Welcome to a tool for finding suitable optical and ultra-violet spectrophotometric standard stars on the sky most appropriate to reduction of astronomical spectroscopic observations.

This resource consists of a set of WWW pages each devoted to a single spectrophotometric standard star and containing positional information, magnitude, a finding chart and plots of the magnitude and flux against wavelength, as shown on an (example page). The Right Ascension and Declination are in the HST Guide Star Catalogue coordinates (equinox 2000).
The finding charts have the conventional orientation, north at the top and east to the left and the image dimensions are indicated. If not arrowed, the standard star is the one in the centre of the field.

Access to the standards is either through:
an RA ordered list;
an RA-Dec sky map with star positions to enable the closest standard star to your observed source to be quickly identified.

The data for the standard stars come from five sources:

• Optical spectrophotometric standards from Oke (1990). Data for 25 stars (7 to 16 mag.) from 3200 to 10200Å based on Hale 5m observations.
• Optical spectrophotometric standards from Hamuy (1992, 1994). Data for 10 bright secondary standards and 19 fainter (10 to 14 mag.) tertiary standards over the wavelength range 3300 to about 10300Å, mostly in the southern hemisphere, taken with CTIO telescopes.
• White Dwarf primary spectrophotometric standards. Data for 4 stars (11 to 13 mag.) from 10Å to 3 microns based on White Dwarf model atmospheres and HST FOS, STIS and NICMOS observations, from the CALSPEC database at STScI.
• X-shooter reference spectra. Data for 6 stars based on X-shooter visible to near-infrared (3000–25000Å) spectra.
• HST UV spectrophotometric standards. Data for 23 stars based on IUE and optical spectra and calibrated by the primary WD standards. Also data on 6 more stars with IUE and model spectra.

The data from which the plots were produced are available here or from the standard star pages.

Some of the finding charts were produced from the Digitized Sky Survey produced by STScI and based on plate material from the UK Schmidt Telescope and the Oschin Schmidt Telescope.

Suggestions for further standard stars to include are welcome.