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921.
G. Y. Liang G. Zhao J. R. Shi 《Monthly notices of the Royal Astronomical Society》2006,368(1):196-202
Theoretical electron density sensitive line ratios R 1 – R 6 of Si x soft X-ray emission lines are presented. We found that these line ratios are sensitive to electron density n e , and the ratio R 1 is insensitive to electron temperature T e . For reliable determination of the electron density of laboratory and astrophysical plasmas, atomic data, such as electron impact excitation rates, are very important. Our results reveal that the discrepancy of the line ratios from different atomic data calculated with the distorted wave (DW) approximation and the R-matrix method is up to 19 per cent at n e = 2 × 108 cm−3 . We applied the theoretical intensity ratio R 1 to the Low Energy Transmission Grating Spectrometer (LETGS) spectrum of the solar-like star Procyon. By comparing the observed value (1.29) with the theoretical calculation, the derived electron density n e is 2.6 × 108 cm−3 , which is consistent with that derived from (C v < 8.3 × 108 cm−3 ) . When the temperature structure of the Procyon corona is taken into account, the derived electron density increases from n e = 2.6 × 108 to 2.8 × 108 cm−3 . 相似文献
922.
The accretion-induced neutron star (NS) magnetic field evolution is studied through considering the accretion flow to drag the field lines aside and dilute the polar-field strength, and as a result the equatorial field strength increases, which is buried inside the crust on account of the accretion-induced global compression of star crust. The main conclusions of model are as follows: (i) the polar field decays with increase in the accreted mass; (ii) the bottom magnetic field strength of about 108 G can occur when the NS magnetosphere radius approaches the star radius, and it depends on the accretion rate as ; and (iii) the NS magnetosphere radius decreases with accretion until it reaches the star radius, and its evolution is little influenced by the initial field and the accretion rate after accreting ∼0.01 M⊙ , which implies that the magnetosphere radii of NSs in low-mass X-ray binaries would be homogeneous if they accreted the comparable masses. As an extension, the physical effects of the possible strong magnetic zone in the X-ray NSs and recycled pulsars are discussed. Moreover, the strong magnetic fields in the binary pulsars PSR 1831−00 and PSR 1718−19 after accreting about 0.5 M⊙ in the binary-accretion phase, 8.7 × 1010 and 1.28 × 1012 G , respectively, can be explained through considering the incomplete frozen flow in the polar zone. As an expectation of the model, the existence of the low magnetic field (∼3 × 107 G) NSs or millisecond pulsars is suggested. 相似文献
923.
Brandt J. C. Snow M. Yi Y. Larson S. M. Mikuz H. Petersen C. C. Liller W. 《Earth, Moon, and Planets》2002,90(1-4):15-33
The plasma tails of comets clearly show the demarcation of the solar wind into distinct equatorial and polar regions (Brandt
and Snow (2000), Icarus
148, 52–64).The boundary is determined by the maximum extent in latitude of the heliospheric current sheet (HCS). The observational
record contains many well-observed equatorial comets, but observations of comets in the polar region are relatively rare.
In addition to its size and brightness, comet Hale–Bopp had an orbital inclination of 89.4° and was well observed for months
in the polar region. We document the comet's large-scale appearance throughout the apparition, including the polar region
and its transition into the equatorial region. The bright dust tail hampered observations of the plasma tail, particularly
near the head, but images taken with a CO+ filter show a very large disconnection event (DE) on May 7 and May 8, 1997. The time of disconnection is estimated at approximately
May 4.0. This DE is associated with a crossing of the HCS. The model calculations of the HCS indicate that other crossings
might have occurred in late April, but given the uncertainty in the calculation, the comet might have missed the HCS. Sparse
observational coverage and the bright dust tail prevent further investigation of the potential earlier HCS crossings. The
plasma tail shows anomalous orientations at the highest latitudes and possible explanations are discussed. 相似文献
924.
G. Pignata F. Patat S. Benetti S. Blinnikov W. Hillebrandt R. Kotak B. Leibundgut P. A. Mazzali P. Meikle Y. Qiu P. Ruiz-Lapuente S. J. Smartt E. Sorokina M. Stritzinger M. Stehle M. Turatto T. Marsh F. Martin-Luis N. McBride J. Mendez L. Morales-Rueda D. Narbutis R. Street 《Monthly notices of the Royal Astronomical Society》2004,355(1):178-190
925.
926.
The possibility of H3+ playing a role as a sink for noble gases has been investigated in the case of Argon. Elaborate quantum methods (ab initio Coupled Cluster and density functional BH&HLYP levels of theory) have been shown to reproduce the rotational constants within 0.3% together with the only known IR frequency on the test case of Ar…D3+. Dissociation energies of (Ar)n…H3+ as a function of cluster size, i.e. 7.2 (n=1), 3.7 (n=2), 3.6 (n=3), 1.6 (n=4), 1.7 (n=5) kcal/mol, follow the pattern established experimentally for (Ar)n…H3+ and (H2)n…H3+ series. Rotational constants and harmonic frequencies of (Ar)n…H3+ (n=1-3) are presented. 相似文献
927.
928.
Using a 2.5-D, time-dependent ideal MHD model in Cartesian coordinates, we carried out numerical simulations to investigate
the equilibrium and evolution properties of a magnetic configuration that consists of a coronal magnetic flux rope and a partly
open photospheric background field, which is equivalent to that produced by a two-patch magnetic source on the photospheric
surface. The axial and annular magnetic fluxes of the flux rope are given and fixed. The global magnetic configuration evolves
in response to three types of changes of the background field: decreasing of the distance between the two sources, shrinking
of the size of each source, and increasing of the shear in the closed component of the background field. As a result, the
geometrical parameters of the flux rope, i.e. the height of the rope axis, the half-width of the rope and the length of the
vertical current sheet below the rope, change due to the variation of the background field. It is shown that for a given coronal
magnetic flux rope in a partly open background field, the variation of the geometrical parameters of the flux rope displays
a catastrophic behavior, namely, there exists a critical point for each case, at which an infinitesimal change of the background
field leads to a loss of equilibrium, and thus a jump of the flux rope. The implication of such a catastrophe in solar active
phenomena is briefly discussed. 相似文献
929.
930.