% Latex text follows
\documentclass[11pt]{article}
\setlength{\topmargin}{-0.5in}
\setlength{\textheight}{9in}
\setlength{\oddsidemargin}{-0.15in}
\setlength{\textwidth}{6.5in}
\usepackage{graphicx,natbib,palatino}
\renewcommand{\baselinestretch}{1.12}
\newcommand{\kms}{km~s$^{-1}$\ }
\def\o2{O$_2$}
\def\h2o{H$_2$O}
\def\bigX{\large \bf X}

\makeatletter
\renewcommand\section{\@startsection {section}{1}{\z@}%
                                   {-2.5ex \@plus -1ex \@minus -.2ex}%
                                   {2.3ex \@plus.2ex}%
                                   {\normalfont\large\bfseries}}
\renewcommand\subsection{\@startsection{subsection}{2}{\z@}%
                                     {-1.5ex\@plus -1ex \@minus -.2ex}%
                                     {1.2ex \@plus .2ex}%
                                     {\normalfont\large\itshape}}
\renewcommand\subsubsection{\@startsection{subsubsection}{3}{\z@}%
                                     {-1.2ex\@plus -1ex \@minus -.2ex}%
                                     {1.0ex \@plus .2ex}%
                                     {\normalfont\normalsize\itshape}}
\makeatother

\begin{document}

\noindent {\Large \bf SUMMARY OF PERSONNEL AND WORK EFFORTS}
\bigskip

\noindent
{\bf PI Walker:} The proposed effort will be a major component 
of the PI's research over the next three years. He will
have overall responsibility for the project and coordinate
activities between the instrument and gondola teams.
He will spend $\sim$2 months per year working on the project.
However, due to the PI's salary being maintained by his 
academic appointment, only 1 month of salary 
per year is being requested.

\smallskip

\noindent
{\bf Co-I Chin} from GSFC is Project Scientist for SWAS and
will play a key role in planning our observational programs
on BLAST. He will also serve as a liaison between the
instrument team at Arizona and the microwave instrument group
at Goddard who will assist in making the instrument
flight worthy. Co-I Chin does not require salary support
from this program.

\smallskip

\noindent
{\bf Co-I Schieder} from the University of Cologne has agreed
to provide the SWAS backup acoustoptical spectrometer (AOS) 
for use with the proposed instrument. The data taken with its twin
on SWAS show that it is exceedingly stable, capable of single
integrations $>$20 hours. Although he will not be paid,
Prof. Schieder and his group will support our efforts to
integrate the AOS into the instrument package.

\smallskip

\noindent
{\bf Co-I Bieging} is an expert in the observation
and modeling of mm/submm emission lines from evolved star
envelopes. His experience will be invaluable in choosing
observing targets and in the interpretation of observations.
He does not request support from this project.  

\clearpage

\medskip
\centerline {\Large \bf A Water- and Oxygen- Seeking Heterodyne Instrument} 
\centerline {\Large \bf for the 2-meter Balloon-Borne Telescope BLAST} 

\section{Introduction}

In our search for origins, for planetary systems like our own that
might harbor life, the cyclical interplay
between the interstellar medium and the stars it forms plays a
pivotal role whose importance cannot be underestimated.  
Questions of particular importance that highlight our incomplete
understanding 
involve the physical and chemical structure of molecular
clouds, the nature of the processes that form stars within these
clouds, the number and nature of planets formed from young
circumstellar debris disks, and the return of potentially 
enriched material from
evolved stars back to the interstellar medium.  Crucial to each of
these phases of evolution is the chemistry of two molecules deemed
essential for life on Earth: oxygen and water.  

Launched in December 1998, the Submillimeter Wave Astronomy Satellite
(SWAS) had one preeminent goal; to conduct the first observations in the
important submillimeter-wave transitions of water (\h2o and
H$_2^{18}$O) and molecular oxygen (\o2), inaccessible to telescopes below the
Earth's atmosphere.  Over the course of three years it has surveyed
nearby molecular cloud cores for \h2o 
and \o2 (refs), leading to new initial conditions and diagnostics for
interstellar chemistry in understanding 
the star formation process.  In particular, the extraordinary 
detection of water vapor toward the evolved carbon-rich star 
IRC+10216 \citep{mel01} may indicate
the extra-solar analog of our own Kuiper Belt around IRC+10216.  If
this interpretation is confirmed by additional observations toward
IRC+10216 and other carbon stars, it will provide a new way of probing
the planet formation process and will yield important constraints to planet
formation models.  Another major result of the SWAS mission is the
non-detection of \o2 in molecular clouds \citep{gold00}.  The nature of oxygen
chemistry in molecular clouds and regions of starbirth has been
rewritten as a result and is providing new insights into the
most relevant interstellar processes, but more questions have been
raised than answered. 

These landmark results from SWAS are therefore not an end in themselves.
Instead, they mark the beginning of a wave of new, more sensitive
observations that will be made possible by the rapid technological
advancements of detector systems at submillimeter and Terahertz (THz)
frequencies.  In particular, the use of cryogenically-cooled
submillimeter detector systems on larger telescopes than the
0.5$\times$0.7-meter aperture of SWAS will reap immediate and
substantial gains. 

We therefore propose to construct a state of the
art, cryogenically-cooled, SIS receiver system (Submillimeter
Astronomy Balloon Expedition Receiver, or SABER) for the
Balloon Large Aperture Submillimeter Telescope (BLAST), a telescope of
2-meter aperture.  Adopted broadband mixer systems are capable of 
observing both the 557~GHz transition of water and the 487~GHz
transition of oxygen with a noise temperature an order of
magnitude lower than SWAS.  
For observations of extended sources, integration times
will be at least 100 times lower and mapping will be more than 100
times faster.  However, the most impressive gains over SWAS are
realized by observing unresolved sources; the BLAST/SABER
combination will perform sensitive observations many {\it thousands}
of times faster.  Crucial followup programs to SWAS, such as the
sensitive survey of evolved stars for water and potential cometary
systems, exceptionally deep
surveys for molecular oxygen in nearby molecular cloud cores, the
evolutionary structure of circumstellar disks, 
and water in Solar System planetary
atmospheres and comets can be performed with exceptional
efficiency, sensitivity, and frequency agility 
unafforded by SWAS and {\it well before} the
Herschel Space Observatory (HSO) launches in (estd.) 2007. 

The use of SABER on BLAST will therefore provide a new,
powerful probe of the interstellar medium and will serve both as a
valuable \& economical follow-up mission to 
SWAS {\it and} as a precursor mission for Herschel.  Although the
system could ultimately be used on long duration balloon flights, even
a comparatively short North American flight has the potential of
providing new, key information on the frequency and origin of planetary 
systems as well as fundamental knowledge of molecular cloud
structure and chemistry.


\section{Scientific Description}


\begin{table}[!hbt]
\begin{minipage}{7in}
\parbox{3.6in}{
\begin{tabular}{|ccc|}
\hline
{\bf Molecule} & {\bf Transition} & {\bf Frequency} (GHz) \\
\hline \hline
{\bf \o2} & $3_3 \rightarrow 1_2$ & {\bf 487.249} \\
HCN & $J=6\rightarrow5$ & 531.716 \\
HNC & $J=6\rightarrow5$ &543.897 \\
$^{13}$CO & $J=5\rightarrow4$ & 550.926 \\
{\bf \h2o} & $1_{10}\rightarrow1_{01}$ & {\bf 556.936} \\
SO & $13_{14}\rightarrow{12}_{13}$ & 560.178 \\ 
H$_2$CO & $8_{18}\rightarrow7_{17}$ & 561.899 \\  
SiO & $J=13\rightarrow12$& 564.243 \\
CN & $J=5\rightarrow4$ & 566.730 \\
NH$_3$ & $1_{00}\rightarrow0_{01}$ & 572.498 \\
CO & $J=5\rightarrow4$ & 576.268 \\
CS & $J=12\rightarrow11$ & 587.616 \\
\hline
\end{tabular}}
\parbox{2.75in}{
\caption{\label{lines} {\small A sample of interesting lines in the
480-590~GHz regime.  As with SWAS, the principal aim of SABER will be
the detection of \h2o and \o2 lines. Unlike SWAS however, SABER's SIS
mixers are frequency-agile, and alternate science programs can also be
pursued.}}}
\end{minipage}
\end{table}


\subsection{Feasibility of \h2o and \o2 Studies from a Balloon}

The wavelength regime between 700 and 200 $\mu$m contains a number
of atomic and molecular emission lines that are key diagnostic probes
of the interstellar medium (c.f. Table~\ref{lines}). 
Ground-based submillimeter telescopes at
high, dry observing sites have some access to the rich features of
this wavelength regime, but are restricted to the spectral ``windows''
of modest atmospheric transmission between supersaturated absorption
features caused by telluric \h2o, \o2, N$_2$O, and O$_3$, among many
others.   However some of these atmospheric species, such as \h2o and
\o2, are themselves of considerable interest in their own right, not
least for their chemical significance to our origins and, on a larger
scale, to the study of life in the Universe.  Although placing an
observatory in space eliminates this problem, it is also possible to
launch a comparatively cheaper, more flexible and reusable
balloon-borne telescope to a height of $\sim$40~km to overfly
nearly all of the atmosphere.  


In Figure~\ref{transmission} we have used an improved version of the
AT program (Grossman 1989) to model the transmission of the
atmosphere in the vicinity of the 556.937~GHz $1_{10}-1_{01}$
transition of \h2o and the $3_3-1_2$ transition of \o2 at 487.25~GHz.
Although telluric \h2o and \o2 features are still saturated even at an 
altitude of 40~km, the width of such lines is fairly narrow. Indeed,
$\sim$90\% transmission is achieved just 10~km~s$^{-1}$ from the \o2
line center, and $\geq$80\% transmission can be found 30~km~s$^{-1}$ from the
center of the \h2o line.  The narrowness of these features at balloon
altitudes makes the
natural shift of the Local Standard of Rest with respect to the
geocentric telluric lines sufficient to move most astronomical
sources into regions of good atmospheric transparency much of the year.  

\begin{figure}[!htb]
\centering
\includegraphics[angle=90,scale=0.34]{Trans_487.ps}
\includegraphics[angle=90,scale=0.34]{Trans_556.ps}
\caption{\label{transmission}{\small Atmospheric transmission in the vicinity
of the 487~GHz \o2 line (left) and 557~GHz \h2o line (right),
calculated using the AT program of (ref), modified to improve its
internal numerical resolution at high resolving power. The solid line
represents the transmission from an altitude of 39~km on a
circumcontinental flight over the Antarctic.  The dotted line
represents a short 1-2 day mission launched to an altitude of 41~km
from North America (Texas).  The weak atmospheric feature at
487.34~GHz is due to O$_3$, and although not modeled in these figures,
will be insignificant over Antarctica.}}
\end{figure}


This statement is depicted most clearly by
Figure~\ref{vlsr}, which demonstrate the frequency shifting of
astronomical spectral lines toward various sources 
due to the Earth's rotation and revolution
about the Sun.  Table~\ref{feasibility} quantitatively demonstrates
the number of days per year that an unbiased 
selection of interesting astronomical sources may be observed with
high efficiency.  

Encouraged by these results, let us explore a few of the exciting
scientific possibilities afforded by the development of the SABER
instrument aboard BLAST. 


\begin{figure}[!htb]
\centering
\includegraphics[angle=-90,scale=0.3]{irc10216.ps} \hspace{0.1in}
\includegraphics[angle=-90,scale=0.3]{orion.ps}  
\includegraphics[angle=-90,scale=0.3]{roph.ps} \hspace{0.1in}
\includegraphics[angle=-90,scale=0.3]{m82.ps}
\caption{\label{vlsr}{\small Spectral line frequency offsets for four
representative sources compared to their telluric counterparts,
expressed in \kms as a function of the day of the year.  
The region between the two dashed horizontal lines
expresses the \o2 ``zone of avoidance'', within $\pm$10~\kms of the
telluric \o2 line center.  The dotted lines represent the \h2o ``zone
of avoidance'', within $\pm$30~\kms of the telluric \h2o line center.}}
\end{figure}

\begin{table}[!hbt]
\begin{minipage}{7in}
\parbox{4.1in}{
\begin{tabular}{|cccc|}
\hline
 & & \multicolumn{2}{c|}{\% of year observable}\\
{\bf Source} & {\bf $V_{lsr}$ (\kms)} & {\bf \o2 } & {\bf \h2o} \\
\hline \hline
\multicolumn{4}{|c|}{\bf Carbon-Rich AGB Stars} \\ \hline
IRC+10216 & -26 & 63 & 41 \\
R Scl & -18 & 70 & 6.5 \\
V384 Per & -17 & 67 & 31 \\
R Lep & 16 & 100 & 56 \\
%RW LMi & -2 & 77 & 0 \\
Y CVn & 24 & 58 & 24 \\
T Dra & -12 & 100 & 47 \\
IRAS 17581 & 23 & 77 & 26 \\
FX Ser & 30 & 73 & 32 \\
IRC+30374 & -12 & 100 & 52 \\
%AFGL 2513 & 19 & 65 & 0 \\
%V Cyg & 15 & 47 & 0 \\
S Cep & -5 & 75 & 0 \\ \hline
\multicolumn{4}{|c|}{\bf Star Forming Regions}  \\ \hline
M16 & 24 & 76 & 26 \\
M17 & 6 & 77 & 23 \\
Orion BN/KL & 5.5 & 67 & 42 \\
NGC 2264 & 6.5 & 63 & 41 \\
AFGL 2591 & -7 & 82 & 39 \\
NGC 7538 & -57 & 100 & 100 \\
$\rho$ Oph A & 4.0 & 77 & 21 \\ \hline
\multicolumn{4}{|c|}{\bf Nearby Galaxies} \\ \hline
IC 342 & 35 & 100 & 51 \\
M82 & 209 & 100 & 100 \\
\hline
\end{tabular}}
\parbox{2.3in}{
\caption{\label{feasibility} {\small A representative sample of
evolved stars, star-forming regions and molecular clouds, and nearby external
galaxies, their intrinsic velocities relative to the Local Standard of
Rest (LSR) and their their observability in the $\sim$500~GHz \o2 and
\h2o lines.  The latter is computed from the fraction of the year that
the observed radial velocities exceed $\pm$10~\kms\ for \o2 ($\sim$90\%
transmission) and $\pm$30~\kms\ for \h2o ($\sim$80\% transmission).}}}
\end{minipage}
\end{table}



\subsection {Survey for Water Vapor in Carbon-Rich Evolved Stars}

\begin{figure}[htb]
\centering
\includegraphics[angle=0,scale=1]{irc+10216.ps}
\includegraphics[angle=0,scale=1.15]{nature.eps}
\caption{\small \label{evap} (left) Artist's conception of the
evaporating comet hypothesis for the water vapor detection of
\citet{mel01} (right) toward IRC+10216.  This result, obtained in
almost 200 hours of on-source integration time with SWAS, is
reproducible in $\approx$5 minutes of on-source integration time with
SABER/BLAST.
}
\end{figure}

The surprising detection of \h2o in the $1_{10}-1_{01}$ 557~GHz line 
toward the carbon-rich
post-main-sequence star IRC+10216 by \citet{mel01} suggests the
use of \h2o emission in such objects as a probe of vaporized cometary systems
in other stellar systems, and hence a measure of the frequency and
nature of planetary systems like our own in the Solar neighborhood.
Such measurements would be a natural complement to the radial-velocity
planet finding methods \citep{Marcy} that are most sensitive to the
detection of 
massive planets orbiting near their parent stars. 
The establishment of a technique to find analogs of ``Kuiper Belts'' around
other stars is certainly exciting, intriguing and has far reaching
consequences for the assessment of habitable planets in the Galaxy.  

However, such powerful statements require equally compelling evidence;
thus this hypothesis needs to be urgently tested.  The combination of
SABER and BLAST provides an outstanding facility for performing  
followup observations toward IRC+10216 and surveying other carbon
stars to establish the frequency and nature of submillimeter \h2o
emission toward carbon-rich AGB stars.  
We also propose to explore alternative explanations with
the SABER observations, however.  Specifically, we believe it is
critically important to examine possible non-equilibrium chemical
models for the presence of oxygen-bearing molecules in carbon star
envelopes.  Most AGB stars, including carbon stars like IRC+10216, are
large-amplitude pulsators, and so must be driving strong shock waves of
$\sim$10-30 \kms through their outer atmospheres every few hundred days.
Willacy \& Cherchneff (1998) computed chemical reactions for a model of
the IRC+10216 envelope, in which pulsationally-driven shocks are the
key non-equilibrium energy source.  They found that some O-bearing
molecules, e.g., SiO, are strongly enhanced to readily detectable
levels.  Observations of submillimeter transitions of SiO by Bieging, Shaked,
\& Gensheimer (2000) showed that the higher energy transitions of SiO
are in fact present at large intensities in many carbon stars, and that
the inferred excitation of the molecule can only be due to formation in
the warm, dense inner circumstellar envelope, with SiO abundances
consistent with formation behind shocks.  Whether \h2o can also be
formed in carbon stars by shock chemistry is unclear.  The pure
gas-phase shock models of Willacy \& Cherchneff (1998) find that \h2o is
enhanced for strong shocks but reduced for slower shocks.
Consequently, this mechanism was rejected by Melnick et al. (2001) as
requiring what they regarded as unrealistic shock parameters.  However,
Hollenbach (private communication) found that \h2o can be produced by
shocks in such environments via grain-CO molecule collisions, which
create free O that rapidly reacts with H to form \h2o.  Recent numerical
hydrodynamic models by Winters et al. (2001) show that in fact,
sufficiently large shock velocities are predicted to occur in regions
of high gas density and high grain condensation fraction, so that the
shock production of \h2o should be given serious consideration.  The
question clearly cannot be resolved without increasing the sample of
AGB carbon stars searched for \h2o emission.

To test this hypothesis, and to compare with the alternative, that \h2o
in carbon star envelopes is an evaporate of primitive icy bodies like
the Kuiper Belt, we will observe a large sample of carbon stars.  The
1000-fold increase in speed that SABER will have over SWAS to reach a
given sensitivity will make this survey feasible.  With a large sample
of stars, we can measure the \h2o line intensity and width, infer \h2o
masses, and compare these results with the known mass-loss properties
of the stellar sample.  If there are correlations with current mass
loss rates and velocities, then the shock hypothesis would be
supported.  If the \h2o is from evaporated KBOs, one would not expect
correlations with current mass loss, which is a function of the star's
current evolutionary state, not its past formation history. 

A further test of the origin of \h2o in carbon-rich stellar envelopes
could be made with a future modification of the SABER receiver, to
access the 1 THz region.  By observing the \h2o $1_{11}-0_{00}$ transition to
the ground state (1.113 THz) as well as the $3_{12}-2_{21}$ line (1.153
THz, 240 K above ground) and the $3_{21}-3_{12}$ line at 1.163 THz (300 K
above ground), we can determine unambiguously the excitation conditions
of gaseous \h2o.  Observations of these \h2o lines, all made with the same
telescope and receiver system, will eliminate uncertainties due to
different beam sizes and calibration.  If produced by shocks in the
inner circumstellar envelope, the higher-energy transitions should be
strong and readily detectable.  In contrast, if \h2o is an evaporate of
ancient icy bodies, it must exist only at large distances from the star
under conditions of relatively low excitation compared with the shock
models.  In this case, the higher excitation lines will be weak or
undetectable.  Hence, comparing lower and higher excitation lines of
\h2o will provide a critical test of the distribution, and therefore of
the formation mechanism, for \h2o in carbon star envelopes.
Additionally, multi-transition data will allow precise \h2o mass
determinations by constraining the molecular excitation temperature.  

We point out that ISO observed and detected only a very few carbon-rich
AGB and post-AGB objects in the IR lines of \h2o.  Herpin and Cernicharo
(2000) found \h2o in the spectrum of CRL618, which is in fact a very
young planetary nebula where the inner envelope chemistry is probably
dominated the UV flux of the hot central star.  Yamamura et al. (2000)
report a tentative detection of \h2o bands with the ISO SWS in the
peculiar carbon star V778~Cygni, an object which shows silicate
absorption features and which may well be a binary with a disk formed
of oxygen-rich stellar ejecta.  In short, these ISO detections of \h2o
are hardly representative of the larger class of carbon-rich AGB stars
which we aim to target with SABER.  The limited spatial and spectral
resolution, and the modest sensitivity of the ISO spectrometers, leave
much room for improvement in searches for \h2o in carbon stars.  The
great advance in sensitivity over SWAS, and in both sensitivity and
spectral resolution over ISO, which SABER should achieve, make our
proposed survey of carbon stars well worth doing.

The first SABER observations on a 1- or 2- day balloon flight will be
able to conservatively observe more than half of the 35 carbon-rich 
sources listed in
the Groenewegen et al. 1999 catalog of AGB stars 
for water vapor emission to noise
levels of 1-2~mK (expected emission is at the 10-20 mK level for a several
$M_{earth}$ source as in IRC+10216).  We plan to allocate about 15 minutes
per source, with 5 minutes for source pointing and set-up overhead,
with 5 minutes total integration on target, and 5 minutes off-target
(standard on-off radio observing strategy). In a full 24-hour duration
flight, SABER can potentially observe 96 sources. During an additional
24-hour flight duration, SABER has the capability to retune in flight
and re-observe the initial set of AGB sources for emission in other
molecular species (e.g. Table~\ref{lines}). 

As a complement to the study of carbon stars, we will also survey a
sample of nearby O-rich (i.e., M spectral type) AGB stars for \h2o, \o2,
and other possible diagnostic lines of inner-envelope shock chemistry.
Water vapor is expected to be a dominant molecule in M-giant stellar
outflows, and has in fact been detected readily in a number of such
stars with ISO (e.g., in R~Cas, by Truong-Bach et al. 1999; and in
several K- and M-giants by Tsuji 2001).  SABER observations of the 
557~GHz \h2o line, with good spectral resolution, will provide crucial
information on the mass loss rates and the \h2o abundance in M-giant
winds.  Existing CO data for these stars will also allow us to compare
molecular abundances with results of theoretical chemical models (e.g.,
Duari et al. 1999).  As a further test of the importance of
pulsationally driven shocks, we will observe two sensitive molecular
indicators in the M-giant sample.  \o2 is predicted by Duari et al.
(1999) to be quite sensitive to processing by shocks, in general being
depleted, but by amounts which vary by a factor of 100 for a change in
shock velocity of only 50\%.  Thus either a detection or an upper limit
on the \o2 abundance can constrain the parameters of shock-driven
chemistry in the circumstellar envelopes of M-giants.  A second
molecular indicator is HCN, which Bieging et al. (2000) detected
readily in the short-mm and long-submm lines toward M-giants.
Theoretical models predict a strong dependence of HCN abundance on
shock parameters (Duari et al. 1999).  Since the models predict that
shock-produced HCN should form in conditions of high density and
temperature, it is crucial to obtain good spectra of the higher-J lines
of HCN to constrain the molecular abundance and excitation.  The high
quality HCN $J=6\rightarrow5$ spectra (531.7 GHz) we will be able to
obtain with SABER, will allow us to model the inner stellar envelopes
with much better accuracy than was possible using only the lower
energy $J=4\rightarrow3$, $3\rightarrow2$, and $1\rightarrow0$ lines
(Bieging et al. 2000).  The HCN $J=6\rightarrow5$ SABER data will be a
critical complement to the ground-based observations made previously.



\subsection {Deep Spectroscopic Searches for Interstellar \o2 in Star
Forming Clouds}

\begin{figure}[htb]
\centering
\begin{minipage}{7in}
\parbox{3.3in}{\includegraphics[angle=0,scale=0.9]{o2.ps}}
\parbox{3in}{\caption{\small \label{o2} The deepest searches for the
interstellar 
\o2 pivotal to models of the chemistry of molecular clouds and
star-forming regions, from \citet{gold00}: the detections (thin lines) 
are measurements of C$^{18}$O
$J=1\rightarrow0$, the non-detections (thick lines) 
are spectra of \o2 at the frequency of the $3_3\rightarrow1_2$ transition. 
These observations from SWAS required
$\sim10^3$ minutes of integration time each, but can be accomplished
in $\leq$5 minutes with BLAST and SABER.  Accounting for the
distribution of oxygen in
star forming clouds is a crucial step in determining the ionization
and thermal balance of clouds; which partly regulates the evolution of
interstellar clouds and their ability to form stars.}}
\end{minipage}
\end{figure}

The distribution of oxygen in atomic and molecular form, both in the gas
phase and on the surfaces of grains is a critical unknown in
understanding the chemistry, the ionization structure, and the thermal
balance of interstellar clouds, and hence in predicting their
evolutionary course. Because of the different chemical reactivities of
O, \o2, \h2o, and their ions, the overall molecular composition in
molecular clouds is
sensitive to the oxygen distribution.  Understanding oxygen chemistry
by establishing the abundance of oxygen-bearing species has been
therefore an important goal of both theoretical and observational
studies. 

Although exhaustive spectral line surveys have only been undertaken
for few sources (e.g. Orion BN/KL and Sgr B2), thousands of lines from
over 100 different molecular species have been detected
\citep{sch99}.  Unfortunately, only about 20\% of the elemental
oxygen measured in the Solar System is accounted for; the remaining
repositories such as O, \h2o, \o2 and their ices lie at frequencies
where atmospheric absorption prohibits their study.  Airborne and space
based telescopes are therefore necessary to probe these species.
However even published studies are inconclusive.  For example, studies of
interstellar O~I 1356 \AA\ absorption \citep{mey98} only probe diffuse
interstellar gas and do not specifically address
dark molecular clouds that constitute the sites of star formation.  In
contrast, [O~I] 63~$\mu$m absorption measurements toward bright
infrared continuum sources suggest that atomic oxygen may be quite
abundant in molecular clouds \citep{pog96,kraemer98,balu97,caux99}.
However as their values range from 10-90\% of the solar abundance,
their interpretation remains controversial.  The spectroscopic
abilities of the Infrared Space Observatory (ISO) were capable of
observing \o2 transitions shortward of 200~$\mu$m, however none of the
observable transitions ($\geq$180~K above the ground state) are
energetically excitable by the cold conditions prevalent in dark
molecular clouds. 

Balloon-borne experiments have searched for \o2 without success.  The most
sensitive of these \citep{olof98} placed 3$\sigma$ limits of
\o2/CO=0.04 toward NGC~7538.  This particular expedition is noteworthy
as it also employed a cryogenic SIS receiver, however the 8 hour
mission was plagued by bad beam coupling ($\eta_{\rm mb} \sim 0.1$) and
garnered only 15 minutes of on-source integration time.  In contrast, we expect
receiver noise temperatures that are nearly 3 times lower
(Section~\ref{rx}), a telescope with $\approx$16 times the collecting
area, and many times better beam coupling efficiency.  

SWAS permitted the most sensitive opportunity for \o2 detection
\citep{gold00}, but \o2 has proven elusive to even very long
integrations.  The most sensitive published limit on \o2 is
toward the nearby $\rho$~Oph~A cloud core: \o2/C$^{18}$O=1.5, or
\o2/CO=0.003 if CO/C$^{18}$O$\sim$500 \citep{wilson94}.  Such low
abundances relative to H$_2$, a few times 10$^{-7}$, are not
explainable by conventional gas-phase chemical models. 

Three principal hypotheses have been invoked to explain the low
abundance of \o2.  All of them are readily testable due to the large
aperture of BLAST and high sensitivity of the cryogenic SIS mixers in
SABER.  It is significant to note that the best detection limit provided by
SWAS toward $\rho$~Oph~A in 10$^3$ minutes of observing time can be
reproduced by the combination of BLAST and SABER in $\leq$5
minutes of on-source integration time.

\medskip

\noindent {\bf \o2 depletion}: The gas-phase fractional abundance of \o2
can be reduced if the gas-phase C/O ratio is raised to $\approx$1 by
preferential depletion of oxygen onto grains in the 
form of \h2o or other species (e.g., Hasegawa \& Herbst 1993). The
details and importance of grain surface depletion, reaction, and
desorption processes are uncertain, but this mechanism could
account for the low gas-phase abundance of \o2 in quiescent clouds.
The return of water-bearing ices to the gas phase in circumstellar
star-forming environments (i.e. in the disk itself, the heated
envelope, or in the warm outflows driven from the central young stellar
object) should liberate oxygen into the gas phase, where some
molecular oxygen might then be observable.  The $\rho$~Oph cloud may
well present a suitable testing ground of this idea; as the $\rho$~Oph~A
cloud core has already been shown to have a low \o2 abundance, and its
neighboring A2 core shows enhanced sulphur abundances (SO, SO$_2$ and
CS) due to a low velocity outflow.  
The newly-formed high mass star AFGL~2591 also 
demonstrates abundant warm gaseous \h2o \citep{hel96} and might be
expected to have returned some of its elemental oxygen to the gas phase.  A
modest sample of sources in varying degrees of thermal evolution should be
sufficient to test this hypothesis, in addition to providing the most
sensitive measurements of the \o2 abundance en route.

\medskip

\noindent {\bf Chemical youth}:  Models of time-dependent chemistry
\citep{berg95,lee96,millar97} require over 10$^5$ years for the \o2
abundance to build up to 10$^{-6}$ in typical shielded molecular
environments of $n_{\rm H} = 10^{3-5}$~cm$^{-3}$.  Thusly, the low abundance
of \o2 could suggest that the molecular material has only recently
been shielded from radiation.  This model can also be tested, as
another indication of chemical youth is a high atomic carbon
abundance, which is observable via fine structure emission lines at
submillimeter wavelengths.  Numerous [C~I] maps exist in the
literature; indeed, the PI's group has mapped a 1600 square arcminutes
of the $\rho$~Oph cloud in the 492~GHz $^3P_1-^3P_0$ line of
carbon, and find a systematically higher carbon abundance in portions of the
cloud \citep{kul02}.  Measurement of \o2 toward several dense cores in
sources like the $\rho$~Oph cloud can test this hypothesis.

\medskip

\noindent {\bf High-ionization solutions}: The bistable solutions to
chemical equilibrium equations lead to an often ignored but plausible
``high-ionization phase'' that may explain the low abundance of \o2,
by favoring atomic oxygen instead \citep{lee98,leb95}.  The
symptoms of the high-ionization solutions are similar to chemical
youth; namely a high atomic carbon, and low \h2o abundance.  
Once again, SABER can provide sensitive 
\o2 and \h2o measurements where SWAS has not yet
ventured, and atomic carbon measurements can be obtained in advance 
via ground based observatories in both northern and southern hemispheres. 


\section{Instrument Description}
\label{rx}

\subsection{Design Goals}

The Schottky Diode mixers on SWAS have a typical DSB noise temperature
of $\sim$2200K DSB (4400K SSB) 
(Melnick et al. 2000). SIS junction based mixers regularly 
achieve noise temperatures of $\sim$100K DSB at the same
frequency. Accordingly, the next
generation ESA orbital submillimeter mission, Herschel, uses SIS
junctions for all the submillimeter bands.  Using BLAST, there are
great opportunities for sub-orbital missions before Herschel launches 
that can expand and improve on many areas of the groundbreaking SWAS
mission. BLAST offers the ability to fly a cryogenic SIS receiver on a
telescope with an aperture $\sim$4 times larger than that of SWAS. These
two features can yield dramatically improved sensitivity to unresolved
sources. We propose to build a dual polarization, state-of-the art,
single sideband SIS receiver that is optimized for observing the 557~GHz
line of water and the 487~GHz line of oxygen using BLAST. The
receiver will be designed and constructed to provide reliable,
low-noise operation within the gondola environment.  It will use a
fixed-tuned silicon etalon as the single sideband filter, a simple
Mylar beamsplitter for the LO diplexer and a wire grid for
polarization diplexing. These optics will efficiently couple the
telescope beam to two SIS mixers and low noise amplifiers, all
contained in a robust and simple liquid cryostat. A backup flight AOS
from the SWAS project will serve as the spectrometer, and we will use
proven computer-controlled bias electronics to monitor and tune the
system in flight. 

\subsection{Optics}

Figure~\ref{diagram} shows a schematic diagram of the receiver
system. All optics 
are cold, with a minimum of moving parts. The cryostat is located just
past the Cassegrain focus of the telescope. The beam enters the
cryostat through a low-loss, AR-coated crystalline quartz window
(Benford et al. 1998) and then proceeds to an offset parabola where it
is collimated. The beam then passes through a quasioptical single
sideband (SSB) filter. Single sideband filters offer advantages in
system noise temperature, sideband calibration, and a reduction in
line confusion (Jewell 1997). While our atmospheric models show that
transmission should be good enough not to require a single sideband
filter, the device does offer a $\sim$100K improvement in system
temperature, in addition to the calibration advantages. Traditionally,
a Martin-Puplett interferometer is used as a quasi-optical single
sideband filter. While this approach has the attractive feature of
frequency agility, they are also complex, and require high precision motion
at 4K. We choose instead to use a silicon etalon as a single sideband
filter. While these devices have narrow bandwidth, they are extremely
simple. They consist of a silicon plate that is ground to the proper
thickness to act as a Fabry-Perot resonant cavity.  They transmit the
desired sideband while reflecting the unwanted sideband to a 4K load
(Mueller 2002). This etalon will be mounted on a linear actuator to
allow it to be removed from the beam for observing brighter lines
where single sideband operation is not critical. A simple Mylar
beamsplitter functions as the LO diplexer. While there are many more
efficient ways to inject the LO signal, they are unnecessary.  LO power
is easily available at ~500 GHz, and not much is required to pump two
mixers. We use a 45$^{\rm o}$ wire grid to split the incoming polarizations to
the two SIS mixers. The mixers are coupled to the telescope beam with
polyethylene coated crystalline quartz lenses and corrugated dual mode
feedhorns, which offer 98\% coupling to the fundamental Gaussian mode.  

\begin{figure}[!htb]
\begin{minipage}{7in}
\parbox{3.8in}{\includegraphics[angle=0,scale=0.5]{diagram.eps}}
\parbox{2.2in}{\caption{\small \label{diagram} Schematic of overall
SABER instrument design}}
\end{minipage}
\end{figure}


\subsection{Mixers and Low Noise Amplifiers}

The current state of the art in SIS mixer design uses suspended
stripline junctions, as pioneered by Blundell \& Tong, with advanced
optimized on-chip tuning structures that allow the use of tunerless
mixer mounts (Blundell et al. 1995). Our mixers are an adaptation of
this proven design. These mixers cover from
425-575 GHz with both high performance and reliability. Mixers
optimized for 460-500 GHz ground based observations exhibit receiver
noise temperatures of $\sim$80K DSB (Kooi et al. 1998). We expect noise
temperatures of 100K or better at 557~GHz.  A ``standard'' 492 GHz
waveguide mixer offers very good performance from 425-575 GHz. We need
only fabricate devices optimized for that frequency. Device runs with
557~GHz junctions are already planned at both JPL and the University
of Virginia. We plan to use Chalmers developed LNAs, which offer 2K
noise temperature, low power dissipation, and a 4-8 GHz IF
bandwidth. The relatively high 6~GHz IF frequency simplifies the
design of the IF processor necessary to feed the SWAS AOS.  

\subsection{Local Oscillator}

A revolution in local oscillator technology has also taken place,
mainly driven by ESA \& NASA's Herschel mission. Past multiplier designs
used whisker-contacted Varactor diodes. These devices exhibited
inconsistent (sometimes time-variable) performance, high capacitance
and low power handling ability. Modern LOs use monolithic diodes made
with micromachining technology to offer very consistent, stable
performance and very high power handling capability. Due to reduced
diode capacitance and very well defined performance characteristics,
exceptional performance is available from LOs with tunerless
multipliers and self biased diodes (Erikson 2001). With only a
backshort and tuner on a Gunn oscillator source, it is possible to
obtain tens of milliwatts of LO power at 557~GHz from an extremely
simple, reliable device. Since we need only adjust the two Gunn
Oscillator micrometers, and a single attenuator micrometer, we can
easily automate the tuning system with three computer controlled
motors and a simple lookup table. No other adjustments are necessary
due to the tunerless SIS mixers and LO multipliers. Since we are
feeding two mixers, each sensitive to a linear polarization orthogonal
to the other, we need to mount the LO such that the polarization of
the LO beam is at 45$^{\rm o}$ to the two mixers. The frequency agility of the
LO and the 700 MHz bandwidth of the backend also allows for the
possibility of frequency switched observations. The BLAST telescope
has no facility for chopping, so frequency switching would be an
efficient observing mode for single point observations. 

\subsection{Backend Spectrometer}

Co-I Schieder, Cologne University, will provide 
the spare SWAS AOS as the backend for the
BLAST heterodyne project (Frerick et al. 1999). This AOS has a 2.1 GHz
input frequency with 1400 MHz bandwidth and 1 MHz frequency
resolution. This is a fully-functional flight-qualified AOS identical
to the device now flying on SWAS. The AOS control electronics are not
spaceflight qualified, but can be repackaged so they are robust enough
for suborbital operations. The AOS data can be accessed every 10ms via
a 16 bit parallel data bus with standard TTL logic. We are responsible
for developing a data handling and storage system, which can be
accomplished with fairly simple electronics and an standard PC running
a real-time operating system (such as RT Linux). 

\subsection{IF Processor}

Similar to what was done on SWAS, we plan to split the AOS passband
into two 700 MHz segments. Each segment would process the spectrum
from one of the two mixer/IF chains. To accomplish this, we need an IF
processor to translate the frequencies of both IFs and combine them
into a single 1.4-2.8 GHz signal. As shown in Figure~\ref{diagram}, we will
amplify each of the 4-8 GHz IF outputs from the mixers and then
downconvert them to 1.75 GHz and 2.45 GHz respectively. Each signal is
then filtered to a 700 MHz bandwidth, amplified, and combined with a
Wilkinson power combiner into a single 1.4-2.8 GHz signal. The signal
from mixer 1 appears from 1.4-2.1 GHz and the signal from mixer 2 is
from 2.1-2.8 GHz.  This IF processor contains off the shelf components
from Miteq Inc. and Mini-Circuits Inc. and requires only two fixed
tuned Miteq oscillators phase locked to a 10 MHz reference signal.  

\subsection{Instrument Control and Integration}

We have already developed a simple, reliable computer controlled bias
system for our array receivers now in operation at the AST/RO
telescope at the South Pole and the Heinrich Hertz Telescope (HHT) on
Mt. Graham, AZ. These systems use rack mounted cards to provide SIS,
magnet and LNA bias to any number of receiver channels. The system can
be controlled by any computer running Linux with a parallel port and a
data acquisition card, and fits into a single 19" wide rack.  A modern
PC can control mixer bias, monitor the total IF power levels, and
serve as the data storage system for the instrument. Via Ethernet,
this type of machine can communicate with any other networkable
computer, allowing great flexibility in communications with the
gondola computer system.  

During the design phase we will keep in close communication with the
BLAST team and GSFC to ensure that the instrument design will be easy
to integrate with blast, and will be able to survive the rigors of a
suborbital mission. To aid in instrument integration, the BLAST team
will provide us with a fully functional duplicate of the BLAST gondola
electronics and data acquisition system. In addition, we will exchange
personnel with both U. Pennsylvania and GSFC during the integration
phase to ensure instrument compatibility and survivability. 

\subsection{Calibration}

In flight calibration is a necessary task that requires more thought
on a suborbital mission than with a ground based receiver. First, to
measure the receiver Y-factor, we need cold and warm loads accessible
during flight. We plan to use a third window in the cryostat that
allows access to a cold load mounted on the 77K radiation shield. A
deployable flip mirror just in front of the main cryostat window will
redirect the receiver beam off a fixed flat into the calibration
window. A second position of the same flip mirror assembly will bring
a warm load directly into the main beam of the receiver.  This warm
load can also be used for chopper wheel calibration. We will be able
to do both continuum and spectral line calibration on planets, as well
as measure beam efficiency. This two-stage calibration, combined with single
sideband operation and fixed-tuned mixers, should provide accurate,
stable calibration. 

\subsection{Sensitivity Estimates}

The sensitivity of a single sideband, heterodyne receiver on BLAST can
be estimated by following the procedures outlined in MMA~Memo~170.  In
this derivation both single sideband operation and atmospheric
contributions are taken into account (Jewell 1997).  

\begin{equation}
T_{SSB,DP} = \frac{2 \, T_{rx}(DSB) + T_A(sky) +
T_{image}}{\sqrt{2} \, \eta_l \, \eta \, \exp (-\tau)}
\end{equation}

\begin{equation}
T_A(sky)= \eta_l \, T_M \left[ 1-\exp(-\tau)\right] + (1-\eta_l) \, T_{spill}
+ \eta_l \, T_{bg} \, \exp(-\tau)
\end{equation}

Table~\ref{parms} lists the parameter values we have chosen to
estimate the BLAST 
system temperature. Since we also detect both polarizations, the
effective system temperature is further improved by the square root of
2. The listed parameters are relatively conservative, assuming an
atmospheric transmission of 80\%. As the atmospheric models presented
earlier show, we expect many objects to have better than 90\%
atmospheric transmission for a significant part of the year. 

\begin{table}[!hbt]
\begin{minipage}{7in}
\parbox{4in}{
\begin{tabular}{|c|c|c|}
\hline
{\bf Parameter} & {\bf Parameter Description} & {\bf Value} \\
\hline \hline
$T_{rx}$ & Receiver Noise Temperature & 100K \\ \hline
$T_{image}$ & Image Temperature & 4.2K \\ \hline
$T_M$ & Atmospheric Temperature & 200K \\  \hline
$T_{spill}$ & Rear Spillover Temperature & 295K \\ \hline
$T_{bg}$ & Background Temperature & 2.7K \\ \hline
$\eta_l$ & Rear Spillover Efficiency & 0.98 \\ \hline
$\eta$ & Main Beam Efficiency & 0.6 \\ \hline
\end{tabular}}
\parbox{2.3in}{
\caption{\label{parms} \small Parameters used for the BLAST/SABER
system temperature estimate following MMA Memo 170.}}
\end{minipage}
\end{table}

With these equations and parameters, we conservatively 
estimate the BLAST system
temperature to be $\sim$550K SSB per mixer. Accounting for dual
polarization operation, this yields a system temperature for co-added
data of $\sim$390K. For comparison, the on orbit verified performance of
SWAS is 2200K DSB, or 4400K SSB (Melnick 2000). 
This is an improvement
of a factor of $\approx$11 in system temperature, or a factor of
$\approx$125 in 
integration time in favor of BLAST. This estimate does not take into
account the increased size of the BLAST telescope. For unresolved
sources, the signal-to-noise ratio (SNR) for a given integration time
increases by the square of the ratio of the beamsizes: 

\begin{equation}
R = \left( \frac{\Omega_{SWAS}}{\Omega_{BLAST}} \right)^2 \propto
\left( \frac{D_{SWAS}}{D_{BLAST}} \right)^2 = \left(
\frac{2.0{\rm m}}{0.625{\rm m}} \right)^2 \simeq 10.2
\end{equation}


This gives BLAST an advantage of a factor of $\approx$115 in signal to
noise ratio (S/N), or $\approx$13,000
in integration time for the same S/N toward objects unresolved with
both instruments. This is why we have chosen to concentrate on
observations of sources with small angular diameter, e.g. evolved
stars, protostellar cores, and external galaxies.  

Another new submillimeter satellite that targets water and oxygen is
Odin. It was recently launched, and hopes to improve on SWAS. Odin has
similar receivers to SWAS, with system temperatures of $\sim$2000K (Eriksson
et al. 2002). Odin has a 1.1-meter telescope, almost twice as large as
SWAS.  BLAST is a factor of 10 more sensitive than Odin, assuming a
2000K system temperature, or a factor of $\sim$100 faster in integration
time. For unresolved sources, the beamsize advantage is lowered to 3.3
rather than 10.2. This gives BLAST an advantage of $\sim$33 in achieving a
given SNR, which corresponds to a reduction of $\approx$1100 in observing
time.  

Pointing is an issue that could potentially lessen the gain in
observing efficiency for unresolved sources. Since the absolute
pointing of the BLAST telescope is no better than 2$'$, we have to use a
more complicated observing strategy to locate the object at the
beginning of an observation. Predecessors to BLAST have demonstrated
relative pointing from a planet to the target object accurate to
within 20$''$. BLAST has a near real-time data link with the control
station that allows quick-look data analysis during flight. We can
remove the single sideband filter from the beam, tune the LO to
CO$(5\rightarrow4)$, 
and quickly make a $3' \times 3'$ map of the area in the vicinity of
the target object.  After downloading this data to the control center,
we can find the centroid of the object and offset the telescope. We
will then insert the SSB filter and tune the LO to water or oxygen for
the deep integration. We expect this procedure will provide relative
pointing accuracy better than 20$''$ since we will be pointing on the
target object, not another source far away. Even in the worst case of
having to make an On-The-Fly map of the entire $3' \times 3'$ region,
with each 
pixel having the same noise per beam, we only lose a factor of 20 in
time. This still yields an integration time improvement over SWAS of a
factor of $\approx$650.  


\section{Plan of Action}

The following list summarizes a brief outline/sketch of some of the
tasks to be accomplished and our expectation as to when and where each
will occur.   

\subsection*{Year 1}

\begin{enumerate}

\item Complete detailed design of receiver front-end, both
electrically and mechanically

\item Procure instrument cryostat, IF amps, LO chain and phaselock,
instrument control computer

\item Assemble receiver front-end and characterize laboratory
performance

\end{enumerate}

\subsection*{Year 2}

\begin{enumerate}
\item Obtain AOS from University of Cologne
\item Construct dual-polarization IF processor
\item Conduct lab tests of AOS/IF processor/front-end combination
using existing AOS control electronics
\item Repackage control electronics for balloon operation and repeat
system tests both in the lab and on the 10-meter Heinrich Hertz
Telescope
\end{enumerate}

\subsection*{Year 3}
\begin{enumerate}
\item Complete development of hardware and software needed for
integration with BLAST
\item Test instrument package with BLAST mock-up control electronics
\item Integrate instrument on BLAST Gondola and perform final system
tests
\item Inaugural flight in North America
\end{enumerate}

\clearpage

\begin{thebibliography}{}
\setlength{\itemsep}{0.1cm}

\bibitem[Baluteau et al.(1997)]{balu97} Baluteau, J.-P.~et 
al.\ 1997, A\&A, 322, L33. 

\bibitem[Benford et al.(1998)]{ben98} Benford, D. J. et al. 9th International Symposium on Space Terahertz Technology, Pasadena, California, March, 1998.

\bibitem[Bergin, Langer, \& Goldsmith(1995)]{berg95} Bergin, 
E.~A., Langer, W.~D., \& Goldsmith, P.~F.\ 1995, ApJ, 441, 222. 

\bibitem[Bieging, Shaked, \& Gensheimer(2000)]{bie00} Bieging, J.H., Shaked, S., \& Gensheimer, P.D. 2000, ApJ 543, 897

\bibitem[Blundell et al.(1995)]{blu95} Blundell et al., Sixth International Symposium on Space Terahertz Technology, Pasadena, Ca., March, 1995.

\bibitem[Caux et al.(1999)]{caux99} Caux, E.~et al.\ 1999, 
A\&A, 347, L1. 

\bibitem[Duari, Cherchneff \& Willacy(1999)]{dua99} Duari, D., Cherchneff, I., \& Willacy, K. 1999, A\&A, 341, L47

\bibitem[Erikson et al.(2001)]{eri01} Erikson, N. et al., 12th  International Symposium on Space Terahertz Technology, San Diego, Ca., February, 2001. 

\bibitem[Eriksson et al.(2002)]{eri02} Eriksson, P. et al.,
Can. J. Phys./Rev. Can. Phys., 80, 1, 2002. 

\bibitem[Frerick et al.(1999)]{fre99} Frerick et al., Proc. SPIE,
3759, 170, 1999.

\bibitem[Goldsmith et al.(2000)]{gold00} Goldsmith, P.~F.~et 
al.\ 2000, ApJL, 539, L123. 

\bibitem[Groenewegen et al.(1999)]{gro99} Groenewegen, M. A. T., et
al., 1999, A\&AS, 140, 197. 

\bibitem[Grossman (1989)]{gro89}  Grossman, E., 1989, AT --
Atmospheric Transmission Software User's Manual, version 1.5, Airhead
Software Co., Boulder, CO

\bibitem[Helmich et al.(1996)]{hel96} Helmich, F.~P.~et al.\ 
1996, A\&A, 315, L173. 

\bibitem[Herpin \& Cernicharo(2000)]{her00} Herpin, F., \& Cernicharo, J. 2000, ApJ, 530, L129

\bibitem[Jewell \& Mangum(1997)]{jew97} Jewell, P.R. \& Mangum,
J.G. MMA Memo 170, 1997.

\bibitem[Kooi et al.(1998)]{koo98} Kooi, J. et al., Proc. SPIE, 3357, 22, 1998

\bibitem[Kraemer, Jackson, \& Lane(1998)]{kraemer98} Kraemer, 
K.~E., Jackson, J.~M., \& Lane, A.~P.\ 1998, ApJ, 503, 785. 

\bibitem[Kulesa, Hungerford, Walker, \& Black(2001)]{kul02} 
Kulesa, C.~A., Hungerford, A.~L., Walker, C.~K., \& Black, J.~H.\ 2001, 
American Astronomical Society Meeting, 198, 5916. 

\bibitem[Lee, Bettens, \& Herbst(1996)]{lee96} Lee, H.-H., 
Bettens, R.~P.~A., \& Herbst, E.\ 1996, A\&AS, 119, 111. 

\bibitem[Lee et al.(1998)]{lee98} Lee, H.-H., Roueff, E., 
Pineau des Forets, G., Shalabiea, O.~M., Terzieva, R., \& Herbst, E.\ 1998, 
A\&A, 334, 1047. 

\bibitem[Le Bourlot, Pineau des Forets, \& Roueff(1995)]{leb95} Le
Bourlot, J., Pineau des Forets, G., \& Roueff, E.\ 1995, A\&A, 297,
251. 

\bibitem[Marcy \& Butler(2000)]{Marcy} Marcy, G.~W.~\& Butler, R.~P.\
2000, PASP, 112, 137 

\bibitem[Melnick et al.(2000)]{mel00} Melnick G., et al. ApJ, 539-2, L77, 2000.

\bibitem[Melnick et al.(2001)]{mel01} Melnick, G.~J., 
Neufeld, D.~A., Ford, K.~E.~S., Hollenbach, D.~J., \& Ashby, M.~L.~N.\ 
2001, Nature, 412, 160. 

\bibitem[Meyer, Jura, \& Cardelli(1998)]{mey98} Meyer, D.~M., 
Jura, M., \& Cardelli, J.~A.\ 1998, ApJ, 493, 222. 

\bibitem[Millar, Farquhar, \& Willacy(1997)]{millar97} Millar, 
T.~J., Farquhar, P.~R.~A., \& Willacy, K.\ 1997, A\&AS, 121, 139. 

\bibitem[(2002)]{mue02} Mueller, E.J. Coherent Inc. Private Communication, 2002.

\bibitem[Olofsson et al.(1998)]{olof98} Olofsson, G.~et al.\ 
1998, A\&A, 339, L81. 

\bibitem[Poglitsch et al.(1996)]{pog96} Poglitsch, A., 
Herrmann, F., Genzel, R., Madden, S.~C., Nikola, T., Timmermann, R., Geis, 
N., \& Stacey, G.~J.\ 1996, ApJL, 462, L43. 

\bibitem[Schilke et al.(1999)]{sch99} Schilke, P., Phillips, T. G., \&
Mehringer, D. M. 1999, in ``The Physics and Chemistry of the
Interstellar Medium'', ed. V. Ossenkopf, J. Stutzki, \& G. Winnewisser
(Herdecke: GCA), 330.

\bibitem[(1999)]{tru99} Truong-Bach, et al. 1999, A\&A, 345, 925

\bibitem[(1999)]{tsu01} Tsuji, T. 2001, A\&A, 376, L1

\bibitem[(1998)]{will98} Willacy, K., \& Cherchneff, I. 1998, A\&A, 330, 676

\bibitem[Wilson \& Rood(1994)]{wilson94} Wilson, T.\ L.\ \& Rood, R.\ 1994, ARA\&A, 32, 191

\bibitem[(2000)]{win00} Winters, J.M., Keady, J.J., Gauger, A., \& Sada, P.V. 2000, A\&A, 359, 651

\bibitem[(2000)]{yam00} Yamamura, I., et al. 2000, A\&A, 363, 629

\end{thebibliography}

\clearpage


\noindent {\Large \bf FACILITIES, EQUIPMENT \& OTHER RESOURCES}


\subsection{\it University of Arizona, Steward Observatory}

Steward Observatory, in
association with the Max Planck Institute for Radioastronomy, has
constructed a 10-meter submillimeter-wave telescope
on Mt. Graham, Arizona (the Heinrich Hertz Telescope, HHT).
At the end of the second year of the proposal effort, we will test the
performance of the BLAST receiver system by using it to observe the
492~GHz [C~I] and 461~GHz CO~$J=4\rightarrow3$ lines on the HHT.

In 1992 the PI 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.
SORAL has $^4$He and $^3$He cryostats available for testing single pixel Nb
and Nb-Au HEB mixers.

The NSF Division of Astronomical Sciences awarded
the PI funds to construct a 7 element array receiver at 345 GHz.
This array will begin operation on the HHT in November, 2001.
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 and 4 pixel
810 GHz array receiver (PoleSTAR) for AST/RO at the South Pole.
The 492/810 GHz receiver has been in operation for 4 years and is the primary
facility receiver for the telescope. The 810 GHz array was commissioned
in November 2000 and is the first array to go into operation in this
important atmospheric window.  This summer SORAL will be working
very closely with Sigfrid Yngvesson at UMass in preparing a
single pixel, 1.5 THz HEB receiver for integration onto AST/RO.
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 awarded the PI
a grant to construct a laser micromachining facility at Steward Observatory.
This system is now fully operational and is being used to manufacture
a variety of THz-frequency waveguide components. 

Through a grant through the Defense University Research Instrumentation
Program (DURIP), SORAL has recently purchased a new laser for the
micromachining system, an e-beam evaporator for metallizing micromachined
components, and a thin film deposition system for depositing nitride
and other films.

SORAL also has licenses for
both Hewlett Packards 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.



\end{document}
