A Not-So-Hot Jupiter?

January 9, 2003 | Hot Jupiters may not be so hot after all. These giant planets, orbiting sunlike stars at extremely close distances, ought to be strong infrared emitters because of their high temperatures. But a team led by Drake Deming (Goddard Space Flight Center) failed to detect the expected signal. Using NASA’s Infrared Telescope Facility at Mauna Kea, Deming measured the 2-micron infrared flux of HD 209458, the star orbited by a well-known transiting hot Jupiter. Measurements were made in September 2001 when the planet was hidden directly behind the star and when it was not. Deming told the AAS meeting in Seattle that no difference was seen between these observations. High reflective clouds could keep the planet cooler than expected, he says. "But if we don’t see the planet later this year with the SIRTF [Space Infrared Telescope Facility], we’ve got a big problem."

A Tossed-Out Brown Dwarf?

January 9, 2003 | Astronomers may be witnessing the ejection of a very young starlike body out of a triple-star system. Dubbed T Tauri South (T Tau S), the system consists of a very tight binary (Sa) and a lower-mass companion (Sb). The trio is slowly orbiting T Tau North, the famous star that lends its name to a whole class of young stellar objects. Now, Laurent Loinard (Universidad Nacional Autónoma de México) claims that Sb is escaping the system after a close encounter with the Sa binary only about seven years ago. This remarkable claim is based on high-precision radio measurements made with the Very Large Array between 1983 and early 2001. If it is real, "this result is extremely significant for astronomy,” comments Charles J. Lada (Smithsonian Astrophysical Observatory); it could shed light on the origin of the many free-floating brown dwarfs in star-forming regions. However, Mark J. Claussen (National Radio Astronomy Observatory) says another analysis of the VLA data fails to support the ejection scenario. Loinard does admit that it’s extremely unlikely for such an ejection to be happening right now as we watch, but he believes Claussen is wrong because Claussen's analysis fails to incorporate the motion of T Tau Sa around T Tau North.

Neptune's Little Buddy

January 8, 2003 | When astronomers from Lowell Observatory discovered a faint object out at Neptune's distance from the Sun 17 months ago, it didn't pique much interest. After all, the observatory's ongoing Deep Ecliptic Survey has tallied more than 250 distant solar-system bodies to date. But within the last two months it's become clear that 2001 QR322 (its official designation) is special. The observing team announced this week that this body shares Neptune's orbit, remaining roughly 60° (4.5 billion kilometers) ahead of the giant planet at all times. Jupiter has more than 1,500 of these so-called Trojan asteroids — most are likely dormant comets — but this is the first one claimed by Neptune or any other outer planet. With an estimated diameter of 230 km, 2001 QR322 takes 166 years (as Neptune does) to orbit the Sun.

For details see the Lowell press release at http://www.lowell.edu/Press/20030108.html

Finding Exoplanets With a 2-inch Scope

January 8, 2003 | The transiting extrasolar planet found in the OGLE survey is probably just the tip of a huge iceberg. So what do you need for an all-sky survey to find large numbers of transiting exoplanets? Nothing more fanciful than a fast 2-inch telescope and a sensitive 16-million-pixel digital camera, according to Josh Pepper, Andrew Gould, and Darren Depoy of Ohio State University. That relatively humble setup turns out to provide the most effective means of monitoring all stars in the sky between 8th and 10th magnitude for possible periodic transits of extrasolar planets. The three astronomers also calculate that a space-based search for transits (like NASA's future Kepler mission) is more likely to find Earth-like planets in habitable zones around red dwarfs than around Sun-like stars.

Andromeda's Second Stream

January 7, 2003 | The Milky Way isn't the only galaxy gobbling up dwarf galaxies that venture too close. Our nearest neighbor, the Andromeda Galaxy (M31) has done it too. In 2001 European scientists found the first telltale stream of stars in the outskirts of Andromeda, probably due to ongoing cannibalism. Now two California astronomers think they may have discovered a second stream. Using spectroscopic data from the Keck telescope, Puragra Guhathakurta (University of California, Santa Cruz) and David Reitzel (University of California, Los Angeles) discovered a subset of red-giant stars in the outer halo of M31, all sharing the same velocity and a similar composition. "I'll bet it's a coherent group," says Reitzel. "Most likely, it has been deposited by a devoured dwarf galaxy."

More Potential Planetary Systems

January 6, 2003 | It seems that another familiar star, Sigma Herculis, may be home to a planetary system. Christine H. Chen (Jet Propulsion Laboratory) and Michael Jura (University of California, Los Angeles) observed the 4th-magnitude double star in Hercules with the orbiting Far Ultraviolet Spectroscopic Explorer (FUSE). While it's been known since 1998 that this 140-million-year-old star system, like many others, is encircled by a dusty disk, Chen and Jura used FUSE to find atomic gas outflowing from the binary. The team believes that the gas comes from collisions between rocky bodies — a hallmark of planet growth — roughly 20 astronomical units (3 billion kilometers) from the system's center. The two astronomers hope to determine the extent and detailed dynamics of the gas with follow-up ultraviolet observations made with the Hubble Space Telescope. Their results appear in the January 1st Astrophysical Journal.


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