IA Porto: TESS First Light on Stellar Physics

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bystander
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IA Porto: TESS First Light on Stellar Physics

Post by bystander » Sat Jun 08, 2019 3:19 pm

TESS First Light on Stellar Physics
Institute of Astrophysics and Space Sciences | University of Porto | 2019 Jun 06

Among the 32,000 stars observed in short cadence in the first two months of science operations, asteroseismic data from the TESS space mission revealed five rare roAp stars, including the fastest pulsator in this class.

roAp.jpeg
Artist's impression of a rapidly oscillating Ap star (roAp), highlighting its complexity.
The diversity of physical phenomena taking place in their outer layers, makes roAp
stars ideal test beds to the modelling of stellar physics. Credit: Victoria Antoci
(Stellar Astrophysics Centre, Aarhus University)

Using asteroseismic techniques, an international team searched for pulsations in a subsample of five thousand stars, from the 32 thousand observed in short cadence in the first two sectors (roughly the first two months of science operations) of NASA‘s Transiting Exoplanet Survey Satellite (TESS), and found five rare rapidly oscillating Ap (roAp) stars. ...

Among the stellar data, the team found the fastest known roAp pulsator, which completes one pulsation every 4.7 minutes. Two of these five stars were found to be particularly challenging to the currently understanding of the field, one because it is cooler than theoretically expected for a roAp star and the other because it exhibits pulsation frequencies that are unexpectedly high. ...

Following an in-depth analysis of 80 stars previously known to be chemically peculiar, the team also found 27 new rotational Ap variables, and derived their rotation periods, based on brightness changes during the star’s rotation, produced by passing chemical spots. ...

For seven roAp stars, previously known from ground-based observations, high-precision photometric data was also gathered. For four of these stars, it was possible to set constraints on the star’s inclination angle and magnetic obliquity. ...

Rotation and Pulsation in Ap Stars: First Light Results from TESS Sectors 1 and 2 ~ M.S. Cunha et al
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Re: IA Porto: TESS First Light on Stellar Physics

Post by neufer » Sat Jun 08, 2019 7:06 pm

http://en.wikipedia.org/wiki/Przybylski%27s_star wrote:
<<Przybylski's Star, or HD 101065, is a peculiar star that is located about 410 light years from the Sun in the constellation Centaurus. In 1961, the Polish-Australian astronomer Antoni Przybylski discovered that this star had a peculiar spectrum that would not fit into the standard framework for stellar classification. Przybylski's observations indicated unusually low amounts of iron and nickel in the star's spectrum, but higher amounts of unusual elements like strontium, niobium, scandium, yttrium, caesium, neodymium, praseodymium, thorium, ytterbium, and uranium. In fact, at first Przybylski doubted that iron was present in the spectrum at all. Modern work shows that the iron-group elements are somewhat below normal in abundance, but it's clear that the lanthanoids and other exotic elements are highly overabundant. As a result of these peculiar abundances this star belongs firmly in the Ap star class. [In fact,] HD 101065 is the prototype star of the roAp star class. It was discovered to pulsate photometrically in 1978 with a period of 12.15 min.

According to the Encyclopedia of Astrobiology, Astronomy, and Spaceflight, Przybylski's Star is…
  • "One of the most chemically peculiar stars known; it is named informally after its discoverer, the Polish-Australian astronomer, Antoni Przybylski.… Apart from the usual lines of hydrogen and the calcium H and K, the strongest lines in HD 101065 are due to singly ionized lanthanides, presenting a spectrum similar to that of an S star, a highly evolved object whose atmosphere is enriched with recently synthesized material from deep within its interior. Yet, in other respects, HD 101065 appears to be a main sequence star or subgiant. One possibility is that it is a cool, extreme Ap star, a theory supported by the discovery of a several kilogauss magnetic field in HD 101065 similar to that of many other Ap stars. The outstanding difficulty with HD 101065 as an Ap star was that its spectrum didn't look like the others. Lines of neutral and first ionized iron are prominent in the spectra of Ap stars, and in some cases, the iron is clearly overabundant.">>
Przybylski's Star also contains many different short-lived actinide elements with actinium, protactinium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium being detected. Other radioactive elements discovered in this star include technetium and promethium. Because of the odd properties of this star, there are numerous theories about why the oddities occur. The most interesting of them is that the star contains some long-lived nuclides from the island of stability (e.g. 298Fl, 304120, or 310126) and that the observed short-lived actinides are the daughters of these progenitors, occurring in secular equilibrium with their parents.>>
Art Neuendorffer

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Re: IA Porto: TESS First Light on Stellar Physics

Post by BDanielMayfield » Mon Jun 10, 2019 2:07 pm

neufer wrote:
Sat Jun 08, 2019 7:06 pm
http://en.wikipedia.org/wiki/Przybylski%27s_star wrote:
<<Przybylski's Star, or HD 101065, is a peculiar star that is located about 410 light years from the Sun in the constellation Centaurus. In 1961, the Polish-Australian astronomer Antoni Przybylski discovered that this star had a peculiar spectrum that would not fit into the standard framework for stellar classification. Przybylski's observations indicated unusually low amounts of iron and nickel in the star's spectrum, but higher amounts of unusual elements like strontium, niobium, scandium, yttrium, caesium, neodymium, praseodymium, thorium, ytterbium, and uranium. In fact, at first Przybylski doubted that iron was present in the spectrum at all. Modern work shows that the iron-group elements are somewhat below normal in abundance, but it's clear that the lanthanoids and other exotic elements are highly overabundant. As a result of these peculiar abundances this star belongs firmly in the Ap star class. [In fact,] HD 101065 is the prototype star of the roAp star class. It was discovered to pulsate photometrically in 1978 with a period of 12.15 min.

According to the Encyclopedia of Astrobiology, Astronomy, and Spaceflight, Przybylski's Star is…
  • "One of the most chemically peculiar stars known; it is named informally after its discoverer, the Polish-Australian astronomer, Antoni Przybylski.… Apart from the usual lines of hydrogen and the calcium H and K, the strongest lines in HD 101065 are due to singly ionized lanthanides, presenting a spectrum similar to that of an S star, a highly evolved object whose atmosphere is enriched with recently synthesized material from deep within its interior. Yet, in other respects, HD 101065 appears to be a main sequence star or subgiant. One possibility is that it is a cool, extreme Ap star, a theory supported by the discovery of a several kilogauss magnetic field in HD 101065 similar to that of many other Ap stars. The outstanding difficulty with HD 101065 as an Ap star was that its spectrum didn't look like the others. Lines of neutral and first ionized iron are prominent in the spectra of Ap stars, and in some cases, the iron is clearly overabundant.">>
Przybylski's Star also contains many different short-lived actinide elements with actinium, protactinium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium being detected. Other radioactive elements discovered in this star include technetium and promethium. Because of the odd properties of this star, there are numerous theories about why the oddities occur. The most interesting of them is that the star contains some long-lived nuclides from the island of stability (e.g. 298Fl, 304120, or 310126) and that the observed short-lived actinides are the daughters of these progenitors, occurring in secular equilibrium with their parents.>>
Thank you for bringing this most fascinating star to our attention Art.

Guesses as to its very strange r-process element mix. Either: (1) The star had a close encounter with a kilo-nova blast from a merger of two neutron stars. Or (2) The star has some rare natural way to accelerate and collide heavy neutron rich nuclei with enough energy to fuse these ultra heavy elements and then dredge this production up to its surface.

But however these heretofore impossible [or nearly impossible] to create on Earth elements are forged, this star is indicating that an "island of stability" further up the periodic table very likely does exist :!:

Bruce
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