8.1 SPY project

The major effort to discover DDs was undertaken by the “ESO Supernovae Ia Progenitors surveY (SPY)” project: a systematic radial velocity survey for DDs with the UVES spectrograph at the ESO VLT (with PI R. Napiwotzky; see [267268373270269Jump To The Next Citation Point] for the details of the project and [269] for the latest published results). The project was aimed at DDs as potential progenitors of type Ia supernovae, but brought as a by-product an immense wealth of data on white dwarfs. More than 1,000 white dwarfs and pre-white dwarfs were observed (practically all white dwarfs brighter than V ≈ 16.5 available for observations from the ESO site in Chile). SPY tremendously increased the number of detected DDs to more than 150. Their system parameters are continuously determined from follow-up observations. Figure 7View Image shows the total masses of the currently known close DDs vs. orbital periods and compares them with the Chandrasekhar mass and the critical periods necessary for merger of components in Hubble time for given M tot (data available in the fall of 2005; R. Napiwotzky, private communication) Altogether, ∼ 5 super-Chandrasekhar total mass DDs are expected to be found by SPY. At the moment, several systems with masses close to the Chandrasekhar limit and merger time shorter than Hubble time, including a probable SN Ia progenitor candidate are already detected. The second candidate super-Chandrasekhar mass binary white dwarf was discovered by Tovmassian et al. [404Jump To The Next Citation Point].
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Figure 7: Known close binaries with two WD components, or a WD and a sd component. Green circles mark systems known prior to the SPY project. Black filled symbols mark the positions of DDs and WD + sd systems detected in the SPY project. A blue triangle marks the positions of the WD component of the binary planetary nebula nucleus PN G135.9+55.9 detected by Tovmassian et al. [404]. (Courtesy R. Napiwotzki.)
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Figure 8: The position of the primary components of known DDs in the “orbital-period–mass” diagram. The underlying gray scale plot is a model prediction from Nelemans et al. [286Jump To The Next Citation Point]. (Figure from [277].)

Figure 8View Image shows the position of the observed components of known DDs vs. the theoretical expectations with account for observational selection effects in the Porbm diagram [288]. The agreement may be considered as quite satisfactory.

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