Properties of the λ2200 Å interstellar absorber

A strong correlation between the equivalent widths of the 2200 Å absorption band in the interstellar extinction curves and the colour excessesE _B-V of the stars was found. The oscillator strength and the damping constant of the 2200 Å transition were estimated. From these findings some conclusions concerning the identification problem were drawn.     

On the nature of interstellar grains

Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, 10⁴⁰ g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals µ^–1 < ;^–2 < 1.94µ^–1 and 2.5µ^–1 < ;^–1 < 3.0 ;^–1. Over the more restricted waveband 4000–5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton pigments. The strongest of the diffuse interstellar bands are provisionally assingned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The 2200 Å interstellar absorption feature could be due to degraded cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths <1800 Å could be due to scattering by virus particles.     

The 2200 Å extinction hump and porous graphite grains

We discuss in this paper the possibility of interpreting the 2200 Å band occurring in the interstellar extinction curves as being attributed to porous graphite. The results show that grains with radii smaller than 0.015 m and a porosity degree within the values 0.02f0.25 are able to fit satisfactorily the peak at 4.6 m^–1 and the band shape between 4 and 5.2 m^–1. Consideration of the expected density for such particles seems to confirm that interstellar grains may be porous but, at the same time, suggests that care must be taken when data concerning dust in the solar system are extrapolated to the interstellar space.     

Aromatic hydrocarbons in very small interstellar grains

We show that the recently observed 3.3 m emission feature in the diffuse radiation from the galactic disk might be due to an ensemble of aromatic molecules distributed within very small interstellar grains. The same particles also provide an explanation of the 2200 Å interstellar absorption feature.     

Contribution to interstellar extinction from an astrophysical microsoot?

The optical constants of a carbon polymorph, calculated using the Drude dispersion theory, are shown to lead to close agreements with the mean interstellar extinction curve over the waveband 0.3 ^-1 5.5 m^-1 for particles of Rayleigh scattering sizes. Astrophysical microsoot grains of radii 50Å may be related to microdiamond grains of similar sizes that have recently been discovered in carbonaceous chondrites. It is postulated that such microsoot particles could contribute to the nearly invariable interstellar extinction law observed over the near IR, visible and near to mid UV spectral regions. Admixtures of microsoot with micron-sized microsoot clumps, microdiamond and hollow organic / biologic grains provide an explanation for the full range of extinction and polarization data.     

The Ultraviolet Absorbance of Presumably Interstellar Bacteria and Related Matters

It is shown that the well-known 2200 Å peak in the extinction of starlight is explained by microorganisms. A mixed culture of diatoms and bacteria, which previously we found to give excellent fits to astronomical data in the infrared, has a peak absorption slightly shortward of 2200 Å, in very close agreement with the absorptions found indirections towards most early-type stars. The peak absorption is measured to be ～ 35000 cm²g^-1. This is in addition to a scattering component of the extinction which has an estimated value for dry microorganisms of ～ 50000 cm²g^-1. The scattering calculated for a size distribution of non-absorbing hollow bacteria with irregularities on the scale of 300 Å produces agreement with both the visual extinction law and the observed λ^-1 type extinction at the far ultraviolet. The contribution to the extinction from a pure scattering bacterial model is about 3.4 mag per kpc path length along the galactic plane at λ =2175 Å. Absorption near this wavelength effectively adds ～ 2.3 mag per kpc, making up precisely the observed total extinction at the peak of 5.7 mag per kpc. The full range of the interstellar extinction observations is now elegantly explained on the basis of a bacterial model alone with no added components or free parameters to be fitted. Photolysis has little effect on the bulk refractive index of the particles and so does not change the scattering component appreciably. But photolysis due to sufficient UV in space can reduce the effectiveness of the 2200 Å absorption in comparison with the scattering, thereby decreasing the height of the absorption peak. An extreme example of this is the Large Magellanic Cloud, where UV emission from a profusion of early-type stars has reduced the absorbance of the particles to about one-quarter of its value for most of our galaxy. The 2200 Å absorption has generally been attributed to small graphite particles. We explain how this belief has come about and why in the past we have been swayed by it.     

Graphite grains,carbon depletion and the 2200 Å feature

In a recent paper Millar has shown that if one assumes that the carbon depleted from the gas phase is all tied up into small graphite grains the observational data raise serious doubts against the hypothesis that these particles are responsible for the 2200 Å extinction hump. In the present paper it is shown that this problem may be overcome if the presence in the interstellar space of graphite grains with sizes greater than 0.02 is taken into account. The derived ratios between the masses of large grains, which do not contribute to the ultraviolet extinction hump, and those of the small ones varies from region to region of the sky and are consistent with those evaluated in the circumstellar shells of carbon stars. Moreover, the largest sizes of the graphite particles we find are in agreement with those needed to fit the interstellar extinction curve over the wavelength range 0.11–<1 .     

Spectroscopic Studies of the Solar Corona – V. Physical Properties of Coronal Structures

Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec^–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec^–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures.     

Multiresolution wavelet analysis of SUMER/SOHO observations in a solar prominence

We have studied through a multiresolution wavelet analysis the oscillations in a limb prominence. Intensity fluctuations in time and height corresponding to different lines of Siiv and Oiv observed with SUMER on board SOHO have been analyzed in the wavelet bands of J₃= 1 min 36 s to 3 min 12 s and J₄=3 min 12 s to 6 min 24 s. For all species, oscillations in the J₄ band were dominant. We found relevant differences between the behavior of line D₁ (1393.76 Å) corresponding to Siiv and the set D₂ (1401.16 Å), D₃ (1404.81 Å), D₄ (1402.77 Å) corresponding to Oiv, Oiv and Siiv respectively. We also report the identification of a pulse in the intensity of the line D₁ that appears in the range of 15–20 min. This disturbance seems to travel with a speed of about 170 km s^–1.     

Околозвездньiе облака поданньiм ультрафиолетовьiх спектров свезл

, ii (2000–3000 Å) i . , i . i (. 2). i i i i + ( 7–10). ii (. 13). ii i i (, 2400 Å) (. 14 15). i i i , iu , i (. 1). i i ii i i . .     

A prominence model based on spectral observations

Intensities and profiles of the H, H, H, K, and D₃ lines are measured in a solar prominence. From the profiles of these lines we estimate T = 6400 K and _t = 5.7 km s^–1. We construct a simple isothermal model which explains the H intensity and profile for an assumed total particle density n _T = 3 × 10¹¹ cm^–3, and a filling factor, = 1/6.From this model we find that the source function in the H line is nearly constant through the prominence. We estimate from the model that the radiative energy loss at the center of the prominence is of the order of 10⁷ erg s^–1 g^–1.     

Spectrophotometry of the corona and a quiescent prominence based on observations of the total solar eclipse of 7 March, 1970 in Mexico

Slit spectrograms of a quiescent prominence and the inner corona (h2.5 arc min) in the range 3400–7000 Å (dispersion 6–10 Å/mm) were obtained. From an analysis of the Stark effect on the Balmer lines (up to number 36) the electron density in the prominence n _e = (7 ± 3) × 10¹⁰ cm^–3 was deduced. The kinetic temperature T _k and the non-thermal velocities _t, found from a simultaneous consideration of the Balmer and metal lines, are T _k 10 000 K and v _t6 km/s. Also the emission measure of the prominence along the line-of-sight was found: ME = 10³¹ cm^–5.In the coronal spectrum 24 coronal lines were found. Thirteen of these lines were identified and measured photometrically to get their absolute intensities, profiles and halfwidths. For nine lines the intensities as a function of the height were studied and on this basis the coronal lines were divided into a few groups. The line-of-sight and non-thermal velocities are _r 10 km/s and _t 25 km/s. The coronal lines originate in at least three types of regions with different temperatures. The emission measure as a function of the ionization temperature was determined. The abundances of four elements of the iron group (V, Cr, Mn, Co) were estimated. The abundances of the other elements of the same group (A, Ca, Fe, Ni), found from EUV-data, are in a good agreement with our observations. The degree of inhomogeneity in the corona was estimated: .     

Correlations between statistical population indices and spectral characteristics of carbon stars

The coefficients of correlation between spectroscopic data published by Yamashita (1967) and others for carbon stars and the statistical population indices calculated for these stars at the Toru Observatory are calculated (Table II). The intensity estimates of Cai 4227 Å, Nai D lines, the C¹³/C¹² ratio, then=n(Li/Ca) index, as well as CN and probably C₂ bands are higher in population I carbon stars. The CH(G) band and probably hydrogen (H, H, H) lines as well as Baii 4554 and 4934 Å lines are stronger in population II carbon stars. The photoelectric colour indices, corrected for interstellar reddening do not show significant population effects. They can be used as spectral type equivalents. For a population criterion the CH/CN intensity ratio is proposed.     

The violet opacity in the red peculiar stars (II)

Moderate dispersion (25-35 Å mm^–1) spectra were obtained from two carbon stars, V Cyg and WZ Cas, in a wide range of wavelengths (3400-6800 Å) with the echelle-spectrometer, ZEBRA, of the 6 m telescope and two-dimensional photon-counting system. Spectral feature identification was carried out from 3850 to 6200 Å. Most of the bands are due to C₂, SiC₂, and CN, however, particularly in WZ Cas, moderate atomic lines of the iron peak and s-process elements are also found. WZ Cas is a so-called lithium star, however, we have found no evidence for a strong line of Li. The spectra of V Cyg contain an emission line of H.     

On the Nature of Prominence Absorption and Emission in Highly Ionized Iron and in Neutral Hydrogen

We have studied the behavior of the emission in the highly ionized EUV lines Feix/x, 171 Å, Fexii, 195 Å, and Fexv, 284 Å observed in quiescent prominences. Kucera, Andretta, and Poland (1998) have explained the absorption of other highly ionized metallic EUV lines as due to absorption in the hydrogen continuum. However, since the authors noticed deviations from the expected ³ dependence of the absorption strengths, we have explored the possibility that emission in EUV iron lines can influence the observations. We propose the existence of a hot, i.e., million-degree plasma component of the prominence–corona transition region (PCTR), where the EUV iron lines originate. We find that (i) neither of the two scenarios alone reproduces observations; (ii) both emission and absorption increase prior to eruption; (iii) the measurements of Kucera, Andretta, and Poland's 14 May event are strongly affected by hot PCTR emission.     

The high-dispersion continuous ultraviolet solar spectrum and the Balmer-jump

Among the intensities, determined at about 200 wavelengths between 3000 and 4100 Å in the spectrum of the centre of the sun's disk (Houtgast, 1965), the 32 highest ones (windows) were plotted and compared with absolute intensities given by other authors.The intensities in between the Fraunhofer lines from 3600 to 4000 Å, as determined here for the first time with high dispersion, reveal a detailed picture of several absorption features, one of which can be attributed to a Balmer jump of 0.03, a value in accordance with that found for stars and in agreement with the strengths of the high Balmer lines.The much higher value of the Balmer jump for the sun, as quoted in literature, in reality refers to the total intensity jump between 4000 and 3600 Å, which is mainly due to the crowding of Fraunhofer lines.     

A unified model for the 3.28 μ emission and the λ2200 å interstellar extinction feature

The 3.28 m feature observed in the diffuse galactic emission and the 2200 Å interstellar extinction feature must have a common source. This requirement rules out graphitic-type PAH molecules such as coronone and tends to favour naturally occurring bi-cyclic ring structures typified by quinoline and its derivatives.     

Observations and analysis of CF Tuc

RecentUBV photometry of the RS CVn binary CF Tuc is discussed and analysed. If we combine the results with previously published spectroscopy we find radii of 1.63R for the hotter (6000 K) and 3.11R for the cooler (4500 K) component; both stars having a mass of about 1.3M . The distance to the system is put at 86±15 pc.Though the photometric data is incomplete in the coverage of some regions out of the minima, there is no significant evidence of the wave-type distortions — a known hallmark of RS CVn stars — and the data can be modeled by a standard eclipsing binary system in which the statistical test of goodness-of-fit (²) produces quite acceptable values for reasonable estimates of observational accuracy (0.01 mag). We, therefore, have no need to postulate any additional photometric complications, and feel entitled to some confidence in the reliability of the derived parameter set.     

The first uv studies of the optical candidate for the X-ray source 1118-61

The X-ray pulsator, 1118-61, discovered in 1975 by the Ariel-5 satellite, has been observed for the first time at UV wavelengths using IUE. Its UV spectrum clearly identifies the optical counterpart as a Be star similar to that seen in other X-ray pulsators. From the 2200 Å absorption feature a distance estimate of 4 kpc is obtained and the carbon-IV profile reveals the mass loss rate from the primary. The discrepancy seen in other similar systems between the optical/UV mass loss rate and that needed to power the X-ray source is also observed in this source. Possible models are reviewed.     

Statistical survey of planetary nebulae: Distances,masses, and distribution in the galaxy

On the basis of empirical (D)-dependency at the frequency of 5 GHz constructed using 15 planetary nebulae with the independently measured distances (10^–171×10^–20 W m^–2 Hz^–1 ster^–1), we evaluated distances of 335 objects. Independent evidence of the correctness of the accepted scale are given. Then(D)-dependency is constructed and it is shown that atD<0.08 pc the mean electron density is higher than the one determined by the Seaton method. We showed that the filling factor diminishes with the increase of the PN diameter (1 atD0.08 pc and 0.2 atD0.4 pc). the ionized mass of 33 PNs is determined. With the diameter increase the ionized mass grows and atD0.4 pc reaches the valueM0.07M . We used the new distance scale when investigating the space distribution of PNs. The mean scale height =130±15 pc and the mean gradient of the change of surface densitym=0.37, which allowed us to estimate the total number of nebulae in the GalaxyN4×10⁴. We divided the PNs according to their velocities (withV _LSR>35 km s^–1 andV _LSR<35 km s^–1) and permitted us to confirm that the PN belong to different sub-systems of the Galaxy. The estimated local formation rate of PNs [=(4.6±2.2)×10^–12 pc^–3 yr^–1] is a little higher than the one of the white dwarfs. That can be explained by a large number of PNs having binary cores, which used in our sample. The statistical estimation of PN expansion velocity showed thatV _ex increases from 5–7 km s^–1 (atD0.03 pc) to 40–50 km s^–1 (atD0.8 pc).