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Astron. Astrophys. 343, 806-812 (1999)
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]](img2.gif)
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
Contents
- 1. Introduction
- 2. Observations
- 2.1. Spectroscopy
- 2.2. Astrometry
- 3. Radial velocities
- 4. Spectroscopic orbits
- 5. Rotational velocities
- 6. Helium lines variability
- 7. Galactic rotation
- Acknowledgements
- References
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999
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