TY  - JOUR
A1  - Leussu, R.
A1  - Usoskin, IIlya G.
A1  - Valliappan, Senthamizh Pavai
A1  - Diercke, Andrea
A1  - Arlt, Rainer
A1  - Denker, Carsten
A1  - Mursula, K.
T1  - Wings of the butterfly
BT  - sunspot groups for 1826-2015
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence since 1826, using the recently digitized data from Schwabe (1826-1867) and Sporer (1866-1880). The wings of the diagram are separated using a recently developed method based on an analysis of long gaps in sunspot group occurrence in different latitude bands. We define characteristic latitudes, corresponding to the start, end, and the largest extent of the wings (the F, L, and H latitudes). The H latitudes (30 degrees-45 degrees) are highly significantly correlated with the strength of the wings (quantified by the total sum of the monthly numbers of sunspot groups). The F latitudes (20 degrees-30 degrees) depict a weak tendency, especially in the southern hemisphere, to follow the wing strength. The L latitudes (2 degrees-10 degrees) show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have a greater wing extent. A strong (5-6)-cycle periodic oscillation is found in the start and end times of the wings and in the overlap and gaps between successive wings of one hemisphere. While the average wing overlap is zero in the southern hemisphere, it is two to three months in the north. A marginally significant oscillation of about ten solar cycles is found in the asymmetry of the L latitudes. The new long database of butterfly wings provides new observational constraints to solar dynamo models that discuss the spatio-temporal distribution of sunspot occurrence over the solar cycle and longer.
KW  - Sun: activity
KW  - sunspots
KW  - history and philosophy of astronomy
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201629533
SN  - 1432-0746
VL  - 599
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Gömöry, Peter
A1  - Balthasar, Horst
A1  - Kuckein, Christoph
A1  - Koza, Julis
A1  - Veronig, Astrid M.
A1  - González Manrique, Sergio Javier
A1  - Kucera, Ales
A1  - Schwartz, Pavol
A1  - Hanslmeier, Arnold
T1  - Flare-induced changes of the photospheric magnetic field in a delta-spot deduced from ground-based observations
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. Changes of the magnetic field and the line-of-sight velocities in the photosphere are being reported for an M-class flare that originated at a delta-spot belonging to active region NOAA 11865. Methods. High-resolution ground-based near-infrared spectropolarimetric observations were acquired simultaneously in two photospheric spectral lines, Fe I 10783 angstrom and Si I 10786 angstrom, with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope (VTT) in Tenerife on 2013 October 15. The observations covered several stages of the M-class flare. Inversions of the full-Stokes vector of both lines were carried out and the results were put into context using (extreme)-ultraviolet filtergrams from the Solar Dynamics Observatory (SDO). Results. The active region showed high flaring activity during the whole observing period. After the M-class flare, the longitudinal magnetic field did not show significant changes along the polarity inversion line (PIL). However, an enhancement of the transverse magnetic field of approximately 550G was found that bridges the PIL and connects umbrae of opposite polarities in the delta-spot. At the same time, a newly formed system of loops appeared co-spatially in the corona as seen in 171 angstrom filtergrams of the Atmospheric Imaging Assembly (AIA) on board SDO. However, we cannot exclude that the magnetic connection between the umbrae already existed in the upper atmosphere before the M-class flare and became visible only later when it was filled with hot plasma. The photospheric Doppler velocities show a persistent upflow pattern along the PIL without significant changes due to the flare. Conclusions. The increase of the transverse component of the magnetic field after the flare together with the newly formed loop system in the corona support recent predictions of flare models and flare observations.
KW  - Sun: magnetic fields
KW  - sunspots
KW  - Sun: photosphere
KW  - Sun: flares
KW  - techniques: polarimetric
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201730644
SN  - 1432-0746
VL  - 602
SP  - 14
EP  - 27
PB  - EDP Sciences
CY  - Les Ulis
ER  -