Balmer line

Most of the stars of our sample have been selected from the H K BPS survey ( Beers, Preston Shectman [1], First, stars were selected from the weakness of their H H lines for the Balmer lines intensity on prism-objective Schmidt telescope plates. Then, the candidate stars were observed with a slit spectrograph in order to have a quantitative estimate of their metallicity. The survey has operated on about 7000 square degrees of the sky, mostly on the polar caps. It has supply a vast amount of metal-poor stars, with hundreds of them more metal-poor than the most metal-poor globular clusters. We selected from this sample stars with metallicities estimated to have [Fe/H] < -2.7. The actual metallicity histogram is given for the sample on fig. 1. 

On a PDA detector, using the spectral energy output from the deuterium lamp, one can also use the sharp calibration lines at 486 and 656nm (Balmer line). 

Balmer lines spect Lines in the hydrogen spectrum, produced by transitions between = 2 and > 2 levels either in emission or in absorption here is the principal quantum number. bobmor, lTnz ... 

Balmer series spect The set of Balmer lines. bobmor sir-ez ... 

When it became possible to obtain the spectrum of one of these objects in 1937, it was obvious that they looked like nothing yet known. All supernovas discovered in subsequent years displayed a remarkable uniformity, both in intensity and in behaviour. This observation led Zwicky to suggest that they might be used as standard candles to calibrate distance across the cosmos. But then, in 1940, a supernova with a completely different spectrum was discovered. It soon became clear that there were at least two classes of supernova, distinguished by their spectral features. It was the presence or absence of the Balmer lines of hydrogen near the maximum of the light curve that provided this classification. 

The R CrB variables and related hydrogen-deficient carbon stars show strong carbon features (except CH) and very weak Balmer lines. The R CrB stars are surrounded by circumstellar dust shells, and continue to eject puffs of new circumstellar material on time scales of a month or two mass loss rates of order 10- Mo yr- are reported by Walker 1986. The compositions of the R CrB stars and hydrogen-deficient carbon stars are were compiled by Lambert (1986). Hydrogen is extremely deficient in both groups (H/He 10 J-10 °), and C/Fe is enriched by typically an order of magnitude over the solar ratio. C/0 is typically 2 (more than is measured in the AGB stars, and [N/Fe] 1. R CrB itself contains a strong lithium... 

The optical spectra for the first 4 days while the supernova was rising to an initial local maximum were rather simple, showing broad Balmer lines. After two days (circa February 25), the spectrum showed He I A.5876 but no sign of Ca H and K or the IR triplet, due, presumably, to the high temperature that ionizes Ca II. After four days (circa... 

The velocities of the absorption minima of the Balmer lines are basically set by the density at a given velocity. The absorption minima are essentially independent of the luminosity of the model for reasonable values of the luminosity. At higher luminosity and temperature more hydrogen is ionized at lower radii and hence velocities, but more of the remaining hydrogen is excited, and these two effects are found to offset one another. Several aspects of the spectra do change significantly with the luminosity. One is the... 

In still other experiments, selective excitation of the H2+ molecular ion in collisions with rare gases at 0.1 to 10 keV was studied by determining the polarizations of the Balmer-a and Balmer-/ lines resulting from the dissociative collision.293... 

While the Bohr atom is of no help in understanding the splittings of the Balmer lines, using it we can calculate the field at which a state is ionized by an electric field. Consider a H atom with its nucleus at the origin in the presence of an electric field in the z direction. The potential experienced by an electron moving along the z axis is given by... 

As the speed of the impacting electrons is still further increased no new processes are observed by the positive ray or clean-up methods. Some experimenters have observed additional ionization setting in at about thirty volts. Of more importance, however, are the results of Franck and Blackett, who showed that the emission of Balmer lines was a primary result of impact of thirty volt or higher speed electrons. In other words, they showed dissociation may occur with excitation of one (or perhaps both) atoms. 

Fig. 1. Numerical values for the coefficients

But experiments to resolve the fine structure of the Balmer lines were difficult as you all know, resolution was impeded by the Doppler broadening of components. So ionized helium comes into the picture, because, as Sommerfeld s formula predicted, fine structure intervals are a function of (aZ)2, so in helium they are of order four times as wide as in hydrogen and one has more chance of resolving the Doppler-broadened lines. So PASCHEN [40], in 1916. undertook an extensive study of the He+ lines and in particular, 4686 A (n = 4->3). Fine structure, indeed, was found and matched against Sommerfeld s formula. The measurements were used to determine a value of a. But the structure did not really match the theory in that the quantum numbers bore no imprint of electron spin, so even the orbital properties - which dominated the intensity rules based on a correspondence with classical radiation theory - were wrongly associated with components, and the value of a derived from this first study was later abandoned. 

Simultaneously the intensity of the atomic Balmer lines (in this case D7) increases by nearly a factor of two. Thus, in the presence of molecules it obviously turns out that corrections to the estimated hydrogen flux may be required in such a form that the atomic S/XB (which is about 15 for densities 1018-1019 m 3 and temperatures above 15 eV) is replaced by an effective one, which is determined by the molecular deuterium flux rd-> ... 

The factor r] accounts for the number of emitted Balmer-a photons per molecule, which involves the type of dissociation process, t] = 1 holds for dissociative excitation with the products D°(n = 3)+D° (Is), i.e., only one atom will directly emit Balmer-a radiation whereas the other is set free already as a proton. In the worst case of a pure molecular flux the total deuterium flux would be underestimated by a factor of 2 by determining it from the Balmer-line emissions solely. More details concerning the energies of the dissociated atoms and accompanying heating mechanisms can be found in [46] and below. 

Early spectroscopic observations showed the Balmer lines, the secondary spectrum, and some of the stronger lines of mercury. The latter gradually disappeared after liquid air had been kept on the traps continually for over two weeks and they had been too weak to observe for several weeks before the final photographs were taken. Incidentally, it is interesting that the relative concentration of H dropped off considerably at the same time, as might be expected from the cessation of collisions of the second... 

There was one additional shortcoming with Bohr s model. In 1891, Albert Ahraham Michelson discovered that the first Balmer line, called H , with a wavelength of 6,562 A, was not one bright line, but two lines with almost equal wavelengths, very close together. Their discovery was made possible by the highly refined optical method Michelson applied to his observation of the Balmer spectral lines. This doublet structure of the Balmer line could not be accounted for by Bohr s model. 

Rate constants for the quenching of Balmer line emis- 678 sion by H2O following the pulse radiolysis of water vapour... 

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