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Direct evidence of a sub-stellar companion around CT Chamaeleontis
Aims: In our ongoing search for close and faint companions around TTauri stars in the Chamaeleon star-forming region, we here presentobservations of a new common proper motion companion to the youngT-Tauri star and Chamaeleon member CT Cha and discuss its properties incomparison to other young, low-mass objects and to synthetic modelspectra from different origins. Methods: Common proper motion ofthe companion and CT Cha was confirmed by direct Ks-band imaging datataken with the VLT Adaptive Optics (AO) instrument NACO in February 2006and March 2007, together with a Hipparcos binary for astrometriccalibration. An additional J-band image was taken in March 2007 toobtain color information for a first classification of the companion.Moreover, AO integral field spectroscopy with SINFONI in J, and H+Kbands was obtained to deduce physical parameters of the companion, suchas temperature and extinction. Relative flux calibration of the bandswas achieved using photometry from the NACO imaging data. Results: We found a very faint (Ks = 14.9 mag, Ks0 = 14.4mag) object, just ~2.67´´ northwest of CT Cha correspondingto a projected separation of ~440 AU at 165 ± 30 pc. We show thatCT Cha A and this faint object form a common proper motion pair and thatthe companion is by ?4? significance not a stationarybackground object. The near-infrared spectroscopy yields a temperatureof 2600 ± 250 K for the companion and an optical extinction ofAV = 5.2 ± 0.8 mag, when compared to spectracalculated from Drift-Phoenix model atmospheres. We demonstrate thevalidity of the model fits by comparison to several other well-knownyoung sub-stellar objects. Conclusions: We conclude that the CTCha companion is a very low-mass member of Chamaeleon and very likely aphysical companion to CT Cha, as the probability for a by chancealignment is ?0.01. Due to a prominent Pa-? emission in theJ-band, accretion is probably still ongoing onto the CT Cha companion.From temperature and luminosity (log(L_bol/L?) = -2.68± 0.21), we derive a radius of R = 2.20_-0.60+0.81RJup. We find a consistent mass of M = 17 ± 6MJup for the CT Cha companion from both its luminosity andtemperature when placed on evolutionary tracks. Hence, the CT Chacompanion is most likely a wide brown dwarf companion or possibly even aplanetary mass object.Based on observations made with ESO telescopes at the ParanalObservatory under program IDs 076.C-0292(A), 078.C-0535(A), &279.C-5010(A).Color versions of Figs. 4, 6, 8 and 11 are only available in electronicform at http://www.aanda.org
| The infrared void in the Lupus dark clouds revisited: a polarimetric approach
The results of B-band CCD imaging linear polarimetry obtained for starsfrom the Hipparcos catalogue are used to re-examine the distribution ofthe local interstellar medium towards the IRAS 100-μm emission voidin the Lupus dark clouds. The analysis of the obtainedparallax-polarization diagram assigns to the dark cloud Lupus1 adistance between 130 and 150pc and assures the existence of a low columndensity region coincident with the observed infrared void. Moreover,there are clear indications of the existence of absorbing material atdistances closer than 60-100pc, which may be associated with theinterface boundary between the Local Bubble and its neighbourhood LoopIsuperbubble.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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