ترغب بنشر مسار تعليمي؟ اضغط هنا

Convection and Overshoot in models of gamma Doradus and delta Scuti stars

348   0   0.0 ( 0 )
 نشر من قبل Catherine Lovekin
 تاريخ النشر 2017
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We investigate the pulsation properties of stellar models representative of $delta$ Scuti and $gamma$ Doradus variables. We have calculated a grid of stellar models from 1.2 to 2.2 M$_{odot}$, including the effects of both rotation and convective overshoot using MESA, and we investigate the pulsation properties of these models using GYRE. We discuss observable patterns in the frequency spacing for $p$ modes and the period spacings for g modes. Using the observable patterns in g mode period spacings, it may be possible to observationally constrain the convective overshoot and rotation of a model. We also calculate the pulsation constant (Q) for all models in our grid, and investigate the variation with convective overshoot and rotation. The variation in Q values of radial modes can be used to place constraints on the convective overshoot and rotation of stars in this region. As a test case, we apply this method to a sample of 22 high amplitude $delta$ Scuti stars (HADS), and provide estimates for the convective overshoot of the sample.



قيم البحث

اقرأ أيضاً

126 - D. R. Xiong , L. Deng , C. Zhang 2018
By using a non-local and time-dependent convection theory, we have calculated radial and low-degree non-radial oscillations for stellar evolutionary models with $M=1.4$--3.0,$mathrm{M}_odot$. The results of our study predict theoretical instability s trips for $delta$ Scuti and $gamma$ Doradus stars, which overlap with each other. The strip of $gamma$ Doradus is slightly redder in colour than that of $delta$ Scuti. We have paid great attention to the excitation and stabilization mechanisms for these two types of oscillations, and we conclude that radiative $kappa$ mechanism plays a major role in the excitation of warm $delta$ Scuti and $gamma$ Doradus stars, while the coupling between convection and oscillations is responsible for excitation and stabilization in cool stars. Generally speaking, turbulent pressure is an excitation of oscillations, especially in cool $delta$ Scuti and $gamma$ Doradus stars and all cool Cepheid- and Mira-like stars. Turbulent thermal convection, on the other hand, is a damping mechanism against oscillations that actually plays the major role in giving rise to the red edge of the instability strip. Our study shows that oscillations of $delta$ Scuti and $gamma$ Doradus stars are both due to the combination of $kappa$ mechanism and the coupling between convection and oscillations, and they belong to the same class of variables at the low-luminosity part of the Cepheid instability strip. Within the $delta$ Scuti--$gamma$ Doradus instability strip, most of the pulsating variables are very likely hybrids that are excited in both p and g modes.
131 - M.-P. Bouabid 2009
Gamma Doradus are F-type stars pulsating with high order g-modes. Their instability strip (IS) overlaps the red edge of the delta Scuti one. This observation has led to search for objects in this region of the HR diagram showing p and g-modes simulta neously. The existence of such hybrid pulsators has recently been confirmed (Handler 2009) and the number of candidates is increasing (Matthews 2007). From a theoretical point of view, non-adiabatic computations including a time-dependent treatment of convection (TDC) predict the existence of gamma Dor/delta Sct hybrid pulsators (Dupret et al. 2004; Grigahcene et al. 2006). Our aim is to confront the properties of the observed hybrid candidates with the theoretical predictions from non-adiabatic computations of non-radial pulsations including the convection-pulsation interaction.
We present the first asteroseismic results for $delta$ Scuti and $gamma$ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilise the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung-Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, $gamma$ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74% for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young $delta$ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.
Observations of the A5p star KIC 8677585 obtained during the Kepler 10-d commissioning run with 1-min time resolution show that it is a roAp star with several frequencies with periods near 10 min. In addition, a low frequency at 3.142 cycles/day is a lso clearly present. Multiperiodic gamma Doradus and delta Scuti pulsations, never before seen in any Ap star, are present in Kepler observations of at least three other Ap stars. Since gamma Doradus pulsations are seen in Ap stars, it is likely that the low-frequency in KIC 8677585 is also a gamma Doradus pulsation. The simultaneous presence of both gamma Doradus and roAp pulsations and the unexpected detection of delta Scuti and gamma Doradus pulsations in Ap stars present new opportunities and challenges for the interpretation of these stars.
As part of the NASA Kepler Guest Observer program, we requested and obtained long-cadence data on about 2700 faint (magnitude 14-16) Kepler stars with effective temperatures and surface gravities that lie near or within the pulsation instability regi on for main-sequence gamma Doradus and delta Scuti pulsating variables. These variables are of spectral type A-F with masses of 1.4 to 2.5 solar masses. The delta Scuti stars pulsate in radial and non-radial acoustic modes, with periods of a few hours (frequencies around 10 cycles/day), while gamma Doradus variables pulsate in nonradial gravity modes with periods 0.3 to 3 days (frequencies around 1 cycle/day). Here we consider the light curves and Fourier transforms of 633 stars in an unbiased sample observed by Kepler in Quarters 6-13 (June 2010-June 2012). We show the location of these stars in the log surface gravity--effective temperature diagram compared to the instability region limits established from ground-based observations, and taking into account uncertainties and biases in the Kepler Input Catalog T_eff values. While hundreds of variables have been discovered in the Kepler data, about 60% of the stars in our sample do not show any frequencies between 0.2 and 24.4 cycles per day with amplitude above 20 parts per million. We find that six of these apparently constant stars lie within the pulsation instability region. We discuss some possible reasons that these stars do not show photometric variability in the Kepler data. We also comment on the non-constant stars, and on 26 variable-star candidates, many of which also do not lie within the expected instability regions.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا