http://arxiv.org/abs/1808.07889
The distributions of the initial main-sequence binary parameters are one of the key ingredients in obtaining evolutionary predictions for compact binary (BH-BH / BH-NS / NS-NS) merger rates. Until now, such calculations were done under the assumption that initial binary parameter distributions were independent. Here we implement the empirically derived inter-correlated distributions of initial binary parameters: primary mass (M1), mass ratio (q), orbital period (P) and eccentricity (e). Unexpectedly, the introduction of inter-correlated initial binary parameters leads to only a small decrease in the predicted merger rates by a factor of 2 $-$ 3, depending on the merger type, relative to the previously used non-correlated initial distributions. Formation of compact object mergers in the isolated classical binary evolution favors initial binaries with stars of comparable masses (q = 0.5 $-$ 1) at intermediate orbital periods (log P (days) = 2 $-$ 4). New distributions slightly shift the mass ratios towards smaller values with respect to the previously used flat q distribution, which is the dominant effect decreasing the rates. New orbital periods (1.3 more initial systems within log P (days) = 2 $-$ 4), together with new eccentricities, only negligibly increase the number of progenitors. Additionally, we discuss the uncertainty of merger rate predictions associated with possible variations of the massive-star initial mass function (IMF). We argue that evolutionary calculations should be normalized to a star formation rate (SFR) that is obtained from the observed amount of UV light at wavelength 1500{\AA} (SFR indicator). In this case, contrary to recent reports, the uncertainty of the IMF does not affect the rates by more than a factor of 2. Any change to the IMF slope for massive stars requires a change of SFR in a way that counteracts the impact of IMF variations on the merger rates.
J. Klencki, M. Moe, W. Gladysz, et. al.
Mon, 27 Aug 18
22/46
Comments: resubmitted to A&A after a minor review
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