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 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 Rotation of Pre-Main Sequence Stars from High S/N Spectroscopy

1988 ◽  
Vol 132 ◽  
pp. 95-98
Author(s):  
J. Bouvier
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Spectroscopic Studies ◽  
Main Sequence Stars ◽  
Rotation Rates ◽  
Large Samples ◽  
Stellar Formation ◽  
Low Mass ◽  
Pms Stars ◽  
Large Telescopes

Until 1980, only a handful of low-mass, active pre-main sequence (pms) stars had known rotation velocities (vsini) /1/. Since then, increasingly sensitive detectors coupled to large telescopes led to high–resolution (a few 104) spectroscopic studies of these faint stars (mv = 10–13), with S/N ratio of the order of 100. The measurement of vsini for large samples of pms stars that resulted brought new insights on various pressing questions related to stellar formation and early stellar evolution : how do the rotation rates of pms stars compare with those expected from models of stellar formation ? how does the stellar angular momentum change during pms evolution ? is pms activity linked with rotation as would be expected if activity were triggered by magnetic processes ?

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 Fu Orionis eruptions and early stellar evolution

1990 ◽  
Vol 137 ◽  
pp. 229-251
Author(s):  
Bo Reipurth
Keyword(s):  
Stellar Evolution ◽  
Accretion Rate ◽  
Circumstellar Disks ◽  
Circumstellar Disk ◽  
Disk Accretion ◽  
Low Mass Stars ◽  
Photometric And Spectroscopic Observations ◽  
T Tauri ◽  
Accretion Model ◽  
Low Mass

The FU Orionis phenomenon has attracted increasing attention in recent years, and is now accepted as a crucial element in the early evolution of low mass stars. The general characteristics of FUors are outlined and individual members of the class are discussed. The discovery of a new FUor, BBW 76, is presented, together with a discussion of photometric and spectroscopic observations of the star. The evidence for circumstellar disks around T Tauri stars is briefly outlined, and the FUor phenomenon is discussed in the context of a disk accretion model. A large increase in the accretion rate through a circumstellar disk makes the disk self-luminous with a luminosity two or more orders larger than that of the star. Massive cool winds rise from FUors, and it is conceivable that they are related to the initiation of Herbig-Haro flows. The FUor phenomenon appears to be repetitive, and newborn low-mass stars may be cycling between the FUor state and the T Tauri state.

scholarly journals Stellar models of rotating, pre-main sequence low-mass stars with magnetic fields

2013 ◽  
Vol 9 (S302) ◽  
pp. 112-113 ◽  
Author(s):  
Luiz T. S. Mendes ◽  
Natália R. Landin ◽  
Luiz P. R. Vaz
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Main Sequence ◽  
Stellar Structure ◽  
Low Mass Stars ◽  
Large Scale Magnetic Field ◽  
Low Mass ◽  
Structure Equations ◽  
Stellar Models

AbstractWe report our present efforts for introducing magnetic fields in the ATON stellar evolution code code, which now evolved to truly modifying the stellar structure equations so that they can incorporate the effects of an imposed, large-scale magnetic field. Preliminary results of such an approach, as applied to low-mass stellar models, are presented and discussed.

scholarly journals A BINARY SCENARIO FOR THE FORMATION OF STRONGLY MAGNETIZED WHITE DWARFS

2011 ◽  
Vol 20 (supp02) ◽  
pp. 29-36 ◽  
Author(s):  
JASON NORDHAUS
Keyword(s):  
Magnetic Fields ◽  
High Field ◽  
White Dwarfs ◽  
Massive Star ◽  
Main Sequence ◽  
High Mass ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass ◽  
Initial Discovery

Since their initial discovery, the origin of isolated white dwarfs (WDs) with magnetic fields in excess of ~1 MG has remained a mystery. Recently, the formation of these high-field magnetic WDs has been observationally linked to strong binary interactions incurred during post-main-sequence evolution. Planetary, brown dwarf or stellar companions located within a few AU of main-sequence stars may become engulfed during the primary's expansion off the main sequence. Sufficiently low-mass companions in-spiral inside a common envelope until they are tidally shredded near the natal white dwarf. Formation of an accretion disk from the disrupted companion provides a source of turbulence and shear which act to amplify magnetic fields and transport them to the WD surface. We show that these disk-generated fields explain the observed range of magnetic field strengths for isolated, high-field magnetic WDs. Additionally, we discuss a high-mass binary analogue which generates a strongly-magnetized WD core inside a pre-collapse, massive star. Subsequent core-collapse to a neutron star may produce a magnetar.

scholarly journals Stellar evolution with turbulent diffusion mixing in low mass stars and 12C/13C ratio in giants of the first ascending branch

1984 ◽  
Vol 105 ◽  
pp. 525-527
Author(s):  
O. Bienaymé ◽  
A. Maeder ◽  
E. Schatzman
Keyword(s):  
Molecular Weight ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Turbulent Transport ◽  
Chemical Species ◽  
Life Time ◽  
Low Mass Stars ◽  
Low Mass ◽  
Red Giant ◽  
Mean Molecular Weight

We consider stellar evolution in low mass stars (1–3 Mo) near the main sequence with the hypothesis that mild turbulence is present within the all star. Turbulent transport of the elements is modeled by diffusion equations where the diffusion coefficient is chosen to be D = R✶eν where ν is the kinematical viscosity and R✶e is a Reynolds number. We consider the effects of the growth of the gradient of the mean molecular weight on turbulence. The main consequences of diffusion on stellar evolution are (1) an increase of the life time near the main sequence and (2) a change of the radial distributions of chemical species (12C, 13C, 14N, 160) (figure 1). The inhibition of the turbulence, when the gradient of mean molecular weight reaches a certain critical value, allows the evolution towards the red giant branch. When stars evolve towards the giant branch, chemical species are dredged up to the surface. At this stage models with and without diffusion, predict substantially different surface abundances (in particular the 12C/13C and C/N ratios). Comparison between models and the available data on giants during the first dredge-up show that abundance anomalies can be explained if turbulent mixing is present during the main sequence phase (figure 2).

scholarly journals A closer look at the transition between fully convective and partly radiative low-mass stars

2018 ◽  
Vol 619 ◽  
pp. A177 ◽  
Author(s):  
Isabelle Baraffe ◽  
Gilles Chabrier
Keyword(s):  
Stellar Evolution ◽  
Structural Changes ◽  
Main Sequence ◽  
Energy Transport ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Mixing Processes ◽  
Nuclear Burning ◽  
Low Mass ◽  
M Dwarf

Recently, an analysis of Gaia Data Release 2 revealed a gap in the mid-M dwarf main sequence. The authors suggested the feature is linked to the onset of full convection in M dwarfs. Following the announcement of this discovery, an explanation has been proposed based on standard stellar evolution models. In this paper we re-examine this explanation. We confirm that nuclear burning and mixing processes of 3He provide the best explanation for the observed feature. We also find that a change in the energy transport from convection to radiation does not induce structural changes that could be visible. Regarding the very details of the process, however, we disagree with the details of the published explanation and propose an alternative.

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