Ultraviolet and optical data for the Hg Mn stars Coronae Borealis and Cancri is being combined with data for the field horizontal branch population II star HD 109995 in order to derive the element abundances in their photospheres. Data collected by IUE is being utilized

Adelman, S. J.

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https://ntrs.nasa.gov/search.jsp?R=19850009604 2020-03-20T20:33:16+00:00Z
(NASA -CR-174298) ELEBLNTAL ABUNDANCES OF
	 N@5-11913
MERCURY-AANGAMESE STAGS INN THE 20PULAIICN 2
TYPE STAB BD 10S995 Semiannual Report, 1
Jul. 1984 - 31 Jul. 1985 (Citadel Coll.)
	 Unclas
6 p HC A02/nF AC1	 CSCL 038 G3/90 13426
ELTMENTAL ABUNDANCES OF MERCURY-MANGANESE STARS AND
THE POPULATION II A TYPE STAR RD 109995
National Aeronautics and Space Administration Grant
No. NAG 5 - 218 (Supplement 2) Semiannual Report
Dr. Saul J. Adelman, Principal Investigator
Department of Physics
The Citadel
Charleston, SC 29409
Grant Duration: July 1, 1984 - July 31, 1985
February 1, 1985
2Dr. David S. Leckrone, Laboratory for Astronomy and Solar
Physics (Code 681), NASA Goddard Space Flight Center, is the co-
investigator for this project. The purpose of our study is to
combine ultraviolet and optical data for the HgMn star% i Coronae
Borealis and K Cancri and the field horizontal branch Population
II star HD 109995 and derive in a thorough self-consistent
analysis the abundances of the elements in their photospheres.
This work is a continuation of our earlier initiated project on
the normF?. late B and early A stars, w Cet, 21 Aql, 134 Tau, v
Cap, o peg, and 9 Leo, which is still in progress and will
provide a standard of comparison for these stars.
The IUE data for i CrB and K Cnc was obtained at the
beginning of January 1985. The high dispersion images are being
coadded and line identification studies will begin soon.
Reduction of the optical region spectrograms should be completed
during a visit to the Dominion Astrophysical Observatory in March
1985 with the completion of the optical region analyses a few
months thereafter.
Much of the IUE data for HD 109995 was obtained in early
summer 1984. The high dispersion images have been coadded and a
line identification study was completed. The last IUE shift for
this star will be on February 5. As soon as that data is
available, a new coaddition will be performed and the line
Identifications, especially in those regions where the new images
substantially improve the signal-to-noise, will be checked and
revised as appropriate. Then Leckrone and I will submit for
3publication our manuscript "The Ultraviolet IUE Spectrum of the
Population II Horizontal Branch A Star HD 109995".
Low noise optical region spectroscopic data of HD 109995
will be obtained in March and April 1985 if the weather
cooperates. During my forthcoming visit :c, the Dominion
Astrophysical Observatory, I have eight nights on their 48"
telescope. My primary goal is obtain several 6.7 A/mm IIaO
spectrograms of HD 109995 and then coadd the resulting spectra
to increase the signal-to-noise ratio. At Kitt Peak National
Observatory in cooperation with Drs. Donald S. Hayes and A. G_
DavisPhilip, I will observe red and infrared C I, N I, and 0 I
lines of several stars including HD 109995 with CCDs in the coude
spectrograph of the 2.1-m telescope.
In the last few months, Leckrone and I have investigated
several factors which affect the accuracy of abundances derived
from IUE spectra including noise, gf- and line damping values,
and the choice of model atmospheres. We studied noise in IUE
high dispersion images by comparing individual images and our
coadditions of normal stars. In well-exposed orders the
amplitude relative to the total signal was 6% for fixed pattern
and 4% for random noise. Further our coaddition procedure
increased the signal-to-noise ratio by a factor of 2 compared
with individual images. At the Tucson American Astronomical
Society Meeting in January 1985, we presented a poster paper
"Investigation of Random and Fixed Pattern Noise in High
Dispersion IUE Spectra" (1984, Bulletin of the American
4Astronomical Society 16, 903). We will shortly submit the
results of our study to a refereed journal.
The choice of gf-values and for strong.lines line damping
constants affects the derived abundances. A standard assumption
for optical region analyses that the line damping is ten times
classical p an lead to incorrect results. R. L. Rurucz in his
current version of WIDTH, a computer program which determines the
abundances given the model atmosphere, the equivalent width, and
the atomic parameters, employs semi-classical approximations to
calculate line damping constants. Only for a few species such as
Fe II (Rurucz, 1981, SAO Special Report 390) have calculations
been performed which permit one to use better approximations to
the true damping constants.
Fe I and Fe II are key species in optical region abundance
analyses as they have many lines. Often the deduced abundances
are calculated for a range of possible microturbulent
velocities. The value of the microturbulent velocity is chosen
so that the derived abundances are not a function of equivalent
width.
Last fall, Dr. J. R. Fuhr, National Bureau of Standards,
completed a new cr tical compilation of Fe II values. I used
these new values and damping constants derived from Rurucz (1981)
to reevaluate optical region abundances from a dozen sharp-lined
B and A stars. Whenever possible, I compared these values to
those derived from Fe I lines, where the gf values came from a
previous critical compilation by Fuhr., and are on the whole of
sslightly better quality than those for Fe II, and the damping
constants were calculated using semi-classical approximations.
The results from Fe I and Fe II lines are in slightly better
agreement than as originally published with a slightly different
set of gf-values for Fe II and ten times classical damping for
both atomic species. Abundance analyses for all other atomic
species were performed for all stars with the new microturbulent
velocities and semi-classical approximations to the damping
constants. The results will be contained in a forthcoming paper.
There are still some minor systematic trends in the optical
abundances of the normal stars. Nevertheless, the results of
optical region studies are useful as initial input parameters for
ultraviolet region analyses. Analyses of ultraviolet lines in
the same stars may help to illuminate the origin of the
systematics. An abundance analysis of 9 Leo based on optical
region data and consistent with the reevaluated optical region
studies just described has also been completed.
When the effective temperature and surface gravity are
determined for optical region abundance studies, one often
compares the predictions of model atmospheres of the appropriate
metallicity with the optical energy distribution, often found by
spectrophotometry, and a measure of a Balmer line, often the
profile of Hy. IUE low dispersion scans can be used to extend
the range over which the energy distributions are known. By
compar'ng this data with model predictions, the model parameters
selected from optical data alone can .be verified or perhaps
}
:t
6refined. This was done for the six normal B and A stars of our
earlier initiated project. Except for o Peg, the previously
selected models were verified.
The first results for the normal stars for FeII X2607 were
presented at the Tucson AAS meeting in January 1985 (D. S.
Leckrone and S. J. Adelman, "Elemental Abundances in Early Type
Stars", 1984, B. A. A. S. 16, 973). The agreement with optical
results was good. Some systematics are present, but more lines
need to be studied to confirm them.
In the process of synthesizing the line profiles, the
necessity for drawing the continuum in the same manner for-all
stars in our program became apparent. Thus Leckrone and I are
planning to analyze the normal, HgMn, and the HB stars at the
same time. We have selected preliminary models for i CrB, K Cnc,
and HD 109995. As soon as we coadd the high dispersion exposures
of these stars, we will include them in our abundance analysis
program. Their abundances will be refined as soon as the optical
abundances are completed. We will first complete the study of
approximately 25 Fe II lines and then proceed to other Laportant
, -tonic species such as C I, N I, 0 I, ;nd Zn II.


Elemental abundances of mercury-manganese stars and the population 2 type star HD 109995

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