NATIONAL RADIO S U M M A R Y ASTRONOMY OBSERVATORY 1991 STATISTICS Cover: The peculiar galaxy NGC 7252. This galaxy is a result of a recent merger, or collision, of two galaxies. The starlight from the merged galaxy is shown as red in this image, light from stars scattered by the force of the collision, or stars unrelated to the galaxy, is shown as green and the radio emission from neutral atomic hydrogen gas is indicated by blue shading. This image demonstrates that when galaxies collide their gas is removed; the final merged system is nearly devoid of gas. The radio image was made with the NRAO Very Large Array radio telescope. The optical image was obtained at the CTIO 4m telescope. VLA Observers: John Hibbard Jacqueline van Gorkom Linda Schweizer NATIONAL RADIO ASTRONOMY OBSERVATORY Observing Summary 1991 Statistics February 1992 SOME HIGHLIGHTS OF THE 1991 RESEARCH PROGRAM The 12 m telescope has been used to detect CO in by far the most distant object to date-the diffuse galaxy IRAS10214+4724, whose optical redshift is 2.29. At so high a redshift, the infrared emission corresponds to a luminosity as great as that of the most luminous QSOs, about 1014 solar luminosities, which if thermal dust emission, correspond to 1010 solar masses of dust. Such a large amount of dust is expected to be accompanied by a still larger mass of (molecular) gas. The CO J=3-2 transition which was detected at the 12 m is shifted from its usual frequency of 345 GHz to 105 GHz, and its 4 mK intensity and 400 km/s width correspond to nearly 1012 solar masses of molecular gas. The detection was confirmed by detecting the redshifted J=2-1 transition at the 12 m, and the J=3-2 transition at the IRAM 30 m. These results suggest that the earliest stages of galaxy formation are preceded by, or contemporary with, the onset of molecular gas and the formation of the first few generations of stars. The first evidence for a primordial "pancake"~a large, flattened agglomeration of hydrogen formed early in the history of the universe-has been detected with the VLA. The object has a redshift of 3.4, and a mass of 3x1014 solar masses, the mass of a large cluster of galaxies. It is interpreted as a protocluster of galaxies undergoing (probably its first) collapse as predicted by Zel'dovich in his "top-down" model in which early matter fluctuations lead first to large structures, which subsequently fragment into smaller structures, eventually galaxies themselves. • The strongest interstellar maser emission yet detected was observed at the 140 ft telescope in 1991 June. It arises from the 51->60 A* transition of methanol (CH3OH) at 6.668 GHz, and it is now seen in 177 Galactic sources, in many at a strength exceeding several thousand Jy. Nearly all CH3OH masers are associated with interstellar OH masers. The new maser will serve as an important tool for the study of proper motions, both in the Milky Way and in external galaxies. The VLA has discovered a previously undetected radio source near the Galactic Center, about 35 arcsec from the powerful Sgr A* source, thought by some to be a massive black hole. The new object was not present in early 1990 December, increased to a maximum in 1991 January, and has decreased (with rapid fluctuations) thereafter. At its strongest, it exceeded Sgr A* in flux. The emission is non-thermal, and is likely synchrotron. The source is verified by HI studies at 21 cm to lie physically close to the Galactic Center, and it also coincides with a strong clump of molecular ammonia near the Center. Such molecular clouds are normally associated with rapid star formation, but in this case they may be responsible for fueling the nucleus of the Galaxy. The nature of the new object remains enigmatic. 1 The first extraterrestrial silicon-nitrogen molecule, SiN, has been detected in the circumstellar envelope of IRC 10216. SiN occurs in the outer envelope, with an abundance SiN/SiQ = NH3/C2H2, indicating that SiN is formed by reaction of Si* with NH3. Since both NH3 and QHj arise in the dense inner core, an efficient means of transporting silicon to the outer envelope must operate. The likely carrier is silane (SiH4). Although these findings indicate considerable quantities of gaseous Si in the outer envelope, the net loss of refractory elements such as Si to the interstellar medium from such mass-losing evolved stars as IRC 10216 is almost entirely in the form of grains. • High resolution VLA observations have detected a pulsar that is "caught in the act" of escaping from the debris created during its violent formation only 15,000 years ago. Using specially designed electronics, a compact nebula at the tip of an unusual protuberance directly outside the arc-shaped radio emission from the SNR G5.4-1.2 was found to harbor the pulsar PSR 1757-24. The young age of the pulsar was measured from its spin-down rate. If the pulsar and the SNR were created in the same supernova event then the current speed of the pulsar is 2400 km/sec, the highest value known for any pulsar. Two eclipsing binary pulsars are known that appear to be evaporating their companions; the evolution of such systems depends directly on the evaporation rate, which has been poorly known. Recent measurements of the pulsar light curve of PSR 1744- 14A in the globular cluster Terzan 5 made with the 140 ft telescope and the VLA at 1.67 GHz reveal that the eclipse is not total, but the pulsar signal is substantially delayed during the eclipse and suffers a maximum attenuation by the ablating material of about 70 percent. Models of the free-free absorption and dispersion of the pulsar signal in an ionized wind explain the frequency dependence of the eclipse duration but predict an evaporation rate such that the companion star is unlikely to be fully ablated in less than a Hubble time, so that in this case ablation may not ultimately form an isolated millisecond pulsar. OBSERVING HOURS 1979 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 Calendar Year MO-Foot 12-Meter iH Interferometer \VLA Fig. 1. This figure shows the hours scheduled for observing on each telescope during the last decade. DISTRIBUTION OF SCHEDULED OBSERVING TIME 12-Meter 140-Foot VLA o X Z3 O 1982 83 84 85 86 87 88 89 90 91 1982 83 84 85 86 87 88 89 90 91 1982 83 84 85 86 87 88 89 90 91 Calendar Year Calendar Year Calendar Year \ NRAO Staff | Visitors Kl Testing and Calibration Fig. 2. These graphs show the number of hours scheduled for calibration and for observing by the NRAO staff and by visitors on each telescope system during the last decade. 12-METER RADIO TELESCOPE SUMMARY 100 A - ^■ "x r m / \ \ i ^s f 80 X A +r> \ r »• \ r > 1 r s n A ^ ^ A / - ] \ J A / ] ( \ \ \ / \ ^ / /■ £ 60 ) ] f A ' A A A \ A ) A f' f k 1 \ - Q- 40 - \ 0 \ V / V V / I V \ / \ \ V \ • 20 J }v/ 1 ^ V J V jJ u V >r > ^ »< ^--^ ■j f .> ^ ^ V ). ^x > v J .'\ s* »^ .y \ > _.--' 0 i/. i I x*' '»' y Calendar Year Observing Installation, Maintenance and Calibration Equipment Failure, Weather and Interference Fig. 3. This summary for each quarter of the calendar year shows the percentage of time the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. The telescope is removed from service for a period of 4-6 weeks each summer during the wet season. This period is used for maintenance and upgrading of the instrument. During the last half of 1982 and most of 1983 the telescope was out of service for the replacement of the reflecting surface and its backup structure. 140-FOOT RADIO TELESCOPE SUMMARY 100 80 ^ 60 u £ 40 20 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Calendar Year Observing Installation, Maintenance and Calibration Equipment Failure, Weather and Interference Fig. 4. This summary for each quarter of the calendar year shows the percentage of time the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. Major improvements to the telescope system include: 1980 - installation of the Model IV autocorrelator receiver; 1982 - brake overhaul and installation of the second channel of the upconverter/maser receiver; 1987 • holographic surface tests and panel readjustments. VERY LARGE ARRAY TELESCOPE SUMMARY - - 80 s , "\ A Sfc " * **" " s -^ '^- ^ ^x *s s^ -^ "^ "*■* -*■"' -" - ^ ^ ^ V >/ - - * 40 -^ — — -> .^ ^ -^ , - ^ /" - ./ N s,. 20 ^x ^. ^. —■ ^ : —. — ^* r: ■ .-- *-«, ^^ — — .-. ^.- -—. _ --— — ■-- ^^ — — """^»." .-. *'■" --H r 0 ~+- Calendar Year — Construction Observing Testing, Maintenance and Calibration Downtime Fig. 5. This summary for each quarter of the calendar year shows the percentage of time the telescope was scheduled for observing; for routine system testing, maintenance, and calibration; and the percentage of time lost due to hardware or software failure, power failure, or bad weather. Time scheduled for completion of the construction was reduced to zero after the first quarter of 1981. FULL-TIME PERMANENT EMPLOYEES 500 200 150 100 50 0 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 Calendar Year V/SkVLA Construction Research and Operations VLB A Construction ESSSl 6BT Construction Fig. 6. This figure shows the total number of NRAO full-time, permanent employees at the end of each year, projected into the future.