Spectral evolution of V838 Monocerotis in the optical and near-infrared in early 2002     

M. T. Rushton  T. R. Geballe  A. V. Filippenko  R. Chornock  W. Li  D. C. Leonard †  R. J. Foley  A. Evans  B. Smalley  J. Th. van Loon  S. P. S. Eyres 《Monthly notices of the Royal Astronomical Society》2005,360(4):1281-1289

We report optical and near-infrared spectroscopy, and optical spectropolarimetry, of the peculiar variable V838 Mon during the multiple outburst phase in early 2002. The spectral evolution is exceptional. Our earliest spectra (2002 January) are noteworthy for their strong absorption lines of barium and strontium in the optical, and bands of CO and circumstellar H₂O in the near-infrared. All but the CO weaken or are absent in later spectra. The behaviour of the CO band during this phase is extraordinary: initially in absorption, it was observed two months later in optically thick emission. The excitation of the CO is probably the result of the propagation of a shock wave at the third maximum. The two spectropolarimetric epochs were taken 6 and 27 d after the second outburst on 2002 February 8. The polarization at both times was measured to be   p_V ≈ 2.7  per cent. Nearly all of the measured polarization is believed to be due to interstellar dust, a conclusion that is consistent with previous studies. At both epochs, however, a weak and variable intrinsic component is thought to be present. Between January and March of 2002 the luminosity of V838 Mon increased by a factor of 15 and the apparent diameter increased fourfold.  相似文献   

Geometrical constraints upon the unipolar model of V407 Vul and RXJ0806.3+1527     

S. C. C. Barros  T. R. Marsh  P. Groot  G. Nelemans  G. Ramsay  G. Roelofs  D. Steeghs  J. Wilms 《Monthly notices of the Royal Astronomical Society》2005,357(4):1306-1312

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Balmer absorption variability and the disc wind of V592 Cassiopeiae     

D. K. Witherick  R. K. Prinja  S. B. Howell  R. M. Wagner 《Monthly notices of the Royal Astronomical Society》2003,346(3):861-870

We present results from time-series optical spectroscopy of the low-inclination, nova-like cataclysmic variable, V592 Cas. The data span the wavelength range from ∼4000 to 5000  Å, and include Balmer lines (Hβ to Hε) as well as He i and He ii . The Balmer lines are generally characterized by shallow absorption troughs with superimposed narrower central emission components. The absorption troughs are variable on time-scales of at least ∼20 min, but the fluctuations are asymmetric such that they are more dominant on the blueward side of the profile out to ∼−2000 km s⁻¹. Fourier analysis reveals modulation periods for emission radial velocities and absorption changes of ∼0.114 and 0.103 d; we support earlier suggestions that the latter is likely to be 1-day alias of the former, which is essentially the system orbital period. However, there is a phase lag of ∼0.3 between absorption and emission changes. The Balmer absorption changes are compared to the predicted behaviour caused by the (stream overflowing) SW Sex phenomenon. There are several discrepancies in this scenario, including the highly asymmetric nature of blueward changes, the velocity amplitudes, and the phase relation to the emission changes. The role of a disc wind in V592 Cas is also discussed; in particular, with this data set, we cannot rule in or rule out the possibility that axisymmetry of the outflow is broken because it is seated on a warped/tilted inner disc, which is implied by previous evidence for negative superhumps in this system.  相似文献   

Spiral waves and the secondary star in the nova-like variable V3885 Sgr     

Louise E. Hartley  James R. Murray  Janet E. Drew  Knox S. Long 《Monthly notices of the Royal Astronomical Society》2005,363(1):285-292

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V型排导槽防治泥石流灾害     

王建强  周道银 《云南地质》2007,26(2):207-212

云南1990年至今推广应用V型槽防治泥石流灾害，对多条泥石流工程防治实践与试验研究的总结，介绍云南泥石流的特点、V型排导槽防治泥石流原来以及V型槽技术治理泥石流灾害的优点。  相似文献   

"03.7"江苏大暴雨凝结潜热的数值模拟   总被引：2，自引：0，他引：2  

濮梅娟  沈树勤  夏瑛  曾明剑  解令运  陆维松 《高原气象》2007,26(2):333-343

运用美国中尺度数值模式(MM5)对2003年7月4~5日江苏省中部的大暴雨过程进行了有无降水凝结潜热加热的数值模拟研究。模拟结果表明,凝结潜热释放能使高层负涡度和低层正涡度强烈发展,形成地面至500 hPa深厚的正涡度柱;使高层辐散、低层辐合和垂直上升运动显著增大一个量级;能诱发低空中尺度涡旋发生发展;使降水量增幅一个量级。凝结潜热释放是暴雨发生和雨量增幅的一种重要物理机制。  相似文献   

Effects of local site and building parameters on damage distribution in Angra do Heroísmo—Azores     

Paula Teves-Costa  Carlos S. Oliveira  M. Luisa Senos 《Soil Dynamics and Earthquake Engineering》2007,27(11):986-999

During the M_w=6.9 January 1, 1980 earthquake in the Azores, the damage distribution in the town of Angra do Heroísmo, in Terceira Island, had a non-homogeneous spatial character. In order to understand the observed pattern of damage a microtremor survey was carried out, using ambient vibrations, and the data were analysed with the J-Sesame software, following the H/V Nakamura methodology. The results are in good agreement with the surface geology and they show a good correlation with the observed damages. Two building surveys were performed, in 1980 on damage evaluation and in 2000 on characterization of few building parameters. With all these elements (surface geology type, soil peak frequency, building type, number of stories and damage level) for 2111 buildings it was possible to perform several interparameter analysis, which enabled the identification of indicators that could be used to improve the damage estimation for future events.  相似文献   

On the Limitation of the H/V Spectral Ratio Using Seismic Noise as an Exploration Tool: Application to the Grenoble Valley (France), a Small Apex Ratio Basin     

Philippe Guéguen  Cécile Cornou  Stéphane Garambois  Julien Banton 《Pure and Applied Geophysics》2007,164(1):115-134

The H/V spectral ratio method based on seismic noise (HVSRN) was used in the Grenoble Basin (France), an Alpine valley characterized by a small apex ratio. The resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1-D theoretical assessment of site responses. Given the abundance of data on the sediments and depth of the basin, the values of the theoretical resonance frequency f_o can be determined quite accurately. However, it has been observed that the effects of basin geometry can disturb f_o measurements using the HVSR method, in particular for a case like the Grenoble Basin, which has a small apex ratio (w/H) and strong suspected 2-D and/or 3-D effects. Interpretation of f_o values in terms of bedrock depth gives rise to estimation errors of about 10% in certain cases, with the most significant errors (>50%) occurring on the edges of the basin, where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated. This study suggests that great care must be taken when using the HVSRN method as an exploration tool, at least in valleys with a small apex ratio.  相似文献   

Reliability of Ambient Noise Horizontal-to-Vertical Spectral Ratio in Urban Environments: The Case of Thessaloniki City (Northern Greece)     

A. A. Panou  N.P. Theodulidis  P.M. Hatzidimitriou  A.S. Savvaidis  C.B. Papazachos 《Pure and Applied Geophysics》2005,162(5):891-912

In the framework of an ambient noise measurement project in the downtown district of the City of Thessaloniki (Northern Greece), several tests and evaluation of noise recordings were performed in selected sites. This data set was processed and compared with previous results for the same sites in terms of horizontal-to-vertical (H/V) spectral ratio obtained from weak and strong motion earthquake data. The recording system used was tested against a reference one. Finally, systematic ambient noise measurements were performed at eight sites in the citys downtown area, to evaluate diurnal and seasonal variations. It was concluded that the recording system used was reliable and the ambient noise H/V spectral ratios were in good agreement with relevant results previously obtained. Diurnal variation of the ambient noise H/V spectral ratio showed that it is preferable to perform measurements during the calm hours of the day, when man-made noise is relatively low. However, no systematic seasonal fluctuation effect on the ambient noise H/V spectral ratio was identified.  相似文献   

X-ray beaming caused by resonance scattering in the accretion column of magnetic cataclysmic variables     

Y. Terada  M. Ishida  K. Makishima  T. Imanari  R. Fujimoto  K. Matsuzaki  H. Kaneda 《Monthly notices of the Royal Astronomical Society》2001,328(1):112-126

Extremely strong ionized Fe emission lines, with equivalent widths reaching ∼4000 eV, were discovered by ASCA from a few Galactic compact objects, including AX J2315−0592, RX J1802.1+1804 and AX J1842.8−0423. These objects are thought to be binary systems containing magnetized white dwarfs (WDs). A possible interpretation of the strong Fe K line is the line-photon collimation in the WD accretion column, as a result of resonance scattering of line photons. The collimation occurs when the accretion column has a flat shape, and the effect is augmented by the vertical velocity gradient, which reduces the resonant trapping of resonant photons along the magnetic field lines. This effect was quantitatively confirmed with Monte Carlo simulations. Furthermore, with ASCA observations of the polar V834 Centauri, this collimation effect was clearly detected as a rotational modulation of the equivalent width of the Fe K emission line. The extremely strong emission lines mentioned above can be explained consistently by our interpretation. Combining this effect with other X-ray information, the geometry and plasma parameters in the accretion column were determined.  相似文献