Tycho Catalogue

Greetings everybody!

There're a couple of issues with the fields of
the Tycho Catalogue I'd need some help with...

I'm looking at the searchable data available through this page
http://www.rssd.esa.int/hipparcos_scripts/hipMultiSearch.pl

The resulting fields of a search are documented in this PDF file:
http://www.rssd.esa.int/Hipparcos/pstex/sect2_02.pdf

Q1 - At page 150 it says:
"Field T11: Trigonometric parallax
The trigonometric parallax, p, is expressed in units of milliarcsec.
The estimated parallax is given for every star, even if it appears to
be insignificant or negative (which may arise when the true parallax
is smaller than its error)."

Am I correct to interpret a negative parallax as a star that is
-likely- to be very far away?

Q2 - And in the same same page:
"Fields T12-13: Proper motion components (epoch J1991.25, ICRS)
The proper motion components, ua* = ua cos d and ud , are
expressed in milliarcsec per Julian year (mas/yr), and are given
with respect to the reference system ICRS.

I don't quite understand that "cosin" based notation. It seems to hint
to the first proper motion component being related and not immediately
orthogonal to the second component.

Can anybody shed some light on these issues?

Thank you!

Manu

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