3,257 research outputs found
Surface waves in solar granulation observed with {\sc Sunrise}
Solar oscillations are expected to be excited by turbulent flows in the
intergranular lanes near the solar surface. Time series recorded by the IMaX
instrument aboard the {\sc Sunrise} observatory reveal solar oscillations at
high resolution, which allow studying the properties of oscillations with short
wavelengths. We analyze two times series with synchronous recordings of Doppler
velocity and continuum intensity images with durations of 32\thinspace min and
23\thinspace min, resp., recorded close to the disk center of the Sun to study
the propagation and excitation of solar acoustic oscillations. In the Doppler
velocity data, both the standing acoustic waves and the short-lived,
high-degree running waves are visible. The standing waves are visible as
temporary enhancements of the amplitudes of the large-scale velocity field due
to the stochastic superposition of the acoustic waves. We focus on the
high-degree small-scale waves by suitable filtering in the Fourier domain.
Investigating the propagation and excitation of - and -modes with wave
numbers \thinspace 1/Mm we find that also exploding granules
contribute to the excitation of solar -modes in addition to the contribution
of intergranular lanes.Comment: 12 pages, 4 figures, to appear in a special volume on Sunrise in
Astrophysical Journal Letter
Transverse component of the magnetic field in the solar photosphere observed by Sunrise
We present the first observations of the transverse component of photospheric
magnetic field acquired by the imaging magnetograph Sunrise/IMaX. Using an
automated detection method, we obtain statistical properties of 4536 features
with significant linear polarization signal. Their rate of occurrence is 1-2
orders of magnitude larger than values reported by previous studies. We show
that these features have no characteristic size or lifetime. They appear
preferentially at granule boundaries with most of them being caught in downflow
lanes at some point in their evolution. Only a small percentage are entirely
and constantly embedded in upflows (16%) or downflows (8%).Comment: Accepted for the Sunrise Special Issue of ApJ
Detection of vortex tubes in solar granulation from observations with Sunrise
We have investigated a time series of continuum intensity maps and
corresponding Dopplergrams of granulation in a very quiet solar region at the
disk center, recorded with the Imaging Magnetograph eXperiment (IMaX) on board
the balloon-borne solar observatory Sunrise. We find that granules frequently
show substructure in the form of lanes composed of a leading bright rim and a
trailing dark edge, which move together from the boundary of a granule into the
granule itself. We find strikingly similar events in synthesized intensity maps
from an ab initio numerical simulation of solar surface convection. From cross
sections through the computational domain of the simulation, we conclude that
these `granular lanes' are the visible signature of (horizontally oriented)
vortex tubes. The characteristic optical appearance of vortex tubes at the
solar surface is explained. We propose that the observed vortex tubes may
represent only the large-scale end of a hierarchy of vortex tubes existing near
the solar surface.Comment: Astrophysical Journal Letters: Sunrise Special Issue, reveived 2010
June 16; accepted 2010 August
Fully resolved quiet-Sun magnetic flux tube observed with the Sunrise IMaX instrument
Until today, the small size of magnetic elements in quiet Sun areas has
required the application of indirect methods, such as the line-ratio technique
or multi-component inversions, to infer their physical properties. A consistent
match to the observed Stokes profiles could only be obtained by introducing a
magnetic filling factor that specifies the fraction of the observed pixel
filled with magnetic field. Here, we investigate the properties of a small
magnetic patch in the quiet Sun observed with the IMaX magnetograph on board
the balloon-borne telescope Sunrise with unprecedented spatial resolution and
low instrumental stray light. We apply an inversion technique based on the
numerical solution of the radiative transfer equation to retrieve the
temperature stratification and the field strength in the magnetic patch. The
observations can be well reproduced with a one-component, fully magnetized
atmosphere with a field strength exceeding 1 kG and a significantly enhanced
temperature in the mid- to upper photosphere with respect to its surroundings,
consistent with semi-empirical flux tube models for plage regions. We therefore
conclude that, within the framework of a simple atmospheric model, the IMaX
measurements resolve the observed quiet-Sun flux tube.Comment: Accepted for publication in The Astrophysical Journal Letters on Aug
11 201
Bright points in the quiet Sun as observed in the visible and near-UV by the balloon-borne observatory Sunrise
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 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, but some display strong
down- or upflows reaching a few km/s.Comment: Accepted for publication in The Astrophysical Journal Letters on
September 08 201
SUNRISE/IMaX observations of convectively driven vortex flows in the Sun
We characterize the observational properties of the convectively driven
vortex flows recently discovered on the quiet Sun, using magnetograms,
Dopplergrams and images obtained with the 1-m balloon-borne Sunrise telescope.
By visual inspection of time series, we find some 3.1e-3 vortices/(Mm^2 min),
which is a factor of 1.7 larger than previous estimates. The mean duration of
the individual events turns out to be 7.9 min, with a standard deviation of 3.2
min. In addition, we find several events appearing at the same locations along
the duration of the time series (31.6 min). Such recurrent vortices show up in
the proper motion flow field map averaged over the time series. The typical
vertical vorticities are <= 6e-3 1/sec, which corresponds to a period of
rotation of some 35 min. The vortices show a preferred counterclockwise sense
of rotation, which we conjecture may have to do with the preferred vorticity
impinged by the solar differential rotation.Comment: To appear in ApJL. 5 Figs, 4 pages. The two animations associated
with the work can be downloaded from
http://www.iac.es/proyecto/solarhr/imaxvortex.html References updated in V
Sunrise: instrument, mission, data and first results
The Sunrise balloon-borne solar observatory consists of a 1m aperture Gregory
telescope, a UV filter imager, an imaging vector polarimeter, an image
stabilization system and further infrastructure. The first science flight of
Sunrise yielded high-quality data that reveal the structure, dynamics and
evolution of solar convection, oscillations and magnetic fields at a resolution
of around 100 km in the quiet Sun. After a brief description of instruments and
data, first qualitative results are presented. In contrast to earlier
observations, we clearly see granulation at 214 nm. Images in Ca II H display
narrow, short-lived dark intergranular lanes between the bright edges of
granules. The very small-scale, mixed-polarity internetwork fields are found to
be highly dynamic. A significant increase in detectable magnetic flux is found
after phase-diversity-related reconstruction of polarization maps, indicating
that the polarities are mixed right down to the spatial resolution limit, and
probably beyond.Comment: accepted by ApJ
The Second INTEGRAL AGN Catalogue
The INTEGRAL mission provides a large data set for studying the hard X-ray
properties of AGN and allows testing of the unified scheme for AGN. We present
analysis of INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly
detected by INTEGRAL above 20 keV. The data analysed here allow a significant
spectral extraction on 148 objects and an optical variability study of 57 AGN.
The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert~2 galaxies are
found to be consistent within the uncertainties, whereas higher cut-off
energies and lower luminosities are measured for the more absorbed / type 2
AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent
with those of Seyfert 1. When applying a Compton reflection model, the
underlying continua appear the same in Seyfert 1 and 2 with photon index 2, and
the reflection strength is about R = 1, when assuming different inclination
angles. A significant correlation is found between the hard X-ray and optical
luminosity and the mass of the central black hole in the sense that the more
luminous objects appear to be more massive. There is also a general trend
toward the absorbed sources and type 2 AGN having lower Eddington ratios. The
black holemass appears to form a fundamental plane together with the optical
and X-ray luminosity of the form Lv being proportional to Lx^0.6 M^0.2, similar
to that found between radio luminosity Lr, Lx, and M. The unified model for
Seyfert galaxies seems to hold, showing in hard X-rays that the central engine
is the same in Seyfert 1 and 2, but seen under different inclination angles and
absorption. (Abridged)Comment: 26 pages, 16 figures, accepted for publication in A&A. Corrections by
language editor included in version
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