Astronomy

Solar Studies At ARIES India

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The institute plans to continue its studies related to the Sun. it proposes to record solar activities, especially solar flares and prominence’s with high temporal and spatial resolution. The CCD array can get solar images with a time resolution of about 25 milliseconds; in other words, it can obtain 40 frames per second capturing the solar phenomena. The resolution of the image, about 1.3 arcsecond, is quite good for recording solar flares. The computer-controlled exposures can be obtained at chosen instants and at the desired time intervals, using Sun-computer software. In order to better understand the mechanism that triggers solar flares, it would be necessary to compare the solar regions that emit hydrogen alpha radiation, and simultaneously observe microwaves and other emissions at a high resolution.

About 30 per cent of the recently discovered soft X-ray sources in the Einstein and ROSAT surveys are late type stars, which exhibit a wide range of chromospheric activities that appear similar to those observed on the Sun.

Stars and Gamma Ray Bursts

Optical studies of the variability in these stars would be needed to identify their optical counterparts for carrying out further studies on the sources. A fast CCD photometer has been commissioned for use with the 104-cm telescope. This would be useful for short, continuous exposures of the order to tens of millisecond in monitoring the optical light variation in X-ray binaries and similar variables. Experience acquired before the ASTROSAT mission of ISRO would be valuable for follow-up observations.

Despite all the satellite probes, it is a sobering thought that only 10 to 20 per cent of the total regions associated with star formation in our galaxy have been scanned with high sensitivity. Young star clusters are excellent tools for tracing the evolution of the galaxy into its current dynamical state. The 104-cm telescope has been used for obtaining images of more than 50 open clusters. These studies will be continued.

Optical observations of the afterglow of gamma ray bursts (GRB) were started in 1997 under a long-term research programme in collaboration with astronomers from all over the world. ARIES observed from India the first two GRB afterglows. So far, more than 20 GRB afterglows have been observed and recorded in spectrometric as well as photometric modes. Gamma ray bursts continue to puzzle astronomers ever since they were discovered in the 1960s. The energy released by the gamma ray bursts is more than what is put out by the Sun. The period of afterglows varied from less than a second to several minutes.

There is another area of research: quasars, the extremely bright objects powered by super massive black holes. However, it is found that only 10 to 20 per cent of the quasars emit radio waves, while the rest barely emit any such radiation. ARIES has taken up a study on the radiation of quasars of different types. Radio-active quasars exhibit a strange behaviour: intense fluctuations at optical wavelengths lasting an hour or so. It is not known if radio quiet quasars too behave similarly.

In collaboration with the National Centre for Radio Astronomy, Pune and the optical telescope at Hanle, simultaneous observations would be possible. While the Giant Metrewave Radio Telescope (GMRT), Pune, can detect radio sources that send faint signals, ARIES can find their optical and near-infrared counterparts. Without such identification, the science targets of GMRT would remain incomplete.

pagoda dark

ARIES is involved in the search for dark matter as well. The nature of the dark matter remains a mystery. In recent years, it is considered that the dark matter consists of some sort of astrophysical “object”, and gravitational lensing technique is used to search for them. Using the 104-cm telescope, ARIES has made observations to detect microlensing events aimed at discovering planets, if any, at thousands of light years from the Earth towards M31, the Andromeda galaxy. The long-duration photometric study (measuring light from sources hundreds of light years away) covers over 4400 stars.

The 2-m class optical telescopes in the country are oversubscribed. The demand for telescope time is thrice the availability. Hence, a 3.6-m class optical telescope and another with a 130-cm mirror are planned at Devasthal, 50 km by road from Nainital, at an altitude of 2500 m. it is an excellent site for optical astronomy at longitude 79º40’57”E and 29º22’6”N. The new site has become necessary, as pollution of light at Manora Peak, the site of ARIES, has significantly increased in recent times. Seeing condition has declined.

The new site has been selected after an extensive 10-year survey of the Kumaon-Garahwal regions of the Shivalik Himalayas. Devasthal has over 200 spectroscopic nights in a year of which 80 per cent are of photometric quality, good for visibility. The relative humidity is generally below 60 per cent and the wind speed, below 20 km per hour, while the temperature variation (due to the telescope itself and the building) has to be maintained within 2º during night time, which is crucial for controlling the seeing conditions.

A 52-cm telescope was installed to determine the characteristics of seeing and the impact of the atmosphere on observing conditions. The proposed 3.6-m glass telescope will have state-of-the-art features. It will have active optics control systems which will keep the primary and secondary mirrors aligned in all observing conditions and temperature variations. Some experiments to introduce adaptive optics would star after the installation of the telescope by 2010.

The telescope will have an alt-azimuth mount, which means it would automatically be brought in line with the desired axis for observation.

The new telescope would be used for both optical and near-infrared observations, sometimes simultaneously. The near-infrared window is useful for studying star formation, which is central to many braches of astrophysics, from the formation and evolution of galaxies to the presence of life on Earth. Current observations cover only 10 to 20 per cent of the total star-forming regions of our galaxy. ARIES intends to carry out near-infrared studies of nearby galaxies as well.

The proposed 1.3-m optical telescope would cater to the immediate needs of the Institute, while providing experience for installing the bigger (3.6 m) telescope.

With the planned launch of ASTROSAT and TAUVEX, a new area of participation will open up for ARIES and other optical telescopes in the country. Ground-based optical follow-up of satellite observations would also be needed. Software development for data reduction and analysis would get a fillip. The experience would enable ARIES to use data from missions launched by other nations as well, including optical telescopes.

sun-blue-sky

ARIES is also a centre for high-altitude atmospheric research in the central Himalayas. The Institute plays a key role in understanding the global weather change and in assessing the impact of human activities on the aerosols in the troposphere (the atmosphere up to about 16 km from the surface). ARIES has undertaken a major initiative in this field. Under the Geosphere-Biosphere programme of ISRO for measuring aerosols since 2002, the findings indicate that in the high altitude (about 2 km) Himalayan region, large size aerosols are quite prominent during the summer than in other times. ARIES has some 50 years of data on the pattern of atmospheric extinction of star light.

The Institute’s instruments for the study of atmospheric sciences include an aethalometer, for measuring aerosol black carbon, an air pollutant; a multi-wavelength radiometer designed by the Space Physics Laboratory of Vikram Sarabhai Space Centre at ISRO, a Sun photometer and an automatic weather station. It is known that aerosol black carbon is a ubiquitous component of combustion emissions.

Recent studies suggest that the clear sky atmosphere absorbs more short-wave radiation than predicted by radiative transfer models. The scientists suspect the presence of an unidentified absorber with optical properties similar to that of black carbon.

ARIES plans to install several observational facilities at Manora Peak, Nainital for the study of the middle atmosphere. ARIES would be linked to ISRO’s Mesosphere, Stratosphere and Troposphere (MST) Radar at Gadanki near Tirupati in Andhra Pradesh.

ARIES aims to play a major role in developing highly skilled human resources by implementing state-of-the-art research projects in astrophysics and atmospheric sciences. The Institute also plans to expand its collaborative programmes with universities and research institutions at home and abroad.

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