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\begin{document}

\begin{titlepage}
\hspace*{\fill} {\Large Isaac Newton Group, La Palma} \hspace*{\fill}
\vfill
\hspace*{\fill} {\Large\bf A User Guide to the INT Faint Object 
Spectrograph} \hspace*{\fill}

\vspace*{20mm}
\hspace*{\fill} {\large\bf D. L. King } \hspace*{\fill}

\vspace*{10mm}
\hspace*{\fill} {\bf May 1992} \hspace*{\fill}

\vspace*{10mm}
\hspace*{\fill} {\bf Version 2.0} \hspace*{\fill}

\vfill
\small
\hspace*{\fill}
\parbox{82mm}{The Isaac Newton Group of Telescopes at the Observatorio del
Roque de los Muchachos del Instituto de Astrophisica de Canarias is operated
by the Royal Greenwich Observatory on behalf of the Science and Engineering
Research Council (UK) and the Nederlandse organisatie voor wetenschappelijk
onderzoek (NL).}
\hspace*{\fill}

\vspace*{20mm}
\normalsize
\end{titlepage}

\renewcommand{\thepage}{\roman{page}}
\tableofcontents
\listoffigures


\chapter{The INT Faint Object Spectrograph}
\markboth{\hfill The INT Faint Object Spectrograph 
\hfill 1992 May}
{chapter \protect\ref{Fos}. \hfill The INT Faint Object Spectrograph \hfill}
\label{Fos}
\setcounter{page}{1}
\renewcommand{\thepage}{\arabic{page}}

\section{Introduction}
\bigskip

This guide attempts to introduce the observer to the Faint Object Spectrograph
(FOS) as used on the Isaac Newton Telescope (INT). No detailed attempt is made 
to educate the reader concerning the workings of the detector (a Charge
Coupled Device (CCD)) used with FOS; if the reader is interested, more 
details can be found in e.g. `A User Guide to the INT Prime Focus CCD',
available in the INT control room, or from the LPUU at RGO.

\medskip
Chapter 1 gives a brief description of the hardware and performance of
FOS, chapter 2 details the setup and operational checks necessary
to see that FOS is working properly, chapter 3 covers the operation of 
FOS in conjunction with the cassegrain Acquisition and Guidance (A\&G) 
box  and the INT Intermediate Dispersion Spectrograph (IDS) and 
chapter 4 shows the procedures contained in the online `quicklook' reduction 
procedures.

\bigskip
The Faint Object Spectrograph (FOS) is a highly efficient fixed
format CCD based spectrograph, designed for low resolution (15-20\AA)
spectrophotometry, over a wide spectral range. The 
optical design, described by Charles Wynne (Optica Acta, 1982, 29,
1557)  is based on a Schmidt camera working without a collimator
in the diverging beam from the f/15 Cassegrain focus of the INT
(see figure ~\ref{fosline}). 
The major components are shown in figures ~\ref{fosdiag} and ~\ref{fosids}).
The dispersion is provided by a transmission grating and a cross
dispersing prism (grism), which together give a multi-order format
covering the wavelength range 3400\AA\  to 10,830\AA. As a result of 
locating the CCD within the camera, there are a small number of
optical surfaces and minimum vignetting, which produces a system
which is more efficient than most conventional spectrographs.
The fixed format enables FOS to have its own set of online data
reduction and analysis procedures; the observer is then able to
have calibrated data within a very short time of the completion
of an exposure.
\medskip

FOS is located beneath the IDS, using the same slit assembly,
comparison sources and acquisition and guiding facilities. The 
change of IDS and FOS modes can indeed be made during the night,
by moving a single folding prism, and installing or removing a
light tight tube. The change from one mode to the other takes
less than half an hour.
\medskip
\section{Hardware description}
\medskip
FOS was an `add on' to the Cassegrain cluster of instruments on the
INT, the IDS and A\&G units having been designed prior to Wynne's
paper. It was thus necessary to find a mounting point on the IDS
which did not cause flexure of the structure (FOS weighs approximately 100kg).
This, combined with the small clearance between the Cassegrain
cluster and the dome floor meant that a folding flat mirror had to
be introduced to accommodate the long path length of the f/15 beam.
Figures ~\ref{fosline}, ~\ref{fosdiag} and ~\ref{fosids} show FOS and 
its relationship to the IDS.
\medskip

\begin{description}
 \item[The FOS frame] is constructed of 3mm steel plate, welded together
to give a rigid structure. Flexure tests of FOS on the telescope
show the rigidity is better than the design specification, the
image of a spectral line shifts by only 0.03 pixels per hour in
the dispersion direction as the telescope tracks through the zenith.
\medskip

 \item[The folding flat] is placed approximately halfway along the light
path from the slit to the grism. It has a plane glass surface,
with an extended blue response silver coating.
\medskip

\item[The Hartmann shutters] are situated between the folding flat and
the grism. They are only used in the initial focussing of the
instrument, not during normal observing. They are pneumatically 
operated and controlled from the instrumentation computer via Camac.
\medskip

 \item[The camera body] has the grism at one end, the mirror at the other,
with the chip between them. The body is fitted to the frame on a 
3-point seat which is adjusted so the spectrum falls on the correct
part of the chip.
\medskip

\item[The grism] has a 150 lines/mm plane transmission grating on the
front surface. A ray from the slit centre to the centre of the
grating surface makes an angle of 6.892 degrees with the normal
to the surface and with the normal to the grating rulings. The
central ray at a wavelength of 8000\AA\   is diffracted normal to the
grating. The grism as a whole is a cemented assembly of the
transmission grating, cross dispersing prisms of Schott SK5 and
LF5 glass, and an aspheric corrector plate of Schott K10 glass.
\medskip

 \item[The camera mirror] is coated with an extended blue response silver
coating and is expected to keep its high reflectivity, as the 
system is not let up to atmospheric pressure, except for 
maintenance.
\medskip

 \item[The CCD] is supported in the camera body by four slender arms
 attached to an outer ring, which is held off the camera
mirror by three invar rods,  resulting in an insignificant 
change in focus position with temperature. The focus position is
initially set up by moving the outer ring in small increments,
using motor micrometers controlled by a microprocessor. It is not
necessary to adjust the focus position during normal observing.
The camera contains an absolute minimum of electronic components,
a temperature control circuit, and some capacitors for
stabilisation. The pcb on which the chip sits is thus very small,
minimising light losses within the camera.
\medskip

 \item[The cryostat] contains sufficient liquid nitrogen to keep the
CCD cool for more than 12 hours, and is bolted to the side of the FOS frame,
connecting via a copper cold finger through the side of the camera
body to the CCD. It could be cooled to 120K, but is normally 
operated at 150K, stability being achieved using a small heater.
\end{description}

\vfill


\section{The CCD electronic system}
\medskip
In common with all other `common user' instruments on the INT, FOS is 
controlled from the instrument computer, a Perkin Elmer 3210,
via the ADAM environment. To obtain data, the chip is cleared of
all previously accumulated charges, and then exposed for the
required time. When the exposure is completed, the pixels are 
clocked out one at a time, the charge from each pixel being
deposited on the gate of the output transistor, and read out as a
voltage. This is amplified, and digitised to 16 bits,whence it is
transmitted to the instrument computer via Camac. It is then stored
and displayed. The process of reading out the chip takes 
approximately 30 seconds.

FOS is currently using an extended blue response GEC P8603 type
chip, coated for the Observatory by ESO. This type of chip is
characterised by very low internal noise, which, coupled with a
small contribution from the pre-amplifier and ADC, gives a total 
noise of around 7 electrons rms. The overall chip characteristics
are excellent, and no preflash facility is included. Details are 
given in appendix C. As the CCD is operated at low temperature,
the thermal noise is negligible, so the charge stored in the 
potential well of each pixel is proportional to the number of
absorbed photons.

The new chip was installed in May 1988. The chip in use prior to this
was an uncoated GEC P8603 which was ineffective in the second order.
The quantum efficiency of the new blue coated chip as measured at Herstmonceux
is shown in Figure ~\ref{rqe}.

\medskip
\section{Performance}
\medskip
The main factors governing the suitability of FOS for astronomical
observations are the spectral resolution and the efficiency.
As far as resolution goes, FOS works at a lower resolution than
most other conventional spectrographs. The dispersion is 450\AA\ /mm;
camera resolution with a narrow slit (0.25 arcsec) is 1.2pixels (12.8\AA)
fwhm, independent of wavelength along the full width of the 4
arcmin slit. Under normal working conditions with a 1-2 arcsec
slit, the resolution is 15-20\AA\  in first order (8-10\AA\  in second
order). Hence it would appear that FOS is suitable for studying
emission line objects (AGN, HII regions, planetary nebulae), or
continuum studies. It is questionable whether FOS is suited to
studies of narrow absorption line objects (solar type stars etc.) where
absorption features would fill only 1-2 pixels.
The principle advantage of FOS is that it is considerably faster
than a conventional spectrograph, and so is likely to be useful
for those objects which are too faint for their spectra to be
obtained at a high enough signal to noise in reasonable integration
times with other instruments. The total throughput of the entire
system (atmosphere,telescope and FOS with the extended blue CCD) in
first order is 12.5\% at peak.
Only a small proportion of this loss occurs in the FOS optics
- the throughput of the FOS minus detector is approximately 70\%
at blaze. The efficiency of FOS in first and second order is shown
in Figure ~\ref{foseff}.

In Figure ~\ref{sn} we show the sky subtracted signal to noise per first
order 10.7\AA\  pixel, assuming the object occupies 3 columns of the
chip, and adopting mode D operation (25 arcsec slot for sky +
object). Adequate classifications of broad features (QSOs,
emission line galaxies, M stars) can generally be made with a s/n
of around 5; absorption line objects usually demand a s/n of better
than 15. The format of the spectrum is shown in Figure ~\ref{fmt}. 
If an object is blue, the curved third order is seen to the left of 
the first two. This is faint; there is no software developed to 
make use of it.

\vfill
\begin{figure}
\centering
\vspace*{185mm}
\caption[Location of FOS]{Location of FOS relative to the IDS and
cassegrain A\&G box}
\label{fosline}
\end{figure}

\newpage

\begin{figure}
\centering
\vspace*{185mm}
\caption[FOS]{FOS}
\label{fosdiag}
\end{figure}

\newpage

\begin{figure}
\centering
\vspace*{185mm}
\caption[FOS and IDS]{3 dimensional view of FOS and the IDS}
\label{fosids}
\end{figure}

\newpage
\begin{figure}
\centering
\vspace*{185mm}
\caption[The Relative Quantum Efficiency of the FOS CCD]{The Relative Quantum
Efficiency of the GEC CCD used in the INT FOS}
\label{rqe}
\end{figure}

\newpage

\begin{figure}
\centering
\vspace*{185mm}
\caption[The Efficiency of FOS]{The Efficiency of the INT FOS}
\label{foseff}
\end{figure}

\newpage

\begin{figure}
\centering
\vspace*{185mm}
\caption[Signal to Noise]{The sky subtracted signal to noise per first order
10.7\AA pixel, assuming the object occupies 3 columns of the chip, and
adopting mode D operation (25 arcsec slot for sky + object)}
\label{sn}
\end{figure}

\newpage

\begin{figure}
\centering
\vspace*{185mm}
\caption[Format of a FOS spectrum]{The format of a FOS spectrum, 
assuming mode D operation (25 arcsec slot for sky + object)}
\label{fmt}
\end{figure}


\chapter{FOS Setup}
\markboth{\hfill The INT Faint Object Spectrograph \hfill 1992 May}
{chapter \protect\ref{setup}. \hfill FOS Setup \hfill}
\label{setup}

\section{Low level operations and calibration checks}
\medskip
As far as the user is concerned, FOS has no moving parts. There
is no need to set up FOS in the same way that say the IDS+CCD
is. In normal use it should not depart from its original
commissioned configuration. There are a few simple checks the astronomer 
and his support astronomer can do.
\medskip
\subsection{Hardware changes}
\medskip
The change from IDS to FOS (or vice versa) is an operation for the
duty technician or the support astronomer. If the FOS cryostat has
been pumped down and cooled, the changeover time is less than half
an hour. It must be made plain that if you want to use FOS when it
has not been scheduled, the technical staff must have been notified via
the support astronomer. The cryostat takes some hours to pump down
to a reasonable vaccuum, and to cool to its operating temperature
(150 degrees K), so more than a days warning is needed.
\medskip

The change from IDS to FOS involves:
\medskip

a) Switching the IDS detector to a safe condition
\smallskip

b) Removing the folding prism which was sending light to the IDS
detector so that the light can enter FOS via the flat mirror.
\smallskip

c) Inserting a light tight tube between the IDS and FOS.
\smallskip

d) Changing the dekker and below slit filter slides with those
specifically for FOS.
\smallskip

e) the camera electronics must be switched on. This involves a 
cable change at the Cassegrain cabinet, so the RGO CCD camera controller
can drive FOS.
\smallskip

f) Finally the software must be re-initialised by restarting ADAM
and selecting the FOS mode at the observer's console.
\medskip
\subsection{System checks}
\medskip
The best way to check that the instrument is operating correctly
is, after having loaded the FOS software, to take a dummy exposure
using the GLANCE command. This checks virtually all status lines,
clears the chip, checks that the shutter opens and closes, reads
out the chip into a data file, and displays the image on the lexidata display.
Keep a watch for any error messages. You can monitor the CCD
telemetry by the command 
\medskip

ADAM$>$TELE --- this only shows telemetry values which are outside
tolerance.
\medskip
\noindent
To see all telemetry values use the command:
\medskip

ADAM$>$TELE QUIET=FALSE
\medskip
\subsection{Focus and alignment.}
\medskip
Experience shows that FOS is very stable, having been removed
from the cass cluster and replaced several times with no noticable
change in focus and alignment (within the measurement errors).
Focussing of FOS is done by moving the CCD detector in 3-D using
the 3 motor micrometers (labelled s r and b). These are not 
adjustable in normal operation, but their status can be obtained
by reading the position sensors (LVDTs) next to each micrometer.
MSTAT can be used to get these values, as well as focus and tilt
angles (HA,VA) of the CCD. These should be within 10 units of the
specification.
e.g.
\medskip

ADAM$>$ MSTAT
\smallskip

focus motor positions are:
\smallskip

MIKES=378 MIKER=481 MIKEB=291
\smallskip

hence FPOSIT=383 HANGLE=95 VANGLE=2
\medskip

\noindent
If these values are outside the tolerance, inform the support 
astronomer. As a further check, expose a copper-argon comparison
lamp and, if available, a mercury comparison lamp, as follows:
\medskip
\begin{tabbing}
111\=111111111111111111111111111111111\=     \kill
   \> ADAM$>$ 2LAMP ON                \> Switch on copper-argon lamp \\

   \> ADAM$>$ ND 1.2                  \> Insert filter ND=1.2 \\

    \>ADAM$>$ DEKKER 3                \> Select 200 micron dekker \\

    \>ADAM$>$ SLIT 50                 \> Select 50 micron slit \\

    \>ADAM$>$ GLANCE 10               \> Expose for 10 seconds
\end{tabbing}
\medskip

\noindent
Using the PROFILE option in PHOTOM you can find the position and width
 of five lines at the following wavelengths:-
\medskip

\begin{tabular}{ccccc}
              9658\AA\  & centred & near & pixel & 135,156\\
              9123\AA\  & " & " & " & 135,206\\
              8265\AA\  & " & " & " & 137,286\\
              6965\AA\  & " & " & " & 141,407\\             
              5461\AA\  & " & " & " & 153,548\\
\end{tabular}
\medskip

The line at 5461\AA\ is from the mercury comparison lamp. All the other
lines are from the copper-argon comparison lamp.
\medskip

\noindent
Use SLICE (from the FOS reduction package) to get accurate
 vertical and horizontal profiles with
rectangular boxes of dimensions [2,8] and [8,2] respectively.
Alternatively, use STARFIT; this routine is really designed to measure
stellar images, but works at least as well on arc lines taken through
a narrow dekker.  
Values for the chip installed in May 1988 are given in table 2.1
The centroids can change absolutely by about 0.5 pixels, and by more than 1
pixel if the folding flat has been moved. Drift with telescope attitude is
about 0.03 pixels per hour, and relative stability is of the same order.
\medskip

Table 2.1 focus and alignment goals (1st order)
\medskip

\begin{tabular}{lcccccc}
           &          &           &          &          &          &        \\
           &    line  &    9658\AA\   &   9123\AA\   &   8265\AA\   &   6965\AA\   &   5461\AA\  \\
           &          &           &          &          &          &         \\
Moments    &     V    &    155.61 &   205.59 &   285.80 &   407.03 &   547.37\\
method     &   sigma  &      0.65 &     0.62 &     0.60 &     0.50 &     0.59\\
           &          &           &          &          &          &         \\
Starfit    &     V    &    155.47 &   205.54 &   285.77 &   406.99 &   547.35\\
method     &   fwhm   &      1.40 &     1.40 &     1.35 &     1.20 &     1.31\\
           &          &           &          &          &          &         \\
           &     H    &    134.65 &   135.41 &   137.22 &   141.62 &   153.13\\
           &   fwhm   &      1.45 &     1.44 &     1.47 &     1.43 &     1.40

\end{tabular}
\bigskip

%Focus and alignment goals (2nd order)

%\medskip

%\begin{tabular}{lcccc}
%           &          &           &          &           \\ 
%           &   line   &    5461\AA\   &   4358\AA\   &     4047\AA\  \\    
%           &          &           &          &           \\
%Moments    &     V    &    37.82  &   243.94 &     302.02\\
%method     &   sigma  &     0.39  &     0.65 &       0.65\\
%           &          &           &          &           \\
%Starfit    &     V    &    37.83  &   243.89 &     301.99\\
%method     &   fwhm   &     0.99  &     1.21 &       1.20\\
%           &          &           &          &           \\
%           &     H    &   153.13  &   174.13 &     184.97\\
%           &   fwhm   &     1.24  &     1.44 &       1.62    
%
%\end{tabular}
%
\bigskip
%
\noindent

NB.    V is in the dispersion direction
\medskip

\noindent

       H is in the cross dispersion direction
\medskip

%All lines shortward of 5461\AA\ are from the mercury comparison lamp.
%\bigskip

The sigma/fwhm estimates are a good indication of focus if you are
concerned about it, but remember that FOS just undersamples, so
fwhm and 2.32 sigma may not quite agree --- two different methods are
used to determine these quantities, and the results will also 
depend quite strongly on the position of the line within the pixel.

\markboth{\hfill The INT Faint Object Spectrograph \hfill 1992 May}
{chapter \protect\ref{operation}. \hfill Operation of FOS \hfill}

\chapter{FOS Operation}
\label{operation}

\section{Operation of FOS and astronomical considerations}
\medskip
\subsection{Overview}
\medskip
The object of this section is to introduce the investigator to
the typical commands used in operating FOS in an observing session.
As stated earlier, FOS is run in the ADAM environment, and many of
the commands are identical to those used to control the IDS + CCD.
Examples are the RUN, GLANCE and PHOTOM commands. The commands
which are missing from the FOS repertoire are those which operate
many of the IDS functions, e.g. grating angles, collimator focus.
Unlike the IPCS, there are few safety precautions, as it is not as 
`delicate', and there is no real time display.

It should be possible to run FOS without reference to any other
guide than this, although this guide cannot be exhaustive, and
details of ADAM and CCD routines are to be found in the 
appropriate manuals.

FOS is run from the observer station, which consists of an ADAM
terminal, from which all the commands are issued, a MIMIC display,
which shows the status of the A\&G box, slit width, above and below
slit filters, and dekker positions, and a LEXIDATA, on 
which the 2-D frame is displayed automatically when an exposure
is completed, and the CCD is read out. Once an exposure has 
finished (and indeed during a subsequent run) the image displayed
on the Lexidata can be extracted, calibrated and plotted using
the dedicated FOS reduction software.
\medskip
\subsection{Starting up}
\medskip
Sit at the observer station and select a free account number from
the white board behind you, say 8. A free account is an account without
anyone's initials against it. Sign on with your observer 
identification (your initials)
\medskip

*SIGNON ABC,8,8       (or si abc,8,8)
\medskip

\noindent
You will be given a few welcoming messages, finishing  with a * as
the invitation to type. Type in 
\medskip

*ADAM
\medskip

\noindent
This leads to a question/answer dialogue, the answers to which
are mostly obvious. You are given the choice of storing your data
on disk or tape --- it is usual to store on disk in the first 
instance as it is possible to dump your data files to tape during
subsequent runs (using FITSOUT). The Perkin Elmer 3210 instrument
computer uses an Egle disk (called sys:) for all software and data
storage - there is space for 500 FOS images, if the disk is relatively
empty. This should be sufficient for several nights observing. The software
informs you on startup how many images there is space for as it is unlikely
that the disk will be completely empty of data files. If this is less than
50, contact a member of the software group, who will endeavour to tidy the 
disk and give you more space. If you have filled the disk with your own files,
then use PURGE to delete files you have already written to tape. It is worth 
giving a word of warning here; it has happened that the Egle disk
crashed losing the observer's data, hence it is a good idea to
dump your data to tape every couple of hours or so.
After five minutes or so, you will get the prompt
\medskip

ADAM$>$
\medskip

\noindent
which is your invitation to type in commands in the ADAM
environment. The three most important commands - after the correct
A\&G box and slit configuration has been set, are the WINK, GLANCE and
RUN commands.
\medskip

ADAM$>$ RUN n "object comments"
\medskip

\noindent
Clears the CCD, opens the shutter for n seconds, closes the 
shutter, reads the exposure into a file SYS:FOSABC.m, where ABC
is your observer id and m is the current run number, e.g. 001.
The image is automatically displayed on the lexidata, erasing
any previously displayed data, and the run number is updated to
m+1.
\medskip

ADAM$>$ GLANCE n
\medskip

\noindent
Clears the CCD, opens the shutter for n seconds, closes the
shutter, reads the exposure into a file SYS:FOSABC.000. The
image is automatically displayed on the lexidata, erasing any
previously displayed image, It will be overwritten by any
subsequent GLANCE. 
If you decide you want to keep the GLANCE
exposure, then you can do so by issuing the ADAM command
\medskip

ADAM$>$ KEEP "object name"
\medskip

\noindent
which copies the GLANCE file into the next file number.
\medskip

A standard GLANCE includes the collection of
FITS packets, So for a GLANCE of less than about 30 seconds,
there is an overhead, while these are being collected.
If the GLANCE is just a test exposure, without any likelihood of 
being saved, use WINK.
\medskip

ADAM$>$ WINK n
\medskip

\noindent
Operates in an identical fashion to a GLANCE command, except
no FITS headers are collected for the output file.
It will be overwritten by any subsequent WINK. If you decide you 
want to keep the WINK exposure, then you can do so by issuing the 
ADAM command
\medskip

ADAM$>$ KEEP "object name"
\medskip

\noindent
which copies the WINK into the next run number. The collection of
FITS headers is done at the stage of the KEEP.
\medskip

One major difference between the GLANCE, WINK and RUN commands is
that GLANCE and WINK always runs as foreground tasks, tying up the
terminal, but a RUN of more than 10 seconds runs as a 
background task, freeing the ADAM terminal so you can
manipulate a previous image, write data to tape etc.
However, if you do decide to use the terminal during a RUN, it
is advisable to make sure you finish before the RUN does. A warning
is given 30 seconds before chip readout comences.

Two other frequently used commands governing runs are ABORT
and TIME, the former stopping an exposure without creating an
output file, the latter amending the exposure time. A manual
of all CCD commands is kept in the INT control room.
\medskip
\subsection{Preparing for observing}
\medskip
Earlier we discussed the absence of any need for lengthy set up
procedures---a few checks as indicated in section 2.1 will reassure the 
observer. Directly the sky is dark enough, the night assistant will acquire a 
bright star, and SNAFU (calibrate out the pointing error)
 onto the centre of the IDS slit. He
will then focus the telescope, thereafter the focus will track automatically
as the temperature changes.
\medskip


\subsection{ FOS observing modes}
\medskip
By now you should have decided on which of the 4 possible FOS
observing modes to use. These modes are selected by selecting
a dekker and field lens configuration via the commands
\medskip

ADAM$>$ DEKKER M
\smallskip

ADAM$>$ BSCF N
\medskip

\noindent
 See appendix A for details of the different choices.
\medskip

It is straightforward to change between these modes, so you
can change as often as necessary during a night to suit your
requirements.
The 4 modes are:
\medskip

Mode A: Beam switching point sources with 5", 2", or 1.2" slots,
12" apart both orders
\medskip

Mode B: Beam switching extended objects with 25"slots, 85" apart,
both orders
\medskip

Mode C: Long slit, 200" slot, first order only
\medskip

Mode D: Single object, 25" slot , both orders.
\medskip

\noindent
The format of the data taken in these modes is shown in appendix A
figure ~\ref{a12}.
Choosing between the modes depends on a variety of factors and
personal preferences. The most commonly used modes of observing are
Modes C and D.
\medskip

\subsubsection{Beam switching or not?}
\medskip

This is a useful facility for eliminating flatfield uncertainties.
Each observation consists of a pair of exposures, I and II, taken
in each of the 2 apertures, L and R.
Sky subtraction can be performed via (L-R)I + (R-L)II, and the
result is a 2-D sky subtracted frame, which is very useful for 
extended objects.
\smallskip

Mode A gives a 5" or less slot, which is rather small. Mode B
gives a 25" slot, which is well suited to work of this nature, but
unfortunately the apertures are 85" apart. This means that the TV
cannot see both apertures simultaneously.
\medskip

For faint object work, where a single 1-D spectra is the required 
final product, these modes could still be used. Modes C and D are
more appropriate particularly since the online software is designed
to handle these modes more effectively.
\medskip

Mode C is a 200" longslit mode used for multiobject work, and very
extended objects.
\medskip

Mode D is a centralised 25" slot offering enough local sky for
interpolative sky subtraction. Flatfielding is required.
\medskip

\subsubsection{Second order or not?}
\medskip

FOS offers two (and possibly three) orders on a cross dispersed
format.
First order covers the region 5170\AA\   to 10830\AA, second order
covers 3400\AA\   to 5670\AA\  and third order approximately 3400\AA\   to
3780\AA. The short wavelength cutoff is governed by the ultraviolet
edge of the glass components in the FOS optics.
 In modes A B and D both orders can be taken simultaneously.
In mode C (long slit) clearly it gets rather confusing, since the
second order signal lies on top of the sky from the first order. If
there are several objects you must be careful that the spectra do 
not overlap. On the other hand the software will do its best to 
subtract any adjacent signal, so there may be occasions when long
slit, two order mode is acceptable, although it is not to be
recommended.

The sensitivity of FOS in the second order is now extremely good,
since the installation of the blue coated GEC CCD in May 1988.
Second order resolution is twice as good as first order, and so
narrow features show up more easily than in first order.

Some third order response is now evident, but little work has been
done on calibrating it.
\medskip

The full chip modes B and C require a field lens in the below
slit colour filter slide to avoid vignetting. To kill second order
insert a GG495 field lens. To keep both orders insert the clear
field lens.
A copper sulphate filter is also available in the below slit 
neutral density slide. This preserves second order but destroys
first order longwards of about 6000\AA. It is useful for multiobject
work in second order.
\medskip
\subsubsection{ Switching Modes}
\medskip
Switching between modes can easily be done via ADAM procedures,
or by typing in a string of ADAM commands. For example
\medskip

\begin{tabbing} 
111\=111111111111111111111111111111111111\= 111111       \kill
   \>ADAM$>$ Procedure longslit \\
   \>Proc$>$ Dekker 0                    \> long slit\\

   \>Proc$>$ bscf 1                      \> clear field lens\\

   \>Proc$>$ end proc                    \>      \\

   \>ADAM$>$
\end{tabbing}
\medskip

\noindent
sets up a command procedure called longslit, which is all you now have to
type to go to that mode. Procedures can be stored in a file by
issuing the command
\medskip 
\noindent

ADAM$>$ put myproc
\medskip

\noindent
and called back again for use on future nights with the command
\medskip
\noindent

ADAM$>$ get myproc
\medskip

\noindent
Don't do this during a run though; you will get the message

\noindent
ADAM ERROR: all procs aborted Dictionary being got from MYPROC.DCT

\noindent
Do not panic. Nothing has happened. Executing a GET during an exposure
is forbidden by the software as it would corrupt the run. Wait until the
run is complete and repeat the command.
\medskip
\subsection{Other variables}
\medskip
The only other variables you can change with FOS are the slit
width and the A\&G facilities (lamps,mirrors, above slit filters.)
These are exactly as for the IDS and the MIMIC display will 
correctly show their current status.
\medskip
\subsection{Other considerations}
\medskip
FOS slightly undersamples its spectrum. 1 GEC pixel (22 micron=
10.7\AA\   in first order) is equivalent to 1.3 arcsec at the slit.
The optimum resolution for a narrow slit is observed to be 1.15
pixels fwhm. In principle to match a 2 pixel fwhm requires a 2.1
arcsec slit, but the resolution is then approximately 21\AA\   fwhm. Narrower
slits will produce sharper features which is generally desirable,
since 21\AA\   resolution is often inadequate for absorption line work.
The online software does not resample the spectrum, so this is an
important point. In good seeing, a 1.0 arcsec slit gives 15\AA\ 
resolution.

With such a wide spectral coverage, another important factor which
is affected by the slit width is light loss due to atmospheric
dispersion. There are two ways to overcome this problem:
\medskip

1) align the slit along the parallactic angle - this is shown
on the telescope status screen, or
\smallskip

2) widen your slit to compensate. As a guide, the following
displacements occur across the orders of FOS at various zenith
distances,
\medskip

\begin{tabular}{ccc}
\multicolumn{3}{c}{ Displacement (arcsec) }\\
\medskip

     z.d. & 1st order & 2nd order\\
\smallskip

    (deg) & (0.5-1.0micron) & (0.4-0.55micron)\\
\smallskip

 30 & 0.61 & 0.64 \\
 45 & 1.05 & 1.10 \\
 60 & 1.82 & 1.90\\
 75 & 3.92 & 4.10
\end{tabular}
\medskip
\subsection{File Allocations}
\medskip
Various sorts of files are used to help the user in his data
analysis. These have the following shorthand notations
\medskip
\begin{tabbing}
111\=11111111\=111111111111111111111111111111\=111    \kill
   \>Rm   \>for SYS:FOSABC.m              \> run files \\

   \>Sm   \>for SYS:FOSSTO.m              \> store files \\

   \>Tm   \>for SYS:FOSTMP.m              \> temporary files 
\end{tabbing}
\medskip

\noindent
Store files can be used for reduced data, temporary files for
intermediate steps in the data reduction.
For example, to display run 6 on the lexidata, simply type
\medskip

ADAM$>$ DISP R6
\medskip

\noindent
In addition, many ADAM procedures adopt the convention of a current
image, which by default is the last image called ( it could be a
GLANCE image or the latest RUN image).
\medskip 
\subsection{Data acquisition}
\medskip
We are now ready to start observing. The target object has been
acquired and put on the slit, and a guide star found. We start 
taking data with
\medskip

ADAM$>$ RUN 1000 "target 1234 1000s"
\medskip

\noindent
The cosmic ray rate is typically 20-30 events per full CCD
frame per 1000 seconds. These can be weeded out of the sky areas by
the reduction software, but if they land on the object spectrum you
can only clean them out by comparing with another exposure. For this 
reason, it is best to limit exposures to less than 1800 seconds.
There is an overhead of about 30 seconds while the chip is read
out and the image displayed before you can issue another RUN 
command. As the sky alone generates between 200 and 1000 adus per
pixel per 1000 seconds, FOS is mostly well above the readout noise
problems in typical exposure times.

All of the normal CCD commands are applicable to FOS, and so the
observer is referred to the CCD userguide, which is kept in the INT control
room.

\chapter{Data Analysis}
\markboth{\hfill The INT Faint Object Spectrograph \hfill 1992 May}
{chapter \protect\ref{data}. \hfill Data Analysis \hfill}
\label{data}

\section{Data Reduction}
\medskip
\subsection{Introduction}
\medskip
FOS reduction is essentially a two stage process at the moment.
The initial stage, as a quick look at the data, is undertaken on the
Perkin Elmer instrument computer, and handles object extraction
and wavelength calibration. The full FOS reduction package has been
rewritten and runs on the main Vax data reduction computers. 
Details may be found in the WHT FOS userguide.
Alternatively it is possible to reduce FOS data using standard packages such 
as FIGARO, which for many users is the preferred option.

\medskip
The aims of the FOS on-line reduction package are to provide

\medskip

1) fully reduced and calibrated spectra so you can see what your data 
represent.
\smallskip

2) facilities for interactive classification and redshift determination.
\medskip

The steps taken to fulfill 1) are easily completed in a few hundred seconds,
enabling the observer to do so while the next exposure is in progress. The 
following points should be noted :
\medskip

1) Modes A and B (beamswitching ) do not have their own dedicated software,
but can be reduced using some of the standard CCD arithmetic routines in
conjunction with the FOS software.
\smallskip

2) Default wavelength and flux calibration is provided. The former should
not worry the observer who can easily take comparison lamp exposures to 
check the calibration. The latter however, is not able to take account of
variations in extinction, and so it is recommended that standard stars are 
observed for this purpose.
\medskip

Following the upgrade of FOS in May 1988, considerable changes were made to 
the software, most of which will be invisible to the observer (except that
now the routines work properly). The most obvious external change is that the
FOS chip is displayed left to right across the Lexidata rather than up and down
This means the full 590 rows are now visible, rather than only 512. The display
is such that the longest wavelengths are to the right.
The following routines have been modified, as it was found they did not
 always handle the arithmetic correctly:
\medskip
\begin{tabbing}
NITPICK \\
FOSCOFS \\
TRIM \\
SPECTRUM \\
SPECPLOT \\
COMBINE \\
SLICE 
\end{tabbing}
\medskip

\noindent
The following routines have been removed:
\begin{tabbing}

ABSCORR        \= this \kill
FADD           \>use ADD it is more general \\

CONVERT        \>use CHFORM it is more general \\

EXTRIC         \>use TRIM and LEXEXT \\

FDIV           \>this was never available \\

OFG            \>this was never available \\

ABSCORR        \>this was never available
\end{tabbing}
\medskip

\noindent
The following routines are original:
\medskip
\begin{tabbing}
DCSUB \\
DOFF \\
FFNORM \\
FMULT \\
VIEW \\
ZAPCOLS \\
ZED
\end{tabbing}

\medskip
For the sake of completeness, several stages of on-line data reduction are 
described which are rarely ever used, as all that is necessary usually is to
extract the spectrum and wavelength calibrate it. The stages which can easily
be ignored are {\em Defect removal, Cosmic ray removal, and Flatfielding}.
So unless you really want to use these facilities, skip on to {\em Spectrum
extraction and Sky subtraction}.

\subsection{Defect removal}
\medskip
ZAPCOLS allows the user to remove column defects. The program prompts for the
first and last column numbers that define the area to be zapped. This area is
then replaced by the mean of the two bordering columns. See Appendix C for
details of the current chip defects. A negative number terminates the prompts.
Routine defect removal should be unnecessary because the sky subtraction
algorithm rejects anomalous pixel values in the sky regions, and of course
the observer should take care to see the object spectrum does not land on a 
defect. Luckily there are very few on the chip currently used in FOS.
\medskip
\subsection{Cosmic ray removal}
\medskip
NITPICK compares two frames, and identifies features which are more than a 
specified significance level away from the value in one and replaces these 
pixel values with the corresponding values from the other. Photon noise is
automatically allowed for, using known CCD statistics. Sky subtraction
software automatically allows for cosmic ray removal, so this is only run 
if the object spectrum is affected. NITPICK only corrects one frame, so you
have to apply the first frame vs the second, and then the second frame vs
the first to correct both frames.

As a general guide, 4 sigma is a good starting level. Care should be taken
not to try to remove too many small variations. NITPICK produces a map of
which pixels have been affected. This image should be displayed; if you 
don't and there is a shift between the two images you are comparing, you
will be unaware that part of your spectrum has been cleaned away.
\medskip
\subsection{Flatfielding}
\medskip
FOS has its own standard flatfield which observers should be able to use
and take home with them. Most observers do like to take their own however.
Use a slit
width similar to that used for your observations, and expose the tungsten
lamp, taking care not to saturate. Use the GG495 filter for first order,
take several 
flatfields, use COMBINE to produce an average flatfield, then use DCSUB
to remove the bias from this image. finally use FFNORM to remove the
strong wavelength dependence. This produces an image which has exactly 
20000 counts where no light fell, and an average of 20000 counts where
light fell, independent of wavelength.

To apply a flatfield, use DOFF which automatically removes the dc bias,
and handles the 20000 count normalisation.
\medskip
\subsection{Spectrum extraction and Sky subtraction.}
\medskip
Normally this is the only part of the online reduction package used by
observers.
The heart of the FOS reduction software is contained in these routines.
Each spectral order presents a curvature which depends primarily on the FOS
optics but also on the atmospheric dispersion when the slit is near the
parallactic angle. The curvature can be mapped at any z.d. as a high order
polynomial fit to an observation of a bright point source. using the routine
FOSCOFFS. The typical observer, working at reasonable z.d. will not have
to worry about this and can use the default calibration.  


The first step is to straighten the separate orders of the spectrum, one at
a time. TRIM prompts you for the order you want to straighten, and then using
the lexidata joystick to delimit this area, straightens the spectrum using the
coefficients stored in frstcofs.dat and scndcofs.dat depending on
which order you are working on. Straightening the data reconfigures the pixels
according to the curvature coefficients, but there is no resampling. If the
observer displays the TRIMmed image each new y value represents a single
spatial point along the slit.

The next step is to carry out the sky subtraction. This is done using the 
routine SPECTRUM. You enter 4 cursor positions using the Lexidata joystick and
control buttons. Depending on how you select your sky area(s), SPECTRUM will 
either interpolate under the object or calculate a straight mean. If you
don't select any sky areas, the object area will not be sky subtracted.

The resulting spectra from TRIM and SPECTRUM are of a standard form --- a spectrum
pair consisting of the sky subtracted object signal, and the sky spectrum along
the slit. The wavelength to channel number relationship
 is very nearly linear, and so there is no need to resample the reduced spectra.
\medskip
\subsection{Flux calibration}
\medskip
Data are flux calibrated by multiplying by the default flux calibration files
referred to by logical names cal1 and cal2, there is no flux calibration for
third order at present. Use FMULT, and you will have relative fluxes at the 
base of the earth's atmosphere. Fluxing is to be recommended, as it makes it
easier to recognise features in the raw spectrum at wavelengths where the CCD
sensitivity is falling off. It must be made clear though, that there is no 
substitute for taking observations of standard stars, and fluxing your data
using the routines contained in say FIGARO. To get absolute fluxes, account
must be made of atmospheric extinction; LPO Technical Note 31 details how to
do this.
\medskip
\subsection{Plotting data}
\medskip
SPECPLOT will now plot your data (object spectrum, or object and sky) on the
lexidata with sensible wavelength limits, with and without autoscaling.
The wavelength calibration is via two ADAM variables, defining channel 0,
and the wavelength interval per bin. Once the plot is complete, you can use
the Lexidata cursor to mark features in the spectrum you might be interested
in. The wavelength of the feature is written both to the Lexidata, and to the
ADAM terminal. Use LEXPLOT if you want a hard copy on the line printer.
\bigskip

Useful procedures for quick FOS data reduction were written by Andy Lawrence
and his team in May 1989, and are reproduced in Appendix D. In its most
automated mode, a plot of a single object was produced in 1 min 58 secs from
issuing the command to execute the procedure.
\bigskip

Again, it must be emphasised that there is no substitute for doing a rigorous
reduction away from the telescope; the on-line reduction facilities are meant
to enable the observer identify the spectrum with ease. To get the best from
the data, use should be made of optimal extraction techniques (this is after
all a Faint Object Spectrograph). Various reduction packages do already
have such facilities.

\appendix

\chapter{Field Lenses, Dekkers, and Observing Modes}
\markboth {\hfill The INT Faint Object Spectrograph 1992 May}
{appendix A. \hfill Field lenses, filters and dekkers \hfill}

\section{Field Lenses}
\begin {center}
\begin {tabular}{l l l l}

{\bf Field lenses}  &\multicolumn{2}{l}  {Below slit colour filter slide}\\
              &\multicolumn{2}{l}  {(upper of pair)}\\
              &           &                  &                             \\
              &  Position &   Action         &       Use \\
              &  BSCF 0   &   Clear no lens  &       Mode D,A(both orders) \\
              &  BSCF 1   &   Clear field lens &     Mode B(both orders) \\
              &  BSCF 2   &   Yellow field lens&     Mode C(1st order only)\\
              &           &                    &             \\
              &           &                    &             \\
\end{tabular}
\end{center}

\section{Filters}
\begin{center}
\begin{tabular}{l l l l}


{\bf Filters}       &\multicolumn{2}{l}  {Below slit neutral density slide}\\
              &\multicolumn{2}{l}  {(lower of pair)}\\
              &           &                    &     \\
              &  Position &   Action           &     Use \\
              &  BSND 0   &   Clear            &     Most of the time \\
              &  BSND 1   &   CuS0$_{4}$       &     Mode C(2nd order only)
\end {tabular}
\end {center}
\section{Dekkers}
\begin{center}
\begin{tabular}{l l l l}

           &  Position &    Action           &     Use \\
           &           &    Clear            &     Long Slit  mode C\\
           &     1     &    25 arcsec slot   &     Short slit mode D\\     
           &     2     &  2x25 arcsec slot   &     Short slit mode B\\     
           &     3     &   1.2 arcsec slot   &     Set up           \\     
           &     4     &    Occulting        &     \\     
           &     5     &    Occulting        &     \\     
           &     6     & 2x1.2 arcsec slot   &     Short slit mode A \\     
           &     7     & 2x2.0 arcsec slot   &     Short slit mode A \\     
           &     8     & 2x5.0 arcsec slot   &     Short slit mode A \\     
\end {tabular}
\end {center}

\begin{figure}[h]
\centering
\vspace*{185mm}
\caption[FOS dekker]{The FOS dekker}
\label{a12}
\end{figure}

\chapter{FOS Commands and Calibrations}
\markboth {\hfill The INT Faint Object Spectrograph 1992 May}
{appendix B\hfill Commands and Calibrations \hfill}
\medskip
\section{ Glossary of on-line commands}
\medskip
 Here is a list of commands you will find useful for operating FOS. It
includes some commands in common with the CCD on the IDS and A\&G box. For
further details see the folder containing a list of commands for all modes
of operation which is kept in the INT control room.
\medskip

\begin{center}
\begin{tabular}{l l l}
      Command        &  Parameters        &  Description\\
                     &                    & \\
      1la(mp)        &  on/off            &  lamp 1\\
      2la(mp)        &  on/off            &  lamp 2\\
      Abo(rt)        &                    &  Abort a run\\
      Afa(rc)        &  n                 &  select A arc filter\\
      Asn(d)         &  n                 &  select above slit neutral density filter\\
      Bfa(rc)        &  n                 &  select B arc filter\\
      Bsc(f)         &  n                 &  select below slit field lens\\
      Bsn(d)         &  n                 &  select CuS04 filter\\
      Comp(mirror)   &  in/out            &  comparison lamp mirror\\
      Centre         &  tv/gd             &  tv/guide probe on axis\\
      Chform         &                    &  change image data format\\
      Combine        &  respond to prompts&  average many exposures\\
      Continue       &                    &  continue a paused run\\
      Dat(a)         &  d/t/n             &  redefine dump device\\
      Dcsub          &  in/out            &  subtract dc offset\\
      Dek(ker)       &  n                 &  select dekker position\\
      Disp(lay)      &  Rn                &  display run n\\
\end{tabular}
\end{center}
\pagebreak
\begin{center}
\begin{tabular}{l l l }
      Command        &  Parameters        &  Description\\
                     &                    &   \\
      Doff           &  in ff out         &  applies flatfield\\
      Ffno(rm)       &  in out            &  normalises to unit count\\
      Fitsdir        &  respond to prompts&  list contents of FITS tape\\
      Fitsin         &  respond to prompts&  read FITS file from tape to disk\\
      Fitsinit       &  respond to prompts&  initialises FITS tape\\
      Fitsout        &  respond to prompts&  writes fits image from disk to tape\\
      Fli(pmirror)   &  in/out            &  flip mirror for tv viewing\\
      Fmult          &  in1 in2 out       &  multiply images preserving descriptor of in1\\
      Fosc(ofs)      &  respond to prompts&  set up curvature polynomial files\\
      Fosp(lot)      &  respond to prompts&  interactive lexidata plotting\\
      Gdx(y)         &  x,y               &  move guide probe\\
      Gla(nce)       &  secs              &  perform glance run\\
      Hartc(los)     &  a/b               &  closes hartmann shutter(s)\\
      Harto(pen)     &  a/b               &  open hartmann shutter(s)\\
      Hstat          &                    &  status of hartmann shutters\\
      Iop(roceed)    &  0/1               &  wait/not wait for command completion\\
      Keep           &  object            &  save glance run as Run file\\
      Lexplot        &  respond to prompts&  hardcopy of lexidata screen\\
      Man(ic)        &  respond to prompts&  create subarrays\\
      Mstat          &                    &  status of FOS motormicrometers\\
      Nd             &  n                 &  comparison beam nd filters\\
      Nextr(un)      &  n                 &  set next run number\\
      Nitpick        &  in1 in2 out       &  compares frames for cosmic rays\\
      Pa(use)        &                    &  pause an active run\\
      Photo(m)       &  defaulted         &  photometry/inspection program\\
      Proc(edure)    &  name              &  create an Adam procedure\\
      Ru(n)          &  secs "title"      &  perform a standard run\\
      Runstat(us)    &                    &  check run status\\
      Shutdown       &                    &  shutdown Adam and instrument safely\\
      Slice          &  respond to prompts&  centroids and profile program\\
      Slit(jaw)      &  n                 &  set slitwidth in microns\\
      Spectrum       &  respond to prompts&  interactive sky subtraction\\
      Tel(e)         &                    &  check CCD telemetry\\
      Time           &  n                 &  change exposure time to n secs\\
      Trim           &  respond to prompts&  interactive straightening of FOS image\\
      Tung(sten)     &  on/off            &  tungsten lamp\\
      Tvx(y)         &  x,y               &  move tv probe\\
      Unz(oom)       &                    &  unzoom Lexidata\\
      View           &  respond to prompts&  print pixel map on Printronix\\
      Wink           &  n                 &  glance n seconds without fits headers\\
      Zapc(ols)      &  respond to prompts&  remove defective ccd columns\\
      Zed            &  respond to prompts&  redshift feature files\\
      Zoom           &  respond to prompts&  zoom Lexidata
\end{tabular}
\end{center}

\pagebreak

\section{Default Calibrations}
\medskip
FOS has several default calibration files. These are listed here for reference.
If you overwrite them, please reset them for the next user.
\medskip

\noindent{\large\bf Curvature coefficients}
\medskip

\noindent{These are stored in the files:}

\begin{tabular}{l l}
                      & \\
Obs:frstcofs.dat      & (first order)\\
                      &              \\
Obs:scndcofs.dat      & (second order).\\
                      &
\end{tabular}

\noindent{The coefficients were carefully determined via observations of 
many standard stars
and should be adequate for general use at low and moderate zenith distances.}
\medskip

\section {Flux calibration}
\medskip

\noindent{The default relative flux calibration files are: }
\medskip

\begin{tabular}{l l} 
Obs:foscal1/g     & (first order)\\
                  &              \\
Obs:foscal2/g     & (second order)\\
                  &
\end{tabular}
\vspace{5mm}

\noindent{Logical names CAL1 and CAL2 can be used in place of these filenames. Divide
your data by these to flux calibrate it.}    

\chapter{Characteristics of the FOS CCD}
\markboth {\hfill The INT Faint Object Spectrograph 1992 May}
{appendix C \hfill CCD characteristics \hfill}

Prior to May, 1988 an uncoated GEC P8603C CCD had been used in FOS.
In May, 1988 a new blue sensitive GEC P8603C CCD was installed. This chip
is extremely clean, with no defects at normal operating temperature,
 and an extremely good blue response. There is one hot column which
appears at 20$\deg$ above operating temperature.
\medskip

\section{CCD Format}
\medskip
Figure ~\ref{ccda31} shows the CCD format; in particular the position of 
the imaging
area within the data frame. This figure shows the appearance of the CCD as
displayed on the Lexidata, which is a mirror image of the actual chip.
\medskip

\noindent{The CCD is mounted with its long axis in the dispersion direction.
 Row 1 is read out first, and appears at the right of the Lexidata screen.
 Row 1 is the red end of the spectrum.}
\medskip

\noindent{Columns 1--12 are the `underscan' region of the CCD, that is, it is
 an area not subject to illumination during an exposure. This region can be
 used to determine the zero reference level for the data frame. This is
 typically 123 $\pm$ 7 adu.}
\medskip

\noindent{Columns 13--397, and rows 1--578 are the true image elements of the
 CCD.}
\medskip

\noindent{Columns 398--400 and rows 579--590 are the overscan regions. They
 contain residual signal, the magnitude of which is indicative of poor charge
 transfer efficiency.} 
\medskip
\section{Signal level calibration and readout noise}
\medskip
The CCD signal charge is converted to a voltage, then amplified and digitised
to 16 bits. The computer measures the signal as an analogue-to-digital
conversion unit (ADU). In the present configuration,
\medskip

\noindent{1 ADU = 0.95 electrons.}
\medskip

\noindent{The readout of any signal charge from a pixel has an intrinsic signal
independent electrical noise introduced by the output circuitry of the CCD
(readout noise). for the current CCD:}
\medskip

\noindent{Readout noise sigma = 7 adu = 7 electrons r.m.s.}
\medskip

\noindent{The measurement of readout noise on an erase (bias) frame, that is a
frame of zero exposure, is a useful test of whether the CCD camera is working
as expected. Photom/stats should reveal a mean background level of 123 adu
with a sigma of 7.}
\medskip

\noindent{The current CCD has a potential well charge of 65535 electrons.
 Linearity is good up to 40000 electrons with no problems. Exposures are
 therefore okay up to 40000 adu.}
\medskip
\section{Other features of operation}
\medskip
\noindent{The CCD is run at a stabilised temperature of 150K. This temperature
 was chosen for optimum overall performance taking into account dark current,
readout noise and charge transfer efficiency.}
\medskip

\noindent{At least two hours should be allowed before serious observations are
 made following the switch-on of the CCD camera. This is because of a charge 
injection effect that is apparent for the first few hours of operation
after power up and which is observed as an excessive dark current count.}
\medskip

\noindent{The cosmic ray detection rate is approximately 15 events/1000 seconds
over the whole chip.}
\medskip
\section{Position of focus in the camera}
\medskip
The camera was focussed in May 1988 after the installation of the new
blue sensitive GEC CCD, the position of which is not expected to move by
very much. To check the focus, run MSTAT from the Adam terminal, which
should give the following values for the relevant parameters:
\medskip

\begin{center}
\begin{tabular}{c c c c c c}
    s  &  r  &  b  &  f  &  ha  &  va \\
       &     &     &     &      &   \\
   378 & 481 & 291 & 383 &  95  &  2  \\
       &     &     &     &      & 
\end{tabular}
\end{center}
\medskip

\noindent{The values obtained using MSTAT should be within 10 units of these.}


\begin{figure}[h]
\centering
\vspace*{185mm}
\caption[CCD format]{CCD format}
\label{ccda31}
\end{figure}


\chapter{FOS reduction procedures}
\markboth {\hfill The INT Faint Object Spectrograph 1992 May}
{appendix D \hfill FOS reduction procedures \hfill}

\section{Useful Procedures for Quick FOS Reduction}
\medskip
In May 1989, Andy Lawrence wrote a set of procedures to automate the TRIM,
SPECTRUM, SPECPLOT and LEXPLOT routines which are used to reduce the FOS data
at the telescope, so that a first order spectrum was produced in about the
time it took to acquire the next object.

Because of ADAM niceties about character strings, and the fact that R1,S1,T1
etc. are psuedo-variables standing for the real file name,(e.g. R1 is
SYS:FOSABC.001, where ABC is the observer's signon initials) it is not obvious 
how to put RUN numbers into procedures. The following (in which parameter names
are arbitrary) will serve as a starting point.
\medskip

\noindent{To reduce the FIRST order spectrum from the raw image and output
a 1D spectrum :-}
\medskip
\begin {tabbing}
111\=11111111111111111111111111111111111111111111111\=11111111 \kill
   \>ADAM$>$ Procedure RED inim outim       \> See notes\\
   \>Proc$>$ DECLARE inim CHAR 20\>      \\
   \>Proc$>$ DECLARE outim CHAR 20\>     \\
   \>Proc$>$ TRIM inim FIRST NO T1     \> See notes\\
   \>Proc$>$ DISP T1                   \> Displays straightened first order\\
   \>Proc$>$ SPECTRUM T1 outim YES       \> Prompts for star and sky positions\\
   \>Proc$>$ End proc                  \>    \\ 
   \>ADAM$>$                           \>    
\end {tabbing}  
\medskip

\noindent{Note:-}

a) Do not use previously defined ADAM variables (e.g. `in' and `out' are
used by the COMPMIRROR command).

b) For well exposed spectra taken using the FOS dekker in position 1, (24
arc seconds, single aperture) TRIM will work well in the automatic mode, and 
find the dekker edge itself.
\medskip

ADAM$>$ put RED\hspace{55mm}(Saves RED for next time).
\medskip

\noindent{You can reduce R1 and put the spectrum in S1 by typing:-}
\medskip

ADAM$>$RED R1 S1
\medskip

\noindent{To plot the spectrum on the LEXIDATA and measure wavelengths on it, 
use the following procedure:-}
\medskip

\begin{tabbing}
111\=111111111111111111111111111111111111111111111\=111111111\kill
   \>ADAM$>$Proc LOOK spec sca\>    \\
   \>Proc$>$DECLARE spec CHAR 20\>    \\
   \>Proc$>$DECLARE sca        \>     \\
   \>Proc$>$SPECPLOT spec LEX 5400 8000 1 1 sca 0\>  (See notes).  \\
   \>Proc$>$End Proc           \>   \\
   \>ADAM$>$                   \>
\end {tabbing}
\medskip

\noindent{Note:-}

a)5400 and 8000 in this line are the minimum and maximum wavelengths,which you
can adjust to suit your requirements

b)SPECPLOT will insist on prompting for a title and comments, but will accept
carriage return as null.

c)The scale should be about int(maxcounts/1000). Maximum counts are output to
the screen by SPECTRUM (and hence by procedure RED).
\medskip

\noindent{You can invoke this with:-}
\medskip

ADAM$>$LOOK S1 6
\medskip

\noindent{In addition to the lexidata display, you can get a hard copy on
the line printer.}
\medskip

\begin{tabbing}
111\=111111111111111111111111111111111111111111111\=1111111111 \kill
   \>ADAM$>$Proc HLOOK sp sc         \> (See note.)\\
   \>Proc$>$DECLARE sp CHAR 20       \>   \\
   \>Proc$>$DECLARE sc               \>   \\
   \>Proc$>$LOOK sp sc               \> (Assumes you have Proc LOOK) \\
   \>Proc$>$LEXPLOT                 \>  (Dumps LEXIDATA to Printer) \\
   \>Proc$>$End Proc                \>  \\
   \>ADAM$>$                        \> 
\end{tabbing}   
\medskip

\noindent{Note:-}

a) Variable names must not be duplicated in your various procedures.
\vspace{5mm}

\noindent{If you are feeling really ambitious, you can do everything from
 the raw image to the hardplot of the spectrum in one fell swoop.}
\medskip

\begin{tabbing}
111\=111111111111111111111111111111111111111111111\=1111111111 \kill
   \>ADAM$>$Proc AUTO raw final        \> \\
   \>Proc$>$DECLARE raw CHAR 20        \>  \\
   \>Proc$>$DECLARE final CHAR 20      \>  \\
   \>Proc$>$RED raw final              \> (Assuming you have Proc RED) \\
   \>Proc$>$HLOOK final 0              \> (See note.) \\
   \>Proc$>$End Proc                   \>   \\
   \>ADAM$>$                           \>
\end {tabbing}
\medskip

\noindent{Note:-}

a) The `0' is the scale for the plot, and is a way of overcoming not
knowing the maximum counts from the start, and will force a prompt.
\medskip

In tests with one object in the slit, and measuring one wavelength from
the SPECPLOT stage, the procedure AUTO took fractionally under 2 minutes
from starting, to returning to the ADAM prompt.
\medskip

\noindent{Run it by typing:-}
\medskip

ADAM$>$AUTO R2 S2.
\medskip

\noindent{Remember to answer the few remaining prompts!}
\end{document}
