Talk:Albireo

Period

I've taken out the phrase about the distance and orbital period of the binary system, since I've found pages saying that the distance between pair stars is 4400 AU with orbital period of 7300 earth year, such as [1]. --Puzzlet Chung 06:58, 20 Mar 2005 (UTC)

Something is not right with these numbers. Kepler's third law can be expressed as $a^{3}=(m_{1}+m_{2})P^{2}$. If we give a total mass of, say, 10 Suns, orbital period of the stars would be still about 92000 years. But in the original article, distance was 44 AU, which is wrong. In that case orbital period would be much less than Pluto's. This article [2] gives possible orbital period of 7800 years. --Jyril 09:04, Mar 20, 2005 (UTC)

Triple

I replaced the section on Albireo as a triple star -- I was some years later and for several years a member of the team which had made the first high-precision measurements in 1976, and made some of the circa 1990 observations myself using the Kitt Peak 4m telescope. The catalogue of interferometric observations by all groups of this object (and all other binary stars) may be found in the Fourth Catalog of Interferometric Measurements of Binary Stars, available at the US Naval Observatory, http://ad.usno.navy.mil/wds/int4.html. -- Don Barry, Cornell University (24.92.255.115 on 26 September 2006)

Orbital elements

This page contains nonsense. There is absolutely no source for the orbital elements (eccentricity, longitude of node, orbital period, separation, etc., etc.). The Washington Double Star Catalog quoted as the source lists all components of the albireo system; it lists no orbital elements. the sixth orbital catalog lists elements only for the spectroscopic Ab,Ac system. At a period of 220,000 years there is no way humanity has in two centuries amassed enough positional change data to compute orbital elements. All these numbers have been made up whole cloth. Macevoy (talk) —Preceding undated comment added 21:35, 24 April 2012 (UTC).

The problem is that the infobox is displaying orbital data for Albireo C, not Albireo B. Is there any way to specify this in the infobox? Should the orbital section be removed from the infobox since it gives the impression that the data is for Albireo B? UPDATE: Under "orbit_footnote" I have added, " for Albireo C" to hopefully make the infobox clearer and less misleading. -- Kheider (talk) 19:15, 17 September 2012 (UTC)

The pair visible in a small telescope is A/B. The pair of stars in the first infobox is Aa/Ac, which is also the pair for which the orbit is given. B is in the second infobox, lower down. Spacepotato (talk) 03:43, 18 September 2012 (UTC)

I disagree. As far as I know, the apparent magnitude of 5.8 is Albireo B (the distant blue-green start) not C (the close star). I have corrected this in the infobox.

Obviously, the infobox is not optimal at present, with parts of it referring to the larger binary system, and others to the smaller. Whoever reads this, please feel encouraged to improve ... Tomeasy _{T C} 23:00, 7 November 2014 (UTC)

The first infobox refers to Aa/Ac, the close spectroscopic binary, and the second to B, the more distant companion. See the Washington Double Star Catalog [3], entry 19307+2758. Spacepotato (talk) 23:37, 7 November 2014 (UTC)

Distances

1.: Distance from earth: The article says "380 light-years (120 pc)" and the infobox says "430 ± 20 ly (133 ± 6 pc)". Now what?
2.: It seems User:PuzzletChung removed the distance from one star to the other in 2005. It's a shame that no one has been able to fill this in in the meantime. I would do the calculation myself if not for 1.
I help out as a guide at an observatory, and thats the first thing people ask: "How far away ist it" / "How much distance between the two". I came here today to get answers, and I'm quite surprised that apparently no one has been able to provide these yet. --BjKa (talk) 17:09, 1 November 2012 (UTC)

That requires that one know the orbit, which we are far from knowing. It is only possible at the present time to get a lower limit to the 3-D separation of the components, that is, the separation of their projection onto the sky plane.Donaldjbarry (talk) 04:01, 22 April 2018 (UTC)

380 is an old value, I believe from the original Hipparcos parallax. The revised Hipparcos parallax gives 430. Note that Albireo B infoxbox still has the old value, hence it is 40 light years from its primary :) Interestingly, the new Hipparcos reduction gives different values for the parallaxes of Alibireo A and B, slightly larger than their joint margins of error, an interesting comment on the accuracy of such things. Fixing. Lithopsian (talk) 17:30, 1 November 2012 (UTC)

Note, confidence intervals are not "margins of error", but rather a statement that the true value is estimated to lie, within some probability, within the bounds stated. The probability is not always stated and the default varies across fields, a frequent bad habit of scientific papers. In astronomy it is usually a 1 sigma result, meaning a 68% probable confinement of the true value, assuming a normal distribution of errors. It is not infrequent, however, that a 2 or 3 sigma result is stated, implying a 95% or 99.8% probability. By comparison, particle physics tends to use a 5 sigma result for claims of novel detections, a 99.99998% assurance based on errors being random, which essentially means that unknown systematic effects are far more likely to effect a false detection than random error.Donaldjbarry (talk) 03:58, 22 April 2018 (UTC)

Pronunciation

Could someone put up a sound file as I am not sure how to pronounce it? Jzlcdh (talk) 13:54, 15 July 2013 (UTC)

Discovering a binary with an interferometer?

The article states: "In 1976, component A was itself discovered to be a binary star, using speckle interferometry and the 2.1-meter telescope at the Kitt Peak National Observatory." This seemed suspicious since determining the binary nature of a star with a spectroscope is generally easier than resolving the pair with an interferometer. So I checked and found that Albireo Aa and Albireo Ac, the pair in question, have separate Henry Draper Catalog numbers, HD 183912 and HD 183913 respectively. They must have been known as a spectoscopic binary pair since 1949 at the latest, the last year that the HDC was updated. So, what happened in 1976 was that a known spectoscopic binary was resolved by interferometry. I will make the appropriate correction when I can get the wording and references right, if someone else does not beat me to it. - Fartherred (talk) 18:24, 27 February 2015 (UTC)

In general there is no guarantee that a binary can be detected spectroscopically. Gowever, Albireo has been known to have a composite spectrum for at least a century. Although one of the speckle references claims that no radial velocity differences had ever been detected, the radial velocity of Albireo A had been reported as early as 1919 to be decreasing slowly. It is now known to be a long period binary directly resolvable by modern equipment. Lithopsian (talk) 20:12, 27 February 2015 (UTC)

Thanks Lithopsian, I should have written that determining the binary nature of a star with a spectroscope is easier than resolving the pair with an interferometer most of the time. Of course there are cases in which the axis to rotation of the binary is parallel to the line of sight. With modern spectroscopy and the high orbital speeds that can be involved, there is a small fraction of cases in which the binary nature of a star eludes the spectroscope. Uncountable binaries are beyond resolution with an interferometer. In this case the binary nature of Albireo A was known long before 1976, as shown by the HD numbers, and that is what is most significant here.

Please note that separate HD numbers are not assigned to spectroscopic binary components. They refer only to the system. Even optical binaries of several arcsecond separation have unique HD numbers.Donaldjbarry (talk) 04:12, 22 April 2018 (UTC)

Another point about the article, the font in the infobox makes the seconds mark in +27° 57′ 34.84″ for the declination of Aa practically illegible on my display. I had to copy it to a larger font to be sure of the text and then just remember what was printed where.- Fartherred (talk) 21:56, 27 February 2015 (UTC)

Albireo Aa and Albireo Ac orbit each other in 213 years. The separation I calculate from the infobox is 0h 0m 0.009s right ascension and 0° 0′ 0.22″ declination. However the separation given on this site is 0.4 arc seconds. If the separation is decreasing it could be near minimum now which would likewise make the radial velocity differences minimum. One could wait fifty-six years to make spectroscope measurements or else read the literature to find what the spectrum differences were when one could detect them. Various websites copy free information with questionable reliability but I hope professional astronomers have access to historical data that they can depend upon. - Fartherred (talk) 22:47, 27 February 2015 (UTC)

Please note, Radial velocity differences are only at a minimum during periastron for circular orbits, a bad assumption for all but extremely close, interacting binaries.Donaldjbarry (talk) 04:12, 22 April 2018 (UTC)

I have made the correction. If someone can improve the wording and give better references, feel free. - Fartherred (talk) 15:47, 1 March 2015 (UTC)

Cub Scout star

Also known as the Cub Scout star; but I'm not too sure how to edit it in without it looking like an abomination. :( — Preceding unsigned comment added by 104.220.56.173 (talk) 01:15, 7 July 2016 (UTC)

Radius

Does this star have a radius of 16 R_☉? If you search the size of Albireo A on the net, you always get 16 R_☉. But where did that come from? Also, where is the actually source for jumk.de 's 109 R_☉?

You're asking in the wrong place. Wikipedia gives its sources (should do anyway), random web pages can just throw any old number out. 69 R_☉ is calculated from a published angular diameter and a published distance. It is unfortunate that they are published in different papers and combined only in WP, but a radius calculated from the bolometric luminosity and effective temperature is comparable. Lithopsian (talk) 17:09, 29 November 2017 (UTC)

Gaia data

A and B have different proper motions

"Star A is moving at 16.66 milliarcseconds per year south by southeast, while Star B is moving at 1.13 mas/yr west by southwest**. The uncertainties in the measurements are relatively small compared to the motion, so I'm confident in saying they're moving in two different directions at two different speeds, and therefore not physically bound together. Their alignment is coincidental." Agmartin (talk) 19:12, 15 August 2018 (UTC)

I wouldn't get too excited just yet. Gaia results are (currently) notoriously unreliable for naked-eye stars because special techniques have to be applied and this hasn't been done for this data release. Some naked-eye stars are still included where the data passes some basic sanity checks. The primary also has a disk that is large compared to the Gaia measurements (meaning it may be observing different parts of the disk at different times), and this would need to be checked and corrected-for before any strong claims could be made. And of course always bear in mind that the quoted margins of error are only one standard deviation, and there are potential systematic errors in addition to the quoted errors. We need to wait for something peer-reviewed. Lithopsian (talk) 20:09, 15 August 2018 (UTC)

Yes, we need something peer reviewed, but the article already mentions the substantial difference in the parallax distances from Hipparcos data (430 versus 400 ly, but with one sigma errors of 20 and 10 ly, so arguably consistent), and the differences in the proper motions mentioned in Sky & Telescope from data in the Washington Double Star Catalog and SIMBAD (and that article also mentions a substantial difference in radial velocity - 24 km/s versus 19 km/s). These details are all in the infobox, cited to Hipparcos and Gaia papers. Taken all together it was already hard to see the data as consistent with a wide physical binary.

That said, the parallax distances quoted in the link above from the Gaia data (328 versus 389 ly) and the proper motions (16 mas/yr "south by southeast" and 1 mas/yr "west by southwest" - what are those compass directions: does he mean SSE and WSW?) do not appear to be consistent with the previously reported measurements. The infobox numbers indicate both A and B are moving roughly to the southwest, albeit at different rates. And I could believe B is at 389 ly (consistent with 400 p/m 10), but why does Gaia show A at 328 ly when Hipparcos said it was 430 p/m 20? Something does not look right. 213.205.240.162 (talk) 15:39, 16 August 2018 (UTC)

"Taken all together" is pretty much a definition of WP:SYNTHESIS, so I removed any statements beyond the bald data that is not contained in a reliable citation. You can speculate all you want and I'm not going to disagree with you, but our speculation can't go in the article. Further to the previous possible reasons for caution, Albireo A is of course itself an unambiguous close binary and it is unclear what effect that has on the astrometric data. I have added error margins lest anyone be misled about the concreteness of the distance differences. Further, I have replaced the blog distances with more scientific values although they aren't much different. Lithopsian (talk) 20:04, 16 August 2018 (UTC)

Oh, sure: but this is just a talk page :) As I said, we need someone to analyse the discrepancies and state the obvious conclusion in a proper reliable source - that is, in a published peer-reviewed journal. But we can at least say that one would expect both elements of a gravitationally bound binary system to (a) lie at approximately the same distance; (b) have approximately the same proper motion; and (c) have similar radial velocities (depending on how the orbit was oriented). Until we have additional reliable sources, there is not much more we can do than state the published facts. 213.205.240.162 (talk) 21:26, 16 August 2018 (UTC)

According to the Gaia catalog, the formal statistical error ellipse is unreliable due to a poor fit to the data. This could be due to either the acceleration of the source or do to photometric problems due to brightness. I've walked back the claim about precise distances. OtterAM (talk) 21:36, 17 August 2018 (UTC)

Albireo Ab

Is there any info about Albireo Ab? The page doesn't seem to mention anything about it. Nussun05 (talk) 06:03, 17 October 2020 (UTC)

You could read this new paper although they don't mention the star. Even detections have been fleeting and there is little hard data on it. WDS has a few notes, but nothing conclusive. MSC shows an Aa/Ab orbit, but may be referring to Aa/Ac. Lithopsian (talk) 13:37, 18 October 2020 (UTC)

Jury is still out?

"It is not known whether the two components β Cygni A and B are orbiting around each other..." So is that still true, nothing definitive? If that's the case, is it because the distances are not known with enough certainty? Assambrew (talk) 18:15, 6 August 2023 (UTC)

Indeed, the distances are not known sufficiently well. They are also a long way apart, regardless of their individual distances, and it is very difficult to tell whether stars are gravitationally bound in such situations. Lithopsian (talk) 16:59, 9 August 2023 (UTC)

Thanks. Has anyone calculated the minimum possible distance between them, assuming that both stars are the same distance from us? Assambrew (talk) 18:25, 13 August 2023 (UTC)

I plugged some numbers into an online calculator. Given angular separation around 35 arcseconds and approximate distance 400 light years for both stars, their minimum separation would be about 4,300 AU, or 0.068 light years. I would put that into the article if it wasn't original research :) Assambrew (talk) 17:09, 20 August 2023 (UTC)

See this and this for sources that give a potential separation. For example, the second paper does a trivial calculation of the average projected separation at 2,927 au, although they still aren't convinced that the two are bound. Lithopsian (talk) 17:38, 20 August 2023 (UTC)