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 [267, 268, 373, 270, 269
] 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
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 7 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
(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. [404
].
Figure 8 shows the position of the observed components of known DDs vs. the theoretical expectations
with account for observational selection effects in the
–
diagram [288]. The agreement may be
considered as quite satisfactory.