A C O M M E N T ON AN A N A L Y T I C A L S T E L L A R M O D E L

(Letter to the Editor)

H E N N I N G K N U T S E N

Stavanger College of Engineering, Stavanger, Norway

(Received 14 June, 1988)

Abstract. Recently, an analytical stellar model was presented. We show that the results are incorrect as they stand.

In a recent paper Duorah and Ray (1987) presented a new analytical stellar model. For their model the pressure isotropy equation takes the form

4 Z x 2 y '' + 2 Z ' x2y ' + ( Z ' x - Z + 1)y = 0, (1)

where the prime means differentiation with respect to x. Duorah and Ray then claim that a simple solution of this equation is of the form

and

Z = (1 + x ) - ' (2)

y = 1 + x . (3)

However, an insertion of these expressions in the isotropy equation shows this is not true. Moreover, this is not just a printing mistake, since the rest of the equations (i.e., their Equations (18), (21), and (22)) are correct.

In addition, this method seems to have been adopted from a paper by Durgapal and Fuloria (1985) which is not listed in the references.

References

Duorah, H. L. and Ray, R.: 1987, Class. Quant. Gray. 4, 1691. DurgapaI, M. C. and Fuloria, R. S.: 1985, Gen. ReL Gray. 17, 671.

Astrophysics and Space Science 150 (1988) 201. �9 1988 by Kluwer Academic Publishers.