CONTACT: Donald Savage NASA Headquarters, Washington, DC (Phone: 202/358-1547)
Tammy Jones Goddard Space Flight Center, Greenbelt, MD (Phone: 301/286-5566)
Ray Villard Space Telescope Science Institute, Baltimore, MD (Phone: 410/338-4514)
Megan Watzke Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (Phone: 617/495-7463)
Although the giant star Mira has been known for about 400years, astronomers have had to wait for NASA's Hubble Space Telescopeto provide the first ultraviolet images of the extended atmosphere ofthe cool red giant star and its nearby hot companion.
By giving astronomers a clear view of the individual members ofthis system, Hubble has provided valuable insights into other types ofdouble star systems where the stars are so close they interact with oneanother.
The separation between Mira and its companion is about 70 timesmore than that between Earth and the Sun, (equal to an angular size ofonly 0.6 arcseconds -- the apparent diameter of a dime at four milesaway) even smaller than the typically fuzzy ground-based telescopicimage of a single star as smeared out by Earth's turbulent atmosphere.
Using the European Space Agency's Faint Object Camera aboardHubble, Margarita Karovska and John Raymond of the Harvard-SmithsonianCenter for Astrophysics, Cambridge, MA; Warren Hack of the SpaceTelescope Science Institute, Baltimore, MD; and Edward Guinan ofVillanova University, Villanova, PA, obtained both ultraviolet andvisible light images and spectra of the two separate stars in the Mirasystem. The results appear in the June 20 Astrophysical JournalLetters.
In ultraviolet light, Hubble has resolved a small hook-likeappendage extending from Mira in the direction of the companion, whichmight be material from Mira being gravitationally drawn toward thesmaller star. Alternately, it could be material in Mira's upperatmosphere being heated due to the companion's presence.
Hubble's visible-light images show that Mira has an odd,asymmetrical shape resembling a football. This may be tied to dramaticchanges occurring during its expansion-contraction cycles, or to thepresence of unresolved spots on its surface. Hubble allows astronomersto measure the star's size at about 60 milliarcseconds, correspondingto a diameter some 700 times larger than our Sun. If Mira were at thecenter of our solar system, it would extend out more than 300 millionmiles, well beyond Mars' orbit and nearly two-thirds of the way toJupiter.
Mira (officially called Omicron Ceti in the constellation Cetus)is the prototype for an entire class of stars known as "Mira-typevariables." Although once like our Sun, Mira is now at the end of itslife, and has evolved into a cool red giant star that is highly variablein brightness. Contracting and expanding every 332 days, Mira shedsvast amounts of material through its powerful "wind" of gas and dust.
Mira's companion is a burned-out star called a white dwarf thatis surrounded by material captured from Mira's wind. At a distance ofabout 400 light-years, Mira is the closest wind-accreting binary systemto Earth.
Separating the spectra of Mira and its companion -- somethingastronomers previously have tried to do through indirect means -- is acrucial step for studies of physical processes associated with windaccretion in binaries.
Mira was discovered on August 13, 1596, by Dutch astronomerDavid Fabricus, who mistook it for a nova because it later faded fromview. He called it Mira, meaning "The Wonderful." Astronomers laterrealized it was really the first case of a variable star.
The Space Telescope Science Institute is operated by theAssociation of Universities for Research in Astronomy, Inc., for NASA,under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperationbetween NASA and the European Space Agency (ESA).
EDITORS NOTE: The Hubble images of Mira are available tomedia representatives by calling the Imaging Branch at NASAHeadquarters at 202/358-1900. Photo number is: (color) 97-HC-537
Image files in GIF and JPEG format and captions may be accessed on theInternet via anonymous ftp from oposite.stsci.edu in /pubinfo.
GIF JPEGPRC97-26 Mira gif/mira.gif jpeg/mira.jpg
Higher resolution digital versions (300 dpi JPEG) of the releasephotograph are available in /pubinfo/hrtemp: 97-26.jpg (color) and97-26bw.jpg (black & white).
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The above story is based on materials provided by National Aeronautics And Space Administration. Note: Materials may be edited for content and length.
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