<i>Chandra</i>Observations of the Pleiades Open Cluster: X‐Ray Emission from Late B‐ to Early F‐Type Binaries

Daniel, Kathryne J.; Linsky, Jeffrey L.; Gagné, Marc

doi:10.1086/340553

Cited by 34 publications

(39 citation statements)

References 60 publications

(189 reference statements)

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“…We find that the B-type primary is detected in 7 out of 11 cases, after resolving it from all known visual companions with Chandra. A trend of the early-type stars to split in two groups was pointed out by Daniel et al (2002) for the Pleiades: Apparent X-ray emitters on the one side, and on the other side X-ray quiet stars with upper limits by 1−2 orders of magnitudes lower than the L x /L bol values of the detected B-type stars. Our observations are consistent with this general picture, although the two populations are not clearly separated.…”

Section: Discussionmentioning

confidence: 93%

Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

Stelzer¹,

Huélamo

Micela³

et al. 2006

A&A

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Context. The X-ray emission from B-type main-sequence stars is a longstanding mystery in stellar coronal research. Since there is no theory at hand that explains intrinsic X-ray emission from intermediate-mass main-sequence stars, the observations have often been interpreted in terms of (unknown) late-type magnetically active companion stars. Aims. Resolving the hypothesized companions requires high spatial resolution observations in the infrared and in X-rays. We use Chandra imaging observations to spatially resolve a sample of main-sequence B-type stars with recently discovered companions at arcsecond separation. Methods. Our strategy is to search for X-ray emission at the position of both the B-type primary and the faint companion. Results. We find that all spatially resolved companions are X-ray emitters, but seven out of eleven intermediate-mass stars are also X-ray sources. If this emission is interpreted in terms of additional sub-arcsecond or spectroscopic companions, this implies a high multiplicity of B-type stars. Firm results on B star multiplicity pending, the alternative, that B stars produce intrinsic X-rays, cannot be discarded. An appropriate scenario would be a magnetically confined wind, as suggested for the X-ray emission of the magnetic Ap star IQ Aur. However, the only Ap star in the Chandra sample is not detected in X-rays, and therefore does not support this picture.

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Section: Discussionmentioning

confidence: 93%

Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

Stelzer¹,

Huélamo

Micela³

et al. 2006

A&A

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“…However, measurements of X-ray luminosity are available only for 10 stars in our sample (Huensch et al 1998;Hünsch et al 1999;Schmitt & Liefke 2004). Among these, only two stars (HIP 21276, HIP 106231) exhibit a higher X-ray luminosity than those in the Pleiades (L 29.00 X = erg s −1 ; Daniel et al 2002). However, these stars have a significantly smaller magnitude excess than the Pleiades members.…”

Section: Stellar Activity Indicesmentioning

confidence: 97%

Spectroscopic Survey of G and K Dwarfs in the Hipparcos Catalog. I. Comparison Between the Hipparcos and Photometric Parallaxes

Kim

Stauffer

et al. 2016

ApJS

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The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data and the development of a new geometric distance measurement for the cluster. A short Pleiades distance from the Hipparcos parallax predicts a number of stars in the solar neighborhood that are sub-luminous at a given photospheric abundance. We test this hypothesis using the spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram. We derive stellar parameters for 170 nearby G-and K-type field dwarfs in the Hipparcos catalog based on high-resolution spectra obtained using KPNO 4 m echelle spectrograph. Our analysis shows that, when the Hipparcos parallaxes are adopted, most of our sample stars follow empirical colormagnitude relations. A small fraction of stars are too faint compared to main-sequence fitting relations bymag, but the differences are marginal at a 2s level, partly due to relatively large parallax errors. On the other hand, we find that the photometric distances of stars showing signatures of youth as determined from lithium absorption line strengths and R HK ¢ chromospheric activity indices are consistent with the Hipparcos parallaxes. Our result is contradictory to a suggestion that the Pleiades distance from main-sequence fitting is significantly altered by stellar activity and/or the young age of its stars, and provides an additional supporting evidence for the longdistance scale of the Pleiades.

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“…Cool stars are also X-ray sources with typical X-ray luminosities 10 26 − 10 30 erg s −1 (Caillault & Helfand 1985;Drake et al 1991;Daniel et al 2002;Schmitt & Liefke 2004). Such X-ray luminosities typically do not influence the subdwarf wind unless the stars are very close.…”

Section: Late-type Main-sequence Companions: Winds In Interactionmentioning

confidence: 99%

Stellar wind models of subluminous hot stars

Krtička

Kubát

Krtičková

2016

A&A

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1Ú stav teoretické fyziky a astrofyziky, Masarykova univerzita, Kotlářská 2, CZ-611 37 Brno, Czech Republic 2 Astronomickýústav, Akademie vědČeské republiky, Fričova 298, CZ-251 65 Ondřejov, Czech Republic Received ABSTRACTContext. Mass-loss rate is one of the most important stellar parameters. Mass loss via stellar winds may influence stellar evolution and modifies stellar spectrum. Stellar winds of subluminous hot stars, especially subdwarfs, have not been studied thoroughly. Aims. We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. Methods. We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. Results. We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived from the observations. The radiative force is not able to accelerate the homogeneous wind for stars with low effective temperatures and high surface gravities. We discussed the properties of winds of individual subdwarfs. The X-ray irradiation may inhibit the flow in binaries with compact components. In binaries with Be components, the winds interact with the disk of the Be star. Conclusions. Stellar winds exist in subluminous stars with low gravities or high effective temperatures. Despite their low mass-loss rates, they are detectable in the ultraviolet spectrum and cause X-ray emission. Subdwarf stars may lose a significant part of their mass during the evolution. The angular momentum loss in magnetic subdwarfs with wind may explain their low rotational velocities. Stellar winds are especially important in binaries, where they may be accreted on a compact or cool companion.

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ChandraObservations of the Pleiades Open Cluster: X‐Ray Emission from Late B‐ to Early F‐Type Binaries

Cited by 34 publications

References 60 publications

Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

Spectroscopic Survey of G and K Dwarfs in the Hipparcos Catalog. I. Comparison Between the Hipparcos and Photometric Parallaxes

Stellar wind models of subluminous hot stars

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