Abstract
By extrapolating to O/H = N/H = 0 the empirical correlations Y–O/H and Y–N/H defined by a relatively large sample of ∼ 45 Blue Compact Dwarfs (BCDs), we have obtained a primordial 4Helium mass fraction Y p=0.2443±0.0015 with dY/dZ=2.4±1.0. This result is in excellent agreement with the average Y p=0.2452±0.0015 determined in the two most metal-deficient BCDs known, I Zw 18 (Z ⊙/50) and SBS 0335–052 (Z ⊙/41), where the correction for He production is smallest. The quoted error (1σ) of ≲ 1% is statistical and does not include systematic effects. We examine various systematic effects including collisional excitation of hydrogen lines, ionization structure and temperature fluctuation effects, and underlying stellar He i absorption, and conclude that combining all systematic effects, our Y p may be underestimated by ∼ 2–4%. Taken at face value, our Y p implies a baryon-to-photon number ratio η=(4.7+1.0 −0.8)×10−10 and a baryon mass fraction Ωb h 2 100=0.017±0.005 (2σ), consistent with the values obtained from deuterium and Cosmic Microwave Background measurements. Correcting Y p upward by 2–4% would make the agreement even better.
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Bania, T.M., Rood, R.T. and Balser, D.S.: 2000, in L.D. Silva, M. Spite and J.R. de Medeiros (eds.), The Light Elements and Their Evolution, ASP San Francisco, p. 214.
Benjamin, R.A., Skillman, E.D. and Smits, D.P.: 1999, Astrophys. J. 514, 307.
Bonifacio, P. and Molaro, P.: 1997, Monthly Notices Roy. Astron. Soc. 285, 847.
Brocklehurst, M.: 1971, Monthly Notices Roy. Astron. Soc. 153, 471.
Brocklehurst, M.: 1972, Monthly Notices Roy. Astron. Soc. 157, 211.
Burles, S. and Tytler, D.: 1998, Astrophys. J. 507, 732.
Davidson, K., and Kinman, T. D.: 1985, Astrophys. J. Suppl. 58, 321.
Hummer, D.G. and Storey, P.J.: 1992, Monthly Notices Roy. Astron. Soc. 254, 277.
Izotov, Y. I. and Thuan, T.X.: 1998, Astrophys. J. 500, 188. (IT98)
Izotov, Y.I. and Thuan, T.X.: 1999, Astrophys. J. 511, 639.
Izotov, Y.I., Chaffee, F.H., Foltz, C.B., Green, R.F., Guseva, N.G. and Thuan, T.X.: 1999, Astrophys. J. 527, 757.
Izotov, Y.I., Thuan, T.X. and Lipovetsky, V. A.: 1994, Astrophys. J. 435, 647. (ITL94)
Izotov, Y. I., Thuan, T.X. and Lipovetsky, V. A.: 1997, Astrophys. J. Suppl. 108,1.(ITL97)
Kingdon, J. and Ferland, G. J.: 1995, Astrophys. J. 442, 714.
Netterfield, C.B. et al.: 2001, Astrphys. J., in press.
Olive, K. and Skillman, E.D.: 2001, New Astron. 6, 119.
Olive, K., Skillman, E.D. and Steigman, G.: 1997, Astrophys. J. 483, 788.
Olofsson, K.: 1995, Astron. Astrophys. 111, 57.
O'Meara, J.M, Tytler, D., Kirkman, D., Suzuki, N., Prochaska, J.X., Lubin, D. and Wolfe, A.M.: 2001, Astrophys. J. 552, 718.
Pagel, B. E. J., Simonson, E. A., Terlevich, R. J. and Edmunds, M. G.: 1992, Monthly Notices Roy. Astron. Soc. 255, 325.
Peimbert, A., Peimbert, M., and Luridiana, V.: 2001, Astrophys. J., in press.
Peimbert, M., Peimbert, A. and Ruiz, M.T.: 2000, Astrophys. J. 541, 688.
Peimbert, M. and Torres-Peimbert, S.: 1974, Astrophys. J. 193, 327.
Pinsonneault, M.H., Walker, T.P., Steigman, G. and Naranyanan, V.K.: 1999, Astrophys. J. 527, 180.
Robbins, R.R.: 1968, Astrophys. J. 151, 497.
Rocca-Volmerange, B., Prévot, L., Ferlet, R., Lequeux, J. and Prévot-Burnichon, M.L.: 1981, Astron. Astrophys. 99,L5.
Ryan, S.G, Norris, J.E. and Beers, T.C.: 1999, Astrophys. J. 523, 654.
Sasselov, D. and Goldwirth, D.: 1995, Astrophys. J. 444,5.
Sauer, D. and Jedamzik, K.: 2001, Astron. Astrophys., in press.
Sawey, P.M.J. and Berrington, K.A.: 1993, Atomic Data Nucl. Data Tables 55, 81.
Smits, D.P.: 1996, Monthly Notices Roy. Astron. Soc. 278, 683.
Spite, F. and Spite, M.: 1982, Astron. Astrophys. 115, 357.
Stasińska, G.: 1990, Astron. Astrophys. 83, 501.
Stasińska, G. and Izotov, Y.I.: 2001, Astron. Astrophys., in press.
Stasińska, G. and Schaerer, D.: 1999, Astron. Astrophys. 351, 72.
Steigman, G., Viegas, S.M. and Gruenwald, R.: 1997, Astrophys. J. 490, 187.
Thuan, T.X., and Izotov, Y.I.: 1998a, in B. Guiderdoni, F.R. Bouchet, T.X. Thuan and J.T.T. Van (eds.), The Birth of Galaxies, The Gioi Publishers, Hanoi, p. 39.
Thuan, T.X. and Izotov, Y.I.: 1998b, Space Sci. Rev. 84, 83.
Thuan, T.X. and Izotov, Y.I.: 2000, in L.D. Silva, M. Spite and J.R. de Medeiros (eds.), The Light Elements and Their Evolution, ASP, San Francisco, p. 176.
Tytler, D., O'Meara, J.M, Suzuki, N. and Lubin, D.: 2000, Phys. Scripta 85, 12.
Vauclair, S. and Charbonnel, C.: 1998, Astrophys. J. 502, 372.
Vílchez, J.M. and Pagel, B.E.J.: 1988, Monthly Notices Roy. Astron. Soc. 231, 257.
Whitford, A.E.: 1958, Astron. J. 63, 201.
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Thuan, T.X., Izotov, Y. The primordial Helium-4 abundance determination: systematic effects. Space Science Reviews 100, 263–276 (2002). https://doi.org/10.1023/A:1015838716176
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DOI: https://doi.org/10.1023/A:1015838716176