| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
|
|
|
Skywatcher Eyes in the Backs of Their Yards With the passing of southern Arizona's steady summer rains, Dave Harvey resumes his ritual for clear desert nights. He crosses his backyard to an 8x8-foot wooden shed, surrounded by prickly pear cactus and palo verde, and slides off its peaked roof. Inside resides a 14-inch Celestron telescope attached to a motorized, industrial-strength mount. He starts to cool the compact charged-coupled device (CCD) camera attached to the eyepiece down from ambient temperature. Then Harvey returns to an office in his house where he can guide the telescope and keep tabs on its celestial sightings from a pair of personal computers. But rather than burn the midnight oil, he will enjoy his evening and a good night's sleep while the camera dutifully takes about 400 pictures. Come morning, Harvey needs only to replace the observatory roof and spend a few minutes at his keyboard to format the previous night's data. Harvey has taken more than 30,000 images of stars in his four years as a bonafide member of the Center for Backyard Astrophysics (CBA), a symbiotic collaboration between amateur astronomers, who often possess the time and the skills to obtain good data, and the professionals who provide expert interpretation. With the right mentor, amateurs--who can access their telescopes whenever they like to view whatever they like--can make significant discoveries. "The whole purpose of the way we do things is to make it as automated as possible so it doesn't take a whole lot of time," Harvey says. "Right now it involves about an hour a day, so it's a fairly minimal impact on my lifestyle." While new data-gathering technology has made observing easier for amateurs, the far reaches of galactic space have also gotten closer thanks to cyberspace. "Every time something pops off in the sky, with the speed of e-mail we can talk to each other and point our telescopes in the right direction, usually the same night," says Columbia University astronomer Joseph Patterson, who since 1980 has conducted this looseknit symphony of star watchers. The CBA network includes 40 members on both Pacific and Atlantic coasts, the Southwest, and others in Belgium, Denmark, Australia, and Japan. About half of CBA's members are active observers. Collaborators in the Midwest, Hawaii, Chile, New Zealand, the United Kingdom, South Africa, and Israel also participate on certain star-watching campaigns. Members appear as co-authors on the more than two dozen research articles that CBA has published in the Publications of the Astronomical Society of the Pacific and other major journals. "The amateurs don't have as good an idea of what to point their telescopes at, and I can help them with that," Patterson says. "All I really need to do is send them the coordinates of my star and my e-mail address." It works just as quickly and easily in reverse. Harvey's computer downloads each image eight seconds after the camera snaps it. He culls from about 300 megabytes of raw data the figures for a target star's varying brightness throughout the night and forwards them to Patterson's electronic mailbox. "I close down by five in the morning," he says, "and Joe has his data by seven." Then Harvey heads to his day job as a programmer for the University of Arizona's Steward Observatory. He wrote the software that operates the Observatory's telescopes atop Kitt Peak, and he runs a private software business for telescope and satellite tracking. When CBA offered to supply his telescope and computers, Harvey reciprocated by providing control system software to other members in the network. CBA was the brainchild of David Skillman, a NASA engineer in suburban Washington, D.C., whose 26-inch-diameter telescope is the largest in the network. In the 1970s, Skillman had an established career but still wanted to make some lasting scientific contribution. He figured that the sky offered ample opportunity for discovery, so he set to work building telescopes and cameras in the days before microprocessors were everyday off-the-shelf items. By 1980 he founded what was then called the Center for Basement Astrophysics, tacking the playful adjective to the name of a renowned research branch of the Harvard-Smithsonian Astrophysical Observatory. "The idea of a subversive organization appealed to me from my days in the sixties," says Skillman. "You know, 'Let's get out there and commit astrophysics.'" But Skillman still needed guidance. With so many stars to choose from, he sought a galactic guru to tell him where to aim his telescope. After a few unsuccessful collaborations with astronomers, Skillman approached Patterson after a lecture and impressed the young professional with his sophisticated questions about photometry, a technique to measure a star's output of energy. Says Skillman, "Most professional astronomers don't want to be associated with nonprofessionals. Basically, Joe was willing to take a chance." Patterson persuaded Skillman to focus his energy on stars in the Milky Way known as cataclysmic variables, which remain the network's target of choice. This subset of the stellar pantheon affords amateurs an opportunity to do novel research firsthand, since most professionals would rather use their precious telescope time looking at less faint and fickle beasts. Cataclysmic variables comprise a pair of stars, one rapidly orbiting the other, which fluctuate in brightness dozens of times each night. Both stars would fit inside our Sun with plenty of space to spare. The primary star in the pair is usually a white dwarf--an aged star that has become a densely packed, volatile mass of matter. (In the case of CR Boo, CBA's 1996 Star of the Year, which the group watched for 100 nights straight, the binary pair are both white dwarfs, "degenerate stars locked in mortal embrace," Patterson calls them.) Hydrogen builds up and burns inside the white dwarf until it explodes like a fusion bomb, causing it to become as visible as the galaxy's brightest star. Unlike the final, fatal implosion of a star that forms a supernova, this explosion only scars the star's surface. Such a so-called dwarf nova eruption can recur millions of times during the star's life. Our galaxy may contain 10,000 dwarf novae, each erupting ten or more times a year, but the CBA keeps tabs on just a few of them. Their task has been made immensely easier through the use of CCD technology. Developed for military surveillance and formerly classified, CCDs are up to 20 times more sensitive than any previous light detectors and perfect for capturing a photon flurry from a faint star. The CCD camera on a telescope works something like a video camcorder, converting light to electrons to create a digital archive of the image in the telescope lens. Now that CCDs are readily available and relatively affordable, they have become standard equipment for the backyard astrophysics set. In order to reduce gaps in the data used to compile a light curve, the pattern of brightness fluctuation from an interacting pair of stars, CBA attempts to overlap the periods for individuals' telescope runs and have the broadest possible geographical spacing of observers. When writing research papers, Patterson combines observations from the amateurs' small scopes with his own data from larger observatories, such as Kitt Peak in Arizona. About half of the CBA star-watching campaigns focus on a peculiarity of cataclysmic variables that has been dubbed a superhump. Superhumps are visible surges of light that vary in periodicity. It turns out that superhumps occur when the orbiting secondary star passes so close to the disk of gas and particles encircling the primary white dwarf star that it illuminates the disk. Superhumps provide an indirect way to keep tabs on the position of the fainter secondary star. And the secondary's mass can also be calculated from the amount of light it generates; some of these secondary stars have just a few percent of the Sun's mass. The same elliptical disk of matter that causes superhumps also makes cataclysmic variables interesting to theoretical astronomers. This so-called accretion disk of matter pulled from the secondary star, as the stars perform their gravitational pas de deux, is thought to be the seed source for planets. Observations of cataclysmic variables could help support or refute ideas about how solar systems form. Sometimes theory and observation see eye to eye. Last spring, the CBA mounted a global campaign to watch the star HZ 29. Though a typical orbital period for a binary star pair is ten days, previous observations of HZ 29 made sense only if the secondary star orbited the white dwarf every 17 minutes. The amateurs gathered five consecutive days worth of light curves from the star, and when the data were analyzed the results came in: HZ 29 did have the briefest orbital period for a binary pair, exactly 17.1 minutes. What the Earth takes a year to accomplish, this star does in the duration of a coffee break. CBA's semiannual newsletter, "Notes from Underground," presents the results of past star-watching campaigns and plans for future ones, complete with wry remarks about various study subjects. Of V603 Agl: "This star is the brightest and most reliable superhumper in the sky, so it merits our Good-Observing Seal of Approval." Or V1974 Cyg, which has been scrutinized for four years: "Oooo, damn interesting star. Funny wiggles in both orbital and superhump periods, carrying some reasonable prospect of deeper understanding, I think." Patterson may exaggerate when he claims that CBA's "data are acquired at no human cost of sweat, tears, insomnia, or psychic stress," but the network does seem to fill a niche at a time when some smaller observatories, including some where Patterson has worked, have gone dark or face closure as astronomers seek more powerful eyes on ever distant reaches of the universe. CBA has survived with modest grants for equipment from the National Science Foundation, and the group recently received $75,000 from the Tucson-based Research Corporation, which supports unconventional science projects. For all its gadgetry and global camaraderie, the Center for Backyard Astrophysics fosters small science and hasn't strayed far from the fundamental fascination with stars that first inspired its members. That's just fine with them. "Most astronomers have gone extragallactic. They're not interested in this galaxy," says Skillman. "We've decided to stick to our own backyard, but it's a big backyard." Blake Edgar is an Associate Editor of California Wild. His email address is bedgar@calacademy.org |
Winter 1998
|
