The Arecibo Observatory hosted fourteen students from colleges and universities in Puerto Rico and in the mainland between May and August. Included in this number were one teacher from a local high school and two students supervised by the Observatory's adjunct staff from the University of Puerto Rico - Rio Piedras. One, Carlos Vargas, continued his work of last summer on hot molecular cores in regions of massive star formation with Peter Hofner. The other, Karin Menendez, helped Carmen Pantoja to develop a dipole antenna and receiver which can be used by high school and college classrooms as a hands-on introduction to radio astronomy. Former REU student Anil Seth (1997) returned for a month to continue his summer student project with Chris Salter, reducing multifrequency VLA data of supernova remnants.

The NSF Research Experience for Undergraduates program sponsored nine undergraduates and one teacher. One of these students was a member of the UPR - Humacao REU program but did her research at the Arecibo Observatory. The NASA Capability Enhancement program, based at the University of Puerto Rico, sponsored two students; a third was supported by a Mellon Minority grant at Williams College and by the Puerto Rico Community Foundation.

The students had many opportunities to observe with the Arecibo dish. All the students were involved in the ongoing summer student observing project, supervised by Murray Lewis. Their monitoring of the spectra of three lines of OH maser emission from OH/IR stars (evolved stars with circumstellar shells) have revealed many interesting and unexpected results over the three years that the project has been conducted. Comparisons of the post-upgrade spectra with pre-upgrade spectra have revealed several sources with dramatic changes which may indicate the evolution of the mass loss system of the stars. Three other students had their own observing programs as their summer projects. They designed and performed all of the observations themselves, reduced and analyzed the data, and will present the results at the AAS meeting in San Diego. (See below for more details.)

The housing situation was much better this past summer. All of the students lived on Observatory property. The boys shared one of the family units on the hill, while seven girls shared a house just outside the Observatory gates. NAIC had recently acquired the house with the view of constructing new VSQ's on the site. Crews from the maintenance department did a great job renovating the old house on the site so that the students could live there. There was only one bathroom (for seven girls!) but the shower at the pool was not far away. When the Esperanza community water failed for several days, the crew connected the house to the Observatory water supply so the girls would at least have water. Since the students lived so close to each other, they could share communal meals and socialize. Several staff members generously offered their cars to make sure that the students had rides to stores, movies and beaches. Organized excursions almost every weekend kept the students from getting "cabin fever". (See Tours) Again, four of the students took the opportunity of warm clear waters to become certified scuba divers. Besides many informal get togethers, Daniel Altschuler hosted a cookout at the pool for the summer students and their advisers.

Supported by NSF REU Funds:

Shawn M. Allison (Penn State University) worked on several aspects of atmospheric science. His main project, supervised by Qihou Zhou, involved radar observations of meteor echos. Previous Arecibo meteor detections showed a puzzling lack of trail echos (only 10 out of 367) with the VHF system. Shawn investigated the possibility that this lack

could be due to the fixed vertical orientation of the Arecibo dish. He analyzed meteor data from the Mu radar in Japan which is stearable. Many meteors were detected, most displaying head echoes but several with trail echoes. Shawn also helped Jonathan Friedman with LIDAR observations.

Sarah Boswell (Bethel College) worked with the aeronomy group (particularly with Nestor Aponte and Sixto González) on two web design projects: the Arecibo Incoherent Scatter Radar Database (AISRD), and a web page that provides up-to-date lists of publications by various members of the aeronomy group. The AISRD provides access to the Arecibo World Day data through a convenient graphing interface. On an image request form, the user selects from appropriate options for the ionospheric altitude region and date of interest. A fully-interactive image provides height and time profiles with adjustable colorbar

scales. Sarah hopes that her web page will be a valuable tool for aeronomers around the world.

Alyson Brooks (Macalester College) mapped portions of the Magellanic Stream in HI with the Arecibo Telescope. She and Snezana Stanimirovic developed their own on-the-fly observing scheme of driving in RA and then stepping in Dec for individual 10 x 11 small maps. These maps were then combined to make a map of the regions MS V and MS VI. With a velocity resolution of 1.3 km/s, the kinematics of the regions could be studied, as well as the structure. Several interesting features were revealed. In MS VI, the tip of the Stream, three clumps were seen, one of which had some head-tail structure and another which was extremely dense with a velocity gradient. MS V had no discernible clumps but

appeared to have two distinct sheets of gas, separated by about 30 km/s. The maps are being analyzed further to test various theories of the origin of the Magellanic Stream and to determine the hierarchy of structure present. The results will be presented in a poster paper at the winter AAS meeting.

Diane Chin (SUNY-Binghamton) searched for extended HI envelopes around low surface brightness (LSB) galaxies in collaboration with Karen O'Neil. The existence (or lack of it) of an HI envelope might shed some light on the evolutionary history of the LSB galaxies and explain their extremely low background star formation rates. Extended envelopes could also have important implications in the search for the source of Lyman-alpha absorption at low redshifts. Diane observed the regions surrounding 4 previously detected LSB galaxies. Three of the four galaxies showed signs of extended HI, although two of them had suspiciously asymmetric distributions. While no detections were made around the remaining galaxy, the upper limits on its H I content were too high to rule out the existence of an extended envelope. Diane's observations will be presented in a poster paper at the winter AAS meeting.

Ernesto Estremera (Quebradillas High School) was the 2000 Teacher-in-Residence at the Arecibo Observatory Visitor and Educational Center (AOVEF), under the supervision of José Alonso. Ernesto shared his longtime hobby of studying local plants and wildlife by developing an exhibit for the AOVEF. He obtained wonderful digital images of the Flora and Fauna of the Observatory grounds and categorized all the varieties he found. The images will be part of a new hypertext exhibit to expand the range of topics to biological subjects. His final presentation impressed all of the Observatory staff with the wealth of beauty in our everyday environment.

Laura J. Hainline (Indiana University) studied the kinematics of dwarf irregular (dIrr) galaxies with Jo Ann Eder. Laura observed high resolution (0.65 km/s) HI spectra of a sample of dIrr galaxies for which previous low resolution (8 km/s) detections indicated narrow single-peaked profiles. A single-peaked profile could result from a face-on orientation or from a small pressure supported galaxy with little or no rotation. However, the high resolution spectra (0.65 km/s) of 9 of the 15 galaxies displayed the double-horned profiles indicative of a rotating gas disk. The velocity dispersion for these galaxies was estimated from the wings of the profile and generally compared well with the estimate obtained from the remaining single-peaked profile of a face-on dwarf. Estimates of the dynamical masses for the double-horned sample indicate high mass-to-light ratios, as compared with other disk galaxies. Laura has already prepared her poster for the winter AAS meeting in San Diego.

Justin B. Kinney (Cornell University) applied his love of mathematics to a very sticky problem - understanding the origin of the large wavenumber tail shown by the spectra of atmospheric gravity waves. Lily Childress, a 1999 REU student working with Mike Sulzer, found that Colin Hines' Doppler spreading theory produced the tail, but with a k(-1) dependence rather that k(-3) as found experimentally. Justin tried many approaches to reconcile the theory with experiment - one-dimensional approximations using Gaussian impulses (--> exponential tail), using a cosine wave (--> k (-1) tail), and a two-dimensional special case of two gravity waves intersecting perpendicularly (--> k (-1) tail assuming a unity Jacobian and k(-3) tail with the exact form of the Jacobian). Justin concludes: "This is a hard problem but it is still accessible. I intend to keep working on it."

Amanda Kirschner (Carleton College) studied pulsar dynamic and secondary spectra for data obtained by her adviser, Ramesh Bhat, with the Ooty Radio Telescope in India. Dynamic spectra (intensity vs. time and frequency) is the result of scintillation of the pulsar signal by the interstellar medium (ISM). The 2D Fourier transform of the dynamic spectrum produces a distribution of points in the plane of inverse frequency and inverse time, called the secondary spectrum. The secondary spectrum can reveal features such as "islands" (ie, periodicities in the dynamic spectrum signifying fringing events) or "wisps". Wisps appear as faint diffuse features extending outward from the origin of secondary spectra. First recognition of wisps came from recent Arecibo observations, and their study is a topic of contemporary research. They are found to lie significantly above the noise floor. The exact cause of wisps is still unknown; they may be either intrinsic to the pulsar or caused by the ISM. Amanda analyzed data for a dozen pulsars. She found no new islands but did find at least four pulsars with evidence for wisps. Amanda described some of the basic properties of these wisps which may help to explain their nature. These results will be presented in a poster paper at the winter AAS meeting.

Ruth Murray (Harvard University) carried out two investigations of pulsar positions with Duncan Lorimer. For the first, Ruth evaluated the unexpected observed bias in the offsets between pulsars and their associated supernova remnants. While the offsets were evenly

distributed in galactic latitude, they showed a marked preference for one direction in galactic longitude. However, Ruth's analysis showed that the errors in the supernova remnant center positions are significantly larger than previously estimated, making the offset result more marginal. The second investigation involved creating a Monte Carlo simulation of the observed pulsar population in an attempt to differentiate between different possible radial distributions for galactic pulsars. The simulation was then applied to the investigation of pulsar/supernova offsets.

Supported by Other Funds:

Darik O. Velez (Williams College), under the guidance of Sixto González, processed over 400 hours of radar topside ionospheric data and calibrated it with Arecibo ionosonde data. This observational data was then compared with the predictions of the International Reference Ionosphere (IRI). Darik found that the IRI model does not predict the hydrogen and helium ion fractions and densities for the topside level of the atmosphere. Contrary to the model, the data indicates that the hydrogen ion percentage continues to rise with height, while the electron density continues to fall. The data also shows a variation in the height of the peak hydrogen density from one night to another. Other discrepancies appeared regarding the intensities and height of the peak helium ion densities. Clearly, the IRI needs to be reevaluated with respect to the topside layer.

Homero Cersosimo (Univ. of Puerto Rico - Humacao), an applied physics major and the son of a former Arecibo Observatory postdoctoral fellow, spent the summer using new engineering computer packages on various projects, under the supervision of Edgar Castro. Homero's favorite project was building and testing a YAGI antenna . He will use the antenna for his ham radio setup at home. Homero also designed a cabinet for the upgrade of Carriage House 1. The upgrade will replace the existing equipment currently housed in three bulky cabinets with more compact versions in one cabinet. Because of support structures and existing doors, the design of this cabinet was very tricky but Homero found a configuration which would work. Homero also mapped all of the AO Fiber Optics, which were recently installed, on a document which can be used for maintenance and repairs - a critical contribution to the future of the Observatory.

Miguel F. Irizarry (Univ. of Puerto Rico - Mayagüez), an engineering student, also worked with Edgar Castro in the Engineering Department on the Carriage House 1 upgrade. He investigated the modern equipment to be put into Homero's cabinet which could be used to replace the older, more bulky equipment. He also designed a cold load which could be used to calibrate the system temperature of the receivers in the Gregorian Dome. Both Homero and Miguel found the practical experience they received at the Arecibo Observatory to be a good complement to their course work.

Karin Menendez (McGill University) was a member of the REU program at UPR - Humacao where she spent several weeks completing computer workshops. However, she worked on a very interesting educational project at Arecibo with Carmen Pantoja. Karin and Carmen designed and built a dipole antenna and receiver in order to observe the radio emission from Jupiter. The antenna, located at the helipad, worked well but Jupiter never rose far enough above the horizon to be detected. Carmen will try later in the year when Jupiter is more cooperative. However, Karin and Carmen demonstrated that the antenna is a low cost and instructive means of introducing radio astronomy in the classroom at either the high school or undergraduate level.

Talks:

Fri, June 16: High Velocity Clouds and the Formation and Evolution of the Milky Way

[Dr. Leo Blitz, UC Berkeley]

Mon, June 19: OH/IR Stars and the Summer Student Observing Project

[Murray Lewis, NAIC/Arecibo]

Wed, June 21: Tour of Platform with Rey Velez, Head of Operations Group

Wed, June 21: Radio Astronomy Principles [Don Campbell, NAIC/Cornell]

Thu, June 22: Low Surface Brightness Galaxies [Karen O'Neil, NAIC/Arecibo]

Tue, June 27: Tour of Platform with Rey Velez

Tue, June 27: Radar Astronomy [Jean-Luc Margot, NAIC/Arecibo]

Thu, June 29: Photogrammetry of the Primary Reflector [Lynn Baker, NAIC/Cornell]

Thu, July 6: Introduction to Pulsar Astronomy [Ramesh Bhat, NAIC/Arecibo]

Fri, July 7: Searching for and Timing Pulsars [Duncan Lorimer, NAIC/Arecibo]

Mon, July 10: Arecibo Observatory: History and Science

[Daniel Altschuler, NAIC/Arecibo]

Wed, July 12: Asteroids [Mike Nolan , NAIC/Arecibo]

Radio Receivers [Dr. R. Ganesan, Raman Institute]

Thu, July 13: Turbulence in the Human Heart and the Equatorial Electrojet:

What Do They Have in Common? [Niel Otani, Case Western Reserve Univ.]

Galaxies Behind the Milky Way and the Great Attractor

[Renee Kraan-Korteweg, Univ. de Guanajuato]

Fri, July 14: Molecular Gas and Dust in High Redshift Galaxies

[Richard Barvainis, National Science Foundation]

Tue, July 18: Geology of the Caribbean Plate [Ellen Howell, NAIC/Arecibo]

Wed, July 19: Probing the Local ISM Using Pulsars [Ramesh Bhat, NAIC/Arecibo]

Mon, July 24: Incoherent Scatter [Mike Sulzer, NAIC/Arecibo]

Wed, July 26: The Upper Atmosphere [Sixto González, NAIC/Arecibo]

Summer Student Symposia:

Wed, July 26: Observing Meteorites [Shawn Allison]

Mon, July 31: Jupiter as a Radio Source [Karin Menendez]

The Flora and Fauna of Arecibo Observatory [Ernesto Estremera]

Mon, Aug 7: Extended H I Disks in Low Surface Brightness Galaxies [Diane Chin]

Building a YAGI Antenna, Designing a Cabinet for the CH1 Upgrade

and Mapping the AO Fiber Optics [Homero Cersosimo]

Wed, Aug 9: Gravity Waves are WEIRD! [Justin Kinney]

Search of CH3OH Masers at the Q-band: A Survey Toward Massive

Star Forming Regions [Carlos Vargas]

Thu, Aug 10: Receiver Cold Load Design and Carriage House One Equipment

Replacement [Miguel Irizarry]

Fri, Aug 11: Kinematics of Dwarf Irregular Galaxies [Laura Hainline]

The Magellanic Stream [Alyson Brooks]

Mon, Aug 14: Understanding the Ionosphere [Darik Velez]

Arecibo Incoherent Scatter Radar Database [Sarah Boswell]

Fri, Aug 18: Two Investigations of Pulsar Positions: Supernova Remnant Offsets

and The Galactic Distribution [Ruth Murray]

Pulsar Dynamic and Secondary Spectra [Amanda Kirchner]

Tours:

* Rey Velez conducted tours of the platform, the new Gregorian system and the receivers.

* Boqueron beach and sunset at the Cabo Rojo lighthouse on a cliff jutting out from the SW corner of the island.

* Snorkeling at the Shacks and watching surfers at Jobos beach.

* Several day trips to Old San Juan with optional tours of the Bacardi Rum Factory and El Morro.

* Tour of the bioreserve, Las Cabezas de San Juan Nature Reserve, in Fajardo.

* All day tour of the El Yunque rain forest and its Visitor Center.

* Overnight on Vieques for a tour and swim in the Bioluminescent Bay.

* Beach party at Sardinera Beach.