scholarly journals Brown Dwarfs are Violet: A New Calculation of Human-eye Colors of Main-sequence Stars and Substellar Objects

2021 ◽  
Vol 5 (9) ◽  
pp. 201
Author(s):  
Steven R. Cranmer
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Main Sequence Stars ◽  
Human Eye ◽  
Substellar Objects

scholarly journals Properties which cannot be explained by Planetary Nebulae's progenitors

1997 ◽  
Vol 180 ◽  
pp. 367-367
Author(s):  
Noam Soker
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Giant Planets ◽  
Main Sequence Stars ◽  
Substellar Objects ◽  
Earth Like Planets ◽  
Low Mass ◽  
Inner Region ◽  
Central Stars

Stellar binary companions account for bipolar PNe (∼ 11% of all PNe1), and some ellipticalls (22%2). The rest of axisymmetrical PNe (40% to 60% of all PNe) are due to substellar objects (planets and brown dwarfs)3. This classification of axi symmetrical PNe suggests that substellar objects are commonly present within several × AU around main sequence stars, and that several substellar objects must be present around most main sequence stars3. Some substellar and low mass stellar companions will enter the primary envelope only as the primary reaches the upper AGB. Thus, the early mass loss episode will be spherical, leading to the formation of a spherical halo around an elliptical inner region. Gas giant planets and brown dwarfs close to the primary, will not allow Earth-like planets to have stable orbits. Systems with no Jupiter-like planets will allow Earth-like planets to be present. These stars will form spherical PNe (10%-20% of all PNe, including spherically ejected PNe that have been deformed by the ISM through which they move4). Systems with substellar objects at large separation, as Jupiter in the solar system, will also allow Earth-like planets to be present. These systems will form PNe with spherical halo. Therefore, life may have been present in planets around the central stars of round PNe and elliptical PNe with round halos.

scholarly journals Atmosphere models for very low mass stars, brown dwarfs and exoplanets

1997 ◽  
Vol 189 ◽  
pp. 227-233
Author(s):  
I. Baraffe ◽  
F. Allard
Keyword(s):  
Main Sequence ◽  
Accurate Determination ◽  
Brown Dwarfs ◽  
Considerable Effort ◽  
Low Mass Stars ◽  
The Past ◽  
Substellar Objects ◽  
Cool Stars ◽  
Low Mass

Over the past decade considerable effort, both observational and theoretical, has been directed towards a more accurate determination of the stellar lower main sequence and of the sub-stellar domain covered by Brown Dwarfs and Planets. Astronomers have been looking for brown dwarfs for more than a decade, either with standard astronomical technics or with microlensing experiments. A breakthrough in the search for brown dwarfs was very recently achieved with the discovery of the first cool brown dwarf GL 229B (Nakajima et al. 1995). At the same epoch, the search for planets blossomed with the discovery of a Jupiter - mass companion of the star 51 Pegasi (Mayor and Queloz 199,5). Now, the number of faint, cool stars and substellar objects is rising rapidly.

scholarly journals Wide Brown Dwarf Companions to Main-Sequence Stars

2003 ◽  
Vol 211 ◽  
pp. 281-286
Author(s):  
John E. Gizis
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Brown Dwarf ◽  
Main Sequence Stars

Many widely separated companions to main-sequence stars have been found using 2MASS. These companions include both stars and brown dwarfs. I discuss a number of systems of particular interest. Present indications are that a few percent of G dwarfs have brown dwarf companions.

scholarly journals The CORALIE survey for southern extrasolar planets

2019 ◽  
Vol 625 ◽  
pp. A71 ◽  
Author(s):  
E. L. Rickman ◽  
D. Ségransan ◽  
M. Marmier ◽  
S. Udry ◽  
F. Bouchy ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Extrasolar Planets ◽  
Brown Dwarfs ◽  
Main Sequence Stars ◽  
Period Range ◽  
Orbital Parameters ◽  
Long Period ◽  
Long Term Trends

Context. Since 1998, a planet-search around main sequence stars within 50 pc in the southern hemisphere has been underway with the CORALIE spectrograph at La Silla Observatory. Aims. With an observing time span of more than 20 yr, the CORALIE survey is able to detect long-term trends in data with masses and separations large enough to select ideal targets for direct imaging. Detecting these giant companion candidates will allow us to start bridging the gap between radial-velocity-detected exoplanets and directly imaged planets and brown dwarfs. Methods. Long-term precise Doppler measurements with the CORALIE spectrograph reveal radial-velocity signatures of massive planetary companions and brown dwarfs on long-period orbits. Results. In this paper, we report the discovery of new companions orbiting HD 181234, HD 13724, HD 25015, HD 92987 and HD 50499. We also report updated orbital parameters for HD 50499b, HD 92788b and HD 98649b. In addition, we confirm the recent detection of HD 92788c. The newly reported companions span a period range of 15.6–40.4 yr and a mass domain of 2.93–26.77 MJup, the latter of which straddles the nominal boundary between planets and brown dwarfs. Conclusions. We report the detection of five new companions and updated parameters of four known extrasolar planets. We identify at least some of these companions to be promising candidates for imaging and further characterisation.

scholarly journals Gravitational waves from bodies orbiting the Galactic center black hole and their detectability by LISA

2019 ◽  
Vol 627 ◽  
pp. A92 ◽  
Author(s):  
E. Gourgoulhon ◽  
A. Le Tiec ◽  
F. H. Vincent ◽  
N. Warburton
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Main Sequence ◽  
Signal To Noise Ratio ◽  
Brown Dwarfs ◽  
Compact Objects ◽  
Main Sequence Stars ◽  
Signal To Noise ◽  
Noise Ratio ◽  
Sgr A

Aims. We present the first fully relativistic study of gravitational radiation from bodies in circular equatorial orbits around the massive black hole at the Galactic center, Sgr A* and we assess the detectability of various kinds of objects by the gravitational wave detector LISA. Methods. Our computations are based on the theory of perturbations of the Kerr spacetime and take into account the Roche limit induced by tidal forces in the Kerr metric. The signal-to-noise ratio in the LISA detector, as well as the time spent in LISA band, are evaluated. We have implemented all the computational tools in an open-source SageMath package, within the Black Hole Perturbation Toolkit framework. Results. We find that white dwarfs, neutrons stars, stellar black holes, primordial black holes of mass larger than 10−4 M⊙, main-sequence stars of mass lower than ∼2.5 M⊙, and brown dwarfs orbiting Sgr A* are all detectable in one year of LISA data with a signal-to-noise ratio above 10 for at least 105 years in the slow inspiral towards either the innermost stable circular orbit (compact objects) or the Roche limit (main-sequence stars and brown dwarfs). The longest times in-band, of the order of 106 years, are achieved for primordial black holes of mass ∼10−3 M⊙ down to 10−5 M⊙, depending on the spin of Sgr A*, as well as for brown dwarfs, just followed by white dwarfs and low mass main-sequence stars. The long time in-band of these objects makes Sgr A* a valuable target for LISA. We also consider bodies on close circular orbits around the massive black hole in the nucleus of the nearby galaxy M 32 and find that, among them, compact objects and brown dwarfs stay for 103–104 years in LISA band with a one-year signal-to-noise ratio above ten.

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.

Planets and brown dwarfs around A–F main-sequence stars: performances of radial-velocity surveys with HARPS and first detections

2010 ◽  
Vol 41 ◽  
pp. 99-102 ◽  
Author(s):  
M. Desort ◽  
A.-M. Lagrange ◽  
F. Galland ◽  
S. Udry ◽  
M. Mayor
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Brown Dwarfs ◽  
Main Sequence Stars

scholarly journals Light Element Depletion in Contracting Brown Dwarfs and Pre–Main‐Sequence Stars

1998 ◽  
Vol 497 (1) ◽  
pp. 253-266 ◽  
Author(s):  
Greg Ushomirsky ◽  
Christopher D. Matzner ◽  
Edward F. Brown ◽  
Lars Bildsten ◽  
Vadim G. Hilliard ◽  
...  
Keyword(s):  
Main Sequence ◽  
Light Element ◽  
Brown Dwarfs ◽  
Main Sequence Stars

Chromospheric activity as a function of age in main-sequence stars

1966 ◽  
Vol 24 ◽  
pp. 40-43
Author(s):  
O. C. Wilson ◽  
A. Skumanich
Keyword(s):  
Main Sequence ◽  
The Sun ◽  
Main Sequence Stars ◽  
Tentative Conclusion ◽  
Chromospheric Activity ◽  
General Field ◽  
Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

Sign in / Sign up

Export Citation Format

Share Document