A&A 389, 537-546 (2002)
DOI: 10.1051/0004-6361:20020593
I. F. Bikmaev1 - T. A. Ryabchikova2,3 - H. Bruntt4 - F. A. Musaev5,6,7 - L. I. Mashonkina1 - E. V. Belyakova1 - V. V. Shimansky1 - P. S. Barklem8 - G. Galazutdinov5,6
1 - Department of Astronomy, Kazan State University, Kremlevskaya 18,
420008 Kazan, Russia
2 -
Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48,
109017 Moscow, Russia
3 -
Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna,
Austria
4 -
Institute for Physics and Astronomy, University of Aarhus, Bygn. 520, 8000 Aarhus C,
Denmark
5 -
Special Astrophysical Observatory RAS, 369167 Nizhnij Arkhyz, Karachai-Circassian Republic,
Russia
6 -
SAO Branch of Isaac Newton Institute, Santiago, Chile
7 -
International Centre for Astronomical, Medical and Ecological Researches (ICAMER),
National Academy of Sciences of Ukraine, 361605 Peak Terskol, Kabardino-Balkaria, Russia
8 - Department of Astronomy and Space Physics, Uppsala University, Box 515, 751-20 Uppsala,
Sweden
Received 26 March 2002 / Accepted 9 April 2002
Abstract
We have performed abundance analysis of two slowly rotating, late A-type stars,
HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtained echelle spectra
covering the spectral range
4000-9850 Å. These spectra allowed us to identify an extensive line list for 31
chemical elements, the most complete to date for A-type stars. Two approaches to
abundance analysis were used, namely a "manual'' (interactive) and a semi-automatic
procedure for comparison of synthetic and observed spectra and equivalent widths.
For some elements non-LTE (NLTE) calculations were carried out and the corresponding
corrections have been applied. The abundance pattern of HD 32115 was found to be very
close to the solar abundance pattern, and thus may be used as an abundance standard
for chemical composition studies in middle and late A stars. Further, its H
line profile shows no core-to-wing anomaly like that found for cool Ap stars and
therefore also may be used as a standard in comparative studies of the atmospheric
structures of cool, slowly rotating Ap stars. HD 37594 shows a metal deficiency
at the level of -0.3 dex for most elements and triangle-like cores of spectral lines.
This star most probably belongs to the
Sct group.
Key words: stars: atmospheres - stars: abundances - stars: individual: HD 32115, HD 37594
HJD-2400000 | ![]() |
n | Reference |
HD 32115 | |||
52333.2007 | 19.15(43) | 67 | this paper |
51929.3035 | 42.08(45) | 71 | this paper |
49405.5333 | 44.61(43) | Grenier et al. (1999) | |
42675.8313 | 43.7 (5) | 14 | Nordström & Andersen (1985) |
42669.8640 | 12.2 (4) | 13 | Nordström & Andersen (1985) |
42379.7278 | 6.8 (6) | 14 | Nordström & Andersen (1985) |
HD 37594 | |||
51930.2146 | 22.52(72) | 69 | this paper |
49736.6142 | 22.04(39) | Grenier et al. (1999) | |
42680.8220 | 22.4 (3) | 15 | Nordström & Andersen (1985) |
42675.8928 | 24.8 (6) | 16 | Nordström & Andersen (1985) |
42380.6909 | 20.2 (7) | 16 | Nordström & Andersen (1985) |
Most sharp-lined stars with temperatures in the range 6700-8000 K belong to different
groups of peculiar stars: Ap, roAp, Am, or
Boo groups. They are usually
believed to have the same or nearly the same atmospheric structure as normal stars.
However, Cowley et al. (2001) found a pronounced core-to-wing anomaly in the Balmer
lines of some Ap stars. They could not compare the H
line profiles of these
stars with normal solar abundance stars because of the lack of reliable spectroscopic
standards in this temperature region. We therefore decided to perform an accurate
spectroscopic investigation of sharp-lined late A- to early F-type stars that are
classified as normal MS stars, using observations of a wide spectral region 4000-9850 Å.
From tabulated rotational velocities (Abt & Morrell 1995) we extracted 27 stars
classified as normal A3-F5-type stars of luminosity classes III-V with
25 km s-1.
Among them only 13 stars have metallicities in the range
0.15 on the basis of
temperature-gravity-metallicity calibrations of the observed Strömgren colours
(a procedure which will be described below). We did not consider the remainder of the
stars, the majority of which have low metallicities [M]<-0.15. In this paper we present
the results of careful atmospheric parameter and abundance determinations for two stars:
HD 32115 and HD 37594. These stars were classified as A8IV (HD 32115) and A8Vs
(HD 37594) by Cowley et al. (1969).
High resolution spectra of the region 4000-9850 Å were obtained for both
stars with the coude-echelle spectrometer (Musaev et al. 1999)
mounted on the 2 m "Zeiss'' telescope at Peak Terskol Observatory near Elbrus
mountain in Russia. The best resolving power of the spectrograph in this
operational mode is R= 45 000, but because of the rather poor seeing we used
a wider slit that resulted in a reduced spectral resolution of
30 000. A Wright Instruments front-side illuminated CCD of 1242 by
1152 pixels (22 mkm) was used as a detector for simultaneous registration of the whole
spectral range in a single exposure. Two spectra were obtained for each star and
they were coadded after cleaning for cosmic events during the reduction procedure.
Blueward of 7100 Å the consecutive orders overlap, while there are gaps of 5 to
55 Å between the orders for
7100 Å. Typical S/N= 150 was estimated
for the centers of the orders close to the H
region, while S/N decreases
to about 100 in the blue and infrared regions. Note that S/N also decreases from
the center to both ends of the order.
An extra spectrum of HD 32115 was obtained recently and was used for radial velocity
measurements, and for equivalent widths measurements of a few lines in the infrared
spectral region.
Table 1 contains the Heliocentric Julian Dates
of the middle of the exposure for each pair of observations. The second column
of Table 1 presents the results of the radial velocity measurements (see below)
together with the data from the literature.
Spectrum processing was realised with the help of a modified version of the PC-based DECH software (Galazutdinov 1992). It includes background subtraction, echelle vectors extraction from the echelle-images, wavelength calibration, continuum rectification, line identification, equivalent widths and radial velocity measurements. We did not divide the stellar image by a flat-field as we found this procedure does not improve the initial S/N= 100-150 for this particular CCD.
Method |
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[M/H] | ![]() |
HD 32115 | ||||
Photometry | 7300(40) | 4.21(01) | 0.03(04) | 2.84(02) |
Parallax | 4.24(05) | 2.84(10) | ||
H![]() |
7250(100) | |||
ATLAS9-newODF | 7250 | 4.30 | ||
Adopted | 7250 | 4.20 | 0.00 | |
HD 37594 | ||||
Photometry | 7170(50) | 4.21(03) | -0.15(04) | 2.98(07) |
Parallax | 4.22(05) | 2.90(07) | ||
H![]() |
7100(100) | |||
ATLAS9-newODF | 7170 | 4.25 | ||
Adopted | 7170 | 4.20 | -0.30 |
Stellar parameters derived with different methods are given in Table 2. We first derived
effective temperatures, gravities, metallicities and absolute magnitudes of our stars
employing Strömgren photometric indices and the calibration of Hauck & Mermilliod
(1998). We used the TEMPLOGG procedure (Rogers 1995), which for A3-F0-type
stars is based on the original calibrations by Moon & Dworetsky (1985) with
improvements by Napiwotski et al. (1993). For the metallicity calibration
TEMPLOGG uses a relation between the Strömgren metallicity index and the
stellar metallicity derived by Smalley (1993).
The quoted formal errors in the stellar parameters from photometry account only for
the reported accuracy of the photometric indices. One can see excellent agreement
between absolute magnitudes obtained here and those obtained from Hipparcos
parallaxes (ESA 1997). In this case the formal errors in the surface gravity include
both the parallax uncertainty and an effective temperature uncertainty of 100 K.
This provides strong support for the surface gravities used in our analysis. Bolometric
corrections do not exceed 0.06 mag. On evolutionary tracks both stars lie close to the
ZAMS and have masses slightly more than 1.5
(Pamyatnykh et al. 1998; Pamyatnykh 2000).
The age of both stars is estimated at 600-700 Myr.
To check the influence of the metal abundances on the derived atmospheric parameters
we calculated a small grid of atmospheric models and corresponding colours with the
abundances typical for our stars (see Sect. 5) and compared the observed and synthetic
colours. Calculations were made with the ATLAS9 code (Kurucz 1993) which is
modified by the inclusion of new line opacities in the form of specifically computed
ODFs (Piskunov & Kupka 2001) and the Canuto-Mazitelli convection treatment
(Smalley & Kupka 1997). We obtained the best fit to Strömgren indices with
= 7250 K and
= 7170 K for HD 32115 and HD 37594, respectively. They are
given in Table 2 as ATLAS9-newODF results. The derived effective temperatures
were also checked by fitting the H
line profile using these models.
Special care was taken to achieve a correct continuum fit in the echelle orders
containing the H
line. The typical length of the orders at 6400-6700 Å
is 90-100 Å, and we have 2 overlapping orders containing the H
line.
The estimated accuracy of our continuum level is
1-2
.
The H
profiles
of the models are computed as described in Barklem et al. (2000), namely, assuming
LTE and using the SYNTH program (Piskunov 1992) with Stark broadening
calculations from Stehlé & Hutcheon (1999) and self-broadening from
Barklem et al. (2000). Radiative broadening and an estimate of the pressure
broadening by helium are also included. A comparison between the observed and
calculated H
line profiles for HD 32115 is shown in Fig. 1.
Plots for HD 37594 show equally satisfactory fits. No atmospheric
model can reasonably fit the core of the H
line in both stars, which is always broader in
the observations. Atmospheric parameters finally adopted for the abundance analysis
are given in Table 2.
![]() |
Figure 1:
A comparison between the observed H![]() |
Open with DEXTER |
A further important parameter in the abundance analysis is microturbulent velocity.
It was derived from the elements with numerous lines and the most accurate atomic data.
Typically the
value as derived from lines of Cr, Mn, Fe, Ni, varies from 2.0 to
2.6 km s-1 in HD 32115, and from 2.2 to 2.8 km s-1 in HD 37594. Ti lines give a
systematically higher microturbulent velocity in both stars, up to 3.2 km s-1.
For abundance calculations we accepted
= 2.3
0.3 km s-1 for HD 32115, and
= 2.5
0.3 km s-1 for HD 37594. These values for turbulent velocity fields
in late A stars agree very well with theoretical predictions (Kupka & Montgomery 2002).
To begin the abundance analysis synthetic spectra are computed for the whole observed
region with the adopted atmospheric parameters and solar abundances. All lines that
have depths greater than 0.5% of the continuum flux in the synthetic spectrum were
extracted from the VALD database (Kupka et al. 1999). For a few elements it was
necessary to make corrections to the atomic line data, and these corrections were made
during the final steps of abundance analysis (see sections below for individual elements
for details). The spectrum synthesis code SYNTH (Piskunov 1992) was used in all
synthetic spectrum calculations. Using these calculations we estimated rotational
velocities for both stars, which were found to be
= 9
2 km s-1 for HD 32115
and
= 17
2 km s-1 for HD 37594.
While for the most part rotational plus instrumental broadening provides adequate fits
to unblended spectral lines in HD 32115, this is not the case for HD 37594. Single
spectral lines in this star often have V-shaped profiles rather than the usual U-shaped
profiles produced by the rotational broadening.
Similar line profiles are observed in
pulsating stars (e.g. the study of the
Sct-type star FG Vir by Mittermayer 2001).
This effect is marginal, and needs a further study with higher spectral resolution.
The final abundance analysis was done by three different methods: classical analysis using equivalent width data, spectral synthesis for strong and partially blended lines, and a semi-automatic procedure which uses both equivalent widths and spectrum synthesis techniques. The results of the first two methods were combined. We found no systematic difference between equivalent widths measured in the Solar Flux Atlas (Kurucz et al. 1984) and in a day-sky spectra obtained at the same dates and with the same spectrograph that was used for the taking the spectra of the program stars. The range of the errors in equivalent width measurements is 2-5 mÅ and depends on S/N ratio (position of the line on the echelle order), and blending effects. For most of the unblended lines this error does not exceed 2-3 mÅ. We also compared two independent sets of equivalent width measurements in the HD 32115 spectrum made by I. Bikmaev with the Gaussian approximation and by H. Bruntt with the Voigt approximation. For 122 lines the mean difference between two sets is 1.2 mÅ with a standard deviation of 2.8 mÅ.
Comparing the synthetic and the observed spectra we selected spectral lines that are
free of substantial blending effects and measured their equivalent widths. The final
abundances were calculated with Kurucz's WIDTH9 code modified by V. Tsymbal
for VALD-format input files. For a few elements, like Ba II which has mostly
very strong lines, or Eu II and Nd III which have only 1-2 partially blended
lines in the whole spectral region, abundances were derived with synthetic spectrum
calculations. Final abundances for 31 chemical elements (41 ions) are collected in
Table 3 (Cols. 2 and 7 for HD 32115 and HD 37594 respectively). The standard deviation
is given in units of the last digit in parentheses. Solar abundances in
=
- 0.04 (correction due to He) are taken from Grevesse & Sauval (1998)
except C, N, O, Mg, Si, and Ba. For these elements, except Ba, the most recent data by
Holweger (2001) are given. We adopted the solar Ba abundance derived by Mashonkina & Gehren (2000).
NLTE corrections were applied for the species marked by asterisks (see details below).
Columns 6 and 11 contain the stellar abundance relative to the sun. We also calculated
line-by-line differences between stellar and solar abundances, which show a close
agreement with the values from Cols. 6 and 11. All individual line abundances are presented in
Table 4 which is available in electronic form only.
This table may be retrieved from http://www.inasan.rssi.ru/~ryabchik.
NLTE corrections are also included in Table 4. These are
probably the most complete abundance data for single A-type stars to date.
Ion | HD 32115 | HD 37954 | Sun | ||||||||
Classical analysis | Semi-automatic | Classical analysis | Semi-automatic | ||||||||
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n |
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n | [
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n |
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n | [
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|
C I | -3.62(17) | 35 | -3.52(24) | 5 | -0.17 | -3.73(15) | 27 | -3.74(05) | 4 | -0.28 | -3.45H |
N I | -4.19(08) | 11 | -4.22(04) | 2 | -0.08 | -4.27(12) | 4 | -0.16 | -4.11H | ||
O I | -3.23(10) | 12 | -3.25(04) | 2 | 0.07 | -3.36(12) | 5 | -3.27(12) | 5 | -0.06 | -3.30H |
Na I* | -5.86(12) | 8 | -0.15 | -6.05(21) | 8 | -0.34 | -5.71 | ||||
Mg I | -4.59(12) | 9 | -4.33(05) | 4 | -0.09 | -4.89(10) | 8 | -4.68(03) | 4 | -0.39 | -4.50H |
Mg II | -4.43(11) | 4 | -4.46 | 1 | 0.07 | -4.79(19) | 3 | -4.65 | 1 | -0.29 | -4.50H |
Al I | -5.69(15) | 4 | -0.12 | -6.15(06) | 2 | -0.58 | -5.57 | ||||
Si I | -4.53(13) | 39 | -4.49(12) | 11 | -0.03 | -4.75(08) | 26 | -4.76(13) | 11 | -0.25 | -4.50H |
Si II | -4.47(12) | 6 | -4.53 | 1 | 0.03 | -4.59(04) | 3 | -4.72(10) | 2 | -0.09 | -4.50H |
P I | -6.42(13) | 2 | 0.17 | -6.59 | |||||||
S I | -4.81(15) | 19 | -4.92(09) | 5 | -0.10 | -5.07(10) | 8 | -5.06(01) | 2 | -0.36 | -4.71 |
Cl I | -6.76 | 1 | -0.22 | -6.54 | |||||||
K I* | -7.05 | 1 | -0.13 | -7.32 | 1 | -0.40 | -6.92 | ||||
Ca I | -5.63(15) | 21 | -5.60(13) | 13 | 0.05 | -5.89(22) | 26 | -5.99(27) | 16 | -0.21 | -5.68 |
Ca II* | -5.69(11) | 7 | -5.58 | 1 | -0.01 | -5.89(04) | 4 | -5.88 | 1 | -0.21 | -5.68 |
Sc II | -8.89(10) | 11 | -8.96(20) | 4 | -0.02 | -9.04(15) | 6 | -9.13 | 3 | -0.17 | -8.87 |
Ti I | -7.20(14) | 21 | -7.18(04) | 4 | -0.18 | -7.43(14) | 3 | -7.42(03) | 2 | -0.41 | -7.02 |
Ti II | -7.03(15) | 27 | -6.92(20) | 13 | -0.01 | -7.23(18) | 19 | -7.38(12) | 8 | -0.21 | -7.02 |
V I | -8.24(25) | 3 | -0.20 | -8.04 | |||||||
V II | -8.17(08) | 5 | -7.95 | 1 | -0.13 | -8.13(25) | 2 | -0.09 | -8.04 | ||
Cr I | -6.40(12) | 39 | -6.40(13) | 7 | -0.03 | -6.71(10) | 11 | -6.75(06) | 5 | -0.34 | -6.37 |
Cr II | -6.27(09) | 20 | -6.22(12) | 7 | 0.10 | -6.63(09) | 17 | -6.55(06) | 6 | -0.26 | -6.37 |
Mn I | -6.87(17) | 20 | -6.76(37) | 6 | -0.22 | -7.14(16) | 9 | -7.04(13) | 4 | -0.49 | -6.65 |
Mn II | -6.72(11) | 2 | -0.07 | -6.65 | |||||||
Fe I | -4.60(12) | 235 | -4.59(11) | 109 | -0.06 | -4.88(13) | 183 | -4.89(12) | 38 | -0.34 | -4.54 |
Fe II | -4.48(14) | 60 | -4.54(11) | 23 | 0.06 | -4.87(11) | 25 | -4.76(11) | 4 | -0.33 | -4.54 |
Co I | -7.16(10) | 5 | -7.16(00) | 2 | -0.04 | -7.43(03) | 3 | -0.31 | -7.12 | ||
Ni I | -5.91(10) | 59 | -5.94(13) | 17 | -0.12 | -6.24(16) | 27 | -6.18(03) | 4 | -0.45 | -5.79 |
Ni II | -5.82 | 1 | -0.03 | -5.79 | |||||||
Cu I | -7.82(26) | 5 | 0.01 | -8.32(06) | 2 | -0.49 | -7.83 | ||||
Zn I | -7.77(16) | 3 | -0.33 | -8.07(05) | 3 | -0.63 | -7.44 | ||||
Sr II* | -9.09(22) | 3 | -0.02 | -9.19(07) | 3 | -0.12 | -9.07 | ||||
Y II | -9.68(15) | 8 | -9.74(08) | 3 | 0.12 | -9.94(08) | 8 | -9.95(07) | 3 | -0.14 | -9.80 |
Zr II | -9.38(16) | 7 | 0.06 | -9.42(20) | 5 | 0.02 | -9.44 | ||||
Ba II* | -9.64(12) | 6 | -9.57(05) | 3 | 0.19 | -9.87(28) | 4 | -9.70(19) | 4 | -0.04 | -9.83MG |
La II | -10.82(08) | 4 | 0.05 | -11.15(13) | 3 | -0.28 | -10.87 | ||||
Ce II | -10.41(19) | 7 | 0.05 | -10.57(16) | 6 | -0.11 | -10.46 | ||||
Nd II | -10.49(25) | 11 | 0.05 | -10.63(01) | 2 | -0.09 | -10.54 | ||||
Nd III | -10.40(07) | 2 | 0.14 | -10.54 | |||||||
Sm II | -11.06 | 1 | -0.03 | -11.38 | 1 | -0.35 | -11.03 | ||||
Eu II | -11.63 | 1 | -0.10 | -11.80 | 1 | -0.27 | -11.53 |
We have written software called VWA for semi-automatic abundance analysis which is described in Bruntt et al. (2002). The code runs though the list of atomic line data extracted from VALD (Kupka et al. 1999) for the target star, and selects lines that suffer from the least amount of blending. For a region around each selected line the synthetic spectrum is calculated for different abundances of the element forming the line until the equivalent widths of the observed and synthetic spectrum match. The computation of the synthetic spectrum is done with SYNTH version 2.5 (Valenti & Piskunov 1996). The code needs the line data from VALD and the adopted atmosphere model as input. When VWA has fitted the selected lines they are inspected visually - and the fit is either accepted, rejected or must be improved manually.
While classical abundance analysis can be performed relatively fast for a star like
HD 32115 that has low
the advantage of using VWA for abundance analysis
is demonstated for HD 37594. Since this star has a moderate value of
one needs
to select lines with some amount of blending to be able to derive abundances of as many
elements as possible. We first used VWA where we only selected unblended Fe lines.
We then adjusted the microturbulence and recalculated abundances with VWA until the
Fei abundance and equivalent width of the lines did not correlate. We thus found
0.3 km s-1. Since the abundance of Fe was now considered to be accurate,
we allowed VWA to select lines of other elements that were mild blends with Fe.
By this method we were able to use lines that could not be used in the classical
abundance analysis which is strictly limited to unblended lines.
When comparing the results of the abundance analysis of the two methods in Table 3 we see that far fewer lines are chosen by VWA but the derived abundances all agree within the error estimates. Hence, VWA is usable for carrying out fast and reliable abundance analysis.
Our derived abundances contain errors from a number of sources of uncertainty,
including the adopted atomic data, most importantly the oscillator strengths, the
equivalent width measurements, the adopted atmospheric parameters and model, and the
observed spectra. For some sources we can directly estimate the associated error.
The estimated uncertainty in equivalent width measurements is 2 mÅ, which
results in 0.20-0.09 dex error in the abundance for lines with equivalent widths 5 to
10 mÅ, 0.05 dex for
= 20 mÅ, and less than 0.03 dex for
40 mÅ.
An error of 100 K in the effective temperature determination results in a systematic
error of 0.05 dex on the the abundance of the most temperature-sensitive atomic species,
e.g. Tii, Vi. For cases where a suitably large number of lines are used, the standard
deviations quoted in Table 3 estimate the total random error associated with all sources
of uncertainty. However, for species where only a small number of lines are available
this cannot be expected to give any indication of this
error. One can see from Table 3 that the standard deviations for most elements with a
sufficient number of spectral lines do not exceed 0.15 dex. Considering this as
indicative for all elements, and taking into account also possible systematic errors
we estimate the total error at about 0.2 dex for the species with 1-3 spectral lines.
Formally, a gravity decrease by 0.2 dex may provide ionization balance for all iron peak elements, since abundances obtained from the ionized lines will be decreased by 0.06-0.09 dex, while abundances from the neutral lines would not be changed. CNO abundances would be reduced by 0.05 dex. However, we stress that the effective gravity for both stars is accurately defined by parallax measurements.
Since most solar photospheric abundances are derived with the semi-empirical model of
Holweger & Müller (1974), it is important to check that our use of theoretical
Kurucz models does not itself introduce any significant differences relative to the
solar abundances. To test this we compared solar Fe abundances derived from Fe II lines in the solar spectrum employing the Holweger-Müller solar atmospheric model
(Holweger & Müller 1974) with those found using the solar model computed with
ATLAS9 and the same convection treatment as for our stars (see Gardiner et al. 1999).
The abundances were calculated from the best 13 Fe II lines (Schnabel et al. 1999)
with oscillator strengths from their paper and from the VALD database.
The results are:
7.42
0.09 (SKH
values, HM model, weighted mean),
7.46
0.11 (SKH
values, our model, unweighted mean),
7.48
0.10 ( VALD
values, our model, unweighted mean).
With our solar model the line-by-line difference (HD 32115-Sun) for 31 common Fe II
lines is -0.02
0.10 and agrees within the error limits with the [Fe/H] value
presented in Table 3.
Oscillator strengths for C and N were taken from Hibbert et al. (1993) and Hibbert et al. (1991) respectively. The same data were used in reevaluation of the solar abundances (Holweger 2001). For oxygen, we employed the oscillator strengths supplied by VALD which originate from the NIST compilation (Wiese et al. 1996). We did not use the IR Oi triplet because of the possibly strong NLTE effects. Expected NLTE corrections are -0.1 dex for C (see Sturenburg 1993; Rentzsch-Holm 1996; Paunzen et al. 1999) and -0.01--0.03 dex for O (Takeda 1997). Both stars show similar small deficiencies of C and N.
These elements are known to be subject to NLTE effects. We also note that the oscillator
strengths for Sii lines in VALD are not accurate, many of them coming from
Kurucz & Peytremann (1975). Therefore we recalculated oscillator strengths for most
of the Sii lines by fitting them to the Solar Flux Atlas (Kurucz et al. 1984)
adopting the solar abundance in Table 3. NLTE corrections were calculated for Nai,
and Ki following atomic models and procedures developed by Mashonkina et al. (2000)
for Na, and Ivanova & Shimansky (2000) for K. Oscillator strength data for Ali
were taken from Baumüller & Gehren (1996). According to this paper NLTE corrections
for the Ali lines used in our abundance analysis are negligible. For Mgi lines
4703, 4730, 5528, 5711 oscillator strengths were taken from Jonsson et al. (1984)
and from Froese Fischer (1975). In both stars the Mg abundance was derived by the
spectral synthesis technique with the Stark and Van der Waals damping constants giving
the best fit for the same Mgi lines in the spectra of Procyon and the Sun
(Fuhrmann et al. 1997; Zhao et al. 1998). Individual LTE and NLTE abundances are
given in Table 4. The largest NLTE corrections were found for the Ki resonance
line
7698.97. They are -0.61 (HD 32115) and -0.41 (HD 37594). Unfortunately,
another Ki resonance line at
7664.91 falls in one of the gaps in our
echelle spectra. We could measure the strongest Cli line
8375.95 in the
spectrum of HD 32115. The solar photospheric Cl abundance is very uncertain,
-6.54
0.3. The Cl abundance in HD 32115 was obtained from just
one weak line but agrees perfectly with the Cl abundance found in meteorites
(Grevesse & Sauval 1998). Two strongest infrared Pi lines
9593.50,
9796.83 measured in the latest spectrum of HD 32115 were used to derive phosphorus abundance.
The iron-group elements usually represent the metallicity of a star. With a few
exceptions we were able to obtain abundances from the lines of neutral and singly-ionized
species for all elements of this group, thus checking the ionization balance in the
atmospheres. The abundances obtained by the neutral and ionized Fe-group elements differ
by 0.13 dex on average. In both our stars the Fe-group elements in the ionized
state are dominating and therefore their lines are less sensitive to temperature
inaccuracy and NLTE effects and hence should provide better abundance estimates.
Among iron-group elements NLTE calculations were carried out for Ca (see below) and Fe
(Rentzsch-Holm 1996). An expected NLTE correction to the abundance obtained from
Fei lines is
+0.1 dex for
7300 K. Applying this correction
as a first approximation to the abundances obtained from the lines of neutral elements
a reasonable ionization balance is obtained.
Five Fe II lines correspondning to 4d-4f transitions with an upper energy level at
around 10.5 eV were measured in the HD 32115 spectrum. For these lines only theoretical
oscillator strengths are available. Both the
values from the Kurucz line
list (included in VALD) (Kurucz 1993) and the more accurate sets of calculated
-values from Raassen & Uylings (1998) agree to within 0.07 dex. Abundances
obtained from these lines do not deviate by more than 0.1-0.2 dex from the mean Fe abundance and thus supports the oscillator strengths for these high excitation Fe II
lines to this level of accuracy.
Fe abundance analysis in HD 32115 is based on about 300 lines well spread through the whole spectral region of 4100-9200 Å. We did not find any clear dependence of the individual abundances on the wavelength (Fig. 2) which might be expected in the primary star if the contribution from the secondary is not negligible.
For the two strongest Ca II lines
8912, 8927 we increased
by 0.3 dex to fit line profiles in the solar spectrum. Stark damping constants for
these lines, which are important, are taken from Dimitrijevic & Sahal-Bréchot (1993).
We also carried out NLTE calculations for Ca II lines using a model of the atom
developed by Ivanova et al. (2002). NLTE corrections are always negative and of
the order of -0.15 dex for
8248, 8912, 8927 lines in both stars,
while they are negligible for weak Ca II lines.
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Figure 2: The dependence of the individual abundances obtained from Fei lines in HD 32115 on wavelength. |
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Abundances of these elements were obtained by spectral synthesis taking into account hyperfine splitting (hfs). Hfs constants were extracted from Biehl (1976). Solar synthetic spectrum calculations showed that for Zni lines we may neglect the hfs effect, while it is strong for Cui lines in the solar spectrum. In both our stars Cui lines are weak, and the hfs effect for Cui and Zni lines is not significant.
Zn shows the largest deviation from the solar abundance in HD 32115, and the largest
deficiency in HD 37594. To our knowledge, there are no NLTE calculations for Cui
or Zni. With ionization energies
= 7.72 eV for Cui and 9.39 eV for Zni
these atoms are minor species similar to Mgi, Ali, Fei in the stellar atmospheres
typical for investigated stars. Based on our experience in NLTE analyses and taking
into account NLTE calculations for atoms with similar atomic parameters and term
structures (Sturenburg 1993; Rentzsch-Holm 1996) Cui and Zni are expected to be
over-ionized. In this case low atomic levels are underpopulated compared
with LTE, and the lower the excitation energy is the greater the departures from LTE
are. Most probably, NLTE effects will weaken the investigated Cui and Zni lines
and NLTE abundance corrections are expected to be positive. Usually NLTE corrections
are increasing with the line intensity. The observed equivalent widths of Zni lines
are 2-3 times larger than for Cui lines, therefore we may also expect larger positive
NLTE corrections for Zn.
NLTE corrections for Sr II lines were calculated using the model atom developed by Belyakova et al. (1997, 1999). They do not exceed 0.1 dex. Hfs effects may be important for Y II lines, but there are no data available. Zr abundances are rather uncertain, because reliable oscillator strengths are only known for a small number of spectral lines. We could not use the solar spectrum fitting for Zr II lines measured in our stars due to strong molecular contributions in the corresponding spectral regions.
NLTE corrections to the Ba abundance were calculated according to Mashonkina et al. (1999).
They are large, up to 0.18 dex, for the two strongest Ba II lines
6141, 6496.
It should be mentioned that the solar Ba abundance used by us was derived by Mashonkina & Gehren (2000)
from the same lines as in our analysis, and it is closer to abundance of Ba found in
meteorites than any previously published solar Ba abundance values (see Grevesse & Sauval 1998).
Stark damping constants for Ba II lines were taken from Dimitrijevic & Sahal-Bréchot (1996),
while for resonance Sr II lines the corresponding values were taken from the NIST
compilation (Konjevic et al. 1984).
New experimental oscillator strengths and hfs constants were used for La II
(Lawler et al. 2001a), Ce II (Palmeri et al. 2000; Zhang et al. 2001), and Eu II lines
(Lawler et al. 2001b). Two weak lines of Nd III
5102, 5295, which are the strongest lines in the Nd III spectrum, were identified in HD 32115. They are
partially blended so abundance estimates were made by spectral synthesis. Oscillator
strengths and other atomic parameters in VALD are taken from Cowley & Bord (1998)
and from Bord (2000). Both lines provide Nd abundances close to that obtained from
the analysis of Nd II lines, thus giving strong support for the Nd III oscillator
strength calculations.
The abundances found for HD 32115 and HD 37594 relative to the sun are shown in Fig. 3
by filled and open circles respectively. Within the typical error limits of 0.15
dex HD 32115 is a solar abundance star (a mean metallicity
).
Therefore this star may be used as a chemical standard in studies of cool peculiar stars.
We also get a standard for further investigation of the hydrogen wing-to-core anomaly
found in cool Ap stars by Cowley et al. (2001). Figure 4 shows a comparison between H
line profiles in HD 32115 and in one of the pulsating Ap (roAp) stars,
HD 24712, with the same effective temperature. It is evident from this comparison that
the Ap-star anomaly occurs in that part of the hydrogen line core that is not reproduced
by our current models.
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Figure 3: The observed relative abundances in HD 32115 (filled circles) and in HD 37594 (open circles). |
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Figure 4:
A comparison between H![]() |
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HD 37594 is slightly metal-deficient. Its mean metallicity
is close
to the value
obtained from photometric calibrations. This error
in the metallicity obtained from photometric calibrations is based only on the errors
in the photometric indices. No systematic errors of the calibration itself are included,
which may be up to 0.1.
Further support for the high accuracy of the metallicities derived from the
Strömgren photometry for normal stars is provided by the results of abundance
analysis of 28 And=HD 2628 (Adelman et al. 2000) and
Boo A=HD 128167
(Adelman et al. 1997). [M] =-0.16
0.29 and -0.29
0.37 were derived for these stars from abundances versus -0.13 and -0.35 from photometric calibration. The
abundance pattern in HD 37594 is similar to that in 28 And (
= 7250 K,
= 4.2,
= 2.3 km s-1,
= 9 km s-1 - see Adelman et al. 2000) which belongs to the
Sct group. The smaller scatter derived in the present paper is explained by more accurate abundance
determinations with NLTE and hfs effects taken into account as well as more careful
choice of the unblended lines which is possible in the red spectral region.
Abundances obtained for HD 32115 and HD 37594 do not follow the predicted abundance
pattern for
28 from consistent stellar evolution models calculated with
radiative forces, opacities and diffusion (Turcotte et al. 1998). Models for
1.5
predict that elements with 5 < Z < 20 will be underabundant
by 0.5 dex relative to Fe, and that iron-peak elements will be generally slightly
overabundant even at early evolutionary phases on the MS. This was not observed in
either of the stars analysed here.
To confirm the derived abundances we have used the software
VWA (Bruntt et al. 2002) which was developed to
be able to make fast semi-automatic abundance analysis.
We find the same abundances as the more careful classical approach.
At present VWA is being applied to the study
of the primary target candidate stars for the asteroseismology missions
COROT and Rømer (Bruntt et al. 2002). Several of these stars have
moderate or high and the amount of work needed to carry out the
analysis using VWA is reduced substantially.
Acknowledgements
We thank G. Wade who provided us with the spectrum of HD 24712 in the Hregion, A. Bondar for the help during the observations, N. Sakhibullin for useful discussions, and F. Kupka for his help in new model atmosphere calculations. T. R. thanks the Fonds zur Förderung der wissenschaftlichen Forschung (project P-14984), the Jubiläumsfonds der Österreichischen Nationalbank (project 7650), the Russian National Program "Astronomy'', and RFBR (grant 00-15-96722) for financial support. IFB, LIM. EVB, VVS acknowledge the Russian National Program "Astronomy'', and RFBR (grant 02-02-17174). FAM and GG thank the Russian National Program "Astronomy'', and RFBR (grant 02-02-17423) for partial funding. The authors thank the referee, C.R. Cowley, for his helpful comments.