What separates the stars from each other



26.07.2011 10:26

New knowledge about the "miraculous" star Mira

Alexander Dworzak Public relations and event management
University of Vienna

The star Omikron Ceti, called Mira, "the miraculous", is extraordinary in two respects: It changes its brightness at regular intervals and has a comet-like tail. An international research team with the leading participation of scientists from the Institute for Astronomy at the University of Vienna provides new findings on structures in the vicinity of the old star. The researchers publish on this in the current issue of the journal "Astronomy & Astrophysics".

For around 20 years, the research of red giants has been the focus of the work of astronomers at the University of Vienna. These final stages of sun-like stars have an above-average size and luminosity, which is up to 1,000 times that of our sun. The red giant Omicron Ceti in the constellation Whale is one of the best-known and most-observed stars in our night sky.

Alleged disappearance of the "miraculous"

The fame of Omikron Ceti is based on its supposed appearance and disappearance, which astonished astronomers as early as the 17th century. Omikron Ceti is easily visible to the naked eye in its brightest phases, but regularly becomes up to 1,500 times weaker. Its fluctuations in brightness are repeated over a period of around 331 days. In his book Historiola Mirae Stellae from 1662 Johannes Hevelius Omikron gave Ceti the name Mira - "the miraculous".

Mira - a double star

Today we know that Mira, about 300 light years from Earth, is a binary star system. It consists of the very bright and pulsating red giant Mira A and the smaller, very faint white dwarf Mira B. Both stars are 55 times the distance between the earth and the sun. X-ray observations from 2005 showed that Mira A transfers part of its mass to Mira B. "Loss of mass in the form of a dusty wind is one of the central features of 'dying' red giant stars," explains Franz Kerschbaum, head of the Institute for Astronomy at the University of Vienna.

Racing star with "comet tail"

Another impressive feature is Mira's movement through the interstellar gas. "The star races through space at around 110 kilometers per second," says Thomas Posch from the Institute for Astronomy at the University of Vienna. The dusty wind is carried backwards, similar to a comet's tail. Spectacular recordings from 2007 showed this for the first time and revealed a strong outflow of mass along the movement path.

Arched and broken structures

New observations with the Herschel infrared telescope of the European Space Agency, which were evaluated at the Institute for Astronomy at the University of Vienna, combine these observations and expand our knowledge of Mira's puzzling appearance. "In the vicinity of the star system, curved and broken structures can be seen, together with a delicate tail," says Andreas Mayer from the Institute for Astronomy at the University of Vienna and first author of the current publication in Astronomy & Astrophysics.

"This is probably due to the interplay of two factors: On the one hand, the movement of the white dwarf by the star wind, which leaves a spiral structure. On the other hand, these spirals are 'pierced' by the strong mass outflow and compressed by the movement of the interstellar medium," explains Mayer.

European project Herschel

"Herschel", the infrared telescope of the European Space Agency ESA, was launched in 2009 with Austrian participation. It observes the sky in the far infrared and, with a mirror diameter of 3.5 meters, is currently the largest space observatory - its light-collecting area is twice as large as that of NASA's "Hubble" telescope. The software was developed at the Institute for Astronomy at the University of Vienna, which enables the data to be compressed enough while on board the satellite to be able to transmit it to Earth.

publication
Herschel's view into Mira's head (A. Mayer, A. Jorissen, F. Kerschbaum, S. Mohamed, S. Van Eck, R. Ottensamer, JADL Blommaert, L. Decin, MAT Groenewegen, Th. Posch, B. Vandenbussche and Ch . Waelkens). In: Astronomy & Astrophysics, Volume 531, July 2011.
DOI: 10.1051 / 0004-6361 / 201117203
Abstract http://www.aanda.org/articles/aa/abs/2011/07/aa17203-11/aa17203-11.html

Scientific contact
Andreas Mayer, Bakk.
Institute for Astronomy
University of Vienna
1180 Vienna, Türkenschanzstrasse 17
M + 43-650-203 53 99
[email protected]

Consultation notice
Mag. Alexander Dworzak
public relation
University of Vienna
1010 Vienna, Dr.-Karl-Lueger-Ring 1
T + 43-1-4277-175 31
M + 43-664-602 77-175 31
[email protected]


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