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Description
The Belgian/UK Ultraviolet Sky Survey Telescope (S2/68) in the ESRO TD1 satellite carried out a controlled scan of the entire sky. It measured the absolute ultraviolet flux distribution between 2740A and 1350A of point sources down to 10th visual magnitude for unreddened early B stars. The S2/68 experiment has been described by Boksenberg et al. (1973MNRAS.163..291B), and the absolute calibration by Humphries et al. (1976A&A....49..389H). The TD1 Catalog of Stellar Ultraviolet Fluxes represents results from the sky-scan experiment on the TD1 satellite of the European Space Research Organization (ESRO), now part of ESA. It lists the absolute fluxes, in four passbands, for 31,215 stars: <pre> Passband Center: 274.0nm 236.5nm 196.5nm 156.5nm Effective Width: 31.0nm 33.0nm 33.0nm 33.0nm </pre> The stars have been selected subject to the constraint that the signal-to-noise ratio should be at least 10.0 in any one of the four passbands. Null values of a flux field and an error field indicate there are no valid data for the star. This usually arises with close pairs of stars whose spectra overlap. Five standard flux error values are greater than 99.99, and were too large for the format of the flux field in the original table. Thus, the flux error values which were greater than 99.99 are given as 99.99. Many of the fainter stars of spectral type later than A5 do not have significant signals in all of the spectrophotometric channels (particularly the 1565A channel). Consequently, after the removal of the background, they can randomly give rise to small negative values of flux. Those negative values were not suppressed, but are given together with their error, as they can be significant when considered as part of a statistical sample. Although the sky coverage is essentially complete, the catalog does not contain the fluxes for all stars that fall within the limit of the sensitivity of the instrument. If any star expected to be present is missing, then its signal is probably blended with that of a nearby star, in which case the data have been discarded. The original contents of the HEASARC's TD1 database table came from a magnetic tape sent to NASA/Goddard Space Flight Center by Dr. G.I. Thompson of the Royal Observatory in Edinburgh, Scotland. The HEASARC recreated this database table in August 2005, based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/II/59B">CDS Catalog II/59B</a> file catalog.dat.gz, in an effort to modernize its parameter names and documentation, as well as to add Galactic coordinates. The data in the CDS version originally came from "Selected Astronomical Catalogs" Vol. 1 CD-ROM released by the NASA Astronomical Data Center (ADC) in 1991. This is a service provided by NASA HEASARC .
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