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III/188 IUE Atlas of B-Type Stellar Spectra (Walborn+ 1995)
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International Ultraviolet Explorer Atlas of B-type Spectra from 1200 to 1900 A
Walborn N.R., Parker J.W., Nichols J.S.
<NASA Reference Publication #1363 (1995)>
=1995N95-28328.....W
Parker J.W., Walborn N.R., Nichols J.S., Gull T.R.
<Bull. American Astron. Soc., 186, #22.21 (1995)>
=1995AAS...186.2221P
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ADC_Keywords: Stars, B-type; Spectra, ultraviolet; Atlases
Abstract:
The IUE Atlas of B-type Stellar Spectra is an atlas of B-type spectra
consisting of short-wavelength, high-resolution data from the
International Ultraviolet Explorer archive, designed to complement the
widely used O-star atlas from the same source (Walborn, Nichols-Bohlin,
& Panek 1985, NASA Reference Publication 1155). The atlas presented here
completes the OB natural group, i.e., to spectral type B3 for the main
sequence and giants, type B5 at class Ib, and B8 at Ia, which is also
the most relevant domain for stellar-wind effects among normal B-type
spectra.
Introduction:
A primary objective of the IUE Atlas of B-type Stellar Spectra is to
chart in detail the gradual disappearance of the stellar-wind features
in normal spectra as a function of spectral type and luminosity class.
As in the O-star atlas, which first demonstrated the strong correlation
between the optical spectral types and the UV wind behavior in the
majority of the stars, the principal selection criterion was the
existence of high-weight optical spectral classifications, which are
quoted here without any revisions based upon the UV data. Some peculiar
categories also are presented including a number of hypergiants, stars
of types BN/BC (and including three of type O9.7 acquired since the O
Atlas), and stars with enhanced winds. 86 images have been selected from
the IUE archive for the atlas. The processing and presentation is as
similar as possible to the O-star atlas, with the SWP data (roughly
1200-1900 angstrom range) rectified and rebinned to a uniform resolution
of 0.25 angstrom.
The conclusions from the B Star Atlas are similar to those from the O
Star Atlas, namely, that the UV stellar-wind features display strong
systematic trends as a functions of spectral type and luminosity class,
and a high degree of correlation with the optical classifications as the
winds decline toward the later types. A somewhat higher rate of
exceptions to these correlations can be recognized among the B spectra
(11%) than the O (2%), but they remain a small fractions of the total
sample and do not prevent clear delineation of the normal behavior.
Indeed, it is only as a result of the latter that the exceptions can be
identified and described.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 79 86 Star IDs, Spectral Types, IUE image
numbers, PI names, atlas plate numbers
spectra.dat 80 68800 Fluxes and data quality flags
splices.dat 74 1118 Splice points of spectra
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- ID HD/HDE or Sanduleak (Sk) number of star
13- 26 A14 --- Name Name of star
29- 44 A16 --- Sp Optical spectral classification
47- 51 I5 --- SWP_num SWP camera image number of observation
54- 69 A16 --- PI_name Name of the IUE principal investigator
72- 73 I2 --- Plate_1 *First atlas plate showing spectrogram
75- 76 I2 --- Plate_2 ?Second atlas plate showing spectrogram
78- 79 I2 --- Plate_3 ?Third atlas plate showing spectrogram
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Note on Plate_1:
Location of of the spectrogram in the printed atlas. Each plate covers two
pages in the atlas (first page covers 1200-1500 A, and the second page
covers 1500-1900 A). Some spectrograms appear on more than one plate.
Byte-by-byte Description of file: spectra.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- ID *HD/HDE or Sanduleak (Sk) number of star
13- 16 I4 0.1nm lambda *Wavelength of first flux/quality pair
18- 26 F9.5 --- flux_1 *Normalized flux at wavelength=lambda
29- 32 F4.2 --- qual_1 *Data quality flag associated with flux_1
34- 42 F9.5 --- flux_2 Normalized flux at wavelength=lambda+0.025 nm
45- 48 F4.2 --- qual_2 Data quality flag associated with flux_2
50- 58 F9.5 --- flux_3 Normalized flux at wavelength=lambda+0.050 nm
61- 64 F4.2 --- qual_3 Data quality flag associated with flux_3
66- 74 F9.5 --- flux_4 Normalized flux at wavelength lambda+0.075 nm
77- 80 F4.2 --- qual_4 Data quality flag associated with flux_4
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Note on ID:
There are 800 records for each star, and the ID appears at the beginning of
each record for a given star.
Note on lambda:
The quoted wavelength value is the wavelength of the flux_1 and qual_1 data
pair. The wavelengths for the subsequent flux/qual data pairs in the
record are in increments of 0.025 nm.
Note on flux_1:
See Appendix A: "Data Preparation" for a brief description of how the
normalized flux was calculated.
Note on qual_1:
See Appendix A: "Data Preparation" for a brief description of how this
normalized quality factor was calculated.
Byte-by-byte Description of file: splices.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- ID *HD/HDE or Sanduleak (Sk) number of star
11- 18 F8.1 0.1nm splice1 *First splice point
19- 26 F8.1 0.1nm splice2 *?Second splice point
27- 34 F8.1 0.1nm splice3 *?Third splice point
35- 42 F8.1 0.1nm splice4 *?Fourth splice point
43- 50 F8.1 0.1nm splice5 *?Fifth splice point
51- 58 F8.1 0.1nm splice6 *?Sixth splice point
59- 66 F8.1 0.1nm splice7 *?Seventh splice point
67- 74 F8.1 0.1nm splice8 *?Eighth splice point
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Note on ID:
There are 13 records for each star, and the ID appears at the beginning of
each record for a given star.
Note on splice*:
Splice points are the wavelength values where overlap of successive orders
of the IUE spectrum have been spliced together. These values come in four
pairs per record, where for each pair:
The first wavelength the beginning of the next (higher) order, and
The second wavelength of the end of the previous (lower) order.
Appendix:
A. Data Preparation:
This section briefly describes the steps involved in selecting and
processing the data comprising this atlas. The following description was
extracted from an edited version of Walborn et al. (1995).
A.1 Selection
As in the O Atlas, the principal selection criterion was the existence
of high-weight optical spectral classifications, which are quoted here
without any revisions based upon the UV data.
A.2 Processing
The processing of the spectral data presented in this Atlas is
substantially similar to that used for the O Atlas. The high-resolution
SWP data were retrieved from the National Space Science Data Center in
their original IUESIPS processed form. Sample wavelength and a data
quality indicator were also included. The spectral data were then
further reduced at the IUE Data Analysis Center. Processing then
proceeded through the following steps:
1. The background was smoothed and subtracted from the on-order
signal to yield the net spectrum.
2. A "ripple" correction was applied to adjust for systematic
variation along each order caused by the varying sensitivity of the
echelle grating. The orders were then spliced at the points where
sensitivities of adjacent orders are equal. These points of overlap
are listed in the second file.
The spectrum was then resampled to 0.25 A resolution:
The complete concatenated spectrogram was rebinned to a uniform
resolution of 0.25 A. The resampled points were computed from a
weighted average of the original points, the weight being based on
the fraction of the original bin that falls within the 0.25 A window
centered at the new wavelength point. A weight of zero was assigned
to any original point possessing an IUESIPS quality flag indicating
reseau contamination, saturation, or a particle hit event. The new
sample points are spaced evenly at 0.25 A intervals from 1150 to
1950 A. A new quality flag was derived for each rebinned point,
computed as the sum of the weights for the original samples
contributing to the new point.
A minor error in this resampling algorithm was detected after
preparation of the O Atlas in 1985. The end points of each bin
overlapped by one extracted point, so that these end points were
included in two bins. The error was subsequently corrected and it
does not affect the data in the present Atlas.
3. The resampled spectrum was then rescaled in order to locate the
stellar continuum at an approximately uniform level:
Each rebinned spectrogram was normalized by dividing by a "continuum
spectrum" created from a highly smoothed version of itself. In a few
cases in which the resulting normalization was unsatisfactory, with
remaining large-scale structure in the continuum, the normalization
was redone manually. Similarly, the data-quality flags were
normalized to remove the effect of the decreasing spectral dispersion
at longer wavelengths, which results in a smaller number of original
samples within each 0.25 A bin. Large geocoronal Lyman-alpha and
particle-hit spikes were manually removed from the data, and in a few
cases of low signal at the shorter wavelengths, noise spikes were
truncated at the borders of the frame [normalized flux values of 0
and 2.5] to avoid overwriting the adjacent spectrograms. [This
truncation also exists for the archived electronic version of these
data, so many spectra will have chopped spikes, particularly in the
region around Lyman-alpha.]
The data-quality flags are coded as numbers between 0 and roughly 1:
small downward spikes are produced when a few of the points in the
bin are contaminated with a reseau mark, and large downward spikes
are produced when all of the points in the bin have reseau or other
contamination. Extracted spectral data points are flagged as
contaminated by a reseau mark if the mark falls near or on the
spectral order. It is possible for one or more rebinned points to
have a near zero quality flag but the spectral data are unaffected by
the reseau mark.
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(End) Joel W. Parker [Code 680/GSFC] 7-Aug-1995