arXiv subjects

Robert J. Rutten

Publications and source records attributed to Robert J. Rutten.

22 records · Page 2Linked to original sources

arXiv2009

Solar Spectroscopy and (Pseudo-)Diagnostics of the Solar Chromosphere

I first review trends in current solar spectrometry and then concentrate on comparing various spectroscopic diagnostics of the solar chromosphere. Some are actually not at all chromospheric but just photospheric or clapotispheric and do not convey information on chromospheric heating, even though this is often assumed. Balmer Halpha is the principal displayer of the closed-field chromosphere, but it is unclear how chromospheric fibrils gain their large Halpha opacity. The open-field chromosphere seems to harbor most if not all coronal heating and solar wind driving, but is hardly seen in optical diagnostics.

astro-ph.SR↗

arXiv2008

DOT Tomography of the Solar Atmosphere VII. Chromospheric Response to Acoustic Events

We use synchronous movies from the Dutch Open Telescope sampling the G band, Ca II and Halpha with five-wavelength profile sampling to study the response of the chromosphere to acoustic events in the underlying photosphere. We first compare the visibility of the chromosphere in Ca II H and Halpha, demonstrate that studying the chromosphere requires Halpha data, and summarize recent developments in understanding why this is so. We construct divergence and vorticity maps of the photospheric flow field from the G-band images and locate specific events through the appearance of bright Ca II H grains. The reaction of the Halpha chromosphere is diagnosed in terms of brightness and Doppler shift. We show and discuss three particular cases in detail: a regular acoustic grain marking shock excitation by granular dynamics, a persistent flasher which probably marks magnetic-field concentration, and an exploding granule. All three appear to buffet overlying fibrils, most clearly in Dopplergrams. Although our diagnostic displays to dissect these phenomena are unprecedentedly comprehensive, adding even more information (photospheric Doppler tomography and magnetograms, chromospheric imaging and Doppler mapping in the ultraviolet) is warranted.

astro-ph↗

arXiv2007

Observing the Solar Chromosphere

This review is split into two parts: one on chromospheric line formation in answer to the frequent question "where is my line formed", and one presenting state-of-the-art imagery of the chromosphere. In the first part I specifically treat the formation of the Na D lines, Ca II H & K, and Halpha. In the second I show DOT, IBIS, VAULT, and TRACE images as evidence that the chromosphere consists of fibrils of intrinsically different types. The straight-up ones are hottest. The slanted ones are filled by shocks and likely possess thin transition sheaths to coronal plasma. The ones hovering horizontally over "clapotispheric" cell interiors outline magnetic canopies and are buffeted by shocks, most violently in the quietest regions. In the absence of integral-field ultraviolet spectrometry, H$α$ remains the principal chromosphere diagnostic. The required fast-cadence profile-sampling imaging is an important quest for new telescope technology.

astro-ph↗

arXiv2007

On the Nature of the Solar Chromosphere

DOT high-resolution imagery suggests that only internetwork-spanning H-alpha "mottles" constitute the quiet-sun chromosphere, whereas more upright network "straws" in "hedge rows" reflect transition-region conditions.

astro-ph↗