Can spicules be detected at disc centre in broad-band Ca ii H filter imaging data?

Beck, C.; Rezaei, Reza; Puschmann, K. G.

doi:10.1051/0004-6361/201220848

Cited by 15 publications

(13 citation statements)

References 64 publications

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“…However, in the presence of strong magnetic fields, the contribution of the line core (through further enhancement of the emission peaks) is much larger than that of the wings (Beck et al 2013). Hence, our images mainly represent chromospheric heights.…”

Section: Observationsmentioning

confidence: 95%

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Jafarzadeh

Solanki

Gafeira

et al. 2017

ApJS

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We present observations of transverse oscillations in slender Ca IIH fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high-(spatial and temporal-) resolutionseeing-free observations in a 1.1 Å wide passband covering the line core of Ca IIH 3969 Å from the second flight of the SUNRISE balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4±0.8 km s −1 and 83±29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9±14 km s −1. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvénic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapidhigh-frequency transverse waves,often produced in the lower photosphere, can penetrate into the chromospherewith an estimated energy flux of ≈15 kW m −2. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.

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Section: Observationsmentioning

confidence: 95%

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Jafarzadeh

Solanki

Gafeira

et al. 2017

ApJS

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“…6 of Eiroa et al 2013), a fact that could potentially contribute to enhancing the relationship between solar physics and the physics of other stars. In the end, such observations may help to resolve a long-standing puzzle in solar physics concerning the very existence of an actual gas temperature inversion at 500 km height and concerning whether this is occurring in the Quiet Sun or in active regions on the Sun (e.g., Leenaarts et al 2011;Beck et al 2013). Theoretical models have hitherto been inconclusive.…”

Section: The Temperature Minima Of α Cen a And α Cen Bmentioning

confidence: 99%

How dusty isα Centauri?

Wiegert

Liseau

Olofsson

et al. 2014

A&A

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Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary α Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the α Cen system. This requires knowledge of their photospheres. Having already detected the temperature minimum, T min , of α Cen A at far-infrared wavelengths, we here attempt to do the same for the more active companion α Cen B. Using the α Cen stars as templates, we study the possible effects that T min may have on the detectability of unresolved dust discs around other stars. Methods. We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in the far infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around α Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunction with radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than α Cen, a fractional dust luminosity−7 could account for SEDs that do not exhibit the T min effect. This is comparable to estimates of f d for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared, slight excesses at the 2.5σ level are observed at 24 µm for both α Cen A and B, which, if interpreted as due to zodiacal-type dust emission, would correspond to f d ∼ (1−3) × 10 −5 , i.e. some 10 2 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dust grains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the α Cen stars, viz. < ∼ 4×10 −6 M of 4 to 1000 µm size grains, distributed according to n(a) ∝ a −3.5 . Similarly, for filled-in T min emission, corresponding Edgeworth-Kuiper belts could account for ∼10 −3 M of dust. Conclusions. Our far-infrared observations lead to estimates of upper limits to the amount of circumstellar dust around the stars α Cen A and B. Light scattered and/or thermally emitted by exo-Zodi discs will have profound implications for future spectroscopic missions designed to search for biomarkers in the atmospheres of Earth-like planets. The far-infrared spectral energy distribution of α Cen B is marginally consistent with the presence of a minimum temperature region in the upper atmosphere of the star. We also show that an α Cen A-like temperature minimum may result in an erroneous apprehension about the presence of dust around other, more distant stars.

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“…A&A 560, A50 (2013) Besides long-slit spectrograms, narrowband filtergrams are often used to study the chromospheric dynamics. This technique provides large area coverage (compared to slit spectra) and high temporal resolution, but a certain mixing of photospheric and chromospheric contributions is unavoidable, as soon as the spectral bandwidth is larger than 0.5 Å (Beck et al 2013a). From a Ca II K filtergram sequence of an inter-network region with a width of 0.3 Å, Wöger et al (2006) describe bright grains with sizes of about 2 and a timescale of 53 s. The same time scale was found by Tritschler et al (2007).…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the Fe II 396.94 nm emission line observed at solar disk center

Schmidt

Fisher

2013

A&A

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Aims. We have studied the structure and dynamics of the upper photosphere and lower chromosphere of the quiet Sun. Methods. We analyzed a sequence of scans of slit spectra of the Ca II H line at 396.8 nm, with a spectral resolution of 850 000, and a spatial resolution of about one arcsec, taken in the quiet Sun at disk center, with a duration of about 55 min and an area coverage of 185 × 3.5 . We used statistical methods to characterize size, lifetime, and dynamics of emission features of the Fe II line at 396.94 nm. Results. We have identified about 780 distinct features where the Fe II line shows emission stronger than 3% above the local continuum. Their lifetime is on the order of one minute, and the spatial extent is about or less than 2 . On average, Fe II emission features show a significant redshift of 1.3 km s −1 , with respect to the position of the absorption line. The redshift of the Fe II emission is absent close to the solar limb. The Fe II emission is coupled with a strongly enhanced intensity level of the Ca II wings. A time line analysis shows that other photospheric lines show significant redshift one minute before, and a blueshift after, the occurrence of an emission event. A redshift of the Ca II H line core precedes the redshift of the Fe II line by about 30 s. The occurrence of the H2v emissions is strongly reduced before and significantly increased after the Fe II emission events. Conclusions. The temporal behavior of the Fe II emission line and both the Ca II H line core and H2v emission suggest a connection between Fe II emission and chromospheric activity. The presence of a significant redshift during the Fe II emissions and the absence of this redshift near the limb suggest that the observed redshift is indeed caused by a downflow in the line-forming region. From our result concerning the intensity fluctuations in the core of the Fe II line, and from the magnitude of the downflow velocities we conclude that the Fe II emissions at 396.94 nm occur in the photosphere.

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Can spicules be detected at disc centre in broad-band Ca ii H filter imaging data?

Cited by 15 publications

References 64 publications

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

How dusty isα Centauri?

Dynamics of the Fe II 396.94 nm emission line observed at solar disk center

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