Distances of Planetary Nebulae

One of the most fundamental physical parameter in astronomy is the distance to the objects we detect in the universe. For many classes of astronomical objects, accurate and proven methods have been developed to determine their distances. Such classes of objects include stars within ∼100 pc from the sun, binary stellar systems, variable stars, stellar clusters, main sequence stars, and other galaxies. It has been, however, more difficult to develop satisfactory methods to determine accurate distances to the more than 1000 planetary nebulae that have been discovered in our galaxy.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900053146 ◽

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.

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Stellar 5 min Oscillations

International Astronomical Union Colloquium ◽

10.1017/s0252921100095828 ◽

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.

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Search for stellar companions of exoplanet host stars by exploring the second ESA-Gaia data release

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2673 ◽

2019 ◽

Vol 490 (4) ◽

pp. 5088-5102 ◽

Cited By ~ 4

Author(s):

M Mugrauer

Keyword(s):

Main Sequence ◽

Stellar Systems ◽

Sequence Evolution ◽

The Sun ◽

M Dwarfs ◽

Primary Star ◽

True Nature ◽

Quadruple System ◽

Data Release ◽

Host Stars

ABSTRACT A new survey is presented, which explores the second data release of the ESA-Gaia mission, in order to search for stellar companions of exoplanet host stars, located at distances closer than about 500 pc around the Sun. In total, 176 binaries, 27 hierarchical triples, and one hierarchical quadruple system are detected among more than 1300 exoplanet host stars, whose multiplicity is investigated, yielding a multiplicity rate of the exoplanet host stars of at least about 15 per cent. The detected companions and the exoplanet host stars are equidistant and share a common proper motion, as it is expected for gravitationally bound stellar systems, proven with their accurate Gaia astrometry. The companions exhibit masses in the range between about 0.078 and 1.4 M⊙ with a peak in their mass distribution between 0.15 and $0.3\, \mathrm{M}_{\odot }$. The companions are separated from the exoplanet host stars by about 20 up to 9100 au, but are found most frequently within a projected separation of 1000 au. While most of the detected companions are early M dwarfs, eight white dwarf companions of exoplanet host stars are also identified in this survey, whose true nature is revealed with their photometric properties. Hence, these degenerated companions and the exoplanet host stars form evolved stellar systems with exoplanets, which have survived (physically but also dynamically) the post-main-sequence evolution of their former primary star.

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A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes

Symposium - International Astronomical Union ◽

10.1017/s0074180900000620 ◽

1970 ◽

Vol 38 ◽

pp. 232-235

Author(s):

W. Becker ◽

R. Fenkart

Keyword(s):

Main Sequence ◽

Milky Way ◽

Absolute Magnitude ◽

Galactic Centre ◽

Density Gradients ◽

The Sun ◽

Main Sequence Stars

The Basel Observatory program of the determination of disc- and halo-density gradients for different intervals of absolute magnitude comprises in addition to Milky Way fields several directions, all pointing to Selected Areas near a plane perpendicular to the galactic equator and passing through the sun and the galactic centre. It was started with SA 51 (Becker, 1965) and continued with Sa 57, 54 and 141 (Fenkart, 1967, 1968, 1969).

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Differential Rotation and Magnetic Activity of the Lower Main Sequence Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100075539 ◽

1980 ◽

Vol 51 ◽

pp. 296-297

Author(s):

G. Belvedere ◽

L. Paterno ◽

M. Stix

Keyword(s):

Spherical Shell ◽

Differential Rotation ◽

Main Sequence ◽

Magnetic Activity ◽

The Sun ◽

Coupling Constant ◽

Main Sequence Stars ◽

Dynamo Theory ◽

Magnetic Cycles ◽

Surface Convection

AbstractWe extend to the lower main sequence stars the analysis of convection interacting with rotation in a compressible spherical shell, already applied to the solar case (Belvedere and Paterno, 1977; Belvedere et al. 1979a). We assume that the coupling constant ε between convection and rotation, does not depend on the spectral type. Therefore we take ε determined from the observed differential rotation of the Sun, and compute differential rotation and magnetic cycles for stars ranging from F5 to MO, namely for those stars which are supposed to possess surface convection zones (Belvedere et al. 1979b, c, d). The results show that the strength of differential rotation decreases from a maximum at F5 down to a minimum at G5 and then increases towards later spectral types. The computations of the magnetic cycles based on the αω-dynamo theory show that dynamo instability decreases from F5 to G5, and then increases towards the later spectral types reaching a maximum at MO. The period of the magnetic cycles increases from a few years at F5 to about 100 years at MO. Also the extension of the surface magnetic activity increases substantially towards the later spectral types. The results are discussed in the framework of Wilson’s (1978) observations.

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The Rotation of Pre-Main Sequence Stars

Highlights of Astronomy ◽

10.1017/s1539299600004822 ◽

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.

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A Survey of Young Stars in Taurus for Multiplicity

International Astronomical Union Colloquium ◽

10.1017/s0252921100006072 ◽

1992 ◽

Vol 135 ◽

pp. 21-29 ◽

Cited By ~ 5

Author(s):

Ch. Leinert ◽

N. Weitzel ◽

M. Haas ◽

R. Lenzen ◽

H. Zinnecker ◽

...

Keyword(s):

Main Sequence ◽

Young Stars ◽

Stellar Systems ◽

Main Sequence Stars ◽

Multiple Systems ◽

Period Distribution

AbstractWe surveyed all stars in Taurus (3h 45m < α < 4h 15m, 15° < δ < 35°) for multiplicity which are contained in the Herbig-Bell catalogue of young stars and have a 2 micron brightness of K ≤ 9.5 mag. This sample consists of 106 stellar systems (single or multiple), of which 43 are double or multiple according to the criteria of our survey, i.e. with separations of ≈0″.2 ≤ d ≤ 10″. Of these, 23 binaries are new detections found in this survey. The resulting degree of multiplicity, 43/106 = 41±6%, is higher than found for main-sequence stars. Provided that the period distribution is the same for young stars as on the main sequence, our result implies that the vast majority of stars are born in binary or multiple systems.

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Narrowband Photometry of Photometrically Peculiar Objects

International Astronomical Union Colloquium ◽

10.1017/s025292110002399x ◽

1989 ◽

Vol 120 ◽

pp. 306-306

Author(s):

Eugenio E. Mendoza V.

Keyword(s):

Short Wavelength ◽

Main Sequence ◽

Spectral Feature ◽

Planetary Nebulae ◽

The Sun ◽

Spectral Emission ◽

Hydrogen Line ◽

Stellar Objects ◽

Solar Type ◽

The Continuum

This work is based upon α(16)A(9)-photometry fot 2 Planets, 11 Wolf-Rayet stars and 7 Planetary Nebulae. The results show anomalous α(16) and A(9)-indices for these objects. Thus, they are photometrically peculiar in this system. The main results are:1) Callisto, Jupiter IV, shows ot(16) and A(9)-indices which can be considered as excellent representatives of solar type stars (G2 V).2) Uranus and Neptune have anomalous A(9)-index, because of a spectral feature in absorption around λ 7805 Å, most likely due to a carbon compound. Thus, they are off the main sequence in the a(16)A(9)-array.3) The Hα-line is possibly stronger in Uranus (marginal) and Neptune than in the Sun.4) Wolf-Rayet stars have anomalous α(16)-inder, because of an extremely wide He II-line (λ 6560 Å), lack of hydrogen and the presence of spectral emission features that fall in the continuum used to determine this index.5) Most WC stars have anomalous A(9)-index, because the presence of spectral emission features in the short wavelength continuum that defines this index.6) Some W-R stars show variations in the strength of He II-line (λ 6560 Å).7) Most WC stars are separated from WN stars in the α(16)A(9)-array.8) Planetary Nebulae have anomalous α(16)-index, because the continuum around the hydrogen line is probably contaminated by [N II]-lines at λ 6548 Å and λ 6583 Å.9) Planetary Nebulae have anomalous A(9)-index, because the short wavelength continuum is heavily contaminated by the [Ar III]-line at λ 7751 Å.10) Planetary Nebulae lie far apart from all kind of stellar objects in the α(16)A(9)-diagram.

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The Existence of Moving Groups and the Disk Heating Problem

Symposium - International Astronomical Union ◽

10.1017/s0074180900230210 ◽

1996 ◽

Vol 169 ◽

pp. 513-514

Author(s):

B. Chen ◽

F. Figueras ◽

J. Torra ◽

R. Asiain ◽

C. Jordi

Keyword(s):

Main Sequence ◽

Velocity Dispersion ◽

A Priori ◽

The Sun ◽

Main Sequence Stars ◽

Large Sample ◽

Objective Evidence ◽

Moving Groups ◽

Input Catalogue ◽

Local Disk

A powerful moving group-finding algorithm has been developed and applied to a large sample of B, A and F main sequence stars from the Hipparcos Input Catalogue. Four moving groups near the Sun (Pleiades, Sirius, IC2391 and Hyades) have been identified without assuming any a priori knowledge of the properties of moving groups. This is the most convincing objective evidence for their existence. After the members of the moving groups are removed from the sample, we investigate the disk heating problem. The results show that the velocity dispersion of the local disk stars increases with age, roughly as ≃ ∞ τ1/5.

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