Using PAN-STARRS1 and WISE to Hunt for Brown Dwarfs at the L/T Transition

A SEARCH FOR L/T TRANSITION DWARFS WITH PAN-STARRS1 AND WISE. II. L/T TRANSITION ATMOSPHERES AND YOUNG DISCOVERIES

Authors:

Best et al

Abstract:

The evolution of brown dwarfs from L to T spectral types is one of the least understood aspects of the ultracool population, partly for lack of a large, well-defined, and well-characterized sample in the L/T transition. To improve the existing census, we have searched ≈28,000 deg2 using the Pan-STARRS1 and Wide-field Infrared Survey Explorer surveys for L/T transition dwarfs within 25 pc. We present 130 ultracool dwarf discoveries with estimated distances ≈9–130 pc, including 21 that were independently discovered by other authors and 3 that were previously identified as photometric candidates. Seventy-nine of our objects have near-IR spectral types of L6–T4.5, the most L/T transition dwarfs from any search to date, and we have increased the census of L9–T1.5 objects within 25 pc by over 50%. The color distribution of our discoveries provides further evidence for the "L/T gap," a deficit of objects with (J − K)MKO ≈ 0.0–0.5 mag in the L/T transition, and thus reinforces the idea that the transition from cloudy to clear photospheres occurs rapidly. Among our discoveries are 31 candidate binaries based on their low-resolution spectral features. Two of these candidates are common proper motion companions to nearby main sequence stars; if confirmed as binaries, these would be rare benchmark systems with the potential to stringently test ultracool evolutionary models. Our search also serendipitously identified 23 late-M and L dwarfs with spectroscopic signs of low gravity implying youth, including 10 with vl-g or int-g gravity classifications and another 13 with indications of low gravity whose spectral types or modest spectral signal-to-noise ratio do not allow us to assign formal classifications. Finally, we identify 10 candidate members of nearby young moving groups (YMG) with spectral types L7–T4.5, including three showing spectroscopic signs of low gravity. If confirmed, any of these would be among the coolest known YMG members and would help to determine the effective temperature at which young brown dwarfs cross the L/T transition.

UScoJ155150.2−213457: A new Free-floating ExoPlanet (Brown Dwarf?) in the Upper Scorpius association

A new free-floating planet in the Upper Scorpius association

Authors:

Ramírez et al

Abstract:

We report on a deep photometric survey covering an area of 1.17 deg2 in the young Upper Scorpius stellar association using VIMOS Iz and UKIDSS ZJHK data taking several years apart. The search for the least massive population of Upper Scorpius (∼5-10 Myr, 145 pc) is performed on the basis of various optical and infrared color-color and color-magnitude diagrams, including WISE photometry, in the magnitude interval J=14.5-19 mag (completeness), which corresponds to substellar masses from 0.028 through 0.004 M⊙ at the age and distance of Upper Scorpius. We also present the proper motion analysis of the photometric candidates, finding that two objects successfully pass all photometric and astrometric criteria for membership in the young stellar association. One of them, UScoJ155150.2−213457, is a new discovery. We obtained low resolution, near-infrared spectroscopy (R∼450, 0.85--2.35 μm) of this new finding using the FIRE instrument. We confirmed its low-gravity atmosphere expected for an Upper Scorpius member (weak alkaline lines, strong VO absorption, peaked H-band pseudocontinuum). By comparison with spectroscopic standards, we derive a spectral type of L6±1, and estimate a mass of ≈0.008-0.010 M⊙ for UScoJ155150.2−213457. The colors and spectral slope of this object resemble those of other young, cool members of Upper Scorpius and σ Orionis (∼3 Myr) and field, high gravity dwarfs of related classification in contrast with the very red indices of field, low gravity, L-type dwarfs of intermediate age. UScoJ155150.2−213457, which does not show infrared flux excesses up to 4.5 μm, becomes one of the least massive and latest type objects known in the entire Upper Scorpius stellar association.

WASP-135b: an Inflated hot Jupiter in a 1.4 day Orbit Around a G5 Dwarf Star

WASP-135b: a highly irradiated, inflated hot Jupiter orbiting a G5V star

Authors:

Spake et al

Abstract:

We report the discovery of a new transiting planet from the WASP survey. WASP-135b is a hot Jupiter with a radius of 1.30 pm 0.09 Rjup, a mass of 1.90 pm 0.08 Mjup and an orbital period of 1.401 days. Its host is a Sun-like star, with a G5 spectral type and a mass and radius of 0.98 pm 0.06 Msun and 0.96 pm 0.05 Rsun respectively. The proximity of the planet to its host means that WASP-135b receives high levels of insolation, which may be the cause of its inflated radius. Additionally, we find weak evidence of a transfer of angular momentum from the planet to its star.

KIC 8462852's Circumstellar Dust Matches the Recent Cometary Breakup Scenario

Constraints on the circumstellar dust around KIC 8462852

Authors:

Thompson

Abstract:

We present millimetre (SMA) and sub-millimetre (SCUBA-2) continuum observations of the peculiar star KIC 8462852 which displayed several deep and aperiodic dips in brightness during the Kepler mission. Our observations are approximately confusion-limited at 850 μm and are the deepest millimetre and sub-millimetre photometry of the star that has yet been carried out. No significant emission is detected towards KIC 8462852. We determine upper limits for dust between a few 10−6 M⊕ and 10−3 M⊕ for regions identified as the most likely to host occluding dust clumps and a total overall dust budget of less than 7.7 M⊕ within a radius of 200 AU. Such low limits for the inner system make the catastrophic planetary disruption hypothesis unlikely. Integrating over the Kepler lightcurve we determine that at least 10−9 M⊕ of dust is required to cause the observed Q16 dip. This is consistent with the currently most favoured cometary breakup hypothesis, but nevertheless implies the complete breakup of ∼ 30 Comet 1/P Halley type objects. Finally, in the wide SCUBA-2 field-of-view we identify another candidate debris disc system that is potentially the largest yet discovered.

KIC 8462852 Needs 648,000 Two Hundred km Comets to Fade as Much as Observed From 1890 to 1989

KIC 8462852 Faded at an Average Rate of 0.165+-0.013 Magnitudes Per Century From 1890 To 1989

Author:

Schafer

Abstract:

The star KIC 8462852 is a completely-ordinary F3 main sequence star, except that the light curve from the Kepler spacecraft shows episodes of unique and inexplicable day-long dips with up to 20% dimming. Here, I provide a light curve of 1232 Johnson B-band magnitudes from 1890 to 1989 taken from archival photographic plates at Harvard. KIC 8462852 displays a highly significant and highly confident secular dimming at an average rate of 0.165+-0.013 magnitudes per century. From the early 1890s to the late 1980s, KIC 8462852 has faded by 0.193+-0.030 mag. This century-long dimming is completely unprecedented for any F-type main sequence star. So the Harvard light curve provides the first confirmation (past the several dips seen in the Kepler light curve alone) that KIC 8462852 has anything unusual going on. The century-long dimming and the day-long dips are both just extreme ends of a spectrum of timescales for unique dimming events, so by Ockham's Razor, all this is produced by one physical mechanism. This one mechanism does not appear as any isolated catastrophic event in the last century, but rather must be some ongoing process with continuous effects. Within the context of dust-occultation models, the century-long dimming trend requires 10^4 to 10^7 times as much dust as for the one deepest Kepler dip. Within the context of the comet-family idea, the century-long dimming trend requires an estimated 648,000 giant comets (each with 200 km diameter) all orchestrated to pass in front of the star within the last century.

The Mass-Metallicity Relation for Giant Planets

The Mass-Metallicity Relation for Giant Planets

Authors:

Thorngren et al

Abstract:

Exoplanet discoveries of recent years have provided a great deal of new data for studying the bulk compositions of giant planets. Here we identify 38 transiting giant planets (20M⊕less than M less than 20MJ) whose stellar insolation is low enough (F∗ less than 2×108ergs−1cm−2, or roughly Teff less than 1000) that they are not affected by the hot Jupiter radius inflation mechanism(s). We compute a set of new thermal and structural evolution models and use these models in comparison with properties of the 38 transiting planets (mass, radius, age) to determine their heavy element masses. A clear correlation emerges between the planetary heavy element mass Mz and the total planet mass, approximately of the form Mz∝M‾‾√. This finding is consistent with the core accretion model of planet formation. We also study how stellar metallicity [Fe/H] affects planetary metal-enrichment and find a weaker correlation than has been previously reported from studies with smaller sample sizes. Our results suggest that planets with large heavy element masses are more common around stars with a high iron abundance, but are not found there exclusively. We confirm a strong relationship between the planetary metal-enrichment relative to the parent star Zplanet/Zstar and the planetary mass, but see no relation in Zplanet/Zstar with planet orbital properties or stellar mass. Suggestively, circumbinary planets are more enriched in heavy elements than similar mass single-star planets, but with only four such planets the effect is not yet significant. The large heavy element masses of many planets (greater than 50M⊕) suggest significant amounts of heavy elements in H/He envelopes, rather than cores, such that metal-enriched giant planet atmospheres should be the rule.

Rayleigh Scattering Detected in Warm Neptune GJ 3470b's Atmosphere

Rayleigh Scattering in the Atmosphere of the Warm Exo-Neptune GJ 3470b

Authors:

Dragomir et al

Abstract:

GJ 3470b is a warm Neptune-size planet transiting a M dwarf star. Like the handful of other small exoplanets for which transmission spectroscopy has been obtained, GJ 3470b exhibits a flat spectrum in the near- and mid-infrared. Recently, a tentative detection of Rayleigh scattering in its atmosphere has been reported. This signal manifests itself as an observed increase of the planetary radius as a function of decreasing wavelength in the visible. We set out to verify this detection and observed several transits of this planet with the LCOGT network and the Kuiper telescope in four different bands (Sloan g', Sloan i', Harris B and Harris V). Our analysis reveals a strong Rayleigh scattering slope, thus confirming previous results. This makes GJ 3470b the smallest known exoplanet with a detection of Rayleigh scattering. We find that the most plausible scenario is a hydrogen/helium-dominated atmosphere covered by clouds which obscure absorption features in the infrared and hazes which give rise to scattering in the visible. Our results demonstrate the feasibility of exoplanet atmospheric characterization from the ground, even with meter-class telescopes.