A&A 451, 285-291 (2006)
Abundance analysis of 5 early-type stars in the young open cluster IC 2391,
Ch. Stütz1,2 -
S. Bagnulo2 - E. Jehin2 -
C. Ledoux2 - R. Cabanac3 - C. Melo2 -
J. V. Smoker2,4
1 - Institute of Astronomy (IfA), University of Vienna,
Türkenschanzstrasse 17, 1180 Vienna, Austria
European Southern Observatory,
Casilla 19001, Santiago 19, Chile
Canada-France-Hawaii Telescope Corporation,
65-1238 Mamalahoa Hwy. Kamuela, Hawaii 96743, USA
4 - Astrophyisics & Planetary Science Research Division,
Department of Physics and Astronomy, The Queen's University
of Belfast, University Road, Belfast, BT7 1NN, UK
Received 25 July 2005 / Accepted 23 January 2006
Aims. It is unclear whether chemically peculiar stars of the upper main sequence represent a class completely distinct from normal A-type stars, or whether there exists a continuous transition from the normal to the most peculiar late F- to early B-type stars. A systematic abundance analysis of open cluster early-type stars would help to relate the observed differences of the chemical abundances of the photospheres to other stellar characteristics, without being concerned by possible different original chemical composition. Furthermore, if a continuous transition region from the very peculiar to the so called normal A-F stars exists, it should be possible to detect objects with mild peculiarities.
Methods. As a first step of a larger project, an abundance analysis of 5 F-A type stars in the young cluster IC 2391 was performed using high resolution spectra obtained with the UVES instrument of the ESO VLT.
Results. Our targets seem to follow a general abundance pattern: close to solar abundance of the light elements and iron peak elements, heavy elements are slightly overabundant with respect to the sun, similar to what was found in previous studies of normal field A-type stars of the galactic plane. We detected a weakly chemically peculiar star, HD 74044. Its element pattern contains characteristics of CP1 as well as CP2 stars, enhanced abundances of iron peak elements and also higher abundances of Sc, Y, Ba and Ce. We did not detect a magnetic field in this star (detection limit was 2 kG). We also studied the star SHJM 2, proposed as a pre-main sequence object in previous works. Using spectroscopy we found a high surface gravity, which suggests that the star is very close to the ZAMS.
Galaxy: open clusters and associations: individual: IC 2391 -
stars: abundances -
stars: evolution -
stars: chemically peculiar -
stars: pre-main sequence
The atmospheres of main sequence A-type stars should be relatively
simple to understand and to model. Convection is apparently absent,
stellar winds are very weak, and little or no photospheric
microturbulence is generally present. Yet, in this group of
stars, a large variety of peculiarities are observed. Among A- and
B-type stars, about 10% are chemically peculiar, i.e., the
analysis of their spectra reveal overabundances (e.g., of iron-peak
and/or rare-earths elements) and/or underabundances (e.g., of He,
Ca, and Sc), compared to the composition of the solar
photosphere. Many of these chemically peculiar (CP) stars exhibit
large scale magnetic fields with a typical strength of a few hundreds up
to a few tens of thousands of Gauss. Furthermore, many of the CP stars
reveal very inhomogeneous atmospheric distributions of numerous
elements. Another characteristic of CP stars is that,
compared to the normal A and B-type stars, most have long rotation
periods - typically several days, but up to a few decades for some
magnetic CP stars. For a more detailed introduction to the variety of
phenomena observed in A and B-type stars see, e.g., Preston
(1974), Wolff (1983).
An important question to address is whether the CP stars represent a
group that is well separated from "normal'' A and B-type stars, or
whether CP stars are the extreme cases of a group of stars
spanning all grades of peculiarity. If a continuous transition from
the very peculiar to the so called normal A-F stars exists, it should
be possible to detect objects with mild peculiarities.
There are several reasons why these stars are so difficult to
identify. Rotation velocities of normal A-type stars are in most cases
too high (
to allow precise
abundance determination. Pronounced chemical peculiarity is mostly
found in slow rotators (
studying a transition from CP to normal stars also implies analysing
objects with higher projected rotation velocities. Thus it is not
clear whether this anticorrelation of
and peculiarity is a
physical one, or if it is due to a selection effect. In other words,
is rotation preventing chemical peculiarity or is it hiding chemical
peculiarity? Hill & Landstreet (1993) explicitly
showed for narrow lined A stars (
of the galactic
plane that the variations in the individual elemental abundances can
be quite large (0.4 dex). The same is reflected
in the work of Adelman and collaborators (e.g. Kocer et al. 2003; Pintado & Adelman 2003).
The proper way to address the questions above is to perform a detailed
abundance analysis of early-type stars of different ages
and rotational velocities. Members of open clusters are of special
interest because one can safely assume that members of the same cluster
are more or less of the same age and chemical composition. They should differ
from each other only by their initial mass. Furthermore, the cluster age
can be determined with much more accuracy than the age of individual stars
in the field.
We thus carried out a detailed study of 5 main sequence stars of
spectral type B - F belonging to the young open cluster IC 2391.
For our investigations we used spectra obtained with UVES, the high
resolution spectrograph of the ESO VLT.
As the stars of IC 2391 we analysed are roughly the same age and were formed
from similar initial chemical composition, we expect that if significant
deviations from the abundance pattern typical for IC 2391 are found, they
will be nearly independent of these two stellar properties. Thus the
probability that weak chemical peculiarity dates back to the birth of
the star is higher than for stars located in the galactic field.
Since the cluster is very young (36 Mys, Lyngå 1987),
main sequence (MS) evolutionary effects are small. One star of our sample,
SHMJ 2, may have not reached the MS yet.
IC 2391 was observed from 7 to 12 February 2001 with the UVES
instrument of the ESO VLT Unit 2 Kueyen within the framework of the
UVES Paranal Observatory Project (Bagnulo et al. 2003). Target selection was performed mainly with the
WEBDA open cluster database
(http://www.univie.ac.at/webda/) developed by J.-C. Mermilliod at
the Institute for Astronomy of the University of Lausanne and
maintained by E. Paunzen at the University of Vienna. Some additional
pre-main sequence stars were selected using the work by Stauffer et al. (1989). Spectra for about 50 candidate cluster
members were obtained using the settings DIC1 (346+580) and DIC2
(437+860) (see UVES user manual VLT-MAN-ESO-13200-1825) with a 0.5''slit width. The resulting spectra cover almost the entire spectral
range from 305 nm to 1040 nm with a spectral resolution of about
80 000. The raw data are available at the ESO archive under
programme ID 266.D-5655.
In total, 50 stars of IC 2391 were observed. For 8 early-type stars
among them, the rotational velocity is low enough and the quality of
the spectral data sufficient for our purposes of detailed abundance
analysis. These stars are listed in Table 1.
Information about membership was extracted from Robichon et al.
(1999), Levato et al. (1988), Perry & Hill
(1969), and Stauffer et al. (1989).
Membership was cross-checked using Hipparcos parallaxes, the most
recent E(b-y) data found in the SIMBAD database and new radial
velocity measurements of UVES POP stars by Noterdaeme et al. (in
preparation). For two objects of Table 1, membership
remains questionable. HD 75029 is not stated as a member in Perry &
Hill (1969), however, its astrometric parameters agree
well with the cluster mean. On the other hand HD 73778,
according to Levato et al. (1988), very likely is not a
member of IC 2391. The Si star HD 74535 was investigated by
Lüftinger et al. (in prep.) parallel to our study.
Candidate target stars for abundance analysis.
Rotation velocities from Noterdaeme et al. (in preparation).
M? denotes questionable membership,
index that is sensitive to CP2 type peculiarity
is taken from Maitzen & Catalano (1986).
A * indicates stars that were selected for the abundance analysis.
We analysed HD 73722, HD 74044, HD 74275,
HD 75029 and SHJM 2. This target selection is the result of a
compromise between keeping the spread of spectral types large and
the projected rotation velocities low.
Data have been reduced by the UVES POP team using an automatic
procedure based on the MIDAS UVES pipeline (Ballester et al. 2000). Science frames were bias-subtracted and divided by
the extracted flat-field, except for the 860 setting, where
the 2D (pixel-to-pixel) flat-fielding was used in order to better
correct for fringing. Because of the high flux of the spectra
the average extraction method was used instead of the
optimal extraction method that is recommended for
spectra characterised by a signal to noise ratio (SNR) 100. Further details about the reduction procedure can be found in
Bagnulo et al. (2003). All reduced spectra can be
obtained with the UVES POP web interface at
Taking advantage of the quality control parameters produced by the
UVES pipeline, we performed a check of the instrument
stability and actual performance. The accuracy of the wavelength
calibration was found to be of the order of 300 m s-1 only because
the Th-Ar reference frames were taken the following morning and not
before and after each observation (the temperature difference between
science exposures and calibrations was typically 1 K). For
this work we used the following wavelength intervals:
3730-4990 Å (characterised by a mean resolution
and a SNR of 100-150);
4760-5770 Å (
and SNR = 210-150);
5840-6840 Å (
and SNR = 170-130).
We found a maximum variation of 3.7% for these mean resolutions.
The targets selected for the abundance analysis
include objects with rotation velocities up to
For such fast rotating stars, the determination of the elemental
abundances depends critically on the accuracy of the continuum
normalisation. To be sure to perform accurate continuum fitting,
we performed some tests using the spectra of HD 74169, a slow
rotating cluster member Ap star that will be analysed in detail in a
forthcoming paper by Lüftinger et al. We normalised the star's high
SNR (300) spectra in two independent ways:
using the merged output of the UVES pipeline,
and using the intermediate "2D unmerged'' spectra, i.e.,
the spectra corresponding to the individual echelle orders (also
available through the UVES POP web interface). The fully merged
spectra are affected by some artefacts mainly due to an imperfect
merging of the echelle orders (for details see Bagnulo et al. 2003, and references therein), hence better results are
expected to be obtained by normalisation of the unmerged spectra.
However, an optimum normalisation could be obtained by dividing the
merged spectra into sub-spectra of a maximum length of
100 Å, and by treating these individually. This way we obtained an
agreement to better than 1% over the whole spectral range for the
two different techniques. The maximum size of the differences
in the normalised spectra obtained with the two methods does not generally
occur at the wavelengths of the the extremes of the echelle
orders. This suggests that the order merging performed by the UVES
pipeline is sufficiently accurate and does not lead to major artefacts
in the abundance analysis.
Our comparison showed that we could not clearly define the continuum for
the hydrogen lines (which are in general broader than 100 Å) and thus
we did not use them to determine fundamental atmospheric parameters.
To identify telluric lines we used the star HD 74196 as
reference. The spectrum of this cluster member does not contain many
lines (spectral type B7V) which are heavily broadened due
to the high rotational velocity of
The starting values for the fundamental parameters of the atmosphere
of the selected stars were estimated via Strömgren
photometry in the case of SHJM 2) and
evolutionary tracks for the cluster interpolated from Schaller et al. (2004). The uncertainties of these estimates are
quite large (typically 200 K in
and 0.25 in
), thus we
tried to improve the fundamental parameters by spectroscopic means.
estimates were improved via elimination of an abundance -
correlation (see Fig. 1).
estimates were improved by making sure that there is no systematic
difference in abundances between different ionisation stages of
chemical elements (called in the following "ionisation equation condition'').
The presence of a magnetic field was checked looking at the correlation of
abundances with Landéfactors, and by searching for magnetically
Excitation potential vs. abundance for the final values of
of HD 74044.
Open circles - Fe I, filled circles -
Fe II. A least squares linear regression
yields: abn = -0.0002
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Together with the mean metallicity of the cluster ([Fe/H] = -0.03,
Randich et al. 2001), these parameters defined the first
atmosphere calculated with LLmodels (Shulyak et al.
2004) in ODF mode (ODF: estimating line absorption via a
pre calculated opacity distribution function). Using this model we
calculated the emerging flux at the center of lines extracted from the
VALD database (Piskunov et al. 1995; Kupka et al. 1999; Ryabchikova et al. 1999) and preselected
only those that make an important contribution to the opacity
are the line and
continuum absorption coefficient).
We determined the initial microturbulence and element abundance
pattern from equivalent widths of unblended lines using the widthV software written by Tsymbal. Assuming that for our set of
spectral lines non-LTE and stratification effects are negligible,
there should be no correlation between abundances determined from the
equivalent widths and the widths themselves or the excitation energy,
and the ionisation equation condition should be fulfilled.
Eliminating the above correlations for the elements where we found
the most unblended or marginally blended lines in the spectra
(typically Fe, Cr, Ti, Ni, Ca)
resulted not only in a fairly good determination of
microturbulence and first abundances, but also in an improvement of
effective temperature and surface gravity. For HD 74275 we had to
perform this step via synthetic line fitting, since this star rotates
and shows only a few unblended lines.
Starting and final set of atmospheric parameters.
UP - UVES POP number.For synthetic line fitting all our models were calculated with LLmodels in the
line-by-line modus (Shulyak et al. 2004). This means that the individual
abundance pattern is included in our atmospheric models as well. The hydrogen
lines were treated using VCS theory (Vidal et al. 1973).
Convection was modelled according to the formalism of Canuto &
Mazzitelli (1991). For atmospheric modelling as well as for the line
synthesis with Synth3 (Piskunov 1992;
Valenti et al. 1998) we extracted the atomic
lines from the VALD line database. To analyse the spectra, in the sense of
deriving noise, deviations between observed and synthesized spectra,
measuring equivalent widths, etc., we developed the "Little Spectrum Analyser'' (Lispan).
The graphical interface for the codes which also controls the automatic
line core fitting is called ATC.
The set of atmospheric modelling and analysis software used for this
investigation can be reviewed on the web at
Once we had fixed
(see Table 2) by synthetic
line fitting of the unblended lines, we determined the elemental abundances in
an iterative process:
This procedure resulted in fundamental atmospheric parameters with internal
errors lower than 150 K in
0.20 dex in
and accurate element abundances (0.1-0.3 dex
in general) for all the program stars except HD 75029 which very likely is
a spectroscopic binary.
For more detailed discussions on internal and absolute errors in modern
abundance analyses see Andrievsky et al. (2002) or
Hill & Landstreet (1993).
- Automatic line core fitting with ATC, Synth3 and Lispan.
This is faster than fitting the whole line, but one has to be
and if present, the magnetic field.
The only free parameters here are the abundances.
- Check for peculiarities and magnetic fields.
- Fine tuning of fundamental parameters (
Check the conditions mentioned above and whether they hold when
peculiarities have been found.
- Edit line selection if blends have been overlooked, certain lines
show non-LTE effects, the quality of line parameters are uncertain,
of members of IC 2391.
Solar values according to Grevesse & Sauval
The atmospheric parameters of our stars were checked by fits of the H
lines. Atomic lines blended by the wings of H Balmer lines were
not used for abundance analysis because we could not precisely
determine the continuum.
In some cases the number of lines suitable for deriving
abundances of a certain element was very small.
For four stars these lines are listed in Table 5.
For the star HD 74044 the complete list of lines used for the
abundance analysis is presented in Table 4.
We found no indications for mean magnetic surface fields larger than 1 kG
in HD 73722, HD 75029 and SHJM 2, or larger than 2 kG in HD 74044 and
We did not find any published high quality abundance analyses
of stars of IC 2391 for a comparison with our work.
In the following we will present the results for the 5 stars we have
For HD 74044 we determined a projected rotation velocity of
Fundamental atmospheric parameters were derived
from Fe, Ca, Cr, Mg, Ni and Ti. We could determine
relatively precise abundances for 10 elements and abundance estimates
for C, Ce, Cu, Mn, O, Y and Zn (see Table 3).
Comparing the abundance pattern of HD 74044 to the other stars
we see indications for a mild chemical peculiarity, which is supported by
the higher abundances of Sc, Y, Ba and Ce (Fig. 2).
The element pattern of HD 74044 contains characteristics of CP1 stars
(enhanced iron peak elements) as well as CP2 stars (enhanced Sc, and
heavy elements). A similar pattern but much more pronounced can be seen
in the cluster star HD 74169 known to be of type CP2
(Lüftinger et al., in prep.).
Due to the rotation velocity of 33.7
detection limit for a mean surface magnetic field is about
2 kG. Polarimetric observations will be necessary to
check for the presence of a magnetic field.
This slowly rotating star (
is listed in the
catalogue of eclipsing and spectroscopic binary stars by
Popova & Kraicheva (1984). But after carefully scanning
our spectra we found no hints of line patterns that could originate from
a stellar companion or a close background star.
Temperature, surface gravity and microturbulence (Table 2)
were confirmed with lines from Fe, Cr, Ti, Ni, Ca, Si and Mn. TiI and
TiII deviated noticeably from the ionisation equilibrium condition.
Their abundances are -7.08 and -7.16 respectively. Typical for this
| < 0.05
for different ionisation stages of the same element.
The abundance of Sr is uncertain because both lines we analysed
(SrII 4161.792 Å and SrI 4607.327 Å) are blended.
The result for oxygen should be considered as an upper limit.
Comparison of the abundances in HD 74044 (open circles) with
those of the CP star HD 74169 (open triangles,
Lüftinger, in prep.) and to
the mean of the other members of IC 2391 (filled circles).
Abundances are in units of
according to Grevesse and Sauval 1998).
Error bars indicate maximum deviations from the mean.
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Elemental abundances relative to the sun.
Solar values according to Grevesse & Sauval
Data points of elements with consecutive atomic numbers are
connected with lines. Errors as in Table 3.
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this is the fastest rotating star we have
analysed. It is also the hottest one. Thus only few lines could be
used and the quality of our Ca, O, Si and Na abundances is
not as good as our internal error estimates may suggest. The
atmospheric parameters were refined from Fe, Cr, Ti and Mg.
In 5 lines (NaI 5889.951, NaI 5895.924, SiII 6347.109,
SiII 6371.371 and HeI 5875.615) we corrected for atmospheric
features (see Sect. 2.4). The remarkable overabundance of Na
(0.7 dex) is probably a non-LTE effect we could not account
for. Takeda (2003) and Asplund (2005) both
suggest non-LTE abundance corrections of up to -0.5 dex for these two
The abundance of helium, determined from 1 line (HeI 5875.615 Å),
is more or less solar.
although the membership of this star may be questionable, we
included it in our analysis, since it was the only slowly rotating
with spectral type between A0 and F5 and no
known peculiarities. A posteriori we found that its
abundances fit quite well in the overall pattern we see for IC 2391.
The star very likely has a faint fast rotating spectroscopic
companion, also noticed by Popova & Kraicheva (1984).
We could not directly separate the spectrum of the companion,
but we found our continuum to be systematically too low for regions
around deeper lines. Strong contamination
due to twilight can be ruled out as the cause because we do not see this
behaviour in the spectra of HD 74275 which has been observed at a
time even closer to dawn. Unfortunately no details about the possible
companion are known so far, hence our results for HD 75029 are
not as accurate as they should be.
Using the UVES observations we could analyse in detail the
spectrum of a very slowly rotating (
star. Stauffer et al. (1989, 1997)
suggested that SHJM 2 has not yet reached the ZAMS. The surface
gravity we determined by spectroscopic means (
surprisingly high if we consider the star to be a PMS object. Evolutionary
tracks for cluster stars give the same value for cluster members with
this effective temperature situated on the ZAMS. Therefore SHJM 2 is
probably at the very end of its pre main sequence phase or
has already reached the ZAMS. Since SHJM 2 is already in the final
stage of its PMS phase and very close to the main sequence, we applied
the techniques developed for main sequence stars for an abundance
analysis. Examining the iron lines FeII 6149.258 and
FeI 6336.8243 we could detect no magnetic field. The star generally
reflects the pattern of the other cluster members (except HD 74044 of
We have carried out a detailed analysis of the atmospheres of 5 A-F stars
in the cluster IC 2391 and have obtained reasonably accurate fundamental
parameters and element abundances accurate within 0.1-0.3 dex.
Specific element patterns were included in our atmospheric models and
the presence of magnetic fields and the possibility of stratification were
checked too (when
Mean abundance pattern of IC 2391 (HD 74044 excluded)
derived in this work compared to the abundance pattern found for
field stars by Hill & Landstreet (1993) and
Hill (1995). Elemental abundances are relative to the
sun with solar values according to Grevesse and Sauval
Data points of elements with consecutive atomic numbers are
connected with lines. Error bars are variances of the mean
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Understanding HD 74044 contributes to our knowledge
of the A star phenomenon. This star shows a mild peculiarity of the
type CP1 and CP2: Sc, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Y and Ce are enhanced by
0.3-0.8 dex relative to the mean of the other cluster members,
and even more so Ba.
Nevertheless we neither can confidently assign HD 74044 to the
group of CP2 nor CP1 stars. We situate this object in the
continuous transition region from the very peculiar to the normal
We did not detect a magnetic surface field, but our detection limit
is rather high (2 kG). Therefore follow-up polarimetric observations
are necessary to clarify its status.
The abundance star to star scatter of the other cluster stars is,
as expected, small (0.1-0.3 dex) compared to what was
found for stars in the galactic plane (0.3-0.5 dex) by
Hill & Landstreet (1993) and Hill (1995)
for 6 and 9 objects respectively.
A comparison of a cluster abundance pattern derived in this work
for 26 elements to the abundances of early A stars in the galactic plane
is shown in Fig. 4. Note that not only the star to star
variations of element abundances are larger in the galactic plane, but they
also seem to increase for faster rotating stars. The latter may not be an
intrinsic effect of rotation, but due to the fact that detailed abundance
studies become rather difficult for faster rotating stars.
For the needed accuracy our technique is limited to a
measured for HD 74275.
Our sample includes the star SHJM 2, probably a PMS star
already close to the ZAMS considering the findings of Stauffer et al.
(1989) and the star's high surface gravity.
Assuming that its atmosphere can be modelled applying the same
physics and approximations as for MS A-F stars, we performed a detailed
abundance analysis in the optical range for this star.
Its abundances reflect the general abundance pattern of IC 2391.
We like to thank Theresa Lüftinger for insight
in her analysis of HD 74169 and Pasquier Noterdaeme for his
data for this cluster. We also thank Martin Stift
for his helpful suggestions on presentation of the results.
Ch. Stütz acknowledges ESO DGDF for a three month studentship at ESO
Santiago/Vitacura and the FWF (project P17890).
S. M., Chernyshova, I. V., Paunzen, E., et al. 2002, A&A, 396,
64 [NASA ADS] (In the text)
- Asplund, M. 2005,
ARA&A, 43, 481 [NASA ADS] (In the text)
- Asplund, M.,
Grevesse, N., & Sauval, A. J. 2004, The solar chemical
composition, Cosmic Abundances as Records of Stellar Evolution and
Nucleosynthesis, ed. F. N. Bash, & T. G. Barnes, ASP Conf.
- Bagnulo, S., Jehin,
E., Ledoux, C., et al. 2003, ESO Messenger, 114, 10 [NASA ADS] (In the text)
- Ballester, P.,
Modigliani, A., Boitquin, O., et al. 2000, ESO Messenger, 101,
31 (In the text)
- Canuto, V. M., &
Mazzitelli, I. 1991, ApJ, 370, 295 [NASA ADS] [CrossRef] (In the text)
Grevesse, N., & Sauval, A. J. 1998, SSR, 85, 161 [NASA ADS] (In the text)
G. M., & Landstreet, J. D. 1993, A&A, 276, 142 [NASA ADS] (In the text)
- Hill, G. M. 1995,
A&A, 294, 536 [NASA ADS] (In the text)
- Levato, H., Garcia,
B., Lustó, C., & Morrell, N. 1988, Ap&SS, 146,
361 [NASA ADS] (In the text)
- Kocer, D., Adelman,
S. J., Caliskan, H., Gulliver, A. F., & Gokmen Tektunali, H.
2003, A&A, 406, 975 [EDP Sciences] [NASA ADS] [CrossRef] (In the text)
- Kupka, F., Piskunov, N.
E., Ryabchikova, T. A., Stempels, H. C., & Weiss, W. W. 1999,
A&AS, 138, 119 [EDP Sciences] [NASA ADS] (In the text)
J. D. 2004, in The A-Star Puzzle, ed. J. Zverko, J. Ziznovsky, S.
J. Adelman, & W. W. Weiss, IAUS, 224, 423
- Levato, H., Garcia, B.,
Lustó, C., & Morrell, N. 1988, Ap&SS, 146, 361 [NASA ADS]
- Lyngå, G.
1987, Catalog of open cluster data (5th edition)
(In the text)
Maitzen, H. M., & Catalano, F. A. 1986, A&AS, 66, 37 [NASA ADS] (In the text)
- Perry, C. L.,
& Hill, G. 1969, AJ, 74, 899 [NASA ADS] [CrossRef] (In the text)
- Pintado, O. I.,
& Adelman, S. J. 2003, A&A, 406, 987 [EDP Sciences] [NASA ADS] [CrossRef] (In the text)
- Piskunov, N.
1992, Stellar Magnetism, Proceedings of the international meeting
on the problem Physics and Evolution of Stars, ed. Yu. V.
Glagolevskij, I. I. Romanyuk, & St. Petersburg, 92
(In the text)
- Piskunov, N. E., Kupka,
F., Ryabchikova, T. A., Weiss, W. W., & Jeffery, C. S. 1995,
A&AS, 112, 525 [NASA ADS] (In the text)
- Popova, M., &
Kraicheva, Z. 1984, Astrofizik. Issledovanija, 18, 64 (In the text)
- Preston, G. W.
1974, ARA&A, 12, 257 [NASA ADS] (In the text)
- Randich, S.,
Pallavicini, R., Meola, G., Stauffer, J. R., & Balachandran, S.
C. 2001, A&A, 372, 862 [EDP Sciences] [NASA ADS] [CrossRef] (In the text)
- Robichon, N.
N., Arenou, F., Mermilliod, J.-C., & Turon, C. 1999, A&A,
345, 471 [NASA ADS] (In the text)
- Ryabchikova, T. A.,
Piskunov, N., Stempels, H. C., Kupka, F., & Weiss, W. W. 1999,
Phys. Scr., T83, 162 [NASA ADS] (In the text)
- Schaller, G.,
Schaerer, D., Meynet, G., & Maeder, A. 2004, A&AS, 96,
269 [NASA ADS] (In the text)
- Shulyak, D.,
Tsymbal, V., Ryabchikova, T., Stütz, Ch., & Weiss, W. W.
2004, A&A, 428, 993 [EDP Sciences] [NASA ADS] [CrossRef] (In the text)
- Stauffer, J.,
Hartmann, L. W., Jones, B. F., & McNamara, B. 1989, ApJ, 342,
285 [NASA ADS] [CrossRef] (In the text)
- Stauffer, J.,
Hartmann, L. W., Prosser, C. F., et al. 1997, ApJ, 479, 776 [NASA ADS] [CrossRef] (In the text)
- Takeda, Y., Zhao,
G., Takada-Hidai, M., et al. 2003, Chin. J. A&A, 3, 316 (In the text)
- Valenti, J. A.,
Piskunov, N., & Johns-Krull, C. M. 1998, ApJ, 498, 851 [NASA ADS] [CrossRef] (In the text)
- Vidal, C. R., Cooper, J.,
& Smith, E. W. 1973, ApJS, 25, 37 [NASA ADS] [CrossRef] (In the text)
- Wolff, S. C. 1983,
The A-stars: Problems and Perspectives, NASA SP-463
(In the text)
Lines used for abundance determination of HD 74044.
Selected lines ([n] < 5) used for abundance determination of
HD 73722, HD 74275, HD 75029 and SHJM 2.
Copyright ESO 2006