1 Introduction

1.1 ASCII tables in astronomy and science

ASCII tables are one of the major data exchange formats used in science. In astronomy, which is the background of AstroAsciiData 's developers, ASCII tables are used for a variety of things like object lists, line lists or even spectra. Every person working in astronomy has to deal with ASCII data, and there are various ways of doing so. Some use the awk scripting language, some transfer the ASCII tables to FITS tables and then work on the FITS data, some use IDL routines. Most of those approaches need individual efforts (such as preparing a format file for the transformation to FITS) whenever there is a new kind of ASCII table with e.g. a different number of columns.

1.2 The project goal

Within the AstroAsciiData project we envision a module which can be used to work on all kinds of ASCII tables. The module provides a convenient tool such that the user easily can:

• read in ASCII tables;
• manipulate table elements;
• save the modified ASCII table;
• read and write meta data such as column names and units;
• combine several tables;
• delete/add rows and columns;
• manage metadata in the table headers.

1.3 Why python?

Python (www.python.org) is in the process of becomming the programming language of choice for astronomers and scientists in general, both for interactive data analysis as well as for large scale software development. A number of interfaces such as PyRAF (http://www.stsci.edu/resources/software_hardware/pyraf) or PyFITS
(http://www.stsci.edu/resources/software_hardware/pyfits) have already been written to bridge the gap between widely used astronomical software packages, data formats and Python.

This makes the development of the AstroAsciiData module for Python a natural choice. Within Python, the AstroAsciiData module may be used interactively, within small scripts, in data reduction tasks and even in data bases.

1.4 Design considerations

In general, the ASCII tables used in astronomy have a relatively small size. As an example, the size of the Wide Field Camera catalogue of Hubble Ultra Deep Field (http://www.stsci.edu/hst/udf) is only 2.2MB. Handling those amounts of data is not a time consuming task for modern day computers. As a consequence, computational speed is not a prime issue in software design and construction, and there was no attempt to implement AstroAsciiData as a particularly fast module. The focus was rather to maximizing convenience and ensuring a steep learning curve for the users.

1.5 The SExtractor table format

There are many ways to store meta data such column name and units in a file together with the table data. Instead of defining our own, proprietary format within the AstroAsciiData module, we have chosen to support the SExtractor header scheme.

This means that the module can read ASCII tables which follow the SExtractor format and extract all column information from the file (see Sect. 3.3). The module also offers to write this information in the SExtractor format back into file.

In the SExtractor format the meta data is stored at the beginning of the file:

#   1 NUMBER          Running object number
#   2 XWIN_IMAGE      Windowed position estimate along x              [pixel]
#   3 YWIN_IMAGE      Windowed position estimate along y              [pixel]
#   4 ERRY2WIN_IMAGE  Variance of windowed pos along y                [pixel**2]
#   5 AWIN_IMAGE      Windowed profile RMS along major axis           [pixel]
#   6 ERRAWIN_IMAGE   RMS windowed pos error along major axis         [pixel]
#   7 BWIN_IMAGE      Windowed profile RMS along minor axis           [pixel]
#   8 ERRBWIN_IMAGE   RMS windowed pos error along minor axis         [pixel]
#   9 MAG_AUTO        Kron-like elliptical aperture magnitude         [mag]
#  10 MAGERR_AUTO     RMS error for AUTO magnitude                    [mag]
#  11 CLASS_STAR      S/G classifier output
#  12 FLAGS           Extraction flags
  1 100.523  11.911   2.783 0.0693 2.078 0.0688  -5.3246   0.0416  0.00  19
  2 100.660   4.872   7.005 0.1261 3.742 0.0989  -6.4538   0.0214  0.00  27
  3 131.046  10.382   1.965 0.0681 1.714 0.0663  -4.6836   0.0524  0.00  17
  4 338.959   4.966  11.439 0.1704 4.337 0.1450  -7.1747   0.0173  0.00  25

The format is rather simple, but nevertheless offers the possibility to save the essential column information.

Potential users who would need or prefer other formats can:

• try to convince us that the alternative format is worth the implementation;
• sub-class the relevant module classes and implement the format support by themselves. We would certainly offer help for this.

1.6 The usage of the User Manual

With more than 70 pages this User Manual is quite voluminous. But to start reading at page 1 and working through it all is pointless. Our recommendations on how to proceed are the following:

• install the module with the the help of Sect. 2;
• get a first impression on AstroAsciiData browsing through Sect. 3;
• start working with the module;
• use Sect. 4 with its detailed examples as a reference manual, preferably in the html form (available at the project site http://www.stecf.org/software/PYTHONtools/astroasciidata/), when looking for a certain functionality or features you need.

1.7 Feedback

Feedback in any form, suggestions, critics, comments, development requests, is very much welcome and will certainly contribute to improve the next versions of the module. The feedback should be sent directly to the developers or to
AstroAsciiData@stecf.org.