P2PP: CRIRES Information

News for Period 81

The `Additional Requirements for CRIRES Finding Charts' were modified.
Under special circumstances the Finding Charts can be skipped by a Phase 2 Waiver Request.

This page contains information specific to the creation of CRIRES Observation Blocks (OBs) for Service Mode programmes. For more general OB creation information, see the P2PP Web page.

Requirement Compliance Policy: Observing runs which do not adhere to the 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.

This document has the following sections:

General

Read the Manuals
CRIRES P2PP tutorial
Additional requirements for CRIRES Finding Charts
Additional Conditions for Waiver Requests
Additional Conditions for the README file
Classification Rules

CRIRES OB Requirements and Recommendations

Observing Modes and Templates

OB Naming Conventions
DIT and NDIT

Guide Stars
Calibration Plan

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 describes how to create Observation Blocks, whereas the more specific CRIRES User Manual gives an overview of the CRIRES instrument and its operating modes and overheads, appropriate for proposal and observation preparation. The Template Reference Manual, the CRIRES calibration plan, and the standard instrument configuration are part of the CRIRES User Manual.

Further useful information and tools for the OB preparation phase can be accessed from the User Support Services and Tools web page, such as links to the Exposure Time Calculator, object visibility, catalogues, etc...

Also, we recommend to check the CRIRES Web pages for the most up-to-date information on the status of the instrument.

CRIRES P2PP Tutorial

A CRIRES P2PP Tutorial has been prepared to guide you through the preparation of successful Observation Blocks (OBs).

Additional Requirements for CRIRES Finding Charts

In addition to the general requirements for finding charts, the following requirements should be fulfilled:

Finding charts should be provided for a field size of 50" x 50", with a clear indication of field orientation. The target should be clearly marked by an arrow. If observations are performed with the derotator in SKY mode, the slit orientation should be clearly drawn.
For high proper motion stars (>1"/year) the present day position should be indicated by an arrow pointing from the target in the chart to the present day position (especially if similar bright sources are around).
Finding charts are to be provided based on existing infrared images obtained in J, H or K-band. Typically, 2MASS or DENIS images are acceptable, although higher spatial resolution is preferable, especially for crowded fields. The finding charts have to show the field in the NIR band closest to the observing wavelength, λ_OBS:
- in J band, if 950 nm < λ_OBS < 1300 nm,
- in H band, if 1300 nm < λ_OBS < 2000 nm, or for very bright targets,
- in K band, if 2000 nm < λ_OBS < 5400 nm.
Note that the ESO infrared digitized sky II actually coerresponds to the I band and should not be used if other infrared images are available.
If the wavelength at which the finding chart has been taken is different from that of the science observation, the user has to clearly describe in the README file section Programme Description how to identify the target at the wavelength of acquisition. Adequate examples of such comments could be:
- the source is the brightest object in the field of view in H-band, or
- two bright sources are expected in our field of view. The science target is the southernmost of the two.
In crowded fields, a second finding chart should be attached to the corresponding OB, with a zoom-in on the science target(s).
For observations using AO it is mandatory to indicate the location of the AO guide star on the finding-chart, because the AO system is operated blindly (i.e. the instrument operator has no image of the field in the optical bandpass used by the AO).
It is mandatory to indicate the location of the SV guide star, if different from the AO guide star and/or science target.
If the AO guide star or the SV guide star are less than 15 arcsec from the edge of the finding chart (centered on the target), another 2' by 2' finding chart should be provided.

The finding chart plugin to SkyCat provides a convenient way to prepare ESO-compliant finding charts. Finding charts must be in JPEG format and must be attached to the corresponding Observation Block in P2PP (see the Finding Chart Tutorial for more information).

Additional Conditions for Waiver Requests

In addition to the general Phase 2 Waiver Request policies, waiver requests have to be submitted for any of the following conditions:

if a DIT larger than 600s is used,
if a DIT larger or equal than 60s is used that is different from the recommended values 60, 90, 120, 180, 300, or 600s,
if a slit width larger than 0.4 arcsec is used,
if a free wavelength setting is used,
if the finding chart should be skipped, which only is possible if the following conditions are met:
- there is no other source within the 50" x 50" field that has a magnitude similar (within 2 mag) to the target star in the observed band (this applies to science targets as well as telluric standards),
- the target/telluric is not variable (to avoid confusion with fainter stars at the faint passage through the variability curve),
- the present day position of a high proper motion target with respect to the surrounding sources fulfills the first condition.
Note that, if the waiver was granted, but nevertheless the target appears double or ambiguous during observations, the night astronomer will either pick one source according to his/her best judgment, or cancel the OB.

Additional Contents for the README file

In addition to the general README policies, the following points should be clearly mentioned in the README file:

the list of OBs that do not require observations of a telluric standard star,
alternatively, any requirements regarding standard stars that deviate from the usual association of 1 telluric OB with 1 science OB,
In NoAO mode, if at least one of the RA or DEC offset between target and Slit Viewer guidestar (SV GS) is larger than 22.5 arcsec. In this case, the SV GS falls outside of the SV field of view. It is used only as a reference star: no guiding on the SV GS will be possible.
In case the finding chart was skipped by a waiver a remark on the unambiguousness of the target in the field of view should be added.

Classification Rules

General Policy:

Quality Control of OBs executed in Service Mode will be based on the user's specified constraints for airmass, atmospheric transparency, seeing, as well as Strehl ratio for AO mode observations. Moon constraints are only necessary in a limited number of cases.

Moon constraints:

Moon does not affect observations obtained by CRIRES. However, as the wavefront sensor is sensitive in the R-band, restricted moon constraints are only meaningful for AO observations with a natural guide star (NGS) fainter than R = 15 mag. In these cases, reducing the FLI constraint to approximately 0.7 and increasing the distance to the Moon to approximately 50 degrees is generally adequate. Even here, it is important not to over-specify the constraints, as this reduces the chances of the Observation Block to be executed.

Note, however, that telescope guiding and active optics can, under certain circumstances, be compromised for moon distances < 30deg.

Seeing: FWHM and on-axis Strehl ratios for adaptive optics observations using a Natural Guide Star:

For closed loop AO observations, the users must specify in the constraint set the desired on-axis Strehl ratio, i.e. the ratio of the maximal intensity of the PSF to the maximal intensity expected for the theoretical PSF with no turbulence. This is the main parameter regarding atmospheric turbulence. It should be set for the K band; this value is produced by the ETC.

In addition, all closed loop AO observations should enter also the FWHM of the seeing, although this constraint is less relevant. The constraint on the seeing refers to the seeing measured by the DIMM or by the guide probe, as they are the most relevant for the MACAO system. It is used as a guide, together with the coherence time, in order to estimate the achievable Strehl ratio.

If the AO star is not the science target, it is worth noting that the isoplanetic angle depends on (airmass)^-8/5, and on the wavelength as λ^6/5. On the other hand, the Strehl ratio, SR, decreases with the angular distance to the AO star θ as SR ∝ exp(-(θ/θ₀)^5/3).

Seeing: FWHM for seeing limited observations, no adaptive optics (NoAO):

For NoAO observations, only the seeing at the wavelength of observations is relevant. The user should therefore specify the FWHM for the respective bands of the science observations. The constraints set and definitions are the same as for all other seeing limited VLT instruments. The input field for the Strehl ratio should remain unchanged.

The classification of each observation will be based either (a) on the measured spatial profile of the spectrum if the object is a point source, or (b) on FWHM of a star seen on the Slit Viewer if there are more stars available, or (c) on the seeing measured on the guide probe otherwise.

Atmospheric transparency

Photometric conditions (PHO) should be asked only for spectrophotometry. Observations in AO mode with an AO star fainter than about R = 15 should preferably require CLR conditions. For all other cases, thin clouds conditions (THN) usually suffice.

Observing Modes and Templates

CRIRES is currently offered in the following two basic modes:

NGS	with adaptive optics using a Natural Guide Star
NoAO	with no adaptive optics

The preparation of Obervation Blocks (OBs) is simple, as the number of relevant templates is small: 2 acquisition templates, each corresponding to one of the 2 above-mentioned observing modes, 3 science observing templates and 3 calibration templates:

Acquisition

CRIRES_spec_acq_NGS (with adaptive optics)
CRIRES_spec_acq_noAO (without adaptive optics)

Science

CRIRES_spec_obs_AutoNodOnSlit (nodding along the slit)
CRIRES_spec_obs_GenericOffset (general nodding offsets)
CRIRES_spec_obs_SpectroAstrometry (multiple slit orientations)

Calibration

CRIRES_spec_cal_LampFlats (lamp flat)
CRIRES_spec_cal_Wave (wavelength calibration)
CRIRES_spec_cal_AutoNodOnSlit (for telluric or spectro-photometric standard stars)

A detailed description of the templates and their parameters is provided in the CRIRES User Manual and the complete list of central wavelengths is also available from the CRIRES instrument page.

The wavelength setting is usually determined by only one input parameter, the reference wavelength, that corresponds to the wavelength at pixel 512 of the 3rd detector. In a small number of cases, this reference wavelength does not unambiguously determine the grating order, which therefore must be given. In these cases, users should refer to the ETC to determine the grating order most suited to achieve their science goal, e.g. based on the S/N at the wavelength of interest.

Standard wavelength settings should preferably be used, as they correspond to settings that can be best calibrated. In particular, the wavelength calibration of these settings is accurate to within 3 pixels in general. Since P80, users must request a Phase 2 waiver for selecting a free wavelength setting.

OB Naming Conventions

When preparing calibration OBs for standard (telluric and/or spectrophotometric) stars the OB name should always starts with the prefix CAL .

OB Comment Fields

Each OB has two Comment Fields: the User Comments and the Instrument Comments. The first field is not mandatory and it is usually used to specify comments relevant to the execution of that specific OB (e.g. it should be followed by its calibration OB).

Instead, it is mandatory to provide some specific information in the Instrument Comments field in P2PP. In the case of CRIRES, this information must include:

targeted S/N ratio per pixel and per single exposure at some reference wavelength
R magnitude of the AO guide star, if relevant
the magnitudes of the SV guide star and of the science target, in the observing band
the spectral type of the telluric star (only in calibration OBs for telluric standard stars) including the range of allowed spectral types

Example for a science OB : S/N=200 @ 2200nm; R_AO=8; H_SV=7.5; H_OBJ=10.
Example for a telluric OB : S/N=200 @ 2200nm; R_AO=8; H_SV=7.5; H_OBJ=10; SpTyp=B2V, range: B1 - B4.

DIT and NDIT

The appropriate choice of DIT and NDIT should be made with the help of the CRIRES ETC. In principle, the choice of the DIT is totally free between the minimum of 1s and the maximum of 900s. In practice, in order to be able to properly calibrate all the nighttime observations during daytime,

observations of bright targets (J,H,K ∼ 8-10 mag) should preferably use one of the following DITs: 1s, 1.5s, 2s, 3s, 5s, 7s, 10s, 15s, 20s, 30s, 45s. In particular, to avoid saturation of the sky, observations in the L or M bands should use a DIT of 10s or less.
for faint targets, only the following DITs can be used: 60s, 90s, 120s, 180s, 300s, 600s. DITs larger than 600s or different from the recommended values can in principle still be accomodated, but a Waiver request must be submitted.

Users should instead change the NDIT parameter in order to achieve the desired S/N ratio.

AO and Slit Viewer Guide Stars for CRIRES

The following constraints exist for Adaptive Optics and Slit Viewer guide stars:

AO guide stars also called Natural Guide Stars (NGS) cannot be brighter than 2nd magnitude. Stars of R = 17 or fainter will not bring any improvement to the image quality.
Slit Viewer Guide Stars (SV GS): reasonable SV guiding on a slit wider than 0.3 arcsec is not possible for objects fainter than J = 14.9, H = 14.5 or K = 14.4 in seeing better than 0.9 arcsec.
Note: Guiding on an offset star in ELEV mode is not implemented.

CRIRES Calibration Plan

The CRIRES instrument is calibrated by the Science Operations staff in the morning after the science observations. All instrument setups used in the science observations are calibrated automatically.

The following table summarises the standard calibration products provided by the observatory.

CRIRES Science Data Calibration Plan
Calibration	Number	Frequency [1/days]	Comments
Flatfields	1	1 / 1	With the same wavelength setting and a slit width of 0.2 arcsec, and DIT of at least 2 seconds.
Darks	3	1 / 1	With the same DIT as the science and standard star observations; each exposure with NDIT=3
Wavelength	1	1/1	Using a 0.2 arcsec slit, with ThAr lamp or N2O gas-cell, depending on reference wavelength. Only if reference wavelength is shorter than 2400 nm.
Bad-pixel maps	1	1 / 180	Derived from Darks and Flatfields (one per detector)
Distortion map	1	1 / 365	To be be checked on a yearly basis or after instrument warm-up

If additional calibrations are required, this must be discussed in advance with the support staff at USD (usd-help@eso.org).

IMPORTANT NOTE: Telluric and/or spectro-photometric standard stars are not part of the Observatory CRIRES Calibration Plan. Users should submit dedicated OBs (using the template CRIRES_spec_cal_AutoNodOnSlit) and the total execution time will be charged to their OPC allocated time. The user is also required to specify in the Instrument Comments field of each 'telluric' OB the spectral type of the standard star, as well as a range of permitted spectral types. This is very important, as the Observatory, in order to optimize the quality of a given observation, may need/decide to observe a different telluric standard star, which will then be chosen according to the spectral type specified by the user. This usually happens if the difference in airmass between the science target and the user-provided telluric star is larger than 0.2 (except if specifically mentioned otherwise in the README file), or if meteorological conditions do not allow to observe the telluric specified by the user. In such case, exposure times will be adjusted according to the targeted S/N ratio per pixel (also to be provided in the Instrument Comments field).

In particular, the README file should explicitly mention OBs that do not require observations of a telluric standard star.

At present no high precision IR atlas of standard stars with bona fida spectra exists, but the CRIRES team plans to compile such a list and make it available on the CRIRES webpage.