JINA-CEE biweekly online seminar

Dear JINA-CEE members and colleagues,

we are hosting a biweekly JINA online seminar series on all topics within the JINA collaboration.

The talks will be streamed online and, thus, can be given from anywhere the speaker wants to.
The talks will be held Fridays, 2pm EST. Everyone is welcome to suggest seminar speakers and
topics.

The seminar is meant to help coordinate and initiate research, and to help junior people establish
collaborations. The format will be a 35-40 min talk followed by 10-15 mins of questions.

list by sending an empty email to Jinacee_online_seminar-join (at) jinaweb.org.

https://msu.zoom.us/j/827950260

Thank you very much in advance. We are looking forward to the seminar series!

P.S.: If you missed a seminar talk, you can watch it by clicking on the title in the list below. You can find
talks from previous semsters at the bottom of the page.

Schedule:

 Date Speaker Title 04/13/18 2pm EST Constantinos Constantinou Enforcing causality in nonrelativistic equations of state We discuss two thermodynamically consistent approaches by whichnonrelativistic (NR) equations of state (EOS) can be modi.ed so thatthey respect causality at all densities and temperatures. We explore their consequences to the state functions of the EOS for entropies-per-baryon of relevance to astrophysical simulations and to the properties of maximum-mass neutron star con.gurations in pure neutron matter for well-known NR models. We also show that, for Skyrme(-like) models, the adiabatic speed of sound is independent of the temperature in the limit of high temperature. 03/30/18 2pm EST James Keegans Postprocessing of Multidimensional Supernova Models Supernova are major contributors to chemical enrichment of galaxies, influencing the abundances of many elements (alpha elements and Fe-group in core collapse supernovae and mostly Fe-group in Type Ia supernovae). Demand for yields from multidimensional simulations of these events has increased in recent years as the effects of non-sphericity have become increasingly apparent in observations. This current work aims to provide nucleosynthetic yields for multidimensional supernovae models, with a reaction network consistent with that used to calculate the abundances of the NuGrid stellar data set. The applications of this new data set to GCE models, and the use of the tools developed to investigate nuclear reaction rate uncertainties should provide a robust framework for future research. 03/16/18 2pm EST Constantinos Constantinou MOVED DUE TO TECHNICAL ISSUE 02/16/18 2pm EST Farrukh Fattoyev Connecting Neutron Skins to Gravitational Waves The historical first detection of a binary neutron star (BNS) merger by the LIGO-Virgo Collaboration has already provided fundamental new insights into the nature of dense neutron-rich nuclear matter. By using a set of realistic models of the equation of state (EOS) that yield an accurate description of the properties of finite nuclei, support neutron stars of two solar masses, and provide a Lorentz covariant extrapolation to dense matter, we confront their predictions against the measured tidal deformability from the BNS merger. Since the gravitational-wave signal is sensitive to the underlying EOS, limits on the tidal deformability inferred from the observation translate into constraints on the neutron-star radius of $R_{1.4} ≲ 13.76$ km. And given the sensitivity of the neutron-skin thickness to the pressure of neutron-rich matter, hence to the neutron star radii, we infer a corresponding upper limit on the neutron skin of about $R_{\rm skin}^{208} ≲ 0.25$ fm. Using the lower bound on the neutron skin thickness as imposed by the Parity Radius Experiment (PREX), we also set a lower limit on tidal polarizabilities of $\Lambda > 490$. We will further discuss observational implications of future PREX-II/CREX measurements, especially should they measure a significantly larger neutron skin thickness. 02/02/18 2pm EST Tony Ahn The first neutron-rich beam induced (alpha,xn) reaction study with the HabaNERO detector Solar abundance pattern tells us historical evidences of element formation in the Universe. Among many different nucleosynthesis processes and astrophysical environments produce the abundancepattern similar to measured one, (.alpha,xn) reactions have been identified as the main production mechanism of Z=38-47 abundances in neutron-rich neutrino driven winds during core-collapse supernovae scenario. Recent sensitivity studies of (alpha.,xn) reaction rates showed that uncertainties of the rates directly affect calculated abundances with an impact that is similar to that from astrophysical uncertainties. Current reaction rate uncertainties are relatively large because very little experimental data exists for (alpha,xn) cross sections with neutron-rich nuclei involved in the nucleosynthesis calculation. We have developed the Heavy ion Accelerated Beam induced (Alpha,Neutron) Emission Ratio Observer (HabaNERO) for the measurement of relevant (.alpha,xn) reactions in the neutrino-wind including 75Ga(.alpha,xn). The HabaNERO is a neutron long counter system which consists of 44 BF3 and 36 3He gas-filled proportional tubes oriented in rings along the beam axis embedded in a polyethylene matrix. The configuration of tubes in the matrix was optimized to obtain a high average neutron detection efficiency as constant as possible in the wide neutron range En = 0.1-19.5 MeV that corresponds to the neutron energies of interest. We have performed the detector commissioning using mono-energetic neutron beams at Edward Accelerator Laboratory, Ohio University, as well as a 75Ga(.alpha,xn) cross section measurement at ReA3, NSCL. This experiment was the first measurement of (.alpha,xn) cross section for neutron-rich nuclei in inverse kinematics. The construction, commissioning, and performance of the detector system will be presented, as well as preliminary results of data analysis. 01/19/18 2pm EST Caroline Robin Nuclear transitions of astrophysical interest in the relativistic nucleon-vibration coupling framework The response of nuclei to external probes has many applications across the field of astrophysics. A precise description of neutral and charge-exchange excitations is necessary to compute the rates of various processes such as neutron-capture, beta-decay, neutrino-scattering or electron-capture, which are needed for the modeling of nucleosynthesis and stellar evolution.In this talk I will present a theoretical approach to the description of the nuclear response. This method describes the nucleus as a system of relativistic protons and neutrons interacting via effective meson exchange, and builds inter-nucleon correlations by accounting for the coupling between single nucleons and collective vibrations of the nucleus. Such correlations typically induce fragmentation and spreading of the transition strength which are essential for a precise description of giant resonances and low-energy modes, and have a great impact on the computing of decay and reaction rates.I will present calculations of various excitation modes and corresponding astrophysical rates in mid-mass and heavy nuclei. Emphasis will be put on recent calculations of Gamow-Teller transitions for beta-decay and electron-capture rates. 12/08/17 2pm EST Alexey Vlasenko Multi-Angle Simulations of Matter-Neutrino Resonance Neutrino flavor transformation can play an important role in astrophysical environments such as compact object mergers and supernovae.  In neutron star mergers, a phenomenon known as the matter-neutrino resonance (MNR) has been shown to efficiently convert electron neutrinos to other flavors, while leaving the anti-neutrino spectra relatively unchanged.  In the past, simulations of MNR were performed in the single-angle approximation, so that the applicability of the results to realistic situations was uncertain.  Our recent work shows that in multi-angle simulations, MNR leads to a distinctive pattern of flavor transformation that is qualitatively different from the single-angle case, but shares with it some common features.  This pattern of flavor transformation appears to be robust, being present under a wide variety of physical conditions.  We conclude that neutrino flavor transformation due to MNR is likely to play an important role in neutron star mergers, with possible consequences for nucleosynthesis, observable signals, and the dynamics of the merger. 11/24/17 Day after Thanksgiving 11/17/17 2pm EST Andre da Silva Schneider Nuclear equation of state for astrophysical simulations The equation of state (EOS) near and above nuclear saturation density is still uncertain. This translates into uncertainties in numerical simulations of core-collapse supernovae and neutron star mergers and in their multi-messenger signatures. Therefore, a wide range of EOSs spanning the allowed range of nuclear interactions are necessary for determining the sensitivity of these astrophysical phenomena and their signatures to variations in input microphysics. I will discuss the effects of the EOS on thermodynamical properties of dense matter, neutron star mass-radius relationship, and in observables of core collapse supernovae. 11/10/17 Veterans Day 10/13/17 2pm EST Alex Deibel Nuclear astrophysics with accreting neutron stars The crusts of accreting neutron stars are heated during active accretion and cool when accretion ends. Thermal evolution models of cooling neutron stars reveal the thermodynamic properties of the dense matter in their crusts. I will discuss how some of the latest observations of cooling neutron stars have allowed us to constrain the properties of nuclear pasta and superfluid neutrons in the neutron star's inner crust. I will also outline new accretion-driven heating mechanisms in the neutron star crust that may reconcile observations of the hottest neutron stars with numerical models.

General remarks:

1) Please join the video conference in time. This way, we have a chance of fixing any problems. Also,
it would be appreciated if attendees meet locally to join the video conference using only one account.

3) If you have any question, please wait until the end of the talk (unless it is necessary for the further
understanding of the talk).
Please also indicate in the chat window that you want to ask a question. If you like, you can also type
the question into the chat window.

4) For the speaker:

How to access the talk:

We will use Zoom for the web seminar. To access the online seminar, please follow the steps below:

https://msu.zoom.us/j/827950260

Or join by phone:

+1 415 762 9988 or +1 646 568 7788 US Toll
Meeting ID: 827 950 260
International numbers available: https://msu.zoom.us/zoomconference?m=yxsDQfz6NMjHbqafkTfe_lhpidS4DVmA

Or join from a H.323/SIP room system:

Dial: 162.255.36.11 (US West) or 162.255.37.11 (US East)
Meeting ID: 827 950 260

3) The seminar speaker will share her/his screen with all participants to give the talk.

Previous Seminars:

Fall 2016 / Spring 2017

 Date Speaker Title 07/28/17 2 pm EST Stephan Stetina The Photon in Dense Nuclear Matter In the core of a neutron star we expect to find a dense plasma comprised of electrons, muons, protons and neutrons interacting via electromagnetic and strong forces. The complicated interplay of these interactions has a profound impact on the spectra of photons traversing through the plasma. The photon spectrum in turn is an important ingredient in the calculation of transport coefficients which for instance determine the damping of hydrodynamic modes or the spin evolution of neutron stars. I will provide a detailed study of the photon spectrum based on the Random Phase Approximation (RPA), placing a particular focus on screening effects and collective modes. 07/07/17 2 pm EST MacKenzie Warren Using the entire toolbox: exploring core-collapse supernovae using spherically symmetric simulations In the era of high performance computing, multidimensional simulations of core-collapse supernovae have provided a valuable window into the explosion mechanism.  However, given the prohibitively high computational cost of each simulation, we cannot yet use them to address some of our biggest questions in core-collapse supernova theory, such as the varying outcomes of different progenitor masses, sensitivities to the nuclear equation of state, and contributions of CCSNe to nucleosynthesis.  So what’s a simulator to do?  I will discuss how we use both 1D and 3D models in conjunction to address some of our biggest open questions and how 1D and 3D models can inform each other for improved physics on both fronts.  In particular, I will present a new method for modeling CCSNe in spherically symmetry that models the turbulence and convection seen in 3D simulations.  This better replicates the physical explosion mechanism, as well as local and global properties of multidimensional simulations, allowing for more reliable predictions of explodability, sensitivities, and nucleosynthesis. 06/09/17 2 pm EST Richard deBoer Understanding the 12C(a,g)16O reaction, its role in stellar evolution and in the laboratory The 12C(a,g)16O reaction is one of the most important for the field of nuclear astrophysics. It strongly influences how massive stars evolve and is even sensitive to the rate of nucleosynthesis of the weak s-process. After 40+ years of measurements, significant improvement in our understanding of the reaction has been achieved, yet the desired level of uncertainty remains just out of reach. In this talk I will give an overview of how this reaction affects nucleosynthesis and stellar evolution as well as the great efforts that have been made to determine its reaction rate experimentally. 05/12/17 2 pm EST Benoit Cote Extending the JINA-NuGrid Galactic Chemical Evolution Pipeline to Cosmological Scales Understanding the origin of abundances patterns observed in the stars of the Milky Way and its satellite galaxies represents a significant challenge as it requires the contribution of several fields of research. To address this challenge, we have developed a series of interconnected codes (NuPyCEE) within the JINA-CEE and NuGrid collaborations in order to bridge stellar evolution with galaxy evolution and to highlight the impact of nuclear astrophysics in a galactic chemical evolution (GCE) context. This numerical pipeline has already been used to investigate the astrophysical sites of odd-Z, first s-process peak, and r-process elements. In this seminar, I will present our effort to extend our GCE pipeline toward cosmological scales by accounting for the mass assembly of galaxies. In particular, I will present our new galaxy model and its interaction with the merger trees extracted from cosmological simulations, the impact of the mass assembly on the star formation history, and the crucial role played by input stellar yields. 04/28/17 2 pm EST Stylianos Nikas Impact of level density and gamma strength function parametrizations on Hauser-Feshbach calculations of neutron capture rates The r-process site remains one of the biggest mysteries in Nuclear Astrophysics. To improve our knowledge behind the synthesis of the heavy elements, Nuclear Physics can be used to limit the scenarios behind the r-process. Reaction rate knowledge is one of the key ingredients to model the r-process nucleosynthesis. However, nuclear statistical properties like level density and gamma-ray strength functions that are used to calculate the corresponding reaction rates using the Hauser-Feshbach theory are not well known away from the valley of stability and need to be constrained. We explore the impact of different models of level densities and gamma ray strength functions to Hauser-Feshbach calculations of (n,g) reaction rates. The main parameters affecting the calculated reaction rates are identified and presented. In addition, we discuss the effect of the variations of the calculated reaction rates, due to the different models of statistical properties used, to the r-process yields. 04/14/17 2 pm EST Matthew Mumpower Reverse engineering nuclear properties from $r$-process abundances The astrophysical r-process of nucleosynthesis is believed to be responsible for the production of most of the rare earth elements. The solar r-process residuals show a small bump in the rare earths around A~160, which is proposed to be formed dynamically during the end phase of the r-process by a pileup of material. This abundance feature is of particular importance as it is sensitive to both the nuclear physics inputs and the astrophysical conditions of the main r-process. We explore the formation of the rare earth peak from the perspective of an inverse problem, using Monte Carlo studies of nuclear masses to investigate the unknown nuclear properties required to best match rare earth abundance sector of the solar isotopic residuals. The feedback provided by this observational constraint allows for the reverse engineering of nuclear properties far from stability where no experimental information exists. We show that the combination of this method with future measurements has potential to resolve the type of conditions responsible for the production of the rare earth nuclei, and provide new insights into the longstanding problem of the astrophysical site(s) of the r-process. 03/03/17 2 pm EST Panagiotis Gastis The details of nucleosynthesis in core collapse supernovae (CCSNe) are important in answering the question about the origin of heavy elements. If the right proton-rich conditions are found vp- process could be contributing to the synthesis of heavy elements beyond iron in the neutrino driven winds of CCSNe. The strength of the vp-process in nucleosynthesis strongly depends on key reactions like the 56Ni(n,p)56Co for which no experimental data currently exist. For this purpose, a cross section measurement of the 56Co(p,n)56Ni reaction (time-inverse) in inverse kinematics, is going to take place at the new ReA3 facility of the National Superconducting Cyclotron Laboratory at Michigan State University. The result will constrain the reaction rate of the astrophysically important 56Ni(n,p)56Co reaction and will provide information about the role of the vp-process in nucleosynthesis. In this presentation, a summary of the vp-process mechanism and a description of the experimental technique for the measurement of the 56Co(p,n)56Ni reaction will be shown. 02/03/17 2 pm EST Kelly Patton Presupernova Neutrinos: Realistic Emissivities from stellar Evolution We present a new calculation of neutrino emissivities and energy spectra from a massive star going through the advanced stages of nuclear burning (presupernova) in the months before becoming a supernova. The contributions from beta decay and electron capture, pair annihilation, plasmon decay, and the photoneutrino process are modeled in detail, using updated tabulated nuclear rates. We also use realistic conditions of temperature, density, electron fraction and nuclear isotopic composition of the star from the state of the art stellar evolution code MESA. Results are presented for a set of progenitor stars with mass between 15 M_sun and 30 M_sun . It is found that beta processes contribute substantially to the neutrino emissivity above realistic detection thresholds of few MeV, at selected positions and times in the evolution of the star. 01/20/17 2 pm EST Kamal Pangeni Gap-Bridging enhancement of modified Urca processes in nuclear matter In nuclear matter at neutron-star densities and temperatures, Cooper pairing leads to the formation of a gap in the nucleon excitation spectra resulting in exponentially strong Boltzmann suppression of many transport coefficients. However, density oscillations of sufficiently large amplitude can overcome this suppression for flavor-changing beta processes via the mechanism of gap bridging. In this talk I will give brief introduction to the mechanism of gap bridging and show that gap bridging can counteract Boltzmann suppression of neutrino emissivity for the realistic case of modified Urca processes with 3P2 neutron pairing. 12/02/16 2 pm EST Matt Caplan Astromaterial Science Stars freeze. But not all of them. Only some parts of some stars will. In white dwarfs and neutron stars, despite temperatures of millions of degrees, the densities and pressures are great enough to compact nuclei into a crystalline lattice millions of times more dense than any material on earth. Deeper still in neutron stars, near the nuclear saturation density, nuclei begin to touch and rearrange into non-spherical structures called 'nuclear pasta.' To interpret observations of neutron stars the composition and structure of the crystal and pasta layers must be understood, as the microscopic properties of the crust determine the macroscopic properties of the star, such as its thermal and electrical conductivity. At Indiana University, we perform computer simulations of these exotic astromaterials to calculate the physical properties of these stars. 11/18/16 2 pm EST Laurens Keek An Exceptionally Long Thermonuclear Burst from IGR J17062-6143: deep ignition and the impact on its surroundings In 2015 a rare day-long Type I X-ray burst was observed from accreting neutron star IGR J17062-6143. Long bursts are thought to be produced by thermonuclear burning deep in the star's envelope, close to the crust. Bursts lasting many hours are typically attributed to the burning of carbon-rich fuel (superbursts). However, our analysis indicates helium-rich fuel, making this possibly the most powerful helium burst ever observed. Such a powerful burst has a strong impact on the surroundings: we find evidence in the spectrum of X-ray reflection off the accretion disk and of disruption of a corona. 11/04/16 2 pm EST Rana Ezzeddine A Non-LTE iron abundance study of Ultra-metal poor stars Accurate determination of the chemical composition of Ultra metal-poor (UMP) stars help to reconstruct the nature of the initial mass function of the First Population III (Pop III) stars. A necessary prerequisite to obtaining high quality chemical abundances are precise and accurate stellar atmospheric parameters, which can be spectroscopically constrained using Fe lines. The photospheres of UMP stars are relatively transparent in the UV, which may lead to large deviations in the Fe line formation from Local Thermodynamic Equilibrium (LTE), an assumption usually relaxed in most chemical abundance analyses. I will present a Non-LTE Fe abundance study of the UMP stars with the lowest iron abundances known to date ([Fe/H] < -4:00). In that, I will suggest a new scale for NLTE Fe abundance corrections for metal-poor stars ([Fe/H] < -2:00) and discuss the corresponding consequences on spectroscopic stellar parameter determinations and comparisons to predicted supernova yields. 10/21/16 2 pm EST Sophia Han Cooling of Transiently Accreting Neutron Stars in Quiescence” Thermal states of neutron stars in soft X-ray transients (SXRTs) are supposed to be determined by deep crustal heating in the accreted matter and cooling via emission of photons and neutrinos from the surface/interior. In this study we assume a global thermal steady-state of the transient system[1] and calculate the heating curves (quiescent surface luminosity vs. mean accretion rate) predicted from theoretical models, taking into account variations in the equations of state, superfluidity gaps, thickness of the light element layer and a phenomenological description of the direct Urca threshold. We further provide a statistical analysis on the uncertainties in these ingredients, and compare the overall results with observations of several SXRTs, in particular the two sources containing the coldest (SAX J1808.4-3658) and the hottest (Aql X-1) neutron stars. Interpretation of the observed data indicates that very likely direct Urca process along with small superfluid gaps is required at least for the most massive stars. For now we exclude the effects from exotic degrees of freedom and defer them to future work.[1] “Neutron Star Cooling”, Ann.Rev.Astron.Astrophys. 42, 169 09/23/16 2 pm EST Zach Meisel Nuclear Thermostats: Urca Pairs in Accreting Neutron Star Oceans and Crusts The thermal structure of the outer layers of accreting neutron stars impacts a number of astronomical observables, such as X-ray bursts, superbursts, and cooling transients following accretion turn-off. Electron capture reactions in the neutron star ocean and crust have the potential to remove or deposit substantial amounts of heat, with potential observational consequences. The presence and strength of electron capture-driven heating and (‘Urca’) cooling reactions in the outer layers of accreting neutron stars are primarily influenced by the properties of individual nuclei, many of which can be determined in the laboratory. In this presentation I will discuss how these nuclei come to be on the neutron star surface and why Urca cooling is likely ubiquitous in the outer layers of accreting neutron stars. I will also briefly discuss recent results regarding the impact of Urca cooling on X-ray superbursts and cooling transient neutron stars. Furthermore, I will highlight some recent and future experimental efforts aimed at reducing the nuclear physics contribution to uncertainties in the presence and strength of Urca cooling pairs.

Spring 2016