2 Andromedae, abbreviated 2 And, is a binary star system in the northern constellation of Andromeda. ''2 Andromedae'' is the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England. They are named for John Flamsteed who first used them while co ...

. It is a faint star system but visible to the naked eye with a combined

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of 5.09. Based upon an annual parallax shift of , it is located 420 light years away. The binary nature of the star was discovered by American astronomer

Sherburne Wesley Burnham Sherburne Wesley Burnham (December 12, 1838 – March 11, 1921) was an American astronomer. For more than 50 years Burnham spent all his free time observing the heavens, mainly concerning himself with binary stars. Biography Sherburne ...

at Lick Observatory in 1889. The pair orbit each other over a

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of 74 years with a high

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.8. The magnitude 5.26 primary, designated component A, is an

A-type main-sequence star An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between ...

based on a stellar classification of A1V or A2V, although it may have already left the main sequence. It was identified as a candidate

Lambda Boötis star A Lambda Boötis star is a type of chemically peculiar star which has an unusually low abundance of iron peak elements in its surface layers. One possible explanation for this is that it is the result of accretion of metal A metal (from Gre ...

, but this was ruled out by Paunzen et al. (2003) as it doesn't match the typical characteristics of these objects. Although 2 And does not display a significant

infrared excess An infrared excess is a measurement of an astronomical source, typically a star, that in their spectral energy distribution has a greater measured infrared flux than expected by assuming the star is a blackbody radiator. Infrared excesses are oft ...

, it is a

shell star A shell star is a star having a spectrum that shows extremely broad absorption lines, plus some very narrow absorption lines. They typically also show some emission lines, usually from the Balmer series but occasionally of other lines. The broa ...

that displays varying absorption features due to circumstellar dust grains. This may indicate it has an orbiting

debris disk A debris disk (American English), or debris disc (Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris di ...

containing gas that is being viewed edge-on. The star is about 100 million years old and is spinning rapidly with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulg ...

of 212 km/s. The magnitude 7.43 secondary companion, component B, is a suspected

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

and may be a

Delta Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a subclass of young pulsating star. These variables as well as classical cepheids are important standard candles and have been used to es ...

. Alternatively, it may be an ellipsoidal variable with a

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

companion. It is an

F-type main-sequence star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII ...

with a class of F1V/F4.

References

External links

Image 2 Andromedae
{{DEFAULTSORT:2 Andromedae A-type main-sequence stars F-type main-sequence stars Delta Scuti variables Shell stars Binary stars Circumstellar disks 02 Andromedae Durchmusterung objects Andromedae, 02 Gliese and GJ objects 217782 113788 8766