共查询到20条相似文献，搜索用时 46 毫秒
1.
A. G. Yeghikyan 《Astrophysics》2011,54(1):87-99
The fluxes of cosmic rays inside typical molecular clouds are calculated. Protons and a-particles with energies of 1 MeVd
≤ ? ≤ 10 GeV penetrate deeply enough to produce irradiation doses in the ice mantle of dust particles on the order of 0.1-1
eV/amu over the 10–50 million year lifetime of clouds with and without star formation regions. The possible use of these results
for interpreting laboratory experiments on the irradiation of ice mixtures of the type H2O:CH3OH:NH3:CO is discussed. Complex organic radiolysis products may play an important role in the prebiological evolution of the dust
component of molecular clouds. 相似文献
2.
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
3.
We investigate numerically the chemodynamical evolution of major disc–disc galaxy mergers in order to explore the origin of
the mass-dependent chemical, photometric and spectroscopic properties observed in elliptical galaxies. We investigate especially
the dependence of the fundamental properties on merger progenitor disc mass (M
d). Three main results are obtained in this study:– More massive (luminous) ellipticals formed by galaxy mergers between more
massive spirals have higher metallicity (Z) and thus show redder colours; the typical metallicity ranges from ∼ 1.0 solar abundance (Z∼ 0.02) for ellipticals formed by mergers with M
d = 1010
M
⊙to ∼ 2.0 solar (Z∼ 0.04) for those with M
d= 1012
M
⊙.– Both the Mg2 line index in the central part of ellipticals (R ≤ 0.1 R
e) and the radial gradient of Mg2 (δ Mg2 / δ log R) are more likely to be larger for massive ellipticals. δ Mg2 / δ log R correlates reasonably well with the central Mg2 in ellipticals. For most of the present merger models, ellipticals show a positive radial gradient of the Hβ line index. – Both M/L
B and M/L
K (where M, L
B, and L
K are the total stellar mass of galaxy mergers, the B-band and the K-band luminosities, respectively) depend on galactic mass in such a way that more massive ellipticals have larger M/L
B and smaller M/L
K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
We present the theoretical analysis of the Al I line formation in the spectra of late-type stars ignoring the assumption of
local thermodynamic equilibrium (LTE). The calculations were based on the 39-level aluminum atom model for one-dimensional
hydrostatic stellar atmosphere models with the parameters: T
eff from 4000 to 9000 K, log g = 0.0–4.5, and metallicity [A] = 0.0;–1.0;–2.0;–3.0;–4.0. The aluminum atom model and the method of calculations were tested by the study of line profiles
in the solar spectrum. We refined the oscillator strengths and Van-der-Vaals broadening constants C
6 of the investigated transitions. We conclude that the Al I atom is in the overionization state: the 3p level is underpopulated in the line formation region. This leads to the line weakening, as compared with the LTE results.
The overionization effect becomes more pronounced with increasing temperature and decreasing metallicity. We show that the
use of various atomic data (ionization cross-sections) for the low levels of Al I does not change the behavior of non-LTE
deviations, whereas the value of these deviations varies essentially. For nine selected Al I lines we calculated the grids
of theoretical non-LTE corrections (ΔX
NLTE = logɛ
NLTE − log ɛ
LTE) to the Al abundances determinedwith the LTE assumption. The non-LTE corrections are positive and significant for the stars
with temperatures T
eff > 6000 K. These corrections weakly depend on log g, and increase with declining stellar metallicity. 相似文献
5.
Ramon J. Quiroga 《Astrophysics and Space Science》1983,93(1):37-54
Statistics in absorption 21-cm data show two main types of clouds at low galactic latitudes: dense small clouds, many of them
with molecular cores, with dispersions σ≈1.5 km s−1 and large clouds forming the fine features of the spiral arms (the shingle like features) with a dispersion range α≈3–4 km
s−1. Sizes and dispersions of both types of clouds are compatible with the Kolmogorov law of turbulence: σ∞d
1/3. The large clouds forming the shingle-like features can be considered as the largest clouds of a Kolmogorov spectrum (the
initial vortices), or as the hydrodynamic features with minimum sizes in the Galaxy. In order to define hydrodynamic motions
in the same sense as given by Ogrodnikov (1965) we use here the tensorial form of the Helmholtz theorem to obtain an approximation
for the hydrodynamic motions depending on distances and seen from the local standard of rest:V
r
∞r. The intermediate range of sizes between turbulent motions and hydrodynamic motions is 100<d<300 pc which is also the range of sizes of the large clouds forming the fine features of the spiral arms.
A classification on of motions in the Galaxy is postulated: (a) a basic rotation motion given by an smooth unperturbed curveΘ
b
(R) associated to the old disk population. (b) Systematic motions of the spiral arms. (c) Systematic motions in the fine structure
of the arms. For scale sizes smaller than these fine features one has turbulent motions according to the Kolmogorov law.
The densities and sizes of the turbulent clouds behave asn
H
∝d
−2 in a range of sizes 7 pc<d<300 pc. The obtained gas densities of the clouds are confirmed with the dust densities from photometric studies. The conditions
for gravitational binding of the clouds are analyzed. Factors as the geometry and the magnetic field within the clouds increases
the critic densities for gravitational binding. When we consider these factors we find that the wide component clouds have
densities below such a critical value.
The narrow component clouds have densities similar or above the critical value; but the real fraction of collapsing clouds
remains unknown as far as the factor of geometry and the inner magnetic field of each cloud are not determinated. 相似文献
6.
Zhe Chen Jiang Zhang YanPing Chen WenYuan Cui Bo Zhang 《Astrophysics and Space Science》2006,306(1-2):33-39
The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metal-poor stars on the left-side [{Ba/Mg}]--[{Mg/H}] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass M
ms ≤ 18 M
⊙ are infertile sources and the SNe II with 20 M
⊙ ≤ M
ms ≤ 40 M
⊙ are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20 M
⊙ ≤ M
ms ≤ 40 M
⊙
with compared to the all massive stars is about∼ 18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced. 相似文献
7.
Using a sample of 57 VLT FORS spectra in the redshift range 1.37< z < 3.40 and a comparison sample with 36 IUE spectra of local (
) starburst galaxies we derive CIV equivalent width values and estimate metallicities of starburst galaxies as a function
of redshift. Assuming that a calibration of the CIV equivalent widths in terms of the metallicity based on the local sample
of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about 0.16 Z
⊙ at the cosmic epoch corresponding to z ≈ 3.2 to about 0.42 Z
⊙ at z ≈ 2.3. A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the
local starburst galaxies our high-redshift objects tend to be overluminous for a given metallicity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
The solar wind quasi-invariant (QI) has been defined by Osherovich, Fainberg, and Stone (Geophys. Res. Lett.
26, 2597, 1999) as the ratio of magnetic energy density and the energy density of the solar wind flow. In the regular solar wind QI is a
rather small number, since the energy of the flow is almost two orders of magnitude greater than the magnetic energy. However,
in magnetic clouds, QI is the order of unity (less than 1) and thus magnetic clouds can be viewed as a great anomaly in comparison
with its value in the background solar wind. We study the duration, extent, and amplitude of this anomaly for two groups of
isolated magnetic clouds: slow clouds (360<v<450 km s−1) and fast clouds (450≤v<720 km s−1). By applying the technique of superposition of epochs to 12 slow and 12 fast clouds from the catalog of Richardson and Cane
(Solar Phys. 264, 189, 2010), we create an average slow cloud and an average fast cloud observed at 1 AU. From our analysis of these average clouds,
we obtain cloud boundaries in both time and space as well as differences in QI amplitude and other parameters characterizing
the solar wind state. Interplanetary magnetic clouds are known to cause major magnetic storms at the Earth, especially those
clouds which travel from the sun to the Earth at high speeds. Characterizing each magnetic cloud by its QI value and extent
may help in understanding the role of those disturbances in producing geomagnetic activity. 相似文献
9.
In this paper we have studied in detail (numerically) the trajectories of charged particles in a magnetic field (dipolar at
infinity) associated with a static star in the framework of Rosen's bimetric theory of gravity. It was found that there do
exist potential wells that allow possible trapping of particles in stable orbits both on and off the equatorial plane. A particularly
interesting feature that has shown up is the fact that the characteristics of the effective potential wellV
eff depend on the ratio of the magnetic field strength parameter λ, and the angular momentumL of the charged particle. For values lower than a critical (λ/L)
c
the potential well lies within the regionr≤2m. 相似文献
10.
A 21 cm absorption measurement over a long path length free of the effects of differential galactic rotation indicates the
existence of two distinct cloud populations in the plane. One of them consisting of cold, dense clouds has been well studied
before. The newly found hot clouds appear to be at least five times more numerous. They have a spin temperature of ~ 300 K,
an rms velocity of ~ 35 km s-1, twice the total mass, and hundred times the kinetic energy of the cold clouds. Over long path lengths, the hot clouds haveN
H/kpc ~ 2 X 1021 cm-2 Kpc-1, and are estimated to have individual column densities ≤ 1020 cm-2. We propose that they are shocked clouds found only within supernova bubbles and that the cold clouds are found in the regions
in-between old remnants, immersed in an intercloud medium. We conclude that the solar neighbourhood must be located between
old supernova remnants rather than within one. 相似文献
11.
We test for age and metallicity gradients in the Galactic Bulgebetween the two low extinction windows Baade's window (l = 1° .1b=−4° .8) and Sagittarius-I (l=1° .3 b=−2° .7). We derive ametallicity difference of ≤ 0.2 dex between BW andSGR-I window. This corresponds to a metallicity gradient
of 1.3 dexkpc-1. This steep gradient is reconcilable with the existence of ashort scale length inner component to the Bulge, most likely
thatprominent in the NIR, which perhaps forms a separate entitysuperimposed on the larger, optical Bulge. Through number counts
incolour-magnitude diagram around the turnoff for several fields andclusters, extending over a range in galactic longitude
we find no evidencefor a significant young stellar population in the GalacticBulge. Previous suggestions of the existence
of a significant youngstellar population have most likely incorrectly identified theforeground disk stars.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
We have detected new HD absorption systems at high redshifts, z
abs = 2.626 and z
abs = 1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170, respectively. Each of these systems consists
of two subsystems. The HD column densities have been determined: log N
HDA = 15.70 ± 0.07 for z
A = 2.626443(2) and log N
HDB = 12.98 ± 0.22 for z
B = 2.626276(2) in the spectrum of J0812+3208 and log N
HDC = 14.83 ± 0.15 for z
C = 1.77637(2) and log N
HDD = 14.61 ± 0.20 for z
D = 1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for three of these subsystems has been found to be considerably higher than its values typical of clouds in our Galaxy.We
discuss the problem of determining the primordial deuterium abundance, which is most sensitive to the baryon density of the
Universe Ωb. Using a well-known model for the chemistry of a molecular cloud, we have estimated the isotopic ratio D/H=HD/2H2 = (2.97 ± 0.55) × 10−5 and the corresponding baryon density Ωb
h
2 = 0.0205−0.0020+0.0025. This value is in good agreement with Ωb
h
2 = 0.0226−0.00060.0006 obtained by analyzing the cosmic microwave background radiation anisotropy. However, in high-redshift clouds, under conditions
of low metallicity and low dust content, hydrogen may be incompletely molecularized even in the case of self-shielding. In
this situation, the HD/2H2 ratio may not correspond to the actual D/H isotopic ratio. We have estimated the cloud molecularization dynamics and the
influence of cosmological evolutionary effects on it. 相似文献
13.
We review selected measurements of the galaxy luminosity function including the field, the local group, the local sphere,
nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that, excluding the super-luminous cD and D
galaxies, the overall cluster luminosity function is fully consistent with the field luminosity function over the magnitude
range in common (–22 ≤ M
B
–5log
h
0.68
≤ –17). We find that only in the core regions of clusters (r ≤ 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function
is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall,
efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
A global iteration method to determine the self-consistent structure of steady plane-parallel radiative shock waves is shown
to converge to the stable solution with upstream front velocities of 15 km/s ≤ U
1≤ 60 km/s and for hydrogen gas of unperturbed temperature T= 3000 K and density ρ = 10−10gcm−3.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
I. Sabbah 《Solar physics》2007,245(1):207-217
Neutron monitor data observed at Climax (CL) and Huancayo/Haleakala (HU/HAL) have been used to calculate the amplitude A of the 27-day variation of galactic cosmic rays (CRs). The median primary rigidity of response, R
m, for these detectors encompasses the range 18 ≤R
m≤46 GV and the threshold rigidity R
0 covers the range 2.97≤R
0≤12.9 GV. The daily average values of CR counts have been harmonically analyzed for each Bartels solar rotation (SR) during
the period 1953 – 2001. The amplitude of the 27-day CR variation is cross-correlated to solar activity as measured by the
sunspot number R, the interplanetary magnetic field (IMF) strength B, the z-component B
z
of the IMF vector, and the tilt angle ψ of the heliospheric current sheet (HCS). It is anticorrelated to the solar coronal
hole area (CHA) index as well as to the solar wind speed V. The wind speed V leads the amplitude by 24 SRs. The amplitude of the 27-day CR variation is better correlated to each of the these parameters
during positive solar polarity (A>0) than during negative solar polarity (A<0) periods. The CR modulation differs during A>0 from that during A<0 owing to the contribution of the z-component of the IMF. It differs during A
1>0 (1971 – 1980) from that during A
2>0 (1992 – 2001) owing to solar wind speed. 相似文献
16.
We have mapped 16 molecular clouds toward a new OB association in the Pup-CMa region to derive their physical properties.
The observations were carried out in the 12CO (J = 1 – 0) line with the Southern millimetre-wave Telescope at Cerro Tololo, Chile. Distances have been determined kinematically
using the rotation curve of Brand with R⊙ = 8.5 kpc and V⊙ = 220 km/s. Masses have been derived adopting a CO luminosity to H2 conversion factor X = 3.8 . 1020 molecules cm-2 (K km/s)-1. The observed mean radial velocity of the clouds is comparable with the mean radial velocity of stars composing an OB association
in Pup-CMa; it is in favor of the close connection of clouds with these stars.
__________
Published in Astrofizika, Vol. 48, No. 4, pp. 491–501 (October–December, 2005). 相似文献
17.
Rosaria Tantalo 《Astrophysics and Space Science》2001,276(2-4):1189-1199
In this paper we present a recent attempt to infer the age, metallicity and abundance ratios for a selected sample of elliptical
galaxies, adopting the line-strength indices Hβ, Mg2 and 〈Fe 〉, which respond in different ways to different parameters such as age (Hβ), metallicity and abundance ratios (〈Fe〉 and Mg2).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Photoelectric Vilnius seven-color photometry is presented and analyzed for a sample of 24 red giant branch and clump stars
in the open cluster NGC 7789. For each star we have determined photometric spectral type, absolute magnitude, interstellar
reddening, effective temperature, metallicity, and surface gravity. From averages over the stars in the sample we find the
mean reddening to the cluster E
Y−V
= 0.21± 0.02 (s.d.), or E
B−V
= 0.25, and the apparent distance modulus (m−M)
V
= 12.21± 0.10 (s.d.), which yield a distance of 1840 pc. The mean overall metallicity is found to be [Fe/H] = −0.18± 0.09
(s.d.). The clump stars, on average, appear to be slightly more metal-rich than the other red giants, which is most probably
caused by evolutionary changes of carbon and nitrogen molecular bands falling in the photometric passbands. A difference in
mass between the two groups of stars has also been detected, which suggests that the clump stars might have undergone extra
mass loss before reaching their core He-burning phase of evolution. 相似文献
19.
R. Surendiranath N. Kameswara Rao Ram Sagar J. S. Nathan K. K. Ghosh 《Journal of Astrophysics and Astronomy》1990,11(2):151-166
bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M)
0 = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1)
× 108 years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor
mass of the planetary nebula on the main sequence is ≥2.5M⊙
Based on observations obtained with the Vainu Bappu Telescope. 相似文献
20.
A comprehensive case and statistical study of CME onsets has been conducted on the solar limb using the CDS, LASCO and EIT
instruments aboard the SOHO spacecraft. This is the first dedicated campaign to establish firmly the EUV signatures of CME
onsets and is based on a series of low-corona observing campaigns made in 2002. The event database consisted of 36 multiple
emission line sequences observed with CDS and the study builds, in particular, on studies of EUV coronal dimming which have
been associated with CME onsets. We witness a range of dimming events in EUV coronal emission line data. Shorter events, commonly
of duration < 4 hours, we find are indirectly associated with CME onsets whereas longer-duration dimmings (> 4 hours) appear
to be either due to coronal evolution or rotational effects. However, for some CME onsets, where the CDS pointing was appropriate,
no dimming was observed. Dimming observed in EIT typically occurred immediately after the launch of a loop or prominence,
and in 5 out of 9 events there is evidence of a matter buildup within the loop before launch. A total of 10 events occurred
where CDS was used to directly observe the CME footprint, but no relationship between these events was found. The results
suggest that the response of the corona to a CME launch differs between the low (1.0 R
⊙≤R≤1.2 R
⊙) and middle (1.2 R
⊙<R≤2.0 R
⊙) corona regions, hence implying a difference between dimming observations conducted with different instruments. 相似文献