Mathematics – Logic
Scientific paper
Apr 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000eso..pres....8.&link_type=abstract
ESO Press Release, 04/2000
Mathematics
Logic
Scientific paper
Astronomers working with a major new instrument at the ESO Very Large Telescope (VLT) at the Paranal Observatory have had a first taste of what is bound to become a research bonanza. Recent test observations with the Ultraviolet-Visual Echelle Spectrograph (UVES) have demonstrated the exceptional science potential of this powerful facility (views from the installation are available as PR Photos 36p-t/99 ).
The first long-exposure test spectra of stars, galaxies and quasars obtained with UVES have thrilled the astronomers by their extraordinary quality. Some have already yielded important results, from unprecedentedly accurate chemical analysis of individual stars in nearby galaxies to abundance measurements of light elements created during the Big Bang. Others provide new insights into the composition of the gas in a galaxy in the early Universe, less than 3 billion years after the Big Bang [1]. One particular set of observations measured an upper limit of the uranium content in a very old star - and thereby a lower limit to the age of the universe. UVES starts operations
UVES began normal operations on April 1, 2000, at the Nasmyth B focus of KUEYEN , the second 8.2-m VLT Unit Telescope, and it is now fully at the disposal of the scientists. The observing time available until the end of September 2000 was assigned to a large number of front-line research projects by the ESO Observing Programmes Committee. For UVES , as for all other VLT instruments, all observations are executed by ESO staff. In "service observing" mode, they choose the targets from a pre-compiled list, taking into account programme priority and sky conditions. In "visitor mode", the ESO astronomer executes the observations according to the sequence chosen by the visiting astronomer who is also present at the telescope.
UVES is the third instrument after FORS1 and ISAAC to enter into regular use at the VLT. It is followed by FORS2 , the second version of FORS that was successfully commissioned earlier this year (cf. ESO PR Photos 05a-c/00 ), and which also started operations on April 1, at the Cassegrain focus of KUEYEN.
UVES achieved "First Light" on September 27, 1999, cf. ESO PR 15/99. This event was followed by three intense weeks of "Commissioning Observations" , by a second tune-up in December 1999 and finally by a very successful period of "Science Verification" in February 2000, cf. the dedicated UVES SV webpage (SV data are being released starting on April 10). A very powerful instrument
The analysis of the test observations has demonstrated that UVES is presently the most powerful astronomical instrument for high-resolution spectroscopy available to the world-wide astronomical community. Its high intrinsic efficiency, at all wavelengths from ultraviolet to red light (e.g., 13% at 360 nm, 18% at 600 nm; [2]), coupled with the large light collecting power of the 8.2-m KUEYEN telescope, makes it perfectly suited for high-resolution spectral observations of faint stellar and extragalactic objects.
UVES achieves "resolving powers" up to 80,000 in the UV-blue spectral region and 115,000 in the red region [3].
UVES has several unique capabilities. First, it can work in parallel at blue and red wavelengths by using a dichroic beam splitter that divides the light from a celestial object at the entrance of the instrument. This observational mode is as efficient as single-spectral-region operation and it implies that it is possible to record light simultaneously over a very broad wavelength interval - up to 500 nm at a time. Secondly, the available CCD detectors register the spectra over 23 million pixels (as compared to 4 million pixels available in similar spectrographs elsewhere). This results in a much better sampling, i.e., a more detailed view, of the spectral features at any given resolving power. First science results from UVES
The instrument operated smoothly during the entire three weeks of the first commissioning. Altogether, only 7 hours were lost due to technical problems of either the instrument or the telescope, a small figure at this stage of operation of a new instrument at a new telescope. A large number of scientific observations were obtained with the aim of testing the limiting capability of UVES for various types of research programmes.
At the same time, the data reduction pipeline was successfully tested; it contributes effectively to the extensive data processing needed to prepare the complex spectra for accurate astrophysical evaluation. Since February 2000, many of these observational data , with a total of more than 90 hours of pure integration time, have been included in the Public Data section of the ESO Science Archive facility.
The analysis of the first scientific data has been carried out by a team of ESO astronomers and by members of the UVES Instrument Science Team [4] who have made available the results to illustrate the impressive capabilities of this powerful instrument as reported below. They cover a wide range of current front-line research areas and they provide an most promising preview of the many observational possibilities with this new instrument.
Short summaries of the first science with UVES are presented here. The titles provide weblinks to detailed reports on each of the eight research topics, attached below.
* A. The beryllium abundance in extremely metal-poor stars
Spectral lines from the light element beryllium in the ultraviolet part of the spectrum close to the atmospheric limit for ground-based observations have been detected in a 3-hour exposure of a very metal-poor, 11-magnitude galactic star. Further observations of this type of a larger sample of stars will provide crucial information about the primordial abundance of this element, and hence about the element-building processes in the early universe.
* B. The isotopic lithium abundance in a metal-poor halo star
An unexpectedly low 6 Li/ 7 Li-ratio of 0.02 is measured in a very-high resolution, very high signal-to-noise spectrum of a 10-mag metal-poor star, obtained during a 3-hour exposure. This new result indicates that it will be necessary to obtain many more measurements of this key isotopic ratio before it can provide significant cosmological information, an observational task for which UVES is very well suited.
* C. Tracking the age of the universe with radioactive elements in stars
A 4-hour exposure of the spectrum of an old 13-mag star allows a firm upper limit to be placed on the uranium abundance in its atmosphere. When used with the measured thorium abundance, this translates into a minimum age of 12 billion years of the universe. Future observations of this and similar stars with longer integration times will be able to set tighter limits to this age determination.
* D. Spectra of individual stars in other galaxies
In an unprecedented observational feat, high-quality spectra of two 18-mag giant stars in the Sagittarius Dwarf Galaxy of the Local Group of Galaxies were obtained from which the abundances of 20 different elements were determined. The deduced fractions of heavier elements were unexpectedly high, a clear sign that this galaxy has experienced more intense chemical reprocessing during its evolution than previously believed, on the basis of less detailed observational data.
* E. Hunting black holes in the nuclei of galaxies
By measuring the exact shape of spectral lines emitted from gas moving around the centre of the spiral galaxy NGC 7782 and using a dynamical model for these motions, it has been possible to determine the mass of the presumed black hole at this centre. An unusually small, upper limit of about 50 million solar masses was derived. Future observations of galactic nuclei of this type will permit interesting demographic studies, for instance the relation(s) between the mass of central black holes and those of galaxy bulges.
* F. A first glimpse at the intergalactic medium in the redshift interval z = 1.5 - 2.0
On its way to us, the light from a remote quasar traverses many intergalactic clouds that leave their signatures in the quasar spectrum in the form of
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