Talk:91 Aquarii

Requested move

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section.

This is the most common name used for the star. Similar to why most people say "55 Cancri" over Rho-1 Cancri, etc. — NuclearVacuum 19:13, 9 June 2008 (UTC)

Agree with move: Bayer designations with superscripts are clumsy to use with Wikipedia article titles (note that a more correct rendering of the Bayer designation would be Psi¹ Aquarii), the Flamsteed designation is valid. Note that the HD designation is more common than either the Bayer or Flamsteed designation however. 131.111.8.96 (talk) 11:18, 10 June 2008 (UTC)

• Support—Fine with me. The current name seems like a less likely search term.—RJH (talk)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

dubious planet data

The 91 Aquarii planetary system

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	>2.9 MJ	0.3	182	0	—	—

I tagged the semimajor in the above table from the article as dubious because Kepler's third law gives 0.85 and not 0.3. One can also see it is wrong without calculating by thinking of our Solar System. I assume it's a typo.

So, at least one of these figures must be wrong: mass star, period, and semimajor axis. I followed the exoplanet.eu reference to http://pasj.asj.or.jp/v57/n1/570109/570109-frame.html which in turn refers to Mitchell et al. 2003 and also notes table data copied from http://obswww.unige.ch/~naef/table.html which is stale and not archived.

However, Four Substellar Companions Found Around K Giant Stars has "91 Aqr has a companion with a minimum mass of 2.9 jupiter masses, and an orbital period of 182 days" but no mention of semimajor axis. That abstract looked like a presentation summary at a conference and did not have any full article attached. -84user (talk) 16:30, 28 November 2009 (UTC)

As can be seen below, the figure 0.3 AU is from exoplanet.eu, and they prob have access to the full paper. When applying Keplers 3rd Law one also have to take into account the stars mass, which in this case is 2.5 Suns. Keplers 3rd Law in its original form is only applicable when comparing two planets in the same solar system, but it might be remedied by dividing each side in the equation with the mass of the central star. ... said: Rursus (^mbork³) 22:22, 9 December 2009 (UTC)

0.85/2.5 = 0.34, so 0.3 is good enough. ... said: Rursus (^mbork³) 22:25, 9 December 2009 (UTC)

Eeeh! Forget it! I got it upside down! The figure remains dubious. Multiply with 2.5 in order to keep the period 182 days, which makes c:a 2.1 AU, not 0.34. ... said: Rursus (^mbork³) 22:33, 9 December 2009 (UTC)

I think the issue of the seemingly low semi-major axis value may be resolved by noting that the paper being sourced by exoplanet.eu, Raghavan et al (2006), actually lists an a sin i value of 0.3 in their Table 2. Hence, this is a lower bound on the semi-major axis. I've updated the table accordingly. Regards, RJH (talk) 16:46, 6 July 2012 (UTC)

I'm not sure what equation you used to get 2.1 AU. That would imply a star of 37 solar masses. The generic form of Kepler's law is: d[AU]^3 = P[years]^2 * M[SolarMasses]. For 91 Aquarii, M is supposed to be 2.5 and P is 0.5 years (182 days), which gives d=cube root of (0.625) which is 0.855. The semi-major axis (d) varies in proportion to the cube root of the star's mass and so is less affected than one might think.

Checking this result with 4*PI^2*d^3 = P^2 * G(M + m), treating m as zero: P^2 = square root (4*PI^2*d^3 / G*M). d=0.855 AU in SI units is 127906290000 metres, M=2.5 solar masses is 4.9723 x 10^30 kg, and G is 6.67300 x 10^-11 m^3 kg^-1 s^-2. Therefore (to three figures only) 4*PI^2*d^3 is 4*PI^2*127906290000^3 = 8.26 × 10^34, and G*M is 3.32 * 10^20, leading to 4*PI^2*d^3 / G*M = (8.26 × 10^34) / (3.32 * 10^20) or 2.49 * 10^14. Square root gives 1.58 * 10^7 seconds or ... 183 days (off by one probably due to my rounding but I doubt we know the mass to this precision in any case). Here's a table:

Planet	Star mass	Period in days	semi-major axis
Earth	1	365	1
Venus	1	225	0.723
Mercury	1	088	0.387
"Half-Earth"	1	182	0.63
91 Aq b P=Ok	2.5	182	0.855
91 Aq b a=Ok	2.5	037.96	0.3
91 Aq b light	0.108	182	0.3
91 Aq b heavy	37	182	2.1

-84user (talk) 23:19, 27 January 2010 (UTC)

Re Dubious Planet Data

With respect to the incorrect orbital data, I made a brief effort at using a downloadable isochrone data base• to estimate 91Aquarii's mass from its effective temperature, luminosity and metallicity. I couldn't quite match the combination of temperature and bolometric luminosity at [Fe/H] = -.085 (Z = 0.016); the star was off the table, too dim by about 0.4 mag. But neglecting that, the nearest matches were solar-mass (.99-1.08) stars at an age of over 10 Ga. The dimmest one was was 0.99 solar masses with an bolometric absolute magnitude of 1.676 (versus an actual Mbol of about 2.0 for 91 Aqr), an effective temperature of 4613K and an age of 12.6 Ga. That exercise makes me believe that the "half-Earth" orbital model is probably close to the truth. If I assume one solar mass, I get a semimajor axis of 0.63 for the planet. Perhaps the "6" got lost somehow and the error has been perpetuated?

• http://stev.oapd.inaf.it/cgi-bin/cmd_2.3

With respect to the hierarchal architecture, I note that the separation for E given in the CCDM is from component BC, not from component D nor component A. I'll note that CCDM is two dimensional and the listings are not predicated on whether components are bound or not.

As I see the system, The K0 giant and the slightly more massive BCE system probably orbit a barycenter with a current major axis of at least 50 arcseconds. Component E is a mid-range M dwarf with a current projected separation about 20 arcseconds from BC. B and C are a couple of late K dwarfs with masses something like 0.60 and 0.52 suns orbiting each other, now at 0.3 arcseconds separation. D is out left field, currently 80 arcseconds east of A, but maybe only 60 arcseconds from the barycenter of the A-(BC)E system. IF we assume we are looking a circular orbits face-on at a distance from us of 148.4 light years, the major axes of these orbits would be something like

D - ABCE ≈ 2800 AU

A - BCE: ≈ 2,000 AU

E - BC: ≈ 900 AU

B - C: ≈14 AU

The ABCE system would have a mass of something like 2.5 solar masses, which is greater than the alpha Centauri system, and the projected separation of D from ABCE is much less than the distance between Proxima and alpha CentauriAB. So, unless E is significantly closer or farther from us than the other stars, It does not at all seem implausible that the entire system would be bound. Of course, people are still debating whether Proxima is bound or not.

Gerald Nordley (27 Dec 10)71.204.166.79 (talk) 01:55, 28 December 2010 (UTC)

umm.. I would like to point out that if you read the exoplanet.eu article on this system. The planet has been confirmed again recently in Jan 03 2011 at the conference " Planetary Systems Beyond the Main Sequence", Bamberg 2010 (Quirrenbach et al). By Conference, means that proponents and opponents of 91 Aquarii b meet and have at least agreed that this exoplanet exists even if its exact nature is of debate.108.206.84.45 (talk) 23:40, 24 January 2012 (UTC)

A major confusion

Disputed

I believe this article is based on some major confusion, or obsolete theories about a quintuple. 91 Aquarii is not a quintuple star, as far as the sources tell me:

• searching the Multiple Star Catalog for HD219449 gives a triple star (* A (BC: B C));
• searching SIMBAD for 91 Aqr (HD 219449) gives one high proper-motion star with a substellar companion, prob a planet,
• following the links GJ 893.2 B (HD 219449B) and GJ 893.2 C (HD 219449C) gives each star in a double system,
• following the link G 157-37 (HD 219430) gives another high proper-motion star, no known companions,
• following the links BD-09 6156D (no HD) and BD-09 6155E (no HD) gives each star in another double system.

Which sums up to: 4 or 5 star systems confused somehow for being one star system. ... said: Rursus (^mbork³) 18:36, 8 December 2009 (UTC)

Fiddling and doodling with my Multiple Star Catalog (MSC) copy in PostgreSQL, there is no quintuple known in Aquarius. The real 91 Aquarii is:

• a triple star of configuration (* A (BC: B C)), it is unknown whether A and BC are really physically connected,
• BC normally goes under the designation GJ 893.2 (BC), which SIMBAD lists as a double, K6+D
• A is instead a high proper-motion star K0III with a "substellar companion" (i.e. a planet), and that planet has the data (according to exoplanet.eu):

Name: HD 219449 b

Discovered in: 2003

Mass: 2.9 Jupiters,

Semi major axis: 0.3 AU,

Orbital period: 182 days.

... said: Rursus (^mbork³) 22:06, 9 December 2009 (UTC)

The CCDM [1] lists five components (CCDM J23159-0905A, ..., J23159-0905E.)

• A is K0, magnitude 4.5.
• BC is a close pair (separation 0.3 arcseconds), which is separated from A by 50 arcseconds.
  • B is K, magnitude 10.3.
  • C is magnitude 11.5.
• D is magnitude 13.5, 80 arcseconds from A.
• E is magnitude 14.3, 20 arcseconds from BC.

Other designations can be equated with these components as follows:

• A = GJ 893.2A = GJ 9815A = HD 219449 = HIP 114855 = LTT 9437 = NLTT 56282.
• BC = G 157-37 = GJ 893.2BC = GJ 9815BC = HD 219430 = LTT 9434 = NLTT 56278.
• D = BD-09 6156D.
• E = BD-09 6155E.

BC is known to be physical [2] and an orbit has been published (IAU Commission 26 Circular 161, [3].) The A/BC system has been classified as physical by Chanamé and Gould (Bibcode:2004ApJ...601..289C, Table 1.) The Washington Double Star Catalog lists [4] D and E as not being physically attached to A/BC. Spacepotato (talk) 04:44, 6 January 2010 (UTC)

I see. Searching SIMBAD for all those CCDM J23159-090/X/, gives that only LTT 9437/HD 219449 has 91 Aqr or ψ¹ Aqr as designation. It is not a quintuple system. There are two systems, HD 219449 and BD-09 6156D/E, and I don't know yet whether CCDM assigns 91 Aqr also for BD-09 6156D/E. I'll take a look, I have to download CCDM and examine it's content with fastest method. Rursus dixit. (^mbork³!) 19:43, 27 January 2010 (UTC)

A fast glance on CCDM makes me convinced that there are no Bayer/Flamsteed type designations in it. I'm pretty convinced that there are two systems:

1.

(HD 219449/91 Aqr/ψ¹ Aqr) + (GJ 893.2)

mult: triple star (ABC: A (BC: B C)), data per above, HD 219449 has a planet

2.

BD-09 6156D

mult: double star (DE: D E), data per above.

I think it should be split. 91 Aqr is HD 219449/GJ 893.2, while BD-09 6156D/E is BD-09 6156D/E. Rursus dixit. (^mbork³!) 19:59, 27 January 2010 (UTC)

A last check of all sources you provided convinced me that nowhere does the name 91 Aqr apply to BD-09 6156D/E. In fact 91 Aqr or Aqr occurred in none of those sources. So a "split" it should be. Rursus dixit. (^mbork³!) 20:07, 27 January 2010 (UTC)

For now I'll just clean away the "D/E components" — they don't belong to the same system as 91 Aqr, and it's a really faint system with few known data. Rursus dixit. (^mbork³!) 20:56, 27 January 2010 (UTC)

Dumping place for CCDM J23159-0905DE

CCDM J23159-0905D/E Orbit Companion CCDM J23159-0905D (BD-09 6156D) Semi-major axis (a) 19.7″ Inclination (i) 341° Orbit Companion CCDM J23159-0905E (BD-09 6155E)

NAME Apparent magnitude (V) Spectral type CCDM J23159-0905D (BD-09 6156D) 13.5 CCDM J23159-0905E (BD-09 6155E) 14.3

Dumped! Rursus dixit. (^mbork³!) 20:56, 27 January 2010 (UTC)

Some fixes now made

It seems pretty obvious by SIMBAD that 91 Aqr applies only to the component A in the star system. I fixed the text accordingly, but I kept info about the subsystem HD 219430BC which all (relevant) sources agree belong to the same system as 91 Aqr. I fixed the text so that 91 Aqr refers to what the former text called 91 Aqr A and so that HD 219430 B and C is used for what was formerly called B and C. Excepting the former component table, that for some confused reason inserted an extra B into the table, getting a sextuple star not the quintuple star claimed by the former text. I also mention CCDM J23159-0905 so that some of the former info about the so called components 91 Aqr D and E is still retained.

The following problems remains:

1. the References and External links list should be reviewed,
2. the above saved data about the system CCDM J23159-0905DE could maybe be put back, claiming that it is arguably an unrelated system that CCDM classifies as belonging to the same system as 91 Aqr,
3. simbad identifications should be added to the infobox
4. the Alcyone software link seems to be a spam link duplicating the info from SIMBAD, and some beautiful day I'm going to throw them from the surface of Earth Grrr!

Rursus dixit. (^mbork³!) 21:53, 27 January 2010 (UTC)

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