A NEO Survey in the
Southern Hemisphere

"B U S C A"

Tancredi G. ⁽¹⁾ , Sosa A. ^{(1) (2)} , Acosta E. ⁽²⁾ & Ceretta A. ⁽²⁾

⁽¹⁾ Depto. Astronomía, Inst. Fisica, Fac. Ciencias, Montevideo, URUGUAY

⁽²⁾ Observatorio Astronómico "Los Molinos'', Ministerio de Educación y Cultura, URUGUAY

Abstract

The efforts to discover NEOs have been concentrated up to now in the Northern Hemisphere where there are already 6 big NEO surveys functioning. The Observatorio Astronómico "Los Molinos" got a grant to install a new observatory fully dedicated to the NEO survey in the countryside of Uruguay (South America). The new telescope is expected to be operational in early 2002.

The program is named "Búsqueda Uruguaya de Supernovas, Cometas y Asteroides - BUSCA".

The problem

The search for NEOs has been concentrated up to now in the northern hemisphere. Six dedicated NEO surveys programs are already in place: 4 located in the Southwest of USA, one in Hawaii and one in Japan.

Figure 1- Sky coverage of the big surveys functioning in March 2001. Note the sharp cut at declination -30° (Created by the Lowell's Asteroid Observing Service - Sky Coverage of NEO Searches, Version 1.2 - http://asteroid.lowell.edu/cgi-bin/koehn/coverage).

None of the surveys mentioned above reach declinations southern than -30°; therefore more than 25% of the celestial sphere is not covered by any project (see e.g. Fig. 1).

Several scientific and political groups have recognized this North-South asymmetry and they appeal for a prompt solution by installing new survey telescopes in the southern hemisphere. There are declarations in this line of arguments by the Spaceguard Foundation, the IAU- Working Group on Near-Earth Objects, and the UK Task Force in NEOs.

Objectives and Methodology

Our main objective is the search for NEOs in the southern sky as well as follow-up observations to determine accurate orbits. With a larger number of known NEOs, we can improve the estimates of the chances that an object could collide with the Earth.

To search for moving objects we require a dedicated telescope and a CCD camera with a wide field of view. We will start our survey with a telescope in the lower range of the already existing surveys. Software for the automatic control of the telescopes will be installed.

Follow-up observations of the discovered objects will be done from other telescopes of our own institute as well through collaboration with colleagues of the South American Spacegaurd Association, with telescopes in Argentina, Brazil, Argentina, Paraguay and Uruguay.

This new survey in the southern hemisphere as well as the follow-up capability would contribute to reach as soon as possible the NASA's goal of locating at least 90 percent of the Earth-approaching asteroids larger than about 1 kilometer in diameter .

The research team

The institutes involved in the project are: the Dept. Astronomy (Fac. of Sciences) and the Observatorio Astronómico "Los Molinos" - OALM (Minister of Education and Culture). Their main research topic is the study of minor bodies of the Solar System.

Some members of our group are members of several IAU Working Group, like the one in on Near-Earth Objects and the one on Comets and Distant Objects. The PI is a founding member of the Spaceguard Foundation.

The staff of the project has large experience in observational research; they have performed observational runs in several telescopes of medium and large size. Our group has been involved in several searches for asteroids and comets using telescope from the European Southern Observatory and the Cerro Tololo Interamerican Observatory.

The OALM has a strong commitment in outreach activities. More than 10.000 persons visit the Observatory every year, most of them are primary and secondary students. Almost hundred people visit us in our monthly open house. Several amateur groups have their instruments in the Observatory campus. The press frequently requests us information about astronomical events.

The present status

The National Research Council of Uruguay (CONICYT) granted the OALM a small project to install a telescope to search for NEOs. The total amount of the awarded fund is US$27000. The money was used to buy a 46cm (f/2.8) telescope (Centurion 18“ by Astroworks, http://www.astroworks.com). With further support from our home institutions (Universidad de Uruguay and the Minister of Education and Culture) we bought PCs and software.

One of the members of our group (Dr. T. Gallardo) got a grant from the Planetary Society to buy a CCD. We bought a CCD camera ST9e and a filter wheel from Santa Barbara Instruments (http://www.sbig.com). Regrettably, the ST9 does not fully cover the available focal plane of the Centurion telescope, but due to our limited budget, this was the larger CCD we could afford. Detectors as large as 30x30 mm could be installed without considerable image distortion.

The characteristics of the system are presented in the following table.

The telescope will be located in a dark area of the countryside, 200 km from Montevideo. We have support from the Local Government of the Province of Maldonado for the buildings. The construction will start in June 2002. Information about the future location:

We have already got some further support from the National Telecommunications Company (ANTEL) and the National Energy Company (UTE) to provide us with telephone connections and alternative energy (solar panels). Several weather monitors like wind, temperature and humidity, sensors; cloud, instantaneous rain and lightning detectors.

Location of the new site in a dark area of the countryside, of the Province of Maldonado.

In the mean time we have installed the telescope at the actual site of the OALM (15 km north of down-town Montevideo in a semi-rural area) where we are testing the software, the hardware and starting our survey observations.

The Centurion telescope in its present location in the OALM

The telescope and the CCD are controlled with the following software: 1) Astronomers Control Program to control the telescope and the dome, 2) MaxIm DL/CCD to acquire the CCD images and pre-processed them; and 3) Pinpoint to detect the moving objects as well as stars of varying brightness.

We plan to concentrate our survey efforts in the region not covered by the northern surveys, i.e. declinations southern than -30 deg..

The telescope will be fully controlled from our home institute in Montevideo. Every afternoon we will submit the jobs for the night and the controller system will decide whether to open the dome and start the observational routines depending on weather conditions. Four frames of each field will be taken separated by half an hour. The software for detection of moving objects will analyze the images and produce a report. Next morning the report of the discoveries as well as the discovery images will be sent them back to Montevideo. After analyzing the information we will submit the discoveries to the MPC.

As mentioned above we actually use a CCD ST9E for the image acquisition. The ST9E has a chip Kodak KAF-0261E thick, front-illuminated of 512x512 pixels of 20x20 mm. Though it is a blue-enhanced chip, the peak QE barely reaches 60% in the visible part of the spectrum. With a focal length of 127cm, the field of view becomes 28'x28' (0.22 square deg.). We plan to take 45 seg. exposures and 4 images per frame. Allowing for time to download the images and move the telescope, in two hours we can cover 30x0.22 = 6.6 sq.deg.. In a typical night of 8 hours, we are able to cover ~26 sq.deg.. The available sky south of -30deg. in declination in any night is ~5000sq.deg. in a month we will be able to cover a tiny fraction on the order of 300 sq.deg..

With a larger CCD (e.g. 1024x1024 pixels of 24mm) we would be able to cover ~150 sq.deg. per nigt, and in a month close to ~1800 sq. deg. This is more than one third of the available sky.

We are also working in many software improvements. An already developed algorithm for automatic detection of trails is being tested (see Ruetalo and Tancredi, Rev. Mexicana Astron. Atrof., Serie de Conf., Vol. 4, 1996, p. 117).

A big part of the region southern of -30 deg. is covered by a dense section of the Milky Way. We plan to implement software to survey in these regions by applying image subtractions techniques.

Since the Centurion survey telescope has the capability to be controlled with the Astronomers Control Program-ACP through the Web, we plan to offer the telescope to the public. The days around full moon are not useful for our survey due to the sky brightness. We plan to let students and amateur groups control the telescope during these days.

For this purpose we are translating the ACP web interface into Spanish.