The Yale Southern Observatory, Inc.

A Brief Description

Historical Background

The Yale Southern Observatory, Inc. is a not-for-profit corporation entered in the corporation books of Connecticut. Its sole purpose is to provide a framework within which Yale faculty members can perform astronomical research in the Southern Hemisphere. The Corporation was founded in 1962 under the name Yale-Columbia Southern Observatory, Inc.(YCSO) in collaboration with Columbia University. Prior to that in the 1920's, Yale had operated an observatory in Johannesburg, South Africa which specialized in the determination of stellar distances, or trigonometric parallaxes. Columbia University subsequently collaborated in that venture and the operation became known as the Yale-Columbia Southern Observatory. In the early 1950's the telescope, a 26-inch refracting telescope, was transferred to the Mt. Stromlo Observatory in Australia and continued to be operated by the Yale-Columbia consortium. Due to changes in scientific interests at Yale and Columbia the telescope was given to the Australian National University in July 1963.

In 1960, initial funding of $750,000 for the purpose of building an observatory to determine the accurate positions and apparent motions of the stars to study the structure of our Milky Way Galaxy was obtained from the Ford Foundation. In 1947 a similar research program had been started at the Lick Observatory in California to study the Northern Milky Way and there was a need to extend that investigation to the Southern Hemisphere. Following a survey of potential sites, the observatory was built at El Leoncito, Argentina, near Barreal in the Province of San Juan, in the eastern foothills of the Andes mountains at an elevation of approximately 8000 feet. The site was provided under terms of a long-term lease by the University of Cuyo and the Observatory was jointly operated by the University of Cuyo's Observatorio Astronomico "Felix Aguilar" (OAFA) in San Juan and the Yale-Columbia Southern Observatory, Inc. In addition, a residence was constructed adjacent to the grounds of the OAFA in San Juan for the technical support and housing of the YCSO personnel while they were in San Juan.

The first survey of the Southern sky was made between the years 1965 and 1974, with the financial support of a series of grants from the National Science Foundation. During that period, the US Naval Observatory relocated a Meridian Circle telescope to El Leoncito for the purpose of determining the positions of stars in the Southern Hemisphere as a part of their project to extend their catalogue of stellar positions to the Southern Hemisphere. The US Naval Observatory returned that telescope to Washington following the completion of its project in 1974. Due to changing research priorities at Columbia University, Columbia withdrew from the Corporation on June 30, 1974 and the name was officially changed to Yale Southern Observatory, Inc. on January 23, 1975. About two years earlier, the University of Cuyo had split into several regionally based units. The one based in San Juan became known as the National University of San Juan (UNSJ) and it assumed the administration of the OAFA and partnership with the YCSO and then the YSO. In 1990 the El Leoncito Observatory was renamed The Dr. Carlos U. Cesco Observatory on the occasion of the 25th anniversary of the beginning of observations in honor of Dr. Cesco's many contributions to the founding and operation of the Observatory.

During the period 1974 - 1983, El Leoncito was run by OAFA under terms of an agreement signed by the OAFA and the YSO. In 1983 a new ten year agreement was negotiated which provided the framework for repeating the Southern Sky survey and this was again extended for another ten year period in 1993. Beginning in 1987, observations were started for the repetition of the Southern Sky Survey but Eastman Kodak terminated the production of our photographic plates after only one-third of our second epoch photography had been completed. In 1997 a grant was received from the NSF to install a CCD detector system on the telescope to replace the photographic plates with the goal of completing the Southern Proper Motion second epoch with the CCD system. Preliminary observations with the CCD system were started immediately after its installation in March 1999 and we anticipate the resumption of the SPM second epoch in 2001 after the full telescope/camera operating system is completed.

The principal telescope of the Cesco Observatory is a Double Astrograph consisting of two lenses each 20-inches in diameter, one designed for blue light and the other for yellow light. The lenses focus the light separately onto two photographic plates with dimensions of 17 x 17 inches. The photographic plates are purchased in the US, shipped to Argentina, where they are exposed in the telescope, developed and then shipped back to the US. In New Haven, Connecticut the plates are measured with a precision measuring machine and the analyses performed which allow us to determine the absolute angular motions, or proper motions, of the stars.

Scientific Research

The principal scientific research program of the YSO and the UNSJ during the initial period of 1965 - 1974 was to photograph the Southern Sky. A comparison of the positions of the stars determined from the first period with those from the second period of photography, which started in 1987, yields the absolute proper motions of stars in our Milky Way Galaxy with respect to the faint and distant galaxies. Most of the stars in our Galaxy are confined to a saucer-like disk structure in which stars at the Sun's distance from the Galactic Center revolve around the center during a period of about 200 million years; those stars located closer to the Galactic Center revolve more quickly than the Sun and those more distant from the Center take a longer time to complete one revolution. By observing the stars from our moving Sun against the distant background of essentially fixed faint galaxies we can determine the rotation characteristics of our Milky Way Galaxy. In addition, if we were to take a star like the Sun moving with a fixed velocity and push it farther and farther away from the Sun, it would appear to be both fainter and move across the sky more slowly. If we now invert this example, then it is possible to estimate stellar distances based on measurements of the apparent brightness and apparent motions of groups of stars. From these data we can then derive the structure of our Milky Way Galaxy.

From 1993 through 1997 a second research program was funded by the National Science Foundation and the UNSJ. As with most astronomical research, the observational programs have been primarily located in the Northern Hemisphere and that is also true for the observation of double stars, which are pairs of stars circling around each other much as the Earth orbits the Sun. By observing the relative motion of one star around the other as a function of time, it is possible to determine the combined mass of the two stars, and those data are then used to provide constraints to the theory of the structure of stars. A new high technology instrument that can correct for the blurring caused by our atmosphere was used at the Cesco Observatory to resolve double stars that are apparently very close together. During the period of operation of this program, the number of high accuracy observations of double stars in the Southern Hemisphere was essentially doubled by our efforts.

A third major research program was initiated by the OAFA Astronomers when the Cesco Observatory was founded and has continued since that time. It deals with the observation and discovery of Minor Planets and Comets. Minor Planets are, as the name suggests, objects that are smaller than Planets and they are normally located in orbits between Mars and Jupiter. By taking long exposures of star fields near the plane of our Solar System and guiding on the stars, the Minor Planets appear as little streaks on the photographs. The positions of the objects over intervals of many years are analyzed and the orbits can then be calculated. This information is used for predicting future appearances of the objects and in some cases it has been used for improving the targeting of NASA spacecraft where very close approaches to the objects are planned. In addition to making observations of previously known objects, a large number of Comets and Minor Planets have also been discovered in this important program. A new phase of this program was started in 1999 with the installation of a new CCD detector system on our telescope. Observations are now also being made of potentially hazadous objects that may pass very close to the earth with the potential of impacting the earth with devastating consequences. These "Near Earth Objects", or NEO's, are generally very faint and move rapidly across the sky and hence require the capabilities of our new CCD detector system.

A fourth research project was initiated in 1978 has been primarily supported by grants from NASA. The Hubble Space Telescope requires that the positions of stars be precisely known for the pointing of the telescope. At the Cesco Observatory we have observed numerous fields of stars with our telescope and determined accurate positions that have been used for the calibration and pointing of the HST.

Financial Support

As mentioned previously, the Cesco Observatory was built with funds from the Ford Foundation and is operated jointly by the UNSJ and the YSO. During the first observation period from 1962 through 1974, the observatory was supported by the YCSO through grants from the US National Science Foundation. In the interim period (1975 -1986) between the first and second observation period the Observatory was supported by the UNSJ and since then it has been supported by both organizations. Starting in 1987 grants were obtained from the NSF to support the observations at the Cesco Observatory in Argentina and the measurement and analyses facilities of the YSO in New Haven. In 1994, a grant from the NSF was also obtained to support the observation of double stars at the Cesco Observatory. While most of the YSO support has gone for the purchase of supplies and equipment, the UNSJ part has been used largely for the support of salaries. This optimum division of funds has made it possible for us to use the highly talented and skilled UNSJ staff and the YSO's scientific equipment to make major contributions to astronomy.
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