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Observing Iummanj Observing iummanj 2005 NATIONAL RADIO ASTRONOMY OBSERVATORY Observin? Jummanj 2005 (tathtio April 2006 Cover Image: A composite of radio (Very Large Array) and optical (Lick Observatory 120-inch and Siding Spring 2.3m telescopes) images of the galaxy cluster Abell 194. This compelling image was awarded an Honorable Mention in the 2005 AUIINRAO Image Contest. Image courtesy of Steve Croft (LLNL) et al. mm Scientific Highlights mSb Ob$emn? Nummary 2005 VLA Provides Key Data on Magnetar Outburst - When the Soft Gamma-ray Repeater SGR 1806-20 underwent a giant flare on December 27, 2004, the VLA became the prime tool for studying the burst's afterglow, in part because the object was at the time too close to the Sun in the sky for many satellite observatories to safely observe. Two teams, including 33 investigators from four continents, used the VLA to study this object, a magnetar. Results from the early observations include measurement of the fireball's expansion speed (0.3c); estimates of the total energy of the flare; a non-spherical and possibly changing shape for the fireball; and polarization measurements. HI absorption measurements by one team possibly have called into question the generally accepted distance to this object, with significant implications for models. VLBA Measures Proper Motion, Rotation of M33 - Using VLBA observations made over a period of 2.5 years, astronomers have directly measured both the proper motion and the rotational motion of M33. This is the first proper-motion detection ever made of a galaxy not a satellite of the Milky Way. Combined with radial-velocity measurements, this work provides the first three-dimensional measurement of the galaxy's motion in space. M33 is a satellite of M31, and this work will refine the orbit of M33 and help determine if it has undergone close encounters with M31 in the past. The measurement of such minuscule angular motion was done by observing water masers in interstellar clouds within M33. Detection of a Water Maser at z=0.66 - The GBT has been used to detect a water maser at a redshift of 0.66 in a Type 2 quasar discovered by the Sloan Digital Sky Survey. This object is more than an order of magnitude farther than any previously known water maser source. Such masers provide information on the nuclear tori and black hole masses of active galactic nuclei. In one case (NGC4258), studies of the water maser emission were used to make a precise distance measurement independent of the usual distance ladder. The spectrum of the new detection has only one emission feature and thus cannot be used for such distance measurements at the present level of sensitivity. Nonetheless, the detection now offers the possibility of finding other megamaser sources in the distant universe that could be used to test deviations from the Hubble Law as inferred from observations of Type la supemovae. White Dwarf's Re-Ignition Spurs New Stellar Evolution Model - In 1996, V4334 Sgr, better known as Sakurai's Object, rapidly brightened. Initially thought to be a nova explosion, the event soon was recognized as the first modem observation of a white dwarf re- igniting after its nuclear burning had ceased. This provided a once-in-a-lifetime opportunity to study the type of event that may be a significant source of carbon and carbonaceous dust in the Galaxy. The re-ignition, only the third ever observed (the others were in 1918 and possibly 1670), is believed to result when a small, hydrogen-rich envelope is convectively ingested into the white dwarf's helium shell, triggering a renewed nuclear flash. Earlier models predicted that this would cause the star's luminosity to increase over a few hundred years. However, this evolution occurred 100 times faster, prompting development of a new model that predicts rapid reheating. The VLA observations revealed radio emission from freshly ionized matter, confirming that the rapid reheating has begun. Scientific Highlights twb Observin? Nummary 2005 Stellar-Wind Collision Region's Motion Is Tracked - The motion of a wind-collision region in the binary pair WR140 has been tracked. The pair consists of a Wolf-Rayet star and an O star. The region where their stellar winds collide is seen as a bow-shaped arc of radio emission that rotates as the orbit progresses. This observation has allowed refinement of the orbit's inclination and a definitive determination of the system's distance. The new data, which is inconsistent with model predictions, will ultimately allow better understanding of the nature both of Wolf-Rayet stars and of wind-collision regions. Observations of 9P/Tempel 1 During Deep Impact - The GBT has been used to carry out eight days of L-Band OH spectroscopy of comet 9P/Tempel 1 in the days immediately following the highly successful Deep Impact mission. Somewhat surprisingly, the impact released considerably lower amounts of volatile gases into the coma than were expected - two orders of magnitude lower production than some pre-mission estimates. In the first week after impact, GBT spectra stood alone offering the only ground-based radio detections of OH. Lines were variable in strength, in part due to the unique nature of the solar UV excitation of OH in cometary atmospheres, and in part due to real variations in gas production. Some days the lines were undetected below a 2 mjy limit, while on July 6 and July 9, lines were detected in excess of 5 mjy. Radio spectra offer information about the kinematics of gases in the coma, and although the data thus far are low signal-to-noise and thus cannot reveal jet structures or small asymmetries, preliminary analysis of the lines reveals that OH is somewhat redshifted from the cometary orbital velocity, and the general outflow of gas from the nucleus is around 0.8 km/s. Analysis is underway to see if variations in gas production are correlated with the favored 40-hour rotation period. VLA Reveals Centimeter-Sized Pebbles in Protoplanetary Disk - Multiwavelength VLA observations of the young star TW Hydrae revealed centimeter-wavelength emission from its dusty protoplanetary disk that indicates particles similar in size to the emission wavelengths. The formation of centimeter-sized particles is considered an important step on the path from dust particles to planets. The star's relatively close distance and its evolutionary stage are ideal for allowing study of the particles in its roughly 0.1-solar-mass dust disk. VLBA Measures Speed of Fastest-Moving Pulsar - Proper-motion and parallax measurements made with the VLBA have shown that the pulsar B1508+55 is moving at nearly 1100 kilometers per second and will inevitably escape the Galaxy. This is the first direct measurement of a neutron-star speed that exceeds 1,000 kilometers per second. The pulsar's path can be traced back from its current position to a birthplace in the Galactic plane near the Cygnus OB association. The high birth velocity of the neutron star constrains evolutionary scenarios, and is greater than that predicted by the latest computer modeling. Scientific Highlights two Observin? Jummanj 2005 A Wealth of Pulsars - Extremely large volumes (i.e. many tens of TB) of pulsar data for timing, searching, and other projects continue to be taken with the GBT and a variety of pulsar backends (including the Spectral Processor, the BCPM, GASP, CGSR2 and the Spigot). One amazing indicator of the GBTs impact in this field is the number of new globular cluster pulsars that the GBT has found: 55 and counting! In only three years, the GBT has discovered more globular cluster pulsars than any other radio telescope has discovered in its lifetime. The vast majority of these pulsars were uncovered using the incredibly sensitive S-Band receiver + Spigot combination. One of these new pulsars, TerzanSad, seems to be the fastest millisecond pulsar yet discovered with a spin period of 1.39ms, finally beating the 23-yr old record set by Backer et al. for PSR B1937+21. TerSad and other new GBT discoveries are beginning to put strong constraints on the Equation of State of matter at supra-nuclear densities. VLA Identifies Afterglow of Short Gamma Ray Burst in an Elliptical Galaxy - The VLA was used to unambiguously identify the afterglow of the short "hard" gamma-ray burst GRB050724, using the rapid-response observing mode put in place earlier in 2005. The identification of the radio afterglow of this burst detected by the Swift satellite showed its association with an elliptical galaxy at z=0.257. The association with a galaxy that is dominated by an old stellar population provides key support for the model in which two compact stellar remnants in a binary system coalesce, giving rise to the gamma-ray burst and the relativistic fireball. VLBA Measures Distance to Perseus Spiral Arm - Using the VLBA, a team of researchers has precisely measured the distance to the Milky Way's Perseus spiral arm. They observed strong methanol masers in the W30H star-forming region, measuring the trigonometric parallax of those masers. Their direct measurement of 1.95 ± 0.04 Kpc resolves a previous factor-of-two discrepancy in the distance to the Perseus spiral arm. The discrepancy arose because of anomalous motions in that part of the Perseus arm. This result, which indicates that the VLBA can measure distances out to 10 Kpc with accuracy 100 times better than the Hipparcos satellite, can lead the way to mapping the spiral structure and full kinematics of massive star-forming regions in the Milky Way. GBT Measurements of the Zeeman Effect - The 21 cm line of HI was measured along two strips, and the Zeeman effect shows that the line-of-sight B field reverses direction across the axis of the molecular cloud.
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