We have recently identified a young, very red (J − Ks = 2.47 mag) late L-type companion at 8.06” ± 0.03” (~102 AU) from a previously unrecognized M dwarf. We determined the parallactic distance of ...the system to be 12.7±1.0 pc. Non-detection of lithium and the kinematics of the primary allowed us to constrain the age of the system in the range of 150–300 Myr. By comparison with theoretical evolutionary models we derived a mass of 73+20−15MJup for the primary, at around the substellar mass regime and 11.2+9.7−1.8MJup for the secondary, near the deuterium burning mass limit.
Context.
The substellar triple system VHS J125601.92−125723.9 (hereafter VHS 1256−1257) is composed of an equal-mass M7.5 brown dwarf binary and an L7 low-mass substellar object. In Guirado et al. ...(2018, A&A, 610, A23) we published the detection of radio emission at 8.4 GHz coming from the central binary and making it an excellent target for further observations.
Aims.
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 ultra-cool dwarfs.
Methods.
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.
Results.
We 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 fluxes detected were 73 ± 4 μJy and 83 ± 13 μJy, 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 three years at 6 GHz. To explain the constraints obtained both from the detections and non-detections, we considered multiple scenarios including thermal and nonthermal emission, and different contributions from each component of the binary.
Conclusions.
Our results can be well explained by nonthermal gyrosynchrotron emission originating at radiation belts with a low plasma density (
n
e
= 300−700 cm
−3
), a moderate magnetic field strength (
B
≈ 140 G), and an energy distribution of electrons following a power-law (d
N
/d
E
∝
E
−
δ
) with
δ
fixed at 1.36. These radiation belts would need to be present in both components and also be viewed equatorially.
The aim of the project is to find the stars closest 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 European Southern Observatory New Technology Telescope 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. This new ultracool dwarf is among the 50 closest 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.
Aims. The aim of the project is to find the stars closest to the Sun and to contribute to the completion of the stellar and substellar census of the solar neighbourhood. Methods. 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 (R ~ 500) optical (600–1000 nm) and near-infrared (900–2500 nm) spectroscopy with instrumentation on the European Southern Observatory New Technology Telescope 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. Results. We classify this new neighbour as an M7.0 ± 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⊙. We also derive a trigonometric distance of 4.4+0.5-0.4 pc, in agreement with the spectroscopic distance estimate, making 2MASS J154043.42−510135.7 (2M1540) the nearest M7 dwarf to the Sun. This trigonometric distance is somewhat closer than the ~6 pc distance reported by the ALLWISE team, who independently identified this object recently. This discovery represents an increase by 25% in the number of M7–M8 dwarfs already known at distances closer than 8 pc from our Sun. We derive a density of ρ = 1.9 ± 0.9 × 10-3 pc-3 for M7 dwarfs in the 8 pc volume, a value similar to those quoted in the literature. Conclusions. This new ultracool dwarf is among the 50 closest 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.
CARMENES input catalogue of M dwarfs Cortés-Contreras, M.; Béjar, V. J. S.; Caballero, J. A. ...
Astronomy and astrophysics (Berlin),
2016, Letnik:
597
Journal Article
Recenzirano
Odprti dostop
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 Sánchez 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. Another six companion candidates require additional astrometry to confirm physical binding. The multiplicity fraction in our observed sample is 16.7 ± 2.0%. The bias-corrected multiplicity fraction in our volume-limited sample is 19.5 ± 2.3% for angular separations of 0.2 to 5.0 arcsec (1.4−65.6 au), with a peak in the distribution of the projected physical separations at 2.5−7.5 au. For M0.0-M3.5 V primaries, our search is sensitive to mass ratios higher than 0.3 and there is a higher density of pairs with mass ratios over 0.8 compared to those at lower mass ratios. Binaries with projected physical separations shorter than 50 au also 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%.
Aims. The aim of the project is to improve our knowledge on the multiplicity of planet-host stars at wide physical separations. Methods. 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. Results. 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 HIP 70849, 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% (1σ 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.
A&A 645, A17 (2021) 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.
Our goal is to characterise the physical properties of the metal-poor brown dwarf population. In particular, we focus on the recently discovered peculiar dwarf WISE J1810055\(-\)1010023. We collected ...optical iz and near-infrared J-band imaging on multiple occasions over 1.5 years to derive accurate trigonometric parallax and proper motion of the metal-depleted ultra-cool dwarf candidate WISE1810. We also acquired low-resolution optical spectroscopy (0.6\(-\)1.0 \(\mu\)m) and new infrared (0.9\(-\)1.3 \(\mu\)m) spectra of WISE1810 that were combined with our photometry, other existing data from the literature and our trigonometric distance to determine the object's luminosity from the integration of the observed spectral energy distribution covering from 0.6 through 16\(\mu\)m. We compared the full optical and infrared spectrum with state-of-the-art atmosphere models to further constrain its effective temperature, surface gravity and metallicity. WISE1810 is detected in the \(iz\) bands with AB magnitudes of \(i\)=23.871\(\pm\)0.104 and \(z\)=20.147\(\pm\)0.083 mag in the PanSTARRS system. It does not show any obvious photometric variability beyond 0.1\(-\)0.2 mag in any of the \(z\)- and \(J\)-band filters. The very red \(z-J \approx 2.9\) mag colour is compatible with an ultra-cool dwarf nature. Fitting for parallax and proper motion, we measure a trigonometric parallax of 112.5\(^{+8.1}_{-8.0}\) mas for WISE1810, placing the object at only 8.9\(^{+0.7}_{-0.6}\) pc, about three times closer than previously thought. We employed Monte Carlo methods to estimate the error on the parallax and proper motion. The object's luminosity was determined at log\(L/L_\odot\)=\(-\)5.78\(\pm\)0.11 dex. From the comparison to atmospheric models, we infer a likely metallicity of Fe/H \(\approx -1.5\) and an effective temperature cooler than 1000K. Abridged
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