Radiative Transfer Effects in He<scp>i</scp>Emission Lines

Benjamin, Robert A.; Skillman, Evan D.; Smits, Derck P.

doi:10.1086/339242

Cited by 92 publications

(116 citation statements)

References 20 publications

Supporting

Mentioning

108

Contrasting

Unclassified

Order By: Relevance

“…Instead, the 10-level numerical calculation program was graciously provided by Bob Benjamin (private communication). Fitting the same functional form to the He I λ10830 optical depth data over the same range (n e = 1-300 cm −3 and T = 1.2-2.0 x 10 4 K), we obtain: f τ (10830) = 1 + (τ /2)[0.0149 + (4.45 × 10 −3 − 6.34 × 10 −5 n e + 9.20 × 10 −8 n e 2 )T )], (2.2) with a maximum fit error of 1.3% (similar to the maximum fit errors reported in [40] available data is very limited. The 3 B-star supergiant spectra (where helium absorption is more significant) reported in Conti & Howarth [41] show equivalent width (EW) underlying absorption of ∼0.5-2.0Å.…”

Section: Introductionsupporting

confidence: 80%

“…The emissivities, including the collisional correction, are adopted from the recent work of Porter, Ferland, Storey, & Detisch [33], as was implemented in AOPS [31], and include He I λ10830. The radiative transfer equations in terms of optical depth come from the work of Benjamin, Skillman, & Smits [40]. That work does not include a fitting formula for He I λ10830, however.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The effects of He I λ10830 on helium abundance determinations

Aver

Olive

Skillman

2015

J. Cosmol. Astropart. Phys.

416

489

View full text Add to dashboard Cite

Abstract. Observations of helium and hydrogen emission lines from metal-poor extragalactic H II regions, combined with estimates of metallicity, provide an independent method for determining the primordial helium abundance, Y p . Traditionally, the emission lines employed are in the visible wavelength range, and the number of suitable lines is limited. Furthermore, when using these lines, large systematic uncertainties in helium abundance determinations arise due to the degeneracy of physical parameters, such as temperature and density. Recently, Izotov, Thuan, & Guseva (2014) have pioneered adding the He I λ10830 infrared emission line in helium abundance determinations. The strong electron density dependence of He I λ10830 makes it ideal for better constraining density, potentially breaking the degeneracy with temperature. We revisit our analysis of the dataset published by Izotov, Thuan, & Stasińska (2007) and incorporate the newly available observations of He I λ10830 by scaling them using the observed-to-theoretical Paschen-gamma ratio. The solutions are better constrained, in particular for electron density, temperature, and the neutral hydrogen fraction, improving the model fit to data, with the result that more spectra now pass screening for quality and reliability, in addition to a standard 95% confidence level cut. Furthermore, the addition of He I λ10830 decreases the uncertainty on the helium abundance for all galaxies, with reductions in the uncertainty ranging from 10-80%. Overall, we find a reduction in the uncertainty on Y p by over 50%. From a regression to zero metallicity, we determine Y p = 0.2449 ± 0.0040, consistent with the BBN result, Y p = 0.2470 ± 0.0002, based on the Planck determination of the baryon density. The dramatic improvement in the uncertainty from incorporating He I λ10830 strongly supports the case for simultaneous (thus not requiring scaling) observations of visible and infrared helium emission line spectra.

show abstract

Section: Introductionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

The effects of He I λ10830 on helium abundance determinations

Aver

Olive

Skillman

2015

J. Cosmol. Astropart. Phys.

416

489

View full text Add to dashboard Cite

show abstract

“…However, since these systematic effects are taken into account in our Y determination, they are not included in the error budget. An exception is the differences between two different sets of He i emissivities by Benjamin et al (1999Benjamin et al ( , 2002 and Porter et al (2005). Treating the different He i line emissivities as systematics affecting the Y wm determination, we obtain Y wm = 0.2500 ± 0.0012 (stat.)…”

Section: Helium Abundancementioning

confidence: 93%

“…It can be seen that the derived He mass fractions Y are very consistent (within < ∼ 1%) in all H ii regions, while the statistical errors 1−5% of the Y values are comparable to those obtained by other authors for different galaxies (see e.g., Peimbert et al 2007). The weighted mean Y derived from all observations shown in Table 8 is equal to Y wm = 0.2485 ± 0.0012 for the emissivities derived by Benjamin et al (1999Benjamin et al ( , 2002 and Y wm = 0.2514 ± 0.0012 for Porter et al (2005) emissivities. These values are very close to the primordial He abundance since the considered H ii regions are of very low-metallicity.…”

Section: Helium Abundancementioning

confidence: 95%

SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies

Izotov

Гусева

Fricke

et al. 2009

A&A

View full text Add to dashboard Cite

Context. We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W.Aims. Our aim is to derive element abundances in different H ii regions of this unique system of galaxies and to study spatial abundance variations.Methods. The electron temperature T e (O iii) in all H ii regions, except for one, is derived from the [O iii] λ4363/(λ4959+λ5007) flux ratio. We determine ionic abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The empirical relations for ionization correction factors are used to derive total abundances of these elements.Results. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different H ii regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of ∼1−2 kpc. Good seeing during FORS observations allowed us to extract spectra of four H ii regions in SBS 0335-052W. The oxygen abundance in the brightest region No. 1 of SBS 0335-052W is 7.22 ± 0.07, consistent with previous determinations. Three other H ii regions are much more metal-poor with an unprecedently low oxygen abundance of 12 + log O/H = 7.01 ± 0.07 (region No. 2), 6.98 ± 0.06 (region No. 3), and 6.86 ± 0.14 (region No. 4). These are the lowest oxygen abundances ever derived in emission-line galaxies, supporting earlier conclusions that SBS 0335-052W is the lowest-metallicity emission-line galaxy known. Helium abundances derived for the brightest H ii regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485 ± 0.0012 and 0.2514 ± 0.0012 for two different sets of He i emissivities. The ratios of neon and sulfur to oxygen abundance are similar to the respective ratios obtained for other emission-line galaxies. On the other hand, the chlorine-to-oxygen abundance ratio in SBS 0335-052E is lower, while the argon-to-oxygen abundance ratio is higher than those in other low-metallicity galaxies. The Fe/O abundance ratios in different regions of SBS 0335-052E are among the highest for emission-line galaxies implying that iron is almost entirely not depleted onto dust grains despite dust being detected in this galaxy in earlier ISO and Spitzer observations. The N/O abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12 + log O/H < 7.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity.

show abstract

“…In spite of this special role have the 447.15 nm (2p 3 P 0 2,1 -4d 3 D 3,2,1 transition), 587.56 nm (2p 3 P 0 2,1 -3d 3 D 3,2,1 transition) and 667.82 nm (2p 1 P 0 1 -3d 1 D 2 transition) neutral helium (He ) spectral lines. Recently, in the work by Benjamin et al (2002) these have been used to investigate the radiative transfer effects for a spherically symmetric nebula with no systematic velocity gradients. Izotov et al (2001) use these lines to derive the 4 He abundance in the Metal-deficient Blue Compact Dwarf Galaxies Tol 1214-277 and Tol 65 1 .…”

Section: Introductionmentioning

confidence: 99%