Pulsation and Long-Term Variability of the High-Amplitude δ Scuti Star AD Canis Minoris

Time-series photometry was made for the large-amplitude δ Scuti star AD CMi in 2005 and 2006. High-quality photometric data provided in the literature were used to analyze the pulsation of the star, with the derived multiple frequencies fitted to our new data. Besides the dominant frequency and its harmonics, one low frequency (2.27402 c d -1) is discovered, which provides a reasonable interpretation for the long-noticed luminosity variation at the maximum and minimum light. Combining the nine new times of light maxima determined from the new data with the 64 times collected from the literature, we analyzed the long-term variability of AD CMi with the O - C technique. The results provide the updated value of period of 0.122974478 days, and seem to be in favor of the model of combination of the evolutionary effect and light-time effect of a binary system, of which some parameters are hereby deduced.     

Time-dependent Behaviour of the Low Amplitude δ Scuti Star HD 52788

Wavelet transform is applied to reanalyze the low amplitude δ Scuti star HD 52788, which exhibits complex light variations with uncertain frequency solutions. We gain an insight into the strong instability of pulsation present in the star. Based on an estimate of the star‘s physical parameters, its evolutionary status is determined. An attempt of asteroseismic modelling failed to predict the observed dense frequencies. Because of its varying pulsation spectrum, HD 52788 is a distinctive and very interesting object among δ Sct stars for testing current models of stellar evolution and pulsation.     

Golden Ratio Sinusoidal Sequences and the Multimode Pulsation of the δ Sct Star V784 Cassiopeiae

Non periodic ordered sequences obtained by production rules in formal grammars are applied to the analysis of the multi-periodicity of the δ-Scuti type variable star V784 Cas. An artificial light curve for V784 Cas is generated by a non deterministic derivation in a context-sensitive grammar by concatenation of two sinusoidal fragments following certain word sequences. The two basic building blocks represent temporal segments in a golden ratio and the number of long and short segments in a word are also in a golden ratio.     

Pulsation analysis of the high amplitude δ Scuti star CW Serpentis

Time-series photometric observations were made for the high amplitudeδScuti star CW Ser between 2011 and 2012 at the Xinglong Station of National Astronomical Observatories,Chinese Academy of Sciences.After performing the frequency analysis of the light curves,we confirmed the fundamental frequency of f=5.28677 c d 1,together with seven harmonics of the fundamental frequency,which are newly detected.No additional frequencies were detected.The O C diagram,produced with the 21 newly determined times of maximum light combined with those provided in the literature,helps to obtain a new ephemeris formula of the times of maximum light with the pulsation period of 0.189150355±0.000000003 d.     

Photometric Observations of the δ Scuti Star UV Trianguli and its Evolutionary Status

UV Tri was observed photometrically from 1999 to 2000 at the Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences, and was also observed with Stroemgren uvby Hβ filter system at the Sierra Nevada Observatory (Spain) in 2000. From period analyses of the data, three pulsation frequencies, 9.3299 c d^-1, 10.8483 cd^-1 and 3.6035 cd^-1 were obtained. We derived color indices: b-y=0.215, m1=0.169, c1=0.783, and β=2.775. With these indices and some calibrations, we obtain:Mv=2.44, Mbol=2.27, logL/L⊙=0.99, and log Teff=3.875. Evolutionary sequences of stellar models with 1.00-2.00 solar masses, at steps of 0.05M⊙,are computed. Each sequence consists of 220 evolutionary intervals. From a comparison between the observed and calculated physical parameters we conclude that UV Tri is in an early evolutionary phase before the turn-off point.     

The Origin of Infrared Emission from the Infrared Luminous Galaxy NGC 4418

We present a study of the origin of infrared (IR) emission in the optically normal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features and continua in the range of 3600-8000 A from the Sloan Digital Sky Survey into a set of simple stellar populations, we derive the stellar properties for the nuclear region of NGC 4418. We compare the observed infrared luminosity with the one derived from the starburst model, and find that star-forming activity contributes only 7% to the total IR emission, that as the IR emission region is spatially very compact, the most possible source for the greater part of the IR emission is a deeply embedded AGN, though an AGN component is found to be unnecessary for fitting the optical spectrum.     

A Catalog of Luminous Infrared Galaxies in the IRAS Survey and Second Data Release of SDSS

We selected a sample of luminous infrared galaxies by cross-identification of the Faint Source Catalogue (FSC) and Point Source Catalogue (PSC) of the IRAS Survey with the Second Data Release of the SDSS. The size of our sample is 1267 for FSC and 427 for PSC by using the 2σ significance level cross-section. The "likelihood ratio" method is used to estimate the individual's reliability and for defining two more reliable subsamples (908 for FSC and 356 for PSC). A catalog of infrared, optical and radio data is compiled and will be used in further work. Some statistical results show that luminous infrared galaxies are quite different from ultra-luminous infrared galaxies. The AGN fractions of galaxies at different infrared luminosities and the radio-infrared correlations are consistent with the previous studies.     

A Multiwavelength Study of the Jets in FR-I Radio Galaxies： I. Data and Analysis

We compile a sample of 11 Fanaroff-Riley type I Radio Galaxies(FR-I RGs)with multi-wavelength observations to address the dynamic behavior of jets in these objects.Optical images acquired by the Hubble Space Telescope(HST)are carefully analyzed.The method and reduction procedure are described in detail. Unresolved optical cores emerge after having properly removed starlight from the host galaxies in eight of the FR-I RGs,of which five are new identifications.Broad band spectral properties of these newly identified compact cores are compared with that previously found in FR-I RGs,as well as the low-energy-peaked BL Lac objects. The similarity between them argues for the same non-thermal synchrotron origin. Well-resolved optical jets with knotty morphologies are found in three FR-I RGs in our sample,namely 3C 15,3C 66B and B20755 37.The optical counterparts to the inner radio/X-ray jets are identified and a clear one-to-one correspondence between the optical,radio and X-ray knots is found.The structure and information on the optical jets are discussed.Physical parameters such as the knots position,flux and size are also presented.Detailed comparison between the multi-wavelength data and radiative and dynamic models of jet will be made in a forthcoming paper.     

Fibonacci Sequences and the Multiperiodicity of the Variable Star UW Herculis

We present an application of the methods recently developed for the study of quasicrystal structures to the analysis of multiperiodicity of semiregular variables. A light curve analysis of UW Her shows frequencies that can be included within the general scheme characterizing the Fourier spectra of Fibonacci quasiperiodic sequences. The analysed data come from the BAA Variable Star Section computerised archive.     

Long-Term Variability in the Magnetic Field of the Ap Star <Emphasis Type="Italic">γ</Emphasis> Equ

New measurements of the longitudinal magnetic field of the Ap star γ Equ obtained with the MSS spectrograph of the 6-m telescope of the SAO RAS in 2002–2018 are present. Analyzing our results together with all the available literature data sources of 〈B_z〉 (441 measurements) we found the rotation period P = 89.1 ± 4.2 years (32 521 days). Fitting all the measurements with double sine-wave function resulted in two periods equal to 95.5 and 17.4 years (with the errors of 3.5 and 2 years correspondingly). According to our new estimate, the transition to positive values of 〈B_z〉, probably, will occur later than previously assumed, literally in 2031.