Primordial 4He abundance: a determination based on the largest sample of H II regions with a methodology tested on model H II regions

Y. I. Izotov; G. Stasińska; N. G. Guseva

doi:10.1051/0004-6361/201220782

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Volume 558 (October 2013)

A&A, 558 (2013) A57

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Table 1

Input parameters for the grid of the photoionised H ii region models.

Parameter	Value

log Q(H)^a	52, 53, 54
Starburst age, Myr	1.0, 2.0, 3.5, 4.0
N _e ^b	10, 10², 10³, var
log f^c	−0.5, −1.0, −1.5, −2.0
Oxygen abundance 12+log O/H	7.3, 7.6, 8.0, 8.3
⁴He mass fraction Y	0.254

Notes.

^(a)

Log of the number of ionising photons in units s^-1.

^(b)

The electron number density in units cm^-3. The electron number density in models labelled “var” is varied along the radius according to Eq. (1).

^(c)

Log of volume-filling factor.

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