Non-thermal Motions Research Articles

DIRECT OBSERVATION OF A SHARP TRANSITION TO COHERENCE IN DENSE CORES

We present NH3 observations of the B5 region in Perseus obtained with the Green Bank Telescope (GBT). The map covers a region large enough (~11'x14') that it contains the entire dense core observed in previous dust continuum surveys. The dense gas traced by NH3(1,1) covers a much larger area than the dust continuum features found in bolometer observations. The velocity dispersion in the central region of the core is small, presenting subsonic non-thermal motions which are independent of scale. However, it is thanks to the coverage and high sensitivity of the observations that we present the detection, for the first time, of the transition between the coherent core and the dense but more turbulent gas surrounding it. This transition is sharp, increasing the velocity dispersion by a factor of 2 in less than 0.04 pc (the 31" beam size at the distance of Perseus, ~250 pc). The change in velocity dispersion at the transition is ~3 km/s/pc. The existence of the transition provides a natural definition of dense core: the region with nearly-constant subsonic non-thermal velocity dispersion. From the analysis presented here we can not confirm nor rule out a corresponding sharp density transition.

THE INITIAL CONDITIONS OF CLUSTERED STAR FORMATION. II. N2H+OBSERVATIONS OF THE OPHIUCHUS B CORE

We present a Nobeyama 45 m Radio Telescope map and Australia Telescope Compact Array pointed observations of N2H+ 1-0 emission towards the clustered, low mass star forming Oph B Core within the Ophiuchus molecular cloud. We compare these data with previously published results of high resolution NH3 (1,1) and (2,2) observations in Oph B. We use 3D Clumpfind to identify emission features in the single-dish N2H+ map, and find that the N2H+ `clumps' match well similar features previously identified in NH3 (1,1) emission, but are frequently offset to clumps identified at similar resolution in 850 micron continuum emission. Wide line widths in the Oph B2 sub-Core indicate non-thermal motions dominate the Core kinematics, and remain transonic at densities n ~ 3 x 10^5 cm^-3 with large scatter and no trend with N(H2). Non-thermal motions in Oph B1 and B3 are subsonic with little variation, but also show no trend with H2 column density. Over all Oph B, non-thermal N2H+ line widths are substantially narrower than those traced by NH3, making it unlikely NH3 and N2H+ trace the same material, but the v_LSR of both species agree well. We find evidence for accretion in Oph B1 from the surrounding ambient gas. The NH3/N2H+ abundance ratio is larger towards starless Oph B1 than towards protostellar Oph B2, similar to recent observational results in other star-forming regions. Small-scale structure is found in the ATCA N2H+ 1-0 emission, where emission peaks are again offset from continuum emission. In particular, the ~1 M_Sun B2-MM8 clump is associated with a N2H+ emission minimum and surrounded by a broken ring-like N2H+ emission structure, suggestive of N2H+ depletion. We find a strong general trend of decreasing N2H+ abundance with increasing N(H2) in Oph B which matches that found for NH3.

HIGH RESOLUTION NEAR-INFRARED SURVEY OF THE PIPE NEBULA. I. A DEEP INFRARED EXTINCTION MAP OF BARNARD 59

We present our analysis of a fully sampled, high resolution dust extinction map of the Barnard 59 complex in the Pipe Nebula. The map was constructed with the infrared color excess technique applied to a photometric catalog that combines data from both ground and space based observations. The map resolves for the first time the high density center of the main core in the complex, that is associated with the formation of a small cluster of stars. We found that the central core in Barnard 59 shows an unexpected lack of significant substructure consisting of only two significant fragments. Overall, the material appears to be consistent with being a single, large core with a density profile that can be well fit by a King model. A series of NH$_3$ pointed observations towards the high column density center of the core appear to show that the core is still thermally dominated, with sub-sonic non-thermal motions. The stars in the cluster could be providing feedback to support the core against collapse, but the relatively narrow radio lines suggest that an additional source of support, for example a magnetic field, may be required to stabilize the core. Outside the central core our observations reveal the structure of peripheral cores and resolve an extended filament into a handful of significant substructures whose spacing and masses appear to be consistent with Jeans fragmentation.

The solar Ba${\sf II}$ 4554 Å line as a Doppler diagnostic: NLTE analysis in 3D hydrodynamical model

The aim of this paper is to analyse the validity of the Dopplergram and lambda-meter techniques for the Doppler diagnostics of solar photospheric velocities using the BaII 4554 A line. Both techniques are evaluated by means of NLTE radiative transfer calculations of the BaII 4554 A line in a three-dimensional hydrodynamical model of solar convection. We consider the cases of spatially unsmeared profiles and the profiles smeared to the resolution of ground-based observations. We find that: (i) Speckle-reconstructed Dopplergram velocities reproduce the ``true'' velocities well at heights around 300 km, except for intergranular lanes with strong downflows where the velocity can be overestimated. (ii) The lambda-meter velocities give a good representation of the ``true'' velocities through the whole photosphere, both under the original and reduced spatial resolutions. The velocities derived from the inner wing of smeared BaII 4554 A line profiles are more reliable than those for the outer wing. Only under high spatial resolution does the inner wing velocities calculated in intergranular regions give an underestimate (or even a sign reversal) compared with the model velocities. (iii) NLTE effects should be taken into account in modelling the BaII 4554 A line profiles. Such effects are more pronounced in intergranular regions. Our analysis supports the opinion that the Dopplergram technique applied to the BaII 4554 A line is a valuable tool for the Doppler diagnostics of the middle photosphere around 300 km. The \lambda-meter technique applied to this line gives us a good opportunity to ``trace'' the non-thermal motions along the whole photosphere up to the temperature minimum and lower chromosphere.

CORONAL NONTHERMAL VELOCITY FOLLOWING HELICITY INJECTION BEFORE AN X-CLASS FLARE

We explore the pre-flare behavior of the corona in a three-day period building up to an X-class flare on 2006 December 13 by analyzing EUV spectral profiles from the Hinode EUV Imaging Spectrometer (EIS) instrument. We found an increase in the coronal spectral line widths, beginning after the time of saturation of the injected helicity as measured by Magara & Tsuneta. In addition, this increase in line widths (indicating nonthermal motions) starts before any eruptive activity occurs. The Hinode EIS has the sensitivity to measure changes in the buildup to a flare many hours before the flare begins.

The gas turbulence in planetary nebulae: quantification and multi-D maps from long-slit, wide-spectral range echellograms

Context. This methodological paper is part of a short series dedicated to the long-standing astronomical problem of de-projecting the bi-dimensional, apparent morphology of a three-dimensional distribution of gas. Aims. We focus on the quantification and spatial recovery of turbulent motions in planetary nebulae (and other classes of expanding nebulae) by means of long-slit echellograms over a wide spectral range. Methods. We introduce some basic theoretical notions, discuss the observational methodology, and develop an accurate procedure disentangling all broadening components (instrumental resolution, thermal motions, turbulence, gradient of the expansion velocity, and fine structure of hydrogen-like ions) of the velocity profile in all spatial positions of each spectral image. This allows us to extract random, non-thermal motions at unprecedented accuracy, and to map them in 1-, 2- and 3-dimensions. Results. We discuss general and specific applications of the method. We present the solution to practical problems in the multidimensional turbulence-analysis of a testing-planetary nebula (NGC 7009), using the three-step procedure (spatio-kinematics, tomography, and 3D rendering) developed at the Astronomical Observatory of Padua (Italy). In addition, we introduce an observational paradigm valid for all spectroscopic parameters in all classes of expanding nebulae. Conclusions. Unsteady, chaotic motions at a local scale constitute a fundamental (although elusive) kinematical parameter of each planetary nebula, providing deep insights on its different shaping agents and mechanisms, and on their mutual interaction. The detailed study of turbulence, its stratification within a target and (possible) systematic variation among different sub-classes of planetary nebulae deserve long-slit, multi-position angle, wide-spectral range echellograms containing emissions at low-, medium-, and highionization, to be analyzed pixel-to-pixel with a straightforward and versatile methodology, extracting all the physical information (flux, kinematics, electron temperature and density, ionic and chemical abundances, etc.) stored in each frame at best.

CO Isotopologues in the Perseus Molecular Cloud Complex: theX‐factor and Regional Variations

We use data gathered by the COMPLETE survey of star-forming regions to find new calibrations of the X-factor and 13CO abundance within the Perseus molecular cloud. We divide Perseus into six subregions, using groupings in a dust temperature vs. LSR velocity plot. The standard X-factor, -->X ? N(H2)/W(12CO) , is derived both for the whole Perseus complex and for each of the six subregions with values consistent with previous estimates. However, the X-factor is heavily affected by the saturation of the emission above -->AV ~ 4 mag, and variations are also found between regions. Linear fits to relate -->W(12CO) and -->AV using only points below 4 mag of extinction yield a better estimate of the -->AV than the X-factor. Linear relations of -->W(13CO) , N(13CO) , and -->W(C18O) with -->AV are derived. The extinction thresholds above which 13CO(1-0) and C18O(1-0) are detected are about 1 mag larger than previous estimates, so that a more efficient shielding is needed for the formation of CO than previously thought. The 12CO and 13CO lines saturate above 4 and 5 mag, respectively, whereas C18O(1-0) never saturates in the whole -->AV range probed by our study (up to 10 mag). Approximately 60% of the positions with 12CO(1-0) emission have subthermally excited lines, and almost all positions have excitation temperatures below the dust temperature. PDR models, using the Meudon code, can explain the 12CO(1-0) and 13CO(1-0) emission with densities ranging between 103 and 104 cm?3. In general, local variations in the volume density and nonthermal motions (linked to different star formation activity) can explain the observations. Higher densities are needed to reproduce CO data toward active star-forming sites, such as NGC 1333, where the larger internal motions driven by the young protostars allow more photons from the embedded high-density cores to escape the cloud. In the most quiescent region, B5, the 12CO and 13CO emission appears to arise from an almost uniform thin layer of molecular material at densities around 104 cm?3, and in this region the integrated intensities of the two CO isotopologues are the lowest in the whole complex.

Spectroscopic studies of solar corona VI: Trend in line-width variation of coronal emission lines with height independent of the structure of coronal loops

We have obtained spectroscopic observations in coronal emission lines by choosing two lines simultaneously, one [Fe x] 6374 A and the other [Fe xi] 7892 A or [Fe xiii] 10747 A or [Fe xiv] 5303 A. We found that in 95 per cent of the coronal loops observed in 6374 A, the FWHM of the emission line increases with height above the limb irrespective of the size, shape and orientation of the loop and that in case of 5303 A line decreases with height in about 89 per cent of the coronal loops. The FWHM of 7892 A and 10747 A emission lines show intermediate behavior. The increase in the FWHM of 6374 A line with height is the steepest among these four lines. We have also studied the intensity ratio and ratio of FWHM of these lines with respect to those of 6374 A as a function height above the limb. We found that the intensity ratio of 7892 A and 10747 A lines with respect to 6374 A line increases with height and that of 5303 A to 6374 A decreases with height above the limb. This implies that temperature in coronal loops will appear to increase with height in the intensity ratio plots of 7892 A and 6374 A; and 10747 A and 6374 A whereas it will appear to decrease with height in intensity ratio of 5303 A to 6374 A lineversus height plot. These findings are up to a height of about 200 arcsec above the limb. The varying ratios with height indicate that relatively hotter and colder plasma in coronal loops interact with each other. Therefore, the observed increase in FWHM with height above the limb of coronal emission lines associated with plasma at about 1 MK may not be due to increase in non-thermal motions caused by coronal waves but due to interaction with the relatively hotter plasma. These findings also do not support the existing coronal loop models, which predict an increase in temperature of the loop with height above the limb.

On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence

The effect of smooth cloud boundaries on the interaction of steady planar shock waves with interstellar clouds is studied using a local adaptive mesh refinement technique with an axisymmetric Godunov hydrodynamic scheme. A three-dimensional calculation is also done to confirm the two-dimensional results. We find that smooth cloud boundaries significantly affect cloud morphology and retard cloud destruction. After shock passage, a sharp density jump formsdue to velocity gradientsgeneratedinthe smooth cloud boundary.Werefer to this density jump as a‘‘slip surface’’because the velocity isshearedparalleltoits surface. Theformation of aslip surface leads tocompletecloud destruction because of the Kelvin-Helmholtz and Rayleigh-Taylor instabilities. We construct analytic models of cloud drag and vorticity generation that compare well with the numerical results. Small shreds formed by the instabilities have significant velocity dispersions of 10%‐20% of the ambient shock velocity. They could be related to the small cold H i clouds recently observed by Stanimirovic´ & Heiles. The dependence of the velocity dispersion on region size, the so-called line width‐size relation, is found to be time-dependent. In the early stages, the line width‐size relation is more or less flat because of the significant small-scale fluctuations generated by the KelvinHelmholtz instability. In the later stages, the small-scale fluctuations tend to damp, leading to a line width that increases with size. The possibility of gravitational instability triggered by shock compression is discussed. We show thatgravitationalcollapsecanbeinducedinaninitiallyuniformcloudbyaradiativeshock( �< 4/3)onlyif itisnot too strong and nonthermal motions are weak. Subject headingg hydrodynamics — ISM: clouds — shock waves — supernova remnants — turbulence

Nonthermal Velocities in Different Temperature Regions of the Solar Lower Transition Region

We analyze the relationship between nonthermal velocities derived from spectral lines of ions formed at different temperatures in the solar lower transition region, using spectra from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO). We find a high degree of correlation among nonthermal motions arising at temperatures ranging from 3 × 104 to 2.5 × 105 K over 1'' spatial scales in quiet-Sun regions. We discuss the implications of these results in terms of the physical nature of the transition region.

Helium Abundance in High‐Temperature Solar Flare Plasmas

In the present work we use emission from dense plasmas late in the decay phase of flares, while the plasmas are still hot [(2-4) × 106 K], to determine the absolute helium abundance in flaring solar corona. To achieve this, we make use of intensity ratios of H I and He II lines and of intensity ratios between the He II lines and the bremsstrahlung continuum radiation emitted by the local postflare plasmas. These ratios are very sensitive to the electron temperature, which is measured by using two different techniques: intensity ratios from lines emitted by heavier elements and from the line width of H I and He II lines. The latter method is made possible by the low atomic weight of H and He and by the high temperature of the plasma, which causes the widths of these lines to exceed 0.6 A (He) and 1.1 A (H). Such values significantly exceed the broadening due to nonthermal mass motions, so line widths can provide accurate temperature measurements. The average helium absolute abundance was found to be 12.2% ± 2.4%.

Complex Variations in the Line-Intensity Ratio of Coronal Emission Lines with Height above the Limb

We obtained spectroscopic observations simultaneously in pairs of coronal emission lines, one line being [Fe X] λ6374 and the other line being [Fe XI] λ7892, [Fe XIII] λ10747, or [Fe XIV] λ5303, and we studied the variations in the intensity and FWHM ratios of these lines with respect to those of 6374 A as a function of height above the limb. We find that the intensity ratio of the 7892 and 10747 A line with respect to the 6374 A line increases with height and that the intensity ratio of 5303 A to 6374 A decreases with height above the limb. This implies that the temperature in coronal loops will appear to increase with height if we consider the intensity ratio of 7892 A to 6374 A a negligible variation in temperature in the case of the 10747 and 6374 A line pair, while the temperature will appear to decrease with height if we consider the intensity ratio of 5303 A to 6374 A. The normalized FWHM (with respect to wavelength) ratio of 6374 A to all the other coronal lines observed increases with height. The FWHM ratio at the limb depends on the pair of emission lines chosen; it is about 1 in the case of the 6374 and 7892 A emission lines, indicating a common temperature and nonthermal velocity in the coronal loops near the limb, and it is about 0.7 at the limb in the case of the 6374 and 5303 A lines and becomes about 1 at a height of 120''. The varying FWHM ratios with height indicate that hotter and colder plasmas in coronal loops mix with each other. Therefore, the observed increase in the FWHM of coronal emission lines, which are associated with plasma at about 1 MK with height, may not be due to an increase in nonthermal motions caused by coronal waves but may be due to an interaction with relatively hotter plasma.

Observations Indicating That ∼1 x 107K Solar Flare Plasmas May Be Produced in Situ from ∼1 x 106K Coronal Plasma

We discuss a set of flare observations obtained at a position of 0.10 R☉ above the solar northwest limb. The data were acquired by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO). We derive time-dependent comparisons of physical properties, such as electron temperature and density, between flare plasma and background coronal plasma observed along the same lines of sight. In addition to temperature and density, we discuss emission measures, elemental abundances, nonthermal mass motions (from line widths), and bulk mass motions (from Doppler shifts). The observations appear to indicate that the flaring plasmas (4 × 106 K ≤ Te ≤ 1 × 107 K) along the lines of sight were formed by in situ heating and possibly by compression of the ambient coronal material (Te ≤ 2 × 106 K).

Physical Conditions in Orion’s Veil

Orion's veil consists of several layers of largely neutral gas lying between us and the main ionizing stars of the Orion Nebula. It is visible in 21 cm H I absorption and in optical and UV absorption lines of H I and other species. Toward θ1 Ori C, the veil has two remarkable properties, a high magnetic field (≈100 μG) and a surprising lack of H2, given its total column density. Here we compute photoionization models of the veil to establish its gas density and its distance from θ1 Ori C. We use a greatly improved model of the H2 molecule that determines level populations in 105 rotational/vibrational levels and provides improved estimates of H2 destruction via the Lyman-Werner bands. Our best-fit photoionization models place the veil 1-3 pc in front of the star at a density of 103-104 cm-3. Magnetic energy dominates the energy of nonthermal motions in at least one of the 21 cm H I velocity components. Therefore, the veil is the first interstellar environment in which magnetic dominance appears to exist. We find that the low ratio of H2/H0 (<10-4) is a consequence of high UV flux incident on the veil due to its proximity to the Trapezium stars and the absence of small grains in the region.

Discovery of a Dusty Ring in the Coalsack: A Dense Core Caught in the Act of Formation?

We present a new infrared extinction study of Globule 2, the most opaque molecular cloud core in the Coalsack complex. Using deep near-infrared imaging observations obtained with the ESO NTT we are able to examine the structure of the globule in significantly greater detail than previously possible. We find the most prominent structural feature of this globule to be a strong central ring of dust column density which was not evident in lower resolution studies of this cloud. This ring represents a region of high density and pressure that is likely a transient structure. For a spherical cloud geometry the ring would correspond to a dense inner shell of high pressure that could not be in dynamical equilibrium with its surroundings since there appear to be no sources of pressure in the central regions of the cloud that could support the shell against gravity and prevent its inward implosion. The timescale for the inward collapse of the ring would be less than 2 x 10^5 years, suggesting that this globule is in an extremely early stage of evolution, and perhaps caught in the process of forming a centrally condensed dense core or Bok globule. Outside its central regions the globule displays a well-behaved density profile whose shape is very similar to that of a stable Bonnor-Ebert sphere. Using SEST we also obtained a C18O spectrum toward the center of the cloud. The CO observation indicates that the globule is a gravitationally bound object. Analysis of the CO line profile reveals significant non-thermal gas motions likely due to turbulence. As a whole the globule may be evolving to a global state of quasi-static dynamical equilibrium in which thermal and turbulent pressure balance gravity.

Properties of the Lower Transition Region: The Widths of Optically Allowed and Intersystem Spectral Lines

The widths of spectral lines in the ultraviolet (UV) and extreme ultraviolet (EUV) spectral regions that are formed in the solar transition region and corona are usually greater than the optically thin widths due to thermal Doppler broadening calculated under the assumption of ionization equilibrium. Although opacity can explain the widths of some lines, there are a host of optically thin lines for which the excess widths are attributed to nonthermal motions. Interest in these motions for coronal heating theories has led to the measurement and comparison of spectral line profiles/widths throughout the solar UV and EUV spectrum. We find that for the quiet Sun the widths of some optically allowed lower transition region lines, deduced from spectra obtained by the Solar Ultraviolet Measurements of Ultraviolet Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft, are considerably larger than predicted from simply scaling previously measured wavelengths of other lines from the same ion. For example, the O III lines of the multiplet near 834 A are considerably wider than predicted from the previously measured (from Skylab) width of the optically thin O III 1666.15 A intersystem line. The excess widths are not due to nonthermal motions, as these are already included in the width of the 1666.15 A line. In this paper, we analyze the widths of some prominent optically allowed lines and discuss possible causes for discrepancies with previous measurements of intersystem lines.

Coronal Loops Heated by Turbulence-driven Alfvn Waves

A two-fluid dynamic model of long-lived coronal loops is presented, whereby heating of the confined plasma is achieved by turbulence-driven Alfven waves. It is assumed that the nonthermal motions inferred from spectral line observations in the transition region are due to Alfven waves. It is also assumed that the turbulence is already fully developed when the waves are injected at the footpoint of the loop while the wave/turbulence energy is readily absorbed by the proton gas. The Coulomb coupling between protons and electrons subsequently heats the electron gas. The model produces a fairly uniform electron temperature in the coronal segment of the loop even though the heating is nonuniform. The model also reproduces electron densities of (1-4) × 109 cm-3, in the range inferred from observations, as well as a moderate flow speed around 10 km s-1 along the loop. The turbulence heating mechanism adopted in this Letter, however, cannot produce stable loops with temperatures T ≤ 1.3 × 106 K.

Free‐Free Emission in the Far‐Ultraviolet Spectral Range: A Resource for Diagnosing Solar and Stellar Flare Plasmas

We report the detection of free-free (bremsstrahlung) emission near 1200 A from a flare at the solar limb observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The observations consist of a time series of slit spectra at a fixed pointing that lasted almost 2 hr, during which the observed solar region produced a C8 flare. Using the free-free continuum intensities in conjunction with intensities of high-temperature (106-107 K) emission lines that appear in the same wavelength range, we derive the flare plasma electron density, electron temperature, emission measure, and nonthermal mass motions before, during, and after the flare. We describe a new diagnostic method for determining the temperature of cooling plasmas. Because the free-free radiation is emitted primarily by the interaction of electrons with nuclei of H and He atoms, we are also able to derive the Fe/H, Al/H, and Ca/H abundance ratios from the line intensities of highly ionized Fe, Al, and Ca lines and the intensities of the free-free emission, assuming a He abundance. The present work demonstrates the exceptional plasma diagnostic potential of ultraviolet free-free continuum radiation when coupled with emission-line intensities. We demonstrate that a similar technique could be employed to diagnose plasma properties of stellar flares using a high-resolution spectrometer with a sufficiently large effective collecting area.

Properties of Solar Plasmas near Solar Maximum above Two Quiet Regions at Distances of 1.02–1.34R⊙

In the present work we have analyzed the spectra emitted by two quiet solar regions observed off the solar disk by the SUMER instrument on board the SOHO satellite. The two complete spectra were recorded when the SOHO north-south axis was rotated relative to the Sun north-south axis by 150° clockwise. As a result, the SUMER slit could be placed so that it is perpendicular to the solar limb in an intermediate orientation between the equator and the poles. The SUMER fields of view consisted of two 1'' wide radial strips of the solar corona from 1.02 to 1.34 R☉. The aim of the present work was to measure the physical properties of the emitting plasma, namely, the electron density and temperature, the plasma emission measure, and the nonthermal mass motions, as a function of the distance from the solar limb. The measurement of the plasma absolute element abundances is deferred to a future paper. In measuring the nonthermal velocities of both source regions, we have discovered a residual instrumental systematic effect to line widths. The plasma in the SUMER field of view is nearly isothermal. The measurements of electron density and temperature allow us to check the hydrostatic assumption commonly adopted in the literature and to find that the plasma is denser than predicted. The wide wavelength range covered by the SUMER instrument includes several Li-like ions, allowing us to investigate the relative contribution of the radiative and collisional excitation mechanisms in the Li-like resonance doublet formation. We confirm the earlier findings that a significant radiative excitation occurs for O VI and Ne VIII resonance lines even at low altitudes.

Nonthermal Mass Motions within the High‐Temperature Plasmas above a Complex Solar Active Region

We report on mass motions in high-temperature plasmas at radial distances of 1.06-1.20 R☉ corresponding to 3.3 × 104-1.3 × 105 km above the west solar limb. The observations were conducted over a 53 hr time period while a complex active region moved across the west solar limb. We found that the nonthermal mass motions in the 2.6 × 106-6.6 × 106 K plasmas that were imaged along the slit were in the 20-35 km s-1 velocity range. The magnitude of the nonthermal mass motions was independent of the plasma temperature or its height above the limb. We also found that the emission measure distribution within the 2.6 × 106-6.6 × 106 K plasma regimes did not change during most of the observations, an indication that on the average the temperature distribution among the various plasma volumes along the line of sight stayed unchanged.