scholarly journals Brown dwarfs in Eddington-inspired Born-Infeld and beyond Horndeski theories

2019 ◽  
Vol 79 (12) ◽  
Author(s):  
A. S. Rosyadi ◽  
A. Sulaksono ◽  
H. A. Kassim ◽  
N. Yusof
Keyword(s):  
Free Parameter ◽  
Brown Dwarfs ◽  
Brown Dwarf ◽  
Hydrogen Burning ◽  
Chi Squared ◽  
Recent Compilation ◽  
Gravity Theories ◽  
Parameter Values

AbstractWe studied herein the mass and the radius of brown dwarfs predicted by beyond Horndeski (BH) and Eddington-inspired Born-Infeld (EiBI) gravity theories by numerically solving the modified non-relativistic hydrostatic equations of both theories. We used a recent compilation of brown dwarf masses and radii obtained from Ref. Bayliss et al. (Astrophys J 153:1, 2016) to constrain the free parameter of both theories. We obtain the range of the corresponding parameters with 1$$\sigma $$σ and 5$$\sigma $$σ confidence by using chi-squared analysis. Furthermore, the minimum chi-squared values can be reached for the cases of $$\kappa = 0.17 \times 10^2 ~\mathrm{m}^5\,\mathrm{kg}^{-1}\,\mathrm{s}^{-2}$$κ=0.17×102m5kg-1s-2 and $$\gamma = -0.1207$$γ=-0.1207 for EiBI and BH theories, respectively. The corresponding parameter values with the minimum chi-squared values are relatively small; therefore, they cannot significantly change the brown dwarf mass limits determined from the equivalence of nuclear and photosphere luminosities for the pp (hydrogen burning) and pp+pd (deuterium burning) reactions.

scholarly journals Lithium in Brown Dwarfs

2000 ◽  
Vol 198 ◽  
pp. 299-309
Author(s):  
Rafael Rebolo
Keyword(s):  
Theoretical Calculations ◽  
Brown Dwarfs ◽  
Solar Neighborhood ◽  
Stellar Clusters ◽  
Brown Dwarf ◽  
Hydrogen Burning ◽  
Resonance Doublet ◽  
Bona Fide ◽  
Li Content ◽  
Made In

Lithium is a key element to establish the substellar nature of brown dwarf candidates. Theoretical calculations show that brown dwarfs with masses below ˜ 0.065 M⊙ preserve a significant fraction of their initial Li content while for higher masses total Li depletion occurs in short timescales. Lithium is preserved at masses well below the hydrogen burning mass. Strong lithium lines have been predicted and discovered in the spectra of brown dwarfs. Most of the bona fide brown dwarfs detected in stellar clusters and in the solar neighborhood have been confirmed to be substellar via detection of the lithium resonance doublet at 670.8 nm. I review these detections and the progress made in understanding the formation of Li lines in very cool high gravity dwarfs.

scholarly journals Greening of the brown-dwarf desert

2019 ◽  
Vol 628 ◽  
pp. A64 ◽  
Author(s):  
Carina M. Persson ◽  
Szilárd Csizmadia ◽  
Alexander J. Mustill ◽  
Malcolm Fridlund ◽  
Artie P. Hatzes ◽  
...  
Keyword(s):  
Mass Density ◽  
Outer Part ◽  
Brown Dwarfs ◽  
Space Mission ◽  
Small Sample ◽  
Brown Dwarf ◽  
Hydrogen Burning ◽  
Stellar Radius ◽  
Tidal Forces ◽  
Photometric Observations

Context. Although more than 2000 brown dwarfs have been detected to date, mainly from direct imaging, their characterisation is difficult due to their faintness and model-dependent results. In the case of transiting brown dwarfs, however, it is possible to make direct high-precision observations. Aims. Our aim is to investigate the nature and formation of brown dwarfs by adding a new well-characterised object, in terms of its mass, radius and bulk density, to the currently small sample of less than 20 transiting brown dwarfs. Methods. One brown dwarf candidate was found by the KESPRINT consortium when searching for exoplanets in the K2 space mission Campaign 16 field. We combined the K2 photometric data with a series of multicolour photometric observations, imaging, and radial velocity measurements to rule out false positive scenarios and to determine the fundamental properties of the system. Results. We report the discovery and characterisation of a transiting brown dwarf in a 5.17-day eccentric orbit around the slightly evolved F7 V star EPIC 212036875. We find a stellar mass of 1.15 ± 0.08 M⊙, a stellar radius of 1.41 ± 0.05 R⊙, and an age of 5.1 ± 0.9 Gyr. The mass and radius of the companion brown dwarf are 51 ± 2 MJ and 0.83 ± 0.03 RJ, respectively, corresponding to a mean density of 108−13+15 g cm−3. Conclusions. EPIC 212036875 b is a rare object that resides in the brown-dwarf desert. In the mass-density diagram for planets, brown dwarfs, and stars, we find that all giant planets and brown dwarfs follow the same trend from ~0.3 MJ to the turn-over to hydrogen burning stars at ~ 73 MJ. EPIC 212036875 b falls close to the theoretical model for mature H/He dominated objects in this diagram as determined by interior structure models. We argue that EPIC 212036875 b formed via gravitational disc instabilities in the outer part of the disc, followed by a quick migration. Orbital tidal circularisation may have started early in its history for a brief period when the brown dwarf’s radius was larger. The lack of spin–orbit synchronisation points to a weak stellar dissipation parameter (Q⋆′ ≳ 108), which implies a circularisation timescale of ≳23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf.

scholarly journals Interferometric Identification of a Pre–Brown Dwarf

Science ◽  
2012 ◽  
Vol 337 (6090) ◽  
pp. 69-72 ◽  
Author(s):  
Philippe André ◽  
Derek Ward-Thompson ◽  
Jane Greaves
Keyword(s):  
Brown Dwarfs ◽  
Spectral Lines ◽  
Continuum Emission ◽  
Small Radius ◽  
Brown Dwarf ◽  
Solar Mass ◽  
Hydrogen Burning ◽  
Dynamical Mass ◽  
Clear Cut ◽  
Solar Type

It is not known whether brown dwarfs [stellar-like objects with masses less than the hydrogen-burning limit, 0.075 solar mass (M☉)] are formed in the same way as solar-type stars or by some other process. Here we report the clear-cut identification of a self-gravitating condensation of gas and dust with a mass in the brown-dwarf regime, made through millimeter interferometric observations. The level of thermal millimeter continuum emission detected from this object indicates a mass ~0.02 to 0.03 M☉, whereas the small radius, <460 astronomical units, and narrow spectral lines imply a dynamical mass of 0.015 to 0.02 M☉. The identification of such a pre–brown dwarf core supports models according to which brown dwarfs are formed in the same manner as hydrogen-burning stars.

scholarly journals A Deep Large area Search for Low Luminosity Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 435-435
Author(s):  
Hugh R.A. Jones ◽  
Mike R.S. Hawkins
Keyword(s):  
Spectral Type ◽  
Low Temperatures ◽  
Current Model ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Spectral Indices ◽  
Late Type ◽  
Brown Dwarf ◽  
Large Area ◽  
M Dwarfs

In a recent survey for faint red stars from a digital stack of Schmidt plates a number of candidate objects were identified. Parallax’s for three of these objects have been reported showing them to have luminosities which interpreted within the available evolutionary models indicate them to be good brown dwarf candidates. Here we examine spectra of these objects and others from the plate stack. Using standard spectral indices we find that for a given spectral type their spectra are more consistent with the Pleiades brown dwarfs (PPL 15, Teide 1 and Calar 3) than with standard late-type M dwarfs. Our interpretation is that this is due to their selection by RF IN colours which at values > 3 preferentially selects objects with relatively low gravities. For late-type M dwarfs and brown dwarfs low gravities are expected to be a reliable indication of youth. We also notice that the stack objects generally have strong FeH absorption for their spectral type. Current model atmospheres suggest that FeH strongly increases in strength toward lower metallicities and lower temperatures. We believe that this is not consistent with the available observational evidence from late-type M dwarfs. It is possible that solid Fe is forming inthe low temperature atmospheres relatively depleting FeH strengths toward lower temperatures. We find some evidence that for dwarfs at low temperatures dust formation is less prevalent in lower gravity objects suggesting that dwarfs at low temperatures stronger FeH may be an indication of youth. In addition to the spectral evidence the three stack objects whose parallax’s have been measured show small tangential velocities which is a further indication of youth.

Bayesian Spectroscopic Characterization of Directly Imaged Planets and Brown Dwarfs and Implications for Ultracool Model Atmospheres

2021 ◽  
Author(s):  
Zhoujian Zhang ◽  
Michael Liu ◽  
Mark Marley ◽  
Michael Line ◽  
William Best
Keyword(s):  
Physical Properties ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Spectroscopic Characterization ◽  
Cool Temperature ◽  
Brown Dwarf ◽  
Modeling Framework ◽  
High Quality ◽  
Model Predictions

&lt;p&gt;Spectroscopic characterization of imaged exoplanets and brown dwarfs is essential for understanding their atmospheres, formation, and evolution, but such work is challenged by the unavoidably simplified model atmospheres needed to interpret spectra. While most previous work has focused on single or at most a few objects, comparing a large collection of spectra to models can uncover trends in data-model inconsistencies needed to improve model predictions, thereby leading to robust properties from exoplanet and brown dwarf spectra. Therefore, we are conducting a systematic analysis of a valuable but underutilized resource: the numerous high-quality spectra of (directly imaged and free-floating) exoplanets and brown dwarfs already accumulated by the community.&lt;span class=&quot;Apple-converted-space&quot;&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt; &lt;p&gt;Focusing on the cool-temperature end, we have constructed a Bayesian modeling framework using the new Sonora-Bobcat model atmospheres and have applied it to study near-infrared low-resolution spectra of &gt;50 late-T imaged planets and brown dwarfs (&amp;#8776;600-1200K, &amp;#8776;10-70 M&lt;sub&gt;Jup&lt;/sub&gt;) and infer their physical properties (effective temperature, surface gravity, metallicity, radii, mass). By virtue of having such a large sample of high-quality spectra, our analysis identifies the systematic offsets between observed and model spectra as a function of wavelength and physical properties to pinpoint specific shortcomings in model predictions. We have also found that the spectroscopically inferred metallicities, ages, and masses of our sample all considerably deviate from expectations, suggesting the physical and chemical assumptions made within these models need to be improved to fully interpret data. Our work has established a systematic validation of cloudless model atmospheres to date and we discuss extending such analysis to wider temperature and wavelength (e.g., JWST) ranges, as well as finding new planetary-mass and brown dwarf benchmarks, in order to validate ultracool model atmospheres over larger parameter space.&lt;/p&gt;

scholarly journals Evidence of a Low-Mass Companion to AB Doradus

1998 ◽  
Vol 164 ◽  
pp. 325-326
Author(s):  
J. C. Guirado ◽  
J. E. Reynolds ◽  
J.-F. Lestrade ◽  
R. A. Preston ◽  
D. L. Jauncey ◽  
...  
Keyword(s):  
Satellite Data ◽  
Main Sequence ◽  
Brown Dwarfs ◽  
Type Star ◽  
Late Type ◽  
Hydrogen Burning ◽  
Late Type Star ◽  
Low Mass

AbstractFrom the combination of VLBI phase-referenced observations and Hipparcos satellite data, we have found evidence of a low-mass object orbiting the late-type star AB Doradus. The mass of the new object is near the hydrogen burning limit and will constitute a precise point for calibrating the low end of the main sequence. This represents the first detection of a low-mass stellar companion using the VLBI technique, which could become an important tool in future searches for planets and brown dwarfs orbiting other stars.

scholarly journals X-Ray Detection of Brown Dwarfs with Chandra

2003 ◽  
Vol 211 ◽  
pp. 447-450 ◽  
Author(s):  
Scott J. Wolk
Keyword(s):  
Brown Dwarfs ◽  
Stellar Clusters ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass ◽  
Vast Range

I review recent observations of brown dwarfs by the Chandra X-ray Observatory. These observations fall in 2 categories, young stellar clusters which contain brown dwarfs and brown dwarf candidates and directed pointings at brown dwarfs and very low mass stars. Surprisingly, there are already over 60 published detections of brown dwarfs by Chandra. A review of the X–ray characteristics shows these objects are subject to flaring and their temperatures and luminosities have a vast range which is related to age.

scholarly journals Sporadic and intense accretion in a 1 Myr-old brown dwarf candidate

2020 ◽  
Vol 634 ◽  
pp. A128
Author(s):  
D. Nguyen-Thanh ◽  
N. Phan-Bao ◽  
S. J. Murphy ◽  
M. S. Bessell
Keyword(s):  
Spectral Energy Distribution ◽  
Brown Dwarfs ◽  
Photometric Data ◽  
Spectral Energy ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
Trigonometric Parallax ◽  
Accretion Process ◽  
Accretion Rates ◽  
Low Mass

Context. Studying the accretion process in very low-mass objects has important implications for understanding their formation mechanism. Many nearby late-M dwarfs that have previously been identified in the field are in fact young brown dwarf members of nearby young associations. Some of them are still accreting. They are therefore excellent targets for further studies of the accretion process in the very low-mass regime at different stages. Aims. We aim to search for accreting young brown dwarf candidates in a sample of 85 nearby late-M dwarfs. Methods. Using photometric data from DENIS, 2MASS, and WISE, we constructed the spectral energy distribution of the late- M dwarfs based on BT-Settl models to detect infrared excesses. We then searched for lithium and Hα emission in candidates that exhibit infrared excesses to confirm their youth and the presence of accretion. Results. Among the 85 late-M dwarfs, only DENIS-P J1538317−103850 (M5.5) shows strong infrared excesses in WISE bands. The detection of lithium absorption in the M5.5 dwarf and its Gaia trigonometric parallax indicate an age of ~1 Myr and a mass of 47 MJ. The Hα emission line in the brown dwarf shows significant variability that indicates sporadic accretion. This 1 Myr-old brown dwarf also exhibits intense accretion bursts with accretion rates of up to 10−7.9 M⊙ yr−1. Conclusions. Our detection of sporadic accretion in one of the youngest brown dwarfs might imply that sporadic accretion at early stages could play an important role in the formation of brown dwarfs. Very low-mass cores would not be able to accrete enough material to become stars, and thus they end up as brown dwarfs.

scholarly journals The Substellar Members of the Pleiades

2003 ◽  
Vol 211 ◽  
pp. 181-182
Author(s):  
Paul D. Dobbie ◽  
Richard F. Jameson ◽  
Samantha L. Osborne ◽  
Simon T. Hodgkin ◽  
David J. Pinfield
Keyword(s):  
Dark Matter ◽  
Spatial Distribution ◽  
Power Law ◽  
Spatial Model ◽  
Total Mass ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Core Radius ◽  
Brown Dwarf ◽  
Limited Sample

We have compiled the largest magnitude limited sample of candidate substellar Pleiads to date. We fit King profiles to their spatial distribution to determine the Pleiades brown dwarf core radius to be Subsequently we have used our improved spatial model to place stringent limits on the shape of the cluster mass function across and below the stellar/substellar regime. We find this to be a power law with index α = 0.41±0.08 (0.3M⊙ ≥M≥ 0.035M⊙). Extrapolation of this mass function to M= 0.012M⊙ indicates that brown dwarfs contribute only ~ 2% to the total mass of the cluster hence we conclude that brown dwarfs do not contribute significantly to disk dark matter.

scholarly journals Ground-Based Optical Deep Pencil Beam Surveys

2003 ◽  
Vol 211 ◽  
pp. 203-210 ◽  
Author(s):  
P. C. Boeshaar ◽  
V. Margoniner
Keyword(s):  
Spatial Distribution ◽  
Large Volume ◽  
Brown Dwarfs ◽  
Scale Height ◽  
Galactic Latitude ◽  
Pencil Beam ◽  
Hydrogen Burning ◽  
High Galactic Latitude ◽  
Low Probability ◽  
Initial Results

The initial results of the Deep Lens Survey (http://dls.bell-labs.com) to identify possible brown dwarfs and extremely metal poor red halo subdwarfs near the hydrogen burning limit are presented. Individual deep CCD high galactic latitude survey fields appear to offer a low probability of discovering field BD's, but taken collectively offer an opportunity to begin addressing questions regarding the scale height and distribution of these objects. In all likelihood, the very depth of such surveys will greatly increase our knowledge of the coolest extreme halo objects, which currently are known in far fewer numbers than T dwarfs. Ultimately, the large volume surveyed by the Large Synoptic Survey Telescope will identify vast numbers of such objects, providing a more complete picture of their spatial distribution.

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