P2PP: VIMOS Information

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Users can define the number of screen flat-field exposures to be taken during attached night-time calibrations. In IFU mode, the mandatory minimum number of screen flat-field exposures is 1 for each grism + filter combination, except for HR_blue grism. The minimum number of attached screen flats for HR_blue grism is 3. Overheads will be charged accordingly to the number of screen flats obtained.

Table of Content

Introduction
Read the Manuals!
Observing Modes
Standard Instrument Configuration
Relative Astrometric Accuracy Requirements
Guide Star information is mandatory - Guidecam
MOS OBs must be submitted soon after Pre-Imaging is obtained
Pre-Imaging
Imaging
VIMOS Observation Block Requirements
VMMPS: The VIMOS Mask Preparation Software
VIMOS Finding Charts

Introduction

This page contains information specific to the creation of Observations Blocks (OBs) for VIMOS Service Mode programmes. 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.

Reminder concerning the quality control grading of VIMOS observations: As stated in the Call for Proposals, any set of MOS data obtained with VIMOS in Service Mode where at least 3 of the 4 arms functioned will be considered an observation completed within constraints.

Read the Manuals!

It is absolutely essential that users read the following manuals:

P2PP User's Manual: this manual describes how to create Observation Blocks
VIMOS User's Manual: this manual gives an instrument overview appropriate for proposal and observation preparation, and includes the Template Reference Manual. The VIMOS calibration plan and the standard instrument configuration are explained here as well as the overhead times.
Guidecam User Manual: this manual describes how to use Guidecam, a tool allowing the user to select a suitable guide star for their (pre-)imaging observations.
VMMPS User's Manual: this manual describes how to use the VIMOS Mask Preparation Software (VMMPS) for the Multi-Object Spectroscopy (MOS) mode.

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 VIMOS service mode WEB page are supplementary to the more general available from the Service Mode Guidelines page.

Further useful information and tools for the OB preparation 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 VIMOS pre-imaging and MOS observations is also available.

Observing Modes

VIMOS is offered in the following instrument modes:

IMA	imaging
MOS	multi-object spectroscopy (masks)
IFU	integral field spectroscopy

Standard Instrument Configuration

General Policy: In order to maintain the calibration needs at a manageable level, a limited number of standard instrument configurations (opto-mechanical components and CCD) can be offered in Service Mode. These standard configurations are summarized below and described in detail in the VIMOS User's Manual. Deviations from these standard configurations or the standard CCD setups for Service Mode must be specifically approved by ESO before you submit your Phase 2 information. Please use the Phase 2 Waiver Request procedure. ESO reserves the right to reject such requests if not sufficiently justified or if they risk imposing an excessive operational burden.

VIMOS standard configuration:

The standard configuration of permanently installed optical components (filters, grisms) is given in the VIMOS User's Manual and summarized here:

FILTERS	GRISMS
Free	Free
U'	HR_red
B	HR_orange
V	HR_blue
R	MR
I	LR_red
z	LR_blue
OS_blue
OS_red
GG435
GG475

The configuration is the same for the 4 channels. All components of the VIMOS standard configuration remain at their nominal location inside the instrument at any time.

VIMOS standard CCD setup:

The standard CCD setups for all VIMOS service mode observations are:

Imaging:	225_Low_Gain
MOS:	225_High_Gain
IFU :	225_High_Gain

Relative Astrometric Accuracy Requirements

The mask preparation with VMMPS requires the use of both input catalogues and pre-images. Highly accurate relative astrometry is required for the MOS mode, in the sense that the object positions in the input catalogue must be known relative to those of reference stars in the field of view to better than 1/6 of the slit widths all over the field of view. The pre-image is, then, used to link the astrometric solution of the input catalogue to the VIMOS FOV. Therefore, pre-images taken with VIMOS are mandatory for VIMOS MOS mode observations.

Guide Star information mandatory for (pre-)imaging: Guidecam

The field of view of VIMOS is large! There is, therefore, very limited unvignetted space in the Nasmyth focus field of view to find a suitable guide star. In some occasions it will not be possible to find a guide star which does not vignet the VIMOS field of view.

Guidecam is a Skycat-based tool that allows to select a guide star from catalogues overlaid on the focal field of view, the VIMOS field of view and of the telescope guide probe. In view of the experience obtained during the previous semesters of VIMOS operations, the selection of a guide star by the user with the Guidecam tool is mandatory for all (pre-)imaging observations. The user must select a guide star which does not vignet the field of view or, in case this is not possible, a guide star that produces acceptable vignetting, for example by blocking only those regions of the detector array where no objects of scientific interest are found.

Once the user selects a guide star, its coordinates must be entered in the OB ('Guide Star RA' and 'Guide Star DEC' entry fields), and the 'Get Guide Star from' entry field in the acquisition template (e.g. VIMOS_img_acq_Preset) should be set to SETUPFILE.

Please select the guide star carefully, especially in the case of imaging observations involving offsets! It is the responsibility of the user to check with Guidecam that the chosen guide star does not produce unacceptable vignetting in any of the frames to be produced by the execution of an OB. ESO will consider as executed within specifications an OB producing vignetted frames, implicitly assuming that such vignetting was already verified by the user and found to be acceptable.

In case that the selected guide star turns out to be inaccessible during the execution of the OB, the telescope operator will try to select an alternative one and use it for the observation, even if this alternative guide star produces vignetting. ESO reserves the right to charge to the time allocated to the run the time spent in identifying and setting up the alternative guide star.

Please consider also the following points:

The Guide Star used during pre-imaging will be automatically used also for the follow-up MOS observations.

The Guidecam tool must be used for the preparation of all VIMOS (pre-)imaging finding charts, which should clearly indicate the guide star to be used.

MOS OBs must be submitted soon after Pre-Imaging is obtained

The lack of atmospheric dispersion correction places severe limits on the time window in which observations through a MOS mask can be successfully executed. In practice the requirements are that both pre-imaging and MOS of the same field must be obtained while the field is plus/minus 2 hours from the meridian. It is the user's responsibility to make sure that the airmass constraints specified in the OBs do not conflict with this operational requirement, i.e. the airmass constraints must be set such that they correspond to +/-2 hours or less from the meridian:

Users may request to waive this rule, but are advised to carefully consider the potentially severe and negative effect this will have on their data quality.

Important information specifically on the rules for submission of follow-up MOS OBs is available. MOS OBs only need to be submitted after pre-imaging is received (no dummy MOS OBs should be submitted at the general Phase 2 deadline).

ESO will make every possible effort to execute all pre-imaging as early as possible, and will release pre-images immediately. In effect all pre-imaging 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.

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 valid OBs are submitted, the earlier the pre-images will be taken, and the higher the probability that follow-up MOS observations will be completed within the narrow window of opportunity.

Pre-Imaging

VIMOS Pre-Imaging is mandatory prior to MOS follow-up. All MOS programs must have a specific Run ID devoted to pre-imaging (i.e., a typical MOS programme consists of a run (A) devoted to pre-imaging, and a run (B) for the ensuing MOS). The following instructions for preparation of pre-imaging OBs should be strictly followed:

Run ID

It is mandatory to use the Run ID corresponding to the pre-imaging run. Please check your Phase 1 proposal if you are unsure as to which run is the one for pre-imaging.

Observation Category: PRE-IMAGE

It is mandatory to set the Observation Category to PRE-IMAGE in the observation template (VIMOS_img_obs_Offset). Failure to do so will result in delays to process and deliver the pre-imaging data, and may result in MOS observations not being carried out.

Pre-imaging Filter

Because the masktoCCD solution is computed using R filter, pre-imaging taken with R filter is mandatory in order to minimize the slit losses.
Should any other filters be required, users must apply for a Phase 2 Waiver before these pre-imaging OBs can be accepted.

Rotator on sky

MOS masks will have the same orientation on the sky as the corresponding pre-images. In order to minimize the slit losses due to atmospheric dispersion, in the case of pre-imaging the rotator on sky, otherwise called position angle on sky, is not a free parameter. The default value (90) corresponds to an orientation of the field with E to the top and N to the left, in which slits are aligned with the parallactic angle at meridian crossing. Users might request to waive this rule, but are advised to carefully consider the potentially severe and negative effect this will have on their data quality.

Effect of atmospheric dispersion

As for MOS OBs, the lack of atmospheric dispersion correction places severe limits on the window in which pre-imaging OBs can be successfully executed. In practice the requirements are that both pre-imaging and MOS of the same field must be obtained while the field is plus/minus 2 hours from the meridian. It is the user's responsibility to make sure that the airmass constraints specified in the OBs do not conflict with this operational requirement, i.e. the airmass constraints must be set such that they correspond to +/-2 hours or less. Users might request to waive this rule, but are advised to carefully consider the potentially severe and negative effect this will have on their data quality.

Typical orientation on sky for spectroscopic follow-up will be such that the slits are oriented along the N-S direction. Deviations from this default value must be specifically approved by ESO before you submit your Phase 2 information. Please use the Phase 2 Waiver Request procedure for this purpose, and note that the waiver may be rejected if not sufficiently justified or if it risks imposing an excessive operational burden.

VIMOS Imaging

The requirements for pure imaging programmes are somewhat different from the pre-imaging requirements.

Observation Category: SCIENCE

The 'Observation Category' entry field must be set to SCIENCE in the observation template (VIMOS_img_obs_Offset).

Rotator on sky

The rotator on sky, otherwise called position angle on sky, can be set to any value for pure imaging programmes, i.e. without immediate spectroscopic follow-up. For future spectroscopic follow-up with VIMOS, it is strongly recommended to keep the default value of 90 degrees for this parameter. This will simplify the design of the masks downstream.

Size of offsets and guide stars

Experience with VIMOS operations has shown that, as a rule, imaging observations involving cumulative offsets greater than about 30 arcsec often result in significant vignetting of the field by the guide probe. For this reason, all dither points for offset patterns used in imaging OBs must fit inside a box of size 30 by 30 arcsec. Should a larger offset pattern be needed, users are requested to use separate OBs for the offset positions, using an appropriate guide star for each of the OBs.

If you have a well justified reason to wish to override the limit on the 30 arcsec offset box within a single OB, then you may submit a Phase 2 Waiver Request. However, you should make sure by using Guidecam in advance to submitting your request that a suitable guide star exists that can be used for all the offset positions, and that any vignetting that may result in the resulting frames is acceptable for the scientific purpose of the observation. In any case, if the waiver is accepted, it will be so under the conditions expressed above.

VIMOS Observation Block Requirements

Users 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's Manual for a general introduction. The available VIMOS templates are described in the VIMOS User's Manual. All observations must be prepared with these templates. Service Mode OBs must be prepared with the version of the P2PP, VMMPS and/or GUIDECAM tools as released on the ESO web page for the current observing period.

General Requirements

Science OB naming conventions:

Instrument mode (PRE/IMG/MOS/IFU) should be clearly specified at the beginning of the OB name; therefore the name of all the imaging OBs should start with IMG (e.g IMG_NGC0000_xxx), and the same applies for the OB names for IFU and MOS. Please see also the naming rules on the Service Mode Guidelines page.

One VIMOS 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.

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 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. For the VIMOS_acq_mos_Mask template the target coordinates are automatically loaded in the OB through the mask definition files (ADP files).

Night calibrations

Night calibrations (arcs) are mandatory for MOS OBs using HR_blue or LR_blue grisms, i.e. when using these grisms the VIMOS_mos_cal_NightCalib template should be attached as the last template to MOS OBs.

Night calibrations (arcs and flats) are mandatory for all IFU OBs, i.e. the VIMOS_ifu_cal_NightCalib template should be attached as the last template to all IFU OBs.

Classification of pre-imaging and science OBs:

For the science OBs the Observation Category must be set to 'SCIENCE', and for pre-imaging OBs to 'PRE-IMAGE'. This is particularly important for pre-imaging OBs, since the keyword will trigger the fast data release which is imperative for successful execution of the follow-up MOS OBs.

Standard Star OBs

VIMOS calibration plan:

The VIMOS User Manual outlines which standard stars exposures are supported by the VIMOS Calibration Plan. If that is sufficient for your calibration goals, no special calibration OBs need to be submitted (more information on the Service Mode Guidelines page).

Calibration OBs

General requirements:

The VIMOS User Manual outlines which calibration exposures are supported by the VIMOS Calibration Plan. If that is sufficient for your calibration goals, no special calibration OBs need to be submitted.

VMMPS: The VIMOS Mask Preparation Software

The VIMOS Mask Preparation Software (VMMPS) plays an essential role in the preparation of VIMOS MOS OBs. In particular, VMMPS is used to generate the configuration files that specify target acquisition and mask manufacture for MOS observations (ADP files). VMMPS is only required for the preparation of MOS OBs, not for the pre-imaging OBs. Since MOS OBs should be submitted as soon as possible after the pre-images have been released, we strongly recommend that Phase 2 proposers with approved MOS runs download the software and test its functionality well ahead of the pre-image release.

A separate VMMPS Installation Page is available.

Critical: never manually edit the ADP files produced by VMMPS!

Critical: never use an old version of the VMMPS software!

VIMOS Finding Charts

General requirements:

All VIMOS finding charts must comply with the specifications given on the general Service Mode Guidelines page.

VIMOS specific requirements for VMMPS users:

The user-selected reference stars have to be identified and the slit alignment checked by the service mode observer interactively. Therefore, the VMMPS tool must be used for the generation of finding charts in MOS mode (the focal field setup can be displayed over the pre-image via the VIMOS-MPS -> Verify ADP File menu in VMMPS). One finding chart per quadrant needs to be produced and attached to the corresponding OB(s). The finding charts prepared with VMMPS must comply with the general specifications given on the Service Mode Guidelines page. The finding chart plugin distributed with the VMMPS software provides a convenient way to do so.

VMMPS-based finding charts must be saved in jpeg format from the VMMPS File -> Make finding chart... window and must contain an overlay of the full VMMPS field clearly showing the reference stars and the slit geometry. The high resolution image generated in this way will allow to verify at the telescope the successful acquisition of the objects in the slits. 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.

VIMOS specific requirements for imaging (including pre-imaging) runs:

The Guidecam tool must be used for the generation of finding charts in imaging mode. The finding chart plugin distributed with the GUIDECAM software provides a convenient way to prepare ESO-compliant finding charts.

VIMOS specific requirements for IFU users:

Since the target to be observed cannot be seen in an acquisition image once the IFU has been deployed, it is often difficult to assess whether or not the telescope is presetting to the desired position. For this reason, the following is required:

A 5' x 5' Digitized Sky Survey view of the field centered on the preset coordinates of the telescope. The field of view of the chosen IFU mode should be clearly indicated on the chart, together with the the distance between the center of the IFU field of view and the closest visible star. The requirement of using the DSS is mandatory, and motivated by the need to ensure that all the objects in the finding chart can be identified in the Guidecam display used at the telescope. The finding chart plugin to SkyCat provides a convenient way to prepare ESO-compliant finding charts.