- P Eridani
Starbox begin
name = p Eridani ABStarbox observe
epoch =J2000.0
constell = Eridanus
ra = RA|01|39|47.2
dec = DEC|-56|11|44
appmag_v = 5.80 / 5.90Starbox character
class = K2V / K3V
r-i =
v-r =
b-v = 0.85 / 0.88
u-b = 0.56 / 0.61
variable = "None"Starbox astrometry
radial_v = +19.5
prop_mo_ra = 286.10
prop_mo_dec = 16.66
parallax = 123.90
p_error = 1.38
parallax_footnote =
dist_ly = 26.3 ± 0.3
dist_pc = 8.07 ± 0.09
space_v_u =
space_v_v =
space_v_w =
absmag_v = 6.25 / 6.35Starbox visbin
reference =
name = p Eridani B
period = 483.66
axis = 7.817
axis_unitless =
eccentricity = 0.5344
inclination = 142.824
node = 13.116
periastron = 1813.494
periarg = Starbox detail
source =
mass = 0.88 / 0.86
radius = 0.79 / 0.6
gravity =
luminosity = 0.28 / 0.25
temperature =
metal =
rotation =
age = Starbox catalog
names = Gliese 66, HR 487, CD -56°328, HD 10360/1, LTT 902, GCTP 352.00, SAO 232490, CP(D)-56 329, WDS 01398-5612, Dunlop 5, HIP 7751Starbox reference
Simbad = HD+10361
ARICNS =p Eridani is a
binary star system approximately 26light-year s away in theconstellation of Eridanus (theRiver ). Its duplicity was discovered in December 1825 byJames Dunlop inAustralia at the SirThomas Brisbane 's Parramatta Observatory.Naming
The name "p Eridani", according to
Nature , p.589 (19th April 1883) has been:"... occasionally miscalled "6 Eridani", which would imply that it was one of Flamsteed's stars. Flamsteed, it is true has a star which he calls "6 Eridani", and which is B.A.C. 926, the binary is B.A.C. 521. The letter p was attached to a star by Lacaille in the catalogue at the end of his Calum Australe Stelliferum. The number '6' is merely borrowed from Bode."
The use of Bode numbers was commonly used in the early 19th century, but this antiquated system has now fallen into disuse for more than a century.
Physical characteristics
p Eridani is one of the most interesting of the many double stars visible in southern skies. This popular binary system lies about 1.1o north of the brilliant bluish coloured star, the 1st magnitude southern star
Achernar . When "p" was first found byJames Dunlop , he adequately describes this bright and fairly wide pair as double (both of the small 6th magnitude). He further went on to say of the telescopic appearance of the system:Since Dunlop's discovery, the stars have significantly widened, and now both stars are easily visible in small telescopes.
We know today it among the stars that are reasonably close to the Sun, which is currently is estimated to lie about 8.07±0.08 pc or 26.6±0.3
light-year s from theSun . The system consists of two visible components that orbit each other in a wide orbit with relatively high eccentricity. The closest that these components will approach each in the orbit is about 29.7astronomical unit s (or AUs) with the maximum orbital separation being 97.7 AU. Widest separation is expected to occur during 2048 A.D., at some 11.8arcsec , with the nextperiastron passage in 2297 A.D. This view may soon change in the near future, depending on the observed measuring positions.Poor Quality
Our knowledge of p Eridani is presently incomplete. As such, the orbit has been deemed as very poor quality in the Sixth Binary Star Catalog being listed as "5" - an "Intermediate" orbit. Most of the problems remains with the original observations made by
James Dunlop in December 1825, being given as an estimated 2.5arcsec through the near northernposition angle of 343o, who unfortunately observed and measured the system after it had past the moment of itsperiastron passage in 1813. His positional errors he presents seems to be quite discordant with observations made since 1825, leaving us uncertain of a critical part of the binary star's apparent orbit. There maybe also problems withJohn Herschel 's early measures made on22 February , 1835, who found the separation as 3.68 arcsec throughposition angle 301.7o. If true, this indicates significant positional changes in just under ten years of observation. Herschel then contributed two other micrometrical measures between 1835 and 1838, which seem also flawed against the current orbit. Much debate continues on the validity and importance of these early measures, all being critical to the accuracy of the determined orbit.Orbit solutions
Several orbits have been calculated, including W.C. Jacob (1850), Bernhard Dawson (1919), W.J. Luyten & E.G. Ebbinghausen (1934), and J.G. Gore (1956) The most recent solution being produced by the Dutch astronomer
Gale Bruno van Albada (1957), while he was acting as the Director of theBosscha Observatory inJava ,Indonesia . Currently van Albada's own orbital elements remain only temporary at best, whose orbital solution is still just considered as approximate. However, it remains fairly good between the measured and calculated positions roughly between 1950 and 2000. This orbital solution will unlike be improved at least until the mid to late- 21st Century, when the orbital motion will again narrow towards periastron.Possible companion
The fainter of the two stars was suspected in the 1960s to have a spectroscopic companion. This information was based on the
Yale Bright Star Catalog for the star HR 486, which is the 'B' component. It seems this conclusion was not properly referenced in the Yale catalogue, and such, no information has appeared in either theWashington Double Star Catalog (WDS), nor by Batten A.H., et.al. in the “Eighth Spectroscopic Binary Catalogue.”.The spectroscopic companion was also suggested in 1957 by G.B. Aldaba in "Note on the Binary Star p Eridani.", to account for the larger parallax, which made the masses smaller. O.J. Eggen in 1956, earlier stated that both stars were under luminous and were probably not main sequence stars. He determined the total mass as 0.63±0.19 M⊙. This problem remained untilHipparcos improved the parallax value of 122.75±1.4mas , making the total masses the more reasonable 1.74±0.08 M⊙. As such, these stars are likely on the main sequence. There is now no need for some unseen companion, and there is no visual or instrumental observations to support this view.Fiction
* In the
Revelation Space fiction series, the system harbours a life supporting planet named Ararat. Much of the book Absolution Gap takes place within the system.References
* William I. Hartkopf & Brian D. Mason, "Sixth Catalog of Orbits of Visual Binary Stars", U.S. Naval Observatory, 2001.
* A.H. Batten, J.M. Hetcher, D.C. MacCarthy; “"Eighth Catalogue of the Orbital Elements of Spectroscopic Binary Systems".”; Publ. Dominion Astrophys. Obs., 17 (1989)
* J. Dunlop; "Approximate Places of Double Stars in the Southern Hemisphere, observed at Paramatta in New South Wales." Mem.Ast.Soc.. London, 3, 257; (1828)Orbit
*W.S. Jacob; "On the Limits of Error in the Elements of the Orbit of α Centauri, and on the Orbits of p Eridani and 61 Cygni"; MNRAS, 10, 170 (1850)
* J.G. Gore; "On the orbit of p Eridani"; MNRAS, 48, 26 (1887)
* B. Dawson; AJ., 32, 144 (1919)
* W.J. Luyten, E.G. Ebbinghausen, PASP, 46, 199 (1934)
* O.J. Eggen; A.J., 61, 361, p. 379 (1956))
* G.B. van Albada; Cont. Bosscha Obs. No. 5. (1956)
* G.B. van Albada; “"Note of the Binary Star p Eridani".”; Astron. J., 62, 282 (1957)External links
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