36 Andromedae
Binary star in Andromeda, part of a triple system.
36 Andromedae is a binary star system located in the northern constellation Andromeda, and it forms part of a triple star system. Its name comes from the star catalog created by English astronomer John Flamsteed, which was first published in 1712. The system is just barely visible without a telescope, with an apparent visual magnitude of 5.45. Based on an annual parallax shift of 26.33 milliarcseconds, it is roughly 124 light-years away from Earth. The system is moving toward the Sun at a radial velocity of −0.8 km/s.
The binary nature of 36 Andromedae was first identified in 1832 by German-Russian astronomer Wilhelm von Struve. The two stars form a wide binary, taking about 169.1 years to orbit each other with an eccentricity of 0.31. Their average separation is 37 astronomical units (AU), which is greater than the distance from the Sun to Neptune. As of 2016, the pair appeared 0.90 arcseconds apart at a position angle of 330°.
The primary star, component A, has a magnitude of 6.12 and is classified as a G8 IV subgiant. The secondary, component B, has a magnitude of 6.54 and is a K3 IV subgiant. Their brightness relative to their temperatures suggests they are evolving subgiant stars, though at least one of them shows flare activity, which could indicate they are actually pre-main-sequence stars.
A third star shares a common proper motion with the inner pair, indicating it is part of the same triple system. This star is separated from the AB pair by 1,407 arcseconds (0.39°). At the system's distance, this corresponds to a projected separation of about 53,000 AU (0.84 light-years), with an estimated orbital period of seven million years. It is a K-type main-sequence star with 0.68 times the Sun's mass and an apparent magnitude of 10.92.
- Apparent magnitude
- 5.45
- Distance
- 124 light years
- Parallax
- 26.33 mas
- Radial velocity
- −0.8 km/s
- Binary discovery year
- 1832
- Binary discoverer
- Wilhelm von Struve
- Orbital period
- 169.1 years
- Eccentricity
- 0.31
- Semi major axis
- 37 au
- Angular separation
- 0.90 arc seconds
Lore & Background
The binary nature of 36 Andromedae was discovered in 1832 by the German-Russian astronomer Wilhelm von Struve. It is a wide binary with an orbital period of 169.1 years and an eccentricity of 0.31. Their semi-major axis is of 37 astronomical units (au), larger than that of Neptune. As of 2016, the pair had an angular separation of 0.90 arc seconds along a position angle of 330°.
The primary, component A, is a magnitude 6.12 G-type star with a stellar classification of G8 IV, while the secondary, component B, has a magnitude of 6.54 and is a K-type star of class K3 IV. Their brightness compared to their temperatures indicate they are evolving subgiant stars. However, at least one of the components is subject to flare activity, which may suggest they are instead pre-main sequence stars.
36 Andromedae makes part of a triple star system. A third star, which shares a common proper motion with the inner pair and hence is believed to form a triple system, is separated by the AB pair by 1,407" (0.39°). At the system's distance, this implies a projected separation of 53,000 astronomical units (0.84 light-years) and an estimated orbital period of seven million years. It is a K-type main-sequence star with 0.68 times the mass of the Sun and an apparent magnitude of 10.92.
Reader's Guide
The system is notable for its wide binary pair, discovered by Wilhelm von Struve in 1832, with an orbital period of 169.1 years and a semi-major axis larger than Neptune's orbit. The primary and secondary are both subgiant stars, but flare activity in at least one component raises the possibility they are pre-main sequence stars instead, leaving their evolutionary status uncertain. The third star, sharing common proper motion, extends the system to a projected separation of 53,000 au and an estimated orbital period of seven million years, making it a hierarchical triple. The system's faint naked-eye visibility (magnitude 5.45) and its inclusion in Flamsteed's 1712 catalogue give it historical cataloguing significance. Its measured parallax of 26.33 mas provides a reliable distance of about 124 light-years, and its radial velocity of −0.8 km/s indicates it is moving toward the Sun.
Did You Know?
- The system's semi-major axis of 37 au is larger than Neptune's orbit.
- At least one component shows flare activity, suggesting it may be a pre-main sequence star.
- The third star is separated by 53,000 au and has an estimated orbital period of seven million years.
Frequently Asked Questions
What is 36 Andromedae?
36 Andromedae is a binary star system in the northern constellation Andromeda that actually belongs to a larger triple-star arrangement. Its designation traces back to John Flamsteed's star catalog, first published in 1712.
How far away is 36 Andromedae from Earth?
Using an annual parallax measurement of 26.33 milliarcseconds, astronomers place the system at roughly 124 light-years from our Sun.
Who first identified 36 Andromedae as a binary star?
German-Russian astronomer Wilhelm von Struve recognized the binary nature of the system in 1832, making it one of the earlier catalogued double stars in Andromeda.
Can 36 Andromedae be seen with the naked eye?
It sits right at the edge of naked-eye visibility, with an apparent visual magnitude of 5.45, so under very dark skies it can just barely be spotted without a telescope.
Is 36 Andromedae moving toward or away from the Sun?
The system has a radial velocity of about −0.8 km/s, meaning it is drifting slowly in our direction, though that speed is negligible on astronomical timescales.
More in Binary and Multiple Stars, Part 2 1-24
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