes of the solutions would be as good a compromise as any.

Grant

Cheers again Grant, I do appreciate this.

I was looking at the catalogue again the other day and noticed that the periods range from fractions of a year to several thousand years, so that's probably a big enough range for my purposes. That should be a pretty wide spread range of distances. (of course, it'd be easier if they told us the mass of the component stars. Surely they know what those are from the period of the orbit, don't they?)

Evil Dr Ganymede wrote:Surely they know what those are from the period of the orbit, don't they?

M+m, at least, even if they don't know the precise mass distribution - but then there's going to be some uncertainty in the estimate for periods that are longer than a century or so, so that's going to introduce an error to the mass estimate.

Grant

The data have just gone off to the contact e-mail address at your Evil Doctor website, Consty.

Grant

Data received. Thank you sir, you're a god amongst men!

Interesting stuff too. I din't know Barnard's Star had three companions, for a start... I thought they ruled that out a while back?

Would you mind if I posted this somewhere for another board I'm on? I'd credit you fully, of course. It seems most of the companions there are within about 800 AU of the primary, which is really what I wanted to know. But it's all very useful indeed.

Many thanks again!

I am sure you are aware of the

Fourth Catalog of Orbits of Visual Binary Stars

http://cdsweb.u-strasbg.fr/viz-bin/Cat?V/39


Bye Fridger

Evil Dr Ganymede wrote:Interesting stuff too. I din't know Barnard's Star had three companions, for a start... I thought they ruled that out a while back?

Yes, the first two are Peter van de Kamp's original orbits for the companions he detected, but which have never been confirmed. I don't know where the eccentric third orbit comes from. Van de Kamp refined his orbits considerably over the years, so it's not clear why the orbits haven't been either a) quietly dropped after his death or b) "updated" with the later elements.

Evil Dr Ganymede wrote:Would you mind if I posted this somewhere for another board I'm on?

No problem.

Evil Dr Ganymede wrote:It seems most of the companions there are within about 800 AU of the primary, which is really what I wanted to know.

I've been thinking that's simply an artefact of the difficulty of orbit determination for long-period companions - 800AU corresponds to 20000yr for a Sun-sized star. Companion stars with undetermined orbits could sit a lot farther out, like Proxima, 33 Lib d, or Fomalhaut B - problem there, of course, is just deciding whether they're gravitationally bound or not.

Grant

t00fri wrote:I am sure you are aware of the

Fourth Catalog of Orbits of Visual Binary Stars

Yes, thanks. But I was under the impression it had been superceded by first the Fifth and then the Sixth Catalog of Orbits of Visual Binary Stars, which is what Consty and I are using. Is that not so?

Grant

granthutchison wrote:

t00fri wrote:I am sure you are aware of the

Fourth Catalog of Orbits of Visual Binary Stars

Yes, thanks. But I was under the impression it had been superceded by first the Fifth and then the Sixth Catalog of Orbits of Visual Binary Stars, which is what Consty and I are using. Is that not so?

Grant

Although I did not do a really thorough research, at least Strasbourg does only seem to offer:

================================================================================
The Fourth Catalog of Orbits of Visual Binary Stars
Worley C.E., Heintz W.D.
<Publ. U.S. Naval Obs. (2) 24, part VII (1983)>
=1983PUSNO..24g...1W (SIMBAD/NED RefCode)

What surprises me is that they are usually more or less complete...

http://cdsweb.u-strasbg.fr/viz-bin/Cat?V/39


But upon explicit comparison, I tend to agree with you.

In fact, there is another interesting catalog:
http://cdsweb.u-strasbg.fr/viz-bin/Cat?J/AJ/111/370

--------------------------------------------------------
Binary star orbits from speckle interferometry.
VIII. Orbits of 37 close visual systems
Hartkopf W.I., Mason B.D., McAlister H.A.
<Astron. J. 111, 370 (1996)>
=1996AJ....111..370H


Abstract:
New orbital elements are presented for 37 close visual systems that
have been observed and in some cases discovered by speckle
interferometry. Periods of these systems range from 5.7 to 425yr,
semimajor axes from 0.06" to 1.1". Four of these systems (Kui 18, Fin
325, StF 2597, and McA 77) had no previously published orbital
analyses, while elements for a number of other systems have undergone
major revisions. Finally, 135 new or revised interferometric
measurements of these systems are also presented, as well as 8
negative results.

-------------------------------------------------------

Bye Fridger

t00fri wrote:Abstract:
New orbital elements are presented for 37 close visual systems that
have been observed and in some cases discovered by speckle
interferometry. Periods of these systems range from 5.7 to 425yr,
semimajor axes from 0.06" to 1.1". Four of these systems (Kui 18, Fin
325, StF 2597, and McA 77) had no previously published orbital
analyses, while elements for a number of other systems have undergone
major revisions. Finally, 135 new or revised interferometric
measurements of these systems are also presented, as well as 8
negative results.

Hmmm. Although the abstract promises orbital elements, the table itself provides only position angles and separations. Perhaps I need to pull the original article ...

Grant