20 research outputs found
ALMA Solar Ephemeris Generator
An online software tool for the easy preparation of ephemerides of the solar
surface features is presented. It was developed as a helper tool for the
preparation of observations of the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA), but it can be used at other
observatories as well. The tool features an easy to use point-and-click
graphical user interface with the possibility to enter or adjust input
parameters, while the result is a table of predicted positions in the celestial
equatorial coordinate system, suitable for import into the ALMA Observing Tool
software. The tool has been successfully used for the preparation and execution
of solar observations with ALMA.Comment: Submitted to The Mining Geological Petroleum Engineering Bulletin
(see https://www.scopus.com/sourceid/101730), 7 pages, 2 figure
Solar differential rotation in the period 1964 - 2016 determined by the Kanzelh\"ohe data set
The main aim of this work is to determine the solar differential rotation by
tracing sunspot groups during the period 1964-2016, using the Kanzelh\"ohe
Observatory for Solar and Environmental Research (KSO) sunspot drawings and
white light images. Two procedures for the determination of the heliographic
positions were applied: an interactive procedure on the KSO sunspot drawings
(1964 - 2008, solar cycles nos. 20 - 23) and an automatic procedure on the KSO
white light images (2009 - 2016, solar cycle no. 24). For the determination of
the synodic angular rotation velocities two different methods have been used: a
daily shift (DS) method and a robust linear least-squares fit (rLSQ) method.
Afterwards, the rotation velocities had to be converted from synodic to
sidereal, which were then used in the least-squares fitting for the solar
differential rotation law. For the test data from 2014, we found the rLSQ
method for calculating rotational velocities to be more reliable than the DS
method. The best fit solar differential rotation profile for the whole time
period is = (14.47 0.01) - (2.66 0.10)
(deg/day) for the DS method and = (14.50 0.01) - (2.87
0.12) (deg/day) for the rLSQ method. A barely noticeable north -
south asymmetry is observed for the whole time period 1964 - 2016 in the
present paper. Rotation profiles, using different data sets (e.g. Debrecen
Photoheliographic Data, Greenwich Photoheliographic Results), presented by
other authors for the same time periods and the same tracer types, are in good
agreement with our results. Therefore, the KSO data set is suitable for the
investigation of the long-term variabilities in the solar rotation profile
First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun
Various solar features can be seen on maps of the Sun in the mm and sub-mm
wavelength range. The recently installed Atacama Large Millimeter/submillimeter
Array (ALMA) is capable of observing the Sun in that wavelength range with an
unprecedented spatial, temporal and spectral resolution. To interpret solar
observations with ALMA the first important step is to compare ALMA maps with
simultaneous images of the Sun recorded in other spectral ranges. First we
identify different structures in the solar atmosphere seen in the optical, IR
and EUV parts of the spectrum (quiet Sun (QS), active regions (AR), prominences
on the disc, magnetic inversion lines (IL), coronal holes (CH) and coronal
bright points (CBPs)) in a full disc solar ALMA image. The second aim is to
measure the intensities (brightness temperatures) of those structures and
compare them with the corresponding QS level. A full disc solar image at 1.21
mm obtained on December 18, 2015 during a CSV-EOC campaign with ALMA is
calibrated and compared with full disc solar images from the same day in
H\alpha, in He I 1083 nm core, and with SDO images (AIA at 170 nm, 30.4 nm,
21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures
of various structures are determined by averaging over corresponding regions of
interest in the ALMA image. Positions of the QS, ARs, prominences on the disc,
ILs, CHs and CBPs are identified in the ALMA image. At 1.21 mm ARs appear as
bright areas (but sunspots are dark), while prominences on the disc and CHs are
not discernible from the QS background, although having slightly less intensity
than surrounding QS regions. ILs appear as large, elongated dark structures and
CBPs correspond to ALMA bright points. These results are in general agreement
with sparse earlier measurements at similar wavelengths. The identification of
CBPs represents the most important new result.Comment: 9 pages, 3 figure
Variation in solar differential rotation and activity in the period 1964-2016 determined by the Kanzelh\"ohe data set
We determined the differential rotation (DR) parameters and
(corresponding to the equatorial rotation velocity and the gradient of the
solar DR) by tracing sunspot groups in sunspot drawings of the Kanzelh\"ohe
Observatory for Solar and Environmental Research (KSO; 1964-2008, for solar
cycles (SC) 20-23) and KSO white-light images (2009-2016, for SC 24). We used
different statistical methods and approaches to analyse cycle related
variations, solar cycle phase-related variations and long-term variations of
the DR. and show statistically significant periodic variability. The
changes in related to solar cycle phase are in accordance with previously
reported theoretical and experimental results (higher during solar minimum,
lower during the maximum of activity), while changes in differ from the
theoretical predictions as we observe more negative values of , that is, a
more pronounced DR during activity maximum. The main result of this paper for
the long-term variations in is the detection of a phase shift between the
activity flip (in the 1970s) and the equatorial rotation velocity flip (in the
early 1990s). During this time period both and activity show a secular
decreasing trend, indicating their correlation. Therefore, the theoretical
model fails in the phase-shift time period that occurs after the modern
Gleissberg maximum, while in the time period thereafter (after the 1990s),
theoretical and experimental results are consistent. The long-term variations
in in general yield an anticorrelation of and activity, as a rise of
is observed during the entire time period (1964-2016) we analysed, during
which activity decreased. We study for the first time the variation in solar DR
and activity based on 53 years of KSO data. Our results agree well with the
results related to the solar cycle phase from corona observations
Variation in solar differential rotation and activity in the period 1964–2016 determined by the Kanzelhöhe data set
Aims. Theoretical calculations predict an increased equatorial rotation and more pronounced differential rotation (DR) during the minimum of solar magnetic activity. However, the results of observational studies vary, some showing less and some more pronounced DR during the minimum of solar magnetic activity. Our study aims to gain more insight into these discrepancies.
Methods. We determined the DR parameters A and B (corresponding to the equatorial rotation velocity and the gradient of the solar DR, respectively) by tracing sunspot groups in sunspot drawings of the Kanzelhöhe Observatory for Solar and Environmental Research (KSO; 1964–2008, for solar cycles 20–23) and KSO white-light images (2009–2016, for solar cycle 24). We used different statistical methods and approaches to analyse variations in DR parameters related to the cycle and to the phase of the solar cycle, together with long-term related variations.
Results. The comparison of the DR parameters for individual cycles obtained from the KSO and from other sources yield statistically insignificant differences for the years after 1980, meaning that the KSO sunspot group data set is well suited for long-term cycle to cycle studies. The DR parameters A and B show statistically significant periodic variability. The periodicity corresponds to the solar cycle and is correlated with the solar activity. The changes in A related to solar cycle phase are in accordance with previously reported theoretical and experimental results (higher A during solar minimum, lower A during the maximum of activity), while changes in B differ from the theoretical predictions as we observe more negative values of B, that is, a more pronounced differential rotation during activity maximum. The main result of this paper for the long-term variations in A is the detection of a phase shift between the activity flip (in the 1970s) and the equatorial rotation velocity flip (in the early 1990s), during which both A and activity show a secular decreasing trend. This indicates that the two quantities are correlated in between 1970 and 1990. Therefore, the theoretical model fails in the phase-shift time period that occurs after the modern Gleissberg maximum, while in the time period thereafter (after the 1990s), theoretical and experimental results are consistent. The long-term variations in B in general yield an anticorrelation of B and activity, as a rise of B is observed during the entire time period (1964–2016) we analysed, during which activity decreased, with the exception of the end of solar cycle 22 and the beginning of solar cycle 23.
Conclusions. We study for the first time the variation in solar DR and activity based on 53 years of KSO data. Our results agree well with the results related to the solar cycle phase from corona observations. The disagreement of the observational results for B and theoretical studies may be due to the fact that we analysed the period immediately after the modern Gleissberg maximum, where for the phase-shift period, A versus activity also entails a result that differs from theoretical predictions. Therefore, studies of rotation versus activity with data sets encompassing the Gleissberg extremes should include separate analyses of the parts of the data set in between different flips (e.g., before the activity flip, between the activity and the rotation flip, and after the rotation flip)
Differences in physical properties of coronal bright points and their ALMA counterparts within and outside coronal holes
Aims. This study investigates and compares the physical properties, such as intensity and area, of coronal bright points (CBPs) inside and outside of coronal holes (CHs) using the Atacama Large Millimeter/submillimeter Array (ALMA) and Solar Dynamics Observatory (SDO) observations.
Methods. The CBPs were analysed using the single-dish ALMA Band 6 observations, combined with extreme-ultraviolet (EUV) 193 Å filtergrams obtained by the Atmospheric Imaging Assembly (AIA) and magnetograms obtained by the Helioseismic and Magnetic Imager (HMI), both on board SDO. The CH boundaries were extracted from the SDO/AIA images using the Collection of Analysis Tools for Coronal Holes (CATCH) and CBPs were identified in the SDO/AIA, SDO/HMI, and ALMA data. Measurements of brightness and areas in both ALMA and SDO/AIA images were conducted for CBPs within CH boundaries and quiet Sun regions outside CHs. Two equal size CBP samples, one inside and one outside CHs, were randomly chosen and a statistical analysis was conducted. The statistical analysis was repeated 200 times using a bootstrap technique to eliminate the results based on pure coincidence.
Results. The boundaries of five selected CHs were extracted using CATCH and their physical properties were obtained. Statistical analysis of the measured physical CBP properties using two different methods resulted in a lower average intensity in the SDO/AIA data, or brightness temperature in the ALMA data, for CBPs within the boundaries of all five CHs. Depending on the CBP sample size, the difference in intensity for the SDO/AIA data, and brightness temperature for the ALMA data, between the CBPs inside and outside CHs ranged from between 2σ and 4.5σ, showing a statistically significant difference between those two CBP groups. We also obtained CBP areas, where CBPs within the CH boundaries showed lower values for the measured areas, with the observed difference between the CBPs inside and outside CHs between 1σ and 2σ for the SDO/AIA data, and up to 3.5σ for the ALMA data, indicating that CBP areas are also significantly different for the two CBP groups. We also found that, in comparison to the SDO/AIA data, the measured CBP properties in the ALMA data show a small brightness temperature difference and a higher area difference between the CBPs within and outside of CHs, possibly because of the modest spatial resolution of the ALMA images.
Conclusions. Given the measured properties of the CBPs, we conclude that the CBPs inside CHs tend to be less bright on average, but also smaller in comparison to those outside of CHs. This conclusion might point to the specific physical conditions and properties of the local CH region around a CBP limiting the maximum achievable intensity (temperature) and size of a CBP. The need for the interferometric ALMA data is also emphasised to get more precise physical CBP property measurements at chromospheric heights
Exploring the Sun with ALMA
The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory opens a new window onto the Universe. The ability to perform continuum imaging and spectroscopy of astrophysical phenomena at millimetre and submillimetre wavelengths with unprecedented sensitivity opens up new avenues for the study of cosmology and the evolution of galaxies, the formation of stars and planets, and astrochemistry. ALMA also allows fundamentally new observations to be made of objects much closer to home, including the Sun. The Sun has long served as a touchstone for our understanding of astrophysical processes, from the nature of stellar interiors, to magnetic dynamos, non-radiative heating, stellar mass loss, and energetic phenomena such as solar flares. ALMA offers new insights into all of these processes.
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