27 Piscium
Binary star with a possible brown dwarf companion.
27 Piscium is a binary star system located in the zodiac constellation Pisces. With an apparent visual magnitude of 4.88, it can be seen without a telescope. The system lies about 234 light-years away, based on a parallax measurement of 13.91 milliarcseconds, and sits close enough to the ecliptic that the Moon can occasionally occult it.
American astronomer S. W. Burnham first identified it as a double star. By 2002, enough positional data had accumulated to confirm orbital motion and derive preliminary orbital elements. The two stars orbit each other with a period of 695 years and a high eccentricity of 0.766. However, these elements do not fully account for the system's radial velocity variations, suggesting the presence of a brown dwarf companion. This candidate object would have a mass of at least 73 times that of Jupiter and orbit at a semimajor axis of about 4 astronomical units.
The primary star, component A, is about 710 million years old. It is a first ascent giant on the red giant branch, with a stellar classification of G8 III—meaning it fuses hydrogen in a shell around an inert helium core. It has 2.4 times the Sun's mass, has expanded to 10 times the Sun's radius, and shines with about 56 times the Sun's luminosity from a photosphere at an effective temperature of 5,014 K. In 2012, the fainter companion, component B, had a magnitude of 8.9 and was observed at an angular separation of 0.80 arcseconds along a position angle of 325°.
- Apparent visual magnitude
- 4.88
- Distance
- about 234 light years
- Parallax
- 13.91±0.28 mas
- Orbital period
- 695 years
- Eccentricity
- 0.766
- Primary classification
- G8 III
- Primary mass
- 2.4 solar masses
- Primary radius
- 10 solar radii
- Primary luminosity
- 56 solar luminosities
- Primary effective temperature
- 5,014 K
Lore & Background
27 Piscium was found to be a double star by American astronomer S. W. Burnham. By 2002, sufficient position data had been gathered that orbital motion could be demonstrated, and preliminary elements were determined. The system has an orbital period of 695 years and an eccentricity of 0.766. However, the orbital elements do not fully explain the radial velocity variations, which may indicate there is a brown dwarf companion. This candidate object would have a mass of at least 73 Jupiter masses and is orbiting with a semimajor axis of around 4 AU.
The primary, component A, is a first ascent giant star on the red giant branch with a stellar classification of G8 III, meaning it is generating energy through hydrogen fusion along a shell surrounding an inert helium core. It has 2.4 times the mass of the Sun and has expanded to 10 times the Sun's radius. The star is radiating about 56 times the Sun's luminosity from its photosphere at an effective temperature of 5,014 K. The system is positioned near the ecliptic and so is subject to occultation by the Moon.
In 2012, the magnitude 8.9 companion, component B, was at an angular separation of 0.80 arcseconds along a position angle of 325°.
Reader's Guide
27 Piscium is significant as a binary system whose orbital motion was confirmed only after sufficient positional data had accumulated by 2002, allowing preliminary orbital elements to be determined. Its long orbital period of 695 years and high eccentricity of 0.766 make it a challenging system for dynamical study. The unresolved radial velocity variations suggest the possible presence of a brown dwarf companion with a mass of at least 73 Jupiter masses, orbiting at about 4 AU. If confirmed, this would add a substellar component to the system, offering insight into the formation and evolution of low-mass companions around evolved stars. The primary star itself is a red giant on the first ascent branch, with an age of about 710 million years, providing a snapshot of stellar evolution after core hydrogen exhaustion. The system's location near the ecliptic allows lunar occultations, which can yield precise astrometric data. The legacy of 27 Piscium lies in its role as a testbed for long-period binary orbital determination and the search for substellar companions via radial velocity anomalies.
Did You Know?
- 27 Piscium is visible to the naked eye with an apparent visual magnitude of 4.88.
- The primary star is a G8 III red giant with 2.4 times the mass of the Sun and 10 times its radius.
- A candidate brown dwarf companion with at least 73 Jupiter masses may exist in the system.
Frequently Asked Questions
Who is 27 Piscium?
27 Piscium is a naked-eye binary star system nestled in the zodiac constellation Pisces, glowing at an apparent magnitude of 4.88 from roughly 234 light-years away. Its primary member is a G8 III orange giant, and the pair appears to be accompanied by a possible brown dwarf companion.
What are 27 Piscium's powers or special traits?
The system's most eye-catching feature is its highly elliptical orbit, with an eccentricity of 0.766, so the two stars swing from very close to very far apart over each 695-year cycle. It also sits close enough to the ecliptic that the Moon can occasionally drift across it and briefly hide it from the sky.
Why is 27 Piscium important to the field?
It stands as a textbook example of how decades of patient astrometry can transform a simple 'double star' catalog entry into a fully characterized orbit with a long period and high eccentricity. The possible brown dwarf companion also makes the system a useful testbed for studying low-mass objects in multi-star configurations.
Who first identified 27 Piscium as a binary?
American astronomer S. W. Burnham was the first to flag the pair as a double star. It took many years of accumulated positional data before a 2002 analysis could confirm true orbital motion and derive the preliminary orbital elements.
More in Binary and Multiple Stars, Part 2 1-24
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