The Ratio of Neutral Hydrogen to Neutral Helium in the Local Interstellar Medium.
Abstract
I describe the results from a sounding rocket borne EUV spectrometer that I designed and built. This instrument operated from 400-1150A with a spectral resolution of ~15A. The instrument effective area was ~1 cm^2 . The instrument was successfully launched, and observed the nearby DA white dwarf G191-B2B. From this observation, I have determined that the stellar effective temperature is 61,000{+6000}atop {-4000}K, and the ratio of helium to hydrogen in the stellar photosphere is 1.0{+2.2} atop{-0.68} times 10^ {-4}. Additionally, the neutral column densities of helium and hydrogen were measured to the star. The neutral helium column density was determined from the first observation of the interstellar absorption edge at 504A. The ratio of neutral helium to neutral hydrogen constrains the mean ionization of the warm gas along the line of sight to G191-B2B. The fractional ionization of hydrogen (H II/H) is <20%, unless significant helium ionization is present as well. The scenario where the fractional ionization of hydrogen is high (H II/H >40%) and the helium is neutral is ruled out with 99% certainty. This result is consistent with some recent theoretical calculations. Using these results, a self-consistent model of the local interstellar medium along the line of sight to G191-B2B is developed. In addition, an unexpected emission feature at 584A was detected in this observation with a high level of significance. Possible sources of this emission are examined, including the companion K dwarf G191-B2A, and an emission nebula near or around G191-B2B.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1989
- Bibcode:
- 1989PhDT.........6G
- Keywords:
-
- Physics: Astronomy and Astrophysics;
- Extreme Ultraviolet Radiation;
- Helium;
- Hydrogen;
- Interstellar Matter;
- Neutral Gases;
- Stellar Temperature;
- Ultraviolet Spectrometers;
- Emission Spectra;
- Gas Ionization;
- Nebulae;
- Photosphere;
- Sounding Rockets;
- Spectral Resolution;
- Stellar Spectra;
- Astrophysics