B. Burningham

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager

An exoplanet extracted from the bright Direct imaging of Jupiter-like exoplanets around young stars provides a glimpse into how our solar system formed. The brightness of young stars requires the use of next-generation devices such as the Gemini Planet Imager (GPI). Using the GPI, Macintosh et al. discovered a Jupiter-like planet orbiting a young star, 51 Eridani (see the Perspective by Mawet). The planet, 51 Eri b, has a methane signature and is probably the smallest exoplanet that has been directly imaged. These findings open the door to understanding solar system origins and herald the dawn of a new era in next-generation planetary imaging. Science, this issue p. 64; see also p. 39 The Gemini Planet Imager detects a Jupiter-like exoplanet orbiting the young star 51 Eridani. [Also see Perspective by Mawet] Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10−6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.

MID-INFRARED PHOTOMETRY OF COLD BROWN DWARFS: DIVERSITY IN AGE, MASS, AND METALLICITY

Original article can be found at: http://www.iop.org/EJ/journal/apj [Full text of this article is not available in the UHRA]

The discovery of a very cool, very nearby brown dwarf in the Galactic plane

We report the discovery of a very cool, isolated brown dwarf, UGPS 0722-05, with the United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Galactic Plane Survey. The near-infrared spectrum displays deeper H2O and CH4 troughs than the coolest known T dwarfs and an unidentified absorption feature at 1.275 mu m. We provisionally classify the object as a T10 dwarf but note that it may in future come to be regarded as the first example of a new spectral type. The distance is measured by trigonometric parallax as d = 4.1(-0.5)(+0.6) pc, making it the closest known isolated brown dwarf. With the aid of Spitzer/Infrared Array Camera (IRAC) we measure H - [4.5] = 4.71. It is the coolest brown dwarf presently known - the only known T dwarf that is redder in H - [4.5] is the peculiar T7.5 dwarf SDSS J1416+13B, which is thought to be warmer and more luminous than UGPS 0722-05. Our measurement of the luminosity, aided by Gemini/T-ReCS N-band photometry, is L = 9.2 +/- 3.1 x 10(-7) L-circle dot. Using a comparison with well-studied T8.5 and T9 dwarfs we deduce T-eff = 520 +/- 40 K. This is supported by predictions of the Saumon & Marley models. With apparent magnitude J = 16.52, UGPS 0722-05 is the brightest of the similar to 90 T dwarfs discovered by UKIDSS so far. It offers opportunities for future study via high-resolution near-infrared spectroscopy and spectroscopy in the thermal infrared.

The discovery of an M4+T8.5 binary system

The original article can be found at: http://www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14620.x

Exploring the substellar temperature regime down to ∼550 K

We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3 (ULAS1238) and ULAS J133553.45+113005.2 (ULAS1335). We detail optical and near-infrared photometry for all three sources, and mid-infrared photometry for ULAS1335. We use near-infrared spectra of each source to assign spectral types T8p (ULAS1017), T8.5 (ULAS1238) and T9 (ULAS1335) to these objects. ULAS1017 is classed as a peculiar T8 (T8p) due to appearing as a T8 dwarf in the J-band, whilst exhibiting H and K-band flux ratios consistent with a T6 classification. Through comparison to BT-Settl model spectra we estimate that ULAS1017 has 750K T8 dwarfs to the rest of the T dwarf sequence, the suggestion of the Y0 spectral class for these objects is premature. Comparison of model spectra with that of ULAS1335 suggest a temperature below 600K, possibly combined with low-gravity and/or high-metallicity. We find ULAS1335 to be extremely red in near to mid-infrared colours, with H [4.49] = 4.34 ± 0.04 . This is the reddest near to mid-infrared colour yet observed for a T dwarf. The near to mid-infrared spectral energy distribution of ULAS1335 further supports Teff < 600K, and we estimate Teff � 550 600K for ULAS1335. We estimate that ULAS1335 has an age of 0.6–5.3 Gyr, a mass of 15–31 MJ and lies at a distance of 8–12 pc.

Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between �24–93pc), identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. (2006). Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations), and find that one of these new T dwarfs may be metal poor, three may have low surface gravity, and one may have high surface gravity. The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y J with decreasing effective temperature, and some interesting colour changes in J H and z J (deserving further investigation) beyond T8. The LAS T dwarf sample from the first and second main data releases show good evidence for a consistent level of completion to J=19. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17±4 >T4 dwarfs in the J 619 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent α between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the α � 1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class.

Eight new T4.5–T7.5 dwarfs discovered in the UKIDSS Large Area Survey Data Release 1

The definitive version is available at www.blackwell-synergy.com Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2007.12023.x

The properties of the T8.5p dwarf Ross 458C

The definitive version can be found at: http://onlinelibrary.wiley.com/ Copyright The Royal Astronomical Society

The physical properties of four ~600 K T dwarfs

We present Spitzer 7.6-14.5 μm spectra of ULAS J003402.77–005206.7 and ULAS J133553.45+113005.2, two T9 dwarfs with the latest spectral types currently known. We fit synthetic spectra and photometry to the near- through mid-infrared energy distributions of these dwarfs and that of the T8 dwarf 2MASS J09393548–2448279. We also analyze near-infrared data for another T9, CFBD J005910.82–011401.3. We find that the ratio of the mid- to near-infrared fluxes is very sensitive to effective temperature at these low temperatures, and that the 2.2 μm and 4.5 μm fluxes are sensitive to metallicity and gravity; increasing gravity has a similar effect to decreasing metallicity, and vice versa, and there is a degeneracy between these parameters. The 4.5 μm and 10 μm fluxes are also sensitive to vertical transport of gas through the atmosphere, which we find to be significant for these dwarfs. The full near- through mid-infrared spectral energy distribution allows us to constrain the effective temperature (K)/gravity (ms^(–2))/metallicity ([m/H] dex) of ULAS J0034–00 and ULAS J1335+11 to 550-600/100-300/0.0-0.3 and 500-550/100-300/0.0-0.3, respectively. These fits imply low masses and young ages for the dwarfs of 5-20 M_(Jupiter) and 0.1-2 Gyr. The fits to 2MASS J0939–24 are in good agreement with the measured distance, the observational data, and the earlier T8 near-infrared spectral type if it is a slightly metal-poor 4-10 Gyr old system consisting of a 500 K and 700 K, ~25 M_(Jupiter) and ~40 M_(Jupiter), pair, although it is also possible that it is an identical pair of 600 K, 30_(M Jupiter), dwarfs. As no mid-infrared data are available for CFBD J0059–01 its properties are less well constrained; nevertheless it appears to be a 550-600 K dwarf with g = 300-2000 ms^(–2) and [m/H] = 0-0.3 dex. These properties correspond to mass and age ranges of 10-50 M_(Jupiter) and 0.5-10 Gyr for this dwarf.

The discovery of a very cool binary system

The definitive version can be found at: http://www3.interscience.wiley.com/ Copyright Royal Astronomical Society