Spectrophotometric Standards (updated 2024)

MODS Primary Spectrophotometry Standards

Because MODS works from 3200 to >~10000 Angstroms, spectrophotometric standard stars with good fluxes from the UV to the near-IR are needed to adequately calibrate the data. A set of 7 stars form the preferred set of spectrophotometric standards for MODS (the “MODS primary spectrophotometric standards”).

The MODS primary spectrophotometric standards are derived from the HST CALSPEC database and are a combination of well-observed northern hemisphere standards from the list of Oke (1990 AJ, 99, 1621) and the 4 (now just 3) HST white dwarf primary spectrophotometric standards of Bohlin, Colina and Findlay (1995, AJ, 100, 1316), which appear in boldface in Table 1 below.

10- and 50-Angstrom Flux Tables

For each primary standard star, flux tables with 10Å bin widths are provided. These tables are in IRAF-style ASCII 3-column format ready to be used with IRAF. Where necessary, HST stellar models or other HST calibration data were used to extend the near-IR wavelength coverage to 10500Å. These tables have the major telluric absorption complexes censored, and the brighter stellar absorption lines have been cut out in most (but not all) tables. They are adequate for grating-mode calibrations, however at the blue end of spectra taken through the dichroic, the resolution may be insufficient to distinguish between the stellar absorption lines and dichroic wiggles.

Tables with 50Å-bin widths are better suited for prism-mode calibrations and these are also provided for most of the stars. The fluxes are based on CALSPEC and the Spec50 flux tables  Massey et al (1988, ApJ 328, 315), with extensions to 1 micron from Massey and Gronwall (1990, ApJ 358, 344)

The original, uncensored flux tables are available from the HST CALSPEC database.

Note that the modsIDL Reduction Pipeline uses the full CALSPEC flux tables which are included in the software distribution.

Data on the MODS Primary Spectrophotometric Standards

Useful information on the MODS primary spectrophotometric standards is provided in Table 1 below. The coordinates, proper motions, spectral type and magnitudes are from Simbad. All of these stars are roughly the same color except the redder BD+33°2642, and span about 3 magnitudes in apparent brightness. Their flux tables, at 10 angstrom and, when available also at 50 angstrom, bins are provided in the links and also in this gzipped tar file. The scripts are available on the mountain (obsN) workstations (in /lbt/lbto/mods/modsScripts/modsSpecPhot/) and also can be generated from the MODS OT library.

Table 1: MODS Primary Spectrophotometric Standards