Description of the Atlas
The aim of this image database is to make available to the community
in electronic-readable form
an atlas of faint photometric structures hidden within the main body
of early-type galaxies.
Each entry contains
image of the galaxy,
the isophotal map,
the Gradient and the
the images . The Atlas will be periodically updated to include
new objects as they will become available.
In the present version, the Atlas includes:
- a sample of 28 early type galaxies observed at the
ESO - NTT during
two observing runs in 1991 and 1992 .
All images have been pre-processed (cosmetics, de-biasing and flat-fielding)
Astrophysikalisches Institut Potsdam
using the November 1993 release of
After pre-processing, the Potsdam Adaptive Filtering Facility (Richter et al.
1978, Richter et al. 1993) was used to produce both the Gradient and the
Laplacian of the original images. These images are not easy to read and
some instructions are given
in How to read the filtered images.
The Atlas is structured as follows:
List of the objects
sorted by right ascension. This list is complemented
by the Observations Log-book
which contains all the relevant data on the
instrumental setup and on the observing conditions. By clicking on the
identification of any object in the list the user can access the corresponding
object-page stored in the Atlas.
Each object page contains the most relevant data on the object
plus at least five small icons. By clicking on either any of the icons or on any
of the underlying short descriptions, the user
can retrieve the corresponding full-size GIF files.
The first five icons in each page refer to the following types of images:
In some cases these five icons are complemented by others containing:
- the original photometric image (details can be found in the underlying
- an enlarged view of the inner regions;
- the uncalibrated isophotal map of the galaxy;
- the Laplacian of the first image;
- the Laplacian of the second image.
In more complex cases, i.e. when structures are color dependent, some
additional icons can provide the Laplacian and the Gradient obtained in
different photometric bands.
All images include a 30 arcsec long bar and are oriented with the North
up and East leftward.
- the Gradient of the first image;
- the Gradient of the second image.
The global parameters section of the Object pages contains the following data
(taken from the
Reference Catalogue of Bright Galaxies (de Vaucouleurs et al. 1991):
The page is completed by a short description of the instrumental setup and
by the notes on structures including links to
the references (also available as complete list from
the cover page of the Atlas).
- Right Ascension and Declination of the object (Epoch 2000.0);
- the mean revised morphological type;
- the total asymptotic magnitude in the BT system;
- the D25 diameter in arcsec;
- the ratio of the major and minor axis at the 25 SBU isophote;
- the weighted average velocity corrected to the 3 K background radiation.
This section of the Atlas is created and mantained by
Petra Böhm, updated: 1999-08-04