The bicanonical map of surfaces with $p_g=0$ and $K^2 \geq 7$

M. Mendes Lopes; R. Pardini

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arXiv · math/9910074

The bicanonical map of surfaces with $p_g=0$ and $K^2 \geq 7$

M. Mendes Lopes·R. Pardini

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Abstract

A minimal surface of general type with $p_g(S)=0$ satisfies $1\le K^2\le 9$ and it is known that the image of the bicanonical map $\fie$ is a surface for $K_S^2\geq 2$, whilst for $K^2_S\geq 5$, the bicanonical map is always a morphism. In this paper it is shown that $\fie$ is birational if $K_S^2=9$ and that the degree of $\fie$ is at most 2 if $K_S^2=7$ or $K_S^2=8$. By presenting two examples of surfaces $S$ with $K_S^2=7$ and 8 and bicanonical map of degree 2, it is also shown that this result is sharp. The example with $K_S^2=8$ is, to our knowledge, a new example of a surface of general type with $p_g=0$.

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BibTeX RIS

M. Mendes Lopes, R. Pardini. 2000-09-18. The bicanonical map of surfaces with $p_g=0$ and $K^2 \geq 7$. https://arxiv.org/abs/math/9910074

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