O. G. Taranova

Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined H

Context. Recent results strongly challenge the canonical picture of massive star winds: various evidence indicates that currently accepted mass-loss rates, u M, may need to be revised downwards, by factors extending to one magnitude or even more. This is because the most commonly used mass-loss diagnostics are affected by “clumping” (small-scale density inhomogeneities), influencing our interpretation of observed spectra and fluxes. Aims. Such downward revisions would have dramatic consequences for the evolution of, and feedback from, massive stars, and thus robust determinations of the clumping properties and mass-loss rates are urgently needed. We present a first attempt concerning this objective, by means of constraining the radial stratification of the so-called clumping factor. Methods. To this end, we have analyzed a sample of 19 Galactic O-type supergiants/giants, by combining our own and archival data for Hα, IR, mm and radio fluxes, and using approximate methods, calibrated to more sophisticated models. Clumping has been included into our analysis in the “conventional” way, by assuming the inter-clump matter to be void. Because (almost) all our diagnostics depends on the square of density, we cannot derive absolute clumping factors, but only factors normalized to a certain minimum. Results. This minimum was usually found to be located in the outermost, radio-emitting region, i.e., the radio mass-loss rates are the lowest ones, compared to u M derived from Hα and the IR. The radio rates agree well with those predicted by theory, but are only upper limits, due to unknown clumping in the outer wind. Hα turned out to be a useful tool to derive the clumping properties inside r < 3 ... 5R� . Our most important result concerns a (physical) difference between denser and thinner winds: for denser winds, the innermost region is more strongly clumped than the outermost one (with a normalized clumping factor of 4.1 ± 1.4), whereas thinner winds have similar clumping properties in the inner and outer regions. Conclusions. Our findings are compared with theoretical predictions, and the implications are discussed in detail, by assuming different scenarios regarding the still unknown clumping properties of the outer wind.

\mathsf{_{\alpha}}

Broad-band UBVRJHKLM photometry of the classical symbiotic binary system Z And obtained at the time of the light maximum of its small-amplitude brightening at the end of 2002 as well as at four epochs before and after this brightening is analysed. The parameters of the symbiotic nebula were obtained from its spectral energy distribution at the epochs of the quiescent state of the system using the energy distribution of the stellar components derived in a previous investigation. The continuum analysis based on the data during the active phase shows that the energy distribution of the compact secondary was changed very little - it remained a hot object emitting mostly in the UV, as in the quiescent state. On the basis of this result the brightening is supposed to be due to a slow expansion to about two times its quiescent size. The possibility of hydrogen burning at the surface of the secondary during quiescence is discussed.

, IR and radio analysis

We discuss our JHKLM photometry for nine carbon Mira stars, eighteen carbon semiregular variables, and two oxygen Mira stars. For fourteen carbon stars, we present and analyze their infrared light and color curves. For all of the observed objects, we have estimated the optical depths of the circumstellar dust envelopes, the angular diameters of the stars, and their temperatures.

Broad-band multicolour observations of the symbiotic binary Z And during quiescence and its activity at the end of 2002

AbstractThe photometric JHKLM observations of the symbiotic novae V1016 Cyg and HM Sge in 1978–1999 are presented. Parameters of the cool stars themselves and the dust envelopes are estimated. The periods of 470±5 days (for V1016 Cyg) and 535±5 days (for HM Sge) are reliably determined from the entire set of our photometric J data for V1016 Cyg and HM Sge. In addition, monotonic light and color variations are observed on a time scale of several thousand days, with the increase in infrared brightness occurring with the simultaneous decrease in infrared color indices; i.e., the dust envelopes in which both components of the systems were embedded before the outburst of their hot sources in 1964 and 1975, respectively, had continued to disperse until late 1999. The amplitudes of these variations for HM Sge are almost twice those for V1016 Cyg. For HM Sge, the dust envelope reached a maximum density near JD 2447500 and then began to disperse. In the case of V1016 Cyg, a maximum density of the dust envelope was probably reached near JD 2444800, and its dispersal has been continuing for about 20 years. Thus, in both symbiotic novae, their dust envelopes reached a maximum density approximately eight years after the outburst of the hot component and then began to disperse. An analysis of the color-magnitude (J–K, J) diagram reveals that grains in the dust envelopes of V1016 Cyg and HM Sge are similar in their optical properties to impure silicates. The observed [J–K, K–L] color variations for the symbiotic novae under study can be explained in terms of the simple model we chose by variations in the Miras photospheric temperature from 2400 to 3000 K and in the dust-envelope optical depth from 1 to 3 at a wavelength of 1.25 µm for a constant grain temperature. The observed J–K and K–L color indices for both symbiotic novae, while decreasing, tend to the values typical of Miras. The dust envelopes of both symbiotic novae are optically thick. The dust envelope around HM Sge is, on the average, twice as dense as that around V1016 Cyg; the Mira in V1016 Cyg is slightly cooler (~2800–2900 K) than that in HM Sge (~2600–2700 K). The dust-envelope density decreases as the Miras temperature increases. The absolute bolometric magnitudes are

Infrared photometry of the symbiotic novae V1016 Cyg and HM Sge in 1978–1999

- 5\mathop .\limits^m 1 \pm 0\mathop .\limits^m 15

Unusual infrared fading of CH Cygni in 2006

for V 1016 Cyg and

Parameters of the dust envelope of the symbiotic star CH Cygni

5\mathop .\limits^m 27 \pm 0\mathop .\limits^m 17