On the non-linear relationships between N(CaII), N(KI) and N(H)

Calculations by Penstonet al. (1969) of the mass distribution of interstellar clouds are reexamined in the light of Hobbs's data on the relationship between N(Caii) and N(H). The mass spectrum is calculated using two different sets of simple assumptions. Two possible explanations of the quadratic dependence of N(Ki) on N(H) are briefly examined.     

The solar hafnium abundance

The solar Hf abundance is determined using nine Hf ii lines in the photospheric spectrum. The transition probabilities were obtained from lifetime measurements performed by the beam-foil technique. The abundance derived from synthetic spectrum calculations is A(Hf) = 0.88 ± 0.08 in the logarithmic A(H) = 12.00 scale.     

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 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.     

The ultraviolet spectrum of the binary system KS Persei (HD 30353)

Nine high- and low-resolution IEU spectra at different orbital phases during different cycles, of the hydrogen-poor single-lined spectroscopic binary KS per (HD 30353) have been studied. The near-UV spectrum is characterized by the presence of several lines of once ionized metals which show the same orbital RV shifts observed in the visual range. The MgII resonance lines present a sharp interstellar + circumstellar core and an emission peak at about 83 and 92 km s^–1. The far UV spectrum is characterized by the presence of strong absorptions of the resonance lines ofNV,CIV, SiIV, SiIII.Direct determination of the IS extinction from the 2200 Å feature givesE(B-V)=0.33. A comparison of corrected logarithmic continuous energy distribution with the theoretical models by Kurucz, indicates that the companion is a hot star,T _e=15000 K; logg=4. A comparison with the recent UV work ofv Sgr, shows that, KS Per is very similar tov Sgr.Based on observations by the International Ultraviolet Explorer (IUE) collected at the Villafrance Satellite Tracking Station and obtained from the IUE data bank.     

On the temperature structure of sunspot umbrae

From a high-resolution spectrum of a sunspot umbra (1.1 < < 2.3 m) we derive models of the temperature stratification in the deep layers of the umbra. The observed spectrum is corrected for straylight using the Hi Paschen line at gl = 1.282 m. A method is described for the iterative fitting of empirical temperature models to spectral information, and the method is applied to the present data. We find that the observed profiles of 3 high-excitation lines of Sii and the observed continuum contrast between umbra and photosphere cannot be reproduced with a single one-component model of the umbral atmosphere: the Si i lines require a model that is 460 K hotter at gt _0.5 = 3 than the continuum model. This indicates that hot and cool components coexist within the umbra. A temperature model derived from the relative intensity in the wings of 3 low-excitation lines of Mgi, Ali, and Sii is not significantly different from the continuum model.Based on observations obtained at Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under contract with the National Science Foundation.     

Diagnostics of solar ions: Ne VI,Mg VI,Si VIII and Mg VIII observed by SERTS

Diagnostics of solar ions Nevi, Mgvi, Siviii, and Mgviii in an active region observed by SERTS have been presented. Density, temperature, and electron pressure in the emitting source have been derived from theoretical line-ratio curves and its EUV spectrum obtained by SERTS. The variation of neon-to-magnesium and silicon-to-magnesium abundances has been discussed in the interpretation of the active region spectrum obtained by SERTS.     

Spectral and photometric observations of the star Y Ori

Data are presented from a spectral and photometric study of the long-period variable star Y Ori, which we have classified as a type M7IIIe near its brightness minimum. In the blue part of the spectrum, features from a star of an earlier spectral class are superimposed on the spectrum of a cool giant, so that a variable excess emission is observed at wavelengths of 4000–4200 Å. As opposed to the monotonically decreasing intensity of the Balmer lines (EWHα > EWHβ > EWHγ > EWHδ) in normal stars belonging to the earlier spectral classes, a reverse relationship, with EWHγ < EWHδ is detected in Y Ori. Translated from Astrofizika, Vol. 51, No. 4, pp. 567–575 (November 2008).     

Spectroscopic study of the eclipsing binary V 367 Cygni

Seventeen coudé spectrograms (dispersion 20 A mm^–1) of the Lyrae-type eclipsing binary V 367 Cygni (P=18.6 d) have been studied. The observations were made at the Haute Provence Observatory during a period of almost two years (May 1973–March 1975). An anomalous behavior for the radial velocities of the spectrograms taken during one cycle (406) was observed; it is suggested that gas eruption under form of prominences may explain it. The spectrum is dominated by shell lines very similar to those present in the spectrum of the supergiant A9 Ia Aurigae. The underlying stellar spectrum is classified as A5 I on the basis of the intensity of the sole clearly visible stellar line, 4481 MgII, of the wings of the stellar Balmer lines, and an estimate of the intensity of the stellarK line. The radial velocity curves for the shell lines of CaII, HI, metallic ions and neutral iron, as well as the phase dependence of the microturbulence, indicate stratification in the shell.     

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 spectrum of Nixix in the solar corona

The wavelengths and intensities of the stronger transitions in the spectrum of Ni xix are reduced from measurements of the X-ray spectra of three coronal active regions. The new measured wavelengths are consistent with prediction by isoelectronic extrapolation from the wavelengths of well established transitions but are about 0.01 Å longer than previously accepted laboratory measurements. This difference appears to be crucial to the correct assignment of features in the coronal spectrum to Ni xix. The relative intensities of our new assignments to Ni xix are in broad agreement with the Loulergue-Nussbaumer calculations.     

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.     

The radial velocity variations of certainOii,Siiii, andNii lines — A confirmation of the shell ejection in the P cygni stellar wind

The radial velocity variations of the components of someOii, Siiii, andNii lines in P Cyg spectrum are investigated during the period 1981–1983. All data are analyzed in terms of a model which implies a multiple ejection of shells in the stellar wind. It is shown that the observed phenomenon is not periodic, but it occurs on a time-scale between 110 and 160 days with the most frequently observed length of the cycle of about 110 days. The shells move away from the star with an acceleration that is greater at low velocities than at high ones. The radial velocity variations ofOii, Siiii, andNii lines agree with these of hydrogen lines if we assume velocity and excitation condition differences inside the shell.     

The forbidden transitions within 3s 2 3p 5 3d of Fe ix and Ni xi and 3s 2 3p 4 3d of Fe x and Ni xii

Improved level values for 3s ² 3p ⁵ 3d and 3s ² 3p ⁴ 3d of Fe ix and Fe x are derived from the observed forbidden lines with special regard to recent accurate measurements in the vacuum-ultraviolet part of the coronal spectrum. A procedure for estimating expected relative intensities is proposed and used for an additional check on the consistency of the identifications, which now comprise 12 lines of Fe IX and 11 lines of Fe x. Finally, by use of a suitable extrapolation technique the wavelengths of corresponding lines in nickel are predicted, which leads to some new identifications and a total of 6 identified lines of Ni xi and 4 of Ni xii.     

The UV spectrum of the binary system SZ Psc

In this paper we study the far-UV as well as the UV spectrum of the spectroscopic binary system SZ Psc in the wavelength ranges 1235–1950 Å and 2710–3090 Å, respectively, from spectra obtained with the International Ultraviolet Explorer (IUE). The UV spectrum of SZ Psc is mainly an emission spectrum. The short wavelength region includes emission lines formed from the low chromosphere to the transition region (e.g., Siiv,Civ, andNv) and also a deep and broad absorption line of Feii.The Mgii[1] resonance doublet at about 2800 Å presents a P Cygni profile and a multiple structure with two emission and two absorption satellite components. We also present the emission measure diagram in the temperature region 4.4T _e <53.     

The photospheric barium spectrum: Solar abundance and collision broadening of Baii lines by hydrogen

A study of the solar Ba ii spectrum leads to a solar abundance of barium of log ba = = 2.11±0.12, on the scale log h = 12. The observed asymmetry of the resonance line 4554 is consistent with an isotopic abundance ratio equal to the terrestrial one. The meteoritic Ba/Si abundance ratio found in carbonaceous chondrites appears to exceed the solar ratio by 0.1 to 0.2 dex (Section 5).The broadening by collisions with hydrogen atoms is determined from the solar spectrum (Section 4). Damping half-widths, h, of the three stronger Ba ii lines turn out to be larger by a factor of about 3.0 than predicted from pure van der Waals interaction of dipoles. Departures from LTE appear to be present in the cores of the resonance lines and of the lines arising from the metastable 5D levels (Section 6). The equivalent widths, however, remain practically unaffected.Equivalent widths of neutral barium lines are predicted and some new identifications of photospheric Ba i lines are suggested (Section 7).     

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.     

Proposed Mg V,Fe XIV and forbidden Fe XVII line identifications in the EUV solar spectrum

Some line identifications in solar disk and limb spectra are proposed on the basis of recent laboratory and theoretical results reported in the literature, including allowed lines of Mgi and Fexiv in the EUV spectrum and an expected forbidden line of Fexvii near 1190 Å.     

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 Solar Spectral Irradiance as a Function of the Mg <Emphasis Type="SmallCaps">ii</Emphasis> Index for Atmosphere and Climate Modelling

We present a new method to reconstruct the solar spectrum irradiance in the Ly α – 400 nm region, and its variability, based on the Mg ii index and neutron-monitor measurements. Measurements of the solar spectral irradiance available in the literature have been made with different instruments at different times and different spectral ranges. However, climate studies require harmonised data sets. This new approach has the advantage of being independent of the absolute calibration and aging of the instruments. First, the Mg ii index is derived using solar spectra from Ly α (121 nm) to 410 nm measured from 1978 to 2010 by several space missions. The variability of the spectra with respect to a chosen reference spectrum as a function of time and wavelength is scaled to the derived Mg ii index. The set of coefficients expressing the spectral variability can be applied to the chosen reference spectrum to reconstruct the solar spectra within a given time frame or Mg ii index values. The accuracy of this method is estimated using two approaches: direct comparison with particular cases where solar spectra are available from independent measurements, and calculating the standard deviation between the measured spectra and their reconstruction. From direct comparisons with measurements we obtain an accuracy of about 1 to 2%, which degrades towards Ly α. In a further step, we extend our solar spectral-irradiance reconstruction back to the Maunder Minimum introducing the relationship between the Mg ii index and the neutron-monitor data. Consistent measurements of the Mg ii index are not available prior to 1978. However, we remark that over the last three solar cycles, the Mg ii index shows strong correlation with the modulation potential determined from the neutron-monitor data. Assuming that this correlation can be applied to the past, we reconstruct the Mg ii index from the modulation potential back to the Maunder Minimum, and obtain the corresponding solar spectral-irradiance reconstruction back to that period. As there is no direct measurement of the spectral irradiance for this period we discuss this methodology in light of the other proposed approaches available in the literature. The use of the cosmogenic-isotope data provides a major advantage: it provides information about solar activity over several thousands years. Using technology of today, we can calibrate the solar irradiance against activity and thus reconstruct it for the times when cosmogenic-isotope data are available. This calibration can be re-assessed at any time, if necessary.