Results of magnetic field measurements in young stars DO Tau, DR Tau, and DS Tau

The results of longitudinal magnetic field measurements B _z in the hot accretion spot in three classical T Tauri stars (CTTS) are reported. In all three stars the magnetic field is detected at a level above 2σ in the formation region of the narrow component of the He I 5876 Å emission line. In the case of DS Tau the longitudinal field B _z in the hot spot was also measured from the narrow emission components of the Na I D lines, implying +0.8 ± 0.3 kG, which is equal to the B _z field component measured from the He I 5876 Å line. Our results suggest that the 6-m telescope of the Special Astrophysical Observatory can be used to study magnetic fields in the hot spots of CTTS with magnitudes down to 13^m, making it possible to double the number of stars of this type with measured B _z values in the accretion zone.     

Spectral Variability of FSRQs

The optical variability of 29 flat spectrum radio quasars in SDSS Stripe 82 region are investigated by using DR7 released multi-epoch data. All FSRQs show variations with overall amplitude ranging from 0.24 mag to 3.46 mag in different sources. About half of FSRQs show a bluer-when-brighter trend, which is commonly observed for blazars. However, only one source shows a redder-when-brighter trend, which implies it is rare in FSRQs. In this source, the thermal emission may be responsible for the spectral behaviour.     

Variability of the spectrum and brightness of RY Tau

The results of spectroscopic observations of the star RY Tau in the ultraviolet based on IUE data and in the visual spectral range obtained at ShAO are presented. Despite significant brightness variability in 1983–1984, the Mg II λ2800 Å emission doublet showed no synchronous variation with the UBV photometric data. Periodic variability of the Mg II λ2800 Å emission intensity with a period of 23 days has been detected for the first time. The periodicity is also observed for a group of such lines as CIV λ1450 Å, He II λ1640 Å, and S II λ1756 Å. The equivalent widths and shifts of the individual components of the Hα, H + H _ε , and CaII K lines also vary with the period found. The observed variability of the emission spectrum can be explained by the existence of a companion in the system in an orbit with a semimajor axis of about 0.13 AU.     

Solar X-Ray Spectral Irradiance Variability

Solar spectral irradiance at X-ray wavelengths show large variations over a period of solar cycle. We use X-ray irradiance data in three narrow spectral regimes deduced from Yohkoh SXT measurements to study coronal irradiance and their possible association with the activity in the lower atmosphere. Time variation of the X-ray irradiance is important in understanding the emergence of magnetic flux and the effects of such variation on the upper atmosphere of the Earth. We note that about 66% of the total (2 – 30 Å) X-ray irradiance arise from 10 to 20 Å spectral range, while 2 – 10 Å contribute only about 3% of the total. The time variation in 2 – 10 and 10 – 20 Å ranges follow each other closely. Further they follow closely the solar indices such as sunspot, F _10.7, and plage indices, although similarity in the variation of 10 – 20 Å is quite apparent. However, the variation in the other spectral band (20 – 30 Å) differ to a large extent except for the solar cycle dependent variation. We infer that in addition to the active regions, the remnants of active regions contribute considerably to the emission in this spectral range.     

Analysis of HST ultraviolet spectra for T Tauri stars: DR Tau

We analyze the spectra of DR Tau in the wavelength range 1200 to 3100 Å obtained with the GHRS and STIS spectrographs from the Hubble Space Telescope. The profiles for the C IV 1550 and He II 1640 emission lines and for the absorption features of some lines indicate that matter falls to the star at a velocity ～300 km s^?1. At the same time, absorption features were detected in the blue wings of the N I, Mg I, Fe II, Mg II, C II, and Si II lines, suggesting mass outflow at a velocity up to 400 km s^?1. The C II, Si II, and Al II intercombination lines exhibit symmetric profiles whose peaks have the same radial velocity as the star. This is also true for the emission features of the Fe II and H₂ lines. We believe that stellar activity is attributable to disk accretion of circumstellar matter, with matter reaching the star mainly through the disk and the boundary layer. At the time of observations, the accretion luminosity was L_ac ? 2L_⊙ at an accretion rate ?10^?7M_⊙ yr^?1. Concurrently, a small (<10%) fraction of matter falls to the star along magnetospheric magnetic field lines from a height ～R_*. Within a region of size ?3.5R_*, the disk atmosphere has a thickness ～0.1R_* and a temperature ?1.5 × 10⁴ K. We assume that disk rotation in this region significantly differs from Keplerian rotation. The molecular hydrogen lines are formed in the disk at a distance <1.4 AU from the star. Accretion is accompanied by mass outflow from the accretion-disk surface. In a region of size <10R_*, the wind gas has a temperature ～7000 K, but at the same time, almost all iron is singly ionized by H I L _α photons from inner disk regions. Where the warm-wind velocity reaches ?400 km s^?1, the gas moves at an angle of no less than 30° to the disk plane. We found no evidence of regions with a temperature above 10⁴ K in the wind and leave open the question of whether there is outflow in the H₂ line formation region. According to our estimate, the star has the following set of parameters: M_* ? 0.9M_⊙, R_* ? 1.8R_⊙, L_* ? 0.9L_⊙, and \(A_V \simeq 0\mathop .\limits^m 9\). The inclination i of the disk axis to the line of sight cannot be very small; however, i≤60°.     

Rapid X-Ray Variability of Seyfert 1 Galaxies

The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert galaxies provided early support for the standard model in which Seyferts are powered by a supermassive black hole fed from an accretion disc. However, since EXOSAT there has been little opportunity to advance our understanding of the most rapid X-ray variability. Observations with XMM-Newton have changed this. We discuss some recent results obtained from XMM-Newton observations of Seyfert 1 galaxies. Particular attention will be given to the remarkable similarity found between the timing properties of Seyferts and black hole X-ray binaries, including the power spectrum and the cross spectrum (time delays and coherence), and their implications for the physical processes at work in Seyferts.     

Spectral Variability of T Tauri Stars in the Optical

We present the results of time variability analysis of the Hα, He I (λ5876 Å) and Na D (λ5890, 5896 Å) lines in two active T Tauri stars, DL Tau and DR Tau. The aim is the study of time behavior of these lines, during one week, as well as possible correlations among them. The observed profiles of some lines are very complex, often showing characteristics of outflow and accretion.     

BLazar天体的光变及多波段能谱特性

本文综述了活动星系核 ,特别是blazar天体的研究现状 ,对blazar天体的多波段与多波段能谱特性研究进行了较为详细的评述。主要的研究工作包括以下内容 :(一 )γ噪blazar天体的短时标光变研究 ,通过对 1 6个γ噪blazar天体 (其中包括全部已证认和观测到VHEγ射线爆发的可能甚高能γ射线源 )自 1 998年的光学观测及光变分析研究表明 ,短时标光变 (小时量级 )是GeVγ噪blazar天体的普遍特性 ,光变幅度通常可达 0 .6mag/h ,对PKS 1 51 0 -0 89类星体的观测发现在一个小时内对象变暗 2个星等 ,对如此激烈的光变变暗目前的理论还不能很好的解释 ,但它同样反映了辐射区域的内部结构 ;而对TBLs的监测表明 ,其光学波段的短时标光变没有其他对象激烈 ,出现的频度和振幅变化都较小 ;(二 )在研究γ噪blazar天体光变时 ,研究了寄主星系对光变的影响 ,得到了 1ES 2 3 44 + 51 4的光变与PSF的FWHM的关联 ,表明随着大气视宁度的下降 (即FWHM变大 ) ,对象变暗 ,即由于寄主星系的影响从而导致假光变的产生 ;(三 )引进两个多波段复合谱指数 ,αxox=αox-αx 及αoro=αor-αo。对样本的统计研究表明 ,RBLs是能谱特性界于XBLs和OVVs之间的一类中间态 ,所得结果支持了Sambrunaetal.( 1 996)大样本多波段能谱分布特性的统计研     

Long-Term Spectral Variability of the Herbig Ae-Star HD 179218

The results of high-resolution long-term spectral monitoring of Herbig Ae star HD 179218 in the region of emission H line and the sodium resonance doublet Na I D are presented. The received data show the existence of short-term variability (about 10 days) and long-term wave-like variability of equivalent width EW, intensity of circumstellar (CS) emission I and parameters of H emission profile. The analysis of these data allows us to suppose the existence of the global variability of parameters of accretion disk.     

NGC 5548的软X射线变化:能谱分析

本文给出了ＲＯＳＡＴＰＳＰＣ对ＮＧＣ５５４８定点观测的分析结果．在ＲＯＳＡＴ观测期间，ＮＧＣ５５４８的计数率显示出大振幅的变化，变化高达１４倍．硬度比与计数率呈负相关，这是由于ＮＧＣ５５４８的软Ｘ射线辐射除幂律分量外还有一个“软超”分量，分别用黑体辐射和热韧致辐射来拟合这个“软超”辐射，得出“软超”的热温度分别为：黑体辐射模型是０．０８ｋｅＶ，热韧致辐射模型是０．２３ｋｅＶ．     

耀变体光学波段的微光变及能谱变化

耀变体在多个波段的微光变和能谱变化多年来是中外天文观测研究的热点课题.耀变体的微光变于20世纪60年代被发现,20世纪80年代以来发现很多源的微光变具有不同的特性,目前对其物理机制的认识和理论、模型的研究还处于发展阶段.该文总结了7个目前观测最多的耀变体(3C 66A,3C 279,3C 454.3,AO 0235+164,BL Lac,OJ 287,S5 0716+714)在光学波段的微光变和能谱变化的观测历史和最新进展,并对其理论模型作了简单介绍.     

Variability of Soft X—ray Spectral Shape in Blazars Observed by ROSAT

1 INTRODUCTION Blazars, including BL Lac objects, highly polarized and optically violently variable quasars,and flat-spectrum radio quasars (FSRQs), are characterized by highly variable non-thermalemission which dominates their characteristics from radio to y-ray bands. The mechanismbelieved to be responsible for their broadband emission is synchrotron radiation followed by in-verse Compton (IC) scattering at higher energies (e.g. Blandford & Konigl 1979). Relativisticbeaming of a jet…     

Variability of Spectral Energy Distribution of Blazar S5 0716+714

The emission from blazars is known to be variable at all wavelengths. The flux variability is often accompanied by spectral changes. Spectral energy distribution (SED) changes must be associated with changes in the spectra of emitting electrons and/or the physical parameters of the jet. Meaningful modeling of blazar broadband spectra is required to understand the extreme conditions within the emission region. Not only is the broadband SED crucial, but also information about its variability is needed to understand how the highest states of emission occur and how they differ from the low states. This may help in discriminating between models. Here we present the results of our SED modeling of the blazar S5 0716+714 during various phases of its activity. The SEDs are classified into different bins depending on the optical brightness state of the source.     

Search for Rapid Optical Variability in Three Gamma-Ray Loud Blazars

I present the search for V, R, I rapid optical variability of three gamma-ray loud blazars, 3C 454.3, 1ES 1959+650, 1ES 2344+514, performed at the Loiano telescope. The source 3C 454.3 was observed during the decline of the May 2005 outburst. 3C 454.3 and 1ES 2344$+$514 showed rapid variability in one band at least. The data in this work and archival data support the correlation between the occurrence of rapid variability and the flux variation suggested by Howard et~al., AJ 127, 17 (2004). PACS 98.54.Cm, 95.75.De     

Solar Cycle 22 UV Spectral Irradiance Variability: Current Measurements by SUSIM UARS

The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) has measured the solar spectral irradiance for wavelengths 115–410 nm on a daily basis since October 11, 1991. The absolutely calibrated solar UV irradiances through January 8, 1996 have been produced. Their time-dependent behavior is similar to that of the Mgii index as measured both by NOAA-9 SBUV and by SUSIM itself. The maximum long-term variation observed by SUSIM is at L and is measured to be in excess of a factor of 2. This maximum variation decreases with increasing wavelength until about 300 nm where no significant long-term variation is directly measured above SUSIM's estimated 1–2% relative accuracy. The wavelength dependence of the measured UV variability is found to roughly correspond to the mean emission height given by solar atmospheric radiative transfer models. Because SUSIM observations began when solar activity was near its peak and now extend to very near its minimum, estimates of the solar cycle 22 UV variability are generated from a combination of these measurements and solar activity proxy indices.     

Effect of Spectral Resolution on the Mg II Index as a Measure of Solar Variability

The solar Mgii core-to-wing ratio is a useful index of UV variability throughout the solar cycle because it has been measured since 1978 in a series of successive satellite missions: Nimbus 7, Solar Mesosphere Explorer (SME), the NOAA 9–14 series, Upper Atmosphere Research Satellite (UARS), and ERS-2. Eventual construction of a single time series from 1978 to the present by combining these measurements will give a long record of almost daily UV variability to serve as a surrogate for estimating both UV and EUV solar radiation. Here we address the effect of spectral resolution on determination of both long-term and short-term solar variability from this index. We use UARS/SOLSTICE measurements of the Mgii line from October 1991 to December 1996 to study the effect of two spectral resolution regimes characteristic of existing measurements, 0.20 to 0.25 nm and 1.10 to 1.15 nm, on determination of the amplitude of 27-day rotational modulation and the more gradual change in chromospheric radiation in the declining phase of solar cycle 22. The two Mgii indices give solar variations that differ by a scaling factor of 2× for both the solar cycle change from 1992 to 1997 and the amplitude of 27-day modulation over the same period. Both types of measurements appear to yield solar signal equally well except at solar minimum when the solar changes become quite small.     

用周期图谱分析方法计算Blazar天体的光变周期

对适用于等间隔时间序列的周期图谱分析方法进行了研究,用模拟信号进行了检验,证实了它适用于有噪声的时间序列.并把这种方法应用到类星体3C 279、3C 345,BL Lac天体OJ 287、ON 231的光变周期分析中,得到它们的光变周期分别为7.14年、10.00年、11.76年、6.80年.结果表明用周期图谱分析方法得到的结论和其他文献用Jurkevich方法得到的结论一致.获得的周期对进一步研究Blazar天体的物理机制很有帮助.还分析了窗函数的影响,指出它们的优缺点,便于在实际工作中做出正确选择.