Nucleosynthesis and Stellar Evolution (original) (raw)
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Stellar Nucleosynthesis and Chemical Evolution of Galaxies
EAS Publications Series, 2007
We present the basic theory of nuclear reactions in stars and sketch the general rules of stellar evolution. Then we shortly review the subject of supernova explosions both by core collapse in massive stars (type II) and carbon-deflagration in binary systems when one of the components is a White Dwarf accreting mass from the companion (type Ia). We also present elementary notions of sand r-process nucleo-synthesis. Finally, we shortly review the topic of galactic chemical evolution and highlight some simple solutions aimed at understanding the main observational data on abundances and abundance ratios.
2003
Among the topics studied by this program, we have selected here a subset including studies of the energetic core-collapse SNe known as `Hypernovae', an investigation of the Star Formation History in Late-Type Galaxies and the effect of both the SN explosions and the Star Formation Rate on the chemical and dynamical evolution of Late-Type Galaxies. In particular: - The recent Type Ic SN 2002ap is spectroscopically a member of the group of Type Ic `Hypernovae' including SN 1998bw/GRB980425, SN 1997ef, and SN1997dq. Analysis of the spectra and of the light curve of SN 2002ap suggest that it ejected less mass and exploded with a smaller kinetic energy than the other hypernovae, but yet the kinetic energy was significantly larger (4-10 times) than in normal core-collapse SNe. We discuss the implication of the energetics and progenitor mass of 2002ap in the context of the general properties of core-collapse SNe. - The approach adopted to derive the Star Formation History (SFH) o...
New Insights into the Early Stage of the Galactic Chemical Evolution
Galaxy Evolution: Connecting the Distant Universe with the Local Fossil Record, 1999
The supernova yields of several heavy elements including α-, iron-group, and r-process elements are obtained as a function of the mass of their progenitor main-sequence stars M ms from the abundance patterns of extremely metal-poor stars with a procedure recently proposed by . The ejected masses of α-and iron-group elements increase with M ms , whereas more Eu is ejected from supernovae with lower M ms . For these several heavy elements, it is shown that the average abundance ratios weighted by the Salpeter initial mass function coincide with the ratios observed in stars with −2 < [Fe/H] < −1 within 0.1 dex. It follows that the correlations of stellar abundance ratios with the metallicity are twofold. One is the abundance ratios for [Fe/H] < −2.5 imprinted by the nucleosynthesis in individual supernovae on the timescale ∼ 10 7 yr and the other for [Fe/H] > −2 results from the mixing of the products from a whole site of the nucleosynthesis, taking place on the timescale longer than 10 9 yr.
The evolution of the Milky Way from its earliest phases: Constraints on stellar nucleosynthesis
Astronomy & Astrophysics, 2004
Ni, and Zn (the solar abundance case) in massive stars from Woosley and Weaver (1995) are the best to fit the abundance patterns of these elements since they do not need any change. We adopted also the yields by Nomoto et al. (1997) and Limongi and Chieffi (2003) for massive stars and discussed the corrections required in these yields in order to fit the observations. Finally, the small spread in the [el/Fe] ratios in the metallicity range from [Fe/H]=-4.0 up to -3.0 dex (Cayrel et al. 2003) is a clear sign that the halo of the Milky Way was well mixed even in the earliest phases of its evolution.
Nucleosynthesis and chemical evolution of intermediate mass stars: results from planetary nebulae
2010
Planetary nebulae (PN) are an excellent laboratory to investigate the nucleosynthesis and chemical evolution of intermediate mass stars. In these objects accurate abundances can be obtained for several chemical elements that are manufactured or contaminated by the PN progenitor stars, such as He, N, C, and also elements that were originally produced by more massive stars of previous generations, namely O, Ne, Ar, and S. Some of these elements are difficult to study in stars, so that PN can be used in order to complement results obtained from stellar data. In the past few years, we have obtained a large sample of PN with accurately derived abundances, including objects of different populations, namely the solar neighbourhood, the galactic disk and anticentre, the galactic bulge and the Magellanic Clouds. In this work, we present the results of our recent analysis of the chemical abundances of He, O, N, S, Ar and Ne in galactic and Magellanic Cloud PN. Average abundances and abundance distributions of all elements are determined, as well as distance-independent correlations. These correlations are particularly important, as they can be directly compared with the predictions of recent theoretical evolutionary models for intermediate mass stars.
The Astrophysical Journal, 2001
Detailed stellar evolution calculations have been performed to quantify the influence of the main sequence mass M MS and the metallicity Z of the progenitor on the structure of the exploding WD which are thought to be the progenitors of SNe Ia. In particular, we study the effects of progenitors on the brightness decline relation M (∆M 15 ) which is a corner stone for the use of SNe Ia as cosmological yard-stick. Both the typical M MS and Z can be expected to change as we go back in time. We consider the entire range of potential progenitors with 1.5 to 7 M ⊙ and metallicities between Z=0.02 to 1 × 10 −10 . Our study is based on the delayed detonation scenario with specific parameters which give a good account of typical light curves and spectra. Based on the structures for the WD, detailed model calculations have been performed for the hydrodynamical explosion, nucleosynthesis and light curves.
Monthly Notices of the Royal Astronomical Society, 2008
This paper presents a mechanism that may modify the extinction law for Type Ia supernovae (SNeIa) observed at higher redshift. Starting from the observations that (i) SNeIa occur predominantly in spiral galaxies, (ii) star formation ejects interstellar medium (ISM) out of the plane of spirals, (iii) star formation alters the extinction properties of the dust in the ISM, and (iv) there is substantially more star formation at higher redshift, I propose that spiral galaxies have a dustier halo in the past than they do now. The ejected material's lower value of R V will lead to a lower average value (R V ) for SNeIa observed at higher redshift.
Constraining Cosmic Evolution of Type Ia Supernovae
The Astrophysical Journal, 2008
We present the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with excellent light-curve information. In addition, we have obtained 397 spectra of low-redshift SNe through a multiple-decade effort at Lick and Keck Observatories, and we have used 45 ultraviolet spectra obtained by HST/IUE. The lowredshift spectra act as a control sample when comparing to the ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra appear very similar. The addition of galaxy light to the Lick composite spectra allows a nearly perfect match of the overall spectral-energy distribution with the ESSENCE composite spectra, indicating that the high-redshift SNe are more contaminated with host-galaxy light than their low-redshift counterparts. This is caused by observing objects at all redshifts with similar slit widths, which corresponds to different projected distances. After correcting for the galaxy-light contamination, subtle differences in the spectra remain. We have estimated the systematic errors when using current spectral templates for K-corrections to be ∼ 0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximumlight SN spectra of ∼3% in the optical and growing toward the ultraviolet. The difference between the maximum-light low and high-redshift spectra constrain SN evolution between our samples to be < 10% in the rest-frame optical.
The Astrophysical Journal, 2006
We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar populations, with observed rates that depend on the stellar mass and mean star-formation rates (SFRs) of their host galaxies. Models where the SN Ia rate depends solely on host galaxy stellar mass are ruled out with >99% confidence. Our analysis is based on 100 spectroscopically-confirmed SNe Ia, plus 24 photometrically-classified events, all from the Supernova Legacy Survey (SNLS) and distributed over 0.2<z<0.75. Using multi-band photometry, we estimate stellar masses and SFRs for the SN Ia host galaxies by fitting their broad-band spectral energy distributions with the galaxy spectral synthesis code, PEGASE.2. We show that the SN Ia rate per unit mass is proportional to the specific SFR of the parent galaxies -more vigorously star-forming galaxies host more SNe Ia per unit stellar mass, broadly equivalent to the trend of increasing SN Ia rate in later-type galaxies seen in the local universe. Following earlier suggestions for a simple "two-component" model approximating the SN Ia rate, we find bivariate linear dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of the host systems. We find that the SN Ia rate can be well represented as the sum of 5.3 ± 1.1 × 10 −14 SNe per year per unit stellar mass, and 3.9 ± 0.7 × 10 −4 SNe per year per M ⊙ yr −1 of star formation.
Planetary nebulae as tracers of galaxy stellar populations
Monthly Notices of the Royal Astronomical Society, 2006
We address the general problem of the luminosity-specific planetary nebula (PN) number, better known as the 'α' ratio, given by α = N PN /L gal , and its relationship with the age and metallicity of the parent stellar population. Our analysis relies on population synthesis models that account for simple stellar populations (SSPs), and more elaborate galaxy models covering the full star formation range of the different Hubble morphological types. This theoretical framework is compared with the updated census of the PN population in Local Group (LG) galaxies and external ellipticals in the Leo group, and the Virgo and Fornax clusters. The main conclusions of our study can be summarized as follows. (i) According to the post-asymptotic giant branch (AGB) stellar core mass, PN lifetime in a SSP is constrained by three relevant regimes, driven by the nuclear (M core 0.57 M), dynamical (0.57 M M core 0.55 M) and transition (0.55 M M core 0.52 M) timescales. The lower limit for M core also sets the minimum mass for stars to reach the AGB thermal-pulsing phase and experience the PN event. (ii) Mass loss is the crucial mechanism to constrain the value of α, through the definition of the initial-to-final mass relation (IFMR). The Reimers mass-loss parametrization, calibrated on Pop II stars of Galactic globular clusters, poorly reproduces the observed value of α in late-type galaxies, while a better fit is obtained using the empirical IFMR derived from white dwarf observations in the Galaxy open clusters. (iii) The inferred PN lifetime for LG spirals and irregulars exceeds 10 000 yr, which suggests that M core 0.65 M cores dominate, throughout. (iv) The relative PN deficiency in elliptical galaxies, and the observed trend of α with galaxy optical colours, support the presence of a prevailing fraction of low-mass cores (M core 0.55 M) in the PN distribution and a reduced visibility timescale for the nebulae as a consequence of the increased AGB transition time. The stellar component with M core 0.52 M , which overrides the PN phase, could provide an enhanced contribution to hotter HB and post-HB evolution, as directly observed in M 32 and the bulge of M 31. This implies that the most UV-enhanced ellipticals should also display the lowest values of α, as confirmed by the Virgo cluster early-type galaxy population. (v) Any blue-straggler population, invoked as progenitor of the M core 0.7 M PNe in order to preserve the constancy of the bright luminosity-function cutoff magnitude in ellipticals, must be confined to a small fraction (a few per cent at most) of the whole galaxy PN population.