[en] The results of an analysis of far-infrared (FIR) and 21-cm data for a sample of 102 spiral galaxies in the Virgo cluster are presented. We show that H I deficient galaxies have lower 60- and 100-μm fluxes and cooler far-infrared colour temperatures than those with normal H I content. We interpret these results in the context of a two-component model for the far-infrared emission: a warm component associated with star formation and H II regions, and a cool 'cirrus-like' component of dust heated by the interstellar radiation field. We find that, for a typical spiral in the core of the cluster, at least half of the diffuse dust has been stripped and the star formation activity suppressed by a factor of 3, compared to normal field galaxies. The dust stripping confirms the presence of a diffuse dust component in Virgo spirals and the validity of current models for the FIR emission in spiral galaxies. (author)

[en] Nearly 15 yr of radial velocity (RV) monitoring and direct imaging enabled the detection of two giant planets orbiting the young, nearby star β Pictoris. The δ Scuti pulsations of the star, which overwhelm planetary signals, need to be carefully suppressed. In this work, we independently revisit the analysis of the RV data following a different approach than available in the literature to model the activity of the star. We show that a Gaussian process (GP) with a stochastically driven damped harmonic oscillator kernel can model the δ Scuti pulsations. It provides similar results to parametric models but with a simpler framework, using only three hyperparameters. It also enables us to model poorly sampled RV data that were excluded from previous analyses, hence extending the RV baseline by nearly five years. Altogether, the orbit and mass of both planets can be constrained from RV only, which was not possible with the parametric modeling. To characterize the system more accurately, we also perform a joint fit of all available relative astrometry and RV data. Our orbital solutions for $\mathrm{\beta <!--\; ??\; -->}\mathrm{P}\mathrm{i}\mathrm{c}$ b favor a low eccentricity of ${0.029}_{-<!--\; ???\; -->0.024}^{+0.061}$ and a relatively short period of ${21.1}_{-<!--\; ???\; -->0.8}^{+2.0}$ yr. The orbit of $\mathrm{\beta <!--\; ??\; -->}\mathrm{P}\mathrm{i}\mathrm{c}$ c is eccentric with ${0.206}_{-<!--\; ???\; -->0.063}^{+0.074}$ with a period of 3.36 ± 0.03 yr. We find model-independent masses of 11.7 ± 1.4 and 8.5 ± 0.5 $M_{\mathrm{J}\mathrm{u}\mathrm{p}}$ for $\mathrm{\beta <!--\; ??\; -->}\mathrm{P}\mathrm{i}\mathrm{c}$ b and c, respectively, assuming coplanarity. The mass of $\mathrm{\beta <!--\; ??\; -->}\mathrm{P}\mathrm{i}\mathrm{c}$ b is consistent with the hottest start evolutionary models, at an age of 25 ± 3 Myr. A direct detection of $\mathrm{\beta <!--\; ??\; -->}\mathrm{P}\mathrm{i}\mathrm{c}$ c would provide a second calibration measurement in a coeval system.

[en] We present a photometric J-band variability study of GU Psc b, a T3.5 co-moving planetary-mass companion (9–13 $M_{\mathrm{J}\mathrm{u}\mathrm{p}}$) to a young (∼150 Myr) M3 member of the AB Doradus Moving Group. The large separation between GU Psc b and its host star (42″) provides a rare opportunity to study the photometric variability of a planetary-mass companion. The study presented here is based on observations obtained from 2013 to 2014 over three nights with durations of 5–6 hr each with the WIRCam imager at Canada–France–Hawaii Telescope. Photometric variability with a peak-to-peak amplitude of 4 ± 1% at a timescale of ∼6 hr was marginally detected on 2014 October 11. No high-significance variability was detected on 2013 December 22 and 2014 October 10. The amplitude and timescale of the variability seen here, as well as its evolving nature, is comparable to what was observed for a variety of field T dwarfs and suggests that mechanisms invoked to explain brown dwarf variability may be applicable to low-gravity objects such as GU Psc b. Rotation-induced photometric variability due to the formation and dissipation of atmospheric features such as clouds is a plausible hypothesis for the tentative variation detected here. Additional photometric measurements, particularly on longer timescales, will be required to confirm and characterize the variability of GU Psc b, determine its periodicity and to potentially measure its rotation period.

[en] We present the discovery of the widest (∼6700 AU) very low mass (VLM) field binary to date, found in a proper motion cross-match of the Sloan Digital Sky Survey and the Two Micron All Sky Survey. Our follow-up J-band imaging provides a 10 year baseline for measuring proper motions. Consequently, we are able to confirm the common proper motion of the pair to within 10 mas, implying a 99.5% probability of their physical association. Near-infrared spectra of the components indicate spectral types of M6 ± 1 and M7 ± 1. The system resides at a spectroscopic distance of 105 ± 13 pc and has an angular separation of 63.''38 ± 0.''05. We have used evolutionary models to infer component masses of 0.105^+0.029_-0.017 M _sun and 0.091^+0.010_-0.007 M _sun. The large separation and low binding energy of this system can provide constraints for formation models of VLM stars.

[en] We have conducted a near-infrared (NIR) proper motion survey, the Sondage Infrarouge de Mouvement Propre, in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging ∼28% of the sky with the Caméra PAnoramique Proche-InfraRouge both in the southern hemisphere at the Cerro Tololo Inter-American Observatory 1.5 m telescope, and in the northern hemisphere at the Observatoire du Mont-Mégantic 1.6 m telescope and comparing the source positions from these observations with the Two Micron All-Sky Survey Point Source Catalog (2MASS PSC). Additional color criteria were used to further discriminate unwanted astrophysical sources. We present the results of an NIR spectroscopic follow-up of 169 M, L, and T dwarfs. Among the sources discovered are 2 young field brown dwarfs, 6 unusually red M and L dwarfs, 25 unusually blue M and L dwarfs, 2 candidate unresolved L+T binaries, and 24 peculiar UCDs. Additionally, we add 9 L/T transition dwarfs (L6–T4.5) to the already known objects.

[en] High-precision radial velocity (RV) measurements have been central in the study of exoplanets during the last two decades, from the early discovery of hot Jupiters, to the recent mass measurements of Earth-sized planets uncovered by transit surveys. While optical RV is now a mature field, there is currently a strong effort to push the technique into the near-infrared domain (chiefly Y, J, H, and K bandpasses) to probe planetary systems around late-type stars. The combined lower mass and luminosity of M dwarfs leads to an increased reflex RV signal for planets in the habitable zone compared to Sun-like stars. The estimates on the detectability of planets rely on various instrumental characteristics but also on a prior knowledge of the stellar spectrum. While the overall properties of M dwarf spectra have been extensively tested against observations, the same is not true for their detailed line profiles, which leads to significant uncertainties when converting a given signal-to-noise ratio to a corresponding RV precision as attainable on a given spectrograph. By combining archival CRIRES and HARPS data with ESPaDOnS data of Barnard’s star, we show that state-of-the-art atmosphere models over-predict the Y- and J-band RV content by more than a factor of ∼2, while under-predicting the H- and K-band content by half.

[en] We present the results of a direct imaging survey for very large separation (>100 au), low-mass companions around 95 nearby young K5–L5 stars and brown dwarfs. They are high-likelihood candidates or confirmed members of the young (≲150 Myr) β Pictoris and AB Doradus moving groups (ABDMG) and the TW Hya, Tucana–Horologium, Columba, Carina, and Argus associations. Images in $i^{\mathrm{\prime <!--\; ???\; -->}}$ and $z^{\mathrm{\prime <!--\; ???\; -->}}$ filters were obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to search for companions down to an apparent magnitude of $z^{\mathrm{\prime <!--\; ???\; -->}}$ ∼ 22–24 at separations ≳20″ from the targets and in the remainder of the wide 5.′5 × 5.′5 GMOS field of view. This allowed us to probe the most distant region where planetary-mass companions could be gravitationally bound to the targets. This region was left largely unstudied by past high-contrast imaging surveys, which probed much closer-in separations. This survey led to the discovery of a planetary-mass (9–13 $M_{\mathrm{J}\mathrm{u}\mathrm{p}}$) companion at 2000 au from the M3V star GU Psc, a highly probable member of ABDMG. No other substellar companions were identified. These results allowed us to constrain the frequency of distant planetary-mass companions (5–13 $M_{\mathrm{J}\mathrm{u}\mathrm{p}}$) to ${0.84}_{-<!--\; ???\; -->0.66}^{+6.73}$% (95% confidence) at semimajor axes between 500 and 5000 au around young K5–L5 stars and brown dwarfs. This is consistent with other studies suggesting that gravitationally bound planetary-mass companions at wide separations from low-mass stars are relatively rare.

[en] We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the β Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as Hα and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in β Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for β Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708 Å equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the β Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age.

[en] We present the results of a search for new circumstellar disks around low-mass stars and brown dwarfs with spectral types >K5 that are confirmed or candidate members of nearby young moving groups. Our search input sample was drawn from the BANYAN surveys of Malo et al. and Gagné et al. Two Micron All-Sky Survey and Wide-field Infrared Survey Explorer data were used to detect near- to mid-infrared excesses that would reveal the presence of circumstellar disks. A total of 13 targets with convincing excesses were identified: 4 are new and 9 were already known in the literature. The new candidates are 2MASS J05010082–4337102 (M4.5), J08561384–1342242 ($\mathrm{M}8\mathrm{\gamma <!--\; ??\; -->}$), J12474428–3816464 ($\mathrm{M}9\mathrm{\gamma <!--\; ??\; -->}$), and J02265658–5327032 ($\mathrm{L}0\mathrm{\delta <!--\; ??\; -->}$); they are candidate members of the TW Hya ($\sim <!--\; ???\; -->10\pm <!--\; ??\; -->3$ Myr), Columba (∼${42}_{-<!--\; ???\; -->4}^{+6}$Myr), and Tucana-Horologium ($\sim <!--\; ???\; -->45\pm <!--\; ??\; -->4$ Myr) associations, with masses of 120 and 13–18 $M_{\mathrm{J}\mathrm{u}\mathrm{p}}$. The M8–L0 objects in Columba and Tucana-Horologium are potentially among the first substellar disk systems aged ∼40 Myr. Estimates of the new candidates’ mean disk temperatures and fractional luminosities are in the ranges ∼$135\text{--}520\mathrm{K}$ and $0.021\text{--}0.15$, respectively. New optical spectroscopy of J0501–4337 reveals strong Hα emission, possibly indicating ongoing accretion, provides a detection of lithium absorption, and shows a radial velocity measurement that is consistent with a membership to Columba. We also present a near-infrared spectrum of J0226–5327 that reveals Paschen β emission and shows signs of low surface gravity, consistent with accretion from a disk and a young age.

[en] We present new JHK spectroscopy (R ∼ 5000) of GQ Lup b, acquired with the Near-Infrared Integral Field Spectrograph and the adaptive optics system ALTAIR at the Gemini North telescope. Angular differential imaging was used in the J and H bands to suppress the speckle noise from GQ Lup A; we show that this approach can provide improvements in signal-to-noise ratio (S/N) by a factor of 2-6 for companions located at subarcsecond separations. Based on high-quality observations and Global Astrometric lnterferometer for Astrophysics synthetic spectra, we estimate the companion effective temperature to T _eff = 2400 ± 100 K, its gravity to log g = 4.0 ± 0.5, and its luminosity to log(L/L _sun) = -2.47 ± 0.28. Comparisons with the predictions of the DUSTY evolutionary tracks allow us to constrain the mass of GQ Lup b to 8-60 M _Jup, most likely in the brown dwarf regime. Compared with the spectra published by Seifahrt and collaborators, our spectra of GQ Lup b are significantly redder (by 15%-50%) and do not show important Paβ emission. Our spectra are in excellent agreement with the lower S/N spectra previously published by McElwain and collaborators.