The National Solar Observatory and its
partners have chosen three candidate sites for a year of detailed
evaluation leading to selection of one site for the 4-meter,
ground-based Advanced Technology Solar Telescope (ATST).
The selected sites are Haleakala, Hawaii; Big Bear Lake, California;
and La Palma, Canary Islands, Spain.
“The ATST Science Working Group recommended these three based on
survey data at each of six sites that we studied for more than a
year,” said Dr. Stephen Keil, director of the National Solar
Observatory. “Each has a unique combination of atmospheric conditions
and other factors that make it an outstanding location for the ATST.
The continued survey will let us determine which one has the best
observing conditions.”
The recommendation was accepted by Keil and the four co-principal
investigators from the principal ATST partners: Robert Rosner,
University of Chicago; Jeffrey Kuhn, University of Hawaii; Michael
Knoelker, High Altitude Observatory, Boulder, CO; and Philip Goode,
New Jersey Institute of Technology. Final selection is anticipated in
late 2004.
The data were collected by the ATST Site Survey Working Group: Frank
Hill (NSO, chair), Rich Radick (U.S. Air Force Research Laboratory),
Steve Hegwer (NSO), John Briggs (University of Chicago), and Steve
Fletcher (NSO).
ATST will be the world’s largest ground-based solar optical
observatory. It will have a 4-meter, open-aperture telescope
employing recent advances in adaptive optics and other technologies
to study the fine structure of details of solar activity including
sunspots, flares, and a range of phenomena too small to be resolved
by current telescopes. Adaptive optics will let it routinely achieve
spatial resolutions as fine as 0.03 arc-second (~20 km) as compared
to the present limit of 0.5 to 0.1 arc-second (~360 to 70 km),
depending on seeing.
The continued ATST site survey will determine which site will
maximize the scientific productivity of the telescope. The desired
daytime atmospheric characteristics of such a site are frequently
clear skies, excellent seeing, low humidity, few aircraft contrails,
and low dust levels.
The initial survey chose six sites as the best of an initial list of
72 potential sites. The three not selected for further study are
Sunspot, NM; Panguitch Lake, UT; and San Pedro Martir, Baja, Mexico.
Except for Panguitch Lake, each of the six sites has solar or
astronomical observatories or both.
The site survey data were released on Nov. 11, 2003, without
rankings. Keil noted, “It was the first time that several sites were
simultaneously evaluated with identical instrumentation.” The data
are aimed at optimizing the new, demanding performance criteria for
the ATST and have no bearing on suitability of those sites and their
current telescopes.
“Five of the sites were selected because they already conduct
front-line solar physics or astrophysics with telescopes that have
been operating for several years,” Keil continued. “Those telescopes
will continue to serve the science community for many years to come.”
ATST is a project of the NSO, the Association of Universities for
Research in Astronomy (NSO’s parent organization), and the National
Science Foundation. It has been highly ranked by the latest Decadal
Survey of Astronomy and Astrophysics (2000) and a National Academy of
Sciences study of ground-based solar astronomy.
Information on the ATST is at http://atst.nso.edu
ATST semi-final candidate sites
Big Bear Lake, CA : Two-hour drive northeast of Los Angeles (34 14 N,
116 58 W; elev. 2.1 km [6717 ft]). Home to the Big Bear Solar
Observatory (BBSO) operated by the New Jersey Institute of Technology.
Haleakela, HA : Atop Haleakala, Maui, third largest of the Hawaiian
Islands (20 42 N, 156 11 S; elev. 3 km [10,023 ft]). Home to the Mees
Solar Observatory operated by the University of Hawaii, and other
observatories.
La Palma, Canary Islands, Spain : Island chain in the Atlantic Ocean,
west of Africa (28 46 N, 17 52 W; elev. 2.4 km [7,800 ft]). Home to
the Instituto de Astrofisica de Canarias, hosting observatories
operated by several European institutions.
Survey instrumentation
The ATST evaluated each site with identical sets of instruments, including:
Solar Dual Image Motion Monitor (S-DIMM) to measure differential
motion of the solar image (caused by atmospheric motion) and to
derive the Fried parameter (a measure of seeing distortions),
Shadow Band Array (SHABAR) to estimate turbulence several hundred
meters above the site,
Coronal photometer to determine sky brightness that would compete
with the faint corona, and
Dust and water vapor monitors to measure dust accumulation on optics
and humidity that may impact infrared observations.
The S-DIMM uses a 30.5 cm (12″) Meade Schmidt-Cassegrain telescope
with its aperture masked but for two 45 mm openings. This allows
measurement of differences in the apparent position of the Sun’s
limb. The SHABAR was mounted on the front of the Meade. It consists
of six miniature telescopes (15 mm f/3.8) focusing a small solar
image through a special lens and onto a photo diode that measures
fluctuations (scintillation) in solar brightness caused by
atmospheric turbulence.
For further information , contact:
Dave Dooling
Outreach and Education Officer,
National Solar Observatory
Sunspot, NM 88349
505-434-7015, dooling@nso.edu
or Jackie Diehl
505-434-7003, diehl@nso.edu
