Vol 13 No 1

Asian Journal of Physics Vol. 13, No 1 (2004) 23-24

Laser- induced fluorescence of Dergaon Meteorite

S Bhattacharyya^l, A Gohain Barua², R Konwar³, R Changmai and G D Baruah
Department of Physics , Dibrugarh University , Dibrugarh 786004, India.
D.C.B. Girls College , Jorhat 785001, India.
'Department of Physics, Gauhati University , Gauhati 781014, India.
³Tinsukia College , Tinsukia 786125, India.

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We report the observation of an emission band system in the region 5700 — 6700 Ǻ from Dergaon stoney iron meteorite ;.sing a 500 mW continuous Ar⁺ laser. The band system is attributed to silicate , the major component of the meteorite. © Anita Publications. All rights reserved.

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1 Introduction

Recent studies on Dergaon meteorite[1, 2] have shown that the 10 and 20 μm bands, characteristics of the valence vibration of SiO₄, a basic component of silicate lattice, are present in its FTIR spectrum. Likewise a wide absorption band at 6150 Ǻ is also observed. These bands are considered as significant in the light of their presence in the interstellar space. The bands at 10 and 20 μm observed in the interstellar space have been identified as the valence vibrations or deformation vibrations respectively, of the SiO₄ tetrahedron in silicates occurring probably as a component of interstellar dust [3, 4]. Measurements made on α' -Orionis [5] revealed clues that 20 μm band in emission was present . Similarly 10μm band was found in a number of super giants and cants [6]. The nature of the interstellar and circumstellar dust presents a problem, unresolved so far by astronomical research. It has been explained only hypothetically in the form of various dust models. According a model interstellar dust is a biproduct of star formation or the 'building waste' of planetary systems respectively. Some bodies of solar systems like meteorites and comets produce even today dust particles obtained by collisions and other splitting up processes which may reach the interstellar space. In the present communication we report an emission band system originating from the Dergaon meteorite [2].

2 Experimental

The laser-induced fluorescence ( or emission ) was recorded photographically on a Glass spectrograph and the intensity distribution of the emission spectrum was measured with the help of a densitometer. The excitation source is a 500 mW Ar⁺ laser. The finely powdered sample is kept near a strong magnet to separate the iron components. The powdered sample without iron was kept between two firmly held glass plates. The optical path or the specimen thickness was 0.05 cm. Commercially available colour film was used to photograph the spectrum.

3 Results and Discussion

Fig 1 demonstrates the general features of the emission band system in the region 5700-6700 Ǻ alongwith the Ar⁺ lasing line at 5145 A as the exciting radiation. The emission band system as its densitometer tracing shown in Fig 2 indicates the diffuse nature of the emission. From the survey of available literature it is seen that the emission spectrum in the visible region has not been reported earlier. The emission would seem to characterize silicate. In earlier work [2] 10 and 20µm silicate bands have already been reported. We may designate the visible system of band in the region as 0.6 μm band. The question arises whether this 0.6 Ǻ m band has been observed in interstellar space. The answer is definitely no. But there seems to be a correlation between the 0.6μm diffuse emission band in the red sector of the spectrum and the reddening law [7]. In 1929 /30 Schalen [7] and Tumpler [8] were in a position to prove that in addition to the strong extinction in individual zones, there will also be another less conspicuous general interstellar extinction in the entire zone of the milky way. This extinction turned out to be wave dependent. Since the shorter waves of the star light are much more attenuated than the longer ones, when passing an accumulation of dust, the stars behind this accumulation have not only a lower light intensity, but also their red colours appear to be deeper. That is why the dependence of the extinction (measured in stellar magnitudes) on the wavelength is called reddening law. To this day, the reddening law represents the most important key, when investigating the properties of the interstellar dust particles; information can also be obtained on the size of these particles. Unfortunately, the law of reddening does not provide any positive information on the chemical composition of the particles. As regards the 0.6µm emission system which we have photographed from a meteorite system, it may be noted that any emission band at 0.6 µm in interstellar space may have possibly been missed due to reddening.

Acknowledgement

We highly acknowledge financial support from DST for assembling an argon ion laser with the help of M/s Suresh Indu Laser for investigation of LIF of the sample.

References

1 Meteoritical Bulletin, No 85 (2001) A295.

2 Gohain Burua A, Baruah B R, Bhattacharyya S, Baruah G D, Pramana—J Phys 60 (2003) 47.

3 Knake R F, Gaustad I E, Gillett F C, Stain W A, Astrophys J 155 (1969) L189.

4 Hackwell I A, Gehrz R D, Woolf N J, Nature 227 (1970) 822.

5 Low F J, Krishna Swami K S, Nature 227(1970) 1334.

6 Gillett F C, F I Low, Stain W A , Astrophys J, 154 (1968) 677.

7 Schalen C, Astron Nachr 236 (1929) 2.

8 Tumpler R J, Lick Bull, No 420 (1930).

[Received: 1.12.2003]

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Asian Journal of Physics Vol 13, No 1,(2004) 69-71

Cosmic ray diurnal anisotropy and geometric Ap index

C M Tiwari¹ and Pankaj K Shrivastava²

¹ Department of Physics, A P S University, Rewa-486 001, India

² Department of Physics, Govt New Science College, Rewa-486 001, India

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Relationship of diurnal anisotropy of cosmic ray intensity with geomagnetic activity disturbace index Ap has been studied for the period of 1989 to 2002. From this correlative analysis, it has been concluded that the yearly mean values of Ap index show good positive correlation with diurnal amplitudes of cosmic ray anisotropic variation. © Anita Publications. All rights reserved.

Total Refs: 7

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Asian Journal of Physics Vol 13, No 1,(2004) 73-76

Inferring tropospheric ozone content at Udaipur

R Pandy and B M Vyas

Department of Physics, M L Sukhadia University, Udaipur-313 002, india

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The total column ozone at Udaipur has been measured using a Microtops II sun photometer. The measurements reveal a diuranal variation in the total column ozone. These diuranal variations in the total column ozone have been attributed to the variation in the tropospheric ozone, produced by the precursor gases like CH₄, CO and NO_x. © Anita Publications. All rights reserved.

Total Refs: 13

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ASIAN JOURNAL OF PHYSICS