SPECIFIC ANGULAR MOMENTUM DISTRIBUTION FOR SOLAR ANALOGS AND TWINS: WHERE IS THE SUN MISSING HIS ANGULAR MOMENTUM?

2012 ◽  
Vol 18 ◽  
pp. 58-62
Author(s):  
J. S. DA COSTA ◽  
J. D. DO NASCIMENTO
Keyword(s):  
Angular Momentum ◽  
Spectral Type ◽  
Momentum Distribution ◽  
Main Sequence ◽  
Mass Range ◽  
Large Mass ◽  
Global Behavior ◽  
The Sun ◽  
Stellar Radius ◽  
Solar Analogs

It is well established that there is a breakdown in the curve of specific angular momentum as a function of mass for stars on the main sequence Ref. 5. Stars earlier than F5 and more massive than the sun, rotate rapidly over a large mass range. For spectral type F5 and later, including the Sun, much smaller rotational velocities are found. We revisit this question from a new sample to shed a light on the basis of a sample solar twins and analogs recently observed by interferometric measurements of stellar radius. Our results clearly show that, as the Sun, the solar twins present similar global behavior from their specific angular momentum. 18 Sco and HIP 100963 have a specific angular momentum one order higher than the solar value, and HIP 55459 and HIP 56948 have a specific angular momentum one order lower than the solar value.

scholarly journals The Rotation of Pre-Main Sequence Stars

1980 ◽  
Vol 5 ◽  
pp. 835-837
Author(s):  
Leonard V. Kuhi ◽  
Stuart Vogel
Keyword(s):  
Angular Momentum ◽  
Spectral Type ◽  
Main Sequence ◽  
Rotational Velocity ◽  
The Sun ◽  
Main Sequence Stars ◽  
Lower Mass ◽  
B Stars ◽  
Large Numbers ◽  
Rapid Deceleration

Kraft (1970) obtained the rotational velocities for large numbers of stars located in the field and in clusters of different ages. He noted that (a) among the field stars those stars with strong Call K emission had larger rotational velocities than those without; (b) stars in the Hyades and Pleiades (which are much younger than the field) had both larger rotational velocities and stronger Call K emission than field stars; (c) there was a pronounced break at spectral type early F in v sini as a function of spectral type and (d) the distribution of angular momentum per unit, mass J(M⊚) was proportional to M0.57 for main sequence stars with mass M > 1.5 Mʘ. This distribution predicted a v sini of ˜75 km/sec for stars of lower mass (e.g. G type) but such high velocities were not seen in the Pleiades nor in the sun. This implied a more rapid deceleration of v sini for lower mass stars and led to estimates of the e-folding time of ˜4×l08 years for stars of 1.2 M⊚ to reduce their v sini from that of the Pleiades to that of the Hyades and ˜4×l09 years to go from the Hyades to the sun’s v sini. We note also that the age of the Pleiades is approximately equal to the pre-main sequence lifetime of a 1.0 M0 star so that the zero-age main sequence cannot have J(M) α M0.57 for ˜1 M0 stars. Skumanich (1972) showed that both the Call k emission and the rotational velocity decayed as the (age)-½ for main-sequence stars.

scholarly journals Stellar 5 min Oscillations

1983 ◽  
Vol 66 ◽  
pp. 469-486
Author(s):  
Jørgen Christensen-Dalsgaard ◽  
Søren Frandsen
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Total Flux ◽  
The Sun ◽  
Major Fraction ◽  
Main Sequence Stars ◽  
Red Supergiants

AbstractEstimates are given for the amplitudes of stochastically excited oscillations in Main Sequence stars and cool giants; these were obtained using the equipartition between convective and pulsational energy which was originally proposed by Goldreich and Keeley. The amplitudes of both velocity and luminosity perturbation generally increase with increasing mass along the Main Sequence as long as convection transports a major fraction of the total flux, and the amplitudes also increase with the age of the model. The 1.5 Mʘ ZAMS model, of spectral type F0, has velocity amplitudes ten times larger than those found in the Sun. For very luminous red supergiants luminosity amplitudes of up to about 0ṃ.1 are predicted, in rough agreement with observations presented by Maeder.

scholarly journals Unbound Close Stellar Encounters in the Solar Neighborhood

2022 ◽  
Vol 163 (2) ◽  
pp. 44
Author(s):  
Bradley M. S. Hansen
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Radial Distance ◽  
Solar Neighborhood ◽  
Limiting Factors ◽  
Line Of Sight ◽  
The Sun ◽  
Finite Set ◽  
Host Stars ◽  
Migration Event

Abstract We present a catalog of unbound stellar pairs, within 100 pc of the Sun, that are undergoing close, hyperbolic, encounters. The data are drawn from the GAIA EDR3 catalog, and the limiting factors are errors in the radial distance and unknown velocities along the line of sight. Such stellar pairs have been suggested to be possible events associated with the migration of technological civilizations between stars. As such, this sample may represent a finite set of targets for a SETI search based on this hypothesis. Our catalog contains a total of 132 close passage events, featuring stars from across the entire main sequence, with 16 pairs featuring at least one main-sequence star of spectral type between K1 and F3. Many of these stars are also in binaries, so that we isolate eight single stars as the most likely candidates to search for an ongoing migration event—HD 87978, HD 92577, HD 50669, HD 44006, HD 80790, LSPM J2126+5338, LSPM J0646+1829 and HD 192486. Among host stars of known planets, the stars GJ 433 and HR 858 are the best candidates.

scholarly journals Lithium Abundances in Solar-Type Stars

2000 ◽  
Vol 198 ◽  
pp. 495-497 ◽  
Author(s):  
L. da Silva ◽  
G. F. Porto de Mello
Keyword(s):  
Angular Momentum ◽  
Momentum Distribution ◽  
The Sun ◽  
Atmospheric Parameters ◽  
Solar Type ◽  
Subgiant Stars ◽  
High Degree ◽  
Li Content

We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. The unevolved stars in this sample present high (> 2.00) Li abundances. We found a few cases of subgiant stars which present high Li content. The Sun seems to be part of a population of nearly unevolved stars which have depleted their Li to a high degree: all other metal-normal, near ZAMS stars in our sample show higher than solar Li content. There seems to be no correlation of the degree of Li depletion with mass, atmospheric parameters or state of evolution: as an example we found a star (HR1532) almost identical to the Sun in its state of evolution and atmospheric parameters, but with over ten times the solar Li abundance. We propose that different histories of angular momentum distribution at star birth, and/or post-birth angular momentum evolution, may account for these differences.

scholarly journals The Present Data Situation for Stars in Open Clusters. II

1980 ◽  
Vol 85 ◽  
pp. 129-133
Author(s):  
J.-C. Mermilliod
Keyword(s):  
Present State ◽  
Spectral Type ◽  
Main Sequence ◽  
Open Clusters ◽  
Photometric Data ◽  
Main Sequence Star ◽  
The Sun ◽  
Previous Version

The present state of astrometric, spectroscopic and photometric data for stars in 63 open clusters nearer to the Sun than 750 pc is summarized. Table I reports the limits of the available data in terms of the apparent V magnitude, in the same way as the previous version (Mermilliod 1977). Information on the apparent V magnitude of the brightest main sequence star (Vbr) and on the number of stars brighter than V=10 (n∗) has been included. In addition, the bluest spectral type on the main sequence has been used as an age estimator (TS).

scholarly journals The Sun in time: age, rotation, and magnetic activity of the Sun and solar-type stars and effects on hosted planets

2008 ◽  
Vol 4 (S258) ◽  
pp. 395-408 ◽  
Author(s):  
Edward F. Guinan ◽  
Scott G. Engle
Keyword(s):  
Main Sequence ◽  
High Energy ◽  
Magnetic Activity ◽  
The Sun ◽  
X Ray ◽  
Multi Wavelength ◽  
Solar Type ◽  
Rotation Age ◽  
Energy Emissions ◽  
Solar Analogs

AbstractMulti-wavelength studies of solar analogs (G0–5 V stars) with ages from ~50 Myr to 9 Gyr have been carried out as part of the “Sun in Time” program for nearly 20 yrs. From these studies it is inferred that the young (ZAMS) Sun was rotating more than 10× faster than today. As a consequence, young solar-type stars and the early Sun have vigorous magnetohydrodynamic (MHD) dynamos and correspondingly strong coronal X-ray and transition region/chromospheric FUV–UV emissions (up to several hundred times stronger than the present Sun). Also, rotational modulated, low amplitude light variations of young solar analogs indicate the presence of large starspot regions covering ~5–30% of their surfaces. To ensure continuity and homogeneity for this program, we use a restricted sample of G0–5 V stars with masses, radii, Teff, and internal structure (i.e. outer convective zones) closely matching those of the Sun. From these analogs we have determined reliable rotation-age-activity relations and X-ray–UV (XUV) spectral irradiances for the Sun (or any solar-type star) over time. These XUV irradiance measures serve as input data for investigating the photo-ionization and photo-chemical effects of the young, active Sun on the paleo-planetary atmospheres and environments of solar system planets. These measures are also important to study the effects of these high energy emissions on the numerous exoplanets hosted by solar-type stars of different ages. Recently we have extended the study to include lower mass, main-sequence (dwarf) dK and dM stars to determine relationships among their rotation spin-down rates and coronal and chromospheric emissions as a function of mass and age. From rotation-age-activity relations we can determine reliable ages for main-sequence G, K, M field stars and, subsequently, their hosted planets. Also inferred are the present and the past XUV irradiance and plasma flux exposures that these planets have endured and the suitability of the hosted planets to develop and sustain life.

scholarly journals Emission of Gravitational Waves from a Magnetohydrodynamic Dynamo in the Center of the Sun

2015 ◽  
Vol 70 (7) ◽  
pp. 545-551
Author(s):  
Friedwardt Winterberg
Keyword(s):  
Magnetic Field ◽  
Gravitational Waves ◽  
Main Sequence ◽  
Fusion Reaction ◽  
Large Mass ◽  
The Sun ◽  
The Moon ◽  
Convection Pattern ◽  
Main Sequence Stars ◽  
The Waves

AbstractBy Birkhoff’s theorem a spherical symmetric convection pattern, as it is assumed to exist for main sequence stars as our sun, cannot lead to the emission of gravitational waves, but all stars that have a magnetic field generated by a magnetohydrodynamic dynamo must by a theorem of Cowling have a non-spherical symmetric convections pattern and for this reason have to emit gravitational waves. The intensity of the thusly emitted gravitational waves depends on the efficiency of this dynamo, expressed by the departure from a spherical convection pattern. The magnitude of the asymmetry is determined by a solution of Elsaesser’s dynamo equations which only recently has become possible with supercomputers. The waves are emitted through large mass motions in the center of the sun by a thermonuclear fusion reaction-driven magnetohydrodynamic dynamo, with thermomagnetic currents in the tachocline shielding the strong magnetic field in the solar core. Using the moon as a large Weber bar, the gravitational waves are focused into the lunar shadow by Poisson diffraction where their effect might become observable during a total solar eclipse.

scholarly journals Shear-turbulence in rotating massive stars

1999 ◽  
Vol 193 ◽  
pp. 260-260
Author(s):  
Eugene Staritsin
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Massive Stars ◽  
Stellar Surface ◽  
Stellar Radius ◽  
Shear Turbulence

Shear-turbulence in a radiative envelopes of rotating main sequence massive stars transports angular momentum from the deeper layers to the stellar surface. This process enlarges the influence of rotation on the stellar radius. As a result, the width of the main sequence increases.

scholarly journals Spectroscopic surveillance of the variable Herbig Ae star AB Aur

1986 ◽  
Vol 118 ◽  
pp. 443-445 ◽  
Author(s):  
U. Finkenzeller ◽  
J.G.V. Schiffer ◽  
H. Mandel
Keyword(s):  
High Resolution ◽  
Spectral Type ◽  
Main Sequence ◽  
High Resolution Spectroscopy ◽  
Rotational Period ◽  
Short Term ◽  
Stellar Radius ◽  
Rotational Modulation ◽  
Outer Atmosphere

AB Aur = HD 31293 = BD + 300741 = MWC 93 = HRC 78n is one of the brightest members of a class of pre-main sequence objects introduced by G. Herbig in 1960. The star is characterized by a spectral type of AOVe, L/L⊙ = 70, mv = 7.2 mag, v sini = 140 km/s, and d = 140 pc. Assuming a stellar radius of a main sequence dwarf R/R⊙ = 3.0, one can estimate the rotational period to be on the order of 28 hours if we see the system edge on. Previous work (Praderie et al. (1985) and Finkenzeller (1983)) has focused on high resolution spectroscopy and shown that AB Aur is subject to short term variations. Finkenzeller's observations have indicated that the emission features can disappear completely within a day. Praderie et al. found evidence of a rotational modulation (45 ± 6 hours) of the MgII λ 2795 and FeII UV lines which is interpreted as due to a non-axisymmetric wind interacting with the outer atmosphere.

EARLY AND MAIN SEQUENCE EVOLUTION OF STARS IN THE RANGE 0.5 TO 100 SOLAR MASSES

1967 ◽  
Vol 45 (11) ◽  
pp. 3429-3460 ◽  
Author(s):  
Dilhan Ezer ◽  
A. G. W. Cameron
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Mass Range ◽  
Energy Stability ◽  
Sequence Evolution ◽  
The Sun ◽  
Solar Mass ◽  
Mass Model ◽  
Evolutionary Study ◽  
Evolutionary Studies

The evolutionary study previously carried out for the sun has been extended to stars of 0.5, 0.7, 2, 5, 10, 20, 50, and 100 solar masses. The evolutionary calculations were started at the threshold of energy stability, carried through the approach to the main sequence, and (with the exception of the 100 solar-mass model) through the depletion of hydrogen on the main sequence. All models were observed to have a completely convective Hayashi phase. There was general agreement, in the appropriate mass range, with the evolutionary studies of Iben, the discrepancies apparently resulting from different opacities used in the calculations. Lines of equal evolutionary age in a Hertzsprung–Russell diagram constructed from these calculations do not agree with the observations of Walker, probably because of the neglect of mass loss and rotation in the early stellar evolutionary histories.

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