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1.
Based on data for 102 OB3 stars with known proper motions and radial velocities, we have tested the distances derived by Megier
et al. from interstellar Ca II spectral lines. The internal reconciliation of the distance scales using the first derivative
of the angular velocity of Galactic rotation Ω′0 and the external reconciliation with Humphreys’s distance scale for OB associations refined by Mel’nik and Dambis show that
the initial distances should be reduced by ≈20%. Given this correction, the heliocentric distances of these stars lie within
the range 0.6–2.6 kpc. A kinematic analysis of these stars at a fixed Galactocentric distance of the Sun, R
0 = 8 kpc, has allowed the following parameters to be determined: (1) the solar peculiar velocity components (u
⊙, v
⊙, ω
⊙) = (8.9, 10.3, 6.8) ± (0.6, 1.0, 0.4) km s−1; (2) the Galactic rotation parameters Ω0 = −31.5 ± 0.9 km s−1 kpc−1, Ω′0 = +4.49 ± 0.12 km s−1 kpc−2, Ω″0 = −1.05 ± 0.38 km s−1 kpc−3 (the corresponding Oort constants are A = 17.9 ± 0.5 km s−1 kpc−1, B = −13.6 ± 1.0 km s−1 kpc−1 and the circular rotation velocity of the solar neighborhood is |V
0| = 252 ± 14 km s−1); (3) the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components,
respectively, f
R
= −12.5±1.1 km s−1 and f
ϑ
= 2.0 ± 1.6 km s−1; the pitch angle for the two-armed spiral pattern i = −5.3° ± 0.3°, with the wavelength of the spiral density wave at the solar distance being λ = 2.3 ± 0.2 kpc; the Sun’s phase in the spiral wave x
⊙ = −91° ± 4°. 相似文献
2.
It is surprising that we hardly know only 4% of the universe. Rest of the universe is made up of 73% of dark-energy and 23%
of dark-matter. Dark-energy is responsible for acceleration of the expanding universe; whereas dark-matter is said to be necessary
as extra-mass of bizarre-properties to explain the anomalous rotational-velocity of galaxy. Though the existence of dark-energy
has gradually been accepted in scientific community, but the candidates for dark-matter have not been found as yet and are
too crazy to be accepted. Thus, it is obvious to look for an alternative theory in place of dark-matter. Milgrom (Astrophys.
J. 270:365, 1983a; 270:371, 1983b) has suggested a ‘Modified Newtonian Dynamics (MOND)’ which appears to be highly successful for explaining the anomalous
rotational-velocity. But unfortunately MOND lacks theoretical support. The MOND, in-fact, is (empirical) modification of Newtonian-Dynamics
through modification in the kinematical acceleration term ‘a’ (which is normally taken as
a=\fracv2ra=\frac{v^{2}}{r}) as effective kinematic acceleration
aeffective = a m(\fracaa0)a_{\mathit{effective}} = a \mu(\frac{a}{a_{0}}), wherein the μ-function is 1 for usual-values of accelerations but equals to
\fracaa0 ( << 1)\frac{a}{a_{0}} (\ll1) if the acceleration ‘a’ is extremely-low lower than a critical value a
0(10−10 m/s2). In the present paper, a novel variant of MOND is proposed with theoretical backing; wherein with the consideration of universe’s
acceleration a
d
due to dark-energy, a new type of μ-function on theoretical-basis emerges out leading to
aeffective = a(1 -K \fraca0a)a_{\mathit{effective}} = a(1 -K \frac{a_{0}}{a}). The proposed theoretical-MOND model too is able to fairly explain ‘qualitatively’ the more-or-less ‘flat’ velocity-curve
of galaxy-rotation, and is also able to predict a dip (minimum) on the curve. 相似文献
3.
This is an account of Allan Sandage’s work on (1) The character of the expansion field. For many years he has been the strongest defender of an expanding Universe. He later explained the CMB dipole by a local velocity of 220±50 km s−1 toward the Virgo cluster and by a bulk motion of the Local supercluster (extending out to ∼3500 km s−1) of 450–500 km s−1 toward an apex at l=275, b=12. Allowing for these streaming velocities he found linear expansion to hold down to local scales (∼300 km s−1). (2) The calibration of the Hubble constant. Probing different methods he finally adopted—from Cepheid-calibrated SNe Ia and from independent RR Lyr-calibrated TRGBs—H 0=62.3±1.3±5.0 km s−1 Mpc−1. 相似文献
4.
Based on the data on a spectral dependence of the geometric albedo of giant planet discs, we obtained depth variations in
the optical thickness τ
a
of the aerosol component and relative concentration γ of methane (Uranium, Neptune) lnτ
a
= −0.720 + 1.507Δlnp (for −2.2085 ≤ lnp ≤ −1.0018), lnτ
a
= +1.224 + 1.160Δlnp (for −1.0018 ≤ lnp ≤ −0.0595), lnτ
a
= +2.318 + 0.192Δlnp (for −0.0595 ≤ lnp), γ = 0.0027 for Jupiter; lnτ
a
= −0.846 + 1.598Δlnp (for −3.3619 ≤ lnp ≤ −2.0575), lnτ
a
= +1.238 + 1.342Δlnp (for −2.0575 ≤ lnp ≤ −1.2074), lnτ
a
= +2.379 + 0.722 (for −1.2074 ≤ lnp ≤ −0.6501), lnτ
a
= +2.781 + 0.326Δlnp (for 0.6501 ≤ lnp), γ = 0.0027 for Saturn; lnτ
a
= −2.694 + 0.087Δlnp (for +0.3685 ≤ lnp ≤ +1.2314), lnτ
a
= −2.619 + 7.341Δlnp (for +1.2314 ≤ lnp ≤ +1.7556), lnτ
a
= +1.229 + 0.956Δlnp (for +1.7556 ≤ lnp) for Uranium; lnτ
a
= −1.861 + 1.248Δlnp (for +0.3204 ≤ lnp ≤ +0.9051), lnτ
a
= −1.131 + 0.347Δlnp (for +0.9051 ≤ lnp) for Neptune; depth-averaged relative methane concentration lnγ = −9.982 + 2.676Δlnp(0.3584 ≤ lnp ≤ 1.5445); ln γ = −9.738 + 2.561Δlnp(0.3237 ≤ lnp ≤ 1.6156) and γ = 0.00382(lnp ≥ 1.6156); 0.00554(lnp ≥ 1.6156) for Uranium and Neptune, respectively (p is in bar). 相似文献
5.
The peculiar galaxy NGC 4650 A (α=12h 42m. 1; = δ—40° 26′; 1950·0) has been studied by means of direct and spectral observations with the ESO 3·6-m telescope. It is
interpreted as a prolate, elliptical galaxy surrounded by a warped ring of H II regions, dust and stars. The distance is 47
Mpc (H
0=55 km s−1 Mpc−1). The ring is seen nearly edge-on (inclination 85°) and it rotates. It has a diameter of about 21 kpc and is bluer than the
elliptical galaxy for which the (M/L
v) ratio is ∼12 in solar units. The observed configuration may be the result of interaction with the nearby galaxy, NGC 4650. 相似文献
6.
Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes,
proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to
the Galactic center R
0, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives.
For R
0 = 8 kpc, we have found the circular velocity of the Sun to be V
0 = 243 ± 16 km s−1, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s−1 kpc−1 and B = −13.5 ± 1.4 km s−1 kpc−1. Our simulation of the influence of a spiral density wave has shown that the peculiar velocity of the Sun with respect to
the local standard of rest and the component (V
⊙)LSR depend significantly on the Sun’s phase in the spiral wave. 相似文献
7.
We present the results of our infrared observations of WR 140 (=V1687 Cyg) in 2001–2010. Analysis of the observations has
shown that the J brightness at maximum increased near the periastron by about 0
m
.3; the M brightness increased by ∼2
m
in less than 50 days. The minimum J brightness and the minimum L and M brightnesses were observed 550–600 and 1300–1400 days after the maximum, respectively. The JHKLM brightness minimum was observed in the range of orbital phases 0.7–0.9. The parameters of the primary O5 component of the
binary have been estimated to be the following: R(O5) ≈ 24.7R
⊙, L(O5) ≈ 8 × 105
L
⊙, and M
bol(O5) ≈ −10
m
. At the infrared brightness minimum, T
g ∼ 820–880 K, R
g ≈ 2.6 × 105
R
⊙, the optical depth of the shell at 3.5 μm is ∼5.3 × 10−6, and its mass is ≈1.4 × 10−8
M
⊙. At the maximum, the corresponding parameters are ∼1300 K, 8.6 × 104
R
⊙, ∼2 × 10−4, and ∼6 × 10−8
M
⊙; the mean rate of dust inflow (condensation) into the dust structure is ∼3.3 × 10−8
M
⊙ yr−1. The mean escape velocity of the shell from the heating source is ∼103 km s−1 and the mean dispersal rate of the shell is ∼1.1 × 10−8
M
⊙ yr−1. 相似文献
8.
It is well known that the interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation
of the ICME and solar wind velocities at 1 AU. This can be understood in terms of an aerodynamic drag force per unit mass
of the form F
D/M=−(ρe
AC
D/M)(V
i−V
e)∣V
i−V
e∣, where A and M are the ICME cross-section and sum of the mass and virtual mass, V
i and V
e the speed of the ICME and solar wind, ρe the solar wind density, C
D a dimensionless drag coefficient, and the inverse deceleration length γ=ρe
A/M. The optimal radial parameterisation of γ and C
D beyond approximately 15 solar radii is calculated. Magnetohydrodynamic simulations show that for dense ICMEs, C
D varies slowly between the Sun and 1 AU, and is of order unity. When the ICME and solar wind densities are similar, C
D is larger (between 3 and 10), but remains approximately constant with radial distance. For tenuous ICMEs, the ICME and solar
wind velocities equalise rapidly due to the very effective drag force. For ICMEs denser that the ambient solar wind, both
approaches show that γ is approximately independent of radius, while for tenuous ICMEs, γ falls off linearly with distance.
When the ICME density is similar to or less than that in the solar wind, inclusion of virtual mass effects is essential. 相似文献
9.
Constantino Tsallis 《Astrophysics and Space Science》2006,305(3):261-271
The cornerstones of Boltzmann-Gibbs and nonextensive statistical mechanics respectively are the entropies S
BG
≡ −k ∑
i = 1
W
p
i
ln p
i
and S
q
≡ k (1−∑
i = 1
W
p
i
q
)/(q−1) (q∊ℜ S
1 = S
BG
). Through them we revisit the concept of additivity, and illustrate the (not always clearly perceived) fact that (thermodynamical) extensivity has a well defined sense only if we specify the composition law that is being assumed for the subsystems (say A and B). If the composition law is not explicitly indicated, it is tacitly assumed that A and B are statistically independent. In this case, it immediately follows that S
BG
(A+B) = S
BG
(A)+S
BG
(B), hence extensive, whereas S
q
(A+B)/k = [S
q
(A)/k]+[S
q
(B)/k]+(1−q)[S
q
(A)/k][S
q
(B)/k], hence nonextensive for q ≠ 1. In the present paper we illustrate the remarkable changes that occur when A and B are specially correlated. Indeed, we show that, in such case, S
q
(A+B) = S
q
(A)+S
q
(B) for the appropriate value of q (hence extensive), whereas S
BG
(A+B) ≠ S
BG
(A)+S
BG
(B) (hence nonextensive). We believe that these facts substantially improve the understanding of the mathematical need and physical origin of nonextensive statistical mechanics, and its interpretation in terms of effective occupation of the W
a priori available microstates of the full phase space. In particular, we can appreciate the origin of the following important fact. In order to have entropic extensivity (i.e., lim
N→∞
S(N)/N < ∞, where N≡ numberof
elements
of
the
system), we must use (i) S
BG
, if the number W
eff of effectively occupied microstates increases with N like W
{{eff}}∼ W ∼ μ
N
(μ ≥ 1); (ii) S
q
with q = 1−1/ρ, if W
{{eff}}∼ N^ρ < W (ρ ≥ 0). We had previously conjectured the existence of these two markedly different classes. The contribution of the present paper is to illustrate, for the first time as far as we can tell, the derivation of these facts directly from the set of probabilities of the W microstates. 相似文献
10.
A large set of limb coronal mass ejections (CMEs) are used to determine the accurate relationship between radial (V
rad) and expansion (V
exp) speeds of CMEs. It is demonstrated that this relation is exceptionally well described by the function f(w)=1/2(1+cot w), representing a full cone model for the CME with a half-width, w. We also demonstrate that for extremely fast CMEs (V
exp>3000 km s−1), it is better to use the approximation V
rad≈V
LE. This implies that such CMEs expand spherically above the solar surface. 相似文献
11.
We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as
massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates
were selected from the Massey et al. catalog based on the following criteria: emission in H
α
, V<18./m 5 and 0.m 35 < (B - V) < 1.m 2. The spectra of both stars reveal a broad and strong H
α
emission with extended wings (770 and 1000 kms−1). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L⊙) = 6.0–6.2 with the value of interstellar extinction A
V
= 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero
Age Main Sequence is M∼ 60–80 M⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts
to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable
variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L⊙) = 6.3 − 6.6, the value of interstellar extinction is A
V
= 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two
thermal components with the temperatures Twarm ∼ 1000K and Tcold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines
indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and
broad H
α emissions allow classifying the studied objects as LBV candidates. 相似文献
12.
A quiescent filament was observed near the center of the disk (N5, W5) with the MSDP spectrograph of the 50 cm refractor of
the Pic-du-Midi Observatory on June 17, 1986. We focus our study on the statistical moments of the Dopplershift,V
1, and the intensity,I
1, at the center of a chord of the Hα profile (±0.256 Å), versus the minimum intensityI
0. We use a statistical model simulating a numbern
max of threads (of optical thicknessτ
0 and source functionS
0), seen over the chromosphere. The threadsj along the same line-of-sighti are identical except for the velocityv
j (gaussian distributionv
0,σ
v). We search for the best fit between the observed and simulated quantities:V
1,σ (V
1),I
1,σ(I
1), and the histogram of theI
0 values over the field of view. A good fit is obtained with: (a) threads characterized byτ
0 = 0.2,S
0 = 0.06 (unit of the continuum at disk center), mean upward velocityv
0 = 1.7 km s−1 and gaussian-type velocity distributionσ
v = 3.5 km s−1. Other possible values ofτ
0 andσ
v are discussed; (b) underlying chromosphere deduced from observed quiet Sun (outside the filament) by modifying the chromospheric
velocities: additional mean upward velocity 0.7 km s−1, standard deviation reduced by a factorF
c ∼ 0.7. The results are discussed in connection with the values deduced from prominence observations. 相似文献
13.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2012,337(1):367-372
Combining the kinematical definitions of the two dimensionless parameters, the deceleration q(x) and the Hubble t
0
H(x), we get a differential equation (where x=t/t
0 is the age of the universe relative to its present value t
0). First integration gives the function H(x). The present values of the Hubble parameter H(1) [approximately t
0
H(1)≈1], and the deceleration parameter [approximately q(1)≈−0.5], determine the function H(x). A second integration gives the cosmological scale factor a(x). Differentiation of a(x) gives the speed of expansion of the universe. The evolution of the universe that results from our approach is: an initial
extremely fast exponential expansion (inflation), followed by an almost linear expansion (first decelerated, and later accelerated).
For the future, at approximately t≈3t
0 there is a final exponential expansion, a second inflation that produces a disaggregation of the universe to infinity. We
find the necessary and sufficient conditions for this disaggregation to occur. The precise value of the final age is given
only with one parameter: the present value of the deceleration parameter [q(1)≈−0.5]. This emerging picture of the history of the universe represents an important challenge, an opportunity for the
immediate research on the Universe. These conclusions have been elaborated without the use of any particular cosmological
model of the universe. 相似文献
14.
S. Bilir T. Güver I. Khamitov T. Ak S. Ak K. B. Coşkunoğlu E. Paunzen E. Yaz 《Astrophysics and Space Science》2010,326(1):139-150
We present CCD BV and JHK
s
2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting
magnitude of V∼19 mag. The star-count method showed that the centre of the cluster lies at α
2000=04
h
09
m
36
s
, δ
2000=49°28′43″ and its angular size is r=10 arcmin. The optical and near-infrared two-colour diagrams revealed the colour excesses in the direction of the cluster
as E(B−V)=0.68±0.06, E(J−H)=0.21±0.02 and E(J−K
s
)=0.33±0.04 mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age
Main-Sequences (ZAMS) provided an average distance modulus of (m−M)0=10.80±0.13 mag, which can be translated into a distance of 1440±80 pc. Finally, using Padova isochrones we determined the
metallicity and age of the cluster as Z=0.015±0.004 ([M/H]=−0.10±0.10 dex) and log (t/yr)=8.40±0.04, respectively. 相似文献
15.
V. P. Arkhipova V. F. Esipov N. P. Ikonnikova G. V. Komissarova A. M. Tatarnikov B. F. Yudin 《Astronomy Letters》2009,35(11):764-779
We present new results of our UBV photometry for HD 179821=V1427 Aql, an F supergiant with an infrared excess, from 2000 to 2008. The semiregular low-amplitude
(ΔV = 0.
m
05−0.
m
20) photometric variability of the star with a cycle period from 130 to 200 days is caused by pulsations, along with the instability
of a variable stellar wind. V1427 Aql also exhibits a long-term trend in the brightness and colors that is probably attributable
to a change in the stellar temperature as a result of mass loss episodes, which cause variations in the continuum formation
level. We present the results of our JHKLM photometry for V1427 Aql in 1992–2008. We trace the trend in the near-infrared brightness, which agrees with the long-term
variability in the V band. Based on broadband photometry, we have determined the color excess for V1427 Aql: E(B−V) = 0.7. Based on low-resolution spectroscopy, we have estimated the stellar temperature and revealed variability of the Hα line caused by a change in the contribution from the emission component. The hypotheses of whether the star belongs to post-AGB
objects or to massive yellow hypergiants are discussed. 相似文献
16.
It is shown (1) that the coefficients Ai of the limb darkening functions I(μ)/Icenter = P5 (μ) = ∑Ai μi (i = 0... 5; μ = cos ϑ), which had been published by Neckel and Labs (Solar Phys. 153, 91, 1994), can well be approximated by analytical functions of wavelength λ, and (2) that at first sight purely formal extrapolation
of the functions P5(μ) to the very limb (μ = 0.0) is not meaningless: in combination with absolute intensities for the disk center these functions
yield ‘limb intensities’ which all correspond to almost the same ‘limb temperature’, Tlimb≈4746 K. Together these results lead to ‘reference functions’ which can quickly yield rather reliable values of the Sun's
continuum intensities, for any values of μ and λ. 相似文献
17.
We investigate the relative motion of three stars, ADS 7446, 9346, and 9701, based on long-term observations with the Pulkovo
26-inch refractor. The relative motion of all three stars shows a perturbation that could be produced by the gravitational
influence of an invisible companion. For ADS 7446, we have determined the orbit of the photocenter with a period of 7.9 yr;
the mass of the companion is more than 0.4M
⊙. For ADS 9346, we have determined the radial velocities of the components: −14.60 km s−1 for A and −13.94 km s−1 for B. For ADS 9346 and 9701, we have determined the dynamical parallaxes, 24 and 20 mas, respectively, which are larger
than those in the Hipparcos catalog by 5 mas, and calculated the orbits by the apparent motion parameter (AMP) method. The
new orbit of ADS 9346 is: a = 5″.2, P = 2035 yr, and e = 0.46 at the system’s mass M = 2.5M
⊙. The new orbits of ADS 9701 are: (a = 2″.9, P = 829 yr, e = 0.54, M = 4.3M
⊙) and (a = 3″.8, P = 1157 yr, e = 0.53, M = 5.0M
⊙). 相似文献
18.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,327(1):111-115
We investigate five-dimensional Brans–Dicke cosmology with spacetime described by the homogeneous, anisotropic and flat spacetime
with the topology M
1×R
3×S
1 where S
1 is taken in the form of a circle. We conjecture throughout this letter that the extra-dimension compactifies as the visible
dimensions expand like b(t)≈a
−1(t) and that the non-minimal coupling between the scalar field and the matter is of the form f(φ)∝
φ
2. The model gives rise to a transition from a decelerated epoch to an accelerated epoch for large values of the Brans–Dicke
parameter ω. The model predicts crossing of the phantom divided barrier unless the universe is governed by a growing matter field. 相似文献
19.
Bianchi Type I string dust cosmological models in presence and absence of magnetic field following the techniques used by
Letelier and Stachel, are investigated. To get the deterministic solution, we have assumed that σ
11 is proportional to the expansion (θ) where σ
11 is the eigen value of shear tensor (σ
i
j
) and which leads to A=N(BC)−n
, n>0 where A,B,C are metric potentials and
, N and ℓ are constants. The behaviour of the models in presence and absence of magnetic field are discussed. The other physical and
geometrical aspects of the model are also discussed. 相似文献
20.
Recent observations with EUV imaging instruments such as SOHO/EIT and TRACE have shown evidence for flare-like processes at
the bottom end of the energy scale, in the range of E
th≈1024–1027 erg. Here we compare these EUV nanoflares with soft X-ray microflares and hard X-ray flares across the entire energy range.
From the observations we establish empirical scaling laws for the flare loop length, L(T)∼T, the electron density, n
e(T)∼T
2, from which we derive scaling laws for the loop pressure, p(T)∼T
3, and the thermal energy, E
th∼T
6. Extrapolating these scaling laws into the picoflare regime we find that the pressure conditions in the chromosphere constrain a height level for flare loop footpoints, which scales
with h
eq(T)∼T
−0.5. Based on this chromospheric pressure limit we predict a lower cutoff of flare loop sizes at L
∖min≲5 Mm and flare energies E
∖min≲1024 erg. We show evidence for such a rollover in the flare energy size distribution from recent TRACE EUV data. Based on this
energy cutoff imposed by the chromospheric boundary condition we find that the energy content of the heated plasma observed
in EUV, SXR, and HXR flares is insufficient (by 2–3 orders of magnitude) to account for coronal heating. 相似文献