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\medskip
\centerline {\Large \bf DesertSTAR~II: The addition of a 230~GHz subarray } \smallskip
\centerline {\Large \bf to an existing 345~GHz array receiver system} 
  
\section{Introduction}

Array receivers have the potential of revolutionizing astronomy at 
millimeter and submillimeter wavelengths. Over the past few years
our group at the University of Arizona has built two 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. DesertSTAR will go into routine operation on the
HHT with an initial complement of 3 pixels in October 2003. The remaining 
four pixels will be implemented next summer.  Work on PoleSTAR 
was funded by the NSF Office of Polar Programs. The 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. 

Here we request funds to add four, 230 GHz pixels to Desert~STAR.
The Desert~STAR closed-cycle, array cryostat was designed to have 
ample thermal capacity and sufficient volume to support the additional 
subarray. The system will be configured to allow simultaneous observations 
with both subarrays.  The large increase in mapping speed afforded by the 
arrays, together with the capability of observing multiple transitions of 
molecules simultaneously, will make Desert~STAR a powerful and unique 
instrument for a variety of projects, including unbiased high resolution 
Galactic Plane CO surveys, deep submillimeter line surveys over extended 
regions, star formation studies, and probing the mass loss from the extended 
envelopes of evolved stars.  Desert~STAR will be a facility instrument 
on the HHT, available to all users. 

In this proposal we describe potential key projects for Desert~STAR 
and provide a technical description of the instrument design and 
expected performance. 

\section {Scientific Motivation}

\begin{table}[!hbt]
\centering
\begin{tabular}{|lccl|}
\hline
{\bf Species} & {\bf Transition} & {\bf Frequency (GHz)} & {\bf
Importance} \\
\hline \hline
$^{12}$CO & J=$2 \rightarrow 1$ & 230.538 &  Excitation and structure \\
$^{12}$CO & J=$3 \rightarrow 2$ & 345.795 &  of molecular clouds; PDR's,\\
$^{13}$CO & J=$2 \rightarrow 1$ & 220.398 &  shocks, protostellar outflows\\
C$^{18}$O & J=$2 \rightarrow 1$ & 219.560 &  star-forming regions \\
C$^{17}$O & J=$3 \rightarrow 2$ & 337.061 &  \& Galactic chemical evolution\\
\hline
CO$^+$ & $3_4 \rightarrow 2_3$ &  354.014 &  Molecules in hostile environments,\\
 & & & UV and X-ray dominated regions \\
\hline
HCN &  J=$3 \rightarrow 2$ & 265.886 &  Dense gas in molecular cloud cores \\
HCN &  J=$4 \rightarrow 3$ & 354.505 &  and circumstellar disks\\
HNC &  J=$3 \rightarrow 2$ & 271.981 &  \\
HNC &  J=$4 \rightarrow 3$ & 362.630 &  \\

\hline
HCO$^+$ & J=$3 \rightarrow 2$ & 267.557 & Excitation and kinematics of\\
HCO$^+$ & J=$4 \rightarrow 3$ & 356.734 &  YSO envelopes, protostellar collapse \\
\hline
SiO &  J=$5 \rightarrow 4$ &  217.504 &  Stellar ejecta \\
SiO &  J=$8 \rightarrow 7$ &  347.330 &  molecular shocks in disks \& outflows \\
\hline
\end{tabular}
\caption{\label{tablelines} {\small Selected spectral line diagnostics in the
200-400 GHz atmospheric windows}}
\end{table}


Desert~STAR in its proposed, upgraded form will be a sensitive,
dual-frequency, 11-pixel, superconducting heterodyne camera for the
800-1400~$\mu$m atmospheric windows.  Its development will serve as a
stepping stone to larger format submillimeter arrays and
significantly broaden the scientific capabilities that submillimeter
spectroscopy can address.  

The atomic and molecular transitions accessible in this spectral range
are important diagnostics of a variety of astronomical phenomena
including planetary atmospheres, molecular clouds, star-forming
regions, young stellar objects, circumstellar envelopes, and planetary
nebulae (Figure~\ref{trans}(a).  The 200--400 GHz atmospheric
windows are relatively well-explored, due to good atmospheric
transmission at high, dry mountain sites.  Figure~\ref{trans}(b) 
depicts the atmospheric transmission for Mt. Graham that is attainable 
25\% (blue curve), 50\% (green curve) and 75\% (red curve) of the
time during the year, based upon tipping radiometer measurements at
225~GHz performed over the last 6 years.  
Labels mark spectral lines of highest importance, and their
frequencies and diagnostic capability are tabulated in
Table~\ref{tablelines}.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.42,angle=-90]{w3_overview.eps}
\hspace{1cm}
\includegraphics[scale=0.37,angle=-90]{transplot.eps}
\begin{minipage}{6.5in}
{\parbox{3.5in}{a)}}
{\parbox{3.5in}{b)}}
\end{minipage}
\caption{\label{trans} {\small a) The 345~GHz spectral line survey toward
    three positions in the W3 molecular cloud by Helmich et al. (1997)
    shows a rich diversity of spectral diagnostics.  b) Modeled
    submillimeter atmospheric transparency for the HHT on Mt. Graham
    in 75 percentile (red), median (green), and 25 percentile (blue)
    atmospheric conditions, derived from 24hour/7day 225~GHz
    radiometer measurements over the last 6 years.}}
\end{figure}

Despite the relative transparency in these atmospheric
windows (compared to the more opaque and transient atmospheric windows at
higher frequencies) and the development of SIS devices that approach the
quantum sensitivity limit to within factors of a few, the
scientific productivity of even modern receivers is severely limited by
their single-beam nature.  This limitation places a stranglehold on the
large-scale mapping capabilities needed to address crucial issues,
such as the Galactic-scale origin and evolution of (molecular) clouds
and their pivotal, delicate interplay with the stars that are born
from them. 

High spatial dynamic range imaging of molecular line 
emission is essential to accurately describe 
interstellar processes that regulate cloud evolution and the 
formation of newborn stars.
High resolution is required to detect the small scale spatial 
variability and compact objects.  Yet one also demands wide field 
imaging to place those features into an environmental context and to
identify patterns that provide clues to interstellar dynamics (ex.
gravitational instabilities).
Heterodyne receiver {\it arrays} will maximize the
scientific return from good submillimeter
weather conditions and revolutionize the spectral line mapping
of interstellar clouds.  For illustration, Figure~\ref{mapping}
portrays the footprint of the 7+4 element arrays on the sky, and the portion
of the $\rho$~Ophiuchi molecular cloud that can be mapped with 15$''$
grid spacing, $<$1~km~s$^{-1}$ spectral resolution, and
1$\sigma$=0.5~K~km~s$^{-1}$ sensitivity in one 4-hour shift at the HHT
with the array, as compared to a conventional single-beam receiver.


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.45,angle=0]{m16array.eps}
\hspace{0.5cm}
\includegraphics[scale=0.45,angle=0]{rho.eps}
\begin{minipage}{6.5in}
{\parbox{3.5in}{a)}}
{\parbox{3.5in}{b)}}
\end{minipage}
\caption{\label{mapping} {\small a) Beam footprints of the 230~GHz
    and 345~GHz arrays at the HHT, atop the HST WFPC image of the
    Eagle Nebula, M16.  Note that the two arrays will actually be
    cospatial on the sky, but are separated in the diagram for
    clarity. b) Heterodyne receiver arrays will
    revolutionize the mapping of molecular clouds and star forming
    regions.  The proposed 7+4~pixel arrays can fully sample the nearby
    $\rho$~Ophiuchi molecular cloud ($40' \times 40'$ ISOCAM image
    from Abergel et al. 1996) at 15$''$ grid spacing in CO~$J=3 
    \rightarrow 2$ and  CO~$J=2 \rightarrow 1$ to 0.5~K~RMS within one
    4-hour shift, with median T$_{sys}$'s of 750 and 450~K, respectively.}}
\end{figure}

While focal plane arrays augment the imaging capability of a telescope,
the productivity of a system can be further increased by multiplexing 
the spectral domain.  A dual frequency system generates 
data on two or more molecular emission lines from which the 
excitation conditions can be derived.  As these spectral lines are measured 
simultaneously, the relative intensities are more reliable leading to 
more accurate modeling of the gas properties.

Lines in the 200-400~GHz atmospheric windows share a number of common
traits; all probe warmer, denser environments ($T > 20$ K, $n \sim
10^{4-7}\ {\rm cm}^{-3}$) than typically observed at longer 
millimeter wavelengths.  These properties
make them unique and powerful probes of energetic molecular gas
which provides the crucial link between luminous stars, their remnant
descendants, and the cold molecular clouds that form them and are
subsequently destroyed by them. 
The following sections describe several key science objectives
for large-format submillimeter arrays on ground-based
submillimeter telescopes, initiated by the 11-pixel array at the HHT
and extended using future $\sim 10 \times 10$ pixel second-generation
instruments.
Among these are studies of molecular 
cloud physics/chemistry, evolved stars, and protostellar 
evolution.  Here we will limit our discussion to a few key research
projects, but the Desert~STAR array will be accessible to all users of
the HHT for targeted PI proposals. 

\subsection{An Unbiased Galactic Plane Survey}

Molecular clouds still pose a host of fundamental questions regarding
their nature and role in the coupling of matter in the interstellar
medium (ISM).  How do molecular clouds form and evolve?  How does star
formation start and propagate through these clouds?   What factors
determine the stellar initial mass function, multiplicity, and
clustering properties?  How does the
molecular ISM respond to the radiation and outflows from the stars 
that form from it, and how does this relate to the global
Galactic evolution?  What are the
mass-spectra and kinematic properties of the clouds and the
substructures that they contain?  How do cloud properties change
across the Galaxy?   What are the relative roles of spiral density
waves, super-bubbles, gravitational instabilities, and Galactic infall
in the formation and destruction of molecular clouds?

Because the dominant H$_2$ molecule lacks a dipole-allowed radio
spectrum, most
of our knowledge of the molecular ISM comes from the second-most
abundant molecule, CO.   
The early surveys of molecular gas were obtained either with large beams
(e.g. $>$ 9$'$, Dame et al. 1987, 2001), or were 
undersampled (e.g. the 3$'$
sampling of the UMass/Stonybrook survey, Solomon et al. 1987; Scoville
et al. 1987).  The development of focal plane 
arrays in the 3mm band over the last 10 years has enabled CO surveys with 
moderate resolution (45$''$) and broad, areal coverage (Heyer et al. 1998; 
ongoing BU-FCRAO Galactic Ring Survey).
However, these
surveys are limited to meauring the J=1$\rightarrow$0 
rotational transitions of CO;
the column density and mass derived from optically thin (isotopic)
J=1$\rightarrow$0 emission is sensitive to the badly constrained
excitation temperature. 

\medskip

\noindent  {\bf The following features represent a definitive CO
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 focused studies with the SMA, CARMA and ALMA}.

\begin{itemize}

\item {\bf Multi-line}:  Surveys carried out in a single line
of $^{12}$CO make it difficult to conclusively disentangle the
competing effects of abundance, line opacity, and excitation.
Significant systematic uncertainties are present with surveys
consisting of one spectral line per species.   At
least two lines of differing excitation are necessary, with at least
one line in an optically-thin isotopomer of CO, such as $^{13}$CO or
C$^{18}$O to diagnose temperature and (column) density.  {\it The simultaneous
  dual-frequency operation of Desert~STAR will dramatically improve the speed, uniformity and scientific return of important new surveys to be undertaken at the HHT. }  These higher-J transition observations
provide a critical complement to the recent surveys of CO and $^{13}$CO
J=1-0 emissions conducted at
the Five College Radio Astronomy Observatory.   Together, these
surveys can place important constraints upon the excitation conditions 
throughout the Galaxy at a resolution of 45$''$
\footnote{Highly sampled DesertStar data smoothed to the resolution of the 
FCRAO 14m 
telescope at 110 GHz will further improve its sensitivity.}.  To 
date, such multi-line, wide field measurements have been made 
at 9$'$ resolution (Sakamoto et al. 1995).  
The derived excitation conditions provide 
a relative barometer to gauge the variation 
of gas pressure with radius in the Galaxy as may be induced by 
the gravitational potential of the disk.
High excitation conditions 
are a valuable beacon/signature to sites of strong interaction with a
molecular cloud 
(ex. supernova remnants, enhanced UV fields) that might otherwise be 
missed with a singular transition.

\item {\bf High 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 1.5~K~km~s$^{-1}$ in the
$J=2\rightarrow1$ transition at a gas density of $n_H=10^4$~cm$^{-3}$, but only
0.7~K~km~s$^{-1}$ if $n_H=10^3$~cm$^{-3}$.  The corresponding
$J=3\rightarrow2$ intensities are 1.2 and 0.2~K~km~s$^{-1}$.  
{\it Even the strongest limit we require in CO $J=2\rightarrow1$ is readily
  detectable (3$\sigma$) within 10 seconds of integration time per independent
  beam in median 230~GHz conditions (T$_{sys}$=500K) at the SMT.
  Detection (or limits) on J=3$\rightarrow$2 in that time would 
  constrain the gas density.}

\item {\bf High Angular Resolution}:  Disentangling the complicated
structures of molecular clouds in the Galaxy requires high angular
resolution.  Low resolution data wash out CO gradients and
enhancements at molecular interface regions.  For example, to resolve a feature
such as the Orion warm ridge at the distance of the Molecular Ring
($\sim$5 kpc) requires better than 1$'$ resolution.   {\it A survey with
30$''$ resolution is needed.  The diffraction-limited beamwidth
of the SMT at 200-400~GHz is 18-35$''$.} 

\item {\bf Unbiased Survey Coverage}:  While specific studies of individual
clouds is highly meritorious, building a statistical picture of the
molecular clouds, cores, and kinematics of the Galaxy requires an
unbiased survey of significant area.  From existing low-resolution
CO maps, the majority of CO emission is found within one degree of the
Galactic Equator, from the Galactic Center to the tangent arms near
$|l| \sim 100^o$.  {\it The mapping efficiency of Desert~STAR will make
large, unbiased mapping surveys possible.}

\end{itemize}

From these requirements, it becomes clear that the unique blend of 
high sensitivity, fine velocity resolution, mapping speed, and high angular
resolution that Desert~STAR offers on the HHT is ideally suited for
such a survey.   Figure~\ref{galacticplane} demonstrates the target
region defined by the 1st Galactic quadrant and ($-1^o < b < +1^o$). 
Because the ``field of view'' of the
230~GHz and 345~GHz arrays is so well matched (90$''$), a survey could be
simultaneously performed in both CO $J=3\rightarrow2$ and
$J=2\rightarrow1$ with comparable sensitivity and identical (resampled)
resolution.  With 2-second integration time per 15$''$-spaced
grid element (i.e. 8 seconds integration per convolved independent beam) 
of an on-the-fly (OTF) map, one square degree of
sky could be mapped to a sensitivity of 1$\sigma$ $\sim$ 0.25~K per 1
km~s$^{-1}$ resolution element in about twelve hours.  180 square degrees of
the 1st quadrant of the Galactic Plane, including the Galactic Center
($0^o < l < 90^o$, $-1^o < b < +1^o$) would then be mappable in
approximately 2000 hours of observing time, or about 80 complete
days of observable weather conditions.  The AST/RO telescope at the
South Pole could extend the survey from the Galactic Center onward.
(The PI is a Co-I on AST/RO and his lab has constructed most of its
receiver systems.)

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.6,angle=0]{Fig2_Dame.eps}
\caption{\label{galacticplane} {\small Overlaid atop the Dame et
al. (1987) CO J=1$\rightarrow$0 map of the Galaxy is the proposed
Desert~STAR key project to map 180 square degrees of the 1st quadrant
of the Galactic Plane, including the Galactic Center ($0^o < l < 90^o$, $-1^o
< b < +1^o$).  AST/RO could extend the Galactic Plane coverage from
the Southern Hemisphere ($-70^o < l < 0^o$) in CO $J=2\rightarrow1$ and
$J=4\rightarrow3$.  The surveys will have a 3$\sigma$ sensitivity of
N(CO)$< 10^{15}$~cm$^{-2}$ per independent beam and will take
approximately 2000 observing hours to complete. }}
\end{figure}

This survey will provide the most detailed ``ecological'' study of
the molecular ISM and the evolution of giant molecular clouds.  It
will probe the entire life cycle of star-forming molecular clouds, and will
allow an unprecedented, unbiased view of the interplay between the
molecular ISM and the stars which are born from it.  It will discover
tens of thousands of star-forming and starless cloud cores and allow
measurement of their statistical properties.  The dynamical evolution
of clouds and their relation to each other and to stars and atomic ISM
components will provide the clearest view of the large scale structure
of the Galaxy.  The proposed survey has the potential of being as 
fundamental to the investigation
of the cold ISM as the IRAS survey is to the study of warm dust, and
the Palomar Sky Survey to the study of the optical sky. 


\subsection{Targeted Deep Surveys of Molecular Clouds and
Star Forming Regions} 

One of the major goals of ground, airborne, and space-based
observational astronomy is the identification and study of
protostellar objects.  A study of protostars provides insight into
the initial conditions required for star formation, protostellar
evolution, and the formation of solar systems like our own. 

Specific molecular clouds at high Galactic longitude will not be included in 
the Unbiased Galactic
Plane Survey.  These regions, such as the Orion, Perseus, Serpens,
Ophiuchus, and Gem OB1 clouds will be targeted separately as a part of
a deep survey of individual clouds.  Like the unbiased survey,
the targeted survey will map a total of 100 square degrees in the
$J=2\rightarrow1$ and $J=3\rightarrow2$ lines of $^{12}$CO,
$^{13}$CO, with more focused mapping in C$^{18}$O or C$^{17}$O as
needed to obtain optically-thin tracers for column density
determination.  Focused mapping in HCO$^+$ will provide density
indicators for the dense core regions.  
This survey is synchronous with
several other contemporary surveys, such as the SIRTF Legacy
program ``From Cores to Disks'', which will map 5 molecular cloud
complexes photometrically from 2-70 microns, and will target specific
sources with low-dispersion mid-IR spectroscopy.  Toward those same
clouds, A. Goodman's COMPLETE survey will add submillimeter continuum
mapping, CO $J=1\rightarrow0$ maps with 45$''$ resolution, and
deep near-infrared imaging.  Our proposed survey will overlap these
regions, adding significant
value to these existing investments of ground- and space-based
telescope time; higher-J transitions of CO will probe the warmer and
denser gas that participates in core evolution and star
formation, and with much less contamination from foreground material.
Well-defined gas excitation conditions provided by a multi-line
analysis will dramatically improve the interpretation of the CO data.  

The multi-beam array will also allow small cloud cores to be mapped in
a spectral survey mode at selected frequencies.  This spectral survey mode will
allow different portions of a star forming
core to be distinguished chemically.  The prospects of using time-dependent 
chemistry as a chronometer for the evolution of protostellar
cores, disks, and outflows is tantalizing, and only made practical through
the use of heterodyne arrays.

Accessibility of high-J CO and HCO$^+$ lines will probe
the physical conditions of the dense, hot envelope gas located much closer 
to the protostar than is currently accessible at lower frequencies
[e.g. 5,6 and references therein].  The statistical 
study of the excitation and structure of star-forming cores versus
starless cores, particularly those uncovered by the Biased and
Unbiased Surveys previously described, is an exciting prospect.  
Furthermore, the excitation and abundance of HCO$^+$~J=$4\rightarrow
3$ with $n_{crit} \sim 10^{7}\ {\rm
cm}^{-3}$ directly reflects the ambient radiation field, provides an
estimate of ionization fraction, and kinematics of protostellar
envelopes.  Indeed, direct detection of infall is 
tractable through these transitions, as the inner envelope is expected
to collapse faster than the colder outer envelope traditionally probed
at lower frequencies.  Linewidth correlations of CO and HCO$^+$
at low- and high-J could provide direct tests of protostellar collapse models. 
The high angular coverage
and resolution provided by the proposed array is critical for
disentangling the complicated kinematics of star-forming environments. 

\subsection{Synergy with Contemporary Surveys}

The surveys conducted with the expanded Desert~STAR system 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{itemize}

\item The SIRTF 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.  Yet, there is no survey of the molecular gas that relates to
this stellar population study that has (even vaguely) comparable resolution.
The proposed Unbiased Galactic Plane Survey will provide the highest
resolution, large-area CO survey to date.  The use of lines with
higher excitation will better account for the
dense cloud material that forms stars,  cloud interaction with
formed stars via their warmed photodissociated surfaces, and their
kinematic disruption by mass ejection, outflow, and supernova remnants. 

\item A second SIRTF Legacy proposal, ''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.  It is
  critical, then, to provide a similar survey of the targeted
  clouds in higher-J CO emission to account (and disentangle) the
  complicated kinematics and physical structures in star-forming
  regions.  The COMPLETE survey of A. 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.  The complementary need of a higher-J
  survey is particularly important for the study of star forming
  regions, where many excitation components are often present and cannot
  be disentangled with only one spectral line.  Our Targeted Deep
  Surveys of selected GMC's will provide thermal and barometric maps that
  will uniquely disentangle the physical structure of 
  these complicated regions and add
  significant value to the baseline $J=1\rightarrow0$ study. 
  
\item 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.
The angular resolution of the survey is 47$''$. The proposed
study will improve upon this 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.  

\item The PI of this proposal has
proposed a NASA SMall EXplorer mission, the Galactic Terahertz
Observatory (GTO), which will map 240 square degrees of the
Galactic Plane ($-60^o < l < +60^o$, $-1^o < b < +1^o$) in the pivotal
fine structure recombination lines of carbon and nitrogen at
158~$\mu$m and 205~$\mu$m.  The [C~II] line is the dominant cooling
line of the atomic ISM, and the [N~II] line is an extinction-free
probe of ionizing photons throughout the Galaxy.  The principal aim of
the survey is to study the life cycle of atomic and molecular clouds.
The [C~II] survey will be able to study H$_2$ clouds that have not yet
recombined into CO -- but it will probe the photoilluminated surfaces 
of the dark CO clouds, not their contents.  A CO survey of comparable
($\sim 1'$) resolution in the higher-J transitions of CO matches
the excitation of the [C~II] line and makes an ideal companion survey
that will enhance the interpretation of [C~II] emission in the Milky Way
and other star forming galaxies. Together, the [C~II] and CO surveys probe 
nearly all stages of carbon in the cold ISM. The proposed Unbiased 
Galactic Plane CO Survey is a perfect match to these goals.  

\end{itemize}


\section {Technical Description}


\subsection {Overview}

The addition of a 4 pixel, 230 GHz subarray to DesertSTAR will make it
an extremely powerful, versatile instrument for probing the ISM in our 
Galaxy and, ultimately (with an expanded backend spectrometer), other
galaxies as well. A schematic diagram of the expanded DesertSTAR system
is shown in Figure~\ref{schematic}. Components to be built or added as part of the 
proposed effort are shown in (bold) red type. Laboratory
measurements indicate the NRAO style, closed-cycle, J-T refrigerator has 
ample capacity (1.8~W at 4~K) to simultaneously cool both the 345 and 230~GHz
subarrays.

\begin{figure}[!hbt]
\centering
\begin{minipage}{7in}
{\parbox{4.8in}{\includegraphics[scale=0.28,angle=0]{DSBlockDiagram.eps}}}
{\parbox{1.6in}{\caption{\label{schematic} {\small Schematic Diagram of DesertSTAR~II. The existing 345~GHz array system is shown in blue/black. The proposed 230~GHz array addition is shown in (bold) red.}}}}
\end{minipage}
\end{figure}

The converging {\it f/13.8} beams from the HHT tertiary first pass through
a 0.5 mil Mylar beamsplitter before entering the array cryostat through a 4.5~in
diameter, low-loss, Zotefoam vacuum window. The Mylar beam splitter is used to inject
the multiple 345~GHz LO beams into the optical path without significant loss
($<$3\%) to either the 345 or 230~GHz sky beams. The beams then pass through
a Gortex 40~K IR blocking filter and are subsequently split into horizontal and
vertically-polarized components by a 45$^\circ$ wire grid. The vertically-polarized
beams are intercepted by 7 hexagonally packed, low-density polyethylene lenses
which provide efficient Gaussian beam coupling to seven, 345 GHz, SIS waveguide mixers.
The physical separation between mixers (29~mm) is three times the Gaussian
beam waist diameter. On the sky this optical configuration separates the
beams by two, full-width-half-maximum (FWHM) spacings (44$^{\prime\prime}$ 
at 345~GHz). The 4-6 GHz intermediate frequency (IF) output of each mixer
passes through an isolator before entering low-noise ($\sim 5$~K), Miteq
amplifiers. The lenses, mixers, isolators, and IF amps are all at $\sim4$~K.
The polarizing grid is at 40~K. At room temperature the signals are further
amplified and downconverted to meet the requirements of the array spectrometer.
In its initial implementation, the 345~GHz array will employ seven, 
250 MHz wide, 1~MHz resolution filterbanks. The seven LO beams needed to drive
the 345~GHz array are produced using a holographic phase grating illuminated by a single
solid-state source. As with the proposed effort, the
development of the 345~GHz array was a collaborative effort between NRAO
(cryostat), the University of Virginia (SIS devices), the University of Massachusetts
(mixer design and fabrication), and the PI's lab at the University of Arizona
(system design and integration). This collaboration has worked extremely well,
yielding excellent receiver performance ($\sim 55$~K DSB at 350~GHz) and a successful
first run. A representative spectrum from the run is shown in Figure~\ref{engineering}a. A photograph of DesertSTAR mounted to the elevation flange of the HHT is shown in Figure~\ref{engineering}b.   

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.65,angle=0]{dr21.eps}
\includegraphics[scale=0.42,angle=0]{DS_at_HHT.ps}
\begin{minipage}{6.5in}
{\parbox{3.5in}{a)}}
{\parbox{3.5in}{b)}}
\end{minipage}
\caption{\label{engineering} {\small The first engineering run with DesertSTAR. a) CO $J = 3\rightarrow2$ spectrum of DR21 made with the first DesertSTAR pixel. b) Photograph of DesertSTAR bolted on the elevation flange of the HHT.}}
\end{figure}

In the proposed expansion, the horizontally polarized beams emerging from
the 40~K wire grid intercept a 2x2 array of dielectric lenses which
in turn couple the light into four, 230~GHz SIS waveguide mixers. Unlike the
simple, single-ended, double-sideband (DSB) mixers used at 345~GHz, the 230~GHz mixers 
will be balanced, sideband-separating mixers based on a successful ALMA design.
In the following sections we will discuss the merits and implementation of the
230~GHz array.

\subsection {Balanced, Sideband-Separating SIS Waveguide Mixers}

Most receivers currently in operation at millimeter and submillimeter-wave
observatories utilize simple, single-ended, DSB mixers. This is because such
mixers are relatively easy to fabricate and implement. However, in most instances
the molecular or atomic lines of interest to the observer appear in only one
of the mixer's sideband. The unwanted image sideband can degrade sensitivity by adding
atmospheric noise and causing spectral confusion. Observatories sometimes use 
quasi-optical devices such as Martin-Pulplett interferometers or Fabry-Perot filters
to suppress the image sideband. However, such devices have limited bandwidth
and require termination of the image sideband in a cold load. These devices are also
often bulky and have significant optical loss. 

In response to the need for large numbers of mm/submm receivers with the best
possible sensitivity and lowest cost, the ALMA project has developed a balanced, 
sideband-separating 230~GHz mixer with the following properties (Claude et al. 2000):

\begin{itemize}
\item{Separates the two sidebands without the use of an interferometer.}
\item{Provides a good 4~K image termination inside the mixer block.}
\item{Makes efficient use of LO power.}
\item{Supresses local oscillator noise.}
\item{Contains no moving parts.}
\end{itemize}

Not surprisingly, these are exactly the desired characteristics in a focal plane
array mixer. Therefore, with the help of NRAO (see support letter from Tony Kerr),
we will base our 230~GHz focal plane array on the ALMA design.

A schematic representation of the mixer architecture to be used in the 230~GHz subarray
is shown in Figure~\ref{250mixer}. 
Sideband separation is achieved by dividing the incoming signal
(RF) with a 90$^o$ phase shift between two balanced mixers (Marked `A' and `B').
Power division and the addition of a phase shift is achieved using a branchline
coupler (a type of waveguide quadrature hybrid; Srikanth and Kerr 2000). The incoming LO power is split and 
coupled in-phase to the balanced mixers. Each of the balanced mixers is itself composed 
of two, single-ended, SIS mixers interconnected by a branchline coupler. The SIS junctions are on
quartz substrates which project into the waveguide outputs of the coupler. 
Impedance matching circuitry and RF choke structures are fabricated on the substrates along 
with the SIS junctions. For balanced operation, the pair of SIS junctions comprising
each balanced mixer must be biased with opposite polarity and their IF outputs combined.
To achieve sideband separation, the single IF output from each pair of SIS 
junctions must be combined in a quadrature hybrid. The IF
quadrature hybrid can exist outside the cryostat as long as it is proceeded by low-noise
amplifiers.  Since the IF hybrid operates at microwave frequencies (here 4-6~GHz), it
can be implemented using a simple 3-branch microstrip coupler. The two outputs of the
IF hybrid are the upper and lower sideband of the incoming radiation.

\begin{figure}[!hbt]
\centering
\begin{minipage}{7in}
{\parbox{4.7in}{\includegraphics[scale=0.28,angle=0]{250HybridMixer.eps}}}
{\parbox{1.7in}{\caption{\label{250mixer} {\small Schematic representation of SSB mixer architecture. The design is based on the ALMA band-6 mixer. }}}}
\end{minipage}
\end{figure}

A preliminary CAD drawing of the proposed 230~GHz mixer subarray is shown in Figure~\ref{2x2cad}.
Radiation is coupled into each mixer by a dielectric lens and corrugated feedhorn.
Each mixer has its own electromagnet for suppressing Josephson noise. The mixer is
designed to split into halves along the centerline of the waveguide. The bottom
half contains the SIS junctions, IF matching networks, and bias-T's. All four SIS junctions
in each SSB mixer can be independently biased. The mixer LO is injected 
through a waveguide port in the back.



\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{3.8in}{\includegraphics[scale=0.33,angle=0]{2502x2Hybrids.8.28.03-5.eps}}}
{\parbox{2.6in}{\caption{\label{2x2cad} {\small  CAD drawing of the proposed 2x2, 230~GHz balanced, sideband-separating
mixer array. Each mixer has an AR grooved, dielectric lens to efficiently couple the 
telescope's beam to a corrugated feedhorn. Four, full-height waveguide, SIS junctions are used 
in each mixer. An electromagnet and field concentrators are used to suppress the
Josephson effect.}}}}
\end{minipage}
\end{figure}

Using this design approach, the ALMA team has constructed and tested a prototype 
sideband-separating mixer. The measured SSB noise temperature and image 
sideband suppression performance are shown in Figures~\ref{kerr}a and \ref{kerr}b. 
The results are excellent, 
with SSB noise temperatures of $\sim 60$K and image suppression greater than 15~dB 
over $\sim 6$~GHz of IF bandwidth (Kerr 2003). In a standard DSB noise measurement 
the mixer's noise temperature would be $\sim 30$~K. The proposed array mixers will
utilize the same waveguide hybrids and SIS devices as the prototype ALMA mixer.
To achieve greater LO coupling efficiency, the array mixers will use a balanced 
configuration. Single-chip (MMIC) balanced and sideband separating mixers have also
been developed by NRAO. These also had excellent performance, however, due
to their large surface area, had low wafer yields. With the waveguide hybrid 
approach, large numbers of devices can be made in a single run.

An exciting aspect of this SSB mixer design approach is its scalability. With conventional
CNC techniques, these mixers can be fabricated to $\sim 700$~GHz. Utilizing new micromachining
techniques together with advances in HEB technology, it should be possible to realize
high performance SSB mixers to $\sim 5$ THz. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.26,angle=0]{Image1.eps}
\includegraphics[scale=0.26,angle=0]{Image2.eps}
\begin{minipage}{6.5in}
{\parbox{3.5in}{a)}}
{\parbox{3.5in}{b)}}
\end{minipage}
\caption{\label{kerr} {\small a) SSB Noise performance and b) image suppression of the 250~GHz ALMA mixers to be used in the DesertSTAR 2x2 array at 230~GHz.}}
\end{figure}


\subsection {Local Oscillator System}

Since the balanced, sideband-separating mixer described above uses four single-ended 
mixers, it may at first seem it requires four times the LO power of the standard
single-ended mixer and this indeed the case. However, in unbalanced applications
these same single-ended mixers require 20~dB LO coupler. A balanced mixer
has an LO port into which all available power can be injected. Therefore, even with 
4 single-ended mixers, a balanced, sideband-separating mixer requires
$\sim 14$dB {\it less} power than the most commonly used single-ended mixer.
All available LO power can be delivered to a single-ended mixer if a Fabry-Perot or
Martin-Pulplett interferometer is used as a diplexer. However, these quasi-optical
devices are bulky and have comparatively limited instantaneous bandwidth.

\begin{figure}[!hbt]
\centering
\begin{minipage}{7in}
{\parbox{5in}{\includegraphics[scale=0.38,angle=0]{2502x2Hybrids.8.28.03-4.eps}}}
{\parbox{1.4in}{\caption{\label{subassembly} {\small 230~GHz subarray assembly.  The LO power divider mounts just behind the mixers. Pamtech isolators are used between the mixers and the Weinreb IF amplifiers. }}}}
\end{minipage}
\end{figure}

A Virginia Diode solid-state, 210-270~GHz LO source will be used to drive the
array. The LO is driven from 
an Agilent K-band synthesizer and does not require subsequent phase locking or mechanical 
tuning. The LO is capable of providing $\sim 2$~mW of power across the band, more than
sufficient to drive the array. The LO power divider is cooled to 4~K, all other
components in the chain operate at room temperature. A standard waveguide vacuum feedthrough
conveys the LO power into the cryostat. The cryostat has a single 40~K radiation
shield. A waveguide thermal choke (Hesler 2003) on the 40~K shield will be used to isolate 
the 300~K input waveguide from the 4~K waveguide going to the LO power splitter.  

Four-way LO power division will be achieved in waveguide using 3 branching, E-plane
Y-junctions (Kerr 2001). The LO power splitter mounts just behind the mixer array 
(See Figure~\ref{subassembly}). Output power from the power divider is coupled to the LO port of each 
mixer through a short length of WR 3.7 waveguide.
A CAD drawing of the full implementation of the DesertSTAR II system as it will look
on the HHT is shown in Figure~\ref{cutaway}.

\begin{figure}[!htb]
\centering
\includegraphics[scale=0.42,angle=0]{DesertSTAR.8.28.03-1.eps}
\caption{\label{cutaway} {\small Cut-away view of the DesertSTAR~II system with both the 345~GHz and 230~GHz arrays implemented.}}
\end{figure}

\subsection {IF System}

As outlined above, each 230~GHz array pixel contains two balanced mixers. The IF bandwidth
of each mixer and the subsequent low-noise amplifier can be made quite broad (4-8~GHz). Indeed, 
for our array application it is the availability of backend spectrometers that limits
system bandwidth. As with the 345~GHz array, we have chosen a 2~GHz IF bandwidth centered
on 5~GHz. The same type of Pamtech 4-6~GHz isolators used between the mixer and 1st IF amplifier of the 345~GHz array will also be used here.
The cryogenic amplifiers for the array will be built by Sandy Weinreb at Caltech
(see attached letter of support). These MMIC amplifiers have excellent performance, providing
$\sim 5$~K noise temperatures and $\sim 35$~dB of gain over our entire IF band. The amplifiers
also have low power dissipation ($\sim 10$~mW). For the entire subarray 8 amplifiers are
needed. The existing cryogenic system can easily cool the amplifiers to 4~K. 
Once at room temperature, the 2 IF outputs of each SSB mixer pass through an IF hybrid.
The two output ports of the hybrid contain the upper and lower sidebands of the incoming
radiation. In the majority of observing programs the desired spectral information resides in
only one of the two sidebands. Naturally, one way to simplify the system and reduce cost is to
perform further processing on just one of the sidebands. However, the optimal sideband can change depending on system performance and atmospheric constraints. Kerr 2003 has demonstrated that 
it is possible to switch sidebands on the output ports of an IF hybrid by simply changing the
polarity of the mixer bias voltages. As with the 345~GHz array, the 230~GHz mixer bias voltages 
will be computer controlled.  This feature will allow us to easily switch between sidebands and 
simplifies the IF processor design.
A block diagram of the IF processor is shown in Figure~\ref{ifprocessor}.

\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
{\parbox{4.3in}{\includegraphics[scale=0.7,angle=0]{downconverter2.eps}}}
{\parbox{2.1in}{\caption{\label{ifprocessor} {\small Block diagram of 230~GHz array IF processsor.}}}}
\end{minipage}
\end{figure}


\subsection {Array Spectrometer}

The room temperature IF chain will amplify, condition, and then downconvert the
IF of each 230 GHz SSB mixer to the baseband frequency required by the spectrometer. 
To service the array we plan to divide the passband of one of the HHT facility 
1~GHz wide, 1~MHz resolution AOS's into four, 250~MHz sub-bands. An effective IF bandwidth 
of 250~MHz means each array pixel will have 326~km/s of velocity coverage at 1.3~km/s resolution. 
This velocity coverage and resolution is well suited to the requirements of a Galactic plane 
survey.

\subsection{Array Bias Control System}

A computer controlled array bias system has already
been developed by the PI's group and is currently being
used with their 4-channel, SIS 810~GHz array (PoleSTAR) on the AST/RO
telescope at the South Pole and the 7-channel, 345~GHz array.
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.
The control system is already designed to be extensible to 100 or 
more channels. The existing DesertSTAR system can be readily modified
to accommodate the additional mixer, magnet, and IF amplier bias 
requirements of the proposed array.

\subsection {On the Fly Mapping}

The most efficient mode of data collection with a focal plane 
array and one 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.  
However, the primary challenge of OTF mapping is data management and the co-add and 
resampling of data onto a regular grid.  This challenge is particularly 
acute with an array for which the data rates are typically 10x larger.
We therefore plan to adopt the scheme 
developed at FCRAO for OTF mapping with the 32 pixel SEQUOIA array
(see {\tt http://www.astro.umass.edu/$\sim$fcrao/library/manuals/otfmanual.html}).
In this scheme, a scan consists of all data from all pixels
taken between and including the two bookend off-source measurements.
An OTF map may be comprised of several of such scans.  The header for 
each scan is written into a relational data base program (MySQL) which 
facilitates efficient logging and retrieval of the data.  The 
observer executes a gui-based program, ({\it otftool}, which accesses
the data base, consolidates the requested scans into a list, 
provides tools for inspecting the raw data, and most importantly,
co-adds and resamples the data onto a regular grid.  The output is 
a FITS cube or Grenoble/CLASS file.  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. 

\subsection{Plan of Action}

\noindent{\it Year 1}

\medskip \noindent
During the first year of funding our efforts will be focused on building and
testing one complete 230~GHz array channel. Critical tasks include:
\begin{enumerate}
\item repackaging the ALMA band 6 (230~GHz) mixer to meet the optical requirements 
of the array. As part of this work we will design, fabricate, and test an IF matching/bias
network for the balanced mixer.
\item building the subarray bias control system. This system will be very similar to
what we have developed for our earlier arrays. The hardware and software will be
expanded to handle the 16 single-ended mixers that make up the 4 balanced, sideband-separation
mixers. 
\item building one complete channel of the IF processor.
\item characterizing the performance of the prototype mixer. Sensitivity,
stability, sideband separation ratios, and beam patterns are some of the properties
that will be measured. This work will be performed using the same cryogenic testbed
(wet dewar, optics, data acquisition system, antenna range) employed in testing the individual 
345~GHz mixers.
\end{enumerate}
\medskip

\noindent{\it Year 2}

\medskip \noindent 
In the second year we will complete the construction of the subarray and conduct
performance tests in the array cryostat. Tasks include:
\begin{enumerate}
\item fabricate and test the remaining three SSB mixers.
\item fabricate and test the 4-way LO power splitter.
\item design and fabricate the cryogenic assembly that houses the mixers,
LO power splitter, isolators, and IF amps.
\item install the subarray in the close-cycle cryostat and characterize its 
performance.
\end{enumerate}

\medskip

\noindent{\it Year 3}

\medskip \noindent 
In the third year our goal will be to install the upgraded, dual-frequency, DesertSTAR
system on the HHT and begin commissioning observations of the Galactic plane and selected
star formation regions.   


\section{Education and Public Outreach}

The proposed 230~GHz array will become part of the DesertSTAR facility instrument on the HHT,
available to all users. A key project for the instrument will be to conduct a sensitive,
high angular resolution, CO $J=3\rightarrow 2$ and $J=2\rightarrow 1$ survey of the Galactic plane.
Survey data products will be made available to the general scientific community via the web in a timely manner.  A Guest Observer Program will be established to facilitate use of the array by outside users.

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. Many students in science and technology have an interest
in astronomy. It is this interest 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 students research.
However, as has been the case for all major projects in the PI's lab, a number of
other students will also participate in making the progress a success. Indeed, 
one of the most important aspects of training students in instrument development
is giving them experience in working in teams. Astronomical instrumentation is
becoming ever more complex, with their successful implementation requiring the talents 
of many individuals. Providing students with both technical training and team-work
experience increases their probability of success. 


\section {Results from Prior NSF Support}

\begin{itemize}

\item A NSF Young Investigator Award (AST-9457445) was made to 
the PI for the period 7/1/94 - 7/1/99
of \$62,500 per year (matching funds have been obtained for all 
5 years). This award was used to support research and teaching
efforts. Research included further development of the laser 
micromachining waveguide technology, the construction of submillimeter
receiver systems at 230 and 490~GHz for the Arizona/MPIfR
Submillimeter Observatory, a 492/810~GHz receiver system
for the AST/RO telescope at the South Pole, the funding
of graduate and undergraduate students for the study of protostellar evolution,
and the construction of a submillimeter polarimeter and student radiotelescope. 
The receiver systems described above are (except for the polarimeter)
facility instruments. We estimate $\sim30$ papers from the HHT and 20 papers
from AST/RO will contain observations made with these instruments. Papers
describing the instruments are Groppi et al. (2000), Walker et al. (2001).

\item A grant (AST-9622569) from the NSF ATI program was made to the PI
to construct the 7-channel, 345~GHz array (DesertSTAR I) for the HHT.
(formal title: ``An 870 micron Array Receiver for the Heinrich Hertz Telescope'')
The award period was from 8/1/96 - 7/31/99 for a total of \$380,931. 
DesertSTAR has been a successful collaboration between the University of
Arizona (PI: system design and construction), NRAO (John Payne: J-T cooler), 
the University of Massachusetts (Gopal Narayanan and Neil Erickson: mixers and LO), 
and the University of Virginia (Art Lichtenberger: SIS junction fabrication).
It will be the first array receiver to operate in the 870 micron atmospheric window (Groppi et al. 2000; 2002).

\item An award (ECS-9800260) from the NSF Physical Foundations of 
Enabling Technologies Program was made to the PI  
to construct and utilize a laser micromachining system at the 
University of Arizona (Drouet d'Aubigny et al. 2001). 
The award period was from 6/1/98 - 5/31/00 
for a total of \$280,000. The system is fully operational 
and has been used to make waveguide components for integrated array
development and prototype quasi-optical structures for NASA's
{\it Terrestrial Planet Finder}.

\item A grant from the NSF ATI program was awarded to the PI and Co-I Daniel
Prober (Yale University) to develop ``An Integrated 370 micron Heterodyne Imaging Array''. 
This is an ongoing effort to combine laser micromachining technology
with recent developments in Hot Electron Bolometer (HEB) mixers to develop
the first truly integrated submillimeter-wave heterodyne imaging arrays (Groppi et al. 2002).
The arrays are being designed to permit scaling to higher frequencies
and formats. The award amount (\$450K) is being divided over a three year
period (02/01/02 to 01/31/05) between the participating institutions.

\item A subaward of \$99,348 was provided to the PI from the NSF ATI program for his 
contribution to ``A 1.5 THz Common User 
Receiver System'' (S. Yngvesson- PI). Over the two year award period (01/01/00 to
12/31/02) the PI's group designed and built the cryogenic, electronic, and optical
system for the TREND 1.5 THz receiver system now on the AST/RO telescope at the
South Pole. The laser LO system and high frequency mixer were provided by the
University of Massachusetts (Yngvesson et al. 2002).  

\item A subaward of \$290K from the NSF Office of Polar Programs was made to
the PI for his group's work in ``Continuing Operation of the Antarctic Submillimeter
Telescope and Remote Observatory'' (A. Stark- PI: OPP-0126090). The PI's group built most
of the facility receivers for AST/RO. This 3 year award 
(02/01/02 to 01/31/05) supports the continued maintenance and upgrade of these
systems (Stark et al. 2002).
\end{itemize}

\end{document}

% STOP HERE!!!!!   The rest of this is old stuff...

\section{\bf FACILITIES, EQUIPMENT \& OTHER RESOURCES}
\subsection{\it University of Arizona}

Steward Observatory, in
association with the Max Planck Institute for Radioastronomy, has 
constructed a 10~m submillimeter telescope
on Mt. Graham, Arizona (the Heinrich Hertz Telescope, HHT). In support
of this 8 million dollar investment, we have established a laboratory 
(the Steward Observatory Radio Astronomy Laboratory, SORAL) for
the development of state-of-the-art submillimeter-wave receiver systems.
The laboratory contains or has ready access to all the equipment 
(spectrum analyzers, network analyzer's, vacuum pumps, cryogenic
support facilities, etc.) needed for the development of receivers.  
The NSF Division of Astronomical Sciences has previously awarded
the PI funds to construct a 7 element array receiver at 345~GHz. 
The laser micromachined mixer arrays will be evaluated using many
of the facilities developed in support of the 345~GHz array.
In the past, SORAL has produced facility 230 and 492~GHz receivers
for the HHT and, recently, was the lead group in the design and
construction of a dual channel 492/810~GHz receiver for AST/RO at
the South Pole. These receiver systems are now in daily use at each
of these observatories. The experience SORAL personnel have gained in 
the design and deployment of these receiver systems will be fully 
utilized in the construction of the proposed prototype systems.

As a result of its successful collaboration with Lincoln Laboratory
in applying laser micromachining technology to the fabrication
of THz components, the Physical Foundations of Enabling Technologies
Program in the Engineering Division of the NSF recently awarded the PI 
a grant to construct a laser micromachining facility at Steward Observatory.
The design of this facility is based on the successful Lincoln
Laboratory system and optimized for the THz applications described
in this proposal. The availability of a state-of-the-art laser micromachining
system at Steward Observatory provides the community with a {\it powerful,
new} ability to develop a wide variety of needed THz components. 
Photolithographic facilities are also available at Steward for fabricating 
the wet-etched portions of the focal plane arrays.

SORAL also has licenses for
both Hewlett Packard's High Frequency Structure Simulator (HFSS) and
Microwave Design System (MDS) software packages. These programs
are used to accurately model and optimize mixers and other
crucial receiver components. 

\section{\bf CURRICULUM VITAE}
\vfill
\eject

\section{\bf CURRENT \& PENDING SUPPORT OF PI}
\subsection{\it Pending Awards}

\noindent
Title: {\it Micromachining of TeraHertz Waveguide and Quasi-Optical
Components for Suborbital and Space-Borne Detctors}, (this proposal), 
\noindent
Agency: NASA: NRA 99-SPA-01, 
\noindent
Budget: \$457,465 from 12/1/1999 to 11/31/02, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it Micromachining of TeraHertz Waveguide and Quasi-Optical
Components for SOFIA, FIRST, and TPF}, 
\noindent
Agency: NASA: NRA 98-OSS-10, 
\noindent
Budget: \$332,043 from 5/1/1999 to 4/30/01, 
\noindent
Commitment: 1 month/yr

\subsection{\it Current Awards}

\noindent
Title: {\it Laser Micromachining of Silicon: A New Technology for
Fabricating THz Imaging Arrays}, 
\noindent
Agency: NSF, 
\noindent
Budget: \$280,000 from 5/1/1998 to 4/30/01, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it NSF Young Investigator Award}, 
Agency: NSF, 
\noindent
Budget: \$312,500 from 7/1/94 to 6/30/99, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it An 870~$\mu$m Array Receiver for 
the Arizona/MPIfR Submillimeter Telescope}, 
\noindent
Agency: NSF, 
\noindent
Budget: \$390,931 from 8/1/1996 to 7/31/99, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it An 810~GHz Array Receiver for 
AST/RO}, 
\noindent
Agency: Smithsonian Astrophysical Observatory, 
\noindent
Budget: \$99,500 from 5/21/1997 to 6/30/99, 
\noindent
Commitment: 1 month/yr
\vfill
\eject

