A study of the X-ray characteristics of mixed-morphology supernova remnants with 1720 MHz OH maser emission

Radio surveys of supernova remnants (SNRs) in the Galaxy have discovered 19 SNRs which are accompanied by the OH maser emission at 1720 MHz. This unusual maser is thought to be produced behind a shock front when a SNR expands into a molecular cloud. An important ingredient of this model is that the X-ray emission from the remnant enhances the production of OH molecules. In this sense, to study the characteristics of the mixed-morphology SNRs accompanied by the OH maser emission at 1720 MHz is important. By studying the X-ray characteristics of the mixed-morphology SNRs accompanied by the 1720 MHz OH maser emission, it is found that the ionization rate of X-ray is not correlated with the physical parameters , D, r, r² and so on, but is correlated with the X-ray luminosity L_x. Meanwhile, L_x is closely correlated with the beam flux density of the weakest feature of the accompanying 1720 MHz OH maser emission. These mean that the X-ray emission from SNRs is sufficient to dissociate the water molecules behind a shock front and to produce the 1720 MHz OH masers.     

Spectroscopic studies of solar corona VI: Trend in line-width variation of coronal emission lines with height independent of the structure of coronal loops

We have obtained spectroscopic observations in coronal emission lines by choosing two lines simultaneously, one [Fe x] 6374 Å and the other [Fe xi] 7892 Å or [Fe xiii] 10747 Å or [Fe xiv] 5303 Å. We found that in 95 per cent of the coronal loops observed in 6374 Å, the FWHM of the emission line increases with height above the limb irrespective of the size, shape and orientation of the loop and that in case of 5303 Å line decreases with height in about 89 per cent of the coronal loops. The FWHM of 7892 Å and 10747 Å emission lines show intermediate behavior. The increase in the FWHM of 6374 Å line with height is the steepest among these four lines. We have also studied the intensity ratio and ratio of FWHM of these lines with respect to those of 6374 Å as a function height above the limb. We found that the intensity ratio of 7892 Å and 10747 Å lines with respect to 6374 Å line increases with height and that of 5303 Å to 6374 Å decreases with height above the limb. This implies that temperature in coronal loops will appear to increase with height in the intensity ratio plots of 7892 Å and 6374 Å; and 10747 Å and 6374 Å whereas it will appear to decrease with height in intensity ratio of 5303 Å to 6374 Å lineversus height plot. These findings are up to a height of about 200 arcsec above the limb. The varying ratios with height indicate that relatively hotter and colder plasma in coronal loops interact with each other. Therefore, the observed increase in FWHM with height above the limb of coronal emission lines associated with plasma at about 1 MK may not be due to increase in non-thermal motions caused by coronal waves but due to interaction with the relatively hotter plasma. These findings also do not support the existing coronal loop models, which predict an increase in temperature of the loop with height above the limb.     

Eclipse observations of coronal emission lines. I. [Fex] 6374Å profiles at the eclipse of 16 February 1980

Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm^-1. The observed line profiles from 1.1 to 1.7 R_⊙ with a spatial resolution of 10 × 22 arcsec², give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 10⁶ K. If temperature of the order of 1.3 × 10⁶ K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s^-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s^-1 to -17 km s^-1. Most of the locations have velocities less than ±5 km s^-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down.     

Relationship between the motion of matter in coronal holes and their evolution

We consider the evolution of a long-lived coronal hole (CH) from February to August 2002 in the zone φ = ?20°…+15°, L = 30°–35°. Active structures emerged in it several times over its lifetime. After their disappearance, the CH was restored to its original form. The Carrington rotation R1989 from May 12 to May 26, 2002, is considered in detail. The relative CH areas have been determined for this rotation from observations in the HeI 1083 nm line. Based on observations in the NiI 676.8 nm line (SOHO, MDI), we have found the periods of the line-of-sight velocity variations. The variations of these periods in CHs are qualitatively compared with those of the CH areas. The oscillation periods in photospheric CH layers have been found to correlate linearly with the CH areas in the chromosphere. For the interval of observations May 12–26, 2002, we have identified 52 sites in CHs for which the area variations in the HeI 1083 nm line were estimated. For times close to the observations in the HeI 1083 nm line, we have determined the average velocities of vertical motion of matter from MDI data. The CH growth and decay have been found to be accompanied, respectively, by upward and downward motions of matter at the photospheric level.     

A new look at the birthrate of supernova remnan

We have reanalysed a homogeneous catalogue of shell-type supernova remnants and we find that the radio data are consistent with a birthrate of one in 22±3 yr. Our approach is based on the secular decrease of surface brightness of the historical remnants whose ages are precisely known. The abovementioned birthrate is significantly higher than most previous estimates which range from one in 50–150 yr, and is consistent with the supernova rate in our galaxy derived from historical observations, as well as with recent estimates of the pulsar birthrate.     

H I observations of galaxies behind the Milky Way in the Puppis region

We report 21-cm H  i line observations of 161 galaxies located behind the Milky Way, in the Puppis region. The observations have been carried out with the Nançay radio telescope, resulting in 101 detections. Most of the galaxies observed appear in the ESO catalogue, and present apparent diameters larger than 1.6 arcmin. We show that the detection rate is strongly related to the apparent diameter; it is as high as 76 per cent for diameters larger than 1.6 arcmin. Half of the non-detections result, in fact, from an insufficient velocity coverage. Global parameters of the detected galaxies are computed, after a careful discussion of the correction for Galactic absorption. Our H  I data are then compared with those obtained by Kraan-Korteweg & Huchtmeier with the Effelsberg radio telescope for 20 galaxies observed in common: the agreement is excellent, implying respective uncertainties on recession velocities and on H  I fluxes lower than 10 km s⁻¹ and 2 Jy km s⁻¹ on average. Finally, we find that the detected galaxies follow well the correlation between the optical linear diameter and the H  I mass found by Haynes & Giovanelli. This result shows that our diameter corrections for Galactic absorption A_B are quite good, except for eight objects which are heavily obscured ( A_B 2.3), or have a very small diameter, lower than 0.5 arcmin.     

The identification of new forbidden coronal lines in the solar EUV spectrum

Identifications are proposed for twenty of the twenty-eight coronal lines observed in the spectra obtained during a rocket flight into the path of the 7 March, 1970 solar eclipse. The methods by which the lines have been identified are discussed. Most of the lines identified are from forbidden transitions between levels in the ground 2p ⁿ and 3p ⁿ configurations in high ions of magnesium, silicon, sulphur, iron, and nickel. The temperature range represented is from 6.9 × 10⁵ K to 2.5 × 10⁶ K. The classification of three lines of Fexii and two of Nixiv has led to a revised identification for the near ultraviolet ² D _3/2-² P _1/2 transition in Fe xii. This transition can be identified with the line at 3072 Å rather than that at 3021 Å as previously suggested in the literature.     

V348 Puppis: a new SW Sex star in the period gap

We present time-resolved optical spectroscopy and photometry of the nova-like cataclysmic variable V348 Puppis. The system displays the same spectroscopic behaviour as SW Sex stars, so we classify V348 Pup as a new member of the class. V348 Pup is the second SW Sex system (the first is V795 Herculis) which lies in the period gap. The spectra exhibit enhanced He  ii λ 4686 emission, reminiscent of magnetic cataclysmic variables. The study of this emission line gives a primary velocity semi-amplitude of     . We have also derived the system parameters, obtaining:     ,         ,     and     . The spectroscopic behaviour of V348 Pup is very similar to that of V795 Her, with the exception that V348 Pup shows deep eclipses. We have computed the '0.5-absorption' spectrum of both systems, obtaining spectra that resemble the absorption spectrum of a B0 V star. We propose that absorption in SW Sex systems can be produced by a vertically extended atmosphere which forms where the gas stream re-impacts the system, either at the accretion disc or at the magnetosphere of the white dwarf (assuming a magnetic scenario).     

1998年9月23 日复杂太阳爆发射电联合观测的初步分析

利用北京天文台1998.09.23日1-2GHz和2.6-3.8GHz频谱仪观测到的一个Ⅲ-Ⅳ型复杂大爆发，结合俄罗斯SSRT和德国分米-米波动态频谱仪的观测资料，进行了初步的比对分析，拓展了关于日冕电子加速和日冕磁结构方面的一些研究内容，简单地注释了一些可研究的现象和运动Ⅳ型爆发及多重脉动的辐射机制。     

STEREO卫星的CME观测研究进展

简要回顾利用"日地关系天文台"(Solar Terrestrial Relations Observatory,STEREO)卫星的立体观测资料在日冕物质抛射(Coronal Mass Ejection,CME)研究方面已取得的一些重要进展,主要包括(1)通过极紫外成像仪观测到的日冕极紫外暗化来更准确地估计CME质量,研究CME演化的结构特征;(2)利用STEREO卫星日冕仪的双角度观测,在CME立体传播特征方面取得的新进展;(3)STEREO卫星日球成像仪具有广阔的视场范围,可以跟踪研究CME从太阳表面爆发到形成行星际日冕物质抛射(Interplanetary CME,ICME),及其在内日球层和近地空间的演化特征以及运动特征等。同时,也介绍了利用三角测量技术测定CME特征物理量的新方法。     

Kinetic properties of coronal mass ejections corrected for the projection effect in Cycle 23

Using Howard et al.'s method, we investigate, before and after the projection correction, the speed and acceleration distributions for 1747 coronal mass ejections (CMEs) associated solely with flares (FL CMEs) and 631 CMEs associated solely with filament eruptions (FE CMEs) observed by the Large Angle and Spectrometric Coronagraph on board the Solar and Heliographic Observatory ( SOHO /LASCO) from 1996 September to 2007 September, corresponding to almost an entire solar cycle. The results show the following. (1) Before the correction, the speed distributions for FL and FE CMEs are statistically different from each other; after the correction, the speed distributions for FL and FE CMEs should also be statistically different from each other. (2) Before the correction, the acceleration distributions for FL and FE CMEs are statistically different from each other. However, after the correction, FL and FE CMEs should have quite similar acceleration distributions.     

A study on the asymmetries in flare lines

We calculate the H and CaII K profiles under different velocity models with chromospheric condensations and investigate the effect of the velocity in different layers on the profiles from a semi-empirical standpoint. The results show that the short-time, H blue asymmetry in the early stage of the flare can be caused by condensations in the transition zone, that the subsequent red asymmetry is the result of the downward motion of matter in the upper chromosphere, while the later CaII K asymmetries can be explained by downward velocities of 10–20 km/s in the middle and lower chromosphere.     

The anomalous intensities of helium lines in a coronal hole

Observations made at the quiet Sun-centre with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instruments on the Solar and Heliospheric Observatory ( SOHO ) have shown that the intensities of the resonance lines of He  i and He  ii are significantly larger than predicted by emission measure distributions found from other transition region lines. The intensities of the helium lines are observed to be lower in coronal holes than in the quiet Sun. Any theory proposed to account for the behaviour of the helium lines must explain the observations of both the quiet Sun and coronal holes. We use observations made with SOHO to find the physical conditions in a polar coronal hole. The electron pressure is found using the C  iii 1175-Å and N  iii 991.5-Å lines, as the C  iii line at 977.0 Å becomes optically thick in some regions at high latitudes. The mean electron pressure is a factor of ≃2 lower than that at the quiet Sun-centre. The mean coronal electron temperature is     . The helium lines are enhanced with respect to other transition region lines but by factors which are ≃ 30 per cent smaller than at the quiet Sun-centre. The mean ratios of the intensities of the He  i 537.0- and 584.3-Å lines and of the He  i and He  ii 303.8-Å lines vary little with the type of region studied. These ratios are compared with those predicted by models of the transition region, taking into account the radiative transfer in the helium lines. No significant variation is found in the relative abundances of carbon and silicon.     

Thermal cyclotron radiation from hot coronal loops and peculiarities of the polarization structure of solar microwave emission sources: I. Brightness temperature

We discuss the possible contribution of the thermal cyclotron radiation from hot coronal magnetic loops to the observed characteristics of the microwave emission from solar active regions. Based on the simplest three-dimensional model of a loop in the shape of a hot torus, we have calculated the expected peculiarities of the frequency and polarization structures of microwave emission sources associated with sunspots and containing coronal loops. Our model calculations of the two-dimensional brightness temperature distributions at various wavelengths for the ordinary and extraordinary modes and the wavelength dependences of the brightness temperatures are presented in the first part of the work. The loop size, the electron density, and the source position on the disk have been found to affect these characteristics. Our numerical calculations of the brightness temperature distributions and spectra have confirmed the well-known assumption that under certain conditions the spectrum of a hot filament can contain cyclotron lines and the sense of the polarization can change over the range. The results obtained here refer to the brightness temperature along the line of sight that crosses the photosphere at a point with given coordinates, i.e., these are the emission characteristics at a fixed point of the source. Integrated characteristics (the flux from the entire source and its polarization) and a discussion of the hot loop model will be given in the second part of the work.     

Thermal cyclotron radiation from hot coronal loops and peculiarities of the polarization structure of solar microwave emission sources: II. Integrated characteristics

We present our calculations of the expected characteristics of the integrated spectrum of thermal cyclotron radiation from a solar active region with a coronal magnetic loop. A hot torus is considered as a three-dimensional loop model. We show that the hot-loop emission can change appreciably the emission characteristics of the active region at centimeter and decimeter wavelengths. At certain loop parameters, the emission frequency spectrum can have a nonmonotonic and complex pattern with several peaks or contain narrow-band cyclotron lines. The polarization structure of the source with a hot loop is also complex and the polarization is repeatedly reversed over the observed frequency range under certain conditions. The revealed spectral-polarization peculiarities are considered from the standpoint of whether some atypical observed properties of the emission sources associated with solar active regions can be explained.     

Features of Kamiokande-II,IMB, and Baksan observations and their interpretation in a two-component model for the signal

We consider the time, angular, and energy distributions of SN 1987A events and discuss the quality of their agreement with the expectations. A global interpretation is made by considering a simple model based on the standard scenario for the explosion. Despite the contrasting and confusing indications, a straightforward fit to the data provides a result that does not contradict but rather supports the expectations. The calculated electron antineutrino flux is applied to predict the relic neutrino signal. The article was translated by the authors.     

X-ray emission lines in the early afterglows of gamma-ray bursts

We computed the thermal time-dependent X-ray spectrum of a hot plasma in the vicinity of a gamma-ray burst (GRB). An allowance for time-dependent processes in a hot rarefied plasma is shown to strongly affect the observed spectrum. These computations can give an alternative explanation for the observed X-ray emission lines in the early afterglows of GRBs (e.g., GRB 011211). Our technique allows the GRB collimation angle and the environment clumpiness parameters to be independently constrained.     

The LMC supernova (SN 1987 A) as a probe for the outcome of stellar collapse

Implications from the available information on the supernova SN 1987 A are discussed for the supernova models. We derive an upper bound of 10–25 eV for the neutrino rest mass.