scholarly journals Photospheric Activity among Early F-Type Stars

1993 ◽  
Vol 137 ◽  
pp. 651-653 ◽  
Author(s):  
L. Mantegazza ◽  
E. Poretti ◽  
E. Antonello ◽  
F. Zerbi
Keyword(s):  
Instability Strip ◽  
Scuti Stars ◽  
Secondary Results ◽  
Hr Diagram

In the last decade stars showing variability of unclear origin have been detected among early F-type stars mainly as secondary results in the context of observational programmes devoted to the study of δ-Scuti and CP stars.For this reason only a small number of these objects has been thoroughly studied: their positions in HR diagram is shown in fig.l.Figure 1: HR diagram of the observed stars.The stars in NGC 2516 have been singled out in a survey work by Antonello and Mantegazza (1986), HD 164615 has been studied by Abt et al.(1983), the variability in 9 Aur has been discovered by Krischinas et al.(1990,1991) and HD 23375 in Pleiades has been pointed out by Breger (1972). The solid line in Fig. 1 is the ZAMS and the dashed lines are the borders of the i-Scuti stars instability strip.

scholarly journals Non-Adiabatic Seismic Study of The Thin Convective Envelope of δ Scuti Stars

2004 ◽  
Vol 193 ◽  
pp. 470-473
Author(s):  
M.-A. Dupret ◽  
A. Grigahcène ◽  
R. Garrido ◽  
J. Montalban ◽  
M. Gabriel ◽  
...  
Keyword(s):  
Instability Strip ◽  
Full Spectrum ◽  
Convective Envelope ◽  
Theoretical Predictions ◽  
Mode Stability ◽  
Different Color ◽  
Mixing Length Theory ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Phase Differences

AbstractFor δ Sct stars, the theoretical predictions of a non-adiabatic pulsation code are very dependent on the characteristics of the thin convective envelope of the models (Balona & Evers 1999). The treatment of the non-adiabatic interaction between convection and pulsation also has a significant impact on the results, particularly near the red edge of the instability strip. The non-adiabatic theoretical predictions can be tested upon observations by comparing them to the amplitude ratios and phase differences as observed in different color passbands (Dupret et al. 2003). In the first part of this paper, we compare the results obtained by adopting different treatments of convection in the interior and atmosphere models: mixing-length theory (MLT) and full spectrum of turbulence (FST) (Canuto et al. 1996, CGM). In the second part, we examine the problem of the interaction between convection and pulsation and compare the mode stability obtained with and without including time-dependent convection in our non-adiabatic code.

scholarly journals Uncertainties in the Position of the β Cephei Instability Strip in the HR Diagram

1995 ◽  
Vol 155 ◽  
pp. 291-292
Author(s):  
A.A. Pamyatnykh ◽  
W.A. Dziembowski ◽  
P. Mikołaj
Keyword(s):  
Heavy Element ◽  
Element Abundance ◽  
Instability Strip ◽  
Metal Mixture ◽  
Hr Diagram

AbstractWe discuss the sensitivity of the theoretical B star instability domains to the heavy element abundance Z, the adopted metal mixture, the assumed overshooting from stellar convective cores and the choice of the opacity data.

scholarly journals Astrophysical Applications of Delta Scuti Stars

1995 ◽  
Vol 155 ◽  
pp. 70-80
Author(s):  
Michel Breger
Keyword(s):  
Main Sequence ◽  
Statistical Significance ◽  
Instability Strip ◽  
Short Period ◽  
Scuti Star ◽  
Systematic Behaviour ◽  
Delta Scuti ◽  
F Stars ◽  
Available Information ◽  
Scuti Stars

AbstractThe δ Scuti stars pulsate with a large number of low-order radial and nonradial p-modes. There also exists some evidence for the presence of g-modes.The pulsational variability outside the classical δ Scuti star instability strip (A1V - F0V on the main sequence) is examined. New measurements do not confirm the short-period variability of the hot B9p star ET And. However, a number of cool, early-F stars shows variability around one day: the γ Dor variables. An explanation involving nonradial g modes appears the most promising.An examination of available information on the multi-periodicity of δ Scuti stars shows no systematic behaviour in which pulsation modes axe excited to an observable level with luminosity and temperature. The asteroseismological potential of δ Scuti vaxiables is briefly examined.So far, the period changes of five luminous Pop. I δ Scuti variables have been studied. While stellar evolution predicts period increases, decreases have been observed and reported for all five stars. The statistical significance of this result and alternative explanations axe briefly examined.

scholarly journals δ Scuti Variables in the HR Diagram

2002 ◽  
Vol 185 ◽  
pp. 322-323
Author(s):  
E. Rodríguez ◽  
M. Breger
Keyword(s):  
Temperature Region ◽  
Abundance Anomalies ◽  
Scuti Stars ◽  
Hr Diagram

The location of the δ Scuti variables in the HR diagram is discussed on the basis of HIPPARCOS parallaxes and uvbyβ photometry together with the R00 catalogue (Rodríguez et al., 2000). In particular, the properties of the α Scuti-type pulsators with nonsolar surface abundances (SX Phe, λ Boo, ρ Pup, δ Del and classical Am stars subgroups) are examined.The latter four classes of stars are spectroscopically defined subclasses with surface abundance anomalies. Although the stars ρ Pup and δ Del are also pulsators, the groups named after these stars should not be regarded as pulsation subclasses of δ Scuti stars. The abundance anomalies in these stars affect the pulsation properties, e.g., the classical Am stars are constant in light or show only small pulsation amplitudes (e.g., HD 1097). These four groups are only a small selection from the bewildering zoo of stars with unusual surface abundances in this temperature region and represent the groups with δ Scuti pulsation.

scholarly journals Frequency Oscillations in the Delta Scuti Star V534 Tauri: Preliminary Results of the STEPHI IX Campaign

2000 ◽  
Vol 176 ◽  
pp. 477-478
Author(s):  
L. Fox Machado ◽  
Z. P. Li ◽  
E. Michel ◽  
M. Alvarez ◽  
M. M. Hernández ◽  
...  
Keyword(s):  
Main Sequence ◽  
Class Iii ◽  
Significant Progress ◽  
Instability Strip ◽  
Preliminary Results ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Scuti Stars ◽  
Made In

The δ Scuti stars are pulsating variables located in the lower part of the Cepheid instability strip with spectral types from A2 to F0 on the main sequence, and from A3 to F5 at luminosity class III. These variables show short periods (< 0.3day) and luminosity amplitudes ranging from a few thousandths of a magnitude to several tenths. Over the last few years, significant progress has been made in the detection of pulsating modes in the framework of the multisite campaigns, e.g. STACC (Frandsen et al. 1996), DSN (Breger et al. 1998), STEPHI (Michel et al. 2000). For the 1998 STEPHI IX photometry campaign, the δ Scuti star V534 Tau of the Pleiades cluster (see Table 1) was monitored during a three week, three continent run. Preliminary results are reported here.

scholarly journals Pulsation of PMS 1.8 M⊙ Stars: A Theoretical Investigation

1998 ◽  
Vol 185 ◽  
pp. 397-398 ◽  
Author(s):  
Doru Marian Suran
Keyword(s):  
Instability Strip ◽  
Before And After ◽  
Deep Layers ◽  
Nuclear Burning ◽  
Similar Range ◽  
M Stars ◽  
Herbig Ae Stars ◽  
Pms Stars ◽  
Scuti Stars ◽  
Δ Scuti Stars

Herbig Ae stars are pre-main sequence of masses ~2M⊙. As they trace their course toward the ZAMS, they cross the classical instability strip. At this stage, their evolution has considerably slowed down. Their structure differs from that of stars evolving after the ZAMS (δ Scuti stars) in the very deep layers where nuclear burning has only recently started. But the outer layers for stars before and after the ZAMS are expected to be similar. As these layers drive the pulsation of δ Scuti stars, it is reasonable to expect that PMS stars in the instability strip also are destabilized by the κ mechanism with a similar range of unstable modes. Indeed, recently a Herbig Ae star has been reported as a variable (Kurtz and Marang 1995).

scholarly journals Probing rotation in pulsating stars from space

2004 ◽  
Vol 215 ◽  
pp. 189-198
Author(s):  
Jaymie M. Matthews
Keyword(s):  
Real Data ◽  
Stellar Rotation ◽  
Instability Strip ◽  
Optical Telescope ◽  
Pulsating Stars ◽  
Rotation Periods ◽  
Diagnostic Potential ◽  
Solar Type ◽  
Ap Stars ◽  
Scuti Stars

At the time of the last Stellar Rotation symposium in 1969, the map of known pulsators in the H-R Diagram covered a lot less territory, being confined mainly to the classical instability strip. Among the new classes of pulsators are the strongly magnetic roAp (rapidly oscillating Ap) stars whose pulsation amplitudes and phases are modulated with their rotation periods. Among the classical pulsators, the δ Scuti stars are now known to show many more eigenmodes and frequency splitting than was ever recognised three decades ago. Both are examples of the diagnostic potential and severe challenges to detect and interpret correctly rotational fine structure in the pulsational frequency spectrum. In a pulsating star, rotation can perturb the structure or dynamics, and it can split degeneracies to serve as a diagnostic of pulsational modes. One tool which should help us exploit the potential and overcome the challenges of studying the interaction between rotation and pulsation is Canada's MOST (Microvariability & Oscillations of STars) microsatellite. MOST is a small optical telescope and ultraprecise CCD photometer designed to detect and characterise acoustic (p-mode) oscillations with periods of minutes and amplitudes as low as 1 micromagnitude in bright stars. While customised to conduct asteroseismology of solar-type stars, the MOST mission will also include roAp stars as prime targets and eventuallly δ Scutis as secondary targets. I present here simulations of MOST observations of such targets with different rotation periods, in advance of the real data expected in the months after the scheduled 30 June 2003 launch.

scholarly journals Hd 24975: A New Delta Scuti Star? (Or A Mild Ap Star with Short Photometric Variations?)

1986 ◽  
Vol 90 ◽  
pp. 253-256
Author(s):  
C. Megessier ◽  
P. North ◽  
M. Burnet
Keyword(s):  
Clear Correlation ◽  
Comparison Star ◽  
Instability Strip ◽  
Precise Location ◽  
Short Period ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Ap Stars ◽  
Hr Diagram

Looking in the literature for short period variations of Ap stars, we found the puzzling case of HD 24975. Used as a comparison star by Weiss (1978), it had been found then to present variations with a peak-to-peak amplitude of 0.01 in U, B and V with a period of about 45mn, but with no clear correlation between the three passbands.HD 24975 has the same spectral type A2 as 21 Com which seems to present photometric variations with P ⋍ 31mn and Δ V < 0,02m (Percy, 1973, 1975). Both stars are near the blue edge of the δ Scuti instability strip in the HR diagram. The lack of photo metric data, however, prevented the precise location of HD 24975 from being found on the HR diagram.

scholarly journals Recent Results on Binary Cepheids

1993 ◽  
Vol 139 ◽  
pp. 398-405
Author(s):  
Nancy Remage Evans
Keyword(s):  
Main Sequence ◽  
Normal Population ◽  
Absolute Magnitude ◽  
Instability Region ◽  
Instability Strip ◽  
Blue Edge ◽  
Convective Overshoot ◽  
Hr Diagram

AbstractIUE observations of hot companions of Cepheids have been used to determine the temperatures of the companions. For companions on the ZAMS, the temperatures can be used to determine the luminosity of the Cepheids from the inferred absolute magnitude of the companion. The accuracy of this method is comparable to the accuracy of calibration using Cepheids in clusters. An over-tone pulsator (SU Cas) has been identified by this technique. The luminosity of the double mode pulsator Y Car agrees with that from the PLC, confirming that is a normal Population I Cepheid. The variation of the width of the instability strip (as a function of luminosity) in the HR diagram is confirmed, and overtone and double mode pulsators are shown to be near the blue edge of the instability strip. Comparison between variables and nonvariables in the HR diagram (from IUE and cluster studies) shows very little overlap. The shape of the observed instability region may be determined both by the boundary between the variables and nonvariables and also the location of the tips of the blue loops of evolutionary tracks. Finally, eight Cepheids with hot companions which are evolved beyond the ZAMS have been studied. Half the systems are matched well by evolutionary tracks with little or no core convective overshoot near the main sequence. At least two and possibly four systems, however, cannot be matched by current isochrones.

scholarly journals Implication of a P-L Relation of Mira Variables

1993 ◽  
Vol 139 ◽  
pp. 103-103
Author(s):  
Hiromoto Shibahashi
Keyword(s):  
Agb Stars ◽  
Single Variable ◽  
Instability Strip ◽  
Thin Line ◽  
Mira Variables ◽  
Stellar Pulsation ◽  
Effective Temperatures ◽  
Function Of Two Variables ◽  
The Masses ◽  
Hr Diagram

Feast et al. (1989) obtained observationally a period-luminosity (P-L) relation of Mira variables in LMC. Basically, fundamental periods of stellar pulsation should be determined by two quantities —a mass and a radius of the star. The existence of a P-L relation implies a special condition that reduces a function of two variables into a function of only a single variable. Though the AGB appears as a thin line in the HR diagram like the Cepheid instability strip, it is an “asymptotically” merged line of evolutionary tracks of stars in a range of about 0.5-3 solar masses. This fact means that the masses of stars on a point of the AGB are not unique though the radii and the effective temperatures are unique, respectively. Therefore we cannot expect, in the case of AGB stars, that a period is reduced to a function of a single variable.

Sign in / Sign up

Export Citation Format

Share Document