A&A 437, 1093-1108 (2005)

DOI: 10.1051/0004-6361:20042000

## Some characteristics of the outer Oort cloud as inferred from observations of new comets

**L. Neslusan and M. Jakubík**

Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia

e-mail: [ne;mjakubik]@ta3.sk

(Received 13 September 2004 / Accepted 10 March 2005)

** Abstract **

We study the outer Oort cloud (OC) by numerical integration
of 126 600 orbits of hypothetical comets representing this cometary reservoir.
We determine the distribution of the semi-major axis *a* for
,
and estimate its population and total mass, as well as some other
characteristics. The distribution of the semi-major axis is found initially
by assuming a constant distribution and then identifying the
theoretically predicted distribution of new comets with their
observed distribution. The semi-major axis of outer-OC comets
ranges from
to typically
on the
decadic-logarithm scale. The relative distribution of this element
can, however, be roughly determined only for
:
d
, where
. The perihelion
distribution of new comets with
is not constant in
the zone of visibility (ZV) and a bias due to the observational selection
cannot be eliminated. The lower limit of the outer OC population is
to
. The currently available cometary
data do not allow us to give a more exact lower estimate or an average
estimate of the population.
The OC has also been depleted by the combined Galactic-tide-planetary
(GTP) perturbation with a local maximum rate at
.
The ratio of these comets that are lost from the outer OC and of new
comets that enter into the ZV in the same time frame is 2.5.
The distributions of the angular elements of new comets at their
previous perihelion passage are used to evaluate the correctness of our
model of the outer OC. Specifically, we calculated the root of mean squares
between the corresponding theoretical and observed distributions of , , and resulting in unexplained
residua.

**Key words:**comets: general

**--**Oort cloud

**--**planets and satellites: formation

SIMBAD Objects

**©**

*ESO 2005*