COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3668 Konkoly Observatory Budapest 4 October 1991 HU ISSN 0374 - 0676 uvby OBSERVATIONS OF SV CEPHEI The irregular variable SV Cephei ( = BD+72d 1031 = IRAS 22205+7325) belongs to a group of evolutionarily young stars called emission-line stars of the Orion Population. Their properties are described in detail in the corresponding catalogue compiled by Herbig and Bell (1988). A comprehensive collection of observational data for SV Cephei can be found in a paper by Friedemann et al. (1992) together with a model of the circumstellar dust shell which gives a consistent explanation of both the optical and infrared data. For SV Cephei and two nearby comparison stars we obtained uvby photometry with the 90 cm telescope of the Jena University Observatory. The observations were carried out on 14 nights from January to September 1991. On each night the atmospheric extinction coefficients and the zero points of the transformation equations were determined from a sample of about 15 standard stars. All of them were taken from the original list of uvby standards published by Crawford and Barnes (1970) including revisions by Perry et al. (1987). The two comparisons b and c in the paper by Friedemann et al. (1992) which contains an identification chart too, are identical with the comparison stars a and b in the list of Wenzel (1969). Both stars were measured on each night and finally taken as secondary local standards. Their magnitudes and colour indices together with its r.m.s. errors (in mag) and the number of observations are given in Table I. Table I. Magnitudes of comparison stars Star y=V r.m.s. b-y r.m.s. m_1 r.m.s. c_1 r.m.s. n b 10.734 0.006 0.248 0.005 0.151 0.006 0.956 0.006 15 c 11.107 0.008 0.437 0.006 0.124 0.009 0.727 0.008 24 A full description of technical details of the used equipment, the reduction procedure, and the transformation equations is given by Reimann et al. (1989). The final photometric results for SV Cephei are collected in Table II. The r.m.s. errors of the photometric data for SV Cephei have been estimated to be +-0.012, +-0.006, +-0.009, and +-0.013 mag in V, b-y, m_1, and c_1, respectively, using the internal agreement of the individual results for the comparison stars obtained in different nights. Table II. Observations of SV Cephei = BD+72d 1031 Julian date y = V b-y m_1 c_1 2448273.454 10.907 0.257 0.071 1.085 2448274.407 10.916 0.267 0.070 1.084 2448288.375 10.842 0.259 0.054 1.032 2448308.377 10.919 0.265 0.076 1.087 2448329.455 10.835 0.270 0.035 1.031 2448330.425 10.851 0.284 0.038 1.020 2448358.527 10.840 0.279 0.046 1.046 2448440.468 10.901 0.303 0.042 1.031 2448448.430 10.909 0.304 0.034 1.033 2448449.405 10.920 0.291 0.058 1.048 2448466.515 10.934 0.294 0.060 1.055 2448502.504 11.101 0.293 0.109 1.106 2448503.512 11.084 0.312 0.103 1.100 2448508.411 11.044 0.290 0.097 1.076 During the time interval covered by our observations SV Cephei exhibited irregular variability only in the order of 0.3 mag with a shallow minimum around JD 2448502.5. From a closer inspection of the colour indices we conclude that during the observed time interval intrinsic stellar colour and brightness changes of the order of 0.1 mag were superimposed on circumstellar cloud obscurations of the order of 0.3 mag of nearly neutral character. The light curve and the magnitudes of the comparison stars are shown in Figure 1. [FIGURE 1] Using the uvby calibrations by Crawford (1975, 1979) and Reimann (1982) for F, A, and B stars, respectively, we deduced for the variable from our observational data a spectral type of B9-9.5, a colour excess E(b-y) = 0.300 mag, and a photometric distance of about 715 pc assuming the luminosity class V. H.-G. REIMANN, C. FRIEDEMANN Universitats-Sternwarte Jena Schillergasschen 2 O-6900 Jena, Germany References: Crawford, D.L.: 1975, AJ 80, 955 [BIBCODE 1975AJ.....80..955C ] Crawford, D.L.: 1979, AJ 84, 1858 [BIBCODE 1979AJ.....84.1858C ] Crawford, D.L. and Barnes, J.V.: 1970, AJ 75, 978 [BIBCODE 1970AJ.....75..978C ] Friedemann, C., Reimann, H.-G., and Gurtler, J.: 1992, Astron. Astrophys. in press [BIBCODE 1992A&A...255..246F ] Herbig, G.H. and Bell, K.R.: 1988., Lick Obs. Bull. No. 1111 [BIBCODE 1988cels.book.....H ] Perry, C.L., Olsen, E.H. and Crawford, D.L.: 1987, PASP 99, 1184 [BIBCODE 1987PASP...99.1184P ] Reimann, H.-G.: 1982, PhD Thesis, Jena University Reimann, H.-G., Bohm, M., and Pfau W.: 1989, Astron. Nachr. 310, 41 [BIBCODE 1989AN....310...41R ] Wenzel, W.: 1969, Mitt. Verand. Sterne, Sonneberg, 5, 75 [BIBCODE 1969MitVS...5...75W ]