Time filter

Source Type

Bangalore, India

The Indian Institute of Astrophysics , with its headquarters in Bangalore , India, is a premier national institute of India for the study of and research into topics pertaining to astronomy, astrophysics and related subjects.The Institute has a network of laboratories and observatories located in various places in India, including Kodaikanal , Kavalur , Gauribidanur, Hanle and Hosakote. Wikipedia.

Sampoorna M.,Indian Institute of Astrophysics
Astrophysical Journal | Year: 2012

Using a previously established theory, we derive a suitable form of the laboratory frame redistribution matrix for the resonance scattering in subordinate lines, allowing for the radiative as well as collisional broadening of both atomic levels involved. The lower level, though broadened, is assumed to be unpolarized. The elastic collisions both in the upper and lower levels are taken into account. We show that, in situations, when elastic collisions in the lower level can be neglected, the redistribution matrix for subordinate lines takes a form that is analogous to the corresponding case of resonance lines. Further, in the case of no-lower-level interactions (i.e., infinitely sharp lower level), we recover the redistribution matrix for resonance lines. We express the redistribution matrix for subordinate lines in terms of the irreducible spherical tensors for polarimetry. For practical applications in one-dimensional polarized radiative transfer problem, we derive the azimuth averaged subordinate line redistribution matrix. © 2012. The American Astronomical Society. All rights reserved.

Javaraiah J.,Indian Institute of Astrophysics
Astronomy and Astrophysics | Year: 2010

Aims: We seek the long-term variations close to the length of a solar cycle in the mean meridional motion of sunspot groups (a proxy of the meridional plasma flow). Methods: Using the largest set of available reliable sunspot group data, the combined Greenwich and Solar Optical Observation Network sunspot group data during the period 1879-2008, we determined variations in the mean meridional motion of the sunspot groups in the Sun's whole northern and southern hemispheres and also in different 10° latitude intervals.We determined the variations from the yearly data and for the sake of better statistics by binning the data into 3-4 year moving time intervals (MTIs) successively shifted by one year. We determined the periodicities in the mean meridional motion from the fast Fourier transform (FFT) power spectrum analysis. The values of the periodicities are determined from the maximum entropy method (MEM) and the temporal dependencies of the periodicities are determined from the Morlet-wavelet analyses. Results: We find that the mean meridional motion of the spot groups varies considerably on a time scale of about 5-20 years. The maximum amplitude of the variation is about 10-15 ms-1 in both the northern and the southern hemispheres. Variation in the mean motion is considerably different during different solar cycles. At the maximum epoch (year 2000) of the current cycle 23, the mean motion is relatively strong in the past 100 years and northbound in both the northern and the southern hemispheres. This abnormal behavior of the mean motion may be related to the low strength and the long duration of the current cycle, and also to the violation of the Gnevyshev and Ohl rule by the cycles pair 22, 23. The power spectral analyses suggest the existence of ≈3.2- and ≈ 4.3-year periodicities in the mean motion of the spot groups in the southern hemisphere, whereas a 13-16 year periodicity is found to exist in the mean motion of the northern hemisphere. There is strong evidence for a latitude-time dependency in the periodicities of the mean motion. The north-south difference in the mean motion also varies by about 10 ms-1. During the recent cycles, the northsouth difference is negligibly small. Approximate 12- and 22-year periodicities are found to exist in the north-south difference. The implications of all these results are briefly discussed. © ESO 2010.

Gangadhara R.T.,Indian Institute of Astrophysics
Astrophysical Journal | Year: 2010

The beamed radio emission from relativistic plasma (particles or bunches), constrained to move along the curved trajectories, occurs in the direction of velocity. We have generalized the coherent curvature radiation model to include the detailed geometry of the emission region in pulsar magnetosphere and deduced the polarization state in terms of Stokes parameters. By considering both the uniform and modulated emissions, we have simulated a few typical pulse profiles. The antisymmetric type of circular polarization survives only when there is modulation or discrete distribution in the emitting sources. Our model predicts a correlation between the polarization angle swing and sign reversal of circular polarization as a geometric property of the emission process. © 2010. The American Astronomical Society. All rights reserved.

Ramesh K.B.,Indian Institute of Astrophysics
Astrophysical Journal Letters | Year: 2010

Recent studies have indicated that the occurrence of the maxima of coronal mass ejection (CME) rate and sunspot number (SSN) were nearly two years apart. We find that the two-year lag of CME rate manifests only when the SSN index is considered and the lag is minimal (two-three months) when the sunspot area is considered. CMEs with speeds greater than the average speed follow the sunspot cycle much better than the entire population of CMEs. Analysis of the linear speeds of CMEs further indicates that during the descending phase of the solar cycle the loss of magnetic flux is through more frequent and less energetic CMEs. We emphasize that the magnetic field attaining the nonpotentiality that represents the free energy content, rather than the flux content as measured by the area of the active region, plays an important role in producing CMEs. © 2010 The American Astronomical Society.

Murthy J.,Indian Institute of Astrophysics
Astrophysical Journal, Supplement Series | Year: 2014

I present tabulations of the diffuse observations made by the GALEX spacecraft in two UV bands (FUV: 1539 Å and NUV: 2316 Å) from the (almost) final data release of the GALEX spacecraft (GR6/GR7). This data release includes all the FUV observations and the majority of the NUV observations. I discuss overall trends in the data but the primary purpose of this paper is to make the data available to the public. The data files described in this paper are hosted by the Mikulski Archive for Space Telescopes at the Space Telescope Science Insitute from whence they may be downloaded. For ease of use, I have also created maps of the diffuse radiation in both bands over the entire observed sky at 6′ resolution. © 2014. The American Astronomical Society. All rights reserved..

Discover hidden collaborations