Yazar "Handler, Gerald" seçeneğine göre listele

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    A tidally tilted sectoral dipole pulsation mode in the eclipsing binary TIC 63328020
    (Oxford University Press, 2021) Rappaport, Saul A.; Kurtz, Donald W.; Handler, Gerald; Jones, D.; Nelson, Lorne A.; Saio, Hideyuki; Fuller, Jim; Holdsworth, Daniel L.; Van Der Burg, Alicia E. Borger; Zak, Jiri; Skarka, Marek; Aiken, Jenny; Maxted, Pierre; Stevens, Daniel; Feliz, Dax L.; aliçavuş, Filiz Kahraman
    We report the discovery of the third tidally tilted pulsator, TIC 63328020. Observations with the TESS satellite reveal binary eclipses with an orbital period of 1.1057 d, and δ Scuti-type pulsations with a mode frequency of 21.09533 d−1. This pulsation exhibits a septuplet of orbital sidelobes as well as a harmonic quintuplet. Using the oblique pulsator model, the primary oscillation is identified as a sectoral dipole mode with l = 1, |m| = 1. We find the pulsating star to have M1 2.5 M, R1 3 R, and Teff, 1 8000 K, while the secondary has M2 1.1 M, R2 2 R, and Teff, 2 5600 K. Both stars appear to be close to filling their respective Roche lobes. The properties of this binary as well as the tidally tilted pulsations differ from the previous two tidally tilted pulsators, HD74423 and CO Cam, in important ways. We also study the prior history of this system with binary evolution models and conclude that extensive mass transfer has occurred from the current secondary to the primary
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    Asteroseismology of Massive Stars with the TESS Mission: The Runaway ? Cep Pulsator PHL 346=HN Aqr
    (Iop Publishing Ltd, 2019) Handler, Gerald; Pigulski, Andrzej; Daszynska-Daszkiewicz, Jadwiga; Irrgang, Andreas; Kilkenny, David; Guo, Zhao; Przybilla, Norbert
    We report an analysis of the first known beta Cep pulsator observed by the Transiting Exoplanet Survey Satellite (TESS) mission, the runaway star PHL 346 = HN Aqr. The star, previously known as a singly periodic pulsator, has at least 34 oscillation modes excited, 12 of those in the g-mode domain and 22 p modes. Analysis of archival data implies that the amplitude and frequency of the dominant mode and the stellar radial velocity were variable over time. A binary nature would be inconsistent with the inferred ejection velocity from the Galactic disk of 420 km s(-1), which is too large to be survivable by a runaway binary system. A kinematic analysis of the star results in an age constraint (23 +/- 1 Myr) that can be imposed on asteroseismic modeling and that can be used to remove degeneracies in the modeling process. Our attempts to match the excitation of the observed frequency spectrum resulted in pulsation models that were too young. Hence, asteroseismic studies of runaway pulsators can become vital not only in tracing the evolutionary history of such objects, but to understand the interior structure of massive stars in general. TESS is now opening up these stars for detailed asteroseismic investigation.
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    On the existence of 'Maia variables'
    (Cambridge Univ Press, 2024) Alicavus, Filiz Kahraman; Handler, Gerald; Chowdhury, Sowgata; Niemczura, Ewa; Jayaraman, Rahul; De Cat, Peter; Ozuyar, Dogus
    There are different classes of pulsating stars in the H-R diagram. While many of those classes are undisputed, some remain a mystery such as the objects historically called 'Maia variables'. Whereas the presence of such a class was suggested seven decades ago, no pulsational driving mechanism is known that could excite short-period oscillations in these late B to early A-type stars. Alternative hypotheses that would render the reports of variability of those stars erroneous have been proposed such as incorrect effective temperatures, binarity or rapid rotation, but no certain conclusions have been reached yet. Therefore, the existence of these variables as a homogeneous class of pulsating star is still under discussion. Meanwhile, many new candidates of these variables have been claimed especially by using photometric observations of space telescopes. In this study, we examined 31 objects that are alleged members of this hypothetical group and carried out detailed spectroscopic and photometric analyses to test the proposed hypotheses for their cause of variability. The T-eff, log g , v sin i , and chemical abundances of the targets were determined and the TESS photometric data were examined. As a result, we found that most of these targets are located inside the delta Scuti, beta Cephei, or SPB star instability strips, a few show evidence for binarity and others for rapid rotation. We give arguments that none of the apparently rapid pulsations in our targets is caused by a star outside any known instability strip. By extrapolation, we argue that most stars proposed as pulsators outside well-established instability domains are misclassified. Hence there is no sufficient evidence justifying the existence of a class of pulsating stars formerly known as the 'Maia variables'.