scholarly journals Possible detection of hydrazine on Saturn’s moon Rhea

2021 ◽  
Vol 7 (4) ◽  
pp. eaba5749
Author(s):  
Mark Elowitz ◽  
Bhalamurugan Sivaraman ◽  
Amanda Hendrix ◽  
Jen-Iu Lo ◽  
Sheng-Lung Chou ◽  
...  
Keyword(s):  
Uv Spectroscopy ◽  
Absorption Feature ◽  
Icy Satellites ◽  
Laboratory Measurements ◽  
Hydrazine Monohydrate ◽  
Broad Absorption ◽  
Plausible Candidate ◽  
Ultraviolet Reflectance ◽  
Far Ultraviolet ◽  
Imaging Spectrograph

We present the first analysis of far-ultraviolet reflectance spectra of regions on Rhea’s leading and trailing hemispheres collected by the Cassini Ultraviolet Imaging Spectrograph during targeted flybys. In particular, we aim to explain the unidentified broad absorption feature centred near 184 nm. We have used laboratory measurements of the UV spectroscopy of a set of candidate molecules and found a good fit to Rhea’s spectra with both hydrazine monohydrate and several chlorine-containing molecules. Given the radiation-dominated chemistry on the surface of icy satellites embedded within their planets’ magnetospheres, hydrazine monohydrate is argued to be the most plausible candidate for explaining the absorption feature at 184 nm. Hydrazine was also used as a propellant in Cassini’s thrusters, but the thrusters were not used during icy satellite flybys and thus the signal is believed to not arise from spacecraft fuel. We discuss how hydrazine monohydrate may be chemically produced on icy surfaces.

scholarly journals Spectrophotometry of the Broad Continuum Features in Magnetic AP Stars

1986 ◽  
Vol 90 ◽  
pp. 201-204
Author(s):  
Diane M. Pyper ◽  
Saul J. Adelman
Keyword(s):  
Color Temperature ◽  
Absorption Feature ◽  
Intensity Maximum ◽  
Energy Distributions ◽  
Broad Absorption ◽  
Solar Abundance ◽  
Normal Star ◽  
Ap Stars ◽  
Relationship Of ◽  
Broad Continuum

The strongest broad absorption feature in the peculiar energy distributions of the Ap stars is that centered at about 5200 Å, thus the Stromgren y band and the Geneva VI band are most affected in stars in which this feature is strong. Fig. 1 shows bandpasses (full width at ½ intensity maximum) of three widely used photometric systems superimposed on two of our scans of Ap stars and two solar abundance line blanketed model atmospheres (Kurucz 1979). It is seen that both the y and VI bands fall entirely within the λ5200 feature. The plot (Fig. 2a) of b-y vs. Tpc (the color temperature of the red end of the Paschen continuum), shows that the b-y colors for most of our sample of Ap stars are displaced to the blue of the b-y, Teff relationship of Relyea and Kurucz (1978). In Fig. 2b, Δ(b−y) = (model b−y) − (observed b−y), for a given temperature is plotted vs. ΔWS2(5200), a spectrophotometric index measuring the equivalent width of the λ5200 feature. There is a strong correlation between Δ(b-y) and ΔWS2(5200), indicating quantitatively the large effect of the λ5200 feature on the y band, previously discussed by Adelman (1979). The deviations in Ap star B2-G values from the normal star B2-G vs. T curve are much less than for b-y, as the Geneva G band is largely outside the λ5200 feature (Fig. 2c). Thus B2-G is a better temperature indicator for Ap stars than is b-y (also see Hauck and North 1982).

Far-Ultraviolet Reflectance Spectra of Ionic Crystals

1971 ◽  
Vol 26 (21) ◽  
pp. 1317-1320 ◽  
Author(s):  
G. W. Rubloff ◽  
J. Freeouf ◽  
H. Fritzsche ◽  
K. Murase
Keyword(s):  
Reflectance Spectra ◽  
Ionic Crystals ◽  
Ultraviolet Reflectance ◽  
Far Ultraviolet

Far-Ultraviolet Spectra of Broad Absorption Line QSOs and Constraints on Models for the Ionization Structure and Metallicity of the BAL-Region Gas

1996 ◽  
Vol 463 ◽  
pp. 110 ◽  
Author(s):  
David A. Turnshek ◽  
Michael, Jr. Kopko ◽  
Eric Monier ◽  
Donette Noll ◽  
Brian R. Espey ◽  
...  
Keyword(s):  
Absorption Line ◽  
Broad Absorption ◽  
Ultraviolet Spectra ◽  
Broad Absorption Line ◽  
Ionization Structure ◽  
Far Ultraviolet

A Discussion on solar studies with special reference to space observations - A high resolution solar ultraviolet spectrum between 200 and 220 nm

1971 ◽  
Vol 270 (1202) ◽  
pp. 29-46 ◽  
Keyword(s):  
High Resolution ◽  
Solar Spectrum ◽  
Ultraviolet Spectrum ◽  
Absorption Feature ◽  
Intensity Analysis ◽  
Echelle Spectrograph ◽  
Broad Absorption ◽  
First Time ◽  
Solar Ultraviolet ◽  
The Continuum

A high resolution solar spectrum in the range 200 to 220 nm has been recorded with an echelle spectrograph launched in, a sun-pointing Skylark rocket. The data have been reduced and are presented as intensity-wavelength plots together with a wavelength list and proposed identifications. A broad absorption feature at 212.4 nm is assigned to a single source and an intensity analysis confirms this to be the non-resonance Sii line at 212.412 nm. The discontinuity in the continuum intensity near 208.7 nm is revealed with high resolution for the first time and is assigned to the photoionization edge of A11. An analysis shows that its intensity drop and wavelength position can only be explained by adjustments to the solar model in the region 0.001 < T 5000 < 0.2.

Ganymede's Far‐Ultraviolet Reflectance: Constraining Impurities in the Surface Ice

2020 ◽  
Vol 125 (9) ◽  
Author(s):  
P. M. Molyneux ◽  
J. D. Nichols ◽  
T. M. Becker ◽  
U. Raut ◽  
K. D. Retherford
Keyword(s):  
Ultraviolet Reflectance ◽  
Far Ultraviolet ◽  
Surface Ice

scholarly journals First detection of bromine and antimony in hot stars

2018 ◽  
Vol 614 ◽  
pp. A96 ◽  
Author(s):  
K. Werner ◽  
T. Rauch ◽  
M. Knörzer ◽  
J. W. Kruk
Keyword(s):  
Model Atmosphere ◽  
Atomic Diffusion ◽  
Laboratory Measurements ◽  
Solar Abundance ◽  
Hot Stars ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
Resonance Doublet ◽  
Chemically Peculiar Stars ◽  
Far Ultraviolet

Bromine (Z = 35) and antimony (Z = 51) are extremely difficult to detect in stars. In very few instances, weak and mostly uncertain identifications of Br I, Br II, and Sb II in relatively cool, chemically peculiar stars were successful. Adopted solar abundance values rely on meteoritic determinations. Here, we announce the first identification of these species in far-ultraviolet spectra of hot stars (with effective temperatures of 49 500–70 000 K), namely in helium-rich (spectral type DO) white dwarfs. We identify the Br VI resonance line at 945.96 Å. A previous claim of Br detection based on this line is incorrect because its wavelength position is inaccurate by about 7 Å in atomic databases. Taking advantage of precise laboratory measurements, we identify this line as well as two other, subordinate Br VI lines. Antimony is detected by the Sb V resonance doublet at 1104.23/1225.98 Å as well as two subordinate Sb VI lines. A model-atmosphere analysis reveals strongly oversolar Br and Sb abundances that are caused by radiative-levitation dominated atomic diffusion.

scholarly journals The Structure and Dynamics of the Outer Atmosphere of ∊ Eri

2004 ◽  
Vol 219 ◽  
pp. 254-258
Author(s):  
S. A. Sim ◽  
C. Jordan
Keyword(s):  
Upper Atmosphere ◽  
Mhd Waves ◽  
New Information ◽  
Sufficient Energy ◽  
Outer Atmosphere ◽  
Measured Line ◽  
Far Ultraviolet ◽  
Semi Empirical ◽  
Imaging Spectrograph ◽  
The Magnetic Field

We present results from our study of the active dwarf ∊ Eri (K2 V) based on ultraviolet spectra recorded with the Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectroscopic Explorer. A combination of simple theoretical arguments and observational constraints derived from measured line fluxes are used to deduce new information about the structure of the upper transition region/corona. The area filling factor of emitting material is determined in the upper atmosphere as a function of temperature. This provides new constraints on how the magnetic field might spread out in the atmosphere of an active main sequence star. Measured emission line widths are used, together with a new semi-empirical model of the atmosphere, to place limits on the energy fluxes carried by MHD waves. These are compared with estimates of the energy input required to support the combined radiative/conductive losses in the upper atmosphere. It is shown that, in principle, waves which propagate at the Alfvén speed could provide sufficient energy to heat the corona.

The Energy Distribution of Several Ap Stars

1976 ◽  
Vol 32 ◽  
pp. 627-632 ◽  
Author(s):  
Johannes Hardorp
Keyword(s):  
Energy Distribution ◽  
Special Interest ◽  
Large Amplitude ◽  
Light Variation ◽  
Light Curves ◽  
Absorption Feature ◽  
Energy Distributions ◽  
Broad Absorption ◽  
Ap Stars ◽  
Absorption Edges

SummaryEnergy distributions were observed in closely spaced 50 Å intervals from 3250 Å to 6000 Å and for some stars to 7950 Å. The broad absorption feature at 5200 Å appears in most Ap stars and persists through all phases of light-variation. No sharp absorption edges were found. Of special interest are the large-amplitude light variables HD 51418 and HD 125248. The main differences of their light curves are explained by different aspects of the oblique rotators.

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