X-ray emission from A-type stars

Schröder, Christian; Schmitt, J. H. M. M.

doi:10.1051/0004-6361:20077429

Cited by 89 publications

(79 citation statements)

References 21 publications

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“…Nevertheless, higher complexity in the magnetic topology is also present. X-ray emission from this system was detected with Einstein (0.15-4.0 keV) at a level of log L X = 28.8 erg s −1 (Schmitt et al 1985) and ROSAT (0.1-2.4 keV) at a level of log L X = 28.6 erg s −1 (Schröder & Schmitt 2007), but it was not resolved in both observations and the contribution from the individual components remained unknown. The field A0p star IQ Aur (HD 34452, HR 1732) belongs to the class of α 2 CVn spectrum variable stars and is thought to be a single star with V = 5.4 and small E B−V 0.01.…”

Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 89%

“…Thus one expects a virtually X-ray dark population at spectral types mid-B to mid-A, where stars neither possess an outer convection zone nor drive strong stellar winds. The overall X-ray detection rate among those stars is with ∼10% quite low indeed, but surprisingly, X-ray emission was detected from several of these stars (Schröder & Schmitt 2007). Consequently, low-mass stars hidden in the vicinity of their optically bright primaries have often been proposed as the true origin of the X-ray emission.…”

Section: Introductionmentioning

confidence: 99%

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New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Robrade

Schmitt

2011

A&A

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Aims. We re-examine the scenario of X-ray emission from magnetically confined/channeled wind shocks (MCWS) for Ap/Bp stars, a model originally developed to explain the ROSAT detection of the A0p star IQ Aur. Methods. We present new X-ray observations of the A0p stars α 2 CVn (Chandra) and IQ Aur (XMM-Newton) and discuss our findings in the context of X-ray generating mechanisms of magnetic, chemically peculiar intermediate mass stars. Results. The X-ray luminosities of IQ Aur with log L X = 29.6 erg s −1 and α 2 CVn with log L X 26.0 erg s −1 differ by at least three orders of magnitude, although both are A0p stars. By studying a sample of comparison stars, we find that X-ray emission is preferably generated by more massive objects such as IQ Aur. Besides a strong, cool plasma component, significant amounts of hot (>10 MK) plasma are present during the quasi-quiescent phase of IQ Aur; moreover, diagnostics of the UV sensitive f /i line ratio in He-like O vii triplet point to X-ray emitting regions well above the stellar surface of IQ Aur. In addition we detect a large flare from IQ Aur with temperatures up to ∼100 MK and a peak X-ray luminosity of log L X ≈ 31.5 erg s −1 . The flare, showing a fast rise and e-folding decay time of less than half an hour, originates in a fairly compact structure and is accompanied by a significant metallicity increase. The X-ray properties of IQ Aur cannot be described by wind shocks only and require the presence of magnetic reconnection. This is most evident in the, to our knowledge, first X-ray flare reported from an A0p star. Conclusions. Our study indicates that the occurrence the of X-ray emission in A0p stars generated by magnetically channeled wind shocks depends on stellar properties such as luminosity, which promote a high mass loss rate, whereas magnetic field configuration and transient phenomena refine their appearance. While we cannot rule out unknown close companions, the X-ray emission from IQ Aur can be described consistently in the MCWS scenario, in which the very strong magnetic confinement of the stellar wind has led to the build-up of a rigidly rotating disk around the star, where magnetic reconnection and centrifugal breakout events occur.

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Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Robrade

Schmitt

2011

A&A

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“…This star sits very low on the A-star color-magnitude diagram (Figure 4). A0 type stars are not intrinsic X-ray sources, yet HIP 16095 was detected in the ROSAT All-Sky Survey (Schroeder & Schmitt 2007) strongly implying the existence of a late-type secondary. At a distance of 88 pc, the X-ray luminosity is 2×10 29 erg s −1 .…”

Section: A1 Probable Octans-near Starsmentioning

confidence: 99%

Young Stars Near Earth: The Octans-Near Association and Castor Moving Group

Zuckerman

Vican

Song

et al. 2013

ApJ

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All cataloged stellar moving groups and associations with ages 100 Myr and within 100 pc of Earth have Galactic space motions (UVW) situated in a "good box" with dimensions ∼20 km s −1 on a side. Torres et al. defined the Octans Association as a group of 15 stars with age "20 Myr?" and located ∼140 pc from Earth, but with average V space velocity −3.6 km s −1 that is well outside of the good box. We present a list of 14 Hipparcos star systems within 100 pc of Earth that we call "Octans-Near"; these systems have UVW similar to those of the much more distant Octans Association. The Octans-Near stars have apparent ages between about 30 and 100 Myr and their relationship to the Octans Association stars is unclear. Six additional star systems have UVW similar to those of Octans-Near stars and likely ages 200 Myr. These six systems include the late-type binary star EQ Peg-6.2 pc from Earth with likely age 100 Myr and thus likely to be the nearest known pre-main sequence star system. The UVW of stars in a previously proposed ∼200 Myr old Castor moving group are not too dissimilar from the UVW of Octans-Near stars. However, stars in the Castor group-if it exists at all-are mostly substantially older than 200 Myr and thus generally can readily be distinguished from the much younger Octans-Near stars.

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“…Peculiar metal abundances are sometimes observed in these stars, "skin diseases" produced by various chemical separation phenomena at the surfaces, such as gravitational settling and radiative levitation, which in more active stars are smothered by mixing processes. This quietness also appears to manifest itself in X-ray quietness-indeed, various ROSAT searches for X-ray emission from normal A-type stars have found most to be Xray dark down to limits of L X < a few 10 27 -10 28 erg s −1 (e.g., Simon et al 1995;Schröder & Schmitt 2007), with significantly lower limits for nearby examples such as Vega. For this A0 V star, Pease et al (2006) obtained L X < 3 × 10 25 erg s −1 from Chandra observations, corresponding to a bolometric fraction limit of L X /L bol < 9×10 −11 (see also Ayres 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Schröder & Schmitt (2007) found that 342 A-type stars in the Bright Star Catalogue (Hoffleit & Jaschek 1991) can potentially be associated with X-ray sources found in ROSAT surveys, corresponding to a detection rate of 10%-15%. But what fraction of the X-ray detections are due to unseen late-type companions?…”

Section: Introductionmentioning

confidence: 99%

Burn Out or Fade Away? On the X-Ray and Magnetic Death of Intermediate Mass Stars

Drake

Braithwaite²,

Kashyap

et al. 2014

ApJ

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The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was L X 1.3 × 10 27 erg s −1 . The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 10 25 erg s −1 . This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

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X-ray emission from A-type stars

Cited by 89 publications

References 21 publications

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Young Stars Near Earth: The Octans-Near Association and Castor Moving Group

Burn Out or Fade Away? On the X-Ray and Magnetic Death of Intermediate Mass Stars

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X-ray emission from A-type stars

Cited by 89 publications

References 21 publications

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

Young Stars Near Earth: The Octans-Near Association and Castor Moving Group

Burn Out or Fade Away? On the X-Ray and Magnetic Death of Intermediate Mass Stars

Contact Info

Product

Resources

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New X-ray observations of IQ Aurigae andα² Canum Venaticorum

New X-ray observations of IQ Aurigae andα² Canum Venaticorum