P2PP: AMBER Information

This page contains information specific to the creation of AMBER Observation Blocks (OBs) for Service Mode programs. 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:

Read the Manuals
AMBER P2PP Tutorial
Target coordinates
Visibility Calculator
Calibrator Selection
Additional Requirements for AMBER README Files
Additional Requirements for AMBER Finding Charts
OB Naming Conventions
Matching of Science target and calibrator OB names
P2PP Constraint Set

Read the Manuals

It is essential that all users read the following manuals:

AMBER User Manual

AMBER Template Manual

P2PP User Manual

It is useful to check the AMBER Web pages for recent updates.

Further useful information and tools for the OB preparation can be found on the User Support Services and Tools Web page (for instance exposure time calculator, object visibility, catalogues, etc.)

P2PP Tutorials

A instrument-specific AMBER P2PP Tutorial has been prepared to guide you through the preparation of successful Observation Blocks (OBs) for AMBER observations.

A general README tutorial is available to guide you through the creation of README information.

A general Finding Chart Tutorial guides you through the attachement of Finding Charts. This tutorial includes also a part dedicated to attaching ephemeris files.

Target coordinates

A special care should be taken when entering the target coordinates in P2PP. We have made best experience with 2Mass coordinates. Also, to ease fringe finding during the observations, proper motion of the target must be entered in P2PP (provided this information exists).

Visibility Calculator

To prepare and plan your VLTI+AMBER observations, we recommend to use the Visibility Calculator VisCalc. The assessment of the feasibility of an observation requires an estimate of the expected visibility for the chosen VLTI configuration. Furthermore, the scientific goal of an interferometric observation campaign can often only be reached if visibility measurements at different projected baseline lengths and/or baseline angles are combined. VisCalc provides calculations of simulated visibilities as a function of hour angle based on software models of the VLTI instruments. The best suited hour angles can be identified using VisCalc, and the corresponding LST (Local Sidereal Time) interval for each OB, i.e. each instantaneous visibility measurement, must be specified in each OB. In case that from a scientific point of view there is no restriction for the LST range to be used, the LST range in the OB must reflect the range when the target is higher than 30 degree above horizon, and when the observation is not unfeasible due to delay line restrictions and shadowing effects (see the section about the LST constraint below). See also plots of the VLTI pointing restrictions in the declination/hour angle space at http://www.eso.org/observing/p2pp/AMBER/vlti_pointing_restrictions.html.

A common problem in interferometric observations is that the proposed target is clearly larger than estimated, and thus over-resolved, we strongly encourage you to collect as much information on your target as possible. It may be advisable to organize imaging studies with single-telescope instruments before conducting AMBER observations if you have strong doubts about the extension of your proposed target.

Calibrator Selection

You are requested to submit a calibration star OB for each science star OB. This pair of science star/calibration star OBs will be executed in a row in order to monitor the atmospheric and instrumental transfer function. To select, for each science target, the calibration target, it is recommended to use the CalVin tool developed by ESO. CalVin selects suitable calibrators from an underlying list based on different user criteria. The underlying list of CalVin calibrators for AMBER is based on these references:
A catalogue of calibrator stars for long baseline stellar interferometry, Borde, P.; Coude du Foresto, V.; Chagnon, G.; Perrin, G. 2002, A&A, 393, 183
A catalog of bright calibrator stars for 200-meter baseline near-infrared stellar interferometry, A. Merand, P. Borde and V. Coude du Foresto 2005, A&A, 433, 1155

The selection of the calibration star should be based on a reasonable compromise between different characteristics such as brightness (not much fainter than the target), distance on sky (close to the target), spectral type (similar to that of the science target), and diameter (unresolved or at least clearly smaller than the target).

VLTI observations are normally performed as pairs of science and calibrator OBs. The LST range of the calibrator OB of the pair must reach from 30 minutes before the start of the LST range of the corresponding science OB to 30 minutes after the end of the LST range of the corresponding science OB. This ensures that a calibrator OB is available at any time when the science target observation may be attempted. In case that a single calibration star cannot be used for the full required range, it is possible to use more than one calibration star OB to cover the required LST range. Only one of these calibration star OBs will be executed depending on the time of the observation of the science target. Paranal Science Operations reserves the right to exchange a user submitted calibrator by another suitable calibrator from CalVin if there is a need to do so.

It is also possible to request additional calibration star OBs so that a sequence of [calibrator - science target - calibrator] is realized. In this case, the sequence must be described in the "Calibration Requirements" field of the OB and in the "Special Calibration" Section of the ReadMe file, as well as in the user comment field of the OB. The execution time for the additional calibrator is subtracted from the allocated time of the programme.

We recommend to select a calibrator from CalVin so that more detailed knowledge on these calibration stars will be acquired rapidly. However, the user has as well the option to use a calibrator which is not in the CalVin database. In this case, the following information is requested in the README file (Section "Special calibration requirements"):

Name
Coordinates
V magnitude
K magnitude
Spectral Type
Uniform Disk (UD) diameter at K, H, J bands with error estimate.
Source of diameter estimate.

We remind that all calibration star data are public as soon as they are listed in the archive.

Additional Requirements for AMBER README Files

In addition to the general requirements for README files, the following AMBER specific recommendations should be followed:

Information about calibrator stars which are not from CalVin (see above), in the Section "Special Calibration information" of the README file.
Information on the variability of guide stars with variable V magnitude (minimum and maximum V magnitude expected during the period).

Additional Requirements for AMBER Finding Charts

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

A 5 x 5 arcmin optical finding chart, centered on the target (whether it is a science object or a calibrator), showing objects brighter than V=17.
If a target is not a single clearly isolated IR source, please request visitor mode.

A description on the creation of Finding Charts using ESO tools can be found here. A tutorial to include the Finding Charts in the OBs is here.

OB Naming Conventions

Any AMBER OB must have its name beginning by one of the two following prefixes, in order to indicate the type of target (either science or calibrator):

SCI_ CAL_

It is recommended that the name of the OB, that follows the prefix, is the name of the target, as written in P2PP, without space characters.

If a scientific target or its calibrators shall be repeated at different hour angles (i.e., LST ranges), there must be as many OBs as desired observations (at different LST ranges). OBs can be duplicated (for scientific targets with the LST range in P2PP modified) and their names completed with a suffix like -sr-n, where sr is the subrun of the programme (A,B,C,...) and n (starting from 1) is the iteration of the observation.

If, instead, a certain observation shall be executed only once, but can be executed at either of several LST ranges, these alternative LST options for one observation must be indicated in one OB.

Matching of Science target and calibrator OB names

In each OB of a scientific target, the name of the corresponding calibrator OB (or OBs) must be indicated in the p2pp comment field labeled "Name of associated OB of SCI/CAL pair". Likewise, in each OB of a calibrator, the name of the corresponding scientific target OB must be indicated in this comment field.

If additional calibrators shall be observed instead of the regular cal/sci pair (sequence of cal/sci/cal), this information has to be inserted into the special calibration sections of the OB and the ReadMe file.

P2PP Constraint Set

Sky transparency

Observations in the IR regime may require clear or photometric conditions, depending on the spectroscopic quality wished. Also for targets close to the brightness limit of AMBER, it is recommended to request clear sky conditions.

Seeing

The specified seeing constraint is compared to the optical seeing delivered by the DIMM. The exact relationship between seeing, MACAO performance, and final data quality is not yet known in detail. However, with the use of MACAO, the injection of flux into the AMBER fibers remains effective, even for moderate to bad seeing conditions. It is therefore recommended not to request constraints on the (optical) seeing more stringent than about 1.6 arcsec. For targets close to the detection limit of AMBER, seeing constraints of about 1.0-1.2 arcsec may be requested. If Coude guiding by the MACAO systems is used, ESO assures that the adaptive optics loop is closed during the entire observation. Otherwise, the OB will be considered for re-execution.

In case that Coude guiding is not used (if the target is fainter than V~17 and no suitable off-axis guide star could be provided), please request excellent seeing conditions of 0.6-0.8 arcsec.

Moon constraints

The sky background introduced by the moon does not significantly affect the AMBER data quality. As a result, the moon constraints are not a part of the AMBER constraint set.

Baseline choice

The choice of the baseline to be used must be indicated in the baseline field of the constraint set in each OB (this applies for UT as well as for AT baselines). Alternative baselines may be mentioned in the ReadMe file.

Intervals of local sidereal time (LST)

Constraints on the local sidereal time (LST) at which the OB has to be executed must be specified in the "Sidereal Time" section of each science OB. Desired constraints on the projected length, azimuth angle of the baseline, or the airmass must be translated into LST intervals, for example by using the ESO Visibility Calculator VisCalc. Furthermore, the specified LST interval must be limited to the time range when the target is above 30 degrees altitude and when the observation is not unfeasible due to the delay line restrictions or shadowing effects. The feasible HA range can be checked with VisCalc. See also plots of the VLTI pointing restrictions in the declination/hour angle space at http://www.eso.org/observing/p2pp/AMBER/vlti_pointing_restrictions.html.

The LST range of the calibrator OB of the pair must reach from 30 minutes before the start of the LST range of the corresponding science OB to 30 minutes after the end of the LST range of the corresponding science OB. This ensures that a calibrator OB is available at any time when the science target observation may be attempted. In case that a single calibration star cannot be used for the full required range, it is possible to use more than one calibration star OB to cover the required LST range.

We recommend to use LST ranges of at least 3 hours. Otherwise it might be difficult to schedule the observation. The minimum accepted LST range is 1 hour. In case that a desired observation shall be done only once, but can be executed at several alternative non-contiguous LST ranges (for instance either some hours before meridian or some hours after meridian), up to five alternative LST intervals can be specified for one OB. The time separation between these intervals must be at least 1 hour. Please be reminded that multiple OBs are needed if your target shall be observed more than once (for instance at different LST intervals).