HD 166 or V439 Andromedae (ADS 69 A) is a 6th magnitude star in the constellation Andromeda, approximately 45 light years away from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. It is a

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 ...

of the BY Draconis type, varying between magnitudes 6.13 and 6.18 with a 6.23 days periodicity. It appears within one degree of the star

Alpha Andromedae Alpha Andromedae (α Andromedae, abbreviated Alpha And or α And), officially named Alpheratz , is 97 light-years from the Sun and is the brightest star in the constellation of Andromeda when Beta Andromedae undergoes its periodi ...

''Autostar Suite Astronomer Edition''. CD-ROM. Meade, April 2006. and is a member of the

Hercules-Lyra association In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as t ...

moving group In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well a ...

. It also happens to be less than 2 degrees from right ascension 00h 00m.

Star characteristics

HD 166 is a

K-type main sequence star A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence star ...

, cooler and dimmer than the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, and has a stellar classification of K0Ve where the ''e'' suffix indicates the presence of

emission lines A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

in the spectrum. The star has a proper motion of 0.422 arcseconds per year in a direction 114.1° from north. It has an estimated visual luminosity of 61% of the

, and is emitting like a

blackbody A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...

with an effective temperature of 5,327K. It has a diameter that is about 90% the size of the Sun and a radial velocity of −6.9 km/s. Age estimates range from as low as 78 million years old based on its chromospheric activity, up to 9.6 billion years based on a comparison with theoretical evolutionary tracks. X-ray emission has been detected from this star, with an estimated luminosity of . An

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 ...

has been detected around HD 166, most likely indicating the presence of a

circumstellar disk A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the ...

at a radius of 7.5 AU. The temperature of this dust is 90 K.

Variability

It has been found that the periodicity in the photometric variability of HD 166 is coincident with the rotation period. This leads to its classification as a

BY Draconis variable BY Draconis variables are variable stars of late spectral types, usually K or M, and typically belong to the main sequence. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in thei ...

, where brightness variations are caused by the presence of large

starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...

s on the surface and by chromospheric activity.

References

External links

Image HD 166

nstars.nau.edu
{{DEFAULTSORT:HD 166 Andromeda (constellation) BY Draconis variables 000166 Spectroscopic binaries K-type main-sequence stars HD, 000166 Andromedae, V439 0008 000544 Durchmusterung objects 0005 Emission-line stars