mercredi 3 août 2011

VISTA Finds 96 Star Clusters Hidden Behind Dust

ESO - European Southern Observatory logo.

3 August 2011

ESO’s infrared survey telescope digs deep into star-forming regions in our Milky Way

VISTA Finds Star Clusters Galore

Using data from the VISTA infrared survey telescope at ESO’s Paranal Observatory, an international team of astronomers has discovered 96 new open star clusters hidden by the dust in the Milky Way. These tiny and faint objects were invisible to previous surveys, but they could not escape the sensitive infrared detectors of the world’s largest survey telescope, which can peer through the dust. This is the first time so many faint and small clusters have been found at once.

This result comes just one year after the start of the VISTA Variables in the Via Lactea programme (VVV) [1], one of the six public surveys on the new telescope. The results will appear in the journal Astronomy & Astrophysics.

“This discovery highlights the potential of VISTA and the VVV survey for finding star clusters, especially those hiding in dusty star-forming regions in the Milky Way’s disc. VVV goes much deeper than other surveys,” says Jura Borissova, lead author of the study.

The majority of stars with more than half of the mass of our Sun form in groups, called open clusters. These clusters are the building blocks of galaxies and vital for the formation and evolution of galaxies such as our own. However, stellar clusters form in very dusty regions that diffuse and absorb most of the visible light that the young stars emit, making them invisible to most sky surveys, but not to the 4.1-m infrared VISTA telescope.

“In order to trace the youngest star cluster formation we concentrated our search towards known star-forming areas. In regions that looked empty in previous visible-light surveys, the sensitive VISTA infrared detectors uncovered many new objects,” adds Dante Minniti, lead scientist of the VVV survey.

By using carefully tuned computer software, the team was able to remove the foreground stars appearing in front of each cluster in order to count the genuine cluster members. Afterwards, they made visual inspections of the images to measure the cluster sizes, and for the more populous clusters they made other measurements such as distance, age, and the amount of reddening of their starlight caused by interstellar dust between them and us.

“We found that most of the clusters are very small and only have about 10–20 stars. Compared to typical open clusters, these are very faint and compact objects — the dust in front of these clusters makes them appear 10 000 to 100 million times fainter in visible light. It’s no wonder they were hidden,” explains Radostin Kurtev, another member of the team.

Since antiquity only 2500 open clusters have been found in the Milky Way, but astronomers estimate there might be as many as 30 000 still hiding behind the dust and gas. While bright and large open clusters are easily spotted, this is the first time that so many faint and small clusters have been found at once.

Furthermore, these new 96 open clusters could be only the tip of the iceberg. “We’ve just started to use more sophisticated automatic software to search for less concentrated and older clusters. I am confident that many more are coming soon,” adds Borissova.


[1]  Since 2010, the VISTA Variables in the Via Lactea programme (VVV) has been scanning the central parts of the Milky Way and the southern plane of the galactic disc in infrared light. This program was granted a total of 1929 hours of observing time over a five year period.  Via Lactea is the Latin name for the Milky Way.

More information:

This research is presented in a paper entitled “New Galactic Star Clusters in the VVV Survey”, to appear in the journal Astronomy & Astrophysics.

The team is composed of J. Borissova (Universidad de Valparaíso, Chile), C. Bonatto (Universidade Federal do Rio Grande do Sul, Brazil), R. Kurtev (Universidad de Valparaíso), J. R. A. Clarke (Universidad de Valparaíso), F. Peñaloza (Universidad de Valparaíso), S. E. Sale (Universidad de Valparaíso; Pontificia Universidad Católica, Chile), D. Minniti (Pontificia Universidad Católica, Chile), J. Alonso-García (Pontificia Universidad Católica), E. Artigau (Département de Physique and Observatoire du Mont Mégantic, Université de Montréal, Canada), R. Barbá (Universidad de La Serena, Chile), E. Bica (Universidade Federal do Rio Grande do Sul), G. L. Baume (Instituto de Astrofísica de La Plata, Argentina), M. Catelan (Pontificia Universidad Católica), A. N. Chenè (Universidad de Valparaíso; Universidad de Concepción, Chile), B. Dias (Universidade de Sao Paulo, Brazil), S. L. Folkes (Universidad de Valparaíso), D. Froebrich (The University of Kent, UK), D. Geisler (Universidad de Concepción), R. de Grijs (Peking University, China; Kyung Hee University, Korea), M. M. Hanson (University of Cincinnati), M. Hempel (Pontificia Universidad Católica), V. D. Ivanov (European Southern Observatory), M. S. N. Kumar (Universidade do Porto; Portugal), P. Lucas (University of Hertfordshire, UK), F. Mauro (Universidad de Concepción), C. Moni Bidin (Universidad de Concepción), M. Rejkuba (European Southern Observatory), R. K. Saito (Pontificia Universidad Católica), M. Tamura National Astronomical Observatory of Japan, Japan), and I. Toledo (Pontificia Universidad Católica).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.


    Research paper:

    Photos of VISTA:

Credit: J. Borissova, Universidad de Valparaiso ESO / Richard Hook, la Silla / Paranal / E-ELT / Survey Telescopes.

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lundi 1 août 2011

NASA'S Dawn Spacecraft Begins Science Orbits Of Vesta

NASA - DAWN Mission patch.

August 01, 2011

NASA's Dawn spacecraft, the first ever to orbit an object in the main asteroid belt, is spiraling toward its first of four intensive science orbits. That initial orbit of the rocky world Vesta begins Aug. 11, at an altitude of nearly 1,700 miles (2,700 kilometers) and will provide in-depth analysis of the asteroid. Vesta is the brightest object in the asteroid belt as seen from Earth and is thought to be the source of a large number of meteorites that fall to Earth.

Animation of Dawn Scanning and Flying Above Vesta's Surface

The Dawn team unveiled the first full-frame image of Vesta taken on July 24:

This image was taken at a distance of 3,200 miles (5,200 kilometers). Images from Dawn's framing camera, taken for navigation purposes and as preparation for scientific observations, are revealing the first surface details of the giant asteroid. These images go all the way around Vesta, since the giant asteroid turns on its axis once every five hours and 20 minutes.

"Now that we are in orbit around one of the last unexplored worlds in the inner solar system, we can see that it's a unique and fascinating place," said Marc Rayman, Dawn's chief engineer and mission manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Image above: NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

After traveling nearly four years and 1.7 billion miles (2.8 billion kilometers), Dawn has been captured by Vesta's gravity, and there currently are 1,800 miles (2,900 kilometers) between the asteroid and the spacecraft. The giant asteroid and its new neighbor are approximately 114 million miles (184 million kilometers) away from Earth.

"We have been calling Vesta the smallest terrestrial planet," said Chris Russell, Dawn's principal investigator at the UCLA. "The latest imagery provides much justification for our expectations. They show that a variety of processes were once at work on the surface of Vesta and provide extensive evidence for Vesta's planetary aspirations."

Engineers still are working to determine the exact time that Dawn entered Vesta's orbit, but the team has reported an approximate orbit insertion time of 9:47 p.m. PDT on July 15 (12:47 a.m. EDT on July 16).

In this image a set of three craters, informally nicknamed "Snowman" by the camera's team members, is located in the northern hemisphere of Vesta. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

In addition to the framing camera, Dawn's instruments include the gamma ray and neutron detector and the visible and infrared mapping spectrometer. The gamma ray and neutron detector uses 21 sensors with a very wide field of view to measure the energy of subatomic particles emitted by the elements in the upper yard (meter) of the asteroid's surface. The visible and infrared mapping spectrometer will measure the surface mineralogy of both Vesta and Dawn's next target, the dwarf planet Ceres. The spectrometer is a modification of a similar one flying on the European Space Agency's Rosetta and Venus Express missions.

Dawn also will make another set of scientific measurements at Vesta and Ceres using the spacecraft's radio transmitter in tandem with sensitive antennas on Earth. Scientists will monitor signals from Dawn and later Ceres to detect subtle variations in the objects' gravity fields. These variations will provide clues about the interior structure of these bodies by studying the mass distributed in each gravity field.

In this image, obtained by the framing camera on NASA's Dawn spacecraft, various craters are visible in the southern equatorial region of the giant asteroid Vesta. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

"The new observations of Vesta are an inspirational reminder of the wonders unveiled through ongoing exploration of our solar system," said Jim Green, planetary division director at NASA Headquarters in Washington.

Dawn launched in September 2007. Following a year at Vesta, the spacecraft will depart in July 2012 for Ceres, where it will arrive in 2015. Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala.

UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team.

For more information about Dawn, visit: 

Images (mentioned), Text, Video, Credits: NASA / JPL-Caltech / UCLA.


Astronomers searching for oxygen can breathe more easily

ESA - HERSCHEL Mission patch.

1 August 2011

ESA’s Herschel space observatory has found molecules of oxygen in a nearby star-forming cloud. This is the first undisputed detection of oxygen molecules in space. It concludes a long search but also leaves questions unanswered.

The oxygen molecules have been found in the nearby Orion star-forming complex. While atomic oxygen has been long known in warm regions of space, previous missions looking for the molecular variety – two atoms of oxygen bonded together – came up largely empty-handed.

Even the observed amount of atomic oxygen is far less than that expected and this created an oxygen ‘accounting problem’ that can be roughly voiced as “where is all the oxygen hiding in the cold clouds?”

Molecular oxygen has been found in the Orion region

NASA’s Submillimetre Wave Astronomy Satellite and Sweden’s Odin mission have both searched for molecular oxygen and established that its abundance is dramatically lower than expected.

One possibility put forward to explain this was that oxygen atoms freeze onto tiny dust grains found floating in space and are converted to water ice, effectively removing them from sight.

If this is true, the ice should evaporate in warmer regions of the cosmos, returning water to the gas and allowing molecular oxygen to form and to be seen.

Paul Goldsmith, NASA’s Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California, and an international team of investigators went looking for it with Herschel.

They used Herschel's HIFI far-infrared instrument and targeted Orion, where they reasoned that the forming stars would heat the surrounding gas and dust.

Using three infrared frequencies of the instrument, the Herschel Oxygen Project team were successful. They found there to be one molecule of oxygen for every million hydrogen molecules.

Hubble’s sharpest view of the Orion Nebula, part of the Orion region

"This explains where some of the oxygen might be hiding," said Dr Goldsmith. "But we didn't find large amounts of it, and still don't understand what is so special about the spots where we find it. The Universe still holds many secrets."

Oxygen, in all its forms, is the third most abundant element in the Universe and a major ingredient of our planet. It is found in our atmosphere, oceans and rocks, and is critical for life itself because we breathe the molecular form.

Although the search continues for it in space, Göran Pilbratt, ESA’s Herschel Project Scientist, believes this is a breakthrough moment: “Thanks to Herschel, we now have an undisputed confirmation that molecular oxygen is definitely out there. There are still many open questions but Herschel’s superior capabilities now enables us to address these riddles.”

Read more:

Observations: Seeing in infrared wavelengths:

Why infrared astronomy is a hot topic:

L2, the second Lagrangian Point:

Herschel in depth:

This story in depth:

Images, Text, Credits: ESA / Digital Sky Survey / NASA / M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team.