The fine structure of prominences

Engvold, O.

doi:10.1007/bf00152636

Cited by 28 publications

(4 citation statements)

References 28 publications

(4 reference statements)

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“…Thus, we believe that the spectral classification of V934 Her made by Garcia et al (1983) using the width of the Ca II K emission line could be biased by the UV variability of this object and by the possible presence of the additional absorption suggested by Gaudenzi & Polcaro (1999). Also, from the data set of Engvold & Rygh (1978), using which Garcia et al (1983) determined the absolute magnitude M V in the V band (and then the spectral type) of V934 Her, it seems that the relation between this quantity and the width of the Ca II K line is very steep for giant stars, i.e. a small variation in the line width reflects in a substantial jump of M V .…”

Section: Optical Spectra and A New Distance Determinationmentioning

confidence: 99%

X–ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her

Masetti¹,

Fiume²,

Cusumano

et al. 2002

A&A

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Abstract. We report on ASCA and BeppoSAX X-ray broad band observations of the galactic low-luminosity X-ray source 4U 1700+24 performed on 1995 and 1998, respectively, and on (quasi-)simultaneous ground observations of its optical counterpart, V934 Her, from the Loiano 1.5-meter telescope. In order to better understand the nature of the source we also analyze public archival ROSAT and RXTE data as well as the RXTE ASM light curve of 4U 1700+24; we also re-analyze a 1985 EXOSAT pointing. The optical spectra are typical of a M2 III star; this allows us to determine a revised distance to the object of ∼400 pc. While these spectra do not show either any spectral change between the two epochs or any peculiar feature apart from those observed in normal red giants, the spectroscopic measurements carried out in X-rays reveal a complex and long-term variable spectrum, with a clear soft excess. The X-ray spectral properties of the source are best described by a thermal Comptonization spectrum plus a soft energy (<1 keV) excess, which can be modeled in the form of a blackbody emission with kTBB ∼ 1 keV; the latter component is not detected at the lowest source flux levels. The ratio between the two components varies substantially with the source flux. The X-ray emission from the object appears to become harder as its luminosity increases: indeed, the RXTE data acquired during an outburst occurred in October-November 1997 display a hard tail, detected up to 100 keV and modeled with a comptonizing cloud which is hotter and less opaque than that seen in the low intensity state. Apart from erratic shot-noise variability on timescales of tens to thousands of seconds, no significant properties (such as pulsations or QPOs) are found from the timing analysis of the X-ray light curves extracted from the observations presented here. With the new distance determination, the 2-10 keV X-ray luminosity range spanned in the considered observations lies between ∼2×10 32 and ∼1×10 34 erg s −1 . All this information, combined with the findings by other authors, allows us to suggest that the scenario which best describes the object consists of a wide binary system in which a neutron star accretes matter from the wind of a M-type giant star. Implications of such a model are discussed.

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Section: Optical Spectra and A New Distance Determinationmentioning

confidence: 99%

X–ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her

Masetti¹,

Fiume²,

Cusumano

et al. 2002

A&A

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“…The observed emission relation (Fig. 3) shows that each prominence is characterized by a well-defined relation; for the fainter prominence E/70N the slope is steeper than for the brighter one E/42N ('branching', cf., Engvold, 1978;Stellmacher and Wiehr, 1995).…”

Section: Ground-based Observationsmentioning

confidence: 99%

Untitled

2003

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We present a comprehensive set of spectral data from two quiescent solar prominences observed in parallel from space and ground: with the VTT, simultaneous two-dimensional imaging of Hβ 4862Å and Ca ii 8542Å yields a constant ratio, indicating small spatial pressure variations over the prominence. With the Gregory, simultaneous spectra of Ca ii 8542Å and He i 10830Å were taken, their widths yielding 8000 < T kin < 9000 K and v nth < 8km/s. The intensity ratio of the helium triplet components gives an optical thickness of τ < 1.0 for the fainter and τ ≤ 2.0 for the brighter prominence. The τ 0 values allow to deduce the source function for the central line intensities and thus the relative population of the helium 3 S and 3 P levels with a mean excitation temperature T mean ex = 3750 K. With SUMER, we sequentially observed 6 spectral windows containing higher Lyman lines, 'cool' emission lines from neutrals and singly charged atoms, as well as 'hot' emission lines from ions like O iv, O v, N v, S v and S vi. The EUV lines show pronounced maxima in the main prominence body as well as 'sidelocations' where the 'hot' lines are enhanced with respect to the 'cool' lines. The line radiance of 'hot' lines blue-wards of the Lyman series limit (λ < 912Å) appear reduced in the main prominence body.This absorption is also visible in TRACE images of Fe ix/x 171Å as fine dark structure which covers only parts of the main ('cool') prominence body.The Lyman lines show a smooth decrease of line widths and radiance with increasing upper level k = 5 through 19. For 5 ≤ k ≤ 8 the level population follows a Boltzmann distribution with T ex > 6 · 10 4 K; higher levels k> 8 appear more and more overpopulated. The larger widths of the Lyman lines require high non-thermal broadening close to that of 'hot' EUV lines. In contrast, the He ii emission is more related to the 'cool' lines.

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“…Velocity measurements for the plasma residing inside prominences or filaments can be determined by Doppler velocity measurements for motion parallel to the line of sight (Engvold 1978;Lin et al 2003;Schmieder et al 2014) and by tracking intensity features in images for motion normal to the line of sight (Engvold 1976;Zirker et al 1994;Berger et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Analysis of Flows Inside Quiescent Prominences as Captured by Hinode/Solar Optical Telescope

Freed

McKenzie

Longcope

et al. 2016

ApJ

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Developing an understanding of how magnetic fields can become entangled in a prominence is important for predicting a possible eruption. This work investigates the kinetic energy and vorticity associated with plasma motion residing inside quiescent prominences (QPs). These plasma flow characteristics can be utilized to improve our understanding of how the prominence maintains a stable magnetic field configuration. Three different contrastenhanced solar prominence observations from Hinode/Solar Optical Telescope were used to construct velocity maps-in the plane of the sky-via a Fourier local correlation tracking program. The resulting velocities were then used to perform the first-ever analysis of the two-dimensional kinetic energy and enstrophy spectra of a prominence. Enstrophy is introduced here as a means of quantifying the vorticity thathas been observed in many QPs. The kinetic energy power spectral density (PSD) produced indices ranging from −1.00 to −1.60. There was a consistent anisotropy in the kinetic energy spectrum of all three prominences examined. Examination of the intensity PSD reveals thata different scaling relationship exists between the observed prominence structure and velocity maps. All of the prominences exhibited an inertial range of at least k 0.8 2.0 rads Mm 1   -. Quasiperiodic oscillations were also detected in the centroid of the velocity distributions for one prominence. Additionally, a lower limit was placed on the kinetic energy density (ò ∼ 0.22-7.04 km s 2 2 -) and enstrophy density (ω ∼ 1.43-13.69 10 s 16 2 --) associated with each prominence.

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The fine structure of prominences

Cited by 28 publications

References 28 publications

X–ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her

X–ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her

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Analysis of Flows Inside Quiescent Prominences as Captured by Hinode/Solar Optical Telescope

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