P Eridani
Encyclopedia
p Eridani is a binary star
system in the constellation
of Eridanus
(the River
) whose distance is approximately 26 light-year
s. It was found to be a double star
in December 1825 by James Dunlop
in Australia
at his home at Paramatta, now spelt Parramatta
.
, p. 589 (19 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. The designated 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.
system that lies about 1.1 degrees north of the brilliant bluish coloured star, the 1st magnitude southern star Achernar
. When "p" was first found by James 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 from the Sun
. The system consists of two visible components that orbit each other in a wide orbit with relatively high eccentricity.
in December 1825, being given as an estimated 2.5 arcsec
through the near northern position angle
of 343o, who unfortunately observed and measured the system after it had past the moment of its periastron 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 may also be problems with John Herschel
's early measures made on 22 February 1835, who found the separation as 3.68 arcsec through position 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.
astronomer Gale Bruno van Albada
(1957), while he was acting as the Director of the Bosscha Observatory
in Java
, 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.
(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 until Hipparcos
improved the parallax value of 122.75±1.4 mas
, 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.
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
system in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Eridanus
Eridanus (constellation)
Eridanus is a constellation. It is represented as a river; its name is the Ancient Greek name for the Po River. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern...
(the River
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
) whose distance is approximately 26 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s. It was found to be a double star
Double star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
in December 1825 by James Dunlop
James Dunlop
James Dunlop was an astronomer's assistant who was hired by Sir Thomas Brisbane to work at his private observatory, once located at Paramatta , New South Wales, about twenty-three kilometres west of Sydney, Australia during the 1820s and 1830s...
in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
at his home at Paramatta, now spelt Parramatta
Parramatta, New South Wales
Parramatta is a suburb of Sydney, in the state of New South Wales, Australia. It is located in Greater Western Sydney west of the Sydney central business district on the banks of the Parramatta River. Parramatta is the administrative seat of the Local Government Area of the City of Parramatta...
.
Naming
The name "p Eridani", according to NatureNature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...
, p. 589 (19 April 1883) has been:
"... occasionally miscalled 6 Eridani, which would imply that it was one of Flamsteed's stars
Flamsteed designation
Flamsteed designations for stars are similar to Bayer designations, except that they use numbers instead of Greek letters. Each star is assigned a number and the Latin genitive of the constellation it lies in...
. Flamsteed, it is true has a star which he calls 6 Eridani. The designated letter 'p' was attached to a star by Lacaille
Nicolas Louis de Lacaille
Abbé Nicolas Louis de Lacaille was a French astronomer.He is noted for his catalogue of nearly 10,000 southern stars, including 42 nebulous objects. This catalogue, called Coelum Australe Stelliferum, was published posthumously in 1763. It introduced 14 new constellations which have since become...
in the catalogue at the end of his Calum Australe Stelliferum. The number '6' is merely borrowed from Bode
Johann Elert Bode
Johann Elert Bode was a German astronomer known for his reformulation and popularization of the Titius-Bode law. Bode determined the orbit of Uranus and suggested the planet's name.-Biography:...
."
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 a southern binary starBinary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
system that lies about 1.1 degrees north of the brilliant bluish coloured star, the 1st magnitude southern star Achernar
Achernar
Achernar , sometimes spelled Achenar, is the brightest star in the constellation Eridanus and the ninth-brightest star in the night sky. Of the top ten apparent brightest stars —Sirius, Canopus, Alpha Centauri, Arcturus, Vega, Capella, Rigel, Procyon, Achernar and Betelgeuse—Achernar is the hottest...
. When "p" was first found by James Dunlop
James Dunlop
James Dunlop was an astronomer's assistant who was hired by Sir Thomas Brisbane to work at his private observatory, once located at Paramatta , New South Wales, about twenty-three kilometres west of Sydney, Australia during the 1820s and 1830s...
, 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 from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The system consists of two visible components that orbit each other in a wide orbit with relatively high eccentricity.
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 DunlopJames Dunlop
James Dunlop was an astronomer's assistant who was hired by Sir Thomas Brisbane to work at his private observatory, once located at Paramatta , New South Wales, about twenty-three kilometres west of Sydney, Australia during the 1820s and 1830s...
in December 1825, being given as an estimated 2.5 arcsec
Arcsec
Arcsec may refer to:* arcsecond, a unit of angular measurement* arcsecant, an inverse trigonometric function...
through the near northern position angle
Position angle
Position angle, usually abbreviated PA, is a measurement derived from observing visual binary stars. It is defined as the angular offset in degrees of the secondary star to the primary, relative to the north celestial pole....
of 343o, who unfortunately observed and measured the system after it had past the moment of its periastron 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 may also be problems with John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
's early measures made on 22 February 1835, who found the separation as 3.68 arcsec through position angle
Position angle
Position angle, usually abbreviated PA, is a measurement derived from observing visual binary stars. It is defined as the angular offset in degrees of the secondary star to the primary, relative to the north celestial pole....
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 DutchNetherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
astronomer Gale Bruno van Albada
Gale Bruno van Albada
Gale Bruno van Albada was a Dutch astronomer.Van Albada obtained his Ph.D. with Antonie Pannekoek at the University of Amsterdam in 1945. He shared Pannekoek's communist ideologies and back in the 1930s his brother Piet van Albada had been an associate of Marinus van der Lubbe...
(1957), while he was acting as the Director of the Bosscha Observatory
Bosscha Observatory
Bosscha Observatory is the oldest observatory in Indonesia. The observatory is located in Lembang, West Java, approximately north of Bandung. It is situated on a hilly six hectares of land and is above mean sea level plateau...
in Java
Java
Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. 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 the Washington Double Star CatalogWashington Double Star Catalog
The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for 102,387 pairs of double stars. The catalog also includes multiple stars...
(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 until Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
improved the parallax value of 122.75±1.4 mas
Mas
Mas or Más may refer to:* Mas , a surnameIn arts:* Más , an album by Spanish singer Alejandro Sanz* "Más", a song by Kinky from their 2002 album Kinky...
, 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 SpaceRevelation SpaceRevelation Space is a 2000 science fiction space opera novel by Welsh author Alastair Reynolds. It was the first novel set in the Revelation Space universe, although the then-unnamed universe had already been established by several published short stories....
fiction series, the system harbours a life supporting planet named Ararat. Much of the book Absolution Gap takes place within the system.
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)