We report the detection and characterization of the transiting sub-Neptune TOI-1759 b, using photometric time-series from TESS and near infrared spectropolarimetric data from SPIRou on the CFHT. ...TOI-1759 b orbits a moderately active M0V star with an orbital period of \(18.849975\pm0.000006\) d, and we measure a planetary radius and mass of \(3.06\pm0.22\) R\(_\oplus\) and \(6.8\pm2.0\) M\(_\oplus\). Radial velocities were extracted from the SPIRou spectra using both the CCF and the LBL methods, optimizing the velocity measurements in the near infrared domain. We analyzed the broadband SED of the star and the high-resolution SPIRou spectra to constrain the stellar parameters and thus improve the accuracy of the derived planet parameters. A LSD analysis of the SPIRou Stokes \(V\) polarized spectra detects Zeeman signatures in TOI-1759. We model the rotational modulation of the magnetic stellar activity using a GP regression with a quasi-periodic covariance function, and find a rotation period of \(35.65^{+0.17}_{-0.15}\) d. We reconstruct the large-scale surface magnetic field of the star using ZDI, which gives a predominantly poloidal field with a mean strength of \(18\pm4\) G. Finally, we perform a joint Bayesian MCMC analysis of the TESS photometry and SPIRou RVs to optimally constrain the system parameters. At \(0.1176\pm0.0013\) au from the star, the planet receives \(6.4\) times the bolometric flux incident on Earth, and its equilibrium temperature is estimated at \(433\pm14\) K. TOI-1759 b is a likely gas-dominated sub-Neptune with an expected high rate of photoevaporation. Therefore, it is an interesting target to search for neutral hydrogen escape, which may provide important constraints on the planetary formation mechanisms responsible for the observed sub-Neptune radius desert.
We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in ...multi-epoch WISE images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer 3.6-4.5 color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1"/yr; our fastest-moving discovery is WISEA J155349.96+693355.2 (total motion ~2.15"/yr), a possible T type subdwarf. We also report a newly discovered wide-separation (~400 AU) T8 comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSR J0002+6357 at 5.5' projected separation (~8,700 AU if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf.
A determination of the initial mass function (IMF) of the current, incomplete census of the 10 Myr-old TW Hya association (TWA) is presented. This census is built from a literature compilation ...supplemented with new spectra and 17 new radial velocities, as well as a re-analysis of Hipparcos data that confirmed HR 4334 (A2Vn) as a member. Though the dominant uncertainty in the IMF remains census incompleteness, a detailed statistical treatment is carried out to make the IMF determination independent of binning, while accounting for small number statistics. The currently known high-likelihood members are fitted by a log-normal distribution with a central mass of \(0.21^{+0.11}_{-0.06}\) \(M_{\odot}\) and a characteristic width of \(0.8^{+0.2}_{-0.1}\) dex in the 12 \(M_{\rm Jup}\)-2 \(M_{\odot}\) range, whereas a Salpeter power law with \(\alpha = 2.2^{+1.1}_{-0.5}\) best describes the IMF slope in the \(0.1-2\) \(M_{\odot}\) range. This characteristic width is higher than other young associations, which may be due to incompleteness in the current census of low-mass TWA stars. A tentative overpopulation of isolated planetary-mass members similar to 2MASS J11472421-2040204 and 2MASS J11193254-1137466 is identified: this indicates that there might be as many as \(10^{+13}_{-5}\) similar members of TWA with hot-start model-dependent masses estimated at \(\sim\) 5-7 \(M_{\rm Jup}\), most of which would be too faint to be detected in 2MASS. Our new radial velocity measurements corroborate the membership of 2MASS J11472421-2040204, and secure TWA 28 (M8.5\(\gamma\)), TWA 29 (M9.5\(\gamma\)) and TWA 33 (M4.5e) as members. The discovery of 2MASS J09553336-0208403, a young L7-type interloper unrelated to TWA, is also presented.
We present the discovery of TOI-2136b, a sub-Neptune planet transiting every
7.85 days a nearby M4.5V-type star, identified through photometric measurements
from the TESS mission. The host star is ...located $33$ pc away with a radius of
$R_{\ast} = 0.34\pm0.02\ R_{\odot}$, a mass of $0.34\pm0.02\ M_{\odot}$ and an
effective temperature of $\rm 3342\pm100\ K$. We estimate its stellar rotation
period to be $75\pm5$ days based on archival long-term photometry. We confirm
and characterize the planet based on a series of ground-based multi-wavelength
photometry, high-angular-resolution imaging observations, and precise radial
velocities from CFHT/SPIRou. Our joint analysis reveals that the planet has a
radius of $2.19\pm0.17\ R_{\oplus}$, and a mass measurement of $6.4\pm2.4\
M_{\oplus}$. The mass and radius of TOI2136b is consistent with a broad range
of compositions, from water-ice to gas-dominated worlds. TOI-2136b falls close
to the radius valley for low-mass stars predicted by the thermally driven
atmospheric mass loss models, making it an interesting target for future
studies of its interior structure and atmospheric properties.
Abbreviated We present the results of a near-infrared (NIR) spectroscopic follow-up survey of 182 M4-L7 low-mass stars and brown dwarfs (BDs) from the BANYAN All-Sky Survey (BASS) for candidate ...members of nearby, young moving groups (YMGs). We confirm signs of low-gravity for 42 new BD discoveries with estimated masses between 8-75 \(M_{Jup}\) and identify previously unrecognized signs of low gravity for 24 known BDs. This allows us to refine the fraction of low-gravity dwarfs in the high-probability BASS sample to \(\sim\)82%. We use this unique sample of 66 young BDs, supplemented with 22 young BDs from the literature, to construct new empirical NIR absolute magnitude and color sequences for low-gravity BDs. We obtain a spectroscopic confirmation of low-gravity for 2MASS J14252798-3650229, which is a new \(\sim\)27 \(M_{Jup}\), L4 \(\gamma\) bona fide member of AB Doradus. We identify a total of 19 new low-gravity candidate members of YMGs with estimated masses below 13 \(M_{Jup}\), seven of which have kinematically estimated distances within 40 pc. These objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments. We find 16 strong candidate members of the Tucana-Horologium association with estimated masses between 12.5-14 \(M_{Jup}\), a regime where our study was particularly sensitive. This would indicate that for this association there is at least one isolated object in this mass range for every \(17.5_{-5.0}^{+6.6}\) main-sequence stellar member, a number significantly higher than expected based on standard log-normal initial mass function, however in the absence of radial velocity and parallax measurements for all of them, it is likely that this over-density is caused by a number of young interlopers from other moving groups. We identify 12 new L0-L5 field BDs, seven of which display peculiar properties.
We describe in this work the BASS survey for brown dwarfs in young moving groups of the solar neighborhood, and summarize the results that it generated. These include the discovery of the 2MASS ...J01033563-5515561 (AB)b and 2MASS J02192210-3925225 B young companions near the deuterium-burning limit as well as 44 new low-mass stars and 69 new brown dwarfs with a spectroscopically confirmed low gravity. Among those, ~20 have estimated masses within the planetary regime, one is a new L4 \(\gamma\) bona fide member of AB Doradus, three are TW Hydrae candidates with later spectral types (L1-L4) than all of its previously known members and six are among the first contenders to low-gravity \(\geq\) L5 \(\beta\)/\(\gamma\) brown dwarfs, reminiscent of WISEP J004701.06+680352.1, PSO J318.5338-22.8603 and VHS J125601.92-125723.9 b. Finally, we describe a future version of this survey, BASS-Ultracool, that will specifically target \(\geq\) L5 candidate members of young moving groups. First experimentations in designing the survey have already led to the discovery of a new T dwarf member of AB Doradus, as well as the serendipitous discoveries of an L9 subdwarf and an L5 + T5 brown dwarf binary.
We present evidence that the recently discovered, directly-imaged planet HD 131399 Ab is a background star with non-zero proper motion. From new JHK1L' photometry and spectroscopy obtained with the ...Gemini Planet Imager, VLT/SPHERE, and Keck/NIRC2, and a reanalysis of the discovery data obtained with VLT/SPHERE, we derive colors, spectra, and astrometry for HD 131399 Ab. The broader wavelength coverage and higher data quality allow us to re-investigate its status. Its near-infrared spectral energy distribution excludes spectral types later than L0 and is consistent with a K or M dwarf, which are the most likely candidates for a background object in this direction at the apparent magnitude observed. If it were a physically associated object, the projected velocity of HD 131399 Ab would exceed escape velocity given the mass and distance to HD 131399 A. We show that HD 131399 Ab is also not following the expected track for a stationary background star at infinite distance. Solving for the proper motion and parallax required to explain the relative motion of HD 131399 Ab, we find a proper motion of 12.3 mas/yr. When compared to predicted background objects drawn from a galactic model, we find this proper motion to be high, but consistent with the top 4% fastest-moving background stars. From our analysis we conclude that HD 131399 Ab is a background K or M dwarf.
JWST's Near-Infrared Imager and Slitless Spectrograph (NIRISS) includes an Aperture Masking Interferometry (AMI) mode designed to be used between 2.7{\mu}m and 4.8{\mu}m. At these wavelengths, it ...will have the highest angular resolution of any mode on JWST, and, for faint targets, of any existing or planned infrastructure. NIRISS AMI is uniquely suited to detect thermal emission of young massive planets and will permit the characterization of the mid-IR flux of exoplanets discovered by the GPI and SPHERE adaptive optics surveys. It will also directly detect massive planets found by GAIA through astrometric accelerations, providing the first opportunity ever to get both a mass and a flux measurement for non-transiting giant planets. NIRISS AMI will also enable the study of the nuclear environment of AGNs.
VISTA Variables in the V\'ıa Láctea (VVV) is one of the six ESO Public Surveys operating on the new 4-meter Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way ...bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated \(K_{\rm S}\)-band tile images for stellar overdensities. Subsequently, we examined the composite \(JHK_{\rm S}\) and \(ZJK_{\rm S}\) color images of each candidate. PSF photometry of \(15\times15\) arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5\,Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solar-metallicity Padova isochrones to the color-magnitude diagrams.
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