Advertisement

The Helium Abundance in the HII Region DR21

  • A. P. Tsivilev
Part of the Astrophysics and Space Science Library book series (ASSL, volume 163)

Abstract

The 36. 5-GHz (H, He)56α and 22. 4-GHz (H. HE)66α radio recombination lines have been observed in the DR21 with RT22(FIAN). These data combined with the other show that the measured relative abundance y+ of ionized helium appears to increase with the angular beamwidth, ϕA, peaking at ϕA = 2‘–2. 5‘, and then to decrease as ϕA further increases what is more complicated than in previous papers. This behaviour is interpreted as a blister-type model nebula which implies the high actual helium abundance y0 =(26±11)% in the DR21 and its expansion rate from 5km s-1 to 20km s-1 by approaching the observed increasing of the hydrogen radial velocity with the frequency decreasing. Discussion has concerned slightly the explanation possibilities of the high helium abundance too.

Keywords

Angular Resolution Helium Abundance Radio Recombination Line Measured Relative Abundance Explanation Possibility 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Barcia A., Gomez-Gonzalez J., Lockman F.E.,and Planesas P. (1985) ‘Radio recombination lines from the galactic plane in Cygnus’ Astr. Ap. 147, 237–240.ADSGoogle Scholar
  2. Churchwell E. and Mezger P. G., Huchtmeier W. (1974) ‘Helium abundance in galactic HII regions’, Astr. Ap. 32, 283–308.ADSGoogle Scholar
  3. Churchwell E.,Smith L.E., Mathis J., Mezger P.C., and Huchtmeier W. (1978) ‘Gradient of НII region electron temperatures and helium abundance in the Galaxy’, Astr.Ap. 70, 719–732.ADSGoogle Scholar
  4. Copetti M. V. F. and Bica L. D. (1983) ‘The volumes of He+ and H+ in HI I regions: the Orion Nebula’, Ap. Space Sci. 91, 381–394.ADSCrossRefGoogle Scholar
  5. Dent W. A. (1972) ‘A flux-density scale for microwave frequecies’ Ap. J. 177, 93–99.ADSCrossRefGoogle Scholar
  6. Dickel H.R., Goss W. M., Rots A. H., and Blount H. M. (1986) ‘VLA observations of the 6 cm and 2 cm lines of H2CO in the direction of DR21’, Astr.Ap. 162, 221–231.ADSGoogle Scholar
  7. Dickel H.R., Lubenow A. F., Goss W. M., Forster J. R., and Rots A. H.(1983) ‘VLA observations of H2CO in DR21’, Astr. Ap. 120, 74–84.ADSGoogle Scholar
  8. Goudis С (1976) ‘The radio and infrared spectrum of DR21’, Ap. Space Sci. 39, L1–L6.ADSCrossRefGoogle Scholar
  9. Guilloteau S., Wilson T. L., Mart in R.N., Batria W., and Pauls T. A. (1983) ‘Ammonia toward DR21: a weak maser in ortho-NH3?’, Astr. Ap. 124, 322–325.ADSGoogle Scholar
  10. Harris S.(1973) ‘5 GHz observations of small-scale structure in DR21’, M. N.R. A.S. 162, 5p–10p.ADSGoogle Scholar
  11. Lichten S. M., Rodrigues L.F.,and Chaisson E.J. (1979) ‘A hydrogen and helium radio recombination-line survey of galactic HII regions at 10 GHz’, Ap. J. 229, 524–532.ADSCrossRefGoogle Scholar
  12. Lockman F.J. and Brown R. L.(1982) ‘A survey of ionized helium in galactic HII regions’, Ap. J. 259, 595-606.ADSCrossRefGoogle Scholar
  13. Matsumoto T.,Hayakawa S., Matsuo H., Murakami H., and Sato S. (1988) ‘The submillimeter spectrum of the cosmic background radiation’, Ap. J. 329, 567–571.ADSCrossRefGoogle Scholar
  14. Pankonin V., Thomasson P., and Barsuhn J.(1977) ‘A survey of radio recombination lines from HI regions and associated HII regions’, Astr. Ap. 54, 335–344.ADSGoogle Scholar
  15. Pitault A.(1980) ‘The “helium problem” in the source DR21’, Astr. Ap. 91, 374–375.ADSGoogle Scholar
  16. Roelfsema P. R.(1987) ‘Radio recombination line observations of HII regions and planetary nebulae’, Ph.D. thesis. University of Groningen.Google Scholar
  17. Roelfsema P. R., Goss W. M., Whiteoak J. T., Gardner F.F., and Pankonin., (1987) ‘VLA hydrogen and helium 76a radio recombination line observations of Sgr B2’, Astr. Ap. 175, 219–230.ADSGoogle Scholar
  18. Ryle M. and Downes D.(1967) ‘High-resolution radio observations of an intense HII region in Cygnus X’, Ap. J. 148, L17–L21(345–349).ADSCrossRefGoogle Scholar
  19. Smirnov G.T.(1985) ‘Electron density in the HII regions DR21 and W3 from Stark broadened radio recombination lines’, Sov. Astron. Lett. 11(1), 7–11.ADSGoogle Scholar
  20. Thum C., Mezger P. G., and Pankonin V.(1980) ‘The helium abundance of galactic HII regions’, Astr. Ap. 87, 269–275.ADSGoogle Scholar
  21. Tsivilev A. P., Ershov A. A., Smirnov G.T.,and Sorochenko R. L. (1986) ‘The Orion A helium abundance’, Sov. Astron. Lett. 12, 355–359.ADSGoogle Scholar
  22. Vallee J. P. (1987) ‘The neutral interface adjoining the HII region DR21’, Ap. Space Sci. 129, 339–351.ADSCrossRefGoogle Scholar
  23. Yoshioka S. and Ikeuchi S.(1987) ‘On the origin of possible deviation from the blackbody spectrum of the cosmic microwave background radiation. Inverse Compton hypothesis based upon the explosion scenario’, Ap. J. 323, L7–L11.ADSCrossRefGoogle Scholar
  24. Zel’dovich J.B., Novikov I. D. (1975) ‘The structure and evolution of Universe’, “Science” Publisher, Moscow.Google Scholar

Copyright information

© Kluwer Academic Publishers 1990

Authors and Affiliations

  • A. P. Tsivilev
    • 1
  1. 1.P.N. Lebedev Physical InstituteAcademy of Sciences of the USSRMoscowUSSR

Personalised recommendations