期刊
ASTROPHYSICAL JOURNAL
卷 757, 期 1, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/757/1/49
关键词
convection; magnetic fields; sunspots
资金
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan
- Spanish Ministerio de Ciencia e Innovacion [AYA2009-14105-C06-06, PCI2006-A7-0624]
- Junta de Andalucia [P07-TEP-02687]
- European FEDER funds
We study the temporal evolution of umbral dots (UDs) using measurements from the CRISP imaging spectropolarimeter at the Swedish 1 m Solar Telescope. Scans of the magnetically sensitive 630 nm iron lines were performed under stable atmospheric conditions for 71 minutes with a cadence of 63 s. These observations allow us to investigate the magnetic field and velocity in and around UDs at a resolution approaching 0.'' 13. From the analysis of 339 UDs, we draw the following conclusions: (1) UDs show clear hints of upflows, as predicted by magnetohydrodynamic simulations. By contrast, we could not find systematic downflow signals. Only in very deep layers, we detect localized downflows around UDs, but they do not persist in time. (2) We confirm that UDs exhibit weaker and more inclined fields than their surroundings, as reported previously. However, UDs that have strong fields above 2000 G or are in the decay phase show enhanced and more vertical fields. (3) There are enhanced fields at the migration front of UDs detached from penumbral grains, as if their motion were impeded by the ambient field. (4) Long-lived UDs travel longer distances with slower proper motions. Our results appear to confirm some aspects of recent numerical simulations of magnetoconvection in the umbra (e. g., the existence of upflows in UDs), but not others (e. g., the systematic weakening of the magnetic field at the position of UDs).
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