共查询到20条相似文献,搜索用时 31 毫秒
1.
S. Hyung L. H. Aller W. A. Feibelman W. B. Lee A. de Koter 《Monthly notices of the Royal Astronomical Society》2000,318(1):77-91
With the Hamilton echelle spectrograph at the Lick Observatory, emission-rich spectral lines of the planetary nebula NGC 6543 were secured in the wavelength range from 3550 to 10 100 Å. We chose two bright regions, ∼8 arcsec east and ∼13 arcsec north of the central star, the physical conditions and chemical abundances of which may differ as a result of the different physical characteristics involving the mass ejection of different epochs. By combining Hamilton echelle observations with archive UV data secured with the International Ultraviolet Explorer ( IUE ), we obtain improved diagnostics and chemical compositions for the two observed regions. The diagnostic diagram gives the average value of T e =8000∼8300 K, and the electron number density near N e ∼5000 cm−3 for most ions, while some low-excitation lines indicate much higher temperatures, i.e. T e ∼10 000 K. With the construction of a photoionization model, we try to fit the observed spectra in a self-consistent way: thus, for most elements, we employ the same chemical abundances in the nebular shell; and we adopt an improved Sobolev approximation model atmosphere for the hydrogen-deficient Wolf–Rayet type central star. Within the observational errors, the chemical abundances do not seem to show any positional variation except for helium. The chemical abundances of NGC 6543 appear to be the same as in average planetary nebulae. The progenitor star may have been an object of one solar mass, most of the heavier elements of which were less plentiful than in the Sun. 相似文献
2.
A. L. Zezas I. Georgantopoulos & M. J. Ward 《Monthly notices of the Royal Astronomical Society》1998,301(4):915-925
We present ROSAT [High Resolution Imager (HRI) and Position Sensitive Proportional Counter (PSPC)] and ASCA observations of the two luminous ( L x ∼ 1041−42 erg s−1 ) star-forming galaxies NGC 3310 and 3690. The HRI shows clearly that the sources are extended with the X-ray emission in NGC 3690 coming from at least three regions. The combined 0.1–10 keV spectrum of NGC 3310 can be described by two components, a Raymond–Smith plasma with temperature kT = 0.81+0.09 −0.12 keV and a hard power law, Γ = 1.44−0.20 −0.11 (or alternatively a harder Raymond–Smith plasma with kT ∼ 15 keV), while there is no substantial excess absorption above the Galactic column value. The soft component emission is probably a super wind while the nature of the hard emission is more uncertain with the likely origins being X-ray binaries, inverse Compton scattering of infrared photons, an active galactic nucleus or a very hot gas component (∼108 K). The spectrum of NGC 3690 is similar, with kT = 0.83+0.02 −0.04 keV and Γ = 1.56+0.11 −0.11 . We also employ more complicated models such as a multi-temperature thermal plasma, a non-equilibrium ionization code or the addition of a third softer component, which improve the fit but not at a statistically significant level (2σ). These results are similar to recent results on the archetypal star-forming galaxies M82 and NGC 253. 相似文献
3.
The multi-transitional observations of CS molecules towards the NGC 2071 core have been re-analysed by using a tri-dimensional Monte Carlo radiative transfer code. Better agreement with the observations is made by an introduction of clumpiness to this model than by smoothly varying density to the 1D microturbulent one. The best-fitting model shows that, when a unique density is assumed for clumps, the volume filling factor of the clumps varies as r −2 with an average of ∼5 per cent over the entire core, and that the H2 number density and the CS abundance of the clump relative to H2 are ∼ 2 × 106 cm−3 and ∼ 6 × 10−10 , respectively. The radial density gradient ∝ r −2 obtained from our clumpy core model is steeper than that (∝ r −1.3 ) obtained from the microturbulent model. Since all clumps are subject to random bulk motions in this 3D clumpy macroturbulent model, synthesized line profiles do not show self-absorption dips even for opaque transitions and the resulting linewidth is in good accordance with the observations. 相似文献
4.
S. Casassus P. F. Roche M. J. Barlow 《Monthly notices of the Royal Astronomical Society》2000,314(4):657-671
We report on advances in the study of the cores of NGC 6302 and 6537 using infrared grating and echelle spectroscopy. In NGC 6302, emission lines from species spanning a large range of ionization potential, and in particular [Si ix ] 3.934 μm, are interpreted using photoionization models (including cloudy ), which allow us to re-estimate the temperature of the central star to be about 250 000 K. All of the detected lines are consistent with this value, except for [Al v ] and [Al vi ]. Aluminium is found to be depleted to one hundredth of the solar abundance, which provides further evidence for some dust being mixed with the highly ionized gas (with photons harder than 154 eV). A similar depletion pattern is observed in NGC 6537. Echelle spectroscopy of IR coronal ions in NGC 6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (<22 km s−1 FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [Ne v ] 3426 Å. We note the absence of a hot bubble, or a wind-blown bipolar cavity filled with a hot plasma, at least on 1 arcsec and 10 km s−1 scales. The systemic heliocentric velocities for NGC 6302 and 6537, measured from the echelle spectra of IR recombination lines, are found to be −34.8±1 km s−1 and −17.8±3 km s−1 . We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle. 相似文献
5.
S. L. Lumsden P. J. Puxley M. G. Hoare 《Monthly notices of the Royal Astronomical Society》2001,320(1):83-102
We have observed a large sample of compact planetary nebulae in the near-infrared to determine how the 21 P–21 S He i line at 2.058 μm varies as a function of stellar effective temperature, T eff . The ratio of this line with H i Br γ at 2.166 μm has often been used as a measure of the highest T eff present in a stellar cluster, and hence of whether there is a cut-off in the stellar initial mass function at high masses. However, recent photoionization modelling has revealed that the behaviour of this line is more complex than previously anticipated. Our work shows that in most aspects the photoionization models are correct. In particular, we confirm the weakening of the 21 P–21 S line as T eff increases beyond 40 000 K. However, in many cases the model underpredicts the observed ratio when we consider the detailed physical conditions in the individual planetary nebulae. Furthermore, there is evidence that there is still significant 21 P–21 S He i line emission even in the planetary nebulae with very hot central stars. It is clear from our work that this ratio cannot be considered as a reliable measure of effective temperature on its own. 相似文献
6.
J. P. Phillips Luis Cuesta S. N. Kemp 《Monthly notices of the Royal Astronomical Society》2005,357(2):548-558
We have undertaken visual spectroscopy of the highly evolved planetary nebulae (PNe) A8, A13, A62, A72, A78 and A83 over a wavelength range 4330 < λ < 6830 Å . This permits us to specify relative line intensities in various sectors of the nebular shells, and to investigate the variation of emission as a function of radius. We determine that the spectrum of the central star of A78 has varied appreciably over a period of 25 yr. There is now evidence for strong P Cygni absorption in the λ4589 and λ5412 transitions of He ii , implying terminal velocities of the order of V ∞ ≅ 3.83 × 103 km s−1 . We also note that the emission-line profiles of the sources can be used to investigate their intrinsic emission structures. We find that most PNe show appreciable levels of emission throughout their volumes; only one source (A13) possesses a thin-shell structure. Such results are in conformity with evolutionary theory, and probably reflect the consequences of adiabatic cooling in highly evolved outflows. 相似文献
7.
S. Casassus P. J. Storey M. J. Barlow P. F. Roche 《Monthly notices of the Royal Astronomical Society》2005,359(4):1386-1392
The core of planetary nebula NGC 6302 is filled with high-excitation photoionized gas at low expansion velocities. It represents a unique astrophysical situation in which to search for hyperfine structure (HFS) in coronal emission lines from highly ionized species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing [Al vi ] 3.66 μm 3 P2 ←3 P1 , obtained with Phoenix on Gemini South at resolving powers of up to 75 000, resolve the line into five hyperfine components separated by 20–60 km s−1 as a result of the coupling of the I = 5/2 nuclear spin of 27 Al with the total electronic angular momentum J . The isotope 26 Al has a different nuclear spin of I = 5 , and a different HFS, which allows us to place a 3σ upper limit on the 26 Al/27 Al abundance ratio of 1/33. We measure the HFS magnetic dipole coupling constants for [Al vi ], and provide the first estimates of the electric quadrupole HFS coupling constants obtained through astronomical observations of an atomic transition. 相似文献
8.
P. Cabella F. K. Hansen M. Liguori D. Marinucci S. Matarrese L. Moscardini N. Vittorio 《Monthly notices of the Royal Astronomical Society》2006,369(2):819-824
We note that H2 emitting planetary nebulae tend to have Zanstra temperatures T Z (He ii ) > 90 kK . This is shown to be consistent with a large evolutionary lifetime, and the kinematic ages of the envelopes. Non-local thermodynamic equilibrium stellar atmospheric modelling also shows that levels of soft X-ray emission increase more rapidly than has previously been assumed, and are preferentially large in H2 emitting sources. It is suggested that this may hold the key to explaining the strengths of the H2 transitions. 相似文献
9.
R. L. C. Starling M. J. Page G. Branduardi-Raymont A. A. Breeveld R. Soria K. Wu 《Monthly notices of the Royal Astronomical Society》2005,356(2):727-733
We present an XMM–Newton observation of the Seyfert–LINER (low-ionization nuclear emission-line region) galaxy NGC 7213. The RGS soft X-ray spectrum is well fitted with a power law plus soft X-ray collisionally ionized thermal plasma ( kT = 0.18+0.03 −0.01 keV) . We confirm the presence of Fe i , Fe xxv and Fe xxvi Kα emission in the EPIC spectrum and set tighter constraints on their equivalent widths of 82+10 −13 , 24+9 −11 and 24+10 −13 eV, respectively. We compare the observed properties together with the inferred mass accretion rate of NGC 7213 with those of other Seyfert and LINER galaxies. We find that NGC 7213 has intermediate X-ray spectral properties lying between those of the weak active galactic nucleus found in the LINER M81 and higher-luminosity Seyfert galaxies. There appears to be a continuous sequence of X-ray properties from the Galactic Centre through LINER galaxies to Seyferts, probably determined by the amount of material available for accretion in the central regions. 相似文献
10.
M. S. Clemens P. Alexander D. A. Green 《Monthly notices of the Royal Astronomical Society》2000,312(2):236-246
This paper describes submm, 12 CO (J = 2–1) observations of the interacting pair of galaxies NGC 4490 and 4485, and together with high resolution H i and multifrequency radio continuum data we investigate the evolution of the ISM in this system. We find the following. (i) The smaller member of the pair, NGC 4485, has had the atomic, molecular and dust components of its ISM stripped via ram pressure during its recent passage through the extended H i distribution of NGC 4490. A bow-shock is identified in the H i ahead of the stripped gas. (ii) Within the disc of NGC 4490 we find a very low H2 -to-H i ratio as well as a strong correlation between thermal emission and mass of H2 suggesting that the star formation rate is limited in this case by the conversion of H i to H2 . (iii) 12 CO emission from an H i and radio-continuum bridge between the two galaxies is detected. 相似文献
11.
S. Bianchi A. Corral F. Panessa X. Barcons G. Matt L. Bassani F. J. Carrera E. Jiménez-Bailón 《Monthly notices of the Royal Astronomical Society》2008,385(1):195-199
We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC 3147. The XMM–Newton spectrum shows that the source is unabsorbed in the X-rays ( N H < 5 × 1020 cm−2 ) . On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low-equivalent width of the iron Kα line (≃130 eV) and the large ratio between the 2–10 keV and the [O iii ] fluxes. It seems therefore inescapable to conclude that NGC 3147 intrinsically lacks the Broad-Line Region, making it the first 'true' type 2 Seyfert galaxy. 相似文献
12.
Using a numerically accurate radiation-gas dynamical method we investigate the winds scenario for aspherical planetary nebulae
(PNe). Our model includes the interaction of two winds: as low high mass-loss rate wind (a `super wind'); and a fast wind;
low mass-loss rate wind. Our model also includes the evolution of the UV spectrum of the PNe centeral star. As stated in the
section3 of Paper I (Ganbari and Khesali, 2001), we consider a three dimensional density distribution ρ(r,θφ for the super wind, in this way we enter the effects of cooling and heating mechanisms in our model. Taking into account
the above assumptions, we introduce the code (DIS3D) and numerically we study the dynamical and ionization properties of the
planetary nebula NGC3132. We show that it is possible by simulations to reproduce the shape of PNe in three dimensions, and
calculating the physical quantities throughout the entire nebula.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Scott Gordon Bärbel Koribalski Keith Jones 《Monthly notices of the Royal Astronomical Society》2003,342(3):939-950
We present the results of Australia Telescope Compact Array (ATCA) H i line and 20-cm radio continuum observations of the galaxy quartet NGC 6845. The H i emission extends over all four galaxies but can only be associated clearly with the two spiral galaxies, NGC 6845A and B, which show signs of strong tidal interaction. We derive a total H i mass of at least 1.8 × 1010 M⊙ , most of which is associated with NGC 6845A, the largest galaxy of the group. We investigate the tidal interaction between NGC 6845A and B by studying the kinematics of distinct H i components and their relation to the known H ii regions. No H i emission is detected from the two lenticular galaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCA J2001−4659 , was detected 4.4 arcmin NE from NGC 6845B and has an H i mass of ∼5 × 108 M⊙ . No H i bridge is visible between the group and its newly detected companion. Extended 20-cm radio continuum emission is detected in NGC 6845A and B as well as in the tidal bridge between the two galaxies. We derive star formation rates of 15–40 M⊙ yr−1 . 相似文献
14.
We present an X-ray spectroscopic study of the prototype far-infrared galaxy NGC 6240 from ASCA . The soft X-ray spectrum (below 2 keV) shows clear signatures of thermal emission well described by a multitemperature optically thin plasma, which probably originates in a powerful starburst. Strong hard X-ray emission is also detected with ASCA and its spectrum above 3 keV is extremely flat with a prominent iron K line complex, very similar to that seen in the Seyfert 2 galaxy NGC 1068 but about an order of magnitude more luminous ( L 3−10keV ≈ 1.4 × 1042 erg s−1 ). The hard X-ray spectrum indicates that only reflected X-rays of an active galactic nucleus (AGN) buried in a heavy obscuration ( N H > 2 × 1024 cm−2 ) are visible. This is evidence for an AGN in NGC 6240, emitting possibly at a quasar luminosity (∼ 1045 erg s−1 ), and suggests its significant contribution to the far-infrared luminosity. 相似文献
15.
Max Spolaor Duncan A. Forbes George K. T. Hau Robert N. Proctor Sarah Brough 《Monthly notices of the Royal Astronomical Society》2008,385(2):667-674
This is the first paper of a series focused on investigating the star formation and evolutionary history of the two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study.
Here, we present new high signal-to-noise ratio long-slit spectroscopic data obtained at the ESO 3.6-m telescope and high-resolution multiband imaging data from the Hubble Space Telescope /Advanced Camera for Surveys and wide-field imaging from Subaru Suprime-Cam. We spatially resolved integrated spectra out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. The radial profiles of the kinematic parameters vrot , σ, h 3 and h 4 are measured. The surface brightness profiles are fitted to different galaxy light models and the colour distributions analysed. The multiband images are modelled to derive isophotal shape parameters and residual galaxy images. The parameters from the surface brightness profile fitting are used to estimate the mass of the possible central supermassive black hole in NGC 1407. The galaxies are found to be rotationally supported and to have a flat core in the surface brightness profiles. Elliptical isophotes are observed at all radii and no fine structures are detected in the residual galaxy images. From our results, we can also discard a possible interaction between NGC 1400, NGC 1407 and the group intergalactic medium. We estimate a mass of ∼1.03 × 109 M⊙ for the supermassive black hole in NGC 1407 galaxy. 相似文献
Here, we present new high signal-to-noise ratio long-slit spectroscopic data obtained at the ESO 3.6-m telescope and high-resolution multiband imaging data from the Hubble Space Telescope /Advanced Camera for Surveys and wide-field imaging from Subaru Suprime-Cam. We spatially resolved integrated spectra out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. The radial profiles of the kinematic parameters v
16.
T.P. Roberts M.R. Goad M.J. Ward R.S. Warwick P.T. O'Brien P. Lira A.D.P. Hands 《Monthly notices of the Royal Astronomical Society》2001,325(2):L7-L11
We report the identification of a possible optical counterpart to the super-Eddington X-ray source NGC 5204 X-1. New Chandra data show that the X-ray source is point-like, with a luminosity of 5.2×1039 erg s−1 (0.5–8 keV) . It displays medium- and long-term X-ray variability in observations spanning a period of 20 yr. The accurate Chandra position allows us to identify a blue optical continuum source ( m v =19.7) at the position of NGC 5204 X-1, using newly obtained optical data from the INTEGRAL instrument on the William Herschel Telescope. The X-ray and optical source properties are consistent with the scenario in which we are observing the beamed X-ray emission of a high-mass X-ray binary in NGC 5204, composed of an O star with either a black hole or neutron star companion. 相似文献
17.
D. R. Gonçalves A. Mampaso R. L. M. Corradi C. Quireza 《Monthly notices of the Royal Astronomical Society》2009,398(4):2166-2176
We obtained optical long-slit spectra of four planetary nebulae (PNe) with low-ionization pair of knots, namely He 1-1, IC 2149, KjPn 8 and NGC 7662.
These data allow us to derive the physical parameters and excitation of the pairs of knots, and those of higher ionization inner components of the nebulae, separately.
Our results are as follows. (1) The electron temperatures of the knots are within the range 9500–14 500 K, similar to the temperatures of the higher ionization rims/shells. (2) Typical knots' densities are 500–2000 cm−3 . (3) Empirical densities of the inner rims/shells are higher than those of the pairs of knots, by up to a factor of 10. Theoretical predictions, at variance with the empirical results, suggest that knots should be denser than the inner regions, by at least a factor of 10. (4) Empirical and theoretical density contrasts can be reconciled if we assume that at least 90 per cent of the knots' gas is neutral (likely composed of dust and molecules). (5) By using the new Raga et al. shock modelling and diagnostic diagrams appropriated for spatially resolved PNe, we suggest that high-velocity shocked knots travelling in the photoionized outer regions of PNe can explain the emission of the pairs of knots analysed in this paper. 相似文献
These data allow us to derive the physical parameters and excitation of the pairs of knots, and those of higher ionization inner components of the nebulae, separately.
Our results are as follows. (1) The electron temperatures of the knots are within the range 9500–14 500 K, similar to the temperatures of the higher ionization rims/shells. (2) Typical knots' densities are 500–2000 cm
18.
G. H. J. Cole C. G. Mundell & A. Pedlar 《Monthly notices of the Royal Astronomical Society》1998,300(3):656-664
Using MERLIN with 0.2-arcsec resolution we have observed neutral hydrogen absorption against the central region of the starburst galaxy NGC 3628. The central region resolves into ∼16 continuum components at 1.4 GHz. From comparison with published 15-GHz data, we infer that these components are supernova remnants, although three components may be consistent with a weak active galactic nucleus. Neutral hydrogen absorption is seen against the continuum emission with column densities ∼1022 cm−2 . The absorption appears to be from two separate absorbing structures. Assuming a simple morphology, the main velocity structure can be attributed to a ring of neutral gas with a radius 130 pc rotating around a central starburst with a velocity gradient of 1270 km s−1 kpc−1 . From simple assumptions, the mass interior to this ring is 0.9 × 109 M⊙ . The second absorption structure may represent outflow from the starburst region or a large-scale galactic structure. Alternatively the absorption structure may be non-axisymmetric, such as a bar. 相似文献
19.
B.Phookun K. R.Anantharamaiah W. M.Goss 《Monthly notices of the Royal Astronomical Society》1998,295(1):156-166
We have used the Very Large Array (VLA) to search for the H92α radio recombination line (RRL) in four starburst galaxies. In NGC 660, the line was detected over a 17Å‐8 arcsec2 region near its starburst nucleus. The line and continuum emission indicate that the RRL-emitting gas is most likely in the form of a cluster of H ii regions with a small filling factor. Using a simple model we find that the total ionized mass in the nuclear region is in the range 2–8Å‐104 M⊙ and the rate of production of UV photons N Lyc ∼1–3Å‐1053 s−1 . The ratio of H92α and Brγ line intensities in NGC 660 indicates that extinction is significant even at λ=2 μm. The velocity field of the ionized gas is consistent with a rotating disc with an average velocity gradient of ∼15 km s−1 arcsec−1 . The dynamical mass within the central 500 pc is ∼4Å‐108 M⊙ and may be about ∼6Å‐107 M⊙ within the central 120 pc. No line was detected in the other galaxies (NGC 520, NGC 1614 and NGC 6946) to a 3σ limit of 300 μJy. In the starburst galaxies in which RRLs have been detected, we find that there is a rough correlation between the integrated H92α line flux density and both the total far-infrared flux density and the radio continuum emission from the central region. 相似文献
20.
G. Lamer P. Uttley I. M. MHardy 《Monthly notices of the Royal Astronomical Society》2003,342(3):L41-L45
We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing Explorer ( RXTE ) since 1999 January. During late 2000 and early 2001 we observed an unusual hardening of the 2–10 keV X-ray spectrum which lasted several months. The spectral hardening was not accompanied by any correlated variation in flux above 8 keV. We therefore interpret the spectral change as transient absorption by a gas cloud of column density 2.6 × 1023 cm−2 crossing the line of sight to the X-ray source. A spectrum obtained by XMM–Newton during an early phase of the hard-spectrum event confirms the obscuration model and shows that the absorbing cloud is only weakly ionized. The XMM–Newton spectrum also shows that ∼10 per cent of the X-ray flux is not obscured, but this unabsorbed component is not significantly variable and may be scattered radiation from a large-scale scattering medium. Applying the spectral constraints on the cloud ionization parameter and assuming that the cloud follows a Keplerian orbit, we constrain the location of the cloud to be R ∼ 10–100 light-days from the central X-ray source, and its density to be n H ∼ 108 cm−3 , implying that we have witnessed the eclipse of the X-ray source by a broad line region cloud. 相似文献