15 research outputs found
Diagnostics for spectropolarimetry and magnetography
An assessment on the capabilities of modern spectropolarimeters and
magnetographs is in order since most of our astrophysical results rely upon the
accuracy of the instrumentation and on the sensitivity of the observables to
variations of the sought physical parameters. A contribution to such an
assessment will be presented in this talk where emphasis will be made on the
use of the so-called response functions to gauge the probing capabilities of
spectral lines and on an analytical approach to estimate the uncertainties in
the results in terms of instrumental effects. The Imaging Magnetograph
eXperiment (IMaX) and the Polarimetric and Helioseismic Imager (PHI) will be
used as study cases.Comment: To be published in "Physics of Sun and Star Spots", Proceedings of
IAU Symp. 273, D.P. Choudhary & A.C. Cadavid (eds.), Cambridge, UK: Cambridge
University Pres
Dynamics of multi-cored magnetic structures in the quiet Sun
We report on the dynamical interaction of quiet-Sun magnetic fields and
granular convection in the solar photosphere as seen by \textsc{Sunrise}. We
use high spatial resolution (0\farcs 15--0\farcs 18) and temporal cadence (33
s) spectropolarimetric Imaging Magnetograph eXperiment data, together with
simultaneous CN and Ca\,\textsc{ii}\,H filtergrams from \textsc{Sunrise} Filter
Imager. We apply the SIR inversion code to the polarimetric data in order to
infer the line of sight velocity and vector magnetic field in the photosphere.
The analysis reveals bundles of individual flux tubes evolving as a single
entity during the entire 23 minute data set. The group shares a common canopy
in the upper photospheric layers, while the individual tubes continually
intensify, fragment and merge in the same way that chains of bright points in
photometric observations have been reported to do. The evolution of the tube
cores are driven by the local granular convection flows. They intensify when
they are "compressed" by surrounding granules and split when they are
"squeezed" between two moving granules. The resulting fragments are usually
later regrouped in intergranular lanes by the granular flows. The continual
intensification, fragmentation and coalescence of flux results in magnetic
field oscillations of the global entity. From the observations we conclude that
the magnetic field oscillations first reported by \citet{2011ApJ...730L..37M}
correspond to the forcing by granular motions and not to characteristic
oscillatory modes of thin flux tubes.Comment: 12 pages, 7 figures. Accepted in ApJ. Animation 1 can be downloaded
from: http://spg.iaa.es/download
The history of a quiet-Sun magnetic element revealed by IMaX/SUNRISE
Isolated flux tubes are considered to be fundamental magnetic building blocks
of the solar photosphere. Their formation is usually attributed to the
concentration of magnetic field to kG strengths by the convective collapse
mechanism. However, the small size of the magnetic elements in quiet-Sun areas
has prevented this scenario from being studied in fully resolved structures.
Here we report on the formation and subsequent evolution of one such
photospheric magnetic flux tube, observed in the quiet Sun with unprecedented
spatial resolution (0\farcs 15 - 0\farcs 18) and high temporal cadence (33 s).
The observations were acquired by the Imaging Magnetograph Experiment (IMaX)
aboard the \textsc{Sunrise} balloon-borne solar observatory. The equipartition
field strength magnetic element is the result of the merging of several same
polarity magnetic flux patches, including a footpoint of a previously emerged
loop. The magnetic structure is then further intensified to kG field strengths
by convective collapse. The fine structure found within the flux concentration
reveals that the scenario is more complex than can be described by a thin flux
tube model with bright points and downflow plumes being established near the
edges of the kG magnetic feature. We also observe a daisy-like alignment of
surrounding granules and a long-lived inflow towards the magnetic feature.
After a subsequent weakening process, the field is again intensified to kG
strengths. The area of the magnetic feature is seen to change in anti-phase
with the field strength, while the brightness of the bright points and the
speed of the downflows varies in phase. We also find a relation between the
brightness of the bright point and the presence of upflows within it.Comment: 13 pages. Accepted in ApJ. Animation 1 can be viewed and downloaded
from: http://spg.iaa.es/downloads.as
IMaX: A magnetograph for SUNRISE
10 pages, 9 figures.-- Published in: "Polarimetry in Astronomy", edited by Silvano Fineschi.-- Contributed to the conference with same title, Waikoloa, HI, USA, Aug 25, 2002.Final full-text version available Open Access at: http://www.iaa.es/~jti/publications/SPIE.pdfThe description of the Imaging Magnetograph eXperiment (IMaX) is presented in this contribution. This is a magnetograph which will fly by the end of 2006 on a stratospheric balloon, together with other instruments (to be described elsewhere). Especial emphasis is put on the scientific requirements to obtain diffraction-limited visible magnetograms, on the optical design and several constraining characteristics, such as the wavelength tuning or the crosstalk between the Stokes parameters.Peer reviewe