Primary eclipse

It is perhaps time that we utilized large telescopes and modern detector technology to study the abundance anomalies in close binaries during total primary eclipse, in a vigorous manner similar to that used, say, in extragalactic research. An up-to-date ephemeris would also be essential in such efforts. 

W Ursae Majoris stars can be understood as contact binary stars with a common envelope (Lucy 1968). They subdivide into two types The A-type are earlier in spectral class than about F5, are believed to have radiative envelopes, and associate primary (deeper) eclipse minimum with transit eclipse. The W-type have spectral classes later than F5, are believed to have convective envelopes, and associate primary minimum with occultation eclipse. Controversy has surrounded the explanation of W-type light curves. 

On the other hand, an ingenious proposal by Mullan (1975) apparently rescues the Lucy model. The Mullan proposal populates the primary component photosphere with starspots. These reduce the average surface brightness, thereby reduce the light loss at transit eclipse, and produce W-type light curves. This proposal has been received favorably by many specialists in the binary star field. 

U Cephei (V = 6.8-9.0, P = 2.493 d) is an eclipsing binary consisting of a B7V primary and a G8DI-IV secondary component. This binary is one of the semidetached Algol systems showing soft X-ray emission which is probably associated with a hot corona surrounding the secondary component (White and Marshall 1983). 

Several chlorinated 1,3-butadienes have been investigated in the gas phase with the primary interest in the influence of chlorination on the conformational properties. In the dichloro derivatives the C—Cl bond distances vary by about 2 pm, depending on the positions of the chlorine atoms. C—Cl bonds which eclipse a geminal C—H bond, such as in 23, are shortest [172.4(2) pm], C—Cl bonds which eclipse the central C—C bond in 24 are intermediate [173.1(3) pm] and C—Cl bonds which eclipse a C=C double bond are longest... 

With both nickel(O) and palladium(O) catalysts distal ring cleavage occurs. Only when nickel is used does efficient rearrangement of the primary intermediates take place. From the pal-ladium(0)-catalyzed reaction of (Z)-5, one diastereomer 7C is obtained selectively in high yield. As an explanation, minimal steric hindrance in the transition state can be assumed, as the C —O bond of the dioxolane is eclipsed only by the C —H bond but not the C —C bond of the cyclopentane moiety. 

Fig. 6. The mass-radius relation for both components in each of fifty eclipsing binary stars. The primaries and secondaries are shown as squares and circles (based on [19])...

Kerbel RS, Kobayashi H, Graham CH, et al. Analysis and significance of the malignant eclipse during the progression of primary cutaneous human melanomas. J Invest Dermatol Symp Proc. 1996 1 183-187. 

In a series of subsequent papers, Manset Bastien (2000b, 2001, 2003) investigated several young binaries and found a weak periodic modulation of the intrinsic linear polarization in a few of them. In most cases, however, the stochastic variability dominates and masks the periodic low-amplitude variations. In the eclipsing binary HAEBE star MWC 1080, the observed periodic variations can be due to the eccentricity of the orbit and/or the asymmetric configuration of CS or CB material. The maximum of the observed polarization coincides (as in the case of UXORs) with the eclipse of the primary in this system. 

The intramolecular insertion of alkylcarbenes appears to involve an eclipsed conformation the energy of which depends on the number of alkyl-alkyl interactions. As a consequence of steric effects, highly-branched alkylcarbenes display an apparent selectivity in favor of primary C-H bonds whereas less-branched structures insert preferentially into seconday C-H bonds . For the example given in scheme (42),... 

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