ADONIS Observing Procedures

Infrared Observing Techniques
Adaptive Optics Terminology
How to take Sky Frames
Observing Overheads
Sumary of Observing Strategy
Data Management
Guiding and Finding Chart

Infrared Observing Techniques

The ADONIS observer should be familiar with the techniques of near infrared observations.

Adonis Adaptive Optics Terminology

The ADONIS observer should be familiar with the following terms:

Science Object

The astronomical object which is under study.

Reference Object

This is the object used for the adaptive optics correction. It must be located less than 30 arcsec away from the science object. Even better, it may be the science object itself, providing its intrinsic angular size is smaller than 3 arcsec. The visual magnitude of the reference star can reach 12.5.

PSF Object

Because residual errors remain on the adaptive optics wavefront sensor, a deconvolution process should be applied. This is done using the point spread function (PSF) determination of a so called PSF star. In order to get the same correction quality with the PSF and the reference star, the PSF should respect a few constraints:

If the science object is not used as the reference object, then the best deconvolution results are obtained by using a binary for which the binary separation is the same as the separation between the science and reference objects. One binary component will be used as the reference and the other as the PSF. Both components should obey the flux and positional constraints listed above. In practice, you have to be lucky to find a suitable nearby binary.

Closing the loop

When the loop is closed, adaptive optic corrections are taking place. That is, the wavefront sensor is monitoring the difference between the actual atmospheric abberations and the most recent position of the deformable mirror.

There are a number of ways to close the adaptive optics loop. The most frequently used methods are as follows:

The observer need only decide what method he/she would prefer. The telescope operator will execute the commands.

Correction of residual abberations

It is very likely that at some point during the observing night a further correction will have to be made for static abberations. Such abberations can appear when observing a scientific target and can change with airmass. To correct for them a series of adjustments are made (e.g. focus, astigmatism, coma, triangular and spherical) by the telescope operator. This process can take up to 15 minutes. The observer need only decide what method he/she would prefer. The telescope operator will execute the commands.

Image centre

Selecting the centre of your desired Adonis image can be confusing if you don't know the difference between the following centres:

The default configuration is for when the reference star is the science object. In this case the IR centre is the same as the WFS centre.

How to take sky frames

Moving the telescope

In this case the on/off (M6) mirror remains fixed. The telescope operator opens the adaptive optics loop and applies an offset to the telescope pointing. Once the sky frame is taken the telescope returns to the original pointing position and the loop is closed without optimization.

They are several reasons to use this mode:

The disadvantage is that this mode has large overheads.

Moving the M6 on/off mirror

In this case the on/off mirror chops so that the camera field of view can be centred on different positions within the available field of view. Double or triple chopping is possible. The observer defines the frequency and amplitude of the chopping via the ADOCAM software.

They are several reasons to use this mode:

The disadvantage is that the sky positional offset must be less than 60" from the reference source. Furthermore, the subtraction of thermal emission from the bench is poor, particularly in K-Band.

Example 1: The scientific target is the reference star for the Wave Front Sensor (WFS).

Example 2: The scientific target is distinct from the reference star.

Observing overheads

In order to plan correctly the time needed for an observation, the astronomer should be aware of the following overheads:

Summary of Observing Strategy

The image quality is limited by various parameters that do not follow the same behaviour. For more information see the article The ESO/ADONIS system: 3 years experience in observing methods by Mignant et al.

Data Management

Image Format

Data are written to one of two disks (/s3 or /h1) on the ADOCAM computer.

Data do not entirely follow the FITS standard. The dimensions of each image are 256x257 pixels. The extra 257th column is used to write the UT time of each individual frame. To reformat the ADONIS FITS to a standard FITS, you can use the ECLIPSE refits command.

The output images are cubes. Each cube contains data from 1 observing cycle, with each plane corresponding to an individual frame.

Here is an example of an Adonis FITS header.

Image Name

At the beginning of the night the observer must enter a name and a nickname which is 3 letters long (e.g. xxx). A directory named xxx_yymmdd_hhmmss.DIR will be created (where y, m, d, h... stand for year, month, day, hour...). This directory will contain a logfile (xxx_yymmdd_hhmmss.LOG) and the raw data files (xxx_yymmdd_hhmmss.FITS).

Observing Logs

For each cube, all the settings of the detector are logged automatically in a file. The settings include integration time, lens scale, filter, observing mode, sequences and ON/OFF position. The user has the option to include the target name and coordinates.

The detector has no communication with the telescope and so does not know what the airmass, seeing or coordinates are. Therefore we suggest that the observer fills out an Adonis log sheet (provided).

The telescope operator will keep a log of the adaptive optic corrections made for each observed source. This log includes the flux and noise measured on the wavefront sensor, the estimated strehl ratio and seeing, type of optimization used and the parameters r0 and lcor. If you would like a copy of this log then please inform the operator.

Data Backups

Each day the operations staff write the previous night's data to dat tape using WDAT. Two copies are made. One copy is for the observer and the other is for ESO.

At the end of each night the observer must list (on a form provided) what directories are to be backed up. If this is not done then the operations staff will not know what directories to backup.

Once the observer receives their dat tape it is essential that they verify its contents as soon as possible. In most cases their data will be deleted from disk before the start of the next night. The dat tapes must be read with WDAT. This is part of the ECLIPSE data reduction package and is available on all machines in the Observer's User Room.
With a DAT driver called /dev/nrst0
To write in the file "listing.lis" the content of the DAT tape:
wdat -d /dev/nrst0 -l= listing.lis

Note: Under no circumstances can data be transferred from the ADOCAM computer to another work station during data acquisition. This will cause ADOCAM to crash and halt observing.

Finding chart & Source List

The observer should have finding charts for each science object as well as for any PSF or standard stars. The telescope has a centre field camera with a field of view of 2.5 x 2.5 arcmin. The display is orientated North (down) and East (left).

It is possible for the telescope software to use a source catalogue file. The file must have the and the following format:
source 033603.2 162802.6 2000.0 2000.0 0.0 0.0 m
where "source" is the object name, "033603.2" is the RA, "162802.6" is the Dec and "2000.0" is the epoch. The line must end with "0.0 0.0 m" which sets the proper motion offsets to zero. The separations must be spaces and not tabs.

This file can easily by ftped to the telescope computer at the beginning of the night.

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