Andrew Yee[_1_]
March 24th 08, 03:30 PM
ESO Education and Public Relations Dept.
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/press-rel/pr-2008/pr-06-08.html
----------------------------------------------------------------------------
Contact:
ESO Press Officer
Dr. Henri Boffin
Phone: +49 89 3200 6222
Science Contact:
Mika Juvela
Helsinki University Observatory
Phone: +358-9-19122909
For Immediate Release: 7 March 2008
ESO Science Release 06/08
Seeing through the Dark
Mapping the interior of interstellar clouds in great detail
Astronomers have measured the distribution of mass inside a dark filament in
a molecular cloud with an amazing level of detail and to great depth. The
measurement is based on a new method that looks at the scattered
near-infrared light or 'cloudshine' and was made with ESO's New Technology
Telescope. Associated with the forthcoming VISTA telescope, this new
technique will allow astronomers to better understand the cradles of newborn
stars.
The vast expanses between stars are permeated with giant complexes of cold
gas and dust opaque to visible light. Yet these are the future nurseries of
stars to be.
"One would like to have a detailed knowledge of the interiors of these dark
clouds to better understand where and when new stars will appear," says Mika
Juvela, lead author of the paper in which these results are reported.
Because the dust in these clouds blocks the visible light, the distribution
of matter within interstellar clouds can be examined only indirectly. One
method is based on measurements of the light from stars that are located
behind the cloud [1] .
"This method, albeit quite useful, is limited by the fact that the level of
details one can obtain depends on the distribution of background stars,"
says co-author Paolo Padoan.
In 2006, astronomers Padoan, Juvela, and colleague Veli-Matti Pelkonen,
proposed that maps of scattered light could be used as another tracer of the
cloud's inner structure, a method that should yield more advantages. The
idea is to estimate the amount of dust located along the line of sight by
measuring the intensity of the scattered light.
Dark clouds are feebly illuminated by nearby stars. This light is scattered
by the dust contained in the clouds, an effect dubbed 'cloudshine' by
Harvard astronomers Alyssa Goodman and Jonathan Foster. This effect is well
known to sky lovers, as they create in visible light wonderful pieces of art
called 'reflection nebulae'. The Chameleon I complex nebula is one beautiful
example.
When making observations in the near-infrared, art becomes science.
Near-infrared radiation can indeed propagate much farther into the cloud
than visible light and the maps of scattered light can be used to measure
the mass of the material inside the cloud.
To put this method to the test and use it for the first time for a
quantitative estimation of the distribution of mass within a cloud, the
astronomers who made the original suggestion, together with Kalevi Mattila,
made observations in the near-infrared of a filament in the Corona Australis
cloud [2] . The observations were made in August 2006 with the SOFI
instrument on ESO's New Technology Telescope at La Silla, in the Chilean
Atacama Desert. The filament was observed for about 21 hours.
Their observations confirm that the scattering method is providing results
that are as reliable as the use of background stars while providing much
more detail.
"We can now obtain very high resolution images of dark clouds and so better
study their internal structure and dynamics," says Juvela. "Not only is the
level of details in the resulting map no longer dependent on the
distribution of background stars, but we have also shown that where the
density of the cloud becomes too high to be able to see any background
stars, the new method can still be applied."
"The presented method and the confirmation of its feasibility will enable a
wide range of studies into the interstellar medium and star formation within
the Milky Way and even other galaxies," says co-author Mattila.
"This is an important result because, with current and planned near-infrared
instruments, large cloud areas can be mapped with high resolution," adds
Pelkonen. "For example, the VIRCAM instrument on ESO's soon-to-come VISTA
telescope has a field of view hundreds of times larger than SOFI. Using our
method, it will prove amazingly powerful for the study of stellar
nurseries."
More Information:
The report appears this week in the journal Astronomy and Astrophysics ("A
Corona Australis cloud filament seen in NIR scattered light - I. Comparison
with extinction of background stars", by Mika Juvela, Veli-Matti Pelkonen,
Paolo Padoan, and Kalevi Mattila). Juvela, Pelkonen and Mattila are
associated with the Helsinki University Observatory (Finland), while Padoan
is at the University of California, San Diego, USA.
Notes:
[1] When the light from the background stars passes through the cloud, it is
absorbed and scattered, resulting in the background stars appearing redder
than they really are. The effect is proportional to the amount of obscuring
material and is therefore largest for stars that are situated behind the
cloud's densest parts. By measuring the degree of this 'reddening'
experienced by stars seen through different areas of the cloud, it is thus
possible to chart the distribution of dust in the cloud. The finer the net
of background stars is, the more detailed this map will be and the better
the information about the internal structure of the cloud. And that is
exactly the problem. Even small clouds are so opaque that very few
background stars can be seen through them. Only large telescopes and
extremely sensitive instruments are able to observe a sufficient number of
stars in order to produce significant results (see ESO 01/01).
[2] Located in the constellation of the same name ('Southern Crown'), the
Corona Australis molecular cloud is shaped like a 45 light year long cigar.
Located about 500 light years away, it contains the equivalent of about 7000
Suns. On the sky, the dark cloud is surrounded by many beautiful 'reflection
nebulae'.
[3] Observations of a star-forming cloud with ESO's VLT and based on
near-infrared scattering is available as ESO Press Photo 26/03.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Denmark: Dr. Michael Linden-Vornle, +45-33-18 19 97
Finland: Ms. Riitta Tirronen, +358 9 7748 8369
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Dr. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
USA: Dr. Paola Rebusco, +1-617-308-2397
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/press-rel/pr-2008/pr-06-08.html
----------------------------------------------------------------------------
Contact:
ESO Press Officer
Dr. Henri Boffin
Phone: +49 89 3200 6222
Science Contact:
Mika Juvela
Helsinki University Observatory
Phone: +358-9-19122909
For Immediate Release: 7 March 2008
ESO Science Release 06/08
Seeing through the Dark
Mapping the interior of interstellar clouds in great detail
Astronomers have measured the distribution of mass inside a dark filament in
a molecular cloud with an amazing level of detail and to great depth. The
measurement is based on a new method that looks at the scattered
near-infrared light or 'cloudshine' and was made with ESO's New Technology
Telescope. Associated with the forthcoming VISTA telescope, this new
technique will allow astronomers to better understand the cradles of newborn
stars.
The vast expanses between stars are permeated with giant complexes of cold
gas and dust opaque to visible light. Yet these are the future nurseries of
stars to be.
"One would like to have a detailed knowledge of the interiors of these dark
clouds to better understand where and when new stars will appear," says Mika
Juvela, lead author of the paper in which these results are reported.
Because the dust in these clouds blocks the visible light, the distribution
of matter within interstellar clouds can be examined only indirectly. One
method is based on measurements of the light from stars that are located
behind the cloud [1] .
"This method, albeit quite useful, is limited by the fact that the level of
details one can obtain depends on the distribution of background stars,"
says co-author Paolo Padoan.
In 2006, astronomers Padoan, Juvela, and colleague Veli-Matti Pelkonen,
proposed that maps of scattered light could be used as another tracer of the
cloud's inner structure, a method that should yield more advantages. The
idea is to estimate the amount of dust located along the line of sight by
measuring the intensity of the scattered light.
Dark clouds are feebly illuminated by nearby stars. This light is scattered
by the dust contained in the clouds, an effect dubbed 'cloudshine' by
Harvard astronomers Alyssa Goodman and Jonathan Foster. This effect is well
known to sky lovers, as they create in visible light wonderful pieces of art
called 'reflection nebulae'. The Chameleon I complex nebula is one beautiful
example.
When making observations in the near-infrared, art becomes science.
Near-infrared radiation can indeed propagate much farther into the cloud
than visible light and the maps of scattered light can be used to measure
the mass of the material inside the cloud.
To put this method to the test and use it for the first time for a
quantitative estimation of the distribution of mass within a cloud, the
astronomers who made the original suggestion, together with Kalevi Mattila,
made observations in the near-infrared of a filament in the Corona Australis
cloud [2] . The observations were made in August 2006 with the SOFI
instrument on ESO's New Technology Telescope at La Silla, in the Chilean
Atacama Desert. The filament was observed for about 21 hours.
Their observations confirm that the scattering method is providing results
that are as reliable as the use of background stars while providing much
more detail.
"We can now obtain very high resolution images of dark clouds and so better
study their internal structure and dynamics," says Juvela. "Not only is the
level of details in the resulting map no longer dependent on the
distribution of background stars, but we have also shown that where the
density of the cloud becomes too high to be able to see any background
stars, the new method can still be applied."
"The presented method and the confirmation of its feasibility will enable a
wide range of studies into the interstellar medium and star formation within
the Milky Way and even other galaxies," says co-author Mattila.
"This is an important result because, with current and planned near-infrared
instruments, large cloud areas can be mapped with high resolution," adds
Pelkonen. "For example, the VIRCAM instrument on ESO's soon-to-come VISTA
telescope has a field of view hundreds of times larger than SOFI. Using our
method, it will prove amazingly powerful for the study of stellar
nurseries."
More Information:
The report appears this week in the journal Astronomy and Astrophysics ("A
Corona Australis cloud filament seen in NIR scattered light - I. Comparison
with extinction of background stars", by Mika Juvela, Veli-Matti Pelkonen,
Paolo Padoan, and Kalevi Mattila). Juvela, Pelkonen and Mattila are
associated with the Helsinki University Observatory (Finland), while Padoan
is at the University of California, San Diego, USA.
Notes:
[1] When the light from the background stars passes through the cloud, it is
absorbed and scattered, resulting in the background stars appearing redder
than they really are. The effect is proportional to the amount of obscuring
material and is therefore largest for stars that are situated behind the
cloud's densest parts. By measuring the degree of this 'reddening'
experienced by stars seen through different areas of the cloud, it is thus
possible to chart the distribution of dust in the cloud. The finer the net
of background stars is, the more detailed this map will be and the better
the information about the internal structure of the cloud. And that is
exactly the problem. Even small clouds are so opaque that very few
background stars can be seen through them. Only large telescopes and
extremely sensitive instruments are able to observe a sufficient number of
stars in order to produce significant results (see ESO 01/01).
[2] Located in the constellation of the same name ('Southern Crown'), the
Corona Australis molecular cloud is shaped like a 45 light year long cigar.
Located about 500 light years away, it contains the equivalent of about 7000
Suns. On the sky, the dark cloud is surrounded by many beautiful 'reflection
nebulae'.
[3] Observations of a star-forming cloud with ESO's VLT and based on
near-infrared scattering is available as ESO Press Photo 26/03.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Denmark: Dr. Michael Linden-Vornle, +45-33-18 19 97
Finland: Ms. Riitta Tirronen, +358 9 7748 8369
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Dr. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
USA: Dr. Paola Rebusco, +1-617-308-2397
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------