Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks
NASA Technical Reports Server (NTRS)
We report on the discovery of the young, nearby, brown dwarf 2MASS J0041353-562112. The object has a spectral type of M7.5; it shows Li absorption and signatures of accretion, which implies that it still has a disk and suggests an age below 10 Myr. The space motion vector and position on the sky indicate that the ...
NASA Astrophysics Data System (ADS)
We propose to continue our investigation of magnetic activity in L and T brown dwarfs in the X-rays with Chandra and in the radio with the VLA and ATCA. We propose to observe three brown dwarfs in the largely unexplored late-L and T regimes with Chandra. Our targets are close, old (~1 Gyr) ...
We compare Smoothed Particle Hydrodynamic simulations of retrogradely precessing accretion disks that have a white dwarf primary and a main sequence secondary with observational data and with theory on retrograde precession via tidal torques like those by the Moon and the Sun on the Earth [1, 2]. Assuming the primary does not accrete ...
We conjecture that brown dwarfs are substellar objects because they have been ejected from small newborn multiple systems that have decayed in dynamical interactions. In this view, brown dwarfs are stellar embryos for which the star formation process was aborted before the hydrostatic cores could build up enough ...
We present a grid of models of accreting brown dwarf systems with circumstellar discs. The calculations involve a self-consistent solution of both vertical hydrostatic and radiative equilibrium along with a sophisticated treatment of dust sublimation. We have simulated observations of the spectral energy distributions and several ...
A long-standing and unverified prediction of binary star evolution theory is the existence of a population of white dwarfs accreting from substellar donor stars. Such systems ought to be common, but the difficulty of finding them, combined with the challenge of detecting the donor against the light from accretion, means that no donor ...
PubMed
We present X-shooter observations of two brown dwarf candidates. We focus on the determination of stellar parameters and their errors. The targets, an accreting class II and a non-accreting class III objects, are members of the ? Orionis star-forming region. We derive the spectroscopic spectral types from the VIS ...
The birth of stars involves not only accretion but also, counter-intuitively, the expulsion of matter in the form of highly supersonic outflows. Although this phenomenon has been seen in young stars, a fundamental question is whether it also occurs among newborn brown dwarfs: these are the so-called 'failed stars', with masses between ...
We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L ...
Energy Citations Database
We review recent theoretical progress aimed at understanding the formation and the early stages of evolution of giant planets, low-mass stars, and brown dwarfs. Calculations coupling giant planet formation, within a modern version of the core accretion model that includes planet migration and disk evolution, and subsequent evolution ...
A star acquires much of its mass by accreting material from a disk. Accretion is probably not continuous but episodic. We have developed a method to include the effects of episodic accretion in simulations of star formation. Episodic accretion results in bursts of radiative feedback, during which a protostar is ...
The regulation of angular momentum is one of the key processes for our understanding of stellar evolution. In contrast to solar-mass stars, very low mass (VLM) objects and brown dwarfs are believed to be fully convective. This may lead to major differences of rotation and activity, since fully convective objects may not host a solar-type dynamo. Here, we ...
This paper extends our previous study of planet/brown dwarf accretion by giant stars to solar-mass stars located on the red giant branch. The model assumes that the planet is dissipated at the bottom of the convective envelope of the giant star. The evolution of the giant is then followed in detail. We analyse the effects of different ...
Brown Dwarf Detectives. Elusive brown dwarfs, the missing link between gas ... The first brown dwarf was not discovered until 1995, yet McLean suspects the ...
NASA Website
Aims. We report the X-ray properties of young (?3 Myr) bona fide brown dwarfs of the Taurus Molecular Cloud (TMC). Methods. The XMM-Newton Extended Survey of the TMC (XEST) is a large program designed to systematically investigate the X-ray properties of young stellar/substellar objects in the TMC. In particular, the area surveyed by 15 XMM-Newton ...
E-print Network
... unique opportunities to study the details of the accretion flow in the cases of normal white dwarfs with accretion disks and magnetic white dwarfs. ...
The lifetimes of optically thick accretion disks around young stars are important because they represent a limit on the amount of time available for the formation of giant planets. Estimating disk lifetimes as a function of stellar mass requires measurements of disk fractions for samples of stars that cover a wide range of ages and masses. Previous photometric surveys with ...
DENIS-P J0041353-562112 is a brown dwarf, with a spectral type of M7.5, which may be younger than 20 Myr. On the basis of its H? emission-line asymmetry, it has been suggested that the object is accreting material. If it is accreting, it is expected to rotate slowly. This paper reports on several photometric ...
In near-infrared NaCo observations of the young brown dwarf 2MASS J0041353-562112, we discovered a companion a little less than a magnitude fainter than the primary. The binary candidate has a separation of 143 mas, and the spectral types of the two components are M 6.5 and M 9.0. Colors and flux ratios of the components are consistent with their locations ...
We explore the properties of an optical transient event formed by the destruction of a planet by a brown dwarf (BD) - a BD-planet mergerburst. When a massive planet approaches a BD towards a merging process it will be tidally destroyed and will form an accretion disc around the BD. The viscosity in the disc sets the characteristic time ...
We argue that brown dwarfs (BDs) and planemos form by the same mechanisms as low-mass hydrogen-burning stars, but that as one moves to lower and lower masses, an increasing fraction of these objects is formed by fragmentation of the outer parts (R ? 100 AU) of protostellar accretion discs around more massive primary protostars, which ...
Recently it has become apparent that proto-stellar-like outflow activity extends to the brown dwarf (BD) mass regime. While the presence of accretion appears to be the common ingredient in all objects known to drive jets fundamental questions remain unanswered. The more prominent being the exact mechanism by which jets are launched, ...
Tags astronomical journal, binaries, brown dwarfs, high angular resolution, nai hawaii team, ... Tags brown dwarfs, nai ua team, spitzer space telescope ...
Jan 22, 2011 ... Title: Prospecting for brown dwarfs in Space Infrared Telescope Facility (SIRTF) ... Citation: Brown Dwarfs IAU Symposium Kona, HI, USA ...
near 1 Myr) brown dwarf candidates, potentially reaching down to isolated objects below the ... members of the brown dwarf population. We will discuss ...
Oct 18, 1998 ... A brown dwarf has a small mass, too low to ignite nuclear fusion. ... It would emit copious infrared radiation, thus the name "brown dwarf". ...
Aug 30, 2000 ... These dim objects are thought to be brown dwarfs and free-floating planets. Brown dwarfs are stars too puny to create energy in their core ...
FUTau belongs to a rare class of young, wide brown dwarf binaries. We have resolved the system in a Chandra X-ray observation and detected only the primary, FUTauA. Hard X-ray emission, presumably from a corona, is present but, unexpectedly, we also detect a strong and unusually soft component from FUTauA. Its X-ray properties, so far unique among ...
Determining the process(es) by which brown dwarfs form is key to understanding their intrinsic nature. If their origins are within circumstellar disks they are akin to giant planets. If, on the other hand, they coalesce from molecular cloud cores, then they share a common lineage with low mass stars. These two mechanisms can be distinguished by ...
DOE Information Bridge
Redshift z=6 marks the end of cosmological reionization due to the formation of the first substantial population of star forming galaxies and accreting black holes. Reionization is a highly inhomogeneous process with significant cosmic variance, and therefore many sightlines are needed to get an accurate picture of the ionization state of the high redshift IGM. We are carrying ...
The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass ac...
National Technical Information Service (NTIS)
... CVs) in which a white dwarf (WD) accretes matter from a main-sequence star (the secondary) filling its Roche lobe by means of an accretion disk. ...
DTIC Science & Technology
Properties of the neutrinos emitted during an accretion of white dwarf matter by a primordial black hole are considered. The possibility of detecting these neutrinos and their oscillations is discussed.
Nov 17, 2009 ... This diagram shows a brown dwarf in relation to Earth, Jupiter, a low-mass star and the sun.
Brown dwarfs are stellar objects with masses less than 0.08 times that of the Sun that are unable to
Article on the surprise solar flare of a brown dwarf star detected by NASA's Chandra X-ray Observatory.
We consider time-dependent accretion onto magnetized white dwarfs. A detailed description of a numerical method of solution to the hydrodynamical equations is given. The postshock flow is cooled by optically thin bremsstrahlung and is thermally unstable. As a result the shock height undergoes periodic oscillations. We consider the properties of this ...
We present high-resolution optical spectroscopy of four candidate members of the nearby TW Hydrae young association including three brown dwarfs (2MASS 1207-3932, 2MASS 1139-3159, and TWA 5B) and one T Tauri multiple star (TWA 5A). Using echelle spectra from the Magellan Baade 6.5 m telescope, we confirm the pre-main-sequence status and cluster membership ...
My talk will focus on the early evolution of low mass objects. I will discuss the main uncertainties on current evolutionary models and the effects of rotation, magnetic field and early accretion history on young object's structure. I will also present possible solutions to the well known spread in HRD observed in star formation regions for objects of a few Myr old.
While the O through K classes are all considered stars, M and L objects are a mixture of stars and brown dwarfs, and T and Y objects are all brown dwarfs.
is a dim star belonging to a class called brown dwarfs; it is the first ultra-cool brown dwarf discovered by NASA's Wide-field Infrared Survey Explorer. Title: Collecting Brown...
Science.gov Websites
Micron All-Sky Survey to derive a preliminary brown dwarf companion ... A brown dwarf wide-companion frequency as low as the 0.5% seen in the brown ...
We present ISOCAM 7 and 15 ?m observations of 12 nearby white dwarfs, 6 of which have been found to have metals such as Ca, Mg and Fe in their photospheres. Our purpose was to search for an excess of infrared emission above the stellar photospheres. We find that none of the white dwarfs other than G29-38 shows a detectable infrared excess and this places ...
The origin of highly magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, such as a planet, ...
PubMed Central
Using the largest high-resolution spectroscopic sample to date of young, very low mass stars and brown dwarfs, we investigate disk accretion in objects ranging from just above the hydrogen-burning limit all the way to nearly planetary masses. Our 82 targets span spectral types from M5 to M9.5, or masses from 0.15 Msolar down to about ...
The brown dwarf desert is the term used to describe the notable absence of brown dwarfs within about 5 AU from the central main- sequence star in binary brown dwarf-stellar systems. Previous work by other researchers has focused on a dynamical mechanism as the origin of the ...
Using the Spitzer Infrared Spectrograph, we have performed mid-infrared spectroscopy on the young binary brown dwarf 2MASS J04414489+2301513 (15 AU) in the Taurus star-forming region. The spectrum exhibits excess continuum emission that likely arises from a circumstellar disk around the primary. Silicate emission is not detected in these data, indicating ...
Jan 22, 2011 ... dc.subject.other, brown dwarfs binaries Hubble Space Telescope 2MASS, en_US. dc. title, Binarity in brown dwarfs: T dwarf binaries discovered ...
There are two dominant models of how stars form. Under gravitational collapse, star-forming molecular clumps, of typically hundreds to thousands of solar masses (M(o)), fragment into gaseous cores that subsequently collapse to make individual stars or small multiple systems. In contrast, competitive accretion theory suggests that at birth all stars are much smaller than the ...
Understanding boundary layer heating is crucial in determining the thermal structure of the accreted envelope of a prenova white dwarf. The matched asymptotic expansion method was used to solve consistently for the structure of accretion disks transferring matter onto rotating white dwarfs. The fraction of ...
Twin Brown Dwarfs Wrapped in a Blanket. 11.23.09. Twin brown dwarfs : Full resolution unannotated jpeg (845 Kb) � : Full resolution tiff (3377 Kb) ...
cooler and less luminous than any other known brown dwarf. Using evolutionary models ... brown dwarf, and its distance of 5.77 PC (Perryman et al. ...
Jan 5, 2009 ... This means the so-called "brown dwarf desert" (the absence of brown dwarfs around solar-type stars) extends to the smallest stars in the ...
Dec 4, 1995 ... A leading candidate is a type of dim, low mass star called a "brown dwarf" star. Our universe could contain more brown dwarfs than any other ...
This talk outlines astrophysical issues related to the long term fate of the universe. We consider the evolution of planets, stars, galaxies, and the cosmos itself over time scales that greatly exceed the current age of the universe. This discussion starts with stellar evolution calculations that follow the development of the low mass (M type) stars that dominate the stellar IMF. We then determine ...
Recent observations and research indicate that interacting binaries may harbor brown dwarfs (BD) as the mass donor if their orbital periods are less than about 90 minutes. One such system, EF Eri, has been proven to contain a BD mass donor (Harrison, Howell, et al, 2004 ApJ, 614, 947). After a correlation of the 2MASS database with known ultra-short period ...
The properties of accretion discs around stars and brown dwarfs in the ?Ori cluster (age 3Myr) are studied based on near-infrared (IR) time series photometry supported by mid-IR spectral energy distributions (SEDs). We monitor ~30 young low-mass sources over eight nights in the J and K band using the duPont telescope at Las Campanas. ...
Brown dwarf formation and star formation efficiency are studied using a nested grid simulation that covers 5 orders of magnitude in spatial scale (10{sup 4}-0.1 AU). Starting with a rotating magnetized compact cloud with a mass of 0.22 M {sub sun}(225 M {sub Jup}), we follow the cloud evolution until the end of the main accretion ...
... Abstract : The prototype of accreting, pulsating white dwarfs (GW Lib) underwent a large amplitude dwarf nova outburst in 2007. ...
We have performed a survey for substellar companions to young brown dwarfs in the Taurus star-forming region using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In these data, we have discovered a candidate companion at a projected separation of 0.''105 from one of the brown ...
Through direct imaging we have discovered a brown dwarf and two low-mass ...... 2004), with estimates for the brown dwarf companion ...
In order to understand what is a brown dwarf, we need to understand the difference between a star and a planet. It is not easy to tell a star from a planet ...
May 1, 2005 ... NAI's Ben Zuckerman of the UCLA team told UCLA, The two objects the giant planet and the young brown dwarf are moving together; ...
mine whether the brown dwarf desert is the expression of two different kinds of .... mature stars suggest a brown dwarf desert between 10 and 50 M ...
... Accession Number : ADA534032. Title : The Pan-STARRS 3-pi Survey and the Brown Dwarf Factory. Descriptive Note : Journal article. ...
Surveying the Solar Neighborhood For Brown Dwarf Companions. Mith the ECLIPSE Discovery Mission. ECLIPSE is a proposed NASA Discovery mission, ...
Nov 23, 2009 ... Spitzer Telescope Observes Baby Brown Dwarf. PASADENA, Calif. .... Space Telescopes Find Trigger-Happy Star Formation ...
Nov 23, 2009 ... NASA's Spitzer Space Telescope has contributed to the discovery of the youngest brown dwarf ever observed -- a finding that, if confirmed, ...
Nov 23, 2009 ... Brown dwarfs are misfits because they fall somewhere between planets and stars in terms of their temperature and mass. ...
WIRE will search for a kind of "failed" star, called a brown dwarf. Brown dwarfs are relatively small objects that shine faintly, mostly in infrared light. ...
the smallest known mass for a brown dwarf. The extrema of the H-R Diagram ..... a possible brown dwarf cuttoff. Any kinks, breaks, or other features will be ...
Jan 21, 2003 ... Artist's concept of platypus and brown dwarf Larger image � star Gliese 229 The star Gliese 229 (left) and a companion brown dwarf 229B ...
Sep 27, 2007 ... Astronomers find companion orbiting brown dwarf candidate ... Scientists believe the star may be a brown dwarf - a failed star that is not ...
Optical spectra for candidate brown dwarfs from the DENIS Mini-survey are provided. These are the spectra used to in Figure 1 of the paper. (12 data files).
Apr 6, 2010 ... Discovery of a planet-like object circling a brown dwarf is the right size for a planet, estimated to be 5-10 times the mass of Jupiter, ...
Feb 18, 2003 ... (PLANETQUEST) -- Researchers at the University of Arizona have released new images of the tightest-orbiting brown dwarf ever observed. ...
Jun 6, 2011 ... If not a binary twin (brown dwarf) and planets spinning clockwise around it ( Nibiru) then please explain to all of us dummies why Earth does ...
Evolution of young brown dwarf disks in the mid-infrared. ... The onset of planet formation in brown dwarf disks. Science, submitted. 12 publications. ...
The first clear evidence of the existence of a brown dwarf was published in 1995 . The evidence consisted of observations from the large, ground-based ...
Jul 12, 2000 ... The Chandra X-ray Observatoryhas detected the first-ever flare from what's known as a brown dwarf, or failed star.
Dec 10, 2008 ... But when NASA's Spitzer Space Telescope observed the brown dwarf with its ... What's more, the Spitzer data revealed the brown dwarf is, ...
are pairs of stars which orbit around their common center of gravity. What is a brown dwarf? Brown dwarfs are objects which are too large to be called planets and too small to...
(1) If we had a black or brown dwarf in our outer solar system, I guess no one could see it right ... For sure, there is no brown dwarf in the solar system. ...
on observations of lithium (6), luminosity and/or surface temperatures (7). However, no direct mass measurement of a brown dwarf has been obtained to date. ...
Mar 1, 2011 ... NASA's Spitzer Space Telescope spotted such a disc around a surprisingly low- mass brown dwarf, or 'failed star.' The brown dwarf, called OTS ...
We present the first observations of a probable brown dwarf, obtained with the new spectrograph X-shooter mounted on the UT2@VLT. The target (2MASS J053825.4-024241) is a 0.06 M_? object in the star-formation region ? Ori. The X-shooter spectrum covers simultaneously the whole range from UV to NIR (300-2500 nm). The J053825.4-024241 spectrum is rich in ...
We present new results on the extended atmosphere of the chromospherically active system UZ Lib. Doppler tomography confirms that the atmosphere of primary is extended to about 3.0 times its radius. Significant downfalls and probably plage regions are present in the atmosphere and we find a rather good correlation between the hydrogen integrated emission and the light curve. We also fix stellar ...
Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many
The eclipsing cataclysmic variable {CV} SDSS J1507 has an orbital period well below the period minimum obeyed by other CVs. Furthermore, it contains a cool, pulsating primary white dwarf {WD} and a sub-stellar brown-dwarf {BD} companion. We have now discovered that J1507 is also a high proper motion star, with a transverse velocity much higher than other ...
We present near-infrared JHKs photometry and light curves of the candidate magnetic white dwarf+brown dwarf binary SDSS J121209.31+013627.7 and report on the detection of near-infrared excess and variability in the Ks band. The observed near-infrared excess can be explained by the presence of an L7 brown dwarf and ...
WZ Sge provides us with an excellent test for numerical codes trying to reproduce the heating and cooling of a white dwarf due to accreted material. This is because of both the many observed quantities of this binary and its long quiescent state. However, a large discrepancy appears between the observed white dwarf`s cooling curve and ...
of the secondary star and accretion of nova abundance-enriched matter back to the white dwarf via the accretion of a nova remnant-like nebula around EY Cyg. Subject Headings: Stars: cataclysmic variables, white dwarfs, related either to donor star contamination by nova ejecta from the accreting ...
First Ground-Based Mid-Infrared Observations of Brown Dwarfs [1] Summary A team of European astronomers [2] have observed eight Brown Dwarfs, i.e., small and faint objects also known as "failed stars", with the TIMMI2 infrared sensitive instrument at the ESO 3.6-m telescope on La Silla. From two of these, ...
The main physical phenomena which occur on accretion disks, are discussed. A numerical simulation of a three dimensional accretion disk model around a white dwarf in a binary system composed of two equal mass stars is developed. The smoothed particle hydr...
It is proposed a new mechanism for high energy gamma ray burst in Supernova type I (SNI) explosion. Presupernova is assumed to be a binary system comprised of a red giant and a white dwarf with a wind accretion. The accretion flow terminates by the accret...
We examine the role of the accretion disk in the steady-burning white dwarf model for supersoft sources. The accretion luminosity of the disk is quite small compared to the nuclear burning luminosity of the central source. Thus, in contrast to standard ac...
Accretion onto and nova events on the surface of a degenerate cold one-solar-mass iron white dwarf are investigated. It is found that, during accretion, hydrogen diffuses deeper into the core than its CNO catalysts, suggesting that the thermonuclear runaway occurs not at the innermost radius achieved by the hydrogen but farther out ...
Context. The accretion processes that accompany the earliest stages of star formation have been shown in recent years to extend to masses well below the substellar limit, and even to masses close to the deuterium-burning limit, suggesting that the features characteristic of the T Tauri phase are also common to brown dwarfs. Aims: We ...
We present new far-ultraviolet observations of the young M8 brown dwarf 2MASS J12073346-3932539, which is surrounded by an accretion disk. The data were obtained using the Hubble Space Telescope-Cosmic Origins Spectrograph. Moderate-resolution spectra (R? 17,000-18,000) obtained in the 1150-1750 � and 2770-2830 � bandpasses reveal ...
We present new far-ultraviolet observations of the young M8 brown dwarf 2MASS J12073346-3932539, which is surrounded by an accretion disk. The data were obtained using the Hubble Space Telescope-Cosmic Origins Spectrograph. Moderate-resolution spectra (R{approx} 17,000-18,000) obtained in the 1150-1750 A and 2770-2830 A bandpasses ...
The dwarf-nova phenomenon could result from a local accumulation of hydrogen being accreted onto the surface of a degenerate dwarf near its magnetic poles. Thermonuclear buring in this hydrogen layer would produce a flare. A magnetic field of (3--30) x 10/sup 6/ gauss is needed to guide the accretion. The origin ...
In this review I describe the basic properties of white dwarfs and their pulsations. I then discuss some of the areas in which the pulsations can provide meaningful results, such as internal chemical profiles, possible emission of ``exotic'' particles, planet detection, crystallization, convection, accretion, and cosmochronology.
If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae an...
core. This marks the dividing line between red dwarf stars and brown dwarfs. The brown dwarf TWA 5B has in the Galaxy--a red dwarf star. Red dwarfs have a mass between approximately 8% and 50% of the mass of the Sun. A red dwarf has ...
We are undertaking an astrometric search for gas giant planets and brown dwarfs orbiting nearby low mass dwarf stars with the 2.5-m du Pont telescope at the Las Campanas Observatory in Chile. We have built two specialized astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S and CAPSCam-N), using two Teledyne ...
We are undertaking an astrometric search for gas giant planets and brown dwarfs orbiting nearby low-mass dwarf stars with the 2.5 m du Pont Telescope at the Las Campanas Observatory in Chile. We have built two specialized astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S and CAPSCam-N), using two Teledyne ...
characteristics that distinguish planetary and brown dwarf compan- ions. Although astrometric studies will be capable of detecting ...
We report on sensitive ground-based measurements of a small sample of young brown dwarf disks. Our detections in the infrared regime, combined with detailed spectral energy distribution modeling, allowed to characterize the structure of brown dwarf disks and infer their dust composition. We also performed submm and ...
... 4. TITLE AND SUBTITLE The Pan-STARRS 3π Survey And the Brown Dwarf Factory 5a. CONTRACT NUMBER 5b. ... Dwarf Factory ...
Stevenson 1994); however, the hotter brown dwarf bands clearly extend blueward to 9250 A. ..... metal-poor thick disk or halo brown dwarf. Further as- ...
Jan 22, 2011 ... Abstract: We report the detection of H alpha emission in the T dwarf (methane brown dwarf) 2MASSW J1237392 + 652615 over three days using ...
The distances and kinematics of brown dwarfs provide key statistical constraints on their ages, moving group membership, absolute brightnesses, evolutionary trends, and multiplicity. Yet fundamental measurements of parallax, proper motion and radial velocity have been made for only a relatively small fraction of the known brown ...
Binary evolution predicts a population of helium core (M < 0.5 M sun) white dwarfs (WDs) that are slowly accreting hydrogen-rich material from low-mass main-sequence or brown dwarf donors with orbital periods less than 4 hr. Four binaries are presently known in the Milky Way that will reach such a ...
This website, by Caltech astronomer Mike Brown, describes dwarf planets and the issues in their classification. A diagram show the "new" solar system, including the approximately 50 dwarf planets in the Kuiper Belt. A table shows the size and distance of each dwarf planet.
NSDL National Science Digital Library
We review the statistical properties of stars and brown dwarfs obtained from the first hydrodynamical simulation of star cluster formation to produce more than a thousand stars and brown dwarfs while simultaneously resolving the lowest mass brown dwarfs (those with masses ...
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 ...
In 2005, Palla & Baraffe proposed that brown dwarfs and very low mass stars (<0.1 solar masses) may be unstable to radial oscillations during the pre-main-sequence deuterium burning phase. With associated oscillation periods of 1-4 hours, this potentially new class of pulsation offers unprecedented opportunities to probe the interiors and evolution ...
We present deep high dynamic range infrared images of young nearby stars in the Tucana/Horologium and ? Pic associations, all � 10 to 35 Myrs young and at � 10 to 60 pc distance. Such young nearby stars are well-suited for direct imaging searches for brown dwarf and even planetary companions, because young sub-stellar objects are still self-luminous ...
Over the past few years, we have been investigating the effects of accretion onto massive white dwarfs and its implications for their growth in mass toward the Chandrasekhar limit, in attempts to identify a possible relationship between SN I and novae. In our studies we have considered accretion at various mass ...
Important aspects of the theory of accretion are reviewed and the theory of the spherical accretion of a polytropic gas is presented. The effect of the termination of the flow at the surface of a neutron star or white dwarf is studied with consideration given to the interaction with a magnetic field anchored to the star. Spherical ...
We have constructed vertically integrated, steady state convective models of accretion disks to explore the mechanism of instability in dwarf novae. The models and observations of dwarf novae suggest a picture in which transferred matter piles up in an optically thin torus. The torus eventually becomes optically thick and the resulting ...
Vertically integrated, steady state convective models of accretion disks have been constructed to explore the mechanism of instability in dwarf novae. The models and observations of dwarf novae suggest a picture in which transferred matter piles up in an optically thin torus. The torus eventually becomes optically thick, and the ...
There has been a long-standing discussion in the literature as to whether core accretion or disk instability is the dominant mode of planet formation. Over the last decade, several lines of evidence have been presented showing that core accretion is most likely the dominant mechanism for the close-in population of planets probed by radial velocity and ...
White dwarfs, the endpoint of stellar evolution for stars with mass < 8 [Special characters omitted.] , possess several attributes favorable for studying planet and brown dwarf formation around stars with primordial masses 1 [Special characters omitted.] . This thesis explores the consequences of post-main-sequence evolution on the ...
We report on the linear polarimetric observations in the Johnson I-band filter of 44 ultracool dwarfs with spectral types between M6 and L7.5, corresponding to effective temperatures in the range 2800-1400 K, and one M4.5-type star. Based on our measurements of polarization (P) and their associated error bars (?P), 11 (10 L and 1 M) dwarfs appear to have ...
Accreting white dwarfs in cataclysmic variables (CVs) have also recently been shown to exhibit non-radial pulsations similar to their non-interacting counterparts; GW Librae was the first accreting pulsator discovered in 1998 (Warner & van Zyl 1998; van Zyl et al. 2000, 2004). When the orbital period of a CV is close to the ...
Observations of novae and theoretical results, in which the authors studied the nova outburst by radially accreting H-rich matter onto an He white dwarf, have convinced them that realistic nova models must be based on accretion that includes the angular momentum of the accreting matter. In the present paper the ...
In this paper we derive a special linear non-vortical wave propagation solution in the shearing sheet, a model of a compressible two-dimensional fluid system with constant density, constant shear and constant Coriolis force, but without self-gravity. The linear analysis of the shearing sheet leads to a single differential equation for the azimuthal velocity perturbation. A detailed derivation of a ...
This review presents a panorama of the research topics that are currently being developed by our strategic research group at the IAC in the field of very low-mass stars, brown dwarfs, extrasolar giant planets and the solar system. Our main goal is to investigate the cosmogony of the least massive stellar and substellar component of the Milky Way. We are ...
We suggest that low-mass hydrogen-burning stars like the Sun should sometimes form with massive extended discs, and we show, by means of radiation hydrodynamic simulations, that the outer parts of such discs (R >~ 100au) are likely to fragment on a dynamical time-scale (103 to 104yr), forming low-mass companions: principally brown dwarfs (BDs), but also ...
Since the first discoveries in 1995, hundreds of field brown dwarfs have been found in DENIS, 2MASS and SDSS. The new generation of large-area surveys uses deeper images and probes a larger volume in the Galaxy, increasing the number of known brown dwarfs. Such surveys are the UKIRT Infrared Deep Sky Survey ...
WZ Sge provides us with an excellent test for numerical codes trying to reproduce the heating and cooling of a white dwarf due to accreted material. This is because of both the many observed quantities of this binary and its long quiescent state. However, a large discrepancy appears between the observed white dwarf's cooling ...
Using the Hubble Space Telescope, the 4 m Blanco Telescope at the Cerro Tololo Inter-American Observatory, and the Spitzer Space Telescope, we have performed deep imaging from 0.8 to 8 ?m of the southern subcluster in the Chamaeleon I star-forming region. In these data, we have discovered an object, Cha 110913-773444, whose colors and magnitudes are indicative of a very low mass ...
The hydrostatic evolution of a carbon-oxygen white dwarf (COWD) experiencing accretion of matter from its companion, a second COWD, is calculated for accretion rates ranging from 10 to the -8th to 10 to the -5th solar masses per year. It is shown that, for accretion rates less than (3.3 + or - 1.5) x 10 to the -6th ...
... targets might include a selection of nearby M-dwarfs to look for astrometric perturbations from faint companions in the brown-dwarf and giant-planet ...
... (2005) success- fully used astrometry to discover a brown dwarf companion to an M dwarf, a promising first step on the path to finding true planets. ...
This mass disparity can be as large as fifteen times or more when comparing an L to a Y dwarf, despite the fact that both objects have the same radius.
Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion. In dwarf novae, an instability is believed to episodically dump much of the ...
The growth of a carbon-oxygen white dwarf is investigated within the framework of the general shell-flash theory of accreting white dwarfs. Account is taken of the envelope restructing in response to the shell flash and to possible mass loss from the white dwarf. Estimates are given for the amount of helium ...
Recent discovery of an unexpectedly large number of low-mass binary pulsars (LMBPs) in globular clusters has instigated active discussions on the evolutionary origin of binary pulsars. Prompted by the possibility that at least some of LMBPs originate from accretion-induced collapse (AIC) of white dwarfs, a reexamination is conducted as to whether or not ...
Our past HST studies of the temperatures of 9 accreting, pulsating white dwarfs in cataclysmic variables show that 3 are in the normal instability strip for single white dwarfs, but the other 6 are much hotter {15,000-16,500K}. This dual strip has been proposed to be due to mass differences in the white dwarfs ...
We have re-analyzed archival HST R and I band images and Subaru CH{sub 4}, H, Ks and L{prime} data of the recently discovered planetary mass companion (PMC) GQ Lup Ab. With these we produce the first R and I band photometry of the companion and fit a radius and effective temperature using detailed model atmospheres. We find an effective temperature of 2338 {+-} 100K, and a radius of 0.37 {+-} ...
We use the data base of spectroscopically identified white dwarfs to isolate a sample of cool degenerates with trace metals. The spatial distribution and space velocity components of the white dwarfs projected onto and perpendicular to the galactic plane are compared with the distribution of local interstellar hydrogen. The results are consistent with the ...
The investigation shows that the superhumps observed in superoutbursts of SU UMa dwarf novae probably result from the excitation of a resonance in the accretion disk near the 3:1 commensurability with the binary orbit. This resonance can only appear for m...
The observations of WZ Sge provide us with the best test for computational codes trying to calculate the accretion process onto a white dwarf. We find that the accreted material on WZ Sge cannot spread over the whole star at least on a time scale of ten y...
Mar 1, 2010 ... Chandra has also revealed unexpected parallels between accretion onto pre-main sequence stars, white dwarfs, neutron stars, stellar-mass and ...
An analytical model calculation of the ionization structure of matter accreting onto a degenerate dwarf was carried out. Self-consistent values of the various parameters are used. The possibility of nuclear burning of the accreting matter is included. We ...
Steady state and time dependent calculations of a model for accretion instability are presented, in which matter accumulates in a cold torus and then undergoes a thermal instability causing the matter to heat and flow down onto the central star. The model...
The rate of accretion of the interstellar medium onto a star is discussed. It is shown that this is a complex, fractionated process. The relative abundances of heavy elements accreting onto the star are very different from the abundances in the ambient medium. These accretion rates are important in determining the abundances on the ...
The magnetospheres of accreting compact stars (neutron stars and white dwarfs) are examined. It is assumed that the compact star possesses a multipole magnetic field. The shape of the magnetosphere for the two-dimensional analog of spherically symmetric accretion and the magnetic-field configuration for the case of disk ...
Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics but it is unclear under what conditions a low mass companion will evaporate, survive the interaction ...
Protostars are precursors to the nearly fully assembled T Tauri and Herbig Ae/Be type stars undergoing quasistatic contraction toward the zero-age main sequence; they are in the process of acquiring the majority of their stellar mass. Although numerous young stars with spatially extended envelope-like structures appear to fit this description, their high extinction has inhibited observers from ...
A simple model of the boundary layer and accretion disk wind of dwarf novae in outburst is briefly described and applied to the Chandra Low Energy Transmission Grating spectra of WZ Sge and SS Cyg in outburst.
DQ Herculis (Nova Herculis 1934) is a deeply eclipsing cataclysmic variable containing a magnetic white dwarf primary. The accretion disk is thought to block our line of sight to the white dwarf at all orbital phases due to its extreme inclination angle. ...
Observational and theoretical studies of the outbursts of classical novae have provided critical insights into a broad range of astrophysical phenomena. Thermonuclear runaways (TNRs) in accreted hydrogen-rich envelopes on the white dwarf (WD) components o...
The AM Her systems are widely believed to be cataclysmic variable systems in which the white dwarf has a magnetic field strong enough to lock the white dwarf to the companion star. The magnetic field channels the accretion flow to the magnetic polar caps ...
The authors present EUVE Deep Survey photometry and AAVSO optical measurements of the 1993 August and 1994 June/July outbursts of the dwarf nova SS Cygni. The EUV and optical light curves are used to illustrate the different response of the accretion disk...
Mar 1, 2011 ... Sagittae are discussed with reference to the similarity between WZ Sge and dwarf novae and the applicability of accretion disk models. ...
The 2006 outburst of GK Persei differed significantly at optical and ultraviolet (UV ) ... liberated during accretion, and interpret the optical/UV outburst profile as ...
A steady-state model of the accretion disk around a white dwarf, including the boundary layer and the hot spot, has been constructed. Calculated distributions of radiation are compared with soft X-ray, ultraviolet, visual, and infrared observations of SS Cyg during outburst as well as with ultraviolet measurements of V 603 Aql and RR Pic. The results ...
In analogy the soft component probably originates from an accretion-heated surface region around the white dwarfs magnetic pole(s). ...
We perform computations using a time-dependent model for the accretion disk limit-cycle mechanism to
In this paper we report 2007-2009 multicolour observations of the dwarf nova AH Her aiming to test the steady-state model for accretion disk emission.
Comets Clash at Heart of Helix Nebula. 02.12.07 ... thought that perhaps the white dwarf was accreting matter onto itself from a hidden companion star. ...
May 2, 2007 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...
Jan 2, 2003 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...
Jul 28, 2008... star, tore material from the surface of a companion sun, until one day so much was accreted that a nuclear deflagration blew the dwarf apart. ...
this vein, V2301 Oph is particularly interesting because it is an ... The BL Hyi data are published in The Astrophysical Journal and the V2301 Oph data ...
Evidence is mounting that cataclysmic variables are weak sources of synchrotron emission. If true, it demonstrates that accretion powered interacting binaries produce such emission whether their primaries are white dwarfs, neutron stars, or black holes.
Dec 7, 2001 ... Cataclysmic Variables (CVs) are close binary systems in which a white dwarf is accreting material from a more or less normal star. ...
In this contribution, we discuss the chemical properties of the complex stellar population of the Galactic globular cluster Omega Centauri.
Accreting high magnetic field neutron stars are observed as X-ray pulsars. ... An examination of a power spectrum of the pulsed emission shows that the peak ...
limiting J magnitude of 17, the probability of two relatively bright T dwarfs randomly lying .... this system on a yearly basis. compared to Gliese 570D, is d&4w - B ..... Hence, improving the statistics for field brown dwarf systems, ...
... 600�750 K for the T9 dwarf 2MASSI J0415195�093506, which supplants Gl 570D as the least luminous and coolest brown dwarf presently known. ...
2/19/09. The Brown Dwarf Kinematics Project (BDKP). What are UltraCool Dwarfs ... KINEMATICS. *Fast* Movers. 3.61 arcsec/yr. *Slower* Movers .32 arcsec/yr ...
The few lowest mass substellar objects discovered in previous imaging surveys are found to have large semi-major axes, typically hundreds of AU. We show that at such large separations and toward old stars one has the best chance to detect the coolest brown dwarf companions, with effective temperatures of <500 K (the so-called 'Y ...
We present the results of near-infrared imaging and low-resolution near-infrared spectroscopy of low-mass objects in the NGC 1333 molecular cloud. A JHK survey of an 11.4?�11.7? area of the northern cluster was conducted to a sensitivity of K<=16 mag. Using near-infrared magnitudes and colors from this and previously published surveys, 25 brown dwarf ...
Jun 24, 2010 ... "We might even find a cool brown dwarf that is closer to us than Proxima Centauri ... The first confirmed brown dwarf was announced in 1995. ...
The brown dwarf orbits the binary stars at a distance about 2.75 times that of ... "Our Chandra data show that the X-rays originate from the brown dwarf's ...
Jul 19, 2010 ... I read on the internet that G1.9 is brown dwarf star and also perhaps a supernova remnant. If this is a brown dwarf star, how close is this ...
We report the discovery of two eclipsing binaries with a brown dwarf (<0.07Msolar) and a 0.15Msolar late main sequence star companion in close orbits around sdB stars.
