Some useful astronomical links

Optical and UV surveys

A list of optical and UV surveys was generated after IAU's Symposium 179 (http://www-gsss.stsci.edu/iauwg/survey_url.home).
Among them:

Optical
€ The Sloan Digital Sky Survey (SDSS) (http://www-sdss.fnal.gov:8000/) will be a complete survey of ¼ steradians using 30 2048x2048 CCDs in five bands and two fiber optics spectrographs. It will consist of a photometric catalog of 108 galaxies, 108 stars and 106 quasars; a spectroscopic catalog including emission and absorption lines, images in five bands and 1-d spectra of 106 galaxies, 105 stars, 105 quasars and 104 clusters. As the size of the SDSS will probably exceed 1010 bytes, maintaining, distributing and querying it will be quite a challenge.

€ ESO slice project (http://boas5.bo.astro.it/~cappi/esokp.html) is a galaxy redshift covering 30 square degrees near the South Galactic Pole, complete up to bJ=19.4. It includes the redshifts of 3,000 galaxies.

€ Two degree Field (2dF) QSO redshift survey: will determine the large scale tridimensional structure of the universe up to z~0.1 by measuring the redshift of 250,000 galaxies. In addition, spectra of 30,000 quasars will be obtained (http://www.aao.gov.au/local/www/rs/qso_surv.html) A mirror site exists in Great Britain (http://www.ast.cam.ac.uk/AAO/www/rs/qso_surv.html)

UV
€ FOCA (http://www.astrsp-mrs.fr/~xbig/foca/node2.html) was a small airborne telescope that surveyed 70 square degrees at 2000Å with an angular resolution of 12" and 20", the generated catalog includes galaxy counts and color distributions for sources between 15 and 18.5mag

€ Alexis (http://alexis-www.lanl.gov) is an EUV/X-ray satellite surveying the sky to map the diffuse soft X-ray background, to study flaring stars and make observations of EUV sources. Any object detected found is immediately compared with lists of known objects to determine its possible nature


Multiwavelength maps

Several institutions provide on-line facilities that create maps of the sky at one or more wavelengths. Among them,

• SKYVIEW (http://skyview.gsfc.nasa.gov/skyview.html) provides an interface to obtain images from radio through gamma ray wavelengths
  
  
• SkyCat (http://archive.eso.org/skycat) accesses the HST, ESO's NTT and CFHT archives to retrieve images and displays them with a variety of options to identify objects on them
  
  
• Astronomical Digital Image Library (http://imagelib.ncsa.uiuc.edu/imagelib.html) contains "books" with FITS images taken at different wavelengths. It provides a convenient way to archive and distribute data.
  
  
  Astrometry

The Hipparcos catalog contains 118,218 astrometric entries (milliarcsecond position, parallax and proper motion) with a median error of 1mas. The Tycho catalog on the other hand includes more than a million objects with a median error of 7mas for the brighter sources and 25mas for the fainter ones. More than 100 epochs were acquired for the photometry of the objects in the Hipparcos catalog. The photometric error is between 0.0004 and 0.0007mag for the brighter stars.

These catalogs are now the astrometry standards. The catalog epoch is J1991.25; the equinox J2000.0

The European Space Agency distributes theses catalogs as a series of 16 books and several CD-ROMs. The catalogs can also be queried in the WWW
(http://astro.estec.esa.nl/SA-general/Macc/hip.html)


Artificial data

Simulated data is useful, among other things, to, for example test algorithms, check photometry results, predict exposure times or optimize an observation using deconvolution techniques.

€ Tiny TIM (http://scivax.stsci.edu/~krist/tinytim.html) creates HST point spread functions. A PSF can be generated for any instrument with any configuration, any wavelength and position. Tiny Tim runs on VAX/VMS, UNIX and Linux

€ The STSDAS (http://ra.stsci.edu/STSDAS.html) synphot package simulates photometric data and spectra as they are observed with the Hubble Space Telescope. Its output is used also in the exposure time calculators that users query to determine the number of orbits needed for their projects. Synphot can be used to estimate count rates obtained by other telescopes by changing the components lookup tables and instrument graph. A manual is available on-line.

€ All instruments currently on board the Hubble Space Telecope have Exposure Time Calculators to estimate either the signal to noise or the exposure time of observations with them.

Other Meta Databases

€ Astrobrowse allows the user to retrieve information from several sites using one single query form. The user only needs to specify a position (or a name that will be resolved into a position), a search radius and a list of the services (as available from different organizations) that can be accessed. At the moment only a prototype exists on-line (http://www.clark.net/pub/warnock/ASTROprofile.html)

€ AMASE (http://amase.gsfc.nasa.gov) is an on-line multi-mission and multi-spectral catalog with pointers to locate data stored in different NASA archives. Besides the information of each object (name, coordinates, color, radial velocity or redshift, proper motion, etc.), AMASE provides the very useful information about the observation: the mission, instrument, instrument configuration and detector used; the pointing, time of observation and roll angle; the target, proposal and principal investigator.

€ The Astronomical Data Center (http://adc.gsfc.nasa.gov/) contains more than 800 catalogs and 750 tables culled from the literature. The ADC produced 3 CD-ROMs with astronomical catalogs (a fourth one will be available at the end of 1997). A list of the recently incorporated catalogs is included in the monthly ADC Newsletter distributed electronically and also stored at the ADC site.