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Galaxies, Volume 9, Issue 1 (March 2021) – 19 articles

Cover Story (view full-size image): This study uses a numerical model to analyze the spatial–temporal variations and prevalence of Extraterrestrial Intelligence (ETI) in the Milky Way Galaxy. It considers key parameters based on known observations and the established theory of star and galaxy evolution, supernova sterilization, abiogenesis, evolutionary timescale, and ETI self-annihilation. The main conclusions are: (1) ETI in the galaxy is most prevalent at ~ 4 kpcs (13,000 light-years) from the galactic center and ~8 billion years since the big bang; (2) self-annihilation is highly influential in the total number of galactic civilizations; (3) most civilizations in the galaxy might be young; (4) our location within the galaxy is outside of the boundary where we expect most ETI to occur. Overall, this study serves as a baseline for analyzing ETI in the Milky Way and providing information for the Search for [...] Read more.
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Article
On the Modeling of Algol-Type Binaries
Galaxies 2021, 9(1), 19; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010019 - 19 Mar 2021
Viewed by 505
Abstract
In earlier papers, we presented a binary evolutionary code for the purpose of reproducing the orbital parameters, masses, radii, and location in the Hertzsprung Russell diagram (abbreviated as HRD) of well-observed Algol systems. In subsequent versions, the effects of mass and angular momentum [...] Read more.
In earlier papers, we presented a binary evolutionary code for the purpose of reproducing the orbital parameters, masses, radii, and location in the Hertzsprung Russell diagram (abbreviated as HRD) of well-observed Algol systems. In subsequent versions, the effects of mass and angular momentum losses and tidal coupling were included in order to produce the observed distributions of orbital periods and mass ratios of Algol-type binaries. The mass loss includes stellar wind and possible liberal evolution, when the gainer star is not capable to absorb all of the matter during mass transfer from the donor star. We added magnetic braking to our code to better reproduce the observed equatorial velocities. Large equatorial velocities of mass-gaining stars are now lowered by tidal interaction and magnetic braking. Tides are mainly at work at short orbital periods, leaving magnetic braking alone at work during longer orbital periods. The observed values of the equatorial velocities of mass gainers in Algol-type binaries are mostly well reproduced by our code. According to our models, Algols have short periods with a strong magnetic field. Full article
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Article
The Dirac Electron Consistent with Proper Gravitational and Electromagnetic Field of the Kerr–Newman Solution
Galaxies 2021, 9(1), 18; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010018 - 17 Mar 2021
Viewed by 631
Abstract
The Dirac electron is considered as a particle-like solution consistent with its own Kerr–Newman (KN) gravitational field. In our previous works we considered the regularized by López KN solution as a bag-like soliton model formed from the Higgs field in a supersymmetric vacuum [...] Read more.
The Dirac electron is considered as a particle-like solution consistent with its own Kerr–Newman (KN) gravitational field. In our previous works we considered the regularized by López KN solution as a bag-like soliton model formed from the Higgs field in a supersymmetric vacuum state. This bag takes the shape of a thin superconducting disk coupled with circular string placed along its perimeter. Using the unique features of the Kerr–Schild coordinate system, which linearizes Dirac equation in KN space, we obtain the solution of the Dirac equations consistent with the KN gravitational and electromagnetic field, and show that the corresponding solution takes the form of a massless relativistic string. Obvious parallelism with Heisenberg and Schrödinger pictures of quantum theory explains remarkable features of the electron in its interaction with gravity and in the relativistic scattering processes. Full article
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Article
Testing Noncommutativity-Like Model as a Galactic Density Profile
Galaxies 2021, 9(1), 17; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010017 - 08 Mar 2021
Viewed by 553
Abstract
Noncommutative-like model (NC-like) is an interesting alternative inspired by string theory to understand and describe the velocity rotation curves of galaxies without the inclusion of dark matter particles. In a natural way, a Gaussian density profile emerges and is characterized by a parameter [...] Read more.
Noncommutative-like model (NC-like) is an interesting alternative inspired by string theory to understand and describe the velocity rotation curves of galaxies without the inclusion of dark matter particles. In a natural way, a Gaussian density profile emerges and is characterized by a parameter θ, called the NC-like parameter. Hence we aim to confront the NC-like model with a galaxy sample of the Spitzer Photometry and Accurate Rotation Curves (SPARC) catalog to constrain the model parameters and compare statistically with the Einasto density profile using the Akaike and Bayesian information criteria. According to our results, some galaxies prefer the NC-like over the Einasto model while others do not support NC-like. Full article
(This article belongs to the Special Issue Dark Cosmology: Shedding Light on Our Current Universe)
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Article
Black Holes and Other Clues to the Quantum Structure of Gravity
Galaxies 2021, 9(1), 16; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010016 - 25 Feb 2021
Cited by 1 | Viewed by 596
Abstract
Bringing gravity into a quantum-mechanical framework is likely the most profound remaining problem in fundamental physics. The “unitarity crisis” for black hole evolution appears to be a key facet of this problem, whose resolution will provide important clues. Investigating this raises the important [...] Read more.
Bringing gravity into a quantum-mechanical framework is likely the most profound remaining problem in fundamental physics. The “unitarity crisis” for black hole evolution appears to be a key facet of this problem, whose resolution will provide important clues. Investigating this raises the important structural question of how to think about subsystems and localization of information in quantum gravity. Paralleling field theory, the answer to this is expected to be an important ingredient in the mathematical structure of the theory. Perturbative gravity results indicate a structure different from that of quantum field theory, but suggest an avenue to defining subsystems. If black holes do behave similarly to familiar subsystems, unitarity demands new interactions that transfer entanglement from them. Such interactions can be parameterized in an effective approach, without directly addressing the question of the fundamental dynamics, whether that is associated with quantum spacetime, wormholes, or something else. Since such interactions need to extend outside the horizon, that raises the question of whether they can be constrained, or might be observed, by new electromagnetic or gravitational wave observations of strong gravity regions. This note overviews and provides connections between these developments. Full article
Review
Survey of CO2 Radiation Experimental Data in Relation with Planetary Entry
Galaxies 2021, 9(1), 15; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010015 - 23 Feb 2021
Viewed by 493
Abstract
This paper focuses on a survey of experimental data related to radiation into CO2 plasma flows, which are encountered during Mars and Venus entries. The review emphasizes on VUV and IR radiation, since recent experimental efforts has been devoted to these wavelength [...] Read more.
This paper focuses on a survey of experimental data related to radiation into CO2 plasma flows, which are encountered during Mars and Venus entries. The review emphasizes on VUV and IR radiation, since recent experimental efforts has been devoted to these wavelength ranges since they contribute mostly to CO2 plasma radiation. The main objective of the study is to identify the most attractive datasets for future crosscheck comparisons with the results obtained during future test campaigns with ESTHER shock-tube. The survey accounts for the results obtained in shock-tubes, expansion tube and plasma arc-jets for Mars and Venus test campaigns. The experimental results obtained for propulsion related studies have also been considered. Full article
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Article
Improvement of the Target Sensitivity in DECIGO by Optimizing Its Parameters for Quantum Noise Including the Effect of Diffraction Loss
Galaxies 2021, 9(1), 14; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010014 - 16 Feb 2021
Cited by 1 | Viewed by 612
Abstract
The DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is the future Japanese, outer space gravitational wave detector. We previously set the default design parameters to provide a good target sensitivity to detect the primordial gravitational waves (GWs). However, the updated upper limit of the primordial [...] Read more.
The DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is the future Japanese, outer space gravitational wave detector. We previously set the default design parameters to provide a good target sensitivity to detect the primordial gravitational waves (GWs). However, the updated upper limit of the primordial GWs by the Planck observations motivated us toward further optimization of the target sensitivity. Previously, we had not considered optical diffraction loss due to the very long cavity length. In this paper, we optimize various DECIGO parameters by maximizing the signal-to-noise ratio (SNR) of the primordial GWs to quantum noise, including the effects of diffraction loss. We evaluated the power spectrum density for one cluster in DECIGO utilizing the quantum noise of one differential Fabry–Perot interferometer. Then we calculated the SNR by correlating two clusters in the same position. We performed the optimization for two cases: the constant mirror-thickness case and the constant mirror-mass case. As a result, we obtained the SNR dependence on the mirror radius, which also determines various DECIGO parameters. This result is the first step toward optimizing the DECIGO design by considering the practical constraints on the mirror dimensions and implementing other noise sources. Full article
(This article belongs to the Special Issue Gravitational Wave Detectors)
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Article
Dark Supernova Remnants Revealed by CO-Line Bubbles in the W43 Molecular Complex along the 4-kpc Galactic Arm
Galaxies 2021, 9(1), 13; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010013 - 04 Feb 2021
Viewed by 554
Abstract
Fine structure of the density distribution in giant molecular clouds (GMCs) around W43 (G31+00+90 km s1at ∼5.5 kpc) was analyzed using the FUGIN* CO-line survey at high-angular (20”∼0.5 pc) and velocity (1.3 km s1) resolutions (*Four-receiver-system Unbiased Galactic Imaging survey with the Nobeyama 45-m telescope). The GMCs show highly turbulent structures, and the eddies are found to exhibit spherical bubble morphology appearing in narrow ranges of velocity channels. The bubbles are dark in radio continuum emission, unlike usual supernova remnants (SNR) or HII regions, and in infrared dust emission, unlike molecular bubbles around young stellar objects. The CO bubbles are interpreted as due to fully evolved buried SNRs in molecular clouds after rapid exhaustion of the released energy in dense molecular clouds. Then, the CO bubbles may be a direct evidence for exciting and maintaining the turbulence in GMCs by SN origin. Search for CO bubbles as “dark SNRs” (dSNR) will have implication to estimate the supernova rate more accurately, and hence the star formation activity in the Milky Way. Full article
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Article
Signatures of Lorentz Violation in Continuous Gravitational-Wave Spectra of Ellipsoidal Neutron Stars
Galaxies 2021, 9(1), 12; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010012 - 29 Jan 2021
Cited by 3 | Viewed by 741
Abstract
We studied the effects of the Lorentz invariance violation on the rotation of neutron stars (NSs) in the minimal gravitational Standard-Model Extension framework, and calculated the quadrupole radiation generated by them. Aiming at testing Lorentz invariance with observations of continuous gravitational waves (GWs) [...] Read more.
We studied the effects of the Lorentz invariance violation on the rotation of neutron stars (NSs) in the minimal gravitational Standard-Model Extension framework, and calculated the quadrupole radiation generated by them. Aiming at testing Lorentz invariance with observations of continuous gravitational waves (GWs) from rotating NSs in the future, we compared the GW spectra of a rotating ellipsoidal NS under Lorentz-violating gravity with those of a Lorentz-invariant one. The former were found to possess frequency components higher than the second harmonic, which does not happen for the latter, indicating those higher frequency components to be potential signatures of Lorentz violation in continuous GW spectra of rotating NSs. Full article
(This article belongs to the Special Issue Lorentz Violation in Astroparticles and Gravitational Waves)
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Review
Radio Constraints of Dark Matter: A Review and Some Future Perspectives
Galaxies 2021, 9(1), 11; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010011 - 28 Jan 2021
Viewed by 695
Abstract
In the past few decades, many studies have analyzed the data of gamma-rays, X-rays, radio waves, electrons, positrons, anti-protons, and neutrinos to search for the signal of dark matter annihilation. In particular, analyzing radio data has been one of the most important and [...] Read more.
In the past few decades, many studies have analyzed the data of gamma-rays, X-rays, radio waves, electrons, positrons, anti-protons, and neutrinos to search for the signal of dark matter annihilation. In particular, analyzing radio data has been one of the most important and effective ways to constrain dark matter. In this article, we review the physics and the theoretical framework of using radio data to constrain annihilating dark matter. We also review some important radio constraints of annihilating dark matter and discuss the future perspectives of using radio detection to reveal the nature of dark matter. Full article
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Article
Quantum Noise in a Fabry-Perot Interferometer Including the Influence of Diffraction Loss of Light
Galaxies 2021, 9(1), 9; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010009 - 26 Jan 2021
Cited by 1 | Viewed by 590
Abstract
The DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is designed to detect gravitational waves at frequencies between 0.1 and 10 Hz. In this frequency band, one of the most important science targets is the detection of primordial gravitational waves. DECIGO plans to use a [...] Read more.
The DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is designed to detect gravitational waves at frequencies between 0.1 and 10 Hz. In this frequency band, one of the most important science targets is the detection of primordial gravitational waves. DECIGO plans to use a space interferometer with optical cavities to increase its sensitivity. For evaluating its sensitivity, diffraction of the laser light has to be adequately considered. There are two kinds of diffraction loss: leakage loss outside the mirror and higher-order mode loss. These effects are treated differently inside and outside of the Fabry-Perot (FP) cavity. We estimated them under the conditions that the FP cavity has a relatively high finesse and the higher-order modes do not resonate. As a result, we found that the effects can be represented as a reduction of the effective finesse of the cavity with regard to quantum noise. This result is useful for optimization of the design of DECIGO. This method is also applicable to any FP cavities with a relatively small beam cut and the finesse sufficiently higher than 1. Full article
(This article belongs to the Special Issue Gravitational Wave Detectors)
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Article
Powerful Jets from Radiatively Efficient Disks, a Decades-Old Unresolved Problem in High Energy Astrophysics
Galaxies 2021, 9(1), 10; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010010 - 26 Jan 2021
Viewed by 829
Abstract
The discovery of 3C 273 in 1963, and the emergence of the Kerr solution shortly thereafter, precipitated the current era in astrophysics focused on using black holes to explain active galactic nuclei (AGN). But while partial success was achieved in separately explaining the [...] Read more.
The discovery of 3C 273 in 1963, and the emergence of the Kerr solution shortly thereafter, precipitated the current era in astrophysics focused on using black holes to explain active galactic nuclei (AGN). But while partial success was achieved in separately explaining the bright nuclei of some AGN via thin disks, as well as powerful jets with thick disks, the combination of both powerful jets in an AGN with a bright nucleus, such as in 3C 273, remained elusive. Although numerical simulations have taken center stage in the last 25 years, they have struggled to produce the conditions that explain them. This is because radiatively efficient disks have proved a challenge to simulate. Radio quasars have thus been the least understood objects in high energy astrophysics. But recent simulations have begun to change this. We explore this milestone in light of scale-invariance and show that transitory jets, possibly related to the jets seen in these recent simulations, as some have proposed, cannot explain radio quasars. We then provide a road map for a resolution. Full article
(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)
Editorial
Acknowledgment to Reviewers of Galaxies in 2020
Galaxies 2021, 9(1), 8; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010008 - 25 Jan 2021
Viewed by 431
Abstract
Peer review is the driving force of journal development, and reviewers are gatekeepers who ensure that Galaxies maintains its standards for the high quality of its published papers [...] Full article
Article
Analysis of the Open Cluster NGC 2281
Galaxies 2021, 9(1), 7; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010007 - 21 Jan 2021
Cited by 1 | Viewed by 673
Abstract
BV observations of an approximately 68×48 field centered on the open cluster NGC 2281 and covering more than 400 nights from 2013 to 2018 are presented. The photometric observations were transformed to the standard system using standards from the American Association of Variable Star Observers Photometric All-sky Survey (APASS) DR10 and analyzed with Gaia DR2 parallaxes and proper motions to determine the distance, age, and metallicity of the cluster. The discovery of an eclipsing binary in the field is discussed. Full article
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Review
Relativistic Effects of Rotation in γ-ray Pulsars—Invited Review
Galaxies 2021, 9(1), 6; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010006 - 18 Jan 2021
Cited by 1 | Viewed by 742
Abstract
In this paper, we consider the relativistic effects of rotation in the magnetospheres of γ-ray pulsars. The paper reviews the progress achieved in this field during the last three decades. For this purpose, we examine the direct centrifugal acceleration of particles and the corresponding limiting factors: the constraints due to the curvature radiation and the inverse Compton scattering of electrons against soft photons. Based on the obtained results, the generation of parametrically excited Langmuir waves and the corresponding Landau–Langmuir centrifugal drive are studied. Full article
(This article belongs to the Special Issue Observations of Gamma-Ray Pulsars)
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Article
A Statistical Estimation of the Occurrence of Extraterrestrial Intelligence in the Milky Way Galaxy
Galaxies 2021, 9(1), 5; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010005 - 18 Jan 2021
Cited by 1 | Viewed by 1624
Abstract
In the field of astrobiology, the precise location, prevalence, and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial–temporal variations and the prevalence of potential ETI [...] Read more.
In the field of astrobiology, the precise location, prevalence, and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial–temporal variations and the prevalence of potential ETI within the Galaxy. This model estimates the occurrence of ETI, providing guidance on where to look for intelligent life in the Search for ETI (SETI) with a set of criteria, including well-established astrophysical properties of the Milky Way. Further, typically overlooked factors such as the process of abiogenesis, different evolutionary timescales, and potential self-annihilation are incorporated to explore the growth propensity of ETI. We examine three major parameters: (1) the likelihood rate of abiogenesis (λA); (2) evolutionary timescales (Tevo); and (3) probability of self-annihilation of complex life (Pann). We found Pann to be the most influential parameter determining the quantity and age of galactic intelligent life. Our model simulation also identified a peak location for ETI at an annular region approximately 4 kpc from the galactic center around 8 billion years (Gyrs), with complex life decreasing temporally and spatially from the peak point, asserting a high likelihood of intelligent life in the galactic inner disk. The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult. Full article
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Article
Gravitational Measurements in Higher Dimensions
Galaxies 2021, 9(1), 4; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010004 - 11 Jan 2021
Cited by 2 | Viewed by 850
Abstract
We attempt to study three significant tests of general relativity in higher dimensions, both in commutative and non-commutative spaces. In the context of non-commutative geometry, we will consider a solution of Einstein’s equation in higher dimensions, with a source given by a static, [...] Read more.
We attempt to study three significant tests of general relativity in higher dimensions, both in commutative and non-commutative spaces. In the context of non-commutative geometry, we will consider a solution of Einstein’s equation in higher dimensions, with a source given by a static, spherically symmetric Gaussian distribution of mass. The resulting metric would describe a regular or curvature singularity free black hole in higher dimensions. The metric should smoothly interpolate between Schwarzschild geometry at large distance, and de-Sitter spacetime at short distance. We will consider gravitational redshift, lensing, and time delay in each sector. It will be shown that, compared to the four-dimensional spacetime, there can be significant modifications due to the presence of extra dimensions and the non-commutative corrected black holes. Finally, we shall attempt to obtain a lower bound on the size of the extra dimensions and on the mass needed to form a black hole in different dimensions. Full article
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Article
A Broadband Signal Recycling Scheme for Approaching the Quantum Limit from Optical Losses
Galaxies 2021, 9(1), 3; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010003 - 01 Jan 2021
Cited by 1 | Viewed by 722
Abstract
Quantum noise limits the sensitivity of laser interferometric gravitational-wave detectors. Given the state-of-the-art optics, the optical losses define the lower bound of the best possible quantum-limited detector sensitivity. In this work, we come up with a broadband signal recycling scheme which gives a [...] Read more.
Quantum noise limits the sensitivity of laser interferometric gravitational-wave detectors. Given the state-of-the-art optics, the optical losses define the lower bound of the best possible quantum-limited detector sensitivity. In this work, we come up with a broadband signal recycling scheme which gives a potential solution to approaching this lower bound by converting the signal recycling cavity to be a broadband signal amplifier using an active optomechanical filter. We will show the difference and advantage of such a scheme compared with the previous white light cavity scheme using the optomechanical filter in [Phys.Rev.Lett.115.211104 (2015)]. The drawback is that the new scheme is more susceptible to the thermal noise of the mechanical oscillator. Full article
(This article belongs to the Special Issue Gravitational Wave Detectors)
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Review
Messengers of the Universe-Cosmic Rays Exploring Supermassive Black Holes
Galaxies 2021, 9(1), 2; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010002 - 29 Dec 2020
Viewed by 648
Abstract
Cosmic rays were discovered over one hundred years ago but there are still unsolved problems. One of the hot problems is the origin of cosmic rays of the highest energies. Sources are still unclear and it is neither clear how particles gain ultra-high [...] Read more.
Cosmic rays were discovered over one hundred years ago but there are still unsolved problems. One of the hot problems is the origin of cosmic rays of the highest energies. Sources are still unclear and it is neither clear how particles gain ultra-high energies. Possible sources of cosmic rays at the highest energies are supermassive black holes. From this perspective we discuss in a popular form some recent developments in cosmic ray studies along with author’s recent results. The paper also offers materials for further reading. Full article
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Article
A Modified Kwee–Van Woerden Method for Eclipse Minimum Timing with Reliable Error Estimates
Galaxies 2021, 9(1), 1; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9010001 - 22 Dec 2020
Viewed by 635
Abstract
The Kwee–van Woerden (KvW) method used for the determination of eclipse minimum times has been a staple in eclipsing binary research for decades, due its simplicity and the independence of external input parameters, which also makes it well-suited to obtaining timings of exoplanet [...] Read more.
The Kwee–van Woerden (KvW) method used for the determination of eclipse minimum times has been a staple in eclipsing binary research for decades, due its simplicity and the independence of external input parameters, which also makes it well-suited to obtaining timings of exoplanet transits. However, its estimates of the timing error have been known to have a low reliability. During the analysis of very precise photometry of CM Draconis eclipses from TESS space mission data, KvW’s original equation for the timing error estimate produced numerical errors, which evidenced a fundamental problem in this equation. This contribution introduces an improved approach for calculating the timing error with the KvW method. A code that implements this improved method, together with several further updates of the original method, are presented. An example of the application to CM Draconis light curves from TESS is given. The eclipse minimum times are derived with the KvW method’s three original light curve folds, but also with five and seven folds. The use of five or more folds produces minimum timings with a substantially better precision. The improved method of error calculation delivers consistent timing errors which are in excellent agreement with error estimates obtained by other means. In the case of TESS data from CM Draconis, minimum times with an average precision of 1.1 s are obtained. Reliable timing errors are also a valuable indicator for evaluating if a given scatter in an O-C diagram is caused by measurement errors or by a physical period variation. Full article
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