Iranian Journal of Astronomy and Astrophysics
https://ijaa.du.ac.ir/
Iranian Journal of Astronomy and Astrophysicsendaily1Mon, 25 Dec 2023 00:00:00 +0330Mon, 25 Dec 2023 00:00:00 +0330Thermodynamics of Horndeski Black Holes with Generalized Uncertainty Principle
https://ijaa.du.ac.ir/article_384.html
Horndeski theory is the most general scalar-tensor extension of General Relativity with second order field equations. It may be interesting to study the effects of the Generalized Uncertainty Principle on a static and asymptotically flat shift symmetric solutions of the Horndeski black holes. With this motivation, here we obtain the modified black hole temperatures in shift symmetric Horndeski gravity by employing the Generalized Uncertainty Principle. Using the corrected temperature, the entropy and heat capacity are calculated with details. We also investigate the tunneling probability of particles from Horndeski black holes horizon and possible correlations between the emitted modes (particles).Dissipation of Magnetohydrodynamic Waves in the Solar Stratified Flux Tubes
https://ijaa.du.ac.ir/article_383.html
Chromosphere is the second layer of the Sun with high variability. The increase of the temperature and the decrease of the density are observed in this layer. This unusual behavior is one of the most important problems in the solar corona. Between the solar chromosphere and the corona, there is a thin transition zone in which the temperature rises very rapidly. Magnetohydrodynamic waves are thought to play an important role in this heating. The dissipation of Alfven waves has been investigated due to phase mixing in the presence of steady flow and sheared magnetic field in a solar stratified flux tube. The temperature variations with height (T0(z)) in the flux tube has been considered. The numerical calculations showed that the amplitude of the tube oscillations decreases with time. Hence, the wave damping takes place in the flux tubes. The temperature and the density variations enhances the wave damping rate compared to the case without temperature effect.Identification of Gamma-Ray Point Sources in Fermi-LAT Data with Minimum Spanning Tree Algorithm
https://ijaa.du.ac.ir/article_385.html
Gamma rays are the most energetic photons in the electromagnetic spectrum, detected with ground-based and space-based detectors in different energy ranges from sources in our galaxy and beyond. Gamma-ray point sources can be identified by special clustering of these photons. The minimum spanning tree (MST) algorithm is a graph-based method in order to find clusters. In this paper, we use the MST algorithm for finding point sources in Fermi gamma-ray space telescope data which is sensitive to photons with energies of 20 MeV up to more than 300 GeV. To this end, we selected eight completely random (10&deg;&times;10&deg;) fields of Fermi gamma-ray sky and tested the algorithm on the 12-year Fermi-LAT sky (Pass 8) at energy ranges above 3 GeV and above 6 GeV and with different cluster selection criteria. The calculation of Precision and Recall for both fields shows that MST is a useful algorithm in order to identify the point.Physics-Informed Deep Learning for Three Dimensional Black Holes
https://ijaa.du.ac.ir/article_387.html
In this paper, we have designed an artificial neural network architecture to produce metric field of planar BTZ and quintessence black holes applying a data-driven approach andleveraging holography principle (according to AdS/DL (Anti de Sitter/ Deep Learning) correspondence given by [1]). Data has been collected by choosing minimally coupled massive scalar field with quantum fluctuations and we try to process two emergent and ground-truth metrics versus the holographic parameter which plays the role of depth of the neural network. Loss or error function which shows rate of deviation of these two metrics in presence of penalty regularization term reaches to its minimum value when values of the learning rate approach to the observed steepest gradient point. Values of the regularization or penalty term of the quantum scalar field has critical role to matching this two mentioned metric. Also, we design an algorithm which helps us to find optimum value for learning parameter and finally, we understand that loss function convergence heavily depends on the number of epochs and learning rate.Astronomy Lab I: Photometric Experiments for Physics Students
https://ijaa.du.ac.ir/article_388.html
As physics laboratories are an integral part of the physics education across the globe, astronomy laboratories are also a necessary part of the astronomy education. However there have been only theoretical astronomy and astrophysics in Iranian universities. We present for the first time a new laboratory course on observational astronomy for bachelor and master students. In this course, students performed observational experiments and learned how to analyze astronomical data. Data are transformed from the camera RAW to the FITS format and later analyzed using Python AstroPy packages. In Astronomy Lab I, students learned to polar align equatorial mounts, measure the read and shot noises, estimate the spatial resolution in long exposure images, measure the solar limb darkening, stack a number of images to get a high signal to noise final image, calculate magnitude using aperture photometry, retrieve the absorption coefficient for each filter, correct for the atmospheric extinction and draw a Hertzsprung-Russell (HR) diagram for open clusters.Modified Gauge Invariant Einstein-Maxwell Gravity and Stability of Spherical Perfect Fluid Stars with Magnetic Monopoles
https://ijaa.du.ac.ir/article_390.html
As an alternative gravity model, we consider an extended Einstein-Maxwell gravity containing a gauge invariance property. An extension is assumed to be an addition of a directional coupling between spatial electromagnetic fields with the Ricci tensor. We will see importance of the additional term in making a compact stellar object and the value of its radius. As an application of this model we substitute ansatz of the magnetic field of a hypothetical magnetic monopole which has just time independent radial component and for matter part we assume a perfect fluid stress tensor. To obtain spherically symmetric internal metric of the perfect fluid stellar compact object we solve the Tolman-Oppenheimer-Volkoff equation with a polytropic form of equation of state as p(&rho;) = a&rho;2. Using dynamical system approach we study stability of the solutions for which arrow diagrams show saddle (quasi stable) for a &lt; 0 (dark stars) and sink (stable) for a &gt; 0 (normal visible stars). We check also the energy conditions, speed of sound and Harrison-Zeldovich-Novikov static stability criterion for obtained solution and confirm that they make stable state.