ABSTRACT We report the discovery of 14 low-mass binary systems containing mid-M to mid-L dwarf companions with separations larger than 250 AU. We also report the independent discovery of nine other ...systems with similar characteristics that were recently discovered in other studies. We have identified these systems by searching for common proper motion sources in the vicinity of known high proper motion stars, based on a cross-correlation of wide area near-infrared surveys (2MASS, SDSS, and SIMP). An astrometric follow-up, for common proper motion confirmation, was made with SIMON and/or CPAPIR at the Observatoire du Mont Mégantic 1.6 m and CTIO 1.5 m telescopes for all the candidates identified. A spectroscopic follow-up was also made with GMOS or GNIRS at Gemini to determine the spectral types of 11 of our newly identified companions and 10 of our primaries. Statistical arguments are provided to show that all of the systems we report here are very likely to be physical binaries. One of the new systems reported features a brown dwarf companion: LSPM J1259+1001 (M5) has an L4.5 (2M1259+1001) companion at ∼340 AU. This brown dwarf was previously unknown. Seven other systems have a companion of spectral type L0-L1 at a separation in the 250-7500 AU range. Our sample includes 14 systems with a mass ratio below 0.3.
ABSTRACT
We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M⋆ = 0.39 M⊙, R⋆ = 0.38 R⊙), which hosts three transiting planets that were recently discovered ...using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M⊕, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the ‘radius valley’ – a region in the radius-period diagram with relatively few members – which has been interpreted as a consequence of atmospheric photoevaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.
The Observational View Artigau, E.
EAS Publications Series,
2012, 2012-00-00, 20120101, Volume:
57
Journal Article
Within less than two decades, the study of low-mass stars and brown dwarfs has bloomed into one of the most active fields in astronomy. The M, L, T and Y dwarfs sequences includes objects spawning ...more than an order of magnitude in absolute temperature, from 4000 K down to room temperature, and nearly fills the entire temperature gap between the coolest stars and our Solar System’s giant planets. I present an overview of the large-scale surveys that led to the discovery of a population of ultracool dwarfs in our immediate galactic vicinity, their classification and various noteworthy spectroscopic features found only in these objects. I provide an outline of photometric variability study of L and T dwarfs, which opens a unique window on the atmospheric phenomenon at play in their atmospheres. Finally, I summarize the capabilities of an upcoming instrument, the SPIRou near-infrared, high-resolution spectropolarimeter, that will be available to the CFHT communities in 2015. SPIRou will be a unique tool for the study of cool dwarfs, and will be used to undertake an ambitious survey of habitable Earth-sized planets around nearby M dwarfs.
We report the discovery of two new exoplanet systems around fully convective stars, found from the radial-velocity (RV) variations of their host stars measured with the nIR spectropolarimeter ...CFHT/SPIRou over multiple years. GJ 3378 b is a planet with minimum mass of $5.26^ on an eccentric 24.73-day orbit around an M4V star of 0.26 GJ 1289 b has a minimum mass of $6.27 in a 111.74-day orbit, on a circular orbit around an M4.5V star of mass 0.21 Both stars are in the solar neighbourhood, at 7.73 and 8.86 pc, respectively. The low-amplitude RV signals are detected after line-by-line post-processing treatment. These potential sub-Neptune class planets around cool stars may have temperate atmospheres and be interesting nearby systems for further studies. We also recovered the large-scale magnetic field of both stars, found to be mostly axisymmetric and dipolar, with polar strengths of 20-30 G and 200-240 G for GJ 3378 (in 2019-21) and GJ 1289 (in 2022-23), respectively. The rotation periods measured with the magnetic field differ from the orbital periods and, in general, stellar activity is not seen in the studied nIR RV time series of both stars. GJ 3378 b detections have not been confirmed by optical RVs and, therefore, they are solely considered a candidate for the present purposes.
Context.
Veiling is ubiquitous at different wavelength ranges in classical T Tauri stars. However, the origin of the veiling in the infrared (IR) domain is not well understood at present. The ...accretion spot alone is not enough to explain the shallow photospheric IR lines in accreting systems, suggesting that another source is contributing to the veiling in the near-infrared (NIR). The inner disk is often quoted as the additional emitting source meant to explain the IR veiling.
Aims.
In this work, we aim to measure and discuss the NIR veiling to understand its origins and variability timescale.
Methods.
We used a sample of 14 accreting stars observed with the CFHT/SPIRou spectrograph, within the framework of the SPIRou Legacy Survey, to measure the NIR veiling along the
YJHK
bands. We compared the veiling measurements with accretion and inner disk diagnostics. We also analyzed circumstellar emission lines and photometric observations from the literature.
Results.
The measured veiling grows from the
Y
to the
K
band for most of the targets in our sample. The IR veiling agrees with NIR emission excess obtained using photometric data. However, we also find a linear correlation between the veiling and the accretion properties of the system, showing that accretion contributes to the inner disk heating and, consequently, to the inner disk emission excess. We also show a connection between the NIR veiling and the system’s inclination with respect to our line of sight. This is probably due to the reduction of the visible part of the inner disk edge, where the NIR emission excess is expected to arise, as the inclination of the system increases. Our search for periods on the veiling variability showed that the IR veiling is not clearly periodic in the typical timescale of stellar rotation – which, again, is broadly consistent with the idea that the veiling comes from the inner disk region. The NIR veiling appears variable on a timescale of a day, showing the night-by-night dynamics of the optical veiling variability. In the long term, the mean NIR veiling seems to be stable for most of the targets on timescales of a month to a few years. However, during occasional episodes of high accretion in classical T Tauri stars, which affect the system’s dynamic, the veiling also seems to be much more prominent at such times, as we found in the case of the target RU Lup.
Conclusions.
We provide further evidence that for most targets in our sample, the veiling that mainly occurs in the
JHK
bands arises from dust in the inner disk.
Context.
Young stellar systems actively accrete from their circumstellar disk and simultaneously launch outflows. The physical link between accretion and ejection processes remains to be fully ...understood.
Aims.
We investigate the structure and dynamics of magnetospheric accretion and associated outflows on a scale smaller than 0.1 au around the young transitional disk system GM Aur.
Methods.
We devised a coordinated observing campaign to monitor the variability of the system on timescales ranging from days to months, including partly simultaneous high-resolution optical and near-infrared spectroscopy, multiwavelength photometry, and low-resolution near-infrared spectroscopy, over a total duration of six months, covering 30 rotational cycles. We analyzed the photometric and line profile variability to characterize the accretion and ejection processes.
Results.
The optical and near-infrared light curves indicate that the luminosity of the system is modulated by surface spots at the stellar rotation period of 6.04 ± 0.15 days. Part of the Balmer, Paschen, and Brackett hydrogen line profiles as well as the HeI 5876 Å and HeI 10830 Å line profiles are modulated on the same period. The Pa
β
line flux correlates with the photometric excess in the
u
′ band, which suggests that most of the line emission originates from the accretion process. High-velocity redshifted absorptions reaching below the continuum periodically appear in the near-infrared line profiles at the rotational phase in which the veiling and line fluxes are the largest. These are signatures of a stable accretion funnel flow and associated accretion shock at the stellar surface. This large-scale magnetospheric accretion structure appears fairly stable over at least 15 and possibly up to 30 rotational periods. In contrast, outflow signatures randomly appear as blueshifted absorption components in the Balmer and HeI 10830 Å line profiles. They are not rotationally modulated and disappear on a timescale of a few days. The coexistence of a stable, large-scale accretion pattern and episodic outflows supports magnetospheric ejections as the main process occurring at the star-disk interface.
Conclusions.
Long-term monitoring of the variability of the GM Aur transitional disk system provides clues to the accretion and ejection structure and dynamics close to the star. Stable magnetospheric accretion and episodic outflows appear to be physically linked on a scale of a few stellar radii in this system.
For several years, the metastable helium triplet line has been successfully used as a tracer to probe atmospheric escape in transiting exoplanets. This absorption in the near-infrared (1083.3\,nm) ...can be observed from the ground using high-resolution spectroscopy, providing new constraints on the mass-loss rate and the temperature characterizing the upper atmosphere of close-in exoplanets. The aim of this work is to search for the He triplet signature in 15 transiting exoplanets ---ranging from super-Earths to ultrahot Jupiters--- observed with SPIRou a high-resolution ($R near-infrared spectropolarimeter at the CFHT, in order to bring new constraints or to improve existing ones regarding atmospheric escape through a homogeneous study. We developed a full data processing and analysis pipeline to correct for the residual telluric and stellar contributions. We then used two different 1D models based on the Parker-wind equations and nonlocal thermodynamic equilibrium (NLTE) radiative transfer to interpret the observational results. We confirm published He triplet detections for HAT-P-11\,b, HD\,189733\,b, and WASP-69\,b. We tentatively detect the signature of escaping He in HD\,209458\,b, GJ\,3470\,b, and WASP-76\,b. We report new constraints on the mass-loss rate and temperature for our three detections and set upper limits for the tentative and nondetections. We notably report improved constraints on the mass-loss rate and temperature of the escaping gas for TOI-1807\,b, and report a nondetection for the debated atmospheric escape in GJ\,1214\,b. We also conducted the first search for the He signature in GJ\,486\,b since its discovery and report a nondetection of the He triplet. Finally, we studied the impact of important model assumptions on our retrieved parameters, notably the limitations of 1D models and the influence of the H/He ratio on the derived constraints.
We have identified CFBDSIR J1458+1013 as a 011 (2.6 AU) physical binary using Keck laser guide star adaptive optics imaging and have measured a distance of 23.1 ? 2.4 pc to the system based on ...near-IR parallax data from the Canada-France-Hawaii Telescope. The integrated-light near-IR spectrum indicates a spectral type of T9.5, and model atmospheres suggest a slightly higher temperature and surface gravity than the T10 dwarf UGPS J0722--05. Thus, CFBDSIR J1458+1013AB is the coolest brown dwarf binary found to date. Its secondary component has an absolute H-band magnitude that is 1.9 ? 0.3 mag fainter than UGPS J0722--05, giving an inferred spectral type of >T10. The secondary's bolometric luminosity of ~2 X 10--7 L makes it the least luminous known brown dwarf by a factor of 4-5. By comparing to evolutionary models and T9-T10 objects, we estimate a temperature of 370 ? 40 K and a mass of 6-15 M Jup for CFBDSIR J1458+1013B. At such extremes, atmospheric models predict the onset of novel photospheric processes, namely, the appearance of water clouds and the removal of strong alkali lines, but their impact on the emergent spectrum is highly uncertain. Our photometry shows that strong CH4 absorption persists in the H band, the J -- K color is bluer than the latest known T dwarfs but not as blue as predicted by current models, and the J -- H color delineates a possible inflection in the blueward trend for the latest T dwarfs. Given its low luminosity, atypical colors, and cold temperature, CFBDSIR J1458+1013B is a promising candidate for the hypothesized Y spectral class. However, regardless of its ultimate classification, CFBDSIR J1458+1013AB provides a new benchmark for measuring the properties of brown dwarfs and gas-giant planets, testing substellar models, and constraining the low-mass limit for star formation.
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