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1.
The upper limit for the absorption cross section σ H ext , of dust in Hii regions in the wave-length range 912–504 Å derived by Mezgeret al. (1974), is compatible with that expected for large dust grains, and a gas-to-dust ratio equal to that in the general interstellar medium. The albedo of the small grains must be high for λ>504 Å. This restriction is lifted if the visual extinction cross section of the grains in Hii regions is less than that for grains in the general interstellar medium. New observations of the Orion Nebula indicate that the visual extinction cross section is within a factor 2 of the value in the general interstellar medium.  相似文献   

2.
Absorption systems observed along the line of sights to distant quasars are observed at all redshifts and the full range of the electromagnetic spectrum is needed to recover the variety of transitions of different elements. However, some important elements are found within the Lyman forest and their absorption line profiles need to be analyzed against the presence of possible Ly-α contamination. Considering the cosmological evolution of the number density of hydrogen clouds, the probability to detect uncontaminated metal lines is higher in the UV-Optical region exploited by CUBES. The list of these elements includes some important ones such as D, H2, O?i, N?i, O?vi, Ar?i, P?ii, C?ii, S?ii and B?ii. The determination of some of them in the Damped Ly-α galaxies and their astronomical interest are briefly discussed.  相似文献   

3.
A study of circumnuclear star-forming regions (CNSFRs) in several early-type spirals has been carried out in order to investigate their main properties: stellar and gas kinematics, dynamical masses, ionising stellar masses, chemical abundances and other properties of the ionised gas. Both high resolution (R～20,000) and moderate resolution (R～5000) have been used. In some cases, these regions (about 100–150 pc in size) are composed of several individual star clusters with sizes between 1.5 and 4.9 pc, estimated from Hubble Space Telescope images. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km?s?1, with the Hβ emission lines being narrower than both the stellar lines and the [Oiii]λ5007 Å lines. The twice ionised oxygen, on the other hand, shows velocity dispersions comparable to those of stars. We have applied the virial theorem to estimate dynamical masses of the clusters, assuming that the systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 107 to 108 M⊙ for the full CNSFRs. We obtain oxygen abundances which are comparable to those found in high-metallicity disc Hii regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC3504, 12+log(O/H)=8.85, about 1.5 times solar. The derived N/O ratios are, on average, larger than those found in high-metallicity disc Hii regions, and they do not seem to follow the trend of N/O vs. O/H which marks the secondary behaviour of nitrogen. On the other hand, the S/O ratios span a very narrow range—between 0.6 and 0.8 times solar. Compared to high-metallicity disc Hii regions, CNSFRs show values of the O23 and the N2 parameters whose distributions are shifted to lower and higher values, respectively. Hence, even though their derived oxygen and sulphur abundances are similar, higher values would in principle be obtained for the CNSFRs if pure empirical methods were used to estimate abundances. CNSFRs also exhibit lower ionisation parameters than their disc counterparts, as derived from [Sii]/[Siii]. Their ionisation structure also seems to be different, with CNSFRs showing radiation-field properties more similar to Hii galaxies than to disc high-metallicity Hii regions.  相似文献   

4.
Considering the host galaxy contribution, a spectral decomposition method is used to reanalyzed the archive data of optical spectra for a narrow line Seyfert 1 galaxy, NGC 4051. The light curves of the continuum f λ (5100 Å), and Hβ, He ii, Fe ii emission lines are given. We find strong flux correlations between line emissions of Hβ, He ii, Fe ii and the continuum f λ (5100 Å). These low-ionization lines (Hβ, Fe ii, He ii) have “inverse” intrinsic Baldwin effects. Using the methods of the cross-correlation function and the Monte Carlo simulation, we find the time delays, with respect to the continuum, are $3.45^{+12.0}_{-0.5}~\mbox{days}$ with the probability of 34 % for the intermediate component of Hβ, $6.45^{+13.0}_{-1.0}~\mbox{days}$ with the probability of 65 % for the intermediate component of He ii. From these intermediate components of Hβ and He ii, the calculated central black hole masses are $0.86^{+4.35}_{-0.33}\times 10^{6}$ and $0.82^{+3.12}_{-0.45}\times 10^{6}~M_{\odot }$ . We also find that the time delays for Fe ii are $9.7^{+3.0}_{-5.0}~\mbox{days}$ with the probability of 36 %, $8.45^{+1.0}_{-2.0}~\mbox{days}$ with the probability of 18 % for the total epochs and “subset 1” data, respectively. It seems that the Fe ii emission region is outside of the Hβ emission region.  相似文献   

5.
We analyze the spectral variability for two narrow line Seyfert 1 galaxies, PG 1700+518 and NGC 4051 using the spectral decomposition method. We focus on their optical Fe ii variability to investigate the origin of Fe ii in AGNs. For PG 1700+518, we find that the Fe ii size is about 200 light-days, which is consistent with the Hβ size derived from the empirical R–L relation. For NGC 4051, the [O iii] 5007 Å flux is strongly correlated with continuum flux, suggesting that we should recalibrate the spectral flux on a scale defined by [O iii] flux. The corrected light curves of Fe ii, Hβ, He ii, f λ (5100 Å) are given here. A detailed analysis will be given in the near future.  相似文献   

6.
Radiative lifetimes for excited states in La ii, Ce ii, Pr ii, Nd ii, Sm ii, Yb i, Yb ii, and Lu ii have been determined by means of the beam-foil technique or the zero-field level-crossing method. The lifetimes for La, Ce, Pr, Nd, Sm, and Yb are shorter than those computed by summing the transition probabilities of Corliss and Bozman by a factor of up to ~5. The large discrepancies between the abundance of La, Ce, Pr, Nd, and Sm in the solar photosphere and in meteorites are eliminated or greatly reduced if the abundance determinations of the solar photosphere are based upon the gf values of Corliss and Bozman, corrected for by the present lifetimes.  相似文献   

7.
It is shown that emission lines, first of all the ultraviolet resonance doublet 2800 Mgii, can be used to decipher the internal dynamic structure of QSOs and active galactic nuclei. The electron temperatures of the emission regions of these objects are determined. A hypothesis is proposed explaining the observed broad profiles of the 2800 Mgii line as a summary effect of emission clouds with a Maxwellian velocity distribution. The main physical parameters of emission clouds in QSOs are obtained. A mechanism of formation of emission clouds is suggested: namely, tidal disruption of stars near to a massive compact object.  相似文献   

8.
Thirty four objects appearing in the SharplessCatalogue of H ii Regions with radio flux densities below 0.1 fu* at 1400 MHz, are studied. It is shown that two of them are planetary nebulae, two are reflection nebulae and two weak emission-reflection nebulae. From statistical arguments it is concluded that six may be evolved planetaries while the remaining are faint nearby Hii regions excited by stars of relatively advanced spectral type.  相似文献   

9.
The existence of compact H?ii regions around massive stellar clusters with ages exceeding several Myr challenges our understanding of the physical processes occurring inside such clusters, and their impact on the interstellar medium of the host galaxy. Here, we summarize our recent results dealing with the hydrodynamics of matter ejected by massive stars inside the cluster and show that compact H?ii regions found around some massive clusters may indicate that these are evolving in a bimodal hydrodynamic regime. The latter is characterized by the accumulation of the injected matter in the central, thermally unstable zone, and by the ejection of mass supplied by massive stars in the outer regions of the cluster.  相似文献   

10.
A rocket-borne spectroheliograph designed to take monochromatic pictures of the sun in the Mgii line at 2795.5 Å was successfully launched from White Sands Missile Range on May 20, 1968. A double ?olc birefringent filter with a spectral bandpass of 2.1 Å was used to select the proper wavelength. Pinhole photographs in the soft X-ray region were also secured in the same flight. The Mgii and X-ray photographs are compared with simultaneous Caii and Hα spectroheliograms, radiomaps at 9.1 cm and 3.3 cm, a Fraunhofer map and a magnetogram and some preliminary results are discussed.  相似文献   

11.
The age decay of two indicators of the stellar magnetic activity (λ 2800 Mgii emission flux and λ 10830 Hei equivalent width) have been studied for field solar-type stars. The Li abundance has been used, in most of the cases, as a stellar age indicator. A calibrated decay law for Mgii has been determined and compared with a similar one, recently published, for the Caii K emission. The greater scatter in the Hei results is atributed to the different rotation rates.  相似文献   

12.
We analyzed transient Ca ii H brightening associated with small-scale canceling magnetic features (CMFs) in the quiet Sun near disk center using Ca ii H filter images and Na D1 magnetograms of Hinode/SOT. We found that in most Ca ii brightening events related to CMFs the Ca ii H intensity peaks after the magnetic flux cancellation. Moreover, the brightening tends to appear as a pair of bright points of similar size and brightness overlying a magnetic bipole. Then a new opposite polarity fragment moves to them and cancels out. These results imply that magnetic reconnection takes place there and is responsible for CMFs.  相似文献   

13.
Based on the calibrated maps in the Hα andV bands, simple shell models for the distributions of ionized gas and dust are calculated for the smallHii regions S237 and S254–S257. In deriving the dust distribution from theV-band maps, it is assumed that scattering particles are made of dirty ice. The results of calculation show that a dust depletion zone should be placed in the central region of each of the observedHii regions. The formation of this dust depletion zone and the evolutionary state of theseHii regions are briefly discussed.  相似文献   

14.
Examination of the stellar spectrum of this star reveals that it has a composite spectrum. It could be classified as (A7V+G5V). It contains three forbidden [Feii] lines which are of the essential features of η Carinae stars. The spectrum also contains H, Hei, Feii, Mni, Tiii, and other different lines. The K-line seems to be sharp double line while other lines appear single ones which suggest early component may be double. This also seems to be true according to radial velocity measurements.  相似文献   

15.
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.  相似文献   

16.
On the coronograph spectrophotographic records taken on 31.372 UT, August 1979, some faint emission features were found which can be ascribed to Siii and Niii. These emissions were obviously a transient phenomena which were detected only 10 hr after the supposed fall of Comet 1979 XI in the Sun's photosphere. It cannot be excluded that the appearance of Si and Ni lines was triggered by the evaporation of dust particles with a high abundance of heavier elements in the solar corona. This assumption is also supported by intensity distribution of the Fex coronal line around the Sun's limb. The maximum coincide with the position angle of the projected path of the comet.  相似文献   

17.
The relative Doppler velocities and linewidths in a polar coronal hole and the nearby quiet-Sun region have been obtained from the Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) observations using emission lines originating at different heights in the solar atmosphere from the lower transition region (TR) to the low solar corona. The observed region is separated into the network and the cell interior, and the behavior of the above parameters were examined in the different regions. It has been found that the histograms of Doppler velocity and width are generally broader in the cell interior than in the network. The histograms of Doppler velocities of the network and cell interior do not show significant differences in most cases. However, in the case of the quiet Sun, the Doppler velocities of the cell interior are more blueshifted than those of the network for the lowermost line He?ii 304 Å, and an opposite behavior is seen for the uppermost line Mg?ix 368 Å. The linewidth histograms show that the network–cell difference is more prominent in the coronal hole. The network has a significantly larger linewidth than the cell interior for the lowermost TR line He?ii 304 Å for the quiet Sun. For the coronal hole, this is true for the three lower TR lines: He?ii 304 Å, O?iii 599 Å, and O?v 630 Å. We also obtained the correlations between the relative Doppler velocity and the width. A mild positive correlation is found for the lowermost transition-region line He?ii 304 Å, which decreases even more or become insignificant for the intermediate lines. For the low coronal line Mg?ix 368 Å, the correlation becomes strongly negative. This might be caused by standing waves or waves propagating from the lower to the upper solar atmosphere. The results may have implications for the generation of the fast solar wind and coronal heating.  相似文献   

18.
A complex eruptive event took place on January 17, 1974 at approximately 19:20 UT in McMath Hulbert Plage No. 12 686, located near N 06o and behind the west limb. The effects were recorded by the XUV spectroheliograph on Skylab from 19:44 UT to 20:46 UT. An eruptive prominence of spray was observed in Heii 304 Å to reach >1R s. It was also photographed in many emission lines at temperatures reaching 1 MK in Mgix. There were at least four other parts of the eruption, each changing character differently with temperature. These first appeared with Ne.vii at 0.6 MK, and were recorded in lines of ions up to Fexvi at 2.6 MK.  相似文献   

19.
We present an investigation of line-of-sight (LOS) velocity oscillations in solar faculae and sunspots. To study the phase relations between chromospheric and photospheric oscillations of the LOS velocity, we measured the time lag of the chromospheric signal relative to the photospheric one for several faculae and sunspots in a set of spectral line pairs. The measured time lags are different for different objects. The mean measured delay between the oscillations in the five-minute band in faculae is 50?s for the Si?i 10?827?Å?–?He?i 10?830?Å pair; for the pair Fe?i 6569?Å?–?Hα 6563?Å the mean delay is 20?s; for the pair Fe?i 4551?Å?–?Ba?ii 4554?Å the mean delay is 7?s; for the pair Si?i 8536?Å?–?Ca?ii 8542?Å the mean delay is 20?s. For the oscillations in the three-minute band in sunspot umbrae the mean delay is 55?s for the Si?i 10?827?Å?–?He?i 10?830?Å pair; for the Fe?i 6569?Å?–?Hα 6563?Å pair it was not possible to determine the delay; for the Fe?i 4551?Å?–?Ba?ii 4554?Å pair the mean delay is 6?s; for the Si?i 8536?Å?–?Ca?ii 8542?Å pair the mean delay is 21?s. Measured delays correspond to the wave propagation speed, which significantly exceeds the generally adopted speed of sound in the photosphere. This raises the question of the origin of these oscillations. The possibility that we deal with slow MHD waves is not ruled out.  相似文献   

20.
This paper contains a model of supernova remnant IC 443 and the interstellar gas surrounding it. The basis of this model is the analysis of the motion of non-spherical adiabatic shock waves due to Kompaneets (1960). Observations of adjacent Hi and Hii regions have been used by several authors to determine the density of gas in the neighbourhood of IC 443. The model gives for the explosion energy and age of IC 443, 1.8×1050 erg and 13 000 yr, respectively. The expansion velocity of IC 443 using the present model is in reasonabel agreement with observations of the remnant.  相似文献   

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