COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1536 Konkoly Observatory Budapest 1979 January 22 ON THE PHOTOMETRIC VARIABILITY OF o Vel AND OF THE He-WEAK STAR HR 3448 Introduction: A systematic survey for He-weak stars conducted by Jaschek et al. (1969) resulted in eight new objects including HR 3448. He-weak stars are known to show periodic spectrum and light variability (Pedersen and Thomsen 1977). However, Pedersen and Thomsen (1977) did not find variability in the strength of the HeI 4026A line of HR 3448 or in its light. HR 3448 was an the present observing program of a search for Beta Cephei stars, as a comparison star to o Vel, a suspected Beta Cephei star (van Hoof 1972); variability in HR 3448 was suspected and it was therefore observed independently against HR 3466 (B9III). o Vel is a suspected Beta Cephei star on the basis of its RV variations reported by van Hoof (1972). However, its light variability has yet to be confirmed (Balona 1977). The observation: reported here suggest that HR 3448 is photometrically variable with a small amplitude of .01 mag in 'b' and o Vel is constant. Observations : The photometric observations were made through the Stromgren 'b' filter during an observing run in March 1977. The University of Toronto 61 cm telescope situated at Las Campanas, Chile, was used. It was equipped with a 1P21 photometer and pulse counting electronics. Table 1 gives observations of HR 3448 and o Vel against HR 3466 obtained on three nights. These are means of two observations. The differential extinction correction was found to be negligible. These observations clearly indicate that variations in o Vel are not more than .005 mag, supporting Balona's (1977) [FIGURE 1] Figure 1: Plots of Delta m_b (o Vel - HR 3466, and HR 3448 - HR 3466) versus JD. [FIGURE 2] Figure 2: A phase diagram of HR 3448 with P=.3880d. conclusion, whereas HR 3448 shows variations of about .01 mag. The observations of HR 3448 and o Vel, obtained on JD 2443213 are plotted in Figure 1. Constancy of HR 3466 is well demonstrated against o Vel. The light curve of HR 3448 shows a characteristic double minimum similar to the light curve of sigma Ori E (Pedersen and Thomsen 1977). Although the observations are not sufficient to determine the period accurately, a period of P=.388d resulted from a statistical technique of period search; it was found to fit very well to all the observations of HR 3448 listed in the Table 1. This period is also supported by the two times of minima observed: JD_min 2443210.5861 and 2443213.6896. This phase diagram is shown in the Figure 2. If this period is right then HR 3448 will be the shortest period He-weak variable. The He-weak variability being a surface phenomenon, in general the period can be accounted for by the rotational velocity of the variable (Pedersen and Thomsen 1977). We could not find in the literature a v * sin i value for HR 3448, which would have provided some kind of indirect check on this proposed period. From the published uvby values for HR 3448 (Crawford et al.1978) one can estimate its luminosity (Mv=-.42, Crawford 1978) and temperature (log Te=4.164, Shaw 1975) and hence its radius (R=3R_Sun). Thus to account for a period of P=.388d, a v * sin i value for HR 3448 is estimated to be of the order of 250 km/s which is slightly large for a normal B8 star. It should be noted that the uvby beta indices used here are not averaged over a cycle and relations used are applicable to normal stars. Another feature of HR 3448 which it shares with sigma Ori E is the fact that HR 3448 also lies away from the zero age main sequence on the [c1], beta plane (Pedersen and Thomsen 1977). More observations are needed to confirm the period and to obtain a complete light curve for HR 3448. The possibility of it being the shortest period He-weak variable and the similarity of the light curve with that of sigma Ori E, a He-rich star, should make this object important. TABLE 1 Observations of HR 3448 and o Vel Against HR 3466 ------------------------------------------------- HR 3448-HR 3466 o Vel-HR 3466 JD Delta m_b JD Delta m_b 2443200+ 2443200+ ----------------------------------------- 10.5208 .087 10.5444 -1.913 10.5368 .088 10.5659 -1.913 10.5653 .094 10.5882 -1.913 10.5861 .095 10.6076 -1.914 10.6201 .090 10.6146 -1.917 13.5157 .088 10.6271 -1.913 13.5402 .092 10.6493 -1.914 13.5659 .091 10.6569 -1.913 13.5965 .089 10.6618 -1.915 13.6215 .087 10.6680 -1.914 13.6576 .089 10.6771 -1.915 13.6896 .097 10.7097 -1.914 13.7285 .088 10.7146 -1.916 13.7646 .084 10.7194 -1.915 20.5229 .088 13.5135 -1.917 20.5444 .091 13.5694 -1.915 20.5736 .095 13.5986 -1.913 20.6166 .087 13.6257 -1.914 13.6618 -1.916 13.6924 -1.913 ------------------------------------------ SHYAM M. JAKATE Department of Astronomy University of Toronto Toronto, Ont. Canada. M5S 1A7 References: Balona, L.A. 1977, Mem. R. Astron. Soc. 84, 101 [BIBCODE 1977MmRAS..84..101B ] Crawford, D.L. 1978, Astron. J. 83, 48 [BIBCODE 1978AJ.....83...48C ] Crawford, D.L., Barnes, J.V., and Golson, J.C. 1971, Astron. J. 76, 621 [BIBCODE 1971AJ.....76..621C ] Jaschek, M., Jaschek, C. and Arnal, M. 1969, Publ. Astron. Soc. Pacific 81, 650 [BIBCODE 1969PASP...81..650J ] Pedersen, H., and Thomsen, B. 1977, Astron. Astrophys. Suppl. 30, 11 [BIBCODE 1977A&AS...30...11P ] Shaw, J.S. 1975, Astron. Astrophys. 41, 367 [BIBCODE 1975A&A....41..367S ] van Hoof, A. 1972. Astron. Astrophys. 18, 51 [BIBCODE 1972A&A....18...51V ]