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A Correction to the GALEX Spectral Fluxes Using CALSPEC and IUE ("GALEX-FLUXCAL")

Bohlin & Bianchi 2018, xx, accepted

Introduction

Description of Data Products

Data Access

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Introduction

CALSPEC spectrum of LDS 749B (purple) overplotted with the GALEX spectrum as small black squares and as large black squares in 50 Å bins. The large black diamonds are the λeff = 1539 and 2316 Å GALEX broad-band photometry that is within 10% of the spectral measures. In the lower panel, the ratio of CALSPEC/GALEX is shown as black circles surrounded by large black diamonds. The GALEX plus CALSPEC statistical uncertainties combined in quadrature appear as small black diamonds connected by a dashed line with a scale in percent indicated on the right axis.
GALEX-FLUXCAL is a collection of 18 IUE spectral energy distributions (SEDs) on the CALSPEC scale that provide a correction to GALEX spectral fluxes. This HLSP also includes the correction in 50 Å bins from 1300 - 3000 Å. While GALEX spectrophotometry is repeatable to only 10-20% in regions of good sensitivity, the average flux correction presented here has a precision of ~3%. You can refer to the full collection of IGM-GAL data products using the DOI http://dx.doi.org/10.17909/T9DX2D You can retrieve the set of IUE data used in this HLSP using the DOI http://dx.doi.org/10.17909/T9FQ2N.

Description of Data Products

Each of the 18 IUE targets have their SEDs available in both TXT and FITS format. The available columns in the SED files are:

  • WAVELENGTH - Wavelength in vacuum in Angstroms.
  • NET - The averaged net signal in linearized IUE Flux Number (FN) units per second.
  • FLUX - The average flux in ergs cm-2 s-1 Angstrom-1.
  • BKG - The background signal (same units as NET column).
  • UNCERTAINTY - The formal, propagated uncertainty as the "error-in-the-mean" (same units as FLUX column).
  • NPTS - The number of observations averaged.
  • TIME - The total exposure time in seconds.
  • RMS - The RMS scatter among the observations as a percent.
There are two slight differences in the column labels between the FITS and TXT files, e.g., "NET" in the FITS versions and "NET/time" in the TXT versions, and "RMS" in the FITS versions and "RMS(%)" in the TXT versions, but both the FITS and TXT columns have the same definition and values. The FITS primary headers also contain a list of all the IUE observation IDs that went into the SED coadd, stored as DATA<nnn> keywords, e.g., DATA001, DATA002, etc.

In addition to the SEDs, a table is provided that has the GALEX-to-CALSPEC flux ratios in different wavelength bins. GALEX spectra should be multiplied by the average corrections in this table to place them on the HST/CALSPEC scale. The text table can be interpolated to define the GALEX correction at intermediate wavelengths.

Data Access

Correction Table GALEX Corrections (TXT)
Target SED Files
BPM16274 TXT FITS
FEIGE59 TXT FITS
G93-48 TXT FITS
GD108 TXT FITS
GD153 TXT FITS
GD50 TXT FITS
HG7-233 TXT FITS
HZ2 TXT FITS
HZ21 TXT FITS
HZ4 TXT FITS
L791-40 TXT FITS
LB227 TXT FITS
LDS749B TXT FITS
Q1302-102 TXT FITS
SK194 TXT FITS
SK196 TXT FITS
STHA190 TXT FITS
WD0416-550 TXT FITS