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| PRI (MPIfR) 04/2009 (1) | Press Release | April 2, 2009 |
A team of astronomers, led by Stefan Kraus and Gerd Weigelt from the Max-Planck-Institute for Radio Astronomy (MPIfR) in Bonn, used ESO's Very Large telescope Interferometer (VLTI) to obtain the sharpest ever image of the young double star Theta 1 Ori C in the Orion Trapezium Cluster, the most massive star in the nearest high-mass star-forming region. The new image clearly separates the two young, massive stars of this system. The observations have a spatial resolution of about 2 milli-arcseconds, corresponding to the apparent size of a car on the surface of the moon. The team was able to derive the properties of the orbit of this binary system, including the masses of the two stars (38 and 9 solar masses) and their distance from us (1350 light-years). The results show the fascinating new possibilities of high-resolution stellar imaging achievable with infrared interferometry.
A particularly
promising way to increase the angular
resolution of conventional optical telescopes is the method
of interferometry. This technique allows astronomers to combine
the light from several telescopes,
forming a huge virtual telescope with a resolving power corresponding to
that of a single telescope of up to 200 m diameter.
The Very Large Telescope Interferometer
(VLTI) now offers this revolutionary technique to European
astronomers and allows them to
directly reconstruct images from the interferometric infrared
data. A team of European astronomers utilized the VLTI and its
near-infrared beam-combination instrument AMBER to demonstrate the imaging
capabilities of this unique facility and to study the intriguing massive
young star Theta1 Ori C in unprecedented detail.
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Figure 1:
Left: Zooming in the center of the Orion star-forming region with the
four bright Trapezium stars (Theta 1 Ori A-D). The dominant star is
Theta 1 Ori C, which was imaged with unprecedented resolution with
the VLT interferometer (lower right).
Right:
The orbit of the binary system (grey line) was derived using position measurements obtained over the last 12 years (yellow points).
The size of the orbit of Jupiter around our sun is shown for comparison.
Collage: MPIfR (Stefan Kraus), combining the VLTI image of Theta 1 Ori C
with images from VLT/ISAAC (Mark Mc Caughrean) and HST (John Bally et al.) (Click images
for higher resolution).
Theta 1 Ori C is the dominant and most luminous star in the Orion star-forming region. Located at a distance of only about 1300 light years, it is the nearest region where massive stars are born and provides a unique laboratory to study the formation process of high-mass stars in detail. The intense radiation of Theta 1 Ori C is ionizing the whole Orion nebula. With its strong wind, the star also shapes the famous Orion proplyds, young stars still surrounded by their protoplanetary dust disks.
Although Theta 1 Ori C appeared to be a single star, both with conventional telescopes and the Hubble Space Telescope, the team discovered the existence of a close companion. "VLTI interferometry with the AMBER instrument allowed us, for the first time, to obtain an image of this system with the spectacular angular resolution of only 2 milli-arcseconds", says Stefan Kraus. "This corresponds to the resolving power of a space telescope with a mirror diameter of 130 meters." The VLTI image reveals that in March 2008 the angular distance between the two stars was only about 20 milli-arcseconds. Fig. 1 shows the VLTI/AMBER image and, in addition, position measurements of the binary system obtained over the last 12 years. These additional observations were obtained using the technique of bispectrum speckle interferometry with 3.6 to 6m-class telescopes, allowing high-angular resolution observations even at visual wavelengths down to 440 nm.
The collection of measurements shows that the two massive stars are on a very eccentric orbit with a period of 11 years. Using Kepler's third law, the masses of the two stars were derived to be 38 and 9 solar masses. Furthermore, the measurements allow a trigonometric determination of the distance to Theta 1 Ori C and, thus, to the very center of the Orion star-forming region. The resulting distance of 1350 light-years is in excellent agreement with the work of another research group led by Karl Menten, also from MPIfR, who measured trigonometric parallaxes of the nonthermal radio emission of Orion Nebula stars using the Very Long Baseline Array. These results are important for studies of the Orion region as well as the improvement of theoretical models of high-mass star formation.
Since 1609, when Galileo Galilei first pointed a telescope towards
the sky, the field of observational astronomy has strongly evolved in
both spectral coverage and angular resolution.
"Our observations demonstrate the
fascinating new imaging
capabilities of the VLTI. This infrared interferometry technique
will certainly lead to many fundamental
new discoveries", says Gerd Weigelt.
Figure 2:
ESO's 8.2m-UT (big domes) and 1.8m-AT telescopes (small domes
in the foreground) on Cerro Paranal.
A virtual telescope of 130 m diameter, formed by
combining the light from three AT's
arranged in three different telescope configurations,
was used to construct the image of Theta 1 Ori C.
Tracing the young massive high-eccentricity binary system
Theta 1 Orionis C through periastron passage,
S. Kraus, G. Weigelt, Y.Y. Balega, J.A. Docobo, K.-H. Hofmann, T. Preibisch, D. Schertl, V.S. Tamazian, T. Driebe, K. Ohnaka, R. Petrov, M. Schoeller, M. Smith, Astronomy & Astrophysics vol. 497, p. 195 (2009).
Max Planck Institute for Radio Astronomy (MPIfR).
Infrared Interferometry Group at MPIfR.
European Southern Observatory (ESO).
Astronomical Multi-BEam combineR (AMBER) at ESO/Paranal.
The distance to the Orion Nebula,
K. M. Menten, M. J. Reid, J. Forbrich, A. Brunthaler,
2007, Astronomy & Astrophysics Vol. 474, pp. 515-520.
High-resolution image of the brightest Orion Trapezium star,
A&A Press Release, April 02, 2009.
Hundred metre virtual telescope captures unique detailed colour image,
ESO Press Release 06/09, February 18, 2009.
Winds of Baby Stars,
PRI (MPIfR) 10/2008 (1), October 10, 2008.
The Growing-up of a Star,
ESO Press Release 03/08, January 29, 2008.
Shedding New Light on the Life Cycle of Stars,
MPIfR & MPG Press Release 02/2007, February 21, 2007.
Dr. Stefan Kraus,
Prof. Dr. Gerd Weigelt,
Dr. Norbert Junkes,
Image: MPIfR (Gerd Weigelt).
(Click image for higher resolution).
Original Paper:
Further Information:
Parallel and earlier press releases:
Contact:
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-395
E-mail: skraus (at)
mpifr.de
Head of Research group Infrared Interferometry,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-243
E-mail: gweigelt (at)
mpifr.de
Public Outreach,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-399
E-mail: njunkes (at)
mpifr.de