Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOn the oxygen abundance of HE0107-5240
152
0
0.0
(
0
)
Authors
M.S. Bessell
Ask ChatGPT about the research
No Arabic abstract
We have determined the oxygen abundance of HE0107-5240 from UV-OH lines detected in VLT/UVES spectra. Using a plane-parallel LTE model atmosphere, we derive [O/Fe] = +2.4, and a similar analysis of CD -38 245 yields [O/Fe] = +1.0. We estimate systematic errors due to 3D effects to be in the order of 0.3 to 0.4 dex. That is, our derived O abundances are likely overestimates: effects from thermal inhomogeneities due to convection may require that the abundances should be reduced by 0.3-0.4 dex or even more. Radial velocity data for HE0107-5240 based on high-resolution spectra show that over a time span of 373 days the radial velocity was constant at 44.5 km/s, with a 1 sigma scatter of the measurements of 0.5 km/s. However, it can not yet be ruled out that HE0107-5240 is a very long period and/or low amplitude binary. These results provide new constraints on scenarios for the origin of the abundance pattern of HE0107-5240. In particular, it seems unlikely that the large overabundances of CNO have been produced in a medium-mass AGB star which later evolved to a white dwarf. The oxygen abundance of HE0107-5240 is significantly smaller than the prediction of Umeda & Nomoto (2003) from calculated yields of a ~25 solar mass Population III star exploding as a supernova of low explosion energy (E_exp = 3 x 10^50 erg) with mixing and fallback. The scenario of Limongi et al. (2003), involving two Population III supernovae, predicts an oxygen abundance of [O/Fe] = +4.1 for HE0107-5240, in strong contradiction with the observed value. In conclusion, none of the above mentioned scenarios, in their present realizations, can satisfactorly explain the abundance pattern of HE0107-5240.
rate research
Read More
We report a detailed abundance analysis for HE0107-5240, a halo giant with [Fe/H]_NLTE=-5.3. This star was discovered in the course of follow-up medium-resolution spectroscopy of extremely metal-poor candidates selected from the digitized Hamburg/ESO objective-prism survey. On the basis of high-resolution VLT/UVES spectra, we derive abundances for 8 elements (C, N, Na, Mg, Ca, Ti, Fe, and Ni), and upper limits for another 12 elements. A plane-parallel LTE model atmosphere has been specifically tailored for the chemical composition of {he}. Scenarios for the origin of the abundance pattern observed in the star are discussed. We argue that HE0107-5240 is most likely not a post-AGB star, and that the extremely low abundances of the iron-peak, and other elements, are not due to selective dust depletion. The abundance pattern of HE0107-5240 can be explained by pre-enrichment from a zero-metallicity type-II supernova of 20-25M_Sun, plus either self-enrichment with C and N, or production of these elements in the AGB phase of a formerly more massive companion, which is now a white dwarf. However, significant radial velocity variations have not been detected within the 52 days covered by our moderate-and high-resolution spectra. Alternatively, the abundance pattern can be explained by enrichment of the gas cloud from which HE0107-5240 formed by a 25M_Sun first-generation star exploding as a subluminous SNII, as proposed by Umeda & Nomoto (2003). We discuss consequences of the existence of HE0107-5240 for low-mass star formation in extremely metal-poor environments, and for currently ongoing and future searches for the most metal-poor stars in the Galaxy.
We discuss the origin of HE0107-5240 which is the most metal poor star yet observed ([Fe/H] = -5.3). Its discovery has an important bearing on the question of the observability of first generation stars. In common with other metal-poor stars (-4 < [Fe/H] < -2.5), HE0107-5240 shows a peculiar abundance pattern (CNO rich, moderate Na rich). We elaborate the binary scenario on the basis of the evolution and nucleosynthesis of extremely metal-poor, low-mass model stars and discuss the possibility of discriminating this scenario from others. In our picture, iron peak elements arise in surface layers of the component stars by accretion of gas from the polluted primordial cloud. To explain the observed C, N, O, and Na enhancements as well as 12C/13C ratio, we suppose that the currently observed star accreted matter from a AGB companion. To estimate the abundances in the matter transferred in the binary, we rely on the results of computations of model stars constructed with up-to-date input physics. Nucleosynthesis in the helium flash convection with hydrogen injected is followed, allowing us to discuss the abundances of s-process elements, in addition to explaining the origin of the observed O and Na enrichments. From the observed abundances, we conclude that HE0107-5240 has evolved from a wide binary with a primary of initial mass, 1.2 ~ 3 Msun. We estimated the present binary separation of ~ 34 AU and period of ~ 150 years. We also conclude that the abundance distribution of the heavy s-process elements, may hold the key to understand the origin of HE0107-5240. An enhancement of [Pb/Fe] = 1 ~ 2 should be observed. If the enhancement of s-process elements is not detected, HE0107-5240 may be a first generation secondary in a binary system with a primary of mass less than 2.5 Msun.
Motivated by the controversy over the surface metallicity of the Sun, we present a re-analysis of the solar photospheric oxygen (O) abundance. New atomic models of O and Ni are used to perform Non-Local Thermodynamic Equilibrium (NLTE) calculations with 1D hydrostatic (MARCS) and 3D hydrodynamical (Stagger and Bifrost) models. The Bifrost 3D MHD simulations are used to quantify the influence of the chromosphere. We compare the 3D NLTE line profiles with new high-resolution, R = 700 000, spatially-resolved spectra of the Sun obtained using the IAG FTS instrument. We find that the O I lines at 777 nm yield the abundance of log A(O) = 8.74 +/- 0.03 dex, which depends on the choice of the H-impact collisional data and oscillator strengths. The forbidden [O I] line at 630 nm is less model-dependent, as it forms nearly in LTE and is only weakly sensitive to convection. However, the oscillator strength for this transition is more uncertain than for the 777 nm lines. Modelled in 3D NLTE with the Ni I blend, the 630 nm line yields an abundance of log A(O) = 8.77 +/- 0.05 dex. We compare our results with previous estimates in the literature and draw a conclusion on the most likely value of the solar photospheric O abundance, which we estimate at log A(O) = 8.75 +/- 0.03 dex.
This paper aims at providing aperture corrections for emission lines in a sample of spiral galaxies from the Calar Alto Legacy Integral Field Area Survey (CALIFA) database. In particular, we explore the behavior of the log([OIII]5007/Hbeta)/([NII]6583/Halpha) (O3N2) and log[NII]6583/Halpha (N2) flux ratios since they are closely connected to different empirical calibrations of the oxygen abundances in star forming galaxies. We compute median growth curves of Halpha, Halpha/Hbeta, O3N2 and N2 up to 2.5R_50 and 1.5 disk R_eff. The growth curves simulate the effect of observing galaxies through apertures of varying radii. The median growth curve of the Halpha/Hbeta ratio monotonically decreases from the center towards larger radii, showing for small apertures a maximum value of ~10% larger than the integrated one. The median growth curve of N2 shows a similar behavior, decreasing from the center towards larger radii. No strong dependence is seen with the inclination, morphological type and stellar mass for these growth curves. Finally, the median growth curve of O3N2 increases monotonically with radius. However, at small radii it shows systematically higher values for galaxies of earlier morphological types and for high stellar mass galaxies. Applying our aperture corrections to a sample of galaxies from the SDSS survey at 0.02<=z<=0.3 shows that the average difference between fiber-based and aperture corrected oxygen abundances, for different galaxy stellar mass and redshift ranges, reaches typically to ~11%, depending on the abundance calibration used. This average difference is found to be systematically biased, though still within the typical uncertainties of oxygen abundances derived from empirical calibrations. Caution must be exercised when using observations of galaxies for small radii (e.g. below 0.5R_eff) given the high dispersion shown around the median growth curves.
We construct maps of the oxygen abundance distribution across the disks of 88 galaxies using CALIFA data release 2 (DR2) spectra. The position of the center of a galaxy (coordinates on the plate) were also taken from the CALIFA DR2. The galaxy inclination, the position angle of the major axis, and the optical radius were determined from the analysis of the surface brightnesses in the SDSS $g$ and $r$ bands of the photometric maps of SDSS data release 9. We explore the global azimuthal abundance asymmetry in the disks of the CALIFA galaxies and the presence of a break in the radial oxygen abundance distribution. We found that there is no significant global azimuthal asymmetry for our sample of galaxies, i.e., the asymmetry is small, usually lower than 0.05 dex. The scatter in oxygen abundances around the abundance gradient has a comparable value, $lesssim 0.05$ dex. A significant (possibly dominant) fraction of the asymmetry can be attributed to the uncertainties in the geometrical parameters of these galaxies. There is evidence for a flattening of the radial abundance gradient in the central part of 18 galaxies. We also estimated the geometric parameters (coordinates of the center, the galaxy inclination and the position angle of the major axis) of our galaxies from the analysis of the abundance map. The photometry-map-based and the abundance-map-based geometrical parameters are relatively close to each other for the majority of the galaxies but the discrepancy is large for a few galaxies with a flat radial abundance gradient.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
