Satellite Line Emission Research Articles

CONSTRAINTS ON OH MEGAMASER EXCITATION FROM A SURVEY OF OH SATELLITE LINES

We report the results of a full-Stokes survey of all four 18 cm OH lines in 77 OH megamasers (OHMs) using the Arecibo Observatory. This is the first survey of OHMs that included observations of the OH satellite lines; only 4 of the 77 OHMs have existing satellite line observations in the literature. In 5 sources, satellite line emission is detected, with 3 of the 5 sources re-detections of previously published sources. The 2 sources with new detections of satellite line emission are IRAS F10173+0829, which was detected at 1720 MHz, and IRAS F15107+0724, for which both the 1612 MHz and 1720 MHz lines were detected. In IRAS F15107+0724, the satellite lines are partially conjugate, as 1720 MHz absorption and 1612 MHz emission have the same structure at some velocities within the source, along with additional broader 1612 MHz emission. This is the first observed example of conjugate satellite lines in an OHM. In the remaining sources, no satellite line emission is observed. The detections and upper limits are generally consistent with models of OHM emission in which all of the 18 cm OH lines have the same excitation temperature. There is no evidence for a significant population of strong satellite line emitters among OHMs.

The Effect of 53 μm IR Radiation on 18 cm OH Megamaser Emission

OH megamasers (OHMs) emit primarily in the main lines at 1667 and 1665 MHz and differ from their Galactic counterparts due to their immense luminosities, large line widths, and 1667/1665 MHz flux ratios, which are always greater than 1. We find that these maser properties result from strong 53 μm radiative pumping combined with line overlap effects caused by turbulent line widths ~20 km s−1; pumping calculations that do not include line overlap are unreliable. A minimum dust temperature of ~45 K is needed for inversion, and maximum maser efficiency occurs for dust temperatures ~80-140 K. We find that warmer dust can support inversion at lower IR luminosities, in agreement with observations. Our results are in good agreement with a clumpy model of OHMs, with clouds sizes 1 pc and OH column densities ~5 × 1016 cm−2, that is able to explain both the diffuse and compact emission observed for OHMs. We suggest that all OH main-line masers may be pumped by far-IR radiation, with the major differences between OHMs and Galactic OH masers caused by differences in line width produced by line overlap. Small Galactic maser line widths tend to produce stronger 1665 MHz emission. The large OHM line widths lead to inverted ground-state transitions having approximately the same excitation temperature, producing 1667/1665 MHz flux ratios greater than 1 and weak satellite line emission. Finally, the small observed ratio of pumping radiation to dense molecular gas, as traced by HCN and HCO+, is a possible reason for the lack of OH megamaser emission in NGC 6240.

K-shell spectra from hot dense aluminum layers buried in carbon and heated by ultrashort laser pulses

Ultrashort laser pulses allow for the generation of hot plasmas near solid state densities. For this purpose a Ti:Sapphire laser was used, which delivers after frequency doubling, pulses of high contrast with an energy of about 60 mJ and a duration of 150 fs at 395 nm . The typical intensity on the target was a few 10 17 W/cm 2 . To achieve a high degree of uniformity we used targets consisting of a 25 nm thin Al tracer layer buried at different depths up to 400 nm in solid carbon. Time-integrated Al K-shell spectra are presented. Characteristic features of the spectra are significant high-order satellite line emission, strong line broadening and a center-of-mass line shift to the red, which was observed in transitions from principal quantum number n=2 or 3 to 1. Accurate measurement of the shift was made possible by using the cold Si K α line as an absolute wavelength calibration. In addition to time-integrated measurements, we used an ultrafast X-ray streak camera to obtain time and spectrally resolved spectra. Typical durations of the Ly α and He α lines are in the range 2–4 ps. The experimental results are compared with a time-dependent model, which combines hydrodynamic simulations, time-dependent atomic kinetics, detailed spectral line shapes including line shifts, and radiation transport.

A high-sensitivity OH 5-cm line survey in late-type stars

We have undertaken a comprehensive search for 5-cm excited OH maser emission from evolved stars representative of various stages of late stellar evolution. Observed sources were selected from known 18-cm OH sources. This survey was conducted with the 100-m Effelsberg telescope to achieve high signal to noise ratio observations and a sensitivity limit of about 0.05 to 0.1 Jy. A total of 65 stellar sources were searched for both main line and satellite line emission. We confirm the previous detection of 5 cm OH in Vy 2-2, do not confirm emission from NML-Cyg and do not report any other new detection within the above sensitivity limit. Implications of these results on the pumping mechanism of the OH radical in circumstellar envelopes are briefly discussed.

Dielectronic satellite contributions to Ne VIII and Ne IXK-shell spectra

K{alpha} spectra of heliumlike neon and associated lithiumlike, berylliumlike, and boronlike satellite line emission have been observed with a high-resolution crystal spectrometer on the Lawrence Livermore Electron Beam Ion Trap. The KLL dielectronic recombination satellites were resolved from their He-like parent lines in electron energy space, and their wavelengths and resonance strengths measured. The wavelength measurements achieved a typical accuracy of a few mAa, with two measurements accurate to better than one part in 10000. By normalizing to the He-like resonance line, w, we measure Li-like satellite resonance strengths that are 10% to 46% lower than predicted by theoretical models. The wavelengths and relative strengths of Be-like KLL satellites were also measured, and absolute strengths were obtained by normalizing to the collisionally excited Li-like qr satellite blend.

DIAGNOSING PLASMA CONDITIONS IN TARGETS IRRADIATED BY INTENSE LIGHT ION BEAMS USING K α SATELLITE LINE INTENSITY RATIOS

The characteristics of K α satellite line emission generated in intense light ion beam experiments is investigated. Inner-shell X-ray lines are emitted from moderate-temperature ( T∼10 1–10 2 eV) plasmas as 2p electrons of the target ions fill in K-shell vacancies created by beam ion-impact ionization. We focus, in particular, on the utilization of line intensity ratios from He-like and Li-like ions to diagnose target plasma temperatures and densities. Although the K α transitions for the He-like and Li-like atomic systems are the same as those in laser-produced and Z-pinch plasmas, the populating mechanisms for their upper states are completely different. That is, the upper states are populated from lower ionization stages by ion-impact ionization. This enables diagnosis of plasmas in the 10–100 eV temperature regime using the extensive instrumentation developed for X-ray crystal spectroscopy. Target plasma characteristics are simulated using a one-dimensional collisional-radiative equilibrium model in which atomic level populations are computed by solving multilevel statistical equilibrium equations self-consistently with the radiation field and ion beam properties. We utilize atomic models which include for all ionization stages a detailed treatment of autoionization states which have K-shell vacancies. Results are presented for Li beam-heated Al and Cl plasmas and proton beam-heated Al plasmas. We find that, as in the case of laser-produced plasmas, the He-like intercombination-to-resonance ratio provides a good density diagnostic. However, because the He α line is produced in ion beam-heated plasmas with a relatively low degree of ionization, it is less susceptible to resonant self-absorption effects as compared to laser plasmas. In addition, the Li-like satellite line structure is significantly different for plasmas heated by ion beams. Unlike laser-produced plasmas, the Li(dabc) and Li(qr) lines tend to be more intense than the Li(kj) lines. Because of this, we find the Li(dabc)-to-He α ratio to be a good temperature diagnostic for intense light ion beam experiments. We also discuss the effects of beam-induced multiple ionization, photoionization, and resonant self-absorption on the line ratio diagnotics.

Hydrogen‐like Ion Emission in the Spectra of Low‐Mass X‐Ray Binaries

We study the emission from H-like ions, particularly oxygen and neon, observed in ASCA spectra of low-mass X-ray binaries (LMXBs). The observed strengths of Lyα emission lines relative to the recombination continua differ from the classical recombination model. This suggests a different excitation mechanism for the lines. Various mechanisms are considered, which include three-body recombination, collisional excitation, recombination satellite line emission, and resonant fluorescent excitation. We find that the detection of Lyman recombination continuum implies that the plasma is photoionized, in agreement with previous studies by Hatchett, Buff, & McCray and Liedahl & Paerels. Under collisional ionization conditions, on the other hand, the Lyman continuum should be negligible unless the temperature were greater than 3 × 106 K. Otherwise, the enhancement of Lyα emission with respect to the continuum may be due to (1) three-body recombination at electron densities greater than 1017 cm-3 and temperatures below 2 × 105 K, (2) contributions to the recombination spectrum from collisional excitation of the H-like ionization stage, (3) contributions to recombination Lyα emission from satellite lines due to recombination onto the He-like ionization stage, and (4) contributions to the recombination spectrum from resonant fluorescence excitation of the H-like ionization stage. Further observations of higher order Lyman series lines and lines from other ionization stages are suggested to discriminate between the various excitation mechanisms. In addition, the implications of the different spectral formation mechanisms to the hydrodynamic accretion model of LMXBs are discussed.

Polarization-dependent spectra of x-ray dielectronic satellite lines of Be-like Fe

We have studied the polarization properties of dielectronic satellite lines in Be-like Fe ions excited through resonant electron capture by an electron beam. Using the photon density-matrix formalism, we have calculated the degree of polarization and polarization-dependent spectra of dielectronic satellite lines, i.e., the spectral intensity distribution of lines associated with a given polarization state. Theoretical results have been compared with experiments performed at the Lawrence Livermore National Laboratory electron-beam ion trap where dielectronic satellite line emission from Fe ions produced at different energies of the electron beam was simultaneously recorded with two crystal spectrometers. These spectrometers had different polarization sensitivities. The experimental spectra recorded by the two spectrometers are reproduced by the theory. This ability to model the polarization dependence of x-ray line spectra is important for the diagnosis of electron beams in plasmas.

Polarization of x-ray Li- and Be-like Fe satellite lines excited by an electron beam

We have calculated the polarization properties of dielectronic satellite lines in Li- and Be-like Fe ions excited through resonance electron capture by a monoenergetic electron beam. Following the density matrix formalism, we have computed the degree of polarization and the spectral intensity distribution of dielectronic satellites associated with a given polarization state. Theoretical results were compared with experiments performed at the Livermore Electron Beam Ion Trap where satellite line emission from Fe ions was simultaneously recorded with two crystal spectrometers. These results are relevant to diagnostic applications of x-ray line polarization spectroscopy in plasmas.

Analysis ofKα line emission from aluminum plasmas created by intense proton beams

X-ray satellite line emission from targets irradiated by intense-light ion beams can be used to diagnose plasma conditions and beam properties. We present results from our analysis of spectroscopic measurements of x-ray K\ensuremath{\alpha} satellites emitted from a target irradiated by an intense-light ion beam. In this experiment, performed on the Particle Beam Fusion Accelerator-II device at Sandia, an Al target was irradiated with a 4--6 MeV proton beam with a peak power density of 1--2 TW/${\mathrm{cm}}^{2}$. Up to 15% of the beam electrical current was in the form of carbon contaminants. A time-integrated spectrum was obtained with a resolution of \ensuremath{\lambda}/\ensuremath{\Delta}\ensuremath{\lambda}>1200. In our analysis, collisional radiative equilibrium (CRE) calculations were performed to study the dependence of the Al K\ensuremath{\alpha} emission spectrum on plasma and beam properties. Good agreement is obtained between calculated satellite spectra and the emission features observed in the experimental spectrum. We find that excited states with M-shell spectator electrons contribute significantly to K\ensuremath{\alpha} satellite emission spectra, exhibiting relatively broad lines at wavelengths blueshifted with respect to those originating from ground-state configurations. Because of opacity effects, it is likely that only radiation emitted from the outer skin of the target plasma was seen by the detector in the experiment. It is also shown that resonant self-absorption can skew the spectrum towards apparent higher ionization stage. Our results suggest that emission spectroscopy of x-ray satellite lines from thin tracer layers offers a potentially valuable technique for determining plasma conditions in intense-light-ion-beam experiments.

Aluminum K-shell line emission as a diagnostic in light ion beam fusion experiments

K α satellite line emission from targets irradiated by intense light ion beams can be used to diagnose plasma temperatures and densities. The fluorescence lines are created as 2p electrons drop down to fill 1s vacancies that result from ion beam-induced ionizations. We present results from collisional-radiative equilibrium calculations for thin Al diagnostic layers to illustrate the dependence of the Kα emission spectrum on temperature, density, and layer thickness. We also discuss the effects of opacity on the spectrum and the contribution from Kα transitions involving excited states.

Time-resolved spectroscopic measurements of high density in Ar-filled microballoon implosions.

We report on the analysis of time-resolved x-ray spectra from direct-drive, Ar-filled polymer shell implosion experiments in which we trace the time evolution of the electron density through stagnation. Very high electron densities in the range 2--8/times/10/sup 24/ cm/sup /minus/3/ are inferred. We also discuss several novel spectral features, including large Stark broadening of satellite line emission, optical thicknesses for resonant transitions lower than expected, and the onset of density-dependent ''blue satellites'' on the high-energy wing of the He/sub /alpha// line.

OH masers in short-period Mira and semiregular variable stars

view Abstract Citations (17) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS OH masers in short-period Mira and semiregular variable stars. Dickinson, D. F. ; Turner, B. E. ; Jewell, P. R. ; Benson, P. J. Abstract The authors have made a systematic search in all four OH lines for maser emission from the short-period Mira variables and the known short-period semiregular maser stars. R Ceti was detected in the main lines, the first short-period (166 days) Mira ever found in OH. None of the short-period Miras searched showed water emission. The authors also present spectra of three SiO detections made in a very limited sample of the short-period Mira variables. Six new OH lines were detected in the semiregular variables; all are Type I stars devoid of any satellite line emission. Both classes of star are weak OH emitters and there is a relative lack of circumstellar material as evidenced by the modest infrared excess shown in the 2.2 - 11 μ color index. These facts are probably related and lend support to the idea that far-infrared radiation is the primary OH maser pump in these stars. Publication: The Astronomical Journal Pub Date: September 1986 DOI: 10.1086/114193 Bibcode: 1986AJ.....92..627D Keywords: Hydroxyl Emission; Interstellar Masers; Mira Variables; Semiregular Variable Stars; Stellar Spectrophotometry; Far Infrared Radiation; Line Spectra; Silicon Oxides; Astrophysics full text sources ADS | data products SIMBAD (102)

Spectroscopic study of stimulated Brillouin scattering

Results are summarized of a diagnostic study of underdense plasma targets, leading to the first observation of stimulated Brillouin scattering arising from thermal-level fluctuations. Included are; (1) a detailed analysis of spectroscopic measurements of the plasma before and during laser heating, (2) computer calculations of plasma evolution during the laser pulse, (3) observations and anlaysis of Brillouin scatter, and (4) spectroscopic observations of forbidden satellite line emission during Brillouin scatter.