AU and AT Microscopii AB

AU Microscopii

This cool and dim, main sequence red dwarf (M0-1 Ve) has only around 0.5 Sol's mass (Paul Kalas), a much smaller of its diameter (Claud H. Lacy, 1977, page 481), and about 10 percent of its brightness (Paul Kalas). However, AU Microscopii is a very young flare star, only around 12 million years old (eight to 20 million years old). Some alternative names and useful star catalogue numbers are: AU Mic, Gl 803, Hip 102409, HD 197481, CD-31 17815, CP(D)-31 6335, SAO 212402, LTT 8214, and V 824.

Paul Kalas, IFA,
University of California at Berkeley


Larger image.



A planet may be creating a hole in
the dust disk of AU Microscopii,
within 17 AUs of the star (more).

Dust Disk

Using the University of Hawaii's 2.2-meter telescope, a team of astronomers (including Paul Kalas, Michael Liu, and others) found that AU Mic had an infra-red excess in its spectrum suggesting hat the star is surrounded by a dusty disk like sister star Beta Pictoris, which was likely to have been born from the same nebula but with three to four times more dust in its disk. Then, to obtain an image of the disk, they blocked out the glare of the star using a device known as a coronagraph and found that the disk extended from 50 to about 210 AUs (21") from the star. In a separate experiment that is to be reported in the Astrophysical Journal, Kalas' group calculated that the disk has a hole in it that extends out to 17 AU from the star that may indicate the presence of a planet. To try and confirm that this is indeed the case, they will now collect sharper images of the star using the Hubble and Spitzer space telescopes.

Hunt for Substellar Companions

The distance from AU Microscopii where an Earth-type planet would be comfortable with liquid water is less than 0.04 AU result in a "day" that last less than 10 hours. At that distance, the rotation of the planet would probably be tidally locked with the star so that one side would have perpetual daylight while the other would be in eternal darkness. Moreover, AU Microscopii's light is so red that Earth-type plants may not be able to photosynthesize very well.

AT Microscopii A

This cool and dim, main sequence red dwarf (M4.5 Vpe) probably has less than half of Sol's mass (RECONS), 11 percent of its diameter (Claud H. Lacy, 1977, page 481), and about 12/1,000,000th of its brightness. However, AT Microscopii is a flare star, probably around 12 million years old like AT Mic. In 1962, it was separated from its companion star by only around 40 AUs -- SepAB= 3.9". Some alternative names and useful star catalogue numbers are: AT Mic A, Gl 799 A, Hip 102141, HD 196982, CD-31 16135 A, CP(D)-31 6181, SAO 212355, LTT 8181, LDS 720, and U or UGP 502.

AT Microscopii B

This cool and dim, main sequence red dwarf (M4.5 Ve) probably has less than half of Sol's mass (RECONS), 11 percent of its diameter (Claud H. Lacy, 1977, page 481), and about 12/1,000,000th of its brightness. However, it is probably around 12 million years old like AT Mic. Some alternative names and useful star catalogue numbers are: AT Mic B, Gl 799 B, CD-31 16135 B, and CP(D)-31 6181 B.