DPS/WFI Survey Release

CURRENT RELEASE Survey ..................... DPS Telescope .................. ESO/MPG 2.2m Instrument ................. WFI Program IDs ................ 169.A-0725; 67.A-0244(A); 164.O-0561 Origin ..................... ESO/EIS Number of regions .......... 3 Region ..................... DEEP1; DEEP2; DEEP3 Number of Fields ........... 11 Passbands .................. U; B; V; R; I Number of Filters .......... 7 EIS Release Number ......... 20 Version .................... 0.7 Total Data Volume .......... 158 Gb Release Date ............... October 2004 Release prepared by ........ EIS/PSG team, A. Mignano

PRODUCTS Product Type ............... Nightly Products Number of Reduced Images ... 287 Data Volume ................ 158 Gb

PREVIOUS RELEASE Origin ..................... ESO/EIS Number of regions .......... 1 Region ..................... DEEP2c Number of Fields ........... 1 Passbands .................. U; B; V; R; I EIS Release Number ......... 11 Version .................... 0.5 Release Date ............... 7 March 2001

PRODUCTS Product Type ............... Survey Products Number of Stacked Images ... 6 Number of catalogs ......... 6

Abstract

Based on ideas submitted by the ESO community and evaluated by ESO's Survey Working Group (SWG), the DPS survey, administered by the ESO Imaging Survey (EIS) and Public Survey Group (PSG) teams, comprises three optical and infrared strategies. The optical part consists of a deep survey covering three regions of 1 square degree on the sky, in U-, B-, V-, R- and I passbands, using the wide-field imager (WFI) mounted on the ESO/MPG 2.2m telescope at La Silla. Each of the three DEEP regions -- 1, 2, 3 -- is covered by circa of four WFI pointings (in five passbands) -- a, b, c, d -- per region. The regions were selected both to enable observations year-round and because they overlapped with regions of other scientific interest. For instance, DEEP1 was chosen to complement deep ATESP radio survey carried out with the Australia Telescope Compact Array (ATCA) covering the region surveyed by the ESO Slice Project, while DEEP2 included the CDF-S field. Finally, DEEP3, was chosen in the northern galactic hemisphere, thus providing an almost year-round coverage (see original proposals for more details). The location and the characteristics of the surveyed regions as well as the planned limiting magnitudes in each passband can be found in the DPS strategy page. One should be aware that in an attempt to improve the performance of the survey, new U and I filters were purchased and used during the course of the observations (see below).

The data contributing to the present release were obtained as part of the ESO Large Programme: 164.O-0561, carried out in visitor mode and its service mode continuation (30 hours) 169.A-0725 (Principal Investigator: J. Krautter, as chair of the SWG), complemented by V- and R-band observations from the following ESO programme (Principal Investigator: P. Schneider): 67.A-0244, covering the DEEP-1 region.

The present release consists of data from the above programs accumulated in observations covering six semesters (Periods 64-69) from November 4, 1999 through September 28, 2002, corresponding to 1872 science exposures, and 246 hours of on-target integration, during a period of 76 nights. About 132 exposures (28 science OBs) in the V- and R-band were taken in 10 nights from the contributing program. About 34% of the V-band and 26% of the R-band data are from the contributing program.

With the present release 90% of the data accumulated by the DPS program, covering 2.5 square degrees, in at least one band, and 1.75 square degrees in five passbands, have been reduced. The remaining 196 exposures include tests, wrong pointings, as well as discarded images. About 10% of the images in all filters have been discarded, with the exception of the B-band.

The 1872 raw WFI exposures (171 Gb) were converted into 312 fully calibrated reduced images, of which 287 are being released. Of the remaining 25 one was observed with the narrow-band I filter # 854 and 24 were rejected by visual inspection namely, 3 B, 5 V, 1 R, and 15 I images.

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 second release of data products associated with the DPS/WFI survey. The complete data set was accumulated from the commissioning of WFI to October 2002, during ESO observing periods 63 through 69.

The present release consists of 287 fully calibrated, reduced ESO/MPG 2.2m WFI images in the following passbands:

The breakdown of these images per region/field is presented in the table below. The table lists: in column (1) a sequence number; in column (2) the EIS region name; in column (3) the EIS field name, and in columns (4)-(10) the number of fully calibrated images (and in parenthesis the number of independent nights on which they were observed) being released in each of the passbands.

#	Region	EIS Field Name	U#877	U#841	B#842	V#843	R#844	I#879	I#845
1	DEEP1	DEEP1a	20 (12)	5 (2)	4 (1)	0 (0)	4 (2)	0 (0)	10 (4)
2	DEEP1	DEEP1b	11 (9)	0 (0)	6 (4)	5 (5)	11 (4)	0 (0)	11 (6)
3	DEEP1	DEEP1c	0 (0)	0 (0)	0 (0)	3 (3)	6 (4)	0 (0)	0 (0)
4	DEEP2	DEEP2a	0 (0)	0 (0)	0 (0)	0 (0)	3 (3)	0 (0)	0 (0)
5	DEEP2	DEEP2b	17 (5)	0 (0)	4 (2)	4 (2)	3 (3)	0 (0)	5 (4)
6	DEEP2	DEEP2c	12 (5)	11 (3)	0 (0)	5 (2)	0 (0)	0 (0)	9 (3)
7	DEEP2	DEEP2d	0 (0)	0 (0)	0 (0)	0 (0)	2 (2)	0 (0)	0 (0)
8	DEEP3	DEEP3a	10 (4)	7 (4)	9 (6)	5 (5)	6 (5)	0 (0)	1 (1)
9	DEEP3	DEEP3b	9 (3)	0 (0)	6 (2)	4 (2)	2 (1)	0 (0)	7 (5)
10	DEEP3	DEEP3c	18 (7)	0 (0)	5 (2)	3 (2)	4 (3)	0 (0)	8 (6)
11	DEEP3	DEEP3d	0 (0)	0 (0)	1 (1)	3 (2)	0 (0)	8 (5)	0 (0)

The data covers 11 fields of the 12 requested distributed in all three regions. The completeness of the coverage can be found in the ``completeness'' plots accessible from the EIS WEB pages.

The OBs used in the observations were typically: in the U-band the OBs varied from five 900 seconds exposures to five 550 second exposures; in the B-band the OBs comprised five 300 sec exposures; in V-band

Note that in the course of the program there were changes in the observing strategy in the U-, to conform to the one hour limit for a single OB, and I-band, to improve the fringing correction. It is important to point out that the chnage in strategy was unrelated to the change in the actual filter used in these passbands.

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 (involving reduced images only) the "data release information section" is followed by a section detailing the "contents" of the release, listing:

NB: note that the assigned grade takes into consideration the type of product considered. For instance, a grade ``A'' stack does not have the same meaning as a grade ``A'' night product associated to one RB

For each survey product the EIS system prepares an extensive ``product'' log from which the process log and the configuration file used can be easily accessed and inspected. This infrastructure provides the means of ensuring the uniqueness of the ingested products. It also provides the information required to understand differences between versions of the same product.

Typically, the product logs consist of seven distinct sections represented in the rendering of the HTML as separate tabs. These sections consist of:

For the time being, a preliminary implementation of this infrastructure is available for the single chip instruments. Work is under way to upgrade and generalize this infrastructure to support all instruments.

In the upper right corner of the data release WEB page there are two buttons (completeness and properties) which link to plots showing the completeness of the dataset being released relative to the original strategy. It also presents different visualizations of the attributes associated with the images being released (for details see Data Quality Assessment section below).

Since the infrastructure is still under development, currently plots are being produced without adequate description. It is foreseen that in the future the these plots will be embedded into HTML files providing captions and statistics.

Comments Specific to this Release

DPS was the first multi-color survey carried out using WFI. In an attempt to improve the performance of the observations in the U- and I-bands new filters were purchased and were deployed following the recommendations of the SWG as they became available. This implies that about 80% of the U observations were carried out with filter #877 first deployed in October 26, 2000, but only 13% of the I observations were carried out with the desired filter #879 first used on the night of March 10, 2002.

Since WFI was first offered as a common user instrument at the ESO/MPG 2.2m telescope in 1999, the available filter set and naming conventions have evolved somewhat. To avoid confusions it is instructive to state explicitly the filter set used when conducting the present survey. The current La Silla Science Operations naming convention assigns all filters which are permanently available at the WFI an ESO identity number. If the filter does not have a special name (U, B, V etc.) then the assigned name is "CWL/FWHM" where CWL is the truncated central wavelength (nm) and FWHM is the truncated full-width at half-maximum (nm). If the filter has a special name, the FWHM of the filter (in nm) is appended to the special name. A full description of the filter names can be found at the WFI Filter Characteristics page of the La Silla Science Operations.

The completeness of the survey in area and passband can be seen in the figures accessible from the release WEB page. This figure shows for each field two superposed histograms showing time versus passband, the latter represented by the ESO filter name convention. The hatched histogram represents the total integration time required by the original strategy (in seconds). The full colored histograms represents the sum of the integration time (TOT-EXPT keyword in the header) of all reduced images in a particular filter. The color code adopted for the filters (passbands) here and elsewhere is as follows: U (#877; blue); U (#841 magenta); B (black); V (green); R (red), I (#879; magenta); and I (#845; yellow). Note that in some cases the R-band exceeds the originally proposed integration time, due to the exposures obtained by the contributing program. In addition, due to the lack of prior information about the new U-filter (#877) and the strong desire to reach the proposed limiting magnitude in U-band, observations taken in less than ideal conditions were repeated also leading to total integration times exceeding those of the original proposal.

This release consists of ``reduced'' images, thus for a given field and filter there may be more than one image product either from the same night (resulting from differently grouped raw images or several similar OBs) or from different nights. Also note that here only exposures for the programs given above are being considered. Considerable more data are available for DEEP-2c when one combines data taken as part of the commissioning period, GOODS observations, COMBO-17 - however, combining all of these data is beyond the scope of the present release. This will be done as part of future releases dealing with the preparation of more advanced survey products.

As explained elsewhere (see EIS Definitions and Conventions) the conventions adopted by EIS to identify a pointing both internally and externally (e.g. OB name, object name, target name, field name) and their graphical representations on the EIS WEB pages have evolved considerably as new procedures were introduced, making it impossible to strictly maintain consistency.

Field names can normally be found in the OBJECT keyword of the FITS header. Since they are, normally, inherited from ``Observation Blocks'' (OBs) which have been prepared by multiple team members, the naming convention may not be homogeneous, and thus it is recommended that the value of the OBJECT keyword should not be, in general, used to rename files.

In the particular case of this survey one should be warned that the contents of the OBJECT keyword do not necessarily correspond to the name convention listed above. For instance, for the DEEP-2c pointing one also finds object names given by AXAF-FX-YY where X represents a passband and YY is the OB identifier.

Comparison to previous release(s)

A first release of optical data for this survey (stacked images for DEEP2c) was carried out 7 March 2001 and described in detail in Arnouts et al. (2001). Since then several improvements have been introduced in the code and are briefly mentioned below.

Data Reduction

The WFI data were reduced using the EIS/MVM image processing library (version 1.0.1). This software package is publicly available and can be retrieved starting from the EIS survey release page.

Each field is the co-addition of a number of sky-subtracted frames (the TOT_IMAG keyword in the FITS image header) grouped in a number of "Reduction Blocks" (RB). The basic reduction methodology is described in Vandame (2004). Significant improvements have been made since the last release of WFI data:

It is important to point out that, most of the data for DPS were reduced slightly earlier than those for XMM and have not benefitted from all the lessons learned from those data. In particular, the construction of the RBs are different from those adopted in the case of XMM and have not been optimized to reduce the number of residual cosmic rays in the final stack. It is also important to note that the observing strategy adopted for the I-band DPS observations was different and involved less exposures of longer integration time per OB. Longer integration times (a factor of 2 compared to the strategy adopted for XMM) has proven to be much more difficult to estimate and remove the fringing pattern. The fact that no external fringing map was used is due to the fact that the DPS regions are at large galactic latitudes.

Astrometry

The astrometric calibration was derived using the GSC2.2 reference catalog and a distortion model described by a second order polynomial. Comparisons yield a typical scatte of 0.2 arcseconds (Vandame 2004). However, comparisons made using exposures of a globular cluster shifted by half a field strongly suggests that the internal accuracy is of about 70 mas. The astrometric calibration is carried out on a chip by chip basis. Possibly, connecting the different solutions may lead to a futher improvement in the accuracy. The WCS in the image header is reported using the CD-matrix notation. The projection adopted is TAN and the orientation is north up and east to the left.

Photometry

It is important to stress that the photometric pipeline being used to automatically extract catalogs, measure fluxes at different apertures, identify those corresponding to known standard stars, and derive from linear fits to these measurements zeropoints, extinction and color terms (if applicable) was originally developed to deal with single chip imagers - only recently systematic tests have been conducted for multi-chip cameras. A number of improvements to the code and more experimentation with the many configurable parameters involved are still possible. Therefore, the solutions presented in this release should not be considered final.

In accordance with the established EIS standard procedures, photometric calibration of the science fields is performed on the Vega magnitude system. Zeropoints are obtained from linear fits to the measured instrumental magnitudes of standard stars in Landolt (1992) fields taken at the same night as the science frames. These fits were obtained using from one (taking some specified values for the extinction and color term) to three free parameters depending on the available airmass and color coverage. Nearly all observations were carried out in visitor mode, by a large number of people, making it difficult to ensure a homogeneous calibration plan.

For the present release photometric solutions were attempted for the 75 nights with observation of standard fields, for the 76 with science observations (including images with grade D). For three nights either no standards were observed (September 27, 2002) or they were missing for a particular filter (November 29, 2000, U-band and June 7 2002, I-band).

A total of roughly 500 standard OBs, nearly all consisting of two images per OB, have been reduced and measured. While this amounts to slightly more than 10 hours on-target (or 4% of the science observations in terms of time), it exceeds the volume of science frames. Depending on the night the number of measurements can range from a few to over 300, covering from 1 to 3 Landolt fields. The period of observations extend over three years.

In practice, the photometric pipeline computes photometric parameters for all possible types of fits (one to three-parameters) and assigns the solution with the smallest zeropoint scatter, to be the ``best solution'' for the night. A night is considered photometric if this scatter is less than a pre-defined value, which at the present time is taken to be below 0.1 mag. If none of the solutions satisfy this criteria and/or the solution found yields unrealistic results (e.g. negative extinction) then the night is considered non-photometric and a default value for the zeropoint is adopted and its error set to -1.

For homogeneity, the default value normally adopted is the median of the zeropoints reported in the trend analysis kept by either the telescope team (depending on the instrument) or the internal EIS database. In the case of WFI, only one solution is currently reported in the WFI WEB pages. It is important to emphasize that EIS has and still is conducting several surveys (e.g. Pilot, DPS, Pre-Flames, XMM and Galex) using WFI, covering its entire operational lifetime. Therefore, in the future a trend analysis of the photometry will become naturally available.

The table below summarizes the number of nights with standard observations and type of ``best solution'' obtained by the photometric pipeline for each passband.

The preparation of this release has shown the need for a number of improvements to be made to the photometric pipeline. Among those either under development or being considered are:

It is important to recall that wide-field multi-chip cameras are complex systems and to obtain a proper calibration depends upon a full understanding of the different effects outlined above. This requires extensive tests which can only be effectively done using automatic procedures as well as versioning infrastructure similar to the ones available in the EIS survey system. In order to carry out these tests efficiently and in a systematic way, a re-factoring of the code, and the implementation of suitable workflows and test-environment are currently underway. This study will be of great importance for defining calibration procedures to be adopted not only for WFI but for other wide-field cameras to be used in large imaging surveys

These photometric solutions were used to calibrate the reduced images. The ZP in the header of a reduced image is given by

where ZP' is the zeropoint at zero airmass (determined from the linear fit), K is the extinction coefficient and X is the airmass in which the image was observed. Therefore, the Vega magnitude is given by

where the flux is the number of counts directly measurable on the images (note that the reduced images are normalized to 1 sec).

In the case of a non-photometric night, a default value for the zeropoint is adopted and the error in zeropoint is set to -1. For nights without observation of fields containing standard stars, a default zeropoint and an error of -2 are assigned to the image. Finally, during quality assessment of the data, calibrated images with zeropoints that deviate significantly from a reference value have the zeropoint in the header changed to a default value and its error set to -3. Note that when a default value is assigned all images will have the same zeropoint in the header regardless of the airmass at which they were observed. It is important to stress that the history of the image calibration process can be retrieved independently of the solutions found for a night.

In the case of stacks, the actual value adopted for the default zeropoint of the reduced images is irrelevant, since those images with default zeropoints have to be re-scaled anyway to match the flux-scale of those images properly calibrated. The final photometric accuracy, however, will depend on the type of solutions and number of independent nights contributing to the final stack.

As a preview, the table below shows for each pointing the best type of solution available for each passband.

From the above table one finds that all pointings/filter combinations have photometric solutions, even though some rely on one-parameter fits. More importantly, in nearly all cases a 3-parameter fit exists for at least one field thus allowing the photometric calibration to be bootstrapped or cross-checked to other fields. The exception is B-band for DEEP-1 and DEEP-2 and R-band for DEEP-3. Another exception is the U-band #841 filter which had poor airmass coverage and only one-parameter fits are available. This filter also does not have a solution from the Telescope Team thus hampering further confirmation.

For detectors formed by a mosaic of individual CCDs, in order to correct for CCD-to-CCD gain variations, median background values sampled in sub-regions bordering adjacent CCDs are used to harmonize the gain to a value common for all CCDs in the mosaic. This has been applied to both science and standard exposures.

It is also known that large-scale variations due to non-uniform illumination over the field of view of wide-field instruments exist. The significance of this effect is passband-dependent and becomes more pronounced with increasing distance from the optical axis (Manfroid et al. 2001; Koch et al. 2004; Vandame et al. 2004). Automated software to correct for this effect has been developed but due to time constraints it has not yet been applied to these data.

Cosmetic Features

In contrast to the previous release of XMM survey data, over 60% of the reduction blocks consist of 5 or less frames. This has the effect of leaving the imprint of the inter-chip gaps and as explained in the README of release #19 leads to a larger number of cosmic rays in the reduced images and in the final stack at the location of the inter-chip gaps. This high number of cosmic rays affects the calculation of the seeing on the image, especially in the U-band.

Note, however, that the reduced images being released do not reflect the quality of the final ``stacked'' image.

The performance of the automatic satellite track masking algorithm has been proven to be very efficient in removing both bright and faint tracks. The frequency for the appearance of these tracks is about 0.9 satellite-tracks/hour, out of which only 1/10 are of the bright type. The extreme case is 3 satellite tracks of varying intensity in a single exposure.

In the case of the U-band images (both filters) the electronic noise is clearly visible because of the low level counts of the background in most exposures (550-900 seconds).

Data Quality Assessment

Before being released the images were examined by eye and graded by the EIS team, with the grade range being from A (best) to D (worst). This grade refers only to the visual aspect of the data (e.g. background, cosmetics). In the future the grade will also include a larger set of quality control parameters (QCP) and will be available for each survey product via a corresponding product log.

Out of 312 reduced images covering the selected DPS fields, 119 (38%) were graded A, 131 (42%) B, 37 (12%) C and 25 (8%) D. From the plots available from the release page on the WEB one finds that the major difficulties in the reduction are for the U-band where most of the images are graded B (primarily due to the electronic noise) and the I-band especially in the case of the filter #845 due to inadequate fringing correction caused by the long integration time used per exposure, which proved inadequate to estimate the fringing map.

Note that images with grade D are not being released, since they have no scientific value. In the table below the 25 images with grade D are presented. The table, ordered by field and date, lists: in column (1) entry number; in column (2) the EIS field name; in column (3) the passband; in column (4) the date when the night started (YYYY-MM-DD); in column (5) the grade given by the visual inspection; and in column (6) the primary motive for the grade.

# Region EIS Field Name Passband Filter Date Grade Comment

1 DEEP1 DEEP1a V #843 2000-07-03 D wrong registration

2 DEEP1 DEEP1a V #843 2000-07-03 D Wrong registration

3 DEEP1 DEEP1a V #843 2000-07-03 D Wrong registration

4 DEEP1 DEEP1a B #842 2000-07-03 D wrong registration

5 DEEP1 DEEP1a I #845 2000-07-04 D Fringing, abusive masking

6 DEEP2 DEEP2b R #844 2000-08-27 D Out of focus

7 DEEP2 DEEP2b B #842 2000-11-27 D Out of focus

8 DEEP2 DEEP2b I #845 2000-11-29 D Fringing, abusive masking

9 DEEP2 DEEP2b I #845 2000-12-26 D fringing, abusive masking

10 DEEP2 DEEP2b I #845 2000-12-26 D Fringing, abusive masking

11 DEEP2 DEEP2b I #845 2001-07-26 D abusive masking

12 DEEP2 DEEP2c I #845 1999-11-04 D very strong fringing

13 DEEP3 DEEP3a I #854 2000-02-26 D I narrow band filter, abusive masking

14 DEEP3 DEEP3a I #845 2000-02-26 D abusive masking

15 DEEP3 DEEP3a I #845 2000-02-26 D absusive masking, fringing, stray light reflexions at the lower left corner

16 DEEP3 DEEP3a I #845 2000-03-29 D abusive masking, stray light reflexions at the upper and lower left corners

17 DEEP3 DEEP3a I #845 2000-03-30 D low level fringing, abusive masking

18 DEEP3 DEEP3a I #845 2000-03-31 D abusive masking

19 DEEP3 DEEP3a I #845 2000-03-31 D abusive masking

20 DEEP3 DEEP3a I #845 2000-04-01 D abusive masking

21 DEEP3 DEEP3a V #843 2000-04-06 D just 1 image of 30 seconds

22 DEEP3 DEEP3b V #843 2001-02-02 D short integration time

23 DEEP3 DEEP3b I #845 2001-02-21 D abusive masking

24 DEEP3 DEEP3b I #845 2001-02-21 D abusive masking

25 DEEP3 DEEP3d B #842 2002-06-07 D suspicious image. Saturated stars show a second rotated blooming cross, needs investigation of the individual images.

The 37 images with grade C are mot listed as shown below about 27% of them are U-band images with a prominent contribution of the eletronic noise to the background and/or masked out strips due oversensitive track detection and I-band images with relative strong residual fringing. However, it should be possible to use these images to contribute to the final stack.

The table below shows for each filter the grade breakdown. The table gives: in column (1) the passband; in column (2) the ESO filter number; in column (3) the number of images; (4)-(7) the ratio of images in a given grade to the total number of images taken with that filter. The table shows that for BVR bands over 84% of the products are grade A, while for U- and I-bands the grade distribution is remarkably different due to the low-counts in the U-band, and the prominence of the eletronic noise, and inadequate fringing correction for the I-band.

Another way to illustrate the above conclusion is shown in the following table. The table lists: in column (1) the grade; in column (2) the total number of images with a given grade; in columns (3)-(8) the fraction of images of a given grade and filter relative to the total number of images with that grade. Inspection of the table clearly shows, for instance, that about 60% of the discarded images were observed in I-band with the filter #854. Somewhat surprising 20% of the discarded images were in V-band - however, all are from the same night July 3, 2000. For these images the astrometric calibration failed.

As part of the photometric calibration, nights with good airmass and color coverage were used to compute complete photometric solutions, namely those for which all parameters (zeropoint, extinction and color term) can be independently estimated. In the table below we show the results giving: in column (1) the passband/filter; in column (2)-(4) the median zeropoint (Zp), extinction, (k), and color term (color) values for all solutions with three parameters.

The photometric solutions computed automatically by the EIS Survey System were compared with the ``best solution'' recently obtained by the 2p2 Telescope team. The results of this comparison are presented in the table below for the general case of 3-parameter fits. The table lists: in column (1) the passband; in columns (2)-(4) the offsets (EIS-Telescope Team) of the zeropoint, extinction and color term.

The solutions are remarkably similar, despite the fact that they are over two years apart.

It is worth emphasizing that, for the present release, the periods of observations of standard stars available to the two teams do not coincide. Also note that there are three (in U, B and I) filters EIS has used for which no solutions have been reported by the telescope team. For these cases, the differences are listed as not-available (n/a).

Not surprisingly, larger offsets are obtained when 2- and 1-parameter fits are included, depending on the passband and estimator used to derive the estimates for extinction and color term, as applicable. Finally, taking into consideration only 3-parameter fit solutions and after rejecting 3 sigma outliers one finds that the scatter of the zeropoints is less than about 0.1 mag. This value for scatter is a reasonable estimate for the current accuracy of the absolute photometric calibration of the DPS survey data.

The quality of the photometric calibration for the dataset being released can be estimated from the table below. The table lists: in column (1) the passband/filter combination; in column (2) the median zeropoint (Zp) including solutions obtained from fits with an arbitrary number of free parameters; in column (3) the estimated rms; in column (4) the largest offset of a night calibration relative to the median; in columns (4)-(7) the same as the three previous columns, except that now the estimate of the median was computed using only 3-parameter fits.

From the above table, one sees that considerable work remains to be done to significantly reduce the photometric calibration error which is typically of the order of 0.1 mag. A notable exception is the wider U#877, for which the rms exceeds 0.2 mag, indicating that this filter will be difficult to obtain a proper calibration.

An important feature of the EIS survey system is that it attempts to provide a backbone infrastructure to enable the user to have a global view of the dataset being released both in terms of the completeness of the survey as well as the quality of the survey products. This is achieved by the production of plots accessible through the release WEB page and the quantitative information (QCP) available in the product logs, so as to make the selection of products with the desired attributes possible. This infrastructure will be complemented by a proper script that will allow the user to select products based on configurable parameters.

The attributes of the released images are summarized in the following figures, available from the WEB release page:

Note that the seeing distribution is bi-modal with one of the peaks corresponding to the pixel size. This is due to the large number of cosmic rays in the individual reduced images, especially in the U-band. This effect is significantly reduced by stacking the images. In the meantime, a new software module is currently being developed to minimize this problem at the level of night products, based on the difference between the typical profile of the cosmics and astronomical sources.

Next Release(s)

Conclusions

This release is the fourth of 2004, and number 20 since March 1998 (of which two were software releases). Since May 2001 a total of over 1741 requests (averaging nearly 80 requests/month in 2004 and 30 requests/month over the period in which information is available) have been made for raw (1111) and reduced (630) data and of the EIS/MVM image processing software (73) . These requests comprised 82,400 files (5.8 Terabytes; 3.2 Tb compressed) of raw data and 7936 files (626 Gb) of survey products (reduced images from different instruments such as SOFI, ISAAC, and WFI). Note that the last public data release was carried out in August 2004.

Over the past few months significant progress has been made in the development of an entire set of administrative tools enabling users of the EIS Survey System to have easy access to a host of information essential for a controlled data release, ensuring a proper accounting of the destination of the accumulated data and a thorough description of the quality of the survey products, including summary plots now also available to the users of the survey data.. Major improvements were also made to the report-facility responsible for the preparation of the material displayed on the WEB and of the statistics of survey products requests. Most of these improvements are illustrated by the contents of the present release, others will be phased-in in subsequent releases.

Since the last release significant progress has also been made in the code used in the photometric calibration of the reduced images providing more information regarding the standards used, easier access to the images of the standard fields as well as more checks regarding the synchronization between solutions and the calibration of the images.

Finally, it is worth mentioning that the present release was a necessary intermediate step which will soon be followed by the release of stacks and more advanced products (single-passband and color catalogs).

References

Koch, A., Grebel, E. K., Odenkirchen, M., Caldwell, J. A. R. 2004 Astronomische Nachrichten 325, 299

Passband	Number of exposures	Integration/exposure (sec)	T (sec)
U	5	900	4500
U	5	550	2750
B	5	300	1500
V	5	300	1500
R	5	300	1500
I	5	600	3000
I	10	300	3000

Passband	ESO Filter Name	ESO Identity Number
U	U350/60	#877
U	U/38	#841
B	B/99	#842
V	V/89	#843
R	Rc/162	#844
I	BB#I_EIS	#879
I	Ic/Iwp	#845

Passband	Filter	# images	A	B	C	D
U	#877	97	0.02	0.88	0.1	0.0
U	#841	23	0.04	0.91	0.04	0.0
B	#842	38	0.87	0.03	0.03	0.08
V	#843	37	0.84	0.03	0.0	0.14
R	#844	42	0.88	0.1	0.0	0.02
I	#879	8	0.63	0.25	0.13	0.0
I	#845	66	0.15	0.26	0.36	0.23
I	#854	1	0.0	0.0	0.0	1.0

Grade	# images	U#877	U#841	B#842	V#843	R#844	I#879	I#845	I#854
A	119	0.02	0.01	0.28	0.26	0.31	0.04	0.08	0.0
B	131	0.65	0.16	0.01	0.01	0.03	0.02	0.13	0.0
C	37	0.27	0.03	0.03	0.0	0.0	0.03	0.65	0.0
D	25	0.0	0.0	0.12	0.2	0.04	0.0	0.6	0.04

Passband	Zp	k	color
U#877	21.94	0.45	0.04
U#841	n/a	n/a	n/a
B#842	24.61	0.26	0.24
V#843	24.2	0.16	-0.11
R#844	24.56	0.11	0.02
I#879	23.33	0.02	0.04
I#845	23.15	0.08	0.2

Passband	default	1-par	2-par	3-par	total
U#877	4	15	7	11	37
U#841	0	9	0	0	9
B#842	2	11	0	4	17
V#843	0	11	2	9	22
R#844	5	6	4	4	19
I#879	1	0	0	3	4
I#845	8	7	0	10	25

Passband	Zp	RMS	$\Delta$ max	Zp	RMS	$\Delta$ max
U#877	22.2	0.27	0.55	21.94	0.32	-0.77
U#841	21.73	0.1	-0.16	n/a	0	n/a
B#842	24.77	0.11	0.23	24.61	0.05	-0.29
V#843	24.13	0.1	-0.18	24.2	0.1	0.24
R#844	24.51	0.1	-0.19	24.56	0.07	0.22
I#879	23.33	0.02	-0.02	23.33	0.02	-0.02
I#845	23.16	0.12	-0.29	23.15	0.11	-0.3