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Astrophysics and Astrononmy
Quiet sun magnetic field evolution observed with Hinode SOT and IRIS
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
06.10.2015
Co-author:
N. Bello González, R. Rezaei
Abstract:
We have calibrated and aligned a co-spatial and co-temporal 3 hour quiet sun time series taken with the Hinode and IRIS satellites. Hinode SOT observed full Stokes profiles of the Fe I 630 line pairs with the Spectro-polarimeter (SP) scanning a 8.7 arcsec region with a cadence of about 70 seconds. The Broadband Filter Imager (BFI) observed in Ca II H with a cadence of 31 s which was complemented by magnetograms and dopplergrams constructed from Na D I 589,6 nm measurements observed by the Narrowband Filter Imager (NFI). The IRIS satellite recorded slit jaw images centered at 2832 Å (112 s cadence), 1390 Å (23 s) and with a cadence of 19 s at 2796 Å. The spectrograph recorded spectra in several passbands including the Mg II k and h lines performing a 2 step raster with a 9.5 s step cadence.
We study magnetic elements seen in SP and NFI data undergoing a magnetic field intensification process accompanied by the development of bright points in the Ca II H images which we identify as convective collapse events. In addition we study pairs of magnetic elements involved in flux cancellation. The magnetic elements pass the IRIS slit at different stages of these processes. The IRIS Magnesium lines spectra are analyzed to investigate the response of the chromosphere to the magnetic events in the photosphere below. We present the temporal evolution of the atmospheric parameters from the photosphere to the transition region during these occurrences and compare the results to convective collapse and flux cancellation models.
Time-series spectroscopy of the eclipsing binary AB Cas with a pulsating component
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
20.07.2016
Co-author:
Jae Woo Lee, Jae-Rim Koo
Abstract:
We present high resolution spectra of the eclipsing binary AB Cas with a δ Sct-type pulsating star, which were obtained using the Bohyunsan Optical Echelle Spectrograph in Korea. The radial velocities (RVs) for the primary and secondary components are measured from a total of 27 spectra, secured during 2 nights on October 2015. In order to obtain the accurate physical properties, we simultaneously analyzed our RV curves together with previously published uvby light-curves. Individual masses, radii, and effective temperatures of both components are determined to be M1=2.01±0.02 Msun, M2=0.37±0.02 Msun, R1=1.84±0.02 Rsun, and R2=1.69±0.03 Rsun, Teff,1=8,000±250 K and Teff,2=4,900±150 K, respectively. In addition, we investigate the evolutionary history of AB Cas using theoretical evolutionary models to give the best representation for their physical parameters. All of these indicates that AB Cas is an oscillating Algol-type eclipsing binary (oEA) with the less massive and cool secondary star filling its inner Roche lobe, which may have experienced rapid mass transfer.
Measurements of helioseismic travel times
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
09.07.2015
Co-author:
Laurent Gizon (MPS), John G. Beck (Stanford)
Abstract:
In time-distance helioseismology wave travel times are measured from the cross-correlation between Doppler velocities recorded at any two locations on the solar surface. All local helioseismology inferences rely critically on the definition of travel time and its accuracy. We compare two different methods to extract the travel times from the noisy cross-correlation functions. The first method consists of fitting a 5-parameter analytic function to the cross-correlation to obtain the phase travel time. The second method consists of linearizing the distance between the observed cross-correlation and a sliding reference cross-correlation (the only parameter is the travel time). We find that the one-parameter fits are more robust with respect to noise. Using SOHO data from the MDI Structure Program for the years 1996–2003, we study in detail the statistical properties of the noise associated with the travel-time measurements for the two different fitting methods.
Recent insights on the penumbra formation process
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
19.06.2018
Co-author:
P. Romano, S. L. Guglielmino, F. Zuccarello
Abstract:
Using high-resolution spectropolarimetric data acquired by IBIS, as well as SDO/HMI observations, we studied the penumbra formation in AR NOAA 11490 and in a sample of twelve ARs appeared on the solar disk on 2011 and 2012, with the β-type magnetic field configuration.
The results concerning the leading polarity of AR NOAA 11490 show that the onset of the classical Evershed flow occurs in a very short time scale, 1-3 hours, while the penumbra is forming to the side away from the opposite polarity of the AR. Conversely, studying the formation of the first penumbral sector around the following proto-spot, we found that a stable penumbra forms in the area facing the opposite polarity, which appears to be located below an AFS, i.e. in a flux emergence region, in contrast with the results of Schlichenmaier et al. (2010).
Analyzing the sample of twelve ARs, we noticed that there is not a preferred location for the formation of the first penumbral sector. We also observed before the penumbra formation an inverse Evershed flow, which changes its sign when the penumbra appears. This confirms the observational evidence that the appearance of the penumbral filaments is correlated with the transition from the inverse Evershed to the classical Evershed flow. Furthermore, the analysis suggests that the time needed to form the penumbra may be related to the location where the penumbra first appears.
New high-resolution observations, like those provided by the European Solar Telescope, are expected to increase our understanding of the penumbra formation process.
OBSERVATIONAL AND PHYSICAL PARAMETERS OF TYPE I CHAINS AND THEIR ASSOCIATION WITH FLARES IN X-RAY
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
19.10.2015
Co-author:
Francisco C. R. Fernandes
Abstract:
We report the analysis of the observational parameters of the two Radio Noise Storms (RNS): one day in the occurrence of the solar flares in X-rays and one day without the presence of the flare. The spectral information about the chains of type I in the events obtained of the network e-CALLISTO (Compact Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory) revealed in 07/05/2011 (day without flare) bandwidth in the range 5.7 {-}{-} 91 MHz, the duration varied from 7 {-}{-} 361 seconds, and the frequency drift-rate was in the range -5.2 {-}{-} +2.5 MHzs$^{-1}$. Day whit flare (01/08/2011) presented bandwidth in the range 4.7 {-}{-} 60 MHz, duration between 6 and 214 seconds and frequency drift-rate varied from -6 to +1.8 MHzs$^{-1}$.
Roles of Ground-based Solar Observations of Hida Observatory toward the Solar-C Era
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
21.10.2015
Co-author:
K. Shibata, K. Ichimoto, S. Nagata (Kwasan and Hida Observatories, Kyoto University, Japan) I. Dorotovič, E. Shahamatnia, R.A. Ribeiro, J.M. Fonseca (CTS-UNINOVA, FCT/UNL, Caparica, Portugal)
Abstract:
For the realization of the Solar-C satellite, discussions about scientific themes and preliminary observations are internationally carried out now. At Hida Observatory of Kyoto University, we will play the following roles toward the Solar-C era by utilizing the Domeless Solar Telescope (DST) and the international solar chromospheric full-disk observation network (CHAIN project) that includes the Solar Magnetic Activity Research Telescope (SMART) with international collaborations, for example, such as the development of image-analysis software by UNINOVA (Portugal) and so on.
1) Roles before the Solar-C launch:
By using DST's focal plane and high-dispersion and wide-wavelength spectroscope, Hida Observatory will play a role as the place of the development of new detectors and focal plane instruments.
On the other hand, we will reveal unclear points in the chromospheric physics and in methods of deriving physical quantities of chromosphere, by carrying out spectrum observations and polarization measurements in various chromospheric absorption lines.
2) Roles after the Solar-C launch:
Promotion of cooperative observations with Solar-C, mainly by observations with the DST.
Our Hida Observatory will perform complimentary observations with satellite's high-spatial-resolution observations that are limited in the spatial FOV and continuous observable time due to the data capacity and lifetime of the satellite, or satellite's spectroscopic observations that are limited in the amount of information along the wavelength direction.
Moreover, we will expand and apply new knowledge provided by Solar-C to the whole of the sun, through our international full-disk solar monitoring network observation (CHAIN project).
It will mediate between the Solar-C and studies of variations of space weather and space climate.
3) Regular roles:
Our observatory continues to provide the place of educational-observation training for students and young researchers where they can gain experiences that they operate instruments by their own hands while watching the Sun in real time.
Moreover, we provide the place that can enforce not only scientific advanced themes, but also other themes that are hard to be accepted in the case of satellites or hard to be carried out by satellites physically, for example, experimental themes, classical scientific themes, themes that need long duration or large data capacity, and educational themes etc.
Some general results on relative magnetic helicity and field line helicity
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
15.12.2017
Abstract:
We present some general considerations on two quantities that are of common use in solar physics:
the relative magnetic helicity H and the field line helicity h of a magnetic field B contained in some
domain D.
1. We show how these two quantities can be expressed in terms of either the magnetic mapping of B or, when B has a simple topology, the boundary values of two pairs of Euler potentials. The well-known topological invariance of H and h can be immediately seen on the formulae that are presented.
2. We compute how the field line helicity varies in time when the plasma in D has finite resistivity and the footpoints of the magnetic lines on the boundary of D are submitted to shearing motions.
Technique for observation derived boundary conditions for Space Weather
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
16.01.2017
Co-author:
Duncan Mackay, Anthony Yeates
Abstract:
We propose a new efficient and accurate modelling technique suitable for the next generation of Space Weather predictive tools. Specifically, we put forward an approach that can provide interplanetary Space Weather forecasting models with an
accurate time dependent boundary condition of erupting flux ropes in the upper Solar Corona. The unique strength of this technique is that it follows the time evolution of coronal magnetic fields directly driven from observations and captures the
full life span of magnetic flux ropes from formation to ejection. To produce accurate and effective boundary conditions we couple two different modelling techniques, MHD simulations with quasi-static non-potential modelling. Our modelling approach
uses a time series of observed synoptic magnetograms to drive the non potential evolution model of the coronal magnetic field to follow the formation and loss of equilibrium of magnetic flux ropes. Following this a MHD simulation captures the
dynamic evolution of the ejection phase of the flux rope into interplanetary space. We focus here on the MHD simulation that describe the ejection of two magnetic flux ropes through the solar corona to the outer boundary. At this boundary we then
produce time dependent boundary conditions for the magnetic field and plasma that in the future may be applied to interplanetary space weather prediction models. We illustrate that the coupling of observationally derived quasi-static nonpotential
magnetic field modelling and MHD simulations can significantly reduce the computational time for producing realistic observationally derived boundary conditions at the boundary between the corona and interplanetary space.
The Early Local Universe – Inside and Outside the Stars
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
15.04.2016
Co-author:
J. Andersen, T. T. Hansen
Abstract:
Extremely metal-poor (EMP) halo stars with [Fe/H] below ~ -3 are considered to be fossil records of conditions in the early halo. In the naïve picture in which iron is a proxy for overall metallicity and indirectly for time, EMP stars formed well before the Galactic globular clusters. Their detailed abundance pattern is very uniform and essentially scaled Solar, except for the α-enhancement typical of halo stars. A minority are, however, dramatically enhanced in carbon (C) and/or r-process elements, with or without a concomitant excess of s-process elements (CEMP-n and CEMP-s stars). How were these elements produced – as a surface contamination deposited locally by a binary companion or far away in the early Galaxy? Are these stars mostly binaries; if so, does it matter? If not, how were the excess elements implanted in the natal clouds of the stars we see today?
The
High cadence observations and analysis of spicular-type events using CRISP onboard SST
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
20.10.2015
Co-author:
J.G. Doyle, E. Scullion, C. Nelson, D. Kuridze
Abstract:
A statistical study of spectral images, taken from the CRISP instrument at the Swedish 1-m Solar Telescope in H-alpha 656.28 nm of fast spicules, present Doppler velocities in the range of -41km/s to +41 km/s. Remarkably, many of these spicules display apparent velocities above 500 km/s, with very short lifetimes of up to 20 s and apparent lengths of around 3500 km. Here we present, the other spectral properties of these events in the line scan. One result is that they are repetitive i.e. appear at the same location but they are not co-temporal or necessarily periodic in nature. In 89 % of the cases there is temporal offset by 3.7 s to 5 s. We interpret the observations as mass motions that appear in the field-of-view of CRISP’s 60 nm filters in the line of sight, along their projection. We observed that 30% of the features showed repetitions at same location. This confirms that these are in fact, elongated mass motions rather than so called sheets, fast spicules or fibrils. Further we observed lateral motion which could be related to waves. With DKIST VTF instrument, having 3 times more spatial resolution than CRISP and much higher temporal resolution, we can being to understand the nature of such fine-scale transient phenomena in greater details.
Comparison of bisectors with inversions based on response functions to infer line-of-sight velocities of the Si I 10827 Å line
Natural Sciences (Astrophysics and Astrononmy)
Sergio Javier González Manrique
Date of upload:
18.06.2018
Co-author:
Sergio Javier González Manrique and Christoph Kuckein
Abstract:
We compare two methods to compute the Doppler shifts and infer the line-of-sight (LOS) velocities of the largely used photospheric Si I 10827 Å line. This line yields information about the upper photosphere. The first method consisted of computing the height-depend bisectors of the line. The second method required much longer computational time since an inversion code was used. For this purpose we used the Stokes inversion based on response function (SIR) code, which provided height-dependent information, in an optical depth scale, of the LOS velocities. The used data set of this study was observed on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS). Small pores and large quiet Sun areas were within the field of view. Two different data sets at different times were exploited for this study. The wavelength positions of the bisectors were computed in 10%-steps of the line depth using linear interpolation in both line wings. The output model from the SIR code covered 55 optical depth positions which range between 1.4 ≥ log τ ≥ -4.0. These LOS velocity maps from SIR at different log τ were compared with those originated from the bisector method at different percentages. The comparison between both methods allowed us to associate the bisector percentages to a specific optical depth. We associated nine LOS velocity bisector maps, in 10% steps of the line depth, starting from the lowest value at 10% and ending at the highest value of 80%. The bisector and SIR velocity maps were compared using the Pearson linear correlation coefficient. Each of the LOS velocity bisector maps was compared and correlated with the SIR LOS velocity maps. High linear correlations in the range of 95-98% were found. Bisector velocities obtained deeper in the line correspond to lower optical depths. The best correlation (97.8%) was achieved for the SIR velocity map at log τ = -2.6, which corresponds to a bisector of 20%. The inferred correspondence between bisector percentage and optical depth can be used to quickly obtain information about the LOS velocity stratification versus optical depth.
Preliminary Results from a Coronal Oscillations Instrument during the 2017 Total Eclipse
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
03.07.2018
Co-author:
Rudawy, P., Radziszewski, K., Berlicki, A., Phillips, K.J.H., Jess, D.B., Keys, P.H., Keenan, F.P.
Abstract:
An instrument using fast-frame cameras has been used during several recent total solar eclipses to search for oscillations in the green-line coronal emission. A much more sophisticated version of the instrument was prepared, tested, and successfully used during the August 21, 2017 total eclipse from a location in the Rocky Mountains, Idaho, USA. A pair of cameras, one observing the corona through a narrow-passband green line filter (wavelength 530.3 nm), and the other the white-light corona, was mounted on a 20 cm f/10 Celestron telescope on a Sky-Watcher EQ8 mounthead.
During the 122 s of totality, 428 images in a field-of-view that included approximately two-thirds of the corona were obtained in the 530.3 nm FeXIV line with an Andor iXon3 885 camera working at approximately 3.5 frames per second. The image format was 1004x1002, with a scale of 1.55 arcsec (1200 km) per pixel. The field-of-view included the loop system above the active region AR12672 which was near the Sun's east limb. Emission is recognizable out to a distance of 150,000 km, and the brightest structures in the active region loop have a strong signal (up to 3000 DN) that enables a search to be made for oscillations and other rapid fluctuations. This compares with a maximum signal of about 60 DN with a frame rate of 40 frames per second in a similar (negative) search by a previous version of this instrument during the 2001 total eclipse visible from central Africa. After dark-current subtraction and flat-fielding, a careful analysis of jitter and drifting motion of the images has enabled the solar coronal images to be placed on a frame that is stable to only 0.1 pixel, or 0.15 arcsec.
As a preliminary result, we did not detect any statistically significant evidence of local periodic variations of the coronal emission in FeXIV green line in any of the 480 000 investigated points . The result is in accordance with our previous findings based on observations collected during the 1999 and 2001 total solar eclipses and it confirms that the wave phenomena of Alfven-type, reported already by Tomczyk et al. (Nature 2007, ApJ 2009), even if common and always present in the solar corona, do not rise periodic fluctuations of the intensity of the coronal emission. An in-depth wavelet analysis of the collected data is under way.
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