Width Of He Research Articles

Line width observation of Heii 4686 � and Hei 4713 � in the chromosphere

Line profiles of He ii 4686 A and He i 4713 A from active regions in the chromosphere were observed during the total solar eclipse of February 16, 1980, with a grazing incidence objective grating spectrograph. The Doppler width of the He i triplet line of 4713 A increases with height and the average width is compatible with width of metallic and hydrogen lines, suggesting that the kinetic temperature of He i triplet emitting region is T ≦ 8000 K. This can only be explained by recombination after photo-ionization due to coronal UV radiation. The Doppler width of the Paschen α line of He ii 4686 is, without any correction for the separation of subcomponents of the line nor non-thermal velocity, 18.4 km s-1. This line width also shows a tendency to increase with height. After comparison with Doppler widths of He i 4713 and the EUV lines, and a necessary subtraction of non-thermal velocity, it is shown that this line is emitted in a 2 × 104 K temperature region, which again supports the view that this line is emitted through the recombination process after photoionization due to coronal XUV radiation below 228 A.

Chemical Composition of Wolf-Rayet Stars: Abundant Evidence for Anomalies

We have observed 45 WN stars in our Galaxy and the LMC with the IUE satellite at a resolution of 6 å. Examination of the spectra reveals surprising differences in line strength, in many cases at a given spectral subtype. This is similar to the description of the visual spectra given by Leep (1982). One generalization that can be made is that the equivalent width of He II λ1640 is correlated with the H/He ratio measured by Perry and Conti (1982), but not with spectral type.

The He II lines in the spectrum of zeta Puppis

Equivalents widths of He II lines in the series n=2,3,4 and 5 are compiled and compared with predictions from plane-parallel, static model atmospheres using a non-LTE theory of line formation. The agreement between observation and prediction for a (50,000,4.0) model atmosphere is good for the upper members of the n=3 and the n=5 series, but the two lines of the n=2 series which are observed and the upper members of the n=4 series (4$Yields$15,4$Yields$17, etc.) are stronger than predicted. Well-determined profiles of lines from the n=3 series indicate v sin i=200 km s$sup -1$. Profiles of the higher members of the n=4 series, however, do not match the predictions, the observed line cores being deeper than predicted. The n=4 level appears to be more overpopulated at moderate depths in the atmosphere than the non-LTE calculations with plane-parallel layers indicate. This may be due to an overlap of the H and He II lines in the even-even series caused by macroturbulent velocities of the hydrogen atoms and helium atoms. (AIP)

Model potential calculations of resonance states in three-electron atoms

A model potential method has been developed for one or more electrons outside a 2S core and applied to calculate the position and widths of autoionizing states. The phase shifts for e+He and e+Li+ scattering predicted by the model are in good agreement with other theories and with experiments while the widths of He-(1s 2s2 2S) resonance is 8 meV, also in agreement with experiment.

Observations of the he II λ10124 Line in O and of Stars

view Abstract Citations (40) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the he II λ10124 Line in O and of Stars Mihalas, Dimitri ; Lockwood, G. W. Abstract Observed equivalent widths of He ii X10124 in absorption-line 0 stars are found to be in agreement with non-LTE computations assuming no overlap of II and He ii lines, and in disagreement with the predictions of LTE and of non-LTE calculations assuming exact coincidence of even-even He ii lines and the corresponding hydrogen lines. it is therefore inferred that pumping of He ii transitions by H lines does not actually occur in the 0 stars. The discovery of the l0124 line in emission in Pup (0Sf) argues further in this direction; and with the often-cited selectivity of the He ii emission mechanism now much weakened, it is suggested that the causes of the emission must involve chromospheric phenomena. Analysis of source-sink terms in equivalent- two-level-atom source functions suggests trends that are compatible with the observed behavior of various lines. Publication: The Astrophysical Journal Pub Date: August 1972 DOI: 10.1086/151596 Bibcode: 1972ApJ...175..757M full text sources ADS | data products SIMBAD (12)

THE ABSOLUTE MAGNITUDE OF THE MAGNETIC STAR HR 1732

HR 1732 (=HD 34452) is classified as AOp in the Henry Draper Catalogue and is a Si-A 4200 peculiar A star. According to Babcock, the star very probably has a magnetic field.1 HR 1732 is the bluest known peculiar A star, with color indices B-V = 0*19 and U-B = 0*63,2 characteristic of a normal dwarf of spectral type around B4 V. The spectrum has presumably been classified as AOp in the HD catalog and as B9p by Osawa3 rather than B4p because, despite the blue color, the lines of helium are abnormally weak. Searle and Sargent have shown that the equivalent width of He i A 4471 is only 230 mÂ,4 about a factor of four lower than the value observed in a normal star having B V = 0*19. Searle and Sargent also showed that the hydrogen line profiles of HR 1732 are characteristic of a B4 V star rather than an A0 V star and concluded that the weakness of the He i lines is due to a deficiency in the abundance of helium by a factor greater than ten. This conclusion would be vitiated if it could be shown that the temperature in the line-forming layers is similar to that of an A0 or B9 star ; however, it should be noted that not all of the apparent abundance anomalies could be removed in this way. For example, the excess abundance of silicon, which amounts to a factor of about 100, is independent of the adopted atmospheric temperature within a very wide range. It is thus obviously important, to know if HR 1732 has the same absolute magnitude as a middle B-type dwarf, as is sug-