Pre-FLAMES (PF) Survey Release (#27)

15 December 2004

Technical Summary

Survey ..................... Pre-FLAMES (PF)
Telescope .................. ESO/MPG 2.2m
Instrument ................. WFI
Program IDs ................ 164.O-0561; 267.A-5729
Number of Fields ........... 7
Passbands .................. B; V; I
Number of Filters .......... 3
EIS Release Number ......... 27
Version .................... 0.7
Release Date ............... December 2004
Release prepared by ........ EIS team, S. Zaggia

Product Type ............... Color Catalogs (DAOPHOT)
Number of catalogs ......... 7
Data Volume ................ 42 Mb

Origin ..................... ESO/EIS
Number of Fields ........... 48
Passbands .................. B; V; R; I (2)
EIS Release Number.......... 21
Version..................... 0.7
Release Date................ 03 November 2004

Product Type................ Nightly Products
Number of Reduced Images.... 287


Based on ideas submitted by the ESO community and evaluated by the Working Group for Public Surveys, the Pre-FLAMES survey, administered by the ESO Imaging Survey (EIS) and Public Survey Group (PSG) teams, is a multi-color survey of selected fields consisting of short- and long-exposures in B-, V-, and I-bands taken using the ESO Wide Field Imager (WFI) at the ESO/MPG 2.2m telescope at the La Silla Observatory. The aim was to gather high quality astrometric and photometric data for fields of high stellar density, to produce object catalogs with the required accuracy to provide input target lists for 160 candidate fields foreseen to be ideally suited to studies using FLAMES, a fibre-fed multiple element spectrograph available on VLT Unit Telescope 2 (Kueyen). The candidate fields consisted of Globular Clusters, Open Clusters, regions of the Milky Way bulge and Halo, a selection of Local Group galaxies, the Sagittarius Dwarf galaxy, and both the Large and Small Magellanic Clouds (LMC and SMC). The definition of the survey and an overal descriprion of its goals are described in Momany et al. (2001) and in Zaggia et al. (2001).

The data contributing to the present release were obtained as part of the ESO Large Programme: 164.O-0561 (Principal Investigator: J. Krautter, as chair of the SWG) and DDT programme 267.A-5729 over ESO's observing periods 64 through 68.

The present release consists of premilinar versions of color catalogs, produced for 7 fields from the images in release 21. The color catalogs were constructed in a single, un-supervised workflow, from the association of single passband catalogs extracted using a combination of SExstractor (Bertin and Arnouts 2000) and DAOPHOT/ALLSTAR program (Stetson 1987) to detect objects, compute the PSF and finally extract photometry. A more detailed description is presented below. These catalogs were produced to help in a preliminary selection of objects for spectroscopic observations using FLAMES.

While still not final, the products being released are meant to illustrate the ongoing work by the survey group and provide data to groups that already have scheduled observations with FLAMES.

For more information about the terminology and conventions used in this document refer to the WEB README pages.

Contents of this Release

This is the fourth official release of reduced data (not including revisions) for the Pre-FLAMES survey, and follows earlier releases of different sets of night products produced with improved reduction techniques.

The present release consists of a sample of 7 catalogs extracted using from fully calibrated ESO/MPG 2.2m WFI images in B-, V-, and I- passbands of 7 different fields. The fields include 4 pointings centered on 1 globular cluster in the Saggittarius dwarf galaxy, 1 pointing covering 1 globular cluster of the Small Magellanic Cloud (SMC) and 2 pointings at the poles of the bulge of the Milky Way (MW). Details about the images can be found in release number 21.

Retrieving EIS Products


Official EIS products can be retrieved via two alternate routes, both originating at the EIS home page. These procedures are described elsewhere (see Retrieving EIS Products). It is worth reiterating that to request data users have to be registered with the ESO Science Archive.

In the case of the present release the "data release information section" is followed by a section detailing the "contents" of the release, listing:

  1. Table entry number (not to be confused with the "Product Identification number" which is reported in the main HEADER of the FITS format catalog);

  2. EIS standard field/region name

  3. Passbands for which the catalogs were produced (Band);

  4. Right Ascension of center of catalog (RA) in J2000.0;

  5. Declination of center of catalog (Dec) in J2000.0;

  6. Total number of objects in the catalog being released, which includes only those detected in all three passbands considered;

  7. Total area (in square degrees) within which objects were extracted;

  8. Grade (A to D, from good to bad) assigned to the catalog, from the visual inspection of the product by the EIS team;

  9. Total volume (in Megabytes) of the selected product;

  10. Hyperlink to the product log;

  11. Interactive check-box which enables the individual product to be selected/de-selected before finally submitting the selection to the ESO Science Archive Facility using "Request Marked Products" at the foot of the page.

Note: All data products are subject to revision and update once released. A report of the changes may be found in the ``COMMENTS'' field next to the particular release (in the release WEB page) and/or in the READMEs of the revised release.

Product Logs

For each survey product the EIS system prepares a ``product'' log from which the process log and the configuration file used can be accessed and inspected. Currently, the product log associated to a Multiple-Passband Catalog just consists of a basic product identification, 1 color-color plot and 1 plot with 2 color-magnitude diagrams.

Even though the product logs are still not in their final form, the logs available in the present release serve to illustrate the type of information the system is able to provide to survey users as a complement to the catalog itself.

Comments Specific to this Release

This is the first release of color catalogs associated with images of release 21. The catalogs were produced using the software suite DAOPHOT/ALLSTAR and SExtractor within the framework of the EIS Data Reduction (Survey) System.

The products in this release are the B, V, and I color catalogs with PSF magnitudes calibrated in both the natural WFI system and the standard Johnson-Cousins system (preliminary).

The catalogs were generated using the photometry of each image obtained with DAOPHOT following the recipes already used for the first Pre-FLAMES release (version 0.5; 6 July 2001) and described in detail in Momany et al. (2001). The present color catalogs consist of the association of the SHORT and LONG exposures of the B, V and I passband (when available) of each single field.

The catalogs are available in the following formats:

  1. FITS file: The full associated color catalogue with all the DAOPHOT measured quantities for each single image and passband as well as the association parameters. Magnitudes are in the WFI and Johnson-Cousins systems. File extension ".fits"

  2. ASCII file: The ascii version of the full fits color catalogue containing only positions and magnitudes. File extension ".asc"

  3. FPOSS file: The FLAMES file allocation catalogue. A reduced version of the full FITS color catalogue to be used with the fibers configuration tool FPOSS. File extension ".fld"

  4. SKYCAT file: A reduced version of the full FITS color catalogue useful for the display of target objects with the SKYCAT catalogue plotting facility. File extension ".scat"

Below a detailed description of these files is provided. Note that the ``product'' being distributed is a gzipped tar file containing all these different formats, as currently there is no mechanism available to allow users to select their desired format.

FITS file

The FITS catalog consists of several binary tables, based on the ``Leiden Data Center'' (LDAC) convention originally adopted by the DENIS project and later expanded in the course of the EIS project. The 2 important tables are the FIELDS_00 and OBJECTS tables. FIELDS_00 contains some basic information such as the name of the field, the RA and DEC range of the field and the detected number of objects. The OBJECTS table contains the DAOPHOT/ALLSTAR measured quantities for all the detected objects. In the latter case there are 239 keywords for each object -- not all of which are important.

The most important keywords for each of the two tables are the following:

-> FIELDS_00
Keywords     Description     
OBJECT       The EIS PF survey name of the observed Field
COLORINFO    The color-number translation of the keywords in 
             the OBJECTS table, e.g. 00 = V, 01 = I, 02 = B
OBJECT_COUNT The number of objects in the color catalogue
METHOD       The name of the program used to measure  magnitudes 
Keywords     Description     
ALPHA_J2000  RA coordinate of the detected object
DELTA_J2000  DEC coordinate of the detected object
MAG_AUTO     DAOPHOT magnitude 
MAGERR_AUTO  DAOPHOT magnitude error 
CHI2DAOPHOT  chi^2 PSF fitting parameter
SHARP        DAOPHOT sharp PSF fitting parameter
ASSOCIATE    Indicies of the associated objects 
N_XX_YY      Number of objects associated
MAG_AUTO_WFI Final WFI calibrated DAOPHOT magnitude
MAG_AUTO_JC  Final Johnson-Cousins calibrated DAOPHOT  magnitude

The MAG_AUTO, MAGERR_AUTO, CHI2, and SHARP of each single image are identified by the subscripts _FAINT, _BRIGHT for the LONG and SHORT exposures respectively and _00, _01 or _02 for the three B, V and I passbands. This means that the keyword relative to the magnitude of the LONG exposure in the B passband is MAG_AUTO_FAINT_02 and so on.

From the association keywords like ASSOCIATE_XX_YY and N_XX_YY (with XX and YY in the range 00, 01 and 02) it is possible to match the magnitudes and the other parameters of the objects.

ASCII file

The ASCII version of the FITS file contains a selection of the most relevant keywords from the OBJECT table in the FITS catalogue. This version of the color catalogue contains a header which reports the description of each keyword. Here we give an example:

# EIS Pre-Flames Survey Release version 0.6 
# ASCII color catalog produced on 2003-04-23T01:16:41.670 
# FIELD: OC99 
# RA: 08 51 24.600 
# DEC:   +11 48 50.688 
# Subscripts Legend 
# 00 = V band magnitude 
# 01 = I band magnitude 
# 02 = B band magnitude 
# JC = Johnson-Cousins calibrated magnitudes  
# WFI = WFI natural calibrated magnitudes 
#   1 SeqNr               Object sequence number (from make_ssc)         
#   2 ALPHA_J2000         Right ascension of barycenter (J2000) [deg]
#   3 DELTA_J2000         Declination of barycenter     (J2000) [deg]
#   4 MAG_AUTO_00         converted to Johnson-Cousin
#   5 MAGERR_AUTO_00      average magnitude error    
#   6 MAG_AUTO_01         converted to Johnson-Cousin
#   7 MAGERR_AUTO_01      average magnitude error    
#   8 MAG_AUTO_02         converted to Johnson-Cousin
#   9 MAGERR_AUTO_02      average magnitude error

FLD file

This an ascii catalogue in FLAMES format (for a description see

The following is an example of the header of the FLD file.

 * EIS Pre-Flames Survey Release version 0.6
 * FPOSS input color catalog produced on 2003-04-15T19:14:25.340
 CENTRE 16 32 32.702 -13 03 11.952
 * OBJECT   RA_J2000   Dec_J2000   Fib PRI MagV Id  MAG_B ERR_B  MAG_V ERR_V   MAG_I ERR_I
 *       hh mm ss.sss ddd mm ss.sss

Comparison to Previous Release(s)

This is the first official release of color catalogs extracted from properly calibrated images. Previously, color catalogs with tentative photometric calibration were distributed on-demand, in particular, to the FLAMES GTO and Science Verification teams and to users with granted observing time at FLAMES. The feedback received was positive regarding the accuracy of the astrometry and the precision of the photometry.

Data Reduction

This release represents a first set of color catalogs extracted from WFI images and created systematically using the EIS Data Reduction/Survey System infrastructure in a fully un-supervised manner. These input images were astrometrically and photometrically calibrated as described in release number 21. The color catalogs being released were produced in the following way. Sources have been extracted and analyzed from each of the 6 single images (3 filters B, V and I for 2 exposures, SHORT and LONG) of each PF Field using the DAOPHOT and ALLSTAR programs. The programs have been fully integrated in the EIS PANEL tool creating an appropriate pipeline which allowed an automatic and un-supervised calculation of the internal PSF of each image and final extraction of PSF magnitudes. Moreover the pipeline also filters and produces automatically the final color catalogs from each single image list of objects. The "recipe" used to obtain the PSF magnitudes is very similar to that already used for the previous PF color catalogue release (version 0.5, see Momany et al. 2001) -- with some modification to the criteria of the selection of the PSF stars.

Before the creation of the color catalogue, an important step is the filtering of the DAOPHOT single image lists to remove possible spurious objects (satellite trails, spurious detections along the gaps, stellar spikes etc.). After some experimentation the 3 quantities ERROR, CHI2 and SHARP calculated by DAOPHOT/ALLSTAR are used to filter out spurious detections in the present release.

In an effort to detect as many sources as possible, the catalogs provided have had conservative filtering thresholds applied: Only sources with uncertainties in the determined magnitude greater than 0.2 have been omitted from the catalogs. Therefore among the numerous source detections, spurious objects will be present. A limited number of additional catalogs with somewhat stricter thresholds applied can be provided upon request.

The final color catalogue is produced in two steps:

  1. For each passband the SHORT and LONG filtered objects lists are combined.

  2. The combined lists for the 3 filters are then associated in the final color catalogue.

In all steps the association is done using the LDAC ASSOCIATE program. The acceptance circle for the association is 1.0 ARCSEC.


The accuracy of the astrometric calibration relies on the astrometric calibration of the reduced images and the reference catalog used. As described in previous releases, it is typically better than 250 mas.


The reduced images were calibrated to the Vega magnitude system based on observations of Landolt (1992) standard stars as described in release number 21. Note that for the reduction of the science frames, a correction for illumination effects has been applied while this is not the case for the standard images. While this correction improves the relative photometry for an image, there may be some offset in the absolute calibration.

The DAOPHOT PSF magnitudes of the final color catalogs are provided calibrated in both the natural WFI system and the standard Johnson-Cousins system (preliminary). The procedure adopted for the calibration is the following:

The calibration in the natural WFI system is performed on each extracted list of objects using the zero-point provided with each image, which is already corrected for atmospheric extinction (see README for release 21). When combining the SHORT and LONG exposures for each passband, the mean zero-point offset is calculated and applied to the LONG exposure to place the whole photometry on the same system. No color correction is applied.

The calibration on the standard Johnson-Cousins system has been performed starting from the calibrated WFI magnitudes and applying the color term correction appropriate for each passband and already listed in the README file of the released images. The following formula is adopted

 mag_JC - mag_WFI = c_term * color_JC   (1)

Using the following color terms:

Passband color term color term (JC)
B_WFI +0.31 (B-V)_JC
V_WFI -0.09 (B-V)_JC
I_WFI +0.18 (V-I)_JC

where JC stands for the Johnson-Cousins system.

In order to obtain each final calibrated magnitude, an appropriate solution is found by coupling formula (1) with the color terms whenever all 3 or only 2 of the B, V and I magnitudes are available.

In the final color catalogue, all the objects only detected in 1 single band and surviving at all the filtering (i.e. suposed to be "real" objects) are NOT calibrated in the JC system and are kept in the natural WFI system.

The photometric calibration (either WFI or JC) used for the present color catalogs is however preliminary since the B-band shows an offset of almost 0.3 magnitudes while the other bands seem correct. The reason of this offset has not been found yet but it could be due to differences in the reduction of the sciences images compared to the standards frames (possibly the illumination correction).

Data Quality Assessment


Before being released the catalogs overlayed on the images were examined by eye and graded by the EIS team, with the grade range being from A (best) to D (worst). The grade is meant as a subjective indication of the quality of the catalog.

Out of the 7 catalogs being released, 2 were graded A and 5 B. The table below presents all cases where comments were made. The table, ordered by increasing grade, lists: in column (1) entry number; in column (2) the region name; in column (3) the EIS field name; in column (4) the grade; and in column (5) a comment.

# Region EIS Field Name Grade Comment
1 SG-C SG-09 B Not complete at the center of the cluster
2 SG-C SG-10 B Not complete at the center of the cluster
3 SG-C SG-11 B Not complete at the center of the cluster
4 SG-C SG-12 B Not complete at the center of the cluster
5 SMC08 SMC08 B Not complete at the area of the cluster. Few bright objects missing
6 MW10 MW10 A Most objects with 3 bands detected. Few bright objects missing
7 MW13 MW13 A Most objects with 3 bands detected. Few bright objects missing

Photometric Calibration

The quality of the photometric calibration of the reduced images has been assessed in the EIS release number 21 and is commented in the previous section.

Next Release(s)

Originally, the following releases were scheduled:

Unfortunately, since the EIS project is scheduled to terminate on December 31, 2004 the EIS team will not be able to complete the work until then.


This release is the eleventh of 2004, and number 27 since March 1998. It is a first temptative release of science-grade color catalogs extracted from stacked products created using the framework of the EIS Data Reduction (Survey) System. The production of the catalogs was done in a completely un-supervised way, with a throughput, varying as a function of the density of the field, of about 0.1 Mpix/sec, a good match to the data rate of other parts of the pipeline. It is important to emphasize that as one goes down the chain of survey products the more complex they become making it difficult to assign a quality for all possible applications. Fine-tuning of parameters may also prove necessary, and may depend on the specific application. Feedback from users would be extremely helpful.


Bertin, E. & Arnouts, S., A&AS, 117, 393

Landolt, A. U., 1992, AJ, 104, 340

Momany, Y. et al. , 2001, A&A, 379, 436

Stetson, P. , 1987, PASP, 99, 191

Zaggia, S. et al., 2001, The Messenger, 105, 25

Remco Slijkhuis 2004-12-15