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1.
There are about 50 galactic planetary nebulae know to have [WR] type nuclei. We have compared their nebular properties with those of the other planetary nebulae in the Galaxy. We have found that the nebular morphological types are similarly distributed in the two groups. Bipolar nebulae constitute only 20% of the total in each group. The distribution of the nebular electron densities and abundance ratios N/O, He/H and C/O are the same in the two groups. The only marked difference is that nebular expansion velocities are larger in the group of planetary nebulae with [WR] central stars. We argue that the WR phenomenon does not preferentially occur in more massive central stars of planetary nebulae, contrary to what has been suggested in some former studies. We demonstrate that, for most of the observed [WR] type objects, the WR phenomenon cannot be triggered by a late helium shell flash event.The results of our investigation are published inAstronomy & Astrophysics 303, 893 (1995) and in the proceedings of the 2nd International Colloquium on Hydrogen-deficient Stars, C.S. Jeffery & U. Heber (eds), Astronomical Society of the Pacific Conference Series, Vol. 96, p. 209 (1996).  相似文献   

2.
The status of planetary nebulae with Wolf-Rayet type central stars([WR] PN) remains one of the most important problems inthe investigation of planetary nebulae. We cannot claim to understand theevolution of low and intermediate-mass stars without answering the questionhow [WR] PN are created.Analyzing the statistical properties of the whole population of [WR] PNand comparing them to other planetary nebulae (non-[WR] PN) bringsimportant information on their origin and evolutionary status. In thisarticle I will summarize our results of this type of studies and show whatlimits they put on the possible evolutionary routes of [WR] PN creation.  相似文献   

3.
We present the first results of a spectroscopy survey of iras sources with colours similar to those of planetary nebulae.Two new planetary nebulae, some H emission line stars, one peculiar source which is probably a pre-Main-Sequence object and a new Seyfert I galaxy have been found.Based on observations collected at the European Southern Observatory, La Silla, Chile.  相似文献   

4.
A number of criteria are elaborated based on the careful analysis of nebulae images which confirm the version of the origin of double-envelope planetary nebulae by means of dynamical separation but not by multiple ejection. The importance of stellar winds in the origin of the gigantic halos around double envelope nebulae is outlined. The problem concerning the existence of two types of filamentary planetary nebulae (Figure 8) is raised: type A, filaments are the fragmentations of the Rayleigh-Taylor instability, the result of dynamical interaction of the envelope with the outer interstellar matter (NGC 6543), and type B, the origin of filaments is connected with the Magnetic field fluctuations (A 43, A 72).The possibility of the origin of three-envelope nebulae in the framework of the dynamic separation version is discussed (NGC 7293). Attention is paid to the impossibility of outbursts with low velocities (20–30 km s–1) from hot stars, i.e., the nuclei of nebulae.  相似文献   

5.
C12 stars in the range 1.04–1.55M are evolved to simulate the core evolution of the possible precursors of planetary nebulae. The nuclear shell burning in stars above 1.2M advances to within about 0.2M of the surface, where the intense radiation interacts with the surface matter and causes mass loss. Comparison between our theoretical results and observations suggests that this may be a mechanism by which planetary nebulae are formed.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.  相似文献   

6.
A principally new, quantitative system of the classification of the spectra of planetary nebulae is proposed. Spectral class of excitation class of the nebulap is determined according to the relative intensities of emission lines (N 1+N 2) [OIII]/4686 HeII and (N 1+N 2) [OIII]/H (Table I, Figure 1). The excitation classes are obtained for 142 planetary nebulae of all classes—low (p=1–3), middle (p=4–8), and high (p=9–12+) (Tables II, III, and IV). An empirical relationship between excitation classp and mean radius of nebulae is discovered (Figure 2). This relationship as well as excitation classp, as an independend parameter, admit an evolutionary interpretation. It is shown that after reaching the highest class of excitationp=12+ the nebulae decrease their class of excitation with the further increases of sizes. The diagram of this relationship has two nearly-symmetric branches — rising and descending with the apogee onp=12+ (Figure 2).  相似文献   

7.
A search (using the Infrared Astronomical Satellite IRAS point source catalogue) for infrared counterparts of the fourteen new candidates for planetary nebulae of low surface brightness detected by Hartl and Tritton (1985), resulted in only five identifications. The infrared sources of four of these candidate nebulae are found within 5 are sec of their optical position and the fifth one within 1 are min. Two of the five nebulae identified with infrared sources are classified as true, one as probable and two as possible by Hartl and Tritton (1985). All the five nebulae are found in regions of high cirrus flux at 100 m. These nebulae are all found to have both point sources as well as small size extended sources (in the IRAS scan windows centred on the sources), with numbers varying from field to field. The infrared emission from these nebulae have dust temperatures 100K (characteristic of planetary nebulae). Four of the nebulae appear to be faint in the infrared (just as in the optical band) with total infrared flux of 2×10–13 W m–2. Only the PN candidate No. 12 appears to be very bright in the infrared. It is likely that part of the emission is from extraneous sources in the line-of-sight to the nebula.  相似文献   

8.
We review our recent results concerning the molecular gas content of young planetary nebulae NGC 2346, M 2–9, and NGC 6720 (the Ring Nebula in Lyra).Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

9.
Three southern planetary nebulae (NGC 2818, He 2-130, and NGC 3132) have been observed with the IDS (Image Dessector Scanner) combined with the Boller and Chivens spectrograph mounted at the Cassegrain focus of the 1.52 m telescope of the ESO in Chile. The spectrograph dispersion was 60 Å mm–1 in the spectral range 6170–7298 Å. The slit aperture was 4×4. Spectra were obtained from an array of positions across each nebula along the E-W direction and/or N-S direction. The data reduction followed the standard IHAP routines for IDS observations. In order to derive electron density, only the [Sii] lines (6617 Å–6731 Å) are given in this paper. The results are in agreement with a shell structure for the observed nebulae.

Toutes les observations ont été faites à l'Observatoire européen Austral (ESO) au Chili.  相似文献   

10.
The central stars of two of the new planetary nebulae found during scans of the AAO/UKST H α Survey of the Milky Way have been found to exhibit Wolf–Rayet (WR) emission features. One (PMR 1) is an early-type star of class either [WO4] or [WC4]. The other (PMR 2) is a late [WC] star which, depending on the classification scheme used, is either intermediate in class between [WC9] and [WC10] or the sole member of the [WC10] class. Both stars exhibit unusual spectral features which may be attributed to enhanced nitrogen in their atmospheres and could be indicative of unusual stellar evolution.  相似文献   

11.
The possiblity of the excitation of a new class of spectral lines, so calledpseudo-resonance absorption lines in the conditions of planetary nebulae, is predicted. These lines are formed by permitted atomic transitions from the metastable levels to the upper subordinate, but not metastable, levels. To observe pseudo-resonance lines of nebular origin is possible only on the spectra of the nuclei of planetary and diffuse nebulae in the form of absorption lines.The preliminary list of pseudo-resonance lines is given in Table I; all of them are located in the region of vacuum ultra-violet (1000–3000 Å), therefore, their observation is possible only under space conditions.In stellar photospheres as well as in the interstellar medium the formation of pseudo-resonance lines is impossible.  相似文献   

12.
The recent evolution of the central star of the planetary nebula LMC-N66 is presented. Before 1987, it showed a weak continuum with aT eff120 000 K andL bol25 000L and in a few years it developed strong WR features (P Cygni line profiles in N v at 124.0 nm and C IV at 155.0 nm, wide Heii emission, etc.) typical of a WN 4.5. Additionally the stellar continuum increased by a large factor and the absolute visual magnitude of the star changed from + 1.24 in 1987 to–2.57 in January, 1995. The WR features and enhanced continuum, evidencing a powerful mass-loss event remained with small variations for more than 5 years. Recent ultraviolet and optical data shows that the mass-loss seems to have diminished abruptly in the last three months.  相似文献   

13.
The evolution of nuclei of planetary nebulae has been calculated from the end of the ejection stage that produces the nebulae to the white, dwarf stage. The structure of the central star is in agreement with the general picture of Finzi (1973) about the mass ejection from the progenitors of planetary nebulae. It has been found that in order to obtain evolutionary track consistent with the Harman-Seaton track (O'Dell, 1968) one has to assume that the masses of the nuclei stars are less than 0.7M . The calculated evolutionary time scale of the central stars of planetary nebulae is 2×104 yr. This time scale is negatively correlated with the stellar mass: the heavier the stellar mass, the shorter the evolutionary time scale.  相似文献   

14.
Pseudo-resonance absorption lines in planetary nebulae: Discovery?   总被引：1，自引：0，他引：1  
The possibility of the formation of pseudo-resonance absorption lines in planetary nebulae is predicted only theoretically. However, this has not been confirmed by direct observations. In the present article an attempt has been made to show, as a result of careful analysis of IUE spectral recordings for a group of planetary nebulae, that the existence of one pseudo-resonance line 1300 SiIII is without doubt at least in spectra of three planetary nebulae: NGC 2610, NGC 3587, and NGC 6891. The presence of this line in the spectra of the other three planetary nebulae, NGC 6210, IC 3568, and IC 4776, seems to be probable. The role of the interstellar selective absorption, the blending effect by the resonance lines of SiII,Oi, andSi in the formation of the pseudo-resonance line 1300 SiIII as well as the possibility of formation of this line in the photosphere of central star of nebula were analysed.  相似文献   

15.
Optical identification of infrared sources from the IRAS Point Source Catalogue (PSC) is made by means of low-dispersion spectra of the First Byurakan Survey (FBS) and Palomar Observatory Sky Survey (POSS) red and blue images. The purpose of this work is to examine the composition of the PSC sample of fainter sources at high galactic latitudes and to reveal QSOs, infrared galaxies, red stars (C and M), planetary nebulae, for their further investigation at the optical range. 100 of 108 unknown IRAS sources in the region with 3h50m 7h40m and + 69° + 73° are optically identified. Optical coordinates, V magnitudes, color indices, and preliminary classes are determined. According to preliminary classification 3 objects turned out to be QSOs, 36 are galaxies with very interesting morphology, 5 are faint planetary nebulae, 9 are carbon stars, and 47 are late M-type stars.Published in Astrofizika, Vol. 38, No. 4, pp. 625–629, October–December, 1995.  相似文献   

16.
The modern self-consistent photoionization model of planetary nebula luminescence is described. All of the processes which play an important role in the ionization and thermal equilibrium of the nebular gas are taken into consideration. The diffuse ionizing radiation is taken into account completely. The construction of the model is carried out for the radial distribution of gas density in the nebular envelope which is consistent with isophotal map of the nebula. The application of the model is illustrated on the example of the planetary nebulae BD+30°3639 and NGC 7293. It is shown that the continuum of the central star at 912 Å does not correspond to the blackbody spectrum but agrees with the spectrum of corresponding non-LTE model atmosphere. The radial distributions of electron density, electron temperature, and other parameters in the nebular envelopes are found.The evolution of the radial distribution of gas density in the planetary nebulae envelopes is investigated. Approximative analytical expression which describe both such distribution and its change with time is adjusted. It is shown that the nebular envelope is formed as a result of quiet evolution of the slow stellar wind of star-precursor, and the formation of the envelope begins from the decrease of star-precursor's mass loss rate. Obtained radial distributions of gas density in the envelopes of young nebulae rule out the idea that the planetary nebula is formed as a result of a rapid ejection of clear-cut envelope. So, there is no necessity for the superwind which is used for this purpose in theoretical calculations.A new method of the determination of planetary nebulae abundances is proposed. Unobserved ionization stages are taken into account with aid of the correlations between relative abundances of various ions which had been obtained from the grid of the photoionization models of planetary nebulae luminescence. Simple approximative expressions for the determination of He/H, C/H, N/H, O/H, Ne/H, Mg/H, Si/H, S/H, and Ar/H are found. The chemical composition of 130 Galactic planetary nebulae is revised. A comparative analysis of the abundances in the Galactic disk, bulge, and halo nebulae is carried out.  相似文献   

17.
We present a detailed, quantitative study of the standard [WC10] Wolf-Rayet central star CPD-56o 8032 based on new high resolution AAT UCLES observations and the Hillier (1990) WR standard model. Our analysis of CPD-56o 8032 gives the wind properties (T *=34500K, lg (L/L )=3.8, lg (M/M a–1)=–5.4,v =225 km s–1) and chemistry (C/He=0.5, O/He=0.1, by number), the latter suggesting an intimate relationship with the Ovi PN central stars and the PG 1159-035 objects. A comparison between the wind properties of CPD-56o 8032 and Sk-66o 40 (WN 10) indicates that low excitation, low wind velocity WR winds are common to both low mass PN central stars (WC sequence) and high mass post-LBV's (WN sequence).  相似文献   

18.
This paper presents new observations of 97 planetary nebulae in the Large Magellanic Cloud (LMC) obtained using the FLAIR system on the UK 1.2-m Schmidt Telescope. These nebulae are mostly at the fainter end of the known population, and about 75 per cent have not been observed before in spectroscopic mode. Radial velocities have been measured using cross-correlation techniques, and represent an increase of 66 per cent in the sample of LMC planetary nebulae with known radial velocities. The major line ratios are given, and are analysed in conjunction with published data. One-quarter of the faint nebulae are Type I objects with very strong [N II ] and [S II ] lines; most of the other faint nebulae have low density, low excitation and relatively strong [S II ] lines.  相似文献   

19.
Linear correlations between the diameter log of ring-shaped nebulae and the total number logN of embedded stars for two absolute magnitude levels of –2m and +2m for the LMC have been found. This shows that less luminous stars are also contributing towards the illumination of the nebulae. A method for the determination of relative ages of these loop nebulae is described.Based on observations collected at the Boyden Observatory, Bloemfontein, South Africa and the European Southern Observatory, La Silla, Chile.  相似文献   

20.
The evolution of 1.40M pure He star is calculated from the stage of the ignition in the center up to the very advanced stage of evolution where mass ejection by the very luminous He shell could occur. It is found that C12 does not ignite by a modest margin. Subsequent evolution and relation to the central stars of planetary nebulae is discussed.  相似文献   

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