COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2454 Konkoly Observatory Budapest 28 December 1983 HU ISSN 0374-0676 HD 104901B AN F-TYPE SUPERGIANT ECLIPSING BINARY HD 104901B has been classified F0Ib-II by Stephenson and Sanduleak (1973), F0Ib/III by Houk and Cowley (1975) and F0IIp by Gahm, Ahlin and Lindroos (1983). The star is 23 arcsec south of the B8Ib/II supergiant HD 104901A. The pair forms Dunlop 117 and the separation has remained fixed for over a century. Observations in 1978 and in 1980 indicated possible variability and the star was monitored for a week in 1981, but significant variation was not noted. However a long run of observations in 1982 and 1983 revealed a variation of 0.35 mag. The intermediate-band and beta observations are listed in Table I and a few (R,I) observations are in Table II. The adopted light elements, max = JD 2445065.0 + 106.6 days were used to compute the phases and the results are shown in Figure 1. A value of P = 53.3 days can not be entirely rejected without additional observations, although the distinct difference in width of the two minima makes the shorter period unlikely. The observations cover a span of 4 years so the periodicity is well established. The star is most likely an eclipsing binary. The components are probably near contact and the slight reddening, shown by (b-y), at both eclipses is normal for such systems. The behaviour of the beta index in Figure 1 is of some interest. There is obviously strong Hbeta emission at some phases and this is confirmed by the spectra taken by Gahm et al. (1983); Table I Intermediate band and Hbeta Observations of HD 104901B JD V b-y M1 C1 beta Phase 244 3637.660 7.67m 0.370m 0.050m 1.572m 2.593 0.610 3638.650 7.69 0.374 0.057 1.562 2.596 0.620 4305.720 7.76 0.381 0.057 1.522 2.608 0.878 4421.605 7.65 0.364 0.075 1.615 2.625 0.964 4670.700 8.00 0.374 0.060 1.470 2.576 0.300 4694.760 7.66 0.359 0.059 1.605 2.618 0.527 4695.795 7.66 0.363 0.063 1.604 2.614 0.537 4698.774 7.65 0.369 0.059 1.575 2.624 0.565 4702.785 7.66 0.370 0.063 1.545 2.604 0.61? 5019.854 7.62 0.364 0.054 1.568 2.624 0.576 5020.847 7.66 0.371 0.050 1.544 2.635 0.586 5025.788 7.76 0.373 0.059 1.540 2.588 0.632 5026.785 7.80 0.386 0.056 1.524 2.586 0.642 5032.750 7.97 0.391 0.074 1.472 2.598 0.697 5049.778 7.77 0.372 0.075 1.579 2.599 0.857 5050.740 7.75 0.373 0.073 1.539 2.601 0.866 5051.757 7.75 0.371 0.064 1.567 2.598 0.876 5057.726 7.64 0.354 0.070 1.593 2.600 0.930 5058.705 7.65 0.366 0.059 1.593 2.598 1.941 5068.667 7.66 0.365 0.059 1.545 2.588 0.035 5069.642 7.69 0.370 0.053 1.603 --- 0.044 5070.656 7.70 0.366 0.067 1.577 2.601 0.053 5083.698 7.84 0.385 0.076 1.426 2.592 0.175 5090.719 7.91 0.375 0.076 1.452 2.569 0.240 5091.670 7.93 0.382 0.068 1.499 2.553 0.250 5119.569 7.65 0.364 0.053 1.664 2.626 0.512 5150.521 7.84 0.374 0.092 1.500 --- 0.802 5151.510 7.84 0.369 0.073 1.550 2.635 0.812 5152.528 7.81 0.385 0.073 1.543 2.619 0.820 5153.503 7.80 0.370 0.079 1.539 2.607 0.830 5353.854 8.01 0.364 0.115 1.415 2.593 0.710 5366.847 7.83 0.380 0.072 1.498 2.599 0.832 5376.805 7.68 0.375 0.066 1.598 2.599 0.925 5377.812 7,72 0.365 0.057 1.629 2.605 0.934 5378.851 7.66 0.363 0.074 1.608 2.624 0.944 5382.858 7.67 0.347 0.069 1.623 2.587 0.982 5383.840 7.67 0.350 0.071 1.669 2.606 0.991 5384.833 7.67 0.355 0.072 1.636 2.606 0.000 5385.840 7.66 0.352 0.062 1.604 2.611 0.010 5386.809 7.67 0.360 0.065 1.591 2.601 0.019 5403.802 7,87 0.391 0.076 1.408 --- 0.178 5412.760 7.90 0.382 0.058 1.467 2.545 0.262 5429.667 7.75 0.380 0.064 1.610 --- 0.421 5430.625 7.73 0.382 0.060 1.613 2.582 0.430 5450.569 7.77 0.375 0.058 1.528 2.604 0.617 5451.587 7.76 0.378 0.054 1.523 2.584 0.626 5459.691 7.93 0.384 0.053 1.448 --- 0.703 5467.639 7.96 0.393 0.075 1.395 2.593 0.777 5493.542 7.69 0.353 0.080 1.687 2.587 0.020 [FIGURE 1] Figure 1 Light and color curves for HD 104901B Table II JD R R-I Phase 244 5074.697 7.54m 0.219 0.091 5089.680 7.63 0.237 0.232 5381.872 7.37 0.230 0.972 5411.680 7.61 0.244 0.252 "Halpha, Hbeta and Hdelta lines show distinct P Cygni profiles with a sharp edge between the emission and absorption components. The peak of the emission components is red-shifted by 90 km/sec relative to the stellar radial velocity as determined from the metallic lines." A striking feature of the beta index is the relative stability with phase and the behaviour of the Hbeta emission must be characterized by some regularity. The run of the beta values in the figure also supports the long period with the largest values of beta (smallest, or non-existent, emission) bracketing the second minimum and the strongest emission (smallest values of beta) occuring near the first minimum. The photometric parameters of the A component (HD 104901, CPD - 61d3933) are listed in Table III. Applying the reddening Table III Photometric Parameters for HD 104901A V b-y M1 C_1 beta Delta^a No. 7.43 0.204 0.021 0.790 2.630 2.5. 5.2 7 E(b-y) [u-b] M_v V_0 Mod. Sp.T.^b 0.240 0.913 -2.9 6.4 9.3 B8Ib/II ^a Mean difference in observed values of (b-y), M1, C1 and beta. ^b Houk and Cowley (1975). and modulus to HD 104901B gives (b-y) = 0.115 mag. and M=-2.7 mag at maximum light. A third component of Dun 117, 26 arcsec north of HD 104901A and apparently a background early type star, gives (V, b-y, M1, C1, beta) = (10.19, 0.136, 0.026, 0.219, 2.650) mag from 7 observations, yielding E(b-y)=0.220 mag, M_V= -2.15 mag and modulus of 11.4 mag. The 10 brightest members of NGC 4103, which is 5deg north, give E(b-y)=0.211 +- 0.015 (sigma) mag and a modulus of 11.45 +- 0.25 (sigma) mag from observations by Stetson (1981). NGC 4755 (kappa Cru cluster) is 6deg north-east with a reddening of E(b-y)=0.230 +- 0.20 (sigma) mag and modulus of 11.4 mag, derived from observations by Shobbrook (1983). The clusters may be part of the association Cru OBI at a distance of 1.9 kpc and containing Dun 117C. Although there is no reason to doubt the validity of the distance derived from HD 104901A, 0.72 kpc, or the assumption that the A and B components are at the same distance, it should be noted that a distance of 1.9 kpc for all three components is not contradicted by other available evidence. Values of M_V=-5.0 and -5.2 mag for components A and B, respectively, do not disagree with the wide luminosity class limits imposed by the available spectral classifications, quoted above. OLIN J. EGGEN Cerro Tololo Inter-American Observatory ^* Casilla 603, La Serena, Chile ^* Cerro Tololo Inter-American Observatory is operated by the Association of Universities for Research in Astronomy, Inc. under contract No. AST 78-27879 with the National Science Foundation. References: Gahm, G., Ahlin, P. and Lindroos, K. (1983). Astron. Astrophys. Suppl. 51, 143. [BIBCODE 1983A&AS...51..143G ] Houk, N. and Cowley, A. (1975). Michigan Spectral Catalogue, Vol. 1. [BIBCODE 1975mcts.book.....H ] Shobbrook, R.R. (1983). Mon. Not. Roy. Astron. Soc. (in press). [BIBCODE 1984MNRAS.206..273S ] Stephenson, B. and Sanduleak, N. (1973). Publ. Warner and Swasey Obs. 1, 3. Stetson, P. (1981). Astron. J. 86, 1500. [BIBCODE 1981AJ.....86.1500S ]