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28 new planets, 7 new brown dwarfs reported by California, Carnegie team

Public release date: 28-May-2007
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley

Honolulu, Hawaii – The world's largest and most prolific team of planet hunters announced today (Monday, May 28) the discovery of 28 new planets outside our solar system, increasing to 236 the total number of known exoplanets.

University of California, Berkeley, post-doctoral fellow Jason T. Wright and newly minted Ph.D. John Asher Johnson reported the new exoplanets at a noon media briefing at the semi-annual meeting of the American Astronomical Society (AAS) in Honolulu. The findings are a result of the combined work of the California and Carnegie Planet Search team and the Anglo-Australian Planet Search team.

The planets are among 37 new objects – all of them orbiting a star, but smaller than a star –discovered by the teams within the past year. Seven of the 37 are confirmed brown dwarfs, which are failed stars that are nevertheless much more massive than the largest, Jupiter-sized planets. Two others are borderline and could be either large, gas giant planets or small brown dwarfs.

Wright said the research teams have become much more sophisticated in their analyses and are able to detect smaller planets as well as planets farther from their parent stars. In both cases, he said, these planets produce much smaller wobbles in the parent star, making them harder to detect.

"We've added 12 percent to the total in the last year, and we're very proud of that," said Wright of the 28 new exoplanets. "This provides new planetary systems so that we can study their properties as an ensemble."

The California and Carnegie Planet Search team is headed by Geoffrey Marcy, professor of astronomy at UC Berkeley; Paul Butler of the Carnegie Institution of Washington; Debra Fischer of San Francisco State University; and Steve Vogt, professor of astronomy at UC Santa Cruz. The Anglo-Australian Planet Search team is headed by Chris Tinney of the University of New South Wales and Hugh Jones of the University of Hertfordshire. They and colleagues Shannon Patel of UC Santa Cruz and Simon O’Toole of the Anglo-Australian Observatory have published their exoplanet results in papers over the past year, but the AAS meeting is the first time the teams have presented their findings together.

In addition to reporting 37 new substellar objects, Wright singled out an exoplanet discovered by their teams two years ago as "extraordinarily rich." Circling the star Gliese 436 (GJ 436), a red M dwarf only 30 light years from Earth, was an ice-giant planet the teams calculated to be at least 22 Earth masses, slightly larger than the mass of Neptune (17 Earth masses). After the discovery in 2004 and publication of the exoplanet's orbit earlier this year, a Belgian astronomer, Michael Gillon at Liege University, observed the planet crossing in front of the star – the first Neptune-sized planet observed to transit a star. Gillon and colleagues reported two weeks ago how this transiting planet allowed them to precisely pin down the mass, 22.4 Earth masses, and to calculate the planet's radius and density, which turns out to be similar to Neptune's.

"From the density of two grams per cubic centimeter – twice that of water – it must be 50 percent rock and about 50 percent water, with perhaps small amounts of hydrogen and helium," Marcy said. "So this planet has the interior structure of a hybrid super-Earth/Neptune, with a rocky core surrounded by a significant amount of water compressed into solid form at high pressures and temperatures."

Its short, 2.6-day orbit around Gliese 436 means the exoplanet is very close to the star – only 3 percent of the sun-Earth distance – making it a hot Neptune, Wright said. It also has an eccentric orbit, not a circular orbit like most giant planets found orbiting close to their parent stars. This orbit, in fact, suggests that the star may have another planetary companion in a more distant orbit.

"I'm sure people will immediately follow up and try to measure the atmospheric composition of this planet." Wright predicted.

Also among the 28 new exoplanets are at least four new multiple-planet systems, plus three stars that probably contain a brown dwarf as well as a planet. Wright said that at least 30 percent of all stars known to have planets have more than one. Because smaller planets and outer planets of a star are harder to detect, he predicts that the percentage will continue to rise as detection methods improve.

"We're just now getting to the point where, if we were observing our own solar system from afar, we would be seeing Jupiter," he said, pointing out that the teams' Doppler technique is now sensitive to stellar wobbles of a meter per second, much less than the 10-meter per second limit they started out with 15 years ago.

Wright keeps track of all known exoplanets for the California and Carnegie Planet Search team's Web site, http://exoplanets.org, which hosts the only peer-reviewed catalog of exoplanets within 200 parsecs (652 light years) of Earth. This includes "everything that is close enough to study and possibly follow up with imaging," he said.

Three of the newly reported planets are around large stars between 1.6 and 1.9 times the mass of our sun. Johnson has focused on exoplanets around massive stars, known as A and F stars, with masses between 1.5 and 2.5 solar masses. Planets around these massive stars are normally very hard to detect because they typically rotate fast and have pulsating atmospheres, effects that can hide or mimic the signal from an orbiting planet. He discovered, however, that cooler "retired" A stars – "subgiant" stars that have nearly completed hydrogen burning and have stabilized for a short period of time – are more stable, making planet-caused wobbles detectable.

So far, Johnson has tracked down six previously discovered exoplanets around retired A stars, and by combining this set with the three newly discovered exoplanets, has been able to draw preliminary conclusions. For one, planets around more massive stars seem to be farther from their host stars, Johnson said.

"Only one of the 9 planets is within 1 AU (astronomical unit, or 93 million miles), and none of them is within 0.8 AU, of their host stars, which is very different than the distribution around sun-like stars," he said, noting that many sun-like stars harbor hot gas giants that whip around their host stars in two to 100 days. Even though such planets are easier to detect, no such planets have been detected orbiting retired A stars, whose typical planets have an orbital distance about equal to Earth's orbit or greater, with an orbital period of a few years.

Based on the results of his search for planets around retired A stars, Johnson has discovered that massive stars are more likely to harbor Jupiter-sized planets than are lower-mass stars. The chance of having a Jupiter-like, giant planet orbiting within 2 AU is 8.7 percent for stars between 1.3 and 2 solar masses, versus 4 percent for sun-like stars with masses ranging from 0.7 solar masses to 1.3 solar masses, and 1.2 percent for M stars with less than 0.7 solar masses. As would be expected from the core accretion model of planet formation, large planets are more often observed around massive stars, probably because these stars start out with more material in their disks during the early formation period.

Johnson will continue to focus on the retired A stars, 450 of which have been added to the teams' target list. As more planets are discovered around subgiants, it should become clearer whether larger orbits are "a result of different formation and migration mechanisms in the disks of A–type stars, or simply a consequence of the small number of massive subgiants currently surveyed," he and colleagues wrote in a paper submitted in April to the Astrophysical Journal.

###

The California and Carnegie Planet Search team uses telescopes at the University of California's Lick Observatory and the W. M. Keck Observatory in Hawaii. The Anglo-Australian Planet Search uses the Anglo-Australian Observatory. Together, these teams have discovered more than half of all known exoplanets.

The work is funded by the National Aeronautics and Space Administration, the National Science Foundation, the W. M. Keck Observatory, the Carnegie Institution of Washington, the Anglo-Australian Observatory and the UC Observatories.


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Public release date:

Spitzer nets thousands of galaxies in a giant cluster 

 

Public release date: 28-May-2007
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Contact: Bob Naeye
Rnaeye@milkyway.gsfc.nasa.gov
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NASA/Goddard Space Flight Center



This false-color mosaic of the central region of the Coma cluster combines infrared and visible-light images to reveal thousands of faint objects (green). Follow-up observations showed that many of these... Click here for more information.

In just a short amount of time, NASA's Spitzer Space Telescope has bagged more than a thousand previously unknown dwarf galaxies in a giant cluster of galaxies.

Despite their diminutive sizes, dwarf galaxies play a crucial role in cosmic evolution. Astronomers think they were the first galaxies to form, and they provided the building blocks for larger galaxies. They are by far the most numerous galaxies in our Universe, and are an important tracer of the large-scale structure of the cosmos. Computer simulations of cosmic evolution suggest that high-density regions of the Universe, such as giant clusters, should contain significantly more dwarf galaxies than astronomers have observed to date.

A team led by Leigh Jenkins and Ann Hornschemeier, both at NASA Goddard Space Flight Center in Greenbelt, Md., used Spitzer to study the Coma cluster, an enormous congregation of galaxies 320 million light-years away in the constellation Coma. The cluster contains hundreds of previously known galaxies that span a volume 20 million light-years across.

Jenkins, Hornschemeier, and their collaborators used data from Spitzer's Infrared Array Camera (IRAC) to study galaxies at the cluster's center. They also targeted an outlying region with the goal of comparing the galaxy populations in the different locations to see how environmental variations influence the evolution of galaxies. They stitched together 288 individual Spitzer exposures, each lasting 70 to 90 seconds, into a large mosaic covering 1.3 square degrees of sky.

The team found almost 30,000 objects, whose catalog will be made available to the astronomical community. Some of these are galaxies in the Coma cluster, but the team realized that a large fraction had to be background galaxies. Using data taken with the 4-meter (13 foot) William Herschel Telescope on the Canary island of La Palma, team member Bahram Mobasher of the Space Telescope Science Institute, in Baltimore, Md., measured distances to hundreds of galaxies in these fields to estimate what fraction are cluster members.

A surprising number turned out to be Coma galaxies. They appear to be comparable or even smaller in mass to the Small Magellanic Cloud, the Milky Way's second largest satellite galaxy. Jenkins estimates that about 1,200 of the 30,000 faint objects are dwarf galaxies in Coma, many more than have been identified in the past. Given that the observations only cover a portion of the cluster, the results imply a total dwarf galaxy population of at least 4,000.

Spitzer made these discoveries possible because it can survey large areas of sky very effectively. Even better, infrared observations in space can probe more deeply than ground-based near-infrared surveys because the sky background is up to 10,000 times darker.

"With Spitzer's superb capabilities, we have suddenly been able to detect thousands of faint galaxies that weren't seen before," says Jenkins. She is presenting these results on Monday at the American Astronomical Society meeting in Honolulu, Hawaii. The discovery paper will also appear in the Astrophysical Journal.

"We're blowing away previous infrared surveys of nearby clusters," adds Hornschemeier. "Thanks to Spitzer, we can observe nearby clusters such as Coma very deeply in a short amount of time. The total observing time is comparable to just a few nights at a ground-based observatory."

Additional Coma dwarf galaxies might be lurking in the Spitzer data, but more follow-up work is needed to determine how many. Hornschemeier and other astronomers are currently making deeper spectroscopic measurements with the 6.5-meter (21 foot) telescope of the MMT Observatory in Arizona, and the 10-meter (32 foot) Keck telescope in Hawaii, to find out how many of the faintest objects belong to the Coma cluster.

###

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's IRAC was built by NASA Goddard. The instrument's principal investigator is Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.


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BGH wrote: Based on the

BGH wrote:

Based on the results of his search for planets around retired A stars, Johnson has discovered that massive stars are more likely to harbor Jupiter-sized planets than are lower-mass stars. The chance of having a Jupiter-like, giant planet orbiting within 2 AU is 8.7 percent for stars between 1.3 and 2 solar masses, versus 4 percent for sun-like stars with masses ranging from 0.7 solar masses to 1.3 solar masses, and 1.2 percent for M stars with less than 0.7 solar masses. As would be expected from the core accretion model of planet formation, large planets are more often observed around massive stars, probably because these stars start out with more material in their disks during the early formation period.

 These are both really interesting articles!  The above paragraph caught my eye...does this have something to do with the gravitational pull of these stars being stronger because of their size or am I oversimplifying?


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jce wrote: These are both

jce wrote:

These are both really interesting articles! The above paragraph caught my eye...does this have something to do with the gravitational pull of these stars being stronger because of their size or am I oversimplifying?

Yeah, it kind of explains it there. A more massive star is theorized to start with more material in the accretion disc where the planets are formed, this would lend to the size of the planets making them naturally bigger.


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Watch Them Revamp

In the future when we start finding life on other planets, it's gonna be funny to see how the theist try to revamp their beliefs to keep their faith. All I hope for is that it happens in my life-time...

Slimm,

Quote:
"When one person suffers from a delusion, it is called Insanity. When many people suffer from a delusion, it is called Religion." - Robert M. Pirsig,


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...and a very cool image

...and a very cool image from the Bad Astronomer:

 


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28 New Exoplanets Discovered

From: http://news.yahoo.com/s/space/20070529/sc_space/28newexoplanetsdiscovered

28 New Exoplanets Discovered

Jeanna Bryner
     Staff Writer
     SPACE.com Tue May 29, 7:01 AM ET

Updated 9:30 pm Eastern

HONOLULU-Astronomers have discovered 28 new planets outside of our solar system, increasing to 236 the number of known exoplanets, revealing that planets can exist around a broad spectrum of stellar types-from tiny, dim stars to giants.

"We added 12 percent to the total in the last year, and we're very proud of that," said one of the study team members Jason Wright of the University of California at Berkeley. "This provides new planetary systems so that we can study their properties as an ensemble."

The planets are among 37 new objects spotted within the past year. Seven of the objects are failed stars called brown dwarfs, with masses that dwarf the largest, Jupiter-sized planets but too small to sustain the nuclear reactions necessary for stellar ignition.

John Johnson of the University of California at Berkeley and his colleagues presented the findings here today at a meeting of the American Astronomical Society (AAS).

Astronomers don't directly spot extrasolar planets, but rather look for stellar wobbles caused by orbiting planets. The planet's size and distance from the parent star affect how strong or weak of a wobble, and more sophisticated techniques for measuring the stellar wobbles has led to an ever-lengthening list of such outer planets. Now they can detect wobbles of a meter per second compared with the 10-meter limit just 15 years ago.


Planet profiles

One of the exoplanets, orbiting a red M dwarf just 30 light-years from Earth, was discovered two years ago, but recent observations have allowed astronomers to pin down its mass, radius and density. The ice-giant planet circles the star Gliese 436 (GJ 436) and has a radius and density that are surprisingly similar to that of Neptune.

Weighing in at 22.4 Earth-masses, the exoplanet is the first Neptune-sized planet observed to transit a star. The previous record holder, dubbed HD 140926b, weighed in at 100 Earth masses, and Jupiter is 320 Earth masses.

"[Gliese 436b] must be 50 percent rock and about 50 percent water, with perhaps small amounts of hydrogen and helium," said head of the planet-search team Geoffrey Marcy, also of UC Berkeley. "So this planet has the interior structure of a hybrid super-Earth/Neptune, with a rocky core surrounded by a significant amount of water compressed into solid form at high pressures and temperatures."

Its 2.6-day orbit around GJ 436 means the hybrid planet circles very close to its star, just 3 percent of the Sun-Earth distance, and making it a hot Neptune. Unlike most giant planets found with such close ties to their stars, this planet has an eccentric orbit. The elongated orbit suggests the parent star could have another planetary companion with a more distant orbit.

"I'm sure people will immediately follow up and try to measure the atmospheric composition of this planet," Wright said.

GJ 436 is an M star and 70 percent of all stars are considered M-type stars, so finding that these dim stars can support planets could mean a boon for planet hunters.


Bigger is better

At least four of the newly spotted planets belong to multiple-planet systems, supporting the idea that at least 30 percent of all planet-parent stars have more than one planetary companion. Since smaller planets and those outside our solar system are trickier to detect, Wright predicts this percentage will continue to rise as detection methods improve.

And three of the just-discovered planets circle stars that boast masses between 1.6 and 1.9 times that of our Sun. Planets orbiting these so-called A- and F-type stars are typically difficult to detect because the stars rotate fast and have pulsating atmospheres.

Due to their extreme rotational velocities and high temperatures, A and F stars only jitter slightly from orbiting planets and so surveys can only pick up wobbles from super-massive planets and brown dwarfs in short-period orbits around these stars.

Johnson discovered that "retired" A stars, which have nearly burned all of their hydrogen and remain stable for a short stint, have slower rotation rates and are not so hot. That makes it easier for astronomers to measure their planet-caused wobbles.

Unlike planets orbiting M-type stars, these exoplanets tend to orbit at least 0.8 astronomical units (AU) from the parent stars.

For this reason, massive stars are more likely to harbor Jupiter-sized planets than are lower-mass stars, Johnson said. And retired A-type stars are twice as likely to support planets compared with Sun-like stars, which Johnson attributes to the fact that bigger stars start out with more material in their disks to feed planet building.

So these massive stars also could represent a treasure trove for places to spot new exoplanets, along with the M stars, Johnson said.

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