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 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 Dynamical masses for the nearest brown dwarf binary: ε Indi Ba,b

2009 ◽  
Vol 5 (H15) ◽  
pp. 761-761
Author(s):  
C. V. Cardoso ◽  
M. J. McCaughrean ◽  
R. R. King ◽  
L. M. Close ◽  
R.-D. Scholz ◽  
...  
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Atmospheric Models ◽  
Brown Dwarf ◽  
Near Ir ◽  
The Earth ◽  
Benchmark System ◽  
Model Independent ◽  
Dynamical Masses

Binary brown dwarfs are important because their dynamical masses can be determined in a model-independent way. If a main sequence star is also involved, the age and metallicity for the system can be determined, making it possible to break the sub-stellar mass-age degeneracy. The most suitable benchmark system for intermediate age T dwarfs is ε Indi Ba,b, two T dwarfs (spectral types T1 and T6; McCaughrean et al. (2004)) orbiting a K4.5V star, ε Indi A, at a projected separation of 1460AU. At a distance of 3.6224pc (HIPPARCOS distance to ε Indi A; van Leeuwen (2007)), these are the closest brown dwarfs to the Earth, and thus both components are bright and the system is well-resolved. The system has been monitored astrometrically with NACO and FORS2 on the VLT since June 2004 and August 2005, respectively, in order to determine the system and individual masses independent of evolutionary models. We have obtained a preliminary system mass of 121±1MJup. We have also analysed optical/near-IR spectra (0.6-5.0μm at a resolution up to R~5000; King et al. (2009)) allowing us to determine bolometric luminosities, compare and calibrate evolutionary and atmospheric models of T dwarfs at an age of 4-8Gyr.

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 A Large, Deep Survey of the Taurus Dark Clouds

2003 ◽  
Vol 211 ◽  
pp. 79-80
Author(s):  
S. L. Osborne ◽  
R. F. Jameson ◽  
P. D. Dobbie ◽  
E. L. Martín
Keyword(s):  
Spectroscopic Data ◽  
Brown Dwarfs ◽  
Theoretical Models ◽  
Late Type ◽  
M Dwarfs ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Deep Survey ◽  
Hα Emission

Preliminary results from a deep R, I and Z band survey of ~ 6 square degrees of the Taurus Dark Cloud region are presented. 186 potential brown dwarfs have been unearthed, with seven having follow-up spectroscopic data. The spectra reveal three mid/late-type M dwarfs, of which two show weak Hα emission. If these objects are members of the TDC region, theoretical models suggest masses in the range 10 – 20 MJ.

scholarly journals Activity and Kinematics of Late M, L, and T Dwarfs

2003 ◽  
Vol 211 ◽  
pp. 437-442
Author(s):  
James Liebert
Keyword(s):  
Spectral Type ◽  
Young Stellar Objects ◽  
Evolutionary Models ◽  
M Dwarfs ◽  
Stellar Objects ◽  
Order Of Magnitude ◽  
Hα Emission ◽  
L Dwarfs ◽  
Larger Sample ◽  
Rule Out

The kinematics of late M and certainly L dwarfs indicate that they have a mean age of no more than a few Gyr. This result does not rule out a mix of young brown dwarfs and ZAMS stars. Relative Hα emission strengths begin to decline in the late M dwarfs, even though about 100% of the M7-8 dwarfs show the weaker emission. Both the frequency and likely strength of this emission declines with spectral type among the L's and T's. A larger sample of late M and L dwarfs, which may provide more definitive tests of the kinematic and activity properties, is being assembled from our NStars project.Two unusual objects, one an M9.5e and the other a T6e, show persistent Hα emission at least an order of magnitude stronger than their counterparts of similar spectral type. If these are hypothesized to be very young stellar objects (≲10 Myr) like some observed in Rho Oph, Sigma Ori and Taurus – evolutionary models would require them to have very low masses: In particular, for an entity to fade to a late T dwarf temperature and luminosity within 10 Myr, its mass should be no more than several Jupiters. This seems implausible for an isolated object not near any obvious site of recent star formation. However, our attempt to show that the emission might be due to accretion in a binary system was unsuccessful.

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 The Brown Dwarf Kinematics Project (BDKP). V. Radial and Rotational Velocities of T Dwarfs from Keck/NIRSPEC High-resolution Spectroscopy

2021 ◽  
Vol 257 (2) ◽  
pp. 45
Author(s):  
Chih-Chun Hsu ◽  
Adam J. Burgasser ◽  
Christopher A. Theissen ◽  
Christopher R. Gelino ◽  
Jessica L. Birky ◽  
...  
Keyword(s):  
Main Sequence ◽  
Formation Rate ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Radial Velocities ◽  
High Resolution Spectroscopy ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
L Dwarfs ◽  
Orbital Periods

Abstract We report multiepoch radial velocities, rotational velocities, and atmospheric parameters for 37 T-type brown dwarfs observed with Keck/NIRSPEC. Using a Markov Chain Monte Carlo forward-modeling method, we achieve median precisions of 0.5 and 0.9 km s−1 for radial and rotational velocities, respectively. All of the T dwarfs in our sample are thin-disk brown dwarfs. We confirm previously reported moving group associations for four T dwarfs. However, the lack of spectral indicators of youth in two of these sources suggests that these are chance alignments. We confirm two previously unresolved binary candidates, the T0+T4.5 2MASS J11061197+2754225 and the L7+T3.5 2MASS J21265916+7617440, with orbital periods of 4 and 12 yr, respectively. We find a kinematic age of 3.5 ± 0.3 Gyr for local T dwarfs, consistent with nearby late M dwarfs (4.1 ± 0.3 Gyr). Removal of thick-disk L dwarfs in the local ultracool dwarf sample gives a similar age for L dwarfs (4.2 ± 0.3 Gyr), largely resolving the local L dwarf age anomaly. The kinematic ages of local late M, L, and T dwarfs can be accurately reproduced with population simulations incorporating standard assumptions of the mass function, star formation rate, and brown dwarf evolutionary models. A kinematic dispersion break is found at the L4–L6 subtypes, likely reflecting the terminus of the stellar main sequence. We provide a compilation of precise radial velocities for 172 late M, L, and T dwarfs within ∼20 pc of the Sun.

scholarly journals Orbital and spectral analysis of the benchmark brown dwarf HD 4747B

2019 ◽  
Vol 631 ◽  
pp. A107 ◽  
Author(s):  
S. Peretti ◽  
D. Ségransan ◽  
B. Lavie ◽  
S. Desidera ◽  
A.-L. Maire ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
High Contrast ◽  
Imaging Data ◽  
Velocity Measurements ◽  
Brown Dwarf ◽  
Contrast Imaging ◽  
Semi Major Axis ◽  
Dynamical Mass

Context. The study of high-contrast imaged brown dwarfs and exoplanets depends strongly on evolutionary models. To estimate the mass of a directly imaged substellar object, its extracted photometry or spectrum is used and adjusted with model spectra together with the estimated age of the system. These models still need to be properly tested and constrained. HD 4747B is a brown dwarf close to the H burning mass limit, orbiting a nearby (d = 19.25 ± 0.58 pc), solar-type star (G9V); it has been observed with the radial velocity method for over almost two decades. Its companion was also recently detected by direct imaging, allowing a complete study of this particular object. Aims. We aim to fully characterize HD 4747B by combining a well-constrained dynamical mass and a study of its observed spectral features in order to test evolutionary models for substellar objects and to characterize its atmosphere. Methods. We combined the radial velocity measurements of High Resolution Echelle Spectrometer (HIRES) and CORALIE taken over two decades and high-contrast imaging of several epochs from NACO, NIRC2, and SPHERE to obtain a dynamical mass. From the SPHERE data we obtained a low-resolution spectrum of the companion from Y to H band, and two narrow band-width photometric measurements in the K band. A study of the primary star also allowed us to constrain the age of the system and its distance. Results. Thanks to the new SPHERE epoch and NACO archival data combined with previous imaging data and high-precision radial velocity measurements, we were able to derive a well-constrained orbit. The high eccentricity (e = 0.7362 ± 0.0025) of HD 4747B is confirmed, and the inclination and the semi-major axis are derived (i = 47.3 ± 1.6°, a = 10.01 ± 0.21 au). We derive a dynamical mass of mB = 70.0 ± 1.6 MJup, which is higher than a previous study but in better agreement with the models. By comparing the object with known brown dwarfs spectra, we derive a spectral type of L9 and an effective temperature of 1350 ± 50 K. With a retrieval analysis we constrain the oxygen and carbon abundances and compare them with the values from the HR 8799 planets.

scholarly journals Spectroscopic Observations of Late-Type Halo M Dwarfs

1978 ◽  
Vol 80 ◽  
pp. 21-22
Author(s):  
Patricia C. Boeshaar
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Late Type ◽  
Main Sequence Stars ◽  
M Dwarfs ◽  
Absorption Bands ◽  
Enhanced Absorption ◽  
Halo Population ◽  
Low Dispersion ◽  
Temperature Class

In the lower main sequence, the coolest halo population stars do not appear to be particularly subluminous in either the standard HR diagram or the (MI, R-I) plane. Earlier type M subdwarf's (e.g., Kapteyn's Star) that lie one or more magnitudes below the main sequence exhibit enhanced hydride absorption bands relative to M dwarfs of the same temperature. From visual region (4500–7000 Å) low dispersion image tube spectrograms we find that the cool halo M dwarfs exhibit enhanced absorption in the CaOH 5530 Å band and Na I resonance lines. Easily noticeable changes in the strength of the CaH “B” band relative to that of the TiO bands was found to be more difficult to determine in halo dwarfs later than spectral type M4. Several M dwarfs with old disk type motions have spectral peculiarities similar to those of the halo dwarfs. In both cases, Balmer emission is not present in most stars, in the rest it is very weak. Therefore, the anomalous strength of the CaOH 5530 Å band and Na resonance lines appear to be a more conveniently utilized qualitative criterion in spectroscopically identifying very cool M dwarfs which are subluminous with respect to most main sequence stars of the same temperature class.

scholarly journals TOI-519 b: A short-period substellar object around an M dwarf validated using multicolour photometry and phase curve analysis

2020 ◽  
Vol 645 ◽  
pp. A16
Author(s):  
H. Parviainen ◽  
E. Palle ◽  
M. R. Zapatero-Osorio ◽  
G. Nowak ◽  
A. Fukui ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Planet Formation ◽  
Thermal Emission ◽  
Brown Dwarfs ◽  
Curve Analysis ◽  
Phase Curve ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
Short Period ◽  
M Dwarf

Context. We report the discovery of TOI-519 b (TIC 218795833), a transiting substellar object (R = 1.07 RJup) orbiting a faint M dwarf (V = 17.35) on a 1.26 d orbit. Brown dwarfs and massive planets orbiting M dwarfs on short-period orbits are rare, but more have already been discovered than expected from planet formation models. TOI-519 is a valuable addition to this group of unlikely systems, and it adds towards our understanding of the boundaries of planet formation. Aims. We set out to determine the nature of the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-519 b. Methods. Our analysis uses a SPOC-pipeline TESS light curve from Sector 7, multicolour transit photometry observed with MuSCAT2 and MuSCAT, and transit photometry observed with the LCOGT telescopes. We estimated the radius of the transiting object using multicolour transit modelling, and we set upper limits for its mass, effective temperature, and Bond albedo using a phase curve model that includes Doppler boosting, ellipsoidal variations, thermal emission, and reflected light components. Results. TOI-519 b is a substellar object with a radius posterior median of 1.07 RJup and 5th and 95th percentiles of 0.66 and 1.20 RJup, respectively, where most of the uncertainty comes from the uncertainty in the stellar radius. The phase curve analysis sets an upper effective temperature limit of 1800 K, an upper Bond albedo limit of 0.49, and a companion mass upper limit of 14 MJup. The companion radius estimate combined with the Teff and mass limits suggests that the companion is more likely a planet than a brown dwarf, but a brown-dwarf scenario is a priori more likely given the lack of known massive planets in ≈ 1 day orbits around M dwarfs with Teff < 3800 K, and given the existence of some (but few) brown dwarfs.

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