J/AJ/155/162 Comparison of IUE and CALSPEC SEDs for 6 WDs (Bohlin+, 2018)
A correction for IUE UV flux distributions from comparisons with CALSPEC.
Bohlin R.C., Bianchi L.
<Astron. J., 155, 162 (2018)>
=2018AJ....155..162B 2018AJ....155..162B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, white dwarf ; Spectra, ultraviolet
Keywords: stars: atmospheres - stars: fundamental parameters -
techniques: spectroscopic - ultraviolet: stars
Abstract:
A collection of spectral energy distributions (SEDs) is available in
the Hubble Space Telescope (HST) CALSPEC database that is based on
calculated model atmospheres for pure hydrogen white dwarfs (WDs). A much
larger set (∼100000) of UV SEDs covering the range (1150-3350 Å) with
somewhat lower quality are available in the IUE database. IUE
low-dispersion flux distributions are compared with CALSPEC to provide
a correction that places IUE fluxes on the CALSPEC scale. While IUE
observations are repeatable to only 4%-10% in regions of good sensitivity,
the average flux corrections have a precision of 2%-3%. Our re-calibration
places the IUE flux scale on the current UV reference standard and is
relevant for any project based on IUE archival data, including our planned
comparison of GALEX to the corrected IUE fluxes. IUE SEDs may be used
to plan observations and cross-calibrate data from future missions, so
the IUE flux calibration must be consistent with HST instrumental
calibrations to the best possible precision.
Description:
The IUE spacecraft was launched 1978 January 26 and was sensitive in each
of two UV channels that cover the far-UV (FUV, 1150-2000 Å) and the
near-UV (NUV, 1850-3350 Å) (Boggess et al. 1978Natur.275..377B 1978Natur.275..377B). Each
spectroscopic channel had both a low-resolution- and an echelle
high-resolution-mode with a prime and a redundant camera for each channel,
i.e., SWP and SWR in the FUV, and LWP and LWR in the NUV.
The IUE data analyzed here are extracted from the Mikulski Archive for
Space Telescopes (MAST; http://archive.stsci.edu/iue/). This Archive
contains both the original IUE data products from the IUESIPS processing
system (Bohlin 1996AJ....111.1743B 1996AJ....111.1743B) and from the NEWSIPS uniform
re-processing of the entire archive (Nichols & Linsky 1996AJ....111..517N 1996AJ....111..517N).
The NEWSIPS version provides a somewhat more photometric product in
most cases and uses the optimal extraction algorithm of Kinney et al.
(1991PASP..103..694K 1991PASP..103..694K).
Six WD stars with multiple IUE spectra and with complete CALSPEC UV
coverage of the IUE spectral range of 1150-3350 Å are selected for
comparison with their NEWSIPS SEDs, as summarized in Table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 74 6 Low-dispersion IUE data used for comparing IUE
and CALSPEC SEDs
table2.dat 31 43 Multiplicative correction for IUE NEWSIPS fluxes
table3.dat 81 5997 IUE SEDs for all six stars
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See also:
J/ApJS/119/207 : IUE echelle spectra of hot white dwarfs (Holberg+, 1998)
J/ApJS/147/145 : IUE low-dispersion spectra of white dwarfs (Holberg+, 2003)
http://www.stsci.edu/hst/observatory/crds/calspec.html : CALSPEC database
http://archive.stsci.edu/iue/ : Mikulski Archive for Space Telescopes (MAST)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- WD WD identifier
13- 14 I2 h RAh Simbad Hour of Right Ascension (J2000)
16- 17 I2 min RAm Simbad Minute of Right Ascension (J2000)
19- 23 F5.2 s RAs Simbad Second of Right Ascension (J2000)
25 A1 --- DE- Simbad Sign of the Declination (J2000)
26- 27 I2 deg DEd Simbad Degree of Declination (J2000)
29- 30 I2 arcmin DEm Simbad Arcminute of Declination (J2000)
32- 35 F4.1 arcsec DEs Simbad Arcsecond of Declination (J2000)
37- 41 F5.2 mag Vmag [11.78/14.69] V band magnitude
43- 65 A23 --- CALSPEC CALSPEC name
67- 68 I2 --- SWP [10/56] Number of good IUE observations for
IUE/SWP camera (in the FUV)
70- 71 I2 --- LWP [1/39] Number of good IUE observation(s) for
IUE/LWP camera (in the NUV)
73- 74 I2 --- LWR [1/10] Number of good IUE observation(s) for
IUE/LWR camera (in the NUV)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 F6.1 0.1nm Wave-SW [1145/1985] IUE/SWP wavelength (Å)
8- 12 F5.3 --- Corr-SW [1.013/1.101] IUE/SWP correction factor
14- 19 F6.1 0.1nm Wave-LW [1850/3350]? IUE/LWP/R wavelength (Å)
21- 25 F5.3 --- Corr-LWP [1.01/1.097]? IUE/LWP correction factor
27- 31 F5.3 --- Corr-LWR [1.042/1.158]? IUE/LWR correction factor
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- WD WD identifier
13- 19 F7.2 0.1nm Wave [1152.26/3346.83] Wavelength (Å)
21- 30 E10.3 s-1 Netavg [-0.01373/12.05] Average net signal (1)
32- 41 E10.3 cW/m2/nm Fluxavg [-2.834e-13/1.963e-11] Average flux
(in erg/s/cm2/Å)
43- 52 E10.3 s-1 Bkg [-0.1135/3.651] Background signal (1)
54- 62 E9.3 cW/m2/nm Sigma [0/3.365e-13] Formal propagated uncertainty as
the error-in-the-mean (in erg/s/cm2/Å)
64- 67 F4.1 --- Nobs [1/56] Number of observation(s) averaged
69- 75 F7.1 s Texp [419.7/38514.8] Total exposure time
77- 81 F5.2 % RMS [0/96.11]?=99 RMS scatter among observations
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Note (1): In linearized IUE Flux Number (FN) units per second.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Nov-2018