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The 1.5 Seyfert galaxy NGC 3516 presents a strong time variability in X-rays. We re-analyzed the 9 observations performed on October 2006 by XMM-Newton and Chandra in the 0.3 to 10 keV energy band. An acceptable model was found to the XMM-Newton data fitting EPIC-PN and RGS spectra simultaneously; later, this model was successfully applied to the contemporary Chandra high resolution data. The model consists of a continuum emission component (power law + blackbody) absorbed by four ionized components (warm absorbers), and ten narrow emission lines. Three absorbing components are warm, producing features only in the soft X-ray band. The fourth ionization component produces FeXXV and FeXXVI in the hard-energy band. We study the time response of the absorbing components to the well detect changes in the X-ray luminosity of this source, and find that the two components with the lower ionization state show clear opacity changes consistent with gas close to photoionization equilibrium. These changes are supported by the models and by differences in the spectral features among the nine observations. On the other hand, the two components with higher ionization state do not seem to respond to continuum variations. The response time of the ionized absorbers allows us to constrain their electron density and location. We find that one component (with intermediate ionization) must be located within the obscuring torus, at a distance 2.7×10 17 cm from the central engine. This outflowing component is likely originated in the accretion disk. The three remaining components are at distances larger than 10 16−17 cm. Two of the absorbing components in the soft X-rays have similar outflow velocities and locations. These components may be in pressure equilibrium, forming a multi-phase medium, if the gas has metallicity larger than the solar one (Z 5Z ). We also search for variations in the covering factor of the ionized absorbers (although partial covering is not required in our models). We find no correlation between the change in covering factor and the flux of the source. This, in connection with the observed variability of the ionized absorbers, suggests that the changes in flux are not produced by this material. If the variations are indeed produced by obscuring clumps of gas, these must be located much closer in to the central source.

Previous publications (1-7) have described some of our work on the chemical constituents of several Helenium species (Compositae), a genus of ca. 50 members (8) located mainly on the American continent. The biological and agricultural importance of this group of plants is well known inasmuch as several species are highly toxic and, when eaten by dairy cattle, impart a bitter taste to their milk (9). Helenanolides are the main constituents of this genus, although its classification by flavonoid chemistry has been proposed (10,11).Here we report that the sesquiterpene lactones carabrone {1] (12) and linifolin A [2] (13,14) were isolated from the extracts of aerial parts of a population of Helenium integrifolium (H.B.K.) Benth. & Hook. [Dougaldta integrifolia (H.B.K.)Cass.].Because of the various stereochemical arrangements and conformational distortions of the cycloheptane ring, and Xray analysis of linifolin A [2] was undertaken. Crystal data for 2 are listed in the Experimental Section. Figure 1 shows the computer generated drawings of two crystallographically independent molecules (A and B) existing in the solid state 'Contribution No.

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