Discussion

Abstract

BONIFACIO: Dr. Adelman, you said that a problem for spectral synthesis analysis is the lack of an ab initio method to fix microturbulence. I totally agree. You also said that you have some ideas of how to get around the problem. I would like to know what they are. ADELMAN: Scott Roby, Chuck Cowley and I have discussed the possibility of using some spectral windows which include a range of clean Fe I or Fe II lines, say. We could compute synthetic spectra with a range of microturbulences. For the correct microturbulence the ratio of the observed to synthetic spectra should be a straight line. Rotation and blends are additional problems. SHORE: (To Adelman) What about using absolute fluxes instead of normalized? ADELMAN: That is possible in principle for those stars whose parallaxes are known with sufficient accuracy. The synthetic spectrum calculations with Kurucz's program SYNTHE are done with appropriate units for such a comparison. SHORE: Vega is like f3 Pic in having a disk with circumstellar material in atomic form. Are any of the other "flat profile weak line" stars IRAS sources? Is it possible that these are post-disk evaporative systems? ADELMAN: I have not checked whether 50 Lib belongs to this class. The other four stars do not show IRAS excesses. I cannot propose any reason why these stars could not be post-disk evaporative systems. MICHAUD: (To Leckrone) Did you suggest that the abundance anomalies in some peculiar stars could be explained by the s-process only and that anomalies in some other peculiar stars could be explained by the r-process? Do you suggest that 204 Hg is produced by the s-process? LECKRONE: My plot of abundance enhancement in x Lup vs. atomic number for Z between 22 and 80 is preliminary and sketchy, yet it is more complete than any abundance information we have had before for a star of this temperature (normal or peculiar). It is perhaps premature to try to draw conclusions about trends, but I can't help noting some interesting features. There is a strong enhancement of the s-process elements Zr, Ru and Ba to abundance values similar to those observed in Ba and S stars (we do not yet have data for Mo or Nb). On the other hand, Pt, Au and Hg are not only the most strongly enhanced elements in terms of overall absolute abundance, they are present in \ Lup's photosphere only in their pure r-process isotopic form: 198 Pt, 197 Au and 204 Hg are all commonly considered to be produced only in a high neutron-flux environment. I am not aware of any previously defined astrophysical scenarios which would produce by nucleosynthesis this complex and bizarre combination of abundance enhancements. That is why I listed in my talk the possibility that diffusion models might produce results that, by coincidence, mimic nucleosynthesis of various kinds. In any event, diffusion theorists might profitably begin to work on elements that we are observing for the first time in very high resolution ultraviolet spectra. SHORE: (To Leckrone) You can predict, if the Ba-star-like abundances are due to Roche lob...