184 research outputs found
Historical solar Ca II K observations at the Rome and Catania observatories
Here we present the little explored Ca II K archives from the Rome and the
Catania observatories and analyse the digitised images from these archives to
derive plage areas.Comment: 5 pages, 3 figures, to be published in "Nuovo Cimento C" as
proceeding of the Third Meeting of the Italian Solar and Heliospheric
Communit
Small-scale flux emergence events observed by Sunrise/IMaX
AbstractThanks to the unprecedented combination of high spatial resolution (0″.2) and high temporal cadence (33 s) spectropolarimetric measurements, the IMaX magnetograph aboard the Sunrise balloon-borne telescope is revealing new insights about the plasma dynamics of the all-pervasive small-scale flux concentrations in the quiet Sun. We present the result of a case study concerning the appearance of a bipole, with a size of about 4″ and a flux content of 5 × 1017 Mx, with strong signal of horizontal fields during the emergence. We analyze the data set using the SIR inversion code and obtain indications about the three-dimensional shape of the bipole and its evolution with time
On the Magnetic Nature of an Exploding Granule as Revealed by Sunrise/IMaX
We study the photospheric evolution of an exploding granule observed in the
quiet Sun at high spatial () and temporal (31.5 s)
resolution by the imaging magnetograph Sunrise/IMaX in June 2009. These
observations show that the exploding granule is cospatial to a magnetic flux
emergence event occurring at mesogranular scale (up to 12 Mm area). Using
a modified version of the SIR code for inverting the IMaX spectropolarimetric
measurements, we obtain information about the magnetic configuration of this
photospheric feature. In particular, we find evidence of highly inclined
emerging fields in the structure, carrying a magnetic flux content up to Mx. The balance between gas and magnetic pressure in the region
of flux emergence, compared with a very quiet region of the Sun, indicates that
the additional pressure carried by the emerging flux increases by about 5% the
total pressure and appears to allow the granulation to be modified, as
predicted by numerical simulations. The overall characteristics suggest that a
multi-polar structure emerges into the photosphere, resembling an almost
horizontal flux sheet. This seems to be associated with exploding granules.
Finally, we discuss the origin of such flux emergence events.Comment: 19 pages, 12 figure + Appendix, accepted for ApJ. Figure 1 and Figure
5 are a low-quality version of the original one
The Relationship Between Plasma Flow Doppler Velocities and Magnetic Field Parameters During the Emergence of Active Regions at the Solar Photospheric Level
A statistical study has been carried out of the relationship between plasma
flow Doppler velocities and magnetic field parameters during the emergence of
active regions at the solar photospheric level with data acquired by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO). We have investigated 224 emerging active regions with different spatial
scales and positions on the solar disc. The following relationships for the
first hours of the emergence of active regions have been analysed: i) of peak
negative Doppler velocities with the position of the emerging active regions on
the solar disc; ii) of peak plasma upflow and downflow Doppler velocities with
the magnetic flux growth rate and magnetic field strength for the active
regions emerging near the solar disc centre (the vertical component of plasma
flows); iii) of peak positive and negative Doppler velocities with the magnetic
flux growth rate and magnetic field strength for the active regions emerging
near the limb (the horizontal component of plasma flows); iv) of the magnetic
flux growth rate with the density of emerging magnetic flux; v) of the Doppler
velocities and magnetic field parameters for the first hours of the appearance
of active regions with the total unsigned magnetic flux at the maximum of their
development.Comment: 14 pages, 8 figures. The results of article were presented at the
ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102-103,
P.4.13,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
The frontier between Small-scale bipoles and Ephemeral Regions in the solar photosphere: Emergence and Decay of an Intermediate-scale bipole observed with IMaX/SUNRISE
We report on the photospheric evolution of an intermediate-scale (~4 Mm
footpoint separation) magnetic bipole, from emergence to decay, observed in the
quiet Sun at high spatial 0".3 and temporal (33 s) resolution. The observations
were acquired by the IMaX imaging magnetograph during the first science flight
of the Sunrise balloon-borne solar observatory. The bipole flux content is 6 x
10^17 Mx, representing a structure bridging the gap between granular scale
bipoles and the smaller ephemeral regions. Footpoints separate at a speed of
3.5 km s-1 and reach a maximum distance of 4.5 Mm before the field dissolves.
The evolution of the bipole is revealed to be very dynamic: we found a proper
motion of the bipole axis and detected a change of the azimuth angle of
90{\deg} in 300 seconds. The overall morphology and behaviour are in agreement
with previous analyses of bipolar structures emerging at granular scale, but we
also found several similarities with emerging flux structures at larger scale.
The flux growth rate is 2.6 x 15 Mx s-1, while the mean decay rate is one order
of magnitude smaller. We describe in some detail the decay phase of the bipole
footpoints which includes break up into smaller structures, interaction with
pre-existing fields leading to cancellation but appears to be dominated by an
as-yet unidentified diffusive process that removes most of the flux with an
exponential flux decay curve. The diffusion constant (8 x 10^2 km^2 s-1)
associated with this decay is similar to the values used to describe the large
scale diffusion in flux transport models.Comment: in press for Ap
The Horizontal Component of Photospheric Plasma Flows During the Emergence of Active Regions on the Sun
The dynamics of horizontal plasma flows during the first hours of the
emergence of active region magnetic flux in the solar photosphere have been
analyzed using SOHO/MDI data. Four active regions emerging near the solar limb
have been considered. It has been found that extended regions of Doppler
velocities with different signs are formed in the first hours of the magnetic
flux emergence in the horizontal velocity field. The flows observed are
directly connected with the emerging magnetic flux; they form at the beginning
of the emergence of active regions and are present for a few hours. The Doppler
velocities of flows observed increase gradually and reach their peak values
4-12 hours after the start of the magnetic flux emergence. The peak values of
the mean (inside the +/-500 m/s isolines) and maximum Doppler velocities are
800-970 m/s and 1410-1700 m/s, respectively. The Doppler velocities observed
substantially exceed the separation velocities of the photospheric magnetic
flux outer boundaries. The asymmetry was detected between velocity structures
of leading and following polarities. Doppler velocity structures located in a
region of leading magnetic polarity are more powerful and exist longer than
those in regions of following polarity. The Doppler velocity asymmetry between
the velocity structures of opposite sign reaches its peak values soon after the
emergence begins and then gradually drops within 7-12 hours. The peak values of
asymmetry for the mean and maximal Doppler velocities reach 240-460 m/s and
710-940 m/s, respectively. An interpretation of the observable flow of
photospheric plasma is given.Comment: 20 pages, 10 figures, 3 tables. The results of article were presented
at the ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102,
P.4.12,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
Effects of heavy ion particle irradiation on spore germination of bacillus spp. From extremely hot and cold environments
Extremophiles are optimal models in experimentally addressing questions about the effects of cosmic radiation on biological systems. The resistance to high charge energy (HZE) particles, and helium (He) ions and iron (Fe) ions (LET at 2.2 and 200 keV/µm, respectively, until 1000 Gy), of spores from two thermophiles, Bacillus horneckiae SBP3 and Bacillus licheniformis T14, and two psychrotolerants, Bacillus sp. A34 and A43, was investigated. Spores survived He irradiation better, whereas they were more sensitive to Fe irradiation (until 500 Gy), with spores from thermophiles being more resistant to irradiations than psychrotolerants. The survived spores showed different germination kinetics, depending on the type/dose of irradiation and the germinant used. After exposure to He 1000 Gy, D-glucose increased the lag time of thermophilic spores and induced germination of psychrotolerants, whereas L-alanine and L-valine increased the germination efficiency, except alanine for A43. FTIR spectra showed important modifications to the structural components of spores after Fe irradiation at 250 Gy, which could explain the block in spore germination, whereas minor changes were observed after He radiation that could be related to the increased permeability of the inner membranes and alterations of receptor complex structures. Our results give new insights on HZE resistance of extremophiles that are useful in different contexts, including astrobiology
Chromospheric signatures of small-scale flux emergence as observed with NST and Hinode instruments
With the ever increasing influx of high resolution images of the solar
surface obtained at a multitude of wavelengths, various processes occurring at
small spatial scales have become a greater focus of our attention. Complex
small-scale magnetic fields have been reported that appear to have enough
stored to heat the chromosphere. While significant progress has been made in
understanding small-scale phenomena, many specifics remain elusive. We present
here a detailed study of a single event of disappearance of a magnetic dipole
and associated chromospheric activity. Based on New Solar Telescope H
data and {\it Hinode} photospheric line-of-sight magnetograms and Ca II H
images we report the following. 1) Our analysis indicates that even very small
dipoles (elements separated by about 0\arcsec.5 or less) may reach the
chromosphere and trigger non-negligible chromospheric activity. 2) Careful
consideration of the magnetic environment where the new flux is deposited may
shed light on the details of magnetic flux removal from the solar surface. We
argue that the apparent collision and disappearance of two opposite polarity
elements may not necessarily indicate their cancellation (i.e., reconnection,
emergence of a "U" tube or submergence of loops). In our case, the
magnetic dipole disappeared by reconnecting with overlying large-scale inclined
plage fields. 3) Bright points seen in off-band H images are very
well-correlated with the Ca II H bright points, which in turn are co-spatial
with G-band bright points. We further speculate that, in general, H
bright points are expected be co-spatial with photospheric BPs, however, a
direct comparison is needed to refine their relationship
The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources
The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper, we present new 150-MHz observations carried out with the LOw-Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6 × 14.7 arcsec and reaches an rms of 160 μJy beam at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of . The median spectral index becomes slightly flatter (increasing from with decreasing flux density down to S_1_5_0 ∼10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample, we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 ultra-steep-spectrum sources and 13 peaked-spectrum sources. We estimate that up to 21 per cent of these could have z > 4 and are candidate high-z radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects
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