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Interacting compact binary systems provide a natural laboratory in which to study irradiated substellar objects. As the mass-losing secondary (donor) in these systems makes a transition from the stellar to [...]

The chemical species containing carbon, nitrogen, and oxygen in atmospheres of giant planets, brown dwarfs (T and L dwarfs), and low-mass stars (M dwarfs) are identified as part of a comprehensive set of thermochemical equilibrium and kinetic calculations for all elements. The calculations cover a wide temperature and pressure range in the upper portions of giant planetary and T-, L-, and M-dwarf atmospheres. Emphasis is placed on the major gases C[H.sub.4], CO, N[H.sub.3], [N.sub.2], and [H.sub.2]O but other less abundant gases are included. The results presented are independent of particular model atmospheres, and can be used to constrain model atmosphere temperatures and pressures from observations of different gases. The influence of metallicity on the speciation of these key elements under pressure-temperature (P-T) conditions relevant to low-mass object atmospheres is discussed. The results of the thermochemical equilibrium computations indicate that several compounds may be useful to establish temperature or pressure scales for giant planet, brown dwarf, or dwarf star atmospheres. We find that ethane and methanol abundance are useful temperature probes in giant planets and methane dwarfs such as Gl 229B, and that C[O.sub.2] can serve as a temperature probe in more massive objects. Imidogen (NH) abundances are a unique pressure-independent temperature probe for all objects. Total pressure probes for warmer brown dwarfs and M dwarfs are HCN, HCNO, and C[H.sub.2]O. No temperature-independent probes for the total pressure in giant planets or T-dwarf atmospheres are identified among the more abundant C, N, and O bearing gases investigated here. Key Words: Jupiter; giant planets; extrasolar planets; brown dwarfs; Gliese 229B; T dwarfs; L dwarfs; M dwarfs; atmospheric chemistry; carbon; nitrogen; oxygen; methane; carbon monoxide; ammonia; thermo-chemical equilibrium.

Observations of brown dwarfs, which are in the interval between the least massive star and the most massive planet, are discussed. They may be almost as common as stars, but seem not to have a dynamically interesting amount of mass. A rough idea of how many occur as solitary objects and how many are in binary systems has now been developed. A first glimpse of atmospheres with temperatures between those of stars and those of planets, in which dust formation is a crucial process has been obtained and led to the proposal of the first new spectral classes in several decades and the need for new diagnostics for classification and setting the temperature scale. All current masses depend on models.

Brown dwarfs are objects with masses between that of stars and planets. Postulated some three decades ago, they remained elusive until recently. Unlike stars, these objects have no sustained energy source and cool as they age. One such cool brown dwarf has been discovered as a companion to a nearby star. The spectrum of this object is similar to that of Jupiter. Single brown dwarfs have been detected in stellar nurseries. Ongoing and planned efforts, from both ground and space, will enable astronomers to decisively determine the population of these elusive and dim objects., Stars are large spheres of gas that are by mass 73% H, 25% He, and 2% 'metals' (elements with atomic number z [is greater than] 2, such as O, N, [...]

The discovery that planets orbit stars 'similar to the sun' has turned the field of extrasolar planet detection into an exciting field of research. Meanwhile, theorists have begun to evaluate the implications of the discoveries on planet formation and star formation theories.

Objects known as brown dwarfs are midway between stars and planets in mass. observations of a hot brown dwarf irradiated by a nearby star will help to fill a gap [...]

Photometry and spectroscopy of the object Cha H[Alpha] 1, located in the Chamaeleon I star-forming cloud, show that it is a ~[10.sup.6]-year-old brown dwarf with spectral type M7.5 to M8 and 0.04 ± 0.01 solar masses. Quiescent x-ray emission was detected in a 36-kilosecond observation with 31.4 ± 7.7 x-ray photons, obtained with the Rontgen Satellite (ROSAT), with 9 Σ detection significance. This corresponds to an x-ray luminosity of 2.57 x [10.sup.28] ergs per second and an x-ray to bolometric luminosity ratio of [10.sup.-3.44]. These are typical values for late M-type stars. Because the interior of brown dwarfs may be similar to that of convective late-type stars, which are well-known x-ray sources, x-ray emission from brown dwarfs may indicate magnetic activity., A brown dwarf (BD) is an object with a mass [is less than or equal to] 0.08 solar masses (M??), which is insufficient to sustain nuclear fusion of hydrogen (1). [...]

Theoretical spectra and evolutionary models that span the giant planet-brown dwarf continuum have been computed based on the recent discovery of the brown dwarf Gliese 229 B. A flux enhancement in the 4- to 5-micrometer wavelength window is a universal feature from jovian planets to brown dwarfs. Model results confirm the existence of methane and water in the spectrum of Gliese 229 B and indicate that its mass is 30 to 55 jovian masses. Although these calculations focus on Gliese 229 B, they are also meant to guide future searches for extrasolar giant planets and brown dwarfs., Brown dwarfs inhabit a realm intermediate between the more massive stars and the less massive planets. Their thermal infrared emission is powered by the release of gravitational potential energy as [...]

G1229B is a cool brown dwarf having a temperature of less than 1200 K. The mass of G1229B is about 20-50 times that of Jupiter and it appears to be a companion of the star G1229. An analysis of coronagraphs indicates that G1229B is positioned 7.69 plus or minus 0.1 arcsec from G1229A at PA = 162 degrees plus or minus 1 degree. Measurement of the parallax with the Hubble Space Telescope should provide evidence for the companionship between G1229B and G1229A.

Brown dwarfs are the opposite of what one normally associates with a star: They're cool, they have clouds and weather, and they emit little or no light. In fact, they [...]

PASADENA, CALIFORNIA--Once upon a time, a star was a star and a planet was a planet and never the twain would meet. But times have changed. Try making a statement [...]

Brown dwarfs are failed stars; born with a low mass, they quickly ran out of deuterium for fusion and became dim cool remnants of stellar material Although many brown dwarfs, [...]

We present the discovery by optical and near-infrared imaging of an extremely red, low-luminosity population of isolated objects in the young, nearby stellar cluster around the multiple, massive star Σ Orionis. The proximity (352 parsecs), youth (1 million to 5 million years), and low internal extinction make this cluster an ideal site to explore the substellar domain from the hydrogen mass limit down to a few Jupiter masses. Optical and near-infrared low-resolution spectroscopy of three of these objects confirms the very cool spectral energy distribution (atmospheric effective temperatures of 1700 to 2200 kelvin) expected for cluster members with masses in the range 5 to 15 times that of Jupiter. Like the planets of the solar system, these objects are unable to sustain stable nuclear burning in their interiors, but in contrast they are not bound to stars. This new kind of isolated giant planet, which apparently forms on time scales of less than a few million years, offers a challenge to our understanding of the formation processes of planetary mass objects., Recent deep photometric and spectroscopic searches have revealed that brown dwarfs, objects unable to stably fuse hydrogen, are very common in star-forming regions, galactic clusters, and the solar neighborhood. Young [...]

Strange, dim objects in the constellation Orion have left astronomers hunting for words. In a young star cluster perched near Orion's belt, a team at the Astrophysics Institute of the [...]

Hubble Space Telescope imaging observations of two nearby brown dwarfs, DENIS-P J1228.2-1547 and Kelu 1, made with the near-infrared camera and multiobject spectrometer (NICMOS), show that the DENIS object is resolved into two components of nearly equal brightness with a projected separation of 0.275 arc second (5 astronomical units for a distance of 18 parsecs). This binary system will be able to provide the first dynamical measurement of the masses of two brown dwarfs in only a few years. Upper limits to the mass of any unseen companion in Kelu 1 yield a planet of 7 Jupiter masses aged 0.5 x 109 years, which would have been detected at a separation larger than about 4 astronomical units. This example demonstrates that giant planets could be detected by direct imaging if they exist in Jupiter-like orbits around nearby young brown dwarfs., Brown dwarfs (BDs) are 'failed stars'; that is, they are not massive enough to sustain stable hydrogen burning but are sufficiently massive to start deuterium burning (1). Brown dwarfs are [...]

Below about 75 times the mass of Jupiter (75 [M.sub.J]), astronomical objects cannot achieve core temperatures hot enough for sustained nuclear fusion of hydrogen. These failed stars are called brown [...]

It's too early for detailed weather forecasts, but two astronomers claim to have detected clouds in the atmosphere of a nearby brown dwarf star. In a paper submitted to the [...]

Differential methane-band imaging is an effective method for detecting brown dwarfs. The method involves removing the image taken in the methane band from a continuum-light image taken in the same spectral region. A strong methane-band absorption in the spectrum helps in the detection of G1229B, a low mass star. The detection of this star requires less than two minutes of integration time. This imaging technique allows the detection of both isolated brown dwarfs in crowded regions and brown dwarfs orbiting around their primary stars.

Spectroscopic measurements of a cool brown dwarf, GI 229B, reveal absorption features attributable to methane in the near infrared much like those of Jupiter. These features are not seen in any star. The presence of methane indicates that the surface temperature of GI 229B is below 1 000 kelvin. Features attributed to water vapor also indicate that GI229B is much cooler than any known star., Stars like our sun fuse hydrogen into helium and in the process produce energy, most of which appears as light. Current stellar models agree that objects less massive than [0.08M.sub.sun], [...]

Steelworkers tell the temperature of a glowing ingot by its color. For astronomers who sift the galaxy in search of the dimly glowing objects called brown dwarfs, however, life is [...]

There is clear evidence of the existence of astronomical objects known as brown dwarfs. Brown dwarfs, also called failed stars, are formed from a protostar of mass less than 0.08 solar masses. They could be a link between huge planets, such as Jupiter, and stars. They grow fainter with a decrease in temperature and are difficult to observe.

Astrophys. J. 714, L84-L88 (2010) Astronomers have found a planet that may have formed like a star--through gravitational collapse. Kamen Todorov of Pennsylvania State University in University Park and his [...]