Pi Andromedae

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Pi Andromedae
Observational Data
Designation Pi And
π Andromedae
29 Andromedae
Right ascension 00h 36m 52.8492s[1][2]
Declination +33° 43′ 09.6383″[1][2]
Constellation Andromeda
Type of object Binary star
Magnitude Apparent Mag: +4.34[3]
Absolute Mag: -2.18[3]
Distance from Earth 598.46 ly[3]
Radial velocity 8.20 ± 0.6 km/s[1][4]
Proper motion RA: 14.75 mas/yr[1][2]
Dec: -3.51 mas/yr[1][2]
Parallax 5.45 ± 0.31 mas[1][2]

Pi Andromedae (Pi And, π Andromedae, 29 Andromedae) is a multiple star system in the constellation of Andromeda.[5] "Pi Andromedae" is the Bayer designation of the star, the "Pi" indicating it is one of the dimmer stars in Andromeda. The system can be easily observed from the Northern hemisphere where it appears as a star of the fourth magnitude.[3] The system is known to contain two stars, though it is thought it may contained four or five.[6] The two main stars were identified through a spectrograph of the system and are thought to be very similar in their properties.

Properties and Structure

The Pi Andromedae system is situated approximately 598.46 light years from Earth.[3] The spectrum of the systems suggests the two main stars are white dwarfs with a spectral class of B5 and a total luminosity 2,000 times larger than that of the Sun.[6] These two stars are thought to be very similar with masses of 4.8 and 5.8 solar masses respectively and radii of roughly 4.7 solar radii. One of the stars is known to have a rotation period of less than 8 days, though it is difficult to determine which star as the two are so similar. The two stars orbit each other in an elliptical orbit, taking 143.53 days to complete one orbit with an average distance between them of 1.3 AU (0.005 seconds of arc as viewed from Earth).[6] The orbit of the stars is fairly eccentric, with the distance between the stars varying from 0.6 AU up to 2.1 AU, or equivalently an eccentricity of e=0.556.[7] The plane of the orbit is very nearly aligned along the line of sight to the Earth.

Further out from the main two stars lies Pi And B, a dwarf star with class A5. The star is significantly fainter than the main two shining at the eight magnitude and is not visible to the unaided eye. It can be found 36 arc-seconds from the main binary pair or 7,200 AU.[6] Further out still is Pi And C, a K type dwarf glowing at the eleventh magnitude roughly 55 second of arc or 11,000 AU from the main two. Whether it really is related to the other three is a matter of some debate. Finally there is a possible fifth star, also a K type dwarf but much closer in, at around 40 AU. Again whether it is related to the Pi Andromedae system or merely lies along the same line of sight is unclear.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Pi Andromedae. Simbad Astronomical Database. simbad.u-strasbg.fr. Retrieved on June 19, 2020.
  2. 2.0 2.1 2.2 2.3 2.4 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics 474 (2): 653-664. doi:10.1051/0004-6361:20078357. Bibcode2007A&A...474..653V.  arXiv:0708.1752
  3. 3.0 3.1 3.2 3.3 3.4 Pi Andromedae (29 Andromedae) Star Facts. universeguide.com. Retrieved on June 19, 2020.
  4. Gontcharov, George (2006). "Pulkovo compilation of radial velocities for 35495 stars in a common system". Astronomy Letters 32: 759-771. doi:10.1134/S1063773706110065. Bibcode2006PAZh...32..844G.  arXiv:1606.08053
  5. Andromeda Constellation. constellation-guide.com. Retrieved on June 19, 2020.
  6. 6.0 6.1 6.2 6.3 Jim Kaler (December 19, 2008). Pi And. Stars. stars.astro.illinois.edu. Retrieved on June 19, 2020.
  7. Eccentricity of the orbit calculated using e=(amax +amin)/(amax+amin)