All Outputs (100)

High-resolution abundance analysis of red giants in the globular cluster NGC 6522 (2014)
Journal Article
Barbuy, B., Chiappini, C., Cantelli, E., Depagne, E., Pignatari, M., Hirschi, R., Cescutti, G., Ortolani, S., Hill, V., Zoccali, M., Minniti, D., Trevisan, M., Bica, E., & Gómez, A. (2014). High-resolution abundance analysis of red giants in the globular cluster NGC 6522. Astronomy & Astrophysics, 570, A76. https://doi.org/10.1051/0004-6361/201424311

Context. The [Sr/Ba] and [Y/Ba] scatter observed in some galactic halo stars that are very metal-poor and in a few individual stars of the oldest known Milky Way globular cluster NGC 6522 have been interpreted as evidence of early enrichment by massi... Read More about High-resolution abundance analysis of red giants in the globular cluster NGC 6522.

The s-process enrichment of the globular clusters M4 and M22 (2014)
Journal Article
Hirschi. (2014). The s-process enrichment of the globular clusters M4 and M22. Astrophysical Journal, https://doi.org/10.1088/0004-637X/795/1/34

We investigate the enrichment in elements produced by the slow neutron-capture process (s-process) in the globular clusters M4 (NGC 6121) and M22 (NGC 6656). Stars in M4 have homogeneous abundances of Fe and neutron-capture elements, but the entire c... Read More about The s-process enrichment of the globular clusters M4 and M22.

Grids of stellar models with rotation - III. Models from 0.8 to 120 Msun at a metallicity Z = 0.002 (2013)
Journal Article
Georgy, C., Ekström, S., Eggenberger, P., Meynet, G., Haemmerlé, L., Maeder, A., Granada, A., Groh, J., Hirschi, R., Mowlavi, N., Yusof, N., Charbonnel, C., Decressin, T., & Barblan, F. (2013). Grids of stellar models with rotation - III. Models from 0.8 to 120 Msun at a metallicity Z = 0.002. Astronomy & Astrophysics, 558, Article A103. https://doi.org/10.1051/0004-6361/201322178

(shortened) We provide a grid of single star models covering a mass range from 0.8 to 120 Msun with an initial metallicity Z = 0.002 with and without rotation. We discuss the impact of a change in the metallicity by comparing the current tracks with... Read More about Grids of stellar models with rotation - III. Models from 0.8 to 120 Msun at a metallicity Z = 0.002.

ADVANCED BURNING STAGES AND FATE OF 8-10M☉STARS (2013)
Journal Article
Jones, S., Hirschi, R., Nomoto, K., Fischer, T., Timmes, F. X., Herwig, F., Paxton, B., Toki, H., Suzuki, T., Martínez-Pinedo, G., Lam, Y. H., & Bertolli, M. G. (in press). ADVANCED BURNING STAGES AND FATE OF 8-10M☉STARS. Astrophysical Journal, 772(2), 150. https://doi.org/10.1088/0004-637x/772/2/150

The reaction of either 4,4′,6,6′-tetramethyl-2,2′-bipyridine, L, or 4,4′,6,6′-tetracarboxy-2,2′-bipyridine, H4L, with Cu(OAc)2·H2O under acidic hydrothermal conditions (50:1 H2O/HNO3; 160 °C) led to the formation of crystalline {[Cu(HL′)(H2O)]·H2O},... Read More about ADVANCED BURNING STAGES AND FATE OF 8-10M☉STARS.

Detailedβ-transition rates for URCA nuclear pairs in 8–10 solar-mass stars (2013)
Journal Article
Toki, H., Suzuki, T., Nomoto, K., Jones, S., & Hirschi, R. Detailedβ-transition rates for URCA nuclear pairs in 8–10 solar-mass stars. Physical Review C - Nuclear Physics, 88(1), Article 015806. https://doi.org/10.1103/physrevc.88.015806

We calculate β-transition rates for URCA nuclear pairs using the sd-shell-model framework of Wildenthal [B. H. Widenthal, Prog. Part. Nucl. Phys. 11, 5 (1984)] with the modified Hamiltonian. We consider many β transitions including excited states nec... Read More about Detailedβ-transition rates for URCA nuclear pairs in 8–10 solar-mass stars.

SILICON CARBIDE GRAINS OF TYPE C PROVIDE EVIDENCE FOR THE PRODUCTION OF THE UNSTABLE ISOTOPE 32 Si IN SUPERNOVAE (2013)
Journal Article
Pignatari, M., Zinner, E., Bertolli, M. G., Trappitsch, R., Hoppe, P., Rauscher, T., Fryer, C., Herwig, F., Hirschi, R., Timmes, F. X., & Thielemann, F.-K. (in press). SILICON CARBIDE GRAINS OF TYPE C PROVIDE EVIDENCE FOR THE PRODUCTION OF THE UNSTABLE ISOTOPE 32 Si IN SUPERNOVAE. Astrophysical Journal Letters, 771(1), L7. https://doi.org/10.1088/2041-8205/771/1/l7

Carbon-rich grains are observed to condense in the ejecta of recent core-collapse supernovae (SNe) within a year after the explosion. Silicon carbide grains of type X are C-rich grains with isotopic signatures of explosive SN nucleosynthesis have bee... Read More about SILICON CARBIDE GRAINS OF TYPE C PROVIDE EVIDENCE FOR THE PRODUCTION OF THE UNSTABLE ISOTOPE 32 Si IN SUPERNOVAE.

Evolution and fate of very massive stars (2013)
Journal Article
Yusof, N., Hirschi, R., Meynet, G., Crowther, P. A., Ekström, S., Frischknecht, U., Georgy, C., Abu Kassim, H., & Schnurr, O. (2013). Evolution and fate of very massive stars. Monthly Notices of the Royal Astronomical Society, 433(2), 1114-1132. https://doi.org/10.1093/mnras/stt794

There is observational evidence that supports the existence of Very Massive Stars in the local universe. First, very massive stars (Mini<=320 M) have been observed in the Large Magellanic Cloud . Second, there are observed SNe that bear the character...

Thes-process in the Galactic halo: the fifth signature of spinstars in the early Universe? (2013)
Journal Article
Cescutti, G., Chiappini, C., Hirschi, R., Meynet, G., & Frischknecht, U. (2013). Thes-process in the Galactic halo: the fifth signature of spinstars in the early Universe?. Astronomy & Astrophysics, 553, Article A51. https://doi.org/10.1051/0004-6361/201220809

Context. Very old halo stars have previously been found to show at least four different abundance anomalies, which models of fast-rotating massive stars (spinstars) can successfully account for: rise of N/O and C/O, low 12C/13C, and a primary-like ev... Read More about Thes-process in the Galactic halo: the fifth signature of spinstars in the early Universe?.

PRODUCTION OF CARBON-RICH PRESOLAR GRAINS FROM MASSIVE STARS (2013)
Journal Article
Pignatari, M., Wiescher, M., Timmes, F. X., de Boer, R. J., Thielemann, F.-K., Fryer, C., Heger, A., Herwig, F., & Hirschi, R. (in press). PRODUCTION OF CARBON-RICH PRESOLAR GRAINS FROM MASSIVE STARS. Astrophysical Journal Letters, 767(2), L22. https://doi.org/10.1088/2041-8205/767/2/l22

About a year after core-collapse supernova, dust starts to condense in the ejecta. In meteorites, a fraction of C-rich presolar grains (e.g., silicon carbide (SiC) grains of Type-X and low density graphites) are identified as relics of these events,... Read More about PRODUCTION OF CARBON-RICH PRESOLAR GRAINS FROM MASSIVE STARS.

THE12C +12C REACTION AND THE IMPACT ON NUCLEOSYNTHESIS IN MASSIVE STARS (2012)
Journal Article
Pignatari, M., Hirschi, R., Wiescher, M., Gallino, R., Bennett, M., Beard, M., Fryer, C., Herwig, F., Rockefeller, G., & Timmes, F. X. (2013). THE12C +12C REACTION AND THE IMPACT ON NUCLEOSYNTHESIS IN MASSIVE STARS. Astrophysical Journal, 762(1), 31. https://doi.org/10.1088/0004-637x/762/1/31

Despite much effort in the past decades, the C-burning reaction rate is uncertain by several orders of magnitude, and the relative strength between the different channels 12C(12C, α)20Ne, 12C(12C, p)23Na, and 12C(12C, n)23Mg is poorly determined. Add... Read More about THE12C +12C REACTION AND THE IMPACT ON NUCLEOSYNTHESIS IN MASSIVE STARS.

The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit (2010)
Journal Article
Hirschi. (2010). The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit. Monthly Notices of the Royal Astronomical Society, 731 -751. https://doi.org/10.1111/j.1365-2966.2010.17167.x

Spectroscopic analyses of H-rich WN5-6 stars within the young star clusters NGC 3603 and R136 are presented, using archival HST & VLT spectroscopy, & high spatial resolution near-IR photometry. We derive high T* for the WN stars in NGC 3603 (T*~42+/-... Read More about The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit.

Massive Stars as Cosmic Engines through the Ages (2008)
Journal Article
Hirschi, R. (2008). Massive Stars as Cosmic Engines through the Ages. Proceedings of the International Astronomical Union, 3-16. https://doi.org/10.1017/S1743921308020292

Some useful developments in the model physics are briefly presented, followed by model results on chemical enrichments and WR stars. We discuss the expected rotation velocities of WR stars. We emphasize that the (C+O)/He ratio is a better chemical in... Read More about Massive Stars as Cosmic Engines through the Ages.

The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars (2008)
Journal Article
Pignatari, M., Gallino, R., Meynet, G., Hirschi, R., Herwig, F., & Wiescher, M. (2008). The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars. Astrophysical Journal, https://doi.org/10.1086/593350

The goal of this paper is to analyze the impact of a primary neutron source on the s-process nucleosynthesis in massive stars at halo metallicity. Recent stellar models including rotation at very low metallicity predict a strong production of primary... Read More about The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars.

Stellar Evolution in the Early Universe (2008)
Journal Article
Hirschi, R., Frischknecht, U., -K. Thielemann, F., Pignatari, M., Chiappini, C., Ekstroem, S., Meynet, G., & Maeder, A. (2008). Stellar Evolution in the Early Universe. Proceedings of the International Astronomical Union, 4(S255), https://doi.org/10.1017/S1743921308024976

Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this paper, we describe the strong impact of rota... Read More about Stellar Evolution in the Early Universe.

GRB progenitors at low metallicities (2007)
Journal Article
Hirschi, R., Meynet, G., & Maeder, A. (2007). GRB progenitors at low metallicities. IL NUOVO CIMENTO B, 10-11, 1183-1187. https://doi.org/10.1393/ncb/i2007-10237-6

We calculated pre-supernova evolution models of single rotating massive stars. These models reproduce observations during the early stages of the evolution very well, in particular Wolf--Rayet (WR) populations and ratio between type II and type Ib,c... Read More about GRB progenitors at low metallicities.

Very low metallicity massive star models: Pre-SN evolution and primary nitrogen production (2006)
Journal Article
Hirschi, R. (2006). Very low metallicity massive star models: Pre-SN evolution and primary nitrogen production. Astronomy & Astrophysics, 461(2), 571 - 583. https://doi.org/10.1051/0004-6361%3A20065356

Two series of models were computed. The first series consists of 20 solar mass models with varying initial metallicity (Z=0.02 down to Z=10^{-8}) and rotation (V_{ini}=0-600 km/s). The second one consists of models with an initial metallicity of Z=10... Read More about Very low metallicity massive star models: Pre-SN evolution and primary nitrogen production.

Stellar evolution with rotation XIII: Predicted GRB rates at various Z (2005)
Journal Article
Hirschi, R., Meynet, G., & Maeder, A. (2005). Stellar evolution with rotation XIII: Predicted GRB rates at various Z. Astronomy & Astrophysics, 443(2), https://doi.org/10.1051/0004-6361%3A20053329

We present the evolution of rotation in models of massive single stars covering a wide range of masses and metallicities. These models reproduce very well observations during the early stages of the evolution (in particular WR populations and ratio b... Read More about Stellar evolution with rotation XIII: Predicted GRB rates at various Z.

Rotating massive stars: Pre-SN models and stellar yields at solar metallicity (2005)
Journal Article
Hirschi, R., Meynet, G., & Maeder, A. (2005). Rotating massive stars: Pre-SN models and stellar yields at solar metallicity. Nuclear Physics A, 758, 234-237. https://doi.org/10.1016/j.nuclphysa.2005.05.041

We present a new set of stellar yields obtained from rotating stellar models at solar metallicity covering the massive star range (9-120 solar masses). The stellar models were calculated with the latest version of the Geneva stellar evolution code de... Read More about Rotating massive stars: Pre-SN models and stellar yields at solar metallicity.

Yields of rotating stars at solar metallicity (2005)
Journal Article
Hirschi, R., Meynet, G., & Maeder, A. (2005). Yields of rotating stars at solar metallicity. Astronomy & Astrophysics, 433(3), 1013-1022. https://doi.org/10.1051/0004-6361%3A20041554

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 de... Read More about Yields of rotating stars at solar metallicity.

Stellar evolution with rotation XII: Pre-supernova models (2004)
Journal Article
Hirschi, R., Meynet, G., & Maeder, A. (2004). Stellar evolution with rotation XII: Pre-supernova models. Astronomy & Astrophysics, 425, 649-670. https://doi.org/10.1051/0004-6361%3A20041095

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 an... Read More about Stellar evolution with rotation XII: Pre-supernova models.