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Table 4

Number of systems with WDs components within 20 pc, see also Fig. 3.

Observations

Single WDs WDMS DWD
Resolved Unresolved Resolved Unresolved

Observed 96.5 ± 3.0 19.2 ± 0.4 0.5 ± 0.6 2.1 ± 0.3 1.0 ± 0.1 (5.0 ± 0.8)
86% complete 112 22 0.58 2.4 1.2 (5.8)
In multiples 4.0 ± 0.01 0 1.0 ± 0.0 1.0 ± 0.6 (2.0 ± 0.6 )

BPS models

Single WDs Mergers WDMS DWD
SFH Period distr. CE Resolved Unresolved Resolved Unresolved

BP Abt γα 126 (3.5) 36 (1.9) 30 (0.8) 2.4 (0.21) 20 (0.63) 8.2 (0.40)
αα 43 (2.1) 2.3 (0.21) 4.0 (0.28)
αα2 50 (2.2) 1.3 (0.16) 2.0 (0.20)

BP Lognormal γα 126 (3.5) 15 (1.2) 40 (0.9) 2.5 (0.22) 28 (0.75) 8.0 (0.40)
αα 19 (1.4) 2.4 (0.22) 4.0 (0.28)
αα2 28 (1.7) 1.5 (0.17) 2.3 (0.22)

cSFR Abt γα 89 (0.5) 26 (0.1) 22 (0.23) 1.8 (0.07) 15 (0.06) 6.1 (0.04)
αα 30 (0.1) 1.9 (0.07) 3.1 (0.03)
αα2 38 (0.1) 1.0 (0.05) 1.5 (0.02)

cSFR Lognormal γα 89 (0.5) 12 (0.05) 29 (0.27) 1.9 (0.07) 21 (0.07) 5.8 (0.04)
αα 14 (0.06) 2.0 (0.07) 3.0 (0.03)
αα2 21 (0.07) 1.2 (0.05) 1.7 (0.02)

Notes. The observed sample is based on Giammichele et al. (2012), but see Sect. 2 for adaptations. For unresolved DWDs, we list two numbers. The first number represents confirmed DWD systems, whereas the number in brackets represents the number of confirmed plus candidate DWDs. The third line lists the number of WD systems in triples and quadruples, which are not included in the first line. The evolution of these systems has not been simulated in the BPS models. The different BPS models are described in Sect. 3 and an overview is given in Table 3. The selection effects described in Sect. 3.7 have been applied to the BPS models. Single WDs are formed by single stellar evolution and mergers in binaries. As such, for a given BPS model, the sum of the “Single stars” column and the “Mergers” column should be compared with the observed number of single WDs. The statistical errors on the BPS simulations are given in brackets.

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