Aims. We present the first results of the ongoing Canada-France Brown Dwarfs Survey-InfraRed, hereafter CFBDSIR, a near infrared extension to the optical wide-field survey CFBDS. Our final objectives ...are to constrain ultracool atmosphere physics by finding a statistically significant sample of objects cooler than 650 K and to explore the ultracool brown dwarf mass function building on a well-defined sample of such objects. Methods. We identify candidates in CFHT/WIRCam J and CFHT/MegaCam z' images using optimised psf-fitting, and follow them up with pointed, near-infrared imaging with SOFI at the NTT. We finally obtain low-resolution spectroscopy of the coolest candidates to characterise their atmospheric physics. Results. We have so far analysed and followed up all candidates on the first 66 square degrees of the 335 square degree survey. We identified 55 T-dwarfs candidates with $z'-J>3.5$ and have confirmed six of them as T-dwarfs, including 3 that are strong later-than-T8 candidates, based on their far-red and NIR colours. We also present here the NIR spectra of one of these ultracool dwarfs, CFBDSIR1458+1013, which confirms it as one of the coolest brown dwarf known, possibly in the 550–600 K temperature range. Conclusions. From the completed survey we expect to discover 10 to 15 dwarfs later than T8, more than doubling the known number of such objects. This will enable detailed studies of their extreme atmospheric properties and provide a stronger statistical basis for studies of their luminosity function.
Aims. We report the discovery of CFBDS J005910.90-011401.3 (hereafter CFBDS0059), the coolest brown dwarf identified to date. Methods. We found CFBDS0059 using i' and z' images from the ...Canada-France-Hawaii Telescope (CFHT), and present optical and near-infrared photometry, Keck laser-guide-star adaptive optics imaging, and a complete near-infrared spectrum, from 1.0 to 2.2 μm. Results. A side-to-side comparison of the near-infrared spectra of CFBDS0059 and ULAS J003402.77-005206.7 (hereafter ULAS0034), previously the coolest known brown dwarf, indicates that CFBDS0059 is ~50 ± 15 K cooler. We estimate a temperature of $T_\mathrm{eff} \sim$ 620 K and gravity of log g ~ 4.75. Evolutionary models translate these parameters into an age of 1–5 Gyr and a mass of 15-30 MJup. We estimate a photometric distance of ~13 pc, which puts CFBDS0059 within easy reach of accurate parallax measurements. Its large proper motion suggests membership in the older population of the thin disk. The spectra of both CFBDS0059 and ULAS J0034 show probable absorption by a wide ammonia band on the blue side of the H-band flux peak. If, as we expect, that feature deepens further for still lower effective temperatures, its appearance will become a natural breakpoint for the transition between the T spectral class and the new Y spectral type. Together, CFBDS0059 and ULAS J0034 would then be the first Y0 dwarfs.
Aims. We present the first results of a wide field survey for cool brown dwarfs with the MegaCam camera on the CFHT telescope, the Canada-France Brown Dwarf Survey, hereafter CFBDS. Our objectives ...are to find ultracool brown dwarfs and to constrain the field-brown dwarf mass function thanks to a larger sample of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i' and z' images using optimised psf-fitting within Source Extractor, and follow them up with pointed near-infrared imaging on several telescopes. Results. We have so far analysed over 350 square degrees and found 770 brown dwarf candidates brighter than $z'_{\rm AB}=22.5$. We currently have J-band photometry for 220 of these candidates, which confirms 37% as potential L or T dwarfs. Some are among the reddest and farthest brown dwarfs currently known, including an independent identification of the recently published ULAS J003402.77-005206.7 and the discovery of a second brown dwarf later than T8, CFBDS J005910.83-011401.3. Infrared spectra of three T dwarf candidates confirm their nature, and validate the selection process. Conclusions. The completed survey will discover ~100 T dwarfs and ~500 L dwarfs or M dwarfs later than M8, approximately doubling the number of currently known brown dwarfs. The resulting sample will have a very well-defined selection function, and will therefore produce a very clean luminosity function.
The SPIRou legacy survey Fouqué, P; Martioli, E; J.-F. Donati ...
Astronomy and astrophysics (Berlin),
04/2023, Volume:
672
Journal Article
Peer reviewed
Open access
Context. The rotation period of stars is an important parameter together with mass, radius, and effective temperature. It is an essential parameter for any radial velocity monitoring, as stellar ...activity can mimic the presence of a planet at the stellar rotation period. Several methods exist to measure it, including long sequences of photometric measurements or temporal series of stellar activity indicators. Aims. Here, we use the circular polarization in near-infrared spectral lines for a sample of 43 quiet M dwarfs and compare the measured rotation periods to those obtained with other methods. Methods. From Stokes V spectropolarimetric sequences observed with SPIRou at the Canada-France-Hawaii Telescope and the data processed with the APERO pipeline, we computed the least-squares deconvolution profiles using different masks of atomic stellar lines with known Landé factor appropriate to the effective temperature of the star. We derived the longitudinal magnetic field to examine its possible variation in 50 to 200 observations of each star. To determine the stellar rotation period, we applied a Gaussian process regression, enabling us to determine the rotation period of stars with evolving longitudinal field. Results. We were able to measure a rotation period for 27 of the 43 stars of our sample. The rotation period was previously unknown for 8 of these stars. Our rotation periods agree well with periods found in the literature based on photometry and activity indicators, and we confirm that near-infrared spectropolarimetry is an important tool for measuring rotation periods, even for magnetically quiet stars. Furthermore, we computed the ages for 20 stars of our sample using gyrochronology.
We report the discovery and characterisation of a giant transiting planet orbiting a nearby M3.5V dwarf (d = 80.4pc, G = 15.1 mag, K=11.2mag, R* = 0.358 ± 0.015 R⊙, M* = 0.340 ± 0.009 M⊙). Using the ...photometric time series from TESS sectors 10, 36, 46, and 63 and near-infrared spectrophotometry from ExTrA, we measured a planetary radius of 0.77 ± 0.03 RJ and an orbital period of 1.52 days. With high-resolution spectroscopy taken by the CFHT/SPIRou and ESO/ESPRESSO spectrographs, we refined the host star parameters (Fe/H = 0.27 ± 0.12) and measured the mass of the planet (0.273 ± 0.006 MJ). Based on these measurements, TOI-4860 b joins the small set of massive planets (>80 ME) found around mid to late M dwarfs (<0.4 R⊙), providing both an interesting challenge to planet formation theory and a favourable target for further atmospheric studies with transmission spectroscopy. We identified an additional signal in the radial velocity data that we attribute to an eccentric planet candidate (e = 0.66 ± 0.09) with an orbital period of 427 ± 7 days and a minimum mass of 1.66 ± 0.26 MJ, but additional data would be needed to confirm this.
Binary systems with a substellar companion are quite rare and provide interesting benchmarks. They constrain the complex physics of substellar atmospheres, because several physical parameters of the ...substellar secondary can be fixed from the much better characterized main-sequence primary. We report the discovery of CFBDS J111807-064016, a T2 brown-dwarf companion to 2MASS J111806.99-064007.8, a low-mass M4.5-M5 star. The brown dwarf was identified from the Canada France Brown Dwarf Survey. At a distance of 50–120 pc, the 7.7′′ angular separation corresponds to projected separations of 390-900 AU. The primary displays no Hα emission, placing a lower limit on the age of the system of about 6 Gyr. The kinematics is also consistent with membership in the old thin disc. We obtained near-infrared spectra, which together with recent atmosphere models allow us to determine the effective temperature and gravity of the two components. We derived a system metallicity of Fe/H = −0.1 ± 0.1 using metallicity-sensitive absorption features in our medium-resolution Ks spectrum of the primary. From these parameters and the age constraint, evolutionary models estimate masses of 0.10 to 0.15 M⊙ for the M dwarf and 0.06 to 0.07 M⊙ for the T dwarf. This system is a particularly valuable benchmark because the brown dwarf belongs to the early-T class: the cloud-clearing that occurs at the L/T transition is very sensitive to gravity, metallicity, and detailed dust properties, and produces a large scatter in the colours. This T2 dwarf, with its metallicity measured from the primary and its mass and gravity much better constrained than those of younger early-Ts, will anchor our understanding of the colours of L/T transition brown dwarfs. It is also one of the most massive T dwarfs, just below the hydrogen-burning limit, and all this makes it a prime probe for brown-dwarf atmosphere and evolution models.
Context.From a 2$^\circ\times$ 2° of NGC 6822 survey we have previously established that this Local Group dwarf irregular galaxy possesses a huge spheroid having more than one degree in length. This ...spheroid is in rotation but its rotation curve is known only within ~$ 15'$ from the center. It is therefore critical to identify bright stars belonging to the spheroid to characterize, as far as possible, its outer kinematics. Aims.We use the new wide field near infrared imager CPAPIR, operated by the SMARTS consortium, to acquire J, Ks images of two $34.8'\times 34.8'$ areas in the outer spheroid to search for C stars. Methods.The colour diagram of the fields allows the identification of 192 C stars candidates but a study of the FWHM of the images permits the rejection of numerous non-stellar objects with colours similar to C stars. Results. We are left with 75 new C stars, their mean Ks magnitude and mean colour are similar to the bulk of known NGC 6822 C stars. Conclusions.This outer spheroid survey confirms that the intermediate-age AGB stars are a major contributor to the stellar populations of the spheroid. The discovery of some 50 C stars well beyond the limit of the previously known rotation curve calls for a promising spectroscopic follow-up to a major axis distance of 40'.
Context. The presence of unresolved binaries on sub-arsecond scales could explain the existence of optically thin inner holes or gaps in circumstellar disks, which are commonly referred to as ..."transitional" or "cold" disks, and it is the first scenario to check before making any other assumptions. Aims: We aim at detecting the presence of companions inside the inner hole/gap region of a sample of five well known transitional disks using spatially-resolved imaging in the near-IR with the VLT/NACO/S13 camera, which probes projected distances from the primary of typically 0.1 to 7 arcsec. The sample includes the stars DoAr 21, HD 135344B (SAO 206462), HR 4796A, T Cha, and TW Hya, spanning ages of less than 1 to 10 Myr, spectral types of A0 to K7, and hole/gap outer radii of 4 to 100 AU. Methods: In order to enhance the contrast and to avoid saturation at the core of the point-spread function (PSF), we use narrow-band filters at 1.75 and 2.12 μm. The "locally optimized combination of images" (LOCI) algorithm is applied for an optimal speckle noise removal and PSF subtraction, providing an increase of 0.5-1.5 mag in contrast over the classic method. Results: With the proviso that we could have missed companions owing to unfavorable projections, the VLT/NACO observations rule out the presence of unresolved companions down to an inner radius of about 0.1 arcsec from the primary in all five transitional disks and with a detection limit of 2 to 5 mag in contrast. In the disk outer regions the detection limits typically reach 8 to 9 mag in contrast and 4.7 mag for T Cha. Hence, the NACO images resolve part of the inner hole/gap region of all disks with the exception of TW Hya, for which the inner hole is only 4 AU. The 5σ sensitivity profiles, together with a selected evolutionary model, allow to discard stellar companions within the inner hole/gap region of T Cha, and down to the substellar regime for HD 135344B and HR 4796A. DoAr 21 is the only object from the sample of five disks for which the NACO images are sensitive enough for a detection of objects less massive than ~13 MJup that is, potential giant planets or low-mass brown dwarfs at radii larger than ~76 AU (0.63 arcsec). Conclusions: These new VLT/NACO observations further constrain the origin of the inner opacity cavities to be owing to closer or lower-mass companions or other mechanisms such as giant planet formation, efficient grain growth, and photoevaporation (for DoAr 21 and HR 4796A).
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