| Observation data EpochJ2000.0 EquinoxJ2000.0 (ICRS) | |
|---|---|
| Constellation | Microscopium |
| Right ascension | 20h 41m 51.15925s[2] |
| Declination | −32° 26′ 06.8283″[2] |
| Apparent magnitude (V) | 11.0/11.1[3] |
| Characteristics | |
| Spectral type | M4 Ve[4] + M4.5e |
| U−Bcolor index | +0.91[5] |
| B−Vcolor index | +1.58[5] |
| Variable type | Flare star |
| Astrometry | |
| Radial velocity (Rv) | 4.5[6] km/s |
| Proper motion (μ) | RA: +270.45[2]mas/yr Dec.: –365.60[2]mas/yr |
| Parallax (π) | 93.50±3.67 mas[2] |
| Distance | 35 ± 1 ly (10.7 ± 0.4 pc) |
| Orbit[7] | |
| Period (P) | 141.39yr |
| Semi-major axis (a) | 2.616″ |
| Eccentricity (e) | 0.607 |
| Inclination (i) | 148.4° |
| Longitude of the node (Ω) | 82.6° |
| Periastronepoch (T) | 2035.10 |
| Argument of periastron (ω) (secondary) | 54.6° |
| Details | |
| AT Mic A | |
| Mass | 0.27+0.04 −0.09[8] M☉ |
| Radius | 0.41[9] R☉ |
| Luminosity | 0.036[3] L☉ |
| Temperature | 3,150[3] K |
| Age | 12+8 −4[8] Myr |
| AT Mic B | |
| Mass | 0.25+0.04 −0.09[8] M☉ |
| Radius | 0.37[9] R☉ |
| Luminosity | 0.033[3] L☉ |
| Temperature | 3150[3] K |
| Other designations | |
| AT Mic,CD−32°16135,GJ 799,HD 196982,HIP 102141,SAO 212355,WDS J20452-3120BC[4] | |
| Database references | |
| SIMBAD | data |
| ARICNS | A |
| B | |
AT Microscopii is abinary star system located at a distance of 35 ly (11 pc) from the Sun in theconstellation ofMicroscopium.[2] Both members areflare stars,[8] meaning they arered dwarf stars that undergo random eruptions that increase their brightness. This pair lies physically near the red dwarf starAU Microscopii, which may mean they form a wide triple star system.[8]
In 1926, Dutch-American astronomerWillem Jacob Luyten reported that the lines in thespectrum 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 inmagnitude. Luyten noted that the star has a largeproper motion, changing its position by 0.43seconds of arc between 1899 and 1923.[10]
By 1927, the object was found to be a pair of stars with anangular separation of 2.95arcseconds. Both were shown to be of 'dwarf Me' type, indicating they arered dwarfs withemission lines in their spectrum. This was the first such pair of matching dwarf Me stars to be discovered. The firstparallax measurements of the pair showed an annual shift of about 0.1arcseconds, while theirradial velocity was measured to be +5 km/s away from the Sun. A nearby star HD 197981, later namedAU Microscopii, 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.[11]
Following the discovery in 1949 that certain types ofvariable stars are characterized by rapid but brief changes in brightness, accompanied byemission lines in their spectrum,[12] in 1954 both HD 196982 A and B were listed as suspectedflare stars by Czech solar physicistZdeněk Švestka.[13]
With the introduction ofphotometric 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 activeflare stars 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.[14] By 1972, the pair had received thevariable star designation AT Microscopii.[15]
Position measurements of the pair made with theHipparcos spacecraft show an annualparallax shift of 0.0935seconds of arc, which is equivalent to a distance of about 35 ly (11 pc) from the Sun.[2] It is abinary star system with anangular separation of 4.0arcseconds.[12] Both members are pre-main sequence,red dwarf stars and are among the youngest of this type in the neighborhood of the Sun.[12] 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.[3]
Both members of this system have activestellar coronae, show luminosity variations of theBY Draconis type, and areX-ray emitters.[8] The average flare rate for the pair is 2.8 per hour.[12][16] Their X-ray spectrum is consistent with a plasma density of around3 × 1010 cm−3 and amagnetic field strength of at least 100 G in the flare regions.[17] Neither star shows any indication oflithium in their spectrum, having depleted this element throughnuclear fusion at their cores.[3]
This binary system is located in close proximity to the young starAU Microscopii, with aprojected separation of46,400 ± 500astronomical units. This indicates that the three may form a wide hierarchical triple system, with the AT Microscopii pair orbiting AU Microscopii over aperiod of 10 million years.[8] All three stars are candidate members of theBeta Pictoris moving group, one of the nearestassociations of stars that share a common motion through space. This group averages a distance of about 100 ly (31 pc) from the Earth, but are scattered across a volume roughly 100 ly (31 pc) in diameter. Estimates for the age of this group range between 10 and 21 million years.[3]
