2010A&A...518A..13G


Query : 2010A&A...518A..13G

2010A&A...518A..13G - Astronomy and Astrophysics, volume 518, A13-13 (2010/7-2)

ΔY/ΔZ from the analysis of local K dwarfs.

GENNARO M., PRADA MORONI P.G. and DEGL'INNOCENTI S.

Abstract (from CDS):

The stellar helium-to-metal enrichment ratio, ΔY/ ΔZ, is a widely studied astrophysical quantity. However, its value has still not been precisely constrained. This paper is focused on studying the main sources of uncertainty that affect the ΔY/ ΔZ ratio derived from the analysis of the low-main sequence (MS) stars in the solar neighborhood. The possibility of inferring the value of the helium-to-metal enrichment ratio from the study of low-MS stars relies on the dependence of the stellar luminosity and effective temperature on the initial helium and metal abundances. The ΔY/ΔZ ratio is obtained by comparing the magnitude difference between the observed stars and a reference, theoretical zero age main sequence (ZAMS) with the related theoretical magnitude differences computed from a new set of stellar models with up-to-date input physics and a fine grid of chemical compositions. A Monte Carlo approach has been used to evaluate the impact of different sources of uncertainty, i.e. observational errors, evolutionary effects, systematic uncertainties of the models. As a check of the procedure, the method was applied to a different data set, namely the low-MS of the Hyades. Once a set of ZAMS and atmosphere models had been chosen, we found that the inferred value of ΔY/ ΔZ is sensitive to the age of the stellar sample, even if we restricted the data set to low-luminosity stars. The lack of an accurate age estimate of low-mass field stars leads to underestimating the inferred ΔY/ ΔZ of ∼2 units. On the contrary, the method firmly recovers the ΔY/ ΔZ value for unevolved samples of stars like the Hyades low-MS. Adopting a solar-calibrated mixing-length parameter and the PHOENIX GAIA v2.6.1 atmospheric models, we find ΔY/ΔZ=5.3±1.4 once the age correction has been applied. The Hyades sample provided a perfectly consistent value. We have demonstrated that assuming that low-mass stars in the solar neighborhood can be considered as unevolved does not necessarily hold, and it may indeed lead to a bias in the inferred ΔY/ΔZ. The effect of the still poorly constrained efficiency of the superadiabatic convection and of different atmosphere models adopted to transform luminosities and effective temperature into colors and magnitudes are also discussed.

Abstract Copyright:

Journal keyword(s): Galaxy: fundamental parameters - solar neighborhood - stars: abundances - stars: low-mass

Simbad objects: 13

goto Full paper

goto View the references in ADS

Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10530 1
2 NGC 346 Cl* 00 59 05.090 -72 10 33.24           ~ 471 0
3 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6555 1
4 NGC 1491 HII 04 03 15.9 +51 18 54           ~ 111 1
5 Cl Melotte 25 OpC 04 29 47 +16 56.9           ~ 2928 0
6 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16509 1
7 M 42 OpC 05 35 17 -05 23.4           ~ 3970 0
8 HD 144628 PM* 16 09 42.7944501960 -56 26 42.541189576 8.449 7.976 7.124 6.643 6.205 K2V 134 0
9 M 8 HII 18 03 37 -24 23.2           ~ 598 1
10 HD 166620 PM* 18 09 37.4162111401 +38 27 27.998016381 7.86 7.27 6.40 5.63 5.14 K2V 414 0
11 NGC 6618 OpC 18 20 47 -16 10.3           ~ 1574 0
12 HD 192263 BY* 20 13 59.8455790536 -00 52 00.769626768 9.447 8.724 7.767 7.231 6.771 K1/2V 232 1
13 HD 222237 PM* 23 39 37.3873674682 -72 43 19.755447187 8.912 8.088 7.087 6.502 5.987 K3+V 151 0

To bookmark this query, right click on this link: simbad:objects in 2010A&A...518A..13G and select 'bookmark this link' or equivalent in the popup menu


2023.01.30-21:23:14

© Université de Strasbourg/CNRS

    • Contact