Protoplanetary Disk found Encircling Mira B

Michael Ireland - CaltechCo-authors: John Monnier (U. Michigan), Peter Tuthill (U. Sydney), Richard Cohen (Keck

Observatory)

Summary

• Planets form in dusty ‘protoplanetary disks’ around young stars.

• What we found: Evidence for a large dusty disk around the companion to Mira, a dying star.

• This is a new type of protoplanetary disk: a planetary system that can be reborn when its companion star dies.

Mira the ‘Miracle’ Star

• In the constellation Cetus, Mira was discovered as a variable star in 1596, demonstrating that the stars were not invariable as Aristotle had thought.• Visible to the naked eye for a month at a time, Mira periodically becomes 1000 times fainter, re-appearing in 11 months.• We now know that Mira is a star like the sun in its death throes, pulsating and ejecting its outer layers on its way to becoming an earth-sized white dwarf.

Mira

Credit AAVSO Website

Mira’s Companion, Mira B: What we knew before

Credit: NASA/CXC/M.Weiss

While Mira A was at its faintest, Mira B has been detected in blue and ultraviolet light. So astronomers have generally thought that Mira B was only a hot, ‘compact’ object (not the kind of place you’d form planets!).

The Keck Long-Wavelength-Spectrometer (LWS) “Segment-tilting” Experiment

Programming the Mirror

Richard Cohen (WMKO) wrote low-level ACS Software

One star is split into four images (blue image falls off detector)

Short-Exposure Images on Keck-LWS at 10.7 microns

10 arcseconds

10 arcsecon

ds

Mira A and B: A colorful conundrum.

Blue: Hubble Space Telescope (actually blue), Green: Infrared 10 microns (silicate), Red: Infrared 12 microns

Solution: A large side-illuminated disk around Mira B

Protoplanetary disks usually located where stars are born

Image credit: NASA/HST

Mira B: A ‘born-again’ protoplanetary disk.

Image credit: NASA Origins

By comparing the measured size of the disk to predictions, and by re-analysing Hubble Space Telescope spectra, we can show that Mira B is an ordinary star 0.5-0.7 times as massive as the sun.

Mira B: A “once-off’ weird system, or something common?• Two out of three stars systems are actually double-stars. One in four will end up like Mira A and B.

• Today in our ‘neighborhood’, stars die 4 times more often than they are born.

• If we turn our telescopes to overlooked nearby stars with white dwarf companions (like Mira A when it dies), we should be able to find many systems that formed like Mira B.

• So… We discovered that around Mira B is a new kind of protoplanetary disk, formed from the wind of a dying star. This is the first detection of this kind of disk.

Mira A and B: Confirm with ISI and Gemini

Mira A and B: Confirm with ISI and Gemini

Infrared Spatial Interferometer (Charlie Townes) early 1990s measurement. Confirms that the ‘clump’ is moving against the wind - so must be connected to Mira B.