From 2001From -2008, we use full-disk, SOHO/EIT 195 Å calibrated images to determine latitudinal and day-to-day variations of the rotation rates of coronal holes (CHs). We estimate the weighted average of heliographic coordinates such as latitude and longitude from the central meridian on the observed solar disk. For different latitude zones between 40• north and 40• south, we compute rotation rates and find that, irrespective of their area, the number of days observed on the solar disk, and their latitudes, CHs rotate rigidly. Combined for all the latitude zones, we also find that CHs rotate rigidly during their evolution history. In addition, for all latitude zones, CHs follow a rigid body rotation law during their first appearance. Interestingly, the average first rotation rate (∼438 nHz) of CHs, computed from their first appearance on the solar disk, matches the rotation rate of the solar interior only below the tachocline.

Context. Long-term sunspot observations are key to understanding and predicting the solar activities and its effects on space weather. Consistent observations, which are crucial for long-term variations studies, are generally not available due to upgradation/modification of observatories over the course of time. We present data for a period of 90 yr acquired from persistent observation at the Kodaikanal observatory in India. Aims. We aim to build a uniform sunspot area time series along with their positions for a 90-yr period between 1921 and 2011, as obtained from the newly digitized and calibrated white-light images from the Kodaikanal observatory. Our aim is to compare this new time series with known sources and confirm some of the earlier reported results with additional new aspects. Methods. We use an advanced semi-automated algorithm to detect the sunspots form each calibrated white-light image. Area, longitude and latitude of each of the detected sunspots are derived. Implementation of a semi-automated method is extremely necessary in such studies as it minimizes the human bias in the detection procedure. Results. Daily, monthly, and yearly sunspot area variations, obtained from the Kodaikanal, compared well with the Greenwich sunspot area data. We find an exponentially decaying distribution for the individual sunspot area for each of the solar cycles. Analyzing the histograms of the latitudinal distribution of the detected sunspots, we find Gaussian distributions, in both the hemispheres, with centers at ∼15 • latitude. The height of the Gaussian distributions are different for the two hemispheres for a particular cycle. Using our data, we show clear presence of Waldmeier effect, which correlates the rise time with the cycle amplitude. Using the wavelet analysis, we explored different periodicities on different time scales present in the sunspot area times series.

The century long H α (656.28 nm) spectroheliograms from Kodaikanal Solar Observatory (KSO) have been recently digitised. Using these newly calibrated, processed images we study the evolution of dark elongated on disk structures called filaments, potential representatives of magnetic activities on the Sun. To our knowledge this is the oldest uniform digitised dataset with daily images available today in H α . We generate Carrington maps for entire time duration and try to find the correspondences with maps of same rotation from Ca II K KSO data. Filaments are segmented from Carrington maps using a semi-automated technique and are studied individually to extract their centroids and tilts. We plot the time-latitude distribution of filament centroids producing Butterfly diagram, which clearly shows presence of poleward migration. We separate polar filaments for each cycle and try to estimate the delay between the polar filament number cycle and sunspot number cycle peaks. We correlate this delay with the same between polar reversal and sunspot number maxima.This provides new insight on the role of polar filaments on polar reversal.

Aims. We study the evolution of the recurrent nova U Scorpii during its outburst in 2010. Methods. Optical spectroscopic observations of the nova were obtained during 0.83-162.5 days after outburst maximum. Optical linear polarisation observations were made before the onset of the super soft X-ray source (SSS) phase and during the SSS phase. Radio continuum observations were made in the 1280 MHz band during the early decline phase, and in the 610 MHz band at the onset and end of the SSS phase. We also present optical spectra obtained in the pre-outburst quiescence phase. Results. The overall spectral evolution during the 2010 outburst is similar to the previous outbursts. However, the dense temporal coverage, especially during the early phases, reveals several short term variations not reported previously. The early phase emission line widths indicate extremely high velocities for the nova ejecta, ∼10 000 km s −1 . The line profiles are broad, boxy and structured. Narrow P-Cygni absorptions, at ∼500 km s −1 are seen associated with the He I lines, and also the Ca II, N I and hydrogen lines (at wavelengths >8000 Å) in the spectrum of day 6.83, obtained immediately after an optical flare. This absorption component could be arising in the plasma emitting the Nitrogen lines seen in X-rays, that probably lies outside the binary orbit. Rapid variations are detected in the strength of the 4660 Å N III feature, which shows a significant increase in the line strength on days 8.83 and 13.82, at orbital phases of 0.75 and 0.25, respectively. Instrinsic polarisation is detected just before the onset, and during the SSS phase, with p v ∼ 1.4% during the SSS phase. The flux variations of the N III feature and the intrinsic polarisation are most likely associated with the reforming accretion disc/stream. We estimate the mass of the ejected (hydrogen) shell to be ∼4.6 × 10 −6 M , for a spherical shell geometry. The non-detection of U Sco in the 1280 MHz and 610 MHz radio bands is consistent with the low mass of the nova ejecta, subgiant nature of the secondary, and the distance to the nova.

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