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The authors have proposed a model geometry for the interior of a regular black hole (BH) mimicker, the frozen star, whose most startling feature is that each spherical shell in its interior is a surface of infinite redshift. The geometry is a solution of the Einstein equations which is sourced by an exotic matter with maximally negative radial pressure. The frozen star geometry is previously presented in singular coordinates for which −gtt$-g_{tt}$ and grr$g^{rr}$ vanish in the bulk and connect smoothly to the Schwarzschild exterior. Additionally, the geometry is mildly singular in the center of the star. Here, the authors present regular coordinates for the entirety of the frozen star. Each zero in the metric is replaced with a small, dimensionless parameter ε; in both −gtt$-g_{tt}$ and grr$g^{rr}$ thus maintaining maximally negative radial pressure. The authors also regularize the geometry, energy density and pressure in the center of the star in a smooth way. The frozen star solution presented here is a completely regular solution of Einstein's equations whose compactness is arbitrarily close to that of a Schwarzschild BH. It obeys the null energy condition, the universally agreed‐upon energy condition, and it is free of any known pathology. As far as it is known, this is the first solution that obeys all of these constraints and, in addition, as will be shown in a future publication, can mimic all of the thermodynamic properties of a standard BH. Our initial analysis uses Schwarzschild‐like coordinates and applies the Killing equations to show that an infalling, point‐like object will move very slowly, effectively sticking to the surface of the star and never coming out. If one nevertheless follows the trajectory of the object into the interior of the star, it moves along an almost‐radial trajectory until it comes within a small distance from the star's center. Once there, if the object has any amount of angular momentum at all, it will be reflected outwards by a potential barrier onto a different almost‐radial trajectory. Finally, using Kruskal‐like coordinates, the causal structure of the regularized frozen star and discuss its ε→0$\varepsilon \rightarrow 0$ limit, for which the geometry degenerates and becomes effectively two dimensional is considered. [ABSTRACT FROM AUTHOR]

The Be stars display variable optical emission lines originating in the circumstellar disc. Here we analyze high resolution spectroscopic observations of Be stars and the distance between the peaks of Hα$$ \mathrm{H}\alpha $$, Hβ$$ \mathrm{H}\beta $$, and Hγ$$ \mathrm{H}\gamma $$ emission lines (ΔVα$$ \Delta {V}_{\alpha } $$,ΔVβ$$ \Delta {V}_{\beta } $$, and ΔVγ$$ \Delta {V}_{\gamma } $$ respectively). Combining published data, spectra from the ELODIE archive (obtained in the period 1998–2003) and Rozhen spectra (obtained 2015–2023) of 93 Be stars, we find a set of relations connecting ΔVα$$ \Delta {V}_{\alpha } $$, ΔVβ$$ \Delta {V}_{\beta } $$ and ΔVγ$$ \Delta {V}_{\gamma } $$. They are effective for 30≤ΔVα≤500kms−1$$ 30\le \Delta {V}_{\alpha}\le 500\kern0.3em \mathrm{km}\kern0.3em {\mathrm{s}}^{-1} $$, 80≤ΔVβ≤600kms−1$$ 80\le \Delta {V}_{\beta}\le 600\kern0.3em \mathrm{km}\kern0.3em {\mathrm{s}}^{-1} $$, and 40≤ΔVγ≤300kms−1$$ 40\le \Delta {V}_{\gamma}\le 300\kern0.3em \mathrm{km}\kern0.3em {\mathrm{s}}^{-1} $$. The new equations are in the form y=ax+b$$ y= ax+b $$ and are valid for a wider velocity range than in previous studies. [ABSTRACT FROM AUTHOR]

The study is about the quasars' cosmological evolution. We used the medium‐band photometric survey at the 1‐m Schmidt telescope of the Byurakan Astrophysical Observatory. The HS47‐22 field with an area of 2.38 square degrees has been selected. We have classified objects and composed a sample of quasars using broadband photometric data and morphological classification from the DECaLS survey (Dey et al. 2019), infrared photometry from the WISE survey (Meisner et al. 2018), spectroscopy from the Sloan Digital Sky Survey (Pâris et al. 2018), ROSAT X‐ray data (Molthagen et al. 1997), FIRST radio data (Becker et al. 1995), and stellar parallax data from the GAIA survey (Gaia Collaboration et al. 2018). We have compiled a sample of 682 quasars, determined their photometric redshifts from the medium‐band photometric data, and calculated the absolute stellar magnitudes. The space density of quasars was calculated for different luminosity ranges at different redshifts using the λ‐CDM model with Ωm=0.3 and Ωλ=0.7 (Hogg 1999). In this paper, we present the comparison of our results with other works. [ABSTRACT FROM AUTHOR]

The main purpose of this scoping review was to summarize the most common tasks and outcome measures in randomized control trials (RCTs) used to assess sensorimotor function following ankle sprain and chronic ankle instability (CAI). We also aimed to summarize the description of inclusion criteria used in articles. We searched for RCTs published between 2008 and 2018 using the following databases: MEDLINE, PubMed, SPORTDiscus, and Web of Science. Eligible studies included participants of either sex who had had at least one ankle sprain with/without subsequent CAI. All articles assessed sensorimotor function. The tasks, outcome measures, and inclusion criteria were categorized, and frequencies of use in each category were calculated. Of 272 publications, 31 met the eligibility criteria. The most common task was single‐limb stance (58% of 31). The most common outcome measure was the posterior‐medial reach distance of the Star Excursion Balance Test (SEBT) (13 of 16 articles, 81%). Different inclusion criteria for a history of ankle sprains or CAI were used. A wide range of sensorimotor assessments and inclusion criteria was used among studies involving individuals with a history of ankle sprain with or without CAI, which could make it difficult to compare and generalize study results. This scoping review provides a baseline for planning future studies exploring outcome measures to assess sensorimotor function of individuals with a history of ankle sprain with or without CAI. [ABSTRACT FROM AUTHOR]

We have reanalyzed the data used by Bessel, von Struve, and Henderson in the 1830s to measure the first parallax distances to stars. We can generally reproduce their results, although we find that von Struve and Henderson have underestimated some of their measurement errors, leading to optimistic parallax uncertainties. We find that temperature corrections for Bessel's measured positions are larger than anticipated, explaining some systematics apparent in his data. It has long been a mystery as to why von Struve first announced a parallax for Vega of 0.″125 only to later revise it to double that value using more data. We resolve this mystery by finding that von Struve's early result used two dimensions of position data, which independently give significantly different parallaxes but, when combined, only fortuitously give the correct result. With later data, von Struve excluded the "problematic" dimension, leading to the larger parallax value. Allowing for likely temperature corrections and using his data from both dimensions reduce von Struve's parallax for Vega to a value consistent with the correct value. [ABSTRACT FROM AUTHOR]

The Gaia mission will have a profound impact on our understanding of the structure and dynamics of the Milky Way. Gaia is providing an exhaustive census of stellar parallaxes, proper motions, positions, colors and radial velocities, but also leaves some glaring holes in an otherwise complete data set. The radial velocities measured with the on-board highresolution spectrograph will only reach some 10 % of the full sample of stars with astrometry and photometry from the mission, and detailed chemical information will be obtained for less than 1 %. Teams all over the world are organizing large-scale projects to provide complementary radial velocities and chemistry, since this can now be done very efficiently from the ground thanks to large and mid-size telescopes with a wide field-of-view and multi-object spectrographs. As a result, automated data processing is taking an ever increasing relevance, and the concept is applying to many more areas, from targeting to analysis. In this paper, I provide a quick overview of recent, ongoing, and upcoming spectroscopic surveys, and the strategies adopted in their automated analysis pipelines. [ABSTRACT FROM AUTHOR]

The Gaia benchmark stars are stars with very precise stellar parameters that cover a wide range in the HR diagram at various metallicities. They are meant to be good representative of typical FGK stars in the Milky Way. Currently, they are used by several spectroscopic surveys to validate and calibrate the methods that analyse the data. I review our recent activities done for these stars. Additionally, by applying our new method to find stellar twins on the Gaia-ESO Survey, I discuss how good representatives of Milky Way stars the benchmark stars are and how they distribute in space. [ABSTRACT FROM AUTHOR]

Introduction: The libration zone of the Moon has not yet been studied accurately enough due to its inaccessibility to direct observations. Nevertheless, while studies on the movement in space of the center of mass of the Moon are being performed and selenodetic reference networks are being created, the construction of accurate models of the lunar relief will not lose its relevance [1-8]. Positional observations make it possible to determine the coordinates of the center of the Moon's figure, which, as it is well known, does not coincide with the center of mass. A difference of up to 0.5" (selenocentric coordinates) can result from the influence of the above factors. In addition, this value is a variable depending on the optical libration. When taking positional observations, the location of the center of the Moon's disk, i.e. approximating circle, can be calculated from the coordinates of a large number of points on its edge, and if we assume that the influence of the microrelief is considered as a random variable obeying the law of normal distribution, the coordinates of the center of mass can be determined by the method proposed in [9]. Methods: The method for creating a digital model of the libration zone of the Moon (DMLZM) is based on the reduction of positional observations [10], when it is impossible to obtain simultaneously a large number of coordinates of points in the libration zone. Therefore, when building DMLZM, adaptive regression modeling is used. The final version of DMLZM should allow accounting for: 1) mutual position of the center of mass and the center of the figure at the moment of observation; 2) errors arising due to the unaccounted influence of the microrelief of the libration zone at the point of observation, which can be as great as several seconds. Therefore, to take into account the irregularities of the edge of the Moon's disk with simultaneous reduction to the center of its mass, models of the relief of the libration zone are used. Results: On the basis of large-scale images of the Moon with stars, a model of the libration zone of the Moon was built in the system of the fundamental catalogue of stars. The studies have shown that the model data center is close to the lunar ephemeris center of mass given by the DE423 theory (created in 2010, includes nutations and librations). It should be noted that, despite a significant number of images of the Moon (over 80 nights of observations), the coordinate plane in some parts turned out to be insufficiently provided with observations, especially in areas near the poles of the Moon. Conclusions: The model of the libration zone of the Moon was studied based on photoelectric observations of the occultations of stars by the Moon using the method described in [11]. The results of this study showed that the weighted average value of ΔR= (R✷☾ - 932.58"), where R✷☾= -0.004" ± 0.593" is topocentric distance between the Moon's center of mass and a star at an average distance from the Earth, and the offset of the center of map data from the center of mass of the Moon, given by the theory of motion DE423, is about 0.1". The constructed model can be used to successfully solve problems related to the orbital motion of the Moon [12], since it is necessary to know the exact position of its center of mass, whose determination from observations is difficult due to the influence of the relief of the libration zone, the nature of mass distribution in the Moon [13], and its rotational parameters [14, 15]. [ABSTRACT FROM AUTHOR]

We present a method of obtaining the most reliable stellar spectral type based on multi-color photometry. The method also allows us to estimate color excess E B-V and distance to the star. Approbation of the method using bright stars with known spectral classification and WBVR photometry permits to estimate its reliability. Stellar spectra models from Pickles (1998) library and Fluks et al. (1994) interstellar extinction law were used in the application of the method. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]