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 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 Disks and Toroids Around Young Stars

1987 ◽  
Vol 115 ◽  
pp. 239-253 ◽  
Author(s):  
L.F. Rodríguez
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Observational Evidence ◽  
Young Stars ◽  
The Other ◽  
Main Sequence Star ◽  
Circumstellar Disk ◽  
The Sun ◽  
Bipolar Outflows ◽  
The One

We review the observational evidence for interstellar and circumstellar size gaseous structures that appear to be collimating the bipolar outflows observed in regions of star formation. In particular, there is growing evidence for circumstellar disk-like objects that may be related to a protoplanetary cloud like the one that once surrounded the Sun. There are similarities between these disks around young stars and that found around the main sequence star β Pictoris. Both flattened structures around L1551 IRS5 and β Pictoris appear to have an inner “hole” with radius of a few tens of AU. On the other hand, there is observational support for focusing and collimation processes acting on the same source from tens of AU (circumstellar dimensions) to tenths of pc (interstellar dimensions).

scholarly journals SOHO: A Prisma Precursor

1993 ◽  
Vol 137 ◽  
pp. 755-757
Author(s):  
P. Lemaire
Keyword(s):  
Main Sequence ◽  
Main Sequence Star ◽  
The Sun ◽  
Atmospheric Structure ◽  
Guide Line ◽  
Stellar Interiors

AbstractProbing the interior of the Sun, a slow rotator G2 V main sequence star, and connecting the atmospheric structure to inside phenomena is one of the objectives of the SOHO mission. An overview of the helioseismology and of the coronal instruments is given. It furnishes a guide line for missions that are dedicated to the probing of stellar interiors in using microvariability and activity as tracers, such as the PRISMA study.

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 Internal Rotation, Mixing and Lithium Abundances

1998 ◽  
Vol 185 ◽  
pp. 25-36
Author(s):  
Brian Chaboyer
Keyword(s):  
Internal Rotation ◽  
Transport Process ◽  
Main Sequence ◽  
Convection Zone ◽  
Nuclear Reactions ◽  
Open Clusters ◽  
Current Status ◽  
The Sun ◽  
Rotation Rates ◽  
Destruction Zone

Lithium is an excellent tracer of mixing in stars as it is destroyed (by nuclear reactions) at a temperature around ~ 2.5 × 106 K. The lithium destruction zone is typically located in the radiative region of a star. If the radiative regions are stable, the observed surface value of lithium should remain constant with time. However, comparison of the meteoritic and photospheric Li abundances in the Sun indicate that the surface abundance of Li in the Sun has been depleted by more than two orders of magnitude. This is not predicted by solar models and is a long standing problem. Observations of Li in open clusters indicate that Li depletion is occurring on the main sequence. Furthermore, there is now compelling observational evidence that a spread of lithium abundances is present in nearly identical stars. This suggests that some transport process is occurring in stellar radiative regions. Helioseismic inversions support this conclusion, for they suggest that standard solar models need to be modified below the base of the convection zone. There are a number of possible theoretical explanations for this transport process. The relation between Li abundances, rotation rates and the presence of a tidally locked companion along with the observed internal rotation in the Sun indicate that the mixing is most likely induced by rotation. The current status of non-standard (particularly rotational) stellar models which attempt to account for the lithium observations are reviewed.

scholarly journals Gaia’s detectability of black hole–main sequence star binaries formed in open clusters

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Minori Shikauchi ◽  
Jun Kumamoto ◽  
Ataru Tanikawa ◽  
Michiko S Fujii
Keyword(s):  
Black Hole ◽  
Main Sequence ◽  
Star Clusters ◽  
Interstellar Extinction ◽  
Open Clusters ◽  
Main Sequence Star ◽  
Chemical Abundance ◽  
Good Test ◽  
Orbital Periods ◽  
Chemical Anomalies

Abstract Black hole–main sequence star (BH–MS) binaries are one of the targets of future data releases of the astrometric satellite Gaia. They are supposed to be formed in two main sites: a galactic field and star clusters. However, previous work has never predicted the number of BH–MS binaries originating in the latter sites. In this paper we estimate the number of BH–MS binaries formed in open clusters and detectable with Gaia based on the results of N-body simulations. By considering interstellar extinction in the Milky Way and observational constraints, we predict that ∼10 BH–MS binaries are observable. We also find that chemical abundance patterns of companion MSs will help us to identify the origin of the binaries as star clusters. Such MSs are not polluted by outflows of the BH progenitors, such as stellar winds and supernova ejecta. Chemical anomalies might be a good test to confirm the origin of binaries with relatively less massive MSs (≲5 M⊙), short orbital periods (∼1.5 yr), and higher eccentricities (e ≳0.1).

scholarly journals Some Aspects of the Evolutionary Status Of W Ursae Majoris Binaries Deduced from Observational Data

1982 ◽  
Vol 69 ◽  
pp. 301-304
Author(s):  
Walter Van Hamme
Keyword(s):  
Observational Data ◽  
Spectral Type ◽  
Main Sequence ◽  
Type A ◽  
Type Systems ◽  
Primary Component ◽  
Main Sequence Star ◽  
Evolutionary Status ◽  
Evolutionary Stage ◽  
Evolutionary State

AbstractWe have developed a test for the evolutionary state of W Ursae Majoris binaries by comparing the observed spectral type of 31 of these systems (14 of type W and 17 of type A) with the expected one when their primary component is an unevolved main sequence star. It appears that both the W- and A-type systems have a primary with a mass and radius too large to be compatible with the observed spectral type,so there is no indication that each type should mark a different evolutionary stage.

scholarly journals Local Variations of the Velocity Ellipsoid

1996 ◽  
Vol 169 ◽  
pp. 525-526
Author(s):  
M. Moreno ◽  
J. Torra ◽  
E. Oblak
Keyword(s):  
Main Sequence ◽  
Photometric Data ◽  
The Sun ◽  
Main Sequence Stars ◽  
Nearby Stars ◽  
Input Catalogue

We have analyzed the distribution of residual velocities of nearby stars (within 200 pc of the Sun) looking for space variations on the velocity ellipsoid. We used a sample of 1071 main sequence stars of spectral types B, A and F selected from the Hipparcos Input Catalogue [7] with uvbyHβ photometric data. Ages have been calculated following [1]. Six subsamples with 8.07 ≤ log(age) ≤ 9.45 have been considered.

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.

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