Precision Spectroscopy in Astrophysics
DOI: 10.1007/978-3-540-75485-5_10
|View full text |Cite
|
Sign up to set email alerts
|

[C/O] Observations in Low-[Fe/H] Halo Stars

Help me understand this report

Search citation statements

Order By: Relevance

Paper Sections

Select...
3
1
1

Citation Types

0
8
0

Publication Types

Select...
5

Relationship

1
4

Authors

Journals

citations
Cited by 6 publications
(8 citation statements)
references
References 5 publications
0
8
0
Order By: Relevance
“…We begin by calculating the IGM metallicity by mass, Z IGM , implied by our measure of Ω C iv : where Ω b = 0.0224/ h 2 (Pettini et al 2008a) is the contribution of baryons to the critical density, is the fraction of carbon which is triply ionized and A C is the mass fraction of metals in carbon. For comparison, in the Sun, Z ⊙ = 0.0122 and A C = 0.178 (Asplund, Grevesse & Sauval 2005); here, we assume that the same value of A C applies at high redshifts because (a) the ratio of carbon to oxygen (the major contributor to Z ⊙ ) is approximately solar at low metallicities (Pettini et al 2008b; Fabbian et al 2009) and (b) any departures are in any case likely to result in only a small correction compared to other uncertainties in the following discussion. We also adopt the conservative limit , as done by Songaila (2001); this is the maximum fractional abundance reached by C iv under the most favourable ionization balance conditions.…”
Section: Discussionmentioning
confidence: 99%
“…We begin by calculating the IGM metallicity by mass, Z IGM , implied by our measure of Ω C iv : where Ω b = 0.0224/ h 2 (Pettini et al 2008a) is the contribution of baryons to the critical density, is the fraction of carbon which is triply ionized and A C is the mass fraction of metals in carbon. For comparison, in the Sun, Z ⊙ = 0.0122 and A C = 0.178 (Asplund, Grevesse & Sauval 2005); here, we assume that the same value of A C applies at high redshifts because (a) the ratio of carbon to oxygen (the major contributor to Z ⊙ ) is approximately solar at low metallicities (Pettini et al 2008b; Fabbian et al 2009) and (b) any departures are in any case likely to result in only a small correction compared to other uncertainties in the following discussion. We also adopt the conservative limit , as done by Songaila (2001); this is the maximum fractional abundance reached by C iv under the most favourable ionization balance conditions.…”
Section: Discussionmentioning
confidence: 99%
“…Nissen et al 2007). In Fabbian et al 2008b, we further investigate this issue, together with a study of the [C/Fe] and [C/O] ratios at low metallicity, via new observational data.…”
Section: Discussionmentioning
confidence: 99%
“…It is expected that non-LTE effects will be enhanced when using 3D atmospheric models, due to their cooler superficial temperatures, to which the highexcitation lines of interest are known to be sensitive. This crucial step forward will allow enhanced abundance analyses and will help to shed light on early Galactic chemical evolution, contributions by SN II and massive stars, time delay of yields from Type Ia SNe, and the reality of the [C/O] upturn at low metallicity (Akerman et al 2004;Spite et al 2005;Fabbian et al 2008b). It is likely that -together with the use of an accurate temperature scalewhen finally taking into account, using detailed calculations with the best available atomic data, the interplay of 3D and non-LTE effects in the formation of the various available abundance indicators (including for the determination of metallicity), it will be possible to in the end fully solve the "oxygen problem".…”
Section: Discussionmentioning
confidence: 99%
“…An initial investigation of such effects by Fabbian et al (2006) seemed to dilute the significance of the results by Akerman et al (2004) by showing that non‐LTE corrections to the C i lines can be as high as −0.4 dex in stars of [Fe/H] ≃−3. A more recent study by the same group, however, has uncovered even larger corrections to the abundance of O at very low metallicities (Fabbian et al 2008a), so that the case for a rise in [C/O] when [O/H] ≲−1 is actually reinforced when non‐LTE effects on the formation of the stellar C i and O i lines are taken into account (Fabbian et al 2008b).…”
Section: The C/o Ratio At Low Metallicitiesmentioning
confidence: 99%