Monday, December 31, 2012

An Image Gallery Gift from NASA's Swift

Of the three telescopes carried by NASA's Swift satellite, only one captures cosmic light at energies similar to those seen by the human eye. Although small by the standards of ground-based observatories, Swift's Ultraviolet/Optical Telescope (UVOT) plays a critical role in rapidly pinpointing the locations of gamma-ray bursts (GRBs), the brightest explosions in the cosmos.

 But as the proxy to the human eye aboard Swift, the UVOT takes some amazing pictures. The Swift team is celebrating eight years of UVOT operations by collecting more than 100 of the instrument's best snapshots in a web-based photo gallery. The images also can be viewed with the free Swift Explorer Mission iPhone app developed by the Swift Mission Operations Center (MOC), which is located in State College, Pa., and operated by Penn State.


The Crab Nebula is the wreckage of an exploded star, or supernova, observed in the year 1054. The expanding cloud of gas is located 6,500 light-years away in the constellation Taurus. This composite of three Swift UVOT ultraviolet images highlights the luminous hot gas in the supernova remnant. The image is constructed from exposures using these filters: uvw1, centered at 2,600 angstroms (shown as red); uvm2, centered at 2,246 angstroms (green); and uvw2, centered at 1,928 angstroms (blue). Credit: NASA/Swift/E. Hoversten, PSU

 Swift has detected an average of about 90 GRBs a year since its launch in 2004. "When we aren't studying GRBs, we use the satellite's unique capabilities to engage in other scientific investigations, some of which produce beautiful images from the UVOT that we're delighted to be able to share with the public," said Michael Siegel, the lead scientist on the UVOT and a research associate in astronomy and astrophysics at the MOC.

 The targets range from comets and star clusters to supernova remnants, nearby galaxies and active galaxies powered by supermassive black holes.

 "One of our more challenging projects in the past was completing an ultraviolet mosaic of M31, the famous Andromeda galaxy," said Stefan Immler, a member of the Swift team at NASA's Goddard Space Flight Center in Greenbelt, Md. "Because the galaxy is so much larger than the UVOT field of view, we had to take dozens of pictures and blend them together to show the whole object."

 An ongoing mosaic project targets the Large and Small Magellanic Clouds, two small satellite galaxies orbiting our own, and makes the Andromeda effort look like child's play. Although the galaxies are much smaller than M31, they are both much closer to us and extend over much larger areas of the sky. The task involves acquiring and aligning hundreds of images and is far from complete.

 With the UVOT's wavelength range of 1,700 to 6,000 angstroms, Swift remains one of few missions that study ultraviolet light, much of which is blocked by Earth's atmosphere.

Omega Centauri (also known as NGC 5139) is the largest, brightest and most massive of our galaxy's retinue of 150 or so globular star clusters. Packing some 10 million stars into a region just 150 light-years across, Omega Centauri is easily visible to the unaided eye despite lying nearly 16,000 light-years away. Unlike other star clusters, whose members all have similar age and chemical makeup, Omega Centauri displays a wide range of age and chemistry, from the ancient (12 billion years) to the relatively recent. The presence of different stellar populations suggests that Omega Centauri is not, in fact, a globular cluster, but the remnant core of a dwarf galaxy torn to shreds by the Milky Way’s gravity. The false-color ultraviolet composite from Swift UVOT's uvw1, uvm2 and uvw2 filters reveals a treasure trove of rare stars in various stages of demise. Credit: NASA/Swift/S. Holland (Goddard), M. Siegel and E. Fonseca (PSU)

 The 6.5-foot-long (2 meter) UVOT is centered on an 11.8-inch (30 cm) primary mirror. Designed and built by the Mullard Space Science Laboratory in Surrey, England, the telescope module includes the primary and secondary mirrors, an external baffle to reduce scattered light, two redundant detectors -- only one has been used to date -- and a power supply.

 Each detector lies behind an identical filter wheel. The wheel holds color filters that transmit a broad range of wavelengths as well as devices called grisms, which spread out incoming light in much the same way as a prism spreads sunlight into a rainbow of component colors. The detectors retain information on the position and arrival time of each photon of light, an operating mode similar to typical X-ray telescopes.

 Because most ultraviolet light never reaches the ground, Swift's UVOT provides a unique perspective on the cosmos. For example, it can measure the amount of water produced in passing comets by detecting the ultraviolet emission of hydroxyl (OH), one of the molecular fragments created when ultraviolet sunlight breaks up water molecules. Other types of UVOT science include exploring emissions from the centers of active galaxies, studying regions undergoing star formation, and identifying some of the rarest and most exotic stars known.

Technicians prepare Swift's UVOT for vibration testing on Aug. 1, 2002, more than two years before launch, in the High Bay Clean Room at NASA's Goddard Space Flight Center in Greenbelt, Md. Credit: NASA's Goddard Space Flight Center. › Larger image

Toward the end of its energy-producing life, a star like the sun will blow away its outer layers as its core transforms into a compact, Earth-sized remnant known as a white dwarf. This chapter of stellar evolution, known to astronomers as the post-asymptotic giant branch phase, lasts only about 100,000 years -- just an eye-blink in comparison to the star's total lifetime. To better understand the process, astronomers need to study large numbers of these unusual stars.

"The UVOT's capabilities give us a great tool for surveying stellar populations and cataloging rare types of ultraviolet-bright stars," Siegel explained.

One of the first targets for the stellar survey was the giant cluster Omega Centauri, which hosts millions of stars and may be the remains of a small galaxy. Thanks to Swift's UVOT, astronomers at Goddard and Penn State have cataloged hundreds of rare stellar types in the cluster and are now comparing their properties and numbers to predictions from theoretical models describing how stars evolve.

Related Links


Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Friday, December 28, 2012

A wanderer dancing the dance of stars and space

Credit: ESA/Hubble & NASA
Acknowledgement: E. Sturdivant

The NASA/ESA Hubble Space Telescope provides us this week with a spectacular image of the bright star-forming ring that surrounds the heart of the barred spiral galaxy NGC 1097. In this image, the larger-scale structure of the galaxy is barely visible: its comparatively dim spiral arms, which surround its heart in a loose embrace, reach out beyond the edges of this frame.

This face-on galaxy, lying 45 million light-years away from Earth in the southern constellation of Fornax (The Furnace), is particularly attractive for astronomers. NGC 1097 is a Seyfert galaxy. Lurking at the very centre of the galaxy, a supermassive black hole 100 million times the mass of our Sun is gradually sucking in the matter around it. The area immediately around the black hole shines powerfully with radiation coming from the material falling in.

The distinctive ring around the black hole is bursting with new star formation due to an inflow of material toward the central bar of the galaxy. These star-forming regions are glowing brightly thanks to emission from clouds of ionised hydrogen. The ring is around 5000 light-years across, although the spiral arms of the galaxy extend tens of thousands of light-years beyond it.

NGC 1097 is also pretty exciting for supernova hunters. The galaxy experienced three supernovae (the violent deaths of high-mass stars) in the 11-year span between 1992 and 2003. This is definitely a galaxy worth checking on a regular basis.

However, what it is really exciting about NGC 1097 is that it is not wandering alone through space. It has two small galaxy companions, which dance “the dance of stars and the dance of space” like the gracious dancer of the famous poem The Dancer by Khalil Gibran.

The satellite galaxies are NGC 1097A, an elliptical galaxy orbiting 42 000 light-years from the centre of NGC 1097 and a small dwarf galaxy named NGC 1097B. Both galaxies are located out beyond the frames of this image and they cannot be seen. Astronomers have indications that NGC 1097 and NGC 1097A have interacted in the past.

This picture was taken with Hubble’s Advanced Camera for Surveys using visual and infrared filters.

A version of this image was submitted to the Hubble’s Hidden Treasures image processing competition by contestant Eedresha Sturdivant.

Source: ESA/Hubble - Space Telescope

 

Thursday, December 27, 2012

Imaging Polarimetry of Circumstellar Environments with ExPo

A team of Dutch astronomers designed and built the innovative imaging polarimeter ExPo (the Extreme Polarimeter), which is a regular visitor instrument at the William Herschel Telescope (WHT). ExPo was designed and built at Utrecht University and has, due to the closure of astronomy in Utrecht, moved to Leiden University.

ExPo makes use of polarised light to study the faint, dust-rich environments around young and evolved stars. The advantage of using polarimetry, over normal intensity images, is that the unpolarised light from the star is easily removed, allowing directly observation of the star's surroundings in scattered (linearly polarised) light. The information contained in the polarised light constrains the properties of the scattering particles (dust), such as their size, albedo and structure.

The ExPo team observed the young binary system Z CMa in 2010, right after its strongest, and as yet unexplained, outburst. This system, comprising an FU Ori and a Herbig Be star, is extremely variable at visible wavelengths. Previous measurements indicate that the Herbig Be star is surrounded by a dust cocoon that blocks its light at visible wavelengths. Using ExPo observations, Cánovas et al. 2011 show direct evidence for a hole in the dust cocoon.  The light escaping through the hole produces a polarised signature that is observable in the ExPo images (see Figure 1, polarised feature 3). This can explain some of the variability of Z CMa when a hole forms in the dust cocoon, the contribution of the Herbig Be star to the total brightness of the system suddenly increases.


Figure 1: Left: Schematic picture of the Z CMa system. The primary Herbig Be-type star is surrounded by an irregular dust cocoon. There is a 3.6-pc jet associated with this star. The secondary FU Ori star is known to drive a jet, at a position angle of ~20 degrees with respect to the primary's jet. The whole system is surrounded by a massive envelope. Right: ExPo image of Z Cma in (linearly) polarised light. The positions of the primary and secondary jets are indicated by black and green lines, respectively. The two stars are unresolved in the ExPo images, and their position is indicated by a green cross at the center of the image. The polarised features labelled as 1 and 2 coincide in position with the primary (black) and secondary (green) jets. The third polarised feature can be explained in terms of polarised light escaping through a hole in the dust cocoon.  [ JPEG ]


Another example of the capabilities of imaging polarimetry for investigating faint circumstellar environments is shown in Figure 2 for the evolved star R CrB. These carbon-rich stars are known to be surrounded by a dust-rich halo and to emit dust clouds at irregular intervals.  The ExPo observations of R CrB were secured when a large dust cloud was emitted along the line of sight to the observer, acting like a natural coronograph. This allowed the astronomers to derive the dust properties in three different regions around R CrB: the "obscuring" cloud, the dust halo that surrounds R CrB, and in one dust cloud that is evident in the ExPo images (see Figure 2). The results are published in Jeffers et al. (2012).


Figure 2.: Left: Schematic picture of R CrB showing the obscuring cloud (Cloud O), the ejected cloud that is detected in ExPo images (Cloud S), and the dusty halo around the star. Right: Polarised intensity image of RCrB, where a dust cloud is clearly detected. An HST image is shown in the right bottom corner for comparison. Combining the HST (intensity) and ExPo (polarised intensity) images, the astronomers were able to derive the properties of this cloud.  [ JPEG ]


More information:

  • Cánovas, H., Min, M. , Jeffers, S. V., Rodenhuis, M. and Keller, C. U., 2012, A&A, 543, A70. Paper.
  • Jeffers, S. V. Min, M., Waters, L. B. F. M., Cánovas, H.,  Rodenhuis, M., Ovelar, M.D.J., Chies-Santos, A.L.,  and Keller, C.U., 2012, A&A, 539, A56. Paper.
 
Contact: Javier Méndez (Public Relations Officer)

Wednesday, December 26, 2012

A Hypergiant Star (Partially) Traversing the Yellow Evolutionary Void

After thirty years of investigation, a team of scientists from six European countries reports that the hypergiant star HR 8752 is partially traversing the Yellow Evolutionary Void, an area in the Hertzsprung-Russell diagram empty of hypergiant stars with surface temperatures between 5000 and 12000 degrees kelvin. 

Some of the observations were carried out using the Utrecht Echelle Spectrograph (UES, now retired) on the William Herschel Telescope. They show that in the twenty years from 1985 to 2005, the star's surface temperature rose from 5000 to 8000 degrees, while undergoing a series of strong mass-loss events. During this time, the radius of HR 8752 shrank from 750 to 400 times that of the Sun. These observations indicate that HR 8752 is traversing (part of) the Yellow Evolutionary Void. 

The astronomers found that the atmospheres of hypergiants are unstable inside the Void because the outward forces in their atmospheres can match or even overcome the inward gravitational pull. The resulting instability of the atmospheres causes these enormous stars to lose huge amounts of mass, and consequently to traverse the Void on a relatively-short timescale. 

The team also discovered that the Void actually consists of two areas where the atmosphere of hypergiants becomes unstable, associated with the ionization of hydrogen and helium gas respectively. Between them, at around 8000 degrees, is a narrow stability strip where the atmospheres are more stable.

Artist's impression of the hypergiant HR 8752 traversing the Yellow Evolutionary Void. The graph shows the star's surface temperature (log Teff) as observed over the last 100 years. It increased from ~5000 to ~8000 degrees between 1985 and 2005, while the hypergiant's radius decreased from 750 to 400 times that of the Sun. Image credit: A. Lobel (ROB).  [ JPEG ]

While an analysis of earlier photometric observations of HR 8752 showed that, at least from ~1900 to ~1980, HR 8752 stayed at a nearly constant surface temperature of 5000 degrees, the team had some indications that around 1985 this remarkable star was fairly close to or even beyond the low-temperature boundary of the Void. Wondering what would happen, the scientists embarked on a long and systematic program of spectroscopic observations that lasted for three decades.

Hypergiants are currently the most luminous stars known in the Universe. The study reported here was of a particular hypergiant called HR 8752, which is about 250000 times as luminous as our Sun. It lies in the constellation of Cassiopeia, and can be seen through binoculars.

The science team mentioned in this news release consists of Dr. H. Nieuwenhuijzen (SRON Laboratory for Space Research, Netherlands), Dr. C. de Jager (NIOZ Royal Netherlands Institute for Sea Research, Netherlands), Dr. I. Kolka (Tartu Observatory, Estonia), Dr. G. Israelian (Instituto de Astrofisica de Canarias, Spain), Dr. A. Lobel (Royal Observatory of Belgium), Dr. E. Zsoldos (Konkoly Observatory, Hungary), Dr. A. Maeder (Observatoire de Geneve, Switzerland), and Dr. G. Meynet (Observatoire de Geneve, Switzerland).

More information:
 
H. Nieuwenhuijzen, C. De Jager, I. Kolka, G. Israelian, A. Lobel, E. Zsoldos, A. Maeder and G. Meynet, 2012, "The hypergiant HR 8752 evolving through the yellow evolutionary void", A&A, 546, A105, which is an Open Access paper (also available at http://www.cdejager.com/hypergiant-publications/).

YouTube video: http://www.youtube.com/watch?v=BOqsPJZoifo, by Orso Byanco.

Contact: Javier Méndez (Public Relations Officer)
Source: Isaac Newton Group of Telescopes

Tuesday, December 25, 2012

"All-Clear" Asteroid Will Miss Earth in 2040

Gemini Multi-Object Spectrograph image of 2011 AG5. The asteroid is the point at the center of the image (circled) with background stars trailing because the telescope tracked on 2011 AG5. This single 300 second exposure is oriented with north up and east left - each background star streak is about 15 arcseconds in length. 2011 AG5 is highly variable in brightness and other Gemini observations on October 27th required longer exposures than the one shown here.

Potential asteroid collision in 2040 is a non-threat based on new Gemini Observatory data.

Using the Gemini North telescope on Mauna Kea, Hawai‘i a team of astronomers from the University of Hawaii’s Institute for Astronomy (IfA) have confirmed that the chance of asteroid 2011 AG5 impacting Earth in 2040 is no longer a significant risk – prompting a collective sigh-of-relief. Previously, scientists estimated that the risk of this 140-meter-diameter (about the length of two American football fields) asteroid colliding with the Earth was as high as one in 500.

If this object were to collide with the Earth it would have released about 100 megatons of energy, several thousand times more powerful than the atomic bombs that ended World-War II. Statistically, a body of this size could impact the Earth on average every 10,000 years.

The observations, using the Gemini Multi-Object Spectrograph (and imager), were especially challenging said team-member Richard Wainscoat. “These were extremely difficult observations of a very faint object,” he said. “We were surprised by how easily the Gemini telescope was able to recover such a faint asteroid so low in the sky.” The Gemini observations were made on October 20, 21, and 27, 2012.

In addition to multiple observations since the asteroid’s discovery, the team had also acquired images about two weeks earlier with the University of Hawai‘i 2.2-meter telescope also on Mauna Kea – however, these data were all less conclusive and required confirmation. Gemini was able to make the follow-up observations rapidly due to the observatory’s scheduling flexibility and availability of several instruments at a moment’s notice.

IfA astronomers David Tholen, Richard Wainscoat, Marco Micheli, and Garrett Elliott conducted the original observations and analysis of the data. Further analysis was performed at NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The updated trajectory of 2011 AG5, based on the Gemini data, has a factor of 60 less uncertainty than the previous observations due in part to the increase in sampling points in the asteroid’s orbit. The original discovery was made from images obtained with the NASA-sponsored Catalina Sky Survey on Mt. Lemmon in Arizona.

According to a press release issued by JPL, while this new result has reduced the interest in 2011 AG5, the experience gained by studying this object and conducting a contingency deflection analysis has demonstrated that astronomers, using NSF and NASA facilities, are well poised to detect and predict the trajectories of Earth-threatening asteroids in the future.

The data for this study are being published by the Minor Planet Center in Cambridge, Massachusetts.

Science Contact:

David Tholen

Astronomer
University of Hawai‘i – Institute for Astronomy
Desk: (808) 956-6930
Cell: 520-461-6925
tholen@ifa.hawaii.edu

Media Contact:

Peter Michaud

Public Information and Outreach Manager
Gemini Observatory, Hilo, Hawai'i
Desk: (808) 974-2510
Cell: (808) 936-6643
pmichaud@gemini.edu

 See the University of Hawaii - Institute for Astronomy release here.

Monday, December 24, 2012

Black holes – no place left to hide!


Very sensitive, wide-field observations with a worldwide network of radio telescopes have uncovered black holes residing in the centre of dust obscured galaxies. In some cases, the amount of dust is so large that even x-rays from the accreting black holes are absorbed in these systems. This is the result of research done by astronomers Chi, Barthel and Garrett from Groningen and Dwingeloo, and is set to appear in an upcoming issue of Astronomy & Astrophysics.

Also in apparently normal galaxies, it seems black holes grow steadily by devouring matter. The bright, exotic radiation, usually the result of these so-called accretion processes, seems to be completely obscured in some galaxies. Only a network of highly sensitive radio telescopes can detect these processes is the conclusion of the Dutch astronomers. The suspicion that the faint radio waves, emitted by many galaxies in the distant early universe is the result of accretion by their black holes, has now been proven.

Traditional radio telescopes, such as the Westerbork Synthesis Radio Telescope (WSRT), cannot determine the exact nature of the radio emission. The technique of Very Long Baseline Interferometry (VLBI) is necessary, in which a network of radio telescopes in different countries or continents observe the same object. The many gigabytes of data of the individual telescopes are then combined. This method digitally simulates a radio telescope of thousands of kilometers in diameter, and as a consequence with a very high resolution and sensitivity.

Using such a VLBI-network of sixteen radio telescopes on two continents (Europe and the United States), a so far unimaginable record sensitivity and resolution could be reached, undoubtedly proving the accretion activity of the distant galaxies.

‘We know many galaxies have black holes. Of course these need to grow to what they are now and it seems that, thanks to these VLBI-observations of the galaxies in the Northern Hubble Deep Field, we can now really observe this growth', say prof. Peter Barthel of the Kapteyn Institute of the University of Gronignen and prof. Michael Garrett of ASTRON, the Netherlands Institute for Radio Astronomy in Dwingeloo.

Barthel adds: ‘We are proud of these results, but what is mostly in our minds is the fact that the one who had the largest part in this study is no longer with us.' Doctoral student Seungyoup Chi, from South-Korea, died from a serious illness in the year he would obtain his PhD doctorate in Groningen. ‘This publication appears posthumous, also in his memory', say Barthel and Garrett, at the time supervisors of Chi.

More information:

Contact:
 

Prof. dr. Peter Barthel, Kapteyn Institute, University of Groningen
Tel: 050-363 4064/ 06-11391826
E-mail: p.d.barthel@rug.nl  

Prof. Michael A. Garrett
General Director & Scientific Director ASTRON Netherlands Institute for Radio Astronomy
Tel: +31 521 595126/+31 521595119
E-mail: garrett@astron.nl

Article: The publication "Deep, wide-field, global VLBI observations of the Hubble Deep Field-North and the Hubble Flanking Fields" by S. Chi, P.D. Barthel and M.A. Garrett is published beginning 2013 in Astronomy & Astrophysics.

 Source: ASTRON

Saturday, December 22, 2012

Masers in Stellar Nurseries

A false-color infrared image of a young star showing outflowing jets as green beams of shocked gas (actually two of the stars in this image have jets). A new study using the SMA has found that bright methanol masers, often seen in such star-forming regions and long thought to indicate only the youngest such stars, are also found around more mature stars. Credit: NASA-Spitzer Space Telescope.  > Low Resolution Image (jpg)

Astronomers have come to realize that the process of star formation, once thought to consist essentially of just the simple coalescence of material by gravity, occurs in a complex series of stages. As the gas and dust in giant molecular clouds comes together into stars, dramatic outflowing jets of material develop around each, as do circumstellar disks (possibly pre-planetary in nature). Other features are present as well: Astronomers in the 1960s were amazed to discover that these star-forming regions sometimes produce natural masers (masers are the bright, radio wavelength analogs of lasers). Clouds of water vapor or methanol vapor in regions of active star formation generate some of the most spectacular masers.

 Although associated with the complex activity of star formation, the role of masers in the building of a new star is thought to be minor (although it is not understood). However masers, because they are so bright, provide valuable diagnostic probes of the regions where star formation is underway. Exactly what they reveal is less clear, but many astronomers have thought that methanol masers can signal the very earliest stages of star formation, perhaps less than about ten thousand years old. One of the key questions masers can possibly help resolve is how stars more massive than the Sun form. Understanding the birth of such massive stars is essential not only in its own right, but also because these stars end up as supernovae which enrich the cosmos with elements essential to life. The birth of massive stars is, however, notoriously tricky to understand because their larger masses prompt the young star to mature very quickly, in less than about one hundred thousand years and much faster than lower-mass stars. As a result, many growth stages are blurred together. Masers are thought to offer a way to probe these earliest times of star formation.

 SAO astronomers Claudia Cyganowski and Qizhou Zhang, with five colleagues, used the Submillmeter Array (SMA) to study regions of massive star formation identified in infrared images as having outflows typical of massive young stars. The SMA was able to identify all of the protostellar cores from their millimeter dust emission. They found one such protocluster of young stars that also contained a variety of types of methanol masers, enabling a comparative study of masers and star- formation activity. Writing in the latest issue of the Astrophysical Journal Letters, the scientists report finding that, contrary to the conventional wisdom, methanol masers thought to be associated with very young stages of star formation are found occurring with more evolved embryos. The new results show for the first time that the mechanisms at work to make these methanol masers, shocks for example, are found in a much wider range of situations than previously suspected. The new results are not atypical of progress in astronomy.


Friday, December 21, 2012

The Needle Galaxy

Credit: ESA/Hubble & NASA
Acknowledgement: Luca Limatola

Like finding a silver needle in the haystack of space, the NASA/ESA Hubble Space Telescope has produced this beautiful image of the spiral galaxy IC 2233, one of the flattest galaxies known.

Typical spiral galaxies like the Milky Way are usually made up of three principal visible components: the disc where the spiral arms and most of the gas and dust is concentrated; the halo, a rough and sparse sphere around the disc that contains little gas, dust or star formation; and the central bulge at the heart of the disc, which is formed by a large concentration of ancient stars surrounding the Galactic Centre.

However, IC 2233 is far from being typical. This object is a prime example of a super-thin galaxy, where the galaxy’s diameter is at least ten times larger than the thickness. These galaxies consist of a simple disc of stars when seen edge on. This orientation makes them fascinating to study, giving another perspective on spiral galaxies. An important characteristic of this type of objects is that they have a low brightness and almost all of them have no bulge at all.

The bluish colour that can be seen along the disc gives evidence of the spiral nature of the galaxy, indicating the presence of hot, luminous, young stars, born out of clouds of interstellar gas. In addition, unlike typical spirals, IC 2233 shows no well-defined dust lane. Only a few small patchy regions can be identified in the inner regions both above and below the galaxy’s mid-plane.

Lying in the constellation of Lynx, IC 2233 is located about 40 million light-years away from Earth. This galaxy was discovered by British astronomer Isaac Roberts in 1894.

This image was taken with the Hubble’s Advanced Camera for Surveys, combining visible and infrared exposures. The field of view in this image is approximately 3.4 by 3.4 arcminutes.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Luca Limatola.

Source: ESA/Hubble - Space Telescope


Spiral Structure of Disk May Reveal Planets

An international team of astronomers has used HiCIAO (High Contrast Instrument for the Subaru Next Generation Optics) (Note 1) to observe a disk around the young star SAO 206462. They succeeded in capturing clear, detailed images of its disk, which they discovered has a spiral structure with two discernable arms. On the basis of their observations and modeling according to spiral density wave theory, the team suspects that dynamic processes, possibly resulting from planets in the disk, may be responsible for its spiral shape. This research may provide the basis for another indirect method of detecting planets.

Scientists have known that planets form in a broad disk of dust and gas surrounding a star, a so-called "protoplanetary disk." However, the composition of these special disks as well as the process by which they give rise to planets have remained a mystery. The bright light of a central star makes it difficult to detect fainter objects around it or to capture a detailed image of the composition of the disk itself. Recent research with HiCIAO, Subaru Telecope's "planet-hunter", has overcome some of those obstacles. By masking the bright light from the central star, the instrument can then detect more detailed features of the star's disk and the objects that it contains.

As part of the SEEDS project (Strategic Exploration of Exoplanets and Disks with the Subaru Telescope) (Note 2), the researchers in the current study used HiCIAO to conduct observations of the disk around the young star SAO 206462 (sometimes referred to as HD 135344B). This star is about 460 light years away from Earth in the constellation Lupus ("the wolf") and is some 9 million years old. The radius of the disk is 20 billion kilometers (12.4 billion miles), about five times greater than Neptune's distance from the Sun in our Solar System.

The researchers captured images of SAO 206462's disk (Figure 1) that clearly reveal its spiral structure and indicate some features of its composition. They then were able to analyze its spiral structure by using density wave theory to infer the properties of the disk. This process allows a productive interface between observational data and a theoretical model.

Figure 1: An image of the disk around SAO 206462 captured with HiCIAO. A coronagraph blocks the direct light of the central star, which appears as the black, circular area in the image. Arrows show the two arms of the spiral structure around the star. (Credit: NAOJ) 

Density wave theory has been applied to explain the spiral arm structure of spiral galaxies. It proposes that a rotating disk of matter would "naturally" develop regions of enhanced density, so-called "spiral density waves", due to differential rotation. The wave-like concentration of dense material grows and forms a spiral pattern. A similar process may be at work in SAO 206462's disk. When the team compared their model with the observational data, they found that it was useful in revealing the features of the disk. (Figure 2)

Figure 2: A comparison of the fit between the theoretical model and observational data. The red dashed line represents the shape of the disk based on modeling from density wave theory. The image shows that the data conform to the predictions of the theory and supports an explanation for the development of the structure in terms of this theory's model. (Credit: NAOJ)  
The team was able to use the model to estimate the temperature of the disk based on dynamic processes and predict the evolution of the spiral structures. The observational data conform to the model. Although they could not specifically identify the origin of the spirals, it is possible that planets embedded in the disk may be the catalysts for the development of its shape. If a planet has already been formed in a disk, its gravity can produce a density wave, which then may result in the creation of a spiral structure in the protoplanetary disk. (Figure 3).

 Figure 3: A representation of how interaction between a protoplanetary disk and planet makes a density wave and affects the disk's structure. A planet in the disk may be one explanation for the formation of the disk's spiral structure. The basis for the simulation is a code in computational fluid dynamics called FARGO that simulates the flow of gases in motion. Colors indicate the surface density of the disk; the darkest colors show the areas with the least density while the white shows those with the greatest density. (Credit: NAOJ)   

Although the observed image does not necessarily show the existence of a planet, the possibility remains that a planet in the disk causes the density wave. This is the first time that density wave theory has been applied to measuring the features of a protoplanetary disk. The research takes an important step in explaining how a spiral disk could form and may mark the development of another indirect means of discovering planets.


References


The research paper entitled "Discovery of Small-Scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory" by Muto et al. was published in Astrophysical Journal Letters, April 2012 (ApJ, 748, L22, 2012)


Note:
  1. HiCIAO (High Contrast Instrument for the Subaru Next Generation Adaptive Optics) is designed to block out the bright direct light from a central star so that it can image nearby faint objects such as planets and detect faint dust disks around the central star.

  2. SEEDS (Strategic Exploration of Exoplanets and Disks with Subaru Telescope) is a large-scale project led by Motohide Tamura at NAOJ (National Astronomical Observatory of Japan). Researchers conduct observations at the Subaru Telescope that focus on the direct imaging and examination of exoplanets and disks to better understand the formation of planetary systems. Over 100 scientists and 25 institutions belong to the international consortium supporting the project . Since 2009, the SEEDS project has yielded a set of impressive findings, including imaging of the detailed structure of disks in AB Aur, LkCa15, HR4796A, and HD 169142.

  1.  

Thursday, December 20, 2012

Armchair Science: Bag and Tag Glowing Galactic Clouds


This is a screen shot from the Clouds game, a new addition to the Milky Way Project, where everyone can help astronomers sort and measure our galaxy. Copyright: 2010-2012 Zooniverse . › Larger image

A new galactic game launching today lets citizen scientists identify the glowing clouds where future stars will be born. The online experience, called Clouds, is a new addition to the Milky Way Project, where everyone can help astronomers sort and measure our galaxy. Clouds features images and data from NASA's Spitzer Space Telescope and the Herschel Space Observatory, a European Space Agency mission with important participation from NASA.
 
In the rapid-fire game, players gauge whether a targeted section of a presented image is a cloud, a "hole" -- an empty region of space -- or something in between. The cataloging of these snapshots of the local cosmos will help astronomers learn more about the architecture and character of our home galaxy, the Milky Way.
 
The organizers of Clouds encourage astronomy enthusiasts to start playing now, because with enough participation, important insights into the Milky Way could come as soon as early next year.
 
"We're really excited to launch Clouds and see results back from our giant volunteer team of amateur scientists," said Robert Simpson, a postdoctoral researcher in astronomy at Oxford University, England, and principal investigator of the Milky Way Project. "We think the community can blast through all these data fairly quickly. We may even be done by the spring, and that would be an amazing result for citizen science."
 
To participate in the Clouds experience by looking for infrared clouds and contributing to the Milky Way Project, visit: http://www.milkywayproject.org/clouds .
 

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Stars Reveal the Secrets of Looking Young

 
The globular cluster NGC 6388 observed by the European Southern Observatory
The globular cluster NGC 6388, 
observed by the NASA/ESA Hubble Space Telescope

NGC 6388 seen from the ground and space

Globular clusters seen by Hubble and from the ground

 Videos
Evolution of globular clusters

Some people are in great shape at the age of 90, while others are decrepit before they’re 50. We know that how fast people age is only loosely linked to how old they actually are — and may have more to do with their lifestyle. A new study using both the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory and the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.
Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity. Relics of the early years of the Universe, with ages of typically 12–13 billion years (the Big Bang took place 13.7 billion years ago), there are roughly 150 globular clusters in the Milky Way and they contain many of our galaxy’s oldest stars.

But while the stars are old and the clusters formed in the distant past, astronomers using the MPG/ESO 2.2-metre telescope and the NASA/ESA Hubble Space Telescope have found that some of these clusters are still young at heart. The research is presented in the 20 December 2012 issue of the journal Nature.

“Although these clusters all formed billions of years ago,” says Francesco Ferraro (University of Bologna, Italy), the leader of the team that made the discovery, “we wondered whether some might be aging faster or slower than others. By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging.”

Star clusters form in a short period of time, meaning that all the stars within them tend to have roughly the same age. Because bright, high-mass stars burn up their fuel quite quickly, and globular clusters are very old, there should only be low-mass stars still shining within them.

This, however, turns out not to be the case: in certain circumstances, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a close neighbour, or if they collide. The re-invigorated stars are called blue stragglers [1], and their high mass and brightness are properties that lie at the heart of this study.

Heavier stars sink towards the centre of a cluster as the cluster ages, in a process similar to sedimentation. Blue stragglers’ high masses mean they are strongly affected by this process, while their brightness makes them relatively easy to observe [2].

To better understand cluster aging, the team mapped the location of blue straggler stars in 21 globular clusters, as seen in images from the MPG/ESO 2.2-metre telescope and Hubble, among other observatories [3]. Hubble provided high resolution imagery of the crowded centres of 20 of the clusters, while the ground-based imagery gave a wider view of their less busy outer regions.

Analysing the observational data, the team found that a few clusters appeared young, with blue straggler stars distributed throughout, while a larger group appeared old, with the blue stragglers clumped in the centre. A third group was in the process of aging, with the stars closest to the core migrating inwards first, then stars ever further out progressively sinking towards the centre.

“Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster,” said Barbara Lanzoni (University of Bologna, Italy), a co-author of the study. “In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the Universe.”

As a cluster’s heaviest stars sink towards the centre, the cluster eventually experiences a phenomenon called core collapse, where the centre of the cluster bunches together extremely densely. The processes leading towards core collapse are quite well understood, and revolve around the number, density and speed of movement of the stars. However, the rate at which they happened was not known until now [4]. This study provides the first empirical evidence of how quickly different globular clusters age.

Notes

[1] Blue stragglers are so called because of their blue colour, and the fact that their evolution lags behind that of their neighbours.

[2] Blue stragglers combine being relatively bright and high mass by the standards of globular cluster stars, but they are not the only stars within these clusters that are either bright or massive.

Red giant stars are brighter, but they have a much lower mass, and therefore are not affected by the sedimentation process in the same way. (It is easy to distinguish these from blue stragglers because their colour is very different.)

Neutron stars, the extremely dense cores of stars much bigger than the Sun that exploded billions of years ago in the early history of globular clusters, have a similar mass to blue stragglers, and are affected by the sedimentation process, but they are incredibly difficult to observe and therefore do not make a useful subject for this study.

Blue stragglers are the only stars within clusters that combine high mass and high brightness.

[3] Of the 21 clusters covered by this research, 20 were studied with Hubble, 12 with the MPG/ESO 2.2-metre telescope, eight with the Canada-France-Hawaii telescope and one with NAOJ’s Subaru Telescope.

[4] Such a rate depends in a complex manner on the number of stars, their density and their velocity within a cluster. While the first two quantities are relatively easy to measure, velocity is not. For these reasons, previous estimates of the rate of globular cluster dynamical aging were based only on theoretical arguments, while the new method allows a totally empirical measurement.

More information

This research was presented in a paper, “Dynamical age differences amongst coeval star clusters as revealed by blue stragglers“, by F. R. Ferraro et al., to appear in the journal Nature on 20 December 2012.

The team is composed of F. R. Ferraro (University of Bologna, Italy), B. Lanzoni (University of Bologna), E. Dalessandro (University of Bologna), G. Beccari (ESO, Garching, Germany), M. Pasquato (University of Bologna), P. Miocchi (University of Bologna), R. T. Rood (University of Virginia, Charlottesville, USA), S. Sigurdsson (Pennsylvania State University, USA), A. Sills (McMaster University, Hamilton, Canada), E. Vesperini (Indiana University, Bloomington, USA), M. Mapelli (INAF-Osservatorio Astronomico di Padova, Italy), R. Contreras (University of Bologna), N. Sanna (University of Bologna), A. Mucciarelli (University of Bologna).

This research is part of the Cosmic-Lab project (www.cosmic-lab.eu) funded by the ERC (European Research Council) for a total amount of € 1.8 million for 5 years. Set up in 2007 by the European Union, the ERC aims to stimulate scientific excellence in Europe by encouraging competition for funding between the very best, creative researchers of any nationality and age. Since its launch, the ERC has funded over 2 500 researchers and their frontier research projects across Europe. The ERC operates according to an "investigator-driven", or "bottom-up", approach, allowing researchers to identify new opportunities in all fields of research (Physical Sciences and Engineering, Life Sciences, and Social Sciences and Humanities). It has also become a benchmark of the competitiveness of national research systems and complements existing funding schemes at national and European levels. The ERC, which is the newest component of the EU's Seventh Research Framework Programme, has a total budget of €7.5 billion from 2007 to 2013. Last year, the European Commission proposed a substantial increase in the ERC's budget for 2014 to 2020 under the new framework programme ('Horizon 2020'). The ERC is composed of an Executive Agency and a Scientific Council. The Scientific Council is made up of 22 top researchers and sets the ERC's scientific strategy. The ERC is led by President Prof. Helga Nowotny and the Scientific Council is represented in Brussels by Secretary General Prof. Donald Dingwell. The ERC Executive Agency implements the "Ideas" Specific Programme and is led by Director (ad int.) Pablo Amor.

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. 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 the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Links


Contacts

 Francesco Ferraro
 University of Bologna
 Italy
 Tel: +39 051 209 5774
 Email:
francesco.ferraro3@unibo.it

 Barbara Lanzoni
 University of Bologna
 Italy
 Tel: +39 051 209 5792
 Email:
barbara.lanzoni3@unibo.it

 Richard Hook
 ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
 Garching bei München, Germany
 Tel: +49 89 3200 6655
 Cell: +49 151 1537 3591
 Email:
rhook@eso.org
Oli Usher
Hubble/ESA
Garching bei München, Germany
Tel: +49 89 3200 6855

WIYN/NOAO: A Panoramic Loop in Cygnus

Giant supernova remnant, Cygnus Loop. The Image Gallery page for this image includes links to the full resolution version, which is more than 24,000 pixels on a side. Image Credit: T.A. Rector (University of Alaska Anchorage), Richard Cool (University of Arizona) and WIYN/NOAO/AURA/NSF
 
As an end of the year finale, the National Optical Astronomy Observatory (NOAO) and WIYN partners offer this new wide-field image of the Cygnus loop.  Three degrees on a side, this image covers an area of the sky about 45 times that of the full moon.  But it does so without sacrificing high resolution.  The image is over 600 million pixels in size, making it one of the largest astronomical images ever made. 

The Cygnus Loop is a large supernova remnant: the gaseous remains of a massive star that exploded long ago. It is located about 1,500 light-years from Earth in the direction of the constellation Cygnus, the Swan.  Astronomers estimate the supernova explosion that produced the nebula occurred between 5,000 to 10,000 years ago. First noted in 1784 by William Herschel, it is so large that its many parts have been catalogued as separate objects, including NGC 6992, NGC 6995 and IC 1340 along the eastern (left) side of the image, NGC 6974 and NGC 6979 near the top-center, and the Veil Nebula (NGC 6960) and Pickering’s Triangle along the western (right) edge.  The bright star near the western edge of the image, known as 52 Cygnus, is not associated with the supernova.

The data were obtained with the NOAO Mosaic 1 camera, with observations in the Oxygen [OIII] (blue), Sulphur [S II] (green) and Hydrogen-Alpha (red) filters.  When mounted on the WIYN 0.9 meter telescope the Mosaic camera has a one square degree field of view.  The Cygnus Loop was observed with nine separate telescope pointings in a 3x3 grid pattern.

The observations were originally obtained in 2003 by Richard Cool, while he was a graduate student at the University of Arizona, as part of a project to precisely measure the distance to the Cygnus Loop. Dr. Cool, now at the MMT Observatory in Arizona, said, “Often, astronomical research reduces images to dry tables of numerical information that we analyze in order to more deeply understand our universe.  Images like this are amazing because they can remind you of the big picture and beauty that surrounds us”.  In 2003 the computing power available was insufficient to process the data into a single, full-resolution color image.  Nine years later, the data were re-reduced and processed by Travis Rector to create the image presented here.  Dr. Rector has produced a remarkable series of color images from NOAO telescopes.  They can be found at his website and on a dedicated NOAO image gallery page.

Images like this demonstrate that even relatively small telescopes when equipped with modern cameras are capable of producing cutting-edge research. The 0.9 meter telescope at Kitt Peak is operated by the WIYN Consortium. It has been in operation since 1960, when the original telescope was first installed at the site now occupied by the WIYN 3.5 meter telescope.  Today, the 0.9 meter is regularly used by graduate students and faculty for a variety of research projects.

The WIYN 0.9 meter Observatory is a partnership including Austin Peay State University, Haverford College, Indiana University, Rochester Institute of Technology, San Francisco State University, University of Wisconsin-Madison, University of Wisconsin- Stevens Point, University of Wisconsin-Whitewater, and Wisconsin Space Grant consortium.

NOAO is operated by Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.

Science Contact

Dr. Travis Rector 
Department of Physics and Astronomy 
University of Alaska Anchorage 
3211 Providence Dr. 
Anchorage, AK 99508 

So These Stars Orbit in a Bar...

Astronomers identify the stellar patrons of the Milky Way bar

Forget the restaurant at the end of the Universe — astronomers now have the clearest understanding yet of the bar at the center of the Milky Way.

Scientists with the Sloan Digital Sky Survey III (SDSS-III) have announced the discovery of hundreds of stars rapidly moving together in long, looping orbits around the center of our Galaxy. "The best explanation for their orbits is that these stars are part of the Milky Way bar," says David Nidever, a Dean B. McLaughin Fellow in the Astronomy Department at the University of Michigan. "We know that the bar plays an important role in determining the structure of the Galaxy, so learning more about these stars will help us understand the whole Galaxy, even out here in the spiral arms."
 
A map of the innermost Milky Way, with circles marking the regions explored by the SDSS-III APOGEE project. Circles marked with "X" show places where the project found high-speed stars associated with the Milky Way's bar moving away from Earth. The lighter regions marked with dots on the other side of the Galactic Center show places where the fourth-generation Sloan Digital Sky Survey hopes to find counterpart bar stars moving toward the Earth.

Illustration Credit: David Nidever (University of Michigan / University of Virginia) and the SDSS-III Collaboration. Background image from the
  Two-Micron All Sky Survey Image Mosaic (Infrared Processing and Analysis Center/Caltech & University of Massachusetts).
Other versions:      300 DPI color JPG
The team's discovery came from accurately measuring the speeds of thousands of stars near the center of the Milky Way. The center of our Galaxy is 30,000 light-years away — close by cosmic standards — yet we know surprisingly little about it, because the Galaxy's dusty disk hides it from view. In spite of this blind spot, though, we do know a key fact about our Galaxy: like many spiral galaxies, the Milky Way has a 'bar' of stars that orbit together around the Galactic Center.
"We know of the bar's existence from many separate lines of evidence," says Gail Zasowski, a National Science Foundation postdoctoral Fellow at The Ohio State University. "What we don't know is which stars are part of the bar, and what the velocities of those stars are. That information will help us understand how the bar formed, and how its stars relate to the stars in the rest of the Galaxy."
The trouble is that there is no obvious way to tell a star in the Milky Way's bar apart from any other star in the same neighborhood. Instead, the key to finding bar stars is to measure the velocities of many stars, then see whether some of those stars are moving together in some unusual pattern. Although interstellar dust blocks nearly all visible light, longer infrared wavelengths can partially shine through. So a survey of stellar positions and velocities that operates in infrared light could finally pierce the veil of dust, and collect data from enough stars in the innermost Milky Way to firmly identify which ones are part of the bar.
Enter SDSS-III's new Apache Point Galactic Evolution Experiment (APOGEE). APOGEE uses a custom-built high-resolution infrared spectrograph attached to the 2.5-meter Sloan Foundation Telescope in New Mexico, and is capable of measuring the velocities and chemical compositions of up to 300 stars at once. "What separates APOGEE from previous spectroscopic surveys is that we are studying the Galaxy using infrared light," Nidever says. APOGEE began observations in June 2011 and has already observed more than 48,000 stars all over our galaxy.
In a paper published recently in the Astrophysical Journal, a worldwide team of scientists including Nidever and Zasowski used data from the first few months of APOGEE observations to measure the velocities for nearly 5,000 stars near the Galactic center. With these velocity measurements, they assembled a picture of how these stars orbit the center of the Milky Way. However, quite unexpectedly, they found that a substantial fraction of stars in the inner Galaxy are moving away from us quickly — about 10 percent of the total stars in their sample are moving at more than 200 kilometers per second (400,000 miles per hour) away from the Earth. The observed pattern of these fast stars is similar in many different parts of the inner Galaxy, and is the same above and below the midplane of the Galaxy — suggesting that these measurements of fast central stars are not just a statistical fluke, but really are a feature of our Galaxy.

An artist's impression of what the Milky Way might look like viewed from above. The small blue dot is where we are on Earth (not to scale). The solid red arrows show the high-speed stars moving away from Earth that were discovered by SDSS-III. The dashed arrows show the stars moving toward Earth that are expected to be seen by the fourth-generation Sloan Digital Sky Survey.

Credit: Jordan Raddick (Johns Hopkins University) and Gail Zasowski (The Ohio State University / University of Virginia).  Milky Way artist's concept by NASA/JPL-Caltech/R. Hurt (SSC-Caltech).

Other versions:      300 DPI color JPG 

The team then compared their observations with the predictions of the bar stars from the latest computer models of the Galaxy — and the observations matched the predictions closely. "Based on the evidence from the model comparisons, I am now confident that these fast-moving stars are part of the bar," Nidever says. "I was actually quite surprised that they showed up so clearly in our survey.

APOGEE's identification of which stars are part of the bar will allow astronomers to study how stars in the bar and in the rest of the galaxy react to one another. "The bar acts like a giant mixer for our galaxy," says Steven Majewski, a professor of astronomy at the University of Virginia and the principal investigator for the APOGEE project. "As the bar rotates, it churns up the motions of nearby stars. Over time, this mixing should have a large effect on the disk of our galaxy, including in spiral arms where we live, but this effect is not well understood. This new sample of definitively-identified bar stars gives us a unique opportunity to learn more about exactly how this giant blender mixes up our galaxy."

But the team's discovery only tells half the story. So far, APOGEE has only observed one side of the bar, the side where the stars are moving away from the Earth. On the other side, the stars must be moving toward Earth. But unfortunately, the Sloan telescope is inconveniently placed: the other half of the Milky Way bar is visible only from Earth's southern hemisphere. Seeing the other side of the bar is one of the motivations for a planned fourth generation of the Sloan Digital Sky Survey. Part of this successor project will implement the same techniques using a 2.5-meter telescope in Chile to observe the rest of the inner Milky Way. The new survey is set to begin in 2014.


Paper announcing the results

D.L. Nidever, G. Zasowski, S.R. Majewski, J. Bird, A.C. Robin, I. Martinez-Valpuesta, R.L. Beaton, R. Schönrich, Ralph; M. Schultheis, J.C. Wilson, M.F. Skrutskie, R.W. O'Connell, M. Shetrone, R.P. Schiavon, J.A. Johnson, B. Weiner, O. Gerhard, D.P. Schneider, C. Allende Prieto, K. Sellgren, D. Bizyaev, H. Brewington, J. Brinkmann, D.J. Eisenstein, P.M. Frinchaboy, A.E. García Pérez, J. Holtzman, F.R. Hearty, E. Malanushenko, V. Malanushenko, D. Muna, D. Oravetz, K. Pan, A. Simmons, S. Snedden, and B.A. Weaver, 2012,
Astrophysical Journal Letters, 755(2), L25, doi:10.1088/2041-8205/755/2/L25.


About SDSS-III

Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/.

SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.

Contacts:
  • David Nidever, University of Michigan, dnidever -at- umich.edu, 734-615-6141
  • Gail Zasowski, The Ohio State University, gail.zasowski -at- gmail.com, 614-292-6925
  • Steven Majewski, University of Virginia, srm4n -at- virginia.edu, 434-924-4893
  •  Michael Wood-Vasey, SDSS-III Spokesperson, University of Pittsburgh, wmwv -at- pitt.edu, 412-624-2751
  • Jordan Raddick, SDSS Public Information Officer, raddick -at- jhu.edu, 410-516-8889


Wednesday, December 19, 2012

Shot Away from its Companion, Giant Star Makes Waves

The giant star Zeta Ophiuchi is having a "shocking" effect on the surrounding dust clouds in this infrared image from NASA's Spitzer Space Telescope. Stellar winds flowing out from this fast-moving star are making ripples in the dust as it approaches, creating a bow shock seen as glowing gossamer threads, which, for this star, are only seen in infrared light. Image credit: NASA/JPL-Caltech . › Full image and caption

Like a ship plowing through still waters, the giant star Zeta Ophiuchi is speeding through space, making waves in the dust ahead. NASA's Spitzer Space Telescope has captured a dramatic, infrared portrait of these glowing waves, also known as a bow shock.

Astronomers theorize that this star was once sitting pretty next to a companion star even heftier than itself. But when that star died in a fiery explosion, Zeta Ophiuchi was kicked away and sent flying. Zeta Ophiuchi, which is 20 times more massive and 80,000 times brighter than our sun, is racing along at about 54,000 mph (24 kilometers per second).

In this view, infrared light that we can't see with our eyes has been assigned visible colors. Zeta Ophiuchi appears as the bright blue star at center. As it charges through the dust, which appears green, fierce stellar winds push the material into waves. Where the waves are the most compressed, and the warmest, they appear red. This bow shock is analogous to the ripples that precede the bow of a ship as it moves through the water, or the pileup of air ahead of a supersonic airplane that results in a sonic boom.

NASA's Wide-field Infrared Survey Explorer, or WISE, released a similar picture of the same object in 2011. WISE sees infrared light as does Spitzer, but WISE was an all-sky survey designed to take snapshots of the entire sky. Spitzer, by contrast, observes less of the sky, but in more detail. The WISE image can be seen at: http://www.jpl.nasa.gov/news/news.php?release=2011-026 .

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov


FOUND: One Planet Orbiting Sun-like Star. Only Twelve Light Years Away. May Be Habitable.


Credit: J. Pinfield for the RoPACS network at the University of Hertfordshire, 2012

Tau Ceti in the early evening sky in constellation of Cetus on Wednesday 19th December from Hatfield, UK

An international team of astronomers using the W. M. Keck Observatory and other telescopes, has discovered that Tau Ceti, one of the closest and most Sun-like stars, may host five planets – with one in the elusive ‘Goldilocks Zone’. Credit: Stellarium software

At a distance of twelve light years and visible with the naked eye in the December evening sky, Tau Ceti is the closest single star that has the same spectral classification as our Sun. Its five planets are estimated to have masses between two and six times the mass of the Earth – making it the lowest-mass planetary system yet detected. One of the planets lies in the star’s habitable zone – the so-called Goldilocks Zone with it’s ‘just right’ temperatures for supporting liquid water – and has a mass around five times that of Earth, making it the smallest planet found to be orbiting in the habitable zone of any Sun-like star. 

The international team of astronomers, from the UK, Chile, the USA, and Australia, combined more than 6,000 observations from three different instruments, including HIRES on the Keck I telescope. Using new techniques, the team has found a method to detect signals half the size previously thought possible. This greatly improves the sensitivity of searches for small planets and suggests that Tau Ceti is not a lone star but has a planetary system.

“We pioneered new data modeling techniques by adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches,” said Mikko Tuomi from the University of Hertfordshire and the first author of the paper. “This significantly improved our noise modeling techniques and increased our ability to find low mass planets.”

“We chose Tau Ceti for this noise modeling study because we had thought it contained no signals,” said Hugh Jones from the University of Hertfordshire. “And as it is so bright and similar to our Sun, it is an ideal benchmark system to test out our methods for the detection of small planets.”

“Tau Ceti is one of our nearest cosmic neighbors and so bright that we may be able to study the atmospheres of these planets in the not too distant future,” said James Jenkins, Universidad de Chile and Visiting Fellow at the University of Hertfordshire. “Planetary systems found around nearby stars close to our Sun indicate that these systems are common in our Milky Way galaxy.”

More than 800 planets have been discovered orbiting other worlds, but planets in orbit around the nearest Sun-like stars are particularly interesting. “This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets,” said Steve Vogt from University of California Santa Cruz. “They are everywhere, even right next door! We are now beginning to understand that nature seems to overwhelmingly prefer systems that have multiple planets with orbits of less than one hundred days. This is quite unlike our own solar system where there is nothing with an orbit inside that of Mercury. So our solar system is, in some sense, a bit of a freak and not the most typical kind of system that nature cooks up.”

“As we stare at the night sky, it is worth contemplating that there may well be more planets out there than there are stars – some fraction of which may well be habitable,” said Chris Tinney from the University of New South Wales.

The W. M. Keck Observatory operates Earth’s two biggest and most scientifically productive telescopes on the summit of Mauna Kea, Island of Hawaii. The twin, 10-meter telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Media Contact:

Steve Jefferson
Communications Officer, Advancement
W.M. Keck Observatory

sjefferson@keck.hawaii.edu
(808)881-3827

Science Contact:

Mikko Tuomi
University of Hertfordshire

miptuom@utu.fi

Hugh Jones
University of Hertfordshire

h.r.a.jones@herts.ac.uk