اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe thermonuclear production of F19 by Wolf-Rayet stars revisited
109
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
New models of rotating and non-rotating stars are computed for initial masses between 25 and 120 Msun and for metallicities Z = 0.004, 0.008, 0.020 and 0.040 with the aim of reexamining the wind contribution of Wolf-Rayet (WR) stars to the F19 enrichment of the interstellar medium. Models with an initial rotation velocity vini = 300 km/s are found to globally eject less F19 than the non-rotating models. We compare our new predictions with those of Meynet & Arnould (2000), and demonstrate that the F19 yields are very sensitive to the still uncertain F19(alpha,p)Ne22 rate and to the adopted mass loss rates. Using the recommended mass loss rate values that take into account the clumping of the WR wind and the NACRE reaction rates when available, we obtain WR F19 yields that are significantly lower than predicted by Meynet & Arnould (2000), and that would make WR stars non-important contributors to the galactic F19 budget. In view, however, of the large nuclear and mass loss rate uncertainties, we consider that the question of the WR contribution to the galactic F19 remains quite largely open.
قيم البحث
اقرأ أيضاً
Radioisotopes are natural clocks which can be used to estimate the age of the solar system. They also influence the shape of supernova light curves. In addition, the diffuse emission at 1.8 MeV from the decay of 26Al may provide a measure of the pres
ent day nucleosynthetic activity in the Galaxy. Therefore, even if radionuclides represent only a tiny fraction of the cosmic matter, they carry a unique piece of information. A large number of radioisotopes are produced by massive stars at the time of their supernova explosion. A more or less substantial fraction of them are also synthesized during the previous hydrostatic burning phases. These nuclides are then ejected either at the time of the supernova event, or through stellar winds during their hydrostatic burning phases. This paper focusses of the non explosive ejection of radionuclides by non-rotating or rotating Wolf-Rayet stars.
Massive stars deeply influence their surroundings by their luminosity and the injection of kinetic energy. So far, they have mostly been studied with spatially unresolved observations, although evidence of geometrical complexity of their wind are num
erous. Interferometry can provide spatially resolved observations of massive stars and their immediate vicinity. Specific geometries (disks, jets, latitude-dependent winds) can be probed by this technique. The first observation of a Wolf-Rayet (WR) star (gamma^2 Vel) with the AMBER/VLTI instrument yielded to a re-evaluation of its distance and an improved characterization of the stellar components, from a very limited data-set. This motivated our team to increase the number of WR targets observed with AMBER. We present here new preliminary results that encompass several spectral types, ranging from early WN to evolved dusty WC. We present unpublished data on WR79a, a massive star probably at the boundary between the O and Wolf- Rayet type, evidencing some Wolf-Rayet broad emission lines from an optically thin wind. We also present new data obtained on gamma^2 Vel that can be compared to the up-to-date interferometry-based orbital parameters from North et al. (2007). We discuss the presence of a wind-wind collision zone in the system and provide preliminary analysis suggesting the presence of such a structure in the data. Then, we present data obtained on 2 dusty Wolf-Rayet stars: WR48a-b and WR118, the latter exhibiting some clues of a pinwheel-like structure from the visibility variations.
We present the analysis of archival Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) observations of the interacting galaxies NGC 4038/39 (a.k.a. the Antennae) at a distance of 18.1 Mpc. Up to 38 young star-forming complexes with e
vident contribution from Wolf-Rayet (WR) stars are unveiled. We use publicly available templates of Galactic WR stars in conjunction with available photometric extinction measurements to quantify and classify the WR population in each star-forming region, on the basis of its nearly Solar oxygen abundance. The total estimated number of WR stars in the Antennae is 4053 $pm$ 84, of which there are 2021 $pm$ 60 WNL and 2032 $pm$ 59 WC-types. Our analysis suggests a global WC to WN-type ratio of 1.01 $pm$ 0.04, which is consistent with the predictions of the single star evolutionary scenario in the most recent BPASS stellar population synthesis models.
The Wolf-Rayet (WR) phenomenon is widespread in astronomy. It involves classical WRs, very massive stars (VMS), WR central stars of planetary nebula CSPN [WRs], and supernovae (SNe). But what is the root cause for a certain type of object to turn int
o an emission-line star? In this contribution, I discuss the basic aspects of radiation-driven winds that might reveal the ultimate difference between WR stars and canonical O-type stars. I discuss the aspects of (i) self-enrichment via CNO elements, (ii) high effective temperatures Teff, (iii) an increase in the helium abundance Y, and finally (iv) the Eddington factor Gamma. Over the last couple of years, we have made a breakthrough in our understanding of Gamma-dependent mass loss, which will have far-reaching consequences for the evolution and fate of the most massive stars in the Universe. Finally, I discuss the prospects for studies of the WR phenomenon in the highest redshift Ly-alpha and He II emitting galaxies.
It has been speculated that WR winds may have contaminated the forming solar system, in particular with short-lived radionuclides (half-lives in the approximate 10^5 - 10^8 y range) that are responsible for a class of isotopic anomalies found in some
meteoritic materials. We revisit the capability of the WR winds to eject these radionuclides using new models of single non-exploding WR stars with metallicity Z = 0.02. The earlier predictions for non-rotating WR stars are updated, and models for rotating such stars are used for the first time in this context. We find that (1) rotation has no significant influence on the short-lived radionuclide production by neutron capture during the core He-burning phase, and (2) 26Al, 36Cl, 41Ca, and 107Pd can be wind-ejected by a variety of WR stars at relative levels that are compatible with the meteoritic analyses for a period of free decay of around 10^5 y between production and incorporation into the forming solar system solid bodies. We confirm the previously published conclusions that the winds of WR stars have a radionuclide composition that can meet the necessary condition for them to be a possible contaminating agent of the forming solar system. Still, it remains to be demonstrated from detailed models that this is a sufficient condition for these winds to have provided a level of pollution that is compatible with the observations.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
