Wednesday Colloquium



Young astronomers meeting at CAMK (CAMK, Warsaw)


"TESS photometry of hot subdwarf stars"

Sumanta Kumar Sahoo (CAMK, Warsaw)

Hot subdwarf stars are extreme horizontal branch stars, consisting of a convective helium-burning core, helium shell, and a thin (in mass) hydrogen envelope. A few of these subdwarfs pulsate, which opens the window to study these stars using asteroseismology. The majority of such pulsating stars detected are B-type stars (sdBV). From the TESS mission, we have detected a few tens of rich gravity mode sdBVs by analyzing their short cadence (SC) light curves and identified their pulsation mode geometries. Apart from the SC data, we also extracted light curves from TESS full frame images for the targets not observed in SC mode and analyzed them to detect pulsations. I will be talking about these pulsating subdwarf stars and our study to understand their pulsation properties.


"Binary coalescences as sources of ultrahigh-energy cosmic rays"

Jonas Pereira (Núcleo de Astrofísica e Cosmologia & Departamento de Física, Universidade Federal do Espírito Santo, Vitória, Brasil and CAMK, W)

Binary coalescences are known sources of gravitational waves (GWs) and they encompass combinations of black holes (BHs) and neutron stars (NSs). I’ll show that when BHs are embedded in magnetic fields (B’s) larger than approximately e10 G, charged particles colliding around their event horizons can easily have ultrahigh energies (≳ e18 eV) and become more likely to escape. Such B-embedding and high-energy particles can take place in BH-NS binaries, or even in BH-BH binaries with one of the BHs being charged (with charge-to-mass ratios as small as e-5, which do not change GW waveforms) and having a residual accretion disk. The number of collisions leading to ultrahigh energy particles is estimated to range from a few up to millions before the merger of binary compact systems. Thus, binary coalescences may also be efficient sources of ultrahigh energy cosmic rays (UHECRs) and constraints to NS/BH parameters would be possible if UHECRs are detected along with GWs.

The presentation will be based on recent PRL work: Binary Coalescences as Sources of Ultrahigh-Energy Cosmic Rays Jonas P. Pereira, Carlos H. Coimbra-Araújo, Rita C. dos Anjos, and Jaziel G. Coelho Phys. Rev. Lett. 132, 091401 – Published 27 February 2024


"Thermal effects in nuclear matter and neutron stars"

Lucas Tonetto (Dipartimento di Fisica, “Sapienza” University of Rome, Italy)

In different astrophysical systems involving neutron stars, such as mergers or newly born stars, a reliable model of a finite-temperature equation of state is needed. Temperature has implications in equilibrium and dynamical phenomena, therefore a fully consistent framework should be able to take into account thermal effects in single-nucleon properties alongside yielding accurate results for average thermodynamic quantities. In this talk, I present the results of employing a recently developed effective interaction based on the Correlated Basis Functions theory, being able to account for nuclear correlations and two- and three-nucleon potentials. After discussing the properties of its generalisation to nonzero temperature, we apply it in the calculation of the neutrino mean free path and emissivity. In the latter, we study how in-medium effects alter the results by using effective weak transition operators.