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10
Naming convention for optical components
This section describes how optical components in use at the VLT and NTT telescopes are named and identified.
Such identifiers are used:
-
by astronomers when selecting a particular observing configuration;
-
by operations staff when setting up the requested optical elements for the upcoming night;
-
by operations staff when operating instruments and performing service observations;
-
by VCS when writing FITS keywords on the data headers;
-
by pipeline software when performing standard data reduction;
-
by astronomers when reducing data off-line;
-
by archive users who prepare archive research programmes.
Astronomers are likely to use names while observatory staff will mostly use identifiers. The convention described in this section was developed with the aim of facilitating all of the tasks mentioned above while at the same time maintaining the discipline needed in order to handle the few hundred elements that will be used at the VLT.
This naming convention will be applied to all VLT and NTT instruments.
10.1 Identification scheme
- guideline-27
- Each optical element, i.e. filters, grisms, etc., in use at any VLT or NTT instrument shall have a unique identifier and a verbose name.
Identifiers are typically sequential numbers which are given to each element when acquired. These identifiers are recorded in the keyword
ID
, e.g.
FILT ID
,
GRIS ID
or
OPTIi ID
(see
section 4.10
for more details). The
ID
serves as the reference to the full characterization file (e.g. transmission and efficiency curves of filters and grisms etc.) which is the authoritative source of information for each component.
Verbose names are recorded in the keyword
NAME
(e.g.
FILT NAME
,
GRIS NAME
or
OPTIi NAME
) and follow the scheme described in
section 10.3
.
- guideline-28
- Identifiers of elements that cease to exist (e.g. a broken filter) are retained in order to ensure the historical validity of the Science Archive.
Identifiers and names are kept in an database which is part of the VLT Instrument Description Database.
- guideline-29
- Instrument Consortia who prepare Data Interface Dictionaries must foresee for the corresponding keywords at least 10 characters space for the ID keyword and 30 characters for the NAME keyword.
10.2
Usage of the
OPTIi
keywords
OPTIi
keywords are used to setup the internal functions of the instrument and to record instrument engineering parameters usually on the operations and configurations logs (see description in
section 4.10
).
The allowed
OPTIn TYPE
values are:
MIRROR FABRYPEROT
FILTER SLIT
GRISM MASK
GRATING FOCUSWEDGE
ECHELLE HARTMANN
WOLLASTON RETARDER
BEAMSPLITTER DICHROIC
FIBER LENS
PRISM FREE
(nothing mounted in the slot)
10.3
Naming scheme
This section describes the scheme applied when assigning a name to optical elements.
- guideline-30
- Optical elements have a technical name that describes its major physical characteristics and may have a short, commonly used conventional name.
Technical names describe the element independently of its context (camera or instrument). The basic rule for technical names is to prefix the name with a four letter mnemonic of the element in question followed by some of its optical characteristics. Conventional names are typically used in user interfaces.
- guideline-31
- Values for wavelengths and other characteristics are rounded to the nearest integer except for slit widths (see below).
10.3.1 Filters
Filters will be characterized by
-
conventional names:
-
the commonly known name, e.g.
K
,
OG590
,
OIII/3000,
when applicable;
-
the system and the name within that system, e.g.
U_BESS
,
U_STRM
;
-
technical names:
-
FILT_
<
central wl in nm
>
_
<
FWHM in nm
> for general filters (at arbitrary wavelengths);
-
FILT_VARi
for variable filters;
i
is a serial number;
-
FILT_
<
50%wavelength in nm
>
_
<
cuton/-off
> for long-/shortpass filters,
where <
cuton/-off
>is
L
for longpass filters or
S
for shortpass filters;
10.3.2 Grisms
Grisms will be characterized by
-
GRIS_
<
#grooves/mm
><
characteristic letter
>
where <
characteristic letter
> indicates the approximate central wavelength (e.g.
R
,
B
).
10.3.3 Gratings
Gratings will be characterized by
-
GRAT_
<
#grooves/mm
><
characteristic letter
>
where <
characteristic letter
> indicates the approximate blaze wavelength (e.g.
R
,
B
) or none if the grating is unblazed.
-
ECHE_
<
#grooves/mm
><
characteristic letter
>
where <
characteristic letter
> indicates the approximate wavelength of use (e.g.
R
,
B
).
10.3.4 Wollaston prisms
Wollaston prisms will be characterized by
-
WOLL_
<
separation angle in arcmin
>
10.3.5 Retarder plates
Retarder plates will be characterized by
-
RETA2
for lambda/2,
RETA4
for lambda/4 plates.
10.3.6 Fabry-Perot etalons
Fabry-Perot etalons will be characterized by
where <
finesse
> is the dimensionless number characterizing the resolving power of the Fabry-Perot interferometer.
10.3.7 Slits
Fixed width slits (e.g. in a punched plate) will be characterized by
-
SLIT_
<
width in arcsec
>
where <
width in arcsec
> is given with one decimal digit (e.g.
1.5
or
0.5
).
Variable width slits, such as those on a decker or with a motorized function are named
-
SLIT_DEKKER
or
SLIT_FUNCTION
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Last updated: November 28, 1997
