Vol 45, No 9 (2019)

Previously we have reported the detection of a sequence of three particle arrival events at energies above 10¹⁹ eV during one day and from a small sky region by two extensive air shower (EAS) arrays. We have shown that the probability of a chance coincidence of the three events is very low and suggested the arrival of a short-lived particle beam at the Earth. Here we refine the energies of the recorded particles and discuss a possible beam formation mechanism that explains the observational results.

For the low-amplitude Cepheid BY Cas we have constructed an O − C diagram spanning a time interval 123 years. The O − C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period, dP/dt = +0.985 (±0.091) s yr⁻¹, which points to the third crossing of the instability strip. The pulsation stability test proposed by Lombard and Koen (1993) confirms that the period increase is real.

We compare the spatial stellar color variations with our three-dimensional analytical model of the spatial dust distribution to refine the properties of the dust layer in Galactic solar neighborhoods. We use a complete sample of 93 992 clump giants with a small admixture of branch giants from the Gaia DR2 catalogue in a spatial cylinder with a radius of 700 pc around the Sun extending to |Z| = 1800 pc along the Galactic Z axis. Accurate parallaxes and photometry of these stars in the Gaia DR2 G_RP and WISE W3 bands have allowed the spatial G_RP - W₃ color variations to be used to calculate the model parameters and two characteristics of the sample, the mode of the dereddened color (G_RP - W3)₀ of the giant clump and the linear change of this mode with coordinate |Z|. As a result, an improved version of the three-dimensional model first proposed by Gontcharov (2009b) has been obtained. As in the previous version, the model suggests two dust layers, along the Galactic equator and in the Gould Belt, that intersect near the Sun at an angle of 18° ± 2°. In contrast to the previous version of the model with a midplane of the Gould Belt dust layer in the form of a circle with the center at the Sun, in the new version this midplane is an ellipse decentered relative to the Sun. A scale height of 170 ± 40 pc has been found for both dust layers. A rather large reddening E(G_RP - W3) = 0.16 ± 0.02 through half of the Galactic dust layer above or below the Sun has been found for giants far from the Galactic plane (|Z| > 600 pc). This can be explained by a possible difference between the extinction law far from the Galactic plane and the commonly adopted law by Cardelli et al. (1989) with R_V = 3.1. The modes of the absolute magnitude M_W3 = -1.70 ± 0.02 and the dereddened color (G_RP - W3)₀ = (1.43 ± 0.01) - (0.020 ± 0.007)|Z|, where Z is expressed in kpc, have been calculated for the giant clump near the Sun. These estimates are consistent with the estimates from the theoretical PARSEC and MIST isochrones for a sample dominated by giants with an age of 2 Gyr and metallicity [Fe/H] = -0.1 in agreement with the TRILEGAL stellar population model. The dispersions of the quantities under consideration have allowed the natural small-scale density fluctuations of the dust medium relative to the mean reddening calculated from the model to be characterized. These fluctuations make a major contribution to the uncertainty in the reddening. Because of them, the reddening of a specific star can differ from the model reddening by a random value that decreases from 80 to <20% of the model reddening when passing from low latitudes far from the Sun to the remaining space.

On July 12, 2014, an unusual light structure was observed in the NOAA 12109 sunspot umbra at the Horizontal Solar Telescope of the Sayan Observatory. It differed from traditional light bridges in that it was entirely within the umbra without any apparent connection with the penumbra or the photosphere. The observed light structure more closely resembles a light “island” in outward appearance. A scan was performed in two spectral ranges: ultraviolet (3930–3975 Å ) and infrared (8490–8560 Å ). Images were constructed from the spectrograms in both continua, two Са II lines (8498 and 3933.6 Å ) and four weak lines (Cr I 3963.7 Å, Fe I 3969.3 Å, Fe I 8514.1 Å, Si I 8556.8 Å). The contrast of the structure has been found to depend on the spectral range and to decrease with height. Within the light structure we have detected upflow line-of-sight velocities of ~500 m s⁻¹ from the infrared lines and up to 3000 m s⁻¹ from the ultraviolet lines relative to the sunspot umbra, in which, in turn, downflows (up to 1000 m s−1) relative to the quiet Sun areas that surrounded the sunspot were observed.