Stellar Physics

Aboriginal Australians have been observing the stars for more than 65,000 years, and many of their oral traditions have been recorded since colonisation. These traditions tell of all kinds of celestial events, such as the annual rising of stars, passing comets, eclipses of the Sun and Moon, auroral displays, and even meteorite impacts. But new research, recently published in The Australian Journal of Anthropology, reveals that Aboriginal oral traditions describe the variable nature of three red-giant stars: Betelgeuse, Aldebaran and Antares. This challenges the history of astronomy and tells us that Aboriginal Australians were even more careful observers of the night sky than they have been given credit for.

transpire v. 1 intr. (of a secret or something unknown) leak out; come to be known 2 intr. disp. a (prec. by it as subject) turn out; prove to be the case. b occur; happen. -J. M. Hughes, P. A. Michell & W. S. Ramson, (1992) The Australian Concise Oxford Dictionary, Oxford University Press, Melbourne. Philip K. Dick, was a seminal U.S. author of science fiction in the late 20th Century. In the 28 years of his prolific career (1954 -82) amongst the hastily written books for a public hungry for paperbacks, he wrote many books that contained detailed and elaborate settings which spawned a host of alternative physical realities, much of which depended for it's impact on detailed descriptions of the environment, it's buildings and the process of design and construction. As a counterpoint to the fabric of reality his visions of the virtual worlds were hauntingly sketched well ahead of their realisation.

The cumulative effect of the magnetized stellar winds on exoplanets dominates over other forms of star-planet interactions. When combined with photoevaporation, these winds will lead to atmospheric erosion. This is directly connected with the concept of Habitable Zone (HZ) planets around late-type stars. Our knowledge of these magnetized winds is limited, making numerical models useful tools to explore them. In this preliminary study, we focus on solar-like stars exploring how different stellar wind properties scale with one another. We used one of the most detailed physics-based models, the 3D Alfvén Wave Solar Model part of the Space Weather ModelingFramework, and applied it to the stellar winds domain. Our simulations showed that the magnetic field topology on the star surface plays a fundamental role in shaping the different stellar wind properties (wind speed, mass loss rate, angular momentum loss rate). We conclude that a characterization of the Alfvén surface is crucial when studying star-planet interaction as it can serve as an inner-boundary of the HZ

Using a new approach, we have obtained a formula for calculating the rotation period and radius of planets. In the ordinary gravitomagnetism the gravitational spin (S) orbit (L) coupling, L • S ∝ L 2 , while our model predicts that L • S ∝ m M L 2 , where M and m are the central and orbiting masses, respectively. Hence, planets during their evolution exchange L and S until they reach a final stability at which MS ∝ mL, or S ∝ m 2 v , where v is the orbital velocity of the planet. Rotational properties of our planetary system and exoplanets are in agreement with our predictions. The radius (R) and rotational period (D) of tidally locked planet at a distance a from its star, are related by, D 2 ∝ M m 3 R 3 and that R ∝ m M a.

The present paper tests one of the important bibliometric law of Bradford’s Law of Scattering for the literature related to “Stellar Physics” for the period 1988 to 2013 as available in the Web of Science Core Collection database. A total of 2738 articles related to Stellar Physics published in journals in English language during the study period are retrieved. Data is analysed with respect to year-wise growth of articles, relative growth rate and doubling time of literature. The 2738 articles are scattered in 188 journals. A list of ranked journals was prepared and it was found that the Astrophysical Journal with 895 articles is the most productive journal publishing Stellar Physics literature followed by Monthly Notices of the Royal Astronomical Society with 507 articles and Astronomy & Astrophysics with 380 articles. In this study, theoretical aspects of Bradford’s Law of Scattering are tested and found that the data does not fit to the present sample as the number of articles in all the three zones is not equal. Leimkuhler model is tested and found to fit the data for Bradford Multiplier (k) at 11.65. Bradford Law is also tested through graphical formulation by drawing Bradford Bibliograph and found to confirm all the three characteristics.

The paper presents the first photometric analysis of two southern eclipsing binary stars, IS Tel and DW Aps. Their V light curves from the All Sky Automated Survey were modelled by using Wilson-Devinney method. The final models give these two Algol-like binary stars as having detached configurations. Absolute parameters of the components of the systems were also estimated.

In the present paper an analysis of the continuous radiation from photosphere of the Sun at equilibrium temperature of it is carried out. The radiation is assumed due to quantum jumps of the electron, in a high density ionized semi-gaseous type material of the photosphere of the Sun, from its amplitude states considering types of damped frequency oscillations and eigen frequency damped oscillations analogous to that exit in a low density plasma with electron-molecule collisions (Nandedkar 2016) [8]. Damped and eigen frequency damped oscillations of the electron result due to density fluctuations of the charge-carriers with opposite signs in the body of the photosphere due to nuclear processes going deep in the core of the Sun. The density fluctuations alternatively builds up and withdraws a d.c. electric field in the body of the photosphere. The necessary damping for the type of damped oscillations mentioned, is provided by electron-ion collision type interaction at equilibrium temperature of the photosphere. The minimum value of the amplitude the electron takes which can be quantized in the field of the neighbouring ion and in the absence of the d.c. electric field when eigen-frequency damped oscillations result, govern the minimum value of the wavelength of radiation from the continuous spectrum of the photosphere. In general the wavelength is shown to be a function of the average density of the charge-carriers. Thus lower limit of the electron density corresponding to an intermediate value of the chromosphere, brings an upper limit for the radiation-wavelength of the radiation spectrum of the photosphere. The continuous radiation from photosphere of the Sun corresponds to electron density N variations in the range 4.774(2) x 10 m ≥ N ≥ 1 x 10 m which corresponds to wavelength λ of radiation in the range 0.2476(8) x 10 m ≤ λ ≤ 8.984(9) x 10 m. However recently the solar spectrum is photographed up to a wavelength of about 0.2099 x 10 m which can be explained due to a mixture of a doubly charged ion and a singly charged ion in right proportion with one of electrons in each cases be considered, then the average distance of the electron from the ion can tend to lower down the minimum value of radiation wavelength.

It has been said that black holes have such immense gravity that they don't allow even light to escape. Although this is apparent in it's effect, the reasoning is flawed. As photon's are mass-less, they do not interact with gravity. A more accurate account of this observed truth is that they space the photon travels through is being pulled in and consumed by the black hole faster than the photon can travel across that space. The photon is still traveling at the speed of light through space, it's just that the black hole is pulling in or consuming that space(electrons) faster than the photons can travel through that space. Thus the photon appears to bend in it's path(e.g. Lensing) or doesn't escape at all as the space itself(electrons) are consumed along with all other matter occupying that space as well. This might seem like an insignificant detail in describing the phenomenon. However, it leads to evidence that faster than the speed of light is not only possible, but is happening continuously throughout space and in the vicinity of black holes, which are continuously breaking the speed of light rule. Once can surmise that the supposed speed of light barrier is not a barrier at all.

Observations of low frequency solar type III radio bursts associated with the ejection of plasma oscillations localized disturbance is due to excitation atoms in the plasma frequency incoherent radiations play a dominant role at the meter and decimeter wavelengths. Here, we report the results of the dynamical structure of solar flare type III that occurred on 9th March 2012 at National Space Centre, Sg Lang, Selangor, Malaysia by using the CALLISTO system. These bursts are associated with solar flare type M6 which suddenly ejected in the active region AR 1429 starting at 03:32 UT and ending at 05:00 UT with the peak at 04:12 UT. The observation showed an initial strong burst occurred due to strong signal at the beginning of the phase. We also found that both solar burst and flares tend to be a numerous on the same day and probability of chance coincidence is high. It is clearly seen that an impulsive lace burst was detected at 4:24 UT and it is more plausible that the energies are confined to the top of the loop when we compared with X-ray results. Associated with this event was type II with velocities 1285 km/s and type IV radio sweeps along with a full halo Coronal Mass Ejections (CMEs) first seen in SOHO/LASCO C2 imagery at 09/0426 Z. We concluded that the significance of study solar burst type III lies in the fact that the emission at decimetric wavelength comes from the role of magnetic field in active region that may provide the key to the energy release mechanism in a flare.

The imaging spectroscopy capabilities of the Reuven Ramaty high energy solar spectroscopic imager (RHESSI) enable the examination of the accelerated electron distribution throughout a solar flare region. In particular, it has been revealed that the energisation of these particles takes place over a region of finite size, sometimes resolved by RHESSI observations. In this paper, we present, for the first time, a spatially distributed acceleration model and investigate the role of inhomogeneous acceleration on the observed X-ray emission properties. We have modelled transport explicitly examining scatter-free and diffusive transport within the acceleration region and compare with the analytic leaky-box solution. The results show the importance of including this spatial variation when modelling electron acceleration in solar flares. The presence of an inhomogeneous, extended acceleration region produces a spectral index that is, in most cases, different from the simple leaky-box prediction. In particular, it results in a generally softer spectral index than predicted by the leaky-box solution, for both scatter-free and diffusive transport, and thus should be taken into account when modelling stochastic acceleration in solar flares.

We present new spectropolarimetric observations of the normal A-type star Vega, obtained during the summer of 2010 with NARVAL at Télescope Bernard Lyot (Pic du Midi Observatory). This new time-series is constituted of 615 spectra collected over 6 different nights. We use the Least-Square-Deconvolution technique to compute, from each spectrum, a mean line profile with a signal-to-noise ratio close to 20,000. After averaging all 615 polarized observations, we detect a circularly polarized Zeeman signature consistent in shape and amplitude with the signatures previously reported from our observations of 2008 and 2009. The surface magnetic geometry of the star, reconstructed using the technique of Zeeman-Doppler Imaging, agrees with the maps obtained in 2008 and 2009, showing that most recognizable features of the photospheric field of Vega are only weakly distorted by large-scale surface flows (differential rotation or meridional circulation).

Dynamics and collapse of collisionless self-gravitating systems is described by the coupled collisionless Boltzmann and Poisson equations derived from f(R) gravity in the weak field approximation.
Specifically, we describe a system at equilibrium by a time-independent distribution function f0(x; v)
and two potentials
Phi0(x) and Psi0(x) solutions of the modified Poisson and collisionless Boltzmann equations. Considering a small perturbation from the equilibrium and linearizing the field equations, it can be obtained a dispersion relation. A dispersion equation is achieved for neutral dust-particle systems
where a generalized Jeans wave number is obtained. This analysis gives rise to unstable modes not present in the standard Jeans analysis (derived assuming Newtonian gravity as weak filed limit of f(R). In this perspective, we discuss several self-gravitating astrophysical systems whose dynamics could be fully
addressed in the framework of f(R) gravity.

Solar flare hard X-ray spectroscopy serves as a key diagnostic of the accelerated electron spectrum. However, the standard approach using the collisional cold thick-target model poorly constrains the lower-energy part of the accelerated electron spectrum, and hence the overall energetics of the accelerated electrons are typically constrained only to within one or two orders of magnitude. Here we develop and apply a physically self-consistent warm-target approach which involves the use of both hard X-ray spectroscopy and imaging data. The approach allows an accurate determination of the electron distribution low-energy cutoff, and hence the electron acceleration rate and the contribution of accelerated electrons to the total energy released, by constraining the coronal plasma parameters. Using a solar flare observed in X-rays by the RHESSI spacecraft, we demonstrate that using the standard cold-target methodology, the low-energy cutoff (and hence the energy content in electrons) is essentially undetermined. However, the warm-target methodology can determine the low-energy electron cutoff with ∼7% uncertainty at the 3σ level and hence permits an accurate quantitative study of the importance of accelerated electrons in solar flare energetics.

Stellar activity cycles are known to be a widespread phenomenon amongst moderately active solar- and late-type stars from long-term periodic variations in chromospheric Ca II H and K emission lines, yet to date only a handful of coronal X-ray cycles are known. We have surveyed serendipitously observed stellar sources in fields observed multiple times in the last decade by XMM-Newton and present our analysis of 9 stars from 6 fields. Since our sample is flux-limited, it is strongly biased towards higher levels of X-ray activity. We fit a single temperature APEC spectrum to each source and search for significant periodicities using a Lomb-Scargle Periodogram (LSP). We use a Monte Carlo (MC) algorithm to yield robust analysis of the statistical significance of cycle detections and non-detections. None of the 9 stellar lightcurves show any convincing indications of periodicity. From MC simulations we simulate the detection capabilities of our methodology and, assuming a uniform distribution of cycle periods and strengths over the domain searched, we conclude with 95% confidence that less than 72% of the stars represented by our sample of active stars have 5-13 year coronal X-ray cycles.

The incidence of planetary systems orbiting red dwarf stars with masses < 0.4 solar masses provides a crucial observational test for the Self-Similar Cosmological Paradigm. The discrete self-similarity of the paradigm mandates the prediction of anomalously few planets associated with these lowest mass red dwarf stars, in contrast to conventional astrophysical assumptions. Ongoing observational programs are rapidly collecting the data necessary for testing this
prediction and preliminary results are highly encouraging. A definitive verdict on the prediction should be available in the near future.

We report the detection of pulsations with ∼ 124 s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX1+4. The pulsations are sinusoidal with modulation amplitude of up to 4 % in blue light and were observed in ten different observing sessions during 1996 April-August using a CCD photometer at the 1.6-m and 0.6-m telescopes of Laboratório Nacional de Astrofísica, in Brazil. The pulsations were also observed with the UBV RI fast photometer. With only one exception the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116 Oph had R magnitude in the range 15.3−15.5 when the pulsed signal was detected, and R = 16.0 − 17.7 when no pulsations were present. The discovery makes GX1+4 only the third of ∼ 35 accretion-powered X-ray pulsars to be firmly detecte...

We report the detection of pulsations with $\sim 124$ s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are sinusoidal with modulation amplitude of up to 4% in blue light and were observed in ten different observing sessions during 1996 April-August using a CCD photometer at the 1.6-m and 0.6-m telescopes of Laboratório Nacional de Astrof\'ısica, in Brazil. The pulsations were also observed with the $UBVRI$ fast photometer. With only one exception the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116~Oph had $R$ magnitude in the range $15.3-15.5$ when the pulsed signal was detected, and $R = 16.0-17.7$ when no pulsations were present. The discovery makes GX 1+4 only the third of $\sim 35$ accretion-powered X-ray pulsars to be firmly detected as a pulsating source in the optical. The presence of flickering and pulsations in V2116 Oph adds strong evidence for an accretion disk scenario in this system. The absolute magnitude of the pulsed component on 1996 May 27 is estimated to be $M_V \sim -1.5$. The implied dimensions for the emitting region are $1.1 R_{\sun}$, $3.2 R_{\sun}$, and $7.0 R_{\sun}$, for black-body spectral distributions with $T = 10^5$ K, $2 \times 10^4$ K, and $1 \times 10^4$ K, respectively.

Aims. We study the polarization of hard X-ray (HXR) sources in the solar atmosphere, including Compton backscattering of photons in the photosphere (the albedo effect) and the spatial distribution of polarization across the source. Methods. HXR photon polarization and spectra produced via electron-ion bremsstrahlung emission are calculated from various electron distributions typical for solar flares. Compton scattering and photoelectric absorption are then modelled using Monte Carlo simulations of photon transport in the photosphere to study the observed (primary and albedo) sources. Polarization maps across HXR sources (primary and albedo components) for each of the modelled electron distributions are calculated at various source locations from the solar centre to the limb. Results. We show that Compton scattering produces a distinct polarization variation across the albedo patch at peak albedo energies of 20-50 keV for all anisotropies modelled. The results show that there are distinct spatial polarization changes in both the radial and perpendicular to radial directions across the extent of the HXR source at a given disk location. In the radial direction, the polarization magnitude and direction at specific positions along the HXR source will either increase or decrease with increased photon distribution directivity towards the photosphere. We also show how high electron cutoff energies influence the direction of polarization at above ∼100 keV. Conclusions. Spatially resolved HXR polarization measurements can provide important information about the directivity and en-ergetics of the electron distribution. Our results indicate the preferred angular resolution of polarization measurements required to distinguish between the scattered and primary components. We also show how spatially resolved polarization measurements could be used to probe the emission pattern of an HXR source, using both the magnitude and the direction of the polarization.

We investigate the temporal spot evolution of the K-giant component in the RS CVn-type binary system zeta Andromedae to establish its surface differential rotation. Doppler imaging is used to study three slightly overlapping spectroscopic datasets, obtained independently at three different observing sites. Each dataset covers one full stellar rotation with good phase coverage, and in total, results in a continuous coverage of almost three stellar rotations ($P_{\rm rot}=$17.8\,d). Therefore, these data are well suited for reconstructing surface temperature maps and studying temporal evolution in spot configurations. Surface differential rotation is measured by the means of cross-correlation of all the possible image pairs. The individual Doppler reconstructions well agree in the revealed spot pattern, recovering numerous low latitude spots with temperature contrasts of up to $\approx$1000\,K with respect to the unspotted photosphere, and also an asymmetric polar cap which is diminishing with time. Our detailed cross-correlation study consistently indicate solar-type differential rotation with an average surface shear $\alpha\approx0.055$, in agreement with former results.

Classical variable stars called RR Lyrae stars have pulsating outer envelopes constituted of excited atoms. Here we demonstrate that the qualitative and quantitative properties of RR Lyrae variables and one subclass of their atomic scale constituents: singly-excited helium atoms undergoing
transitions between Rydberg states, share a remarkable degree of self-similarity.  In terms of masses, radii, oscillation periods, morphologies and kinematics the stellar and atomic analogues obey a simple set of discrete self-similar scaling
equations. The concept of stellar/atomic self-similarity may prove useful in the search for a deeper understanding of both stellar and atomic systems.

This paper presents a new viewpoint to explain why the outer core of Earth is liquid. The conclusion is based on these factors: iron and nickel are the principle elements of core; isotopes 57Fe, 61Ni can harvest low energy 14keV and 67keV respectively from concentrated neutrinos current, then convert to heat; unlike thermal neutron's optic refractive index n<1 and very close to 1, the low energy (<100keV) neutrino's can be n > 2, so as to form caustic zone inside Earth, confirmed by the fact that night observed value of solar neutrinos is 3.2% more than day. Why the outer core of Earth is liquid? Radius of the Earth is about 6371km, and the outer core of Earth counts from radius 1210km to 3510km, i.e. total thickness = 2300km, and modern seismic measurements have confirmed that the outer core of Earth is in liquid state. Of course, the simplest answer is that: too hot can make anything liquid. But how and where does the heating energy come from? Our textbooks are giving the wrong answer or alternative facts. My new research result shows the answer should have relation with the mystery neutrinos, especially the very low energy neutrinos. Don't forget the Sun is producing tremendous neutrinos after wake of fusion reaction. The great nature sets a mechanism to dissipate about 40% energy from beta decay. Although most

We calculate collision strengths and their thermally-averaged Maxwellian values for electron excitation and de-excitation between the fifteen lowest levels of singly-ionised cobalt, Co+, which give rise to emission lines in the near- and mid-infrared. Transition probabilities are also calculated and relative line intensities predicted for conditions typical of supernova ejecta. The diagnostic potential of the 10.52, 15.46 and 14.74 micro-metre transition lines is briefly discussed.

We consider a spherically symmetric internal solution within the context of Einstein–Chern–Simons gravity and derive a generalized five-dimensional Tolman–Oppenheimer–Volkoff (TOV) equation. It is shown that the generalized TOV equation leads, in a certain limit, to the standard five-dimensional TOV equation.

University Centre for Space Research and Technologies, Sofia University 
performs  scientific  and  applied  research,  and  education  in  Space  Research  and
Technologies, which have applications in Monitoring of Pollutions and Protection of the
Environment,  Prevention  of  Forest  Fires,  Global  Change,  GIS,  Electronics,
Telecommunications, Geophysics, Meteorology, Ecology, Archaeology and other fields.
It also performs research on properties of materials for space technology.
The  Centre  coordinates  and  manages  efforts  of  scientists  from  various  departments  of  Sofia
University and external institutions in temporary research teams, which accomplish scientific and
applied tasks related to Space Research and Technologies. Centre forms temporary laboratories on
different high- priority hot topics. It ensures higher flexibility than this of most scientific institutes
and university departments in the country. 
The  Centre  have  affiliated  companies  (O&K,  Hydroloc,  etc),  internationally  recognized
Astronomical  observatory  IAU-  79  and  active  Astronomical  student  circle,  which  also  performs
scientific research. 
Applied  research  fields  of  the  Centre  includes  development  of  IR,  UV  and  visible  imaging
systems and photometry for remote sensing observations from aircrafts, UAVs and satellites, Solar
and Space Impacts on the Environment and  applications of Space Research and Technologies in
Archaeological research and prospecting. 
Main  educational  activity  of  the  Center  are  master's  Programs  on  “Space  research”  and
“Aerospace engineering”. 
Center’s web page is: 
http://www.phys.uni-sofia.bg/eng/departments/ucsrt/index.html
Center’s YouTube channel is:
https://www.youtube.com/channel/UCyH3fFqMfKjLLI9jS4xnWHw
Center forms temporary laboratories, which work in its current directions of research, as its
laboratory in Archaeo-geophysics:
http://www.phys.uni-sofia.bg/bul/departments/ucsrt/agpl/index.html