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Magnetic Stars, 2011, pp. 410 ­ 414

Stars with Discrepant v sin i as Derived from the Ca I I 3933 and Mg I I 4481 ° Lines A
z Zverko J.1 , Zinovsky J.1 , Iliev I.2 , Barzova I.2 , Romanyuk I.3 , Kudryavtsev D.3 , ´ 3 Semenko E.
1 2 3

Astronomical Institute, Slovak Academy of Sciences, Tatransk´ Lomnica, Slovak Republic a Institute of Astronomy, NAO Rozhen, Sofia, Bulgaria Special Astrophysical Observatory, Nizhny Arkhyz, Russia

Abstract. Axial rotation of a star plays an important role in its evolution, physical conditions in its atmosphere and the shape of its spectrum. Methods of determining v sin i are based on comparison of the observed profiles of spectral lines with the theoretical ones. Their accuracy depends on the type and quality of spectrograms, as well as on the algorithms used. A frequently used method is a simple comparison of one line, e.g. the Ca ii at 3933 ° or Mg ii at 4481 A ° This, however, may result in a false value of v sin i in the case when lowA. dispersion spectra are used. We investigate the spectra of stars with a significant discrepancy of their rotational velocities introduced in various sources, and analyze the corresponding spectral region from the point of view of possible admixed features, which may mask the true line profiles. We use the CCD spectra of the stars having this discrepancy to compare with theoretical spectra. We also studied the photographic spectra, obtained during the 1970s and 1980s.

1

Intro duction

Selecting chemically peculiar stars using an ambiguous classification of their peculiarity types from the catalogue by Bertaud & Floquet (1974), we found large differences between the values of v sin i introduced in the catalogs of Palmer et al. (1968) and Wolf & Preston (1978). While the former work is based on the Ca II 3933 ° line, the latter uses the Mg ii 4481 ° line. One of the stars was A A 53 Aur in which we detected a spectrum of a companion (Zverko et al., 2008). We found other 24 such stars, five of which were classified as chemically peculiar in Bertaud & Floquet (1974), and further three in Renson (1991). The stars are listed in Table 1. Besides the main discrepancy, two groups can be easily distinguished, namely, 15 stars with v sin i (Ca) > v sin i (Mg), and 9 stars of the opposite inequation. In this paper we bring a progress report on our investigations of high dispersion, high S/N CCD spectra of the stars collected. We also investigate the photographic spectra obtained during the seventh and eighth decades of the past century, which may help to disclose how the misestimation of the value of the rotational velocity could occur. They may also contain information on the eventual radial velocity variation.


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Table 1: List of program stars and actual observations v sin i Palm Wolff 260 125 135 35 215 175 50 250 170 50 65 300 50 125 95 50 120 50 160 350 90 13 0 175 0 125 60 16 180 350 0 175 75 40 95 42 70 25 100 30 95 150 100 25 190 120 180 125 Classification Palm Cow ley B9.5 V A0 III ::Si B9 IV A0 V A0 V B8 Vn ?SiSr B9 V B8 III Si, var B8 III ?Pec B9 V Ap A0p Si(Cr) Si, var B9 V B7 III B9p MnHg B9 Vn B8V B9 V1) Ap B8 HgMn B9p B6 He w1) B9.5 III A0 III : B7 III B9.5 V B8 V2) Observations MSS MSS MSS MSS, NAO, E MSS E MSS, NAO

HD 2913 8837 9531 25152 31592 44783 45563 47964 51688 53744 90599 113797 114376 129174 136849 138527 172044 175132 182255 183986 188485 199892 204862 214923
1) 2)

MSS, NES, NAO, E NAO NAO NES NAO, E NES, NAO NES NES MSS, NES, E MSS

MSS MSS, E

Palm = Palmer et al. (1968), Wolff = Wolff & Preston (1978), Cow ley = Cowley et al. (1969) Renson (1991) Hoffleit (1964)

2

Observations, the Metho d

The photographic spectra were obtained with the coude spectrographs of the 2­m telescopes at the Astronomical Institute of the Academy of Sciences of the Czech Republic, Ond v and the rejo National Astronomical Observatory, Bulgarian Academy of Sciences, Rozhen (NAO). The spectral region was usually 3650 ­ 4900 ° Kodak IIaO or IIaOb emulsion, reciprocal dispersion 8.5 ° A, A/mm. These spectra are digitized using a computerised microdensitometer in the Astronomical Institute, Tatransk´ Lomnica. a The CCD spectra were obtained at the NAO and the Special Astrophysical Observatory, Nizhnii Arkhyz, Russia (SAO RAS). The NAO spectra were taken with the Photometric AT200 CCD camera with the SITe SI003AB 1024 â 1024 at the 3rd optical camera of the coude spectrograph of the 2­ m RCC telescope, with R = 22 000. The IRAF standard procedures were used for the spectra reduction. The Ca II region extends from 3898 to 3967 ° and the Mg II one from 4447 to 4550 ° A A. The SAO spectra were obtained either with the Nasmyth Echelle Spectrograph (NES), equipped with a 2048 â 2048 CCD camera with resolution R = 50 000 (Panchuk et al., 2002), and the Main


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Stellar Spectrograph (MSS), equipped with a 2048 â 2048 CCD camera with R = 17 000 using a Zeeman analyser with the slicer (Chountonov, 2004) of the 6­m BTA telescope of the SAO. The NES spectral region is 4226 ­ 5654 ° while the MSS spectra were obtained within 4453 ­ 4695 ° The A, A. ZEEMAN context (Kudryavtsev, 2000), written with the ESO MIDAS, and REDUCE software package (Piskunov & Valenti, 2002) were used to reduce the SAO spectra. The available public archival data were also used. The SYNSPEC code (Hubeny et al., 1994; Krti a, 1998) was used to compute the synthetic ck spectra, detailed line profiles of the Ca ii 3933 and Mg ii 4481 lines, and to derive the elemental abundances by means of comparing with the observed lines. The atmosphere models are interpolated from the grid of Castelli & Kurucz (2003). Effective temperature and surface gravity values were derived using the codes UVBYBETA (Moon & Dworetsky, 1985) and TEFFLOGG (Smalley & Dworetsky 1995) with the uv by data extracted from SIMBAD. Radial velocities were derived using the CCF method (Zverko et al., 2007).

3

First Results

HD 2913
Teff = 11 120 K, log g = 4.31. The Catalog of Components of Double and Multiple Stars (Dommanget, 1983) gives a remark "Double or Multiple Star". Two MSS spectra, S/N = 1000, separated by 8 months do not indicate radial velocity or line profile change. Apparently the lines of two different values of v sin i are present in the spectra. While for the strong lines of Mg II at 4481 and of He I at 4471 ° v sin i = 170 km/s is suitable, the weak lines need a remarkably lower value. At the same time, A the abundance of weak lines indicates a lower effective temperature. Tentatively we summed two synthetic spectra, one of which with temperature, gravity and v sin i as introduced above, and the other with Teff = 7 500 K, log g = 4.0, and v sin i = 45 km/s. This shows that the observed spectrum may be composed of two components that contribute in a ratio L1 : L2 = 0.9 : 0.1. The stronger component seems to be mildly underabundant in helium by a factor of 0.8 and overabundant in magnesium by a factor of 3. The spectrum of the weak component is shifted by RV = -15 km/s relative to the stronger one. The barycentric radial velocity values derived from the two CCD spectra correspond to -24.0 (±0.7) and +26 (±0.7) km/s, while the relative velocities of the two components remain constant. Two photographic spectra were separated by 3.3 years. Radial velocities were derived by using the central sections ±2.5 ° from the central wavelength of the Balmer lines H4 ­ A H11. The barycentric values were 3.0 (±4.1) and 5.6 (±3.4) km/s. The BS catalogue (Hoffleit, 1964) gives +19 km/s.

HD 25152
Teff = 10 530 K, log g = 3.94. MSS (S/N = 300) and NAO (S/N = 180) spectra fit perfectly the value of v sin i = 127 km/s. Helium and calcium are in deficit (0.9â and 0.45â, magnesium is slightly overabundant (1.5â) with respect to the solar abundances, the microturbulence is zero. Around the Ca II line, (S/N = 110) in the continuum, weak lines of Al and He are compatible with v sin i = 127 km/s. A narrow absorption, shifted 0.3 ° longward from the centre of the Ca II line, and 0.42 ° A A ° may be of interstellar origin. Welsh et al. (2010) give for the (32 km/s) of FWHM with EW = 33 mA nearest star HD 23625, which is 380 pc distant, the equivalent width EW = 66 m° for the interstellar A component. The distance of HD 25152 is 123 pc.


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HD 44783
A spectrum (4000 ­ 6800 ° of this star A) shell feature in the Balmer line, as well Wolf & Preston (1978) from the Mg II by Palmer et al. (1968) corresponds to was retrieved from the ELODIE public archive. It shows a as in many metal lines. The high value of v sin i derived by line corresponds to this type of stars. The low value given the narrow absorption peak at the Ca II line.

HD 47964
Teff = 12 360 K, log g = 3.43. The pro jected v sin i = 60 km/s fits Mg II as well as the Ca ii line. The Ca II line itself, however, features a peak shifted from the central position. Its EW = 41 m° measured A under the synthetic profile is in agreement with the observation by Welsh et al. (2010).

HD 90569
Teff = 10 710 K, in the NES spe and Mg II lines He and Ca are log g = 3.97. The value of pro jected rotational velocity derived from the Mg II line ctrum corresponds to v sin i = 8 km/s. In the NAO spectra, the profiles of the Ca II satisfy v sin i = 13 km/s. Fe and Cr are overabundant by factors of 15 and 70, while in deficit by the factors of 0.05 and 0.15, respectively.

HD 113797
Teff = 11 200 K, log g = 4.16. The value of the pro jected rotational velocity is v sin i = 137 km/s. Magnesium is overabundant by a factor of 2, while calcium is in deficit by a factor of 0.5. A weak narrow feature is seen near the centre of Ca II line corresponding to v sin i 8 km/s, and EW = 14 m° Welsh et al. (2010) give EW = 13.6 m° for the interstellar component. A. A

HD 114376
Teff = 14 030 Helium and feature near 1 in l and b K, log g = 3.53. The pro jected rotational velocity corresponds to v sin i = 125 km/s. calcium are underabundant by the factors of 0.55 and 0.1, respectively. A narrow the centre of the Ca II line of EW = 0.48 m° is present. This star, 351 pc away, is only A off the previous star which is 87 pc away.

HD 136849
Teff = 10 970 K, log g = 4.24. The value of the pro jected rotational velocity is v sin i = 220 km/s. Magnesium is mildly overabundant by a factor of 2, while calcium is in a deficit by a factor of 0.5. The value of the pro jected rotational velocity is too high for the He I 4471 line, for which v sin i = 185 km/s is more suitable. A narrow peak occurs at the center of the wide Ca II 3933 line. Its central depth under the mean profile amounts to 0.03 corresponding to EW = 5 m° Welsh et al. A. off HD 136849 and 95 p c (2010) has measured the interstellar extinction for HD 138749, which is 3 away. They give EW(Ca II) = 6.7 m° HD 138749 is 76 pc away. A.

HD 138 527
Teff = 11 200 K, log g = 4.08. For Mg II 4481 line v sin i = 140 km/s, for the Ca II 3933 line v sin i = 120 km/s. Mg and Ca are underabundant by the factors of 0.5 and 0.15, respectively. A narrow feature at the centre of Ca II 3933 line is present. Its EW = 9 m° Welsh et al. (2010) give 8 m° the A, A. absence of metal lines when comparing with the synthetic spectrum suggests a possible Boo­type star. However, a need of remarkably lower abundances to reach the fit of the Mg II 4481, Ca II 3933,


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and He I 4471 ° lines does not exclude a possible component star, contributing its fraction to the A spectrum.

HD 172044
Teff = 14 480 K, log g = 3.60. The value v sin i = 40 km/s is confirmed by our observations. Abundances of helium, nitrogen and sulphur must be reduced by factors of 0.01, 0.5 and 0.5 respectively in order to fit the observed spectrum. The same reason leads to the abundances of phosphorus, manganese and gallium increased by factors of 30, 2000 and 10 000.

HD 175132
Teff = 11 360 K, log g = 3.18, v sin i = 30 km/s. Abundances reduced for helium (by a factor of 0.1), magnesium (0.2), aluminium (0.1) and sulphur (0.1) and increased for silicon (4), chromium (10), manganese (20) and iron (8) fits the observed spectrum. However, there remain many weak unidentified lines.
Acknowledgements. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and the VALD database for atomic data operated by the University of Vienna. For some stars public data were extracted from The ELODIE Archive. This work is partly supported by the VEGA grant 2/0074/09, Russian Foundation for Basic Research (RFBR grant no. 09­02­0002), the Federal Programs Scientific Schools (grant no. NSh­5473.2010.2), the Scientific and Scientific­Pedagogical Cadres of Innovative Russia (grant no. P­1244).

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