Engineering topics
Publications and source records attributed to Hall, Douglas S..
Differential B-band photometry of BV Dra and BW Dra, obtained in 1965, is presented. Times of primary and secondary minima are derived and combined with published times for a period study. Period variations are found in both binaries and magnetic cycles are proposed as an explanation. The cycle length is 19 years in BV Dra and 8 years in BW Dra.
Times of minimum derived from photometry obtained in 1963, 1967, 1978, and 1979 are presented. With these and previously published times, the period is studied. A constant period increase (quadratic ephemeris) represents most of the times but there was a period decrease in 1934 and possibly in 1984. A 50-year magnetic cycle is discussed.
The photometric variability of the Ap star HD 10783 = UZ Psc is discussed. New UBV photometry, obtained between late 1965 and early 1969, is presented and it is combined with existing published photometry to derive an improved ephemeris for times of maximum brightness: 2439758.00 + 4d.1328 n. It is concluded that the results are not very sensitive to the small shifts applied to the blue photometry.
The amplitude of the ellipticity effect, the mass function, and the V sin i in ten long-period RS CVn SB1 binaries are used to compute limits on the masses of the two stars and the radius of the primary: zeta And, UV CrB, V1764 Cyg, V826 Her, V350 Lac, GX Lib, V1197 Ori, AP Psc, 33 Psc, and EE UMa. Explicit masses and radii are computed for three SB2 systems: BL CVn, V1817 Cyg, and TZ Tri. The primary in several is found to fill 95 percent or more of its Roche lobe. The two minima produced by the ellipticity effect are unequal in depth, with the effect largest when i is near 90 deg and the primary nearly fills its Roche lobe. The greatest inequality found, in UV CrB, was 0.08 mag.
An analysis of 11 yr of photometry of HR 1362 = EK Eri has shown a well-established photometric period of 335 days. This confirms an earlier period determination of about 310 days from 3 yr of APT data and is consistent with a new v sin i determination of 2 + or - 2 km/s. Recent Ca II H and K observations show moderately strong H and K emission lines at a flux level of log F prime (K) of about 6.5 ergs sq m/s. If the photometric period is interpreted as the rotation period, this surface flux is more than one order of magnitude larger than what can be expected from empirical activity versus rotation relationships. The spectrum and the U-B and B-V colors are consistent with a single G8 III-IV spectral classification, while the V-R and V-I values indicate a small color excess, typical of chromospherically active stars.
Differential UBV photometry of V478 Lyrae from 1980 to 1988 is given and analyzed as 22 separate light curves, each spanning an average of a dozen rotation cycles. It is shown that spots on V478 Lyr appear to have lifetimes on the order of several months to a year. The amplitude of the light loss produced by a spot can change by a factor of 2 within 20 days. In the only four determinate cases, a spot came into existence at one of the two conjunctions, that is, in the middle of the hemisphere facing (or opposing) the companion star. This finding provides additional support for the picture of a four-sector longitudinal structure, aligned with the major axis of the binary, which determines where magnetically active regions develop.
Differential UBVRI photometry of the double-lined BY Dra system HD 80715 (K3 V + K3 V) obtained in December 1987 is presented. The star is found to be a variable with a full amplitude of 0.06 mag in V and a period similar or equal to the orbital period of 3.804 days. The mechanism of the variability is interpreted as rotational modulation due to dark starspots. In an attempt to detect chromospheric activity, high-resolution CCD spectra were obtained at Ca II H and K and at Fe I 6430 A and Ca I 6439 A, the photospheric lines normally used for Doppler imaging. HD 80715 shows double H and K emission features at a constant flux level for each component.
BM Camelopardalis (=12 Cam) is a chromospherically active binary star with a relatively large orbital eccentricity. Systems with large eccentricities usually rotate pseudosynchronously. However, BM Cam has been a puzzle since its observed rotation rate is virtually equal to its orbital period indicating synchronization. All available photometry data for BM Cam have been collected and analyzed. Two models of modulated ellipticity effect are proposed, one based on equilibrium tidal deformation of the primary star and the other on a dynamical tidal effect. When the starspot variability is removed from the data, the dynamical tidal model was the better approximation to the real physical situation. The analysis indicates that BM Cam is not rotating pseudosynchronously but rotating in virtual synchronism after all.