Two-telescope-based solar seeing profile measurement simulation

Measurements of the daytime seeing profile of the atmospheric turbulence are crucial for evaluating a solar astronomical site so that research on the profile of the atmospheric turbulence as a function of altitude C n 2 ( h n ) becomes more and more critical for performance estimation and optimization of future adaptive optics (AO) including the multi-conjugate adaptive optics (MCAO) systems. Recently, the S-DIMM+ method has been successfully used to measure daytime turbulence profiles above the New Solar Telescope (NST) on Big Bear Lake. However, such techniques are limited by the requirement of using a large solar telescope which is not realistic for a new potential astronomical site. Meanwhile, the A-MASP (advanced multiple-aperture seeing profiler) method is more portable and has been proved that can reliably retrieve the seeing profile up to 16 km with the Dunn Solar Telescope (DST) on the National Solar Observatory (Townson, Kellerer et al.). But the turbulence of the ground layer is calculated by combining A-MASP and S-DIMM+ (Solar Differential Image Motion Monitor+) due to the limitation of the two-individual-telescopes structure. To solve these problems, we introduce the two-telescope seeing profiler (TTSP) which consists of two portable individual telescopes. Numerical simulations have been conducted to evaluate the performance of TTSP. We find our TTSP can effectively retrieve seeing profiles of four turbulence layers with a relative error of less than 4% and is dependable for actual seeing measurement.

Near-infrared and Visible Opacities of S-type Stars: The B1Π—X1Σ+ Band System of ZrO

The ZrO B1Π—X1Σ+ transition is an important opacity source in the near-infrared and optical spectrum of S-type stars. The 0–0, 0–1, 0–2, 1–0, 1–2, 1–3, 2–0, 2–1, 2–3, 2–4, 3–1, 3–4, and 4–2 bands of the 90Zr16O B1Π—X1Σ+ transition are reanalyzed using a high-temperature (2390 K) high-resolution (0.04 cm−1) emission spectrum collected at the National Solar Observatory (Kitt Peak). A modern spectroscopic analysis was performed using the PGOPHER program to provide updated spectroscopic constants and to produce a high-precision line list with line strengths based on an ab initio calculation of the transition dipole moment.

Surges of the weak magnetic field in the photosphere of the Sun

<p>The properties of the magnetic fields of the solar photosphere are investigated, in particular, the distribution of fields of different polarity over the solar surface. As primary data, synoptic maps of the photospheric magnetic field of the Kitt Peak National Solar Observatory for 1978-2016 were used. Using the vector summation method, the non-axisymmetric component of the magnetic field is determined. It was found that the nonaxisymmetric component of weak magnetic fields B < 5 G changes in antiphase with the flux of these fields. Magnetic fields of B < 5 G constitute a significant part of the total magnetic field of the Sun, since they occupy more than 60% of the area of the photosphere. The fine structure of the distribution of weak fields can  be observed by setting the upper limit to the strength of the  fields  included in the time–latitude diagram. This allows to eliminate the contribution of the strong fields of sunspots.</p><p>On the time-latitude diagram for weak magnetic fields (B < 5 G), bands of differing colors correspond to the streams of the magnetic fields moving in the direction to the Sun’s poles.. These streams or surges show the alternation of the dominant polarity - positive or negative - which is clearly seen in all four cycles. The slopes of the bands indicate the velocity of the fields movement towards the poles. The surges can be divided into two groups. The surges of the first group belong to the so-called Rush-to-the-Poles. These are bands with the width of about three years, which begin at approximately 40° of latitude and have the same polarity as the trailing sunspots. They reach high latitudes and cause the polarity reversal of the polar field. However, in addition to these surges, for most of the solar  cycle (the descending phase, the minimum and the ascending phase), there are narrower surges of both polarities (with the width less than one year), which extend from the equator almost to the poles. These surges are most clearly visible in the southern hemisphere when the southern pole is positive. Consideration of the latitude-time diagrams separately for positive and negative polarities showed that the alternating dominance of one of the polarities is associated with the antiphase development  of the positive and negative fields of the surges. The widths of surges and the periodicity of their appearance vary significantly for the two hemispheres and from one solar cycle to the other. The mean period of the polarity alternation is about 1.5 years.</p>

Analysis of the He i chromosphere in relation to the magnetic field activity over solar cycle time periods

ABSTRACT Solar synoptic maps of both He i 10 830 Å intensity and the magnetic field, which are observed by the Vacuum Telescope at National Solar Observatory/Kitt Peak from 2005 July to 2013 March are utilized to study relationship of He i intensity of the weakly magnetized chromosphere with the respective magnetic field strength. Strong absorption in He i intensity presents the butterfly-pattern latitude migration zone as active regions do, indicating that strong magnetic field corresponds to high-temperature structures of the active chromosphere. For He i intensity and magnetic field strength, their distribution at the time-latitude coordinate and their time series at each of the 180 measurement latitude are found to be significantly negatively correlated with each other in most cases. When a solar hemisphere is divided into three latitude bands: low, middle, and high latitude bands, and even after large magnetic field values not taken into account, they are still negatively correlated in most cases, and further when large magnetic field values are subtracted He i intensity varies more sensitively with magnetic field strength than the corresponding cases when large magnetic field values are not subtracted. He i intensity in the quiet chromosphere thus mainly presents a negative correlation with the magnetic field, and the heating of the quiet chromosphere is inferred to be caused mainly by small-scale magnetic elements.

Intelligent Recognition of Time Stamp Characters in Solar Scanned Images from Film

Prior to the availability of digital cameras, the solar observational images are typically recorded on films, and the information such as date and time were stamped in the same frames on film. It is significant to extract the time stamp information on the film so that the researchers can efficiently use the image data. This paper introduces an intelligent method for extracting time stamp information, namely, the convolutional neural network (CNN), which is an algorithm in deep learning of multilayer neural network structures and can identify time stamp character in the scanned solar images. We carry out the time stamp decoding for the digitized data from the National Solar Observatory from 1963 to 2003. The experimental results show that the method is accurate and quick for this application. We finish the time stamp information extraction for more than 7 million images with the accuracy of 98%.

Monitoring solar activity with PEPSI

Synoptic Sun-as-a-star observations are carried out with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), which receives light from the Solar Disk-Integration (SDI) telescope. Daily spectra are produced with a high signal-to-noise ratio, providing access to unprecedented quasi-continuous, long-term, disk-integrated spectra of the Sun with high spectral and temporal resolution. We developed tools to monitor and study solar activity on different time-scales ranging from daily changes, over periods related to solar rotation, to annual and decadal trends. Strong chromospheric absorption lines, such as the Ca ii H & K λ3934 & 3968 Å lines, are powerful diagnostic tools for solar activity studies, since they trace the variations of the solar magnetic field. Other lines, such as Hα λ6563 Å line and the near-infrared (NIR) Ca ii λ8542 Å line, provide additional information on the physical properties in this highly complex and dynamic atmospheric layer. Currently, we work on a data pipeline for extraction, calibration, and analysis of the PEPSI/SDI data. We compare the SDI data with daily spectra from the Integrated Sunlight Spectrometer (ISS), which is part of the Synoptic Long-Term Investigation of the Sun (SOLIS) facility operated by the U.S. National Solar Observatory (NSO). This facilitates cross-calibration and validation of the SDI data.

Synoptic Magnetic Fields Measurements of the Solar Chromosphere from SOLIS/VSM at NSO

Full disk magnetic field measurements of the photosphere and chromosphere have been performed at National Solar Observatory (NSO), USA for many decades. Here we briefly describe recent upgrades made to this synoptic observing program. In particular, we present the full Stokes polarimetry observations made using the chromospheric Ca II 854.2 nm spectral line. These new observations have the potential to probe vector nature of magnetic field in the chromosphere above the active regions and provide improved estimates of magnetic free-energy, which is released during flares and coronal mass ejections (CMEs). We emphasize that these observations could improve estimates of polar fields, as compared to photospheric observations, due to magnetic field expansion in higher layers and perspective effect near the polar regions. The global coronal potential field models and solar wind speed estimates depend critically on polar field measurements.

Design of a Full Stokes Polarimeter for Chromospheric Measurements with SOLIS/VSM

The synoptic observations of the magnetic field of the Sun have continued at the National Solar Observatory (NSO) since 1970s. The daily full-disk maps of the longitudinal magnetic field are regularly combined to form Carrington maps of the photospheric magnetic flux per solar rotation. These maps continue to be used by the international research community for a variety of studies related to solar magnetism as well as for space weather studies. The current NSO synoptic facility is the Synoptic Optical Long-term Investigation of the Sun (SOLIS), which regularly provides photospheric vector and chromospheric longitudinal full-disk magnetograms, among other data products. In the near future, an upgrade of SOLIS to produce chromospheric vector magnetograms is planned. We present the design of a new polarization modulator package for full Stokes polarimetry of the chromospheric Ca II 854.2 nm spectral line.

Asymmetry in the periodicities of solar photospheric fields: A probe to the unusual solar minimum prior to cycle 24

Employing wavelet and Fourier methods, we investigate temporal variations of periodicities in the photospheric fields obtained from synoptic magnetograms of the National Solar Observatory at Kitt Peak (NSO/KP) spanning the years 1975-2009. A north-south asymmetry is noticed in the periodicities of photospheric fields in the latitude range, 45°-78°, when the data is grouped into fields prior to and after 1996. This asymmetry when coupled with the fact that both solar fields in the latitude range, 45°-78°, and the micro-turbulence levels in the inner heliosphere began declining ~ 1995-1996 suggests that active changes occurred in the underlying basic solar processes which eventually initiated, at the end of solar cycle 23, the build-up of the deepest solar minimum, in the past 100 years.