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2.
徐钧  韩金林  王陈 《天文学报》2011,52(3):180-189
脉冲宽度的测量方法有几种.最常用的脉冲宽度有Wpp（两峰值点的间距）、W50（最高峰值强度50%处的宽度）和W10（最高峰值强度10%处的宽度）.另外,还有测量两个最外成分各自强度50%处的宽度Wc50和各自强度10%处的宽度Wc10.利用16颗双锥峰脉冲星和7颗核锥三峰脉冲星样本在1.4 GHz的脉冲轮廓数据,测量了5种脉冲宽度.利用有磁倾角α和撞击角β数据的脉冲星,导出了对应的辐射束半径ρ,并验证其与脉冲星周期P之间的关系ρ∝P-0.5.通过比较5种脉冲宽度导出的ρ与P关系的好坏,发现最外成分之间的宽度比前面3种宽度更好,其中Wc50宽度得出的相关关系最好.由此认为Wc50是最能反映辐射束宽度的测量值.还讨论了脉冲轮廓的对称性,发现后随的锥辐射成分与先导的锥辐射成分相比,更靠近核心辐射成分,两个锥辐射成分的宽度在统计上基本相同.  相似文献   

3.
We consider the two-photon positron and electron annihilation in flight, it means the annihilating particles exhibit the middly relativistic momenta in a super strong magnetic field. Such particles are present in the corona of pulsars and magnetars. The paper presents how the total emission rate for the two-photon process is affected not only by magnetic field but also by the relativistic momentum of the annihilating particles. We found that the momenta influence significantly the total emission rate and the directions of the emitted photons. Additionally, the total emission for the two-photon process is comparable to that for the one-photon process at the momentum of annihilating particles of about m0, where m0 is the electron mass, and the magnetic field close to the critical Schwinger value of 4.41 × 1013 G. The latter is reported as a main annihilation channel in a super strong magnetic field. We calculated also the energetic spectra of annihilating photons emitted, which are also affected by the magnetic field and the momenta of the annihilating particles.  相似文献   

4.
《New Astronomy》2007,12(4):353-355
We give a tracker solution for the quintessence scalar field for Ratra–Peebles or SUGRA potentials, holding before, during and after the equality epoch (ρm = ρr) and nicely fitting the numerical behavior.  相似文献   

5.
Millisecond pulsars have a very high rotation stability, which can be applied to many research fields, such as the establishment of the pulsar time standard, the detection of gravitational wave, the spacecraft navigation by using X-ray pulsars and so on. In this paper, we employ two millisecond pulsars PSR J0437-4715 and J1713+0743, which are observed by the International Pulsar Timing Array (IPTA), to analyze the precision of pulsar clock parameter and the prediction accuracy of pulse time of arrival (TOA). It is found that the uncertainty of spin frequency is 10?15 Hz, the uncertainty of the first derivative of spin frequency is 10?23 s?2, and the precision of measured rotational parameters increases by one order of magnitude with the accumulated observational data every 4～5 years. In addition, the errors of TOAs within 4.8 yr which are predicted by the clock model established by the 10 yr data of J0437-4715 are less than 1 μs. Therefore, one can use the pulsar time standard to calibrate the atomic clock, and make the atomic time deviate from the TT (Terrestrial Time) less than 1 μs within 4.8 yr.  相似文献   

6.
This paper reports the results from three targeted searches of Milagro TeV sky maps: two extragalactic point source lists and one pulsar source list. The first extragalactic candidate list consists of 709 candidates selected from the Fermi-LAT 2FGL catalog. The second extragalactic candidate list contains 31 candidates selected from the TeVCat source catalog that have been detected by imaging atmospheric Cherenkov telescopes (IACTs). In both extragalactic candidate lists Mkn 421 was the only source detected by Milagro. This paper presents the Milagro TeV flux for Mkn 421 and flux limits for the brighter Fermi-LAT extragalactic sources and for all TeVCat candidates. The pulsar list extends a previously published Milagro targeted search for Galactic sources. With the 32 new gamma-ray pulsars identified in 2FGL, the number of pulsars that are studied by both Fermi-LAT and Milagro is increased to 52. In this sample, we find that the probability of Milagro detecting a TeV emission coincident with a pulsar increases with the GeV flux observed by the Fermi-LAT in the energy range from 0.1 GeV to 100 GeV.  相似文献   

7.
We present observations of the O2(a1Δg) nightglow at 1.27 μm on Mars using the SPICAM IR spectrometer onboard of the Mars Express orbiter. In contrast to the O2(a1Δg) dayglow that results from the ozone photodissociation, the O2(a1Δg) nightglow is a product of the recombination of O atoms formed by CO2 photolysis on the dayside at altitudes higher than 80 km and transported downward above the winter pole by the Hadley circulation. The first detections of the O2(a1Δg) nightglow in 2010 indicate that it is about two order of magnitude less intense than the dayglow (Bertaux, J.-L., Gondet, B., Bibring, J.-P., Montmessin, F., Lefèvre, F. [2010]. Bull. Am. Astron. Soc. 42, 1040; Clancy et al. [2010]. Bull. Am. Astron. Soc. 42, 1041). SPICAM IR sounds the martian atmosphere in the near-IR range (1–1.7 μm) with the spectral resolution of 3.5 cm?1 in nadir, limb and solar occultation modes. In 2010 the vertical profiles of the O2(a1Δg) nightside emission have been obtained near the South Pole at latitudes of 82–83°S for two sequences of observations: Ls = 111–120° and Ls = 152–165°. The altitude of the emission maximum varied from 45 km on Ls = 111–120° to 38–49 km on Ls = 152–165°. Averaged vertically integrated intensity of the emission at these latitudes has shown an increase from 0.22 to 0.35 MR. Those values of total vertical emission rate are consistent with the OMEGA observations on Mars-Express in 2010. The estimated density of oxygen atoms at altitudes from 50 to 65 km varies from 1.5 × 1011 to 2.5 × 1011 cm?3. Comparison with the LMD general circulation model with photochemistry (Lefèvre, F., Lebonnois, S., Montmessin, F., Forget, F. [2004]. J. Geophys. Res. 109, E07004; Lefèvre et al. [2008]. Nature 454, 971–975) shows that the model reproduces fairly well the O2(a1Δg) emission layer observed by SPICAM when the large field of view (>20 km on the limb) of the instrument is taken into account.  相似文献   

8.
We present spectral and spatial information for major volatile species in Comet 10P/Tempel 2, based on high-dispersion infrared spectra acquired on UT 2010 July 26 (heliocentric distance Rh = 1.44 AU) and September 18 (Rh = 1.62 AU), following the comet’s perihelion passage on UT 2010 July 04. The total production rate for water on July 26 was (1.90 ± 0.12) × 1028 molecules s?1, and abundances of six trace gases (relative to water) were: CH3OH (1.58% ± 0.23%), C2H6 (0.39% ± 0.04%), NH3 (0.83% ± 0.20%), and HCN (0.13% ± 0.02%). A detailed analysis of intensities for water emission lines provided a rotational temperature of 35 ± 3 K. The mean OPR is consistent with nuclear spin populations in statistical equilibrium (OPR = 3.01 ± 0.18), and the (1σ) lower bound corresponds to a spin temperature >38 K. Our measurements were contemporaneous with a jet-like feature observed at optical wavelengths. The spatial profiles of four primary volatiles display strong enhancements in the jet direction, which favors release from a localized vent on the nucleus. The measured IR continuum is much more sharply peaked and is consistent with a dominant contribution from the nucleus itself. The peak intensities for H2O, CH3OH, and C2H6 are offset by ～200 km in the jet direction, suggesting the possible existence of a distributed source, such as the release of icy grains that subsequently sublimed in the coma. On UT September 18, no obvious emission lines were present in our spectra, nevertheless we obtained a 3σ upper limit Q(H2O) < 2.86 × 1027 molecules s?1.  相似文献   

9.
The central and outer components from the radiation beam of a pulsar are called the core and cone components, respectively. It was found in some early researches that a proportion of 0.7 exists between the widths of core and cone components of pulsars. 33 pulsars with signi?cant core and cone components are selected to verify it. The component separations are made by ?tting the integrated pulse pro?les of these pulsars with Gaussian functions, so as to obtain the widths and errors of all the core and cone components. The relation between the widths of core and cone components is investigated for the triple-peaked and quintuple-peaked pulsars, respectively. We ?nd that there are no signi?cant differences between the widths of core and cone components, the proportion of between the widths of core and cone components that reported by previous studies does not exist.  相似文献   

10.
《New Astronomy》2007,12(7):590-596
We assume that the helium-I lines emitted by the massive binary system η Carinae are formed in the acceleration zone of the less-massive secondary star. We calculate the Doppler shift of the lines as a function of orbital phase and of several parameters of the binary system. We find that a good fit is obtained if the helium lines are formed in the region where the secondary wind speed is vzone = 430 km s−1. The acceptable binary eccentricity is in the range 0.90 ≲ e ≲ 0.95, and the inclination angle (the angle between a line perpendicular to the orbital plane and the line of sight) is in the range 40° ≲ i ≲ 55°. Lower values of e require higher values of i, and vice versa. The binary system is oriented such that the secondary star is in our direction (closer to us) during periastron passage. The orbital motion can account in part to the Doppler shift of the peak in X-ray emission.  相似文献   

11.
The neutral, singly, doubly and triply ionized mercury (Hg I–IV, respectively) spectral line shapes and line center positions have been investigated in the laboratory helium plasma at electron densities ranging between 9.3 × 1022 m?3 and 1.93 × 1023 m?3 and electron temperatures around 19,500 K, both interesting for astrophysics. The mercury (natural isotope composition) atoms were sputtered from the cylindrical amalgamated gold plates located in the homogenous part of the pulsed helium discharge operating at a pressure of 665 Pa in a flowing regime. The mercury spectral line profiles were recorded using the McPherson model 209 spectrograph and the Andor ICCD camera as the detection system. This research presents Stark broadening parameters, the width (W) and the shift (d), of one Hg I, 19 Hg II, 6 Hg III and 4 Hg IV lines, not investigated so far. Our experimental W values were compared with the data calculated applying various approaches. The shape and intensity of astrophysically important 398.4 nm Hg II spectral line was discussed taking into account the isotope shift, hyperfine structure and Penning effects. At the mentioned plasma parameters the Stark broadening is found to be a main line broadening mechanism of the lines (λ > 200 nm) in the Hg I–IV spectra.  相似文献   

12.
Augusto Carballido 《Icarus》2011,211(1):876-884
Numerical magnetohydrodynamic (MHD) simulations of a turbulent solar nebula are used to study the growth of dust mantles swept up by chondrules. A small neighborhood of the solar nebula is represented by an orbiting patch of gas at a radius of 3 AU, and includes vertical stratification of the gas density. The differential rotation of the nebular gas is replaced by a shear flow. Turbulence is driven by destabilization of the flow as a result of the magnetorotational instability (MRI), whereby magnetic field lines anchored to the gas are continuously stretched by the shearing motion. A passive contaminant mimics small dust grains that are aerodynamically well coupled to the gas, and chondrules are modeled by Lagrangian particles that interact with the gas through drag. Whenever a chondrule enters a region permeated by dust, its radius grows at a rate that depends on the local dust density and the relative velocity between itself and the dust. The local dust abundance decreases accordingly. Compaction and fragmentation of dust aggregates are not included. Different chondrule volume densities ρc lead to varying depletion and rimmed-chondrule size growth times. Most of the dust sweep-up occurs within ～1 gas scale-height of the nebula midplane. Chondrules can reach their asymptotic radius in 10–800 years, although short growth times due to very high ρc may not be altogether realistic. If the sticking efficiency Q of dust to chondrules depends on their relative speed δv, such that Q < 10?2 whenever δv > vstick ≈ 34 cm/s (with vstick a critical sticking velocity), then longer growth times result due to the prevalence of high MRI-turbulent relative velocities. The vertical variation of nebula turbulent intensity results in a moderate dependence of mean rimmed-chondrule size with nebula height, and in a ～20% dispersion in radius values at every height bin. The technique used here could be combined with Monte Carlo (MC) methods that include the physics of dust compaction, in a self-consistent MHD-MC model of dust rim growth around chondrules in the solar nebula.  相似文献   

13.
Vertical distributions and spectral characteristics of Titan’s photochemical aerosol and stratospheric ices are determined between 20 and 560 cm?1 (500–18 μm) from the Cassini Composite Infrared Spectrometer (CIRS). Results are obtained for latitudes of 15°N, 15°S, and 58°S, where accurate temperature profiles can be independently determined.In addition, estimates of aerosol and ice abundances at 62°N relative to those at 15°S are derived. Aerosol abundances are comparable at the two latitudes, but stratospheric ices are ～3 times more abundant at 62°N than at 15°S. Generally, nitrile ice clouds (probably HCN and HC3N), as inferred from a composite emission feature at ～160 cm?1, appear to be located over a narrow altitude range in the stratosphere centered at ～90 km. Although most abundant at high northern latitudes, these nitrile ice clouds extend down through low latitudes and into mid southern latitudes, at least as far as 58°S.There is some evidence of a second ice cloud layer at ～60 km altitude at 58°S associated with an emission feature at ～80 cm?1. We speculate that the identify of this cloud may be due to C2H6 ice, which in the vapor phase is the most abundant hydrocarbon (next to CH4) in the stratosphere of Titan.Unlike the highly restricted range of altitudes (50–100 km) associated with organic condensate clouds, Titan’s photochemical aerosol appears to be well-mixed from the surface to the top of the stratosphere near an altitude of 300 km, and the spectral shape does not appear to change between 15°N and 58°S latitude. The ratio of aerosol-to-gas scale heights range from 1.3–2.4 at about 160 km to 1.1–1.4 at 300 km, although there is considerable variability with latitude. The aerosol exhibits a very broad emission feature peaking at ～140 cm?1. Due to its extreme breadth and low wavenumber, we speculate that this feature may be caused by low-energy vibrations of two-dimensional lattice structures of large molecules. Examples of such molecules include polycyclic aromatic hydrocarbons (PAHs) and nitrogenated aromatics.Finally, volume extinction coefficients NχE derived from 15°S CIRS data at a wavelength of λ = 62.5 μm are compared with those derived from the 10°S Huygens Descent Imager/Spectral Radiometer (DISR) data at 1.583 μm. This comparison yields volume extinction coefficient ratios NχE(1.583 μm)/NχE(62.5 μm) of roughly 70 and 20, respectively, for Titan’s aerosol and stratospheric ices. The inferred particle cross-section ratios χE(1.583 μm)/χE(62.5 μm) appear to be consistent with sub-micron size aerosol particles, and effective radii of only a few microns for stratospheric ice cloud particles.  相似文献   

14.
We present a spectroscopic study of Mg II k&h emission lines in the 2000–3000 Å region of 91 high resolution IUE spectra of α Orionis obtained during the period 1978–1996. There are absorption and emission components on the blue sides of the k&h emission lines, these components may be coming from the dust envelope located inside the extended atmosphere of α Orionis. A set of 91 Mg II k&h emission lines have been identified and measured to determine their fluxes and widths. We found that there is a spectral variability for these physical parameters with phase, similar to that found for the light curve, which we attribute to the changes of density and temperature of the regions from which these emission lines are coming, as a result of the semi-regular pulsation and the variability of mass loss of the red supergiant.Also we present a study of C II and Fe II emission features in the 2000–3000 Å region of 55 high resolution IUE spectra during the period 1978–1996. A set of 55 C II and Fe II emission lines have been identified and measured to determine their fluxes and widths. We found the same result as with the Mg II emission lines.  相似文献   

15.
The ZrO molecule has been detected in sunspot umbrae through the identification of following laboratory molecular transitions: 1Σ+ ? X1Σ+ (0, 0), A3Φ2 ? X2Δ1 (0, 0), A3Φ3 ? X2Δ2 (0, 0), A3Φ4 ? X2Δ3 (0, 0), B3Π2 ? X3Δ3 (0, 0), B3Π1 ? X3Δ2 (0, 0) and B3Π0 ? X3Δ1 (0, 0) in red – infrared region using high resolution, visible range Fourier Transform Spectrum of sunspot umbra observed at the National Solar Observatory in Kitt Peak (NSO/KP). Much new identification has been made in the searched spectral wavenumber region from 16650 cm?1 to 18007 cm?1 of sunspot spectrum. Equivalent widths of well resolved lines, versus rotational quantum number J have been used to determine the effective rotational temperature for seven bands of the ZrO molecule. This result agrees well with the temperatures derived for other molecules’ presence in sunspot umbrae. It is evident that ZrO molecular lines are formed in higher layers of the atmosphere of relatively “cold” sunspots.  相似文献   

16.
M.R. Sanad 《New Astronomy》2010,15(5):409-416
The main aim of this study is to use archival low-dispersion spectra from the International Ultraviolet Explorer (IUE) in an attempt to follow up the spectral behavior of two symbiotic Mira systems RR Tel and RX Pup of the period from 1978–1995 and 1979–1989 for two systems respectively. We concentrated on studying N IV 1486 Å intercombination line, coming from the emission nebulae (Bryan and Kwok, 1991, Muerset et al., 1991, Murset and Nussbaumer, 1994), by calculating the line fluxes and line widths of N IV 1486 Å. We found that there is a disparity of spectral variability for these physical parameters at different times for both systems. For RR Tel, both line fluxes and line widths are increasing with the phase, while for RX Pup, both line fluxes and line widths are decreasing with the phase. There is a relation between the parameters of this emission line (line flux, line width) and phase, which we attribute to the variations of temperature of the emission nebulae at different times, as a result of the activity of the hot component.  相似文献   

17.
We examine spectral properties of the SDSS quasar J093201.60 + 031858.7, in particular the presence of strong blue peaks in the Balmer emission lines offset from the narrow lines by approximately 4200 km s?1. Asymmetry in the broad central component of the Hβ line indicates the presence of a double-peaked emitter. However, the strength and sharpness of the blue Hβ and blue Hγ peaks make this quasar spectrum unique among double-peaked emitters identified from SDSS spectra. We fit a disk model to the Hβ line and compare this object with other unusual double-peaked quasar spectra, particularly candidate binary supermassive black holes (SMBHs). Under the binary SMBH scenario, we test the applicability of a model in which a second SMBH may produce the strong blue peak in the Balmer lines of a double-peaked emitter. If there were only one SMBH, a circular, Keplerian disk model fit would be insufficient, indicating some sort of asymmetry is required to produce the strength of the blue peak. In either case, understanding the nature of the complex line emission in this object will aid in further discrimination between a single SMBH with a complex accretion disk and the actual case of a binary SMBH.  相似文献   

18.
《New Astronomy》2007,12(6):435-440
A detailed analysis of emission lines of carbon-like silicon reveals that some ratios of n = 3 → 2 line intensities are sensitive to the electron density, ne. The ratio between two groups of 3d → 2p transition lines of 55.246 Å and 55.346 Å provides a good diagnostic of ne because of the combined characteristic of sensitivity to electron density and relative insensitivity to temperature. From this ratio, a lower limit of the electron density of 0.6 × 108 cm−3 was set for Procyon, which is consistent with the values constrained by C V and Si X emission lines. Significant discrepancies were found between theoretical predictions and observations for the 3s → 2p lines relative to 3d → 2p lines in Procyon, recently measured using the Chandra high-resolution transmission grating instrument. The difference of more than a factor of 3, cannot be explained by uncertainties of atomic data. Ness and co-workers also suggested that the effect of opacity appeared not to be a major factor for the discrepancy. For the 3s → 2p line at 61.611 Å, present work indicates that the large discrepancy may be from the contamination of a S VIII line at 61.645 Å. For lines at 61.702 and 61.846 Å, we suggest that the discrepancies may be attributed to contaminations by currently yet-unknown spectral lines.  相似文献   

19.
We present the photoionisation modelling of the intrinsic absorber in the bright quasar HS 1603 + 3820. We constructed the broad-band spectral energy distribution using the optical/UV/X-ray observations from different instruments as inputs for the photoionisation calculations. The spectra from the Keck telescope show extremely high Civ to Hi ratios, for the first absorber in system A, named A1. This value, together with high column density of Civ ion, place strong constraints on the photoionisation model. We used two photoionisation codes to derive the hydrogen number density at the cloud illuminated surface. By estimating bolometric luminosity of HS 1603 + 3820 using the typical formula for quasars, we calculated the distance to A1. We could find one photoionization solution, by assuming either a constant density cloud (which was modelled using cloudy), or a stratified cloud (which was modelled using titan), as well as the solar abundances. This model explained both the ionic column density of Civ and the high Civ to Hi ratio. The location of A1 is 0.1 pc, and it is situated even closer to the nucleus than the possible location of the Broad Line Region in this object. The upper limit of the distance is sensitive to the adopted covering factor and the carbon abundance. Photoionisation modelling always prefers dense clouds with the number density n0 = 1010 − 1012 cm−3, which explains intrinsic absorption in HS 1603 + 3820. This number density is of the same order as that in the disk atmosphere at the implied distance of A1. Therefore, our results show that the disk wind that escapes from the outermost accretion disk atmosphere can build up dense absorber in quasars.  相似文献   

20.
《New Astronomy Reviews》2000,44(7-9):511-517
The width of the broad Hβ emission line is the primary defining characteristic of the NLS1 class. This parameter is also an important component of Boroson and Green’s optical “Eigenvector 1” (EV1), which links steeper soft X-ray spectra with narrower Hβ emission, stronger Hβ blue wing, stronger optical Fe II emission, and weaker [O III] λ5007. Potentially, EV1 represents a fundamental physical process linking the dynamics of fueling and outflow with the accretion rate. We attempted to understand these relationships by extending the optical spectra into the UV for a sample of 22 QSOs with high quality soft-X-ray spectra, and discovered a whole new set of UV relationships that suggest that high accretion rates are linked to dense gas and perhaps nuclear starbursts. While it has been argued that narrow (BLR) Hβ means low Black Hole mass in luminous NLS1s, the C IV λ1549 and Lyα emission lines are broader, perhaps the result of outflows driven by their high Eddington accretion rates. We present some new trends of optical-UV with X-ray spectral energy distributions. Steeper X-ray spectra appear associated with stronger UV relative to optical continua, but the presence of strong UV absorption lines is associated with depressed soft X-rays and redder optical–UV continua.  相似文献   

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