CARMENES input catalogue of M dwarfs Cortes-Contreras, M; Bejar, V J S; Caballero, J A ...
Astronomy and astrophysics (Berlin),
1/2017, 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 1.5m 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-spectra l 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 14pc. 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+ or -2.0%. The bias-corrected multiplicity fraction in our volume-limited sample is 19.5+ or -2.3% for angular separations of 0.2 to 5.0arcsec (1.4-65.6au), with a peak in the distribution of the projected physical separations at 2.5-7.5au. For M0.0-M3.5V 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 50au also tend to be of equal mass. For 26 of our systems, we estimated orbital periods shorter than 50a, 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 0.2arcsec, longer than 5.0arcsec, 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.
Our objective is the optical and near-infrared spectroscopic characterisation of 2MASS J0249−0557 c, a recently discovered young planetary mass companion to the
β
Pictoris (~25 Myr) member ...2MASS J0249−0557.
Methods.
Using the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey and the Two Micron All Sky Survey (2MASS) data, we independently identified the companion 2MASS J0249−0557 c. We also obtained low-resolution optical spectroscopy of this object using the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy spectrograph at the Gran Telescopio Canarias, and near-infrared spectroscopy using the Son of Isaac spectrograph on the New Technology Telescope.
Results.
We classified 2MASS J0249−0557 c with a spectral type of L2.5 ± 0.5 in the optical and L3 ± 1 in the near-infrared. We identified several spectroscopic indicators of youth both in the optical and in the near-infrared that are compatible with the age of the
β
Pictoris moving group: strong absorption due to oxides, weak alkaline atomic lines, and a triangular shape of the
H
-band pseudo-continuum. We also detect a strong H
α
emission, with a pseudo-equivalent width (pEW) of −90
−40
+20
Å, which seems persistent at timescales from several days to a few years. This indicates strong chromospheric activity or disk accretion. Although many M-type brown dwarfs have strong H
α
emission, this target is one of the very few L-type planetary mass objects in which this strong H
α
emission has been detected. Lithium absorption at 6708 Å is observed with pEW ≲5 Å. We also computed the binding energy of 2MASS J0249−0557 c and obtained an (absolute) upper limit of
U
= (−8.8 ± 4.4) × 10
32
J.
Conclusions.
Similarly to other young brown dwarfs and isolated planetary mass objects, strong H
α
emission due to accretion or chromospheric activity 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.
Abstract
We demonstrate that the previously identified L/T transition brown dwarf SDSS J213154.43−011939.3 (SDSS 2131−0119) is a widely separated (82${^{\prime\prime}_{.}}$3, ∼3830 au) common proper ...motion companion to the low-mass star NLTT 51469, which we reveal to be a close binary itself, separated by 0${^{\prime\prime}_{.}}$64 ± 0${^{\prime\prime}_{.}}$01 (∼30 au). We find the proper motion of SDSS 2131−0119 of μαcos δ = −100 ± 20 mas yr−1 and μδ = −230 ± 20 mas yr−1 consistent with the proper motion of the primary provided by Gaia DR2: μαcos δ = −95.49 ± 0.96 mas yr−1 and μδ = −239.38 ± 0.96 mas yr−1. Based on optical and near-infrared spectroscopy, we classify the primary NLTT 51469A as an M3 ± 1 dwarf, estimate photometrically the spectral type of its close companion NLTT 51469B at ∼M6, and confirm the spectral type of the brown dwarf to be L9 ± 1. Using radial velocity, proper motion, and parallax, we derived the UVW Galactic 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 a 670.8 nm Li i absorption line, and absence of H α emission, detected X-rays, or UV excess, indicate that the system is likely a member of the thin disc population and is older than 1 Gyr. For the parallactic distance of 46.6 ± 1.6 pc from Gaia DR2, we determined luminosities of $-1.50^{+0.02}_{-0.04}$ and −4.4 ± 0.1 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 ± 0.02 M⊙ for the primary, and 1400–1650 K and 0.05–0.07 M⊙ for the wide companion. For the ∼M6 component, we estimated Teff = 2850 ± 200 K and m = 0.10$^{+0.06}_{-0.01}$ M⊙.
Aim. With the purpose of investigating 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. Methods. We observed in phase-reference mode the system VHS 1256–1257 with the Karl G. Jansky Very Large Array at X band and L band and with the European VLBI Network at L band in several epochs during 2015 and 2016. Results. We discovered radio emission at X band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 μJy. We determined a spectral index α = −1.1 ± 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 3σ upper limit of 20 μJy. 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 3σ upper bound to the radio flux density of the L7 object of 9 μJy at 10 GHz.
ABSTRACT
We present the results of a 4-month, spectroscopic campaign of the Wolf–Rayet dust-making binary, WR137. We detect only small-amplitude random variability in the C iii λ5696 emission line ...and its integrated quantities (radial velocity, equivalent width, skewness, and 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 H α, H β, H γ, He ii λ6678, and He ii λ5876 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 disc 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 disc 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 disc 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.
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 μm) reaching a 3σ 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 μm 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 M
Jup (T
eff > 400 K), ages of a few Gyr, and located in ∼3.6–18 au orbits with a 3σ confidence level. This minimum mass is approximately 5 M
Jup smaller than any previous imaging survey that explored the surroundings of Barnard's Star could restrict.
A method is defined for identifying late-T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the ...WISE multiframe measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space, we use a control sample of isolated non-moving non-variable point sources from the Sloan Digital Sky Survey (SDSS), and identify a sample of 158 WISE
W2-only candidates down to a signal-to-noise limit of eight. For signal-to-noise ranges >10 and 8-10, respectively, ∼45 and ∼90 per cent of our sample fall outside the selection criteria published by the WISE team, mainly due to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (∼1.3 and ∼1.8 arcsec yr−1). Both objects show a mid-infrared/near-infrared excess of ∼1-1.5 mag and are K band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disc) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late-T and Y dwarfs may have a higher thick-disc/halo population fraction than earlier objects.
Abstract
We report on the discovery of a fourth component in the HD 221356 star system, previously known to be formed by an F8V, a slightly metal poor primary (Fe/H = −0.26), and a distant M8V+L3V ...pair. In our ongoing common proper motion search based on Visible and Infrared Survey Telescope for Astronomy (VISTA) Hemisphere Survey (VHS) and Two Micron All Sky Survey (2MASS) catalogues, we have detected a faint J = 13.76 ± 0.04 mag comoving companion of the F8 star located at angular separation of 12.13 ± 0.18 arcsec (position angle of 221°.8 ± 1°.7), corresponding to a projected distance of ∼317 au at 26 pc. Near-infrared spectroscopy of the new companion, covering the 1.5-2.4 μm wavelength range with a resolving power of R ∼ 600, indicates an L1 ± 1 spectral type. Using evolutionary models the mass of the new companion is estimated at ∼0.08 M⊙, which places the object close to the stellar-substellar borderline. This multiple system provides an interesting example of objects with masses slightly above and below the hydrogen-burning mass limit. The low-mass companions of HD 221356 have slightly bluer colours than field dwarfs with similar spectral type, which is likely a consequence of the subsolar metallicity of the system.
The direct detection of extrasolar planets is the only technique that leads to the most complete characterization of their physical properties. Here, we report on mid-IR observations of five directly ...imaged substellar companions (DF Tau B, FU Tau B, κ And b, GJ 758 B, and GJ 504 b) obtained with the Si-2 filter (8.7 µm) in the CanariCam instrument mounted on the 10-m Gran Telescopio de Canarias (GTC). We show the detection of FU Tau B, and we set upper limits of 11.5-12.0 mag in the 8.7 µm band for the other substellar targets. These data are useful to constrain their effective temperature and the presence of mid-IR flux excesses that may be due to surrounding disks.
Aims.
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 1810055−1010023.
Methods.
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 WISE J1810055−1010023. We also acquired low-resolution optical spectroscopy (0.6−1.0 μm) and new infrared (0.9−1.3 μm) spectra of WISE J1810055−1010023 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 μm. 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.
Results.
WISE J1810055−1010023 is detected in the
iz
bands with AB magnitudes of
i
= 23.871 ± 0.104 and
z
= 20.147 ± 0.083 mag in the Panoramic Survey Telescope and Rapid Response System (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
≈ 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
−8.0
+8.1
mas for WISE J1810055−1010023, placing the object at only 8.9
−0.6
+0.7
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
⊙
= −5.78 ± 0.11 dex. From the comparison to atmospheric models, we infer a likely metallicity of Fe/H ≈ −1.5 and an effective temperature cooler than 1000 K. The estimated luminosity and temperature of this object are below the known substellar limit. Despite its apparent low metallicity, we derive space motions that are more typical of the old disc than the halo of the Milky Way. We confirm that WISE J1810055−1010023 has an ultra-cool temperature and belongs to a new class of objects with no known spectral counterparts among field L- and T-type dwarfs.
Conclusions.
WISE J1810055−1010023 is a very special substellar object and represents a new addition to the 10 pc sample. The optical to near-infrared spectra show strong features due to water vapour and H
2
collision induced absorption. Our trigonometric distance has strong implications on the density of metal-poor brown dwarfs in the solar vicinity, which may be higher than that of metal-poor stars.
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