Data Formats

The data for each stars are stored in a combination of an ASCII “DAT” file and FITS “spectra” files.

DAT file

The ASCII file is the only required file. This file gives the photometry and links to the FITS files that contain the spectroscopy. Many dat files for stars used in literature dust extinction curves are provided in the extstar_data repository <https://github.com/karllark/extstar_data>_.

An example of such a file (for a star from Valencic et al. 2004) that gives the Johnson photometry, location of IUE spectrum, and spectral types is below. This includes the photometry and associated uncertainties in Vega magnitudes. Comments taking an entire line are allowed if they start with a “#” character.

# data file for observations of HD 38023
V = 8.870 +/- 0.020
B = 9.190 +/- 0.030
U = 8.870 +/- 0.030
J = 8.080 +/- 0.020
H = 7.990 +/- 0.060
K = 7.900 +/- 0.020
IUE = IUE_Data/hd038023_iue.fits
sptype = B4V
uvsptype = B4IV

A more complicated example giving photometry and spectroscopy from different sources is below (from a star from Gordon et al. 2021; Decleir et al. 2022 among other studies). The Johnson photometry is provided mainly as colors in this example. Photometry from IRAC/IRS/MIPS is provided in mJy. The different photometry units are converted to the measure_extinction internal units when read into StarData. In addition, there are comments provided after data using the “;” character.

# data file for observations of HD 29647
V = 8.31 +/- 0.017 ; UBVRI ref = Slutskij, Stalbovskij & Shevchenko 1980 (1980SvAL....6..397S)
(U-B) = 0.47 +/- 0.030
(B-V) = 0.91 +/- 0.019
(V-R) = 0.96 +/- 0.024
(V-I) = 1.71 +/- 0.030
J = 5.960 +/- 0.030 ; JHK ref = IRSA 2MASS All-Sky Point Source Catalog
H = 5.593 +/- 0.021
K = 5.363 +/- 0.020
# IRAC 1 and 2 seem off
IRAC1 = 2.23E+03 +/- 4.45E+01 mJy
IRAC2 = 1.50E+03 +/- 3.00E+01 mJy
IRAC3 = 1.06E+03 +/- 2.16E+01 mJy
IRAC4 = 5.42E+02 +/- 1.09E+01 mJy
IRS15 = 3.14E+02 +/- 6.51E+00 mJy
MIPS24 = 6.76E+01 +/- 1.89E+00 mJy
# WISE have extended source contamination, contaminated by scattered moonlight
# WISE 1, 2 and 3 spurious detection of scattered light halo
# WISE 1 and 2 seem off, have saturated pixels
WISE1 = 5.179 +/- 0.150 ; WISE ref = IRSA AllWISE Source Catalog
WISE2 = 4.905 +/- 0.068
WISE3 = 4.882 +/- 0.023
WISE4 = 3.821 +/- 0.033
IUE = IUE_Data/hd029647_iue.fits
SpeX_SXD = SpeX_Data/hd029647_SXD_spex.fits
SpeX_LXD = SpeX_Data/hd029647_LXD_spex.fits
IRS = IRS_Data/hd029647_irs.fits
sptype = B7IV ; sptype ref = Murakawa, Tamura & Nagata 2000 (2000ApJS..128..603M)
uvsptype = B8III ; uvsptype ref = Valencic+2004 (2004ApJ...616..912V)

Spectra

The spectra are stored in FITS files with standard columns and wavelength grids. The standard columns are “WAVELENGTH”, “FLUX”, “SIGMA”, and “NPTS”. These files are created using the “merge_xxx_spec” functions provided in merge_obsspec. These ensure that all the spectra from a specific source (e.g., IUE) have the same wavelength grid, units, and standard columns.

For some of the types of spectra (e.g., IUE, STIS, SpeX, NIRCam SS), there is commandline code in the measure_extinction/utils subdirectory to create such files from the commandline.

When using a stellar model for the comparison, each type of spectra supported is simulated/mocked using code in the measure_extinction/utils subdirectory. See Stellar Models as Standards.