Harvard-Smithsonian Center for Astrophysics|
The CfA Almanac Vol. XIII No. 1, March 2000
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Anxious astronomers, uncertain whether to run for cover or to tool up their telescopes, now at least will get their needed answers faster, thanks to a new high-speed computer at the world's asteroid and comet early-alert center.
A grant from the Tamkin Foundation of Los Angeles, CA, has permitted the creation of a high-speed computer network for the Minor Planet Center, the international clearing house for astronomical information based at the CfA, that will allow more rapid determination of the paths of newly discovered asteroids and comets, including those on possible crash courses with Earth.
The Minor Planet Center, operated for the International Astronomical Union (IAU), serves the world scientific community by collecting, checking, and disseminating positional observations and orbital data for asteroids and comets. Tracking many thousands of objects simultaneously, the Center distributes initial and updated data by means of the Minor Planet Electronic Circulars (issued via email several times a day) and monthly consolidations of the data in the printed Minor Planet Circulars. The new Tamkin Foundation Computing Network will greatly enhance the level of service the Center can provide to astronomers around the world.
Steven M. Tamkin, Executive Vice-President, presented his family foundation's contribution to Irwin I. Shapiro, CfA director, at an informal ceremony in Cambridge late last fall.
From left, SAO Development Officer Amanda Preston, Steven Tamkin, and Brian Marsden, in the CfA Computation Facility.
An amateur astronomer with a deep interest in near-Earth asteroids and other objects with the potential to collide with our planet, Mr. Tamkin noted that "this is the Foundation's first investment in nonmedical scientific research, and we look forward to a long and fruitful partnership in supporting the Center's work."
The combination of observational and computational research is vital in astronomy, according to Brian Marsden, Associate Director for Planetary Sciences. "During the past few years new technology has completely revolutionized the way astronomers make their observations," says Marsden.
"At numerous observatories around the world, computer programs examine an electronic image of the sky, immediately reduce the data for each asteroid or comet to a string of numbers, and then communicate those numbers to us at the Minor Planet Center," he says.
"Our computer programs automatically establish which observations belong to the same asteroid or comet and make successive improvements to the orbital solutions that are then added to the database used to identify further observations," Marsden explains. "It is very rewarding for us that the Tamkin Foundation will support the computing technology that is integral to this kind of research."
The Minor Planet center currently keeps tabs on the orbits of some 60,000 asteroids and 1,050 comets. In 1999 alone, there were some 30,000 new asteroids and 60 comets discovered.
Historic view of "Observatory Hill," now known as 60 Garden Street.
The earthly abode of the CfA now has its own place in space. The Minor Planet 1997 YB8, discovered by the Czech astronomers J. Ticha and M. Tichy, has been renamed "Sixtygarden" in honor of--obviously, for those who abide there--the street address of the CfA in Cambridge, MA.
According to the November 23, 1999, Minor Planet Circular, "observers of minor planets and comets know [this address] as the seat of the Minor Planet Center and the Central Bureau for Astronomical Telegrams, which communicate fast-breaking news of astronomical discoveries to the international community."
(The SAO operates both services for the world's scientific community through the IAU.)
By tradition, tempered by the IAU's official rules on nomenclature, the discoverers of asteroids have the privilege of suggesting names for these small bodies of the solar system. While family, friends, and fellow astronomers are the most common recipients of asteroid names, some discoverers have more cosmic--or eclectic--tastes.
For example, the crop of renamed minor planets that included "Sixtygarden" would otherwise seem a tribute to popular culture. Among the names among the stars are several already seen "up in lights." For example, there is "Audrey," honoring the late Audrey Hepburn; "Hitchcock," for the director of "Psycho"; "Davidlean," for the director of "Ryan's Daughter"; "Forman," for Milos, director of "One Flew Over the Cuckoo's Nest" and the current "Man on the Moon"; and "Jerrylewis."
A unique detector of astronomical radiation, developed at the CfA and tested at the Heinrich Hertz Submillimeter Telescope (HHT) on Mount Graham, Ariz., has made the first ground-based measurements of radio emission from interstellar molecules in the "terahertz waveband"--a virtually unexplored part of the astronomical spectrum.
The detector is a superconducting hot-electron bolometer (HEB),a device analogous to the familiar AM radio receiver, but operating at terahertz frequencies, which are about a million times higher than AM radio frequencies. The key to the HEB is a detector made of a superconducting thin film of niobium nitride, developed in a collaboration between the SAO 's Submillimeter Receiver Laboratory and a group at the Moscow State Pedagogical University.
The new receiver is capable of detecting and amplifying very-high-frequency signals with very fine frequency resolution, so it can detect the spectral lines, or chemical fingerprints, of interstellar molecules which emit radio signals at terahertz frequencies--the highest frequencies ever detected with a radio receiver. The wavelengths corresponding to terahertz frequencies are smaller than one-third of a millimeter, that is, closer to infrared, about midway between optical emissions and frequencies usually observed by large radio telescopes such as the VLA at Socorro, N.M.
The receiver was installed on the HHT, a joint project of the Steward Observatory at the University of Arizona (UA) in Tucson and the Max-Planck-Institute for Radioastronomy in Bonn, Germany. The high, dry location of the 10-meter-diameter (33-foot) telescope allows the high-frequency signals to reach the telescope with minimum atmospheric absorption.
Scientists from the CfA and UA groups collaborated in making the observations with the new receiver, detecting emission from molecules of carbon monoxide (CO) in the Kleinmann-Low Nebula in the Orion Molecular Cloud. The CO emission indicates that some of the gas in this star-forming cloud is some ten times hotter than average.
More important, these observations demonstrate that a "terahertz window on the universe" can be opened for ground-based astronomy. Several groups are now preparing instruments to exploit this new opportunity.
Among the scientists involved in the first terahertz observations were Ray Blundell, Todd Hunter, Scott Paine, Cosmo Papa, and Edward Tong at the CfA; former CfA grad student Jonathon Kawamura now at Caltech; and Eugene Gershenzon and Gregory Gol'tsman of the Moscow State Pedagogical University.
Astronomers have long known that pulsating stars either expand or contract at any one time; but, thanks to new spectra and images of Betelgeuse taken with the Hubble Space Telescope (HST), they have now discovered regions on that star's surface where gas is sometimes being expelled at one side while simultaneously splashing down at the other.
Observations by Alex Lobel and Andrea Dupree of the CfA in Cambridge and Ronald Gilliland of the Space Telescope Science Institute have provided the first direct evidence for such complex flows in the gas surrounding cool, oscillating stars.
From early 1998 to spring 1999, the Space Telescope Imaging Spectrograph (STIS) was used to scan Betelgeuse's disk four times and to record spectra from small slices cut across its surface.
"We found the upper atmosphere or chromosphere warmer than the region below it and we observed that it also contracted and expanded during this period," says Lobel. "But, most surprisingly, a scan in fall 1998 suggests streams of gas that are heading in opposite directions--with velocities of about 10,000 miles per hour."
The astronomers can measure these differences in direction because moving material scatters light out of bright spectral emission lines that emerge from the chromosphere, leaving two distinct peaks. By using knowledge of the Doppler effect (like the change of pitch while a jet flies over or a train passes by), the astronomers inferred that gas is falling to the star when the peak corresponding to the lowest-frequency peak is higher than its companion. When gas is blown off into space, the relative height of the two peaks is reversed.
Throughout the same period, the Faint Object Camera (FOC) was used to make new images of Betelgeuse's chromosphere in ultraviolet (UV) light. While the intensity of UV emitted by the chromosphere varied with the star's pulsation, brighter and rather subtle intensity patterns appeared at different locations on the stellar disk. Although an FOC observation by Dupree and colleagues in 1995 revealed a bright spot-like area on Betelgeuse's surface, the new images--with their improved resolution--now also revealed that a bright 'arc-like' structure spanned a large portion of the disk in September 1998.
One out of a million stars in our galaxy is a supergiant and fewer yet are cool supergiants. Not only is Betelgeuse a cool supergiant, but it is also the seventh brightest star visible in the northern hemisphere, appearing in the shoulder of the constellation Orion at a distance of 425 light-years from Earth. Because its surface temperature can drop to below 3,000 K degrees, it shines reddish. Its atmosphere is like a big puffy cloud, ten million times less dense than our Sun's atmosphere; and, under such conditions, slight perturbations have dramatic effects on movements of its atmospheric gases.
Indeed, this star is so big that, if it replaced the Sun at the center of our Solar System, its pulsating atmosphere would extend almost to the orbit of Jupiter. Additional measurements by Lobel, Dupree, and Gilliland revealed that the star is wrapped in an even bigger and less dense envelope of warmer gas. Its chromosphere extends up to 5,000 times the radius of our Sun, or out to Neptune's orbit, where the temperature can increase to about 5,000 K.
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