Multiplicity of stars as a function of mass

• Applicant: Dr. Klaus Fuhrmann
• Subject Area: Astrophysics and Astronomy
• Term: from 2010 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 163865239

Although it is usually asserted that most stars form as binaries, more recent investigations on low-mass stars suggest that M-, L- and T-type dwarfs are mostly single. Being the dominant population by number, this has even led to the suggestion that the majority of all hydrogen-burning stars in the Milky Way Galaxy are single. However, the considerable observational progress in recent years has also brought to light that up to about one quarter of all stars may consist of higher level star systems; this fraction is believed to be even much higher as indicated by massive stars in the Orion Trapezium. Thus, hierarchical multiples appear to be an important part of general star formation and it is a key question to what extent the stellar mass is involved.It is proposed to investigate the multiplicity fraction for stars in the mass range of 0.8 - 100 M☉ based on about 1000 stars with high-resolution spectroscopy. The southern sample consists of all (~ 250) O stars from the compilation of Galactic O Stars as well as of 260 B and 170 F/G stars, all to be observed by multi-epoch spectroscopy. The northern sample comprises about 350 nearby F- and G-type stars where high-resolution spectra have already been taken. Apart from the O stars, all objects form unbiased and volume-complete samples taken from the Hipparcos archive.From the data we wish to obtain the fraction of the SB1 and SB2 systems as a function of stellar mass. We intend to determine the spectral types and/or the basic stellar parameters of the stars and shall relate these data in terms of the derived stellar multiplicities, metallicities and masses.

• DFG Programme: Research Grants