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Edge-on disk around the T Tauri star [MR81] H? 17 NE in Corona Australis
Aims: Using the speckle camera SHARP at the 3.5 m ESO NTT, Köhlerand collaborators found an object ˜ 3.5 mag fainter in K only1.3'' north-east of the T Tauri star [MR81] H? 17 in the CoronaAustralis (CrA) star-forming region, which could be either a brown dwarfor a T Tauri star with an edge-on disk. We attempt to study this faintobject in detail. Methods: We acquired deep VLT NACOnear-infrared images at three epochs to determine, whether [MR81]H? 17 and the nearby faint object are comoving and to measure theinfrared colors of both objects. We obtained optical and infraredspectra of both objects with the VLT using FORS and ISAAC, respectively,to determine spectral types and temperatures as well as ages and masses. Results: The T Tauri star [MR81] H? 17 and the faint nearbyobject have a projected separation of 1369.58 mas, i.e. 178 AU at 130pc. They share the same proper motion (~ 5 ?), so that they mostcertainly form a bound binary pair. The apparently fainter component[MR81] H? 17 NE has a spectral type of M2e, while the apparentlybrighter component [MR81] H? 17 SW, the previously known T Tauristar, has a spectral type of M4-5e. We can identify a nearly edge-ondisk around [MR81] H? 17 NE by visual inspection, which has adiameter of at least 30 to 50 AU. We are able to detect strong emissionlines in [MR81] H? 17 NE, which are almost certainly due toongoing accretion. The NE object is detectable only by means of itsscattered light. Conclusions: If both objects are co-eval (2-3Myr) and located at the same distance (˜ 130 pc as CrA), then theapparently fainter [MR81] H? 17 NE is more massive (primary)component with a nearly edge-on disk and the apparently brigthercomponent [MR81] H? 17 SW is less massive (companion). Both arelow-mass T Tauri stars with masses of ˜ 0.5 and 0.23 ± 0.05M?, respectively.Based on observations collected at the European Southern Observatory,Chile in runs 67.C-0213, 71.C-0206(D), 71.C-0522(B), 073.C-0164(A),073.C-0167(B) and 081.C-0393(A).
| 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
| Confirmation of the binary status of Chamaeleon H? 2 - a very young low-mass binary in Chamaeleon
Context: Neuhäuser & Comerón (1998, Science, 282, 83;1999, A&A, 350, 612) presented direct imaging evidence, as well asfirst spectra, of several young stellar and sub-stellar M6- to M8-typeobjects in the Cha I dark cloud. One of these objects is Cha H? 2,classified as brown dwarf candidate in several publications andsuggested as possible binary in Neuhäuser et al. (2002, A&A,384, 999). Aims: We have searched around Cha H? 2 for closeand faint companions with adaptive optics imaging. Methods: Twoepochs of direct imaging data were taken with the Very Large Telescope(VLT) Adaptive Optics instrument NACO in February 2006 and March 2007 inKs-band together with a Hipparcos binary for astrometric calibration.Moreover, we took a J-band image in March 2007 to get color information.We retrieved an earlier image from 2005 from the European SouthernObservatory (ESO) Science Archive Facility, increasing the availabletime coverage. After confirmation of common proper motion, we deducephysical parameters of the objects by spectroscopy, like temperature andmass. Results: We find Cha H? 2 to be a very close binaryof 0.16 arcsec separation, having a flux ratio of 0.91, thus havingalmost equal brightness and indistinguishable spectral types within theerrors. We show that the two tentative components of Cha H? 2 forma common proper motion pair, and that neither component is a non-movingbackground object. We even find evidence for orbital motion. A combinedspectrum of both stars spanning optical and near-infrared parts of thespectral energy distribution yields a temperature of 3000 ± 100K, corresponding to a spectral type of M6 ± 1 and a surfacegravity of log{g} = 4.0+0.75-0.5, both from acomparison with GAIA model atmospheres. Furthermore, we obtained anoptical extinction of AV ? 4.3 mag from this comparison.Conclusions: We derive masses of 0.110 M?(?0.070 M?) and 0.124 M? (?0.077M?) for the two components of Cha H? 2, i.e.,probably low-mass stars, but one component could possibly be a browndwarf.Based on observations made with ESO telescopes at the ParanalObservatory under programme IDs 076.C-0292A, 076.C-0339B, 078.C-0535A,at the La Silla Observatory under programme ID 065.L-0144B, the HubbleSpace Telescope under programme ID GO-8716 and on observations made withthe European Southern Observatory telescopes obtained from theESO/ST-ECF Science Archive Facility.Color version of Fig. [see full textsee full text] is only available inelectronic form athttp://www.aanda.org
| Astrometric and photometric monitoring of GQ Lupi and its sub-stellar companion
Context: Neuhäuser et al. (2005, A&A, 435, L13) presenteddirect imaging evidence for a sub-stellar companion to the young T Tauristar GQ Lupi. Common proper motion was highly significant, but noorbital motion was detected. Faint luminosity, low gravity, and alate-M/early-L spectral type indicated that the companion is either aplanet or a brown dwarf. Aims: We have monitored GQ Lupi and itscompanion in order to detect orbital and parallactic motion andvariability in its brightness. We also search for closer and faintercompanions. Methods: We have taken six more images with the VLTAdaptive Optics instrument NACO from May 2005 to Feb. 2007, always withthe same calibration binary from Hipparcos for both astrometric andphotometric calibration. By adding up all the images taken so far, wesearch for additional companions. Results: The position of GQLupi A and its companion compared to a nearby non-moving backgroundobject varies as expected for parallactic motion by about one pixel (2\cdot ? with parallax ?). We could not find evidence forvariability of the GQ Lupi companion in the K_s-band (standard deviationbeing ±0.08 mag), which may be due to large error bars. Noadditional companions are found with deep imaging. Conclusions:There is now exceedingly high significance for common proper motion ofGQ Lupi A and its companion. In addition, we see for the first time anindication for orbital motion ( 2 to 3 mas/yr decrease in separation,but no significant change in the position angle), consistent with a nearedge-on or highly eccentric orbit. We measured the parallax for GQ LupiA to be ? = 6.4 ± 1.9 mas (i.e. 156 ± 50 pc) and forthe GQ Lupi companion to be 7.2 ± 2.1 mas (i.e. 139 ± 45pc), both consistent with being in the Lupus I cloud and bound to eachother.Based on observations collected at the European Southern Observatory,Chile in runs 073.C-0164, 075.C-0710C, 076.C-0339B, 077.C-0264B,078.C-0552B, and 078.C-0535A.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| Photographic observations of visual double stars
Photographic observations of 238 pairs of visual binaries obtained on770 plates using the 60-cm visual refractor of Bosscha Observatory(Lembang, Java) during 1976-1979 are reported, continuing the catalog ofvan Albada-van Dien (1983). The data-reduction procedures are brieflydescribed, and the data are presented in a table.
| Photographic observations of visual double stars
Mean positions, the corresponding epochs, relative separations, positionangles, and mean errors are presented for 95 pairs of visual doublestars, mostly in the Southern Hemisphere. The results were obtained bymeasuring plates taken with the 60-cm visual refractor of BosschaObservatory, Lembang, Indonesia, over a 16-yr period. The reductionmethod used in determining the mean positions, epochs, and errors isdiscussed.
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