The Nainital-Cape Survey: A search for variability in Ap and Am stars

The “Nainital-Cape Survey” program for searching photometric variability in chemically peculiar (CP) stars was initiated in 1997 at ARIES, Nainital. We present here the results obtained to date. The Am stars HD 98851, HD 102480, HD 13079 and HD 113878 were discovered to exhibit δ Scuti type variability. Photometric variability was also discovered in HD 13038, for which the type of peculiarity and variability is not fully explained. The null results of this survey are also presented and discussed.     

Coupled nature of evening-time ionospheric electrodynamics

The F region evening electrodynamics in the equatorial region is characterized by a pre-reversal enhancement (PRE) in the zonal eastward electric field. Although the theoretical mechanisms for PRE are known, its variability, particularly day-to-day variability is not fully resolved. PRE is a large scale phenomenon driven by the F region dynamo after the sunset hours. This paper investigates whether the variability of the E region conductivity (particularly the one associated with the sporadic E, Es) has any influence on the F region dynamo and hence on the PRE of zonal electric field. Interestingly, ionosonde observations have indicated a higher occurrence of the blanketing type Es (Esb) over the low latitude on days with highly suppressed PRE of zonal electric field in comparison with the days with significantly larger PRE. Observational evidences presented in this paper suggests that the formation of the Esb in the evening hours is a sovereign process, not always controlled by the sheared F region vertical electric field of equatorial origin, mapping along the magnetic field line on to the low latitude E region. Model computations of the PRE suppression based on the measured Es densities have further substantiated the observational findings presented in this paper. These results clearly indicate that the low latitude Es has the potential to suppress the PRE of zonal electric field and possibly can play a vital role in explaining the PRE variability, particularly the day-to-day variability. Results have been discussed in light of earlier reports on PRE mechanisms and E-F region coupling processes.     

The optical variability of the Seyfert galaxies NGC 4051 and NGC 1068

The optical (BV) monitoring data for the Seyfert galaxies NGC 4051 and NGC 1068 are presented in this paper. NGC 4051 showed a variation of 0.43 mag in 21 minutes in B band from its bright nucleus, and the nucleus of NGC 1068 exhibited a variability of 0.46 mag in B band in a timescale of 1.8 hours. These results argued that the optical emission from the nuclei of the two Seyfert galaxies could be dominated by the nonthermal radiation. The data in this paper, however, are only marginal evidence on the rapid optical variability of these two Seyferts, and further monitoring is needed to confirm this type of variability.     

Simultaneous optical and ultraviolet observations of variability in HD 50896

In this paper, simultaneous optical and ultraviolet observations of spectral variability of the WN5 star HD 50896 are presented. Night-to-night and shorter timescale changes were found in the shape and intensity of most emission lines and P Cygni profiles in both wavelength ranges but there is no clear link between the ultraviolet and optical variability. There are some indications that the ultraviolet variations occur in phase with the well-known 3.766-day period often associated with this star.     

Long-term V(RI)_c CCD photometry of pre-main-sequence stars in the association Cepheus OB3

Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented. These stars are located in the association Cepheus OB3, in the field of the young star V733 Cephei. Photometric observations, especially concerning the long-term variability of the stars, are missing in the literature. We present the first longterm V(RI)_c monitoring for them, that cover 13 years. Results from our study indicate that all of the investigated stars manifest strong photometric variability. The presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.     

Annual and Diurnal Variation of Meteor Rates by the Forward-Scatter Radio Observation

Forward-scatter radio meteor observations have been made at Japan since 1996 using inexpensive and low-end equipment. The activity of some major meteor showers and the seasonal variability of sporadic meteors in 2006 are presented.     

Variation in comet P/Halley

Photoelectric photometry (UBV) of Comet P/Halley performed on April 29, 1986 has been presented. The observations show short-term variability in light. The amplitude of variability in U filter is much more than in B and V filters.     

斯坦福大学太阳物理组的研究项目

为了弄清太阳变化的来源及其对地球环境的影响 ,我们积极地参与了各式各样的正在和即将进行的研究项目。本文对这些项目作了综述 ,并介绍了我们有关的一些活动。     

High-Speed BVRI Photometry of SS Cyg at Quiescence and at Outburst

BVRI photometry of SS Cyg from the end of 1996 and the beginning of 1997 is presented. The star underwent an eruption around December 11. The amplitude of which was slightly bigger than those of observed earlier eruptions. We saw some indication of the future outburst in the decreasing of brightness in all colours by about 0.4 mag during the last two weeks before the event. The emission of the system moved strongly to the shorter wavelengths at outburst. Our multicolour data confirm the existence of a light variability with the orbital (spectroscopic) period at quiescence. Moreover we found for the first time that this variability exists also at outburst but its amplitude is 3–5 times smaller. Whereas the amplitudes of the orbital variability at quiescence decrease to the longer wavelengths, they increase at outburst to the longer wavelengths. The orbital folded curve at quiescence has two-wave shape and was fitted well by the different visibility of two diametrical opposite hot spots (210000 K) with angular size 10⁰ on the magnetic poles of the white dwarf. An analogy between the two basic states of the U Gem-star SS Cyg, the polar AM Her and Z Cam-star RX And was found.     

X-ray variability in a deep, flux-limited sample of QSOs

We present an analysis of X-ray variability in a flux-limited sample of quasi-stellar objects (QSOs). Selected from our deep ROSAT survey, these QSOs span a wide range in redshift (0.1< z <3.2) and are typically very faint, so we have developed a method to constrain the amplitude of variability in ensembles of low signal-to-noise ratio light curves. We find evidence for trends in this variability amplitude with both redshift and luminosity. The mean variability amplitude declines sharply with luminosity, as seen in local active galactic nuclei (AGN), but with some suggestion of an upturn for the most powerful sources. We find tentative evidence that this is caused by redshift evolution, since the high-redshift QSOs ( z >0.5) do not show the anticorrelation with luminosity seen in local AGN. We speculate on the implications of these results for physical models of AGN and their evolution. Finally, we find evidence for X-ray variability in an object classified as a narrow-emission-line galaxy, suggesting the presence of an AGN.     

The infrared variability of QSO 3C 273

The near-infrared data of the quasar 3C273 are collected from available literature and are used to analyze its variability properties. The largest amplitudes of variations are ΔJ = 1.0, ΔH = 0.9, and ΔK = 0.86. The color indices are J − H = 0.82, J − K = 1.96, and H − K = 1.13. Analysis with the discrete correlation function (DCF) method indicates that the variability between any two infrared bands is correlated without any time lag. The relation between the color index and brightness is also investigated and the result indicates that the spectrum steepens when the source first dims, while it flattens after the source has dimmed to a some extent, suggesting that the emission of 3C 273 at near-IR consists of at least two components. Some discussions are presented.     

Short variability of the radio flux density from the blazar J0530+1331

The results of observations of the quasar J0530+1331 (B0528+134) with the radio telescopes RATAN-600 at frequencies of 4.6, 8.2, 11.2, 21.7 GHz and RT-32 at the Zelenchukskaya and Badary observatories of the Quasar network of the Institute of Applied Astronomy, the Russian Academy of Sciences, at frequencies of 4.84 and 8.57 GHz in 2014–2015 are presented. A strong variability on a timescale of 20 days at 4.6–11.2 GHz has been detected over three months of daily RATAN-600 observations; the variability indices are V = dS/〈S〉; = 0.65?0.39. The spectrum of the variable component is falling toward high frequencies with an index α = ?0.76. The structure and autocorrelation functions at 4.6 GHz show an additional process on a timescale of 7 days. No delay of the main process has been detected between 11.2 and 8.2 GHz; the delay between 8.2 and 4.6 GHz does not exceed two days. The most likely cause of the observed variability is the scattering by inhomogeneities of the interstellar medium. The variability has been obtained at theminimum activity phase of the source. The intraday variability (IDV) has been searched for at both RT-32 telescopes since April 2014. Out of 38 successful observing sessions for the source, only three have shown a variability on a timescale of four hours or more at a significance level no higher than 0.1%. This confirms our conclusion drawn from the previous IDV measurements for other sources that the IDV is observed mainly at the maximum phases of long-term variability of the sources.     

VST OmegaCAM difference image analysis

We present a modified version of the difference image analysis software developed by the OGLE collaboration (DIAPL) and its implementation within AstroWISE environment. Python interface and parallel execution are described. Examples of graphical output on simulated data set are presented. The tool will be used in VST surveys for photometric variability search.     

Improved correlation between the variability and peak luminosity of gamma-ray bursts

A new procedure for smoothing a gamma-ray burst (GRB) light curve and calculating its variability is presented. Applying the procedure to a sample of 25 long GRBs, we have obtained a very tight correlation between the variability and the peak luminosity. The only significant outlier in the sample is GRB 030329. With this outlier excluded, the data scatter is reduced by a factor of ∼3 compared to that of Guidorzi et al., measured by the deviation of fit. Possible causes for the outlier are discussed.     

天体物理非线性问题初探-活动星系核的光变及引力的局部近似

展示活动星系核研究和引力研究中的一些难点,揭示了某些天体的光变存在分形结构的可能性。我们提出了活动星系核的中心黑洞具有某种随机微活动性的假设,该假设可解释活动星系核的一些观测现象。我们发现Ｗｅｉｅｒｓｔｒａｓ函数的分形图形可以用来很好地拟合ＯＪ２８７的短时标光变。一个用Ｗｅｉｅｒｓｔｒａｓ函数构造的分形曲线与ＯＪ２８７的历史光变的线性相关系数达到了０．７３。我们计算了ＯＪ２８７光变曲线的计盒维数,信息维数和关联维数,结果表明,这些维数均大于１。我们研究了两个活动星系核（ＯＪ２８７和３Ｃ３４５）的历史光变,发现在星等和这两个物体滞留在这个星等之下的时间长度的对数之间存在线性关系。这种关系可能源于光变的分形结构。我们提出,空时点及附于该点的一个标架与Ｍｉｎｋｏｗｓｋｉ空间上的一个３阶反对称张量场对应。场中的张量取自于一个固定的张量集合。我们得到了Ｒｉｅｍａｎｎ正则坐标下引力场的一个级数表示式。我们还计算了Ｒｉｃｃｉ张量的线性近似和一级非线性近似。这有利于强引力场下的局部非线性结构分析。期望对于引力的进一步研究,通过非线性科学这门新方法的桥粱,沟通极端天文现象与基本引力相互作用之间的鸿沟     

A survey of emission-line stars in the CMa star formation region

A survey of emission-line stars was carried out in the CMa star formation region, based on spectral observations with the Kiso Schmidt telescope. In total, 128 emission-line stars were detected, ranging fromV=6 to 15, and the majority are found withV between 11 and 14. A comparison with the existing catalogues shows that some emission-line stars are common with ours, while some exhibit no detectable emission line on our plates, suggesting the variability of emission-line strength. The two-colour (U–B, B–V) diagram is also shown for the detected stars.Paper presented at the IAU Third-Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.On leave from the Bosscha Observatory, Institute of Technology Bandung, Indonesia.     

光学选类星体样本的光变

利用测光数据研究时间跨度为１８年的光学选类星样本的光变,发现此样本的光变比例约４０％。还发现光变类星体的光变幅与光度反相关,即光度越大,光变越小;且光变幅与红移可能有相关性。     

A systematic study of variability in a sample of ultraluminous X-ray sources

We present results from a study of short-term variability in 19 archival observations by XMM–Newton of 16 ultraluminous X-ray sources (ULXs). Eight observations (six sources) showed intrinsic variability with power spectra in the form of either a power-law or broken power-law-like continuum and in some cases quasi-periodic oscillations (QPOs). The remaining observations were used to place upper limits on the strength of possible variability hidden within. Seven observations (seven sources) yielded upper limits comparable to, or higher than, the values measured from those observations with detectable variations. These represented the seven faintest sources, all with   f_x < 3 × 10⁻¹² erg cm⁻² s⁻¹  . In contrast, there are four observations (three sources) that gave upper limits significantly lower than both the values measured from the ULX observations with detectable variations, and the values expected by comparison with luminous Galactic black hole X-ray binaries (BHBs) and active galactic nuclei (AGN) in the observed frequency bandpass (10⁻³–1 Hz). This is the case irrespective of whether one assumes characteristic frequencies appropriate for a stellar mass  (10 M_⊙)  or an intermediate mass  (1000 M_⊙)  black hole, and means that in some ULXs the variability is significantly suppressed compared to bright BHBs and AGN. We discuss ways to account for this unusual suppression in terms of both observational and intrinsic effects and whether these solutions are supported by our results.     

Polarization Position Angle Swings caused by Relativistic Effects

Polarization position angle swings of - 180 ° observed in extragalactic radio sources are a regular behavior of variability in polarization. They should be due to some kind of physically regular process. We consider relativistic shocks which propagate through and 'illuminate' regular configurations of magnetic field, producing polarization angle swing events. Two magnetic field configurations (force-free field and homogeneous helical field) are considered to demonstrate the results. It is shown that the properties of polarization angle swings and the relationship between the swings and variations in total and polarized flux density are critically dependent on the configuration of magnetic field and the dynamical behavior of the shock. In particular, we find that in some cases polarization angle swings can occur when the total and polarized flux densities only vary by a very small amount. These results may be useful for understanding the polarization variability with both long and short timescales obser     

Variability of long-period pulsating stars. II. Additional parameters for classifying stars

Results are presented from an analysis of observations in a sample of 53 long-period pulsating stars (44 of which are Mira-type and 9 are semiregular variables). A catalog of the characteristics of the individual pulsation cycles of the light curves is obtained for these stars. A correlation analysis of the characteristics of the individual pulsation cycles is carried out for each star. A number if diagrams relating the variability of the characteristics of the individual cycles to the average parameters of the variability of the stars and to their spectral classes. New criteria for classifying long-period variables are proposed on the basis of these diagrams. __________ Translated from Astrofizika, Vol. 49, No. 4, pp. 595–612 (November 2006).