The Omega nebula M17 from the VLT survey telescope

Image credits: ESO/Phil Plait/Discover magazine
Rounding up some of the latest exoplanet and brown dwarf news from the literature this week: firstly I noted the direct imaging discovery of the Jovian analogue GJ 504b which has a projected (on the plane of the sky) separation from its parent (G0V) star of 43.5 AU, causing some problems for the core accretion scenario of planet formation, as explained by Paul Glister over at Centauri Dreams, here.

Direct imaging and cancellation of starlight works well to discover planets in rather distant orbits: microlensing, on the other hand, is a useful method to find closer in planets, although the method is limited by the requirement of close on the sky alignment between the foreground system with planet and a background target star. Recently a 2 Jupiter mass planet has been found only 0.87 AU from an old, field brown dwarf. Neptune mass planets have been found by the method. Microlensing resources can be found here, here and here. From the first linked paper of these:

Gravitational microlensing occurs when a foreground star happens to pass very close to our line of sight to a more distant background star. The foreground star acts as a lens, splitting the light from the background source star into two images, which are typically unresolved. However, these images of the source are also magnified, by an amount that depends on the angular separation between the lens and source. The relative motion between the lens and source therefore results in a time-variable magnification of the source: a microlensing event. If the foreground star happens to host a planet with projected separation near the paths of these images, the planet will also act as a lens, further perturbing the images and resulting in a characteristic, short-lived signature of the planet.

Elsewhere, in a paper accepted to MNRAS, Pinfield et al. have identified two late T dwarfs from WISE which have kinematics (space motions) consistent with them being old objects belonging to the galactic thick disk or even halo population. Schneider et al. inform us of a study of HD 166191, a young F8 star, which shows how WISE data can be used to study infrared excesses above the stellar photosphere, indicating circumstellar and likely planet-forming material. This warm dust disk (~ 150K) is a rarity, hinting perhaps at a phase of ongoing collisional planet-building. Lastly, and on a cosmological note, a gamma ray burst has been found at redshift z ~ 5.9. The burst, one of the most distant yet seen, marks the death of a massive star from a time when the Universe was only enriched in metals – elements heavier than hydrogen and helium forged in stellar interiors – to one tenth of the present day value.

Update: astrometry is the direct positional measurement of the period of a secondary, or companion, from which masses and semi-major axes can be deduced using various Keplerian methodologies. Like microlensing, astrometry is also sensitive to planets at small to intermediate separations, especially for low-mass primaries, as shown by this recent discovery around another field brown dwarf, in a 246 day orbit.


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