Temperature Sensitive Line Ratios Research Articles

Low-ionization structures in planetary nebulae – III. The statistical analysis of physico-chemical parameters and excitation mechanisms

ABSTRACT Nearly 30 yr after the first detailed studies of low-ionization structures (LISs) in planetary nebulae (PNe), we perform a statistical analysis of their physical, chemical, and excitation properties, by collecting published data in the literature. The analysis was made through the contrast between LISs and high-ionization structures – rims or shells – for a large sample of PNe, in order to highlight significant differences between these structures. Our motivation was to find robust results based on the largest sample of LISs gathered so far. (i) Indeed, LISs have lower electron densities (Ne[S ii]) than the rims/shells. (ii) The nitrogen electron temperatures (Te[N ii]) are similar between the two groups, while a bimodal distribution is observed for the Te based on [O iii] of the rims/shells, although the high- and low-ionization structures have Te[O iii] of similar median values. (iii) No significant variations are observed in total abundances of He, N, O, Ne, Ar, Cl, and S between the two groups. (iv) Through the analysis of several diagnostic diagrams, LISs are separated from rims/shells in terms of excitation. From two large grids of photoionization and shock models, we show that there is an important overlap between both mechanisms, particularly when low-ionization line ratios are concerned. We found a good tracer of high-velocity shocks, as well as an indicator of high- and low-velocity shocks that depends on temperature-sensitive line ratios. In conclusion, both excitation mechanisms could be present; however, shocks cannot be the main source of excitation for most of the LISs of PNe.

High-Resolution Spectroscopy of T Tauri Stars

We have conducted high-resolution spectroscopic observations of a sample of both classical and weak-line T Tauri stars embedded in the Taurus-Auriga molecular cloud using the Okayama Astrophysical Observatory’s 188 cm telescope equipped with HIDES (HIgh Dispersion Echelle Spectrograph). Utilizing the ratios of equivalent widths of specific lines, we efficiently eliminated the effects of “veiling” and determined the atmospheric parameters individually for each object. Eight pairs of temperature-sensitive line-ratios were selected to derive the effective temperature with high precision and reliability. As for the surface gravity, we have developed a new method to determine the value. The method was first tested on observed spectral standards, and the derived surface gravities had a less than 5% deviation from the values in the literature. The derived surface gravities are well within the range of the assumed values for T Tauri stars.

Temperature-sensitive line ratio diagnostics based on Si satellite-to-resonance line ratios for 1s 2–1s np transitions

Dielectronic satellite lines due to 1s 2 n′l′–1s np n′l′ ( n = 3, 4) transitions in Li-like Si (Si XII) occur at 5.818 and 5.565 Å, on the long wavelength side of the He-like Si (Si XIII) 1s 2–1s3p and 1s 2–1s4p lines at 5.681 and 5.384 Å, respectively. They have been extensively observed with the RESIK crystal spectrometer on the Russian spacecraft CORONAS-F. As with corresponding satellites 1s 2 nl–1s2p nl on the long-wavelength side of the Si XIII 1s 2–1s2p resonance line, there is an inverse temperature dependence of the intensity ratio of the satellites to the He-like ion lines ( I sat/ I He). New atomic data are used to calculate the Si XII satellite line intensities and thus the I sat/ I He ratio. RESIK observations of the ratio in solar flares, together with temperatures from the ratio of the two GOES X-ray channels, are compared with theoretical variation of the ratio with temperature. The good agreement indicates this to be a valuable temperature diagnostic for solar flares and laboratory plasmas such as tokamaks. There are implications for similar satellites in Fe line spectra which are observed with broad-band resolution by the RHESSI solar flare mission.

Possible Density Determination of the Nebular Component of Cataclysmic Variables with the N III 4641/4635 Line Ratio

The dependence of the N III 4641/4635 line ratio on the electron density is presented. It is shown that this ratio may be an important diagnostic tool in cataclysmic variables.Pérez-Tijerina, Bohigas & Machorro (2001) used the Chianti code and database developed by the U.S. Nautical Observatory (Landi, 200) in order to find density and temperature sensitive line ratios in the conditions occuring in plasmas produced in pulsed laser deposition experiments for thin film deposition, i.e., around 1018 cm 3 and 104 K. Level populations are determined considering only radiative decay and collisional excitation and de-excitation.

Temperature Measurements in the Solar Transition Region Using NiiiLine Intensity Ratios

UV emission from B-like N and O ions a rather rare opportunity for recording spectral lines in a narrow wavelength range that can potentially be used to derive temperatures relevant to the solar transition region. In these ions, the line intensity ratios of the type (2s2p(sup 2) - 2p(sup 3)) / (2s(sup 2)2p - 2s2p(sup 2)) are very sensitive to the electron temperature. Additionally, the lines involving the ratios fall within a range of only - 12 A; in N III the lines fall in the 980 - 992 A range and in O IV in the 780 - 791 A range. In this work, we explore the use of these atomic systems, primarily in N III, for temperature diagnostics of the transition region by analyzing UV spectra obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory (SOHO). The N III temperature-sensitive line ratios are measured in more than 60 observations. Most of the measured ratios correspond to temperatures in the range 5.7x10(exp 4) - 6.7x10(exp 4) K. This range is considerably lower than the calculated temperature of maximum abundance of N III, which is approx. 7.6x10(exp 4) K. Detailed analysis of the spectra further indicates that the measured ratios are probably somewhat overestimated due to resonant scattering effects in the 2s(sup 2)2p - 2s2p(sup 2) lines and small blends in the 2s2p(sup 2) - 2p3 lines. Actual lower ratios would only increase the disagreement between the ionization balance calculations and present temperature measurements based on a collisional excitation model. In the case of the O IV spectra, we determined that due to the close proximity in wavelength of the weak line (2s2p(sup 2)-2p3 transitions) to a strong Ne VIII line, sufficiently accurate ratio measurements cannot be obtained. Subject headings: atomic data --- atomic processes --- Sun: transition region --- Sun: U V radiation --- techniques: spectroscopic

Using Strong Lines to Estimate Abundances in Extragalactic H ii Regions and Starburst Galaxies

We have used a combination of stellar population synthesis and photoionization models to develop a set of ionization parameter and abundance diagnostics based only on the use of the strong optical emission lines. These models are applicable to both extragalactic H II regions and star-forming galaxies. We show that, because our techniques solve explicitly for both the ionization parameter and the chemical abundance, the diagnostics presented here are an improvement on earlier techniques based on strong emission-line ratios. Our techniques are applicable at all metallicities. In particular, for metallicities above half solar, the ratio [N II]/[O II] provides a very reliable diagnostic since it is ionization parameter independent and does not have a local maximum. This ratio has not previously been used historically because of worries about reliable calibration over such a long baseline, and reddening correction concerns. However, we show that the use of classical reddening curves and standard calibration are quite sufficient to allow this [N II]/[O II] diagnostic to be used with confidence as a reliable abundance indicator. As we had shown, the commonly used abundance diagnostic R23 depends strongly on the ionization parameter, while the commonly used ionization parameter diagnostic [O III]/[O II] depends strongly on abundance. The iterative method of solution presented here allows both of these parameters to be obtained without recourse to the use of temperature-sensitive line ratios involving faint emission lines. We compare three commonly used abundance diagnostic techniques and show that individually, they contain systematic and random errors. This is a problem affecting many abundance diagnostics, and the errors generally have not been properly studied or understood due to the lack of a reliable comparison abundance, except for very low metallicities, where the [O III] λ4363 auroral line is used. Here we show that the average of these techniques provides a fairly reliable comparison abundance indicator against which to test new diagnostic methods. The cause of the systematic effects are discussed, and we present a new optimal abundance diagnostic method based on the use of line ratios involving [N II], [O II], [O III], [S II], and the Balmer lines. This combined diagnostic appears to suffer no apparent systematic errors, can be used over the entire abundance range and significantly reduces the random error inherent in previous techniques. Finally, we give a recommended procedure for the derivation of abundances in the case that only spectra of limited wavelength coverage are available so that the optimal method can no longer be used.

Density and temperature sensitive line ratios in plasmas generated by laser ablation

Solving the statistical equilibrium equations we find line intensity ratios of C III, N III, O III, Si III, and Al III in the visible and ultraviolet range, that are sensitive to electron density and/or temperature in the regime commonly found in pulsed laser deposition. For thin film deposition, the plasma density is between 1012 and 1018 cm−3 and the temperature is close to 104 K. Our results are consistent with experimental data on Al II and Al III, previously reported in the literature. These line intensity ratios are a promising tool to diagnose the physical state of plasmas generated through laser ablation in thin film deposition techniques.

On the oxygen abundance determination in HII regions.

This is our second paper devoted to the problem of line intensity - oxygen abundance calibration starting from the idea of McGaugh (1991) that the strong oxygen lines contain the necessary information to determine accurate abundances in HII regions. The high-metallicity HII regions are considered. A relation of the type O/H=f(P,R23) between oxygen abundance and the value of abundance index R23 introduced by Pagel et al. (1979) and the excitation parameter P (which is defined here as the contribution of the radiation in [OIII]4959,5007 lines to the "total" oxygen radiation) has been derived empirically using the available oxygen abundances determined via measurement of a temperature-sensitive line ratio [OIII]4959,5007/[OIII]4363 (Te - method). By comparing oxygen abundances derived with the Te - method and those derived with the suggested relations (P - method), it was found that the precision of oxygen abundance determination with the P - method is around 0.1 dex and is comparable to that of the Te - method. A relation of the type Te=f(P,R23) between electron temperature and the values of abundance index R23 and the excitation parameter P was derived empirically using the available electron temperatures determined via measurement of temperature-sensitive line ratios. The mean difference between electron temperatures derived through the Te=f(P,23 relation and determined via measurement of the temperature-sensitive line ratio is around 500K.

Visible and Near‐Infrared Spectroscopy of Seyfert 1 and Narrow‐Line Seyfert 1 Galaxies

This paper studies the continuum and emission-line properties of a sample composed of 16 normal Seyfert 1 and seven narrow-line Seyfert 1 (NLS1) galaxies using optical and near-IR CCD spectroscopy. The continuum emission of the galaxies can be described in terms of a combination of stellar population, a nonstellar continuum of power-law form, and Fe II emission. A significative difference in the optical spectral index between NLS1's and normal Seyfert 1's is observed; the latter is steeper. Most NLS1's show Fe II/Hβ ratios larger than those observed in the other Seyfert 1's. In the IRAS band, both groups of galaxies have very similar properties. We have searched for the presence of optically thin gas in the broad-line region (BLR) of the galaxies by comparing the broad O I λ8446 and Hα emission-line profiles. Our analysis show that in the NLS1's, both profiles are similar in shape and width. This result contradicts the hypothesis of thin gas emission in the high-velocity part of the BLR to explain the narrowness of broad optical permitted lines in these objects. Evidence of narrow O I λ8446 emission is found in six galaxies of our sample, implying that this line is not restricted to a pure BLR phenomenon. In the narrow-line region, we find similar luminosities in the permitted and high-ionization lines of NLS1's and normal Seyfert 1's. However, low-ionization lines such as [O I] λ6300, [O II] λ3727, and [S II] λλ6717, 6731 are intrinsically less luminous in NLS1's. Physical properties derived from density- and temperature-sensitive line ratios suggest that the [O II] and [S II] emitting zones are overlapping in normal Seyfert 1's and separated in NLS1's.

N II] AND [O III] MEAN ELECTRON TEMPERATURES IN PLANETARY NEBULAE

ABSTRACT Mean electron tempertures for 106 planetary nebulae are presented, which have been derived using calculations of the values of electron temperature-sensitive line ratios involving forbidden transitions among the 2s2 2p2 3P, 1D, and 1S levels of N+ and O++, based on new electron impact rates and transition probabilities. Comparison of these results with values of Te[N II] and Te[O III] determined previously by Kaler reveal that the present electron temperatures are systematically lower for both ions, and that this discrepancy is correlated with the electron density in the nebula. It is also shown that the average difference tween Te[N II] and Te[O III] in a planetary nebula is somewhat smaller than that derived by Kaler, with the present results implying that the N II and O III temperatures disagree on average by 2070 K as opposed to the 2210 K average found by Kaler.

On the temperature measurement from the O IV emission lines

The new calculations of the Oiv temperature-sensitive EUV line ratios are presented and compared with previous results.

Observational tests for nonequilibrium ionization in the solar corona

Nonequilibrium ionization may be produced by a variety of processes in the solar corona, for example, by mass flows through the large temperature gradients of the transition region or by impulsive heating and cooling. Any deviation from equilibrium ionization would have a strong effect on the radiation from the corona and on the interpretation of solar observations; hence, it is important to determine observational signatures of nonequilibrium. The temperature-sensitive line ratios can be used as such signatures. We examine the line ratios: C IV I(1548.2 A)/I(312.4 A), O IV I(789.4 A)/I(554.4 A), O V I(629.7 A)/I(172.2 A), O VI I(1031.9 A)/I(173.0 A) and O VI I(1031.9 A)/I(150.1 A). These line ratios are calculated for four coronal loop models that have a steady flow and that are known to have significant departures from equilibrium ionization. Our results indicate that, in general, nonequilibrium causes a considerable reduction in the line ratios, more than an order of magnitude in the downflowing leg of the loop model with the largest mass flows. We find that the C IV line ratio is the most sensitive to nonequilibrium. We discuss the implications of our results for observations, specifically, the observations expected from the upcoming SOHO mission.

Temperature-sensitive line ratios of the lithium-like ion O vi

The intensity ratios of emission lines from the lithium-like ion Ovi are calculated as a function of electron temperature using recent computations of collision strengths by Zhang, Sampson, and Fontes (1990). The line ratios are strongly dependent on temperature and are appropriate as a diagnostic of hot thin plasmas such as in the solar transition region and corona.

H II region abundances - Model oxygen line ratios

An extensive, homogeneous grid of H II region models, is presented. It is found that the behavior of the strong oxygen lines can be modeled by taking proper account of the softening of the ionizing spectra produced by stars of increasing metallicity. This provides a calibration of the abundance indicating line ratio ([OII] λ3727 + [OIII] λλ4959, 5007)/Hβ which is comparable in accuracy to that obtainable by direct methods when a temperature-sensitive line ratio is available. No metallicity dependence of the IMF is required to explain the systematic softening of stellar spectra with increasing metallicity.

Predicted extreme-ultraviolet and X-ray spectrum of a microflare-heated corona

Sturrock et al. (1990) have proposed that a distribution of microflares produces the solar coronal and transition-region emission. This paper presents computed EUV and X-ray emission spectra from that distribution, including the effects of time-dependent ionization. The overall agreement of the predicted spectrum with observations is fairly good, although the predicted emission from the upper transition region is high by a factor of 2. Time-dependent ionization greatly enhances the He II 304-A line, improving the agreement with observation compared with ionization equilibrium models. The predicted effects on temperature-sensitive line ratios of other ions cannot yet be tested against observations due to uncertainties in instrumental calibration and atomic rates.

Use of Al xii and Mg xi lines as solar plasma diagnostics

We present three sets of observations of n = 1 to n = 2 lines due to helium-like aluminium (Alxii), made during two solar flares (25 August, 1980 and 19 October, 1986), using the X-Ray Polychromator on the SMM satellite. The observed temperature-sensitive line ratio G is shown to be consistent with the close-coupling calculations of Keenan and McCann (1987), although the ratio R, which is both temperature and density-sensitive for lower-Z elements, is not sufficiently well determined from these data to say more than that the observed values of R are not inconsistent with the theoretical calculations. This region of the spectrum also includes the helium-like magnesium (Mgxi) 11 S - 31 P line, and it is shown that the ratio of this line to the Alxii resonance (11 S - 21 P) line is a more sensitive indicator of electron temperature than are the Alxii G and R ratios. We demonstrate that the three ratios may be used together in order to derive values of emission measure, electron temperature and electron density during these flares.

Effect on Deuteron Temperature on Iron Forbidden Line Intensities in RF-Heated Tokamak Plasmas

AbstractTwo line ratios, the forbidden line at 845.5 Å to the allowed line at 135.7 Å in Fe XXII and the forbidden line at 592.1 Å to the forbidden line at 1118.2 Å in Fe XIX, have been measured as ion temperature-sensitive line ratios during rf heating in the Princeton Large Torus. The results indicate that deuteron collisions in plasmas of high deuteron temperature have a noticeable effect on the intensity of the forbidden lines. Measured relative intensities are compared with values from level population calculations which include deuteron collisional excitation between the levels of the ground configuration. The agreement between the observed and calculated ratios is within 30%. A method for deuteron (or proton) temperature measurement in tokamak plasmas is discussed.1More details about this experiment can be found in Ref. 2.

Properties of solar coronal active regions deduced from X-ray line spectra

view Abstract Citations (22) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Properties of Solar Coronal Active Regions Deduced from X-Ray Line Spectra McKenzie, D. L. Abstract Spectra from the SOLEX B RAP spectrometer have been used to analyze the temperature and density structure of over 100 nonflaring solar active regions. Density measurements that used the R ratio of O VII indicated that few regions have electron densities higher than ≡3×109cm-3. In a few cases, flare-productive regions had measured densities approximately twice this high. Temperature-sensitive line ratios in the helium-like ions O VII, Ne IX, and Mg XI were used to decude the general properties of the differential emission-measure function B(T) for nonflaring regions. B(T) falls off with increasing temperature above a peak temperature that is almost always lower than Tm(O VII) = 1.8×106K. Publication: The Astrophysical Journal Pub Date: November 1987 DOI: 10.1086/165747 Bibcode: 1987ApJ...322..512M Keywords: Line Spectra; Solar Activity; Solar Corona; Solar X-Rays; X Ray Spectra; Electron Density (Concentration); Emission Spectra; Radiant Flux Density; Solar Temperature; Temperature Dependence; Solar Physics; SUN: CORONA; SUN: X-RAYS; X-RAYS: SPECTRA full text sources ADS |

Temperature diagnostic line ratios of Fe XVII

Based on extensive calculations of the excitation rates of Fe XVII, four temperature-sensitive line ratios are investigated, paying special attention to the contribution of resonances to the excitation rates and to the contributions of dielectronic recombination satellites to the observed line intensities. The predictions are compared to FPCS observations of Puppis A and to Solar Maximum Mission (SMM) and SOLEX observations of the sun. Temperature-sensitive line ratios are also computed for emitting gas covering a broad temperature range. It is found that each ratio yields a differently weighted average for the temperature and that this accounts for some apparent discrepancies between the theoretical ratios and solar observations. The effects of this weighting on the Fe XVII temperature diagnostics and on the analogous Fe XXIV/Fe XXV satellite line temperature diagnostics are discussed.

Spectroscopic Measurement of Electron Temperature during Lower Hybrid Current Startup in JIPP T-IIU Tokamak

A simple diagram method is applied to obtain the time evolution of the electron temperature from the time history of the impurity line radiation which appears during the early phases of lower hybrid current startup in the JIPP T-IIU tokamak. This method makes it possible to survey the dependence of the time behavior of impurity emission on various plasma parameters (impurity influx rate, impurity confinement time, etc.). The electron temperature thus obtained agrees well with that derived from the temperature-sensitive line ratio and from Thomson scattering.