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K. Hulek

Publications and source records attributed to K. Hulek.

22 records · Page 2Linked to original sources
arXiv1994

Degenerations of abelian surfaces and Hodge structures

In this paper the authors consider a certain toroidal compactification of the moduli space of degenerations of (1,p)-polarized abelian surfaces with (canonical) level structure. Using Hodge theory we give a proof that a degenerate abelian surface associated to a corank 1 boundary point is (almost) completely determined by the boundary point. The crucial ingredient in the proof is the Local Invariant Cycle theorem which relates the variation of Hodge structure to the mixed Hodge structure on the singular surface.

alg-geom↗
arXiv1993

Very ample linear systems on abelian varieties

Let $(X,L)$ be a polarized complex abelian variety of dimension $g$ where $L$ is a polarization of type $(1,...,1,d)$. For $(X,L)$ genberic we prove the following: (1) If $d \ge g+2$, then $ϕ_L\colon X \to {\bf P}^{d-1}$ defines a birational morphism onto its image. (2) If $d > 2^g$, then $L$ is very ample. We show the latter by checking it on a suitable rank-$(g-1)$-degeneration.

alg-geom↗
arXiv1993

The Geometry of Bielliptic Surfaces in P^4

In 1988 Serrano \cite{Ser}, using Reider's method, discovered a minimal bielliptic surface in $\PP^4$. Actually he showed that there is a unique family of such surfaces and that they have degree 10 and sectional genus 6. In this paper we describe, among other things, the geometry of the embedding of the minimal bielliptic surfaces. A consequence of this description will be the existence of smooth nonminimal bielliptic surfaces of degree 15 in $\PP^4$. We also explain how to construct the degree 15 surfaces with the help of the quadro-cubic Cremona transformation of $\PP^4$. Finally, we remark that the quintic elliptic scroll and the abelian and bielliptic surfaces of degree 10 and 15 are essentially the only smooth irregular surfaces known in $\PP^4$ (all others can be derived via finite morphisms $\PP^4\to\PP^4 $).

alg-geom↗