Search

Understanding the global rotational profile of the solar atmosphere and its variation is fundamental to uncovering a comprehensive understanding of the dynamics of the solar magnetic field and the extent of coupling between different layers of the Sun. In this study, we employ the method of image correlation to analyze the extensive dataset provided by the Atmospheric Imaging Assembly of the Solar Dynamic Observatory in different wavelength channels. We find a significant increase in the equatorial rotational rate ($A$) and a decrease in absolute latitudinal gradient ($|B|$) at all temperatures representative of the solar atmosphere, implying an equatorial rotation up to $4.18\%$ and $1.92\%$ faster and less differential when compared to the rotation rates for the underlying photosphere derived from Doppler measurement and sunspots respectively. In addition, we also find a significant increase in equatorial rotation rate ($A$) and a decrease in differential nature ($|B|$ decreases) at different layers of the solar atmosphere. We also explore a possible connection from the solar interior to the atmosphere and interestingly found that $A$ at $r=0.94\,\mathrm{R}_{\odot}, 0.965\,\mathrm{R}_{\odot}$ show an excellent match with 171 Angstrom, 304 Angstrom and 1600 Angstrom, respectively. Furthermore, we observe a positive correlation between the rotational parameters measured from 1600 Angstrom, 131 Angstrom, 193 Angstrom and 211 Angstrom with the yearly averaged sunspot number, suggesting a potential dependence of the solar rotation on the appearance of magnetic structures related to the solar cycle or the presence of cycle dependence of solar rotation in the solar atmosphere., Comment: 18 pages, 11 figures, Accepted in The Astrophysical Journal

Ca II K observations of the Sun have a great potential for probing the Sun's magnetism and activity, as well as for reconstructing solar irradiance. The Kodaikanal Solar Observatory (KoSO) in India, houses one of the most prominent Ca II K archives, spanning from 1904 to 2007, obtained under the same experimental conditions over a century, a feat very few other sites have achieved. However, the KoSO Ca II K archive suffers from several inconsistencies (e.g., missing/incorrect timestamps of observations and orientation of some images) which have limited the use of the archive. This study is a step towards bringing the KoSO archive to its full potential. We did this by developing an automatic method to orient the images more accurately than in previous studies. Furthermore, we included more data than in earlier studies (considering images that could not previously be analyzed by other techniques as well as 2845 newly digitized images), while also accounting for mistakes in the observational date/time. These images were accurately processed to identify plage regions along with their locations, enabling us to construct the butterfly diagram of plage areas from the entire KoSO Ca II K archive covering 1904-2007. Our butterfly diagram shows significantly fewer data gaps compared to earlier versions due to the larger set of data used in this study. Moreover, our butterfly diagram is consistent with Sp\"orer's law for sunspots, validating our automatic image orientation method. Additionally, we found that the mean latitude of plage areas calculated over the entire period is 20.5%+/-2.0 higher than that of sunspots, irrespective of the phase or the strength of the solar cycle. We also studied the North-South asymmetry showing that the northern hemisphere dominated plage areas during solar cycles 19 and 20, while the southern hemisphere dominated during solar cycles 21--23., Comment: 15 pages, 9 figures, Under Review in Solar Physics

This work studies the kinematics of the leading edge and the core of 6 Coronal Mass Ejections (CMEs) in the combined field of view of Sun Watcher using Active Pixel System detector and Image Processing (SWAP) on-board PRoject for On-Board Autonomy (PROBA-2) and the ground-based K-Cor coronagraph of the Mauna Loa Solar Observatory (MLSO). We report, for the first time, on the existence of a critical height h$_\mathrm{c}$, which marks the onset of velocity dispersion inside the CME. This height for the studied events lies between 1.4-1.8 R$_{\odot}$, in the inner corona. We find the critical heights to be relatively higher for gradual CMEs, as compared to impulsive ones, indicating that the early initiation of these two classes might be different physically. We find several interesting imprints of the velocity dispersion on CME kinematics. The critical height is strongly correlated with the flux-rope minor radius and the mass of the CME. Also, the magnitude of velocity dispersion shows a reasonable positive correlation with the above two parameters. We believe these results will advance our understanding of CME initiation mechanisms and will help provide improved constraints to CME initiation models., Comment: 16 Pages, 9 Figures, Accepted for publication in The Astrophysical Journal Letters

Full-disk spectroscopic observations of the solar corona are highly desired to forecast solar eruptions and their impact on planets and to uncover the origin of solar wind. In this paper, we introduce a new multi-slit design (5 slits) to obtain extreme ultraviolet (EUV) spectra simultaneously. The selected spectrometer wavelength range (184-197 \r{A}) contains several bright EUV lines that can be used for spectral diagnostics. The multi-slit approach offers an unprecedented way to efficiently obtain the global spectral data but the ambiguity from different slits should be resolved. Using a numerical simulation of the global corona, we primarily concentrate on the optimization of the disambiguation process, with the objective of extracting decomposed spectral information of six primary lines. This subsequently facilitates a comprehensive series of plasma diagnostics, including density (Fe XII 195.12/186.89 \r{A}), Doppler velocity (Fe XII 193.51 \r{A}), line width (Fe XII 193.51 \r{A}) and temperature diagnostics (Fe VIII 185.21 \r{A}, Fe X 184.54 \r{A}, Fe XI 188.22 \r{A}, Fe XII 193.51 \r{A}). We find a good agreement between the forward modeling parameters and the inverted results at the initial eruption stage of a coronal mass ejection, indicating the robustness of the decomposition method and its immense potential for global monitoring of the solar corona., Comment: 14 pages, 5 figures, 2 tables. Accepted on 2024 April 18 for publication in ApJ. Published on 2024 May 30. The name of first author changed once from Linyi Chen (simplified Chinese) to Lami Chan (traditional Chinese) but for the same person

One of the intriguing mechanisms of the Sun is the formation of the bipolar magnetic regions (BMRs) in the solar convection zone which are observed as regions of concentrated magnetic fields of opposite polarity on photosphere. These BMRs are tilted with respect to the equatorial line, which statistically increases with latitude. The thin flux tube model, employing the rise of magnetically buoyant flux loops and their twist by Coriolis force, is a popular paradigm for explaining the formation of tilted BMRs. In this study, we assess the validity of the thin flux tube model by analyzing the tracked BMR data obtained through the Automatic Tracking Algorithm for BMRs (AutoTAB). Our observations reveal that the tracked BMRs exhibit the expected collective behaviors. We find that the polarity separation of BMRs increases over their normalized lifetime, supporting the assumption of a rising flux tube from the CZ. Moreover, we observe an increasing trend of the tilt with the flux of the BMR, suggesting that rising flux tubes associated with lower flux regions are primarily influenced by drag force and Coriolis force, while in higher flux regions, magnetic buoyancy dominates. Furthermore, we observe Joy's law dependence for emerging BMRs from their first detection, indicating that at least a portion of the tilt observed in BMRs can be attributed to the Coriolis force. Notably, lower flux regions exhibit a higher amount of fluctuations associated with their tilt measurement compared to stronger flux regions, suggesting that lower flux regions are more susceptible to turbulent convection., Comment: 16 pages, 10 figures. Under consideration in ApJ. Comments are welcome

This study addresses the limitations of single-viewpoint observations of Coronal Mass Ejections (CMEs) by presenting results from a 3D catalog of 360 CMEs during solar cycle 24, fitted using the GCS model. The dataset combines 326 previously analyzed CMEs and 34 newly examined events, categorized by their source regions into active region (AR) eruptions, active prominence (AP) eruptions, and prominence eruptions (PE). Estimates of errors are made using a bootstrapping approach. The findings highlight that the average 3D speed of CMEs is $\sim$1.3 times greater than the 2D speed. PE CMEs tend to be slow, with an average speed of 432 km $s^{-1}$. AR and AP speeds are higher, at 723 km $s^{-1}$ and 813 km $s^{-1}$, respectively, with the latter having fewer slow CMEs. The distinctive behavior of AP CMEs is attributed to factors like overlying magnetic field distribution or geometric complexities leading to less accurate GCS fits. A linear fit of projected speed to width gives a gradient of 2 km $s^{-1}deg^{-1}$, which increases to 5 km $s^{-1}deg^{-1}$ when the GCS-fitted `true' parameters are used. Notably, AR CMEs exhibit a high gradient of 7 km $s^{-1}deg^{-1}$, while AP CMEs show a gradient of 4 km $s^{-1}deg^{-1}$. PE CMEs, however, lack a significant speed-width relationship. We show that fitting multi-viewpoint CME images to a geometrical model such as GCS is important to study the statistical properties of CMEs, and can lead to a deeper insight into CME behavior that is essential for improving future space weather forecasting., Comment: Accepted for publication in Space Weather Journal

We present low-frequency radio observations of the Galactic symbiotic recurrent nova RS Ophiuchi during its 2021 outburst. The observations were carried out with the upgraded Giant Metrewave Radio Telescope (uGMRT) spanning a frequency range of 0.15$-$1.4 GHz during 23$-$287 days post the outburst. The average value of the optically thin spectral index is $\alpha \sim$ $-$0.4 ($F_{\nu} \propto \nu^\alpha$), indicating a non-thermal origin of the radio emission at the observed frequencies. The radio light curves are best represented by shock-driven synchrotron emission, initially absorbed by a clumpy ionized circumbinary medium. We estimate the mass-loss rate of the red giant companion star to be $\dot{M} \sim$ 7.5 $\times$ 10$^{-8}$ $M_{\odot}$ yr$^{-1}$ for an assumed stellar wind velocity of 20 km/s. The 0.15--1.4 GHz radio light curves of the 2021 outburst are systematically brighter than those of the 2006 outburst. Considering similar shock properties between the two outbursts, this is indicative of a relatively higher particle number density in the synchrotron emitting plasma in the current outburst., Comment: Accepted for publication in MNRAS, 5 Figures, 4 Tables

The tilt of the bipolar magnetic region (BMR) is crucial in the Babcock-Leighton process for the generation of the poloidal magnetic field in the Sun. We extend the work of Jha et al. (2020) and analyze the recently reported tracked BMR catalogue based on AutoTAB Sreedevi et al. (2023) from Michelson Doppler Imager (1996-2011) and Helioseismic and Magnetic Imager (2010-2018). Using the tracked information of BMRs based on AutoTAB, we confirm that the distribution of bmax reported by Jha et al. (2020) is not because of the BMRs are picked multiple times at the different phases of their evolution instead it is also present if we consider each BMRs only once. Moreover, we find that the slope of Joy's law initially increases slowly with the increase of bmax. However, when bmax>2.5 kG, gamma_0 decreases. The decrease of observed $gamma_0$ with bmax provides a hint to a nonlinear tilt quenching in the Babcock-Leighton process., Comment: 4 Pages, 2 Figures; IAUS 365 Proceedings Series

The study of the differential rotation in the chromosphere of the Sun is of significant importance as it provides valuable insights into the rotational behaviour of the solar atmosphere at higher altitudes and the coupling mechanism between the various layers of the solar atmosphere. In this work, we employed the image correlation technique, explicitly focusing on plages, intending to estimate the chromospheric differential rotation. For this purpose, we have utilized Ca II K spectroheliograms (1907-2007) from the Kodaikanal Solar Observatory (KoSO), recently calibrated with a better technique to ensure accuracy. Our analysis indicates that plages in the chromosphere exhibit faster rotation and a smaller latitudinal gradient when compared to the rotation rate obtained through sunspot tracking. Furthermore, we investigate the temporal analysis of the chromospheric differential rotation parameters across various solar cycles., Comment: 4 pages, 3 figures, Proceedings of IAUS 365

Full disc observations of the Sun in the H$\alpha$ line provide information about the solar chromosphere and in particular about the filaments, which are dark and elongated features that lie along magnetic field polarity inversion lines. This makes them important for studies of solar magnetism. Since full disc H$\alpha$ observations have been performed at various sites since 1800s, with regular photographic data having started in the beginning of the 20th century, they are an invaluable source of information on past solar magnetism. In this work we aimed at deriving accurate information about filaments from historical and modern full disc H$\alpha$ observations. We have consistently processed observations from 15 H$\alpha$ archives spanning 1909-2022. Our data processing includes photometric calibration of the data stored on photographic plates. We have constructed also Carrington maps from the calibrated H$\alpha$ images. We find that filament areas are affected by the bandwidth of the observation. Thus, cross-calibration of the filament areas derived from different archives is needed. We have produced a composite of filament areas from individual archives by scaling all of them to the Meudon series. Our composite butterfly diagram shows very distinctly the common features of filament evolution, that is the poleward migration as well as a decrease in the mean latitude of filaments as the cycle progresses. We also find that during activity maxima, filaments on average cover about 1% of the solar surface. We see only a weak change in the amplitude of cycles in filament areas, in contrast to sunspot and plage areas. Analysis of H$\alpha$ data for archives with contemporaneous Ca II K observations allowed us to identify and verify archive inconsistencies, which will also have implications for reconstructions of past solar magnetism and irradiance from Ca II K data., Comment: 21 pages, 14 figures, accepted for publication in A&A

The kinematics of coronal mass ejections (CMEs) are essential for understanding their initiation mechanisms and predicting their planetary impact. Most acceleration and deceleration occur below 4 R$\odot$, which is crucial for initiation understanding. Furthermore, the kinematics of CMEs in the inner corona ($<$ 3 R$_\odot$) are closely related to their propagation in the outer corona and their eventual impact on Earth. Since the CME kinematics are mainly probed using coronagraph data, it is crucial to investigate how imaging cadence affects the precision of data analysis and conclusions drawn and also for determining the flexibility of designing observational campaigns with upcoming coronagraphs. We study ten CMEs observed by the K-Coronagraph of the MLSO. We manually track the CMEs using high cadence (15 s) white-light observations of K-Cor and vary the cadence as 30 s, 1 min, 2 min, and 5 min to study the impact of cadence on the kinematics. We also employed the bootstrapping method to estimate the fitting parameters. Our results indicate that the average velocity of the CMEs does not have a high dependence on the imaging cadence, while the average acceleration shows significant dependence on the same, with the confidence interval showing significant shifts for the average acceleration for different cadences. The decrease in cadence also influences the determination of acceleration onset time. We further find that it is difficult to find an optimum cadence to study all CMEs, as it is also influenced by the pixel resolution of the instrument and the speed of the CME. However, except for very slow CMEs (speeds less than 300 Kms$^{-1}$), our results indicate a cadence of 1 min to be reasonable for the study of their kinematics. The results of this work will be important in the planning of observational campaigns for the existing and upcoming missions that will observe the inner corona., Comment: 21 Pages, 7 Figures, 18 Figures in Supplementary material, accepted for publication in Frontiers in Astronomy and Space Sciences

The primary objective of this study is to connect the coronal mass ejections (CMEs) to their source regions, primarily creating a CME source region (CSR) catalogue, and secondly probing into the influence the source regions have on different statistical properties of CMEs. We create a source region catalogue for 3327 CMEs from 1998 to 2017, thus capturing the different phases of cycle 23 and 24. The identified source regions are segregated into 3 classes, Active Regions (ARs), Prominence Eruptions (PEs) and Active Prominences (APs), while the CMEs are segregated into slow and fast based on their average projected speeds. We find the contribution of these three source region types to the occurrences of slow and fast CMEs to be different in the above period. A study of the distribution of average speeds reveals different power-laws for CMEs originating from different sources, and the power-law is different during the different phases of cycles 23 and 24. A study of statistical latitudinal deflections showed equator-ward deflections, while the magnitude of deflections again bears an imprint of the source regions. An East-West asymmetry is also noted, particularly in the rising phase of cycle 23, with the presence of active longitudes for the CMEs, with a preference towards the Western part of the Sun. Our results show that different aspects of CME kinematics bear a strong imprint of the source regions they originate from, thus indicating the existence of different ejection and/or propagation mechanisms of these CMEs., Comment: 29 Pages, 18 Figures. Accepted in The Astrophysical Journal Supplement Series (APJS)

Decayless kink oscillations are omnipresent in the solar atmosphere and a viable candidate for coronal heating. Though there have been extensive studies of decayless oscillations in coronal loops with a few hundred Mm lengths, the properties of these oscillations in small-scale ($\sim$10 Mm) loops are yet to be explored. In this study, we present the properties of decayless oscillations in small loops embedded in the quiet corona and coronal holes. We use high resolution observations from the Extreme Ultraviolet Imager onboard Solar Orbiter with pixel scales of 210 km and 5 s cadence or better. We find 42 oscillations in 33 coronal loops with loop lengths varying between 3 to 23 Mm. The average displacement amplitude is found to be 136 km. The oscillations period has a range of 27 to 276 s, and the velocity amplitudes range from 2.2 to 19.3 km s$^{-1}$. The observed kink speeds are lower than those observed in active region coronal loops. The variation of loop length with the period does not indicate a strong correlation. Coronal seismology technique indicated an average magnetic field value of 2.1 G. We estimate the energy flux with a broad range of 0.6-314 W m$^{-2}$. Moreover, we note that the short-period decayless oscillations are not prevalent in the quiet Sun and coronal holes. Therefore, our study suggests that decayless oscillations in small-scale coronal loops are unlikely to provide enough energy to heat the quiet Sun and accelerate solar wind in the coronal holes., Comment: Accepted for publication in the Astronomy & Astrophysics

Bipolar Magnetic Regions (BMRs) provide crucial information about solar magnetism. They exhibit varying morphology and magnetic properties throughout their lifetime, and studying these properties can provide valuable insights into the workings of the solar dynamo. The majority of previous studies have counted every detected BMR as a new one and have not been able to study the full life history of each BMRs. To address this issue, we have developed an Automatic Tracking Algorithm (AutoTAB) for BMRs, that tracks the BMRs for their entire lifetime or throughout their disk passage. AutoTAB uses the binary maps of detected BMRs to automatically track the regions. This is done by differentially rotating the binary maps of the detected regions and checking for overlaps between them. In this first article of this project, we provide a detailed description of the working of the algorithm and evaluate its strengths and weaknesses by comparing it with existing algorithms. AutoTAB excels in tracking even for the small BMRs (with flux $\sim 10^{20}$ Mx) and it has successfully tracked 9152 BMRs over the last two solar cycles (1996--2020), providing a comprehensive dataset that depicts the evolution of various properties for each BMR. The tracked BMRs exhibit the well-known latitudinal-time distribution and 11 year cyclic variation except for small BMRs which appear at all phases of the solar cycle and show weak latitudinal dependency. Finally, we discuss the possibility of adapting our algorithm to other datasets and expanding the technique to track other solar features in the future., Comment: 14 pages including 9 figures; Re-submitted in ApJS; Comments are welcome

The thermodynamic evolution of Coronal Mass Ejections (CMEs) in the inner corona (< 1.5 R$_{sun}$) is not yet completely understood. In this work, we study the evolution of thermodynamic properties of a CME core observed in the inner corona on July 20, 2017, by combining the MLSO/K-Cor white-light and the MLSO/CoMP Fe XIII 10747 {\AA} line spectroscopic data. We also estimate the emission measure weighted temperature (T$_{EM}$) of the CME core by applying the Differential Emission Measure (DEM) inversion technique on the SDO/AIA six EUV channels data and compare it with the effective temperature (T$_{eff}$) obtained using Fe XIII line width measurements. We find that the T$_{eff}$ and T$_{EM}$ of the CME core show similar variation and remain almost constant as the CME propagates from ~1.05 to 1.35 R$_{sun}$. The temperature of the CME core is of the order of million-degree kelvin, indicating that it is not associated with a prominence. Further, we estimate the electron density of this CME core using K-Cor polarized brightness (pB) data and found it decreasing by a factor of ~ 3.6 as the core evolves. An interesting finding is that the temperature of the CME core remains almost constant despite expected adiabatic cooling due to the expansion of the CME core, which suggests that the CME core plasma must be heated as it propagates. We conclude that the expansion of this CME core behaves more like an isothermal than an adiabatic process., Comment: Accepted for publication in Frontiers in Astronomy and Space Sciences, 19 pages, 10 figures

Despite investments in multiple space and ground-based solar observatories by the global community, the Sun's polar regions remain unchartered territory - the last great frontier for solar observations. Breaching this frontier is fundamental to understanding the solar cycle - the ultimate driver of short-to-long term solar activity that encompasses space weather and space climate. Magnetohydrodynamic dynamo models and empirically observed relationships have established that the polar field is the primary determinant of the future solar cycle amplitude. Models of solar surface evolution of tilted active regions indicate that the mid to high latitude surges of magnetic flux govern dynamics leading to the reversal and build-up of polar fields. Our theoretical understanding and numerical models of this high latitude magnetic field dynamics and plasma flows - that are a critical component of the sunspot cycle - lack precise observational constraints. This limitation compromises our ability to observe the enigmatic kilo Gauss polar flux patches and constrain the polar field distribution at high latitudes. The lack of these observations handicap our understanding of how high latitude magnetic fields power polar jets, plumes, and the fast solar wind that extend to the boundaries of the heliosphere and modulate solar open flux and cosmic ray flux within the solar system. Accurate observation of the Sun's polar regions, therefore, is the single most outstanding challenge that confronts Heliophysics. This paper argues the scientific case for novel out of ecliptic observations of the Sun's polar regions, in conjunction with existing, or future multi-vantage point heliospheric observatories. Such a mission concept can revolutionize the field of Heliophysics like no other mission concept has - with relevance that transcends spatial regimes from the solar interior to the heliosphere., Comment: This White Paper was submitted in 2022 to the United States National Academies Solar and Space Physics (Heliophysics) Decadal Survey

With over 100 years of solar observations, the Kodaikanal Solar Observatory (KoSO) is a one-of-a-kind solar data repository in the world. Among its many data catalogues, the `suncharts' at KoSO are of particular interest. These Suncharts (1904-2020) are coloured drawings of different solar features, such as sunspots, plages, filaments, and prominences, made on papers with a Stonyhurst latitude-longitude grid etched on them. In this paper, we analyze this unique data by first digitizing each suncharts using an industry-standard scanner and saving those digital images in high-resolution `.tif' format. We then examine the Cycle~19 and Cycle~20 data (two of the strongest cycles of the last century) with the aim of detecting filaments. To this end, we employed `k-means clustering' method and obtained different filament parameters such as position, tilt angle, length, and area. Our results show that filament length (and area) increases with latitude and the pole-ward migration is clearly dominated by a particular tilt sign. Lastly, we cross-verified our findings with results from KoSO digitized photographic plate database for the overlapping time period and obtained a good agreement between them. This work, acting as a proof-of-the-concept, will kick-start new efforts to effectively use the entire hand-drawn series of multi-feature, full-disk solar data and enable researchers to extract new sciences, such as the generation of pseudo magnetograms for the last 100 years., Comment: 12 pages, 7 Figures, Accepted for publication in ApJ

We present observations of the active M-dwarf binary AT Mic (dM4.5e+dM4.5e) obtained with the orbital observatory AstroSat. During 20 ks of observations, in the far ultraviolet ($130-180$ nm) and soft X-ray ($0.3-7$ keV) spectral ranges, we detected both quiescent emission and at least five flares on different components of the binary. The X-ray flares were typically longer than and delayed (by $5-6$ min) with respect to their ultraviolet counterparts, in agreement with the Neupert effect. Using X-ray spectral fits, we have estimated the parameters of the emitting plasma. The results indicate the presence of a hot multi-thermal corona with the average temperatures in the range of $\sim 7-15$ MK and the emission measure of $\sim (2.9-4.5)\times 10^{52}$ $\textrm{cm}^{-3}$; both the temperature and the emission measure increased during the flares. The estimated abundance of heavy elements in the corona of AT Mic is considerably lower than at the Sun ($\sim 0.18-0.34$ of the solar photospheric value); the coronal abundance increased during the flares due to chromospheric evaporation. The detected flares had the energies of $\sim 10^{31}-10^{32}$ erg; the energy-duration relations indicate the presence of magnetic fields stronger than in typical solar flares., Comment: Accepted for publication in Research in Astronomy and Astrophysics

Kodaikanal Solar Observatory (KoSO) possesses one of world's longest and homogeneous records of sunspot observations that span more than a century (1904-2017). Interestingly, these observations (originally recorded in photographic plates/films) were taken with the same setup over this entire time period which makes this data unique and best suitable for long-term solar variability studies. A large part of this data, between 1921-2011, were digitized earlier and a catalog containing the detected sunspot parameters (e.g., area and location) was published in Mandal et al.(2017). In this article, we extend the earlier catalog by including new sets of data between 1904-1921 and 2011-2017. To this end, we digitize and calibrate these new datasets which include resolving the issue of random image orientation. We fix this by comparing the KoSO images with co-temporal data from Royal Greenwich Observatory. Following that, a semi-automated sunspot detection and automated umbra detection algorithm are implemented onto these calibrated images to detect sunspots and umbra. Additionally, during this catalog updation, we also filled data gaps in the existing KoSO sunspot catalog (1921-2011) by virtue of re-calibrating the 'rouge' plates. This updated sunspot area series covering nearly 115 years (1904-2017) are being made available to the community and will be a unique source to study the long term variability of the Sun, Comment: 13 Pages, 7 Figures, Accepted for Publication in Frontiers in Astronomy and Space Sciences Stellar and Solar Physics

The middle corona, the region roughly spanning heliocentric altitudes from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential physical transitions and processes that govern the behavior of coronal outflow into the heliosphere. Eruptions that could disrupt the near-Earth environment propagate through it. Importantly, it modulates inflow from above that can drive dynamic changes at lower heights in the inner corona. Consequently, this region is essential for comprehensively connecting the corona to the heliosphere and for developing corresponding global models. Nonetheless, because it is challenging to observe, the middle corona has been poorly studied by major solar remote sensing missions and instruments, extending back to the Solar and Heliospheric Observatory (SoHO) era. Thanks to recent advances in instrumentation, observational processing techniques, and a realization of the importance of the region, interest in the middle corona has increased. Although the region cannot be intrinsically separated from other regions of the solar atmosphere, there has emerged a need to define the region in terms of its location and extension in the solar atmosphere, its composition, the physical transitions it covers, and the underlying physics believed to be encapsulated by the region. This paper aims to define the middle corona and give an overview of the processes that occur there., Comment: Working draft prepared by the middle corona heliophysics working group

The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 mission of ISRO that will measure and monitor the solar radiation emitted in the near-ultraviolet wavelength range (200-400 nm). SUIT will simultaneously map the photosphere and the chromosphere of the Sun using 11 filters sensitive to different wavelengths and covering different heights in the solar atmosphere and help us understand the processes involved in the transfer of mass and energy from one layer to the other. SUIT will also allow us to measure and monitor spatially resolved solar spectral irradiance that governs the chemistry of oxygen and ozone in the stratosphere of Earth's atmosphere. This is central to our understanding of the Sun climate relationship., Comment: 5 Figures, Published in Current Science

Images of the extended solar corona, as observed by white-light coronagraphs as observed by different white-light coronagraphs include the K- and F-corona and suffer from a radial variation in intensity. These images require separation of the two coronal components with some additional image-processing to reduce the intensity gradient and analyse the structures and processes occurring at different heights in the solar corona within the full field of view. To process these bulk coronagraph images with steep radial-intensity gradients, we have developed an algorithm: Simple Radial Gradient Filter (SiRGraF). This algorithm is based on subtracting a minimum background (F-corona) created using long-duration images and then dividing the resultant by a uniform intensity gradient image to enhance the K-corona. We demonstrate the utility of this algorithm to bring out the short time-scale transient structures of the corona. SiRGraF could be used to reveal and analyse such structures. It is not suitable for quantitative estimations based on intensity. We have successfully tested the algorithm on images of the LASCO-C2 onboard the Solar and Heliospheric Observatory (SOHO), and COR-2A onboard the STEREO with good signal to noise ratio (SNR) along with low-SNR images of STEREO/COR-1A and the KCoronagraph. We also compared the performance of SiRGraF with Normalising Radial Gradient Filter (NRGF). We found that when hundreds of images have to be processed, SiRGraF works faster than NRGF, providing similar brightness and contrast in the images and separating the transient features. Moreover, SiRGraF works better on low-SNR images of COR-1A than NRGF, providing better identification of dynamic coronal structures throughout the field of view. We discuss the advantages and limitations of the algorithm., Comment: 18 pages, 6 figures. Accepted for publication in Solar Physics journal

We present multi-epoch optical and near-infrared observations of the highly reddened, \pion{Fe}{ii} class slow nova V2891 Cygni. The observations span 15 months since its discovery. The initial rapid brightening from quiescence, and the presence of a $\sim$35 day long pre-maximum halt, is well documented. The evidence that the current outburst of V2891 Cyg has undergone several distinct episodes of mass ejection is seen through time-varying P Cygni profiles of the O\,{\sc i} 7773\,$\AA$ line. A highlight is the occurrence of a dust formation event centred around $\sim$+273d, which coincides with a phase of coronal line emission. The dust mass is found to be $\sim0.83-1.25 \times 10^{-10} M_{\odot}$. There is strong evidence to suggest that the coronal lines are created by shock heating rather than by photoionization. The simultaneous occurrence of the dust and coronal lines (with varying velocity shifts) supports the possibility that dust formation is shock-induced. Such a route for dust formation has not previously been seen in a nova, although the mechanism has been proposed for dust formation in some core-collapse supernovae. Analysis of the coronal lines indicates a gas mass and temperature of 8.35--8.42$\times10^{-7}$ M$_\odot$ and $\sim(4.8-9.1)\times10^{5}$~K respectively, and an overabundance of aluminium and silicon. A Case B analysis of the hydrogen lines yields a mass of the ionized gas of ($8.60\pm1.73)\times10^{-5}$ M$_{\odot}$. The reddening and distance to the nova are estimated to be $E(B-V)$ = 2.21$\pm$0.15 and $d$ = 5.50 kpc respectively., Comment: Accepted for Publication in MNRAS

Detailed study of the solar magnetic field is crucial to understand its generation, transport and reversals. The timing of the reversals may have implications on space weather and thus identification of the temporal behavior of the critical surges that lead to the polar field reversals is important. We analyze the evolution of solar activity and magnetic flux transport in Cycles 21--24. We identify critical surges of remnant flux that reach the Sun's poles and lead to the polar field reversals. We reexamine the polar field buildup and reversals in their causal relation to the Sun's low-latitude activity. We further identify the major remnant flux surges and their sources in the time-latitude aspect. We find that special characteristics of individual 11-year cycles are generally determined by the spatiotemporal organization of emergent magnetic flux and its unusual properties. We find a complicated restructuring of high-latitude magnetic fields in Cycle~21. The global rearrangements of solar magnetic fields were caused by surges of trailing and leading polarities that occurred near the activity maximum. The decay of non-Joy and anti-Hale active regions resulted in the remnant flux surges that disturbed the usual order in magnetic flux transport. We finally show that the leading-polarity surges during cycle minima sometimes link the following cycle and a collective effect of these surges may lead to secular changes in solar activity. The magnetic field from a Babcock--Leighton dynamo model generally agrees with these observations., Comment: Accepted for publication in MNRAS; 5 pages including 5 figures

Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to $\gamma$-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass white dwarf. The optical pre-outburst detection of a 501.42s oscillation suggests a magnetic white dwarf. This is the first time that an oscillation of this magnitude has been detected in a classical nova prior to outburst. We report X-ray outburst observations from {\it Swift} and {\it Chandra} which uniquely show: (1) a very strong modulation of super-soft X-rays at a different period from reported optical periods; (2) strong pulse profile variations and the possible presence of period variations of the order of 0.1-0.3s; and (3) rich grating spectra that vary with modulation phase and show P Cygni-type emission lines with two dominant blue-shifted absorption components at $\sim 3000$ and 9000 km s$^{-1}$ indicating expansion velocities up to 11000 km s$^{-1}$. X-ray oscillations most likely arise from inhomogeneous photospheric emission related to the magnetic field. Period differences between reported pre- and post-outburst optical observations, if not due to other period drift mechanisms, suggest a large ejected mass for such a fast nova, in the range $2\times 10^{-5}$-$2\times 10^{-4} M_\odot$. A difference between the period found in the {\it Chandra} data and a reported contemporaneous post-outburst optical period, as well as the presence of period drifts, could be due to weakly non-rigid photospheric rotation., Comment: 11 pages, 5 figures. Accepted for publication in Astrophysical Journal Letters

Despite studying Coronal Mass Ejections (CMEs) for several years, we are yet to have a complete understanding of their kinematics. In this regard, the change in kinematics of the CMEs, as they travel from the inner corona ($<$ 3R$_\odot)$ to the higher heights is essential. We do a follow up statistical study of several 3D kinematic parameters of 59 CMEs studied by Majumdar et al. (2020). The source regions of these CMEs are identified and classified as Active Regions (ARs), Active Prominences (APs), and Prominence Eruptions (PEs). We study several statistical correlations between different kinematic parameters of the CMEs. We show that the average kinematic parameters change as they propagate from the inner to the outer corona, indicating the importance of the region where normally the common practice is to perform averaging. We also find that the parameters in the outer corona is highly influenced by those in the inner corona, thus indicating the importance of inner corona in the understanding of the kinematics. We further find that the source regions of the CMEs tend to have a distinct imprint on the statistical correlations between different kinematic parameters, and that an overall correlation tends to wash away this crucial information. The results of this work lends support towards possibly different dynamical classes for the CMEs from active regions and prominences which is manifested in their kinematics., Comment: 10 pages, 4 figures and 1 Table; Accepted for publication in The Astrophysical Journal

Hand-drawn synoptic maps from the Meudon Observatory (1919 onwards) and the McIntosh archive (1967 onwards) are two important sources of long-term, manually recorded filament observations. In this study, we calibrate the Meudon maps and subsequently identify filaments through an automated method. We extract physical parameters from this filament database and perform a comparative study of their long-term evolution focusing on the cotemporal period of McIntosh and Meudon observations. The spatio-temporal evolution of filaments manifests in the form of a filament butterfly diagram, indicating further that they are intimately related to the large-scale solar cycle. Physical descriptors such as the number and length of filaments, which are tracers of solar surface magnetic field, have cycles which are phase-locked with the 11 year sunspot cycle. The tilt angle distribution of filaments - both near or distant from active region locations - indicates that their origin is due to either large-scale surface magnetic field or inter-active region field evolution. This study paves the way for constructing a composite series of hand-drawn filament data with minimal gaps stretching the time span of solar filament observations to a century. On the one hand, this would serve as useful constraints for models of magnetic field emergence and evolution on the Sun's surface over multiple solar cycles, and on the other hand, this filament database may be used to guide the reconstruction of filament-prominence associated eruptive events before the space age, Comment: Accepted for publication in ApJ; (18 pages, 13 figures)

Aditya-L1 is India's first solar mission with Visible Emission Line Coronagraph (VELC) consisting of three spectral channels taking high-resolution spectroscopic observations of the inner corona up to 1.5 Rsun at 5303 \AA, 7892 \AA, and 10747 \AA. In this work, we present the strategy for the slit width optimization for the VELC using synthetic line profiles by taking into account the instrument characteristics and coronal conditions for log(T) varying from 6 to 6.5. The synthetic profiles are convolved with simulated instrumental scattered light and noise to estimate the signal-to-noise ratio (SNR), which will be crucial to design the future observation plans. We find that the optimum slit width for VELC turns out to be 50 microns providing sufficient SNR for observations in different solar conditions. We also analyzed the effect of plasma temperature on the SNR at different heights in the VELC field of view for the optimized slit width. We also studied the expected effect of the presence of a CME on the spectral channel observations. This analysis will help to plan the science observations of VELC in different solar conditions., Comment: Accepted for publication in Frontiers in Astronomy and Space Sciences. (18 pages, 5 figures and 5 tables)

As one of the most spectacular energy release events in the solar system, solar flares are generally powered by magnetic reconnection in the solar corona. As a result of the re-arrangement of magnetic field topology after the reconnection process, a series of new loop-like magnetic structures are often formed and are known as flare loops. A hot diffuse region, consisting of around 5-10 MK plasma, is also observed above the loops and is called a supra-arcade fan. Often, dark, tadpole-like structures are seen to descend through the bright supra-arcade fans. It remains unclear what role these so-called supra-arcade downflows (SADs) play in heating the flaring coronal plasma. Here we show a unique flare observation, where many SADs collide with the flare loops and strongly heat the loops to a temperature of 10-20 MK. Several of these interactions generate clear signatures of quasi-periodic enhancement in the full-Sun-integrated soft X-ray emission, providing an alternative interpretation for quasi-periodic pulsations that are commonly observed during solar and stellar flares., Comment: Published in The Innovation; Animations are available in the Journal's Website

The rotational profile of the Sun is considered to be one of the key inputs in a solar dynamo model. Hence, precise and long-term measurements of this quantity is important for our understanding of solar magnetism and its variability. In this study, we use the newly digitized, white light sunspot data (1923 -- 2011) from Kodaikanal Solar Observatory (KoSO) to derive the solar rotation profile. An automated correlation based sunspot tracking algorithm is implemented to measure the rotation parameters, $A$, the equatorial rotation rate and $B$, the latitudinal gradient. Our measurements of $A=14.381\pm0.004$ and $B=-2.72\pm0.04$ compare well with previous studies. In our analysis, we find that the bigger sunspots (with area $>$400~$\mu$Hem) rotate slower than the smaller ones. At the same time, we do not find any variation in the rotation rates between activity extremes, i.e solar maxima and minima. Lastly, we employ our tracking algorithm on the Michelson Doppler Imager (MDI) data and compare the MDI results with our KoSO values., Comment: 16 pages, 7 figures, accepted for publication in Solar Physics

Solar eruptions such as Coronal Mass Ejections (CMEs) observed in the inner solar corona (up to 4 R$_{\odot}$) show acceleration profiles which appear as parabolic ridges in height-time plots. Inspired by the white-light automated detection algorithms, Computer Aided CME Tracking System (CACTus) and Solar Eruptive Events Detection System (SEEDS), we employ the parabolic Hough Transform for the first time to automatically detect off-disk solar eruptions {from height-time plots. Due to the limited availability of white-light observations in the inner corona, we use Extreme UltraViolet (EUV) images of the Sun. In this paper we present a new algorithm, CME Identification in Inner Solar Corona (CIISCO), which is based on Fourier motion filtering and the parabolic Hough transform, and demonstrate its implementation using EUV observations taken from {\it Atmospheric Imaging Assembly} (AIA) on-board the Solar Dynamics Observatory (SDO), {\it Extreme Ultra Violet Imager} (EUVI) on-board the STEREO-A and B satellites, and {\it Sun Watcher using Active Pixel System detector and Image Processing} (SWAP) Imager on-board PROBA2. We show that CIISCO is able to identify any {off-disk} outward moving feature in EUV images. The use of automated detection algorithms, like CIISCO, can potentially be used to provide early warnings of CMEs if an EUV telescope is located at $\pm$ 90$^{\circ}$ from the Sun-Earth line, providing CME characteristics and kinematics close to the Sun. This paper also presents the limitations of this algorithm and the prospects for future improvement., Comment: Accepted for publication in Solar Physics; 27 pages, 10 figures, 1 table

We investigate the occurrence of the "extended solar cycle" (ESC) as it occurs in a host observational data spanning 140 years. Investigating coronal, chromospheric, photospheric and interior diagnostics we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) using previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder's butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of 55\degree\ latitude in the evolution, and possible production, of solar magnetism., Comment: 29 pages, 15 figures. Movies of Fig.14 panels available on request to mscott@ucar.edu. Submitted to Solar Physics

We investigate the properties of plasmoids observed in the current sheet formed after an X-8.3 flare followed by a fast CME eruption on September 10, 2017 using Extreme Ultraviolet (EUV) and white-light coronagraph images. The main aim is to understand the evolution of plasmoids at different spatio-temporal scales using existing ground- and space-based instruments. We identified the plasmoids in current sheet observed in the successive images of {\it Atmospheric Imaging Assembly} (AIA) and white-light coronagraphs, K-Cor and LASCO/C2. We found that the current sheet is accompanied by several plasmoids moving upwards and downwards. Our analysis showed that the downward and upward moving plasmoids have average width of 5.92 Mm and 5.65 Mm, respectively in the AIA field of view (FOV). However, upward moving plasmoids have average width of 64 Mm in the K-Cor which evolves to a mean width of 510 Mm in the LASCO/C2 FOV. Upon tracking the plasmoids in successive images, we observe that downward and upward moving plasmoids have average speeds of $\sim$272 km s$^{-1}$ and $\sim$191 km s$^{-1}$ respectively in the EUV passbands. We note that the plasmoids become super-Alfv\'enic when they reach at LASCO FOV. Furthermore, we estimate that the null-point of the current sheet at $\approx$ 1.15 R$_\odot$ where bidirectional plasmoid motion is observed. We study the width distribution of plasmoids formed and notice that it is governed by a power law with a power index of -1.12. Unlike previous studies there is no difference in trend for small and large scale plasmoids. The presence of accelerating plasmoids near the neutral point indicates a longer diffusion region as predicted by MHD models., Comment: Accepted for the publication in Astronomy & Astrophysics (A&A). 10 pages, 11 figures. Animations can be found at https://www.dropbox.com/sh/g0wjq2awxai1hy4/AAClkTHPFkTa5JU-Zulf9a75a?dl=0

The regular observation of the solar magnetic field is available only for about last five cycles. Thus, to understand the origin of the variation of the solar magnetic field, it is essential to reconstruct the magnetic field for the past cycles, utilizing other datasets. Long-term uniform observations for the past 100 years as recorded at the Kodaikanal Solar Observatory (KoSO) provide such opportunity. We develop a method for the reconstruction of the solar magnetic field using the synoptic observations of the Sun's emission in the Ca II K and H$\alpha$ lines from KoSO for the first time. The reconstruction method is based on the facts that the Ca II K intensity correlates well with the unsigned magnetic flux, while the sign of the flux is derived from the corresponding H$\alpha$ map which provides the information of the dominant polarities. Based on this reconstructed magnetic map, we study the evolution of the magnetic field in Cycles 15--19. We also study bipolar magnetic regions (BMRs) and their remnant flux surges in their causal relation. Time-latitude analysis of the reconstructed magnetic flux provides an overall view of magnetic field evolution: emergent magnetic flux, its further transformations with the formation of unipolar magnetic regions (UMRs) and remnant flux surges. We identify the reversals of the polar field and critical surges of following and leading polarities. We found that the poleward transport of opposite polarities led to multiple changes of the dominant magnetic polarities in poles. Furthermore, the remnant flux surges that occur between adjacent 11-year cycles reveal physical connections between them., Comment: 6 pages including figures; accepted for publication in ApJL

SU Lyn, a star that ostensibly appears to be an unremarkable late M type giant, has recently been proposed to be a symbiotic star largely based on its hard X-ray properties. The star does not display, in low-resolution optical spectra, the high excitation lines typically seen in the spectra of symbiotic stars. In the present work, UV, optical, and near-infrared observations are presented, aimed at exploring and strengthening the proposed symbiotic classification for this star. Our Far-UV 1300-1800$\AA$ spectrum of SU Lyn, obtained with the ASTROSAT mission's UVIT payload, shows emission lines of Si IV, C IV, OIII and N III in a spectrum typical of symbiotic stars. The UV spectrum robustly confirms SU Lyn's symbiotic nature. The detection of high excitation lines in a high-resolution optical spectrum further consolidates its symbiotic nature. As is being recognized, the potential existence of other similar symbiotic systems could significantly impact the census of symbiotic stars in the galaxy., Comment: Accepted for publication in MNRAS-Letters

Since Coronal Mass Ejections (CMEs) are the major drivers of space weather, it is crucial to study their evolution starting from the inner corona. In this work we use Graduated Cylindrical Shell (GCS) model to study the 3D evolution of 59 CMEs in the inner ($<$ 3R$_{\odot}$) and outer ($>$ 3R$_{\odot}$) corona using observations from COR-1 and COR-2 on-board Solar TErrestrial RElations Observatory (STEREO) spacecraft. We identify the source regions of these CMEs and classify them as CMEs associated with Active Regions (ARs), Active Prominences (APs), and Prominence Eruptions (PEs). We find 27 $\%$ of CMEs show true expansion and 31 $\%$ show true deflections as they propagate outwards. Using 3D kinematic profiles of CMEs, we connect the evolution of true acceleration with the evolution of true width in the inner and outer corona. Thereby providing the observational evidence for the influence of the Lorentz force on the kinematics to lie in the height range of $2.5-3$ R$_{\odot}$. We find a broad range in the distribution of peak 3D speeds and accelerations ranging from 396 to 2465 km~s$^{-1}$ and 176 to 10922 m~s$^{-2}$ respectively with a long tail towards high values coming mainly from CMEs originating from ARs or APs. Further, we find the magnitude of true acceleration is be inversely correlated to its duration with a power law index of -1.19. We believe that these results will provide important inputs for the planning of upcoming space missions which will observe the inner corona and the models that study CME initiation and propagation., Comment: 22 Pages, 8 Figures, 1 Table; Accepted for publication in The Astrophysical Journal