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Register a new userThe First Spectrum of the Coldest Brown Dwarf
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The recently discovered brown dwarf WISE 0855 presents our first opportunity to directly study an object outside the Solar System that is nearly as cold as our own gas giant planets. However the traditional methodology for characterizing brown dwarfs---near infrared spectroscopy---is not currently feasible as WISE 0855 is too cold and faint. To characterize this frozen extrasolar world we obtained a 4.5-5.2 $mu$m spectrum, the same bandpass long used to study Jupiters deep thermal emission. Our spectrum reveals the presence of atmospheric water vapor and clouds, with an absorption profile that is strikingly similar to Jupiter. The spectrum is high enough quality to allow the investigation of dynamical and chemical processes that have long been studied in Jupiters atmosphere, but now on an extrasolar world.
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Context: WISE J085510.83-071442.5 (W0855) is a unique object: with Teff ca. 250 K, it is the coldest known brown dwarf (BD), located at only ca.2.2 pc form the Sun. It is extremely faint, which makes any astronomical observations difficult. However, at least one remotely similar ultra-low-mass object, the M9 dwarf TVLM 513-46546, has been shown to be a steady radio emitter at frequencies up to 95 GHz with superimposed active states where strong, pulsed emission is observed. Aims: Our goal is to determine the millimeter radio properties of W0855 with deep observations around 93 GHz (3.2 mm) in order to investigate whether radio astrometry of this object is feasible and to measure or set an upper limit on its magnetic field. Methods: We observed W0855 for 94 min at 85.1-100.9 GHz on 24 December 2019 using 44 of the Atacama Large millimeter Array (ALMA) 12 m antennas. We used the standard ALMA calibration procedure and created the final image for our analysis by accommodating the Quasar 3C 209, the brightest nearby object by far. Furthermore, we created a light curve with a 30 s time resolution to search for pulsed emission. Results: Our observations achieve a noise RMS of 7.3 {mu}Jy/beam for steady emission and of 88 {mu}Jy for 30 s pulses in the aggregated bandwidth (Stokes I). There is no evidence for steady or pulsed emission from the object at the time of the observation. We derive 3 {sigma} upper limits of 21.9 {mu}Jy on the steady emission and of 264 {mu}Jy on the pulsed emission of W0855 between 85 GHz and 101 GHz. Conclusions: Together with the recent non-detection of W0855 at 4-8 GHz, our constraints on the steady and pulsed emission from W0855 confirm that the object is neither radio-loud nor magnetospherically particularly active.
Variations of eclipse arrival times have recently been detected in several post common envelope binaries consisting of a white dwarf and a main sequence companion star. The generally favoured explanation for these timing variations is the gravitational pull of one or more circumbinary substellar objects periodically moving the center of mass of the host binary. Using the new extreme-AO instrument SPHERE, we image the prototype eclipsing post-common envelope binary V471 Tau in search of the brown dwarf that is believed to be responsible for variations in its eclipse arrival times. We report that an unprecedented contrast of 12.1 magnitudes in the H band at a separation of 260 mas was achieved, but resulted in a non-detection. This implies that there is no brown dwarf present in the system unless it is three magnitudes fainter than predicted by evolutionary track models, and provides damaging evidence against the circumbinary interpretation of eclipse timing variations. In the case of V471 Tau, a more consistent explanation is offered with the Applegate mechanism, in which these variations are prescribed to changes in the quadrupole moment within the main-sequence star
This White Paper to the National Academy of Sciences Astro2010 Decadal Review Committee highlights cross-disciplinary science opportunities over the next decade with cold brown dwarfs, sources defined here as having photospheric temperatures less than ~1000 K.
We report the discovery of OGLE-2016-BLG-1190Lb, which is likely to be the first Spitzer microlensing planet in the Galactic bulge/bar, an assignation that can be confirmed by two epochs of high-resolution imaging of the combined source-lens baseline object. The planets mass M_p= 13.4+-0.9 M_J places it right at the deuterium burning limit, i.e., the conventional boundary between planets and brown dwarfs. Its existence raises the question of whether such objects are really planets (formed within the disks of their hosts) or failed stars (low mass objects formed by gas fragmentation). This question may ultimately be addressed by comparing disk and bulge/bar planets, which is a goal of the Spitzer microlens program. The host is a G dwarf M_host = 0.89+-0.07 M_sun and the planet has a semi-major axis a~2.0 AU. We use Kepler K2 Campaign 9 microlensing data to break the lens-mass degeneracy that generically impacts parallax solutions from Earth-Spitzer observations alone, which is the first successful application of this approach. The microlensing data, derived primarily from near-continuous, ultra-dense survey observations from OGLE, MOA, and three KMTNet telescopes, contain more orbital information than for any previous microlensing planet, but not quite enough to accurately specify the full orbit. However, these data do permit the first rigorous test of microlensing orbital-motion measurements, which are typically derived from data taken over <1% of an orbital period.
The very recent discovery of planets orbiting very low mass stars sheds light on these exotic objects. Planetary systems around low-mass stars and brown dwarfs are very different from our solar system: the planets are expected to be much closer than Mercury, in a layout that could resemble the system of Jupiter and its moons. The recent discoveries point in that direction with, for example, the system of Kepler-42 and especially the system of TRAPPIST-1 which has seven planets in a configuration very close to the moons of Jupiter. Low-mass stars and brown dwarfs are thought to be very common in our neighborhood and are thought to host many planetary systems. The planets orbiting in the habitable zone of brown dwarfs (and very low-mass stars) represent one of the next challenges of the following decades: they are the only planets of the habitable zone whose atmosphere we will be able to probe (e.g. with the JWST).
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