Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.sao.ru/hq/lizm/conferences/pdf/2003/2003_p93.pdf Äàòà èçìåíåíèÿ: Wed Apr 21 16:48:55 2010 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 16:37:01 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 63

Magnetic stars, 2004, 93-100

New magnetic CP stars
Kudryavtsev D.O.1 , Romanyuk I.I.1 , Elkin V.G.
1 2

1,2

Special Astrophysical Observatory of RAS, Nizhny Arkhyz 369167, Russia Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK

Abstract. Observations with the 6 m telescop e have revealed 25 new magnetic chemically p eculiar stars. We selected candidates by analyzing the depression profile at a wavelength of 5200° This technique for selecting candidate magnetic stars is A. shown to b e efficient: we have found magnetic fields in 25 from 40 ob jects that were selected for observations with the Zeeman analyzer. 11 of the rest 15 ob jects have wide lines and therefore the accuracy of measuremets is low in these cases, so it is not unlikely that part of these stars are magnetic to o. We found several stars with very strong magnetic fields, among them HD 178892 and HD 343872 with the surface magnetic fields not less than 20 kG and 9 kG, resp ectively. In spite of the go o d efficiency of our metho d for selecting candidates, we have not found any correlation b etween the intensity of the depression profile and the value of the magnetic field. Key words: stars: chemically p eculiar ­ stars: magnetic fields

1

Intro duction

At present we know only slightly more than 200 magnetic CP stars (Romanyuk 2000), which is about 3% of the total number of known CP stars (Renson et al. 1991). Such a small number is caused by the fact that investigations of magnetic fields can be carried out only with large telsecopes, where observational time is severely limited. Moreover, before the appearance of CCD detectors it was possible to observe stars with a magnitude of up to 8 only, even with large telescopes. Now the appearance of new detectors allows us to search for and investigate magnetic fields of stars with magnitudes of up to 11 using the 6 m telescope. Thus, great possibilities for extending the number of magnetic stars are opened. It also allows us to expand the space limits, within which the magnetic stars are observed, and for the first time make a comparative analysis of different characteristics of magnetic stars in relation with the Galaxy structure in the surroundings of the Sun. The large number of CP stars that is available for Zeeman observations poses two problems. First, we have to choose for the researches such stars, study of which can give new results as soon as possible. Second, we need a criterion which could make it possible to select with a high probability such CP stars which have strong magnetic fields. First of all, we decided to observe the spatially close stars and stars in open clusters. It is well known that investigation of stars in clusters can give answers to some questions concerning the evolution of stars. From this point of view it would be extremely interesting to obtain data on characteristics of stellar magnetic fields in clusters of different ages. Now we know approximately 70 magnetic stars which are members of open clusters. But if one considers an individual cluster, then the number of known magnetic stars in it will barely exceed 10 at best. It is clear that no comparative analysis is possible in this case, and the list of magnetic stars needs to be extended. Investigations of spatially close stars attract our attention as a result of our statistical analysis of the spatial distribution and motions of magnetic CP stars (Kudryavtsev and Romanyuk 2003; Romanyuk and
c Sp ecial Astrophysical Observatory of the Russian AS, 2004


94

KUDRYAVTSEV, ROMANYUK, ELKIN

Kudryavtsev 2001) pointing to some primary orientation of magnetic fields of close stars. However these conclusions are based on an insufficient number of data which must be increased. Therefore since 2000 we have been searching for new magnetic CP stars basing on the catalogs of Egret and Jaschek (1981), Renson (1992), Kopylov (1987), Niedzielski and Muciek (1988). In this paper we mainly consider the spatially close stars, for this reason candidates for magnetic stars were chosen from the catalogue of CP stars in stellar groups (Egret and Jaschek 1981). We observed mainly SrCrEu stars. Obtaining Zeeman spectra for all stars would take a lot of observational time at the 6 m telescope, so we need a criterion pointing with some probability to the presence of a strong magnetic field. We used the analysis of the 5200 ° depression profile. As early as 1980, Cramer and Maeder (1980) showed that the A depth of the 5200 ° depression could be an indicator of the presence of a magnetic field. Our method may A be considered as some modification of Cramer and Maeder's method, but it differs from it by the fact that we use low resolution spectra but the photometric index. Stars were preliminarily observed with the low resolution spectrograph UAGS at the 1 m telescope of SAO, and after that we selected candidates with the depth of spectral features not less than 10% in the 5200 ° region. A The data for a part of new magnetic stars presented in this paper were published earlier (Elkin et al. 2002; Elkin et al. 2003), but now we present another 11 stars for which magnetic field measurements are published for the first time.

2

Observations

The initial selection of candidates was made by analysis of the 5200 ° depression profile in low resolution A spectra observed with the spectrograpth UAGS at the 1 m telescope of SAO. For the following Zeeman observations we selected stars with a depth of spectral features not less than 10% of the continuum. The search for magnetic field was performed by measuring its longitudinal component using Zeeman spectra observed with the Main Stellar Spectrograph of the 6 m telescope with analyzers of circular polarization (Naidenov and Chountonov 1976; Chountonov 2000). The spectra were observed at 4500 ° with a resolution A of about 15000. The Zeeman shift in spectra of magnetic stars is a very subtle effect, therefore we observed not less than three spectra for each star on different dates to exclude any fortuities and also to avoid, where possible, the hit at the phase of zero longitudinal magnetic field. The data reduction was made in ESO MIDAS using the programs for reduction of Zeeman spectra (Kudryavtsev 2000). On the whole, a search for magnetic field in 40 candidate stars has been conducted so far. Some data on them are presented in Table 1. The information for spectral class and peculiarity was taken from the catalog of Renson et al. (1991). The stars are divided in two groups: a) stars with detected magnetic field; b) stars the detection of magnetic field in which had no success.

3

Magnetic field measurements

The measurements were made in a classical manner. Zero standards and stars with the well-known magnetic field were observed for the calibration. Measurements of standard stars show a good agreement with previous studies. Table 2 presents the results of our measurements of the magnetic field Be for the detected magnetic stars. The measurements of the spectra of the stars in which we failed to detect magnetic field are listed in Table 3. As one can see from Table 3, the measurements of the ma jority of "non-magnetic" stars were performed with a large r.m.s. error . This is probably due to their fast rotation (period of rotation is unknown) and fact that the lines of the given stars are very broad. Only for 4 sharp-line stars out of 15 stars the measurements were made with the standard accuracy reachable with the MSS of the 6 m telescope. Thus, it is possible that part of the presented stars also have rather strong magnetic fields; however instrument and methods of higher precision are required to detect them. Four stars with very large extrema of the longitudinal component of the magnetic field: HD 178892 (B e = 8490 ± 380), HD 293764 (Be = 4040 ± 230), HD 343872 (Be = 4590 ± 350), HD 349321 (Be = 5560 ± 310), attract attention. Additional observation are presently being made for them with the purpose of determination of the rotational period and construction of models. For HD 178892 and HD 343872 even now it is possible to make a certain analysis which we present below in Section 4.


NEW MAGNETIC CP STARS

95

Table 1: Observed stars HD/BD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD HD M
V

6757 7.7 29925 8.3 38823 7.3 39658 8.8 40711 8.4 115606 8.6 134793 7.5 142554 9.8 158450 8.6 168796 7.9 169887 9.0 170565 9.1 170973 6.4 Stars in 1677 7.3 3473 9.0 4478 9.0 27505 6.5 31362 6.3 34427 8.7 37642 8.0 68703 6.5

Pec HD/BD MV Sp Pec New magnetic stars A0 CrEuSi HD 178892 8.9 B9 SrCrEu B9 Si HD 189963 9.9 A0 SrCrEu A5 SrEu HD 196691 8.6 A0 Si A0 CrEu HD 209051 8.8 A0 SrCrEu A0 SrCrEu HD 231054 10.0 Ap SiSr A2 Cr HD 293764 9.5 A2 SrCrEu A4 SrEuCr HD 338226 9.8 A0 Si A0 CrEu HD 343872 9.9 Ap SrCrEu A0 SrCrEu HD 349321 9.3 A1 Si A0 SiCrSr BD +173622 8.8 A2 SrCrEu Ap Si BD +322827 9.9 Ap SrEuCr BD +353616 9.5 F0 SrEu A3 SrCrEu A0 SiCrSr which the presence of magnetic field is questionable A2­F0 HD 103498 7.0 A1 CrEuSr A2 SiMg HD 138218 9.8 A2 Sr B9 Si HD 141461 8.5 B9 Si HD 158352 5.4 A0 CrEu HD 164827 9.3 A0 Si HD 205087 6.7 A0 SrSiCr B9 He weak Si HD 290665 9.4 A0 CrEuSr A8

Sp

4
4.1

Stars with strong magnetic fields
HD 178892

During ob jective­prism observations Bond (1970) found the star to be peculiar. In the SIMBAD database, it is listed as a star in a binary system. Our observations with the 1 m telescope revealed a prominent feature at a wavelength near 5150 ° We A. were able to obtain four Zeeman spectra for this star. It possesses a strong magnetic field whose longitudinal component is not less than 8 kG. At present, we know only one star (HD 215441) 1 with longitudinal component Be exceeding this value and one star (HD 175362) with a comparable longitudinal component (see the catalog of Romanyuk (2000). HD 215441 is a hot silicon star (Te = 16000 K), while HD 175362 is a star with anomalous helium lines (Te = 17000 K) (Glagolevskij 1994). Among the numerous and cooler (with T e of the order of 8000 K) SrCrEu stars, HD 178892 can be a record holder by its magnetic field strength. Using our measurements of the longitudinal component of the magnetic field Be , we determined the rotational period as P = 8d 27 ± 0d08. The curve of variation of Be is displayed in Fig. 4.1. We also attempted . . to determine the period of rotation using Hipparcos photometry data; however, the star showed no significant light variability. The photometry data fitted with the period 8d 27 are shown at the bottom of the Fig.4.1. . Using the Be variability curve, we estimated lower limits of the dipole field strength on the magnetic pole as Bd 30 kG and the surface magnetic field Bs 19.8 kG. The corresponding theoretical curve in an approximation of a simple dipolar field is shown in the upper part of Fig. 4.1 with a solid line. Modeling the profile of the line H in HD 178892 showed the best fit to the model with Te = 8000 K, lg g = 4.0. Values of v sin i measured from different lines range from 20 to 45 km/s depending on the Lande factor. Thus, the influence of magnetic broadening of lines is evident. A star with a temperature T e = 8000 K has a radius of the order of 1.85R (Kopylov 1967). Then the equatorial rotational velocity at the period of
1 As we were preparing this publication Bagnulo et al. (2004) discovered a longitudinal magnetic field of 9 kG in the star NGC 2244­334.


96

KUDRYAVTSEV, ROMANYUK, ELKIN

Table 2: Magnetic field measurements for new magnetic stars
JD 2450000+ HD 6757 2544.539 2544.554 2545.465 2545.488 2625.296 2626.257 2689.170 2690.148 HD 29925 1807.508 2129.543 2153.521 2189.458 HD 38823 1892.493 2624.440 2625.452 2626.411 2689.241 HD 39658 2624.599 2625.640 2626.310 2661.537 2662.543 2689.213 HD 40711 1807.554 1892.538 2130.553 2153.557 HD 115606 1952.438 2333.454 2333.479 2417.254 HD 134793 2624.642 2660.592 2661.591 2689.483 HD 142554 2417.448 2805.274 2807.305 2830.311 HD 158450 2130.269 2805.373 2807.375 2812.415 HD 168796 2129.291 2130.291 2190.225 2458.396 Be ± (G) +2727 +2720 +2166 +3099 +2960 +2848 +2625 +2456 ± ± ± ± ± ± ± ± 144 196 249 258 170 159 144 124 JD 2450000+ HD 169887 2128.492 2129.358 2130.360 2807.357 HD 170565 2805.413 2831.384 2835.403 HD 170973 2688.645 2805.360 2807.521 HD 178892 2459.449 2459.473 2625.140 2626.139 2660.652 2661.645 2688.614 2689.577 2805.343 2807.392 2812.372 2830.403 2831.435 2832.496 2834.431 2835.380 2838.390 2840.433 HD 189963 2457.447 2459.421 2805.473 2830.462 2835.455 HD 196691 2130.304 2417.500 2454.473 2457.419 HD 209051 2130.456 2191.258 2454.498 2458.420 HD 231054 2127.502 2128.417 2129.395 2130.395 Be ± (G) -2340 +540 +1210 +2019 ± ± ± ± 290 230 240 247 JD 2450000+ HD 293764 1806.558 1807.529 1864.505 HD 338226 2127.545 2128.458 2129.433 HD 343872 1768.504 1770.391 1798.267 1799.286 1800.432 1802.347 1803.401 1804.315 1806.185 1807.185 1893.122 1952.640 1952.655 1953.622 2069.458 2127.283 2128.283 2130.435 2805.503 2840.349 HD 349321 2805.432 2807.418 2830.380 2831.409 2832.471 2834.407 2835.358 2839.308 2840.396 BD +17 3622 1275.555 2069.512 2127.417 BD +32 2827 2191.208 2417.341 2457.417 BD +35 3616 2128.485 2626.168 2805.320 2807.448 2835.508 Be ± (G) +4040 ± 230 +3770 ± 310 +3590 ± 290

+1583 ± 182 +1706 ± 187 +1956 ± 134

+1040 ± 230 +440 ± 180 +1490 ± 170

-1100 + -200 -810 -890

±190 ± 360 ± 250 ± 150

+634 ± 43 -399 ± 46 -343 ± 47

-939 ± 138 -2493 ± 96 -1412 ± 113 -23 ± 66 +1523 ± 85

-971 ± 91 -642 ± 214 +1349 ± 123 +1332 ± 182 +101 ± 157 -481 ± 306

-230 ± 60 +330 ± 110 -630 ± 310 -650 ± 90

+6320 +6260 +8150 +8490 +5773 +5277 +1729 +4917 +4940 +7767 +1665 +6143 +7795 +7752 +6181 +5097 +4780 +5762

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

480 530 390 380 519 500 225 457 543 407 340 626 474 398 520 553 602 535

+3590 +2160 +660 -760 -600 +3860 +1960 +2730 +1980 +1510 +2210 +3580 +2880 +2950 +2850 +2870 +3810 +2660 +4179 +4589

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

300 400 340 220 300 250 790 370 350 190 350 180 290 210 200 230 230 210 173 351

-210 +680 +640 -760

± ± ± ±

130 120 110 150

+255 ± 140 +212 ± 200 +301 ± 73 -695 ± 91 +355 ± 57

-5555 +1869 -4700 -1647 +1774 +2192 -5153 +1858 -3445

± ± ± ± ± ± ± ± ±

312 334 279 455 318 213 306 948 620

-140 ± 114 -812 ± 122 +900 ± 83 +953 ± 96

-1940 +2290 +1920 +630

± ± ± ±

240 360 240 250

+1600 ± 160 +1510 ± 240 +980 ± 130

+1737 +1744 +447 -771

± ± ± ±

260 245 364 263

-3300 -2580 -2980 -1040

± ± ± ±

580 460 730 700

-770 ± 180 -470 ± 150 +60 ± 130

+240 -528 -2975 +812

± ± ± ±

100 116 196 236

+960 +1840 +2530 +380

± ± ± ±

250 250 270 170

+250 ± 150 -517 ± 52 -13 ± 71 +310 ± 67 +541 ± 69

-610 ± 110 -290 ± 110 -870 ± 90 +510 ± 110


NEW MAGNETIC CP STARS

97

Table 3: Measurements for stars in which the presence of magnetic field is questionable JD 2450000+ HD 1677 2544.506 2544.521 2625.232 2626.243 2689.157 2690.170 HD 3473 2129.485 2130.528 2153.252 2625.252 HD 4478 2153.296 2625.276 2834.468 HD 27505 2624.320 2625.338 2626.331 HD 31362 2333.293 2544.572 2544.580 2545.411 2545.440 2624.339 2625.347 2626.341 Be ± (G) -916 -471 -275 +255 +120 +337 ± ± ± ± ± ± 431 462 289 305 513 403 JD 2450000+ HD 34427 2191.474 2625.384 2626.375 HD 37642 * 2624.419 2625.437 2626.394 HD 68703 2333.272 2544.591 2544.600 2624.507 2625.657 2626.571 2661.519 HD 103498 2662.569 2689.365 2689.391 2690.398 2830.278 2831.277 HD 138218 2417.378 2457.328 2660.614 Be ± (G) +1850 ± 1810 +2800 ± 1910 -442 ± 1528 JD 2450000+ HD 141461 2333.563 2333.581 2661.610 2662.593 HD 158352 2688.639 2689.559 2830.346 HD 164827 2805.392 2830.433 2831.359 2835.426 HD 205087 2805.524 2830.537 2831.504 2832.536 HD 290665 2624.388 2625.412 Be ± (G) -1450 ± 1300 -760 ± 1360 +513 ± 638 +93 ± 1342

+2143 ± 890 +4640 ± 1250 +2630 ± 2302

-70 +1310 -890 +88

± ± ± ±

640 590 970 380

+343 ± 772 +590 ± 878 +2187 ± 1265

+1277 ± 919 +533 ± 898 -1004 ± 719

+390 +213 -325 -219 +176 +196 +338

± ± ± ± ± ± ±

210 285 278 193 218 180 212

+1276 ± 450 +1623 ± 525 -2325 ± 1131 -1075 ± 352

-2488 ± 1094 -78 ± 728 +2262 ± 1585

+79 +1364 +332 +213 -67 +171 +411 +149

± ± ± ± ± ± ± ±

380 623 335 250 437 188 309 296

-242 ± 56 -5 ± 85 -25 ± 94 +8 ± 106 +86 ± 45 -29 ± 36

+3 ± 78 +239 ± 95 +126 ± 101 +63 ± 100

+7406 ± 2886 +309 ± 2930

-1770 ± 2051 -3518 ± 1545 +1391 ± 1084

* Magnetic field of HD 37642 was discovered by Borra (1981) using balmer-line polarimeter. Star has very broad lines that made impossible accurate Zeeman spectroscopy.


98

KUDRYAVTSEV, ROMANYUK, ELKIN

HD178892 JD2452452.217 + 8.27320 (+0.078,-0.077)
10000 8000

Be, G

6000 4000 2000 0 0 9,1 0,2 0,4 0,6 0,8 Bs >= 19.8 kG Bd >= 30 kG 1

9,05

m
9 8,95

0

0,2

0,4

phase

0,6

0,8

1

Figure 1: Longitudinal magnetic field variability and Hipparcos photometry for HD 178892.

8d 27 will be of the order of 10 km/s. The instrumental profile of the MSS of the 6 m telescope corresponds to . 20 km/s, thus, the entire broadening that we observe is most likely caused by the magnetic field of the star.

4.2

HDE 343872

HDE 343872 was first classified as a Si peculiar star by Bidelman (1983) on the basis of ob jective­prism spectra. Schneider (1986) included it in the list of CP2 stars to be observed in Stromgren's system to determine its photometric indices, H and a. Schneider's studies revealed a variable depression at 5200 ° in A HDE 343872, which is the largest among all the previously observed CP stars, with a from 0.067 to 0.146. Because of the small number of observations, Schneider (1986) was able to estimate the variability period only roughly: from 7 to 9 days. Subsequently, Kroll (1992) carried out spectroscopic observations of the star. He found T e = 10500 K and lg g = 3.1, suggesting that HDE 343872 is an evolved star. Its spectrum exhibits enhanced chromium and iron lines. Thus, we had strong grounds for including the CP star HDE 343872 with the largest depression ever observed, which also exhibited the largest periodic variations, in our program of observations with the 6 m telescope to search for and thoroughly study its magnetic field. We obtained about 20 Zeeman spectra of the star. Using measurements of the longitudinal component of the magnetic field we determined the rotational period of the star as P = 8d 79±0d02. To estimate the period, . . we also attempted to employ Tycho photometry; however, the star showed no considerable variability within the measurement errors. The curve of variability of the magnetic field longitudinal component and Tycho photometry with the period of 8d 79 days are shown in Fig. 4.2. . Preliminary modeling the curve of the longitudinal magnetic field in an approximation of a simple dipole yields lower limits of the dipole strength, Bd 13.5 kG, and of the surface magnetic field, Bs 8.7 kG. The corresponding theoretical curve of Be is shown in the upper part of Fig. 4.2 with a solid line. With such a surface field Bs magnetic broadening can contribute 50% of the total line width, depending on the Lande factor of the line. Values of v sin i determined from different lines range from 25 to 35 km/s,


NEW MAGNETIC CP STARS

99

HD343872 JD2451759.802 + 8.78843 (+-0.021)
5000 4000 3000 2000 1000 0 -1000 0 11,5 11 10,5 10 9,5 9 8,5 0 0,2 0,4 0,6 0,8 1 0,2 0,4 0,6 Bs >= 8.7 kG Bd >= 13.5 kG 0,8 1

m

Be (G)

phase

Figure 2: Longitudinal magnetic field variability and Tycho photometry for HD 343872.

depending on the Lande factor, which is also evidence of magnetic broadening. The contribution of magnetic broadening cannot be ignored when studying the chemical composition of the stellar atmosphere. The attempt of modeling hydrogen line profiles showed a result rather curious for a magnetic star -- log g = 3.0, which, however, is in excellent agreement with the data of Kroll (1992) mentioned earlier. However, we were unable to define unambiguously the temperature of the star using hydrogen lines. Note also that the modeling of metallic lines represents in this case a task which is far from being trivial. The star is extremely interesting for further more detailed investigations.

5

Results

So, by the present time, we have observed 40 candidates for magnetic stars, selected on the basis of analyzing the profile of the depression at 5200 ° In 25 of them (62.5% of the sample) magnetic fields were found, A. including 4 stars with extremely strong magnetic fields. Among the rest of the stars 11 out of 15 stars have very broad lines, and that is why the magnetic measurements were made with low accuracy. It is not unlikely that part of them are magnetic as well. If one considers only the stars with narrow lines, then we found fields in 25 (86.2%) from 29 candidates. Thus, it can be stated that our technique of selecting the candidates turned out to be efficient enough. Nevertheless, it should be taken into account that most of the candidates were of SrCrEu type of peculiarity, and the frequency of occurence of magnetic fields in these stars is very high, which, probably, affected the assessment of the technique presented above. We attempted to establish a possible relation between the depth of one of the characteristic features on the profile of the depression at 5200 ° and the magnetic field magnitude. Since in the ma jority of cases A we had no curves of variations of the longitudinal field and accurate magnetic field models, we took as the estimate its maximum value, Bextr . The relationship between the depth of the detail at 5200 ° and Bextr A is shown in Fig. 5. As it can be seen from the figure, we found no correlation between these two values. Although the abovedescribed procedure of estimation of the given relationship is rather rough, we do not expect any qualitative


100

KUDRYAVTSEV, ROMANYUK, ELKIN

8000

6000

Be extremum, G

4000

2000

0 0,75 0,8 0,9 0,85 Depth of the depression profile at 5150A

Figure 3: Relation between the depth of a detail at 5200 AA depression profile and the observed extremum of the longitudinal magnetic field.

changes when specifying the magnetic star models. Thus, direct measurements are necessary even in statistical studies of magnetic field of stars.
Acknowledgements. We thank the Program Committee for observing time at the 6 m telescope. The work was partially supported by the Russian Foundation for Basic Research (grant 03­02­16342).

References
Bagnulo S., Hensberge H., Landstreet J. D., Szeifert T., Wade G. A., 2004, Astron. Astrophys., 416, 1149 Bidelman W. P., 1983, Astron. J., 88, 1182 Bond H. E., 1970, Publ. Astr. Soc. Pacific, 82, 321 Borra E.F., 1981, Astrophys. J., 249, L39. Chountonov G. A., 1997, in: "Stellar magnetic fields", eds.: Yu. V. Gladolevskij and I. I. Romanyuk, 229 Cramer N., Maeder A., 1980, Astron. Astrophys. Suppl. Ser., 41, 111 Egret D., Jaschek M., 1981, Comptes Rendus Symp. Liege, No. 23, 495 Glagolevskij Yu. V., 1994, Bull. Spec. Astrophys. Obs., 38, 152 Kopylov I. M., 1987, Izv. CrAO, 1967, 36, 134 Kopylov I. M., 1987, Astrofiz. Issled. (Izv.SAO), 24, 44 Kroll R., 1992, in: Proc. of IAU Coll. 138, "Peculiar Versus Normal Phenomena in A­type and Related Stars", eds.: Dworetsky M. M., Castelly F., Farragiana R., ASP Conf. Ser., 44, 75 Kudryavtsev D. O., 2000, in: "Magnetic Fields of CP and Related Stars", eds.: Yu. V. Gladolevskij and I. I. Romanyuk, 84 Kudryavtsev D. O., Romanyuk I. I., 2003, Astrophysics, 46, 234 Naidenov I. D., Chuntonov G. A., 1976, Soobshch. Spec.Astrofiz.Obs., 16, 63 Niedzielski A., Muciek M., 1988, Acta Astronomica, 38, 225 Renson P., Gerbaldi M., Catalano F., 1991, Astron. Astrophys. Suppl. Ser., 89, 429 Renson P., 1992, Bull. Inf. Centre Donnees Stellaires, 40, 97 Romanyuk I. I., 2000, in: "Magnetic Fields of CP and Related Stars" eds.: Yu. V. Gladolevskij and I. I. Romanyuk, 18 Romanyuk I. I., Kudryavtsev D. O., 2001, ASP Conf. Ser., 248, 299 Schneider H., 1986, Astron. Astrophys., 161, 203