scholarly journals Radial Pulsation in Variable Stars with Mass Loss

1993 ◽  
Vol 137 ◽  
pp. 575-577
Author(s):  
Frank P. Pijpers
Keyword(s):  
Mass Loss ◽  
Outer Boundary ◽  
Variable Stars ◽  
Radial Pulsation ◽  
Long Period ◽  
Classical Formulation ◽  
Long Period Variables ◽  
The Stability ◽  
Resonance Cavity

AbstractIt is possible to show that cool giants with very large photospheric scale heights do not perfectly reflect pulsational waves at the photosphere. This means that for these stars the classical formulation of pulsation in which the outer boundary for the resonance cavity is assumed to be perfectly reflecting is not valid. This can have significant consequences for the eigenfrequencies of the pulsation of Long Period Variables such as Mira type variables as well as for the stability of their pulsation.

scholarly journals A Search for Variable Stars at the Galactic Center

1989 ◽  
Vol 136 ◽  
pp. 487-492 ◽  
Author(s):  
Joseph W. Haller ◽  
Marcia J. Rieke
Keyword(s):  
Stellar Population ◽  
Galactic Center ◽  
Ccd Camera ◽  
Variable Stars ◽  
Detector Array ◽  
High Luminosity ◽  
Bolometric Luminosity ◽  
Long Period ◽  
Long Period Variables ◽  
K 13

A study of the Galactic Center stellar population is continuing with a sensitive 2μm CCD camera. Using a 64 × 64 detector array, background limited images are recorded with modest amounts of observing time (tobs ≈ 20 sec to reach K=13). Magnitudes have been extracted using DAOPHOT from repeated imaging of the central 5′ × 5′ to search among approximately 1500 stars for long period variables (LPV's, P > 200d), particularily Miras. Miras have a well defined period-luminosity relationship as well as one in period-mass. This program investigates the nature of highly luminous stars at the Galactic Center. Presently 12 variables have been found and have several characteristics consistent with Miras. They have a maximum bolometric luminosity of −4.4 mag, which supports the case that high luminosity stars in the central 6 pc are young supergiants.

scholarly journals Long Period Variables in the Magellanic Clouds and the Galaxy

1993 ◽  
Vol 139 ◽  
pp. 192-200 ◽  
Author(s):  
S.M.G. Hughes
Keyword(s):  
Mass Loss ◽  
Galactic Disk ◽  
Magellanic Clouds ◽  
Pulsation Mode ◽  
Long Period ◽  
Long Period Variables ◽  
The Galaxy ◽  
Loss Rates

AbstractNew results (∼last two years) on mainly observational properties of Long Period Variables (LPVs) in the Magellanic Clouds and the Galaxy are reviewed. These properties include the effects of metallicity variations on their mass loss rates, the use of AGB LPVs to map the stellar distributions of the Galactic disk and bulge, and using detailed observations of nearby Miras to investigate their structure and to obtain new parallax distances, with implications for the pulsation mode of Miras.

scholarly journals Cepheids and LPVs in and around Magellanic Cloud Clusters

1995 ◽  
Vol 155 ◽  
pp. 383-384
Author(s):  
K.M. Sebo ◽  
P.R. Wood
Keyword(s):  
Variable Stars ◽  
Magellanic Cloud ◽  
Ccd Photometry ◽  
Long Period ◽  
Cloud Clusters ◽  
Long Period Variables ◽  
Young Clusters

AbstractV and I band CCD photometry of the young clusters NGC 330 (SMC), NGC 1850, NGC 2058 and NGC 2065 (LMC) has been used to find variable stars in and around the clusters. The variables detected are mostly Cepheids and long-period variables (LPVs). Here we outline some results of these studies.

Some Dependences for Long-Period Variables and a Possible Scheme of their Evolution

1989 ◽  
Vol 131 ◽  
pp. 451-451
Author(s):  
I. L. Andronov ◽  
L. S. Kudashkina ◽  
G. M. Rudnitskij
Keyword(s):  
Light Curve ◽  
Color Index ◽  
Variable Stars ◽  
Maser Emission ◽  
Long Period ◽  
General Catalogue ◽  
Long Period Variables ◽  
Molecular Lines ◽  
Visual Light

Some dependences between the parameters for approximately 150 stars, of which 81 are sources of maser emission in molecular lines, are constructed. The following parameters are considered: period P, asymmetry (M-m) of the visual light curve, visual amplitude A, color index (I-K). We use the data of the General Catalogue of Variable Stars. For the stars Z Cyg, R Tau, R Peg, RT Vir, RX Boo, PZ Cas, U Her, and R Cas, some parameters were determined by the authors.

scholarly journals Wind properties of variable B supergiants

2018 ◽  
Vol 614 ◽  
pp. A91 ◽  
Author(s):  
M. Haucke ◽  
L. S. Cidale ◽  
R. O. J. Venero ◽  
M. Curé ◽  
M. Kraus ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Empirical Relationship ◽  
Variable Stars ◽  
Stellar Winds ◽  
Radial Pulsation ◽  
Line Profiles ◽  
Stellar Radius ◽  
Wind Variability ◽  
Loss Rates

Context. Variable B supergiants (BSGs) constitute a heterogeneous group of stars with complex photometric and spectroscopic behaviours. They exhibit mass-loss variations and experience different types of oscillation modes, and there is growing evidence that variable stellar winds and photospheric pulsations are closely related. Aims. To discuss the wind properties and variability of evolved B-type stars, we derive new stellar and wind parameters for a sample of 19 Galactic BSGs by fitting theoretical line profiles of H, He, and Si to the observed ones and compare them with previous determinations. Methods. The synthetic line profiles are computed with the non-local thermodynamic equilibrium (NLTE) atmosphere code FASTWIND, with a β-law for hydrodynamics. Results. The mass-loss rate of three stars has been obtained for the first time. The global properties of stellar winds of mid/late B supergiants are well represented by a β-law with β > 2. All stars follow the known empirical wind momentum–luminosity relationships, and the late BSGs show the trend of the mid BSGs. HD 75149 and HD 99953 display significant changes in the shape and intensity of the Hα line (from a pure absorption to a P Cygni profile, and vice versa). These stars have mass-loss variations of almost a factor of 2.8. A comparison among mass-loss rates from the literature reveals discrepancies of a factor of 1 to 7. This large variation is a consequence of the uncertainties in the determination of the stellar radius. Therefore, for a reliable comparison of these values we used the invariant parameter Qr. Based on this parameter, we find an empirical relationship that associates the amplitude of mass-loss variations with photometric/spectroscopic variability on timescales of tens of days. We find that stars located on the cool side of the bi-stability jump show a decrease in the ratio V∞∕Vesc, while their corresponding mass-loss rates are similar to or lower than the values found for stars on the hot side. Particularly, for those variable stars a decrease in V∞∕Vesc is accompanied by a decrease in Ṁ. Conclusions. Our results also suggest that radial pulsation modes with periods longer than 6 days might be responsible for the wind variability in the mid/late-type. These radial modes might be identified with strange modes, which are known to facilitate (enhanced) mass loss. On the other hand, we propose that the wind behaviour of stars on the cool side of the bi-stability jump could fit with predictions of the δ−slow hydrodynamics solution for radiation-driven winds with highly variable ionization.

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