Image Credit:P. Kalas, University of California, Berkeley
Copyright, please do not reproduce without permission from the authors.

AU Mic at 0.8 microns

HD 197481       SAO 56680     HIP 102409
RA (J2000) = 20 45 09.5318      Dec (J2000) = -31 20 27.238
SpT = M1Ve    V = 8.65 mag    d = 9.9 pc
Proper Motion (mas/yr) =279.96 -360.61

The disk around AU Microscopii (AU Mic) was first seen in this image obtained by Paul Kalas on October 15, 2003, from the University of Hawaii 2.2-m telescope on Mauna Kea, Hawaii.

The image shows a black disk in the center that is suspended by four thin wires at the focus of the telescope. The black disk produces an artificial eclipse of AU Mic, just like the Moon occasionally produces a total eclipse of the Sun. Therefore we do not see the star AU Mic - it's hidden behind the spot - but we see the faint nebulosity around it. The nebulosity is produced by dust grains that orbit the star in a relatively flat disk, much like the Kuiper Belt of our Solar system. The image was recorded on a CCD with 2048 x 2048 pixels.

In the image gallery, AU Mic is the closest circumstellar disk that can be seen in optical reflected light. It is only 10 pc from the Sun (33 light years). AU Mic's disk is detected in the image above as close as 50 AU radius from the star, and as far as 210 AU radius (1 AU = 1 astronomical unit = 93 million miles).

AU Mic is also important because it is beta Pic's sister star. beta Pic, AU Mic, and approximately 20 other stars appear to move together in the galaxy and have similar ages. The young stars comprising the "beta Pic Moving Group" probably formed together from the same interstellar cloud of gas and dust.

The image above shows beta Pic (left) and AU Mic (right) side-by-side with the same angular scale and sensitivity. In both images, the black disk in the center has diameter 10 arcseconds, which corresponponds to 193 AU at beta Pic, and only 99 AU at AU Mic. Remarkably, both disks appear to have an edge-on orientation when viewed from Earth. Beta Pic's disk appears to be much brighter, though. Why? First, beta Pic is a brighter star and therefore dust around it reflects more light. Second, beta Pic's disk probably has 3-4 times more dust mass than AU Mic's disk. AU Mic could be called beta Pic's "little sister".

Basic facts about AU Mic:

1) Stellar Mass = 0.5 Msun, Stellar luminosity = 0.1 Lsun

2) Radius of Disk = 210 AU (21")

3) Radius of central depletion of dust = 17 AU

4) Age = 8-20 Million Year