Photometry, Database and Extinction Module Optimization for Chimera
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Photometry, Database and Extinction Module Optimization for Chimera. Joshua J. Brown, Adam Biesenbach, Earl Bellinger, Michael Meyers, Joshua Primrose, Dennis Quill, Paulo Henrique de Silva3, Prof. Antonio Kanaan 1 , Prof. Shashi Kanbur 2

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Results, Problems and Solutions

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Results problems and solutions

Photometry, Database and Extinction Module Optimization for Chimera

Joshua J. Brown, Adam Biesenbach, Earl Bellinger, Michael Meyers, Joshua Primrose, Dennis Quill, Paulo Henrique de Silva3, Prof. Antonio Kanaan1, Prof. Shashi Kanbur2

1. Universidade Federale de Santa Catarina, 2. State University of New York, Oswego

Agreement with Independent Extinction Verification

Improvement of the extinction module will continue until the module can accurate predict to within a reasonable tolerance the actual extinction values independently obtained by astronomers. To this end, the following steps are going to be taken:

- Refinement of the aperture selection and aperture integration methods for photometry of stars.

- Continued effort to better integrate IRAF photometry tools into the photometry and extinction module.

- A more intelligent data-set picking method which more strictly enforces that stars all share the same exposures.

- Elimination of large, saturated stars from use In determining extinction.

Database Values to Extinction

The data in the database is fundamentally organised into exposures, which contain information about time and properties specific to one image, and stars, which hold general information about items observed in various exposures. These stars can be organised into catalogues for convenience. This simplified diagram represents the database structure:

Introduction

Chimera was developed by Paulo Henrique de Silva and Prof. Antonio Kanaan at the Departmento de Fisica as a modular, easily implemented remote observatory automation program.

In 2009 photometric processing, database storage, and extinction coefficient calculation functionality were developed by Jillian Neely, Peter Thompson, and Brandon Gilfus

. However, these modules did not interface well with the existing Chimera framework. It was thus necessary to optimise these modules to run more natively in Chimera with added functionality.

Introduction

Chimera was developed by Paulo Henrique de Silva and Prof. Antonio Kanaan at the Departmento de Fisica as a modular, easily implemented remote observatory automation program.

In 2009 photometric processing, database storage, and extinction coefficient calculation functionality were developed by Jillian Neely, Peter Thompson, and Brandon Gilfus.

However, these modules did not robustly produce reliable extinction values. Thus it was necessary to examine and optimise the entire data flow to improve the accuracy of the extinction values produced.

Results, Problems and Solutions

The results obtained using the extinction module were initially consistently poor, using simple methods for choosing objects to calculate extinction values. Small sets, manually specified, were often unrepresentative of data overall.

The first step in fixing the issue was to use more intelligent selection of data. The extinction module was modified to look for all the exposures taken on a given date and then use only the stars that were found in every exposure or the greatest possible number of exposures.

Eventually the need for a more robust method of photometric processing was realised, and Source Extractor's photometry processing was replaced by IRAF's APPHOT module. Further testing is planned to determine the efficacy of this method, although initial results look positive. The chart on the previous column is an example of the results obtained through this method.

Aim

The current goal in developing photometric, database, and extinction capabilities in a robotic system is the complete automation of extinction calculation. The ideal process would require no human intervention to run for the entirety of a night collecting data and computing an extinction coefficient which could be used to calibrate data for research.

Database Improvements

In addition to the principle changes made to the extinction module, many large improvements were made to the database to improve functionality:

- More query options to allow more specific data selection

- Improved ability to delete objects from the database.

- Ability to add all stars from an exposure from Simbad to improve extinction accuracy.

- Improved, more intuitive logic in parsing option input.

- Partial functionality for a light curve generation utility.

- More robust management of various non-Chimera generated FITS file headers.

- Better user interaction, including warnings, error messages, and confirmation prompts for deletion.

Each cell holds the instrumental magnitude of a given star for each exposure in which it is found. Note that not all stars are in every exposure!

Extinction values are calculated by plotting the magnitude of each star against the airmass through which the star is observed. Then the slope of the resulting line is called the extinction coefficient, in magnitudes per airmass.

Photometry

This image shows the sources detected by Chimera's Source Extractor implementation.

Once the stars are identified the total pixel counts within a predefined aperture are summed and either converted directly to magnitudes by Source Extractor or passed to IRAF for more accurate processing.

Acknowledgements

The authors thank Dr. Kanbur and Dr. Kanaan, as well as Paulo Henrique de Silva, Peter Thompson, Jilian Neely, Brandon Gilfus, and all past contributors to the project. Furthermore, the authors thank NSF OISE award 0755646, and the Laboratorio Nacional de Astrofisica

After the stars' locations have been identified the coordinates of the star are fed to a part of IRAF, APPHOT, which determines how bright each star is by summing the total pixel counts inside a given aperture (green circle) and subtracting the average background value.

For optimal results, the average slope for many stars is used. These numbers can be made even more accurate by querying the actual zero-airmass magnitudes of stars in the catalogue to provide a known magnitude for calibration.


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