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1.
During the formation of heavy elements in the neutron star merger (NSM) scenario with a fairly long duration of the r-process, most of the seed nuclei rapidly burn out at the initial stage. The nucleosynthesis wave rapidly reaches the region
of actinoids, where beta-delayed, neutron-induced, and spontaneous fission are the main reaction channels. The fission products
of transuranium elements are again drawn into the r-process as new seed nuclei to form the yields of elements with mass numbers A > 100. The contribution from the various types of fission to the formation of heavy and superheavy nuclei is investigated.
The proposed r-process model applied to the NSM scenario describes well the observed abundances of chemical elements, which confirms the
formation of the main r-process component in the NSM scenario. Simple extrapolations of the spontaneous fission half-lives are shown to be inapplicable
for the region of nuclei with N ∼ 184, because the formulas do not reflect the increase in half-life when the shell structure changes as the number of neutrons
approaches 184. The formation of superheavy elements in the r-process is possible, but their survival depends to a large extent on how reliable the predictions of nuclear parameters,
including the half-lives of the forming nuclei from the island of long-lived isotopes, are. The contributions from various
types of fission—neutron-induced, beta-delayed, and spontaneous one—to the formation of heavy elements in the main r-process have been determined. 相似文献
2.
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more
than 60 000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of stars in the range 4500≲T
eff≲9000 K. Our preliminary results indicate that the majority of the sample is formed by main sequence F- and G-type stars,
with metallicity [M/H]≳−1 dex. 相似文献
3.
Possibilities for the development of an r-process in the helium shell of a supernova under the action of free neutrons appearing as a result of inelastic neutrino scattering by 4He nuclei are investigated. The conditions in the outer part of the helium shell in metal-poor stars are shown to be favorable for the reproduction of a weak r-process component. 相似文献
4.
A. N. Gerashchenko 《Astronomy Letters》2009,35(9):625-632
We describe a method for simultaneous determination of the metallicity and interstellar reddening of globular clusters that
uses parameters of the giant branch on the V vs. (B-R) color-magnitude diagram: the slope of the giant branch, its color at the level of the horizontal branch, and the apparent
magnitude V of the horizontal branch. Applying this method to the globular cluster NGC 7006 gives the metallicity [Fe/H] = −1.78 ± 0.11
and interstellar reddening E
B-R
= 0.25 ± 0.02. 相似文献
5.
Neeraj Pant 《Astrophysics and Space Science》2011,334(2):267-271
The paper presents a class of interior solutions of Einstein-Maxwell field equations of general relativity for a static, spherically
symmetric distribution of the charged fluid. This class of solutions describes well behaved charged fluid balls. The class
of solutions gives us wide range of parameter K (0.3277≤K≤0.49), for which the solution is well behaved hence, suitable for modeling of super dense star. For this solution the mass
of a star is maximized with all degree of suitability and by assuming the surface density ρ
b
=2×1014 g/cm3. Corresponding to K=0.3277 with X=−0.15, the maximum mass of the star comes out to be M=0.92M
Θ with radius r
b
≈17.15 km and the surface red shift Z
b
≈0.087187. It has been observed that under well behaved conditions this class of solutions gives us the mass of super dense
object within the range of white-dwarf. 相似文献
6.
David A. Juckett 《Solar physics》2010,262(1):3-17
Wolff (Astrophys. J.
193, 721, 1974) introduced the concept of g-mode coupling within the solar interior. Subsequently, Wolff developed a more quantitative model invoking a reciprocal interaction
between coupled g modes and burning in the solar core. Coupling is proposed to occur for constant values of the spherical harmonic degree [ℓ] creating rigidly rotating structures denoted as sets(ℓ). Power would be concentrated near the core and the top of radiative zone [RZ] in narrow intervals of longitude on opposite
sides of the Sun. Sets(ℓ) would migrate retrograde in the RZ as function of ℓ and their intersections would deposit extra energy at the top of the RZ. It is proposed that this enhances sunspot eruptions
at particular longitudes and at regular time intervals. Juckett and Wolff (Solar Phys.
252, 247, 2008) detected this enhancement by viewing selected spherical harmonics of sunspot patterns within stackplots twisted into the
relative rotational frames of various sets(ℓ). In subsequent work, the timings of the set(ℓ) intersections were compared to the sub-decadal variability of the sunspot cycle. Seventeen sub-decadal intersection frequencies
(0.63 – 7.0 year) were synchronous with 17 frequencies in the sunspot time-series with a mean correlation of 0.96. Six additional
non-11-year frequencies (periods of 8.0 to 28.7 year) are now shown to be nearly synchronous between sunspot variability and
the model. Two additional intersections have the same frequency as the solar cycle itself and peak during the rising phase
of the solar cycle. This may be partly responsible for cycle asymmetry. These results are evidence that some of the solar-cycle
variability may be attributable to deterministic components that are intermixed with a broad-spectrum stochastic and long-term
chaotic background. 相似文献
7.
V. I. Burnashev B. A. Burnasheva 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):63-67
From the results of long-term observations, data on the energy distribution in the spectra of 116 variable stars of different
types have been obtained. From the published response curves of the UBV system, the magnitudes and color indexes were calculated. The mean accuracy of the calculated values is σ
v
≃ 0.
m
04, σ
bv
≃ 0.
m
03, and σ
ub
≃ 0.
m
06. 相似文献
8.
I. V. Panov 《Astronomy Letters》2003,29(3):163-169
The concept of the r-process path is considered from the standpoint of a dynamic model. Rapid nucleosynthesis is shown to proceed not along certain preferential lines called the r-process paths but in the region of nuclei bounded on the one side by the existing nuclei and on the other side by nuclei upon reaching which the r-process enters a cooling phase. This view is shown to account for the main heavy-element abundance patterns. 相似文献
9.
M. R. Setare 《Astrophysics and Space Science》2010,326(1):27-31
In this paper, we study a cosmological application of the new agegraphic dark energy density in the f(R) gravity framework. We employ the new agegraphic model of dark energy to obtain the equation of state for the new agegraphic
energy density in a spatially flat universe. Our calculations show, taking n<0, that it is possible to have w
Λ crossing −1. This implies that one can generate a phantom-like equation of state from a new agegraphic dark energy model
in a flat universe in the modified gravity cosmology framework. Also, we develop a reconstruction scheme for the modified
gravity with f(R) action. 相似文献
10.
HE1005-1439是一颗金属丰度极低([Fe/H] ~ - 3.0)的碳增丰贫金属星(Carbon Enhanced Metal-Poor,CEMP), 该星的s-过程元素显著超丰([Ba/Fe] = 1.16±0.31, [Pb/Fe] = 1.98±0.19), 而r-过程元素温和超丰([Eu/Fe] = 0.46±0.22), 使用单一的s-过程模型和i-过程模型均不能拟合该星中子俘获丰度分布. 采用丰度分解的方法探究该星化学元素的天体物理来源可有助于理解CEMP星的形成和化学演化. 利用s-过程和r-过程的混合模型对其中子俘获元素的丰度分布进行拟合, 发现该星的中子俘获元素主要来源于低质量低金属丰度AGB伴星的s-过程核合成, 而r-过程核合成也有贡献. 相似文献
11.
We show that for the discussed scenario of a neutron-star merger in highly neutronized ejecta (Y e ?0.1), neutron-induced fission plays a major role in the r-process cycling and is the main obstacle to the formation of superheavy elements. At the final stage of the r-process, when the free-neutron density is already too low to maintain rapid nucleosynthesis and only beta-decay and beta-delayed fission take place, the leading role in forming the final abundances of chemical elements passes to delayed fission. The latter ultimately changes the abundances of individual isotopes in the region before the second peak and heavier than lead, which, in particular, affects the determination of the age of the Galaxy. 相似文献
12.
The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] μm bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: M Z = ?0.20 ± 0.04, M Y = ?0.470 ± 0.045, M[3.6] = ?1.70 ± 0.03, M[4.5] = ?1.60 ± 0.03, M[5.8] = ?1.67 ± 0.03, and M[8.0] = ?1.70 ± 0.03. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [M/H] ? 0.40 (Z ? 0.038) with an error of [M/H] ? 0.1 dex, while the effective temperature is 4250± 150 K. Stars with an age of 9–10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of ~8 Gyr can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200–8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one. 相似文献
13.
Rogemar A. Riffel 《Astrophysics and Space Science》2010,327(2):239-244
I briefly describe a simple routine for emission-line profile fitting by Gaussian curves or Gauss–Hermite series. The profit (line-profile fitting) routine represent a new alternative for use in fits data cubes, as the ones from Integral Field Spectroscopy or Fabry–Pérot
Interferometry, and may be useful to better study the emission-line flux distributions and gas kinematics in distinct astrophysical
objects, such as the central regions of galaxies and star forming regions. The profit routine is written in IDL language and is available at . 相似文献
14.
P.E. Nissen 《Astrophysics and Space Science》1999,265(1-4):249-256
Recent determinations of precise abundance ratios for nearby halo and thick disk stars in the metallicity range −1.3 < [Fe/H]
< −0.5 have revealed a significant cosmic spread in the abundances of oxygen, magnesium, sodium, nickel, s-process and r-process elements relative to iron. Possible explanations of these variations are reviewed. In particular, it is discussed
if the differences in abundance ratios are correlated with the kinematics of the stars, and hence can be used to identify
stellar populations in the Galaxy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
The Franck-Condon factors and r-centroids, which are very closely related to vibrational transition probabilities, have been evaluated by the more reliable
numerical integration procedure for the bands of B
2∑+ − X
2∑+, F
2∑+ − X
2∑+ systems of SrF and C
1∑+ − X
1∑+, G
1Π − X
1∑+ systems of ScF molecules of astrophysical interest, using a suitable potential. 相似文献
16.
R. Rampazzo F. Annibali A. Marino L. Bianchi A. Bressan L. M. Buson M. Clemens P. Panuzzo W. W. Zeilinger 《Astrophysics and Space Science》2011,335(1):201-206
We detected recent star formation in nearby early-type galaxies located in low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of star formation may be present in the nucleus and in outer rings/arm like structures.
Our study suggests that such star formation may be induced by different triggering mechanisms, such as the inner secular evolution
driven by bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV) color vs. Mg2 correlation, and suggest that it relates to “downsizing” in galaxy formation. 相似文献
17.
Bogdan Valcu Peter L. Smith Larry D. Gardner John C. Raymond Mari-Paz Miralles John L. Kohl 《Solar physics》2007,243(1):93-104
We have tracked the spectral responsivity of the ultraviolet channels of the UVCS (Ultraviolet Coronagraph Spectrometer) instrument
on SOHO by repeated observations of a stable hot star. We demonstrate first that the ultraviolet spectral irradiance of the
Be star ζ Tau (HD 37202) for the 100- to 125-nm wavelength range has been sufficiently constant for our purposes when measured periodically
over the course of the SOHO mission. We then use ζ Tau as a radiometric transfer standard to determine an average decrease beginning in November of 1998 of 13.0% per year in
the responsivity of the UVCS O vi channel for wavelengths near H i Ly α and for a particular UVCS unvignetted aperture used for science observations. The calibration tracking method involves
separating two ζ Tau spectral regions that are overlapped on part of the detector. The change in the responsivity of UVCS/SOHO began in late
1998 as determined by comparison of simultaneous observations of the corona carried out with UVCS/SOHO and the freshly-calibrated
UVCS instrument on the Spartan 201 satellite in early November of 1998.
B. Valcu now at BrainLAB, Inc, 3 Westbrook Corporate Ctr., Tower 3, Suite 400, Westchester, IL 60154, USA, e-mail: bogdan.valcu@brainlab.com
or Bogdan_valcu@hotmail.com 相似文献
18.
V. G. Klochkova V. E. Panchuk N. S. Tavolganskaya V. V. Kovtyukh 《Astronomy Letters》2003,29(11):748-762
High-resolution CCD spectra have been obtained for the first time for the W Virginis star V1 (K 307) in the globular cluster M12 and its closest neighbor K 307b (m pg=14m; the angular distance from the W Vir star is δ<1 arcsec). We determined the fundamental parameters (T eff=5600 K, logg=1.3, and T eff=4200 K, logg=1.0 for the W Vir star and the neighboring star, respectively) and their detailed chemical composition. The derived metallicities of the two stars ([Fe/H]=?1.27 and ?1.22 relative to the solar value) are in good agreement with the metallicities of other cluster members. Changed CNO abundances were found in the atmosphere of the W Vir star: a small carbon overabundance, [C/Fe]=+0.30 dex, and a large nitrogen overabundance, [N/Fe]=+1.15 dex, with oxygen being underabundant, [O/Fe]≈?0.2 dex. The C/O ratio is ≥1. Na and the α-process elements Mg, Al, Si, Ca, and Ti are variously enhanced with respect to iron. We found an enhanced abundance of s-process metals relative to iron: [X/Fe]=+0.34 for Y, Zr, and Ba. The overabundance of the heavier metals La, Ce, and Nd with respect to iron is larger: [X/Fe]=+0.49. The largest overabundance was found for the r-process element europium, [Eu/Fe]=+0.82. The spectrum of the W Vir star exhibits the Hα and Hβ absorption-emission profiles and the He I λ5876 Å emission line, which are traditionally interpreted as a result of shock passage in the atmosphere. However, the radial velocities determined from absorption and emission features are in conflict with the formation pattern of a strong shock. The high luminosity log L/L ⊙ = 2.98, the chemica peculiarities, and the spectral peculiarity are consistent with the post-AGB evolution in the instability strip. The pattern of relative elemental abundances [X/Fe]in the atmosphere of the neighboring star K 307b is solar. Statistically significant differences were found only for sodium and α-process elements: the mean overabundance of light metals is [X/Fe]=+0.35. 相似文献
19.
The aim of this paper is to determine the flux emergence rate due to small-scale magnetic features in the quiet Sun using
high-resolution Hinode SOT NFI data. Small-scale magnetic features are identified in the data using two different feature identification methods
(clumping and downhill); then three methods are applied to detect flux emergence events. The distribution of the intranetwork
peak emerged fluxes is determined. When combined with previous emergence results, from ephemeral regions to sunspots, the
distribution of all fluxes are found to follow a power-law distribution which spans nearly seven orders of magnitude in flux
(1016 – 1023 Mx) and 18 orders of magnitude in frequency. The power-law fit to all these data is of the form
|
\fracdNdY = \fracn0Y0\fracYY0-2.7,\frac{\mathrm{d}N}{\mathrm{d}\Psi} = \frac{n_0}{\Psi_0}\frac{\Psi}{\Psi _0}^{-2.7}, 相似文献
20.
We discuss our JHKLM photometry for nine carbon Mira stars, eighteen carbon semiregular variables, and two oxygen Mira stars. For fourteen carbon stars, we present and analyze their infrared light and color curves. For all of the observed objects, we have estimated the optical depths of the circumstellar dust envelopes, the angular diameters of the stars, and their temperatures. 相似文献
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