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  • 1
    Electronic Resource
    Electronic Resource
    Chemical Evolution of the Galaxy (1991)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 29 (1991), S. 129-162 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.29.090191.001021
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  • 2
    Electronic Resource
    Electronic Resource
    Absorption effects of intergalactic natural graphite whiskers on observations at microwave and radio frequencies (1979)
    Springer
    Astrophysics and space science 66 (1979), S. 173-190 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An attempt has been made to explain the microwave background within the framework of the steady state theory by invoking thermalizers in the form of long whiskers of semi-metallic grains such as natural graphite. An ad hoc but general method has been sought for the description of a cosmic thermal system in terms of absorption coefficients of such grains in the proper Rayleigh limit. We have found that typically natural graphite grains, having axial ratios of the order of 104 to 105 and a temperature about 4 K, have a broad absorption peak only at decimetre wavelengths and thus cannot adequately thermalize the background. It is also shown that the effects of such an absorbing medium on such radio astronomical tests as the number count test or the angular size test can be very severe, especially in Friedmann cosmologies. These effects are marginal in the steady state theory. The desirable physico-optical properties of such semi-metallic thermalizers have also been investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648369
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  • 3
    Electronic Resource
    Electronic Resource
    Absorption effects due to intergalactic long whiskers of pyrolytic graphite and the cosmic microwave background (1980)
    Springer
    Astrophysics and space science 71 (1980), S. 123-133 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Earlier (Rana, 1979, 1980) it was shown that an intergalactic medium containing natural graphite whiskers could not adequately thermalize the ambient radiations to generate 3 K microwave backgroud. In the present paper we have carried out a similar investigation with whiskers of pyrolytic graphite. Provided the abundance is about 10−34 g cm−3, the model is capable of thermalizing the background. Some of the observational consequences have been studied with reference to extragalactic astronomy and quasistellar objects. No conflicting evidence has been found so far.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646913
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray absorption effects due to intergalactic abundance of carbon (1980)
    Springer
    Astrophysics and space science 67 (1980), S. 201-204 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The absorption effects at the soft X-ray and hard ultraviolet wavelengths due to some model abundance of intergalactic carbon material have been investigated for different cosmologies. Even though the local density, 2 × 109 〈ϱ 0 = 1.0 × 10−34 g cm−3 of the absorbing component of the intergalactic material in the form of carbon is not adequate for the thermalization of the discrete background radiation, the amount of absorption in the X-rays up to the Hubble radius is not negligible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00651876
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  • 5
    Electronic Resource
    Electronic Resource
    Past history of star formation in the solar neighbourhood from the observed white dwarf luminosity distribution (1990)
    Springer
    Astrophysics and space science 163 (1990), S. 229-240 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is known that intermediate and low-mass stars evolve finally to white dwarfs of mass characteristically centred around 0.6M ⊙. The observed luminosity distribution and the theoretical cooling curves of such white dwarfs are used in this work to estimate the rate of formation of these and, hence, of their progenitors (although not uniquely) in the solar neighbourhood as a function of time. It is found that the star formation rate has remained fairly constant over the past 10–12 billion years, and that the observed number density of the local white dwarfs match quite well with the one expected from the mass functions of the local stars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00655744
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  • 6
    Electronic Resource
    Electronic Resource
    Coordinate gauge conditions in theN-body equations of motion in the first-order post-Newtonian approximation of general relativity (1990)
    Springer
    Astrophysics and space science 167 (1990), S. 125-138 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The explicit forms of the metric as well as the equations of motion in the first-order post-Newtonian approximation are worked out under several gauge conditions. It is noted that the so-called EIH (Einstein, Infeld, and Hoffman) equation of motion for an assembly ofN finite mass points mutually interacting via gravitation is identically obtained under three different gauge conditions, namely the harmonic gauge, Chandrasekhar gauge and a composite Chandrasekhar gauge used by Misneret al. (1970), even though the solutions for the metric are found to be all different. In one case the metric has a component apparently diverging, but finally generates regular affine connections so that the equations of motions become free from any singularity. By use of the Chandrasekhar gauge and his formulation, the second-order contribution to the acceleration of planets in the limit of test particle motion around the Sun has been calculated, the inclusion of which in the EIH set of the equations of motion would extend the relative accuracy of computing the total acceleration of any planet to better than one part in 1017.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642068
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  • 7
    Electronic Resource
    Electronic Resource
    G-dwarf metallicity distribution curves assuming an inhomogeneous interstellar medium (1992)
    Springer
    Astrophysics and space science 196 (1992), S. 1-21 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that the explicit assumption of a chemically inhomogeneous interstellar medium allows a better reproduction of the metallicity distribution of G-dwarfs in the solar neighbourhood. The inhomogeneity is considered by assuming that at any time stars are born with a spread in their metallicities, the spread being a Gaussian in the logarithm of the metallicity around the mean metallicity of that epoch. We show that for various simple models of chemical evolution, the fit to the G-dwarf metallicity curve improves considerably once the above assumption is applied. We show that the parameters obtained from the fitting also give acceptable predictions for the age-metallicity relation. We also find that if we use a G-dwarf metallicity function corrected for the scale height inflation of stars, the conventional models of chemical evolution cannot match the shape of the curve, at least under the instantaneous recycling approximation applied to a chemically homogeneous ISM. Under the inhomogeneous ISM approximation, the predicted shapes are found to be better, though not totally satisfactory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00645237
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  • 8
    Electronic Resource
    Electronic Resource
    Distribution of metals in dwars stars in the solar neighbourhood (1990)
    Springer
    Astrophysics and space science 168 (1990), S. 317-330 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A preliminary method is proposed to handle the intrinsic chemical inhomogeneity in models of chemical evolution of the solar neighbourhood. If we assume a Gaussian spread in metallicity (z≡[Fe/H]) about a ‘mean’ metallicity in the birth function of stars, the metallicity distribution of stars as a function of time is investigated, assuming that the mean metallicityz evolves linearly with time. Metallicity ([Fe/H]) histograms are plotted for A-, F-, G-, and K-dwarfs of the local disk population based on our compilation of data from several sources, and compared with the existing ones. We have applied the above method on these distributions to check whether distribution of the local A-, F-, and K-dwarfs could be fitted reasonably well with a single set of parameters derived from a fit to the metallicity distribution of the G-dwarfs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00636876
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  • 9
    Electronic Resource
    Electronic Resource
    On the definition of mass-energy of a static spherically-symmetric mass in the post-newtonian approximation of general relativity (1993)
    Springer
    Astrophysics and space science 207 (1993), S. 145-150 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recently we (Roy and Rana, 1990a) critically examined the self-consistency of the EIH equations of motion. A static spherically symmetric body as was pointed out there may not appear as a point mass with all its mass concentrated at its centre to a particle placed outside the body. An attempt to analyse this aspect further is made here in the context of the Chandrasekhar gauge. A comparison is also made with the general solutions obtained by Schwarzschild in the standard co-ordinates. Certain difficulties still exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00659138
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  • 10
    Electronic Resource
    Electronic Resource
    Astration of deuterium during the evolution of the solar neighbourhood (1993)
    Springer
    Astrophysics and space science 207 (1993), S. 129-132 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is here shown that the stellar astration of deuterium in the solar neighbourhood of the Galactic Disc over 13 Gy corresponds to a factor of about 2 only in a closed model of chemical evolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00659136
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