AU Microscopii

AU Microscopii

AU Microscopii, J band image, 2MASS.
Observation data Epoch J2000      Equinox J2000
Constellation	Microscopium
Right ascension	20h 45m 09.53250s[1]
Declination	–31° 20′ 27.2379″[1]
Apparent magnitude (V)	8.73[2]
Characteristics
Spectral type	M1Ve[2]
Apparent magnitude (V)	8.627±0.052[3]
Apparent magnitude (J)	5.436±0.017[3]
U−B color index	1.01
B−V color index	1.45
Variable type	Flare star
Distance		31.683 ± 0.007 ly (9.714 ± 0.002 pc)
Absolute magnitude (MV)	8.61
Details
Myr
LTT 8214, SAO  212402, Vys 824, LDS 720 A.
Database references
SIMBAD	data
ARICNS	data

AU Microscopii (AU Mic) is a young

AU Microscopii has been observed in every part of the

AU Microscopii's debris disk has an asymmetric structure and an inner gap or hole cleared of debris, which has led a number of astronomers to search for planets orbiting AU Microscopii. By 2007, no searches had led to any detections of planets.[24]^[25] However, in 2020 the discovery of a Neptune-sized planet was announced based on transit observations by TESS.^[7] Its rotation axis is well aligned with the rotation axis of the parent star, with the misalignment being equal to 5⁺¹⁶
₋₁₅°.^[26]

Since 2018, a second planet, AU Microscopii c, was suspected to exist. It was confirmed in December 2020, after additional transit events were documented by the TESS observatory.^[27]

A third planet in the system was suspected since 2022 based on transit-timing variations,^[28] and "validated" in 2023, although several possible orbital periods of planet d cannot be ruled out yet. This planet has a mass comparable to that of Earth.^[6] Radial velocity observations have also found evidence for a fourth, outer planet as of 2023.^[3]

Debris disk

AU Microscopii harbors its own disk of dust, first resolved at optical wavelengths in 2003 by Paul Kalas and collaborators using the University of Hawaii 2.2-m telescope on Mauna Kea, Hawaii.^[5] This large debris disk faces the earth edge-on,^[30] and measures at least 200 AU in radius. At these large distances from the star, the lifetime of dust in the disk exceeds the age of AU Microscopii.^[5] The disk has a gas to dust mass ratio of no more than 6:1, much lower than the usually assumed primordial value of 100:1.^[31] The debris disk is therefore referred to as "gas-poor". The total amount of dust visible in the disk is estimated to be at least a lunar mass, while the larger planetesimals from which the dust is produced are inferred to have at least six lunar masses.^[32]

The spectral energy distribution of AU Microscopii's debris disk at submillimetre wavelengths indicate the presence of an inner hole in the disk extending to 17 AU,^[33] while scattered light images estimate the inner hole to be 12 AU in radius.^[34] Combining the spectral energy distribution with the surface brightness profile yields a smaller estimate of the radius of the inner hole, 1 - 10 AU.^[24]

The inner part of the disk is asymmetric and shows structure in the inner 40 AU.^[35] The inner structure has been compared with that expected to be seen if the disk is influenced by larger bodies or has undergone recent planet formation.^[35]

The surface brightness (brightness per area) of the disk in the near infrared ${\displaystyle \scriptstyle I}$ as a function of projected distance ${\displaystyle \scriptstyle r}$ from the star follows a characteristic shape. The inner ${\displaystyle \scriptstyle r\,<\,15AU}$ of the disk appear approximately constant in density and the brightness is unchanging, more-or-less flat.^[34] Around ${\displaystyle \scriptstyle r\,\approx \,15AU}$ the density and surface brightness begins to decrease: first it decreases slowly in proportion to distance as ${\displaystyle \scriptstyle I\,\propto \,r^{-1.8}}$; then outside ${\displaystyle \scriptstyle r\,\approx \,43AU}$, the density and brightness drops much more steeply, as ${\displaystyle \scriptstyle I\,\propto \,r^{-4.7}}$.^[34] This "broken power-law" shape is similar to the shape of the profile of β Pic's disk.

In October 2015 it was reported that astronomers using the Very Large Telescope (VLT) had detected very unusual outward-moving features in the disk. By comparing the VLT images with those taken by the Hubble Space Telescope in 2010 and 2011 it was found that the wave-like structures are moving away from the star at speeds of up to 10 kilometers per second (22,000 miles per hour). The waves farther away from the star seem to be moving faster than those close to it, and at least three of the features are moving fast enough to escape the gravitational pull of the star.^[36]

Methods of observation

AU Mic's disk has been observed at a variety of different

Optical observations have been made with the Hubble Space Telescope and

See also

• List of exoplanets discovered in 2020 - AU Microscopii b and c
• List of exoplanets discovered in 2023 - AU Microscopii d

References

External links

Wikimedia Commons has media related to AU Microscopii.

• "AU and AT Microscopii AB". SolStation. 2004. Archived from the original on 11 November 2006. Retrieved 2006-12-20.