archive: SETI A Star-Forming Region in Ara

SETI A Star-Forming Region in Ara

Larry Klaes ( )
Tue, 04 May 1999 12:59:38 -0400

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>Subject: A Star-Forming Region in Ara
>Subject: A Star-Forming Region in Ara (Forwarded)
>Date: Fri, 30 Apr 1999 20:57:11 -0400
>From: Andrew Yee <>
>Organization: via Internet Direct
>ESO Education and Public Relations Dept.
>Text with all links is available on the ESO Website at URL:
>Information from the European Southern Observatory
>ESO Press Photos 21a-b/99
>For immediate release: 30 April 1999
>A Star-Forming Region in Ara
>New Wide-Field Camera at La Silla Looks at RCW 108
>The new Wide-Field Imager (WFI) at the MPG/ESO 2.2-m telescope at the La
>Silla observatory continues to obtain impressive images of the southern sky,
>see also ESO PR Photos 18a-d/99.
>Recently, a series of images were obtained of areas in the Milky Way band,
>including some in which interstellar nebulae of gas and dust are seen. Each
>frame records 8184 x 8196, or over 67 million, pixels in a sky field of 32 x
>32 arcmin2.
>The present photos show the RCW 108 complex of bright and dark nebulae in
>the southern association Ara OB1, a star-forming region in the constellation
>Ara (The Altar), deep in the southern sky.
> ESO PR Photo 21a/99 ESO PR Photo 21b/99
> PR Photo 21a/99 displays (very nearly) the full extent of the WFI field,
> while PR Photo 21b/99 shows a smaller area in more detail.
> In PR Photo 21a/99, the resolution has been degraded by reducing the
> number of pixels in one direction from about 8000 to 3000 in the
> "High-Resolution version", in order to make the image transportable over
> the web without incurring completely unacceptable transfer times. Still it
> is very large, even in the highly compressed jpeg-format, reflecting the
> great amount of details visible. The "Normal" and "Preview" versions are
> smaller and may be acquired much faster, but with a corresponding loss of
> detail. The "Full-Resolution" version of PR Photo 21b/99 retains the
> original pixel structure and image sharpness. It covers an area that
> corresponds to about 1/7 of the full WFI field.
>The Ara OB1 association contains many young and bright stars (of types O and
>B; hence the name). It is located at a distance of about 4000 light-years
>(1.3 kpc) from the Sun; the part shown in PR Photo 21a/99 covers an area of
>about 40 light-years across (approx. 12 x 12 pc) and includes most of RCW
>RCW 108 is a molecular cloud that is in the process of being destroyed by
>intense ultraviolet radiation from heavy and hot stars in the nearby stellar
>cluster NGC 6193, seen to the left in the photos. Most of this radiation
>comes from the bright object near the center of the image, which is actually
>a binary system composed of two O-type stars. The red glow that pervades the
>field is emission in the red H-alpha spectral line of hydrogen. It reveals a
>massive stream of gas that flows away from the molecular complex as it is
>being heated and ionized.
>The small bright patch with several stars near the darkest part of the
>nebulosity, to the right in the photos, is the infrared source IRAS
>16362-4845. It marks a site where a small cluster of stars is being formed
>at present.
>The designation RCW 108 refers to the inclusion of this object in "A
>catalogue of H-alpha emission regions in the southern Milky Way", published
>by three astronomers (A.W. Rodgers, C.T. Campbell and J.B. Whiteoak) in
>Technical information: This colour picture is a composite made from 12
>separate images, obtained with the WFI on 27 March 1999. The blue component
>corresponds to the B filter, the green to the V filter, and the red to the
>H-alpha filter. The images in each filter are the composite of 4 individual
>frames obtained with the telescope pointing at slightly different positions
>on the sky, so that the parts of the sky falling in the gaps between the 8
>individual 2k x 4k CCDs in any given frame are recorded on the others. The
>monochromatic images are then produced by superimposing the individual
>frames, correcting for the telescope offsets; this ensures that the complete
>field is well covered. This procedure is not simple, as the observing
>conditions may change slightly from exposure to exposure, resulting in small
>differences. Finally, the combined images in each filter are aligned and
>colour-coded to produce the colour picture.
>For the processing of this large photo (8k x 8k; 256 Mbytes), a minimum of
>contrast correction was made and very faint lines may still be perceived in
>some places where the individual frames were joined. It may also be noted
>that there is a slight misalignment of the individual colours in stellar
>images at the extreme corners of the large field. This is due to the effect
>of differential atmospheric refraction, i.e. light rays of different colours
>are bent differently in air.
>The exposure time was 300 sec for each frame in H-alpha, and 60 sec in B and
>V. East is to the left and North to the top.
>This is the caption to ESO PR Photos 21a-b/99. They may be reproduced, if
>credit is given to the European Southern Observatory.
> Copyright ESO Education & Public Relations Department
> Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
>Andrew Yee