You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
we discuss constraints on the universal baryonic mass - density parameter @xmath5 and a hubble parameter @xmath6 , using all available microlensing ( ml ) data and considering flattened galactic dark halo . since @xmath7 and @xmath3 are uncertain and correlated , we tried to break this degeneracy with the other cosmological information : measured optical depths from ml . in recent paper
we examined the relation between galactic halo flattening and baryonic dark matter ( samurovi , irkovi & miloevi - zdjelar 1999 , smz ) , using mass density for flattened instead of spherical halo , and optical depth @xmath8 as a function of galactic coordinates , derived by sackett & gould 1993 ( eqs .
2.1 and 2.5 ) .
comparing solutions for lmc , smc , m31 and a source at 50 kpc with all available ml data , we obtained @xmath0 for halo flattening . assuming that machos have finite mass - to - light ratio ( white or brown dwarfs ) , in smz we determined total mass of the macho halo as a function of flattening ( eq .
9 ) , and cosmological density parameter @xmath9 ( eq .
recent estimate of total halo mass within 50 kpc is @xmath10 ( wilkinson & evans 1999 ) . that can be obtained when we assume flattening parameter @xmath11 .
spherical halo has serious problems concerning bbns limits .
value @xmath4 is in accord with @xmath12 obtained by combining the baryon budget with cmbr measurements ( hannestad 1999 ) .
realistic flattening and macho - dominance in the inner halo are incompatible with @xmath13 .
fig . 1 : dependence of @xmath14 on @xmath3 for flattening @xmath15 , truncation radius 50 kpc , macho halo mass within 50 kpc for @xmath15 .
the sum of main baryonic components is @xmath16 .
high value @xmath17 , is within constraints of cmb observations : @xmath18 ( lineweaver et al . 1997 ) , and recent bbns and light element abundances constraints ( burles et al . 1999 ) . at higher redshifts ,
high @xmath19 can account for observational results of ly@xmath20 forest .
our results fit into theoretical requirements of high resolution spectroscopy of the igm ( e.g. burles & tytler 1998 ) .
burles , s. , nollett , k.m . , truran , j.n . ,
& turner , m.s . 1999 ,
lett . , 82 ( 21 ) , 4176 burles , s. , & tytler , d. 1998 , apj , 499 , 699 hannestad , s. 1999 , mnras , in press , preprint astro - ph/9906246 lineweaver , c. h. , barbosa , d. , blanchard , a. , & bartlett , j. g. 1997 , a & a , 322 , 365 sackett , p. d. , & gould , a. , 1993 , apj , 419 , 648 samurovi , s. , irkovi , m. m. , & miloevi - zdjelar , v. 1999 , mnras , in press ( smz ) , preprint astro - ph/9907165 wilkinson , m.i .
, & evans , n.w . 1999 , mnras , in press , preprint astro - ph/9906197
microlensing observations can be used for determining the shape of the milky way s halo . 
 it can be shown that the data are best described with moderately flattened halo , @xmath0 . 
 we discuss , by taking into account this result , the constraints on the baryonic mass - density parameter , @xmath1 , and their implications on the value of the hubble constant @xmath2 , i.e. @xmath3 . our conclusion is that current data , in order to satisfy bbns and galaxy dynamics constraints , strongly suggest that @xmath3 should take values within the lower part of the permissible range , @xmath4 .