But How About More Massive Stars That Will Become Supernova? TESS To

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But How About More Massive Stars That Will Become Supernova? TESS To

Massive star evolution put to the test with Kepler/TESS M. G. Pedersen1, M. Michielsen1, C. Aerts1,2,3 and P. I. Pápics1 1Institute of Astronomy, KU Leuven, Leuven, Belgium | 2Department of Astrophysics/ IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands | 3MPIA, Heidelberg, Germany Internal mixing has a high Effect of mixing on the main-sequence evolution of stars with convective cores impact on stellar evolution, Envelope but remains a poorly CBM mixing calibrated quantity for massive stars in particular. y c y y n t t i i e i s s Asteroseismology allows us c o o i Extent depends f n n f i to probe the stellar interiors, i E on f H CBM p m m g u and determine the efficiency u n L L i of the internal mixing from x i the core to the surface of the M Starting level star. g o defined by Dext L However, the number of O- and f ∈ [0.01, 0.04] H D ∈ [10, 2000] cm2 s-1 B-type stars suitable for CBM p ext asteroseismic modeling has Center Surface Temperature Temperature been limited! Gravity modes Based on Kepler observations x u l F Gravity mode instability strip Time g s n n i o c i t a a p s l s u d p o i d r e t e i P c x B-type stars e Pulsation Period f o # But how about more massive stars that will TESS to Revisiting the Kepler field has lead to a four-fold increase in the become supernova? the rescue! number of B-type stars suitable for asteroseismic modeling Take away We found 4x more B-type pulsators in the Kepler data suitable for asteroseismic modeling compared to previous findings (summary in Szewczuk et al. 2018) Due to the choice of field-of-view, no stars more massive than ~8.5 M☉ revealed suitable pulsation modes from the nominal Kepler mission, while K2’s time span is too short. The TESS continuous viewing zone is therefore crucial for the calibration of stellar structure and evolution models of the most massive stars in the Universe. Pedersen et al. 2019 Stellar variability detected in 90% of all OB-type stars observed in 2-min cadence by TESS in sectors 1 and 2, covering masses up to ~45 M☉.

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Plotting Variable Stars on the H-R Diagram Activity
Pulsating Variable Stars and the Hertzsprung-Russell Diagram The Hertzsprung-Russell (H-R) Diagram: The H-R diagram is an important astronomical tool for understanding how stars evolve over time. Stellar evolution can not be studied by observing individual stars as most changes occur over millions and billions of years. Astrophysicists observe numerous stars at various stages in their evolutionary history to determine their changing properties and probable evolutionary tracks across the H-R diagram. The H-R diagram is a scatter graph of stars. When the absolute magnitude (MV) – intrinsic brightness – of stars is plotted against their surface temperature (stellar classification) the stars are not randomly distributed on the graph but are mostly restricted to a few well-defined regions. The stars within the same regions share a common set of characteristics. As the physical characteristics of a star change over its evolutionary history, its position on the H-R diagram The H-R Diagram changes also – so the H-R diagram can also be thought of as a graphical plot of stellar evolution. From the location of a star on the diagram, its luminosity, spectral type, color, temperature, mass, age, chemical composition and evolutionary history are known. Most stars are classified by surface temperature (spectral type) from hottest to coolest as follows: O B A F G K M. These categories are further subdivided into subclasses from hottest (0) to coolest (9). The hottest B stars are B0 and the coolest are B9, followed by spectral type A0. Each major spectral classification is characterized by its own unique spectra.
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(NASA/Chandra X-Ray Image) Type Ia Supernova Remnant – Thermonuclear Explosion of a White Dwarf
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Variable Star
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Asteroseismology
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``But I Am Constant As the Northern Star of Whose True-Fixed and Resting Quality There Is No Fellow in the Firmament.'' William
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Neilson et al., JAAVSO Volume 44, 2016 179 Period Changes and Evolution in Pulsating Variable Stars Hilding R. Neilson John R. Percy Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada; [email protected], [email protected] Horace A. Smith Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320; [email protected] Invited review paper, received October 18, 2016 Abstract We review ways in which observations of the changing periods of pulsating variable stars can be used to detect and directly measure their evolution. We briefly describe the two main techniques of analysis—(O–C) analysis and wavelet analysis— and results for pulsating variable star types which are reasonably periodic: type I and II Cepheids, RR Lyrae stars, β Cephei stars, and Mira stars. We comment briefly on δ Scuti stars and pulsating white dwarfs. For some of these variable star types, observations agree approximately with the predictions of evolutionary models, but there still exist significant areas of disagreement that challenge future models of stellar evolution. There may be a need, for instance, to include processes such as rotation, mass loss, and magnetic fields. There may also be non-evolutionary processes which are contributing to the period changes. 1. Introduction known constant period P. When (O–C) is plotted against time, it produces a straight line if the period is constant, a parabola Star lives are measured in billions of years, millions of opening upward if the period is increasing linearly, a parabola years for very rare massive stars.
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Pulsating Stars: Stars That Breathe
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The Wolf-Rayet Stars in M 31? I
A&A 563, A89 (2014) Astronomy DOI: 10.1051/0004-6361/201323240 & c ESO 2014 Astrophysics The Wolf-Rayet stars in M 31? I. Analysis of the late-type WN stars A. Sander, H. Todt, R. Hainich, and W.-R. Hamann Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany e-mail: [ansander;htodt]@astro.physik.uni-potsdam.de Received 12 December 2013 / Accepted 22 January 2014 ABSTRACT Context. Comprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpected similarities between the WR populations of these different galaxies. Analyzing the WR stars in M 31 will extend our understanding of these objects in different galactic environments. Aims. The present study aims at the late-type WN stars in M 31. The stellar and wind parameters will tell about the formation of WR stars in other galaxies with different metallicity and star formation histories. The obtained parameters will provide constraints to the evolution of massive stars in the environment of M 31. Methods. We used the latest version of the Potsdam Wolf-Rayet model atmosphere code to analyze the stars via fitting optical spectra and photometric data. To account for the relatively low temperatures of the late WN10 and WN11 subtypes, our WN models have been extended into this temperature regime. Results. Stellar and atmospheric parameters are derived for all known late-type WN stars in M 31 with available spectra. All of these stars still have hydrogen in their outer envelopes, some of them up to 50% by mass.
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