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.

If you want to receive notifications for future online seminars, you can sign up for the seminar email
list by sending an empty email to Jinacee_online_seminar-join (at) jinaweb.org.
 
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
 05/26/17
 2 pm EST
 Stephan Stetina
 
   
 05/12/17
 2 pm EST
 Benoit Cote
 
   
 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 EzzeddineA 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 HanCooling 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.


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.

2) Please mute your microphone during the talk.

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:
    It would be great if you could answer the question, how JINA can help your field of research.



How to access the talk:

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

1) Register and download the Zoom software under https://www.zoom.us.

2) To join the Zoom meeting from PC, Mac, iOS or Android, please follow the link
     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.

If you encounter any problems or have any questions, please contact Ingo Tews (itews (at) uw.edu).




Previous Seminars:

Spring 2016

 Date       Speaker Title
 05/06/16
 2 pm EST
 Xilin Zhang
 Hot and dense matter beyond relativistic mean field theory
  I will talk about our recent work (arXiv:1602.07665, to be published in Physics Review C) on properties of hot and dense nuclear matter. The study is based on the framework of quantum hadro-dynamics, and includes contributions from two-loop (TL) diagrams arising from the exchange of iso-scalar and iso-vector mesons between nucleons. Our extension of relativistic mean-field theory (MFT) employs the same five coupling which are calibrated using the empirical properties at the equilibrium density of iso-spin symmetric matter. I will compare the MFT and TL calculations for the matter conditions that are relevant for astrophysics. As you will see, the TL results for the equation of state (EOS) of cold neutron matter at sub- and near-nuclear densities agree well with those of modern quantum Monte Carlo and effective field-theoretical approaches. At high density the neutron matter's EOS in the TL calculation is substantially softer than its MFT counterpart, but it is able to support a two-solar-mass neutron star required by recent determinations. In contrast to MFT, the TL results also give a better account of the single-particle or optical potentials extracted from analyses of medium-energy proton-nucleus  and heavy-ion experiments. I will also discuss the ratio of the thermal components of pressure and energy density expressed as Gamma_th = 1 + (Pth/Eth), which is often used in astrophysical simulations.
 04/22/16
 2 pm EST

 David Radice
Double Neutron Star Mergers
  Neutron star mergers are among the most violent events in the Universe.  They are one of the targets of the nascent gravitational-wave astronomy and could be linked with a number of possible electromagnetic transients.  In this talk, I will discuss recent results from numerical simulations of neutron star mergers, focusing on their gravitational-wave signature, the evolution of the merger remnant, and the dynamical ejection of neutron rich material.
 04/08/16
 2 pm EST
 Chris Sullivan
The Sensitivity of Core-collapse Supernovae to Nuclear Electron Capture
  An open source weak-rate library aimed at investigating the sensitivity of astrophysical environments to variations of electron-capture (EC) rates on medium-heavy nuclei has been developed. With this library, the sensitivity of the core-collapse and early post-bounce phases of core-collapse supernovae (CCSNe) to nuclear EC has been examined. In this study, the EC rates were adjusted by factors consistent with uncertainties indicated by comparing theoretical rates to those deduced from charge-exchange and β-decay measurements. To ensure a model-independent assessment, sensitivity studies across a comprehensive set of progenitors and equations of state were performed. Variations of the protoneutron star inner-core mass and peak electron-neutrino luminosities were observed to be 5 times larger when varying the EC rates than what is observed when fixing the rates and utilizing a wide array of progenitor models. Furthermore, the simulations were found to be particularly sensitive to the reduction in rates for neutron-rich nuclei near the N = 50 closed neutron shell. As measurements for medium-heavy (A>65) and neutron-rich nuclei are sparse, and because accurate theoretical models that account for nuclear structure considerations of individual nuclei are not readily available, rates for these species may be overestimated. In this talk, I will describe the impact this overestimate may have to the core-collapse trajectory, the detailed sensitivity of the core-collapse and bounce phases of CCSNe to EC rates, and I will suggest specific areas of focus for future experimental and theoretical efforts.
 03/11/16
 2 pm EST
 Alessandro Roggero
Thermal conductivity and impurity scattering in the accreting neutron star crust
  In this talk I will present our recent quantum calculations of the dynamical properties of the strongly correlated multi-component plasma expected in the outer layers of accreting neutron star's crust. The use of Path Integral Monte Carlo techniques allows us to isolate the low energy response of the ions and use it to estimate the electron thermal conductivity that results reduced by a factor 2-4 when compared to earlier calculations based on the simpler electron-impurity scattering formalism. These findings directly impact our interpretation of the thermal relaxation observed in transiently accreting neutron stars.
 02/26/16
 2 pm EST
 Maxime Brodeur
High precision mass measurements for Nuclear Astrophysics
  

The production of isotopes via explosive nucleosynthesis processes such as the rapid (r-) neutron and the rapid proton (rp-) capture process depend sensitively on the atomic mass of the nuclide involved. The development of new radioactive ion beam facilities and measurement techniques now allows to extend the reach where precise and accurate mass measurements can be done into unexplored territories. The importance of high precision mass measurements for nuclear astrophysics will be discuss, as well as some of the state-of-the-art measurements techniques and some current and future developments.

 02/12/16
 2 pm EST
 Jonas Lippuner
r-Process nucleosynthesis in neutron star mergers
  Stellar fusion and nuclear burning in type Ia supernovae can only produce elements up to the iron-peak (A ~ 56). Heavier elements can only be produced via neutron capture. I this talk, I will discuss nucleosynthesis via the rapid neutron capture process (r-process) in neutron star mergers. I will give an overview of binary neutron star and neutron star--black hole mergers and their expected observables. Then I will introduce the nuclear reaction network SkyNet and briefly discuss how the nucleosynthesis calculation work. The main focus will then be on various nucleosynthesis calculation results in the context of neutron star mergers.
 01/29/16
 2 pm EST
 Sean M. Couch
Simulations of Supernovae and Their Massive Star Progenitors in 3D
  Core-collapse supernovae are the luminous explosions that herald the death of massive stars.  While core-collapse supernovae are observed on a daily basis in nature, the details of the mechanism that reverses stellar collapse and drives these explosions remain unclear.  While the most recent high-fidelity simulations show promise at explaining the explosion mechanism, there remains tension between theory and observation.  This is likely telling us we are missing important physics in our simulations.  I will discuss some interesting candidates for such missing physics that could be crucial to the supernova mechanism.  In particular, I will describe our efforts to develop more realistic initial conditions for supernova simulations with fully 3D massive stellar evolution calculations.  Such realistic 3D initial conditions turn out to be favorable for successful explosions, in large part because they result in stronger turbulence behind the stalled supernova shock.  I will also discuss the important role turbulence is playing in the supernova mechanism and what might be required for accurately modeling the turbulence in our simulations.
 01/15/16
 2 pm EST
 Sebastien Guillot
How to measure the radius of a neutron star?

 Constraints on the equation of state (EoS) of matter at densities above nuclear density can be obtained by the study of neutron stars (NS). Several methods exist to determine the EoS of dense matter. They involve measurement of the NS mass or radius, of the NS moment of inertia, or of the chirp frequency of gravitational waves emitted during the last instant of a NS/NS mergers. In the past few years, the most robust constraints on the EoS came from the precise mass measurements of two NSs with M~2 Msun. However, further constraints on the EoS from NS masses will only be achieved by NS masses higher than the previously measured highest NS masses. In the past few years, however, the most promising constraints on the EoS arose from measurements of the NS radius. A variety of sub-classes of NSs offers of variety of methods producing NS radius measurements. In this talk, I will present these methods and their resulting constraints on the dEoS. I will also address their advantages and their drawbacks, and how these measurements could be improved in the future.