Aims. We investigate the variability in temperature as a function of time among a sample of coronal X-ray bright points (XBPs). Methods. We analysed a 7-h (17:00-24:00 UT) long time sequence of soft X-ray images observed almost simultaneously in two filters (Ti_poly and Al_mesh) on April 14, 2007 with X-ray telescope (XRT) onboard the Hinode mission. We identified and selected 14 XBPs for a detailed analysis. The light curves of XBPs were derived using the SolarSoft library in IDL. The temperature of XBPs was determined using the calibrated temperature response curves of the two filters by means of the intensity ratio method. Results. We find that the XBPs show a high variability in their temperature and that the average temperature ranges from 1.1 MK to 3.4 MK. The variations in temperature are often correlated with changes in average X-ray emission. It is evident from the results of time series that the XBP heating rate can be highly variable on short timescales, suggesting that it has a reconnection origin.

Aims. Our aim is to investigate the intensity oscillations in coronal X-ray Bright Points (XBPs). Methods. We analysed a 7 h long time sequence of the soft X-ray images obtained on April 14, 2007 with a 2 min cadence using the X-Ray Telescope (XRT) on-board the Hinode mission. We use SSW in IDL to derive the time series of 14 XBPs and 2 background regions. For the first time, we have tried to use power spectrum analysis on XBP data to determine the periods of intensity oscillations. Results. The power spectra of XBPs show several significant peaks at different frequencies corresponding to time scales that range from a few minutes to hours. The light curves of all the XBPs give the impression that the XBPs can be grouped into three classes depending on emission levels: (i) weak XBPs; (ii) bright XBPs; and (iii) very strong XBPs. The periods of intensity oscillation are consistent in all the XBPs and are independent of their brightness level, suggesting that the heating mechanisms in all the three groups of XBPs are similar. The different classes of XBPs may be related to the different strengths of the magnetic field with which they have been associated.

The exact nonlinear cylindrical solution for incompressible Hall -magnetohydrodynamic (HMHD) waves, including dissipation, essentially from electron -neutral collisions, is obtained in a uniformly rotating, weakly ionized plasma such as exists in photospheric flux tubes. The ω -k relation of the waves, called here Hall -MHD waves, demonstrates the dispersive nature of the waves, introduced by the Hall effect, at large axial and radial wavenumbers. The Hall -MHD waves are in general elliptically polarized. The partially ionized plasma supports lower frequency modes, lowered by the factor δ ≡ ratio of the ion mass density to the neutral particle mass density, as compared to the fully ionized plasma (δ = 1). The relation between the velocity and the magnetic field fluctuations departs significantly from the equipartition found in Alfvén waves. These short-wavelength and arbitrarily large amplitude waves could contribute toward the heating of the solar atmosphere.

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High-resolution spectral profiles of Na i D lines from the interstellar medium towards 64 stars in the direction of the Vela supernova remnant are presented. This survey conducted mostly between 2011-12 complements an earlier survey of the same stars by Cha & Sembach done in the 1993-96 period. The interval of 15 to 18 years provides a base line to search for changes in the interstellar profiles. Dramatic disappearance of strong absorption components at low radial velocity is seen towards three stars -HD 63578, HD 68217, HD 76161 -over 15-18 years; HD 68217 and HD 76161 are associated with the Vela SNR but HD 63578 is likely associated with the wind bubble of γ 2 Velorum. The vanishing of these cold neutral clouds in the short time of 15 to 18 years needs some explanation. Other changes are seen in high-velocity Na D components.