Here we report the first measure in radio emission of differential rotation as a function of height in the solar corona. This is derived from the disk-integrated simultaneous daily measurements of solar flux at 11 radio frequencies in the range of 275-2800 MHz. Based on the model calculations, these radio emissions originate from the solar corona in the estimated average height range of ∼ km above the photosphere. The 4 (6-15) # 10 investigations indicate that the sidereal rotation period at the highest frequency (2800 MHz), which originates from the lower corona around km, is ∼24.1 days. The sidereal rotation period decreases with height to 4 6 # 10 ∼23.7 days at the lower frequency (405 MHz), which originates at ∼ km. It is difficult to identify clearly 4 13 # 10 the rotational modulation at 275 MHz, perhaps because these emissions are significantly affected by the turbulence in the intervening medium. Since these investigations are based on disk-integrated solar flux at radio frequencies, it is difficult to say whether these systematic variations in sidereal rotation period are partly due to the latitudinal differential rotation of the solar corona. It will be interesting to investigate this possibility in the future.

We present here the detection of giant-pulse emission from PSR B0950+08, a normalperiod pulsar. The observations, made at 103 MHz and lasting for about ten months, have shown on a number of days the frequency of occurrence of giant pulses to be the highest among the known pulsars. The flux-density level of successive giant pulses fluctuates rapidly and their occurrence rates within a day's observations as well as between neighboring days show large variations. While on some days PSR B0950+08 shows a large number of giant pulses, there are other days when it shows only "quasinulls" with no detectable emission in the power spectrum or in the folded pulse data. The cumulative intensity distribution of these giant pulses appears to follow a power law, with index −2.2. After eliminating instrumental, ionospheric, interplanetary and interstellar diffractive and refractive scintillation effects as the cause, it appears that these intensity variations are intrinsic to the pulsar. We suggest that the giant pulse emission and nulling may be opposite manifestations of the same physical process, in the former case an enhanced number of charges partaking in the coherent radiation process giving rise to an extremely high intensity while in the latter case the coherence could be minimal.

We report on analysis of 308.3 hrs of high speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope (WET) during the 2008 international observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897 µHz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l=1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004-2007 archival data, confirms these identifications, provides constraints on additional frequencies, and finds an average period spacing of 41 s. Building on this foundation, we present nonlinear fits to high signal-to-noise light curves from the SOAR 4.1m, Mc-Donald 2.1m, and KPNO 2m telescopes. The fits indicate a time-averaged convective response timescale of τ 0 = 99.4 ± 17 s, a temperature exponent N = 85 ± 6.2 and an inclination angle of θ i = 32.9 ± 3.2 • . We present our current empirical map of the convective response timescale across the DA instability strip.

The present study is an attempt to investigate the long term variations in coronal rotation by analyzing the time series of the solar radio emission data at 2.8 GHz frequency for the period 1947 - 2009. Here, daily adjusted radio flux (known as Penticton flux) data are used. The autocorrelation analysis shows that the rotation period varies between 19.0 to 29.5 sidereal days (mean sidereal rotation period is 24.3 days). This variation in the coronal rotation period shows evidence of two components in the variation; (1) 22-years component which may be related to the solar magnetic field reversal cycle or Hale's cycle, and (3) a component which is irregular in nature, but dominates over the other components. The crosscorrelation analysis between the annual average sunspots number and the coronal rotation period also shows evidence of its correlation with the 22-years Hale's cycle. The 22-years component is found to be almost in phase with the corresponding periodicities in the variation of the sunspots number.Comment: 9 pages, 5 figures, Accepted for publication in MNRA

In the present work, we perform time‐series analysis on the latitude bins of the solar full disc (SFD) images of Nobeyama Radioheliograph (NoRH) at 17 GHz. The flux modulation method traces the passage of radio features over the solar disc and the autocorrelation analysis of the time‐series data of SFD images (one per day) for the period 1999–2001 gives the rotation period as a function of latitude extending from 60°S to 60°N. The results show that the solar corona rotates less differentially than the photosphere and chromosphere, i.e. it has smaller gradient in the rotation rate.

The aim of this paper is to study the latitudinal variation in the solar rotation in soft X‐ray corona. The time series bins are formed on different latitude regions of the solar full disc (SFD) images that extend from 80°S to 80°N. These SFD images are obtained with the soft X‐ray telescope (SXT) on board the Yohkoh solar observatory. The autocorrelation analyses are performed with the time series that track the SXR flux modulations in the solar corona. Then for each year, extending from 1992 to 2001, we obtain the coronal sidereal rotation rate as a function of the latitude. The present analysis from SXR radiation reveals that: (i) the equatorial rotation rate of the corona is comparable to the rotation rate of the photosphere and the chromosphere, (ii) the differential profile with respect to the latitude varies throughout the period of the study; it was more in the year 1999 and least in 1994, and (iii) the equatorial rotation period varies systematically with sunspot numbers and indicates its dependence on the phases of the solar activity cycle.

No abstract

No abstract