A Discussion on astronomy in the ultraviolet - The Celescope survey and the galactic distribution of interstellar absorption

1975 ◽  
Vol 279 (1289) ◽  
pp. 345-354 ◽  
Keyword(s):  
Interstellar Dust ◽  
Interstellar Extinction ◽  
Astronomical Observatory ◽  
Digital Television ◽  
National Observatory ◽  
Interstellar Absorption ◽  
The Galaxy ◽  
Galactic Distribution

The Celescope experiment consisted of four 31 cm aperture telescopes equipped with digital television photometers, installed in the Orbiting Astronomical Observatory, launched 7 December 1968. We used this instrument to conduct a survey in four ultraviolet colours: U l (2100-3200 A), U2 (1550—3200 A), U3 (1350— 2150 A) and U4 (1050-2150 A). We have published the observational results in the Celescope catalog of ultraviolet stellar observations (Davis, Deutschman & Haramundanis 1973). I have studied these results, together with relevant ground-based data, to determine the distribution of interstellar dust and variations of the interstellar extinction law with the position in the galaxy. Results from the data contained in the Celescope catalogue have been prepared for publication (Peytremann & Davis 1974)- These results have now been refined and expanded to include new ground-based U, B, V, and H(3 photometry acquired at Kitt Peak National Observatory, as well as new observations by W. A. Deutschman and R. Schild at Cerro Tololo Inter-American Observatory

scholarly journals Dust absorption and scattering in the silicon K-edge

2019 ◽  
Vol 627 ◽  
pp. A16 ◽  
Author(s):  
S. T. Zeegers ◽  
E. Costantini ◽  
D. Rogantini ◽  
C. P. de Vries ◽  
H. Mutschke ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Galactic Center ◽  
Interstellar Extinction ◽  
Line Of Sight ◽  
X Rays ◽  
Laboratory Measurements ◽  
Galactocentric Distance ◽  
Synchrotron Facility ◽  
The Galaxy ◽  
Low Mass

Context. The composition and properties of interstellar silicate dust are not well understood. In X-rays, interstellar dust can be studied in detail by making use of the fine structure features in the Si K-edge. The features in the Si K-edge offer a range of possibilities to study silicon-bearing dust, such as investigating the crystallinity, abundance, and the chemical composition along a given line of sight. Aims. We present newly acquired laboratory measurements of the silicon K-edge of several silicate-compounds that complement our measurements from our earlier pilot study. The resulting dust extinction profiles serve as templates for the interstellar extinction that we observe. The extinction profiles were used to model the interstellar dust in the dense environments of the Galaxy. Methods. The laboratory measurements, taken at the Soleil synchrotron facility in Paris, were adapted for astrophysical data analysis and implemented in the SPEX spectral fitting program. The models were used to fit the spectra of nine low-mass X-ray binaries located in the Galactic center neighborhood in order to determine the dust properties along those lines of sight. Results. Most lines of sight can be fit well by amorphous olivine. We also established upper limits on the amount of crystalline material that the modeling allows. We obtained values of the total silicon abundance, silicon dust abundance, and depletion along each of the sightlines. We find a possible gradient of 0.06 ± 0.02 dex/kpc for the total silicon abundance versus the Galactocentric distance. We do not find a relation between the depletion and the extinction along the line of sight.

scholarly journals Evidence for biodegradation products in the interstellar medium

2009 ◽  
Vol 9 (1) ◽  
pp. 29-34 ◽  
Author(s):  
Kani Rauf ◽  
Chandra Wickramasinghe
Keyword(s):  
Interstellar Dust ◽  
Bituminous Coal ◽  
Interstellar Extinction ◽  
Full Width ◽  
Absorption Profile ◽  
Substantial Fraction ◽  
Mid Infrared ◽  
Interstellar Absorption ◽  
Aromatic Molecules ◽  
Absorption Features

AbstractThe interstellar absorption band centred on 2175 Å that is conventionally attributed to monodisperse graphite spheres of radii 0.02 μm is more plausibly explained as arising from biologically derived aromatic molecules. On the basis of panspermia models, interstellar dust includes a substantial fraction of biomaterial in various stages of degradation. We have modeled such an ensemble of degraded biomaterial with laboratory spectroscopy of algae, grass pigments, bituminous coal and anthracite. The average ulrtraviolet absorption profile for these materials is centred at 2175 Å with a full width at half maximum of 250 Å, in precise agreement with the interstellar extinction observations. Mid-infrared spectra also display general concordance with the unidentified interstellar absorption features found in a wide variety of astronomoical sources.

scholarly journals Interstellar Extinction in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 341-351
Author(s):  
K. Nandy
Keyword(s):  
Interstellar Dust ◽  
Interstellar Extinction ◽  
Magellanic Clouds ◽  
Absorption Feature ◽  
Early Type ◽  
Distribution Law ◽  
Broad Absorption ◽  
Grain Sizes ◽  
The Galaxy ◽  
The Difference

The extinction properties of interstellar dust in the Large and Small Magellanic Clouds have been systematically investigated, using recent UV observations of early type Cloud members along with complementary visible data. The extinction curves differ systematically from the standard Galactic curve. The latter shows a broad absorption feature centred near 2200Å in virtually all sight lines but this is absent or only weakly present in the SMC; also the SMC extinction in the far UV is the largest known relative to EB-V. Dust in the LMC appears to be intermediate in extinction properties between the SMC and normal Galactic material. However, exceptions from the average extinction curves have been found in both Clouds.Model computations show that the range of grain sizes and their number distribution law may not be significantly different in the Clouds and the Galaxy; the difference in extinction laws can be accounted for by varying the graphite contribution relative to silicate.

scholarly journals Analysis of Interstellar Extinction towards the Hypergiant Cyg OB2 No. 12

2016 ◽  
Vol 25 (1) ◽  
Author(s):  
O. V. Maryeva ◽  
E. L. Chentsov ◽  
V. P. Goranskij ◽  
S. V. Karpov
Keyword(s):  
Interstellar Extinction ◽  
Stellar Association ◽  
The Galaxy ◽  
The Mean

AbstractThe Cyg OB2 stellar association hosts an entire zoo of unique objects, and among them – an enigmatic star Cyg OB2 No. 12 (Schulte 12, MT 304). MT 304 is enigmatic not only due to its highest luminosity (according to various estimates, it is one of the brightest stars in the Galaxy), but also because its reddening is anomalously large, greater than the mean reddening in the association. To explain the nature of anomalous reddening (

scholarly journals DIBs, Interstellar Dust, and Extinction

2013 ◽  
Vol 9 (S297) ◽  
pp. 147-152 ◽  
Author(s):  
G. C. Clayton
Keyword(s):  
Interstellar Medium ◽  
Interstellar Dust ◽  
Dust Grains ◽  
Weak Correlation ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
The Relationship

AbstractThe relationship between DIBs and dust is still unknown. The correlation between reddening and DIB strength means that the DIBs are mixed in with the dust and gas in interstellar clouds. The DIBs are relatively stronger in the diffuse interstellar medium than in dense clouds. There is only a weak correlation between the DIBs and the UV extinction parameters including the 2175 Å bump strength and the far-UV rise. In addition, the bump dust grains are sometimes polarized, while the DIBs are not. However, observations of DIBs in the SMC show that when the 2175 Å bump is weak or missing so are the DIBs. Two of the four sightlines that deviate strongly from the CCM UV extinction in the Galaxy show weak DIBs.

scholarly journals Polyaromatic disordered carbon grains as carriers of the UV bump: Far-UV to mid-IR spectroscopy of laboratory analogs

2017 ◽  
Vol 607 ◽  
pp. A73 ◽  
Author(s):  
L. Gavilan ◽  
K. C. Le ◽  
T. Pino ◽  
I. Alata ◽  
A. Giuliani ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Interstellar Dust ◽  
Vacuum Ultraviolet ◽  
Interstellar Extinction ◽  
Electronic Transitions ◽  
Mid Infrared ◽  
Pressure Experiment ◽  
Circumstellar Extinction ◽  
Integrated Intensities ◽  
Far Ultraviolet

Context. A multiwavelength study of laboratory carbons with varying degrees of hydrogenation and sp2 hybridization is required to characterize the structure of the carbonaceous carriers of interstellar and circumstellar extinction. Aims. We study the spectral properties of carbonaceous dust analogs from the far-ultraviolet to the mid-infrared and correlate features in both spectral ranges to the aromatic/aliphatic degree. Methods. Analogs to carbonaceous interstellar dust encountered in various phases of the interstellar medium have been prepared in the laboratory. These are amorphous hydrogenated carbons (a-C:H), analogs to the diffuse interstellar medium component, and soot particles, analogs to the polyaromatic component. Thin films (d < 100 nm) have been measured in transmission in the vacuum-ultraviolet (VUV; 120–210 nm) within the atmospheric pressure experiment (APEX) chamber of the DISCO beam line at the SOLEIL synchrotron radiation facility. Spectra of these films were further measured through the UV-Vis (210 nm–1 μm) and in the mid-infrared (3–15 μm). Results. Tauc optical gaps, Eg, are derived from the visible spectra. The major spectral features are fitted through the VUV to the mid-infrared to obtain positions, full-widths at half maximum (FWHM), and integrated intensities. These are plotted against the position of the π-π∗ electronic transitions peak. Unidentified or overlapping features in the UV are identified by correlations with complementary infrared data. A correlation between the optical gap and position of the π-π∗ electronic transitions peak is found. The latter is also correlated to the position of the sp3 carbon defect band at ~8 μm, the aromatic C=C stretching mode position at ~6 μm, and the H/C ratio. Conclusions. Ultraviolet and infrared spectroscopy of structurally diverse carbon samples are used to constrain the nanostructural properties of carbon carriers of both circumstellar and interstellar extinction, such as the associated coherent lengths and the size of polyaromatic units. Our study suggests that carriers of the interstellar UV bump should exhibit infrared bands akin to the A/B classes of the aromatic infrared bands, while the circumstellar bump carriers should exhibit bands corresponding to the B/C classes.

scholarly journals Flare Stars Investigations at the Department of Astronomy and the Rozhen National Astronomical Observatory

1989 ◽  
Vol 104 (2) ◽  
pp. 151-154
Author(s):  
M.K. Tsvetkov ◽  
B.Zh. Kovachev
Keyword(s):  
Spectral Type ◽  
Astronomical Observatory ◽  
National Observatory ◽  
Flare Stars ◽  
Nonstable Star

In the frames of the programme of nonstable star investigations in the Department, of Astronomy and National Astronomical Observatory the investigations of flare stars- stars of spectral type dK - dM whose nonstabi1ity appears first of all through the quick brightness increases take an essential place. The programme of systematic observations was initiated in 1979 with setting into operation of the telescopes of the Rozhen National Observatory.

scholarly journals Wolf-Rayet Binaries: Evolutionary Causes for their Distribution in the Galaxy

1984 ◽  
Vol 80 ◽  
pp. 175-190
Author(s):  
Bambang Hidayat ◽  
A. Gunawan Admiranto ◽  
Karel A. Van Der Hucht
Keyword(s):  
Galactic Plane ◽  
Small Mass ◽  
The Sun ◽  
Relative Importance ◽  
Galactocentric Distance ◽  
Evolutionary Scenario ◽  
The Galaxy ◽  
Binary Evolution ◽  
Mass Functions ◽  
Galactic Distribution

AbstractOn the basis of the most recent data, the fraction of known Wolf-Rayet binaries is 0.22. In the solar neighbourhood (d < 2.5 kpc) this fraction is 0.34In order to assess the relative importance of massive binary evolution as one of the ways to produce WR stars, the galactic distribution of WR binaries is compared with that of single WR stars using improved intrinsic parameters and new data for the fainter WR stars.In the galactic plane the increase of the binary frequency with galactocentric distance is confirmed.In a direction perpendicular to the galactic plane it is demonstrated at all distances from the Sun that the single-line spectroscopic WR binaries with small mass functions have definitely larger |z|-distances than the ‘single’ WR stars and the WR binaries with massive companions. This is consistent with the evolutionary scenario for massive binaries summarized by van den Heuvel (1976). Among the ‘single’ WR stars the fraction of those with large |z|-distances is increasing with galactocentric distance, like the fraction of the known binaries. This implies that among the high-ļzļ ‘single’ WR stars as well as among the WR stars with lower |z|-values many binaries are still to be discovered.The total WR binary frequency in the Galaxy could be well above 50 %.

Interstellar Extinction in the Galaxy.

1965 ◽  
Vol 141 ◽  
pp. 923 ◽  
Author(s):  
Harold L. Johnson
Keyword(s):  
Interstellar Extinction ◽  
The Galaxy
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