Observations of Subarcsecond Bright Dots in the Transition Region Above Sunspots With the Interface Region Imaging Spectrograph

Kleint, Lucia; Peter, Hardi; Weber, Mark; Testa, Paola; DeLuca, E. E.; Golub, L.; Schanche, N.

doi:10.1088/2041-8205/790/2/l29

Cited by 80 publications

(124 citation statements)

References 37 publications

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“…The bright dots are shortlived (25 s) and appear at the footpoints of large-scale coronal loops. Tian et al (2014a) found similar subarcsecond bright dots above sunspots in the transition region (TR) with the observations of the Interface Region Imaging Spectrograph (IRIS;De Pontieu et al 2014).…”

Section: Introductionsupporting

confidence: 70%

Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

Zhang

2016

A&A

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Context. The new Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of UV spectra and slit-jaw images (SJIs). These data have become available for investigating the dynamic features in the transition region (TR) below the on-disk filaments. Aims. The driver of "counter-streaming" flows along the filament spine is still unknown yet. The magnetic structures and the upflows at the footpoints of the filaments and their relations with the filament mainbody have not been well understood. We study the dynamic evolution at the footpoints of filaments in order to find some clues for solving these questions. Methods. Using UV spectra and SJIs from the IRIS, along with coronal images and magnetograms from the Solar Dynamics Observatory (SDO), we present the new features in a quiescent filament channel: subarcsecond bright points (BPs) and quasi-periodic upflows.Results. The BPs in the TR have a spatial scale of about 350−580 km and lifetimes of more than several tens of minutes. They are located at stronger magnetic structures in the filament channel with a magnetic flux of about 10 17 −10 18 Mx. Quasi-periodic brightenings and upflows are observed in the BPs, and the period is about 4−5 min. The BP and the associated jet-like upflow comprise a "tadpole-shaped" structure. The upflows move along bright filament threads, and their directions are almost parallel to the spine of the filament. The upflows initiated from the BPs with opposite polarity magnetic fields have opposite directions. The velocity of the upflows in the plane of sky is about 5−50 km s −1 . The emission line of Si IV 1402.77 Å at the locations of upflows exhibits obvious blueshifts of about 5−30 km s −1 , and the line profile is broadened with the width of more than 20 km s −1 . Conclusions. The BPs seem to be the bases of filament threads, and the upflows are able to convey mass for the dynamic balance of the filament. The "counter-streaming" flows in previous observations may be caused by the propagation of bi-directional upflows initiated from opposite polarity magnetic fields. We suggest that quasi-periodic brightenings of BPs and quasi-periodic upflows result from small-scale oscillatory magnetic reconnections, which are modulated by solar p-mode waves.

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Section: Introductionsupporting

confidence: 70%

Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

Zhang

2016

A&A

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“…Recently, Tian et al (2014) reported on IRIS observations of bright dots in sunspots, the majority of which were observed in the penumbrae. The dot-like brightenings in their Si IV slit-jaw images appear to have properties similar to the PMJs in our data: they have similar small round shapes, lifetimes on the order of a minute, and those that show proper motion have comparable speeds of 10-40 km s −1 (our PMJs fall on the lower end of that range).…”

Section: Discussionmentioning

confidence: 99%

Evidence for a Transition Region Response to Penumbral Microjets in Sunspots

Vissers

Voort

Carlsson

2015

ApJ

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Penumbral microjets (PMJs) are short-lived, fine-structured, and bright jets that are generally observed in chromospheric imaging of the penumbra of sunspots. Here we investigate their potential transition region signature by combining observations with the Swedish 1-m Solar Telescope in the Ca II H and Ca II 8542 Å lines with ultraviolet imaging and spectroscopy obtained with the Interface Region Imaging Spectrograph (IRIS), which includes the C II 1334/1335 Å, Si IV 1394/1403 Å, and Mg II h & k 2803/2796 Å lines. We find a clear corresponding signal in the IRIS Mg II k, C II, and Si IV slit-jaw images, typically offset spatially from the Ca II signature in the direction along the jets: from base to top, the PMJs are predominantly visible in Ca II, Mg II k, and C II/Si IV, suggesting progressive heating to transition region temperatures along the jet extent. Hence, these results support the suggestion from earlier studies that PMJs may heat to transition region temperatures.

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“…Those inside penumbrae are more compact, isolated, and ephemeral. In this study, we only focus on the subarcsecond and short-lived BDs within the penumbral area studied by Tian et al (2014b).…”

Section: Discussionmentioning

confidence: 99%

“…The recently launched Interface Region Imaging Spectrograph (IRIS; De Pontieu et al 2014) mission provides unprecedented observations of the solar TR and chromosphere with high cadence (several seconds), high spatial (0 167 pixel −1 ), and spectral resolution. Using IRIS 1400 and 1330 Å slit-jaw images (SJIs), Tian et al (2014b) revealed numerous short-lived subarcsecond bright dots (BDs) in the TR above every sunspot they investigated (located mainly in the penumbrae). These TR penumbral BDs often have intensities that are a few times stronger than their surrounding background in the 1400 Å SJIs.…”

Section: Introductionmentioning

confidence: 99%

Multi-Wavelength Study of Transition Region Penumbral Subarcsecond Bright Dots Using Iris and NST

Deng

Yurchyshyn

Kleint

et al. 2016

ApJ

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Using high-resolution transition region (TR) observations taken by the Interface Region Imaging Spectrograph (IRIS) mission, Tian et al. revealed numerous short-lived subarcsecond bright dots (BDs) above sunspots (mostly located in the penumbrae), which indicate yet unexplained small-scale energy releases. Moreover, whether or not these subarcsecond TR brightenings have any signature in the lower atmosphere and how they are formed are still not fully resolved. This paper presents a multi-wavelength study of the TR penumbral BDs using a coordinated observation of a near disk center sunspot with IRIS and the 1.6 m New Solar Telescope (NST) at the Big Bear Solar Observatory. NST provides high-resolution chromospheric and photospheric observations with narrowband Hα imaging spectroscopy and broadband TiO images, respectively, complementary to IRIS TR observations. A total of 2692 TR penumbral BDs are identified from a 37 minute time series of IRIS 1400 Å slit-jaw images. Their locations tend to be associated more with downflowing and darker fibrils in the chromosphere, and weakly associated with bright penumbral features in the photosphere. However, temporal evolution analyses of the BDs show that there is no consistent and convincing brightening response in the chromosphere. These results are compatible with a formation mechanism of the TR penumbral BDs by falling plasma from coronal heights along more vertical and dense magnetic loops. The BDs may also be produced by small-scale impulsive magnetic reconnection taking place sufficiently high in the atmosphere that has no energy release in the chromosphere.

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Observations of Subarcsecond Bright Dots in the Transition Region Above Sunspots With the Interface Region Imaging Spectrograph

Cited by 80 publications

References 37 publications

Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

Evidence for a Transition Region Response to Penumbral Microjets in Sunspots

Multi-Wavelength Study of Transition Region Penumbral Subarcsecond Bright Dots Using Iris and NST

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