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\twocolumn[
\centerline {\bf \large Terahertz Astronomy From The Coldest Place on Earth}
\normalsize
\begin{center}
Christopher K. Walker \& Craig A. Kulesa \\
Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson
AZ 85721\\ 
e-mail: cwalker@as.arizona.edu \& ckulesa@as.arizona.edu\\
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\noindent
{\bf Abstract}
\medskip

Many atoms and molecules have emission lines that occur at THz frequencies. 
These emission lines can be used to probe the conditions in Giant
Molecular Clouds (GMCs) throughout our galaxy. From studying the star
formation process 
in GMCs we will gain a better understanding of the origin of planetary
systems like our own. The high Antarctic plateau offers unique
opportunities for observatories optimized for this important
wavelength regime.   

\medskip
\noindent
{\bf Introduction}
\medskip

All stars and planets originate in cold clouds of gas and dust that
permeate interstellar space. The original clouds contained only
hydrogen and helium with trace amounts of lithium and
deuterium. Indeed the first generation of stars contained only these
elements. Over the lifetime of the Universe many generations of high
mass stars have come and gone depositing the products of
nucleosynthesis (C, N, O, Si, P, etc.) into the interstellar
medium. Within the shielded environments of Giant Molecular Clouds
(GMCs) these elements are able to combine to form a plethora of
molecules. Through radiative transitions, these molecules play an
important role in determining the energy balance within star forming
clouds and the interstellar medium as a whole.  They partially regulate the 
formation of stars and planets and can be used to diagnose the physical
conditions (composition, temperature, density, velocity fields) within
these regions. 

\begin{figure}[!ht]
\centering
\includegraphics[scale=0.31,angle=-90]{./ngc6334.ps}
\caption{\label{ngc6334} {\small \it Left): The southern giant
    molecular cloud NGC~6334 imaged in the light from the J=4-3
    rotational transition 
    (0.46~THz) of CO with the AST/RO telescope. Right): A sample 0.81~THz
    spectrum of neutral atomic carbon and the J=7-6 rotational
    transition of CO observed toward a star forming region. }}
\end{figure}

Most of the dominant atomic and molecular features are 
found at submillimeter wavelengths ($>$0.3 THz, see
Figure~\ref{ngc6334}), one of the last largely unexplored wavelength
frontiers in modern astronomy. The extreme dryness and cold of the Antarctic plateau make it the best
location for conducting infrared and submillimeter astronomy from the ground.
Sites of particular astronomical interest on the plateau are shown in
Figure~\ref{continent}.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{./antarctica-map.eps}
\caption{\label{continent} {\small \it Map of the Antarctic continent showing
    the locations of South Pole, and the high-elevation sites of
    Dome~A, Dome~C, and Vostok station. }} 
\end{figure}

\medskip
\noindent
{\bf The Antarctic Submillimeter Telescope \& Remote Observatory}
\medskip

Over the past decade the Antarctic
Submillimeter Telescope \& Remote 
Observatory (AST/RO, see Figure~\ref{astro}) has been in operation at the
Amundsen-Scott South Pole Station. AST/RO was conceived as a
submillimeter-wave survey instrument and a prototype telescope for
automated winter operations in Antarctica. It is designed to
carry out large-scale mapping of the southern Galactic plane, the
Galactic Center, nearby galaxies, and selected star-formation regions
using a wide variety of submillimeter-wave heterodyne receiver 
systems.  Principal targets are the 0.5 THz fine-structure line
of atomic carbon and rotationally excited lines of carbon
monoxide (CO) from 0.46-0.81~THz.  The 1.7-meter aperture 
yields a beamsize of 1-2~arcminutes at these frequencies, large enough
to permit large-scale mapping programs, yet small enough to map
distant clouds in the Galaxy [1].

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{./astro.eps}
\caption{\label{astro} {\small \it The 1.7-meter Antarctic
    Submillimeter Telescope 
    and Remote Observatory (AST/RO) has been in continual operation at
    the Amundsen-Scott South Pole Station since 1994. }}
\end{figure}

\medskip
\noindent
{\bf The South Pole Telescope}
\medskip

Based upon the success of astronomical experiments at
the South Pole, new submillimeter facilities are being conceived and
constructed.  The largest of these, the 10-meter South Pole Telescope (SPT)
is now under construction and is scheduled for completion in 2007
(Figure~\ref{spt}). 
It will be used to study the formation and
evolution of the early Universe as well as the interstellar medium in
our and other galaxies [2].

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.55,angle=0]{./sptisosm.eps}
\caption{\label{spt} {\small \it Conceptual drawing of the 10-meter
    South Pole Submillimeter Telescope. }}
\end{figure}


\medskip
\noindent
{\bf HEAT: A Terahertz Observatory for Dome~A}
\medskip

Building upon the heritage of AST/RO, 
a new 0.5-meter observatory, the High Elevation Antarctic Terahertz Telescope
(HEAT), is being proposed for Dome~A in Antarctica (Figure~\ref{heat}) [3].
Dome~A is the highest (4.1~km), driest, coldest site on the ice plateau. From
its summit, observations of the astrophysically important 1.46 and
1.9~THz lines from N$^+$ and C$^+$ should be routinely
possible.  From remote sites such as Dome~A, the next generation of THz
instrumentation can be field tested, providing an invaluable dress
rehearsal for future space missions. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.5,angle=0]{../figures/AASTINO.eps}
\caption{\label{heat} {\small \it The High Elevation Antarctic
    Telescope will be a dedicated observatory for astronomical
    investigations at THz frequencies.  It will rest atop an Automated
    Astrophysical Site-Testing InterNational Observatory (AASTINO),
    built by the University of New South Wales.  Equipped with
    sensitive SIS and HEB
    receivers, HEAT is designed to perform an automated survey of the southern
    Galactic Plane from Dome~A, the highest point on the Antarctic
    plateau, starting in 2008. }}
\end{figure}

\medskip
\noindent
{\bf References}
\medskip

\noindent [1] Martin, C. L., Walsh, W. M., Xiao, K., Lane, A. P.,
Walker, C. K., and Stark, A. A. 2004, ``The AST/RO Survey of the
Galactic Center Region. I. The Inner 3 Degrees'', Astrophysical Journal
Supplement, v150, p. 239-262. 

\smallskip

\noindent [2] Ruhl, J., et al.\ 2004, ``The South Pole Telescope'',
Proc. SPIE, 5498, 11 

\smallskip

\noindent [3] Walker, C.~K., et al.\, ``Forecast for HEAT on Dome A,
Antarctica: the High Elevation Antarctic Terahertz Telescope'', 2004,
Proc. SPIE, 5489, 470 


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