Using a population synthesis technique , we have calculated detailed models of the present-day field population of objects that have resulted from the merger of a giant primary and a main-sequence or brown dwarf secondary during common-envelope evolution .
We used a grid of 116 stellar and 32 low-mass/brown dwarf models , a crude model of the merger process , and followed the angular momentum evolution of the binary orbit and the primary ’ s rotation prior to merger , as well as the merged object ’ s rotation after the merger .
We find that present-day merged objects that are observable as giant stars or core-helium burning stars in our model population constitute between 0.24 % and 0.33 % of the initial population of ZAMS binaries , depending upon the input parameters chosen .
The median projected rotational velocity of these merged objects is \sim 16 km sec ^ { -1 } , an order of magnitude higher than the median projected rotational velocity in a model population of normal single stars calculated using the same stellar models and initial mass function .
The masses of the merged objects are typically less than \sim 2 M _ { \odot } , with a median mass of 1.28 M _ { \odot } , which is slightly more than , but not significantly different from , their normal single star counterparts .
The luminosities in our merged object population range from \sim 10 - 100 L _ { \odot } , with a strong peak in the luminosity distribution at \sim 60 L _ { \odot } , since the majority of the merged objects ( 57 % ) lie on the horizontal branch at the present epoch .
The results of our population synthesis study are discussed in terms of possible observational counterparts either directly involving the high rotational velocity of the merger product or indirectly , via the effect of rotation on envelope abundances and on the amount and distribution of circumstellar matter .