scholarly journals Primeval very low-mass stars and brown dwarfs – VII. The discovery of the first wide M + L extreme subdwarf binary

2019 ◽  
Vol 489 (1) ◽  
pp. 1423-1435 ◽  
Author(s):  
ZengHua Zhang (张曾华)
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
High Surface ◽  
Brown Dwarfs ◽  
Mass Range ◽  
Surface Gravity ◽  
Late Type ◽  
Low Mass Stars ◽  
Classification Schemes ◽  
Low Mass

ABSTRACT I present the discovery of the first wide M + L extreme subdwarf binary system Gaia J0452−36AB. The binary is located at a distance of 137.27 $^{+0.68}_{-0.67}$ pc with a projected separation of 15828 ± 78 au. I classified Gaia J0452−36AB as esdM1 and esdL0 subdwarfs, respectively. Gaia J0452−36AB have typical halo kinematics, metallicity of [Fe/H] ≈−1.4, and temperature of ∼ 3550 and 2600 K, respectively. Gaia J0452−36AB is a pair of very low-mass stars with masses of 0.151 $^{+0.029}_{-0.019}$ and 0.0855$^{+0.0014}_{-0.0010}$ M$\odot$, and is a gravitationally bound system. I tested the metallicity consistency of existing M subdwarf classification schemes with Gaia J0452−36AB and a sample of M and L subdwarfs with known metallicity. I found that the metallicity of each M subclass defined by the the metallicity index ζCaH/TiO is not consistent from mid-to-late M subtypes. Because late-type M and L subdwarfs have dusty atmospheres and high surface gravity which have significant impacts on CaH and TiO indices that used in the classification. The metallicity scale of late-type M subdwarfs would be overestimated by the ζCaH/TiO index. I discussed the mass range of M subdwarfs, and explained the lack of late-type M extreme and ultra subdwarfs, and decreasing binary fraction from sdM, to esdM, and usdM subclasses. The four M subclasses have different mass ranges. The comparison between M subclasses is between populations in different mass ranges. I also present the discovery of Ruiz 440-469B, an M8 dwarf wide companion to a cool DA white dwarf, Ruiz 440-469.

scholarly journals Spectral library of age-benchmark low-mass stars and brown dwarfs

2019 ◽  
Vol 491 (4) ◽  
pp. 5925-5950 ◽  
Author(s):  
E Manjavacas ◽  
N Lodieu ◽  
V J S Béjar ◽  
M R Zapatero-Osorio ◽  
S Boudreault ◽  
...  
Keyword(s):  
Near Infrared ◽  
High Surface ◽  
Spectral Characteristics ◽  
Brown Dwarfs ◽  
Surface Gravity ◽  
Test Surface ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Bolometric Luminosity ◽  
Ring Structures

ABSTRACT In recent years, some extremely red brown dwarfs have been discovered. They were believed to have a low surface gravity, but many of their spectral characteristics are similar to those of high-surface-gravity brown dwarfs, showing that the spectral characteristics of young brown dwarfs are poorly understood. We aim to test surface-gravity indicators in late-M and early-L brown dwarf spectra using data obtained with the X-shooter spectrograph at the Very Large Telescope. We select a benchmark sample of brown dwarf members of Chamaeleon I (∼2 Myr), Upper Scorpius (5−10 Myr), the Pleiades (132 ± 27 Myr) and Praesepe (590−790 Myr) with well-constrained ages and similar metallicities. We provide a consistent spectral classification of the sample in the optical and in the near-infrared. We measure the equivalent widths of their alkali lines, finding that they have a moderate correlation with age, especially for objects with spectral types M8 and later. We use spectral indices defined in the literature to estimate surface gravity, finding that their gravity assignment is accurate for 75 per cent of our sample. We investigate the correlation between red colour and age, finding that after ∼10 Myr, the colour does not change significantly for our sample with spectral types M6.0–L3.0. In this case, the red colours might be associated with circumstellar discs, ring structures, extinction, or viewing angle. Finally, we calculate the bolometric luminosity, and J and K bolometric corrections for our sample. We find that six objects are overluminous compared with other members of the same association. These objects are flagged as binary candidates by the Gaia survey.

Circumstellar disk fragmentation and the origin of massive planetary companions, brown dwarfs, and very low-mass stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 239-240 ◽  
Author(s):  
M. B. N. Kouwenhoven ◽  
Yun Li ◽  
D. Stamatellos ◽  
S. P. Goodwin
Keyword(s):  
Binary Systems ◽  
Brown Dwarfs ◽  
Mass Range ◽  
Mass Function ◽  
Initial Mass Function ◽  
Low Mass Stars ◽  
Triple Systems ◽  
Low Mass ◽  
Viable Mechanism

AbstractThe low-mass end of the initial mass function remains poorly understood. In this mass range, very low-mass stars, brown dwarfs, and massive planets are able to form through a variety of physical processes. Here, we study the long-term evolution of disk-fragmented systems around low-mass stars, for the epoch up to 10 Myr (the typical lifetime of an embedded cluster) and up to 10 Gyr (the age of the Milky Way). We carry out N-body simulations to study the decay of disk-fragmented systems and the resulting end products. Our simulations indicate rapid decay and frequent physical collisions during the first 10 Myr. We find that disk fragmentation provides a viable mechanism for explaining hierarchical triple systems, the brown dwarf desert, single and binary brown dwarfs, and very low-mass binary systems in the solar neighbourhood.

scholarly journals BANYAN. V. A SYSTEMATIC ALL-SKY SURVEY FOR NEW VERY LATE-TYPE LOW-MASS STARS AND BROWN DWARFS IN NEARBY YOUNG MOVING GROUPS

2014 ◽  
Vol 798 (2) ◽  
pp. 73 ◽  
Author(s):  
Jonathan Gagné ◽  
David Lafrenière ◽  
René Doyon ◽  
Lison Malo ◽  
Étienne Artigau
Keyword(s):  
Brown Dwarfs ◽  
Late Type ◽  
Low Mass Stars ◽  
Sky Survey ◽  
Low Mass ◽  
Moving Groups

scholarly journals Optical Spectroscopy of Young Brown Dwarfs in Orion

2003 ◽  
Vol 211 ◽  
pp. 69-70
Author(s):  
Fiona C. Riddick ◽  
Patrick F. Roche ◽  
Philip W. Lucas
Keyword(s):  
Optical Spectroscopy ◽  
Spectral Characteristics ◽  
Brown Dwarfs ◽  
Late Type ◽  
Low Mass Stars ◽  
Cluster Membership ◽  
Show Evidence ◽  
Low Mass ◽  
Orion Trapezium

Red spectra of a sample of low-mass stars and brown dwarfs in the Orion Trapezium cluster are discussed. They show late-type spectral characteristics confirming cluster membership and some show evidence of circumstellar activity.

scholarly journals Pebble-driven planet formation around very low-mass stars and brown dwarfs

2020 ◽  
Vol 638 ◽  
pp. A88 ◽  
Author(s):  
Beibei Liu ◽  
Michiel Lambrechts ◽  
Anders Johansen ◽  
Ilaria Pascucci ◽  
Thomas Henning
Keyword(s):  
Mass Fraction ◽  
Planet Formation ◽  
Water Mass ◽  
Giant Planet ◽  
Brown Dwarfs ◽  
Mass Range ◽  
Protoplanetary Disk ◽  
Low Mass Stars ◽  
Streaming Instability ◽  
Low Mass

We conduct a pebble-driven planet population synthesis study to investigate the formation of planets around very low-mass stars and brown dwarfs in the (sub)stellar mass range between 0.01 M⊙ and 0.1 M⊙. Based on the extrapolation of numerical simulations of planetesimal formation by the streaming instability, we obtain the characteristic mass of the planetesimals and the initial mass of the protoplanet (largest body from the planetesimal populations), in either the early self-gravitating phase or the later non-self-gravitating phase of the protoplanetary disk evolution. We find that the initial protoplanets form with masses that increase with host mass and orbital distance, and decrease with age. Around late M-dwarfs of 0.1 M⊙, these protoplanets can grow up to Earth-mass planets by pebble accretion. However, around brown dwarfs of 0.01 M⊙, planets do not grow to the masses that are greater than Mars when the initial protoplanets are born early in self-gravitating disks, and their growth stalls at around 0.01 Earth-mass when they are born late in non-self-gravitating disks. Around these low-mass stars and brown dwarfs we find no channel for gas giant planet formation because the solid cores remain too small. When the initial protoplanets form only at the water-ice line, the final planets typically have ≳15% water mass fraction. Alternatively, when the initial protoplanets form log-uniformly distributed over the entire protoplanetary disk, the final planets are either very water rich (water mass fraction ≳15%) or entirely rocky (water mass fraction ≲5%).

scholarly journals The Late-Type Extension to MoVeRS (LaTE-MoVeRS): Proper Motion Verified Low-mass Stars and Brown Dwarfs from SDSS, 2MASS, andWISE

2017 ◽  
Vol 153 (3) ◽  
pp. 92 ◽  
Author(s):  
Christopher A. Theissen ◽  
Andrew A. West ◽  
Guillaume Shippee ◽  
Adam J. Burgasser ◽  
Sarah J. Schmidt
Keyword(s):  
Proper Motion ◽  
Brown Dwarfs ◽  
Late Type ◽  
Low Mass Stars ◽  
Low Mass ◽  
Late Movers

scholarly journals The coolest extremely low-mass white dwarfs

2018 ◽  
Vol 614 ◽  
pp. A49 ◽  
Author(s):  
Leila M. Calcaferro ◽  
Leandro G. Althaus ◽  
Alejandro H. Córsico
Keyword(s):  
Mass Transfer ◽  
Mass Loss ◽  
White Dwarf ◽  
Binary Systems ◽  
Mass Range ◽  
Surface Gravity ◽  
Slight Reduction ◽  
Mechanisms Of Formation ◽  
Nuclear Burning ◽  
Low Mass

Context. Extremely low-mass white dwarf (ELM WD; M⋆ ≲ 0.18–0.20 M⊙) stars are thought to be formed in binary systems via stable or unstable mass transfer. Although stable mass transfer predicts the formation of ELM WDs with thick hydrogen (H) envelopes that are characterized by dominant residual nuclear burning along the cooling branch, the formation of ELM WDs with thinner H envelopes from unstable mass loss cannot be discarded. Aims. We compute new evolutionary sequences for helium (He) core WD stars with thin H envelopes with the main aim of assessing the lowest Teff that could be reached by this type of stars. Methods. We generate a new grid of evolutionary sequences of He-core WD stars with thin H envelopes in the mass range from 0.1554 to 0.2025 M⊙, and assess the changes in both the cooling times and surface gravity induced by a reduction of the H envelope. We also determine, taking into account the predictions of progenitor evolution, the lowest Teff reached by the resulting ELM WDs. Results. We find that a slight reduction in the H envelope yields a significant increase in the cooling rate of ELM WDs. Because of this, ELM WDs with thin H envelopes could cool down to ~2500 K, in contrast to their canonical counterparts that cool down to ~7000 K. In addition, we find that a reduction of the thickness of the H envelope markedly increases the surface gravity (g) of these stars. Conclusions. If ELM WDs are formed with thin H envelopes, they could be detected at very low Teff. The detection of such cool ELM WDs would be indicative that they were formed with thin H envelopes, thus opening the possibility of placing constraints on the possible mechanisms of formation of this type of star. Last but not least, the increase in g due to the reduction of the H envelope leads to consequences in the spectroscopic determinations of these stars.

scholarly journals Giant planets around AF and M stars

2013 ◽  
Vol 8 (S299) ◽  
pp. 64-65
Author(s):  
Julien Rameau ◽  
Gaël Chauvin ◽  
Anne-Marie Lagrange ◽  
Philippe Delorme ◽  
Justine Lannier
Keyword(s):  
Giant Planets ◽  
Early Type ◽  
Late Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Planetary Mass ◽  
Nearby Stars ◽  
Low Mass ◽  
M Stars ◽  
The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

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