共查询到20条相似文献，搜索用时 46 毫秒
1.
R. J. Barber S. Miller N. Dello Russo M. J. Mumma J. Tennyson P. Guio 《Monthly notices of the Royal Astronomical Society》2009,398(3):1593-1600
High-resolution spectra of comet 8P/Tuttle were obtained in the frequency range 3449.0–3462.2 cm−1 on 2008 January 3 ut using CGS4 with echelle grating on United Kingdom Infrared Telescope. In addition to observing solar pumped fluorescent lines of H2 O, the long integration time (152 min on target) enabled eight weaker H2 O features to be assigned, most of which had not previously been identified in cometary spectra. These transitions, which are from higher energy upper states, are similar in character to the so-called SH lines recorded in the post Deep Impact spectrum of comet Tempel 1. We have identified certain characteristics that these lines have in common, and which in addition to helping to define this new class of cometary line give some clues to the physical processes involved in their production. Finally, we derive an H2 O rotational temperature of and a water production rate of (1.4 ± 0.3) × 1028 molecules s−1 . 相似文献
2.
Paolo A. Mazzali 《Monthly notices of the Royal Astronomical Society》2001,321(2):341-346
The spectrum of the normal Type Ia SN 1990N observed very early on (14 days before B maximum) was analysed by Fisher et al., who showed that the large width and the unusual profile of the strong line near 6000 Å can be reproduced if the line is assumed to be due to C ii 6578, 6583 Å and if carbon is located in a high-velocity shell. This line is one of the characterizing features of SNe Ia, and is usually thought to be due to Si ii . A Monte Carlo spectrum synthesis code is used to investigate this suggestion further. The result is that if a standard explosion model is used, the mass enclosed in the shell at the required high velocity (25 000–35 000 km s−1 ) is too small to give rise to a strong C ii line. At the same time, removing silicon has a negative effect on the synthetic spectrum at other wavelengths, and removing carbon from the lower velocity regions near the photosphere makes it difficult to reproduce two weak lines which are naturally explained as C ii , one of them being the line which Fisher et al. suggested is responsible for the strong 6000-Å feature. However, synthetic spectra confirm that although Si ii can reproduce most of the observed 6000-Å line, the red wing of the line extends too far to be compatible with a Si ii origin, and that the flat bottom of the line is also not easy to reproduce. The best fit is obtained for a normal SN Ia abundance mix at velocities near the photosphere (15 500–19 000 km s−1 ) and an outer carbon–silicon shell beyond 20 000 km s−1 . This suggests that mixing is not complete in the outer ejecta of an SN Ia. Observations at even earlier epochs might reveal to what extent a carbon shell is unmixed. 相似文献
3.
E. Brannigan M. Takami A. Chrysostomou J. Bailey 《Monthly notices of the Royal Astronomical Society》2006,367(1):315-322
We demonstrate that artificial bipolar structure can be detected using spectro-astrometry when the point spread function (PSF) of a point source suffers distortion in a relatively wide slit. Spectro-astrometry is a technique which allows us to probe the spatial structure of astronomical sources on milliarcsec (mas) scales making it possible to detect close binaries and to study the geometry and kinematics of outflowing gas on scales much smaller than the seeing or the diffraction limit of the telescope. It is demonstrated that a distorted PSF, caused by tracking errors of the telescope or unstable active optics during an exposure, can induce artificial signals which may be misinterpreted as a real spectro-astrometric signal. Using simulations, we show that these may be minimized by using a narrow slit relative to the seeing. Spectra should be obtained at antiparallel slit position angles (e.g. 0° and 180°) for comparison in order to allow artificial signatures to be identified. 相似文献
4.
5.
6.
7.
Thorsten Tepper García 《Monthly notices of the Royal Astronomical Society》2006,369(4):2025-2035
The Voigt–Hjerting function is fundamental in order to correctly model the profiles of absorption lines imprinted on the spectra of bright background sources by intervening absorbing systems. In this work, we present a simple analytic approximation to this function in the context of absorption-line profiles of intergalactic H i absorbers. Using basic calculus tools, we derive an analytic expression for the Voigt–Hjerting function that contains only fourth-order polynomial and Gaussian functions. In connection with the absorption coefficient of intergalactic neutral hydrogen, this approximation is suitable for modelling Voigt profiles with an accuracy of 10−4 or better for an arbitrary wavelength baseline, for column densities up to N H I = 10 22 cm−2 , and for damping parameters a ≲ 10−4 , that is, the entire range of parameters characteristic to all Lyman transitions arising in a variety of H i absorbing systems such as Lyman α (Lyα) forest clouds, Lyman limit systems and damped Lyα systems. We hence present an approximation to the Voigt–Hjerting function that is both accurate and flexible to implement in various types of programming languages and machines, and with which Voigt profiles can be calculated in a reliable and very simple manner. 相似文献
8.
S.A. Sim 《Monthly notices of the Royal Astronomical Society》2001,326(2):821-832
The importance of partial redistribution (PRD) in the modelling of the Lyman α and Lyman β emission lines of hydrogen in stellar atmospheres is examined using simple atmospheric models of a range of late-type stars. These models represent the subgiant Procyon (F5 IV–V), and the two giants β Gem (K0 III) and α Tau (K5 III). These stars are selected to span a wide range of surface gravities: 1.25< log g <4.00 . The calculations are performed using the computer code multi with the modifications made by Hubeny & Lites. It is found that PRD effects are highly significant, both in the direct prediction of the Lyman line profiles and in the application of hydrostatic equilibrium to calculate the atmospheric electron density in static atmospheric models. 相似文献
9.
10.
11.
Sergei A. Levshakov & Wilhelm H. Kegel 《Monthly notices of the Royal Astronomical Society》1998,301(2):323-327
We show that spatial correlations in a stochastic large-scale velocity field in an otherwise smooth intergalactic medium (homogeneous comoving density) superposed on the general Hubble flow may cause a 'line-like' structure in QSO spectra similar to the population of unsaturated Lyα forest lines which usually are attributed to individual clouds with 1011 ≲ N H i 5 × 1013 cm−2 . Therefore there is no clear observational distinction between a diffuse intergalactic medium and discrete intergalactic clouds. It follows that the H i density in the diffuse intergalactic medium might be substantially underestimated if it is determined from the observed intensity distribution near the apparent continuum in high-resolution spectra of QSOs. Our tentative estimate implies a diffuse neutral hydrogen opacity τGP ∼ 0.3 at z ∼ 3 and a current baryon density ΩIGM ≃ 0.08, assuming a Hubble constant H 0 = 70 km s−1 Mpc−1 . 相似文献
12.
L. Binette 《Monthly notices of the Royal Astronomical Society》1998,294(3):L49-L51
The line ratios from coronal gas in Seyferts can be successfully fitted with photoionized clouds of high densities and low volume filling factor. The ionization parameter implied is sufficiently high that models must consider the effect of radiation pressure from the active nucleus. In spite of the gravitational force of the nucleus, radiation pressure is sufficiently strong to compress and radially accelerate the internally stratified gas clouds provided that these contain small amounts of dust (≃ 10 per cent of the solar neighbourhood value). This radial acceleration could explain the blueshift of the coronal lines relative to the systemic velocity without the need to invoke an ambient 'pushing' wind. Embedded dust has the interesting effect of making the photoionized clouds marginally ionization-bounded instead of matter-bounded. 相似文献
13.
G. A. Galazutdinov J. Kre&#;owski F. A. Musaev 《Monthly notices of the Royal Astronomical Society》1999,310(4):1017-1022
The recent hypothesis that some of the diffuse interstellar bands originate in bare carbon chains such as and is tested using echelle spectra covering the whole range of possible (i.e. found in the laboratory) transitions of these molecules. Most of the expected features are below the level of detection in astrophysical spectra, and even those observed show intensity ratios that are different from those in the laboratory. Thus the hypothesis is very unlikely to be true. 相似文献
14.
We have measured the line widths and nonthermal velocities in 12 solar regions using high resolution EUV data taken by Hinode/EIS. We find that there exists a positive correlation between the intensity and nonthermal velocity for the Fe XII emission line as well as some other lines. The correlation coefficients decrease from the disk center to the limb. However, the nonthermal velocities of a particular spectral line do not vary much in different regions, so they are considered isotropic. In particular, we find that for a coronal loop structure, the largest widths and nonthermal velocities occur at the footpoints, where outflows appear. Based on these observational results, we discuss several physical processes responsible for coronal heating. 相似文献
15.
16.
We report the first extensive measurements of hyperfine structure in Ta ii . Spectra of Ta ii were recorded by high-resolution Fourier transform spectrometry in the region 10 000–53 000 cm-1 (1886–10 000 Å) and the majority of observed lines show significant hyperfine structure. Computer fits to several hundred of these line profiles have yielded values of the magnetic dipole hyperfine interaction constant A for 88 energy levels with an uncertainty of between 0.5 and 10 per cent for the majority of A factors. The A factors range from −0.078 to +0.065 cm−1 for the even levels and from −0.064 to +0.083 cm−1 for the odd levels. For the majority of these A factors no previous measurements are known. Approximate values of the electric quadrupole hyperfine interaction constant B were found for 73 levels. These measurements of A and B factors allow, for the first time, the effects of hyperfine structure in Ta ii lines to be correctly accounted for both in abundance analysis and in the resolution of blended lines in astrophysical spectra. 相似文献
17.
18.
Hua-Xiang Wang Xin-Ji WuDepartment of Astronomy Peking University Beijing Urumqi Astronomical Station National Astronomical Observation Urumqi CAS-PKU Joint Beijing Astrophysics Center Beijing 《中国天文和天体物理学报》2003,3(5)
Using the method of Gaussian Fit Separation of Average Profile (GF-SAP), we re-examine the average profiles of nine pulsars at several frequencies, ranging from 408-1642 MHz. This method enables us to obtain the number of components for each pulsar, and the parameters for each component, the width, position and amplitude. The ρ-P relation for the inner cone and outer cone are studied separately, and the results are, respectively, ρ = p-0.51±0.05 and ρ= p-0.42±0.06 The results can be interpreted as a confirmation of the double-cone structure of pulsar emission beams. The altitudes of emission region, and the radius-to-frequency-map (RFM) are also examined; for the outer cone, we obtained γ(v) ∝v-0.19±0.09. 相似文献
19.
[OIII] 5007 Å line profiles at high spectral and spatial resolution have been obtained at a single slit position near the Trapezium cluster in the Orion Nebula (M42, NGC1976) using the Manchester Echelle Spectrometer (MES). The very long integration time at this position confirms the earlier tentative identification of a shell on the nearside of the Trapezium cluster with a relative velocity of -100 kms–1 and a radius of 1 arcminute. No receding counterpart is found. We believe this is the first detection of this feature at optical wavelengths, previous spectroscopic work (O' Dellet al., 1993),(Baldwinet al., 1991),(Castaneda, 1988) having concentrated on the main nebular material at relatively low velocities. 相似文献
20.
I. A. Crawford R. Lallement & B. Y. Welsh 《Monthly notices of the Royal Astronomical Society》1998,300(4):1181-1188
We present ultra-high-resolution (0.35 km s−1 FWHM) observations of the interstellar Ca K line towards seven nearby stars. The spectral resolution was sufficient to resolve the line profiles fully, thereby enabling us to detect hitherto unresolved velocity components, and to obtain accurate measurements of the velocity dispersions ( b values). Absorption components with velocities similar to those expected for the Local Interstellar Cloud (LIC) and the closely associated 'G cloud' were identified towards six of the seven stars. However, in most cases the b values deduced for these components were significantly larger than the b ≈ 2.2 km s−1 (i.e. T k ≈ 7000 K, v t ≈ 1 km s−1 ) expected for the LIC, and it is argued that this results from the presence of additional, spectrally unresolved, components having similar velocities and physical conditions. For two stars (δ Vel and α Pav) we detect interstellar components with much smaller b values (1.1 ± 0.3 and 0.8 ± 0.1 km s−1 , respectively) than are expected for low-density clouds within the Local Bubble. In the case of the narrow α Pav component, we also find an anomalously large Na i /Ca ii column density ratio, which is indicative of a relatively high density. Thus it is possible that, in addition to LIC-type clouds, the local interstellar medium contains a population of previously undetected cooler and denser interstellar clouds. 相似文献