Stochastic data in astronomy. II. Search for harmonic components of time series with very large gaps

This is an analysis of certain aspects of using the CLEAN algorithm for Fourier analysis of short segments of time series and of time series consisting of short segments of length ΔT separated by very long irregular gaps. It is assumed that the time series contain a harmonic component of amplitude A with a period longer than the length of the longest of the segments of the time series plus white noise with dispersion N². Reliability plots are constructed for determining the ranges of the parameters (ν, ϕ) for which the CLEAN procedure can be used to determine the values of ν, the frequency, and ϕ, the phase of the harmonic component, with a given accuracy. The results of this analysis are used to search for harmonic components in the variation of the Hβ line profile in spectra of the triple star δ Ori A obtained in 2004 with the BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 281–297 (May 2007).     

3C 66A: Variability in 2007–2015

The results of photometric (BV RIJHK) and polarimetric (R)monitoring of the blazar 3C 66A performed at the St. Petersburg State University and the Central AstronomicalObservatory of the Russian Academy of Sciences in 2007–2015, radio observations performed by the Boston University team with the Very Long Baseline Array at 43 GHz, and a gamma-ray light curve based on observations with the Fermi SpaceObservatory are presented. Color variations of the object are studied. Changes in the optical spectral energy distribution are observed at some times, indicating the appearance and disappearance of individual variable sources. A variable source with a degree of polarization of 36% is identified, which is responsible for the polarization variations observed during one episode. The correlations between the variations in the different spectral ranges indicate that the optical and gamma-ray radiation originates near the radio core detected at 43 GHz. The presence of five superluminal components emerging from the core is detected.     

He,C, N,and O abundances in an ensemble of galactic planetary nebulae

The He, C, N, and O abundances in more than 120 planetary nebulae (PNe) of our Galaxy and the Magellanic Clouds have been redetermined by analyzing new PNe observations. The characteristics of PNe obtained by modeling their spectra have been used to compile a new catalog of parameters for Galactic and extragalactic PNe, which is accessible at http://www.astro.spbu.ru/staff/afk/GalChemEvol.html. The errors in the parameters of PNe and their elemental abundances related to inaccuracies in the observational data have been analyzed. The He abundance is determined with an accuracy of 0.06 dex, while the errors in the C, N, and O abundances are 0.1–0.2 dex. Taking into account the inaccuracies in the corrections for the ionization stages of the elements whose lines are absent in the PNe spectra increases the errors in the He abundance to 0.1 dex and in the C, N, and O abundances to 0.2–0.3 dex. The elemental abundances in PNe of various Galactic subsystems and the Magellanic Clouds have been analyzed. This analysis suggests that the Galactic bulge objects are similar to type II PNe in Peimbert’s classification, whose progenitor stars belong to the thin-disk population with ages of at least 4–6 Gyr. A similarity between the elemental abundances in PNe of the Magellanic Clouds and the Galactic halo has been established.     

Evolution of elemental abundances in planetary nebulae

We study the evolution of elemental abundances in an ensemble of Galactic planetary nebulae as a function of the masses of the central stars (M _cs) and their progenitors (M _ini). We derive the dependences of the C, N, Ne, Cl, Ar, and S abundances on M _cs and M _ini for a large sample of nebulae. We calculate the theoretical elemental abundances in nebulae under the assumption of complete mixing of the progenitor’s matter ejected at different stages of its evolution. The theoretical dependences of the C and N abundances on M _ini have been found to correspond to the observed ones. At the same time, the observed mean O abundance is approximately half its theoretical value. The Ne, Cl, Ar, and S abundances monotonically increase with increasing mass of the progenitor star, which reflects an increase in the mean abundances of heavy elements during the chemical evolution of the Galaxy. We have derived the relation between the abundances of the elements under consideration in planetary nebulae and the masses of their central stars. This relation is used to construct the mass function for the nuclei of planetary nebulae.     

Variability of the Blazar 1156+295 in 2005–2020

Astronomy Reports - We present and analyze the monitoring results of the blazar 1156+295 in radio, optical, and gamma ranges in 2005–2020. After a long period of relative quietness at the end...