[Weltevreden SA (Dana)]

Good old Level 5 comes through again. I hadn't looked into the Stellar Spectra part of its huge list of goodies before. Thanks to your suggestion, I downloaded the abridged Gray survey. Alas, it's a little too abridged. Now I have to start saving the pennies to buy the original, which in SA will take a lot of pennies.

I have a couple of questions. First, I notice in Ch. 11 that the bottom three stars, Vega, A Leonis, and HD 23194, all have broad-sloped lines in the Hbeta at ~4100 and Hdelta ~4348 bands. These shoulders are not so pronounced in other bands in the same spectra. Only a few other spectra, e.g. 23585 in Ch. 18, exhibit this feature, one of the lines being the ~4100 Hbeta. Would broad shoulders like this indicate high rotation rates in the photospheres?

Since the pattern is not mimicked cross all the bands, I wonder if we have a case of magnetic field circulation in the stellar photospheres. In thick stellar atmospheres, an upper altitude (not core-to-surface) convection cycle can develop, which is analogous to the Earth's upper atmospheric weather pattern cycling from the equator to the poles and back. As with the earth and its weather, stars with polar circulation are affected by the Coriolis Force, which in stars produces magnetic turbulence akin to our earthly weather fronts. The effect would be greatest in mid-latitudes and least at the equator and poles. The effect on spectra could be variable line smearing.

Second, starting with the bottom 3 spectra in Ch. 24 and becoming notable by Ch. 26 HR 3577 and BK Vir, the gradual-rise, sharp-drop sawtooth effect I mentioned yesterday becomes very evident. This becomes even more evident in Ch. 29 with S and R Leonis (though HR 3577 and BK Vir are repeated as well). Other lines in the same spectra don't feature this sawtooth effect. Also, the sawtooth lines are the strongest of all lines in all the affected charts. This is a feature common to most M dwarfs. It can't be due to rotation because other lines don't repeat the pattern, but I can't figure out what might cause the behaviour.

In Ch. 31 V Cancri has a remarkably spiky, bright Hbeta emission line. This appears again in both spectra in Ch. 34. What would cause such a bright peak in Hbeta that isn't reflected in other spectra or even in other lines in these same spectra?

An observation: the He-rich subdwarf in C.33 is probably a He white dwarf dropping off the bottom of the Horiz Branch "Blue Tail" into true WD territory. These are unusual stars and there are not many of them. They are normal Horiz Branch blue stars, all of which have a core mass of 0.487 Msol, but have lost their entire H atmospheres and become almost totally He. They have no more heat input from nuclear processes (too cold for Carbon ignition) so cannot ascend the AGB branch and become planetary shedders like most pre-WDs. They are produced mostly in low-metallicity, and therefore low-opacity, GCs, which convert atmospheric mass into solar wind more easily. Compare this spectra with Barnard 26 in Ch. 32, which is a former Horiz Branch star that retained enough of a He atmosphere to evolve upward into the AGB, where it is now busily becoming a planetary-nebula parent.

Thanks again for all the links. I already have Kaler's 'Stars and Their Spectra', so the Gray is a welcome expansion into the territory. It's fun being introduced to new stuff.

=Dana in SA