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Physics of Magnetic Stars, 2007, pp. 214217

Magnetic field measurements for 1 Ori C with the 6-meter telescope
G.A. Chuntonov
Special Astrophysical Observatory of the Russian AS, Nizhnij Arkhyz 369167, Russia chunt@sao.ru

Abstract. The longitudinal magnetic field is measured for the star 1 Ori C at ° ° eight p oints in its p erio d using the CIV 5801 A and 5812 A absorption lines. The measurements were made on the 6-meter telescop e using a circular p olarization analyzer with an image slicer and in the back-and-forth mo de. The maximum value was +231 ± 47 G.
The star 1 Ori C (HD 37022) is the brightest (mv = 5.1) in the Trap ezium of Orion. Its age is estimated at 200000 years (Howarth and Prinja 1989). It is on the ZAMS. This star is the main source of ionization of the Orion nebula. This is a multiple system. It consists of two hot comp onents (O 5.5

Figure 1: Fragments of a Zeeman sp ectrum in the region of 5850 ° A

CIV 5801.33 CIV 5811.98 He I 5875.72

Figure 2: Fragments of sp ectra in three phases of rotation. 214

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Figure 3: Fragments of extracted Zeeman sp ectra in the neighb orho o d of CIV 5801 ° and 5812 ° A A lines in phase 0.64.

Figure 4: Variation in the magnetic field of 1 Ori C with phase of rotation.

and O 9.5), K 7 comp onent, and a cold ob ject with temp erature of 190 K (Vitrichenko 2004, Kraus, Balega et al. 2007). Parameters of hot comp onents are: M = 34.0 M and 15.5 M , Tef f = 39900 K and 31900 K, the distance -- 414±7 p c (Menten et al. 2007), the p erio d of rotation -- 15.426 days (Stahl et al. 1996). Chemical comp osition: He, C, O, Si, Fe, Ni, Zn -- in deficit, Ne -- in excess; N, P, S, Mn -- at the solar abundance. A satellite at a distance of 0.033" has b een rep orted (Weigelt et al. 1999). The minimum cycle time makes according to 8 years. Walb orn, 1981 has found p erio dic variations of broad H-alpha emission line in the sp ectrum of 1 Ori C, and detailed researches have revealed that many emission and photospheric absorption lines change with the same p erio d, 15 d .426 ± 0.002. The strictly p erio dic change of lines allows one to b elieve that the case of a magnetic rotator is p ossible. The star shows a variability of brightness with an amplitude of 0 m .06 (Kukarkin 1982). Gagne et al. (1997) have found that the X-ray flux from this star changes with a p erio d of ab out 16 days. To explain this phenomenon, Bab el and Montmerle (1997) have offered a mo del of an oblique rotator with a surface magnetic field Bs = 300 G. Since 1966 (see, for example, Kudryavtsev et al.

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Table 1: Magnetic field vs phase. +2450000.00 Be, G phase sigma, G 3339.27 190 0.01 63 3339.35 174 0.127 51 3279.50 123 0.247 38 2678.78 ** 86 0.30 49 3747.29 -72 0.57 90 3748.33 18 0.64 67 3366.38 231 0.879 47 2950.46 * 201 0.917 28 3367.25 183 0.936 35 * observations were made in a back-and-forth mo de ** Bagnulo et al. (2006)

2000), unsuccessful attempts to find magnetic field in this star have b een undertaken. The difficulty of detection consists in the small numb er of sp ectral lines suitable for measurements. In 19992000 at the Anglo-Australian observatory Donati et al. (2002) have registered a magnetic field. They rep orted detection of a p erio dically changing longitudinal magnetic field of ab out 300 G with a p erio d conterminous to the p erio d of change of sp ectral lines. Estimations of the surface field gave a value of ab out 1 kG. The authors give the following parameters of the rotator: the inclination of the axis of the magnetic dip ole to the axis of rotation of the star is 42 ± 6 and the angle of inclination of the axis of rotation of the star to the observer is ab out 45 . Smith and Fullerton (2005) have revised the mo del of this star. While in last pap ers the attention is fo cused on a full structure ultra-violet CIV and NV resonant lines, they analyze blue and red wings of these lines. On the basis of this analysis of the b ehaviour of resonant sp ectral lines, a mo del of the star in which magnetic lines are broken off at some distance from the star is constructed. The comp onent of the star wind shows absorption shifted towards the blue part of the sp ectrum. The geometry of the internal parts is more complex. Particles of the star wind move from p oles along magnetic lines and collide at the magnetic equator. In collision emission o ccurs, and the particles fall on the star along magnetic lines. The high temp erature of these falling condensates causes a red-shited emission. Observations were made withn the Main Stellar Sp ectrograph of the 6-meter telescop e with use of an analyzer of circular p olarization and a double slicer (Chountonov 2004). One measurement was carried out in a back-and-forth mo de (Chountonov et al. 2000). Instead of the Savart plate (an element from Iceland spar) usually used in the analyzer, a dichroic p olarizer consisting of two glass prisms stuck together, to the diagonal side of which a multilayer dielectric covering is applied, is employed. The p olarizer in contrast to the element of Icelandic spar do es not cause disp ersion at the slit of the sp ectrograph. The image slicers pro duce 7 slices 5 arcsec in height for each p olarization, which increases the efficiency of measurements by a factor of 25. A diaphragm placed in front of the p olarizer do es not allow the Zeeman sp ectra to overlap. The magnetic field measurement data are listed in Table 1. This star is b eyond the range of magnetic chemically p eculiar stars. The magnetic moment of such massive stars as 1 Ori C is so great that such stars may app ear to b e predecessors of magnetars (single neutron stars with magnetic fields up to 10 15 G).

Acknowledgements. I am grateful to Yu.Yu. Balega for helpful discussions.

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References
Babel J. and Montmerle T., 1997, Astrophys. J., 485, L29 Bagnulo S, Landstreet J. D., Mason E. et al., 2006, Astron. Astrophys., 450, 777 Chountonov G.A., Murzin V.A., Ivashchenko N.G., Afanasieva I.V., 2000, in: Proc. of the Intern. Conf. "Magnetic fields of chemically peculiar and related stars", Yu.V. Glagolevskij and I.I. Romanyuk. (eds.), 249, Moscow Chountonov G.A., 2004, in: Proc. of the Intern. Conf. "Magnetic stars", Yu.V. Glagolevskij, D.O. Kudryavtsev and I.I. Romanyuk. (eds.), 286, Nizhnij Arkhyz Donati MJ-F., Babel J., T. J. Harries T. J. et al., 2002, Mon. Not. R. Astron. Soc., 333, 55 Gagne M., Caillault J.-P., Stauffer J., and Linsky J. L., 1997, Astrophys. J., 478, L87 Howarth I.D. and Prinja R.K., 1989, Astrophys. J. Suppl. Ser., 69, 527 Kraus S., Balega Yu.Yu., Berger J.-P., et al., 2007, Astron. Astrophys., 466, 649 Kudryavtsev D. O., Piskunov N.E., Romanyuk I.I., Chountonov G.A., and Shtol V.G., 2000, in: Proc. of the Intern. Conf. "Magnetic fields of chemically peculiar and related stars.", Yu.V. Glagolevskij and I.I. Romanyuk. (eds.), 64, Moscow Kukarkin B.V. et al., 1982, New Catalog of Stars Suspected of Brightness Variations [in Russian], Nauka, Moscow Menten K.M., Reid M.J., Forbrich J., Brunthalen A., 2007, Astron. Astrophys., in press Smith M.A. and Fullerton A.W., 1994, Publ. Astr. Soc. Pacific, 117, 13 Stahl O., Kaufer A., Rivinius Th. et al., 1996, Astron. Astrophys.,312, 539 Vitrichenko E.A., 2004, The Trapezium of Orion [in Russian], Nauka, Moscow, 304 Walborn N. R., 1981, Astrophys. J., 243, L37 Weigelt G., Balega Yu., Preibisch T. et al., 1999, Astron. Astrophys., 347, L15