Hot subluminous stars: Highlights from the MUCHFUSS and<i>Kepler</i>missions

Heber, U.; Geier, S.; Gänsicke, B. T.

doi:10.1051/epjconf/20134304002

Cited by 9 publications

(10 citation statements)

References 15 publications

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“…The strong magnetic fields so far measured in white dwarfs tend to be dipole fields with strengths on the order of several MG, with weaker fields at the tens of kG level also having been detected in a small number of these stars (Landstreet et al 2012b;. Similarly, the recently discovered magnetic He-sdO star (Heber et al 2013) has a magnetic fields strong enough to induce clear Zeeman splitting (hundreds of kG). We would have been extremely unlucky to have missed anything remotely comparable to these in LS IV-14 • 116 .…”

Section: No Evidence For a Magnetic Fieldmentioning

confidence: 93%

“…Similarly, the recently discovered magnetic He-sdO star (Heber et al 2013) has a magnetic field strong enough to induce clear Zeeman splitting (hundreds of kG). We would have been extremely unlucky to have missed anything remotely comparable to these in LS IV-14 • 116.…”

Section: No Evidence For a Magnetic Fieldmentioning

confidence: 97%

“…An independent analysis based on spectro-polarimetry obtained with ESPaDOnS at the CFHT (Petit et al 2012) also failed to measure a magnetic field in two hot subdwarfs for which a positive detection had previously been claimed. In this context, it was with great interest that we noted the first detection of a very strong (several hundred kG) magnetic field in a He-rich subdwarf O (sdO) star (Heber et al 2013). Given that magnetic fields are relatively common among white dwarfs, they should also be present for a sizeable fraction of their hot subdwarf (sdB and sdO) progenitors.…”

Section: Introductionmentioning

confidence: 99%

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The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

Randall¹,

Bagnulo

Ziegerer

et al. 2015

A&A

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The intermediate helium subdwarf B star LS IV-14 • 116 is a unique object showing extremely peculiar atmospheric abundances as well as long-period pulsations that cannot be explained in terms of the usual opacity mechanism. One hypothesis invoked was that a strong magnetic field may be responsible. We discredit this possibility on the basis of FORS2 spectro-polarimetry, which allows us to rule out a mean longitudinal magnetic field down to 300 G. Using the same data, we derive the atmospheric parameters for LS IV-14 • 116 to be T eff = 35 150 ± 111 K, log g = 5.88 ± 0.02 and log N(He)/N(H) = −0.62 ± 0.01. The high surface gravity in particular is at odds with the theory that LS IV-14 • 116 has not yet settled onto the helium main sequence, and that the pulsations are excited by an mechanism acting on the helium-burning shells present after the main helium flash. Archival UVES spectroscopy reveals LS IV-14 • 116 to have a radial velocity of 149.1±2.1 km s −1 . Running a full kinematic analysis, we find that it is on a retrograde orbit around the Galactic centre, with a Galactic radial velocity component U = 13.23 ± 8.28 km s −1 and a Galactic rotational velocity component V = −55.56 ± 22.13 km s −1 . This implies that LS IV-14 • 116 belongs to the halo population, an intriguing discovery.

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Section: No Evidence For a Magnetic Fieldmentioning

confidence: 93%

Section: No Evidence For a Magnetic Fieldmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

Randall¹,

Bagnulo

Ziegerer

et al. 2015

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“…In the course of the MUCHFUSS project (Geier et al 2011), which aims at finding hot subdwarf binary systems with massive companions, we have discovered a possible progenitor for such a supernova consisting of a hot subdwarf B star (sdB) and a white dwarf in an extremely compact binary (Heber et al 2013;Geier et al 2013). This system, CD-30 • 11223, was also independently discovered by Vennes et al (2012).…”

Section: Introductionmentioning

confidence: 99%

A progenitor binary and an ejected mass donor remnant of faint type Ia supernovae

Geier

Marsh

Wang

et al. 2013

A&A

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116

159

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Type Ia supernovae (SN Ia) are the most important standard candles for measuring the expansion history of the universe. The thermonuclear explosion of a white dwarf can explain their observed properties, but neither the progenitor systems nor any stellar remnants have been conclusively identified. Underluminous SN Ia have been proposed to originate from a so-called double-detonation of a white dwarf. After a critical amount of helium is deposited on the surface through accretion from a close companion, the helium is ignited causing a detonation wave that triggers the explosion of the white dwarf itself. We have discovered both shallow transits and eclipses in the tight binary system CD-30 • 11223 composed of a carbon/oxygen white dwarf and a hot helium star, allowing us to determine its component masses and fundamental parameters. In the future the system will transfer mass from the helium star to the white dwarf. Modelling this process we find that the detonation in the accreted helium layer is sufficiently strong to trigger the explosion of the core. The helium star will then be ejected at such high velocity that it will escape the Galaxy. The predicted properties of this remnant are an excellent match to the so-called hypervelocity star US 708, a hot, helium-rich star moving at more than 750 km s −1 , sufficient for it to leave the Galaxy. The identification of both progenitor and remnant provides a consistent picture of the formation and evolution of underluminous SNIa.

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“…A first helium-rich hot O-type subdwarf (He-sdO) star with a significant magnetic field (≈300 -700 kG) was identified spectroscopically by Heber et al (2013), although this star has not been analysed to date. Here we present the first spectroscopic analysis of a hot subdwarf star with a strong magnetic field, the He-sdO Gaia DR2 5694207034772278400 (henceforth J0809-2627).…”

Section: Introductionmentioning

confidence: 99%

Discovery of a highly magnetic He-sdO star from a double-degenerate binary merger

Dorsch

Reindl

Pelisoli

et al. 2022

A&A

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Helium-rich hot subdwarf stars of spectral type O (He-sdO) are considered prime candidates for stellar merger remnants. Such events should lead to the generation of strong magnetic fields. However, no magnetic He-sdO has yet been unambiguously discovered despite the high magnetic rate (20%) among white dwarf stars, the progeny of hot subdwarfs. Here we present the discovery of a strong magnetic field (B = 353 ± 10 kG) from Zeeman-split hydrogen, helium, and metal lines in the optical X-shooter spectrum of an He-sdO and present the first spectroscopic analysis of any magnetic hot subdwarf. For this we used line-blanketed TLUSTY non-local thermodynamic equilibrium models and assumed a simple homogeneous magnetic field. The derived atmospheric parameters Teff = 44 900 ± 1000 K and log g = 5.93 ± 0.15 are typical for He-sdO stars, while the star is less hydrogen-poor than most He-sdOs at log n(He)/n(H) = + 0.28 ± 0.10. The star is a slow rotator (vrot sin i < 40 km s−1). Its chemical composition is N-rich and C- and O-poor, and the Si and S abundances are close to solar. Combining the atmospheric parameters with Gaia parallax and photometry, the stellar radius and luminosity are found to be typical for He-sdOs and place the star on the helium main sequence in the Hertzsprung-Russell diagram. Its mass of 0.93−0.30+0.44 M⊙, although uncertain, appears to be remarkably high. The strong magnetic field along with the atmospheric parameters and metal abundances provide overwhelming evidence for the double-degenerate merger scenario.

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Hot subluminous stars: Highlights from the MUCHFUSS andKeplermissions

Cited by 9 publications

References 15 publications

The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

A progenitor binary and an ejected mass donor remnant of faint type Ia supernovae

Discovery of a highly magnetic He-sdO star from a double-degenerate binary merger

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