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P2PP: FORS1 and FORS2 Information |
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Table of Contents
Introduction
This page contains information specific to the creation of
Observation Blocks (OBs) for FORS1 and FORS2 Service Mode programs.
For more general OB creation information and rules, see the
P2PP page or the
Service Mode Guidelines for Phase 2
preparation.
Requirement Compliance Policy:
Observing runs which do not adhere
to procedures and policies presented in this document will not be scheduled
for execution. If you feel you must violate one of these procedures or
policies, you must submit a Phase 2
Waiver Request before submitting any Phase 2 material.
Read the Manuals!
It is absolutely essential that all users read the following manuals:
The manuals above are listed in a hierarchical way - the most general p2pp
manual on the top and the more specific below. Similarly the instrument
specific instructions on this FORS service mode WEB page are supplementary
to the more general P2PP Service Mode
page.
Further useful information and tools for the OB preparation phase
can be accessed from the User Support
Department's Web pages (such as links to the Exposure Time Calculator,
object visibility, catalogues, etc.).
A tutorial on the use of P2PP
to prepare FORS observations is also available.
Observing Modes
FORS1:
For Service Mode observations during the coming observing period FORS1 is
offered with the following instrument modes:
| Mode Name | Observing method | Acquisition Mode |
IMA | imaging | fast & RRM |
| OCC | imaging with occulting bars | FIMS |
| MOS | multi-object spectroscopy (movable slits) | FIMS
|
| LSS | longslit spectroscopy | fast & RRM |
| IPOL | imaging polarimetry | fast & RRM |
| PMOS | multi-object spectropolarimetry | FIMS & fast -
SR mode only |
FORS2:
For Service Mode observations FORS2 is offered
with the following instrument modes:
| Mode Name | Observing method | Acquisition Mode |
IMA | imaging | fast & RRM |
| OCC | imaging with occulting bars | FIMS |
| MXU | multi-object spectroscopy (masks) | FIMS - SR
mode only |
| MOS | multi-object spectroscopy (movable slits) | FIMS -
SR mode only |
| LSS | longslit spectroscopy | fast & RRM |
| HITI | high time resolution imaging | fast - SR mode only |
The Rapid Response Mode (RRM), is offered for observations of transient phenomena such as Gamma-ray bursts or Supernovae in semi-automatic mode.
RRM is available for service observations only.
Some observing modes are only offered with the standard resolution (SR)
collimator. Mask preparation with FIMS is required for
observing modes OCC, MOS, MXU and PMOS.
Standard Instrument Configuration
General Policy:
Service Mode users can only request the standard instrument
configurations (opto-mechanical components and CCD) as summarized below and
as described in detail in the FORS
User Manual.
Deviations from these standard configurations or the standard CCD
setups for Service Mode must be specifically requested from ESO
before you submit your Phase 2 information. Please use the Phase 2 Waiver Request procedure.
ESO reserves the right to reject all such requests.
FORS1 standard configuration:
The standard configuration of permanently installed optical
(filters, grisms, retarder plates, collimator, Wollaston) and
mechanical components (slits, masks) is given in the FORS User Manual and summarized here
for the three filter wheels in the parallel beam and the two
interference filter wheels in the converging beam:
| wheel 1 | wheel 2 | wheel 3 | IF wheel 4 |
IF wheel 5 |
| Wollaston | GRIS_300V | GG375+30 | g_GUNN |
idle |
| g_HIGH+115 | idle | GG435+31 | idle |
idle |
| V_BESS+35 | GRIS_600B | OG590+72 | idle |
idle |
| R_BESS+36 | GRIS_600R | u_HIGH+112 | idle |
idle |
| idle | GRIS_150I | b_HIGH+113 | |
|
| GRIS_600V | GRIS_1200B | v_HIGH+114 | |
|
| idle | GRIS_1200g | I_BESS+37 | |
|
This standard configuration supports the vast majority of instrument
setups typically requested for visitor and service observing with the
following exceptions:
- Imaging polarimetry with FORS1 in g_HIGH, V_BESS and R_BESS and
spectro-polarimetry using grism 600V is not supported since the
subsequent optical components are in the Wollaston wheel.
- At most 6 interference filters can be requested for a service mode
project and at most up to 2 interference filters may be used in a
single OB.
All components of the FORS1 standard configuration remain at their
nominal location inside the instrument at any time. Interference
filters (IF) will be mounted into the idle positions, if so requested by
the service mode users.
FORS1 standard CCD setup:
The standard CCD setups for all FORS1 service mode observations are:
| Mode | Readout mode |
Imaging: |
200kHz,2x2,low |
| Spectroscopy: |
100kHz,2x2,high |
| Imaging polarimetry: |
200kHz,2x2,low |
| Spectropolarimetry: |
100kHz,2x2,high |
FORS2 standard configuration:
The standard configuration of permanently installed optical (filters,
grisms, collimator) and mechanical components (slits, masks) is given
in the FORS User Manual and
summarized here for the three filter wheels in the parallel beam and the two
interference filter wheels in the converging beam:
| wheel 1 | wheel 2 | wheel 3 | IF wheel 4 |
IF wheel 5 |
| GRIS_300V | GRIS_1028z | GG375 | FILT_465_250
| idle |
| GRIS_300I | GRIS_1400V | GG435 | U_SPECIAL |
idle |
| GRIS_200I | GRIS_600B | OG590 | idle |
idle |
| GRIS_150I | GRIS_1200R | B_BESS | idle |
idle |
| XGRIS_600B | GRIS_600I | V_BESS | |
|
| GRIS_600RI | z_GUNN | R_SPECIAL | |
|
| GRIS_600z | idle | I_BESS | |
|
Please note the following restrictions:
- FORS2 MXU and MOS observations are only supported in Standard Resolution
mode (SR).
- FORS1 MOS observations are only supported in Standard Resolution
mode (SR).
- At most 6 interference filters can be requested for a service mode
project.
- Not more than 10 MXU masks will be punched for a service mode project.
The components of the FORS2 standard configuration remain at their
nominal location inside the instrument at any time. Interference filters (IF)
will be mounted if requested by the service mode users into the idle
positions.
FORS2 standard CCD setup:
The standard CCD setups for all FORS2 service mode observations are:
| Mode | Readout mode |
Imaging: |
200kHz,2x2,low |
| Spectroscopy: |
100kHz,2x2,high |
No special and user-provided filters in service mode:
The use of non-standard or user provided filters during Service Mode
is not permitted for FORS1 or FORS2 Service Mode programmes.
Relative Astrometric Accuracy Requirements
Highly accurate relative astrometry is required for any observing mode which
will make use of FIMS or blind offset acquisitions. The mask
preparation with FIMS requires input images which are astrometrically
corrected within the definitions and precision given below. DSS images will,
in almost all cases, not be suitable for the task.
The target acquisition procedures have been reviewed and improved since
March 2003 based on new astrometric measurements. Earlier restrictions for
the use of contributed images from other telescopes are obsolete. Accurate
astrometry and properly defined world coordinate systems in the fits headers
are however required in this case. The relative astrometry must be known
better than 1/6 of the slit widths all over the field of view.
It is recommended to cross check the
values for the image scale and field distortion in other fields (in fields
with
astrometric standard stars).
These relative astrometric calibrations are fulfilled, if your
FIMS preparation is based on images taken with FORS1 after March 22, 2003
or on any FORS2 data (SITE and MIT CCDs). Pre-images taken with both
FORS1 (after March 22, 2003) and FORS2 (all dates) can be used
for mask preparations for both FORSes; FORS2 MXU mask preparation does
not anymore require pre-images which were explicitly taken with FORS2!
We recommend to search in the VLT
Science Archive for released FORS imaging data.
FIMS users with pre-imaging from wide field mosaic imagers should read
the important
note
regarding the World Coordinate System (WCS) keywords.
Submission of pre-imaging and MOS/MXU OBs
ESO will make every possible effort to execute all preimaging
as early as at all possible, and will release pre-images immediately. In
effect all pre-image OBs will be treated as ``carry-under OBs'', meaning
that they will be executed as soon as they are ready even if that is before
the period starts. To allow the immediate release of pre-imaging data,
it is important to set the Observation Category to 'PRE-IMAGE' within
any pre-imaging OBs.
For the Phase 2 proposers this means that it is important to submit
pre-imaging OBs as soon as possible, even long before the deadline.
The earlier we have the OBs, the earlier the pre-images will be taken,
and the higher the probability that follow-up MOS/MXU observations will be
completed within the narrow window of opportunity.
For the Phase 2 proposers it also means that it is important to
prepare the follow-up MOS/MXU OBs as soon as the pre-imaging data is released.
Since MOS/MXU is typically a dark time mode, it effectively means that Phase
2 proposers should strive to submit MOS/MXU OBs such that they are ready
for execution during the darktime following that of the pre-images. If one
darktime is missed, this limits the window of opportunity. If two darktimes
are missed, the OBs will be in jeopardy of failing to find a slot in the
schedule.
Pre-imaging data delivery: As soon as a pre-image is successfully
taken, the data will be immediately transfered to the ESO data archive in Garching,
where it will be automatically reduced (bias subtraction and flat fielding).
Reduced and raw data will then be available on a dedicated ftp account. Detailed
instructions on where to retrieve the data from, as well as further information
is send to the user by e-mail, typically the day after the pre-image was taken.
Please note that the data must be fetched from its ftp location within a certain
range of time, usually within a week. The data delivery process starts as soon
as the first pre-image is taken, i.e. not only after the whole pre-imaging run is
completed.
FORS Observation Block Requirements
Readers are assumed to be familiar with Observation Block (OB)
preparation and with the fact that OBs are constructed from observing
templates. If you are not familiar with these concepts, please see
the P2PP User Manual for a
general introduction. The available FORS templates are described in
the FORS Template Manual.
All observations must be prepared with these templates. Service Mode
OBs must be prepared with the version of the P2PP and FIMS software packages as
released on the ESO web page for the subsequent observing period.
General Requirements
Science OB naming conventions:
Please follow the naming rules on the
Service Mode Guidelines page.
One FORS mode per OB:
As a general rule, observing modes of the instrument must not be
mixed within a single OB. This implies that each OB should contain the
acquisition and observation description templates corresponding to the
selected instrument mode. In this respect, fast and FIMS based
observations in PMOS mode are to be considered as separate
instrument modes, i.e. the respective templates must not be mixed in
the OBs.
OB target coordinates are required:
Each science OB must have a target attached which gives the
presetting coordinates for the telescope.
The only exceptions from this rule are target-of-opportunity (ToO) OBs
for which the target coordinate default values (i.e. 0:00:00.0, 0:00:00.0)
should be used if the actual coordinates of the targets are not yet known
by the time of OB submission.
Classification of pre-imaging, science and standard star OBs:
For the science OBs the Observation Category must be set to 'SCIENCE', for
standard star OBs to Observation Catagory 'STANDARD' and for pre-images to
'PRE-IMAGE'. This is particularly important for urgent pre-imaging
OBs, since the keyword will trigger the fast data release.
FORS2 sky brightness and maximum integration times in I_BESS,
z_GUNN and order sorting filters
The maximum exposure times for R_SPECIAL, I_BESS and z_GUNN imaging
observations in dark time are 600s, 240s and 100s in dark time,
respectively. Exposure times for images without filters or order
separation filters (GG375, GG435 and OG590) should be kept below
1 minute during dark time. In case of longer integration times the
saturation level can be reached for the binned standard CCD mode.
With the bright moon above the horizon the maximum exposure times may
be even shorter.
Using acquisition images for science?
The acquisition images to center the target on the slit may be skipped
or shortened for operational reason even if there is a request in the
ReadMe file not to do so. You must submit an imaging OB if your science
depends on these images.
Spectroscopic and high-time resolution mode OBs
Through-slit images required:
Any FORS spectroscopic OB must include a through-slit imaging template
after the acquisition template but before the first science template.
In other words, all spectroscopic Observation Descriptions must have the
following order:
- FORS1/2_MODE_acq(_fast)
- FORS1/2_MODE_obs_slit(_fast)
- FORS1/2_MODE_obs_off(_fast)
The through-slit exposure time should be defined so that it allows
the service observer to see the target(s) or (a) user selected
reference object(s) in the slit(s). The exposure time should be
calculated for the specified OB Constraint Set.
The high-time resolution imaging mode requires to center a star on the
slit and it will require a through-slit image to center the target like
the spectroscopic observations.
Standard Star OBs
FORS calibration plan:
The FORS User Manual outlines which standard star exposures are supported
by the FORS Calibration Plan. If that is sufficient for your calibration
goals, no special calibration OBs need to be submitted
(more information on the P2PP Service Mode
page).
A list of
FORS1 and
FORS2 Standard Fields and Stars is available on the WEB.
Calibration OBs
General requirements:
The FORS User Manual outlines which calibration exposures are supported
by the FORS Calibration Plan. If that is sufficient for your calibration
goals, no special calibration OBs need to be submitted.
Lamp calibrations should never be attached to science OBs to be executed
during nighttime.
All FORS calibration OBs must begin with the template FORS1_img_cal_coll or
FORS2_img_cal_coll and end with the respective templates to obtain flat
field and arc exposures:
- FORS1/2_img_cal_coll
- FORS1/2_MODE_cal_scrflat(_fast)
- FORS1/2_MODE_cal_wave(_fast)
Lamp calibrations only at daytime:
It is not possible to obtain calibration lamp exposures during the night.
Only daytime lamp calibrations will be taken. The level of accuracy
achievable with such calibrations is described in the
FORS User Manual.
FIMS: The FORS Instrumental Mask Simulator
The FORS Instrumental Mask
Simulator (FIMS) plays an essential role in the preparation of
FORS OBs. In particular, FIMS is used to generate configuration files that
specify target acquisition and focal plane assembly setups for many FORS
configurations, including MOS, MXU, PMOS and imaging
observations with occulting bars. For the MXU mode, FIMS also produces
the file which specifies how to manufacture the MXU mask on the laser
punching machine.
A separate FIMS Installation
Page is available. Please consult the
FIMS Manual about how to use
FIMS for the mask preparation.
The FIMS tool supports both FORS instruments. However, users must be
careful to select the correct instrument, because the FORS1 and FORS2 FIMS
files are incompatible due to intrinsic optical differences between these
two instruments:
- unix> fims.sh 1
for all FORS1 observations
- unix> fims.sh 2
for all FORS2 observations
Critical: never manually edit the P_TARG, P_FOCF, or P_GBR files
produced by FIMS! Most editors may add some bytes like hidden return
characters which can cause failures at the execution time!
Save your FIMS output files:
Three or four (MXU only) output files will be created (suffixes
.p_targ, .p_focf, .p_gbr, .fims) in directory .fims/SET/ whenever a FORS
focal plane setup is saved. We strongly recommend that you retain these
files as well as the respective input image for future reference.
We may request these files from you for review during the troubleshooting
process in case of problems.
FIMS or fast:
Observation in modes IMG, IPOL, LSS and single target observations in
"PMOS" mode can be done without using FIMS. For
faint targets we support blind offset acquisition modes for all the fast modes,
but the astrometric requirements are similar for blind fast acquisitions and
FIMS acquisitions. In general the OB execution won't be much faster, but the
OB preparation will!
Important special constraints for MXU reference slits:
The MXU reference slits are not selectable by the users but
there will be by default 6 reference pinholes defined automatically.
FIMS highlights their location with a red line. WARNING: these
pre-defined reference holes have to be within the boundary of the
pre-image (no matter if in the vignetted area or not) to apply
the conversion from pixels to world coordinates.
FIMS will remove the pinholes which are outside the image and will save a
valid output file which can be used for the target acquisitions.
To get all six reference slits back you must press (FORS2> Reset Mode)
before preparing any new masks.
FORS Finding Charts
General requirements:
All FORS finding charts must comply with the specifications given
on the general P2PP
Service Mode page. Note that since ESO Period 73, all Finding Charts
must be created as Jpeg files and directly attached to one or more OBs withing P2PP.
More information on this change is available on the general
Service Mode
Guidelines web-page, as well as in
the P2PP User Manual
FORS specific requirements for FIMS users:
Occasionally the user selected reference stars have to be identified
by the service mode observer interactively. Therefore the
finding charts generated with the FIMS tool are mandatory for all
FIMS based observing modes: OCC, MOS, MXU and PMOS.
The finding charts prepared with FIMS must comply with the general
specifications given on the P2PP
Service Mode page. The finding
chart plugin distributed with the FIMS software provides a
convenient way to do so. Please note that some popular tools to view
jpeg files, most notably xv,
do not display the files at full resolution, and the chart may appear
of low quality. When attached to OBs with P2PP, however, the full
resolution of the finding charts is preserved.
Please include the following requirements:
- Use the label option of the FIMS tool to get the FORS specific
labeling of the finding chart automatically correct (i.e. this gives
the coordinates of the field center, the rotator angle, indicates the
field of view, the reference and target objects, the slit geometry,
wavelength coverage etc.)
- For FIMS based OBs the finding chart must contain an overlay
of the full FIMS field clearly showing the reference stars and the slit
geometry.
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