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\begin{document}

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\twocolumn[
\Large 
\centerline {\bf Project Description}
\normalsize
\vspace{0.5cm}
]


\section{Results from Prior NSF Support}
Over the past few years, the PI's group at the University of Arizona
has built two spectroscopic heterodyne array receivers;
{\it PoleSTAR}, a 4 pixel 810 GHz
receiver now in operation on the 1.7~m AST/RO telescope at the South
Pole and {\it DesertSTAR}, a 7 pixel 345~GHz array receiver for the
10-meter Heinrich Hertz Telescope (HHT) on Mt. Graham,
Arizona.  Both instruments are the very first of their kind.  PoleSTAR has been fully integrated with
the AST/RO telescope and offers excellent 
(T$_{rec}<700$~K) receiver performance on all
4 pixels. % (Figure~\ref{polestar}).  
DesertSTAR went into routine operation on the HHT with an
initial complement of 3 pixels in October 2003.  First-light spectra
and a photograph of the instrument mounted at the f/13.8 Nasmyth focus of the
HHT are shown in Figures~\ref{desertstar1}--\ref{desertstar2}.  
Excellent main-beam efficiencies (80\%) were derived from observations
of Mars.  DesertSTAR will be expanded
to the final hexagonal array of 7 pixels during summer 2004.   Both
instruments were funded by NSF programs; work on PoleSTAR 
was funded by the NSF Office of Polar Programs (A. Stark--PI: OPP-0126090),
and DesertSTAR 
development has been a joint effort between the University of Arizona,
the University of Massachusetts, and the University of Virginia with
partial funding through the NSF ATI program (AST-9622569).  The experience and
heritage of many constructive collaborations gained in the
construction of both arrays will be exploited in the proposed development of 
the first large-format, integrated submillimeter heterodyne camera. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.4,angle=0]{../figures/new_mount.eps}
\caption{\label{desertstar1} {\small DesertSTAR mounted at the Nasmyth
    focus of the HHT during its first multipixel engineering run.}}
\end{figure}

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.37,angle=0]{../figures/orion.eps}
\caption{\label{desertstar2} {\small  First multipixel light of
    DesertSTAR at the HHT from the Orion 
    Molecular Cloud.  The $10' \times 10'$ On-The-Fly (OTF) 
    map was performed in
    1~hour; the 2-pixel noise floor is 1.4 times lower than that of a single
    pixel.}}
\end{figure}

%\begin{figure}[!hbt]
%\centering
%\includegraphics[scale=0.3,angle=0]{../figures/ngc6334-final.eps}
%\caption{\label{polestar} {\small Simultaneous 4-channel spectra from
%    PoleSTAR, the PI's 810~GHz array
%    receiver, now in operation at the AST/RO telescope at the South
%    Pole.  Every imaged point in a heterodyne map of a molecular cloud also
%    represents a high-resolution ($\lambda/\Delta \lambda \approx
%    10^6$) spectrum.}} 
%\end{figure}

\vspace{-0.25cm}

\section{Research Activities}

The proposed SuperCam instrument will enable
innumerable new astronomical research opportunities as a facility
instrument at the HHT, {\bf open to all users.}  However, 
its high angular and spectral resolution,
coupled with an exceptional field of view makes it {\it a truly exceptional
Galactic Survey instrument}.  Here, we outline a SuperCam ``key project'', a
submillimeter CO survey of the Galactic Plane observable from
Arizona.  Indeed, the scientific requirements of this survey define the
characteristics of the SuperCam instrument, which is then presented in
detail in Section~\ref{instrument}. 


\subsection{Introduction}

From the Milky Way to the highest-redshift protogalaxies at the onset
of galaxy formation, the internal evolution of galaxies is defined by
three principal ingredients that closely relate to their interstellar
contents: 
\begin{enumerate}
\setlength{\topsep}{-1ex}
\setlength{\partopsep}{-1ex}
\setlength{\itemsep}{-0.4ex}
\setlength{\parsep}{-0.4ex}

\item the transformation of neutral, molecular 
gas clouds into stars and star clusters (star formation). 

\item the interaction of the interstellar medium
(ISM) with the young stars that are born from it, a regulator of
further star formation. 

\item the return of enriched stellar material to the
  ISM by stellar death, eventually to form future generations of stars.

\end{enumerate}

\noindent The evolution of (the stellar population of) galaxies is
therefore determined to a large extent by the life cycles of
interstellar clouds: their creation, star-forming properties, and
subsequent destruction by the nascent stars they spawn.  


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.38,angle=0]{../figures/LifeCycle-ISM.eps}
\caption{\label{cycles} {\small Life Cycles of the ISM}} 
\end{figure}

The life cycle of interstellar clouds is summarized pictorially in
Figure~\ref{cycles}.   Although these clouds are largely comprised of
neutral hydrogen in both atomic and molecular form and atomic helium, these
species are notoriously difficult to detect under typical interstellar
conditions.  Atomic hydrogen is detectable in cold clouds via the
21~cm spin-flip transition at 1420~MHz, but because the emission line
is insensitive to gas density, cold (T$\sim$70K) atomic clouds are not
distinguishable from the warm (T$\sim$8000K) neutral medium that
pervades the Galaxy.  Furthermore, neither atomic helium nor molecular hydrogen
(H$_2$) have accessible emission line spectra in the prevailing
physical conditions in cold interstellar clouds.   Thus, it is generally
necessary to probe the nature of the ISM via rarer trace elements. 
Carbon, for example, is found in ionized form (C$^+$) in neutral HI clouds,
eventually becoming atomic (C), then molecular as carbon monoxide (CO)
in dark molecular clouds.  The dominant ionization state(s) of carbon
accompany each stage of a cloud's life in Figure~\ref{cycles}.  

In general, however, only global properties can be gleaned from the
coarse spatial resolution offered by studies of external galaxies.
Therefore detailed interstellar studies of the widely varying
conditions in our own Milky Way Galaxy
serve as a crucial diagnostic template or ``Rosetta
Stone'' that can be used to translate the global properties of distant
galaxies into reliable estimators of star formation rate and state of
the ISM.   These studies are very incomplete, however.  
Though we are now beginning to understand star formation, the
formation, evolution and destruction of molecular clouds remains
shrouded in uncertainty. 

The need to understand the evolution of interstellar clouds as they
directly 
relate to star formation has become acute.  The National Research Council's
most recent Decadal Survey, under the the advisory of a distinguished
committee, has identified the study of star formation as one of
the key recommendations for new initiatives in this decade.
Similarly, understanding the processes that give rise to star and
planet formation represent the central theme of NASA's ongoing Origins
program.  

%\fbox{\parbox{2.9in}{
\noindent A new, comprehensive survey of the
Galaxy must address the following questions to make significant progress
toward a complete and comprehensive view of Galactic star formation:
\begin{itemize}
\setlength{\topsep}{-1ex}
\setlength{\partopsep}{-1ex}
\setlength{\itemsep}{-0.4ex}
\setlength{\parsep}{-0.4ex}

\item How do molecular clouds form, evolve, and get disrupted?  How
  do typical atoms and grains cycle through the ISM?

\item How and under what conditions do molecular clouds form stars?

\item   How do the energetic byproducts of stellar birth, UV radiation
  fields and (bipolar) mass outflows regulate further star formation
  in molecular clouds?

\item How does the Galactic environment impact the formation of clouds
  and stars?   What are the specific roles of spiral arms, central
  bars, and infall and other influences from outside the Galaxy?

\end{itemize}
%}}

\subsection{Properties of the Proposed Survey}


\noindent \fbox{\parbox{3in}{The following features represent a definitive
survey that would not only provide the clearest view of the star
forming clouds in the Galaxy, but would also serve as the reference
map for future focused studies with the LMT, and SMA, CARMA and ALMA
interferometers.  }}

\subsubsection{High Resolution Spectroscopic Imaging}


%\vspace{-0.3cm}
\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.48,angle=0]{../figures/supercam-b33.eps}
\caption{\label{beams} {\small The 64 beams of SuperCam overlaid upon
    the Horsehead Nebula (B33).  Each beam will measure a
    high-resolution spectrum, a small portion (15\%) of which is shown
    at right. The depicted spectrum was taken with the existing
    345~GHz facility receiver at the HHT, and resampled to match
    the spectral resolution of the proposed SuperCam instrument.}}
\end{figure}


Techniques commonly used to diagnose the molecular ISM 
include submillimeter continuum mapping of dust
emission \citep{hild83} and dust extinction mapping at optical and
near-infrared wavelengths \citep{lada94}.  Large format detector
arrays in the infrared are now 
commonplace, and with the advent of bolometer arrays like SCUBA at the
JCMT and SHARC at the CSO, both techniques have performed degree-scale
maps of molecular material.  However, these techniques have limited
applicability to the study of the large-scale evolution of molecular
clouds due to the complete lack of kinematic information.   

The confluence of many clouds along most Galactic lines of sight can only 
be disentangled with spectral line techniques.  Fitting to a model of
Galactic rotation is often the
only way to determine each cloud's distance and location within the
Galaxy.  With
resolution finer than 1~\kms, a cloud's kinematic location can
be even distinguished from other phenomena that alter the lineshape, such as 
turbulence, rotation, and local effects such as protostellar
outflows.  These kinematic components play a vital role in the
sculpting of interstellar clouds, and a survey that has the goal of
understanding their evolution must be able to measure them.  

CO is second only to H$_2$ as the most abundant molecule in the ISM,
and it remains the most accurate, most sensitive tracer of
H$_2$ on large scales (Figure~\ref{beams}). 
The proposed SuperCam instrument will resolve the
intrinsic profiles of Galactic CO lines, with a per-channel
resolution of 0.2~\kms\ over 230~\kms\ of spectrometer
bandwidth, comparable to the Galactic rotational velocity.  


\subsubsection{First Submillimeter Galactic Plane Survey}

%\vspace{-0.4cm}
Molecular line surveys have been performed over the entire sky in the
light of the 2.6 millimeter 
$J=1-0$ line of \co, and have been used to synthesize our
best understanding of the molecular content of the Galaxy.  Still, our
understanding of Galactic molecular clouds is incomplete.  Early
results were obtained with large beams, e.g., $>$9$'$
\citep{dame87,dame01}); were undersampled, e.g., 3$'$ for the
UMass/Stonybrook survey -- \citep{solo87, scov87}; or had limited
areal coverage, e.g., the early FCRAO surveys -- \citep{carp95, star89, ball91, miec94}.  The Galactic
Ring Survey (GRS) at FCRAO is by far the most comprehensive survey of
the inner Galaxy to date \citep{simo01}.  However, this survey traces
only the $J=1-0$ line of \tco, which is less sensitive to warm, low-opacity,
high velocity gas such as produced by outflows, photodissociation
regions (PDRs), and shocks.  
This point is illustrated in Figure~\ref{synthcloud},  
with images of a synthetic model cloud constructed in the
integrated light of different spectral lines of CO.  
The model cloud is externally illuminated by a B
star and cloud excitation, temperature and
chemical abundances are determined self-consistently using Monte
Carlo methods.  The integrated spectral 
line images show that the
heated portion of the cloud is largely missed by the J=1-0 lines,
but captured by the J=3-2 lines.   Reconstruction of the cloud based
on observation of the \tco\ J=1-0 line alone recovers only 60\% of
the total cloud mass, whereas the combination of J=1-0 and
J=3-2 lines recovers 90\% of the H$_2$ mass.

\medskip

\noindent 
\fbox{\parbox{3.1in}{A more comprehensive view of molecular clouds can
therefore be gleaned from
measurement of the submillimeter lines of CO and its isotopes, in
combination with existing millimeter-wave observations. 
The gas probed by
higher-J transitions is of greatest interest to our posed 
questions -- it is the {\it energetic} gas that 1) participates
in molecular outflows, 2) senses radiation fields at the
photodissociated surfaces of clouds, and 3) is warmed by 
star-formation in cloud cores.  Higher-J lines are also needed to
properly interpret even basic properties of clouds derived from 
existing CO~$1-0$ observations. }}

\medskip

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.4,angle=0]{../figures/COmaps.eps}
\caption{\label{synthcloud} {\small {\bf The need for a submillimeter
    survey}:  Simulated image of a fractal molecular
    cloud in several CO transitions. 
    The energetic gas that interacts with stars is far 
    better probed by the $3-2$
    lines, however both $1-0$ and $3-2$ lines are needed together to
    extract a comprehensive understanding of cloud properties,
    dynamics \& evolution. }}
\end{figure}

%\vspace{-0.3cm}
%\begin{figure}[!hbt]
%\centering
%\begin{minipage}{3.3in}
%{\parbox{1.8in}{\includegraphics[scale=0.45,angle=0]{../figures/COmissing.eps}}}
%{\parbox{1.3in}{\caption{\label{missing} {\small The simulated cloud from
%    Figure~\ref{synthcloud} further demonstrates the {\bf need for a
%      submillimeter survey}.  Shown as grayscale images are the actual
%    model H$_2$ column densities (top) and the values that would be
%    derived using only the \tco $1-0$ line (using the same conversion
%    as the Galactic Ring Survey) (middle) and as derived using a
%    dataset comprised of $1-0$ and $3-2$ data (bottom).  
%    Most of the energetic warm gas is
%    missed by only using the \tco\ $1-0$ data. }}}}
%\end{minipage}
%\end{figure}

Due to the prevailing physical conditions in the interstellar medium, 
the 870~$\mu$m (320-370~GHz) atmospheric window is one of the richest in the 
electromagnetic spectrum (Figure~\ref{trans}-a). %Frequencies of
				%spectral lines of special diagnostic
				%capability are tabulated in Table~\ref{tablelines}.  
This window also has the highest 
atmospheric transmission of any submillimeter band.  At this
wavelength the HHT has the 
highest aperture efficiency (80\%) of any submillimeter telescope in the 
world and excellent atmospheric transmission more than 40\% of the
time (Figure~\ref{trans}-b). These prospects make the design of a large
format multibeam receiver in the 345~GHz atmospheric window most attractive. 

\begin{figure*}[!bt]
\centering
\begin{minipage}{6.5in}
{\parbox{4in}{\includegraphics[scale=0.5,angle=0]{../figures/345window.eps}}}
{\parbox{2.5in}{\caption{\label{trans} {\small a) The 345~GHz spectral
	line survey toward 
    three positions in the W3 molecular cloud by \cite{helm97}
    shows a rich diversity of spectral diagnostics.  b) Modeled
    submillimeter atmospheric transparency for the HHT on Mt. Graham
    in 75 percentile (top), median (middle), and 25 percentile (bottom)
    atmospheric conditions, derived from 24 hour 225~GHz
    radiometer measurements over the last 6 years.}}}}
\end{minipage}
\begin{minipage}{4in}
{\parbox{1.5in}{a)}}
{\parbox{1.5in}{b)}}
\end{minipage}
\end{figure*}


\subsubsection{High Angular Resolution}

Angular resolution is a critical aspect of improvement for a new
Galactic survey.   Figure~\ref{resolution} depicts the model cloud of
Figures~{\ref{synthcloud}, projected to distances of
500~pc and 5~kpc.  Clearly, disentangling different clouds and cloud
components can only be accomplished with sub-arcminute angular
scales.  The angular resolution of SuperCam at the HHT
is 23$''$ at 345~GHz.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.4,angle=0]{../figures/resolution.eps}
\caption{\label{resolution} {\small {\bf The need for high angular
    resolution: } The synthetic cloud from 
    Figures~\ref{synthcloud} as seen in the \co\
    $J=3-2$ transition at a distance of 500~pc (left) and at 5~kpc,
    with beam sizes of $30''$ (top) and $2'$ (bottom).  The structure
    of the cloud is essentially lost in the larger beam.  In order to
    probe cloud structure and excitation over the entire Galactic
    disk, high angular resolution is vital. }} 
\end{figure}


\subsubsection{High Sensitivity}
\label{sensitivity}

CO survives in the ISM in part because of
the UV shielding from dissociation provided by H$_2$; thus CO's
survivability depends upon a molecular, H$_2$-dominated
environment.  For typical molecular clouds, the sharp transition
from H to H$_2$ typically occurs by a visual
extinction of $\sim$1 magnitude in the local interstellar radiation
field, or N(H)$=1.8\times 10^{21}$~cm$^{-2}$.
We therefore aim to detect all CO down to this hydrogen column density limit.
This corresponds to a 3$\sigma$ 
detection limit of N($^{12}$CO)$\sim 10^{15}$~cm$^{-2}$, which
implies an integrated intensity for cold gas 
(10K $<$ T$_k$ $<$ 50K) of 1.2~K~\kms\ in the
$J=3\rightarrow2$ transition at a gas density of $n_H=10^4$~cm$^{-3}$.
This sensitivity limit is achievable (3$\sigma$) within 10 seconds of
integration time per independent beam in {\it median} atmospheric
conditions (T$_{sys}\sim$700K) at the HHT, or (100/\#pixels) hours per mapped square degree, with 10$''$ grid spacing.  Detection (or limits) on
J=3$\rightarrow$2 in that time would constrain the gas density, based
upon the line brightness of millimeter wave transitions. 

\subsubsection{Mapping Coverage of the Galactic Plane}

\begin{figure*}[!hbt]
\centering
\includegraphics[scale=0.7,angle=0]{../figures/Fig2Dame.eps}
\caption{\label{area} {\small The power of SuperCam:  a definitive
    chemical and kinematic survey of star forming clouds in \co\ \&
    \tco\ J=3-2 over 500
    square degrees (\co) of the sky can be performed in 33
    full days per spectral line. 
    A corresponding survey with contemporary single
    pixel receivers would take over 6 years each. }}
\end{figure*}

Figure~\ref{area} demonstrates the needed sky coverage of a
submillimeter-wave Galactic plane survey.  From previous CO surveys it
is known that the scale height of CO emission toward the inner Galaxy 
is less than one degree \citep{dame87,dame01}.  
The interstellar pressure, abundances, and physical
conditions vary strongly as a function of Galactocentric radius, so it is
necessary to probe the inner Galaxy, the outer Galaxy, and the
$l=\pm 100^o$ tangent arms to obtain a statistically meaningful survey
that encompasses the broad dynamic range of physical conditions in the
Galaxy.  We propose therefore to 
probe the entire Galactic plane as seen from Arizona ($0
< l < 240^o$).  Below $l=90^o$, a {\it completely unbiased survey} will be
undertaken, covering 180 square degrees ($-1^o < b < 1^o$).  
This ``inner'' Galaxy survey will coincide
with two synergistic surveys: the FCRAO-BU Galactic Ring Survey (GRS)
and GLIMPSE, a Spitzer Space Telescope (SST) Legacy Program \citep{benj03}. 
Above $l=90^o$, most of the CO emission is located at
higher Galactic latitude, so the same solid angle will be distributed
according to the \cite{dame87,dame01} survey to follow the CO $1-0$
distribution and the best characterized star forming regions in the
Galaxy -- while maximizing
synergies with the ``Cores to Disks'' SST Legacy program
\citep{evans}, and other SST GTO programs. 

As discussed in Section~\ref{instrument}, the proposed SuperCam
array exceeds all of these needs and constitutes
the ideal Galactic survey instrument.


\subsection{Survey Activities}

\subsubsection{Mapping Strategy}

The most efficient mode of data collection with a focal plane 
array and which produces the highest fidelity images is 
On-the-Fly (OTF) mapping.  In this mode, the telescope continuously 
scans back and forth across a field while the backends are 
read-out at a sufficent rate to eliminate aliasing and beam smearing
(typically 4x/beam).  The primary advantage of OTF mapping with an array 
is that a given position on the sky is observed by all pixels in the 
array.  This redundancy removes any noise and gain imhomogeneities between 
pixels
and reduces the degree to which the data are correlated as a singular 
off-source measurement is distributed to on-source data. 
Mapping projects at the HHT routinely and efficiently use the OTF technique.  

The broad coverage of the Galactic Plane Survey lends itself naturally
to efficient, 24-hour/day mapping.   Only the region defined by $0 < l < 40^o$
enters the $30^o$ Sun-avoidance circle (during the month of December),
and $150 < l < 210^o$ during May-June.  With 64
pixels, SuperCam can reach the requisite sensitivity of
1$\sigma$=0.35K over a full square degree in 1.6 hours 
(Section~\ref{sensitivity}).  A Galactic
Plane Visibility diagram (Figure~\ref{visibility}) shows the nominal observing
strategy in which the entire survey can be accomplished in 2 months of
observing time per spectral line.  
We will therefore use a total of 4 months of observing time
over two years to perform the baseline survey; year \#1 of observing will
be devoted to \co\ $J=3-2$ mapping (346~GHz), and year \#2 will be devoted to
\tco\ $J=3-2$ mapping (331~GHz), with followup spectroscopy in
e.g. HCO$^+$ $J=4-3$ (356~GHz) and  C$^{18}$O $J=2-1$ (230~GHz
facility receiver) to identify the most opaque, densest cloud
cores.  {\it SuperCam's wide instantaneous IF bandwidth
  (ultimately 8~GHz; see Section~\ref{IF} for details) also allows sensitive detection of 870~$\mu$m dust continuum
  emission.}
Thusly, we will also simultaneously record total power scans and construct
dust continuum maps, particularly in regions where the \tco\ lines
become optically thick. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.33,angle=-90]{../figures/visibility.eps}
\caption{\label{visibility} {\small The entire Galactic Plane survey
    can be accomplished in 2 months of observing time per spectral
    line.  This visibility diagram denotes how the Galactic Plane
    will be partitioned for efficient observing. }} 
\end{figure}


\subsubsection{Science Products and Dissemination}

The primary challenge of OTF mapping is data management, which becomes
particularly 
acute with an array for which the data rates are typically 100x larger.
We therefore plan to adopt the scheme 
developed at FCRAO for OTF mapping with the 32 pixel SEQUOIA array
(see {\it
  http://www.astro.umass.edu/$\sim$fcrao/library/manuals/}), whereby
coadded and regridded data is written as a FITS cube or
CLASS file, and headers for 
each scan are written into a MySQL relational database, which 
facilitates efficient logging and retrieval of the data.
Our most demanding storage
requirements for a 500 square degree map, gridded to 10$''$ spacing,
with 1024 spectral points per grid position, is 130~GB.  The total
disk requirements for the survey will be about 260 GB.  Even today,
this volume can be readily handled by a single computer with a
redundant disk array for data integrity. 
Access to these data products to the greater scientific community
will be provided through a Java-based web browser interface that will
interface with MySQL and the FITS data cubes. 

\noindent \fbox{\parbox{3.1in}{All science tools, packaged reduction software,
    data products and 
    science products will be made available from the SuperCam survey's web
    page.}}

\medskip

\noindent   In addition to data products, important science tools
    include the following: 

\medskip 

\noindent {\it Clumpfinder} and {\it Outflowfinder}:  All Galactic
  cloud cores and star forming 
  regions will be separated,
  identified and analyzed from the master dataset as a function of
  position in the Galaxy.  An unbiased survey of 
  Galactic outflows, and their energy inputs to the ISM will be tabulated. 

\medskip 

\noindent {\it CO Analysis Package and Cloud Models}:  Numerous tools used to
  extract physical properties of clouds, such as volume density and
  temperature, will be released.  These tools will include statistical
  equilibrium calculations, radiative transfer codes
  based upon LTE, LVG, and Monte Carlo techniques, basic chemical network
  capable of following hydrogen and carbon chemistries, and foundational 
  models of molecular clouds and photodissociation regions.

\medskip 

\noindent {\it 2MASS Extinction Maps and the Formation of Molecular
  Clouds}:  The release of the 
  2~$\mu$m All Sky Survey will be used to make extinction maps in the
  photometric J, H, and K bands, to be
  compared with the measured CO emission and used to search for
  molecular cloud formation in the Galaxy; regions where large
  amounts of gas have become molecular, but CO has not yet formed.
  The ideal probe of nascent H$_2$ is the
  158 $\mu$m fine-structure line of the C$^+$ ion, owing to its intensity and
  utility as a densitometer \citep{kauf99}, but very 
  limited far-IR
  spectroscopic observations are available, and none have the requisite
  angular resolution.   Instead, we will adopt the innovative use
  of recombination lines of carbon \citep{rosh02} 
  to probe the [C~II] emission and hence the
  H$_2$ in forming clouds, just as H$\alpha$ emission at visible
  wavelengths is used to probe hydrogen-ionized regions.  
  We will use SuperCam to make selected deep pointings in the
  26$\alpha$ recombination line of carbon at 353~GHz, 
  in combination with similar
  measurements of the 39$\alpha$ line from the Kitt Peak 12-meter (or
  FCRAO 14-meter) and
  high-$n$ lines from, for example, the NRAO Green Bank Telescope or the
  VLA.  {\it These measurements will enable the crucial 
  first measurement of the formation of Galactic molecular clouds.}

\medskip 

\noindent {\it Systematic calibration of the dataset}:
  D-PI Kulesa is executing a unique survey of Galactic
  molecular clouds, using high resolution infrared absorption line
  spectroscopy of H$_2$ and \co, using ARIES (Arizona Infrared Image
  and Echelle Spectrometer) at the 6.5-meter MMT.  
  These observations directly measure
  the \co\ and \tco\ abundances relative to a precisely measured
  column density of H$_2$ \citep{kule04}. 
  These pointed measurements will be used to
  calibrate the submillimeter dust continuum maps and
  molecular line observations provided by SuperCam and the 
  generated infrared extinction maps from the 2MASS survey. 


\subsubsection{Roles of the Collaboration Participants}

Personnel who will initially develop and use the SuperCam instrument
comprise the Science~(S) and Instrument~(I) Teams tabulated in
Table~\ref{roles}.  They are also represented in an organization
chart, Figure~\ref{orgchart} in Section~\ref{management}.  {\it In addition
to the two teams, numerous students will participate in the instrument
and science development; at least 4 graduate students and 2 undergraduates at
the University of Arizona, and at least one graduate student each at UVa and
Caltech. }

\begin{table*}[!hbt]
\centering
\small
\begin{tabular}{|l|c|c|l|}
\hline
{\bf Participant} & {\bf Team} & {\bf Affiliation} & {\bf Partipation
  Activity} \\
\hline \hline
Christopher Walker & I, S & U. Arizona &  Project PI \\
 & & & Establishes science \& instrument requirements \\
 & & & Reviews and approves operations plans and execution \\
 & & & Reviews and approves science data products \\
\hline
Hop Bailey & I & U. Arizona & Project Manager \\
 & & & Manages science and instrument implementation \\
\hline
Craig Kulesa & I, S & U. Arizona &  DPI: Electronics, bias
systems \& software for SuperCam. \\
 & & & Lead for survey science products, data processing pipeline. \\
 & & & Collaborative activities with 2MASS and SST surveys. \\
\hline
Harry Fagg & I & U. Arizona & Project Systems Engineer, integration with HHT \\
\hline
Chris Groppi & I, S & NRAO & Array systems, dynamics of star forming regions \\
\hline
Sander Weinreb & I & JPL & PI for IF Amplifiers and IF processing
chain \\
\hline
Mark Heyer & S & U. Mass & Provides synergistic access to GRS
survey data \\
 & & & Leads integration of data pipeline with FCRAO OTF tools \\
 & & & Experience with Galactic Surveys and physics of the ISM \\
\hline
Alyssa Goodman & S & Harvard & Provides synergistic access to COMPLETE
survey data \\
 & & & Integration of C2D \& COMPLETE with SuperCam survey\\
\hline
J\"{u}rgen Stutzki & S & U. K\"{o}ln & Physics \& Chemistry of the ISM \\
\hline
Gopal Narayanan & I, S & U. Mass & Mixer design, star formation studies \\
\hline
John H. Bieging & S & U. Arizona & Integration of SuperCam data with 3-2-1
survey \\ 
\hline
Ed Churchwell & S & Wisconsin & Provides synergistic access to GLIMPSE SST
survey \\
\hline
Neil Erickson & I & U. Mass & mm/submm array receivers  \\
\hline
Larry d'Addario & I & NRAO &  Correlators and cryogenics \\
\hline
Jacob Kooi & I & Caltech & Broadband mixer design and device integration \\
\hline
Art Lichtenberger & I & UVa & PI for SIS device fabrication \\
\hline
John Payne & I & NRAO & mm-wave receiver systems \\ 
\hline
\end{tabular}
\caption{\label{roles} \small Activities of the Science ({\bf S}) and
  Instrumentation ({\bf I}) Teams}
\end{table*}


\section{Description of Research Instrumentation and Needs}
\label{instrument}

\subsection{Overview}

In order to achieve our scientific objectives we propose to build the first
large format (64 pixel) superheterodyne camera (SuperCam) at
submillimeter wavelengths. 
The advent of such a system will provide an order of magnitude
increase in mapping speed over what is now available and revolutionize
how observational astronomy is performed in this important wavelength regime. 

Unlike the situation with bolometric detectors, heterodyne 
receiver systems are coherent, retaining information about both the amplitude 
and phase of the incident photon stream. From this information a high
resolution 
spectrum of the incident light can be obtained without multiplexing. Indeed,
{\bf each} SuperCam pixel will provide 1,024 simultaneous spectral
measurements. 
In terms of raw power, each observation made with {\it SuperCam} will provide
{$\bf \sim 65,536$} independent measurements of the properties of the
object under 
study. High resolution spectroscopy can, in 
principle, be performed in this same wavelength regime using incoherent 
detectors together with frequency dispersive quasi-optical devices such as 
gratings and Fabry-Perot interferometers. However, the size requirement of 
quasi-optical devices and/or the need to scan in order to construct a 
spectrum make them too cumbersome or insensitive for the scientific objectives
of the proposed study. 

The possibility of large format arrays at submillimeter wavelengths
has been discussed for more than two decades
\citep{gil79}, but was prohibited by several factors:

\begin{itemize}
\setlength{\topsep}{-1ex}
\setlength{\partopsep}{-1ex}
\setlength{\itemsep}{-0.4ex}
\setlength{\parsep}{-0.4ex}

\item Sensitive mixing devices either did not exist or were difficult to
   fabricate.

\item When mixers were available, their performance would often vary
   significantly from device to device.

\item There was insufficient LO power to simultaneously pump more than
   one or two detectors.

\item Stacking more than a few mixer blocks together in the focal plane
   with their associated backshorts (if necessary), IF amps, magnets,
   bias lines, etc. was mechanically complex and could overload the
   cryogenic system.

\item The cost of the frontend components and the required backend
   spectrometer were prohibitive.

\end{itemize}

\noindent However, through the arduous efforts of many researchers in the
field, these hurdles have now been overcome. In realizing SuperCam,
the design team will pull heavily on the experience gained building a
variety of submillimeter-wave heterodyne receiver systems,
including:

\begin{itemize}
\setlength{\topsep}{-1ex}
\setlength{\partopsep}{-1ex}
\setlength{\itemsep}{-0.4ex}
\setlength{\parsep}{-0.4ex}

\item 230, 345, 490, and 810~GHz single pixel receivers for the Heinrich
Hertz Telescope (HHT) and Antarctic Submillimeter Telescope and Remote
Observaory (AST/RO).

\item the first 345 GHz array receiver ({\it DesertSTAR} on the HHT).

\item the first 810 GHz array receiver ({\it PoleSTAR} on AST/RO).
\end{itemize}
 
\noindent 
{\it SuperCam} represents the next phase in the evolution of high spectral
resolution imaging systems. The technology developed in the proposed effort 
has applications in a number of research areas outside of astronomy. 
These include remote imaging, space-based communications, and hazardous 
material detection.


\subsection{\it Proposed Design}

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.33,angle=0]{../figures/polestar-top.eps}
\caption{\label{polestar-cryostat} {\small Inside the PoleSTAR dewar. }} 
\end{figure}

Unlike all other millimeter/submillimeter arrays composed of individual
mixers and discrete components, the proposed array has a high degree of
integration. Well conceived, efficient packaging is essential to the
successful implementation of large format
systems. Figure~\ref{polestar-cryostat} shows the crowded 
interior of the 4 pixel (\it PoleSTAR}) array cryostat built by the PI's team
from discrete components.  The enormous 
complexity of even a small discrete system suggests 
a more integrated approach for larger systems.
A 3D rendering of the proposed SuperCam
array cryostat together with a block diagram of the full system is
shown in Figure~\ref{blockdiagram}.  At the heart of the array is an 
8x8 integrated 
array of low-noise mixers. The array mixer block is mounted on a motherboard  
containing mixer bias and first stage, low-noise, MMIC IF
amplifiers.  The motherboard design is depicted in Figure~\ref{motherboard}.

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{../figures/345-motherboard.eps}
\caption{\label{motherboard} {\small The high degree of integration in the SuperCam design also extends to the ``motherboard'' that houses the mixers and IF chain. }} 
\end{figure}


\begin{figure*}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{4.2in}{\includegraphics[scale=1.13,angle=0]{../figures/345blockdiagram.eps}}}
{\parbox{2.2in}{\caption{\label{blockdiagram} {\small Block diagram of
	the 345~GHz, 64-pixel SuperCam heterodyne array.}}}}
\end{minipage}
\end{figure*}

The mixers  
and IF amplifiers operate at 4~K. Novel microstrip ribbon cables carry
the IF's from all 64 mixers in the array to break-out boards attached to the 
inside of the vacuum housing of the array cryostat. The microstrip
ribbon cables  
are heat sunk to the 45~K stage of the closed-cycle refrigerator to
reduce thermal 
loading at 4~K. A single waveguide-coupled, solid-state source 
provides sufficient local oscillator power to pump all the mixers in
the array.  SuperCam is fully automated, 
with a field-proven control system that provides the user with a full
range of instrument control and characterization options. Below we discuss 
SuperCam's key components.

\subsection{\it Mixer Array}

In the 300-400~GHz range no amplifiers exist, so incoming
signals must first be down-converted to frequencies where low noise
amplifiers are available. At these high frequencies two types of mixing
devices are currently in use;  Schottky diodes
and superconductor-insulator-superconductor (SIS) junctions.
Schottky diode mixers have been in use on ground, airborne, and
space-based platforms for many years. They are reliable and provide modest
sensitivity that improves as they are cooled.  However, they require
prodigious amounts ($\sim$mW) of local oscillator (LO) power to efficiently
pump a single mixer.
State-of-the-art SIS mixers in the 350~GHz band have 20 times the sensitivity 
of Schottky mixers. Their greater sensitivity and lower LO power
requirements make SIS mixers the best choice for array applications. 
To operate, these mixers must be cooled to $\sim 4$~K. We
propose to develop a compact, sensitive, 64 pixel array of SIS mixers
optimized for operation in the 320-360~GHz atmospheric window.

The two dimensional, 8x8 array will be composed of eight, 1x8 subarrays.
The array mixers will utilize the same simple, single-ended, double-sideband
design that was successfully employed in our existing 7-pixel, 345~GHz array
(DesertSTAR). Indeed, the same SIS devices used in DesertSTAR
will be initially used in the proposed SuperCam instrument development. 
The measured DSB
noise temperature of a typical DesertSTAR mixer (50~K) is excellent and  
essentially frequency independent across the band.  
The 1x8 mixer subarrays will be composed of three major parts; a horn block,
an LO power injection block, and a junction block. The blocks are machined 
out of copper using standard split-block construction techniques.
Stainless steel guide pins and screws are used to ensure proper alignment 
and good contact between parts.  An assembly diagram is shown in 
Figure~\ref{assembly}.

\begin{figure*}[!hbt]
\centering
\includegraphics[scale=0.75,angle=0]{../figures/MixerBlock1x8-assembly.eps}
\caption{\label{assembly} {\small Assembly diagram of an
    integrated $8 \times 8$ pixel mixer array.}} 
\end{figure*}


Figure~\ref{IFblock} is a pictoral representation of one mixer in a
1x8 subarray. 
A low-loss, dielectric lens couples energy from the telescope into an
efficient, broadband, dual-mode feedhorn \citep{neil02} located in the
Horn Block.  
The horn uses an optimized nonlinear taper to generate multimodes,
which have a fundamental Gaussian  
mode power fraction of 99\%. This power fraction rivals that of
corrugated feedhorns but without the associated difficulties in
fabrication. The energy in the horn passes 
through a circular to full-height rectangular transition before
entering the LO injection 
block. The LO injection block consists of a $\lambda$/2 length of
waveguide with 
a half-height transition on the output. One or two small holes are drilled
into the sidewall of the waveguide to permit LO power ($\le 2\,\mu$W) 
from a waveguide running along the backside of the block to be coupled
into the mixer.  LO power distribution details are discussed in
Section~\ref{LOsection}, below. The sky signal
and LO energy 
then enter the Junction Block. The Junction Block consists of a 1/2
wavelength section 
of half-height waveguide, a slot for the SIS junction, a fixed-tuned 
backshort, and a small microstrip board. The SIS junction is a $\sim
1 \times 1$~$\mu$m Nb/AlO$_{\rm x}$/Nb 
device fabricated on a 3~mil crystalline quartz substrate.  Tuning structures
fabricated on the substrate permit broadband, low-noise operation. The junction
resides in a suspended stripline slot \citep{grop03}.  In the current
design, one end of the device 
is grounded to the mixer block. The other, ``hot'' end of the device
serves as both  
IF output and DC bias input and connects to the microstrip board
located on the facing 
half of the split-block via a spring loaded contact. The microstrip
connects the  
IF output/DC bias input of the mixer to the array motherboard via a
contact pad on the  
bottom edge of the junction block. 
  
Several companies have the capability of machining the mixer array. In
particular, 
Custom Microwave of Longmont, CO has a proven track record of
fabricating high quality, 
submillimeter-wave waveguide mixers and feedhorn arrays. We include
the cost of Custom  Microwave fabricating the mixer array in our budget. 

\begin{figure*}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{4.6in}{\includegraphics[scale=0.3,angle=0]{../figures/Mixer.eps}}}
{\parbox{1.8in}{\caption{\label{IFblock} {\small Assembly diagram of a
	single mixer block.}}}}
\end{minipage}
\end{figure*}


\subsection{Local Oscillators}
\label{LOsection}

With an array receiver, LO power must be efficiently distributed among
pixels. Depending on the mechanical and optical constraints of the array,
a balanced distribution can be achieved using quasioptical techniques or
waveguide injection. With the quasioptical approach, dielectric beam splitters
or holographic phase gratings are used to divide the LO energy between array
pixels. The multiple LO beams are then combined with the corresponding
sky beams  
before entering the array mixers using a beam splitter, Martin-Puplett
interferometer, or Fabry-Perot interferometer. The quasioptical approach 
works well for modest sized arrays. However, for the large format system being
proposed here, the size of the required quasi-optical power splitter and 
diplexer become prohibitive. Therefore we have chosen to use waveguide LO
power injection. Waveguide LO injection has the added advantage that
the optical 
alignment issues associated with the quasioptical approach are nonexistent.

The LO power for the array will be provided by a single solid-state,
synthesizer-driven source 
available from Virginia Diode Inc. 
The active multiplier chain consists of a high power solid-state 
amplifier followed by a series of tunerless broadband multipliers. An example
of such an LO chain is shown in Figure~\ref{LO}. There 
are no mechanical tuners, so the output frequency simply tracks the 
synthesized input frequency. The chain utilizes a series of broadband 
varactor doublers that have been developed at Virginia Diode Inc. 
These doublers have a tunerless bandwidth of 15-20\% and exhibit efficiencies 
from 60\% at 50 GHz to 10-20\% at 300 GHz. In order to increase output
power and reduce waveguide path length loss, the final multipler in the chain
will be mounted on the 45~K radiation shield of the array cryostat. With the
final multiplier cooled to this temperature, the output power of the LO chain
from 320-360 GHz is expected to be in excess of 5~mW. Using realistic estimates
for waveguide path length loss, this power level is $\sim8$ times greater than 
that required by the array. The output of the array is coupled to an eight-way
waveguide power divider located on one side of the array. Each of the eight outputs
provides the drive power for a 1x8 subarray. Power is delivered to each 
array pixel via a coupling hole as described above. A 
similar LO power injection
scheme was successfully used by Erickson (priv. comm.) 
in the 100~GHz, 
15 pixel, Quarry array. A novel waveguide ``thermal choke'' 
is used between the 45 and 4~K stages of the cryostat to minimize heat
loading (Hesler, private comm.). 


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.25,angle=0]{../figures/300x2chain.eps}
\caption{\label{LO} {\small Virginia Diode solid state LO chain.}} 
\end{figure}

\subsection{IF/Bias Distribution system}

\subsubsection{IF Amplifiers}
\label{IF}

The IF outputs from the array mixers are conveyed via microstrip
to 4, $1\times 16$ low-noise, InP MMIC amplifier modules located on
the array motherboard. 
These amplifier modules have been designed and fabricated by Sander Weinreb's 
group at Caltech. Initially, the IF center frequency of the array will
be 5~GHz.
This is the standard IF frequency at the HHT and lies within the
operating range of the existing generation of IF amplifier modules. 

During the past 4 years wideband, very low noise, cryogenic monolithic
microwave integrated circuit (MMIC) amplifiers have been developed with
design and testing at JPL and Caltech and foundry fabrication at TRW (now
Northrop Grumman Space Systems,  NGST) and HRL.  These LNA's utilize 
indium phosphide, 0.1~$\mu$m gate length, high electron-mobility transistors 
(HEMT's) and match the requirements needed for densely packed focal plane 
arrays in terms of noise temperature,  chip size,  DC power dissipation, 
yield,  and bandwidth.  

Prototype chips tested at 12~K and higher temperatures are available with 
frequency ranges of 4 to 12~GHz,  1 to 60~GHz, and 1 to 110~GHz with noise 
temperature increasing with frequency. The 4 to 12~GHz chip is 
most appropriate for this application because of its match to the
IF bandwidth of SIS and HEB devices and its very low noise and power 
consumption.   A typical 4--12~GHz  amplifier is described in 
Figure~\ref{IFamps}.  The chip
achieves noise temperature of $<$ 5~K consuming 20~mW  of power at 12~K when 
driven from a 50 ohm generator impedance.   The input match of the LNA is 
close to 50 ohms over the 4 to 12~GHz range;  this is often required for 
stable operation with an SIS mixer.
% (but not with an HEB mixer where a lower 
%frequency IF is advantageous).   
We propose to optimize the LNA using external microstrip
input circuit design and chip revisions if needed,  for the proposed mixers 
in terms of frequency range, power consumption at 4~K, input match, and noise 
temperature.  Ultimately, we plan to raise the center IF frequency of
the array to 8~GHz to take advantage of the wide bandwidth of these IF
amplifier modules. 

Compact packaging compatible with large focal-plane arrays is also
important to this program.  A custom-designed 
ribbon cable with alloy conductors 
for low thermal conductivity and ground-signal-ground coplanar waveguide 
output transmission lines will be designed and tested for cross-talk and 
impedance matching.  
The ``ground'' conductors can be at RF ground but also serve 
as DC conductors for transistor and mixer bias. Miniature strip connectors 
with 0.5~mm conductor spacing are available.  We believe this  strip MMIC IF 
amplifier approach can be realized with pixel spacing in the 2 to 5~mm range. 
As isolation of the amplifier input and output is also important, 
we will design appropriate shields and absorbers.


\begin{figure}[htb]
\centering
\includegraphics[angle=0,scale=0.4]{../figures/IF-performance.eps}
\caption{\small \label{IFamps} Performance of the 
4--12~GHz IF amplifiers produced by S. Weinreb's group at Caltech.  Noise 
temperatures are $\le $5~K, with gains of $\sim$35~dB when cooled to 12~K.}
\end{figure}


\subsubsection{Array Spectrometer}

A backend spectrometer is required to create the spectrum of each pixel 
from the downconverted base-band signal. Recent advanced in on-chip
integration  
make autocorrelators an efficient, low-cost approach for achieving the
bandwidth (~256 MHz) and spectral resolution (~0.25 MHz) required for
the proposed science program.  Spaceborne Inc. has built a number of
autocorrelator systems for radio 
astronomy applications and can provide an array spectrometer for SuperCam that
meets the proposed science requirements (Table~\ref{spectrometer}).

\begin{table}[!hbt]
\centering
\begin{tabular}{|l|}
\hline
a) 64 spectrometers enclosed in a VXI mainframe \\
b) 300 MHz maximum sampling clock \\
c) 300  MHz maximum analog bandwidth \\
d) 1024 frequency channels per spectrometer \\
e) integration timer from 150ms to 20s \\
f) packaged in a VXI,  C-size enclosure \\
g) 1000 W power consumption \\
h) computer interface via a fast USB port of a PC \\
i) virtual instrument software for Windows 2000 \\
\hline
\end{tabular}
\caption{\label{spectrometer} \small Spaceborne digital autocorrelator
  specifications}
\end{table}

A photograph of a Spaceborne correlator chip (here a 2~GHz bandwidth device)
is shown in Figure~\ref{correlator}a, and laboratory measurement of
the spectral response is shown in Figure~\ref{correlator}b. 
The SuperCam correlator chips will be fabricated with a 0.18~$\mu$m
CMOS process and provide efficient (87\%)  2-bit/4-level digital
correlation with 1024 lags.  The correlator
cost includes two separate device runs to ensure a sufficient number
of devices are
available. The SuperCam correlator will be delivered as a ``turn-key''
system with virtual
instrument software. A backend computer will communicate with the correlator,
perform the first-order data reduction, and store the reduced scans. 

We will construct an IF processor that downconverts each of the
64, 5~GHz IF's from the array to the 0-500~MHz frequency range required
at the input of the correlator.  The IF processor will also provide a
measurement of the total power level in each of the IF channels.  This
total power level will be used for characterizing the array
performance independent of the spectrometer and to sample the
broad-band continuum emission from astronomical objects.  A second IF
processor will be constructed to combine the 64 IF inputs of the
array correlator into eight, 2~GHz wide channels to be used as a
backend spectrometer for DesertSTAR.  {\it This
addition will allow DesertSTAR to reach its
full potential as an extragalactic instrument and will preserve its value
alongside SuperCam at the HHT.}  Funds for the second IF
processor are not being requested here. 

\begin{figure*}[htb]
\centering
\begin{minipage}{6.5in}
{\parbox{4.5in}{\includegraphics[angle=0,scale=0.5]{../figures/correlator.eps}}}
{\parbox{2in}{\caption{\small \label{correlator} The Spaceborne digital
  autocorrelator provides an ideal ``off-the-shelf'' multichannel
  spectrometer for SuperCam. a) 2~GHz Spaceborne correlator chip.  b)
  Laboratory measurement of spectral response. }}}
\end{minipage}
\end{figure*}

\subsection{Array Cryostat}

A 3-D rendition of the SuperCam cryostat is shown in
Figure~\ref{blockdiagram}. 
The cryostat's
outer dimensions are $\sim$546x546x481~mm. Light from the telescope enters
the cryostat through a 127~mm (5$''$) diameter AR coated, crystalline
quartz vacuum
window and passes through an IR blocking filter on the 50~K radiation
shield before illuminating the 4~K mixer array. 
SuperCam will use a Sumitomo Model a SRDK-415E-A71A cryocooler. The
cooler has 1.5~W 
of thermal load capacity at 4.2~K and 45W at 50K with 
orientation-independent operation. 
The operating temperature of the cryocooler is stabilized by the
addition of a helium  
gas pot on the 2nd stage. Once the 2nd stage cools to 4~K, the helium
gas liquifies. 
The SuperCam array motherboard is heat-sunk to this pot via low-loss,
vibration-damping 
copper straps. Calculations indicate the SRDK-415E load capacity is
sufficient to cool 
the mixers, magnets, and amplifiers to the proper operating
temperatures.  Should additional 
cooling become necessary, the cryostat is designed to permit the
addition of second 
cryocooler.  Janis Research is the Sumitomo distributor in the
US. Janis has reviewed 
our array cryostat drawings and given us an estimated cost for the complete 
cryostat/cryocooler system.

\subsection{Bias Control System \& Software}

A computer-controlled array bias system has already been developed by the
PI's group at Arizona and is currently being used with their 4-pixel,
SIS 810~GHz array (PoleSTAR) on the AST/RO telescope at the South Pole and
a 7-pixel, 345~GHz SIS array (DesertSTAR) on the HHT.
The system allows manual tuning of each mixer and amplifier, plus
automated bias point selection.  All voltages (and currents) are
controlled and monitored through a flexible graphical user interface (GUI)
written in C and controlled by a single Linux-based PC. The hardware and
control software have been specifically designed to 
support SIS arrays of $\approx 100$~pixels. 

\subsection{Optics}

The existing secondary mirror of the Heinrich Hertz Telescope provides
a f/13.8 beam
at the Nasmyth focus. The clear aperture available through the
elevation bearing prevents the possibility of a large format array at
this position. To efficiently 
illuminate a large format array like SuperCam, the telescope focus
must fall within 
the apex room located just behind the primary. A new f/7.5 secondary is 
required. The new secondary will be optimized to guarantee a Strehl
ratio (coupling efficiency)
greater than 0.9 across the whole field of view of the array. The
relatively fast focal ratio
permits simpler and smaller re-imaging optics to match the f/5 beams of the 
array receiver. Since the physical separation between array elements
in the instrument 
focal plane scales as $2 f \lambda$, lower f/\#'s
serve to
reduce the overall size of the
instrument. The reimaging optics are composed of two offset parabolas and three
flat mirrors. The two off-axis parabolas are in a coma-canceling
configuration \citep{sera95}. 
All the re-imaging optics can be mounted on a single vertical optical
breadboard and left in 
the apex room.  Only one flat mirror needs to be rotated to take the
reimaging optics (and SuperCam) 
out of the telescope's optical path. The secondary can be changed in
under an hour.  The optical system is depicted in
Figure~\ref{integration}. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.9,angle=0]{../figures/345-integration.eps}
\caption{\label{integration} {\small Optical system matching SuperCam
    to the HHT}} 
\end{figure}


\section{Impact of Infrastructure Projects}


\subsection{Institutional Impact}

SuperCam will provide an order of magnitude leap in the mapping 
speed of the HHT and serve as a technological roadmap for the realization 
of large format heterodyne arrays at submillimeter and far-infrared 
wavelengths. At the design wavelength of SuperCam (870 $\mu$m) the HHT 
has one of the highest aperture efficiency of any submillimeter telescope 
in the world (80\%) and excellent atmospheric transmission more 
than 40\% of the time.  SuperCam
will be an order of magnitude larger than any existing spectroscopic
imaging array at submillimeter-wavelengths, will be the most powerful
instrument for probing the history of
star formation in our Galaxy, and will put the University of 
Arizona at the forefront of research and technology in 
this wavelength regime.  This will in turn attract more highly qualified
students, technical staff, and faculty to the University, not just 
in Astronomy, but also Chemistry, Optical Sciences, and Electrical 
Engineering.  The technological spin-offs from building and 
operating SuperCam will be substantial and place the University in an 
excellent position to propose for even larger arrays for use on ground, 
airborne, or space platforms.  

\subsection{Educational Impact}


The training of students in the development of state-of-the-art
instrumentation  
is essential to the future of science. This is particularly true in
mm/submm astronomy where technological advances are happening so rapidly.
Ironically, there are only a handful of laboratories in the world
where students 
gain hands-on experience in the design, fabrication, and fielding of
radio astronomy 
instrumentation. In the PI's lab we have been fortunate to have had a number of
talented students pursue their research. Over the past 10 years the
lab has produced  
6 Ph.D.'s and numerous undergraduate senior projects. All the Ph.D.'s are still
pursuing astronomical research and a number of the undergraduates have
gone on to 
receive Ph.D's at other institutions. In recent years research in the
lab has drawn 
an increasing number of students from other departments, particularly
optical sciences and electrical engineering.  It is interest in
astronomy and the interdisciplinary nature of the research 
that attracts them to the PI's lab.  In an effort to reach this
population of students, 
the PI and fellow faculty members in other departments are seeking to
establish an 
interdisciplinary program in astronomical instrumentation. Two of the PI's past
Ph.D. students have received majors and minors in different
departments. The PI currently 
has 4 graduate and 2 undergraduate students participating in
interdisciplinary studies. 

In the proposed budget, funds for only one graduate student are
requested. The development 
and ultimate use of the array on the HHT will be the focus of the
student's research. 
However, as is customary in the PI's lab,
many 
other students will also participate in making the program a success. Indeed, 
one of the most important aspects of training students in instrument
development 
is experience in working in teams. Astronomical instrumentation is
becoming ever more complex, and requires the talents  
of many individuals. Providing students with both technical training
and team-work experience increases their probability of success. 

\subsection{Global Impact: Survey Synergies}
\label{synergies}

The surveys conducted with the SuperCam array receiver on the HHT
will serve as a ``finder chart'' for future, more focused surveys 
(e.g. with ALMA) and markedly improve the interpretation,
and enhance the value of numerous contemporary surveys.

\begin{figure*}[!htb]
\centering
\begin{minipage}{6.5in}
{\parbox{4.2in}{\includegraphics[angle=0,scale=0.3]{../figures/OrganizationChart.eps}}}
{\parbox{2.3in}{\caption{\small \label{orgchart} SuperCam Organizational Chart}}}
\end{minipage}
\end{figure*}


\subsubsection{SST Galactic Plane Survey}

The Spitzer Space Telescope Legacy program GLIMPSE, 
headed by E. Churchwell, will provide a thermal infrared survey of the
Galactic plane that provides a complete census of star formation, the
stellar structure of the molecular ring, will map the warm
interstellar dust, constrain extinction laws as a function of
galactocentric radius and will detect all young embedded O and B
stars.  
The proposed Galactic Plane survey will provide the best corresponding
molecular cloud survey that will account for the 
dense cloud material that forms stars,  cloud interaction with
formed stars, and kinematic disruption by mass ejection, outflow, and supernova
remnants.  Collaborator E. Churchwell 
will provide guidance in accessing and interpreting this data for
comparison with the SuperCam survey.

\subsubsection{ From Molecular Clouds to Young Stars}
A second SST
Legacy proposal, ``From Cores to Disks'', or ``C2D'', will survey a sample of
giant molecular clouds and complexes in infrared continuum emission
to provide a complete base for nearby star formation and to follow
the transition from starless cloud cores to low-mass disks. 
  The COMPLETE survey of Alyssa Goodman will provide a
reference study of the millimeter wave dust continuum emission in
these clouds and their molecular line survey will support the
$J=1\rightarrow0$ lines of CO and $^{13}$CO using the FCRAO Sequoia
array.  Our target surveys of Outer Galaxy and high latitude 
GMC's add significant value to the baseline by providing
higher-J CO data critical for the study of star forming
regions where many excitation components are often present and cannot
be disentangled with only one spectral line.   
Collaborator Alyssa Goodman (CfA)
will provide assistance in accessing COMPLETE data
for combination with the SuperCam survey.  The ``C2D'' Legacy
project data itself will be available in 2005.

\subsubsection{Molecular Ring Survey} The ongoing FCRAO Molecular
Ring Survey led by J. Jackson 
will provide the most sensitive study of the inner Galaxy to
date, but will only map the $^{13}$CO $J=1\rightarrow0$ line.
This proposed
study will improve upon the GRS resolution by up to a factor of 4 in 
area and yield the crucial higher-J lines that make proper
interpretation of existing CO surveys possible.  Collaborator Mark
Heyer (U.Mass) is a member of the GRS team and will provide
assistance in accessing this data for combination with SuperCam
surveys. 

\subsubsection{3-2-1 Survey}  John Bieging (Arizona) has proposed
``3-2-1'', a collaborative survey of \co\ $J=2-1$, $J=3-2$, and \tco\ $J=2-1$
in the inner 50 square degrees of the Galaxy over the next 3 years,
using the existing HHT and KPNO 12-meter facilities.  The SuperCam
Galactic Plane surveys will dovetail with the coverage that 3-2-1 
obtains by the time SuperCam is completed.  Many of the science
products and tools will be shared between the two surveys, and the
OTF data acquisition and archival methods will be identical.  Nearly all of
the collaborators of 3-2-1 are collaborators in SuperCam as well.  In
particular, John Bieging will provide guidance in merging the
SuperCam and 3-2-1 surveys and products.

\subsubsection{2MASS \& Formation of Molecular Clouds}
The 2 Micron All Sky Survey (2MASS) has imaged the northern and
southern hemisphere skies in the photometric J, H, and K bands from
1--2.5~$\mu$m.  This survey will be used to construct extinction
maps over the entire region to be surveyed by SuperCam
\citep{lada94,alves99}, which will be used to locate
%  Additional sensitivity will be acquired as
%  needed using the ARIES and PISCES infrared imagers at the Univ. of Arizona
%  2.3-meter refector on Kitt Peak, and the 6.5-meter MMT on
%  Mt. Hopkins, Arizona.  
%We will use them to locate
regions in the Galaxy where new molecular clouds are being formed;
i.e. where gas has become molecular (i.e. H$_2$), but CO has not yet
formed.   These measurements will enable the crucial 
first measurement of the formation of Galactic molecular clouds, and
will leverage the investment of the 2MASS survey in an innovative way. 


\section {Project Management}
\label{management}

SuperCam is an exciting, challenging project that requires the coordinated 
participation of scientists and engineers from several academic institutions
and leading-edge companies to succeed. We have developed an organizational
structure (shown in Figure~\ref{orgchart}) 
to meet this task. Collectively the SuperCam
team members represent many years of successful instrument development and
observing programs. The organizational structure of the SuperCam project 
provides effective control of the project while allowing the delegation 
of authority to be made at the proper level within the organization.
The main components of the organization are the PI, who has overall 
responsibility for the project and coordinates the activities of the 
participants, the DP-I (Kulesa) who assists the PI and is responsible 
for developing the bias control system and writing SuperCam support 
software, the Project Manager (PM-Bailey) who oversees the fiscal realities
of the project, the Project Engineer (PE--H. Fagg) who will oversee the
integration of the array hardware, and the Science and Instrument Teams
who will provide extensive scientific and technical guidance throughout
the course of the project.
Table~\ref{roles} provides a listing of the roles and responsibilities of each
member in the organization.     

A schedule of key project milestones and tasks is provided in
Figure~\ref{gantt}. 
Routine communications between project participants is essential.
There will be quarterly telecons between Science and Instrument team
members to monitor progress, provide insight into solutions to
emerging problems, and redefine priorities as needed. There will
be weekly telecons and quarterly meeting (either in person or through
teleconferencing) between the PI, D-PI, PM, PE, and IF technical lead
Weinreb (CIT) and Device technical lead Lichtenberger (UVa).  

\begin{figure}[!htb]
\centering
\includegraphics[angle=0,scale=0.58]{../figures/gantt.eps}
\caption{\small \label{gantt} SuperCam Organizational Timeline }
\end{figure}


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\end{document}

