The physical parameters and exciting stars of six Hii regions

The radio spectra of particular radio sources (mainly Hii regions) are plotted on the same graph for comparison. Various physical parameters of these objects are obtained from the radio data through a model. Predictions about the number and the nature of the exciting stars of six Hii regions are made. A comparison with the so far identified exciting stars is also presented.     

Study of a triple emission nebula in Orion

The Hii regions S254, 255 and 257 in the constellation of Orion are close together on the sky and appear like a triple object. Fabry-Pérot radial velocities of the Hii regions as well asUBV photo-electric magnitudes of their exciting stars are obtained. The data show that (1) all three nebulae are at a distance of 2.5 kpc; (2) an excess extinction is observed in S255 and S257 while S254 shows no excess extinction; (3) S255, identified as an IR and a molecular source, is the youngest object of the group. It is concluded that the three Hii regions are at different evolutionary stages.     

The radio spectra and physical parameters of some extended radio sources in monoceros

The radio spectra of the Rosette Nebula, the source S280 and the Monoceros Nebulosity are established over a wide range of frequencies. The radio spectra of the Rosette Nebula and S280, show a typical thermal shape. Physical parameters of both Hii regions are derived by adopting a spherical model.The radio spectrum of the Monoceros Nebulosity shows a non-thermal shape (sp. index –0.66) but the exact nature of the object is not clear. Assuming it is an SNR some of its physical characteristics are estimated.     

On the observed infrared fluxes from extragalactic Hii regions

We have calculated for extragalactic Hii regions, the expected relationship between the radio flux at 11 cm and the infrared flux at 11 and 20 m based on the grain models and the parameters which fit the observations of galactic Hii regions. It is shown that the measured infrared fluxes of extragalactic Hii regions are consistent with the expected infrared fluxes for these objects.     

Physical conditions in NGC 6164-5

From spectroscopic observations of the emission lines H, 4959 and 5007[Oiii], H, 6584[Nii], 6717 and 6731[Sii] and some interferometric data in H and [Nii] it was established that NGC 6164 and NGC 6165 have characteristics of normal Hii regions for Ne and Te. They are embedded in a very tenuous medium nearly coincident with the Strömgren sphere of the central star HD 148937, corresponding to the outer peripheral structure described by Westerlund. Variations of the relative abundances of N, O, and S are discussed.     

Giant infrared bubble in Cepheus

A ring-shaped infrared emission region is recognizable on the IRAS Sky Flux images of a Cepheus region which happens to include the association Cepheus OB 2. The ring is easily visible both at 60 and 100 microns. The approximate galactic coordinates of its centre arel=102°.8 andb=+6°.7, with an outer diameter of 7 deg. IC 1396 and several otherHii regions, such as S 129, S 133, S 134, and S 140 are apparently parts of the ring. If it is assumed that these Hii regions are physically connected to the ring its distance must be about 900 pc and its diameter 120 pc. The existence of several arc-shaped H filaments along the ring, the proper motion of the nearby runaway star Cephei, and the possible presence of the [Fex] 6375 interstellar line in the spectra of two stars of Cep OB 2 combine to suggest that the infrared ring might well be a result of a supernova explosion which occurred in this region about 2–3 million years ago.     

Solar Cii resonance line profiles

The profiles of the solar Cii resonance doublet λ1334.6 A are presented. Possible broadening mechanisms are discussed.     

The forbidden line [Ca ii] λ7323 in the fraunhofer spectrum

New observations of the [Caii] 7323 Fraunhofer line are reported. The blending H₂O line was weak at the time of observation. Accurate estimates of the centre-limb variation of the equivalent width of the [Caii] transition are obtained and shown to be consistent with the calcium abundance log N(Ca) = 6.33.     

Observations des bords brillants dans NGC 281, IC 434 et M 16

Sommaire Les photographies monochromatiques en H, [Nii] 6584 et [Oiii] 5007 ont été obtenues sur NGC 281, IC 434 et M 16 eu vue de la détection et de l'étude des bords brillants. A partir de ces photos, on accède à la carte d'égal rapport [Nii]/H grâce à la méthode décrite par Louise et Sapin (1972). A l'exclusion des bords brillants, ce rapport varie très peu à l'intérieur d'une même nébuleuse. Par contre à l'approche des fronts d'ionisation, il augmente de façon spectaculaire et systématique.Le renforcement de la raie [Oiii] vers les bords brillants suggère la présence des inhomogénéités (globules ou/et filaments) et le rôle possible que jouent les mécanismes d'échange de charges étudiés par Aller et Keyes (1980).

---

Observations of bright rims in NGC 281, IC 434 and M 16

Monochromatic plates are obtained in H, [Nii] 6584 and [Oiii] 5007 lines for three Hii regions: NGC 281, IC 434 and M 16. They allow both detection and physical studies of bright rims. Indeed, it is shown that bright rims appear most contrasted on [Nii] and [Oiii] plates. Furthermore, maps of ratio [Nii]/H are derived from the method described by Louise and Sapin (1972). This ratio remains practically constant within the nebula, except for bright rims where it increases. This may be understood by means of both increasing abundanceN(N⁺/N(H⁺) and temperature following to the model of Mallik (1975).The [Oiii] enhancement towards bright rims in M 16 suggests the presence of inhomogeneities (globules or/and filaments) and the possible role played by charge exchange mechanisms as pointed out by Aller and Keyes (1980).

     

Preliminary results from the spectra of V471 tauri

The findings about this unusual eclipsing variable which possesses a white-dwarf component are reported. It was found that the H and K absorption lines of Caii are strongly pressure-broadened, and exhibit two double-reversal emission components. The radial velocities derived from the central strong emission components of Caii (H and K) are in agreement with the mean radial velocity curve obtained from the metallic absorption lines of the existing elements, whereas H (4340.47 Å) does not conform with the mean radial velocity curve. In certain orbital phases the H (6562.82 Å) line occurs in emission.     

A systematic radial velocity survey of the HII regions IC 1318a and HS 191

The results of a systematic radial velocity survey of two Hii regions in the Cygnus-X complex are presented. The [Nii] emission line components obtained at many positions over each object have been compared and correlated with other phenomena. It is suggested that they are probably connected objects and may be part of a giant shell or cylinder.     

The velocity structure of S54 and S142

The velocity structures of two extended, low-density and low-temperature Hii, regions S54 and S142, have been examined. Both exhibit an ionized sheet structure.     

Chemical abundances of the WR-ring nebulae NGC 2359 and RCW 78

We report on extensive spectroscopic observations of the WR-ring nebulae NGC 2359 and RCW 78, respectively, excited by the WN5 stars HD 56925 and WN8 HD 117688. For the first object we have determined abundances for O/H, Ne/H, N/H, and He/H in many different positions, including the ionized gas in the bubble, inside the optical shell structure, and the outermost zones associated with the S 298 Hii region. We do not find any significant difference in the N/H and O/H abundances over the entire nebula. The O/H and N/H abundances expected are close to those for a normal Hii region located at similar distance. In the case of He/H we find indication of local enhancements which sum to the abundance of metal rich galactic Hii regions like M17. RCW 78 appears to show slight overabundances of He/H and N/H in the two observed positions.The ionising temperature for the WN central star (HD 56925) of NGC 2359 is determined from the observed Hii region spectrum giving a value of 50000 K, appropriate to its spectral type.     

The Balmer 9 and Balmer 11 lines of He ii in the Sun

We identify the Balmer 9 and 11 lines of He ii at 959 Å and 942 Å in solar spectra. These lines are produced mainly by recombination following photoionization of He ii by coronal XUV radiation. From analysis of the line intensities, we confirm the theoretical model of Avrett et al. (1976), who found that an appreciable amount of He⁺⁺ is present at temperatures of 1–2 × 10⁴ K and that the anomalously strong He ii 304 line is produced primarily by collisional excitation. We also confirm the suggestion of Kohl (1977) that the photoionization-recombination process is more important in active regions than in the quiet Sun, and we find that the 304 line is produced largely by recombination in solar flares.     

Narrow band CCD imagery of southern galaxies in strong lines and continua: NGC 613

CCD narrow band imagery of the southern barred spiral NGC 613 has been obtained in the light of H, H, [Oiii] 5007 Å, [Oii] (3726+29) Å and continua at 3765, 5230, and 6500 Å. Absolute fluxes have been obtained for the lines H and [Oiii] 5007 Å and continua at 5230 and 6500 Å. Distribution of ages, monochromatic colour vs absolute brightness and [Oiii]/H are discussed.     

Raies nébulaires et coronales dans le spectre infrarouge de la Nova Delphini

Nova Delphini 1967 has been observed in the red and photographic infrared at the Haute-Provence Observatory from September 7 to November 12, 1968. Dispersions range from 230 Å/mm to 4 Å/mm. The slope of the continuous spectrum in the region 1.3–1.7 ^–1 leads to a gradient of 3.06, which did not appear to vary during the observing period. This gradient is, however, very different from the value 1.71 measured on plates secured in August 1968. Lines ofHi, Hei, Heii, Feii,Oi,Cii and forbidden transitions due toOi,Oii, Fevii, Fex, Fexi,Siii,Aiii,Av,Axi and Nixv have been identified. Their intensities at various dates are given in Table II. Line profiles could be measured for a few lines taken on a 39 Å/mm spectrogram on October 3. Hei 6678 and 7065 are displayed on Figures 2 and 3. Figure 4 gives the [Oii] doublet at 7319–7330, while the H profile, obtained on October 4 can be seen on Figure 5. The line extends over more than 45 Å and narrow absorptions are seen at 6551.05; 6555.75; 6563.15; 6571.49; 6574.45. Due to the absence of published data on radial velocities of absorption lines in the visible spectrum at that time, it is not possible to give a clear identification for these features. Some of them may belong to H, while others are probably due to metals.     

Some physical considerations on NGC 1313

The ionized gas in NGC 1313 was studied by spectrophotometric means. The radial behaviour of theI(H)/I(6584),I(6717)/I(6731),N(Nii)/N(Hii), andN(Nii)/N(Sii) ratios and the deduced electron densities are discussed. The abundance ratiosN(N)/N(H) andN(N)/N(S) for the nucleus and two emission regions were also derived and compared with previous data.     

Planetary nebula with a neutral envelope?

IUE ultraviolet spectral recording for a low excitating planetary nebula NGC 6369 is obtained. The very strong doublet 2800 Mgii in emission as well as not less strong absorption line 2852 Mgi are discovered in the spectrum of this nebula. It is shown that the resonance line 2852 Mgi may originate only in a neutral envelope, around the nebula, consisting of neutral hydrogen, neutral magnesium, and dust particles (Hi+Mgi). The importance of this absorption line as a powerful indicator of the discovery of neutral envelopes around the planetary nebulae is outlined.The possibility of the existence of one more envelope—transition zone—immediately contacting with the bright that is ionized part of nebula (Hii+Mgii) is also shown. The transition zone consists of neutral hydrogen, ionized magnesium, and dust particles (Hi+Mgii), main parameters of this zone are also obtained (Table IV).The temperature of the central star of this nebula is obtained for the first time:T _*=48000 K. Continuous background in the interval 2600–3000 Å is identified with Balmer continuum with electron temperatureT _e =12500 K.     

The UV spectrum of the binary system TY Pyx

A detailed list and analysis of line identifications of five UV spectra of the RS CVn-type binary system TY Pyxidis are presented. These spectra are recorded at different phases with the International Ultraviolet Explorer (IUE). Two of them are in the wavelength range1235–1950 Å while the other three in the range2700–3110 Å.The far-UV spectrum of TY Pyx is mainly an emission spectrum dominated by the emission lines of the ions:Ci, Oi, Cii, Siii, Heii, Alii, and Feiii. We also pointed out the existence of a Feiii [34] line in absorption.The UV spectrum between 2700–3110 Å is dominated by weak absorption lines. Two satellite components are indicated for many lines, which correspond to the two stars of the system, in the two out of the three spectra (LWP 13386 and LWP 13347).Violet emission wings are observed for Fei [1], Tii [1],Oiv [1], and Siiii [1]. The UV spectrum of TY Pyx is also characterized by the multi-structure of Mgii [1] resonance lines.Based on data from the International Ultraviolet Explorer, de-archived from the Villafranca Data Archive of the European Space Agency.     

Theoretical models of planetary nebulae

Sets of theoretical models of spherically symmetrical gaseous nebulae are calculated for a fixed chemical composition and with central star, energy distributions given by Cassinelli (1971) and by Kunasz, Mihalas and Hummer (1975). A central region of constant densityN _H=100 cm^–3 is surrounded by a broken shell consisting of zones of different density and optical thickness. It is found that for a fixed chemical composition and central star flux, a considerable range can be found in the emitted fluxes of certain lines such as 4686 which are often used to fix the level of excitation of a nebula. Although it is possible to produce models yielding a variety of nebular line ratios in this way, these truncated inhomogeneous shell models have not reproduced the integrated spectra of nebulae that simultaneously show extreme features of high and low excitation with great strength-e.g. [Nii], [Oii] and 4686 Heii.