Evolution du spectre de la Nova Delphini 1967 en 1971 et 1972

Continued spectroscopic observations of Nova Del 67 during 1971 and 1972 show a general decrease of the nebular and coronal emission with respect to the local continuum. The continuous spectrum exhibits a strong Balmer emission (figure 1). Equivalent widths of Hi, Hei, Heii, Oi, [Oi], Oii, [Oii], Oiii, [Oiii], Niii, [Sii], [Aiii], [Neiii], [Nev], [Fevi], [Fevii], [Fex], [Fexi], [Fexiv], [Nixvi], [Nixv] are listed in tables 1 and 2.Figures 5 to 10 show several line profiles, which can be interpreted in terms of a model proposed by Hutchings (1972). Kinematical properties of the nova envelope do not seem to have changed in the 1968–1972 time interval. However, a study of the [Oiii] (4959 Å) line indicates that the physical conditions in the polar blobs in 1972 (T _e=10 660 K,N _e=5,5×10⁵ cm^–3) are different from those prevailing in equatorial rings (T _e=9×100 K,N _e=7×10⁵ cm^–3).

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Le matérial d'observation utilisé pour cette étude a été obtenu à l'aide de téléscopes de 120 cm, 152 cm et 193 cm de l'Observatoire de Haute-Provence (CNRS).     

Spectral evolution of Nova V400 Per (1974) and Nova V373 Sct (1975)

Photographic and spectroscopic observations of the two galactic novae, V400 Per and V373 Sct, which appeared in 1974 and 1975, have been carried out at Asiago. The light curves of the two novae were characterized by the presence of brightness oscillations during the early decline. The spectral evolution was quite normal: the spectra showed at first, over a relatively strong continuum, wide emission bands of moderate excitation, accompanied by blueshifted absorptions, with radial velocities of –1760 km s^–1 (Nova Per) and –1260 km s^–1 (Nova Sct). Later, after the novae entered the nebular stage, the continuum weakened, the absorption disappeared and the novae displayed the usual emission spectrum, with permitted and forbidden lines of high excitation ([Oiii], Niii, Hei, Heii). Forbidden lines of Fevi and Fevii-and in Nova Sct, also Fex and Ax-were present for a time, but they soon disappeared, so that at the end the spectrum was dominated by the [Oiii] nebular lines, even stronger than H.     

Densities and mass motions in transition-zone plasmas in solar flares observed from Skylab

We studied the EUV line spectra of three flare observed with the NRL slit spectrograph on Skylab. The electron densities in the flare transition-zone plasmas are determined from density-sensitive lines of Si iii and O iv. The electron densities in all three flares studied were greatest during the flare maximum with values of the order of 10¹² cm^–3. The density decreases by a factor of 2 to 3 in the decay phase of the flares. The intensities of EUV lines from the flare chromospheric and transition-zone plasmas all are greatly enhanced. In contrast to lines for Oi, Ci, Feii and other chromospheric ions, the lines of Oiv and Nv and other transition-zone lines are not only enhanced but also very much broadened.Fitting of the N v 1242 Å line with a two-gaussian model shows that for two of the flares studied, there is a red-shifted component in addition to an unshifted component. The shifted component in the N v line profiles is interpreted as due to a dynamic and moving plasma with a bulk motion velocity of 12 km s^–1 for one flare and more than 70 km s^–1 for the other. The broadened line profiles indicate that there are large turbulent mass motions with random velocities ranging from 30 to 80 km s^–1.Ball Corporation. Now with NASA/Marshall Space Flight Center.     

Nova Delphini 1967. Observations du spectre nebulaire entre 5600 et 8800 Å en 1970

Five 230 Å/mm infrared spectra of Nova Delphini 1967 have been obtained from May to September 1970 on Kodak hypersensitized IN plates. Visual brightness has dropped by one magnitude between fall 1969 and fall 1970. The continuous spectrum remains strong and a mean value of 2.35 is found for the gradient in the region 6000–8000 Å, indicating a slight increase in temperature since 1969. Permitted lines ofHi,Oi, Hei, Feii are weakening, while intensities of forbidden transitions due [Nii], [Fevii], [Oi], [Oii], [Aiii], [Av], [Fevii], [Fex], [Fexi], [Fexi], [Nixv] are much more stable At the dispersion of our spectra, there is little evidence of activity in the nova shell during 1970. Temperature seems to be slightly increasing in the lower layers as well as in the external, low density regions.

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Les observations ont été effectuées à l'Observatoire de Haute-Provence (C.N.R.S.)     

The far UV spectrum of the Be star AX Monocerotis

In this paper we study the main features of the far UV spectrum of the binary star AX Mon, observed with the IUE satellite at phase 0.568.Ions indicating a large range of ionization stages, going fromCi,Oi,Ni toSiv,Civ,Nv are present.The spectrum is dominated by shell absorption lines of Feii, Feiii, Siiii,Cii, Alii, Mgii and Niii.Two satellite components are clearly indicated in all these lines except for Niii which presents only one. Their mean velocities are +10±5 km s^–1, –75±10 km s^–1, and –260±15 km s^–1.Red emission wings are observed in the Mgii resonant doublet at 2800 Å, which shows a P Cygni profile. Each of the absorption lines of the Mgii doublet is formed by a narrow component, which is blended with the Mgii interstellar line and a broad component, which shows a complex structure.Broad and asymmetrical profiles are observed for the Siiv,Civ, andNv resonance lines with blue edge velocities about –700±30 km s^–1.     

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.     

Rosat and EUVE observations of B stars

Recent observations of the X-ray and EUV emission of non-supergiant B stars are summarized. As compared with O stars, the X-rays of most of the near-main-sequence B stars are soft, and the stars show a departure from theL _x = 10^?7 L _bol relation. Using line driven wind models to provide an estimate of the density distribution, it is concluded that a major fraction of the wind emission measure is hot, whereas in shocked wind theory less than 10 percent of the wind emission measure should be hot. The X-ray observations suggest that all of the B stars are X-ray emitters with a basal X-ray luminosity of about 10^?8.5 L _bol . A hard component dominates the X-ray emission of τ Sco, and possible causes are discussed. For the Be stars, the X-ray emission is that which is expected from a normal B-star wind coming from the poles, as in the Wind Compressed Disk (WCD) model of Be stars. None of the stars, including theβ Cep stars, show noticeable variability in their X-rays.EUVE observations of∈ CMa B2 II, find it to be the brightest object in the EUV sky at 500 to 700 Å. It shows a Lyman continuum flux that is a factor of 30 higher than line blanketed model atmospheres. The continuum is seen on both sides of the He I 504 Å edge, and the discrepancy with model atmospheres is even greater shortward of 504 Å. TheEUVE spectra show emission lines both from high stages of ionization ( Feix to Fexvi) and from low stages (Heii and Oiii). The Heii Lymanα results from recombination following X-ray photoionization in the wind, and the Oiii resonance line is found to be present because of the Bowen fluorescence mechanism. Thus, there is and interesting coupling between the wind production by the EUV photospheric emission, the production of X-ray and line EUV emission by winds, and the production of fluorescence by recombination in the wind; all of these processes are now observable in B stars.     

Oscillations in EUV emission lines during a loop brightening

Oscillations in the emission in the ultraviolet lines of Cii, Oiv, and Mg x, detected by the Harvard College Observatory EUV spectroheliometer on Skylab are observed on August 7, 1973, during a loop brightening. The intensity of the EUV lines varies with a period of 141 s during the time of enhanced intensity of the coronal loop, lasting 10 min. The periodic oscillation is not only localized in the loop region but extends over a larger area of the active region, maintaining the same phase. We suggest that the intensity fluctuation of the EUV lines is caused by small-amplitude waves, propagating in the plasma confined in the magnetic loop and that size of the loop might be important in determining its perferential heating in the active region.On leave from the University of Torino, Italy.     

The temperatures of the nuclei of high-excitation planetary nebulae

An empirical relationship between the ratio of the intensities of emission lines in spectra of planetary nebulae, 4686 Heii/H andN ₁+N ₂[Oiii]/4868 Heii, is established (see Equation (1), curve in Figure 1). A new statistical temperature scale based on this empirical relationship is proposed for the determination of lower limits of the temperatures of the nuclei of planetary nebulae. The well-known method 4686 Heii/H gives the upper level of the temperature of the nucleus. A simultaneous application of both methods has been carried out for 97 planetary nebulae, in order to determine both the upper and lower limits of the temperature of their nuclei (last two columns in Table I). A new quantitative system for the determination of excitation classes of nebulae is proposed (Tables IV and V).     

Spectroscopic evidence for mass loss from CH Cygni

Some high-dispersion spectrograms of CH Cygni taken in epochs at which only the M6 spectrum is visible and after the explosions of June 1967 and July 1968 have been studied. The strong negative radial velocities of the Caii chromospheric absorptions and the turbulent motions broadening the emission, lines ofHi, Hei, Feii, [Feii] prove that mass is lost from the star at a rate of the order of 10^–8 solar masses per year. Arguments are given in favour of the hypothesis that CH Cygni is a close binary composed of an M giant and a blue unstable subdwarf.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.     

The spectrum of RR Telescopii in 1968

The nova-like variable RR Telescopii observed at Cerro Tololo Observatory in 1968 displayed an unusually rich emission line spectrum ranging in excitation from Mgi to [Feviii]. A list of lines with their suggested identifications and approximate intensities covers the range from 3100 to 6700. Only a semi-quantitative discussion is possible since photographic measurements of line intensities could not be calibrated photoelectrically.The spectrum can be interpreted as coming from a highly, inhomogeneous stratified shell illuminated by an extremely hot source. Radiation of Mgi [Oi], [Nii], and [Sii] arises from dense pockets shielded from ionizing radiation. The [Oiii] and [Neiv] radiation appears to originate in strata with densities of the order of 5×10⁶ ions/cm³ and a temperature of the order of 18000 K. The abundance of iron appears to be comparable with that of neon. The helium/hydrogen ratio may be about 0.24.     

The symbiotic stellar lines at 6830 Å, 7088 Å; An origin in optically thick fluorescence

The question of the origin of the symbiotic stellar lines at 6830 Å and 7088 Å, recently proposed to arise from Raman scattering of ultraviolet Ovi lines by hydrogen, is examined quantitatively by comparing line intensities expected from this process with the intensity of an Feii line photoexcited by one of the same Ovi lines. It appears that Raman scattering does not yield sufficient intensity to account for the symbiotic lines. An alternative mechanism for producing the lines exists, however, in off-line-center photoexcitation of optically thick hydrogen by the Ovi lines. This gives intensities which are higher than Raman intensities, and which are more consistent with the Feii fluorescent line intensity. Observed further redward shifts are also explained by the mechanism. It is therefore suggested that the proposed hypothesis of Ovi–Hi interaction may be valid, but that the process involved is probably not second-order Raman scattering but first-order fluorescent scattering.     

Forbidden high excitation lines and TiO bands in the symbiotic system QW Sge = MHα80-5

The suspected symbiotic nature of MH80-5=AS 360 was confirmed for the first time by spectra taken in 1967 at Asiago Observatory (Marini, 1969) showing the [Oiii] and [Neiii] forbidden lines, together with strong Heii lines and TiO bands. According to Allen (1984) nebular lines were absent in 1978, while we recorded them again in 1985. Further excitation strengthening up to [Fevii] andOvi, in 1990 were noted by Munari and Buson (1991). The evolution implies density variability in the thick nebula surrounding this new variable system.     

Analysis of the emission line spectra of a solar flare observed from Skylab

The EUV emission spectra in the wavelength range 110–1900 Å of the 5 September 1973 flare observed with the NRL slit spectrograph on Skylab are studied. The results are: (1) The chromospheric and transition-zone lines are greatly enhanced during the flare. In particular, the allowed lines are enhanced more than the intersystem lines. The Ni ii and P ii lines show the greatest enhancement with a factor of 800 increase in intensity. Other lines such as O i, C i, Si iii, S iii, S iv, O iv, O v, and N v show increases in intensity 10–100 times during the flare. (2) The chromospheric lines, although greatly enhanced during the flare, maintain their sharp and gaussian profiles and are not appreciably broadened. The transition zone lines, on the other hand, show a red-shifted component during the initial phase of the flare. The deduced downward velocity in the transition zone is 50 km s^–1. In addition, there are large turbulent mass motions. The downward mass motion is probably caused by the pressure imbalance between the flare hot plasma at 13 × 10⁶ K and the cooler plasma at 10⁵ K. (3) The density of the 10⁵ K flare plasma, as deduced from density-sensitive lines, is greater than 10¹² cm^-3. The depth of the 10⁵ K plasma in the flare transition zone is only of the order of 0.1 km, giving a steep temperature gradient. Consideration of the energy balance between the conductive flux and the radiative energy losses shows that, indeed, the high density in the transition zone requires that its thickness be very small. This is a consequence of the maximum radiative efficiency at the temperature around 10⁵ K in the solar plasma.Ball Brothers Research Corporation.     

Solar EUV emission line profiles of Si ii and Si iii and their center to limb variations

Spectral line profiles of Si ii and Si iii are presented which were observed both at solar center and near the quiet solar limb with the Naval Research Laboratory EUV spectrograph of ATM/SKYLAB. Absolute intensities and line profiles are derived from the photographic data. A brief discussion is given of their center-to-limb variations and of the optical thickness of the chromosphere in these lines. Nonthermal broadening velocities are found for the optically thin lines from their full width at half maximum intensity (FWHM).Also at High Altitude Observatory for part of this work.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

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.     

Extreme ultraviolet spectrum of the solar flare of 2114 UT March 27, 1967

Scanning spectrometer measurements in the range 1310–270 Å, observed from the satellite OSO 3, are reported for the solar flare of 2114 UT March 27, 1967. This flare was a long lasting sequence of bursts with EUV spectra consisting of enhanced lines and recombination continua normally emitted from the chromosphere and chromosphere-corona transition region, with unusually small increases in lines normally emited from the corona. An EUV flare spectrum is presented and suggested as one example for interpreting broadband observations of EUV bursts. Any broadband continuum other than known recombination continua contributed less than 6 % of the meassured line and hydrogen recombination continua in the range 270–1310 Å. The ratio of photon flux of Ciii 1176 Å to that of Ciii 977 Å was 0.86, which suggests an ambient density in the region of emission greater than 10¹² cm^-3 at temperatures near 60000 K.     

Nova Vulpeculae 1968 No. 2 (Kohoutek)

Nova Vul 1968 No. 2 (Kohoutek) has been studied on Asiago material obtained before and after the announcement of discovery. The nova, fainter than 20 magnitude at minimum, brightened on July 16. The maximum (9.25 B) was reached on July 19. From the light curve the star can be classified as a normal fast nova. Objective prism spectra taken near maximum display the presence of absorption systems with radial velocities from –550 to –2200 km/sec. On slit spectrograms obtained at the end of October, the nova was found in the nebular stage with wide emission bands of H, Hei, Heii,Nii,Niii and forbidden lines ofOiii,Nii,Oi. The degree of excitation is slowly increasing.The nova is strongly reddened by interstellar absorption.     

Line intensities in the photosphere-chromosphere transition region

Eclipse observations of total line intensities (Cr i: two groups of lines; Ti ii, Fe ii and Cr ii: two lines each) are interpreted in terms of departures from LTE. The same method as described in Paper III (van Dessel, 1974) is used. The HSRA model is used to compute the LTE populations. A distribution of NLTE-coefficients is obtained for each group of lines. The lines discussed in the present paper are seen to remain in emission down to some 1000 km inside the limb. As a consequence, interpretation is less simple than for the Fe i lines (Paper III); population and excitation temperatures are found to be rather divergent from Holweger's temperature, which was used for a first approximation.     

Solar XUV limb brightening observations

Limb brightening of XUV lines of the ions Ciii Niii, Niv, Oiii, Oiv, Ov and Siiv is compared with that predicted by a modified version of a coronal model developed by Dupree and Goldberg. Systematic differences between the predicted and observed limb brightening are found. These differences can be eliminated by introducing into the model the effects of spicules that extend up into the chromospheric-coronal transition region. The spicules are assumed to be opaque to radiation between 500 and 900 Å because of absorption in the hydrogen Lyman continuum.