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Centro de Astrofísica da Universidade do Porto

Finding proto-spectroscopic binaries
Precise multi-epoch radial velocities of 7 protostars in ρ Ophiuchus

P. Viana Almeida, C. Melo, N. C. Santos, P. Figueira, M. Sterzik, J. F. Gameiro

Abstract
The formation of spectroscopic binaries (SB) may be a natural byproduct of star formation. The early dynamical evolution of multiple stellar systems after the initial fragmentation of molecular clouds leaves characteristic imprints on the properties of young, multiple stars. The discovery and the characterization of the youngest SB will allow us to infer the mechanisms and timescales involved in their formation. Our work aims to find spectroscopic companions around young stellar objects (YSO). We present a near-IR high-resolution (R ~ 60000) multi-epoch radial velocity survey of 7 YSO in the star forming region (SFR) ρ Ophiuchus. The radial velocities of each source were derived using a two-dimensional cross-correlation function, using the zero-point established by the Earth’s atmosphere as reference. More than 14 spectral lines in the CO Δν = (0-2) bandhead window were used in the cross-correlation against LTE atmospheric models to compute the final results. We found that the spectra of the protostars in our sample agree well with the predicted stellar photospheric profiles, indicating that the radial velocities derived are indeed of stellar nature. Three of the targets analyzed exhibit large radial velocity variations during the three observation epochs. These objects - pending further confirmation and orbital characteristics - may become the first evidence for proto-spectroscopic binaries, and will provide important constraints on their formation. Our preliminary binary fraction (BF) of ~71% (when merging our results with those of previous studies) is in line with the notion that multiplicity is very high at young ages and therefore a byproduct of star formation.

Keywords
binaries: close – stars: formation – stars: pre-main sequence – binaries: spectroscopic – stars: protostars

Notes
Based on observations collected with the CRIRES spectrograph at the VLT/UT1 8.2-m Antu Telescope (ESO run ID. 081.C-0395(A)) at the Paranal Observatory, Chile.
Table 1 is available in electronic form at http://www.aanda.org

Astronomy and Astrophysics
Volume 539, Page A62_1
March 2012

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