Wednesday, May 25, 2016

GOODS-S 29323: NASA Telescopes Find Clues For How Giant Black Holes Formed So Quickly

GOODS-S 29323
Credit: X-ray: NASA/CXC/Scuola Normale Superiore/Pacucci, F. et al, Optical: NASA/STScI; 
Illustration: NASA/CXC/M.Weiss.


Using data from NASA's three Great Observatories, scientists have found the best evidence to date of a mechanism that produced supermassive black holes in the early Universe. If confirmed, this result, described in our latest press release, could lead to new insight into how black holes were formed and grew billions of years ago.

This artist's illustration depicts a possible "seed" for the formation of a supermassive black hole, that is an object that contains millions or even billions of times the mass of the Sun. In the artist's illustration, the gas cloud is shown as the wispy blue material, while the orange and red disk is showing material being funneled toward the growing black hole through its gravitational pull.

Researchers found evidence that two objects could have formed in this way, by directly collapsing into a black hole from a large cloud of gas. These two candidates for being "direct collapse black holes" are so distant that they may have formed less than one billion years after the Big Bang

The inset boxes show data from the Hubble Space Telescope (right) and Chandra X-ray Observatory (left) of one of the objects described above. The Hubble image shows the faint, distant galaxy at the center of the image and the Chandra image shows X-ray emission from material falling onto the black hole in the same galaxy.

The researchers used computer models of black hole seeds combined with a new method to select candidates for these objects from long-exposure images from Chandra, Hubble, and Spitzer (not shown in this graphic). By analyzing the combined light from the three telescopes, the team was able to search through thousands of objects to look for any that had properties that matched those predicted by their models.

Two candidates emerged that had the expected red color, seen by Hubble and Spitzer, as well as the X-ray profile predicted from Chandra. These objects were found in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Great Observatories Origins Deep Survey-South surveys. The next steps will involve getting more data on these two intriguing objects as well as extending the analysis to other surveys to look for more direct collapse black hole candidates.

These results will appear in the June 21st issue of the Monthly Notices of the Royal Astronomical Society and is available online. The authors of the paper are Fabio Pacucci (SNS, Italy), Andrea Ferrara (SNS), Andrea Grazian (INAF), Fabrizio Fiore (INAF), Emaneule Giallongo (INAF), and Simonetta Puccetti (ASI Science Data Center). NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.


Fast Facts for GOODS-S 29323:

Scale: Image is about 15 arcsec across. (about 212,000 light years)
Category: Black Holes, Cosmology/Deep Fields/X-ray Background
Observation Date: 54 pointings between Oct 15, 1999 to Jul 22, 2010
Observation Time: 1111 hours 6 min (46 days 7 hours 6 min).
Obs. ID: 441, 581-582, 1431, 1672, 2239, 2312-2313, 2405-2406, 2409, 8591-8597, 9575, 9578, 9593, 9596, 9718, 12043-12055, 12123, 12128-12129, 12135, 12137-12138, 12213, 12218-12220, 12222-12223, 12227, 12230-12234
Instrument: ACIS
References: Pacucci, F. et al, 2016, MNRAS, 459, 1432; arXiv:1603.08522
Color Code: X-ray (Blue), Optical (Gold)
Distance Estimate: About 13.2 billion light years (z=9.73)


Puffy Giant Planet Discovered by KELT-S Transit Survey

The discovery lightcurve of exoplanet KELT-10b is overlaid on an image of the KELT-S Telescope in South Africa. The lightcurve was obtained using 4967 observations over about 4-years. A 30-minute binned lightcurve is shown in red. Image Credit: R. Kuhn & Vanderbilt University/SAAO.


Transiting planets orbiting bright stars provide a golden opportunity to learn about the nature of exoplanets, their composition and origin. A robotic survey of the southern sky, designed to detect such systems, has discovered its first exoplanet: KELT-10b, a highly inflated giant planet. Although it is only 2/3 the mass of Jupiter, KELT-10b is 40% larger than Jupiter in radius. Because of its large size, when the planet passes in front of its star, it blocks out a whopping 1.4% of the star’s light, generating a transit signal that is relatively easy to detect. As one of only 25 planets known to transit bright stars (V < 11) in the southern hemisphere, KELT-10b is an attractive target for future studies aimed at characterizing planetary atmospheres. 

KELT-10b was discovered by the Kilodegree Extremely LIttle Telescope-South (KELT-S) transit survey. KELT-S is a robotic telescope located at the Sutherland site of the South African Astronomical Observatory. It is operated by Vanderbilt University and the South African Astronomical Observatory. NOAO astronomer David James is a founding member of the project. 

Describing his enthusiasm for the KELT-S project, James explained, “Efforts to detect and characterize extra-solar planets are driven by the deep-rooted desires of humanity to understand the origin of the solar system and their place in it. Although small aperture planet-hunting telescopes like KELT-S are typically are modest in budget, they deliver a strong return in science. They are also a powerful educational experience for students.” 

James is excited by the future of exoplanet research, as it moves from the era of exoplanet detection and taxonomy to the characterization of their atmospheres and searches for bio-signatures. He mused, “When my daughter is my age, perhaps having detected exoplanets of her own, she may well be using a 30-50m class telescope to describe their biology and potential for hosting life.”

Links to resources and press releases:

Tuesday, May 24, 2016

The Little Fox and the Giant Stars

Copyright ESA/Herschel/PACS, SPIRE/Hi-GAL Project


New stars are the lifeblood of our Galaxy, and there is enough material revealed by this Herschel infrared image to build stars for millions of years to come.

Situated 8000 light-years away in the constellation Vulpecula – latin for little fox – the region in the image is known as Vulpecula OB1. It is a ‘stellar association’ in which a batch of truly giant ‘OB’ stars is being born.
The vast quantities of ultraviolet and other radiation emitted by these stars is compressing the surrounding cloud, causing nearby regions of dust and gas to begin the collapse into more new stars. In time, this process will ‘eat’ its way through the cloud, transforming some of the raw material into shining new stars.

The image was obtained as part of Herschel’s Hi-GAL key-project. This used the infrared space observatory’s instruments to image the entire galactic plane in five different infrared wavelengths.

These wavelengths reveal cold material, most of it between -220ºC and -260ºC. None of it can be seen at ordinary optical wavelengths, but this infrared view shows astronomers a surprising amount of structure in the cloud’s interior.

The surprise is that the Hi-GAL survey has revealed a spider’s web of filaments that stretches across the star-forming regions of our Galaxy. Part of this vast network can be seen in this image as a filigree of red and orange threads.

At visual wavelengths, the OB association is linked to a star cluster catalogued as NGC 6823. It was discovered by William Herschel in 1785 and contains 50–100 stars. A nebula emitting visible light, catalogued as NGC 6820, is also part of this multi-faceted star-forming region.

The giant stars at the heart of Vulpecula OB1 are some of the biggest in the Galaxy. Containing dozens of times the mass of the Sun, they have short lives, astronomically speaking, because they burn their fuel so quickly.

At an estimated age of two million years, they are already well through their lifespans. When their fuel runs out, they will collapse and explode as supernovas. The shock this will send through the surrounding cloud will trigger the birth of even more stars, and the cycle will begin again.



Monday, May 23, 2016

Are mystery Mars plumes caused by space weather

Copyright visual images: D. Parker (large Mars image and bottom inset) & W. Jaeschke (top inset)
All other graphics courtesy D. Andrews

Observations of a mysterious plume-like feature (marked with yellow arrow) at the limb of the Red Planet on 20 March 2012. The observation was made by astronomer W. Jaeschke. The image is shown with the north pole towards the bottom and the south pole to the top.  Copyright: W. Jaeschke

Mysterious high-rise clouds seen appearing suddenly in the martian atmosphere on a handful of occasions may be linked to space weather, say Mars Express scientists.

Amateur astronomers using telescopes on Earth were the first to report an unusual cloud-like plume in 2012 that topped-out high above the surface of Mars at an altitude around 250 km. The feature developed in less than 10 hours, covered an area of up to 1000 x 500 km, and remained visible for around 10 days.

The extreme altitude poses something of a problem in explaining the features: it is far higher than where typical clouds of frozen carbon dioxide and water are thought to be able to form in the atmosphere.

Indeed, the high altitude corresponds to the ionosphere, where the atmosphere directly interacts with the incoming solar wind of electrically charged atomic particles.

Speculation as to their cause has included exceptional atmospheric circumstances, auroral emissions, associations with local crustal anomalies, or a meteor impact, but so far it has not been possible to identify the root cause.

Unfortunately, the spacecraft orbiting Mars were not in the right position to see the 2012 plume visually, but scientists have now looked into plasma and solar wind measurements collected by Mars Express at the time.
They have found evidence for a large ‘coronal mass ejection’, or CME, from the Sun striking the martian atmosphere in the right place and at around the right time.

“Our plasma observations tell us that there was a space weather event large enough to impact Mars and increase the escape of plasma from the planet’s atmosphere,” says David Andrews of the Swedish Institute of Space Physics, and lead author of the paper reporting the Mars Express results.

“But we were not able to see any signatures in the ionosphere that we can categorically say were due to the presence of this plume.

“One problem is that the plume was seen at the day–night boundary, over a region of known strong crustal magnetic fields where we know the ionosphere is generally very disturbed, so searching for ‘extra’ signatures is rather challenging.”

To go further, the scientists have looked at the chances of these two relatively rare events – a large and fast CME colliding with Mars, and the mysterious plume – occurring at the same time.

They have been searching back through the archives for similar events, but they are rare.

For example, the Hubble Space Telescope observed a similar high plume in May 1997, and a CME was registered hitting Earth at the same time.

Although that CME was widely studied, there is no information from Mars orbiters to judge the scale of its impact at the Red Planet. 

Similarly, CMEs have been detected at Mars without any associated plume being reported, although changes in distance and visibility of Mars from Earth makes it difficult to acquire good ground-based images at all times.

“The jury is still out as to what physics is at play here, but given the altitude of the plume, we think that plasma interactions must be important,” says David.

“One idea is that a fast-travelling CME causes a significant perturbation in the ionosphere resulting in dust and ice grains residing at high altitudes in the upper atmosphere being pushed around by the ionospheric plasma and magnetic fields, and then lofted to even higher altitudes by electrical charging.

“This could lead to a plume effect that is significant enough to be detected from Earth by astronomers.”

“A number of processes could be responsible, but if these plumes are indeed driven by space-weather disturbances, this adds an important angle to our understanding of how Mars may have lost much of its atmosphere in the past, changing from a warm, wet world and becoming the cold, dry, dusty place it is today,” says Dmitri Titov, Mars Express project scientist.

“The plume also emphasises the scientific potential for continuous monitoring of Mars by both orbiters and ground-based observatories. In particular, we are now going to use the webcam on Mars Express for more frequent coverage of the planet.”


Notes for Editors


Plasma observations during the Mars atmospheric “plume” event of March–April 2012, by D. Andrews et al has been accepted for publication in the Journal of Geophysical Research.

The measurements were conducted by the Mars Express Analyzer for 
Space Plasmas and Energetic Atoms (ASPERA-3) plasma instrument suite and the Mars Advanced Radar for Sub-Surface and Ionospheric Sounding (MARSIS).


For further information, please contact:

David Andrews
Swedish Institute of Space Physics
Tel: +46 (0) 184715922 
Email: david.andrews@irfu.se

Dmitri Titov
ESA Mars Express project scientist
Email: Dmitri.titov@esa.int

Markus Bauer





 ESA Science and Robotic Exploration Communication Officer







Tel: +31 71 565 6799







Mob: +31 61 594 3 954







Email: markus.bauer@esa.int

Source: ESA

Faintest Early-Universe Galaxy Ever, Detected and Confirmed

Color image of the cluster taken with Hubble Space Telescope (images in three different filters were combined to make an RGB image). In the inset we show three spectra of the multiply imaged systems. They have peaks at the same wavelength, hence showing that they belong to the same source. Credit: Bradac/HST/W. M. Keck Observatory


MAUNAKEA, Hawaii – An international team of scientists has detected and confirmed the faintest early-Universe galaxy ever using the W. M. Keck Observatory on the summit on Maunakea, Hawaii. In addition to using the world’s most powerful telescope, the team relied on gravitational lensing to see the incredibly faint object born just after the Big Bang. The results are being published in The Astrophysical Journal Letters today.

The team detected the galaxy as it was 13 billion years ago, or when the Universe was a toddler on a cosmic time scale.

The detection was made using the DEIMOS instrument fitted on the ten-meter Keck II telescope, and was made possible through a phenomenon predicted by Einstein in which an object is magnified by the gravity of another object that is between it and the viewer. In this case, the detected galaxy was behind the galaxy cluster MACS2129.4-0741, which is massive enough to create three different images of the object.

"Keck Observatory's telescopes are simply the best in the world for this work," said Marusa Bradac, a proefssor at University of California, Davis who led the team. "Their power, paired with the gravitational force of a massive cluster of galaxies, allows us to truly see where no human has seen before."

“Because you see three of them and the characteristics are exactly the same, that means it was lensed,” said Marc Kassis, staff astronomer at Keck Observatory who assists the discovery team at night. “The other thing that is particularly interesting is that it is small. The only way they would have seen it is through lensing. This allowed them to identify it as an ordinary galaxy near the edge of the visible Universe.”

“If the light from this galaxy was not magnified by factors of 11, five and two, we would not have been able to see it,” said Kuang-Han Huang, a team member from UC Davis and the lead author of the paper. “It lies near the end of the reionization epoch, during which most of the hydrogen gas between galaxies transitioned from being mostly neutral to being mostly ionized (and lit up the stars for the first time). That shows how gravitational lensing is important for understanding the faint galaxy population that dominates the reionization photon production.”

The galaxy’s magnified images were originally seen separately in both Keck Observatory and Hubble Space Telescope data. The team collected and combined all the Keck Observatory/DEIMOS spectra from all three images, confirming they were the same and that this is a triply-lensed system.

“We now have good constraints on when the reionization process ends – at redshift around 6 or 12.5 billion years ago – but we don’t yet know a lot of details about how it happened,” Huang said. “The galaxy detected in our work is likely a member of the faint galaxy population that drives the reionization process.”

This galaxy is exciting because the team infers a very low stellar mass, or only one percent of one percent of the Milky Way galaxy,” Kassis said. “It’s a very, very small galaxy and at such a great distance, it’s a clue in answering one of the fundamental questions astronomy is trying to understand: What is causing the hydrogen gas at the very beginning of the Universe to go from neutral to ionized about 13 billion years ago. That’s when stars turned on and matter became more complex.”

The core of the team consisted of Bradac, Huang, Brian Lemaux, and Austin Hoag of UC Davis who are most directly involved with spectroscopic observation and data reduction of galaxies at redshift above seven.
Keck Observatory astronomers Luca Rizzi and Carlos Alvarez were instrumental in helping the team collect the DEIMOS data. Tommaso Treu from University of California, Los Angeles and Kasper Schmidt of Leibniz Institute for Astrophysics Potsdam were also part of the team. They lead the effort that obtains and analyzes spectroscopic data from the WFC3/IR grism on Hubble.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and world-leading laser guide star adaptive optics systems.

DEIMOS (the DEep Imaging and Multi-Object Spectrograph) boasts the largest field of view (16.7 arcmin by 5 arcmin) of any of the Keck instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

Keck 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.

By Steve Jefferson


Friday, May 20, 2016

Busy bees

 Credit:ESA/Hubble & NASA
Acknowledgement: Judy Schmidt (
Geckzilla)


This NASA/ESA Hubble Space Telescope image shows star clusters encircling a galaxy, like bees buzzing around a hive. The hive in question the an edge-on lenticular galaxy NGC 5308, located just under 100 million light-years away in the constellation of Ursa Major (The Great Bear).

Members of a galaxy type that lies somewhere between an elliptical and a spiral galaxy, lenticular galaxies such as NGC 5308 are disc galaxies that have used up, or lost, the majority of their gas and dust. As a result, they experience very little ongoing star formation and consist mainly of old and aging stars. On 9 October 1996, one of NGC 5308’s aging stars met a dramatic demise, exploding as a spectacular Type la supernova.

Lenticular galaxies are often orbited by gravitationally bound collections of hundreds of thousands of older stars. Called globular clusters, these dense collections of stars form a delicate halo as they orbit around the main body of NGC 5308, appearing as bright dots on the dark sky.

The dim, irregular galaxy to the right of NGC 5308 is known, rather prosaically, as SDSS J134646.18+605911.9.



Thursday, May 19, 2016

Hubble Takes Mars Portrait Near Close Approach

Mars Near 2016 Oppostion (Annotated)
Credit: NASA, ESA, and L. Frattare (STScI)
 
Bright, frosty polar caps, and clouds above a vivid, rust-colored landscape reveal Mars as a dynamic seasonal planet in this NASA Hubble Space Telescope view taken on May 12, 2016, when Mars was 50 million miles from Earth. The Hubble image reveals details as small as 20 to 30 miles across.

The large, dark region at far right is Syrtis Major Planitia, one of the first features identified on the surface of the planet by seventeenth century observers. Christiaan Huygens used this feature to measure the rotation rate of Mars. (A Martian day is about 24 hours and 37 minutes.) Today we know that Syrtis Major is an ancient, inactive shield volcano. Late-afternoon clouds surround its summit in this view.

A large oval feature to the south of Syrtis Major is the bright Hellas Planitia basin. About 1,100 miles across and nearly five miles deep, it was formed about 3.5 billion years ago by an asteroid impact.

The orange area in the center of the image is Arabia Terra, a vast upland region in northern Mars that covers about 2,800 miles. The landscape is densely cratered and heavily eroded, indicating that it could be among the oldest terrains on the planet. Dried river canyons (too small to be seen here) wind through the region and empty into the large northern lowlands.

South of Arabia Terra, running east to west along the equator, are the long dark features known as Sinus Sabaeus (to the east) and Sinus Meridiani (to the west). These darker regions are covered by dark bedrock and fine-grained sand deposits ground down from ancient lava flows and other volcanic features. These sand grains are coarser and less reflective than the fine dust that gives the brighter regions of Mars their ruddy appearance. Early Mars watchers first mapped these regions.

An extended blanket of clouds can be seen over the southern polar cap. The icy northern polar cap has receded to a comparatively small size because it is now late summer in the northern hemisphere. Hubble photographed a wispy, afternoon, lateral cloud extending for at least 1,000 miles at mid-northern latitudes. Early morning clouds and haze extend along the western limb.

This hemisphere of Mars contains landing sites for several NASA Mars surface robotic missions, including Viking 1 (1976), Mars Pathfinder (1997), and the still-operating Opportunity Mars rover. The landing sites of the Spirit and Curiosity Mars rovers are on the other side of the planet.

This observation was made just a few days before Mars opposition on May 22, when the sun and Mars will be on exact opposite sides of Earth, and when Mars will be at a distance of 47.4 million miles from Earth. On May 30, Mars will be the closest it has been to Earth in 11 years, at a distance of 46.8 million miles. Mars is especially photogenic during opposition because it can be seen fully illuminated by the sun as viewed from Earth.

The biennial close approaches between Mars and Earth are not all the same. Mars' orbit around the sun is markedly elliptical; the close approaches to Earth can range from 35 million miles to 63 million miles.

They occur because about every two years Earth's orbit catches up to Mars' orbit, aligning the sun, Earth, and Mars in a straight line, so that Mars and the sun are on "opposing" sides of Earth. This phenomenon is a result of the difference in orbital periods between Earth's orbit and Mars' orbit. While Earth takes the familiar 365 days to travel once around the sun, Mars takes 687 Earth days to make its trip around our star. As a result, Earth makes almost two full orbits in the time it takes Mars to make just one, resulting in the occurrence of Martian oppositions about every 26 months.


For additional information, contact:

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514

dweaver@stsci.edu / villard@stsci.edu

Jim Bell
Arizona State University, Tempe, Arizona
480-965-1044

jim.bell@asu.edu

Michael Wolff
Space Science Institute, Boulder, Colorado
262-352-2910

mjwolff@spacescience.org


Source: HubbleSite

A Beautiful Instance of Stellar Ornamentation

The glowing gas cloud LHA 120-N55 in the Large Magellanic Cloud

PR Image eso1616b
LHA 120-N55 in the constellation of Dorado


Videos

Zooming in on the glowing gas cloud LHA 120-N55 in the Large Magellanic Cloud

Close-up view of the glowing gas cloud LHA 120-N55 in the Large Magellanic Cloud
Close-up view of the glowing gas cloud LHA 120-N55 in the Large Magellanic Cloud


In this image from ESO’s Very Large Telescope (VLT), light from blazing blue stars energises the gas left over from the stars’ recent formation. The result is a strikingly colourful emission nebula, called LHA 120-N55, in which the stars are adorned with a mantle of glowing gas. Astronomers study these beautiful displays to learn about the conditions in places where new stars develop.

LHA 120-N55, or N55 as it is usually known, is a glowing gas cloud in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way located about 163 000 light-years away. N55 is situated inside a supergiant shell, or superbubble called LMC 4. Superbubbles, often hundreds of light-years across, are formed when the fierce winds from newly formed stars and shockwaves from supernova explosions work in tandem to blow away most of the gas and dust that originally surrounded them and create huge bubble-shaped cavities.

The material that became N55, however, managed to survive as a small remnant pocket of gas and dust. It is now a standalone nebula inside the superbubble and a grouping of brilliant blue and white stars — known as LH 72 — also managed to form hundreds of millions of years after the events that originally blew up the superbubble. The LH 72 stars are only a few million years old, so they did not play a role in emptying the space around N55. The stars instead represent a second round of stellar birth in the region.

The recent rise of a new population of stars also explains the evocative colours surrounding the stars in this image. The intense light from the powerful, blue–white stars is stripping nearby hydrogen atoms in N55 of their electrons, causing the gas to glow in a characteristic pinkish colour in visible light. Astronomers recognise this telltale signature of glowing hydrogen gas throughout galaxies as a hallmark of fresh star birth.

While things seem quiet in the star-forming region of N55 for now, major changes lie ahead. Several million years hence, some of the massive and brilliant stars in the LH 72 association will themselves go supernova, scattering N55’s contents. In effect, a bubble will be blown within a superbubble, and the cycle of starry ends and beginnings will carry on in this close neighbour of our home galaxy.

This new image was acquired using the FOcal Reducer and low dispersion Spectrograph (FORS2) instrument attached to ESO's VLT. It was taken as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.


More Information

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 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Contacts

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org


Source: ESO

Wednesday, May 18, 2016

NRAO Media Tip Sheet: May 2016

ALMA image of dusty cometary ring around HR 8799, the only star where multiple planets have been imaged. The new data suggest the planets either migrated or another undiscovered planet is present. The zoom-in portion of the image, taken with ESO's Very Large Telescope, shows the location of the known planets in this system in relation to a graphical representation of the central star. Credit: Booth et al., ALMA (NRAO/ESO/NAOJ); A. Zurlo, et al.

VLBA image of Compact Symmetric Object J13262+3152, called "an archetypical example" of such an object.
Credit: Tremblay, et al., NRAO/AUI/NSF

Patent for surface treatment for self-calibrating radiometer awarded to NRAO engineer Galen Watts.
Credit: NRAO/AUI/NSF

NRAO engineers Tod Boyd and Matt Morgan, recipients of the 2015 IEEE Antenna and Propagation Society Harold A. Wheeler Applications Prize Paper Award. Credit: NRAO/AUI/NSF



1. Cometary Belt around Distant Multi-planet System Hints at Hidden or Wandering Planets

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made the first high-resolution image of the cometary belt (a region analogous to our own Kuiper belt) around HR 8799, the only star where multiple planets have been imaged directly. The shape of this dusty disk, particularly its inner edge, is surprisingly inconsistent with the orbits of the planets, suggesting that either they changed position over time or there is at least one more planet in the system yet to be discovered. "These data really allow us to see the inner edge of this disk for the first time," explains Mark Booth from Pontificia Universidad Católica de Chile and lead author of the study. "By studying the interactions between the planets and the disk, this new observation shows that either the planets that we see have had different orbits in the past or there is at least one more planet in the system that is too small to have been detected." The disk, which fills a region 150 to 420 times the Sun-Earth distance, is produced by the ongoing collisions of cometary bodies in the outer reaches of this star system. ALMA was able to image the emission from millimeter-size debris in the disk; according to the researchers, the small size of these dust grains suggests that the planets in the system are larger than Jupiter. Previous observations with other telescopes at shorter wavelengths did not detect this discrepancy in the disk. It is not clear if this difference is due to the low resolution of the previous observations or because different wavelengths are sensitive to different grain sizes, which would be distributed slightly differently. HR 8799 is a young star approximately 1.5 times the mass of the Sun located 129 light-years from Earth in the direction of the constellation Pegasus. "This is the very first time that a multi-planet system with orbiting dust is imaged, allowing for direct comparison with the formation and dynamics of our own Solar System," explains Antonio Hales, co-author of the study from the National Radio Astronomy Observatory in Charlottesville, Va. The astronomers are reporting their results in the Monthly Notices of the Royal Astronomical Society.

Reference: "Resolving the Planetesimal Belt of HR 8799 with ALMA," Booth et al.; Monthly Notices of the Royal Astronomical Society [http://dx.doi.org/10.1093/mnrasl/slw040], May 2016. Preprint: http://arxiv.org/abs/1603.04853

2. VLBA Study Doubles Sample of Youngest Radio Galaxies

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) have found 15 new examples of a rare type of object that may yield valuable clues about how radio-emitting galaxies and their environments evolve in their early stages of development. The objects, called compact symmetric objects (CSOs), are small, young versions of the supermassive black hole-powered "engines" that propel fast-moving jets of material outward from radio galaxies. Following up on a large-scale VLBA survey done in 2006, the scientists made more-detailed observations of objects they identified as possible CSOs. Of 103 such candidates, they confirmed 24, 15 of which are newly identified as CSOs. Using McDonald Observatory's Hobby-Eberly Telescope, they determined distances to some of the objects, which allowed them to measure the objects' sizes. "This doubles the number of these objects known," said Steven Tremblay, of Curtin University in Australia. Enlarging the sample of known CSOs, the astronomers said, can be a big help to understanding radio galaxies in general. With sizes as small as 5 light-years across, and ages from only 20 to 2,000 years, CSOs represent an important early stage in the development of the much larger and older radio-emitting galaxies. Even at this early stage, the scientists said the CSOs in their sample show a distinction between higher-powered and lower-powered objects that also typifies older radio galaxies. "Understanding these young objects is vital to understanding their larger cousins," said Greg Taylor, of the University of New Mexico. The astronomers are reporting their results in the Monthly Notices of the Royal Astronomical Society.

Reference: "Compact Symmetric Objects and Supermassive Binary Black Holes in the VLBA Imaging and Polarimetry Survey," Tremblay et al.; Monthly Notices of the Royal Astronomical Society, May 2016. Preprint: http://arxiv.org/abs/1603.03094

3. Innovation from NRAO Engineer Yields New Patent

Galen Watts, an engineer at the National Radio Astronomy Observatory's Green Bank Microwave Electronics Group, received a patent (U.S. Patent Number: 9,343,815) for a surface treatment application for radiometers that aids in their self-calibration. Radiometers are devices that measure the actual energy of microwaves and other forms of electromagnetic radiation. Radio astronomers and other researchers use microwave radiometry to discover the molecular and atomic composition as well as the temperature of many objects on Earth and even the most distant celestial objects. They do this by examining the content of these objects’ naturally emitted microwave signals. To make accurate readings, however, a radiometer has to be properly calibrated. The new surface treatment application, developed by Watts, aids in radiometer self-calibration by reflecting an image of the feed horn back onto itself in a manner that doesn't set up standing waves. Similar applications could also be useful for reducing antenna side-lobes (extraneous readings in radio astronomy), reducing radar cross-sections of objects, and eliminating resonances from stray reflections in quasi-optical component assemblies.

4. NRAO Engineers Receive IEEE Antenna and Propagation Society Award

NRAO engineers Mathew A. Morgan and Tod A. Boyd have been awarded jointly the 2015 IEEE Antenna and Propagation Society Harold A. Wheeler Applications Prize Paper Award, which is presented to the authors of the best applications paper published in the IEEE Transactions on Antennas and Propagation during the previous year. Their paper, "A 10-100 GHz Double-Ridged Horn Antenna and Coax Launcher," was published in August 2015 and reports on the development of a novel radio antenna. It is described as an ultra-wideband, double-ridged horn antenna with a bandwidth that covers a ten-fold range in frequencies. This is believed to be the first such decade-bandwidth horn in the millimeter-wave frequency range, covering -- in this case -- 10-100 GHz. Such horns can be used for test and measurement applications, including material characterization. It was originally designed as a scale model for an even higher-frequency horn covering 100 GHz - 1 THz. For this award, they will each receive a certificate and share in the $1,000 honorarium. The award will be presented at the IEEE APS/URSI Symposium Awards Ceremony, June 29, 2016, in Fajardo, Puerto Rico.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of South Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.

Contacts:

Charles Blue, Public Information Officer
(434) 296-0314; cblue@nrao.edu

Dave Finley, Public Information Officer
(575) 835-7302; dfinley@nrao.edu


Jupiter blasted by 6.5 fireball impacts per year on average Further information

March 17th fireball captured by Gerrit Kernbauer and John McKeon
Image processed by Sebastian Voltmer
Credit: G. Kernbauer, J. McKeon, S. Voltmer

Animation of 17th March impact observed by John McKeon
Credit: J McKeon


Jupiter is hit by an average of 6.5 objects per year that create impacts large enough to be visible from Earth, according to preliminary results from a worldwide campaign by amateur astronomers to observe the giant planet.  The estimate was presented at an international workshop on Jupiter for professional and amateur astronomers organised by Europlanet 2020 Research Infrastructure at the Observatoire de la Côte d’Azur in Nice, France.

Meteors impacting Jupiter’s upper atmosphere can create spectacular fireballs, such as the one observed by amateur astronomers Gerrit Kernbauer and John McKeon on 17th March 2016. This was the fourth in a series of fireballs in Jupiter observed serendipitously by amateur astronomers since June 2010. Groups of amateurs worldwide have coordinated efforts to obtain improved estimates of the number of small bodies around Jupiter and how they interact with the planet.

Marc Delcroix, who coordinates a 60-strong group of amateur astronomers worldwide said, “Dramatic impacts with Jupiter can be captured with standard amateur equipment and analysed with easy-to-use software.  But to get a good estimate of how often these events occur, we need observers around the world who are willing to collaborate to create a programme of more-or-less continuous monitoring of Jupiter.  It takes time and commitment – observations of no impacts are just as important as detecting a fireball.  In 3 years since our programme started, amateur contributors from Europe, the US and Australia have analysed the equivalent of more than 56 days of videos – around 53 000 videos — without discovering an impact. 

This is a result in itself and, together with the reports of amateur astronomer John McKeon, has helped us come up with our preliminary estimate which slightly reduces previous estimates of the flux of impacting objects in Jupiter. We are now working to further enhance our software to improve its usability, while maintaining its simplicity and efficiency, to reach an even wider participation by amateurs. This should help in refining the impact estimations for Jupiter, and hopefully discover new impacts.”

Isshi Tabe and Dr Jun-ichi Watanabe, of the Association of Lunar and Planetary Observers (ALPO) in Japan, set up the Find Flash project following the observation of an impact flash by four Japanese amateur astronomers on 20th August 2010.

Tabe explained, “We recognised the importance of impact flashes for estimating the number of small bodies around Jupiter. We have perhaps more than 50 Japanese amateur astronomers in our association who take video images almost every night. We also have around 10 nights per year observation time on bigger telescopes in public and professional observatories, which allows us to employ a narrow band methane filter to detect fireballs in Jupiter’s upper atmosphere more efficiently. We’ve carried out the observational campaign for three years, but unfortunately we have never yet detected any impact flashes. We expect to have an increasing of number of observations over the next few years and to get valuable data both from bigger and smaller telescopes. However, in northern hemisphere of Earth, especially in Japan, we can only get consistently good observational conditions in summer, so it is important that we work together with other amateur groups around the world to get more data.”

John McKeon, who observed the St Patrick’s Day impact said, “Collaboration is extremely important in the amateur astronomer community. On March 28th I became aware that an amateur astronomer in Austria, Gerrit Kernbauer, had discovered a possible impact on Jupiter on March 17th. I remembered I had been filming Jupiter around the same time, with the intention of illustrating a double moon transit of the planet. I’d filmed a total of 207 short 55 second movies of the planet over a period of about 3 and half hours and had processed them to create a time-lapse animation. When I checked back through my videos, I found the impact in the second last video I had taken. This secondary observation helped to confirm the impact event. Having a hand in this discovery, and the input and support from other amateurs in the analysis of the event, has changed and improved my imaging process for the future.”

“The new estimate of 6.5 impacts a year of comparable size objects lies at the bottom part of our previous estimate of impacts in Jupiter,” said Ricardo Hueso of the University of the Basque Country and chair of the workshop’s scientific organising committee. “Constraining this number is important to improve our expectancies of observing large impacts in the planet, such as the Shoemaker-Levy impact in 1996 and the 2009 impact. Unfortunately, we are still dealing with the statistics of a very few number of impacts detected, but plans to improve our detection methods and perform systematic searches will help us to detect more of these objects. That will allow us to know more about the current architecture of the outer Solar System and the role of Jupiter in protecting the Earth from comparable impacts.”


Further information



Science contacts

Isshi Tabe
tabe@libra-co.com

Marc Delcroix
delcroix.marc@free.fr

John Mckeon
john.mckeon@gmail.com

Prof Ricardo Hueso Alonso
Escuela Técnica Superior de Ingeniería
Universidad del País Vasco/Euskal Herriko Unibertsitatea
Bilbao
+ 34 94601 4262

ricardo.hueso@ehu.es


Media contact

Anita Heward
Europlanet Media Centre
Tel: +44 7756 034243

anita.heward@europlanet-eu.org

Source: Europlanet




About Europlanet

Since 2005, Europlanet has provided Europe’s planetary science community with a platform to exchange ideas and personnel, share research tools, data and facilities, define key science goals for the future, and engage stakeholders, policy makers and European citizens with planetary science.

The Europlanet 2020 Research Infrastructure (RI) has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208 to provide access to state-of-the-art research facilities across the European Research Area and a mechanism to coordinate Europe’s planetary science community. The project builds on a €2 million Framework 6 Coordination Action and €6 million Framework 7 Research Infrastructure funded by the European Commission.  The Europlanet collegial organisation, linked by a Memorandum of Understanding (MoU), has a membership of over 70 research institutes and companies.

Europlanet project website: www.europlanet-2020-ri.eu
Europlanet outreach website: www.europlanet-eu.org
Follow on Twitter via @europlanetmedia

Tuesday, May 17, 2016

Kepler-223 System: Clues to Planetary Migration

These animations show approximately 200,000 years of orbital evolution in the Kepler-223 planetary system. The planets’ interactions with the disk of gas and dust in which they formed caused their orbits to shrink toward their star over time at differing rates.YouTube version

Sean Mills (left) and Daniel Fabrycky (right), researchers at the University of Chicago, describe the complex orbital structure of the Kepler-223 system in a new study. Credits: Nancy Wong/University of Chicago


The four planets of the Kepler-223 star system appeared to have little in common with the planets of our own solar system today. But a new study using data from NASA's Kepler space telescope suggests a possible commonality in the distant past. The Kepler-223 planets orbit their star in the same configuration that Jupiter, Saturn, Uranus and Neptune may have had in the early history of our solar system, before migrating to their current locations.

"Exactly how and where planets form is an outstanding question in planetary science," said the study's lead author, Sean Mills, a graduate student in astronomy and astrophysics at the University of Chicago in Illinois. "Our work essentially tests a model for planet formation for a type of planet we don't have in our solar system."

The puffy, gaseous planets orbiting Kepler-223, all of which are far more massive than Earth, orbit close to their star. "That's why there's a big debate about how they formed, how they got there and why don't we have an analogous planet in our solar system," Mills said.

Mills and his collaborators used data from Kepler -- its mission is now known as K2 -- to analyze how the four planets block their stars' light and change each other's orbits. This information also gave researchers the planets' sizes and masses. The team performed numerical simulations of planetary migration that generate this system's current architecture, similar to the migration suspected for the solar system's gas giants. These calculations are described in the May 11 Advance Online edition of Nature.

The orbital configuration of our own solar system seems to have evolved since its birth 4.6 billion years ago. The four known planets of the much older Kepler-223 system, however, have maintained a single orbital configuration for far longer.

Astronomers call the planets of Kepler-223 "sub-Neptunes." They likely consist of a solid core and an envelope of gas, and they orbit their star in periods ranging from only seven to 19 days. They are the most common type of planets known in the galaxy, even though there is nothing quite like them around our sun.

Kepler-223's planets also are in resonance, meaning their gravitational influence on each other creates a periodic relationship between their orbits. Planets are in resonance when, for example, every time one of them orbits its sun once, the next one goes around twice. Three of Jupiter's largest moons, where the phenomenon was discovered, display resonances. Kepler-223 is the first time that four planets in an extrasolar system have been confirmed to be in resonance.

"This is the most extreme example of this phenomenon," said study co-author Daniel Fabrycky, an assistant professor of astronomy and astrophysics at the University of Chicago.


Formation scenarios

The Kepler-223 system provides alternative scenarios for how planets form and migrate in a planetary system that is different from our own, said study co-author Howard Isaacson, a research astronomer at the University of California, Berkeley, and member of the California Planet Search Team.

"Data from Kepler and the Keck Telescope were absolutely critical in this regard," Isaacson said. Thanks to observations of Kepler-223 and other exoplanetary systems, "We now know of systems that are unlike our sun's solar system, with hot Jupiters, planets closer than Mercury or in between the size of Earth and Neptune, none of which we see in our solar system. Other types of planets are very common."

Some stages of planet formation can involve violent processes. But during other stages, planets can evolve from gaseous disks in a smooth, gentle way, which is probably what the sub-Neptune planets of Kepler-223 did, Mills said.

"We think that two planets migrate through this disk, get stuck and then keep migrating together; find a third planet, get stuck, migrate together; find a fourth planet and get stuck," Mills explained.

That process differs completely from the one that scientists believe led to the formation of Mercury, Venus, Earth and Mars, which likely formed in their current orbital locations.

Earth formed from Mars-sized or moon-sized bodies smacking together, Mills said, in a violent and chaotic process. When planets form this way, their final orbital periods are not near a resonance.


Substantial movement

But scientists suspect that the solar system's larger, more distant planets of today -- Jupiter, Saturn, Uranus and Neptune -- moved around substantially during their formation. They may have been knocked out of resonances that once resembled those of Kepler-223, possibly after interacting with numerous asteroids and small planets (planetesimals).

"These resonances are extremely fragile," Fabrycky said. "If bodies were flying around and hitting each other, then they would have dislodged the planets from the resonance." But Kepler-223's planets somehow managed to dodge this scattering of cosmic bodies.

NASA's Ames Research Center in Moffett Field, California, manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.


For more information about the Kepler and K2 missions, visit:  http://www.nasa.gov/kepler
 

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425

elizabeth.landau@jpl.nasa.gov

Michele Johnson
NASA Ames Research Center, Moffett Field, Calif.
650-604-6982

michele.johnson@nasa.gov

Written by Steve Koppes
University of Chicago
773-702-8366

skoppes@uchicago.edu

Editor: Tony Greicius



Monday, May 16, 2016

Did Star Formation Regulation Change as the Universe Evolve?

An international team led by scientists at the Subaru Telescope and Eidgenössische Technische Hochschule (ETH) Zürich in Switzerland used the W. M. Keck Observatory (Note 1) to study the role of star formation rates in metal contents of distant galaxies. What they discovered is that the amount of metals is very similar irrespective of galaxies' star formation activity, raising new questions about star-forming theory. Their findings were published in the Astrophysical Journal this week.

Using the Keck I telescope – one of the two world's largest optical and infrared telescopes at Keck Observatory – equipped with the MOSFIRE (Note 2) instrument, the scientists gathered data on 41 normal, star-forming galaxies found in the Universe 11 billion years from today (Figure 1).

Figure 1: A galaxy observed in this study (surrounded by a blue rectangle). The light we received from the galaxy in the distant Universe tells us - from hydrogen, oxygen, and neon emission lines - that they followed a different rule to produce the heavy elements. (Credit: 3D-HST / NASA / ESA / STScI)


The team found typical galaxies forming stars in the Universe 2 billion years after the Big Bang have only twenty percent of metals (elements heavier than Helium) compared with those in the present day Universe. They also discovered the metal content is independent of the strength of the star-formation activity – in stark contrast with what is known for recently formed, or nearby galaxies (Figure 2). 

"The galaxies we studied are very faint because they are so far away that light needs more than 11 billion years to reach us," said Masato Onodera, the lead author of the paper. "Therefore, the superb light-gathering ability of the 10 meter Keck Observatory telescope was crucial to accomplish this study." He led the study while he was at ETH Zürich and hence moved to the Subaru Telescope.

Gathering the photons is only part of the job; breaking it down into data that could be analyzed by the team was the job of Keck Observatory's latest instrument, MOSFIRE.

"MOSFIRE allowed us to observe multiple objects simultaneously with an exquisite sensitivity, enabling us to collect spectra of many galaxies very efficiently," he said. "We saw number of spectral features emitted by ionized atoms in the galaxies such as hydrogen, oxygen, and neon, which allowed us to determine the metal content of the galaxies."

In addition to the telescope time awarded to them through the California Institute of Technology, the team utilized time exchange program between the 8.2-meter Subaru Telescope and the telescopes of Keck Observatory to complete the research.

Metal content in star-forming galaxies is the result of a complex interplay between gas coming into the galaxy, star formation in the galaxy, and gas outflowing from the galaxy in the cosmological context. How much metal is in the system and whether the correlation between the metal content and star formation activity exists provide important clues how galaxy evolve in a distant Universe.

Figure 2: A diagram showing the star formation rate (SFR) of distant galaxies (11 billion years ago) and today's galaxies (present) versus their metallicity. The former does not show any distinction in the metallicities with respect to the SFRs, while the latter is divided into two distinct metal contents according to their SFRs. Horizontal axis is the weight of the galaxy in the unit of solar mass. (Credit: NAOJ)


"If you extrapolate what is known in the local Universe, you would have expected a higher metallicity in less active star-forming galaxies than they found," said Hien Tran, staff astronomer at Keck Observatory who was not part of the finding. "It's part of the normal stellar and galaxy evolution. Onodera's team realized the role of star formation is not as strong at great distances as it is at zero distance. Understanding the interplay between metallicity, star formation rates and the mass of star forming galaxies will help us better understand galaxy evolution."

Because the team did not see any influence of the strength of star formation in the metal enrichment in distant galaxies, it is telling that the physical condition regulating star formation in galaxies in the early Universe is possibly different from that seen in the present-day Universe. This could be related to the fact that star formation rate cannot keep up with the gas accretion rate from the cosmic web.

The research paper appeared in May 1, 2016 issue of the on-line version of the Astrophysical Journal titled "ISM excitation and metallicity of star-forming galaxies at z~3.3 from near-IR spectroscopy" by Onodera, M., Carollo, C.M., Lilly, S., Renzini, A., Arimoto, N., Capak, P., Daddi, E., Scoville, N., Tacchella, S., Tatehora, S., and Zamorani, G.; doi:10.3847/0004-637X/822/1/42.
  

Notes
  1. The W. M. Keck Observatory operates the two, 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaiʻi, neighboring the Subaru Telescope.
  2. MOSFIRE (Multi-Object Spectrograph for Infrared Exploration) is a highly efficient instrument that can take images or up to 46 simultaneous spectra. A sensitive state-of-the-art detector and electronics system enables MOSFIRE to obtain observations of very faint objects.

  Research Team
  • M. Onodera: Institute for Astronomy, ETH Zürich, Switzerland and Subaru Telescope, USA
  • C. M. Carollo: Institute for Astronomy, ETH Zürich, Switzerland
  • S. Lilly: Institute for Astronomy, ETH Zürich, Switzerland
  • A. Renzini: INAF-Osservatorio Astronomico di Padova, Italy
  • N. Arimoto: Subaru Telescope, USA and SOKENDAI, Graduate University for Advanced Studies, Japan
  • P. Capak: Infrared Processing and Analysis Center (IPAC), USA and California Institute of Technology, USA
  • E. Daddi: CEA, Laboratoire AIM-CNRS-Universite Paris Diderot, France
  • N. Scoville: California Institute of Technology, USA
  • S. Tacchella: Institute for Astronomy, ETH Zürich, Switzerland
  • S. Tatehora: SOKENDAI, Graduate University for Advanced Studies, Japan
  • G. Zamorani: INAF-Osservatorio Astronomico di Bologna, Italy

Links
  • Preprint is available here.
  • Press release from ETH Zürich is here.
  • Press release from Keck Observatory is here.



Sunday, May 15, 2016

A Cosmic Hit and Run

Credit: ESO. Acknowledgements: Jean-Christophe Lambry

This Picture of the Week shows the Vela ring galaxy, visible as a bright core surrounded by a baby blue halo. As the name suggests, this ring galaxy — located in the southern constellation of Vela (The Sails) — is notable due to its compact core and large circular belt of gas and stars.

It is thought that ring galaxies like this are created when larger galaxies are punctured by a smaller galactic aggressor, which, passing through the heart of its more sizeable victim, triggers a shock wave that spreads outwards. This pushes gas to the galaxy’s periphery, where it begins to collapse and form new stars. The Vela ring galaxy is unusual in that it actually exhibits at least two rings, suggesting that the collision was not a recent one.

This picture also features a galaxy known as ESO 316-33, seen just above and to the left of the Vela ring galaxy, and a bright star known as HD 88170.

Source:  ESO/Images

Saturday, May 14, 2016

Helium’s Role in the Pulsation of Early White Dwarfs

Light curves (left) and Fourier amplitude spectra (right) for the three new pulsating low-mass white dwarfs. The red tick marks denote the significant frequencies which lie above the detection threshold of four times the average noise level. Hi-res image


Before low-medium mass stars become white dwarfs they pulsate wildly and eventually spew their outer layers into space – often forming beautiful planetary nebulae. The same stars are predicted to continue pulsating during their transformation to a white dwarf, if they have helium in their atmospheres. A team from the University of Oklahoma used Gemini North, in conjunction with the 1.5-meter FLWO telescope in Arizona, to observe a much-sought-after link between these pulsations and helium in the star’s atmospheres.

The researchers studied a trio of low mass white dwarf precursors, each with a mass less than one-third the mass of our Sun, and with pulsations ranging from approximately 5-10 minutes. According to team leader Dr. Alexandros Gianninas these observations appear to confirm the predictions of models based on non-adiabatic pulsation theory that predict the helium connection. 

“The nature of the observed pulsations matches almost perfectly with the predictions of our models,” said Gianninas. “Helium is the crucial ingredient that allows these stars to pulsate; models that don't include it don't predict pulsations. Our discovery represents the first concrete proof that these soon-to-be white dwarfs must still have helium at or near the surface.” The team plans to continue with additional observations to pinpoint the thickness of the hydrogen layer, and how it interacts with the helium, to better understand the dynamics of the oscillations. 

Dr. Alexandros Gianninas is a postdoctoral fellow at the University of Oklahoma and was assisted in this work by undergraduate student Brandon Curd, Professor Mukremin Kilic, Professor Gilles Fontaine at Université de Montréal and Dr. Warren Brown at the Smithsonian Astrophysical Observatory. 

The team’s results are published in The Astrophysical Journal Letters, 822, L27.


Paper Abstract: 


We report the discovery of pulsations in three mixed-atmosphere, extremely low-mass white dwarf (ELM WD, M ≤ 0.3 M⊙) precursors. Following the recent discoveries of pulsations in both ELM and pre-ELM WDs, we targeted pre-ELM WDs with mixed H/He atmospheres with high-speed photometry. We find significant optical variability in all three observed targets with periods in the range 320–590 s, consistent in timescale with theoretical predictions of p-mode pulsations in mixed-atmosphere ≈0.18 Me He-core pre-ELM WDs. This represents the first empirical evidence that pulsations in pre-ELM WDs can only occur if a significant amount of He is present in the atmosphere. Future, more extensive, timeseries photometry of the brightest of the three new pulsators offers an excellent opportunity to constrain the thickness of the surface H layer, which regulates the cooling timescales for ELM WDs.