Authors:Ishihara et alAbstract:Context:Debris disks are important observational clues for understanding planetary-system formation process. In particular, faint warm debris disks may be related to late planet formation near 1 AU. A systematic search of faint warm debris disks is necessary to reveal terrestrial planet formation.Aims:Faint warm debris disks show excess emission that peaks at mid-IR wavelengths. Thus we explore debris disks using the AKARI mid-IR all-sky point source catalog (PSC), a product of the second generation unbiased IR all-sky survey.Methods:We investigate IR excess emission for 678 isolated main-sequence stars for which there are 18 micron detections in the AKARI mid-IR all-sky catalog by comparing their fluxes with the predicted fluxes of the photospheres based on optical to near-IR fluxes and model spectra. The near-IR fluxes are first taken from the 2MASS PSC. However, 286 stars with Ks<4 .5="" 1.4="" 1.8="" 14="" 2mass="" accuracy="" accurate="" africa="" and="" applying="" average.="" band="" br="" density="" due="" errors="" filters="" flux="" fluxes="" for="" from="" h="" have="" imager="" improved="" in="" infrared="" irsf="" j="" ks="" large="" m="" measured="" near-ir="" neutral="" on="" our="" phi="" photometry="" sample="" saturation.="" simultaneous="" south="" survey="" telescope="" the="" thus="" to="" unbiased="" we="">
Results:
We identified 53 debris-disk candidates including eight new detections from our sample of 678 main-sequence stars. The detection rate of debris disks for this work is ~8%, which is comparable with those in previous works by Spitzer and Herschel.
Conclusion:
The importance of this study is the detection of faint warm debris disks around nearby field stars. At least nine objects have a large amount of dust for their ages, which cannot be explained by the conventional steady-state collisional cascade model.
Saturday, December 3, 2016
Faint Warm Debris Disks Around Nearby Bright Stars
Friday, December 2, 2016
L-band Spectroscopy with Magellan-AO/Clio2: First Results on Young Low-Mass Companions
Authors:Stone et alAbstract:L-band spectroscopy is a powerful probe of cool low-gravity atmospheres: The P, Q, and R branch fundamental transitions of methane near 3.3 μm provide a sensitive probe of carbon chemistry; cloud thickness modifies the spectral slope across the band; and H+3 opacity can be used to detect aurorae. Many directly imaged gas-giant companions to nearby young stars exhibit L-band fluxes distinct from the field population of brown dwarfs at the same effective temperature. Here we describe commissioning the L-band spectroscopic mode of Clio2, the 1-5 μm instrument behind the Magellan adaptive-optics system. We use this system to measure L-band spectra of directly imaged companions. Our spectra are generally consistent with the parameters derived from previous near-infrared spectra for these late M to early L type objects. Therefore, deviations from the field sequence are constrained to occur below 1500 K. This range includes the L-T transition for field objects and suggests that observed discrepancies are due to differences in cloud structure and CO/CH4 chemistry.
Pleiades HII 3441B: a Brown Dwarf Companion
Authors:Konishi et alAbstract:We find a new substellar companion to the Pleiades member star, Pleiades HII 3441, using the Subaru telescope with adaptive optics. The discovery is made as part of the high-contrast imaging survey to search for planetary-mass and substellar companions in the Pleiades and young moving groups. The companion has a projected separation of 0".49 +/- 0".02 (66 +/- 2 AU) and a mass of 68 +/- 5 M_J based on three observations in the J-, H-, and K_S-band. The spectral type is estimated to be M7 (~2700 K), and thus no methane absorption is detected in the H band. Our Pleiades observations result in the detection of two substellar companions including one previously reported among 20 observed Pleiades stars, and indicate that the fraction of substellar companions in the Pleiades is about 10.0 +26.1/-8.8 %. This is consistent with multiplicity studies of both the Pleiades stars and other open clusters.
Looking for Radio Flares From Brown Dwarfs
Authors:Route et alAbstract:We describe our second installment of the 4.75 GHz survey of ultracool dwarfs (UCDs) conducted with the Arecibo radio telescope, which has observed 27 such objects and resulted in the detection of sporadic flaring from the T6 dwarf, WISEPC J112254.73+255021.5. We also present follow up observations of the first radio-emitting T dwarf, 2MASS J10475385+2124234, a tentatively identified radio emitting L1 dwarf, 2MASS J1439284+192915, and the known radio-flaring source, 2MASS J13142039+132011 AB. Our new data indicate that 2MASS J1439284+192915 is not a radio flaring source. The overall detection rate of our unbiased survey for radio-flaring UCDs is ~5% for new sources, with a detection rate for each spectral class of ~5-10%. Evidently, radio luminosity of the UCDs does not appear to monotonically decline with spectral type from M7 dwarfs to giant planets, in contradiction to theories of the magnetic field generation and internal structure of these objects. Along with other, recently published results, our data exemplify the unique value of using radio surveys to reveal and study properties of substellar magnetic activity.
Thursday, December 1, 2016
A Detection of the Secondary Eclipse of hot Jupiter Qatar-1b
Authors:Cruz et alAbstract:Qatar-1b is a close-orbiting hot-Jupiter (Rp≃1.18 RJ, Mp≃1.33 MJ) around a metal-rich K-dwarf, with orbital separation and period of 0.023 AU and 1.42 days, respectively. We have observed the secondary eclipse of this exoplanet in the Ks-band with the objective of deriving a brightness temperature for the planet and providing further constraints to the orbital configuration of the system. We obtained near-infrared photometric data from the ground by using the OMEGA2000 instrument at the 3.5 m telescope at Calar Alto (Spain), in staring mode, with the telescope defocused. We have used Principal Component Analysis (PCA) to identify correlated systematic trends in the data. A Markov chain Monte Carlo analysis was performed in order to model the correlated systematics and fit for the secondary eclipse of Qatar-1b using the occultation model by Mandel & Agol (2002). We measured a secondary eclipse depth of 0.196%+0.071%−0.051%, which indicates a brightness temperature in the Ks-band for the planet of 1885+212−168 K. We also measured a small deviation in the central phase of the secondary eclipse of −0.0079+0.0162−0.0043, which leads to a value for ecosω of −0.0123+0.0252−0.0067. However, this last result should be confirmed with more data. This work highlights that ground-based secondary eclipse observations are capable of providing useful constraints on the orbital configuration of bright, giant planets that can be used to probe the architecture and multiplicity in hot Jupiter systems.
KELT-12b: A Highly Inflated Hot Jupiter Transiting a Mildly Evolved Hot Star
Authors:Stevens et alAbstract:We report the discovery of KELT-12b, a highly inflated Jupiter-mass planet transiting a mildly evolved host star. We identified the initial transit signal in the KELT-North survey data and established the planetary nature of the companion through precise follow-up photometry, high-resolution spectroscopy, precise radial velocity measurements, and high-resolution adaptive optics imaging. Our preferred best-fit model indicates that the V=10.64 host, TYC 2619-1057-1, has Teff=6278±51 K, logg⋆=3.89+0.054−0.051, and [Fe/H] = 0.19+0.083−0.085, with an inferred mass M⋆=1.59+0.071−0.091M⊙ and radius R⋆=2.37±0.18R⊙. The planetary companion has MP=0.95±0.14MJ, RP=1.79+0.18−0.17RJ, loggP=2.87+0.097−0.098, and density ρP=0.21+0.075−0.054 g cm−3, making it one of the most inflated giant planets known. The time of inferior conjunction in BJDTDB is 2457088.692055±0.0009 and the period is P=5.0316144±0.0000306 days. Despite the relatively large separation of ∼0.07 AU implied by its ∼5.03-day orbital period, KELT-12b receives significant flux of 2.93+0.33−0.30×109 erg s−1 cm−2 from its host. We compare the radii and insolations of transiting giant planets around hot (Teff≥6250 K) and cool stars, noting that the observed paucity of known transiting giants around hot stars with low insolation is likely due to selection effects. We underscore the significance of long-term ground-based monitoring of hot stars and space-based targeting of hot stars with the Transiting Exoplanet Survey Satellite (TESS) to search for inflated giants in longer-period orbits.
Hot Jupiter WASP-103b Really Does Have an Anomalous Transmission Spectrum
Contamination from a nearby star cannot explain the anomalous transmission spectrum of the ultra-short period giant planet WASP-103b
Authors:
Southworth et al
Abstract:
The planet in the WASP-103 system is an excellent candidate for transmission spectroscopy because of its large radius and high temperature. Application of this technique found a variation of radius with wavelength which was far too strong to be explained by scattering processes in the planetary atmosphere. A faint nearby star was subsequently detected, whose contamination of the transit light curves might explain this anomaly. We present a reanalysis of published data in order to characterise the faint star and assess its effect on the measured transmission spectrum. The faint star has a mass of 0.72 +/- 0.08 Msun and is almost certainly gravitationally bound to the planetary system. We find that its effect on the measured physical properties of the planet and host star is small, amounting to a planetary radius larger by 0.6 sigma and planetary density smaller by 0.8 sigma. Its influence on the measured transmission spectrum is much greater: the spectrum now has a minimum around 760 nm and opacity rises to both bluer and redder wavelengths. It is a poor match to theoretical spectra and the spectral slope remains too strong for Rayleigh scattering. The existence of the faint nearby star cannot therefore explain the measured spectral properties of this hot and inflated planet. We advocate further observations of the system, both with high spatial resolution in order to improve the measured properties of the faint star, and with higher spectral resolution to confirm the anomalous transmission spectrum of the planet.
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