AT Microscopii is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

system located at a distance of from the Sun in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Microscopium Microscopium ("the Microscope") is a minor constellation in the southern celestial hemisphere, one of twelve created in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. The nam ...

. Both members are

flare star A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to the magnetic energy stored in th ...

s, meaning they are

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

stars that undergo random eruptions that increase their brightness. This pair lies physically near the red dwarf star

AU Microscopii AU Microscopii (AU Mic) is a young small star located about away – about 8 times as far as the closest star after the Sun. The apparent visual magnitude of AU Microscopii is 8.73, which is too dim to be seen with the naked eye. It w ...

, which may mean they form a wide triple star system.

Observational history

In 1926, Dutch-American astronomer

Willem Jacob Luyten Willem Jacob Luyten (March 7, 1899 – November 21, 1994) was a Dutch-American astronomer. "Willem Jacob Luyten", ''Marquis Who's Who'', 2006. Life Jacob Luyten was born in Semarang, Java, at the time part of the Dutch East Indies. His ...

reported that the lines in the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of this star underwent variation. A photographic plate taken on June 23, 1895, showed bright lines of hydrogen that were much weaker on a plate taken June 29, 1895. A photograph taken on July 1, 1903, showed no such lines. The net variation in brightness of the star was small, not exceeding 0.5 in

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

. Luyten noted that the star has a large

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

, changing its position by 0.43 seconds of arc between 1899 and 1923. By 1927, the object was found to be a pair of stars with an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 2.95

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s. Both were shown to be of 'dwarf Me' type, indicating they are

s with

emission line 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 ...

s in their spectrum. This was the first such pair of matching dwarf Me stars to be discovered. The first

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements of the pair showed an annual shift of about 0.1

s, while their

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

was measured to be +5 km/s away from the Sun. A nearby star HD 197981, later named

, was shown to have a similar radial velocity of +10 km/s. For this reason it was suggested that the three stars are physically associated. Following the discovery in 1949 that certain types of

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 ...

s are characterized by rapid but brief changes in brightness, accompanied by

s in their spectrum, in 1954 both HD 196982 A and B were listed as suspected

s by Czech solar physicist

Zdeněk Švestka Zdeněk Švestka (30 September 1925 – 2 March 2013) was a Czech astronomer. For several decades he was the world's leading expert on solar flares. He studied mathematics and physics at Charles University, Prague, until graduating in 1948. Togeth ...

. With the introduction of photometric instruments to astronomy, the variability of stars could now be monitored over intervals of time. Measurements of HD 196982 during 1969 showed them to be the most active

s known at that time: over a period of 16.31 hours, 54 flares were observed. The flares increased the combined magnitude of the pair by more than 0.05 for more than half of this observation period. By 1972, the pair had received the

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

AT Microscopii.

Properties

Position measurements of the pair made with the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

spacecraft show an annual

shift of 0.0935 seconds of arc, which is equivalent to a distance of about from the Sun. It is a

system with an

of 4.0

arcseconds A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

. Both members are pre-

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

stars and are among the youngest of this type in the neighborhood of the Sun. Relative to the Sun, component A has about 27% of the mass and 3.6% of the luminosity, while component B has 25% of the mass and 3.3% of the luminosity. Both members of this system have active

stellar corona A corona ( coronas or coronae) is the outermost layer of a star's atmosphere. It consists of plasma. The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. It is most easily seen during a total solar ...

e, show luminosity variations of the BY Draconis type, and are

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

emitters. The average flare rate for the pair is 2.8 per hour. Their X-ray spectrum is consistent with a plasma density of around and a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

strength of at least 100 G in the flare regions. Neither star shows any indication of

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...

in their spectrum, having depleted this element through

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...

at their cores. This binary system is located in close proximity to the young star

, with a

projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

of . This indicates that the three may form a wide hierarchical triple system, with the AT Microscopii pair orbiting AU Microscopii 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 10 million years. All three stars are candidate members of the

Beta Pictoris moving group The Beta Pictoris Moving Group is a young moving group of stars located relatively near Earth. A moving group, in astronomy, is a group of stars that share a common motion through space as well as a common origin. This moving group is named for B ...

, one of the nearest associations of stars that share a common motion through space. This group averages a distance of about from the Earth, but are scattered across a volume roughly in diameter. Estimates for the age of this group range between 10 and 21 million years.

References

External links

* {{DEFAULTSORT:AT Microscopii Microscopium M-type main-sequence stars Binary stars Flare stars BY Draconis variables 196982 0799 102141 CD-32 16135 Microscopii, AT