On the mass of supernova progenitors: the role of the 12^{12}C+12+^{12}C reaction

A precise knowledge of the masses of supernova progenitors is essential to answer various questions of modern astrophysics, such as those related to the dynamical and chemical evolution of Galaxies. In this paper we revise the upper bound for the mass of the progenitors of CO white dwarfs (\mup) and the lower bound for the mass of the progenitors of normal type II supernovae (\mups). In particular, we present new stellar models with mass between 7 and 10 \msun, discussing their final destiny and the impact of recent improvements in our understanding of the low energy rate of the \c12c12 reaction.Comment: To be published on the proceedings of NIC 201

Low and intermediate-mass close binary evolution and the initial - final mass relation

Using Eggleton's stellar evolution code, we carry out 150 runs of Pop I binary evolution calculations, with the initial primary mass between 1 and 8 solar masses the initial mass ratio between 1.1 and 4, and the onset of Roche lobe overflow (RLOF) at an early, middle, or late Hertzsprung-gap stage. We assume that RLOF is conservative in the calculations, and find that the remnant mass of the primary may change by more than 40 per cent over the range of initial mass ratio or orbital period, for a given primary mass. This is contrary to the often-held belief that the remnant mass depends only on the progenitor mass if mass transfer begins in the Hertzsprung gap. We fit a formula, with an error less than 3.6 per cent, for the remnant (white dwarf) mass as a function of the initial mass of the primary, the initial mass ratio, and the radius of the primary at the onset of RLOF. We also find that a carbon-oxygen white dwarf with mass as low as 0.33 solar masses may be formed if the primary's initial mass is around 2.5 solar masses.Comment: 7 pages for main text, 11 pages for appendix (table A1), 12 figure

The surface carbon and nitrogen abundances in models of ultra metal-poor stars

We investigate whether the observed high number of carbon- and nitrogen-enhanced extremely metal-poor stars could be explained by peculiar evolutionary properties during the core He flash at the tip of the red giant branch. For this purpose we compute a series of detailed stellar models expanding upon our previous work; in particular, we investigate if during the major He flash the penetration of the helium convective zone into the overlying hydrogen-rich layers can produce carbon- and nitrogen-rich abundances in agreement with current spectroscopic observations. The dependence of this phenomenon on selected model input parameters, such as initial metallicity and treatment of convection is examined in detail.Comment: 8 pages, 4 figures, submitted to A&

AlterBBN: A program for calculating the BBN abundances of the elements in alternative cosmologies

We describe AlterBBN, a public C program for evaluating the abundances of the elements generated by Big-Bang nucleosynthesis (BBN). This program enables the user to compute the abundances of the elements in the standard model of cosmology, and additionally provides possibilities to alter the assumptions of the cosmological model in order to study their consequences on the abundances of the elements. In particular the baryon-to-photon ratio and the effective number of neutrinos, as well as the expansion rate and the entropy content of the Universe during BBN can be modified in AlterBBN. Such features allow the user to test the cosmological models by confronting them to BBN constraints. A presentation of the physics of BBN and the features of AlterBBN is provided here under the form of a manual.Comment: 15 pages, 1 figure, 1 table. AlterBBN can be obtained from https://alterbbn.hepforge.org

Stellar evolution with rotation VII: Low metallicity models and the blue to red supergiant ratio in the SMC

We calculate a grid of models with and without the effects of axial rotation for massive stars in the range of 9 to 60 M$_{\odot}$ and metallicity $Z$ = 0.004 appropriate for the SMC. Remarkably, the ratios $\Omega/\Omega_{\mathrm{crit}}$ of the angular velocity to the break-up angular velocity grow strongly during the evolution of high mass stars, contrary to the situation at $Z$ = 0.020. The reason is that at low $Z$, mass loss is smaller and the removal of angular momentum during evolution much weaker, also there is an efficient outward transport of angular momentum by meridional circulation. Thus, a much larger fraction of the stars at lower $Z$ reach break-up velocities and rotation may thus be a dominant effect at low $Z$. The models with rotation well account for the long standing problem of the large numbers of red supergiants observed in low $Z$ galaxies, while current models with mass loss were predicting no red supergiants. We discuss in detail the physical effects of rotation which favour a redwards evolution in the HR diagram. The models also predict large N enrichments during the evolution of high mass stars. The predicted relative N-enrichments are larger at $Z$ lower than solar and this is in very good agreement with the observations for A-type supergiants in the SMC.Comment: 18 pages, 16 figures, in press in Astronomy and Astrophysic

The thermonuclear production of F19 by Wolf-Rayet stars revisited

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.Comment: 9 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Routes To the Renaissance for Pittsfield, MA

The goal of the Master of Regional Planning Studio is to develop a student’s techniques for collecting, analyzing, and synthesizing spatial and non-spatial data and then presenting that collective data in a manner (i.e., report, video, presentation, and charettes) that is understandable to academics, professionals, and the public. Planning Studio allows students to integrate knowledge from coursework and research, and apply such knowledge to resolving representative planning problems. At UMASS Amherst, these problems are found in neighborhood, rural, urban, and/or regional settings. In the fall of 2015, the City of Pittsfield contracted the MRP Studio to create a vision plan to connect the goal’s of its Master Plan in 2009 to current development regulations that encourage development and redevelopment of an appropriate size, scale and design that meets the short term and long term vision of the community. The vision plan encompasses the following: Spatial and Physical Boundaries of Major Gateway Corridors: Analyze the major gateways and develop tools to make them more welcoming. Permitted Use Table and Definitions: Review, clarify, and consolidate the land-uses listed in the table to assess deficiencies and unclear definitions. Design Guidelines: Create a manual to guide architectural aesthetic standards for new retail developments. Sign Ordinance: Implement a streamlined regulation that improves sign quality. Site Plan Review: Develop thresholds to create clearer processes for review of development projects. Resolution for Split Parcels: Identify all properties that fall within two zoning districts and develop a mitigation tool. Pro Forma and Multi-Family Housing: Develop a financial model that will estimate the construction and maintenance cost of multi-family housing units and make projections for new development’s financial return

Yields of rotating stars at solar metallicity

We present a new set of stellar yields obtained from rotating stellar models at solar metallicity covering the massive star range (12-60 solar masses). The stellar models were calculated with the latest version of the Geneva stellar evolution code described in Hirschi et al (2004). Evolution and nucleosynthesis are in general followed up to silicon burning. The yields of our non-rotating models are consistent with other calculations and differences can be understood in the light of the treatment of convection and the rate used for C12(a,g)O16. This verifies the accuracy of our calculations and gives a safe basis for studying the effects of rotation on the yields. The contributions from stellar winds and supernova explosions to the stellar yields are presented separately. We then add the two contributions to compute the total stellar yields. Below about 30 solar masses, rotation increases the total metal yields, Z, and in particular the yields of carbon and oxygen by a factor of 1.5-2.5. As a rule of thumb, the yields of a rotating 20 solar masses star are similar to the yields of a non-rotating 30 solar masses star, at least for the light elements considered in this work. For very massive stars (around 60 solar masses), rotation increases the yield of helium but does not significantly affect the yields of heavy elements.Comment: 11 pages, 4 figures; accepted for publication in A&

Stellar evolution with rotation XII: Pre-supernova models

We describe the latest developments of the Geneva stellar evolution code in order to model the pre-supernova evolution of rotating massive stars. Rotating and non-rotating stellar models at solar metallicity with masses equal to 12, 15, 20, 25, 40 and 60 solar masses were computed from the ZAMS until the end of the core silicon burning phase. We took into account meridional circulation, secular shear instabilities, horizontal turbulence and dynamical shear instabilities. Most of the differences between the pre-supernova structures obtained from rotating and non-rotating stellar models have their origin in the effects of rotation during the core hydrogen and helium burning phases. The effects of rotation on pre-supernova models are significant between 15 and 30 solar masses. Indeed, rotation increases the core sizes (and the yields) by a factor ~ 1.5. Above 20 solar masses, rotation may change the colour of the supernova progenitors (blue instead of red supergiant) and the supernova type (Ib instead of II). Rotation affects the lower mass limits for radiative core carbon burning, for iron core collapse and for black hole formation. For Wolf-Rayet stars (M > 30 solar masses), the pre-supernova structures are mostly affected by the intensities of the stellar winds and less by rotational mixing. Finally, the core of our rotating WR stars contain enough angular momentum to produce GRBs.Comment: 23 pages, 23 figures, accepted for publication in A&