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Spirit panorama
This amazing panorama of the martian surface at Columbia Hills was taken by the Spirit rover. Expert narration is provided by camera scientist Jim Bell. (2min 12sec file)
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Update on Mars rovers
Mars Exploration Rover project manager Jim Erickson and panoramic camera lead scientist Jim Bell offer comments on the status of the Spirit and Opportunity missions (1min 33sec file)
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Delta rocket assembly
The first stage of Boeing's Delta 2 rocket that will launch NASA's Swift gamma-ray burst detection observatory in November is erected on pad 17A at Cape Canaveral, Florida. (4min 52sec file)
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Solid boosters arrive
The three solid-fueled rocket boosters for the Boeing Delta 2 vehicle that will launch the Swift satellite are hoisted into the pad 17A mobile service tower. (4min 55sec file)
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SRBs go for attachment
The mobile service tower carries the solid boosters into position for attachment to the Delta 2 rocket's first stage. (3min 08sec file)
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Swift nose cone
The two halves of the 10-foot diameter rocket nose cone that will enclose NASA's Swift satellite during launch aboard a Boeing Delta 2 vehicle are lifted into the pad 17A tower. (4min 26sec file)
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ISS talk with students
The International Space Station crew holds an educational event to answers questions live with students at the Maryland Science Center. (24min 01sec file)
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Genesis to Houston
The solar wind samples retrieved by NASA's Genesis spacecraft finally arrive at Johnson Space Center facilities from the Utah landing site. (2min 51sec file)
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SpaceShipOne team chats with ISS
SpaceShipOne pilots and Burt Rutan call the International Space Station for an informal chat with Expedition 9 commander Gennady Padalka and flight engineer Mike Fincke the day after winning the X Prize. (13min 07sec file)
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Gordon Cooper tribute
The flight of Gordon Cooper and Mercury's Faith 7 mission is remembered in this NASA tribute film. (20min 42sec file)
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X Prize launch
SpaceShipOne with pilot Brian Binnie rocket into space on the second of two flights needed to win the $10 million X Prize. (2min 32sec file)
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Monday's flight
This longer length clip of SpaceShipOne's second X Prize launch following the ascent, feathering of the wings and the start of re-entry. (5min 56sec file)
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Safe landing
Brian Binnie, the world's second private astronaut, brings SpaceShipOne to a safe landing at Mojave airport to capture the X Prize. (5min 55sec file)
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Launch of SpaceShipOne
Watch the hair-raising flight of SpaceShipOne during the first of two launches needed to win the $10 million X Prize. The craft experienced a major rolling motion and early engine shutdown. (3min 40sec file)
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X-43A test
NASA's X-43A research craft and its Pegasus rocket booster complete a captive carry test flight aboard a B-52 launch aircraft. (1min 48sec file)
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See the KSC damage
See damage to the Vehicle Assembly Building, the Saturn 5 Center and other facilities at Kennedy Space Center caused by Hurricane Jeanne. (4min 31sec file)
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Cape damage report
Jim Kennedy, director of the Kennedy Space Center, and Col. Mark Owen, 45th Space Wing commander, hold a news conference on Monday, Sept. 27 to provide a preliminary report on damage from Hurricane Jeanne at KSC and Cape Canaveral Air Force Station. (49min 30sec file)
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Hurricane Jeanne
Cameras aboard the International Space Station captured these views of Hurricane Jeanne on Saturday, Sept. 25 as the storm approached Florida. (3min 59sec file)
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Station news briefing
International Space Station program manager Bill Gerstenmaier holds a news conference Sept. 24 to discuss problems with the oxygen generation system and Expedition 10 launch preparations. (44min 06sec file)
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Galaxy clusters collide
Scientists describe a cosmic hurricane in this news conference from Sept. 23, explaining how two merging galaxy clusters churn high-pressure shock waves that leave thousands of galaxies strewn in the wake. (53min 24sec file)
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Station chat with kids
Expedition 9 commander Gennedy Padalka and flight engineer Mike Fincke talk about life aboard the International Space Station during an in-flight educational event with students at the Carnegie Science Center in Pittsburgh. (19min 00sec file)
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ISS educational event
The International Space Station's Expedition 9 crew hold an educational talk with students and members of the National Guard Bureau in Charleston, West Virginia. (19min 53sec file)
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What is it? Mystery object discovered by astronomers
Posted: October 8, 2004

Astronomers using the Gemini North and Keck II telescopes have peered inside a violent binary star system to find that one of the interacting stars has lost so much mass to its partner that it has regressed to a strange, inert body resembling no known star type.

A close-up view of the EF Eridanus system as it might appear today given that most of the radiation emitted by the system is in the infrared part of the specrum and not visible to the human eye. Credit: Gemini Observatory/Jon Lomberg
Unable to sustain nuclear fusion at its core and doomed to orbit with its much more energetic white dwarf partner for millions of years, the dead star is essentially a new, indeterminate type of stellar object.

"Like the classic line about the aggrieved partner in a romantic relationship, the smaller donor star gave, and gave, and gave some more until it had nothing left to give," says Steve B. Howell, an astronomer with Wisconsin-Indiana-Yale-NOAO (WIYN) telescope and the National Optical Astronomy Observatory, Tucson, AZ. "Now the donor star has reached a dead end - it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star. There's no true category for an object in such limbo."

The binary system, known as EF Eridanus (abbreviated EF Eri), is located 300 light-years from Earth in the constellation Eridanus. EF Eri consists of a faint white dwarf star with about 60 percent of the mass of the Sun and the donor object of unknown type, which has an estimated bulk of only 1/20th of a solar mass.

Howell and Thomas E. Harrison of New Mexico State University made high- precision infrared measurements of the binary star system using the spectrographic capabilities of the Near Infrared Imager (NIRI) on the Gemini North telescope and NIRSPEC on Keck II, both on Mauna Kea in Hawaii, in December 2002 and September 2003, respectively. Supporting observations were made with the 2.1-meter telescope at Kitt Peak National Observatory near Tucson in September 2002.

EF Eri is a type of binary star system known as magnetic cataclysmic variables.

This class of systems may produce many more of these 'dead' objects than scientists have realized, says Harrison, co-author of a paper on the discovery to be published in the October 20 issue of the Astrophysical Journal. "These types of systems are not generally accounted for within the usual census figures of star systems in a typical galaxy," Harrison says. "They certainly should be considered more carefully."

The white dwarf in EF Eri is a compressed, burnt-out remnant of a solar-type star that is now about the same diameter as the Earth, though it still emits copious amounts of visible light. Howell and Harrison observed EF Eri in the infrared because infrared light from the pair is naturally dominated by heat and longer wavelength emissions from the secondary object.

The scientific detective work to deduce the components of this binary system was complicated greatly by the cyclotron radiation emitted as free electrons spiral down the powerful magnetic field lines of the white dwarf. The white dwarf's magnetic field is about 14 million times as powerful as the Sun's. The resulting cyclotron radiation is emitted primarily in the infrared part of the spectrum.

"In our initial spectroscopy of EF Eri, we noted that some parts of the infrared continuum light became about 2-3 times brighter for a time period, then went away. This brightening repeated every orbit, and thus had to have an origin within the binary," Howell explains. "We first thought the brightness change resulted from the difference between a heated side and a cooler side of the donor object, but further observations with Gemini and Keck instead pointed to cyclotron radiation. We 'see' this additional infrared component at the phases which occur when the radiation is beamed in our direction, and we do not see it when the beaming points in other directions."

The 81-minute orbital period of the two objects was probably four or five hours when the mass transfer process began about five billion years ago. Originally, the secondary object may also have been similar in size to the Sun, with perhaps 50-100 percent of a solar mass.

"When this interactive process of mass transfer from the secondary star to the white dwarf begin, and why it stopped, both remain unknown to us," Howell says. During this process, repeated outbursts and novae explosions were very likely. The physics of the process also caused the two objects to spiral closer to each other. Today, the two objects orbit each other at about the same separation as the distance from the Earth to the Moon. The donor object has regressed to a body with a diameter roughly equal to the planet Jupiter.

The combined observing power of the Gemini 8-meter and Keck 10-meter telescopes and their large primary mirrors, which were essential to this research, Howell says, makes it clear that neither spectral features of the donor nor its composition match any known type of brown dwarf or planet.

Derek Homeier (University of Georgia) created a series of computer models that attempt to replicate the conditions at EF Eri, but even the best of these do not match perfectly.

The shape of the spectra indicate a very cool object (about 1,700 degrees Kelvin, equivalent to a cool brown dwarf), yet they do not have the same detailed shape or key features of brown dwarf spectra. The coolest normal stars (very low mass M-type stars) are about 2,500 degrees K, and Jupiter is 124 degrees K. The close-in "hot Jupiter" exoplanets detected indirectly by other astronomers using their gravitational effect on their parent stars are estimated to be 1,000-1,600 degrees K.

There is a small chance that the EF Eri system could have originally consisted of the progenitor of the present-day white dwarf star and some sort of "super -planet" that survived the evolution of the white dwarf to result in the system observed now, but this is considered unlikely.

"There are about 15 other known binary systems out there that may be similar to EF Eri, but none has been studied enough to tell," Howell says. "We are working on some of them right now, and trying to improve our models to better match the infrared spectra."

Co-authors of this paper on EF Eri are Paula Szkody of the University of Washington in Seattle, and Joni Johnson and Heather Osborne of New Mexico State.

The WIYN 3.5-meter telescope is located at Kitt Peak National Observatory, 55 miles southwest of Tucson, AZ. Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF).

The national research agencies that form the Gemini Observatory partnership include: the US National Science Foundation (NSF), the UK Particle Physics and Astronomy Research Council (PPARC), the Canadian National Research Council (NRC), the Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnologico (CNPq). The Observatory is managed by AURA under a cooperative agreement with the NSF.

The W.M. Keck Observatory is operated by the California Association for Research in Astronomy (CARA), a scientific partnership of the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.