COMMISSION 27 OF THE I. A. U.
	 INFORMATION BULLETIN ON VARIABLE STARS
		     Number 2645


			   	   Konkoly Observatory
				   Budapest
				   17 December 1984

				   HU ISSN 0374 - 0676

   DETERMINATION OF THE MAGNETIC FIELD IN THE STAR V 474 Mon

  V 474 Mon (HD 40535) is a variable star of Delta Scuti type with the primary
period of light variation P=0.1361260d showing the Blazhko-effect with P =
7.746d+-0.001d (Romanov, Fedotov, 1979). Both the primary period and the
Blazhko-effect period are exhibiting stability according to published 
observations. An abnormally great variation of light amplitude is present with 
the Blazhko-effect period; from 0.04m to 0.36m (Millis, 1973).

  Spectral observations of this star were carried out with the second camera
of the main stellar spectrograph of the 6-m telescope, SAO, Academy of Sciences,
USSR, in September, 1982. Spectrograms of the stars alpha^2 CVn and beta CrB were also
obtained from 1980 to 1982. These magnetic stars have been investigated more
completely and have been used as standards of magnetic field.
  An achromatic analyzer of circular polarization with a Fresnel rhomb has been
used as a phaseshifting element along with a crystal of Iceland spar which
provide the 5" separation of circularly polarized light beams at the 
spectrograph slit (Glagolevsky et al., 1978). All the spectrograms were obtained 
with an inverse linear dispersion of 9 A/mm. Time resolution used was 4-7 minutes
for V 474 Mon and 1-3 minutes for alpha^2 CVn and beta CrB. Kodak emulsion 103aO 
hypersensibilized with hydrogen according to the procedure developed at the Odessa
Astronomical Observatory has been used The spectral interval of wavelength
is 3900-5000 A.

  From 20 to 70 lines have been measured in each spectrogram in the spectral.
range 4000-4600 A. Probable error of one measurement amounts to 130-280
gauss for V 474 Mon, 300-550 gauss for alpha^2 CVn and 100-300 gauss for beta CrB.
The determinations of magnetic field strength for alpha^2 CVn and beta CrB agree with
those of other authors in all phases.

  Variation of the magnetic field strength. for V 474 Mon are given in Fig 1.
Phases of the fundamental pulsation period were calculated according to the
ephemeris: Max hel. J.D. = 2441661.1668 + 0.13612600d E and phases of the
Blazhko-effect in the star according to : J.D. max 
(O-C)=2441664.962+7.74639d N
(Romanov, Fedotov, 1979). These elements are in a good agreement with all known
observations.

                               [FIGURE 1]

  It is seen from Fig. 1 that the magnetic field strength changes with the
phase of stellar pulsation. The large scatter of points results from both
errors of measurements and the Blazhko-effect process. The character of this
variation is not yet found. It should be noted that not only the magnetic 
field strength changes, but also the field sign changes.
  To solve the problems connected with pulsations and magnetic field variations
further spectroscopic and photometric observations of V 474 Mon are extremely
needed.


		     Yu.S. ROMANOV, S.N. UDOVICHENKO
		     Odessa Astronomical Observatory, USSR

		     M.S. FROLOV
		     Astronomical Council of the USSR
		     Academy of Sciences, USSR


References:

Glagolevsky, Yu.V. et al., 1978, Soobshchenia SAO, 24, p. 61. [BIBCODE 1978SoSAO..23...61G ]
Millis, R.L., 1973, Publ.Astron.Soc.Pacif., vol. 85, p. 410. [BIBCODE 1973PASP...85..410M ]
Romanov, Yu.S., Fedotov, Yu.T., 1979, Astron. Tsirk., No. 1071. [BIBCODE 1979ATsir1071....6R ]