Mathematics – Logic
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998eso..pres...12.&link_type=abstract
ESO Press Release, 09/1998
Mathematics
Logic
Scientific paper
Two Weeks of Intensive Observations Successfully Concluded
After a period of technical commissioning tests, the first 8.2-m telescope of the ESO VLT (UT1) has successfully performed an extensive series of "real science" observations , yielding nearly 100 hours of precious data. They concern all possible types of astronomical objects, from distant galaxies and quasars to pulsars, star clusters and solar system objects.
This intensive Science Verification (SV) Programme took place as planned from August 17 to September 1, 1998, and was conducted by the ESO SV Team at the VLT Observatory on Paranal (Chile) and at the ESO Headquarters in Garching (Germany).
The new giant telescope lived fully up to the high expectations and worked with spectacular efficiency and performance through the entire period. All data will be released by September 30 via the VLT archive and the web (with some access restrictions - see below). The Science Verification period
Just before the beginning of the SV period, the 8.2-m primary mirror in its cell was temporarily removed in order to install the "M3 tower" with the tertiary mirror [1]. The reassembly began on August 15 and included re-installation at the Cassegrain focus of the VLT Test Camera that was also used for the "First Light" images in May 1998. After careful optical alignment and various system tests, the UT1 was handed over to the SV Team on August 17 at midnight local time.
The first SV observations began immediately thereafter and the SV Team was active 24 hours a day throughout the two-week period. Video-conferences between Garching and Paranal took place every day at about noon Garching time (6 o'clock in the morning on Paranal). Then, while the Paranal observers were sleeping, data from the previous night were inspected and reduced in Garching, with feedback on what was best to do during the following night being emailed to Paranal several hours in advance of the beginning of the observations.
The campaign ended in the morning of September 1 when the telescope was returned to the Commissioning Team that has since continued its work. The FORS instrument is now being installed and the first images from this facility are expected shortly. Observational circumstances
During the two-week SV period, a total of 154 hours were available for astronomical observations. Of these, 95 hours (62%) were used to collect scientific data, including calibrations, e.g. flat-fielding and photometric standard star observations. 15 hours (10%) were spent to solve minor technical problems, while another 44 hours (29%) were lost due to adverse meteorological conditions (clouds or wind exceeding 15 m/sec).
The amount of telescope technical downtime is very small at this moment of the UT1 commissioning. This fact provides an impressive indication of high technical reliability that has been achieved and which will be further consolidated during the next months.
The meteorological conditions that were encountered at Paranal during this period were unfortunately below average, when compared to data from the same calendar period in earlier years. There was an excess of bad seeing and fewer good seeing periods than normal; see, however, ESO PR Photo 35c/98 with 0.26 arcsec image quality.
Nevertheless, the measured image quality on the acquired frames was often better than the seeing measured outside the enclosure by the Paranal seeing monitor. Part of this very positive effect is due to "active field stabilization" , now performed during all observations by rapid motion (10 - 70 times per second) of the 1.1-m secondary mirror of beryllium (M2) and compensating for the "twinkling" of stars. Science Verification data soon to be released
A great amount of valuable data was collected during the SV programme. The available programme time was distributed as follows: Hubble Deep Field - South [HDF-S; NICMOS and STIS Fields] (37.1 hrs); Lensed QSOs (3.2 hrs); High-z Clusters (6.2 hrs); Host Galaxies of Gamma-Ray Bursters (2.1 hrs); Edge-on Galaxies (7.4 hrs); Globular cluster cores (6.7 hrs); QSO Hosts (4.4 hrs); TNOs (3.4 hrs); Pulsars (1.3 hrs); Calibrations (22.7 hrs).
All of the SV data are now in the process of being prepared for public release by September 30, 1998 to the ESO and Chilean astronomical communities. It will be possible to retrieve the data from the VLT archive, and a set of CDs will be distributed to all astronomical research institutes within the ESO member states and Chile.
Moreover, data obtained on the HDF-S will become publicly available worldwide, and retrievable from the VLT archive.
Updated information on this data release can be found on the ESO web site at http://www.eso.org/vltsv/.
It is expected that the first scientific results based on the SV data will become available in the course of October and November 1998. First images from the Science Verification programme
This Press Release is accompanied by three photos that reproduce some of the images obtained during the SV period.
ESO PR Photo 35a/98
ESO PR Photo 35a/98 [Preview - JPEG: 671 x 800 pix - 752k] [High-Res - JPEG: 2518 x 3000 pix - 5.8Mb]
This colour composite was constructed from the U+B, R and I Test Camera Images of the Hubble Deep Field South (HDF-S) NICMOS field. These images are displayed as blue, green and red, respectively.
The first photo is a colour composite of the HDF-S NICMOS sky field that combines exposures obtained in different wavebands: ultraviolet (U) + blue (B), red (R) and near-infrared (I). For all of them, the image quality is better than 0.9 arcsec. Most of the objects seen in the field are distant galaxies. The image is reproduced in such a way that it shows the faintest features scaled, while rendering the image of the star below the large spiral galaxy approximately white. The spiral galaxy is displayed in such a way that the internal structure is visible.
A provisional analysis has shown that limiting magnitudes that were predicted for the HDF-S observations (27.0 - 28.5, depending on the band), were in fact reached.
Technical information : Photo 35a/98 is based on 16 U-frames (~370 nm; total exposure time 17800 seconds; mean seeing 0.71 arcsec) and 15 B-frames (~430 nm; 10200 seconds; 0.71 arcsec) were added and combined with 8 R frames (~600 nm; 7200 seconds; 0.49 arcsec) and 12 I-frames (~800 nm; 10150 seconds; 0.59 arcsec) to make this colour composite. Individual frames were flat-fielded and cleaned for cosmics before combination. The field shown measures 1.0 x 1.0 arcmin. North is up; East is to the left.
ESO PR Photo 35b/98
ESO PR Photo 35b/98 [Preview - JPEG: 679 x 800 pix - 760k] [High-Res - JPEG: 2518 x 3000 pix - 5.7Mb]
The colour composite of the HDF-S NICMOS field constructed by combining VLT Test Camera images in U+B and R bands with a HST NICMOS near-IR H-band exposure. These images are displayed as blue, green and red, respectively. The NICMOS image was smoothed to match the angular resolution of the R-band VLT image. The boundary of the NICMOS image is also shown.
The next photo is similar to the first one, but uses a near-IR frame obtained with the Hubble Space Telescope NICMOS instrument instead of the VLT I-frame. The HST image has nearly the same total exposure time as the VLT images. Their combination is meaningful since the VLT and NICMOS images reach similar depths and show more or less the same faint objects. This is the result of several effects compensating each other: while more distant galaxies are redder and therefore better visible at the infrared waveband of the NICMOS image and this image has a better angular resolution than those from the VLT, the collecting area of the UT1 mirror is over 11 times larger than that of the HST.
It is interesting to note that all objects in the NICMOS image are also visible in the VLT images, with the exception of the very red object just left of the face-on spiral. The bright red object near the bottom has not before been detected in optical images (to the limit of R ~ 26 mag), but is clearly present in all the VLT Test Camera coadded images, with the exception of the U-band i
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