Mass-to-radius profiles of Newtonian polytropic spheres: Low-mass main-sequence stars in Palatini gravity versus dark-matter-admixed low-mass stars in general relativity

2019 ◽  
Vol 99 (10) ◽  
Author(s):  
Ilídio Lopes ◽  
Grigoris Panotopoulos
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Low Mass

scholarly journals Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mai Yamashita ◽  
Yoichi Itoh ◽  
Yuhei Takagi
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Emission Lines ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Pms Stars ◽  
Infrared Triplet ◽  
Narrow Emission

Abstract We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca ii infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter were used. The small ratios of the equivalent widths indicate that Ca ii IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca ii IRT lines to the stellar bolometric luminosity, $R^{\prime }_{\rm IRT}$, of the PMS stars with narrow emission lines are as large as the largest $R^{\prime }_{\rm IRT}$ of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.

scholarly journals The rotational evolution of young low mass stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 231-240 ◽  
Author(s):  
Jérôme Bouvier
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Main Sequence ◽  
Young Stars ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Rotational Evolution ◽  
Low Mass

AbstractStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.

scholarly journals Effect of mass gain on stellar evolution

1981 ◽  
Vol 59 ◽  
pp. 361-371
Author(s):  
R. Ebert ◽  
H. Zinnecker
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Accretion Rate ◽  
Mass Gain ◽  
Point Mass ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Low Mass ◽  
Cloud Material

AbstractIn this paper we present a fully hydrodynamical treatment of the stationary isothermal accretion problem onto a moving gravitating point mass. The derivation is purely analytical. We find that the accretion rate is more than a factor of 50 higher than the accretion rate derived from the partially non-hydrodynamical treatment by Hoyle and Lyttleton (1939) or Bondi and Hoyle (1944). This result may have some bearing on the evolutionary tracks of young pre-Main Sequence stars still embedded in their parent protocluster cloud. We discuss the work by Federova (1979) who investigated the pre-Main Sequence evolution of degenerate low mass ‘stars’ with strong accretion of protocluster cloud material. We suggest that the stars which lie below the Main Sequence in young clusters could strongly accrete matter at the pre-Main Sequence stage.

scholarly journals Doppler Detection of Extrasolar Planets

1999 ◽  
Vol 170 ◽  
pp. 121-130
Author(s):  
G. W. Marcy ◽  
R. Paul Butler ◽  
D. A. Fischer
Keyword(s):  
Main Sequence ◽  
Extrasolar Planets ◽  
Mass Function ◽  
Solar Neighborhood ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Pile Up ◽  
Solar Type ◽  
Low Mass ◽  
M Dwarf

AbstractWe have measured the radial velocities of 540 G and K main sequence stars with a precision of 3−10 ms−1 using the Lick and Keck échelle spectrometers. We had detected 6 companions that have m sin i < 7 MJup. We announce here the discovery of a new planet around Gliese 876, found in our Doppler measurements from both Lick and Keck. This is the first planet found around an M dwarf, which indicates that planets occur around low-mass stars, in addition to solar-type stars. We combine our entire stellar sample with that of Mayor et al. to derive general properties of giant planets within a few AU of these stars. Less than 1% of G and K main sequence stars harbor brown dwarf companions with masses between 5 and 70 MJup. Including Gliese 876b, 8 companions exhibit m sin i < 5 MJup which constitute the best planet candidates to date. Apparently, 4% of stars have planetary companions within the range m sin i = 0.5 to 5 MJup. Planets are distinguished from brown dwarfs by the discontinuous jump in the mass function at 5 MJup. About 2/3 of the planets orbit within just 0.3 AU due in part to their favorable detectability, but also possibly due to a real “pile up” of planets near the star. Inward orbital migration after formation may explain this, but the mechanism to stop the migration remains unclear. Five of eight planets have orbital eccentricities greater than that of our Jupiter, eJup = 0.048, and tidal circularization may explain most of the circular orbits. Thus, eccentric orbits are common and may arise from gravitational interactions with other planets, stars, or the protoplanetary disk. The planet-bearing stars are systematically metal-rich, as is the Sun, compared to the solar neighborhood.

scholarly journals Observational Searches for Dark Halos

1987 ◽  
Vol 117 ◽  
pp. 415-424 ◽  
Author(s):  
P.C. van der Kruit
Keyword(s):  
Dark Matter ◽  
Spectral Type ◽  
Main Sequence ◽  
Large Fraction ◽  
Main Sequence Stars ◽  
Upper Limits ◽  
Low Mass ◽  
Rule Out ◽  
K Band

A review of observational searches reveals the following constraints for the constituents of dark halos: (1) Optical searches show that these halos are not for a large fraction of their mass made up of dwarfs of spectral type M5 or earlier. (2) K-band (2.2 μ) searches virtually rule out all H- burning Main Sequence stars. (3) IRAS upper limits are consistent with black dwarfs of any age or Jupiters. (4) The inferred metallicity and M/L variations in the spheroid of NGC 7814 are consistent with the hypothesis that the dark matter consists of low mass objects that formed along with the luminous population II.

scholarly journals A Note about Multiple Systems of Dense Molecular Clouds

1982 ◽  
Vol 69 ◽  
pp. 105-108
Author(s):  
Peter Vanýsek
Keyword(s):  
Main Sequence ◽  
Space Distribution ◽  
Main Sequence Stars ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Multiple Systems ◽  
Ob Stars ◽  
Ir Sources ◽  
Low Mass ◽  
The Individual

AbstractThe space distribution of some small dense clouds with point-like IR sources, resembles the clustering of young OB stars. It can be assumed that such objects contain heavy obscured high-luminosity stars on the ZAMS. From the comparison of infrared and radio data it follows that in typical cases, only one B star is the source of the radiation of the cloud. The total mass of the cloud is of the order of one solar mass. If the individual fragments of the cloud are gravitationally unstable, then in the later stage of the evolution only low-mass stars are formed. One can therefore expect that young OB stars are most frequently accompanied by low-mass pre-Main Sequence stars.

scholarly journals Solar and Stellar Dynamos

2010 ◽  
Vol 6 (S271) ◽  
pp. 247-260
Author(s):  
Nigel O. Weiss
Keyword(s):  
Main Sequence ◽  
Solar Magnetic Field ◽  
Mean Field ◽  
Doppler Imaging ◽  
Main Sequence Stars ◽  
Dynamo Theory ◽  
Cyclic Activity ◽  
Low Mass Stars ◽  
Theoretical Approaches ◽  
Low Mass

AbstractRecords of the solar magnetic field extend back for millennia, and its surface properties have been observed for centuries, while helioseismology has recently revealed the Sun's internal rotation and the presence of a tachocline. Dynamo theory has developed to explain these observations, first with idealized models based on mean-field electrodynamics and, more recently, by direct numerical simulation, notably with the ASH code at Boulder. These results, which suggest that cyclic activity relies on the presence of the tachocline, and that its modulation is chaotic (rather than stochastic), will be critically reviewed. Similar theoretical approaches have been followed in order to explain the magnetic properties of other main-sequence stars, whose fields can be mapped by Zeeman-Doppler imaging. Of particular interest is the behaviour of fully convective, low-mass stars, which lack any tachocline but are nevertheless extremely active.

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