Overstability of nonradial pulsations in rotating early type stars

1994 ◽  
Vol 162 ◽  
pp. 128-129
Author(s):  
Hideyuki Saio ◽  
Umin Lee
Keyword(s):  
Numerical Analysis ◽  
Angular Dependence ◽  
Free Parameter ◽  
Main Sequence ◽  
Evolutionary Model ◽  
Angular Frequency ◽  
Early Type ◽  
Early Type Stars ◽  
Rotating Star ◽  
Nonradial Pulsation

We present the result of nonadiabatic analysis for nonradial pulsations in uniformly rotating main sequence models.The angular dependence of the amplitude of a nonradial pulsation mode with an azimuthal order m in a rotating star is represented by a sum of terms proportional to spherical harmonics Ylm(θ, ø) with l = |m|, |m| + 2,… (even mode) or l = |m| + 1, |m| + 3,… (odd mode; see e.g. Saio and Lee 1991 for detail). (In this paper we consider only even modes.) This property makes the analysis complex compared with the case without rotation, in which a single Ylm expresses the angular dependence of a given mode. In our numerical analysis the summation is truncated, in which only first two terms are taken into account. Lee and Saio (1987) give the differential equations for nonadiabatic nonradial pulsations in a uniformly rotating star. Treating the angular frequency of rotation as a free parameter, we applied the nonadiabatic analysis to a main-sequence evolutionary model, for which the effect of rotation is neglected.

scholarly journals The Connection with B[e] stars

2000 ◽  
Vol 175 ◽  
pp. 26-36 ◽  
Author(s):  
Franz-Josef Zickgraf
Keyword(s):  
Common Property ◽  
Main Sequence ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Circumstellar Envelopes ◽  
Early Type Stars ◽  
Uniform Group

AbstractThe characteristics of the various types of B[e] stars are discussed and compared with those of classical Be stars. Both groups of stars are characterized by the presence of emission lines in their spectra, in particular of hydrogen. However, there are also significant differences between these classes. Classical Be stars lack hot circumstellar dust and strong forbidden low-excitation emission lines, which are typical characteristics produced by B[e]-type stars. While classical Be stars are a rather uniform group of early-type stars, B[e]-type stars form a quite heterogeneous group, very often of poorly known evolutionary status, comprising such diverse types of objects as near main-sequence objects, evolved lowmass proto-planetray nebulae and massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars sometimes find their way into the group of B[e] stars. However, despite these dissimilarities classical Be stars and B[e]-type stars, share a common property, namely the nonsphericity of their circumstellar envelopes.

scholarly journals A Comparison of Luminosity Calibrations for MK Classifications of OB Stars

1979 ◽  
Vol 47 ◽  
pp. 81-86
Author(s):  
Janet Rountree Lesh
Keyword(s):  
Main Sequence ◽  
Early Type ◽  
Class V ◽  
Ob Stars ◽  
Early Type Stars

It has been apparent for some time that there is a need for a single luminosity calibration to be used with modern MK types for early-type stars, at least from 0 through middle B. The widely used calibration of Blaauw (1963) has to be replaced because the refinement of the MK system - as reflected in the large collections of spectral types by Lesh (1968), Hiltner, Garrison, and Schild (1969) and Walborn (1971) - has led to a lower mean luminosity for most main sequence subgroups of early-type stars, as the higher luminosity stars tend to move out of class V. Thus the calibrations of Lesh (1968) and Walborn (1972, 1973) are systematically fainter than Blaauw’s

Interstellar Reddening at High Galactic Latitudes

1973 ◽  
Vol 52 ◽  
pp. 263-267
Author(s):  
A. G. Davis Philip
Keyword(s):  
Main Sequence ◽  
Galactic Plane ◽  
Galactic Latitude ◽  
Early Type ◽  
High Galactic Latitude ◽  
Early Type Stars

Measures in the Strömgren four-color and Hβ systems provide an accurate way to determine color excesses of early-type stars. Fourteen areas at high galactic latitude have now been searched for faint A stars which are then measured photoelectrically to obtain the color excesses. Non-main sequence A stars, which are easily detected by means of the four-color photometry, are not included in the analysis. Within 40° of each pole, the reddening is essentially zero, Eb–y = 0.00 north of the galactic plane and Eb–y = 0.01 south of the plane.

scholarly journals Photospheric and “Chromospheric” CIV Lines in B-Main-Sequence Stars

1986 ◽  
Vol 116 ◽  
pp. 113-116
Author(s):  
Fiorella Castelli ◽  
Carlo Morossi ◽  
Roberto Stalio
Keyword(s):  
High Temperature ◽  
Stellar Wind ◽  
High Velocity ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Uv Spectra ◽  
Spectral Lines ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.

scholarly journals Be Phenomena in Young Early-type Stars: Various Forms of Interaction between the Star and the Circumstellar Gaseous Envelope

2000 ◽  
Vol 175 ◽  
pp. 344-347
Author(s):  
M. Pogodin
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Main Sequence ◽  
Stellar Surface ◽  
High Resolution Spectroscopy ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Early Type Stars ◽  
Gaseous Envelope

AbstractNew results of high-resolution spectroscopy of four pre-main sequence Ae/Be stars are presented. An analysis of parameters of lines originating in different regions of the circumstellar (CS) envelope (Hα, Hβ, He I 5876, DNal) allows to reconstruct a picture of the interaction between the star and the CS environment which can be displayed in different forms. At least two separate processes seem to impact the structural and kinematical properties of the envelope: the stellar wind from the stellar surface and the matter infall onto the star from the CS media. A possible relation between these two phenomena is discussed in the framework of different models. Some similarity between observational phenomena in Herbig Ae/Be and classical Be stars is noted in spite of their difference in evolutionary status.

scholarly journals 3D mapping of young stars in the solar neighbourhood with Gaia DR2

2018 ◽  
Vol 620 ◽  
pp. A172 ◽  
Author(s):  
E. Zari ◽  
H. Hashemi ◽  
A. G. A. Brown ◽  
K. Jardine ◽  
P. T. de Zeeuw
Keyword(s):  
Main Sequence ◽  
Three Dimensional ◽  
Young Stars ◽  
Solar Neighbourhood ◽  
Mass Star ◽  
Early Type ◽  
Star Forming ◽  
Star Forming Regions ◽  
Density Maps ◽  
Early Type Stars

We study the three dimensional arrangement of young stars in the solar neighbourhood using the second release of the Gaia mission (Gaia DR2) and we provide a new, original view of the spatial configuration of the star-forming regions within 500 pc of the Sun. By smoothing the star distribution through a Gaussian filter, we construct three dimensional (3D) density maps for early-type stars (upper-main sequence, UMS) and pre-main sequence (PMS) sources. The PMS and the UMS samples are selected through a combination of photometric and astrometric criteria. A side product of the analysis is a 3D, G-band extinction map, which we use to correct our colour-magnitude diagram for extinction and reddening. Both density maps show three prominent structures, Scorpius-Centaurus, Orion, and Vela. The PMS map shows a plethora of lower-mass star-forming regions, such as Taurus, Perseus, Cepheus, Cassiopeia, and Lacerta, which are less visible in the UMS map due to the lack of large numbers of bright, early-type stars. We report the finding of a candidate new open cluster towards l, b ∼ 218.5° , − 2°, which could be related to the Orion star-forming complex. We estimate ages for the PMS sample and we study the distribution of PMS stars as a function of their age. We find that younger stars cluster in dense, compact clumps, and are surrounded by older sources, whose distribution is instead more diffuse. The youngest groups that we find are mainly located in Scorpius-Centaurus, Orion, Vela, and Taurus. Cepheus, Cassiopeia, and Lacerta are instead more evolved and less numerous. Finally, we find that the 3D density maps show no evidence for the existence of the ring-like structure which is usually referred to as the Gould Belt.

scholarly journals Observations of stellar winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 1-18
Author(s):  
Peter S. Conti
Keyword(s):  
Resonance Line ◽  
Optical Spectrum ◽  
Main Sequence ◽  
Emission Lines ◽  
Stellar Winds ◽  
Be Stars ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars ◽  
Line P

I have been asked to review the “observations” of winds in “early-type” stars. This normally means stars of spectral type OB and those of the Wolf-Rayet (WR) class. In this paper I will concentrate on the massive population I stars of these types, and primarily the O and WR classes on which most of the recent work has been done. The early B type supergiants share many of the wind properties of the O stars but the later supergiant types, Be stars, and main sequence stars may not. Stellar winds are a ubiquitous phenomenon among these early type stars (Snow and Morton 1976). We see evidence of their winds in the resonance line P Cygni profiles in the UV region, in the emission lines of Hα and λ4686 He II in the optical spectrum, and in the free-free emission from the ionized plasma as observed in the IR and radio regions of the spectrum.

scholarly journals A Study of Main Sequence Early Type Stars

1979 ◽  
Vol 47 ◽  
pp. 483-490
Author(s):  
Ulf Sinnerstad
Keyword(s):  
Main Sequence ◽  
Photometric Study ◽  
Line Profiles ◽  
Early Type ◽  
Fundamental Parameters ◽  
Preliminary Results ◽  
Early Type Stars ◽  
Hydrogen Lines ◽  
Line Strengths

AbstractA spectroscopic and photometric study of 75 normal main sequence B2-B6 stars has been carried out. From the spectra (12 Å/mm, 3700-4800 Å) are determined: equivalent widths of all measurable lines, line profiles of hydrogen lines and v sin i. The photometric work includes besides uvby and β photometry, also photoelectrically determined line strengths of Hα and He I 4471 Å. Some preliminary results concerning the relation between the MK types and the atmospheric fundamental parameters (Teff, log g) of the stars are briefly discussed.

scholarly journals Effects of rotation on the main sequence evolution of a 5M⊙ star

1994 ◽  
Vol 162 ◽  
pp. 147-148
Author(s):  
J. Fliegner ◽  
N. Langer
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Chemical Elements ◽  
Sequence Evolution ◽  
Early Type ◽  
Mixing Processes ◽  
Core Mass ◽  
Convective Core ◽  
Early Type Stars ◽  
Effects Of Rotation

The way rotation influences the main sequence evolution of early type stars depends strongly on their internal angular momentum distribution. Their convective core mass is not always decreased as a consequence of a reduced “effective mass” due to rotation, since rotation laws close to uniform specific angular momentum may increase Δrad and thereby the convective core mass (Clement). In addition, rotationally induced mixing processes may redistribute angular momentum and chemical elements inside the stars (e.g. Endal & Sofia 1978).

scholarly journals Evolution of rotation in rapidly rotating early-type stars during the main sequence with 2D models

2019 ◽  
Vol 625 ◽  
pp. A89 ◽  
Author(s):  
D. Gagnier ◽  
M. Rieutord ◽  
C. Charbonnel ◽  
B. Putigny ◽  
F. Espinosa Lara
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Main Sequence ◽  
Massive Stars ◽  
Early Type ◽  
Wind Regime ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Rotational Evolution ◽  
Early Type Stars

The understanding of the rotational evolution of early-type stars is deeply related to that of anisotropic mass and angular momentum loss. In this paper, we aim to clarify the rotational evolution of rapidly rotating early-type stars along the main sequence (MS). We have used the 2D ESTER code to compute and evolve isolated rapidly rotating early-type stellar models along the MS, with and without anisotropic mass loss. We show that stars with Z = 0.02 and masses between 5 and 7 M⊙ reach criticality during the main sequence provided their initial angular velocity is larger than 50% of the Keplerian one. More massive stars are subject to radiation-driven winds and to an associated loss of mass and angular momentum. We find that this angular momentum extraction from the outer layers can prevent massive stars from reaching critical rotation and greatly reduce the degree of criticality at the end of the MS. Our model includes the so-called bi-stability jump of the Ṁ − Teff relation of 1D-models. This discontinuity now shows up in the latitude variations of the mass-flux surface density, endowing rotating massive stars with either a single-wind regime (no discontinuity) or a two-wind regime (a discontinuity). In the two-wind regime, mass loss and angular momentum loss are strongly increased at low latitudes inducing a faster slow-down of the rotation. However, predicting the rotational fate of a massive star is difficult, mainly because of the non-linearity of the phenomena involved and their strong dependence on uncertain prescriptions. Moreover, the very existence of the bi-stability jump in mass-loss rate remains to be substantiated by observations.

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