Context. The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution. Aims. We aim to derive new constraints on the structure of the transition disk MWC 758, to detect non-axisymmetric features and understand their origin. Methods. We obtained infrared polarized intensity observations of the protoplanetary disk MWC 758 with VLT/SPHERE at 1.04 µm to resolve scattered light at a smaller inner working angle (0.093 ) and a higher angular resolution (0.027 ) than previously achieved. Results. We observe polarized scattered light within 0.53 (148 au) down to the inner working angle (26 au) and detect distinct nonaxisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H/r ∼ 0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Conclusions. Our observations reveal the complex morphology of the disk MWC 758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed.

We present J-band imaging and H+K-band low-resolution spectroscopy of the 2MASS1207-3932AB system, obtained with the VLT NIR-AO instrument (NACO). Our J-band astrometry is consistent with AB being a co-moving system, in agreement with the recent results of Chauvin et al. (2005a). For the putative planetary mass secondary, we find J = 20.0±0.2 mag. The shapes of the HK spectra for both components imply low gravity, as expected for this young (5-10 Myr-old) system, as well as a dusty atmosphere for the secondary. Comparisons to the latest synthetic spectra yield T ef f −A ≈ 2550±150K, and T ef f −B ≈ 1600±100K. These temperatures are consistent with the late-M and mid-to-late L spectral types derived earlier for 2M1207A and B respectively. For these T eff , and an age of 5-10 Myrs, the latest theoretical evolutionary tracks imply M A ≈ 24±6 M Jup and M B ≈ 8±2 M Jup . Independent comparisons of the theoretical tracks to the observed colors, spanning ∼I to L ′ (including recent HST photometry), also yield the same mass and temperature estimates. Our mass for the primary agrees with other recent analyses; however, our secondary mass, while still in the planetary regime, is 2-3 times larger than claimed previously. The roots of this discrepancy can be traced directly to the luminosities: while the absolute photometry and M bol of the primary are in excellent agreement with theoretical predictions (especially with the recently derived d = 53±6 pc for the system), the secondary appears ∼ 2.5±0.5 mag fainter than expected in all photometric bands from I to L ′ as well as in M bol . This anomalous under-luminosity accounts for the much lower secondary mass (and temperature) derived in earlier studies. We argue that this effect is highly unlikely to result from: (i) a large -2overestimation of our secondary T eff ; (ii) serious overestimation of luminosities by the theoretical evolutionary models; (iii) very large distance/age variations between the two components; or (iv) faintness in the secondary due to formation via core-accretion. These conclusions are bolstered by the absence of any luminosity problems with the primary in our analysis. Similarly, we find no luminosity discrepancies in the recently discovered sub-stellar companion AB Pic B, which is also young (age ∼30 Myr) and comparable in spectral classification (∼L-type) and temperature (∼1700K) to 2M1207B. We therefore suggest grey extinction in 2M1207B, due to occlusion by an edge-on circum-secondary disk. This scenario is consistent with the observed properties of edge-on disks around T Tauri stars, and with the known presence of a high-inclination evolved disk around the primary. Finally, the system's implied mass ratio of ∼0.3 suggests a binary-like formation scenario.Subject headings: stars: low-mass, brown dwarfs -stars: pre-main sequencestars: formation -circumstellar matter -planetary systems -techniques: spectroscopic what T eff this mass corresponds to, the evolutionary models he uses Baraffe et al. 2003) indicate T eff ∼900-1050K, at the adopted age of...

Context. TW Hya is a classical T Tauri star that shows significant radial-velocity variations in the optical regime. These variations have been attributed to a 10 M Jup planet orbiting the star at 0.04 AU. Aims. The aim of this letter is to confirm the presence of the giant planet around TW Hya by (i) testing whether the observed RV variations can be caused by stellar spots and (ii) analyzing new optical and infrared data to detect the signal of the planet companion. Methods. We fitted the RV variations of TW Hya using a cool spot model. In addition, we obtained new high-resolution optical & infrared spectra, together with optical photometry of TW Hya and compared them with previous data. Results. Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54• can reproduce the reported RV variations. The model also predicts a bisector semi-amplitude variation <10 m s −1 , which is less than the errors of the RV measurements discussed in Setiawan et al. (2008, Nature, 451, 38). The analysis of our new optical RV data, with typical errors of 10 m s −1 , shows a larger RV amplitude that varies depending on the correlation mask used. A slight correlation between the RV variation and the bisector is also observed although not at a very significant level. The infrared H-band RV curve is almost flat, showing a small variation (<35 m s −1 ) that is not consistent with the published optical orbit. All these results support the spot scenario rather than the presence of a hot Jupiter. Finally, the photometric data shows a 20% (peak to peak) variability, which is much larger than the 4% variation expected for the modeled cool spot. The fact that the optical data are correlated with the surface of the cross-correlation function points towards hot spots as being responsible for the photometric variability. Conclusions. We conclude that the best explanation for the RV signal observed in TW Hya is the presence of a cool stellar spot and not an orbiting hot Jupiter.

We present initial results from time-series imaging at infrared wavelengths of 0.9 deg 2 in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 μm data over 40 consecutive days. We extracted light curves with ∼3% photometric accuracy for ∼2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (I c ) and/or near-infrared (JK s ) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5 μm variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs-YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.

Context. T Cha is a young star surrounded by a cold disk. The presence of a gap within its disk, inferred from fitting to the spectral energy distribution, has suggested on-going planetary formation. Aims. The aim of this work is to look for very low-mass companions within the disk gap of T Cha. Methods. We observed T Cha in L and K s with NAOS-CONICA, the adaptive optics system at the VLT, using sparse aperture masking.Results. We detected a source in the L data at a separation of 62 ± 7 mas, position angle of ∼78 ± 1 degrees, and a contrast of ΔL = 5.1 ± 0.2 mag. The object is not detected in the K s band data, which show a 3-σ contrast limit of 5.2 mag at the position of the detected L source. For a distance of 108 pc, the detected companion candidate is located at 6.7 AU from the primary, well within the disk gap. If T Cha and the companion candidate are bound, the comparison of the L and K s photometry with evolutionary tracks shows that the photometry is inconsistent with any unextincted photosphere at the age and distance of T Cha. The detected object shows a very red K s − L color, for which a possible explanation would be a significant amount of dust around it. This would imply that the companion candidate is young, which would strengthen the case for a physical companion, and moreover that the object would be in the substellar regime, according to the K s upper limit. Another exciting possibility would be that this companion is a recently formed planet within the disk. Additional observations are mandatory to confirm that the object is bound and to properly characterize it.

The original article can be found at: http://www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14620.xWe report the discovery of a T8.5 dwarf, which is a companion to the M4 dwarf Wolf 940. [Please see original online abstract for complete version with correct notation

Context. Whilst there is a generally accepted evolutionary scheme for the formation of low-mass stars, the analogous processes when moving down in mass to the brown dwarf regime are not yet well understood. Aims. In this first paper, we try to compile the most complete and unbiased spectroscopically confirmed census of the population of Collinder 69, the central cluster of the Lambda Orionis star forming region, as a first step in addressing the question of how brown dwarfs and planetary mass objects form. Methods. We study age dependent features in optical and near-infrared spectra of candidate members to the cluster (such as alkali lines and accretion-associated indicators). In addition, we complement that study with the analysis of other youth indicators, such as X-ray emission or mid-infrared excess. Results. We confirm the membership to Collinder 69 of ∼90 photometric candidate members. As a byproduct, we determine a temperature scale for young M, very low-mass stars, and brown dwarfs. We assemble one of the most complete initial mass functions from 0.016 to 20 M . Finally, we study the implications of the spatial distribution of the confirmed members for the proposed mechanisms of brown dwarf formation.

Aims. We search for brown dwarfs at the Class 0/I evolutionary stage, or proto brown dwarfs.Methods. We present a multi wavelength study, ranging from optical at 0.8 μm to radio wavelengths at 6 cm, of a cool, very faint, and red multiple object, SSTB213 J041757, detected by Spitzer toward the Barnard 213 dark cloud, in Taurus.Results. The SED of SSTB213 J041757 displays a clear excess at long wavelengths resembling that of a Class I object. The mid-IR source has two possible counterparts, A and B, in the near-IR and optical images, and the 350 μm observations detect clear extended emission, presumably from an envelope around the two sources. The position of A & B in the (Ic − J) versus (J − [3.6]) colour-colour diagram is consistent with them being Galactic sources and not extragalactic contaminants. A proper-motion study confirms this result for A, while it is inconclusive for B. The temperature and mass of the two possible central objects, according to COND evolutionary models, range between 1550−1750 K and 3−4 M Jupiter , and 950−1300 K and 1−2 M Jupiter , for A and B, respectively. The integrated SED provides bolometric temperatures and luminosities of 280 K and 0.0034 L , assuming that the emission at wavelengths >5 μm is associated with component A, and 150 K and 0.0033 L , assuming that the emission at wavelengths >5 μm is associated with component B, which would imply the SSTB213 J041757 object has a luminosity well below the luminosity of other very low luminosity objects discovered up to date. Conclusions. With these characteristics, SSTB213 J041757 seems to be a promising, and perhaps double, proto brown dwarf candidate.