We obtained deep images of G 196-3 B and VHS J1256-1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter ...Array (ALMA) and Very Large Array (VLA) data of VHS J1256-1257 b at 0.87 mm and 0.9 cm, respectively. Neither G 196-3 B nor VHS J1256-1257 b were detected in the NOEMA, ALMA and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G 196-3 B) and 0.153 mJy (VHS J1256-1257 b) with a 3-sigma confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 0.016 M\(_{\rm Earth}\) and 0.004 M\(_{\rm Earth}\) for the mass of any cold dust that might be surrounding G 196-3 B and VHS J1256-1257 b, respectively. We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20 M\(_{\rm Jupiter}\) and ages between 1 and a few hundred million years. Only two very young objects are detected out of a few tens concluding, as other groups did before, that the disks around these very low-mass objects must have small masses and possibly reduced sizes. If debris disks around substellar objects scale down in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper for being able to detect and characterize their surrounding debris disks.
The substellar triple system VHS J125601.92\(-\)125723.9 is composed by an equal-mass M7.5 brown dwarf binary and a L7 low-mass substellar object. In this work, we aim to identify the origin of the ...radio emission occurring in the central binary of VHS 1256\(-\)1257 while discussing the expected mechanisms involved in the radio emission of ultracool dwarfs (UCDs). We observed this system with the Karl G. Jansky Very Large Array, the European very-long-baseline interferometry (VLBI) Network, the enhanced Multi Element Remotely Linked Interferometer Network, the NOrthern Extended Millimeter Array, and the Atacama Large Millimetre Array at frequencies ranging from 5 GHz up to 345 GHz in several epochs during 2017, 2018, and 2019. We have found radio emission at 6 GHz and 33 GHz coincident with the expected position of the central binary of VHS~1256\(-\)1257. The Stokes I density flux detected were 73 \(\pm\) 4 \(\mu\)Jy and 83 \(\pm\) 13 \(\mu\)Jy, respectively, with no detectable circular polarisation or pulses. No emission is detected at higher frequencies (230 GHz and 345 GHz) nor at 5 GHz with VLBI arrays. The emission appears to be stable over almost 3 years at 6 GHz. To explain the constraints obtained both from the detections and non-detections we considered multiple scenarios including thermal and non-thermal emission, and different contributions from each component of the binary. Our results can be well explained by non-thermal gyrosynchrotron emission originating at radiation belts with a low plasma density (n\(_e\) = 300\(-\)700 cm\(^{-3}\)), a moderate magnetic field strength (B \(\approx\) 140 G), and an energy distribution of electrons following a power-law (\(d N / d E \propto E^{- \delta}\)) with \(\delta\) fixed at 1.36. These radiation belts would need to be present in both components and also be viewed equatorially.
Aims: Our objective is the optical and near-infrared spectroscopic characterisation of 2MASS J0249-0557 c, a recently discovered young planetary mass companion to the \(\beta\) Pictoris member 2MASS ...J0249-0557. Methods: Using the Visible and Infrared Survey Telescope for Astronomy (VISTA) Hemisphere Survey (VHS) and the Two Micron All Sky Survey (2MASS) data, we independently identified the companion 2MASS J0249-0557 c. We obtained low-resolution optical spectroscopy of this object using the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy (OSIRIS) spectrograph at the Gran Telescopio Canarias (GTC), and near-infrared spectroscopy using the Son of Isaac (SofI) spectrograph on the New Technology Telescope (NTT). Results: We classified 2MASS J0249-0557 c with a spectral type of L2.5\(\pm\)0.5 in the optical and L3\(\pm\)1 in the near-infrared. We identified spectroscopic indicators of youth that are compatible with the age of the \(\beta\) Pictoris moving group. We also detect a strong H\(\alpha\) emission, with a pEW of -90\(^{+20}_{-40}\)A, which seems persistent in time. This indicates strong chromospheric activity or disk accretion. Although many M-type brown dwarfs have strong H\(\alpha\) emission, this target is one of the very few L-type planetary mass objects in which this strong H\(\alpha\) emission has been detected. Lithium absorption at 6708 A is observed with pEW \(\lesssim\) 5A. We also computed the binding energy of 2MASS J0249-0557 c and obtained an (absolute) upper limit of \(U=(-8.8\pm4.4) 10^{32}\) J. Conclusions: Similarly to other young brown dwarfs and isolated planetary mass objects, strong H\(\alpha\) emission is also present in young planetary mass companions at ages of some dozen million years. We also found that 2MASS J0249-0557 c is one of the wide substellar companions with the lowest binding energy known to date.
We demonstrate that the previously identified L/T transition brown dwarf SDSS J213154.43-011939.3 (SDSS 2131-0119) is a widely separated (82.3'', \(\sim\)3830 au) common proper motion companion to ...the low-mass star NLTT 51469, which we reveal to be a close binary itself, separated by 0.64''\(\pm\)0.01'' (\(\sim\)30 au). We find the proper motion of SDSS 2131-0119 of \(\mu_{\alpha}\cos\delta=-100\pm20\), \(\mu_{\delta}=-230\pm20\) mas/yr consistent with the proper motion of the primary provided by Gaia DR2: \(\mu_{\alpha}\cos\delta=-95.49\pm0.96\), \(\mu_{\delta}=-239.38\pm0.96\) mas/yr. Based on optical and near-infrared spectroscopy we classify NLTT 51469A as a M3\(\pm\)1 dwarf, estimate photometrically the spectral type of its close companion NLTT 51469B at \(\sim\)M6 and confirm the spectral type of the brown dwarf to be L9\(\pm\)1. Using radial velocity, proper motion and parallax we derived the \(UVW\) space velocities of NLTT 51469A, showing that the system does not belong to any known young stellar moving group. The high \(V, W\) velocities, lack of 670.8 nm Li I absorption line, and absence of H\(\alpha\) emission, detected X-rays or UV excess, indicate that the system is likely a member of the thin disk population and is older than 1 Gyr. For the parallactic distance of \(46.6\pm1.6\) pc from Gaia DR2 we determined luminosities of \(-1.50^{+0.02}_{-0.04}\) and \(-4.4\pm0.1\) dex of the M3 and L9, respectively. Considering the spectrophotometric estimation which yields a slightly lower distance of \(34^{+10}_{-13}\) pc the obtained luminosities are \(-1.78^{+0.02}_{-0.04}\) and \(-4.7^{+0.3}_{-0.5}\) dex. We also estimated their effective temperatures and masses, and obtained 3410\(^{+140}_{-210}\) K and \(0.42\pm0.02 M_{\odot}\) for the primary, and 1400-1650 K and \(0.05-0.07 M_{\odot}\) for the wide companion. For the \(\sim\)M6 component we estimated \(T_{eff}=2850\pm200 K\) and \(m=0.10^{+0.06}_{-0.01} M_{\odot}\).
We present the results of a four-month, spectroscopic campaign of the Wolf-Rayet dust-making binary, WR137. We detect only small-amplitude, random variability in the CIII5696 emission line and its ...integrated quantities (radial velocity, equivalent width, skewness, kurtosis) that can be explained by stochastic clumps in the wind of the WC star. We find no evidence of large-scale, periodic variations often associated with Corotating Interaction Regions that could have explained the observed intrinsic continuum polarization of this star. Our moderately high-resolution and high signal-to-noise average Keck spectrum shows narrow double-peak emission profiles in the Halpha, Hbeta, Hgamma, HeII6678 and HeII5876 lines. These peaks have a stable blue-to-red intensity ratio with a mean of 0.997 and a root-mean-square of 0.004, commensurate with the noise level; no variability is found during the entire observing period. We suggest that these profiles arise in a decretion disk around the O9 companion, which is thus an O9e star. The characteristics of the profiles are compatible with those of other Be/Oe stars. The presence of this disk can explain the constant component of the continuum polarization of this system, for which the angle is perpendicular to the plane of the orbit, implying that the rotation axis of the O9e star is aligned with that of the orbit. It remains to be explained why the disk is so stable within the strong ultraviolet radiation field of the O star. We present a binary evolutionary scenario that is compatible with the current stellar and system parameters.
With the purpose to investigate the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92\(-\)125723.9 (hereafter VHS ...1256\(-\)1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8\,pc. We observed in phase-reference mode the system VHS 1256\(-\)1257 with the Karl G. Jansky Very Large Array at \(X\)- and \(L\)- band and with the European VLBI Network at \(L\)-band in several epochs during 2015 and 2016. We discovered radio emission at \(X\)-band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 \(\mu\)Jy. We determined a spectral index \(\alpha = -1.1 \pm 0.3\) between 8 and 12 GHz, suggesting that non-thermal, optically-thin, synchrotron or gyrosynchrotron radiation is responsible for the observed radio emission. Interestingly, no signal is seen at \(L\)-band where we set a 3-\(\sigma\) upper limit of 20 \(\mu\)Jy. This might be explained by strong variability of the binary or self-absorption at this frequency. By adopting the latter scenario and gyrosynchrotron radiation, we constrain the turnover frequency to be in the interval 5--8.5 GHz, from which we infer the presence of kG-intense magnetic fields in the M7.5 binary. Our data impose a 3-\(\sigma\) upper bound to the radio flux density of the L7 object of 9 \(\mu\)Jy at 10\,GHz.
Aims: We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES ...exoplanet survey. Methods: We obtained high-resolution images in the I band with the lucky imaging instrument FastCam at the 1.5 m Telescopio Carlos Sanchez for 490 mid- to late-M dwarfs. For all the detected binaries, we measured angular separations, position angles, and magnitude differences in the I band. We also calculated the masses of each individual component and estimated orbital periods, using the available magnitude and colour relations for M dwarfs and our own MJ-spectral type and mass-MI relations. To avoid biases in our sample selection, we built a volume-limited sample of M0.0-M5.0 dwarfs that is complete up to 86% within 14 pc. Results: From the 490 observed stars, we detected 80 companions in 76 systems, of which 30 are new discoveries. The multiplicity fraction in our observed sample is 16.7+-2.0% . In our volume-limited sample it is 19.5+-2.3% for angular separations of 0.2 to 5.0 arcsec (1.4-65.6 au), The distribution of the projected physical separations peaks at 2.5-7.5 au. For M0.0-M3.5 V primaries, our search is sensitive to mass ratios higher than 0.3. Binaries with projected physical separations shorter than 50 au tend to be of equal mass. For 26 of our systems, we estimated orbital periods shorter than 50 a, 10 of which are presented here for the first time. We measured variations in angular separation and position angle that are due to orbital motions in 17 of these systems. The contribution of binaries and multiples with angular separations shorter than 0.2 arcsec, longer than 5.0 arcsec, and of spectroscopic binaries identified from previous searches, although not complete, may increase the multiplicity fraction of M dwarfs in our volume-limited sample to at least 36%.
We have performed mid-infrared imaging of Barnard's Star, one of the nearest stars to the Sun, using CanariCam on the 10.4 m Gran Telescopio Canarias. We aim to investigate an area within 1-10 arcsec ...separations, which for the 1.83 pc distance of the star translates to projected orbital separations of 1.8-18 AU (P > 12 yr), which have not been explored yet with astrometry or radial velocity programs. It is therefore an opportunity to enter the domain of distances where most giant planets are expected to form. We performed deep imaging in the N-band window (Si-2 filter, 8.7 {\mu}m) reaching a 3{\sigma} detection limit of 0.85+/-0.18 mJy and angular resolution of 0.24 arcsec, close to the diffraction limit of the telescope at this wavelength. A total of 80 min on-source integration time data were collected and combined for the deepest image. We achieved a dynamical range of 8.0+/-0.1 mag in the 8.7 {\mu}m band, at angular separations from ~2 to 10 arcsec and of ~6-8 mag at 1-2 arcsec. No additional sources were found. Our detectability limits provide further constraints to the presence of substellar companions of the Barnard's Star. According to solar metallicity evolutionary models, we can exclude companions of masses larger than 15 MJup (Teff > 400 K), ages of a few Gyr, and located in ~3.6-18 AU orbits with a 3{\sigma} confidence level. This minimum mass is approximately 5 MJup smaller than any previous imaging survey that explored the surroundings of Barnard's Star could restrict.
The aim of the project is to improve our knowledge on the multiplicity of planet-host stars at wide physical separations. We cross-matched approximately 6200 square degree area of the Southern sky ...imaged by the Visible Infrared Survey Telescope for Astronomy (VISTA) Hemisphere Survey (VHS) with the Two Micron All Sky Survey (2MASS) to look for wide common proper motion companions to known planet-host stars. We complemented our astrometric search with photometric criteria. We confirmed spectroscopically the co-moving nature of seven sources out of 16 companion candidates and discarded eight, while the remaining one stays as a candidate. Among these new wide companions to planet-host stars, we discovered a T4.5 dwarf companion at 6.3 arcmin (~9000 au) from HIP70849, a K7V star which hosts a 9 Jupiter mass planet with an eccentric orbit. We also report two new stellar M dwarf companions to one G and one metal-rich K star. We infer stellar and substellar binary frequencies for our complete sample of 37 targets of 5.4+/-3.8% and 2.7+/-2.7% (1 sigma confidence level), respectively, for projected physical separations larger than ~60-160 au assuming the range of distances of planet-host stars (24-75 pc). These values are comparable to the frequencies of non planet-host stars. We find that the period-eccentricity trend holds with a lack of multiple systems with planets at large eccentricities (e > 0.2) for periods less than 40 days. However, the lack of planets more massive than 2.5 Jupiter masses and short periods (<40 days) orbiting single stars is not so obvious due to recent discoveries by ground-based transit surveys and space missions.
The aim of the project is to find the stars nearest to the Sun and to contribute to the completion of the stellar and substellar census of the solar neighbourhood. We identified a new late-M dwarf ...within 5 pc, looking for high proper motion sources in the 2MASS-WISE cross-match. We collected astrometric and photometric data available from public large-scale surveys. We complemented this information with low-resolution optical and near-infrared spectroscopy with instrumentation on the ESO NTT to confirm the nature of our candidate. We also present a high-quality medium-resolution VLT/X-shooter spectrum covering the 400 to 2500 nm wavelength range. We classify this new neighbour as an M7.0\(\pm\)0.5 dwarf using spectral templates from the Sloan Digital Sky Survey and spectral indices. Lithium absorption at 670.8 nm is not detected in the X-shooter spectrum, indicating that the M7 dwarf is older than 600 Myr and more massive than 0.06 M\(_{\odot}\). We also derive a trigonometric distance of 4.4 pc, in agreement with the spectroscopic distance estimate, making 2MASS\,J154043.42\(-\)510135.7 the nearest M7 dwarf to the Sun. This trigonometric distance is somewhat closer than the \(\sim\)6 pc distance reported by the ALLWISE team, who independently identified this object recently. This discovery represents an increase of 25\% in the number of M7--M8 dwarfs already known at distances closer than 8\,pc from our Sun. We derive a density of \(\rho\)\,=\,1.9\(\pm\)0.9\(\times\)10\(^{-3}\)\,pc\(^{-3}\) for M7 dwarfs in the 8 pc volume, a value similar to those quoted in the literature. This new ultracool dwarf is among the 50 nearest systems to the Sun, demonstrating that our current knowledge of the stellar census within the 5 pc sample remains incomplete. 2M1540 represents a unique opportunity to search for extrasolar planets around ultracool dwarfs due to its proximity and brightness.
