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Astron. Astrophys. 343, 806-812 (1999)

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Kinematics and binaries in young stellar aggregates *

I. The trapezium system BD+00°1617 in Bochum 2

Ulisse Munari 1 and Lina Tomasella 2

1 Osservatorio Astronomico di Padova, Sede di Asiago, I-36012 Asiago (VI), Italy (munari@pd.astro.it)
2 Osservatorio Astrofisico del Dipartimento di Astronomia, Università di Padova, I-36012 Asiago (VI), Italy (tomasella@pd.astro.it)

Received 9 July 1998 / Accepted 24 November 1998

Abstract

Internal kinematics, spectroscopic binaries and galactic motion are investigated for the trapezium system BD+[FORMULA]1617 (which lies at the heart of the young open cluster Bochum 2) by means of 73 high resolution Echelle+CCD spectra secured over the period 1994-98. Two of the three O-type member stars are found to be binaries on close and highly eccentric orbits of 6.8 and 11.0 day period. The spectra of the two binaries show large variations in the half-intensity and equivalent widths of the HeI absorption lines, which are intrinsic to the primaries and are not correlated to the orbital phase. Astrometric and radial velocities exclude that one of the component is leaving as a runaway star, but upper limits are still compatible with the trapezium evaporating at very low relative velocities. The projected rotational velocities of the three constituent O-type stars are low. This conforms to expectations from the high frequency of binaries. The observed radial velocity of Bochum 2 agrees with Hron (1987) expression for the Galaxy rotation inside the latter's quoted errors.

Key words: stars: binaries: spectroscopic – stars: early-type – stars: fundamental parameters – stars: individual: BD+00O 1617 – stars: kinematics – Galaxy: open clusters and associations: individual: Bochum 2

* Tables 2 and 3 are only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr/pubs/cats/J/A+A/343/806 (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/343/806

Send offprint requests to: U. Munari

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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