The 2nd Conference of Young Researchers at CAMK PAN

Session

Student presentations

23 Jun 2020, 09:00

Zoom

11. A bright ultraluminous X-ray source in NGC 5055

NGC 5055 X-1 is the brightest ultraluminous X-ray (ULX) source with luminosity $2.3\times10^{40}$ erg/sec, located in the outskirt of the spiral galaxy NGC 5055. We present the first, detailed X-ray spectral analysis of this source. We fit the data with the phenomenological model composed of multi-color disk plus powerlaw and thermal Comptonization model. We found that the disk temperature...

19. Asteroseismology of pulsating subdwarf B stars using TESS data

Subdwarf B (sdB) stars are extreme horizontal branch stars, consisting of a convective helium burning core, helium shell and a very thin (in mass) hydrogen envelope. Few of these sdBs pulsate (sdBV), which opens the window to study these stars using asteroseismology. From the TESS mission, we have detected a few tens of rich gravity mode sdBVs by analysing their lightcurves and periodograms...

15. BLR size and R-L relation in realistic FRADO model

The effective size of Broad Line Region (BLR), so-called the BLR radius, in galaxies with active galactic nuclei (AGN) scales with the source luminosity. Therefore by determining this location either observationally through reverberation mapping or theoretically, one can use AGNs as an interesting laboratory to test cosmological models. Focusing on the theoretical side of BLR based on the...

3. Boosting the heat

The search for a relativistic theory of dissipation has lasted for 80 years. In the gravitational-wave era, we need, more than ever, a definitive answer to the question "how do heat and viscosity really work in relativity?". Our interpretation of the data coming from neutron-star mergers crucially depends on this. We need a theory which is formulated as a well-posed initial-value problem,...

22. Distance determinations using RR Lyrae stars and the new reddening maps of the Magellanic Clouds

During my talk, I will present preliminary results concerning the calibration of the Baade-Wesselink method of distance determinations for RR Lyrae stars.
I will shortly introduce the new reduction - standardization pipeline that I've written for the purpose of the reduction of photometric data.
I will also talk about the new reddening maps of the Magellanic Clouds that were published earlier...

24. Eclipse Timing of Detached Eclipsing Binaries using SOLARIS network of telescopes

The multiplicity of stellar systems has a quite high incidence. The presence of multiple bodies around a Detached Eclipsing Binary (DEB) can be observed through the Light Time Effect (LTE). Measuring the precise moments of minima (eclipse timing) takes advantage of the manifestation of LTE due to circumbinary bodies and the periodicity of the DEBs. I talk about the preliminary work to create a...

20. General relativistic radiation hydrodynamic simulations of levitating atmospheres

Some accreting neutron stars may produce near-Eddington luminosity. In general relativity, the atmosphere of a sufficiently luminous neutron star is disconnected from and levitates above its surface. The atmosphere is centered at a radius where the gravitational and radiation forces balance each other. We aim to simulate optically thin and thick levitating atmospheres of a near Eddington...

4. High metal content of highly accreting quasars

We present an analysis of 23 quasar UV spectra believed to belong to extreme Population A (xA) quasars, aimed at the estimation of the chemical abundances of the broad line emitting gas. Metallicity estimates for the broad line emitting gas of quasars are subject to a number of caveats, although present data suggest the possibility of an increase along the quasar main sequence along with...

2. Kinetic numerical simulations of particle acceleration mechanisms in relativistically magnetized jets of blazars

High-energy astrophysical phenomena reveal signatures of non-thermal particle energy distributions. Among them stand blazars with very broad photon spectra, from radio up to very high energy ($\sim$ TeV) gamma rays and variability on timescales ranging from decades to minutes. Relativistic magnetic reconnection offers an attractive scenario for the explanation of efficient particle...

8. Magnetic field evolution of neutron stars

Neutron stars are incredibly dense compact objects having the strongest magnetic field in the universe known to date. To study the field evolution in real-time, we performed magnetohydrodynamic simulations using the publicly available code PLUTO. The field undergoes a cataclysmic rearrangement in few Alfven timescales which develops a toroidal component with field strength 50% of the poloidal...

18. MOCCA Survey Database: Extra Galactic Globular Clusters. Method and first results

Over the last few decades, exhaustive surveys of extra Galactic globular clusters (EGGCs) have become feasible. Only recently, kinematical information of globular clusters (GCs) were available through Gaia DR2 spectroscopy and also proper motions. On the other hand, simulations of GCs can provide detailed information about the dynamical evolution of the system. We present a preliminary study...

17. On the spectral-timing properties of Cygnus X-1 in its hard state.

During an outburst, Black Hole X-Ray Binaries (BHXRBs) present two main spectral states: the soft and the hard. The geometry of the system is thought to change throughout the outburst but its exact evolution is unknown. In particular, for the hard state, there is still no agreement on its exact geometry. In Cygnus X-1, the spectral components observed in the hard state can be explained in...

12. Partially accreted crusts of Neutron Stars

Neutron stars in binary systems may accrete matter from their companion star ; so far, only the case of a crust fully replaced by accreted matter has been considered in detailed calculations. However if the star has only accreted a small amount of matter, the crust is not fully but only partially accreted. This could be for example the case of IGR J17480−2446. The observed decrease of its...

23. Pulsating subdwarf B stars in the oldest open cluster NGC6791

NGC6791 is the oldest metal rich ([Fe/H]=0.4) open cluster with an age of 8Gyr. The evolution of this cluster is still an enigma. Subdwarf B stars are extreme horizontal branch core helium burning objects with a very thin hydrogen envelope. We study the evolution of subdwarf B stars in this cluster by means of asteroseismology to derive the parameters of the stars. We have analyzed Kepler...

10. Scaling of magnetic dissipation and particle acceleration in ABC fields

Using particle-in-cell (PIC) numerical simulations, we study how the efficiencies of magnetic dissipation and particle acceleration scale with the initial effective wavenumber $k_{\rm eff}$ of the two-dimensional “Arnold-Beltrami-Childress” (ABC) magnetic field configurations.All simulations are run for at least 25 light crossing times in order to achieve a saturation stage.We confirm the...

16. Stellar Pulsation studies

Pulsating stars offer a window to look into key aspects of
stellar evolution and also serve as a tool (especially Cepheids) to
distance scale measurements. Their ubiquitous nature can reveal a lot
about the structure and evolution of our Galaxy and the Magellanic
Clouds. In this talk, I will discuss two important classes of pulsating
stars, Cepheids and RR Lyrae, in general, and then dive into...

21. Stratification of hot accretion flow of MAXI J1820+070

Spectral and timing results show that the inner accretion flow in the hard state of black hole X-ray binaries (BHXRB) appears more inhomogeneous than assumed in standard spectral fits.
These studies hint at a stratified hot medium, with the inner parts being hotter and emitting a harder spectrum. Such complex structure implies that time-averaged energy spectra cannot be fitted with simple...

7. Studying the southern Beta Cephei stars using TESS

The TESS satellite provides us with precise high quality time series data for stars including hot O- and B-type stars, which was mostly skipped in other missions. We make use of this photometric data to study variabilities in B type stars. Analysis of HN Aqr (Handler et al. 2019), already showed the prospectives for massive star asteroseismology based on such data, along with realizing the...

14. Testing the reliability of AGN torus X-ray spectral models

Numerous X-ray spectral models have been developed to model emission reprocessed by an AGN torus, e.g., UXCLUMPY, CTORUS, MYTORUS. They span a range of assumed torus geometries and morphologies – some posit smooth gas distributions, others posit distributions of clouds. It is suspected that given the quality of currently available data, certain model parameters (such as photon index and torus...

9. The CaFe Project: Search for the correlation between Fe+ and Ca+ in active galaxies

Resolving the complexity in Fe II species in quasar spectra has been an ongoing work for over 40 years. First identified and reported for the prototypical Narrow-line Seyfert 1 galaxy I Zw 1 ([Phillips 1978a][1]), the study has made a niche of its own in the field of AGN research. Seminal works led by [Boroson & Green (1992)][2], [Verner et al. (1999)][3], [Sigut & Pradhan (2003)][4] and...

6. The hunt for peculiar Eu and Ba abundances in metal-poor stars using *Gaia* and GALAH surveys

The lanthanide-rich ejecta observed in the spectroscopic follow up of the neutron-star merger and gravitational wave event GW170817 has shed light on a possible r-process nucleosynthesis site. However, abundances of r-process elements measured in metal-poor stars suggest that neutron-star mergers are not the only site for this kind of nucleosynthesis. Metal-poor stars provide information...

13. The origin of inequality. Isolated formation of 30 Msun and 10 Msun BH-BH merger.

The LIGO/Virgo collaboration has reported the detection of GW190412, a black hole-black hole (BH-BH) merger with the most unequal masses to date: m1 = 24.4–34.7 Msun and m2 = 7.4–10.1 Msun, corresponding to a mass ratio of q = 0.21–0.41 (90% probability range). Additionally, GW190412’s effective spin was estimated to be χeff = 0.14–0.34, with the spin of the primary BH in the range aspin =...

25. Tools for Period Searching in AGN in the Era of ``Big Data''

AGN persistently emit across the electromagnetic spectrum; emission is dominated by stochastic, aperiodic variability that overwhelms any periodic/quasi-periodic signal (QPO) if one exists. Pure stochastic red noise processes can spuriously mimic few-cycle sinusoid-like periodicities. Hence, while using different statistical tools one needs to account for red noise which can impact the...

5. X-ray variability studies from GRMHD simulations

Long term observations of black-hole X-ray binaries show that these systems exhibit extreme, aperiodic variability on time scales of few milliseconds to seconds. The observed light-curves display various characteristic features like log-normal distribution and linear rms-flux relation, which indicates that the underlying variability process is stochastic in nature and is thought to be...