Tutorial

What is APES

APES is an astronomical software that allows to prepare narrow angle astrometry observations conducted at the VLTI with PRIMA. APES allows the astronomer to schedule his observations, to compute the target exposure time, as well as to create parameter files that can be loaded into P2PP.

Environment :

APES is a java application that should run, in principle, on any operating system, ie. Mac OS X (10.4 or later), windows XP, Linux and Unix provided that the Java Runtime Environnement v1.50 is installled on your computer. However, APES is beeing developped on Mac OS X Leopard (10.5) and has not been fully tested on other operating system.

Launching the java application with webstart :
APES

Starting from Scratch :

A>Description of APES main panel

The APES main window, is composed of several panels.
The first top panels give general informations such as the name of the observing run, the date, the baseline and the science target name. On the second top panel, observational parameters such as Airmass, LST, Hour angle, Julian date, UT and Local Chilean time are given.
REM : In order to have access to the coordinate of the target its magnitudes and other information relevant to the target, the user sould open a catalog or enter the demonstration mode of APES.

The middle panel is an elevation plot of a given science target (Airmass or elevation versus time). The target trajectory is shown (thick yellow line) as well as the moon trajectory. This panel is interactive, therefore you can use the mouse to select the observation time of your target. Most of fields will be updated according to the Airmass/Time location of the target.

The 2 bottom-left panels represent the astrometric motion of your target with the the orientation of the projected baseline overplotted for a given date and time. The length of the of the vector is proportional to inverse of the expected astrometric error. The smaller the error, the larget the vector.

The bottom-right panels correspond to the exposure time calculator. You can select to compute the error on the differential phase given a total integration time of 30minutes or to compute the integration time necessary to reach an accuracy of 30 micro arcseconds.

The Make a PAF button will pop-up a window which will display the main parameters of your target/reference star. At this stage of the observation preparation, you are able to modify the integration times computed by the ETC. You should then validate your choices and an Parameter File will created.

Additional information about the orientation of the Baseline and target is displayed at the bottom of the bottom-right panel.

In Service mode, APES main panel is slightly changed. The middle panel ie. the one that represent the observing night, not longer represent the observing night for a given night but for au given period of time (an observing run or even a full observoing period). The Y-axis, therefore represent the airmass as well as the date within the observing period. This is why the beginning and the end of the night change along the Y-Axis. The horizontal dark-blue line represents the day at which the observations are carried out during the observing period.

B> Demonstration example : observability, astrometric motion & accuracy

- Menu=>Demo=>Demonstration Mode
in the new panel "Demonstration Mode" click on :
Ra-Dec: Move the sliders. You will see the target trajectory on the airmass panel moving with respect to the night.
Date: Move the sliders. You will see the night canvas moving. Orbit: Move the sliders. You will see the effect of a change of orbital elements on the astrometric orbit.
ref Star : Move the sliders and place your mouse on the airmass trajectory of the target. The integration time necessary to reach 30 microarcsec accuracy will be displayed on the main panel. You can see how the separation between the target and its references affect the integration time.

-Menu=>Setup=>Choose baseline
Select "expert mode" and "enable all positions". Move the slider to select different baselines and place your mouse on the airmass trajectory of the target. Have a look at the astrometric motion panels (both relative parallactic motion and orbital motion). You will see a representation of the projected baseline on the astrometric motion, which will allow the observer to select an optimal baseline orientation to contrain both the relative parallactic and orbital motion.

C>Create your own science target catalog :

First of all you should load a science target catalog into APES containing a list of target stars and reference stars. A full description of the catalog format is given catalog format web page .
However, a demostration catalog can be downloaded from http://obswww.unige.ch/~segransa/apes/catalog_demo.rdb in order to start the APES tutorial.
Creating the catalog is very important since several of the catalog fields will be passed the PAFs as well as in the OBs and, in the end and to the fitsheaders. Therefore, when scheduling real observations, make sure that all the catalog fields are correct. The format of the catalog is "tab separated columns" with a 2 line header. You should probably start from the demo catalog to create your own (Catalog menu->Open a demo Catalog). Starbase is an ASCII relational database for UNIX ( http://cfa-www.harvard.edu/~john/starbase/starbase.html ) that allows to manipulate this kind of catalog.

D> Phase 1 observation example

In addition to the demonstration example, for the Phase 1 of the observation preparation, you'll need to use the exposure time calculator and therefore feed APES with the magnitude of both the target and reference star as well as of the atmospheric conditions. You need a catalog.
-Menu=>Demo=>Open a demonstration catalog
Select with your mouse a target and a reference into the catalog panel.
-Menu=>Setup=>Choose baseline. Move the slider to select different baselines.
-Menu=>File=>Initiate a new observing run
Select a range of date for Phase I observations and validate.

On the astrometric motion panel of your target, you will see a yellow shadow that cover the time range you have selected.
Use the date slider at the bottom of the main panel and you will see the target moving with a given lst on the astrometric motion curves. You can now choose the date (or date range) at which you want your observations to be carried out by choosing the best orbital phases.
You can also select a range of date that are acceptable to carry-out these observation with the Duration slider at the bottom of the main panel. A black thick line will be printed over the parallactic motion and the airmass trajectory panel will change shape in order to take into account the change of bight duration in your observing date range.

You can then select the lst (or baseline orientation) at which you want to observe by doouble clicking on the science target airmass curve.

You should now repeat the same set of operation with the detailed ETC panel open. (Menu=>View=>Detailed ETC panet). You will see the all the details about the ETC. You should worry if the SNR /pix and per frame on the science target is lower than 3. That would mean that you cannot fringe-track on the target (Have to check wether it's 3 or 5 or 10).

In the preference panel (Menu=>Apes=>Preferences=>ETC) you can change the values of the seeing, the coherence time and of the number of reads per coherence time for the fringe tracking. You can now repeat the same set of operation and see how it affects the results of the ETC and of the final accuracy (integration time) in the main panel.

E> Phase 2 observation example : Visitor Mode

-Menu=>Demo=>Open a demonstration catalog Select with your mouse a target and a reference into the catalog panel. -Menu=>File=>Initiate a new observing run Select the range of date and the baseline (for this period) for Phase II observations and validate.
Continue in the same way as for phase 1 to select a optimal baseline configuration (lst), date and reference star.
Once you are happy with your setup you can click onto the "Make a PAF" button on the main panel. The PAF panel will then pop-up and you will be able to modify some of the fields (those which are in white) before creating the parameter file.
Repeat this process with all your targets until your observing run/night has been created.

You can also visualize how your PAF are organised within one nigh by displaying the night-schedule. Keep it on display when creating on observing night.

F> Phase 2 observation example : Service Mode

-Menu=>Demo=>Open a demonstration catalog or
-Menu=>Setup=>Open a local input catalog Select with your mouse a target and a reference into the catalog panel. -Menu=>File=>Initiate a new observing run Select the range of date and the baseline for Phase II observations and validate.
Continue in the same way as for phase 1 to select a optimal baseline configuration (lst), date and reference star.
Once you are happy with your setup you can click onto the "Make a PAF" button on the main panel. The PAF panel will then pop-up and you will be able to modify some of the fields (those which are in white) before creating the parameter file.
Repeat this process with all your targets until your service observing run has been created.
You can also visualize how your PAF are organised within one observing period (LST organized) by displaying the night-schedule.

G> Reload your observing night - observing run - Service mode observations

- open the night schedule panel (-Menu=>View=>Night Schedule)
On the night schedule panel click on the import button and select the directory where your PAF are stored.
You now have a graphical representation of your observing run on the night schedule panel ie. PAFs as a function of sideral time. Clicking on given PAF allow to select it. The corresponding target will be displayed on APES main panel will all the corresponding information. If you are not happy with the position of an OB on the night schedule, you can move it using the main panel. All the parameters of the PAF will be updated according to the new lst.
On the night schedule, you can also remove PAFs from your observing run.