The acquisition of short wavelength spectra of Beta Cephei variable stars from the International Ultraviolet Explorer is reported. A total of 122 images of 10 variable stars and 3 comparison stars were obtained. All of the images were observed in the high dispersion mode through a small aperture. The development of image processing methods is also briefly discussed

Lesh, J. R.

English

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Velocity Fields and Spectrum
_
 Peculiarities in Beta Cephei Stars
by
Janet Rountree Leah
Department of Physics
University of Denver
Denver, Colorado 80208
(NASA-CR- 16386O) VELOCITY FIELDS AND	 N $1-15914
SPECTRU8 PECULIARITIES IN BETA CEPHEI STARS
Final Technical Report, May 1979 - Nov. 1980
(Denver Univ . ) 6 p HC A02/MF A01	 CSCL 03A	 Uncl.as
63/89 29743
3i'^^ ^`y^1a
Final Technical Report
NASA Grant NSG- 5 3 67
TvMa l^  1979 November 1980
i
^u
I. Introduction
The purpose of this project is td^;, 'vbtain high- resolution, short-wavelength
IVE spectra of a number of Beta Cephei variable star s
 at frequent phase
intervals during their pulsation cycles (typical periods are 4 to 6 hours),
and to study the profile variations 'in several ultraviolet spectral Lines in
order to determine the velocity field s
 in the stellar atmospheres. This study
is intended to point the way to answers to questions like the following;.
1) Are these stars radial or nonracial pulsators? Can the actual
pulsation n°iode l,e determined? Does the specified mode support or
eliminate any candidate for the instability iiiechwnism?
2) Are theses stars losing mass at a significant rate (as evidenced by
an accelerating valocity gradient)? If so, does this affect the stability or
the future evolution of the star?
A secondary objective is to compare the mean spectra of the variable
stars with those: of nonvariable stars of the sane spot-tral type, to see if
some of the anomalies indicated by ultraviolet photometry and low-dispersion
spectroscopy are borne out when the spectra are examined at high dispersion.
In particular, anomalous luminosity indicators have been reported in a
.few cases.
II. Conxpleted Work
`Dine 8-hour shifts of observing time with the IVE satellite were scheduled
for this project, in the second year of operations. All of theses observing
shifts were used profitably in May 197 '9, to obtain a total of 122 images of
r	 .
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r
lQ variable stars and 3 comparison stars. The complete list at targets
observed, and the number of Images obtained for each one, is given in
the table below. All the iniages were observed in the high-dispersion node,
through the small aperture. Most of them are well expose d and usable.
3.
Object
Xi l CMS
Sigma Sco
Alpha, Pyx
Alpha Vir
Beta iru
Tau t Lup
V9 g 6 Qpt^
Camma Peg
Zeta Cite
Data, CMa
16 Lac
1 Cas
12 Lac
`p 'e
'Variable
Variable
Con-1pa rlao n
Variable
Variable
Variable
Variable?
Variable
Cowipar s o
Variable
Variable
Comparis on
Var iable
5Wp Images
It
lz
1
11
9
3
LWR Images
2
1
I
1
Thirty-three Guest Investigator tapes, containing raw images,
geometrically and photometrically corrected iwAage3 p , and extracted
apectra were received by then Principal Investigator in June through
September 1979. Fhotowrites and 10 9/in tracings, as well an a
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4,
selection of 1 AO / in tracings, were also received. The q ,-%tracted spectra
were read from the GO tapes and written, in order of observation, on a
set of four more closely packed, merged tapes. This work was performed
using the minicomputer facility at the Goddard Space Flight Center.
Just as the merging of the spectra on the original GO tapes was being
completed, it was discovered that all the spectr* obtained for this project
had been reduced with the incorrect Image Transfer Function. Since we
are looking for small variations in the spectral line profiles, the type of
distortion introduced by the incorrect Image Transfer Function would have
invalidated our results. Therefore all analysis of the spectra was stopped
pending receipt of the reprocessed images. These were received over a
period of several months from June through September 1980. The re-
merging of the reprocessed spectra was completed by the end of October
1980.
Meanwhile, with the help of Richard Fahey, we composed a set of
FORTH words ( subroutines) to perform the desired operations on our
IUE spectra, again using the GSFC minicomputer. In an interactive mode,
u
the routines enable one to locate and identify selected spectral lines, draw
t=
	
	in the continuum, rectify the line profiles, and compute the central depth,
half-width, equivalent width, and asymmetry parameter (a measure of the
I,
	
relative steepness of the red and violet wings.
A FORTRAN program, which had been previously written to reduce
ground-based and Copernicus spectra, was adapted for use with the IUE data.
rf
G.
r^
.
1 ,
This program a?,so rectifier the profiles and computes central depths,
half-widths, equivalent widths, and asymmetry parameters, as well as the
radial velocity associated with the deepest point In the line. The FORTRAN
program, runs on the GSFC 360-91 computer, in the batch mode. Its advantage
over the FORTH program (in addition to speed) is that it consistently sets
the continuum at exactly the same wavelengths in each spectrum. However,
since the observer does not see the spectrum as the computation is being
made, he has no opportunity to correct for instrumental artifacts and
other possible errors without a second iteration.
Both the FORTH and the FORTRAN program were tested on a few of
the original spectra, 'while we were waiting for the reprocessed spectra
to be delivered. In spite of its disadvantages, the FORTH program appears
to give better results, because it allows one to compensate for anomalies
both in the instrument (shifts in the wavelength scale, reseaux, etc. ) and
in the star (real changes in the spectral line width) in a realistic manner.
III. Work in Progress
Because of the late arrival of the reprocessed spectra, little analysis
was completed on our data before the end of the grant period. A preliminary
examination of the spectra does not reveal any gross changes in the
equivalent widths, such as were reported by Fischel a.n d Sparks for the
1 C IV and N V lines in Beta Cephei ("The Universe in Ultraviolet Wavelengths;
The First Two Years of IUE, 11 Goddard Space Flight Center, 1980). However,
since Fischel and Sparks did not find any such anomalies for any of the other
k	
1
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t..
stars in their program, It is beginning to appear that Beta Cephei is a
unique object In this respect.
A comparison of the l R/In tracings of Gamma Peg (a variable star)
and Zeta Cam (a nonvariable star of the same spectral type, BZ IV), which
were obtained In this program, was mad by Anna Underhill for inclusion.
In a Bore she is co-editing with the Principal Investigator ( ► 'B Mars With
and Without Eti—fission Lines, ►► NASA and CNRS, in press), There were
surprising differences in the line widths in the two spectre -- differences
that may be greater than we can account for on the basis of rotation alone.
This result is unexpected, since previous low-dispersion work (sash and
Bohlin, PAST S_`?, $87, l 9'; 5) has indicated that the ultraviolet spectra of
these two stars are nearly identical. This point will, be pursued, to see it
it has any connection with the pulsation of Gamma Peg.
We intend to complete our plan of measuring the central depths, half-
widths, equivalent widths, and asymmetry parameters of selected lines in
all the spectra obtained for this program, both of variable stars and non-
variable stars. The FORTH routine on the minicomputer will probably be
used for this purpose, since it apparently gives more reliable results.
These parameters will then be plotted against phase for the variable stars,
and the mean values for the variable. , stars will be compared with the values
for the nonvariable stars.
It is anticipated that this phase of the project w ll be completed by
August 1981. Subsequent analysis will depend upon Oiee nature of the variations
detected. If consistent results are obtained, they will be compared with the
predictions of radial, and nonradial pulsation theory.


Velocity fields and spectrum peculiarities in Beta Cephei stars

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