ON THE QUESTION OF THE HELIUM ABUNDANCE IN ORION A MEASURED BY RADIO RECOMBINATION LINES. AND THE PRIMORDIAL HELIUM ABUNDANCE

Автор(и)

  • A. P. Tsivilev Pushchino Radio Astronomy Observatory of Lebedev Physical Institute RAS, Russian Federation

DOI:

https://doi.org/10.18524/1810-4215.2020.33.216303

Ключові слова:

Cosmology, Radio astronomy, HII regions, radio recombination lines

Анотація

Recombination radio lines (RRLs)
of hydrogen (H), helium (He-4), and carbon (C) are
a powerful tool for studying the interstellar medium
(ISM) in space. The RRLs observations allow to obtain
the physical parameters of regions of ionized hydrogen
(HII regions) as well as of the photo-dissociation
regions; and to estimate the effective temperature
of stars that ionize the HII region. There is also an
important cosmological task for RRL – measuring
Primordial helium abundance produced at the stage of
Primordial nucleosynthesis of the Universe. It turned
out that the Orion A nebula is an interesting object
for the latter task. At the time, the recombination
radio lines observations of hydrogen, helium (H, He),
and carbon (C) at a number of positions in the Orion
A HII region were carry out with the RT22 radio
telescope (Pushchino) at wavelengths of 8 and 13 mm.
The relative helium abundance, y + = n(He + )/n(H + ),
in these positions was obtained. The behavior of
this value over the nebula showed that the helium
ionization zone is smaller than the hydrogen one with
different ratios for the core and halo. The location
where the maximum y + value is expected was also
determined. For the established ionization structure,
it means that the actual helium abundance in Orion
A, n(He)/n(H), will not be less than the maximum
y + value. This allows to estimate the limitations on
the Primordial helium abundance. In this work, new
H and He RRL observations were made at 13 mm in
the direction of the expected maximum of y + . RRLs
were observed in two transitions - 65α and 66α. It was
found that the maximum y + value is in the range of
10 − 12%. Hence, we can expect that the Primordial
helium abundance (Yp, the ratio He/H by mass)
lies in the range of ≈ 26.4 − 29%, and the number
of light neutrino-type particles during Primordial
nucleosynthesis may exceed the standard value. To
refine the result the work will be continue.

Посилання

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Опубліковано

2020-11-15

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Розділ

Cosmology, gravitation, astroparticle physics, high energy physics