COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2501 Konkoly Observatory Budapest 3 April 1984 HU ISSN 0374-0676 HD 172256 REVISITED + Variations of the Be star HD 172256 (SAO 187112) have already been reported by Heck and Manfroid (1982) from 30 uvby observations obtained over seven consecutive nights in August 1981. The observed (peak-to-peak) amplitudes were 0.103m, 0.023m, 0.026m and 0.069m for V, b-y, m1, and c1 respectively, while the absolute internal accuracy for stars of a similar type was 0.011m, 0.005m, 0.007m, and 0.009m respectively. The variations were therefore highly significant, In particular, significant variations of up to 0.1m occurred within a single night. On that basis, HD 172256 was added to the growing list of Be stars showing variations on a time scale less than a day or two (Percy, 1982). Table I Variations of HD 172256 during, June 1983 (observations at ESO 50 Danish telescope) JDo V b-y m c 2,445,000+ 500.6002 8.694 0.099 0.025 0.108 500.8347 8.759 0.115 0.003 0.129 501.8070 8.751 0.116 -0.008 0.141 502.5775 8.697 0.114 0.004 0.113 504.6313 8.713 0.112 0.005 0.121 504.7729 8.713 0.131 -0.023 0.123 505.5828 8.714 0.089 0.050 0.083 505.7601 8.698 0.119 -0.016 0.141 506.7184 8.731 0.119 -0.010 0.130 506.8243 8.731 0.115 -0.006 0.135 508.5654 8.686 0.125 -0.001 0.092 508.6523 8.725 0.128 -0.015 0.128 508.7458 8.731 0.120 -0.016 0.137 508.8312 8.704 0.110 0.005 0.122 508.8734 8.708 0.113 -0.013 0.133 509.6011 8.724 0.110 -0.011 0.145 509.7108 8.708 0.121 -0.007 0.120 509.8014 8.719 0.120 -0.013 0.130 509.8661 8.710 0.108 0.006 0.120 509.9035 8.706 0.111 -0.009 0.150 + Based on observations collected at the European Southern Observatory, La Silla, Chile Table II Variations of HD 172256 during July 1983 (observations at ESO 1m telescope) JDo V b-v m1 c1 2,445,000+ 518.5521 8.683 0.127 -0.015 0.142 518.6826 8.727 0.120 -0.013 0.145 518.8725 8.721 0.120 -0.014 0.131 542.6204 8.733 0.119 -0.004 0.142 542.6631 8.745 0.122 -0.008 0.141 542.7812 8.725 0.117 -0.002 0.126 545.5036 8.707 0.116 -0.004 0.108 545.5936 8.746 0.077 0.043 0.120 546.5020 8.692 0.119 -0.002 0.128 546.5913 8.723 0.121 -0.006 0.137 546.7245 8.820 0.116 -0.013 0.160 546.7508 8.802 0.116 -0.001 0.138 547.4952 8.677 0.125 -0.015 0.126 547.5527 8.708 0.125 -0.014 0.127 547.6415 8.747 0.112 0.001 0.129 547.6751 8.736 0.117 0.000 0.126 547.7302 8.743 0.112 0.012 0.101 547.7727 8.752 0.114 -0.012 0.114 548.4856 8.712 0.115 -0.002 0.139 548.6516 8.725 0.106 0.014 0.116 548.6761 8.719 0.109 0.004 0.123 548.6965 8.743 0.102 0.014 0.116 Table III Peak-to-peak amplitudes of HD 172256 variations V b-y m1 c1 August 1981 0.103 0.023 0.026 0.069 June 1983 0.073 0.042 0.073 0.042 July 1983 0.126 0.050 0.058 0.059 June-July 1983 0.126 0.054 0.073 0.059 In several stars, such variations have been attributed to non-radial pulsation. Models involving rotation or duplicity have also been proposed. The observations of Heck and Manfroid (1982) were analyzed for periodicity using Deeming's (1975) method. The V observations could be fit by periods of 0.308d, 0.236d or 0.444d (in order of decreasing significance: these periods are related by 1 cycle/day), but the c1 observations could not. Additional observations have therefore been carried out in June and July 1983 at La Silla, Chile, with the 50 cm Danish and 1m ESO telescopes, respectively, The data collected are presented in Tables I and II. The amplitudes [FIGURE 1] Figure 1 Correlation between b-y and m1 for HD 172256 in observations carried out in August 1981, June 1983 and July 1983. are given in Table III and are large compared to the absolute internal errors estimated here to be 0.011m, 0.005m, 0.007m and 0.009m for V, b-y, m1 and c1 respectively in June 1983, and 0.012m, 0.006m, 0.008m and 0.011m in July 1983. Again, there are variations of several hundredths of a magnitude on many nights, including a variation of 0.128m within 0.22d on JD 2445546. It has not been possible, however, to extract any strict periodicity from the data, and in particular, those mentioned earlier are not present again. Moreover, the variations in the different colours are mostly uncorrelated. Only b-y and m1 seem clearly anticorrelated (see figure), with m1 varying more than b-y. Since m1 = (v-b) - (b-y), this would mean that (v-b) is also anticorrelated to (b-y). A. HECK (1), MANFROID (2)**, J.R. PERCY (3) 1 Observatoire Astronomique, 11 rue de l'Universite, F-67000 Strasbourg, France 2 Departement Astrophysique de l'Universite de Liege, avenue de Cointe 5, B-4200 Cointe-Ougree, Belgium 3 Department of Astronomy, University of Toronto, Toronto, Ontario M5S 1A1, Canada ** Research Associate, National Fund for Scientific Research References : Deeming, T.J. 1975, Astrophys.Space Sci. 36, 137 [BIBCODE 1975Ap&SS..36..137D ] Heck, A. and Manfroid, J. 1982. IAU Comm. 27 Inform.Bull.Var. Stars No. 2198 Percy, J.R. 1982, IAU Comm. 29 Be Star Newsletter No. 6, 8 [BIBCODE 1982BeSN....6....8P ] [From IBVS 2537] Emendation Table III and the legend of Figure 1 in I.B.V.S. No. 2501 is not legible on most of the copies because of bad printing. For the sake of completeness we repeat Table III and the figure caption here: Table III Peak-to-peak amplitudes of HD 172256 variations V b-y m1 c1 August 1981 0.103 0.023 0.026 0.069 June 1983 0.073 0.042 0.073 0.042 July 1983 0.126 0.050 0.058 0.059 June-July 1983 0.126 0.054 0.073 0.059 Legend of the figure: Correlation between b-y and m1 for HD 172256 in observations carried out in August 1981, June 1983 and July 1983. Editors