Other
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000eso..presp..25.&link_type=abstract
ESO Press Release, 10/2000
Other
Scientific paper
The R Coronae Australis complex of young stars and interstellar gas clouds is one of the nearest star-forming regions, at a distance of approx. 500 light-years from the Sun. It is seen in the southern constellation of that name (The "Southern Crown").
Images of this sky area were recently obtained with the Wide Field Imager (WFI) , a 67-million pixel digital camera that is installed at the 2.2-m MPG/ESO Telescope at ESO's La Silla Observatory.
Some of these exposures have been combined into a magnificent colour image, here reproduced as PR Photo 25a/00 . The field shown measures about 4.7 x 4.7 light-years 2. It displays the central part of the complex, its brightest stars, and the nebulosity that they illuminate. The interstellar clouds that are associated with the complex are visible all across this field and also beyond its borders (on other exposures), due to the obscuring effect of the dust particles that "dim" the light of stars behind these clouds. This effect is particularly noticeable in the lower left corner where very few stars are seen.
R Coronae Australis , the bright star from which the entire complex is named, is located at the center of the field and illuminates the reddish nebula around it. The bright star in the lower part, illuminating a somewhat bluer nebula, is known as TY Coronae Australis .
The brightness of these two stars and several others in the same field is variable. They belong to the so-called "T Tauri" class , a type that is quite common in star-forming regions. T Tauri stars are in the early stages of stellar evolution and display various observable characteristics of this phase, e.g. emission at visible and infrared wavelengths due to the accretion of matter left over from their formation, as well as X-ray emission.
The nebulosity seen in this picture is mostly due to reflection of the stellar light by small dust particles. The stars in the R Coronae Australis complex do not emit sufficient ultraviolet light to ionize a substantial fraction of the surrounding hydrogen, and thereby cause this gas to glow.
However, some smaller features are also visible (one is seen in the upper left corner of PR Photo 25b/00 ) which emit light by a different mechanism. These are so-called Herbig-Haro objects , i.e., dense clumps of gas ejected from the immediate vicinity of newly formed stars with velocities of about 200 km/sec. When such clumps ram into the gas, the atoms are heated (excited) and start to shine. See also ESO PR Photo 40c/99 of the object HH-34 in Orion.
Other WFI images are available at the WFI Photo Gallery.
Tecnical information : The observations were obtained on the night of 30 August 2000. The image is a combination of twelve large (8000 x 8000 pix) CCD frames taken through B, V, and R filters. Four exposures of 5 min each were obtained in each filter, with the telescope pointing at slightly different positions so that the gaps among the eight individual CCD-chips of the detector can be adequately filled. All frames were carefully aligned, and the intensity levels were cut in order to achieve the proper colour balance. A logarithmic intensity scale was used to improve the dynamical range. PR Photo 25a/00 displays the full field and was rebinned to a smaller scale in order to allow transportation over the web. PR Photo 25b/00 shows part of this field at the original resolution. The images were prepared by Fernando Comeron (ESO).
This is the caption to ESO PR Photos 25a-b/00 . They may be reproduced, if credit is given to the European Southern Observatory.
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