COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3850 Konkoly Observatory Budapest 26 February 1993 HU ISSN 0374 - 0676 OPTICAL VARIABILITY AND H-ALPHA EMISSION FOR THE BRIGHT O STAR HR 2806 HR 2806 (HD 57682) has been classified as a sharp-lined O9V star (Slettebak, 1956). Its v sin i is truly small: values from 17 (Conti et al., 1977) to 40 km/sec (Buscombe, 1970) have been quoted. There has been some past speculation that it has possessed emission lines at some epochs. Peterson & Scholz (1971) observed possible emission at H alpha and H beta Conti (1974) found emission shortward of H alpha and elsewhere. However, Jaschek et al. (1964) and Zinn (1970) found no emission at H alpha. The star is the exciting object for the IC 2177 nebulosity and a member of the CMa OB1 association. The author obtained a spectrum centered at H alpha with the Kitt Peak coude feed telescope and RCA2 CCD on JD2446878.73. It was immediately apparent that there was a noticeable single emission component at H alpha. Later, two other spectra in the same region were also acquired on JD 2448644.90 and 8645.80 with the same telescope, but this time with the T1KA CCD. They were virtually identical in appearance, with both showing a single emission component at H alpha and a strong, uncontaminated lambda 6678 He I. The spectra from JD 6878 and 8645 are shown in Figure 1. The intensity of H alpha emission seems to have increased slightly. The velocity of the H alpha emission peak has not changed much (-5.6, -11.4, and -12.0 km/sec for 3 spectra), nor has that of He I lambda 6678 (+17.9, +19.3, +21.0 km/sec). These last are in good agreement with the published radial velocities of +22.6, +21.9, and +23.9 (Abt & Biggs, 1972). In view of its possible variability, the star was added to the BV photometric monitoring program of the Corralitos Observatory. Along with its 0.6-m. telescope, two different photometers were used, the first being an ambient temperature EMI 9924A tube-based system, and the second based on an R4457 tube. Care was devoted to the observation of standard stars so that there were no measurable transformation errors between the two systems. Two comparison stars were utilized: HR 2798 (V=6.549; B-V= +.513) and HR 2739 (V=6.001; B-V = -.135). The average standard errors for the two comparison stars were .018 magnitudes in V and B-V. 51 observations over the time period JD 2446754-8724 were obtained. They appear in Table 1 and graphically in Figure 2. Clearly, HR 2806 is minorly variable, showing a range of 0.111 in V and .100 in B-V. A plot of V vs. B-V shows no correlation. It would also seem that the range of variability in V magnitude changes: seasons 3 and 4 show larger dispersion than 1, 2, and 5. The cause of variability of this star cannot be ascertained from the data taken. It may proceed from changing conditions in the circumstellar material or HR 2806 may be a rapid variable akin to Zeta Ophiuchi, an O9.5Ve star which shows light variations with periods of 0.193 and 1.075 days (Percy, 1987). The author wishes to most gratefully acknowledge a Theodore Dunham, Jr. Grant of the Fund for Astrophysical Research for purchase of photometric equipment. [FIGURE 1] Figure 1. Coude spectra in the region of H alpha for HR 2806. The ordinate is in units of continuum intensity. Dates of spectra are in the text. [FIGURE 2] Figure 2. V magnitudes for HR 2806. Julian Date is JD - 2440000. Table 1 BV magnitudes for HR 2806 Numbers following magnitudes in parentheses are standard errors in millimags. Julian Date V(SE) B-V(SE) Julian Date V(SE) B-V(SE) (2440000+) (2440000+) 6754.9471 6.406(-) -.162(-) 8243.8361 6.404(1) -.119(19) 6777.8721 6.416(-) -.158(-) 8243.8377 6.402(-) -.171(-) 6795.8928 6.434(-) -.187(-) 8244.8375 6.397(13) -.147(13) 6816.8416 6.447(-) -.141(-) 8292.8410 6.341(-) -.152(-) 6833.7912 6.431(-) -.197(-) 8293.7806 6.452(11) -.173(16) 6867.7748 6.402(-) -.133(-) 8313.7616 6.439(-) -.181(21) 7124.9447 6.407(-) -.186(-) 8328.7042 - -.189(-) 7183.8243 6.407(-) -.174(-) 8348.6847 6.430(-) -.185(-) 7212.7448 6.384(-) -.147(-) 8350.6694 6.447(10) -.105(23) 7232.7124 6.403(-) -.146(-) 8364.6573 6.439(-) -.154(-) 7259.6546 6.392(-) -.118(-) 8597.9493 6.365(17) -.124(6) 7878.9333 6.379(4) -.140(20) 8598.9188 6.386(15) -.145(-) 7881.8076 6.374(1) -.132(4) 8621.8215 6.394(-) -.191(20) 7896.8132 6.383(18) -.109(9) 8635.8917 6.359(16) -.147(4) 7897.8014 6.426(6) -.154(13) 8635.8931 6.364(-) -.179(-) 7915.7646 - -.123(-) 8636.8153 6.358(13) -.164(-) 7916.8319 6.372(-) -.119(-) 8637.8028 6.360(-) -.162(19) 7917.7764 6.430(-) -.160(4) 8674.8090 6.369(21) -.158(1) 7952.6750 6.350(-) -.097(10) 8679.8101 6.359(-) -.196(-) 7965.7139 6.410(19) -.125(-) 8677.7667 6.383(4) -.149(1) 7985.6403 6.402(16) -.142(-) 8695.6993 6.384(2) -.160(19) 7986.6694 6.409(14) -.150(-) 8711.6576 6.390(-) -.140(4) 8002.6313 6.360(-) -.190(-) 8722.6410 6.378(1) -.160(1) 8176.9660 6.382(9) -.123(29) 8723.6368 6.385(2) -.144(14) 8205.8896 6.390(5) -.131(24) 8724.6417 6.393(1) -.166(4) 8225.8979 6.411(11) -.123(2) ELAINE M. HALBEDEL Corralitos Observatory P.O. Box 16314 Las Cruces, NM U.S.A. 88004 References: Abt., H. A. & Biggs, E. S., 1972, Bibliography of Stellar Radial Velocities (New York: Latham) [BIBCODE 1972bsrv.book.....A ] Buscombe, W., 1970, MNRAS, 148, 75 [BIBCODE 1970MNRAS.148...75B ] Conti, P. S., 1974, ApJ, 187, 539 [BIBCODE 1974ApJ...187..539C ] Conti, P. S., Leep, E. M., & Lorre, J. J., 1977, ApJ, 214, 759 [BIBCODE 1977ApJ...214..759C ] Jaschek, C., Jaschek, M., & Kucewicz, B., 1964, ZfAp, 59, 108 [BIBCODE 1964ZA.....59..108J ] Percy, J. R., 1987, in Physics of Be Stars, ed. A. Slettebak & T. P. Snow (Cambridge: Cambridge Univ. Press) Peterson, D. M. & Scholz, M., 1971, ApJ, 163, 51 [BIBCODE 1971ApJ...163...51P ] Slettebak, A., 1956, ApJ, 124, 173 [BIBCODE 1956ApJ...124..173S ] Zinn, R. J., 1970, ApJ, 162, 909 [BIBCODE 1970ApJ...162..909Z ]