Terrestrial World OGLE-2016-BLG-1195Lb Orbits a Brown Dwarf at 1.16 AU

An Earth-mass Planet in a 1-AU Orbit around an Ultracool Dwarf

Authors:

Shvartzvald et al

Abstract:
We combine Spitzer and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass (1.43+0.45−0.32M⊕) planet OGLE-2016-BLG-1195Lb at 1.16+0.16−0.13 AU orbiting a 0.078+0.016−0.012M⊙ ultracool dwarf. This is the lowest-mass microlensing planet to date. At 3.91+0.42−0.46 kpc, it is the third consecutive case among the Spitzer "Galactic distribution" planets toward the Galactic bulge that lies in the Galactic disk as opposed to the bulge itself, hinting at a skewed distribution of planets. Together with previous microlensing discoveries, the seven Earth-size planets orbiting the ultracool dwarf TRAPPIST-1, and the detection of disks around young brown dwarfs, OGLE-2016-BLG-1195Lb suggests that such planets might be common around ultracool dwarfs. It therefore sheds light on the formation of both ultracool dwarfs and planetary systems at the limit of low-mass protoplanetary disks.

Can we Detect Exoplanets Transitiong L & T Class Brown Dwarfs?

POLARIMETRIC DETECTION OF EXOPLANETS TRANSITING T AND L BROWN DWARFS

Author:

Sengupta

Abstract:

While scattering of light by atoms and molecules yields large amounts of polarization at the B-band of both T and L dwarfs, scattering by dust grains in the cloudy atmosphere of L dwarfs gives rise to significant polarization at the far-optical and infrared wavelengths where these objects are much brighter. However, the observable disk-averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed large polarization of several L dwarfs, rotation-induced oblateness or horizontally inhomogeneous cloud distribution in the atmosphere is invoked. On the other hand, when an extra-solar planet of Earth-size or larger transits the brown dwarf along the line of sight, the asymmetry induced during the transit gives rise to a net non-zero, time-dependent polarization. Employing atmospheric models for a range of effective temperature and surface gravity appropriate for T and L dwarfs, I derive the time-dependent polarization profiles of these objects during the transit phase and estimate the peak amplitude of polarization that occurs during the inner contact points of the transit ingress/egress phase. It is found that peak polarization in the range of 0.2%–1.0% at I and J band may arise of cloudy L dwarfs occulted by Earth-size or larger exoplanets. Such an amount of polarization is higher than what can be produced by rotation-induced oblateness of even rapidly rotating L dwarfs. Hence, I suggest that time-resolved imaging polarization could be a potential technique for detecting transiting exoplanets around L dwarfs.

Hunting for Close-in Circum Brown Dwarf Exoplanets

First limits on the occurrence rate of short-period planets orbiting brown dwarfs

Authors:

He et al

Abstract:

Planet formation theories predict a large but still undetected population of short-period terrestrial planets orbiting brown dwarfs. Should specimens of this population be discovered transiting relatively bright and nearby brown dwarfs, the Jupiter-size and the low luminosity of their hosts would make them exquisite targets for detailed atmospheric characterisation with JWST and future ground-based facilities. The eventual discovery and detailed study of a significant sample of transiting terrestrial planets orbiting nearby brown dwarfs could prove to be useful not only for comparative exoplanetology but also for astrobiology, by bringing us key information on the physical requirements and timescale for the emergence of life.

In this context, we present a search for transit-signals in archival time-series photometry acquired by the Spitzer Space Telescope for a sample of 44 nearby brown dwarfs. While these 44 targets were not particularly selected for their brightness, the high precision of their Spitzer light curves allows us to reach sensitivities below Earth-sized planets for 75% of the sample and down to Europa-sized planets on the brighter targets. We could not identify any unambiguous planetary signal. Instead, we could compute the first limits on the presence of planets on close-in orbits. We find that within a 1.28 day orbit, the occurrence rate of planets with a radius between 0.75 and 3.25 R⊕ is {\eta} < 67 ± 1%. For planets with radii between 0.75 and 1.25 R⊕, we place a 95% confident upper limit of {\eta} < 87 ± 3%. If we assume an occurrence rate of {\eta} = 27% for these planets with radii between 0.75 and 1.25 R⊕, as the discoveries of the Kepler-42b and TRAPPIST-1b systems would suggest, we estimate that 175 brown dwarfs need to be monitored in order to guarantee (95%) at least one detection.

Polarimetric Detection of Exoplanets Transiting T- and L- Brown Dwarfs

Polarimetric Detection of Exoplanets Transiting T- and L- Brown Dwarfs

Author:

Senjugupta

Abstract:

While scattering of light by atoms and molecules yields large amount of polarization at the B-band of both T- and L-dwarfs, scattering by dust grains in cloudy atmosphere of L-dwarfs gives rise to significant polarization at the far-optical and infra-red wavelengths where these objects are much brighter. However, the observable disk averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed large polarization of several L-dwarfs, rotation-induced oblateness or horizontally inhomogeneous cloud distribution in the atmosphere is invoked. On the other hand, when an extra-solar planet of Earth-size or larger transits the brown dwarf along the line of sight, the asymmetry induced during the transit gives rise to a net non-zero, time dependent polarization. Employing atmospheric models for a range of effective temperature and surface gravity appropriate for T- and L-dwarfs, I derive the time dependent polarization profiles of these objects during transit phase and estimate the peak amplitude of polarization that occurs during the inner contact points of the transit ingress/egress phase. It is found that peak polarization in the range of 0.2-1.0 % at I- and J-band may arise of cloudy L dwarfs occulted by Earth-size or larger exoplanets. Such an amount of polarization is higher than that can be produced by rotation-induced oblateness of even the rapidly rotating L-dwarfs. Hence, I suggest that time resolved imaging polarization should be a potential technique to detect transiting exoplanets around L-dwarfs.

Circum Brown Dwarf Gas Giant 2M1207b has Heterogeneous Clouds and a 11 Hour Rotation

Discovery of Rotational Modulations in the Planetary-Mass Companion 2M1207b: Intermediate Rotation Period and Heterogeneous Clouds in a Low Gravity Atmosphere

Authors:

Zhou et al

Abstract:

Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution. Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We present here, for the first time, time-resolved high-precision photometric measurements of a planetary-mass companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photon-noise limited accuracy for both the primary and the secondary. While the primary is consistent with a flat light curve, the secondary shows modulations that are clearly detected in the combined light curve as well as in different subsets of the data. The amplitudes are 1.36% in the F125W and 0.78% in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period of 10.7+1.2−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b is very similar to a field brown dwarf that has identical spectral type but different J-H color. Importantly, our study also measures, for the first time, the rotation period for a directly imaged extra-solar planetary-mass companion.

OGLE-2013-BLG-0723LB/Bb: A Brown Dwarf With a Venus-Mass Exoplanet in Orbit

A Venus-Mass Planet Orbiting a Brown Dwarf: Missing Link between Planets and Moons

Authors:

Udalski et al

Abstract:

The co-planarity of solar-system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the {\it Kepler} satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. We report here the discovery of an intermediate system OGLE-2013-BLG-0723LB/Bb composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled down version of a planet plus star or as a scaled up version of a moon plus planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us to suggest that formation processes of companions within accretion disks around stars, brown dwarfs, and planets are similar.