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In mathematics, Enriques surfaces are algebraic surfaces such that the irregularity q = 0 and the canonical line bundle K is non-trivial but has trivial square. Enriques surfaces are all projective (and therefore Kähler over the complex numbers) and are elliptic surfaces of genus 0. Over fields of characteristic not 2 they are quotients of K3 surfaces by a group of order 2 acting without fixed points and their theory is similar to that of algebraic K3 surfaces. Enriques surfaces were first studied in detail by Enriques (1896), though some of the Reye congruences introduced earlier by Reye (1882) are also examples of Enriques surfaces.

Enriques surfaces can also be defined over other fields. Over fields of characteristic other than 2, Artin (1960) showed that the theory is similar to that over the complex numbers. Over fields of characteristic 2 the definition is modified, and there are two new families, called singular and supersingular Enriques surfaces, described by Bombieri & Mumford (1976).

Invariants

The plurigenera Pn are 1 if n is even and 0 if n is odd. The fundamental group has order 2. The second cohomology group H2(X, Z) is isomorphic to the sum of the unique even unimodular lattice II1,9 of dimension 10 and signature -8 and a group of order 2.

Hodge diamond:

1
0 0
0 10 0
0 0
1

Marked Enriques surfaces form a connected 10-dimensional family, which Kondo (1994) showed is rational.

Characteristic 2All Enriques surfaces are elliptic or quasi elliptic.

In characteristic 2 there are some new families of Enriques surfaces, sometimes called quasi Enriques surfaces or non-classical Enriques surfaces or (super)singular Enriques surfaces. In characteristic 2 the definition of Enriques surfaces is modified: they are defined to be minimal surfaces whose canonical class K is numerically equivalent to 0 and whose second Betti number is 10. (In characteristics other than 2 this is equivalent to the usual definition.) There are now 3 families of Enriques surfaces:

All Enriques surfaces are elliptic or quasi elliptic.


Examples

for some general homogeneous polynomial Q of degree 2. Then its normalization is an Enriques surface. This is the family of examples found by Enriques (1896).

See also

list of algebraic surfaces
Enriques–Kodaira classification

References

Artin, Michael (1960), On Enriques surfaces, PhD thesis, Harvard
Compact Complex Surfaces by Wolf P. Barth, Klaus Hulek, Chris A.M. Peters, Antonius Van de Ven ISBN 3-540-00832-2 This is the standard reference book for compact complex surfaces.
Bombieri, Enrico; Mumford, David (1976), "Enriques' classification of surfaces in char. p. III.", Inventiones Mathematicae 35 (1): 197–232, doi:10.1007/BF01390138, ISSN 0020-9910, MR 0491720
Cossec, François R.; Dolgachev, Igor V. (1989), Enriques surfaces. I, Progress in Mathematics 76, Boston: Birkhäuser Boston, ISBN 978-0-8176-3417-9, MR 986969
Enriques, Federigo (1896), "Introduzione alla geometria sopra le superficie algebriche.", Mem. Soc. Ital. delle Scienze 10: 1–81
Enriques, Federigo (1949), Le Superficie Algebriche, Nicola Zanichelli, Bologna, MR 0031770
Kondo, Shigeyuki (1994), "The rationality of the moduli space of Enriques surfaces", Compositio Mathematica 91 (2): 159–173
Reye, T. (1882), Die Geometrie der Lage, Leipzig

External links

Enriques surfaces

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