protoplanetary disk found encircling mira b michael ireland - caltech co-authors: john monnier (u....
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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.