Lettre de l'OHP No.18 - Table de Matières

HFA: the Hypercat FITS Archive

Grégory MAUBON, Philippe PRUGNIEL, Valeri GOLEV, François SIMIEN

Observatoire de Lyon


This paper presents the development of a FITS Archive, mainly supplied by OHP observations, and suggests to generalize this approach to other observational projects.

Presentation

The HST imposed, 10 years ago, a new approach of the archiving and distribution of the astronomical data. Later all major observatories implemented archival systems. In practice the archival of space-based telescope data is easier for two main reasons. First, the conditions of observation are much more stable than for ground-based telescopes. In the latter case, the analysis on the data deeply relies on notes taken by the observer.

Second, the conditioning of the data is, from the beginning, designed with the scope to store them in an archive. These reasons make that archived ground-based observations are generally difficult to use by others than the observers themselves: the description of the observations is too often insufficient in both quality and quantity.

Classical analysis procedures are used to deal with such under-described data: missing information is asked to the user whenever they are needed along the data reduction. If the data need to be re-processed, for example with an improved method, same actions may have to be repeated. For instance, it happens that the correct identification of an astronomical object is set very late in the work, sometimes only when the paper is being written. This means that when going back to the data, possibly years after, one has to cross-correlate again the names given by the observer (maybe something like "obj. #333) into a standard identification (eg. NGC3379).

We actually met this problem when re-reducing the CARELEC spectra accumulated in the period 1992-1997 in order to analyse the stellar population of galaxies [Golev et al. 1999 A&A in press]. We realized that it would not be more time consuming to store at once all informations in the image keywords and that it would anticipate over a possible re-use of these data. In addition, well-described data can be used to feed pipeline processings which are much more efficient than the tailor-made approach we were accustomed to.

These considerations led us to develop, in the frame of the Hypercat database, http://www-obs.univ-lyon1.fr/hypercat/, a FITS Archive (hereafter HFA, Hypercat FITS Archive).
We have adopted for the archive the Flexible Image Transport System (FITS) standard because it is widely accepted by astronomical community and because its flexibility allows to mix images and tables. Moreover, this standard is in permanent but controlled evolution, and so adapted to present and future conditions of astronomy.

In the next section we describe the present content of the HFA, its internal organization and the access to the data. Finally we anticipate over future developments of this project.


The archive


Perspective

The HFA is in rapid evolution. We continue to feed the archive with other datasets, from OHP and other observatories, in relation with our projects about stellar kinematics and populations in galaxies.

The pipeline procedures are also being developed. We are implementing functions for cosmetic processing (e.g. removal of spikes due to cosmic rays), but the most ambitious part consists in implementing also sophisticated analysis procedures. We plan to offer, after 1999 June, the classical kinematical and spectrophotometric analysis algorithms online. Hence, the output of the pipeline will eventually be more than a FITS file containing observations: it will also deliver rotation curves or spatial profiles of line-strength indices.

The interest of the project is not to reproduce analysis already performed (and published). It allows to address completely new problems. In particular, the main present limitation to the accuracy of the stellar kinematics is the template miss-matching: HFA and the analysis pipelines will allow to check the analysis against different templates and, in a few months, to use synthetic templates based on the PEGASE program [Fioc & Rocca 1997] and on the ÉLODIE stellar library [Soubiran et al. 1998].

The development of Hypercat is led by our scientific projects. However, the experience we have acquired can undoubtly be applied to other projects. We believe that adopting this approach for the data management could both profit to the scientific project themselves and enhance the utility of the small-telescope observations.

Our team could provide some support to any project considering to follow the approach.


References


Fioc & Rocca 
 1997, A&A, 326, 950

Golev V., Prugniel Ph., Simien F., Longhetti M.
 1999 A&A in press

Prugniel & Heraudeau
 1998, A&AS, 128, 299

Simien and Prugniel
 1997a, A&AS, 122, 521

Simien and Prugniel
 1997b, A&AS, 126, 15

Simien and Prugniel
 1997c, A&AS, 126, 519

Simien and Prugniel
 1998, A&AS, 131, 287

Soubiran et al.
 1998, A&AS, 133, 221


Lettre de l'OHP No.18 - Table de Matières