c Pleiades Publishing, Inc., 2011. ISSN 1063-7737, Astronomy Letters, 2011, Vol. 37, No. 10, pp. 718–725. c I.A. Usenko, L.N. Berdnikov, V.V. Kravtsov, A.Yu. Kniazev, R. Chini, V.H. Hoffmeister, O. Stahl, H. Drass, 2011, published in Pis’ma v Astronomicheski˘ı Original Russian Text Zhurnal, 2011, Vol. 37, No. 10, pp. 781–788.
Spectroscopic Studies of Southern-Hemisphere Cepheids: WW Car, SX Car, UZ Car, UY Car, GX Car, HW Car, YZ Car I. A. Usenko1* , L. N. Berdnikov2 , V. V. Kravtsov2, 3 , A. Yu. Kniazev2, 4, 5 , R. Chini3, 6 , V. H. Hoffmeister6 , O. Stahl7 , and H. Drass6 1
Department of Astronomy, Odessa National University, Shevchenko Park, Odessa, 65014 Ukraine 2 Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119992 Russia 3 Instituto de Astronomia, Universidad Catolica del Norte, Avenida Angamos 0610, Antofagasta, Chile 4 South African Astronomical Observatory, P.O. Box 9, Observatory, Cape Town, 7935 South Africa 5 South African Large Telescope, P.O. Box 9, Observatory, Cape Town, 7935 South Africa 6 Astronomisches Institut, Ruhr-Universitat ¨ Bochum, Bochum, 44780 Germany 7 Landersternwarte Heidelberg, Germany Received April 28, 2011
Abstract—For seven faint southern Cepheids (WW Car, SX Car, UZ Car, UY Car, GX Car, HW Car, YZ Car), we have determined their atmospheric parameters and chemical composition for the first time based on ten high-resolution (R = 50 000) spectra taken with the 1.5-m Hexapod telescope at the Joint Observatory of the Northern Catholic University (Antofagasta, Chile) and the Ruhr University (Bochum, Germany). Six objects from the list demonstrate atmospheric parameters and chemical composition typical of Cepheids that have passed through the first dredge-up phase, while WW Car is probably an anomalous Cepheid. According to our preliminary estimates, it has an overabundance of CNO, a deficit of sodium and aluminum, and a slight deficit of magnesium, with iron and other elements being underabundant relative to the Sun. DOI: 10.1134/S1063773711100070 Keywords: Cepheids, spectra, atmospheric parameters, chemical composition.
INTRODUCTION Analysis of the spatial distribution of Cepheids with known chemical composition reveals a decrease in their metallicity with distance from the Galactic center (Andrievsky et al. 2002a–2002c; Luck et al. 2003; Lemasle et al. 2007, 2008; Romaniello et al. 2008). Andrievsky et al. (2010) pointed out that the region in Carina turned out to be least studied in this respect. As was already noted in our first paper (Berdnikov et al. 2010), Cepheids are very convenient objects for determining the Galaxy’s metallicity gradient: bright yellow supergiants with low rotation velocities have many narrow absorption spectral lines of various chemical elements. Knowing the abundances of these elements in Cepheid atmospheres will help us understand the formation and evolution of the Galaxy. Therefore, we initiated a project to determine the chemical composition of Cepheids in this region to refine the above metallicity gradient. In this paper, we present our first results: the atmospheric parameters *
E-mail:
[email protected]
and chemical composition of WW Car, SX Car, UZ Car, UY Car, GX Car, HW Car, and YZ Car. OBSERVATIONS AND PRIMARY REDUCTION Our spectroscopic observations of the programm stars were performed at the Joint Observatory of the Northern Catholic University and the Ruhr University (Bochum) near Cerro Armazones in Chile. For the spectroscopy, we used the BESO spectrograph connected by a fiber cable with the Cassegrain focus of the 1.5-m Hexapod telescope (information about the instrument is given in Fuhrmann et al., 2011). Ten spectra in the wavelength range 3530–8860 A˚ with a spectral resolution R = 50 000 were taken in April 2009. The exposure time for each spectrum was 1800 s. Each spectrum consists of 89 orders, 60 A˚ each. The automated (streaming) reduction of our spectroscopy was performed with the same software package in the ESO-MIDAS system that is also used for the FEROS spectrograph at the La Silla 718
SPECTROSCOPIC STUDIES OF SOUTHERN-HEMISPHERE CEPHEIDS
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1.0 0.8
r
0.6 0.4 0.2 0 6250
6255
6260 6265 Wavelength, Å
6270
6275
˚ Fragment of the spectrum for the Cepheid YZ Car in the wavelength range 6250–6275 A.
Observatory. The primary CCD image reduction for the spectra obtained included standard procedures, in particular, debiasing, flat-fielding, and image resampling. The next step was the extraction of each individual echelle order, the wavelength calibration and the normalization to the continuum. The final step was the removal of cosmic-ray particle hits. The wavelength calibration was made using calibration lamps; it was subsequently improved based on the telluric bands near 6900 and 7600 A˚ using the spectra of standard stars as telluric templates. The improved system of radial velocities is stable up to 100 m s−1 , as was shown by the radial velocity difference between the spectral bands mentioned above. We did not check the absolute zero point of the system. Since the blue part of the spectrum is very noisy, for our analysis we used only spectral lines in the range 4840– 8860 A˚ (67 orders). As an example, the figure shows a fragment of the spectrum for the Cepheid YZ Car ˚ All basic inin the wavelength range 6250–6275 A. formation about our observations of the Cepheids is given in Table 1; it presents the object names, their coordinates, pulsation periods, mean magnitudes, exposures times, and signal-to-noise ratios. MODEL PARAMETERS AND LIGHT ELEMENTS We determined three basic parameters of stellar atmospheres, namely the effective temperature Teff , surface gravity log g, and microturbulent velocity Vt , as follows: —the effective temperatures Teff were determined using spectroscopic criteria (Kovtyukh 2007) by a method based on the depth ratios of selected pairs of spectral lines most sensitive to the temperature; ASTRONOMY LETTERS
Vol. 37 No. 10 2011
—the microturbulent velocities Vt were determined from the condition for the abundance of ionized iron, FeII, derived from a set of lines being independent of their equivalent widths (Kovtyukh and Andrievsky 1999); —the surface gravities log g were determined from the ionization equilibrium condition for the Fe I and Fe II atoms. More detailed information about the methods for determining the atmospheric parameters of the program stars and their measurement errors is given in our previous paper (Berdnikov et al. 2010). All of the atmospheric parameters we derived are presented in Table 2. For Teff , we provide the error of the mean at an uncertainty in the zero point of 150–200 K. When calculating the atmospheric parameters and chemical composition, we used solar oscillator strengths from Kovtyukh and Andrievsky (1999) and model atmospheres from Kurucz (1992). To improve the light elements for all our program Cepheids, we used their observations from the ASAS3 catalog (Pojmanski 2002). Using the method by Hertzsprung (1919), whose computer implementation was proposed by Berdnikov (1992), we determined the seasonal times of maximum light over the last 5–7 years from which we obtained the current light elements by the least-squares method included in Table 2, along with the atmospheric parameters we derived (Teff , log g, Vt ) and the phases for all spectra of the program Cepheids. CHEMICAL COMPOSITION We determined the chemical composition of the program stars in the LTE approximation using the WIDTH9 code and the grid of models from Kurucz (1992). Tables 3, 4, and 5 present the derived elemental abundances relative to the Sun [El/H], their
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Table 1. Information about the objects and their observations Cepheid
α (2000.0)
δ (2000.0)
P , days
V
HJD 2450000+
Signal-to-noise ratio
WW Car
10 51 35.8
–59 23 06
4.68
10.6
4944.5966
30
SX Car
10 46 05.8
–57 32 51
4.86
10.0
4944.5738
50
UZ Car
10 36 17.8
–61 00 45
5.21
10.2
4939.6299
30
UY Car
10 32 04.4
–61 46 57
5.54
9.8
4937.6230
75
4940.6055
75
4944.5508
75
GX Car
09 55 26.2
–58 25 47
7.20
10.4
4929.6877
35
HW Car
10 39 20.3
–60 09 09
9.20
9.4
4940.6490
65
YZ Car
10 28 16.9
–59 21 01
18.16
8.7
4937.5997
75
4940.5835
75
Table 2. Atmospheric parameters and light elements for the program Cepheids Initial time of max. 2450000+
Period, days
Phase
4.50
3866.2487
4.6768
0.573
2.00
4.70
4008.8428
4.8600
0.537
5374 ± 58
2.00
4.20
4474.4145
5.2046
0.386
4937.6230
5900 ± 30
2.20
4.20
3988.7538
5.5438
0.159
4940.6055
5550 ± 30
2.10
4.20
0.697
4944.5508
5700 ± 30
2.00
3.40
0.409
GX Car
4929.6877
5451 ± 26
2.00
5.40
4638.2815
7.1969
0.491
HW Car
4940.6490
5702 ± 28
1.70
4.50
3552.7920
9.1992
0.867
YZ Car
4937.5997
5323 ± 31
1.25
4.50
4236.1486
18.1692
0.607
4940.5835
5600 ± 30
1.90
5.50
Object
HJD 2450000+
Teff , K
log g
Vt , km s−1
WW Car
4944.5966
5012 ± 46
1.70
SX Car
4944.5738
5433 ± 43
UZ Car
4939.6299
UY Car
errors σ, and the number of lines used for a given element NL. We published full information about the influence of uncertainties in the atmospheric parameters on the abundances of chemical elements in our previous paper (Berdnikov et al. 2010). DISCUSSION Among the seven objects we investigated, only for YZ Car did Petterson et al. (2004) determine one of the atmospheric parameters, the mean Teff = 5900 K, by hydrodynamic modeling based on the mass–luminosity relation (Chiosi et al. 1993). The
0.771
values we found at light curve phases 0P. 607 and 0P. 771 (the ascending branch) are slightly lower. This can be explained by the existence of a hot companion to YZ Car with a period of 657.3 days (Petterson et al. 2004). According to the data in Tables 3, 4, and 5, six Cepheids from our list (except WW Car) have a nearly solar iron abundance or a slight deficit of iron (GX Car and HW Car). The CNO abundances in their atmospheres are quite typical of yellow supergiants that have passed through the first dredge-up phase: a deficit of carbon, an overabundance of nitrogen, and a nearly solar oxygen abundance. The scatter of ASTRONOMY LETTERS
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Table 3. Elemental abundances for WW Car, SX Car, and UZ Car WW Car
Element [El/H]
σ
CI
+0.30
NI
SX Car
UZ Car
NL
[El/H]
σ
NL
[El/H]
σ
0.38
8
–0.41
0.19
10
–0.43
0.15
9
+0.95
0.07
6
+0.62
0.31
5
+0.64
0.13
6
OI
+0.22
0.26
3
+0.12
0.11
2
+0.07
0.10
5
Na I
–0.46
0.18
4
–0.07
0.14
2
–0.14
0.14
3
Mg I
–0.12
0.28
7
–0.27
0.17
7
–0.28
0.13
7
Al I
–0.16
0.14
7
+0.11
0.10
7
–0.06
0.11
5
Si I
–0.07
0.21
36
–0.15
0.20
38
–0.12
0.24
41
Si II
+0.16
–
1
+0.07
0.28
2
–0.18
0.05
2
SI
+0.16
0.18
6
+0.04
0.22
6
+0.03
0.18
7
KI
+0.66
–
1
+0.63
–
1
+0.70
–
1
Ca I
–0.44
0.29
8
–0.30
0.20
11
–0.44
0.30
12
Sc I
+0.01
0.29
4
+0.30
0.24
3
–0.06
0.06
3
Sc II
–0.90
0.18
9
–0.42
0.17
7
–0.21
0.17
6
Ti I
–0.27
0.38
38
–0.13
0.33
59
–0.14
0.33
55
Ti II
–0.23
0.28
6
–0.54
0.09
7
–0.19
0.26
5
VI
–0.01
0.28
7
–0.23
0.32
14
–0.24
0.18
12
V II
–0.29
0.05
3
–0.07
0.08
4
–0.21
0.23
4
Cr I
–0.21
0.25
21
–0.15
0.27
27
+0.04
0.29
22
Cr II
–0.35
0.27
14
–0.12
0.19
12
–0.00
0.39
11
Mn I
–0.61
0.29
9
–0.38
0.29
13
–0.46
0.14
7
Fe I
–0.30
0.25
237
–0.16
0.20
264
–0.02
0.27
268
Fe II
–0.33
0.21
33
–0.18
0.17
42
–0.01
0.22
42
Co I
–0.33
0.35
19
–0.05
0.28
20
+0.04
0.31
31
Ni I
–0.32
0.31
73
–0.29
0.29
96
–0.32
0.31
85
Cu I
–0.53
0.33
3
–0.42
0.30
4
–0.26
0.47
4
Zn I
–0.50
–
1
–0.17
–
1
+0.21
–
1
Sr I
+0.18
0.31
3
+0.68
–
1
+0.40
0.05
2
YI
–
–
–
–0.16
–
1
–0.07
–
1
Y II
–0.17
0.30
6
+0.02
0.29
7
–0.07
0.09
6
Zr II
–0.11
0.09
3
+0.02
0.17
2
+0.00
0.16
4
Ru I
+0.34
–
1
+0.29
0.62
2
+0.03
–
1
La II
–0.29
0.29
2
–0.60
0.01
2
+0.01
0.02
3
Ce II
–0.55
0.11
5
–0.22
0.32
7
–0.13
0.13
4
Pr II
–0.30
0.20
2
–0.37
–
1
–0.17
0.01
3
Nd II
–0.36
0.19
9
–0.16
0.21
4
+0.09
0.24
11
Eu II
+0.09
0.20
2
+0.10
0.21
4
+0.24
0.43
2
Gd II
–0.36
–
1
–0.80
–
1
+0.01
–
1
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Table 4. Elemental abundances for UY Car (JD 2454937.6230, JD 2454940.6055, and JD 2454944.5508) JD 4937.6230
Element
JD 4940.6055
[El/H]
σ
NL
[El/H]
σ
CI
–0.47
0.27
11
–0.52
NI
+0.41
0.26
6
OI
+0.01
–
Na I
+0.03
Mg I
JD 4944.5508 NL
[El/H]
σ
0.16
8
–0.31
0.17
6
+0.35
0.04
3
+0.47
0.31
6
1
+0.11
0.32
3
+0.11
0.13
6
0.29
5
–0.13
0.08
3
–0.02
0.07
4
–0.38
0.18
5
–0.27
0.31
5
–0.33
0.30
6
Al I
–0.09
0.19
6
+0.08
0.17
7
–0.03
0.15
6
Si I
–0.04
0.20
48
+0.04
0.23
41
+0.02
0.20
45
Si II
–0.08
0.19
2
–0.07
0.49
2
–
–
–
SI
+0.01
0.20
7
+0.05
0.17
7
–0.03
0.14
7
KI
+0.12
–
1
+0.61
–
1
+0.71
–
1
Ca I
–0.24
0.22
12
–0.18
0.35
11
–0.14
0.25
12
Sc I
–
–
–
–0.08
0.05
2
+0.08
–
1
Sc II
–0.20
0.18
9
–0.15
0.22
7
–0.17
0.07
6
Ti I
–0.03
0.38
52
+0.08
0.24
45
–0.00
0.21
46
Ti II
–0.15
0.15
9
–0.17
0.15
3
–0.10
0.20
5
VI
+0.02
0.22
13
+0.02
0.24
12
–0.12
0.18
8
V II
–0.12
0.18
4
–0.06
0.25
5
+0.10
0.18
4
Cr I
+0.18
0.37
28
–0.02
0.33
28
–0.06
0.22
21
Cr II
–0.02
0.22
15
–0.01
0.27
12
+0.09
0.23
12
Mn I
–0.43
0.22
9
–0.24
0.27
12
+0.10
0.43
13
Fe I
–0.07
0.23
333
–0.05
0.25
273
–0.06
0.22
273
Fe II
–0.06
0.22
55
–0.06
0.22
36
–0.06
0.21
47
Co I
–0.02
0.22
21
–0.04
0.27
21
+0.02
0.19
27
Ni I
–0.15
0.24
78
–0.19
0.24
68
–0.09
0.27
91
Cu I
–0.30
0.07
5
–0.18
0.21
3
–0.28
0.37
6
Zn I
–0.08
–
1
–0.24
–
1
–0.04
–
1
Sr I
+0.59
0.26
2
–
–
–
+0.59
0.22
2
Y II
+0.11
0.10
5
+0.03
0.08
4
–0.16
0.15
6
Zr II
+0.01
0.18
6
+0.19
0.36
6
–0.01
0.11
4
Ru I
–0.14
–
1
+0.20
–
1
–
–
–
La II
+0.24
0.06
2
+0.18
0.08
2
–
–
–
Ce II
–0.18
0.24
7
+0.06
0.16
5
+0.07
0.25
8
Pr II
–0.11
–
1
+0.29
0.28
2
+0.04
0.16
2
Nd II
+0.09
0.18
12
+0.09
0.25
14
+0.04
0.22
12
Eu II
+0.02
0.09
3
+0.21
0.19
3
+0.18
0.35
3
Gd II
+0.05
–
1
–0.13
–
1
–
–
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– 2011
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Table 5. Elemental abundances for GX Car, HW Car, and YZ Car (JD 2454937.5997 and JD 2454940.5835) GX Car
Element
HW Car
YZ Car
[El/H]
σ
NL
[El/H]
σ
NL
[El/H]
σ
NL
[El/H]
σ
NL
CI
–0.44
0.24
15
–0.48
0.27
15
–0.23
0.13
9
–0.55
0.16
14
NI
+0.46
0.20
4
+0.53
0.21
4
+0.31
0.17
3
+0.25
0.25
3
OI
+0.06
0.18
6
–0.17
0.14
4
+0.10
0.08
3
–0.01
0.16
4
Na I
–0.12
0.19
4
+0.07
0.07
2
–0.13
0.17
3
–0.10
0.39
4
Mg I
–0.44
0.27
6
–0.41
0.21
6
–0.33
0.13
3
–0.22
0.15
9
Al I
–0.03
0.14
7
+0.15
0.21
5
+0.10
0.12
5
–0.13
0.19
9
Si I
–0.09
0.19
49
–0.18
0.21
57
–0.08
0.17
39
–0.06
0.14
39
Si II
–0.07
0.07
2
–0.19
0.49
2
+0.06
0.36
2
+0.05
–
1
SI
–0.10
0.25
7
–0.02
0.17
7
+0.05
0.28
6
–0.06
0.17
6
KI
–
–
–
+0.57
–
1
–
–
–
–
–
–
Ca I
–0.35
0.19
11
–0.20
0.14
8
–0.35
0.25
10
–0.32
0.15
10
Sc I
+0.24
0.22
4
+0.03
0.19
4
–0.35
0.08
3
–0.11
0.12
2
Sc II
–0.14
0.21
7
–0.21
0.28
6
–0.21
0.24
3
–0.23
0.09
4
Ti I
–0.12
0.26
50
–0.04
0.23
63
–0.08
0.24
46
–0.11
0.28
50
Ti II
–0.25
0.25
4
–0.15
0.15
8
–0.16
0.31
4
–0.16
0.15
4
VI
–0.05
0.45
19
–0.11
0.12
13
–0.11
0.23
14
+0.03
0.19
10
V II
–0.11
0.17
5
–0.33
0.38
4
–0.07
0.28
3
–0.06
0.18
3
Cr I
–0.13
0.24
21
+0.03
0.28
32
–0.15
0.20
25
+0.04
0.26
21
Cr II
–0.05
0.23
13
–0.13
0.22
13
–0.07
0.30
12
–0.04
0.13
13
Mn I
–0.34
0.28
13
–0.15
0.22
15
–0.21
0.13
9
–0.29
0.29
11
Fe I
–0.12
0.24
294
–0.15
0.22
303
–0.04
0.20
257
–0.08
0.24
304
Fe II
–0.13
0.19
46
–0.16
0.12
42
–0.04
0.12
31
–0.10
0.15
30
Co I
–0.06
0.22
26
+0.14
0.41
31
–0.06
0.22
26
+0.06
0.22
25
Ni I
–0.23
0.31
90
–0.22
0.26
102
–0.16
0.27
84
–0.25
0.26
88
Cu I
–0.25
–
1
–0.00
0.32
4
–0.23
0.15
3
–0.03
0.32
4
Zn I
–0.25
–
1
–0.07
–
1
+0.07
–
1
–0.01
–
1
Sr I
+0.46
0.40
2
+0.44
–
1
+0.57
–
1
+0.20
–
1
YI
–0.18
0.01
2
+0.14
–
1
+0.24
–
1
–
–
–
Y II
–0.01
0.17
6
+0.01
0.06
6
+0.04
0.22
5
+0.05
0.19
7
Zr II
–0.05
0.18
5
+0.01
0.18
4
+0.15
0.19
4
+0.17
0.12
4
Ru I
+0.45
–
1
–
–
–
+0.30
–
1
–
–
La II
+0.11
0.21
3
+0.27
0.07
3
–0.19
–
1
+0.40
0.01
2
Ce II
–0.12
0.23
4
–0.22
0.24
7
+0.02
0.28
6
–0.03
0.25
5
Pr II
–0.08
0.01
2
+0.04
0.01
2
–0.23
0.11
3
–0.09
0.16
3
Nd II
+0.02
0.16
15
–0.14
0.20
13
–0.10
0.16
13
+0.01
0.16
13
Eu II
–0.03
0.25
3
–0.12
0.10
2
+0.21
0.05
3
+0.12
0.04
3
Gd II
–0.07
–
1
–0.57
–
1
–
–
–
–0.76
–
1
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0.1 dex in the carbon abundances for UY Car is quite acceptable and is most likely explained by the quality of the spectra. The abundance difference for YZ Car is much larger (about 0.3 dex) and is probably due to the large extent of the atmosphere of this long-period Cepheid with a pulsation period of 18.16 days. There is no clear correlation of the CNO abundances with the Cepheid pulsation periods. As regards the remaining “key elements” of the evolution of yellow supergiants (Na, Mg, Al), here we do not observe any noticeable overabundance of sodium, as for the Cepheids in our previous papers (Berdnikov et al. 2010; Usenko et al. 2011). No dependence of the sodium abundance on the pulsation period is observed either. However, there is an increase in the magnesium abundance (except for YZ Car). In this case, its deficit (with respect to the Sun) for these six stars is much larger than that for the Cepheids with similar pulsation periods from our previous papers. The situation with the aluminum abundance is similar to that for sodium: either a nearly solar abundance or a slight overabundance. The observed picture is consistent with the results of the Ne–Na and Mg–Al cycles in the hydrogenburning shell (Mowlavi 1999a, 1999b; Andrievsky and Kovtyukh 1996; Andrievsky et al. 2002a–2002c; Andrievsky et al. 2004; Kovtyukh et al. 2005; Luck et al. 2003, 2006; Usenko et al. 2001a–2001c). It only remains to assume that the initial abundances of sodium, magnesium, and aluminum in the atmospheres of these stars before the first dredge-up stage were much lower. For the α-elements (Si, S, K, Ca), we observe either a slight deficit or a nearly solar abundance (as we see from Tables 3, 4, and 5, it is slightly lower than the iron abundance). The significant overabundance of potassium in most objects is apparently related to partial blending of the KI 6938.763 A˚ line. As a rule, the iron-group elements (Sc, Ti, V, Cr, Co, Ni) exhibit nearly solar abundances or those comparable to the iron abundance. As regards the r- and sprocess elements, here we see either a nearly solar abundance or a slight deficit, especially for nickel, copper, and several “heavy” s-process elements. An overabundance of strontium related to the sensitivity of its lines to non-LTE effects is noticeable virtually for all objects. WW Car is a completely unique object. According to the SIMBAD database, this supergiant is an F0 star, but the values of Teff = 5012 K and log g = 1.70 we derived do not correspond to a Cepheid with such a spectral type and a pulsation period of 4.68 days: the effective temperature and the gravity should be near 7000 K and log g = 2.0, respectively. If we turn our attention to the chemical composition of WW Car (Table 3), then the first thing that is
immediately apparent is an overabundance of CNO, a deficit of sodium (the lowest abundance among the program stars), and a deficit of aluminum. In contrast, the abundance of magnesium is highest among these supergiants. At the same time, the abundance of iron in the atmosphere of WW Car is lowest: about −0.3 dex. A deficit of calcium, a large spread in Sc I and Sc II abundances, and a deficit of all iron-group elements and r- and s-process elements are noticeable. This object resembles the bright semiregular supergiant R Pup in carbon overabundance (though the carbon abundance in R Rup is an order of magnitude higher), sodium deficit, and iron abundance (Usenko et al. 2011). In addition, the abundances of all the remaining elements in R Pup, except for oxygen, sulfur, and potassium, are close to those in WW Car. Thus, we can hypothesize that WW Car is an object with anomalous chemical composition. One of the explanations for such an anomaly can be the presence of a companion whose existence was suspected by Madore and Fernie (1980). Therefore, further thorough spectroscopic studies of this supergiant are needed. CONCLUSIONS During our work, we used the 1.5-m Hexapod telescope at the Joint Observatory of the Northern Catholic University (Antofagasta, Chile) and the Ruhr University (Bochum, Germany) to obtain ten high-spectral-resolution spectra for seven classical Cepheids: WW Car, SX Car, UZ Car, UY Car, GX Car, HW Car, and YZ Car. The reduction of these spectra allowed us to determine for the first time the atmospheric parameters (effective temperature Teff , surface gravity log g, and microturbulent velocity Vt ) and detailed chemical composition of these stars. We showed that six Cepheids from our list have a nearly solar metallicity and that the abundances of the “key elements” for stellar evolution (CNO, sodium, magnesium, and aluminum) in their atmospheres are typical of supergiants that had passed through the first dredge-up phase. WW Car shows anomalous abundances of the key elements, with the abundances of iron ([Fe/H] = −0.3 dex) and other elements being low. Thus, WW Car is a Cepheid with anomalous chemical composition probably due to the presence of a companion. ACKNOWLEDGMENTS This study was supported in part by the Russian Foundation for Basic Research (project no. 10-0200489). We wish to thank V.V. Kovtyukh for his help. A.Yu. Kniazev is grateful to the National Research Foundation of South Africa for support. ASTRONOMY LETTERS
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SPECTROSCOPIC STUDIES OF SOUTHERN-HEMISPHERE CEPHEIDS
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Translated by N. Samus’
