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1.
Terry Moon 《Astrophysics and Space Science》1985,117(2):261-270
A linear relation is found to exist between the Barnes-Evans visual surface brightness parameterF
V
and the (b-y)0 colour index ofuvby photometry for spectral types later than G0. Using this relation, and a previously determined relation for spectral types B0-G0, tables of intrinsic colours and indices, absolute magnitude and stellar radius are given for the ZAMS and luminosity classes Ia-V over a wide range of spectral types. Comparison of absolute magnitudes and radii calculated fromuvby photometry with values obtained using the visual magnitude, parallax and angular diameter indicates thatuvby photometry can be used to determineM
V
to ±0
m
.2 and log(R/R
) to ±0.05. 相似文献
2.
Photopolarimetry of the classic Herbig Ae star VV Ser was carried out at the Crimean Astrophysical Observatory as a part of the longterm program of UX Ori type stars monitoring. An exceptionally deep minimum, down to V = 14m8, was observed in 1998. For the first time for this star the blueing effect was detected in U – B and B – V color indexes. Record-high for UX Ori stars linear polarization (12.8 ± 1.4% in B) was observed in this minimum. 相似文献
3.
The twelfth list of blue stellar objects in the second part of the First Byurakan Spectral Sky Survey (FBS) is presented. This list contains 143 objects in the region -3° +1° at high latitudes with an area of approximately 992 square degrees (62 fields). The objects have magnitudes V of 11.8-18.1 and B-V colors ranging from -0.82 to +0.81. Of the 143 objects, 51 have been discovered for the first time. Equatorial coordinates, V magnitudes, color indices, and preliminary classifications of the objects are given. DSS identification charts are given for the newly discovered objects. 相似文献
4.
In the present paper, the effects of free convection currents and the viscous dissipation on the unsteady flow of an electrically conducting and viscous incompressible fluid around an uniformly accelerated vertical porous plate subjected to a suction or injection velocity inversely proportional to the square root of time, in presence of a transverse magnetic field, have been investigated. Analytical solutions for the velocity and the temperature distributions, the skin-friction and the rate of heat transfer are obtained for small magnetic parameterM. During the course of discussion the effects of the Grashof number Gr, the Eckert number Ec, the suction/injection parametera have been considered for unit value of the Prandtl number Pr.Nomenclature
a
suction/injection parameter
-
C
p
specific heat at constant pressure
-
B
0
magnetic induction
-
g
acceleration due to gravity
- Gr
Grashof number (g(T
w
–T
)/U
0
3
)
-
K
thermal conductivity
-
M
magnetic field parameter (B
0
2
/U
0
2
)
- Pr
Prandtl number (C
p/K)
-
T
temperature of the fluid near the plate
-
T
w
temperature of the plate
-
T
temperature of the fluid at infinity
-
t
time
-
t
dimensionless time (tU
0
2
/)
-
u
velocity of the fluid
-
u
non-dimensional velocity (u/U
0)
-
U
velocity of the plate
-
U
dimensionless velocity of the plate (U/U
0)
-
U
0
reference velocity
-
v
0
suction velocity
-
v
0
non-dimensional suction velocity (v
0/U
0)=at
–1/2
- Ec
Eckert number ((U
0)2/3/C
p(T
w
–T
))
-
T
dimensionless temperature of the fluid near the plate ((T–T
)/(T
w
–T
))
-
x, y
coordinates along and normal to the plate
-
x, y
dimensionless coordinates (y=yU
0/)
-
kinematic viscosity
-
coefficient of volume expansion
-
electric conductivity of the fluid
-
y/2t
1/2
-
density of the fluid
-
skin-friction
-
dimensionless skin-friction
-
q
rate of heat transfer
-
q
non-dimensional rate of heat transfer
-
coefficient of viscosity
- e
magnetic permeability
On leave of absence from Department of Mathematics, University of Dhaka, Bangladesh 相似文献
5.
The eleventh list of blue stellar objects in the second part of the First Byurakan Spectral Sky Survey (FBS) is presented. The list consists of 64 objects located in the region +80 +90° and 2h 08m a 20h 15m. The objects haveV magnitudes in the range 12.3–17.4 andB–V color indices in the range -0.55-+0.55. Of the 98 objects, 56 are newly discovered. Tentative classifications are given for 28 objects, of which there is one planetary nebula, 6 possible quasars, 15 possible white dwarfs, and 6 possible cataclysmic variables. Two of the latter are possibly novae having erupted at the epoch of exposure of the FBS plates in this region.Translated fromAstrofizika, Vol. 39, No. 4, pp. 531–540, November, 1996. 相似文献
6.
General theory of electrical conductivity of a multicomponent mixture of degenerate fermions in a magnetic fieldB, developed in the preceding article (this volume), is applied to a matter in neutron star interiors at densities 0, where 0 = 2.8×1014 g cm–3 is the standard nuclear matter density. A model of free-particle mixture ofn, p, e is used, with account for appearance of –-hyperons at >
c
, where
c
40. The electric resistivities along and acrossB, and , and the Hall resistivity
H
are calculated and fitted by simple analytical formulae at
c
and >
c
for the cases of normal or superfluid neutrons provided other particles are normal. Charge transport alongB is produced by electrons, due to their Coulombic collisions with other charged particles; is independent ofB and almost independent of the neutron superfluidity. Charge transport acrossB at largeB may be essentially determined by other charged particles. If
c
, one has = [1 + (B/B
0)2] for the normal neutrons, and for the superfluid neutrons, while
H
=
B/B
e
for both cases. HereB
e
109
T
8
2
G,B
01011
T
8
2
G, andT
8 is temperature in units of 108 K. Accordingly for the normal neutrons atBB
0, the transverse resistivity suffers an enhancement, 1/4 1. When 50 andB varies from 0 toBB
p
1013
T
8
2
G, increases by a factor of about 103–104 and
H
changes sign. WhenBB
p
, remains constant for the superfluid neutrons, and
H
B
2 for the normal neutrons, while
H
B for any neutron state. Strong dependence of resistivity onB, T, and may affect evolution of magnetic fields in neutron star cores. In particular, the enhancement of at highB may noticeably speed up the Ohmic decay of those electric currents which are perpendicular toB. 相似文献
7.
Unsteady laminar free convection flow of a viscous incompressible and electrically conducting fluid past an accelerated vertical infinite porous plate subjected to a suction velocity proportional to (time)–1/2 is studied in presence of a uniform horizontal magnetic field. Results are discussed with the effects of the Grashof number Gr, and the magnetic field parameterM for Pr (the Prandtl number)=0.71 and 7.0 representing air and water respectively at 20 °C.Nomenclature
a
suction/injection parameter
-
C
p
specific heat at constant pressure
-
B
0
magnetic induction
-
g
acceleration due to gravity
- Gr
Grashof number (vg(T'w-T')/U
0
3
)
-
K
thermal conductivity
-
M
magnetic field parameter (B
0
2
e
2
/U
0
2
)
- Pr
Prandtl number (C
p/K)
-
T'
temperature of the fluid near the plate
-
T'
w
temperature of the plate
-
T'
temperature of the fluid at infinity
-
t'
time variable
-
t
dimensionless time (t' U
0
2
/v)
-
u
non-dimensional velocity (u'/U
0)
-
U'
velocity of the plate
-
U
dimensionless velocity of the plate (U'/U
o)
-
U
0
reference velocity
-
v'
0
suction velocity
-
v
0
nondimensional suction velocity (v'
0/U
0)=at–1/2
-
v'
normal velocity component
-
v
dimensionless normal velocity
- Ec
Eckert number ((vU
0)2/3/C
p(T'
w
-T'
))
-
T
dimensionless temperature of the fluid near the plate ((T'-T'
)/T'
w
–T'
))
-
x',y'
coordinates along and normal to the plate
-
y
dimensionless ordinate (=y' U
o/v)
-
v
kinematic viscosity
-
coefficient of volume expansion
-
electric conductivity of the fluid
-
similarity variable (y/2t)
- w
density of the fluid at the plate
-
density of the fluid at infinity
- '
skin-friction
-
dimensionless skin-friction
-
coefficient of viscosity
- e
magnetic permeability 相似文献
8.
V. G. Fainshtein 《Solar physics》1991,136(1):169-189
By analyzing observational data, it has been possible to determine quantitative relationships that represent the role of the interaction of fast and slow solar wind (SW) streams in the formation of characteristic SW properties at the Earth's orbit.It is shown that maximum values of magnetic field B
M and density n
M peaks in the neighbourhood of the sector boundary (SB) at the base of the high-speed stream front are associated with solar wind characteristics such as the SW minimum velocity near the SB, V
m, the maximum velocity in the central part of the fast stream, V
M, and the slope of the magnetic field neutral line to the solar equatorial plane at R = 2.5 R
(R
is the solar radius).It is concluded that enhancements of absolute values of the z-component of the magnetic field, ¦B
z¦, recorded at the Earth's orbit, are largely attributable, at sufficiently large values of , to the interaction of different-velocity SW streams. 相似文献
9.
UBVR
c
I
c observations of SN 2002ap during February, October, and November 2002 at the Crimean Astrophysical Observatory are reported. An examination of our photometric data, along with published data, shows that over a period of about a year from the day the SN 2002ap supernova burst, the light curve passed through three developmental stages: a sharp rise, followed by a stage of rapid exponential decrease, and then a slower fading. Based on the shape of the light curve, this supernova is of type SN I, but according to the variation in its color indices, it more likely belongs to the SN Ic supernovae. In the premaximum stage, the energy distribution from 3000 to 6000 resembles the emission from a star of spectral class F5V. In the second stage of the light curve evolution, when the brightness falls off rapidly, the changes in the color indices are associated with a change in the radiation temperature indicative of rapid cooling of the ejected material. Taking the effective radiation temperature in the premaximum stage to be T
eff 6500 K, we estimate the expansion velocity of the quasiphotosphere to be about 9700 km/s. 相似文献
10.
J. David Bohlin 《Solar physics》1971,18(3):450-457
Two-dimensional isophotes of the extreme solar corona (r
max 45 R
) have been derived from integrated vidicon pictures taken from the Moon's surface by the unmanned probes Surveyors 6 and 7. These data were calibrated through use of previously published values for the coronal brightness gradient along the ecliptic. The resulting structure of the outer corona is compared to ground-based observations of the innermost corona 1.125 r/R
2.0 made by the High Altitude Observatory K-coronameter. The possible existence of a streamer seen by Surveyor 7 is analyzed over the region 15 r 22.5 R
. 相似文献
11.
It is shown that a cylindrical plasma column supporting a longitudinal fieldB
z
and an azimuthal fieldB
has a fastest-growing mode in whichkR
01 (k=wave number,R
0=radius of the column). If we assume that plasma is ejected from a galaxy to form a jet, filament or bridge of length 5 kpc,R
00.5 kpc, density 10–24 gm cm–3 with a dragged-out field of strengthB
z
10–5 Gauss (from a parent field 10–6 Gauss), such a column must eventually fragment by the action of a hydromagnetic instability, breaking up into a number 10 of regularly-spaced condensations. It is, therefore, predicted that features like the M87 jet should show incipient nucleation with 3–10 knots, and that periodically-spaced objects of the type noted by Arp may have resulted from the action of such an instability. 相似文献
12.
Two sets of accurate approximate expressions for the gyrosynchrotron radiation in the transverse propagation case are presented for the first time. They contain emissivity –/BNand absorptivity –
B/Nfor e-mode, effective temperature T
effand frequency of peak brightness p. The expressions are designed for the range 2 to 7 of electron energy spectral index and for the ranges from 2 to 10 and 10 to 100 of harmonic numbers s(=/B). Their statistical error is, respectively, ±18% and ±29% for –/BNand –
B/Nfor 10/B100, ±128% and and ±170% for 2/B10. 相似文献
13.
The 2 m RCC telescope of the Rozhen National Observatory (Bulgaria) was used to obtain the colour-magnitude and colour-colour diagrams of OB110 and OB112 associations which form the largest star grouping in the southern region of M33. The stars withV andU20.4 andB21 were measured. TheV magnitude, the coloursB - V, U - B and the respective identification charts are given. This allowed to construct the luminosity function of OB110+OB112. The group has an integrated magnitudeM
VT=–11.8 which is by 0
m
.5 fainter than OB78 (M31). The mean absorption and the foreground were examined as well. 相似文献
14.
G. S. Lakhina 《Astrophysics and Space Science》1982,85(1-2):369-380
The velocity gradients of the contrastreaming electron beams observed in the Earth's magnetosphere can excite three types of ordinary mode instabilities, namely (i) B-resonance electron instability, (ii) ion cyclotron instability, and (iii) unmagnetized ion instability. The B-resonance electron instability occurs at small values of the shear parameter 10–4<S<10–3, whereS = [(1/e){dU
o(x)}/(dx)] (U
0(x) and
e
being the streaming velocity of the electron beams and the electron cyclotron frequency, respectively). Near the equatorial plane of the bouncing electron beams region, this instability can generate electromagnetic waves having frequenciesf(0.045–0.2) Hz and wavelentghs
(0.5–10)km, and the wave magnetic field is polarised in a radial direction. This instability can also occur in the plasma sheet region during the earthwards and tailwards plasma flows events and can generate waves, with wave magnetic field polarised along north-south direction, in the frequency rangef(0.007–0.02) Hz with
(10–100)km nearR=–35R
E
. For 10–3<S<10–2, the ion cyclotron instability is excited and it can generate waves up to 5th harmonic or so of ion cyclotron frequency. ForS>10–2, the unmagnetized ion instability is excited which can generate electromagnetic waves having frequences from 5 to 50 Hz and typical wavelengths
(0.5–6)km. The growth rates of all the three velocity shear driven instabilities are reduced in the presence of cold background plasma. The turbulence generated by these instabilities may give rise to enhanced effective electron-electron and electron-ion collisions and broaden the bouncing electron beams. 相似文献
15.
P. D. Singh A. M. Gomez Balboa J. A. De Freitas Pacheco 《Astrophysics and Space Science》1985,108(1):153-160
Spontaneous emission rates and absorption oscillator strengths for prominent V4 sequence bands of theB
2+-A
2i transition of the CN molecule are estimated. The wavelengths of some lines observed in the coma spectrum of the comet Bradfield 1980t as well as in several comets coincide with these V4 sequence LeBlanc bands of the CN radical. Formation and destruction of the CN radical in the coma of a comet are discussed in the framework of gas phase reactions.Work supported by CNPq, Brasília, under contract numbers: Processos 401236-83 and 4076/77-FA01. 相似文献
16.
A technique is proposed for separating the rays of the streamer belt with quasi-stationary and non-stationary solar wind (SW) flows. It is shown that the lifetime of rays with a quasi-stationary SW can exceed 20 days. A new method has been developed for measuring the relative density distribution of a quasi-stationary slow SW flowing along the streamer belt's ray of increased brightness, based on the LASCO/SOHO data. It is shown that the density n for such SW flows varies with the radius R according to the relationship nR
–, where =13.3–3.9 within 4 R
0 R 6 R
0 (here R
0 is the solar radius), and decreases gradually further away. It is also shown that the V(R)-profiles in some rays of the streamer belt differ little from each other, although the value of the mass flow density, j
E, at the Earth's orbit in them can vary more than by a factor of 4. This distinguishes in a crucial respect a slow SW in the streamer belt's rays from a fast SW originating in coronal holes, for which j
Econstant and the dependences V(R) in different fast flows can differ greatly. 相似文献
17.
I. R. Tuohy N. Visvanathan D. T. Wickramasinghe 《Astrophysics and Space Science》1986,118(1-2):291-294
We report AAT observations of two southern AM Herculis variables, H0139-68 and E1405-451. H0139-68 was found to be in an unusually faint state (V17), and this has permitted the first measurement of the magnetic field of the white dwarf,B
p3×107 G. Linear polarimetry of E1405-451 has revealed a substantial position angle variation with phase, corresponding to an orbital inclination of 60° and a colatitude of 20° for the magnetic pole of the white dwarf.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
18.
J. Puls A. Feldmeier U. W. E. Springmann S. P. Owocki A. W. Fullerton 《Astrophysics and Space Science》1994,221(1-2):409-426
On the basis of a a careful analysis of resonance line formation (both for singlets and doublets) in structured winds, presenttime dependent models of the line driven winds of hot stars (Owocki et al., this volume; Feldmeier, this volume) are shown to be able to explain a number of observational features with respect to variability and structure: they are (in principle) able to reproduce theblack andbroad troughs (without any artificial turbulence velocity) and the blue edge variability observed in saturated resonance lines; they might explain the long lived narrow absorption components often observed in unsaturated lines at high velocities; they predict a relation between the edge velocity of UV-lines and the radiation temperature of the observed X-ray emission.As a first example of the extent to which theoretical models can be constrained by comparisons between observations and profiles calculated by spectrum synthesis from structured winds, we show here that models with deep-seated onset of structure formation ( 1.1R
*
) produce resonance lines which agreequalitatively with observational findings; in contrast, the here presented models with structure formation only well out in the wind ( 1.6R
*
) fail in this respect. 相似文献
19.
The results of spectrophotometric observations of CH Cyg in an active phase and during emergence from it are given: the spectral energy distribution in the 3225-7500 range with 23 resolution, the absolute monochromatic illuminances at eight selected wavelengths in the 3225-8015 , and the emission fluxes in the H and H lines. The features of the energy distribution in the stellar spectrum and the observed forms of variability, different between the short-wavelength and red parts of the spectrum, are determined by the instability of both of the system's components. In the active phase, CH Cyg's emission in the observed spectral range can be represented as the total emission from a cool M6 III giant and a hot hydrogen gas with a temperature T
e
= 10,000-15,000 K. In the low-brightness state, the star's energy distribution fully corresponds to that of a cool giant, the spectrum of which varies from M6 III to M7 III. The photometric variability of the cool component in the 8015 range is 0
m
.3-0
m
.4. An increase in the brightness of the cool giant preceded a bright outburst of the hot component. 相似文献
20.
Very Large Array (VLA) observations of compact transient sources on the Sun at 2 cm wavelength are presented. These sources have angular sizes of 5–25, brightness temperatures of T
B 1–3 × 105 K, and lifetimes ranging between a few minutes to several hours. The emission originates in regions of diffuse plage and quiet Sun, where the photospheric magnetic fields are relatively weak (H 100 G). In some cases the 2 cm radiation may be explained as the thermal bremsstrahlung of a dense (N
e 1010 cm-3) plasma in the transition region. For other sources, the relatively high circular polarization (
c 40–50 %) suggests a nonthermal emission mechanism, such as the gyrosynchrotron radiation of mildly relativistic electron with a power-law spectrum. 相似文献