He^{3} in Several Magnetic Stars

Abstract

view Abstract Citations (8) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS He^{3} in Several Magnetic Stars Zirin, Harold Abstract The presence of He3 in 3 Cen A, ~ UMa, and ~y1 Vir is indicated by the shift in wavelength of the line He i X10830. In several other stars no X10830 is observed. Sargent and Jugaku (1961) found that the neutral helium lines in 3 Cen A correspond essentially to wavelengths expected for the isotope He3. Because the isotope shifts in the helium lines are small in the visual region (only XX4922 and 6878 have substantial z~X/X shifts), I attempted, at Sargent's suggestion, to measure the shift in the X10830 line in various magnetic stars. According to Fred et i1. (1951), the He3 shift in X10830 is 1.15 A, a value about twice as large as that for the lines in the visual region, although ~X/X is the same. In any event, X10830, being such a strong line, should be more easily detectable in A stars than is the X5876 line. As part of our program of chromospheric studies of the X10830 line (Vaughan and Zirin 1968), I obtained spectrograms of a number of peculiar A stars with the 72-inch camera of the coudé spectrograph of the Hale telescope, using a single-stage RCA image converter kindly lent by the Carnegie image-tube committee. The dispersion is 17 A mm-'; a 1-hour exposure is required for stars of infrared magnitude, I = 4. In the spectrograms taken before plate No. 10835, the helium doublet (1 A separation, 8:1 ratio) is barely separated. For plates after No. 10835, a transfer lens consisting of two Canon f/0.9, 50-mm lenses, face to face, was used. This made it possible to reach a magnitude of I = 5 in 1 hour; the resolution then improved to 0.5 A. Uncertainty is caused by the presence of an atmospheric line at 10832.14 A, the weakness of the helium line, and the low contrast of image-tube spectra. Of course, if no He i line is observed, we cannot comment on the existence of He3. Table 1 lists the magnetic stars observed, the plate numbers, the measured and cor- rected wavelengths, the line strength on a scale O-5, and a conclusion. Figure 1 (Plate L7) shows spectra of E UMa and 3 Cen A, along with the X10830.31 comparison line. In 3 Cen A, a broad line is observed at 10830.8 A; the velocity correction of 0.5 A places the initial stellar wavelength at 10831.3 A, close to the predicted He3 position. Aside from the fact that the uncorrected wavelength does not agree with the atmospheric line, the general weakness of the other atmospheric lines makes it unlikely that the line seen is only X10832.14. In a2 CVn, a weak line may be present at the He3 position. In `y' Vir, a broad complex line reaches from 10830 to 10831 A; hence both He4 and He3 may be present. This star has a radial-velocity shift of - 1.74 A, so that there is no confusion with the atmospheric line. In a And (plate No. 8993), radial velocity shifts the He3 line to the red; a broad feature appears on the blue portion of the atmospheric line. However, plate No. 10835, taken December 11, 1967, shows no helium line. In UMa, we find a broad line at 10833.7 A. The radial-velocity correction listed is +0.7; however, the strongest line observed in this spectrum, the Si i line at 10750.26 A, would require a correction of - 0.87 A. Adopting this correction, we get a wavelength * This work was supported in part by NASA grant NGR 05-002-034 Publication: The Astrophysical Journal Pub Date: June 1968 DOI: 10.1086/180206 Bibcode: 1968ApJ...152L.177Z full text sources ADS | data products SIMBAD (8)