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.
Muthumariappan C.,Indian Institute of Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2017
We analyse the characteristics of dust and its distribution in the planetary nebula IRAS 18333- 2357 located in M22 using a three-dimensional radiative transfer code HOCHUNK3D. The spectral energy distribution was constructed using ultraviolet, optical and infrared archival data. We also have used Spitzer 8-μm and Wide-field Infrared Survey Explorer (WISE) 22-μm images for our study. Taking into account that the dust shell is carbon-rich, models are presented for amorphous carbon and graphite grains. The spectral energy distribution and the thermal images are fit better by the amorphous carbon model than the graphite model. The stellar photospheric temperature is (50 000 ± 3000) K. IRAS 18333-2357 has a (40 ± 2)° inclined equatorial disc and a thin spherical shell around it, similar to the inner geometry of the born-again planetary nebula A30. Disc inner and outer radii are (2.8 ± 0.1) and (6.0 ± 0.6) arcsec, respectively. The inner and outer radii of the shell are (13.3 ± 1.5) and (25 ± 4) arcsec, respectively. Incorporating a very small grain population, we explain the excess emission in the region of 3-12 μm. The stellar bolometric luminosity is (2460 ± 800) L⊙ and the luminosity reprocessed by dust is (630 ± 200) L⊙. The masses of very small grain population and the classical dust grains are (9.4 ± 0.75) × 10-4 M⊙ and (3.1 ± 0.24) × 10-3 M⊙, respectively, resulting in a total dust mass of (4.1 ± 0.31)× 10-3 M⊙. The derived gas-to-dust mass ratio is 7 ± 1. We discuss a possible origin of IRAS 18333-2357 from a born-again event. The faint envelope seen in the WISE 22-μm image may contain H-rich matter ejected before the H-deficient nebula. © 2017 The Author. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
Vemareddy P.,Indian Institute of Astrophysics
Astrophysical Journal | Year: 2017
We study the magnetic field evolution in AR 12371, related to its successive eruptive nature. During the disk transit of seven days, the active region (AR) launched four sequential fast coronal mass ejections (CMEs), which are associated with long duration M-class flares. Morphological study delineates a pre-eruptive coronal sigmoid structure above the polarity inversion line (PIL) similar to Moore et al.'s study. The velocity field derived from tracked magnetograms indicates persistent shear and converging motions of polarity regions about the PIL. While these shear motions continue, the crossed arms of two sigmoid elbows are being brought to interaction by converging motions at the middle of the PIL, initiating the tether-cutting reconnection of field lines and the onset of the CME explosion. The successive CMEs are explained by a cyclic process of magnetic energy storage and release referred to as "sigmoid-to-arcade-to-sigmoid" transformation driven by photospheric flux motions. Furthermore, the continued shear motions inject helicity flux with a dominant negative sign, which contributes to core field twist and its energy by building a twisted flux rope (FR). After a limiting value, the excess coronal helicity is expelled by bodily ejection of the FR, which is initiated by some instability as realized by intermittent CMEs. This AR is in contrast with the confined AR 12192 with a predominant negative sign and larger helicity flux, but much weaker (-0.02 turns) normalized coronal helicity content. While predominant signed helicity flux is a requirement for CME eruption, our study suggests that the magnetic flux normalized helicity flux is a necessary condition accommodating the role of background flux and appeals to a further study of a large sample of ARs. © 2017. The American Astronomical Society. All rights reserved.
News Article | February 22, 2017
Sunlight beams through the dome of the solar tunnel telescope at the Kodaikanal Solar Observatory, India, February 3, 2017. REUTERS/Danish Siddiqui KODAIKANAL, India (Reuters) - In the early morning darkness, Devendran P. walks up a hill to a solar observatory in India's southern hill town of Kodaikanal, trudging the same path his father and grandfather walked in a century-old family tradition of studying the sun. Once inside, he pulls a rope to open shutters in the dome and positions a six-inch telescope used since 1899 to photograph the sun and preserve a daily record of its activity. "The sun, like stars, has a lifetime of 10 billion years," Devendran told Reuters during a recent visit to the observatory in India's southern state of Tamil Nadu. "If you want to know about any small changes, you need to have a large amount of data." The observatory run by the Indian Institute of Astrophysics has a key role in providing a continuous stream of data on the sun and its influence on Earth and surrounding space, said R. Ramesh, a professor at the institute. "Some of the discoveries made, based on data obtained in the Kodaikanal observatory, are so fundamental to solar physics that they vastly improved techniques used at observatories even today," Ramesh said. The Evershed effect of gas motion in sunspots, discovered in 1909 by the then director of the observatory, John Evershed, is one such example, he added. In the observatory library, shelves stretch to the ceiling, packed with volumes of handwritten records and thousands of film plates of the sun. Authorities have launched a project to digitize and preserve the data collected over the past century. Devendran's grandfather, Parthasarty, joined the observatory in 1900, a year after it relocated from Madras, the state capital, to Kodaikanal, situated more than 2,000 meters (6,562 feet) above sea level, offering ideal weather to study the sun. Like his father and grandfather, Devendran has no formal education in astronomy. His interest was piqued during a visit to the observatory when he was a child. He became a fulltime sunwatcher in 1986 and says the six-inch (15-cm) telescope has never failed his family. "It has never required any major overhaul, or change of parts, because we all take care of it," he said. More than three decades of observation has made him feel close to the sun, despite its distance of more than 149 million kms (93 million miles) from Earth. It's a feeling enhanced by the devout family's worship of the Hindu sun god Surya, he said. "I feel more religious than other people, as I can see that there is a universal power which is controlling everything," he said. His 23-year-old son, Rajesh, expects to carry on the family tradition, but with one difference. He has a master's degree in physics. "I get amazed by what my father does here," said Rajesh. "I think observing the Sun is in my blood."
Sampoorna M.,Indian Institute of Astrophysics
Astrophysical Journal | Year: 2011
The present paper concerns the derivation of polarized partial frequency redistribution (PRD) matrices for scattering on a two-level atom in arbitrary magnetic fields. We generalize the classical theory of PRD that is applicable to a J = 0 → 1 → 0 scattering transition, to other types of atomic transitions with arbitrary quantum numbers. We take into account quantum interference between magnetic substates of a given upper J-state. The generalization proceeds in a phenomenological way, based on the direct analogy between the Kramers-Heisenberg scattering amplitude in quantum mechanics and the Jones scattering matrix in classical physics. The redistribution matrices derived from such a generalization of classical PRD theory are identical to those obtained from a summed perturbative quantum electrodynamic treatment of the atom-radiation interaction. Our semi-classical approach has the advantage that it is non-perturbative, more intuitive, and lends itself more easily to further generalization (like the inclusion of J-state interference in the PRD theory). © 2011. The American Astronomical Society. All rights reserved.
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.
Javaraiah J.,Indian Institute of Astrophysics
Solar Physics | Year: 2012
We have analyzed the combined Greenwich and Solar Optical Observing Network (SOON) sunspot group data during the period of 1874 - 2011 and determined variations in the annual numbers (counts) of the small (maximum area A M<100 millionth of solar hemisphere, msh), large (100≤A M<300 msh), and big (A M≥300 msh) spot groups. We found that the amplitude of an even-numbered cycle of the number of large groups is smaller than that of its immediately following odd-numbered cycle. This is consistent with the well known Gnevyshev and Ohl rule (G-O rule) of solar cycles, generally described by using the Zurich sunspot number (R Z). During cycles 12 - 21 the G-O rule holds good for the variation in the number of small groups also, but it is violated by cycle pair (22, 23) as in the case of R Z. This behavior of the variations in the small groups is largely responsible for the anomalous behavior of R Z in cycle pair (22, 23). It is also found that the amplitude of an odd-numbered cycle of the number of small groups is larger than that of its immediately following even-numbered cycle. This might be called the 'reverse G-O rule'. In the case of the number of the big groups, both cycle pairs (12, 13) and (22, 23) violated the G-O rule. In many cycles the positions of the peaks of the small, large, and big groups are different, and considerably differ with respect to the corresponding positions of the R Z peaks. In the case of cycle 23, the corresponding cycles of the small and large groups are largely symmetric/less asymmetric (the Waldmeier effect is weak/absent) with their maxima taking place two years later than that of R Z. The corresponding cycle of the big groups is more asymmetric (strong Waldmeier effect) with its maximum epoch taking place at the same time as that of R Z. © 2012 Springer Science+Business Media B.V.
Javaraiah J.,Indian Institute of Astrophysics
Solar Physics | Year: 2011
Using the combined Greenwich (1874 - 1976) and Solar Optical Observatories Network (1977 - 2009) data on sunspot groups, we study the long-term variations in the mean daily rates of growth and decay of sunspot groups. We find that the minimum and the maximum values of the annually averaged daily mean growth rates are ≈ 52% day-1 and ≈ 183% day-1, respectively, whereas the corresponding values of the annually averaged daily mean decay rates are ≈ 21% day-1 and ≈ 44% day-1, respectively. The average value (over the period 1874 - 2009) of the growth rate is about 70% more than that of the decay rate. The growth and the decay rates vary by about 35% and 13%, respectively, on a 60-year time scale. From the beginning of Cycle 23 the growth rate is substantially decreased and near the end (2007 - 2008) the growth rate is lowest in the past about 100 years. In the extended part of the declining phase of this cycle, the decay rate steeply increased and it is largest in the beginning of the current Cycle 24. These unusual properties of the growth and the decay rates during Cycle 23 may be related to cause of the very long declining phase of this cycle with the unusually deep and prolonged current minimum. A ≈ 11-year periodicity in the growth and the decay rates is found to be highly latitude and time dependent and seems to exist mainly in the 0° - 10° latitude interval of the southern hemisphere. The strength of the known approximate 33 - 44-year modulation in the solar activity seems to be related to the north-south asymmetry in the growth rate. Decreasing and increasing trends in the growth and the decay rates indicate that the next 2 - 3 solar cycles will be relatively weak. © 2011 Springer Science+Business Media B.V.
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..
Bilham R.,University of Colorado at Boulder |
Gaur V.,Indian Institute of Astrophysics
Science | Year: 2013
The enforcement of sound building practices would substantially reduce future fatalities from earthquakes in south central Asia.