共查询到20条相似文献，搜索用时 15 毫秒
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《Icarus》1986,65(1):1-12
The tidal gravitational field of the Galaxy directed into the galactic plane changes the angular momentum of comets in the Oort cloud. For comet orbits with semimajor axis greater than 2 × 104 AU, the change of angular momentum in one orbit is sufficient to bring comets from the Oort cloud into the visible region, causing the infall of “new” comets. The limiting size orbit is weakly dependent on the angle between the major axis of the comet orbit and the galactic plane. The flux of comets into the inner Solar System caused by the galactic tidal field will be continuous and nearly isotropic. This effect appears to exclude any determination of the trajectories of passing stars by analysis of the angular distribution of new comets. The production of intense comet showers by the tidal field of a solar companion or of an interstellar cloud is considered. We show that the direction of a solar companion cannot be found from the present distribution of observable comets. The frequency of comet showers induced by encounters with interstellar clouds is found to be much lower than that from passing stars, and the tidal fields of interstellar clouds are not strong enough to cause comet showers of sufficient intensity to result in Earth impacts. 相似文献
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用紫金山天文台青海站的１３７ｍ射电望远镜,对１０个行星状星云给出了新的ＣＯ（１－０）谱线观测结果．其中４个行星状星云：ＮＧＣ６４４５,Ｍ１５９,Ｍ４９和Ｍ２５１,已有过ＣＯ（２１）的观测,本文第一次给出了它们的ＣＯ（１０）的测量结果;对２个别人曾经观测过但未测到ＣＯ的行星状星云：Ｓｈ２７１和Ｍ４１８,本文第一次证认了它们的ＣＯ发射;对４个别人从未进行过ＣＯ搜寻的行星状星云：ＶＶ１８,Ｍ２５２,Ｈｅ２４５９和Ｋ３３１,本文第一次进行了观测,并得到了它们的ＣＯ（１０）谱．由ＣＯ的发射谱征可见,ＶＶ１８可能是一个误分类的行星状星云 相似文献
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利用紫金山天文台青海站的 １３．７ ｍ毫米波望远镜,对 Ｏｒｉｏｎ Ａ分子云中的 ＯＭＣ－３区域,进行了较高分辨率的１３ＣＯ（Ｊ＝１－０）和Ｃ１８Ｏ（Ｊ＝１－０）分子辐射的成图观测．给出了该分子云中１３ＣＯ和 Ｃ１８Ｏ云核分布的整体结构和平均物理参数．观测发现,该分子云的１３ＣＯ和 Ｃ１８Ｏ的云核中心分别与最年轻的天体－Ｃｌａｓｓ ０类源 ＭＭＳＩ, ＭＭＳ４,ＭＭＳ６和ＭＭＳ７,ＭＭＳ８;ＭＭＳ９成协．此外,通过分析ＯＭＣ－３整个区域的速度场结构,发现沿 Ｃ１８Ｏ和１３ＣＯ云核方向从南到北有一个～ １．７ｋｍ／ｓ的速度场梯度,而分子云的红、蓝移团块则分别趋于云的北部和南部．并对ＯＭＣ－３区的恒星形成特征进行了讨论． 相似文献
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Dale P. Cruikshank Joshua P. Emery Katherine A. Kornei Emiliano d’Aversa 《Icarus》2010,205(2):516-527
We obtained time-resolved, near-infrared spectra of Io during the 60-90 min following its reappearance from eclipse by Jupiter on five occasions in 2004. The purpose was to search for spectral changes, particularly in the well-known SO2 frost absorption bands, that would indicate surface-atmosphere exchange of gaseous SO2 induced by temperature changes during eclipse. These observations were a follow-on to eclipse spectroscopy observations in which Bellucci et al. [Bellucci et al., 2004. Icarus 172, 141-148] reported significant changes in the strengths of two strong SO2 bands in data acquired with the VIMS instrument aboard the Cassini spacecraft. One of the bands (4.07 μm [ν1 + ν3]) observed by Bellucci et al. is visible from ground-based observatories and is included in our data. We detected no changes in Io’s spectrum at any of the five observed events during the approximately 60-90 min during which spectra were obtained following Io’s emergence from Jupiter’s shadow. The areas of the three strongest SO2 bands in the region 3.5-4.15 μm were measured for each spectrum; the variation of the band areas with time does not exceed that which can be explained by the Io’s few degrees of axial rotation during the intervals of observation, and in no case does the change in band strength approach that seen in the Cassini VIMS data. Our data are of sufficient quality and resolution to show the weak 2.198 μm (4549.6 cm−1) 4ν1 band of SO2 frost on Io for what we believe is the first time. At one of the events (June 22, 2004), we began the acquisition of spectra ∼6 min before Io reappeared from Jupiter’s shadow, during which time it was detected through its own thermal emission. No SO2 bands were superimposed on the purely thermal spectrum on this occasion, suggesting that the upper limit to condensed SO2 in the vertical column above Io’s surface was ∼4 × 10−5 g cm−2. 相似文献
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We present new radio observations of molecular lines in the region of high mass star formation, namely G122.0-7.1. A large-scale
map of the emission observed in the 12CO (J = 1−0) and 13CO (J = 1−0) lines covers the area of 15′ × 9′, revealing two dense regions. The molecular bipolar outflows have been resolved
in ASO1 region. It is associated with the known candidate YSO nearby IRAS 0042 + 5530. Also, a new dense region has been discovered
in the North-Western part of the G122.0-7.1 at a distance of 5′ from IRAS 0042 + 5530. Its position is close to the peak of
4850 MHz emission.
The text was submitted by the authors in English. 相似文献
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Suresh Chandra 《Astrophysics and Space Science》1994,218(1):29-33
Collisional vibrational deexcitation rate constantsk
10 for diatomic molecules have been calculated and used by a number of authors. But sometimes scientists use some fit-formula instead of the actual expression. This may be caused by difficulties in understanding the actual formula. Here, I discuss the calculations of collisional deexcitation rate constants for diatomic molecules by using the actual expression. 相似文献
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利用日本名古屋大学天体物理系的毫米波射电望远镜对CepheusC的C18O（J＝1－0）分子辐射首次进行了观测，得到了强度分布图．从强度分布图上，我们发现C18O（J＝1－0）分子的分布呈现三个核．通过计算得到了三个核的物理参数． 相似文献
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Nadjinangar Gotoum Kamel Hammami L. C. Owono?Owono Nejm-Eddine Jaidane 《Astrophysics and Space Science》2012,337(2):553-561
Rotational excitation cross sections and rate coefficients of AlF collisions with para-H2 are computed at low temperature, i.e., for T≤70 K. Prior to collisional calculations, a four-dimensional (4D) potential energy surface (PES) for the AlF-H2 system is calculated at the ab initio Coupled-Cluster level of the theory with an aug-cc-pVQZ Gaussian basis set. This 4D-PES is further reduced to a two-dimensional
(2D) PES based on the considerations related to collisional studies with para-H2. The [Al-F] and [H-H] bond lengths are frozen at their experimental equilibrium value r
e
=1.654369 bohr and r
e
=1.4011 bohr respectively. The interaction energy presents a global minimum located ∼63 cm−1 below the AlF-H2 dissociation limit. With this PES, cross sections are determined in the Close-Coupling (CC) approach and rate coefficients
are inferred by averaging the cross sections over a Maxwell-Boltzman distribution of kinetic energies. These quantities are
significantly magnified in comparison with their AlF-He counterparts. The already observed propensity towards ΔJ=1 transitions for AlF-He remains. 相似文献
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We report spectroscopy of Comet C/1991 T1 (McNaught-Hartley) at 3-13 μm on January 31.62 and February 1.7 2001 UT (delta=1.29 AU, r=1.40 AU) using the broadband array spectrograph system on the IRTF. The spectrum showed a silicate emission feature extending about 20% above the continuum. Two emission features at 10.3 and 11.2 μm appeared above the silicate band, the latter seemingly indicative of crystalline olivine. The 10.3-μm feature is only a 1-2 sigma detection but if real could indicate the presence of hydrated silicates. The color temperature at 8-13 μm was 260±10 K, approximately 6% above the blackbody radiative equilibrium temperature of 235 K. The magnitude at [N] was 3.13±0.02. On the second night, the comet had brightened slightly ([N]=2.98±0.02) and the two prominent emission features were absent, although the silicate emission feature maintained its trapezoidal shape with shoulders at 9.5 and 11.2 μm. 相似文献
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《天文和天体物理学研究(英文版)》2014,(8)
We present large scale observations of C18O(1–0) towards four massive star forming regions: MON R2,S156,DR17/L906 and M17/M18. The transitions of H2CO(110–111),C18O(1–0) and the 6 cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non–LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 – 8 K. The excitation of the H2 CO absorption line is affected by strong background continuum emission. From a comparison of H2 CO and C18 O maps,we found that the extent of H2 CO absorption is broader than that of C18 O emission in the four regions. Except for the DR17 region,the maximum in H2 CO absorption is located at the same position as the C18 O peak. A good correlation between intensities and widths of H2 CO absorption and C18 O emission lines indicates that the H2 CO absorption line can trace the dense,warm regions of a molecular cloud. We find that N(H2CO) is well correlated with N(C18O) in the four regions and that the average ratio of column densities is N(H2CO)/N(C18O) ～ 0.03. 相似文献
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We have observed carbon monoxide in the stratosphere of Venus at phase angles of 180 and 120° via the J = 0 → 1 rotational transition at 115.2712 GHz. The mixing ratio profile of CO has been obtained by fitting the theoretical spectrum produced by a small number of layers with constant CO mixing ratio to the line profile, and the results suggest that the CO mixing ratio below the 1-mb level increased by at least a factor of 10 between 180 and 120° phase angles. The depletion of CO on the nightside of the planet was not anticipated and may require either a new loss mechanism for CO which can operate without sunlight or an increase in the amount of vertical mixing on the nightside. 相似文献
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俞志尧 《中国天文和天体物理学报》1999,(1)
分析ＣｅｐｈｅｕｓＥ中Ｃ１８Ｏ（Ｊ＝１－０）的速度位置图,发现相对于峰速度的红移速度成分主要分布在中心位置附近的核区,而相对于峰速度的蓝移速度成分除了分布在中心位置附近的核区外,还可以在向东和向西北方向的外流中找到。这说明强度分布图中的分子外流的不准直分布是由相对于峰速度的蓝移速度成分的不准直分布所引起的。 相似文献
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Previous observations have revealed an accretion disk and outflow motion in the high-mass starforming region G192.16–3.84, but collapse has not been reported before. Here we present molecular line and continuum observations toward the massive core G192.16–3.84 with the Submillimeter Array. C18 O(2–1) and HCO+(3–2) lines show pronounced blue profiles, indicating gas infalling in this region. This is the first time that infall motion has been reported in the G192.16–3.84 core. Two-layer model fitting gives infall velocities of 2.0±0.2 and 2.8±0.1 km s-1. Assuming that the cloud core follows a power-law density profile(ρ∝ r1.5), the corresponding mass infall rates are(4.7±1.7)×10-3 and(6.6±2.1)×10-3 M⊙yr-1 for C18 O(2–1) and HCO+(3–2), respectively. The derived infall rates are in agreement with the turbulent core model and those in other high-mass star-forming regions, suggesting that high accretion rate is a general requirement for forming a massive star. 相似文献
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Results from optical photometric observations of the PMS star V 1735 Cyg are reported. The star is located in the IC 5146
dark cloud complex—a region of active star formation. On the basis of observed outburst and spectral properties, V 1735 Cyg
was classified as a FUor object. We present data from BVRI CCD photometric observations of the star, collected from March 2003 to January 2009. Plates from the Rozhen Schmidt telescope
archive were scanned for a brightness estimation of the star. A sequence of sixteen comparison stars in the field of V 1735
Cyg was calibrated in BVRI bands. The data from photographic observations made from 1986 to 1992 show a strong light variability (ΔV=1⋅m2). In contrast, the recent photometric data obtained from 2003 to 2009 show only small amplitude variations (ΔI=0⋅m3). The analysis of existing photometric data shows a very slow decrease in star brightness—1⋅m8 (R) for a 44 year period. The possibilities for future photometric investigations of V 1735 Cyg using the photographical
plate archives is discussed briefly. 相似文献
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《天文和天体物理学研究(英文版)》2020,(9)
High energy photon radiations of gamma-ray bursts(GRBs) and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s) follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ_0) of GRBs.It is shown that the AGN sample does not agree with the L_p-E_(p,z)-Γ_0 relation of GRBs.In addition,we obtain a tight relation of ■ for FSRQs and NLS1 galaxies,where L_(syn) is the luminosity at peak photon energy E_(syn,p) of the synchrotron radiations.This relation is different from the L_p-E_(p,z)-Γ_0 relation of GRB s.The dependence of L_(syn) to δ is consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue that Γ_0 may be a representative of the kinetic power of the radiating region and the tight L_p-E_(p,z)-Γ_0 relation is shaped by the radiation physics and the jet power together. 相似文献