Talk:Stuart Pottasch

Untitled

Can someone add the following to this wikipedia article? Stuart Pottasch wrote this to me in november 2015.

"I have been thinking about the most important research I have done over the years and I have come up with the three following subjects.

The first concerns the abundance of iron in the sun. The situation at the time, which must have been 1958 to 1960 (a long time ago) was that the abundance of iron was found to have a surprisingly low value in the photosphere of the sun. Some people interpreted this as meaning that for some reason iron was removed from the photosphere whereas a few people thought the reason was that there was something wrong with the physical theory for determining the abundance. My contribution had to do with determining the abundances of elements in the solar corona, the outside regions of the solar atmosphere. Using newly determined spectra of the corona I was able to determine the abundances of about 8 elements found there and could show that iron was indeed a factor of about 10 higher in the corona as that found in the photosphere. After showing that i was unlikely that the abundances were changing as a function of position in the solar atmosphere, it was possible to conclude that for some reason the iron abundance in the photosphere was wrong, which was generally accepted in the years following.

The second subject concerns the abundances in planetary nebulae. these were rather difficult to obtain accurately because the spectra in the visual part of the spectrum contains only a limited number of ions. In addition the spectra must be corrected for absorption by material in the interstellar medium, which is often difficult to do. I was able to determine much more accurate abundances by using spectra which were made in satellites. These spectra not only contained many more ions, but they were made in regions of the spectra where correction by the interstellar medium is easier to determine (and also because it plays a much smaller role in these parts of the spectrum which are inaccessible from the surface of the earth). It is surprisingly simpler to obtain such spectra than you might expect.

The third subject also concerns planetary nebulae, involving the determination of both the temperature and the luminosity of the central star of the nebular, and comparing this with predictions made by theory. Here there are several problems which make this difficult. Some of it can be helped by spectra taken from satellites and correcting them properly. One big problem is due to the fact that the distances to planetary nebulae are poorly known. I have used various ways to determine distances but I obtain answers which differ rather considerably from theoretical determinations. This question is not solved at present, but there is a satellite flying now which will better determine distances to planetary nebulae. The results will be known in about 4 or 5 years. I hope that I am around to see them.

If you have any questions let me know." — Preceding unsigned comment added by 217.122.232.107 (talk) 21:25, 7 April 2018 (UTC)