
\appendix

\chapter{Flux Standards}

With the proliferation of linear detectors on Cassegrain spectrographs,
spectrophotometry has become a common byproduct of many spectroscopic 
observations. The cornerstone of such studies is the system of 
spectrophotometric standards. Useful references are:

{\supersingle
\reference{Filippenko, A.V., Greenstein, J.L.}{1984}{\pasp}{96}{530}
\reference{Oke, J.B., Gunn, J.E.}{1983}{\apj}{266}{713}
\reference{Massey \etal }{1988}{\apj}{328}{315}}

For observers with access to a STARLINK node, the main Figaro directory (logical 
name FIGARO\_PROG\_S) contains a   number of files, including those recently
compiled by Roderick Johnstone (IoA) giving the published flux densities of 
standard stars, all with a .TAB extension according to FIGARO convention.

       The  VMS  DIRectory  command may be used to find which
  files are available as tables.  The command

\begin{verbatim}
     $DIR FIGARO_PROG_S:*.TAB
\end{verbatim}

  will list all the table files supplied in the  main  directory.   
Not  all of these are intended for flux calibration; some may be
  extinction tables, etc.  These are all  text  files,  and
have comments at the start describing their function.  
       For most of the flux standards for which Figaro supplies  tables,
  two  tables are provided:  one in AB magnitudes, usually a direct copy
  of the published data, and one in (milli- or micro-) Janskys,  usually
  the  result  of  a  semi-automatic conversion from the former.  If you
  particularly like $ergs\;s^{-1}\;cm^{-2}\:\AA^{-1}$ , then you can 
  either provide your own
  flux tables in these units and work from them directly, or you can use
  the FLCONV command to convert from a spectrum  calibrated  in  Janskys
  into these units.


The  command
\begin{verbatim}
     $TYPE FIGARO_PROG_S:file.TAB
\end{verbatim}
  will list the file. For example, the file G158M100.TAB  begins
  as follows -
\begin{verbatim}
     *                   G 1 5 8 - 1 0 0
     *
     *   Table file for G158-100, faint object flux standard,
     *   based on Filippenko and Greenstein (1984) P.A.S.P.
     *   96, 530. Note that these are fitted continuum 
     *   fluxes, not directly measured fluxes, and should 
     *   be used accordingly.   This file is designed for
     *   use with the Figaro routine GSPIKE.  The data here is
     *   given to 3 decimal places and was supplied directly by
     *   Alex Filippenko.
     *
     SET .Z.UNITS = "micro-Janskys"
     SET .Z.LABEL = "Flux"
     *
      3300   891.251
      3400   990.831
      3500  1135.534
      3600  1282.331
      3700  1432.187
      3800  1599.556
      3900  1770.110
\end{verbatim}

       The lines beginning with asterisks are treated as  comments,  and
  the  lines  that  begin with `SET' are used to set data objects in the
  file created from this table.  


An alternative version of this file  is G158M100A.TAB, the A added after the star 
name indicates that the list is in AB magnitudes. It contains the lines
\begin{verbatim}
     SET .Z.UNITS = "AB Magnitudes"
     SET .Z.LABEL = "Flux"
     SET .Z.REVSCALE = 1
     SET .Z.MAGFLAG = 1
     *
      3300   16.525
      3400   16.410
      3500   16.262
      3600   16.130
      3700   16.010
      3800   15.890
\end{verbatim}
       The functions of the .Z.UNITS and .Z.LABEL lines should be fairly
  obvious.   Setting  .Z.REVSCALE to 1 in a file indicates to SPLOT that
  the data should be plotted with the flux scale reversed,  and  setting
  .Z.MAGFLAG  indicates  that the scale is in logarithmic units.  Tables
  based on data from, for example, Oke and Gunn's 1983 paper  will  also
  include the line

     SET .Z.BANDWIDTH = 40

  to indicate the  40  Angstrom  bandwidth  used  by  their  data.   The
  Filippenko  and Greenstein data represents fitted continuum fluxes, so
  does not have a bandwidth. From the .TAB files already supplied, it should 
  be possible
  for you to deduce how to create your own, should that be necessary.

 
Table~1 lists the stars available in FIGARO main directory (Column~1), 
name of the file (Column~2), wavelength coverage (Column~3) and comments
(Column~4).

         The files listed contain stellar fluxes in  milli-janskys.   AB
    magnitude  files have the same name, but with an A after the star's
name. 
Files are called after the star with +
    and - signs replaced by P and  M  respectively.   Some
    files  have  been  included more than once under aliases of the star
    name.

         Numerical values  of  wavelength,  flux,  bandwidth  and  order
    changeover  wavelengths  have  been  checked  and are believed to be
    correct.  


         Note that there are several different magnitude  systems  which
    determine  the  fluxes presented in these tables.  These are defined
    through different calibrations of the primary standard Vega and  use
    different ways of transferring the magnitude system from Vega to the
    fainter secondary standards.  In general the stars listed  here  are
    not  actual standards but are just good calibrations of non-variable
    stars.  The user is strongly advised to read the  paper  from  which
    the numbers come (listed at the top of each file) to gain an idea of
    both the random and the systematic errors in the fluxes as  well  as
    the magnitude system from which the fluxes derived.

Special thanks to Doreen Oliver at RGO who typed
    in most of the original files and to Carolyn Crawford who gave
    invaluable help checking the numbers.

\begin{verbatim}

    Star            File            Coverage        Comments
    ====            ====            ========        ========
     
    40 Eri B        40ERIB.TAB      3320-9880
    AM CVn          HZ29.TAB        3340-8720
    BD+25 3941      BDP253941.TAB   3200-8370
    BD+28 4211      BDP284211.TAB   3200-8370
    BD+33 2642      BDP332642.TAB   3200-8370
    BD+40 4032      BDP404032.TAB   3200-8370
    BD+82 2015      BDP82015.TAB    3200-8370
    EG  5           VMA2.TAB        3260-10640      Used 2nd order
                                                    values at overlap
    EG 11           L870M2.TAB      3210-7220
    EG 28           LB1240.TAB      3210-7220
    EG 29           LB227.TAB       3210-7220
    EG 31           HZ2.TAB         3210-7220
    EG 33           40ERIB.TAB      3320-9880
    EG 39           HZ7.TAB         3210-7220
    EG 42           HZ14.TAB        3230-7420
    EG 50           HE3.TAB         3340-9440
    EG 54           L745M46AA.TAB   3320-10520      Cosmetic change to
                                                    lambda_double
    EG 63           LDS235B.TAB     3320-8920       Cosmetic change to
                                                    lambda_double
    EG 67           SA29M130.TAB    3210-10200
    EG 76           AL970M30.TAB    3180-7040       40A bins in 2nd order
    EG 76           BL970M30.TAB    3320-9880       80A bins in 2nd order
    EG 77           TON573.TAB      3340-8160
    EG 79           R627.TAB        3160-10840
    EG 86           HZ21.TAB        3340-9660
    EG 91           HZ29.TAB        3340-8720
    EG 98           HZ43.TAB        3320-10520
    EG 99           W485A.TAB       3320-9880
    EG 102          GRWP705824.TAB  3210-10200
    EG 119          ROSS640.TAB     3320-10520
    EG 129          GRWP708247.TAB  3340-9200
    EG 133          L1573M31.TAB    3336-10073
    EG 139          W1346.TAB       3210-10640
    EG 144          GRWP738031.TAB  3340-9440
    EG 148          L1363M3.TAB     3316-10520
    EG 149          L930M80.TAB     3320-9240       Cosmetic change to
                                                    lambda_double and
                                                    correct value at 4510
    EG 162          L1512M34B.TAB   3210-10040
    EG 182          G47M18.TAB      3340-9280
    EG 184          GD140.TAB       3160-10560
    EG 192          AGD185.TAB      3200-7240       80A bins 2nd order
    EG 192          BGD185.TAB      5820-9780       360A bins
    EG 247          G191B2B.TAB     3320-10520
    Feige 110       F110.TAB        3200-8370       _S: file seems to have
                                                    wrong bandwidth and
                                                    lambda_double
    Feige 15        F15.TAB         3200-8370
    Feige 25        F25.TAB         3200-8370
    Feige 34        F34.TAB         3200-8370
    Feige 56        F56.TAB         3200-8370
    Feige 92        F92.TAB         3200-8370
    Feige 98        F98.TAB         3200-8370
    G191B2B         G191B2B.TAB     3320-10520
    G47-18          G47M18.TAB      3340-9280
    GD 140          GD140.TAB       3160-10560
    GD 185          AGD185.TAB      3200-7240       80A bins 2nd order
    GD 185          BGD185.TAB      5820-9780       360A bins
    GD-248          GDM248.TAB      3300-10000      Not from SPICA
    Grw+70 5824     GRWP705824.TAB  3210-10200
    Grw+70 8247     GRWP708247.TAB  3340-9200
    Grw+73 8031     GRWP738031.TAB  3340-9440
    He 3            HE3.TAB         3340-9440
    HZ 14           HZ14.TAB        3230-7420
    HZ 15           HZ15.TAB        3200-8370
    HZ 2            HZ2.TAB         3210-7220
    HZ 21           HZ21.TAB        3340-9660
    HZ 29           HZ29.TAB        3340-8720
    HZ 43           HZ43.TAB        3320-10520
    HZ 44           HZ44.TAB        3316-10520      Ambiguity in bandwidth
                                                    at changeover to
                                                    first order
    HZ 7            HZ7.TAB         3210-7220
    Kopff 27        KOP27.TAB       3200-8370
    L1363-3         L1363M3.TAB     3316-10520
    L1403-49        TON573.TAB      3340-8160
    L1512-34B       L1512M34B.TAB   3210-10040
    L1573-31        L1573M31.TAB    3336-10073
    L745-46A        L745M46AA.TAB   3320-10520      Cosmetic change to
                                                    lambda_double
    L870-2          L870M2.TAB      3210-7220
    L930-80         L930M80.TAB     3320-9240       Cosmetic change to
                                                    lambda_double and
                                                    correct value at 4510
    L970-30         AL970M30.TAB    3180-7040       40A bins in 2nd order
    L970-30         BL970M30.TAB    3320-9880       80A bins in 2nd order
    LB1240          LB1240.TAB      3210-7220
    LB227           LB227.TAB       3210-7220
    LDS235B         LDS235B.TAB     3320-8920       Cosmetic change to
                                                    lambda_double
    R627            R627.TAB        3160-10840
    Ross 640        ROSS640.TAB     3320-10520
    SA29-130        SA29M130.TAB    3210-10200
    Ton573          TON573.TAB      3340-8160
    VMa 2           VMA2.TAB        3260-10640      Used 2nd order
                                                    values at overlap
    W1346           W1346.TAB       3210-10640
    W485A           W485A.TAB       3320-9880
\end{verbatim}

Table~2 has been compiled for the WHT manual by Janet Sinclair (RGO) and 
includes 1950.0 positions, proper motions, m$_{5556}$ and spectral type
of spectrophotometric standards.
\vfill
\newpage
r
\newpage
r
\newpage
r

\chapter{Data Reduction}

We hesitate to include this appendix, because we realize that probably there 
are as many ways of reducing data as CCD users in the astronomical 
comunity.

We would like anyway to make some general comments, based on our personal
experience, for the benefit of first time users.

\section{Data format}

The observer takes home a copy of the data tapes, that has been produced in
FITS format. The original D-tape is archived at RGO. The header information on 
the data is kept on-line
on a Vax computer, and can be accessed using the La Palma Data Archive 
(E.J.~Zuidewijk, 1989, Technical Note \# 69) by the owner and, after one year,
by anyone interested in the data.

Prior to 16/1/1989, the data from the CCD was copied into tape as produced:
unsigned 16 bit. FITS data conventions are unsigned 8 bit; signed 16 bit and
signed 32 bit. STARLINK FITS routines therefore considered the data as supported
by the conventions which is fine for count values in the range 0 to 
($2^{15}-1$)=32767. For output in the range ($2^{15}-1$) to ($2^{16}-1$) the
routines would produce negative numbers in the range $-2^{15}$ to $-1$. This
data looks as if it is saturated. The simplest recipe is to search for
negative numbers, and add to them $2^{16}=65536$. This is done by simple 
routines available in STARLINK.

Changes have been introduced to handle CCD data at the telescope in a consistent
and correct manner.
After the 16/1/1989, CCD images created on the INT are labelled internally 
on disc as U2 (unsigned 16 bit) and FITS tapes now conform exactly to the 
international FITS standard.

\section{Bias}

You would have obtained during the night (read again Chapter 4) several frames 
with no illumination
to determine the modulations of the ``zero'' level, or dark current, across the 
chip. This zero
level also changes during the night, so we find convenient to use the
underscan columns for each frame (1-11 in the GEC CCDs) to determine it.

We proceed as follows:

\begin{enumerate}
\item Average all the bias frames and smooth them slightly (e.g.~top-hat 3 
pixels).

\item Check for -- and eliminate -- hot spots.

\item Trim the four edges to get rid of rubbish that will otherwise ruin your
mean values, but taking care to leave some 
of the underscan columns (columns 7-10 is usually enough; 1-4 after trimming).
The dark level for each frame is to be obtained from them.

\item Subtract the mean value of the whole frame to obtain a new frame with the
modulations and a mean value of $\sim$ zero. This we will call, in what follows,
the bias frame.

\end{enumerate}

\section{Preflash}

If the chip used needed preflash, you would have obtained some preflash frames 
at the beginning and end of the night, plus one or two flash maps (see Chapter 
4).

\begin{enumerate}

\item Average the flash maps.

\item Check for -- and eliminate -- hot spots. Smooth the frame.

\item Trim the edges to the same size of the bias frame.

\item Obtain the mean value of the dark current from the underscan columns
(now 1-4, for example) and add that number to the bias frame.

\item Subtract the resulting frame from the one obtained after step 3.

\end{enumerate}

Proceed likewise with the preflash frames. The ratio of mean values of these two
frames should be similar to the ratio of flash units used. You can divide the
flash map by this ratio and use this ``scaled'' preflash as the one to 
subtract from the data frames. Use the preflash frames to check for consistency.

\section{Flat field}

You can repeat steps 1-5 from B.3 using the flat field frames; this time 
without smoothing  as you are interested in the pixel to pixel variations. Then 
subtract the ``scaled'' preflash (if used) from the resulting frame. You will 
have obtained a flat field frame; divide it by its mean value and you have a 
normalized flat field that is now ready to be used in the data reduction.

For extended objects, it is important to obtain during twighlight several
well exposed ($\sim 10^4$  counts) sky frames, because the illumination of the
slit by a lamp might not be uniform. These flat skies are reduced as flat 
fields.
\section{Objects}

You have finished now preparing the ``initial'' frames (bias, preflash and 
flat field) for the reduction of
one night's objects. You might have different flat fields for each telescope
configuration.

Object by object you can proceed as follows: 
\begin{enumerate}

\item Check for -- and eliminate -- hot spots. 

\item Trim the edges to the same size of the bias frame.

\item Obtain the mean value of the dark current from the underscan columns
(now 1-4, for example) and add that number to the bias frame.

\item Subtract the resulting frame from the one obtained after step 3.

\item Subtract the ``scaled'' preflash (if used).

\item Divide by the normalized flat field. 
\end{enumerate}
Calibration frames are treated as objects.
\section{Calibrations}

It is important to prepare your calibration tactics before your observing
trip. These preparations include 

\begin{description}
\item [a)] Selecting the lamps to use at each telescope configuration (see 
Appendix C).

\item [b)] Selecting the stars to correct for atmospheric absorptions (F8 stars
make good calibrators).

\item [c)] Selecting the flux standards to use (see Appendix A).

\end{description}

Back home after your trip, and after steps B.1 to B.5 of the reduction, you will
be able to use your favourite calibration package. FIGARO, for instance, allows
you to calibrate in wavelength in 2-D which is very useful, specially if you
are working with extended objects. You can then extract 1-D spectra and 1-D sky
to subtract, and you will be ready to eliminate atmospheric absorptions, 
calibrate in flux and write your papers.
\vfill

\chapter{Calibration Arcs}

``A Spectral Atlas of calibration lamps in use with IDS'' (E.J.Zuiderwijk and
J.Knapen 1989) is being issued by RGO. It contains maps of a Cu-Ar arc with 
high, intermediate and low
dispersion (1200, 400 and 150 lines mm$^{-1}$ gratings), Cu-Ne with high and 
low dispersion (1200 and 150 lines mm$^{-1}$ gratings), Th-Ar with high 
dispersion (1200 lines mm$^{-1}$ grating), Cu-He with low dispersion (150 
lines mm$^{-1}$ grating) and Al/Ca/Mg-Ne with intermediate dispersion
(632 lines mm$^{-1}$ grating).

The main features of the different lamps are described also here, so that users
can decide which lamps are more adequate for their observations. Some of the
comments that follow, only apply to CCD observations and not to IPCS ones, due 
to the difference in dynamic range between both detectors. The best way to 
judge is actually by inspecting the arc atlas.

\section{Comparison lamps}

Several lamps are available in the INT A\&G unit for wavelength calibration.
Two lamps are allowed to be simultaneously used, and they are by default
Copper-Argon in position 1 and Copper-Neon in position 2. Users wanting 
a different one should specify their requirements in advance so that the 
lamp is installed by the duty technician in place of the standard ones.

\subsection{Cu-Ar lamp}

The Copper-Argon lamp presently in use with the IDS shows only ArI and ArII
spectra. Copper lines are not seen. It  shows two distinct spectral regions:

\begin{enumerate}
\item  Between 3900 \AA\ and 6965 \AA\ the spectrum contains a large number
of relatively faint lines, which can be used in both low and high dispersion
work. The region 3900~\AA \ to 5100~\AA\ is particularly useful both with CCD 
and IPCS detectors. Between 5200~\AA\ and 5500~\AA , although there are a
large number of lines, they are comparatively weak and large exposure times
are needed. One may be better off with the Th-Ar lamp for this region.

\item Redwards of 6965~\AA\ up to 9784~\AA , the spectrum contains a large 
number of strong and very strong emission lines, which give the argon arc
its characteristic red colour. However between these strong lines there are
gaps devoid of even very weak lines, particularly redwards of 7500~\AA .
There the spectrum is only useful at low dispersion (150, 300 and 400 
g/mm gratings) or at high dispersion, in combination with another lamp
(e.g.~Cu-Ne).

\end{enumerate}
This lamp is normally located in position 1, enabled by the Adam command
1LAMP ON.

\subsection{Cu-Ne lamp}

The Neon spectrum between 3100~\AA \ and 9600~\AA \ can be roughly divided in
three sections: very strong features due to NeI dominate the
wavelength range 5850-7440~\AA ; another group of prominent features are present
between 7500 and 9600~\AA , although these are as much as ten times fainter
than those in the former range. Bluewards, neon lines, both NeI and NeII,
appear only weakly, and the copper spectrum provides the strongest features.
Even so, the strong copper line CuI $\lambda$ 5105~\AA\ is barely 
one-twentieth  the intensity of the principal NeI lines described earlier.

This implies that for wavelength calibrations in the red, 
the copper-neon lamp is only really
useful for low-dispersion work whilst the red features are so
spaced that at high dispersion very few lines may be present in certain
wavelength intervals. In the blue, at intermediate and high dispersions, it
may be useful to supplement the argon spectrum in regions where this is a
bit sparse e.g.~3300-4000~\AA , but significantly longer exposures would be 
necessary to bring up the few NeII lines below 3250~\AA .
To reach a few weaker lines redward of 9700~\AA, in particular in the region
1.0--1.1$\mu$m, careful second-order filtering is required, and also 
considerable patience.

This lamp is normally located in position 2, enabled by the ADAM command
2LAMP ON.

\subsection{Th-Ar lamp}

This lamp gives a very  rich emission line spectrum over a wide wavelength
range and is thus very useful for high dispersion work, particularly in the red
where the Cu-Ar and Cu-Ne ones are rather sparse. Our lamp produces very weak
lines to the red of 7200~\AA \ and long exposures are required which will 
produce the undesirable effect of overexposing the very strong Argon features.
On the other hand, it is not
recommended for medium and low dispersion work because of the severe problems
which line-blending would introduce.

This is not a standard lamp, so users must notify their SA in advance for the 
lamp to be installed.

\subsection{Cu-He lamp}

The spectrum is that of pure HeI with some contamination by very weak hydrogen;
copper lines are not seen.

Between 3800~\AA\ and 5050~\AA\ it has 12 well defined lines which makes it 
useful at low dispersion. Between 5875~\AA\ and 7281~\AA\ the spectrum contains
4 strong emission lines, while beyond 7282~\AA\ only a few weak lines are 
present. The only strong feature in the far red is the line at 
$\lambda$~10830.3~\AA .
Apart from this far red line, the lamp could be useful  in combination with
another  one to fill gaps (e.g.~Cu-Ar) or for very low dispersion 
spectroscopy with FOS.

This is not a standard lamp, so users must notify their SA in advance for it
to be installed.

\subsection{Al/Ca/Mg-Ne lamp}

This lamp was originally acquired for the wavelength calibration of TAURUS
data. The spectrum contains, apart from the NeI features, a large number
of multiplets of CaI, MgI and AlI, which dominate the blue spectral range. In
the far red, some of these multiplets neatly fill gaps  between the NeI lines.
This lamp is useful at high dispersion CCD work in narrow selected regions.  
\vfill


\chapter{Filters, gratings and masks}

\section{Filter sets}

Neutral density and colour filters are available to use either above or
below the spectrograph slit.

\subsubsection{Order sorting filters}

The standard ASCF (above slit colour filter) has 6 positions that correspond
to 

\begin{table}[h]
\begin{center}
\begin{tabular}{cc}
\\*
Position & Filter \\
\\
0        & Clear \\
1        & WG360 \\
2        & GG495 \\
3        & RG630 \\
4        & BG38\ \\
5        & GG385 \\
\end{tabular}
\end{center}
\end{table}



These are general order sorting filters or other $\lambda$ discrimination.
Figure 2.5 gives their wavelength dependent transmission. All filters are 
2mm thick with selective antireflection coatings added.

A non-standard slide (ASCF \#0) is available for users to request special 
setups. The slide can accomodate 5 standard-size filters (45mm by 60mm by 3mm)
or 4 standard-size filters plus one 50mm diameter which requires a special
mounting to insert it into the tray. Users may provide their own filters
in advance for an observing session, to be mounted on this slide by local 
support.

The slide BSCF (below slit colour filter) can carry filters in positions 1 and
2, 0 is clear. If you use below slit filters, the collimator has to be moved
to account for the change in the optical path length.

\subsubsection{Neutral density filters}

The above slit neutral density filters are put in position by issuing the 
ADAM command ASND~n, where n, valued from 0-5 corresponds to


\begin{table}[h]
\begin{center}
\begin{tabular}{cc}
\\*
Position & Filter \\
\\
0        & Clear \\
1        & 0.3 \\
2        & 0.6 \\
3        & 1.2 \\
4        & 1.8 \\
5        & 3.0 \\
\end{tabular}
\end{center}
\end{table}

\subsubsection{Calibration lamp filters}

Two filter wheels (A and B) are available for the calibration lamps. AFARC~n
and BFARC~m put in position n and m the filters in wheels A and B; n and m 
are numbers between 0 and 7 corresponding to

\begin{table}[h]
\begin{center}
\begin{tabular}{cll}
\\*
Position & AFARC & BFARC \\
\\
0        & Clear & Clear \\
1        & 0.236 & 0.33 \\
2        & 0.61  & 0.498 \\
3        & 0.80  & 0.89 \\
4        & 1.74 & 1.20 \\
5        & 3.0 & 2.1 \\
6        & empty\ at & empty\ at \\
7        & present   & present
\end{tabular}
\end{center}
\end{table}

Wheels A and B are used together in any combination, giving a density range
between clear and 5.10. By specifying ND {\it x} the software will choose
the combination of A and B equal or greater than {\it x}.

\section{Gratings}

The gratings available for use with the IDS are given in Tables~3.1 and 3.2, and
their efficiency as a function of wavelength, in Figure~2.4.

The R or H prefix in the name of the grating indicates whether it is 
conventionally ruled (R) or ``holographic'' (H). The number indicates the
frequency of groves/mm. And the last letter refers to the region of the spectrum
where maximum efficiency occurs.

Graphs of grating settings are given in Dataset~5 of the IPCS Cook Book.

\section{Dekker masks}

Dekker masks with the CCD are normally used only for set-ups and in the clear 
(0) position.
The  default is the IPCS dekker mask. It has 9 positions corresponding to

\begin{table}[h]
\begin{center}
\begin{tabular}{clc}
\\*
Position & arcsec & mm \\
\\
0        & Clear & Clear \\
1        & 0.5 & 0.10 \\
2        & 1.0 & 0.18 \\
3        & 1.5 & 0.32 \\
4        & 2.5 & 0.52 \\
5        & 3.5 & 0.70 \\
6        & comb & \\
7        & 7.5 & 1.53 \\
8        & 5.0 & 1.05 
\end{tabular}
\end{center}
\end{table}
Users of the cross disperser might find convenient the FOS dekker. 
\vfill
