1. Department of Astronomy, University of Barcelona, Marti i Franques 1, E-08028 Barcelona, Spain
2. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
3. European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
4. Isaac Newton Group, PO Box 321, Santa Cruz de La Palma, Tenerife, Canary Islands, E-38780 Spain
5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
6. Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, California 94720-3411, USA
7. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
8. Department of Physics, Stockholm University, AlbaNova University Center, SE-108 91 Stockholm, Sweden
9. Observatoire de Strasbourg, 11, rue de l'Université, F-67000 Strasbourg, France

Correspondence to: Pilar Ruiz-Lapuente^1,2 Email: pilar@am.ub.es

Abstract

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion^{1, 2, 3}. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova^{4, 5} is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0–G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.

1. Department of Astronomy, University of Barcelona, Marti i Franques 1, E-08028 Barcelona, Spain
2. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
3. European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
4. Isaac Newton Group, PO Box 321, Santa Cruz de La Palma, Tenerife, Canary Islands, E-38780 Spain
5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
6. Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, California 94720-3411, USA
7. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
8. Department of Physics, Stockholm University, AlbaNova University Center, SE-108 91 Stockholm, Sweden
9. Observatoire de Strasbourg, 11, rue de l'Université, F-67000 Strasbourg, France

Correspondence to: Pilar Ruiz-Lapuente^1,2 Email: pilar@am.ub.es

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