Kepler

[bystander]

NASA's Kepler Spacecraft Takes Pulse of Distant Stars
NASA Ames Research Center | M10-91 | 26 Oct 2010

An international cadre of scientists that used data from NASA's Kepler spacecraft announced Tuesday the detection of stellar oscillations, or "starquakes,” that yield new insights about the size, age and evolution of stars.

The results were presented at a news conference at Aarhus University in Denmark by scientists representing the Kepler Asteroseismic Science Consortium (KASC). The team studied thousands of stars observed by Kepler, releasing what amounts to a roster of some of humanity's most well-characterized stars.

Analysis of stellar oscillations is similar to how seismologists study earthquakes to probe the Earth's interior. This branch of science, called astroseismology, produces measurements of stars the Kepler science team is anxious to have.
...
In the results presented Tuesday, one oscillating star took center stage: KIC 11026764 has the most accurately known properties of any star in the Kepler field. In fact, few stars in the universe are known to similar accuracy. At an age of 5.94 billion years, it has grown to a little over twice the diameter of the sun and will continue to do so as it transforms into a red giant. The oscillations reveal that this star is powered by hydrogen fusion in a thin shell around a helium-rich core.
...
KASC scientists also reported on the star RR Lyrae. It has been studied for more than 100 years as the first member of an important class of stars used to measure cosmological distances. The brightness, or light wave amplitude, of the star oscillates within a well-known period of about 13.5 hours. Yet during that period, other small cyclic changes in amplitude occur -- behavior known as the Blazhko effect.

The effect has puzzled astronomers for decades, but thanks to Kepler data, scientists may have a clue as to its origin. Kepler observations revealed an additional oscillation period that had never been previously detected. The oscillation occurs with a time scale twice as long as the 13.5-hour period. The Kepler data indicates the doubling is linked to the Blazhko effect.
...
For more information about the Kepler mission, visit: http://www.nasa.gov/kepler
For more information about the findings by the KASC scientists, visit: http://astro.phys.au.dk/KASC/

• Slides: The science panel's slide show (pdf)
• Text: Extended press release (pdf)
• AUDIO: Daniel Huber's Red Giant Oscillation Symphony (mp3)

NASA’s Kepler Mission changing how astronomers study distant stars
Iowa State University | 26 Oct 2010

The quantity and quality of data coming back from NASA's Kepler Mission is changing how astronomers study stars, said Iowa State University's Steve Kawaler.
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Kepler launched March 6, 2009, from Florida's Cape Canaveral Air Force Station. The spacecraft is orbiting the sun carrying a photometer, or light meter, to measure changes in star brightness. The photometer includes a telescope 37 inches in diameter connected to a 95 megapixel CCD camera. That instrument is continually pointed at the Cygnus-Lyra region of the Milky Way galaxy. Its primary job is to use tiny variations in the brightness of the stars within its view to find earth-like planets that might be able to support life.

The Kepler Asteroseismic Investigation is also using data from that photometer to study stars. The investigation is led by a four-member steering committee: Kawaler, Chair Ron Gilliland of the Space Telescope Science Institute based in Baltimore, Jorgen Christensen-Dalsgaard and Hans Kjeldsen, both of Aarhus University in Aarhus, Denmark.

And Kepler has already buried the star-studiers in data.
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Some of the data describe a binary star system - two stars held together by their gravity and orbiting a common center of mass. In this case, one star is a white dwarf, a star in the final stages of its life cycle; the other is a subdwarf B star, a star in an intermediate stage of development. Kepler not only returned information about the star system's velocity and mass, but also data providing a new demonstration of Einstein's Theory of Relativity.
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Kawaler said another Kepler advantage is its ability to collect data on a lot of stars. It is expected to continuously observe about 170,000 stars for at least three and a half years.

That gives researchers a much better idea about the average star, Kawaler said.
...
Kepler, for example, is giving researchers a better picture of red giant stars by more precisely measuring their oscillations or changes in brightness. Studies of those star quakes can answer questions about the interior properties of stars such as their density, temperature and composition. It's similar to how geologists study earthquakes to learn about the Earth's interior.

Our sun will evolve into a red giant in about five billion years. It will exhaust its hydrogen fuel, expand enormously and shine hundreds of times brighter than it does today. After that, it will be similar to the stars that Kawaler's group has been studying.

[neufer]

NASA's Kepler Spacecraft Takes Pulse of Distant Stars
NASA Ames Research Center | M10-91 | 26 Oct 2010

KASC scientists also reported on the star RR Lyrae. It has been studied for more than 100 years as the first member of an important class of stars used to measure cosmological distances. The brightness, or light wave amplitude, of the star oscillates within a well-known period of about 13.5 hours. Yet during that period, other small cyclic changes in amplitude occur -- behavior known as the Blazhko effect.

The effect has puzzled astronomers for decades, but thanks to Kepler data, scientists may have a clue as to its origin. Kepler observations revealed an additional oscillation period that had never been previously detected. The oscillation occurs with a time scale twice as long as the 13.5-hour period. The Kepler data indicates the doubling is linked to the Blazhko effect.

• AUDIO: Daniel Huber's Red Giant Oscillation Symphony (mp3)

<<The Blazhko effect, which is sometimes called long-period modulation, is a variation in period and amplitude in RR Lyrae type variable stars. It was first observed by Sergey Blazhko in 1907 in the star RW Dra. The cause of this effect is currently a matter of debate, with there being two primary hypotheses. The first, referred to as the resonance model, predicts that the cause of modulation is non-linear resonance in the star interior. The second, known as the magnetic model, assumes the variation to be caused by the magnetic field being inclined to the rotational axis, deforming the main radial mode.>>

[Ann]

In the results presented Tuesday, one oscillating star took center stage: KIC 11026764 has the most accurately known properties of any star in the Kepler field. In fact, few stars in the universe are known to similar accuracy. At an age of 5.94 billion years, it has grown to a little over twice the diameter of the sun and will continue to do so as it transforms into a red giant. The oscillations reveal that this star is powered by hydrogen fusion in a thin shell around a helium-rich core.

And there's no information on the star's color!! How am I to understand this star if I don't know what color it is?

Ann

[neufer]

In the results presented Tuesday, one oscillating star took center stage: KIC 11026764 has the most accurately known properties of any star in the Kepler field. In fact, few stars in the universe are known to similar accuracy. At an age of 5.94 billion years, it has grown to a little over twice the diameter of the sun and will continue to do so as it transforms into a red giant. The oscillations reveal that this star is powered by hydrogen fusion in a thin shell around a helium-rich core.

And there's no information on the star's color!! How am I to understand this star if I don't know what color it is?

Probably a deep orange or red Thermally Pulsing AGB (TP-AGB).

Evolution of stars of different masses are represented in the Hertzsprung-Russell diagram. The asymptotic giant branch is marked AGB in the case of a star of 2 solar masses.

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The AGB phase is divided into two parts, the early AGB (E-AGB) and the thermally pulsing AGB (TP-AGB). During the E-AGB phase the main source of energy is helium fusion in a shell around a core consisting mostly of carbon and oxygen. During this phase the star swells up to giant proportions to become a red giant again. The star's radius may become as large as one astronomical unit. After the helium shell runs out of fuel, the TP-AGB starts. Now the star derives its energy from fusion of hydrogen in a thin shell, inside of which lies the now inactive helium shell. However, over periods of 10,000 to 100,000 years, the helium shell switches on again, and the hydrogen shell switches off, a process known as a helium shell flash or thermal pulse. Due to these pulses, which only last a few thousand years, material from the core region is mixed into the outer layers, changing its composition, a process referred to as dredge-up. Because of this dredge-up, AGB stars may show S-process elements in their spectra. Subsequent dredge-ups can lead to the formation of Carbon stars.

AGB stars are typically long period variables, and suffer large mass loss in the form of a stellar wind. A star may lose 50 to 70% of its mass during the AGB phase.>>

<<A long period variable (LPV) is a type of variable star in which variations in brightness occur over long timescales of months or years. Long period variables are giant stars and brighter, from spectral class F and redwards, but most are red giants and AGB giants, meaning spectral class M, S or C. They are usually deep orange or red.

The following well defined variable star classes use to be counted into the LPV category:

* Mira variables, long rather regular pulsation periods in the range between 80 to 1000 days and grand light variations, from 2.5 magnitudes up to 11,
* semiregular variables, the periods in the same range as Miras, but lower amplitude and often irregularities that makes the period determination hard,
* slow irregular variables, stars similar to the semiregulars, but whose period cannot be determined, because of the irregularity of the light change.>>

[Ann]

Probably a deep orange or red Thermally Pulsing AGB (TP-AGB).

Probably not!

At an age of 5.94 billion years, it has grown to a little over twice the diameter of the sun and will continue to do so as it transforms into a red giant.

A star which is 5.94 billion years old and already begining to turn into a red giant was never a small red or deeply orange dwarf star to begin with. It was probably a star like the Sun or even a star slightly more massive and hotter than the Sun. But please note, too, that it has only swelled to a little more than twice the diameter of the Sun. That is not a lot for a red giant, and it will not give the star any sort of deep red color. Consider Pollux. This well-known star is, intrinsically, one of the lesser of the famous red giants in the sky. Its diameter is only about nine or ten the diameter of the Sun, which really isn't that much for a red giant, but it is still much, much larger than the star called KIC 11026764. Because of the puny red-giant diameter of Pollux, it is pale as red giants go: Its color index is about 0.99, which is less than Big Dipper red giant Dubhe (1.06) and still less than famous Arcturus (1.24). Pollux pales even more in comparison to red supergiants like Betelgeuse (whose color index in Johnson is given as 1.500 ± 0.510 - that's a huge margin of error!) or Antares (1.865 ± 0.014).

What about the Thermally Pulsing AGB stars? You quoted wikipedia and said:

The AGB phase is divided into two parts, the early AGB (E-AGB) and the thermally pulsing AGB (TP-AGB). During the E-AGB phase the main source of energy is helium fusion in a shell around a core consisting mostly of carbon and oxygen. During this phase the star swells up to giant proportions to become a red giant again. The star's radius may become as large as one astronomical unit. After the helium shell runs out of fuel, the TP-AGB starts. Now the star derives its energy from fusion of hydrogen in a thin shell, inside of which lies the now inactive helium shell.

It doesn't say how big the star is during its thermally pulsing stage, but I find it very hard to believe that it would shrink from a size close to an astronomical unit to a size just over twice the diameter of the Sun.

Mira is the most famous Long Period Variable in the sky. Interestingly, my software claims that Mira's color index is very pale and measly indeed: 0.966 ± 0.299. According to Professor emeritus Jim Kaler,

Mira, however, is so close that we can easily measure its angular radius, hence physical radius, which ranges from about 2 Astronomical Units (500 solar radii) at visual wavelengths to double that in the infrared, or from 20 percent bigger than the orbit of Mars to nearly half the size of the orbit of Jupiter. From a typical temperature (found from the angular size) of around 3000 Kelvin (other estimates going as low as 2000 Kelvin) and the radius itself, we find a luminosity of around 8500 times that of the Sun, close to that deduced from the visual brightness, distance, and an estimate of the huge amount of infrared radiation produced by the cool "surface." The star is approaching the last stages of its life. Long ago, the hydrogen fusion that powered its core ran out, and then the by-product of that fusion, helium, fused to carbon and oxygen, and now the helium has also run out. The result of these internal changes is a hugely distended, very luminous star.

Mira is huge. KIC 11026764, which is just a little more than twice the diameter of the Sun, is big but not huge. It has not swelled to a great size, and therefore it has probably not changed color dramatically. And given the fact that it was never red or orange to begin with (not during its main sequence phase), it will not have become orange or red now.

And that is precisly why I would so dearly love to know what color it is now! Who knows, maybe it is the color of Capella (0.795 ± 0.019). Ah, but Capella is so much bigger than KIC 11026764, since Capella consists of two stars with radii of 13.6 and 8.3 solar, versus only a bit more than twice solar for KIC 11026764.

The current size of KIC 11026764 makes it rather similar in size to Altair, whose diameter is 1.8 that of the Sun, although Altair is strikingly oblate. Anyway, Altair has a diameter similar to KIC 11026764 but a mass similar to Pollux: 1.7-1.8 solar for Altair versus about 1.8 solar for Pollux. All this makes me wonder if KIC 11026764 is in any way similar to Altair or Pollux. Probably not, because KIC 11026764 is probably not much more massive than the Sun.

In any case, KIC 11026764 is not a Thermally Pulsing AGB, not a Long Period Variable and not a deeply orange or red star! It might be the color of Capella, if I may venture a guess.

Ann

[Chris Peterson]

And there's no information on the star's color!! How am I to understand this star if I don't know what color it is?

Keep in mind that star color is a crude measurement at best, not intrinsically interesting but simply a limited means to understanding more important stellar properties. In this case, we have a G-type star that has had its properties measured much more rigorously than any color classification can provide, so it isn't surprising that the concept of "color" plays little role in this work, and isn't mentioned in the press release. Furthermore, the data was derived photometrically, not spectrometrically, so no color information is intrinsic to the primary measurements. That said, an accurate understanding of the metallicity of the star required obtaining ground based spectrometry, and the paper discusses the star's atmosphere and temperature (~5700 K).

[Ann]

The star's temperature is ~5700 K? That strongly suggests to me that it is very similar in color to the Sun, so it is definitely not orange or red.

Thanks, Chris. I think you confirmed my color assessment of this star. If anything, it is probably a little bit bluer than I would have guessed.

Ann

[Chris Peterson]

The star's temperature is ~5700 K? That strongly suggests to me that it is very similar in color to the Sun, so it is definitely not orange or red.

One key point of the study is examining sun-like stars, of which this is an example.

[bystander]

Kepler Mission Discovers Its First Rocky Planet
NASA JPL-Caltech Kepler | 2011 Jan 10

Artist concept: Kepler 10b shown in front of host star. [i](Credit: NASA)[/i]

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Artist concept of Kepler 10b. [i](Credit: NASA)[/i]

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NASA's Kepler mission confirmed the discovery of first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.

The discovery of this planet, called an exoplanet, is based on more than eight months of data collected by the spacecraft from May 2009 to early January 2010.

"All of Kepler's best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our sun," said Natalie Batalha, Kepler's deputy science team lead at NASA's Ames Research Center in Moffett Field, Calif., and primary author of a paper on the discovery accepted by the Astrophysical Journal. "The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it's beginning to pay off."

Kepler's ultra-precise photometer measures the tiny decrease in a star's brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star.

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet's surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.

Kepler-10 was the first star identified that could potentially harbor a small transiting planet, placing it at the top of the list for ground-based observations with the W.M. Keck Observatory 10-meter telescope in Hawaii. Scientists waiting for a signal to confirm Kepler-10b as a planet were not disappointed. Keck was able to measure tiny changes in the star's spectrum, called Doppler shifts, caused by the telltale tug exerted by the orbiting planet on the star.

"The discovery of Kepler 10-b is a significant milestone in the search for planets similar to our own," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Although this planet is not in the habitable zone, the exciting find showcases the kinds of discoveries made possible by the mission and the promise of many more to come."

Knowledge of the planet is only as good as the knowledge of the star it orbits. Because Kepler-10 is one of the brighter stars being targeted by Kepler, scientists were able to detect high-frequency variations in the star's brightness generated by stellar oscillations, or starquakes. This analysis allowed scientists to pin down Kepler-10b's properties.

There is a clear signal in the data arising from light waves that travel within the interior of the star. Kepler Asteroseismic Science Consortium scientists use the information to better understand the star, just as earthquakes are used to learn about Earth's interior structure. As a result of this analysis, Kepler-10 is one of the most well-characterized planet-hosting stars in the universe.

That's good news for the team studying Kepler-10b. Accurate stellar properties yield accurate planet properties. In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter -- similar to that of an iron dumbbell.

Big news: first “solid” exoplanet found!
Discover Blogs | Bad Astronomy | 2011 Jan 10

Space scope finds scorched super-Earth
Nature News | Space & Astronomy | 2011 Jan 10

[bystander]

Click to play embedded YouTube video.

[Céline Richard]

Thank you for both the article and the video
This is a very good news, although unfortunately, this planet is not habitable.
We couldn't live in a landscape covered with lava, we need some water...

Céline

[BMAONE23]

Just curious
I am wondering how many of these proposed exoplanets might actually be misinterpreted long lived sunspot activity.
A Sunspot the size of Jupiter that passes by on a star that is rotating every 4 or 5 days could resemble a planet with a 4 or 5 day orbit period.

[orin stepanek]

http://www.kepler.arc.nasa.gov/news/nas ... &NewsID=94
I can't imagine how hot it must be on this planet! How cold could the dark side be?

[orin stepanek]

http://www.nasa.gov/home/hqnews/2011/ja ... epler.html I'll be watching on TV.

[rstevenson]

I can't imagine how hot it must be on this planet! How cold could the dark side be?

From one of the pages at the Kepler site...

The daytime temperature’s expected to be more than 2,500 degrees Fahrenheit, hotter than lava flows here on Earth.

If the planet's day is the same length as its year, as you might expect for a planet that close to its star, the night side (the only side you'd want to touch down on) could be very cold indeed since there seems to be no atmosphere to transfer heat around to that side. But I expect that the planet itself is mighty warm all the way through. So your space suit would have to keep you warm except for the soles of your boots, where it will likely have to keep you cool. Interesting problem.

Rob

[orin stepanek]

http://www.kepler.arc.nasa.gov/news/nas ... &NewsID=98
Kepler's been busy!

[neufer]

[url=http://www.cartage.org.lb/en/themes/sciences/earthscience/Geology/Earthquakes/CauseofEarthquakes/EarthsInterior/EarthsInterior.htm]The center of the Earth ~ 8,000 degrees Fahrenheit[/url]

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The center of the Earth is 8,000ºF but that doesn't seem
to have melted much snow on the ground around here.

The subsolar point of Mercury reaches about 800ºF
during perihelion yet the floors of deep craters at
Mercury's poles remain below -276ºF

I can't imagine how hot it must be on this planet! How cold could the dark side be?

From one of the pages at the Kepler site...

The daytime temperature’s expected to be more than 2,500 degrees Fahrenheit, hotter than lava flows here on Earth.

If the planet's day is the same length as its year, as you might expect for a planet that close to its star, the night side (the only side you'd want to touch down on) could be very cold indeed since there seems to be no atmosphere to transfer heat around to that side. But I expect that the planet itself is mighty warm all the way through. So your space suit would have to keep you warm except for the soles of your boots, where it will likely have to keep you cool. Interesting problem.

[bystander]

http://www.kepler.arc.nasa.gov/news/nas ... &NewsID=98
Kepler's been busy!

http://asterisk.apod.com/vie ... 31&t=22814

[bystander]

Kepler gives astronomers a look inside red giant stars
Iowa State University | 2011 Mar 30

[attachment=0]NGC6791-800px.jpg[/attachment]

NASA's Kepler Mission is giving astronomers such a clear view of changes in star brightness that they can now see clues about what's happening inside red giant stars.

"No one anticipated seeing this before the mission launched," said Steve Kawaler, an Iowa State University professor of physics and astronomy and a leader of the Kepler Asteroseismic Investigation. "That we could see so clearly down below a red giant star's surface was unexpected."

The astronomers' preliminary findings are published in two papers in the journals Science and Nature.

Both papers describe how Kepler tracks tiny, regular changes in star brightness. Their regularity resembles steady drumbeats at different, precise rhythms. Each rhythm can be thought of as an individual tooth of a comb. Astronomers have studied those oscillations from ground-based telescopes to determine star basics such as mass and radius. But they noticed departures from the steady patterns in the Kepler data - "dandruff on the comb," Kawaler said.

These other patterns are caused by gravity mode oscillations. And those waves are allowing researchers to probe a star's core. The result, according to the Science paper, is information about the density and chemistry deep inside a star.

And, according to the Nature paper, the data also shows researchers whether a red giant star burns hydrogen in a shell surrounding the star or whether it has evolved to an age that it burns helium in the core. That's something astronomers hadn't been able to determine before Kepler.

"The stars burning helium in the core survived a helium flash," Kawaler said. "That transformation from stars burning a hydrogen shell is mysterious. We think it happens quickly and perhaps explosively. Now we can tell which stars have done that and which stars will do that."

That information will help astronomers better understand the life cycle of red giant stars. Our sun will evolve into a red giant in about 5 billion years.

Star Cluster NGC 6791 from Kepler First Light Image

Kepler-Detected Gravity-Mode Period Spacings in a Red Giant Star - PG Beck et al

• Science Brevia (Online 17 March 2011) DOI: 10.1126/science.1201939

Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars - TR Bedding et al

• Nature 471(7340) 608 (31 Mar 2011) DOI: 10.1038/nature09935

New Technique Separates the Modest Red Giants From the … Giant Red Giants
Universe Today | Anne Minard | 2011 Mar 30

Starquakes Reveal Pulse of Giant Stars
Space.com | Science and Astronomy | Charles Q Choi | 2011 Mar 30

[bystander]

Giant stars reveal inner secrets for the first time
University of Sidney | NASA ARC Kepler | 2011 Mar 30

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University of Sydney astrophysicists are behind a major breakthrough in the study of stars known as red giants, finding a way to peer deep into their cores to discover which ones are in early infancy, which are fresh-faced teenagers, and which are facing their dying days.

The discovery, published in the latest edition of the journal Nature and made possible by observations using NASA's powerful Kepler space telescope, is shedding new light on the evolution of stars, including our own sun.

The paper's lead author, the University of Sydney's Professor Tim Bedding, explains that "red giants are evolved stars that have exhausted the supply of hydrogen in their cores that powers nuclear fusion, and instead burn hydrogen in a surrounding shell. Towards the end of their lives, red giants begin burning the helium in their cores."

The Kepler space telescope has allowed Professor Bedding and colleagues to continuously study star light from hundreds of red giants at an unprecedented level of precision for nearly a year, giving a window into the stars' cores.

"The changes in brightness at a star's surface is a result of turbulent motions inside that cause continuous star-quakes, creating sound waves that travel down through the interior and back to the surface," Professor Bedding said.

"Under the right conditions, these waves interact with other waves trapped inside the star's helium core. It is these 'mixed' oscillation modes that are the key to understanding a star's particular life stage. By carefully measuring very subtle features of the oscillations in a star's brightness we can see that some stars have run out of hydrogen in the centre and are now burning helium, and therefore at a later stage of life."

Astronomer Travis Metcalfe of the US National Center for Atmospheric Research, in a companion piece in the same Nature issue which highlights the discovery's significance, compares red giants to Hollywood stars, whose age is not always obvious from the surface. "During certain phases in a star's life, its size and brightness are remarkably constant, even while profound transformations are taking place deep inside."

Professor Bedding and his colleagues work in an emerging field called asteroseismology. "In the same way that geologists use earthquakes to explore Earth's interior, we use star quakes to explore the internal structure of stars," he explained.

Professor Bedding said: "We are very excited about the results. We had some idea from theoretical models that these subtle oscillation patterns would be there, but this confirms our models. It allows us to tell red giants apart, and we will be able to compare the fraction of stars that are at the different stages of evolution in a way that we couldn't before."

Daniel Huber, a PhD student working with Professor Bedding, added: "This shows how wonderful the Kepler satellite really is. The main aim of the telescope was to find Earth-sized planets that could be habitable, but it has also provided us with a great opportunity to improve our understanding of stars."

[bystander]

Echoes from the depth of a red giant star
NASA ARC Kepler | 2011 Apr 07

Click to play embedded YouTube video.

Today an international team of astronomers reports the discovery of waves inside a star that travel so deep that they reach the core. The discovery was published in the renowned journal Science, and was possible thanks to precise measurements with the Kepler space telescope. Waves traversing stars, similar to sound waves here on Earth, were already known to exist, but up to now only waves in the outer part of the star were observed. They travel hundred thousands of kilometers deep, and at a certain depth the stellar material gets too dense to penetrate so that the waves bounce back to the surface. The team now unexpectedly found the signature of waves that run all the way to the center of the star.

Astronomers love this kind of waves, or stellar oscillations as they call them. Just like a doctor listens to the sound of your heart to make a diagnosis, or like seismologists use earthquakes on Earth to probe the inside of our planet, the scientific discipline of asteroseismology studies stellar oscillations to draw a detailed picture of stellar interiors. The detection of waves that are able to “sense” the conditions in the core of a star opens a window to an inferno which otherwise would remain unreachable and hidden.

The discovery was made in a red giant star. These are elderly stars which our Sun will become in about 5 billion years. By that time our Sun will have inflated more than 10 times its current size, and will be about 50 times brighter. At the same time its color will have changed from yellowish to reddish, hence their name.

“Having a view into the core of these red giants will teach us exactly what will happen to our Sun when it grows older.”, says Paul Beck, a PhD student at Leuven university in Belgium. Paul is one of the many young researchers that are given the opportunity to work with Kepler data. He, Tim Bedding of The University of Sydney, and Marc-Antoine Dupret from the University of Liège were the first to notice that some oscillations seemed to behave differently, “out of key”. After comparing the observations with theoretical models, they soon realized that they were looking at waves that feel the conditions in the heart of the star.

At the star's surface the oscillations manifest themselves as patches where the temperature changes slightly, more or less periodically over time. Overall, this causes tiny variations in the brightness the star, and after the light traveled for hundreds of years through empty space these changes are now carefully recorded by NASA's space telescope Kepler.

The team that made the discovery is part of KASC, the Kepler Asteroseismic Science Consortium, currently one of the largest consortia in astronomy, consisting of more than 440 astronomers specialized in probing stellar interiors. Its headquarters are located in Aarhus, Denmark. “Astronomers of all over the world are taking part in this huge effort to exploit Kepler data to better understand the interiors of stars”, says Hans Kjeldsen of Aarhus university, the coordinator of KASC. “The measurements provided by Kepler are so incredibly precise that we see things we never saw before. It's like traveling in a whole new world.”

The spacecraft is expected to operate for at least another 2 years, and will continue to measure the same stars, making the datasets better every day. For sure to be continued.

[bystander]

Kepler Listens to an Orchestra of Solar-Type Stars
NASA ARC Kepler | 2011 Apr 07

An international team of asteroseismologists, led by the University of Birmingham, has used data from the NASA Kepler Mission to sample the ‘stellar music’ of 500 stars similar to the Sun, according to research published today (8 April 2011) in the journal Science. The team used the information from these natural resonances, which is coded in pulses of starlight, to measure the properties of these stars and will now be able to compare their findings with predictions based on models of the Milky Way galaxy.

The Kepler spacecraft is monitoring the brightness of more than 150,000 stars in the galaxy. Its data are being used to search for planets and also to monitor the natural oscillations of the stars, the field of asteroseismology. The oscillations lead to miniscule changes or pulses in brightness, and are caused by sound trapped inside the stars.

Dr Bill Chaplin from the University of Birmingham’s School of Physics and Astronomy, who leads the international collaboration, said, ‘The sound inside the stars makes them ring or vibrate like musical instruments. If you measure the pitch of the notes produced by an instrument it can tell you how big the instrument is. The bigger the instrument is, the lower the pitch and deeper the sound. This is how we can tell how big a star is - from its stellar music’.

He continued, ‘Thanks to the Kepler Mission we can measure and weigh the stars and look at the range of sizes and masses. Previously astronomers have predicted the population of stars in the Milky Way by creating computer models of the stars and planets. It has been difficult to verify aspects of these models in great detail due to lack of data and levels of precision. We now have the tools to be able test and interrogate the models in much more detail than we could before, to build an accurate picture of star populations in our galaxy.’

The team, which is part of one of the biggest international collaboration in astronomy, the Kepler Asteroseismology Science Consortium (KASC), found 500 stars that ring like the Sun. Dr Hans Kjeldsen from Aarhus, who coordinates KASC, said ‘Before Kepler we had asteroseismic data on only about 20 such stars. We now have an orchestra of stars to play with, and this opens up huge possibilities for probing stellar evolution and obtaining a clearer picture of the past and future of our own Sun and how our galaxy, and others like it, has evolved over time. We can, for example, pick out stars that weigh the same as the Sun but have different ages, to, in effect, follow the Sun in time...’

Ensemble Asteroseismology of Solar-Type Stars with the NASA Kepler Mission - WJ Chaplin et al

• Science 332(6026) 213 (08 Apr 2011) DOI: 10.1126/science.1201827

NASA’s Kepler helps Iowa State’s Kawaler, astronomers update census of sun-like stars
Iowa State University | Mike Krapfl | 2011 Apr 07

NASA's Kepler Mission has detected changes in brightness in 500 sun-like stars, giving astronomers a much better idea about the nature and evolution of the stars.

Prior to Kepler's launch in March 2009, astronomers had identified the changes in brightness, or oscillations, of about 25 stars similar to our sun in size, age, composition and location within the Milky Way galaxy.

The discoveries are reported in a paper, "Ensemble Asteroseismology of Solar-Type Stars with the NASA Kepler Mission," in the April 8 issue of the journal Science. The lead author of the paper is Bill Chaplin of the University of Birmingham in the United Kingdom.

The paper says Kepler is a big boost to asteroseismology, the study of stars by observations of their natural oscillations. Those oscillations provide clues about star basics such as mass, radius and age as well as clues about the internal structure of stars.

"This helps us understand more about the formation of stars and how they evolve," said Steve Kawaler, an Iowa State University professor of physics and astronomy, a co-author of the paper and a leader of the Kepler Asteroseismic Investigation. "These new observations allow us to measure the detailed properties of stars at an accuracy that wasn't possible before."

The Kepler spacecraft is orbiting the sun carrying a photometer, or light meter, to measure changes in star brightness. The photometer includes a telescope 37 inches in diameter connected to a 95 megapixel CCD camera. The instrument is continually pointed at the Cygnus-Lyra region of the Milky Way. It is expected to continuously observe about 170,000 stars for at least three and a half years.

Kepler's primary job is to use tiny variations in the brightness of the stars within its view to find earth-like planets that might be able to support life.

The Kepler Asteroseismic Investigation is using Kepler data to study different kinds of stars. The investigation is led by a four-member steering committee: Kawaler, Chair Ron Gilliland of the Space Telescope Science Institute based in Baltimore, Jorgen Christensen-Dalsgaard and Hans Kjeldsen, both of Aarhus University in Denmark.

Kepler has provided astronomers with so much new information, the Science paper says they're "entering a golden era for stellar physics."

Data from 500 sun-like stars gives astronomers a much better understanding of the stars, their properties and their evolution. It also gives astronomers data to test their theories, models and predictions about the stars and the galaxy. And it gives astronomers enough data to make meaningful statistical studies of the stars.

"But this is just the start of things," Kawaler said. "This is a first broad-brush analysis of the data we've seen. This is a preview of this new tool and the kind of detailed census that we'll be able to do."

Among the projects to come, according to the Science paper, are studies to determine the ages of all these sun-like stars and studies of the host stars of the earth-like planets discovered by Kepler.

[bystander]

Kepler discovery of a unique triply eclipsing triple star
NASA ARC Kepler | 2011 Apr 07

[attachment=0]HD181068_1024.jpg[/attachment][/i]

Click to play embedded YouTube video.

Animation of HD181068 system and light curve

While the quest for Earth-like planets around other stars using the NASA's Kepler space telescope has recently produced many exciting discoveries, other branches of stellar astrophysics also benefit from the ultraprecise space photometry offered by the revolutionary Kepler satellite. An international group of European, Australian and American researchers report on the discovery of a unique stellar system in a paper accepted for publication in the Science magazine. The object, catalogued as HD 181068 and known as Trinity' within the authorship team, is a 7th magnitude star that is almost visible to the naked eye, and the seemingly single star is in reality a complex triple system in which three stars reside in a very special geometry, showing mutual eclipses as each of the stars gets behind or in front of the others. The most luminous object is a red giant star around which a close pair of two red dwarfs orbits with a period of 45,5 days.

"Thanks to the fortunate viewing angle from Earth, the combined light from the three stars change very characteristically: there are sharp brightness decreases with a period of 0.9 days produced by the mutual eclipses of the close pair of dwarfs, while it takes 2 days for the close pair to pass in front of or behind the red giant" - says Aliz Derekas (Eotvos University and Konkoly Observatory, Budapest, Hungary), the lead author of the paper. A mind-boggling feature of the variations is that when the red dwarfs are in front of the red giant, their short-period eclipses disappear. This is because the surface brightnesses of the three stars are actually very similar, and just as a white rabbit cannot be seen in snow-fall, the red dwarfs in front of the red giant are also almost invisible, hence no light is lost when they eclipse each other.

The authors discovered this interesting system in June 2010 and consequently took ground-based observations. "The spectroscopic measurements revealed the periodic motion of the largest star in the system with the wide orbital period of 45,5 days. The 2-day long eclipses are so similar at first sight that we thought that the outer orbital period is 22.7 days. Only after having obtained the whole radial velocity curve, we realised the tiny differences in the long period minima and that the real period was the double of it.'- says Laszlo Kiss (Konkoly Observatory), the second author of the discovery paper. Further observations using interferometry were used to measure the angular size of the red giant. "Combining the angular diameter with the known distance of the system we were able to measure the absolute radius of the red giant, which was a great achievement given its large distance of 800 light years" - adds Daniel Huber (University of Sydney, Australia), who led the interferometric observations using the Center for High-Angular Resolution Astronomy (CHARA) at Mount Wilson Observatory in California, USA. The results show that the largest star in the system is 12.4 times larger than our Sun. The scientists could also estimate the mass of the main component as 3 times that of the Sun.

The discovery of this complex system is significant because HD 181068 is a real astrophysical labaratory where changes in the orbital elements, unlike in the usual cases in astronomy, can be detected in a few years from now, i.e. we can compare theoretical predictions and observed changes on human timescale. In addition, HD 181068 has further peculiar features. Careful analyses of red giant stars observed by Kepler have shown that all red giant stars should exhibit oscillations similar to those in the Sun. The frequency of these oscillations can be theoretically determined knowing the basic physical paremeters of the red giant (mass, temperature, radius). However, there is no sign of such oscillations in the red giant component of HD 181068 which means there must be a mysterious mechanism that suppresses the pulsation. "Surprisingly, we do detect some variability but with periods that are closely linked to the orbital period of the close pair in the system" - told Dr. Derekas. This may indicate that tidal forces of the close pair induce vibes in the surface of the red giant.

The intriguing nature of this unique system remained unnoticed until now despite its brightness. We really needed Kepler with its unprecedentedly precise and uninterrupted photometric monitoring to uncover such a rare gem - she added.

HD 181068: A Red Giant in a Triply Eclipsing Compact Hierarchical Triple System - A Derekas et al

• Science 332(6026) 216 (08 Apr 2011) DOI: 10.1126/science.1201762

Astronomers discover Kepler's trinity
University of Sidney | Allison Muir | 2011 Apr 08

NASA's revolutionary Kepler satellite has discovered a unique triply eclipsing triple star, reports an international team of astronomers.

The group's discovery of a unique stellar system was published in today's Science magazine.

The object, catalogued as HD 181068 and nicknamed `Trinity' by the research team, and is a seventh magnitude star that is almost visible to the naked eye.

University of Sydney astronomer Daniel Huber from the School of Physics says: "We found what was a seemingly single star is in reality a complex triple system in which three stars reside in a very special geometry.

The observations we have show mutual eclipses as each of the stars gets behind or in front of the others. The most luminous object is a red giant star around which a close pair of two red dwarfs orbits with a period of 45.5 days."

Lead author on the paper Aliz Derekas from the Eotvos University and Konkoly observatory, Budapest, Hungary says: "Thanks to the fortunate viewing angle from Earth, the combined light from the three stars change very characteristically. There are sharp brightness decreases with a period of 0.9 days produced by the mutual eclipses of the close pair of dwarfs, while it takes two days for the close pair to pass in front of or behind the red giant.

"A mind-boggling feature of the variations is that when the red dwarfs are in front of the red giant, their short-period eclipses disappear.

This is because the surface brightness of the three stars are actually very similar, and just as a white rabbit cannot be seen in snow-fall, the red dwarfs in front of the red giant are also almost invisible, hence no light is lost when they eclipse each other."

Huber who led the interferometric observations using the Center for High-Angular Resolution Astronomy (CHARA) at Mount Wilson Observatory in California, USA says further observations using interferometry were used to measure the angular size of the red giant.

"Combining the angular diameter with the known distance of the system we were able to measure the absolute radius of the red giant, which was a great achievement given its large distance of 800 light years," states Huber.

The results show that the largest star in the system is 12.4 times larger than our Sun. The scientists could also estimate the mass of the main component as 3 times that of the Sun.

The discovery of this complex system is significant because HD 181068 is a real astrophysical labaratory where changes in the orbital elements can be detected in a few years from now.

In addition, HD 181068 has further peculiar features. Careful analyses of other red giant stars observed by Kepler have shown that all red giant stars should exhibit oscillations similar to those in the Sun.

"The frequency of these oscillations can be theoretically determined knowing the basic physical parameters of the red giant, their mass, temperature, and radius.

"However, there is no sign of such oscillations in the red giant component of HD 181068 which means there must be a mysterious mechanism that suppresses the pulsation.

"Surprisingly, we do detect some variability but with periods that are closely linked to the orbital period of the close pair in the system," states Dr Derekas. This may indicate that tidal forces of the close pair induce vibes in the surface of the red giant.

[orin stepanek]

Kepler is still finding more candidates. Latest! http://www.kepler.arc.nasa.gov/news/ind ... NewsID=128

Click to view full size image

[orin stepanek]

kepler discovers inviible world! http://www.kepler.arc.nasa.gov/news/nas ... NewsID=148

Click to view full size image

What does Kepler-19c look like? We don't know—we have have very few clues. “Kepler-19c has multiple personalities consistent with our data. For instance, it could be a rocky planet on a circular 5-day orbit, or a gas-giant planet on an oblong 100-day orbit,” said co-author Daniel Fabrycky of the University of California, Santa Cruz (UCSC). This a depiction of the Kepler-19 system by artist David Aguilar..