scholarly journals Constraining the multiplicity statistics of the coolest brown dwarfs: binary fraction continues to decrease with spectral type

2018 ◽  
Vol 479 (2) ◽  
pp. 2702-2727 ◽  
Author(s):  
Clémence Fontanive ◽  
Beth Biller ◽  
Mariangela Bonavita ◽  
Katelyn Allers
Keyword(s):  
Spectral Type ◽  
Brown Dwarfs

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.

scholarly journals The First Young Brown Dwarf in the Serpens Cloud

2003 ◽  
Vol 211 ◽  
pp. 83-86
Author(s):  
Jean-Louis Monin ◽  
Emmanuel Caux ◽  
Alain Klotz ◽  
Nicolas Lodieu
Keyword(s):  
Star Formation ◽  
Spectral Type ◽  
Near Infrared ◽  
Nir Spectroscopy ◽  
Brown Dwarfs ◽  
Brown Dwarf ◽  
Star Formation Region ◽  
Formation Region

We report the discovery of the first young brown dwarf in the Serpens cloud (BD-Ser 1). It is obscured by more than ten magnitudes of visual absorption as indicated by near infrared (NIR) photometric survey at the NTT and confirmed by NIR spectroscopy at the VLT. We estimate the mass of this brown dwarf to be M ~ 0.05 M⊙ and its age to be ~ 3.5 Myr. Available NIR indices in the literature (designed for field brown dwarfs) fail to provide its current spectral type but using a model they correctly determine its future spectral type to be T. This is the first young brown dwarf ever found deeply embedded in the Serpens star formation region

scholarly journals The Search for Brown Dwarfs around White Dwarfs

2003 ◽  
Vol 211 ◽  
pp. 289-292 ◽  
Author(s):  
J. Farihi ◽  
E. E. Becklin ◽  
B. Zuckerman
Keyword(s):  
Spectral Type ◽  
White Dwarf ◽  
Proper Motion ◽  
White Dwarfs ◽  
Near Field ◽  
Brown Dwarfs ◽  
Wide Field ◽  
M Dwarfs ◽  
Recent Phase ◽  
Motion Search

The infrared search for substellar companions to nearby white dwarfs has been going on for a little more than a decade. The most recent phase has been a wide field proper motion search carried out primarily at Steward Observatory, where we are complete down to J = 18. Earlier phases included near field searches at the IRTF and Keck Observatory. In the last year we have discovered ten previously unrecognized faint proper motion companions. Of the recent discoveries, most are white dwarfs and a few M dwarfs. GD165B, discovered in 1988 as part of our program, is still the only known companion to a white dwarf with spectral type later than M.

scholarly journals Photometric Properties of L and T Dwarf Binaries

2021 ◽  
Vol 5 (12) ◽  
pp. 286
Author(s):  
Alyssa C Leone ◽  
William M. J. Best ◽  
Michael C. Liu ◽  
Eugene A. Magnier ◽  
Trent J. Dupuy
Keyword(s):  
Spectral Type ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Supporting Evidence ◽  
Limited Sample

Abstract Recent studies using volume-limited samples of brown dwarfs have revealed the photometric evolution of single L and T dwarfs and unresolved binaries as they age and cool, in particular as they transition from L to T spectral types. We demonstrate that the near-infrared photometric evolution of the resolved components of L and T dwarf binaries is consistent with that of single objects using a volume-limited sample. In addition, we provide supporting evidence that the L9 dwarf WISE J185101.83+593508.6 is an unresolved binary and identify three more candidate or confirmed unresolved binaries all from being overluminous for their spectral type. We calculate a new binary fraction of 13.1% ± 1.8% for L0–T8 dwarfs.

scholarly journals Primeval very low-mass stars and brown dwarfs – VI. Population properties of metal-poor degenerate brown dwarfs

2019 ◽  
Vol 486 (1) ◽  
pp. 1260-1282 ◽  
Author(s):  
Z H Zhang (张曾华) ◽  
A J Burgasser ◽  
M C Gálvez-Ortiz ◽  
N Lodieu ◽  
M R Zapatero Osorio ◽  
...  
Keyword(s):  
Transition Zone ◽  
Spectral Type ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Absolute Magnitude ◽  
Wide Field ◽  
Low Mass Stars ◽  
Low Mass ◽  
Infrared Survey ◽  
K Band

ABSTRACT We presented 15 new T dwarfs that were selected from UKIRT Infrared Deep Sky Survey, Visible and Infrared Survey Telescope for Astronomy , and Wide-field Infrared Survey Explorer surveys, and confirmed with optical to near-infrared spectra obtained with the Very Large Telescope and the Gran Telescopio Canarias. One of these new T dwarfs is mildly metal-poor with slightly suppressed K-band flux. We presented a new X-shooter spectrum of a known benchmark sdT5.5 subdwarf, HIP 73786B. To better understand observational properties of brown dwarfs, we discussed transition zones (mass ranges) with low-rate hydrogen, lithium, and deuterium burning in brown dwarf population. The hydrogen burning transition zone is also the substellar transition zone that separates very low-mass stars, transitional, and degenerate brown dwarfs. Transitional brown dwarfs have been discussed in previous works of the Primeval series. Degenerate brown dwarfs without hydrogen fusion are the majority of brown dwarfs. Metal-poor degenerate brown dwarfs of the Galactic thick disc and halo have become T5+ subdwarfs. We selected 41 T5+ subdwarfs from the literature by their suppressed K-band flux. We studied the spectral-type–colour correlations, spectral-type–absolute magnitude correlations, colour–colour plots, and HR diagrams of T5+ subdwarfs, in comparison to these of L–T dwarfs and L subdwarfs. We discussed the T5+ subdwarf discovery capability of deep sky surveys in the 2020s.

scholarly journals Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope

2022 ◽  
Vol 924 (2) ◽  
pp. 68
Author(s):  
Johanna M. Vos ◽  
Jacqueline K. Faherty ◽  
Jonathan Gagné ◽  
Mark Marley ◽  
Stanimir Metchev ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Spectral Type ◽  
Brown Dwarfs ◽  
High Mass ◽  
Occurrence Rate ◽  
Spitzer Space Telescope ◽  
Photometric Variability ◽  
Space Telescope ◽  
Rotation Periods ◽  
Low Mass

Abstract We present a survey for photometric variability in young, low-mass brown dwarfs with the Spitzer Space Telescope. The 23 objects in our sample show robust signatures of youth and share properties with directly imaged exoplanets. We present three new young objects: 2MASS J03492367+0635078, 2MASS J09512690−8023553, and 2MASS J07180871−6415310. We detect variability in 13 young objects, and find that young brown dwarfs are highly likely to display variability across the L2–T4 spectral type range. In contrast, the field dwarf variability occurrence rate drops for spectral types >L9. We examine the variability amplitudes of young objects and find an enhancement in maximum amplitudes compared to field dwarfs. We speculate that the observed range of amplitudes within a spectral type may be influenced by secondary effects such as viewing inclination and/or rotation period. We combine our new rotation periods with the literature to investigate the effects of mass on angular momentum evolution. While high-mass brown dwarfs (>30M Jup) spin up over time, the same trend is not apparent for lower-mass objects (<30M Jup), likely due to the small number of measured periods for old, low-mass objects. The rotation periods of companion brown dwarfs and planetary-mass objects are consistent with those of isolated objects with similar ages and masses, suggesting similar angular momentum histories. Within the AB Doradus group, we find a high-variability occurrence rate and evidence for common angular momentum evolution. The results are encouraging for future variability searches in directly imaged exoplanets with facilities such as the James Webb Space Telescope and 30 m telescopes.

scholarly journals X-ray Emission from Brown Dwarfs

2004 ◽  
Vol 219 ◽  
pp. 285-295
Author(s):  
Thomas Preibisch
Keyword(s):  
Free Energy ◽  
Spectral Type ◽  
Effective Temperature ◽  
Plasma Temperature ◽  
Brown Dwarfs ◽  
Low Mass Stars ◽  
Electrical Currents ◽  
X Ray ◽  
Magnetic Free Energy ◽  
Low Mass

During the last few years, X-ray emission has been detected from numerous brown dwarfs. Most of the X-ray detected brown dwarfs are very young objects with ages of at most 107 years, and all are still relatively warm, with late M spectral types. Their typical fractional X-ray luminosities are (LX/Lbol) ∼ 10—4 — 10—3, i.e. very similar to the values observed for active very-low mass stars. Their X-ray lightcurves show low-level variability, but in most cases no large flares; this implies that the young brown dwarfs are able to produce quiescent X-ray emission, not only occasional flares. An analysis of the Chandra X-ray spectra of several brown dwarfs yields surprisingly low plasma temperatures between 3 MK and 10 MK for some of the M8-9 dwarfs and indicates a decline in plasma temperature with decreasing effective temperature (or increasing age). The lack of X-ray detections for dwarfs cooler than spectral type M9 is consistent with the strong drop of activity observed in Hα at spectral types around M9. The observed X-ray emission from the young brown dwarfs with late M spectral type can be understood as a consequence of the fact that these objects are still warm enough to maintain partially ionized atmospheres which are capable of sustaining electrical currents. In the cooler, essentially neutral atmospheres of the older L and T dwarfs such currents are probably shut off, preventing the buildup of magnetic free energy and the support for magnetically heated chromospheres and coronae.

scholarly journals Parallaxes of Brown Dwarfs at USNO

2003 ◽  
Vol 211 ◽  
pp. 409-412
Author(s):  
Hugh C. Harris ◽  
Conard C. Dahn ◽  
Frederick J. Vrba ◽  
Harry H. Guetter ◽  
Blaise Canzian ◽  
...  
Keyword(s):  
Spectral Type ◽  
Tangential Velocity ◽  
Brown Dwarfs ◽  
Absolute Magnitude ◽  
Rotation Velocity ◽  
Measurable Parameter ◽  
Trigonometric Parallaxes ◽  
Hα Emission ◽  
L Dwarfs ◽  
Absolute Magnitudes

Trigonometric parallaxes have been measured by Dahn et al. (2002) for 28 cool dwarfs and brown dwarfs, including 17 L dwarfs and three T dwarfs. Broadband CCD and near-IR photometry (VRIz*JHK) have been obtained for these objects and for 24 additional late-type dwarfs. These data have been supplemented with astrometry and photometry from the literature, including parallaxes for the brighter companions of ten L and two T dwarfs. The absolute magnitudes and colors are reviewed here. The I - J color and the spectral type are both good predictors of absolute magnitude for late-M and L dwarfs. MJ becomes monotonically fainter with I - J color and with spectral type through late-L dwarfs, then brightens for early-T dwarfs. In contrast, the J - K color correlates poorly with absolute magnitude for L dwarfs. Using several other parameters from the literature (Li detection, Hα emission strength, projected rotation velocity, and tangential velocity), we fail to uncover any measurable parameter that correlates with the anomalous J - K color.

scholarly journals Magnetic Activity of Pre-main Sequence Stars near the Stellar-Substellar Boundary

2015 ◽  
Vol 10 (S314) ◽  
pp. 126-127
Author(s):  
David Principe ◽  
Joel. H. Kastner ◽  
David Rodriguez
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Brown Dwarfs ◽  
Magnetic Activity ◽  
Main Sequence Stars ◽  
Coronal Emission ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass ◽  
Age Range

AbstractX-ray observations of pre-main sequence (pre-MS) stars of M-type probe coronal emission and offer a means to investigate magnetic activity at the stellar-substellar boundary. Recent observations of main sequence (MS) stars at this boundary display a decrease in fractional X-ray luminosity (LX/Lbol) by almost two orders of magnitude for spectral types M7 and later. We investigate magnetic activity and search for a decrease in X-ray emission in the pre-MS progenitors of these MS stars. We present XMM-Newton X-ray observations and preliminary results for ~10 nearby (30-70 pc), very low mass pre-MS stars in the relatively unexplored age range of 10-30 Myr. We compare the fractional X-ray luminosities of these 10-30 Myr old stars to younger (1-3 Myr) pre-MS brown dwarfs and find no dependence on spectral type or age suggesting that X-ray activity declines at an age later than ~30 Myr in these very low-mass stars.

Some Results of the Spectroscopic Study of Four Close Binary Systems of Early Spectral Types

1965 ◽  
Vol 5 ◽  
pp. 120-130
Author(s):  
T. S. Galkina
Keyword(s):  
Spectroscopic Study ◽  
Spectral Type ◽  
Spectroscopic Investigation ◽  
Binary Systems ◽  
Quantitative Information ◽  
Close Binary ◽  
Physical Parameters ◽  
Absorption And Emission ◽  
Close Binary Systems ◽  
Quantitative Estimates

It is necessary to have quantitative estimates of the intensity of lines (both absorption and emission) to obtain the physical parameters of the atmosphere of components.Some years ago at the Crimean observatory we began the spectroscopic investigation of close binary systems of the early spectral type with components WR, Of, O, B to try and obtain more quantitative information from the study of the spectra of the components.

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