Bright Points in the Quiet Sun as Observed in the Visible and Near-Uv by the Balloon-Borne Observatory Sunrise

Abstract

Bright points (BPs) are manifestations of small magnetic elements in the solar photosphere. Their brightness contrast not only gives insight into the thermal state of the photosphere (and chromosphere) in magnetic elements, but also plays an important role in modulating the solar total and spectral irradiance. Here, we report on simultaneous high-resolution imaging and spectropolarimetric observations of BPs using Sunrise balloon-borne observatory data of the quiet Sun at the disk center. BP contrasts have been measured between 214 nm and 525 nm, including the first measurements at wavelengths below 388 nm. The histograms of the BP peak brightness show a clear trend toward broader contrast distributions and higher mean contrasts at shorter wavelengths. At 214 nm, we observe a peak brightness of up to five times the mean quiet-Sun value, the highest BP contrast so far observed. All BPs are associated with a magnetic signal, although in a number of cases it is surprisingly weak. Most of the BPs show only weak downflows, the mean value being 240 m s −1 , but some display strong down-or upflows reaching a few km s −1 .

The Sunrise Mission

“…The total observing time with image stabilization was more than 33 h, in which SuFI collected nearly 56 000 images in the wavelength range between 210 nm to 400 nm, being above most of the ozone layer in the Earth's atmosphere. In the blue channels at 214 nm, 300 nm, and 312 nm, the solar surface could be observed for the first time at high angular resolution and with unprecedented intensity contrasts Riethmüller et al, 2010;Hirzberger et al, 2010b), thanks to the high optical quality of the instrumentation. IMaX collected high resolution Doppler-and magnetograms with an unprecedented combination of angular resolution and magnetic sensitivity .…”

The Filter Imager SuFI and the Image Stabilization and Light Distribution System ISLiD of the Sunrise Balloon-Borne Observatory: Instrument Description

“…A careful analysis of the data (Hirzberger et al, 2010a;Riethmüller et al, 2010;Solanki et al, 2010) reveals that the observed intensity contrasts are remarkably high, showing the extraordinary optical performance of the total system of telescope and instrument, especially the virtual lack of straylight contamination.…”

Comparison of solar photospheric bright points between Sunrise observations and MHD simulations

“…2, panel h) find that most of the BPs are only weakly polarized. We use the BP detection method applied by Riethmüller et al (2010) for a direct comparison with their results.…”

“…Furthermore, the noise levels of the two data sets were comparable. We also calculated the histogram of the circular polarization degree of the set of V5-6 BPs analyzed by Riethmüller et al (2010) (not shown) and compared it with their histogram of the total polarization degree, i.e., Q 2 + U 2 + V 2 integrated over λ in the line, shown in Fig. 2, panel (h) of Riethmüller et al (2010).…”

“…We also calculated the histogram of the circular polarization degree of the set of V5-6 BPs analyzed by Riethmüller et al (2010) (not shown) and compared it with their histogram of the total polarization degree, i.e., Q 2 + U 2 + V 2 integrated over λ in the line, shown in Fig. 2, panel (h) of Riethmüller et al (2010). From the similarity of the two histograms we concluded that the Stokes Q and U signals are negligible in BPs, so that the lack of Q and U signals in the L12-2 data should not affect our conclusions.…”