Spectra of celestial bodies in the far ultraviolet region
Atmospheric and interstellar absorption, and spectra of celestial bodies in far ultraviolet
ATMOSPHERIC ABSORPTION↗
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Results for “ULTRAVIOLET SPECTRA”
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Circumstellar material around rapidly rotating B stars. II - On the nature of ultraviolet shell lines in the spectra of Be and shell stars
Using high-resolution (FWHM approximately 0.05 A) ultraviolet spectral data obtained with Copernicus, the nature of shell lines in Be and shell stars. Scans were obtained for various excited fine-structure lines of Fe III, Si II, and O I. It is found that Be stars, in general, do not display shell lines in the ultraviolet, contrary to the findings of previous work at lower resolution. The only Be stars that display strong UV shell lines are the 'classical' shell stars, i.e., stars that also display shell lines in the optical region. Furthermore, it is found that the shell lines, when present, have essentially zero velocity shift with respect to the star. The resonance shell lines seen in the shell stars are generally asymmetric on the short-wavelength side, indicating that the lines are formed in a low-velocity outflowing region. The results presented here argue strongly in favor of a flattened disk structure for the shell line forming region, and against some recent scenarios involving spherical symmetry.
Oegerle, W. R.↗
Jupiter in the Ultraviolet: Acetylene and Ethane Abundances in the Stratosphere of Jupiter from Cassini Observations between 0.15 and 0.19 μm
At wavelengths between 0.15 and 0.19 μm, the far-ultraviolet spectrum of Jupiter is dominated by the scattered solar spectrum, attenuated by molecular absorptions primarily by acetylene and ethane, and to a lesser extent ammonia and phosphine. We describe the development of our radiative transfer code that enables the retrieval of abundances of these molecular species from ultraviolet reflectance spectra. As a proof-of-concept we present an analysis of Cassini Ultraviolet Imaging Spectrograph (UVIS) observations of the disk of Jupiter during the 2000/2001 flyby. The ultraviolet-retrieved acetylene abundances in the upper stratosphere are lower than those predicted by models based solely on infrared thermal emission from the mid-stratosphere observed by the Composite Infrared Spectrometer (CIRS), requiring an adjustment to the vertical profiles above 1 mbar. We produce a vertical acetylene abundance profile that is compatible with both CIRS and UVIS, with reduced abundances at pressures <1 mbar: the 0.1 mbar abundances are 1.21 ± 0.07 ppm for acetylene and 20.8 ± 5.1 ppm for ethane. Finally, we perform a sensitivity study for the JUICE ultraviolet spectrograph, which has extended wavelength coverage out to 0.21 μm, enabling the retrieval of ammonia and phosphine abundances, in addition to acetylene and ethane.
79 ASTRONOMY AND ASTROPHYSICS↗
Soft X-ray and EUV emission spectra of beryllium plasma produced by neodymium-glass laser radiation with broad frequency and angular spectra
We present the results of an experimental study of soft X-ray (SXR) and extreme ultraviolet emission spectra of the plasma produced by exposing a plane solid beryllium target to laser radiation with broad frequency and angular spectra. SXR lines up to 1s – 9p of Be IV as well as the plasma continuum are recorded for a laser focal-spot intensity of 5.3 × 10{sup 13} W cm{sup −2}. To model the SXR beryllium plasma spectra, simulations are carried out using the INDHAUS programme and the FLYCHK code in the framework of local thermodynamic equilibrium model, which agree nicely with experimentally obtained results. (laser plasma)
36 MATERIALS SCIENCE↗
Cooling of the white dwarf in U Geminorum between outbursts
We have obtained far-ultraviolet (1150-1610 A) spectra of U Gem with the Faint Object Spectrograph on the Hubble Space Telescope approximately 13 and 70 days after the end of a normal dwarf nova outburst of the system. Both spectra appear dominated by the White Dwarf (WD) in U Gem. At 1400 A, the flux from U Gem declined approximately 28% between the two observations. Detailed comparison of the spectra with solar abundance WD models suggest that average surface temperature of the WD surface cooled from approximately 39,400 K to approximately 32,100 K between the two observations. The main features which are not fitted well by WD models are absorption due to N V lambda lambda-1239, 1243 and emission at Lyman-alpha. These observations provide unambiguous confirmation that the WD in U Gem cools during quiescence, as was suggested by analyses of far-ultraviolet spectra obtained with International Ultraviolet Explorer (IUE) and Hopkins Ultraviolet Telescope (HUT).
Long, Knox S.↗
Isophotal diameters of galaxies at high redshifts
New ultraviolet observations and archival spectra are presented for the bright disk of the galaxy NGC 4736 to derive the ultraviolet surface brightness profile. This is used to predict the appearance of such a galaxy at high redshift. The profiles in red light of 100 galaxies determined by S. Kent (1984) are used with assumed ultraviolet spectra to predict the isophotal diameters of these galaxies as a function of redshift. The results show that, for ground-based imagery, normal spiral galaxies should be resolvable to the largest redshifts (z roughly 1). For space-based imagery, much smaller but brighter galactic disks characterized by extensive star formation will be those resolved at the highest redshifts (z roughly 2.5).
Weedman, Daniel W.↗
Organic Compounds Produced by Photolysis of Realistic Interstellar and Cometary Ice Analogs Containing Methanol
The InfraRed (IR) spectra of UltraViolet (UV) and thermally processed, methanol-containing interstellar / cometary ice analogs at temperatures from 12 to 300 K are presented. Infrared spectroscopy, H-1 and C-13 Nuclear Magnetic Resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry indicate that CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), HCO (the formyl radical), H2CO (formaldehyde), CH3CH2OH (ethanol), HC([double bond]O)NH2 (formamide), CH3C([double bond]O)NH2 (acetamide), and R[single bond]C[triple bond]N (nitriles) are formed. In addition, the organic materials remaining after photolyzed ice analogs have been warmed to room temperature contain (in rough order of decreasing abundance), (1) hexamethylenetetramine (HMT, C6H12N4), (2) ethers, alcohols, and compounds related to PolyOxyMethylene (POM, ([single bond]CH2O[single bond](sub n)), and (3) ketones (R[single bond]C([double bond]O)[single bond]R') and amides (H2NC([double bond]O)[single bond]R). Most of the carbon in these residues is thought to come from the methanol in the original ice. Deuterium and C-13 isotopic labeling demonstrates that methanol is definitely the source of carbon in HMT. High concentrations of HMT in interstellar and cometary ices could have important astrophysical consequences. The ultraviolet photolysis of HMT frozen in H2O ice readily produces the 'XCN' band observed in the spectra of protostellar objects and laboratory ices, as well as other nitriles. Thus, HMT may be a precursor of XCN and a source of CN in comets and the interstellar medium. Also, HMT is known to hydrolyze under acidic conditions to yield ammonia, formaldehyde, and amino acids. Thus, HMT may be a significant source of prebiogenic compounds on asteroidal parent bodies. A potential mechanism for the radiative formation of HMT in cosmic ices is outlined.
Bernstein, Max P.↗
Echelle spectra image processing for the International Ultraviolet Explorer
This paper presents the techniques needed to convert the International Ultraviolet Explorer (IUE) high-resolution echelle spectra into useful scientific data. The image is obtained with a digitally controlled vidicon camera system. The processes that must be carried out on the image include: noise removal, correction for geometric and optical distortion, nonuniform photometric corrections, and two-dimensional wavelength determination. Results from the breadboard camera system are presented.
Klinglesmith, D. A.↗
Ultraviolet and optical spectroscopy of Cn 1-1 (= HDE 330036)
Ultraviolet and optical spectra of Cn 1-1 are presented. This stellar object has strong emission lines superposed on the absorption spectrum of an F5 III-IV star. It has been called both a symbolic star and a planetary nebula. Optical spectra taken over a period of two years do not show any variations in radial velocities. The radial velocities of the absorptionand emission-line spectra appear to be the same. The ultraviolet and optical spectra did not show variations in appearance over the period of observations. The interstellar extinction and distance are estimated by various methods, and values of c = 0.4 and d = 450 pc are adopted. The emission-line region is characterized by high-electron density and temperature and by enhancements over solar values in C/O and N/O. It is proposed that Cn 1-1 is a dense planetary nebula involved in a binary system. If so, the enhancements in abundances derived from the observations suggest that the planetary nebula is associated with a relatively massive progenitor star.
Lutz, J. H.↗
The Spectrum of Jupiter's Great Red Spot: The Case for Ammonium Hydrosulfide (NH4SH)
Here we present new ultraviolet-visible spectra of irradiated ammonium hydrosulfide (NH4SH), a reported Jovian atmospheric cloud component, for a range of temperatures and radiation doses and make assignments to the spectral features. We show that the combination of radiolysis and thermal annealing of NH4SH causes the originally featureless ultraviolet-visible reflectance spectrum to evolve into one that absorbs in the ultraviolet-visible region. Furthermore, we find that our laboratory spectra resemble HST (Hubble Space Telescope) spectra below 500 nanometers, suggesting that the more stable reaction products of NH4SH radiolysis are likely an important component of the Great Red Spot.
Jupiter's Great Red Spot (GRS)↗
The Spectrum of Jupiters Great Red Spot: the Case for Ammonium Hydrosulfide (NH4SH)
Here we present new ultraviolet-visible spectra of irradiated ammonium hydrosulfide (NH4SH), a reported Jovian atmospheric cloud component, for a range of temperatures and radiation doses and make assignments to the spectral features. We show that the combination of radiolysis and thermal annealing of NH4SH causes the originally featureless ultraviolet-visible reflectance spectrum to evolve into one that absorbs in the ultraviolet-visible region. Furthermore, we find that our laboratory spectra resemble HST (Hubble Space Telescope) spectra below 500 nanometers, suggesting that the more stable reaction products of NH4SH radiolysis are likely an important component of the Great Red Spot.
Jupiter Atmosphere↗
Hubble Space Telescope Eclipse Observations of the Nova Like Cataclysmic Variable UX Ursae Majoris
We present and analyze Hubble Space Telescope observations of the eclipsing nova-like cataclysmic variable UX UMa obtained with the Faint Object Spectrograph. Two eclipses each were observed with the G160L grating (covering the ultraviolet waveband) in 1994 August and with the PRISM (covering the near-ultraviolet to near-infrared) in November of the same year. The system was about 50% brighter in November than in August, which, if due to a change in the accretion rate, indicates a fairly substantial increase in Mass accretion by about 50%. The eclipse light curves are qualitatively consistent with the gradual occultation of an accretion disk with a radially decreasing temperature distribution. The light curves also exhibit asymmetries about mideclipse that are likely due to a bright spot at the disk edge. Bright-spot spectra have been constructed by differencing the mean spectra observed at pre- and posteclipse orbital phases. These difference spectra contain ultraviolet absorption lines and show the Balmer jump in emission. This suggests that part of the bright spot may be optically thin in the continuum and vertically extended enough to veil the inner disk and/or the outflow from UX UMa in some spectral lines. Model disk spectra constructed as ensembles of stellar atmospheres provide poor descriptions of the observed posteclipse spectra, despite the fact that UX UMa's light should be dominated by the disk at this time. Suitably scaled single temperature model stellar atmospheres with T(sub eff) approximately equals 12,500-14,500 K actually provide a better match to both the ultraviolet and optical posteclipse spectra. Evidently, great care must be taken in attempts to derive accretion rates from comparisons of disk models to observations. One way to reconcile disk models with the observed posteclipse spectra is to postulate the presence of a significant amount of optically thin material in the system. Such an optically thin component might be associated with the transition region ("chromosphere") between the disk photosphere and the fast wind from the system whose presence has been suggested by Knigge and Drew. In any event, the wind/ chromosphere is likely to be the region in which many, if not most, of the UV lines are formed. This is clear from the plethora of emission lines that appear in the mideclipse spectra, some of which appear as absorption features in spectra taken at out-of-eclipse orbital phases.
Knigge, Christian↗
Photoabsorption and photoionization of N2 near the first ionization threshold
The photoabsorption and photoionization spectra of molecular nitrogen, N2, near the first ionisation threshold display numerous intense resonances that have not been satisfactorily assigned to date. Principal among these is a pair of broad resonances between 126,200 and 126,600 cm−1 commonly referred to as the ”cathedral” bands. Here, we present new double-resonance photoionization spectra in this region recorded via the 𝑎′′ 1Σ+ 𝑔,𝑣′=0 intermediate state as well as new high-resolution, vacuum-ultraviolet photoabsorption spectra of 14N2,14N15N, and 15N2 to provide additional insight into the assignment of these features. Progress towards a fully consistent interpretation of the existing data on these bands is discussed, and a route towards a comprehensive description of the N2 absorption spectrum up to the 𝐵 2Σ+ 𝑢 state of N+ 2 is proposed.
Nitrogen, vacuum ultraviolet absorption, photoioni↗
Ultraviolet spectroscopy of R Coronae Borealis
Observations of the hydrogen-deficient supergiant R CrB were obtained with the IUE over an interval of 54 days in order to study the nature of this star's irregular, small-amplitude variations in light. By chance, the series of observations coincided with a dip in the light intermediate between the normal fluctuations and the deep declines associated with the formation of an obscuring dust cloud. High-resolution spectra have been used to search for radial velocity variations, while low-resolution spectra yield ultraviolet light curves down to 1810 A. Both types of spectra have been analyzed for indications of temperature changes. It is found that a combination of photospheric temperature variation and variable extinction is necessary to account for the details of the observations. A simple, ad hoc, periodic model is presented in which the amount of obscuring dust varies in proportion to the drop in temperature, but at a later time, reproduces the wavelength dependence of both the amplitudes and phase shifts of the light curves. The radial velocities are consistent with pulsation being responsible for the temperature variation.
Holm, A. V.↗
Reassignment of the Iron (3) Absorption Bands in the Spectra of Mars
Absorption features in the near-infrared and visible region reflectance spectra of Mars have been assigned to specific Fe (3+) crystal-field and o(2-) yields Fe(3+) charge transfer transitions. Recently, near-ultraviolet absorption spectra of iron oxides were obtained and the energies of o(2-) yields Fe(3+) charge-transfer (LMCT) transitions were determined from accurate SCF-X # alpha-SW molecular orbital calculations on (FeO6)(9-) and (FeO4)(5-) clusters. Both the theoretical and experimental results, together with existing data in the literature, show that some of the previous Fe(3+) band assignments in the spectra of Mars need to be revised. The theory of Fe(3+) spectra in minerals is discussed and applied to the spectrum of Mars.
Sherman, D. M.↗
Low resolution ultraviolet and optical spectrophotometry of symbiotic stars
Low resolution International Ultraviolet Explorer spectra combined with optical spectrophotometry provide absolute flux distributions for seven symbiotic variables from 1200 to 6450 A. For five stars (EG And, BF Cyg, CI Cyg, AG Peg, and Z And) the data are representative of the quiescent/out-of-eclipse energy distributions; for CH Cyg and AX Per, the observations were obtained following their atest outburst in 1977 and 1978, respectively. The de-reddened distributions reveal a remarkable diversity of both line spectra and continua. While the optical and near infrared regions lambda = 5500 A) are well represented by single component stellar models, multicomponent flux distributions are required to reproduce the ultraviolet continua.
Slovak, M. H.↗
Chromospheres of classical Cepheids
The International Ultraviolet Explorer spectra of five classical Cepheids were obtained in the short and the long wavelength regions at low dispersion, curves and emission line strengths were obtained from the low resolution spectra. The amplitudes of the light curves increase with decreasing wavelength except around 1550 A where the amplitude is surprisingly small. The emission line fluxes behave differently in the various stars and it appears that bumps in the ultraviolet light curves are related to the behavior of the chromospheres. However, the strengths of the emission lines are roughly comparable to nonvariable stars of similar temperature and luminosity. The high resolution spectra were used to study the fluxes of the emission from the Mg II h and k lines. It is found that the emission components come and go during the cycles and the behavior differs from one star to another, with generally stronger and more persistent emission at longer periods. This is compared with the times of appearance of the Ca II H and K emission features and provides insight into the way in which the chromosphere reacts to shock waves generated by the pulsation of the star.
Schmidt, E. G.↗
Neutral Gas Temperature Estimates in an Inductively Coupled CF4 Plasma by Fitting Diatomic Emission Spectra
This work examines the accuracy of plasma neutral temperature estimates by fitting the rotational band envelope of different diatomic species in emission. Experiments are performed in an inductively coupled CF4 plasma generated in a Gaseous Electronics Conference reference cell. Visible and ultraviolet emission spectra are collected at a power of 300 W (approximately 0.7 W/cc) and pressure of 30 mtorr. The emission bands of several molecules (CF, CN, C2, CO, and SiF) are fit simultaneously for rotational and vibrational temperatures and compared. Four different rotational temperatures are obtained: 1250 K for CF and CN, 1600 K for CO, 1800 K for C2, and 2300 K for SiF. The vibrational temperatures obtained vary from 1750-5950 K, with the higher vibrational temperatures generally corresponding to the lower rotational temperatures. These results suggest that the different species have achieved different degrees of equilibration between the rotational and vibrational modes and may not be equilibrated with the translational temperatures. The different temperatures are also related to the likelihood that the species are produced by ion bombardment of the surface, with etch products like SiF, CO, and C2 having higher temperatures than species expected to have formed in the gas phase.
Cruden, Brett A.↗