X-ray emission from early-type stars in the Orion Nebula Cluster

B. Stelzer, E. Flaccomio, T. Montmerle, G. Micela, S. Sciortino, F. Favata, T. Preibisch, E. D. Feigelson

Research output: Contribution to journalArticle

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Abstract

The X-ray properties of twenty ∼1 Myr old O, B, and A stars of the Orion Trapezium are examined with data from the Chandra Orion Ultradeep Project (COUP). On the basis of simple theories for X-ray emission, we define two classes separated at spectral type B4: hotter stars have strong winds that may give rise to X-ray emission in small- or large-scale wind shocks, and cooler stars that should be X-ray dark due to their weaker winds and absence of outer convection zones where dynamos can generate magnetic fields. Emission by late-type magnetically active companions may be present in either class. Sixteen of the 20 stars are detected with a wide range of X-ray luminosities, log L X (ergs s -1) ∼ 29-33, and X-ray efficiencies, log (L X/L bol) ∼ -4 to -8. Only two stars, θ 1 Ori D (B0.5) and NU Ori (B1), show exclusively the constant soft-spectrum emission at log(L X/L bol) ∼ -7 expected from the standard model involving many small shocks in an unmagnetized radiatively accelerated wind. Most of the other massive O7-B3 stars exhibit some combination of soft-spectrum wind emission, hard-spectrum flaring, and/or rotational modulation indicating large-scale inhomogeneity. Magnetic confinement of winds with large-scale shocks can be invoked to explain these phenomena. This is supported in some cases by nonthermal radio emission and/or chemical peculiarities, or direct detection of the magnetic field (θ 1 Ori C). Most of the stars in the weak-wind class exhibit X-ray flares and log L X < 31 ergs s -1, consistent with magnetic activity from known or unseen low-mass companions. In most cases, the X-ray spectra can be interpreted in terms of a two-temperature plasma model with a soft component of 3-10 MK and a hard component up to 40 MK. All nondetections belong to the weak-wind class. A group of stars exhibit hybrid properties - flarelike behavior superimposed on a constant component with log L X ∼ 32 ergs s -1 - which suggest both magnetic activity and wind emission.

Original languageEnglish (US)
Pages (from-to)557-581
Number of pages25
JournalAstrophysical Journal, Supplement Series
Volume160
Issue number2
DOIs
StatePublished - Oct 1 2005

Fingerprint

Orion nebula
stars
x rays
erg
shock
magnetic field
A stars
rotating generators
O stars
B stars
hot stars
plasma temperature
radio emission
coolers
magnetic fields
inhomogeneity
flares
emission spectra
convection
luminosity

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Stelzer, B., Flaccomio, E., Montmerle, T., Micela, G., Sciortino, S., Favata, F., ... Feigelson, E. D. (2005). X-ray emission from early-type stars in the Orion Nebula Cluster. Astrophysical Journal, Supplement Series, 160(2), 557-581. https://doi.org/10.1086/432375
Stelzer, B. ; Flaccomio, E. ; Montmerle, T. ; Micela, G. ; Sciortino, S. ; Favata, F. ; Preibisch, T. ; Feigelson, E. D. / X-ray emission from early-type stars in the Orion Nebula Cluster. In: Astrophysical Journal, Supplement Series. 2005 ; Vol. 160, No. 2. pp. 557-581.
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abstract = "The X-ray properties of twenty ∼1 Myr old O, B, and A stars of the Orion Trapezium are examined with data from the Chandra Orion Ultradeep Project (COUP). On the basis of simple theories for X-ray emission, we define two classes separated at spectral type B4: hotter stars have strong winds that may give rise to X-ray emission in small- or large-scale wind shocks, and cooler stars that should be X-ray dark due to their weaker winds and absence of outer convection zones where dynamos can generate magnetic fields. Emission by late-type magnetically active companions may be present in either class. Sixteen of the 20 stars are detected with a wide range of X-ray luminosities, log L X (ergs s -1) ∼ 29-33, and X-ray efficiencies, log (L X/L bol) ∼ -4 to -8. Only two stars, θ 1 Ori D (B0.5) and NU Ori (B1), show exclusively the constant soft-spectrum emission at log(L X/L bol) ∼ -7 expected from the standard model involving many small shocks in an unmagnetized radiatively accelerated wind. Most of the other massive O7-B3 stars exhibit some combination of soft-spectrum wind emission, hard-spectrum flaring, and/or rotational modulation indicating large-scale inhomogeneity. Magnetic confinement of winds with large-scale shocks can be invoked to explain these phenomena. This is supported in some cases by nonthermal radio emission and/or chemical peculiarities, or direct detection of the magnetic field (θ 1 Ori C). Most of the stars in the weak-wind class exhibit X-ray flares and log L X < 31 ergs s -1, consistent with magnetic activity from known or unseen low-mass companions. In most cases, the X-ray spectra can be interpreted in terms of a two-temperature plasma model with a soft component of 3-10 MK and a hard component up to 40 MK. All nondetections belong to the weak-wind class. A group of stars exhibit hybrid properties - flarelike behavior superimposed on a constant component with log L X ∼ 32 ergs s -1 - which suggest both magnetic activity and wind emission.",
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Stelzer, B, Flaccomio, E, Montmerle, T, Micela, G, Sciortino, S, Favata, F, Preibisch, T & Feigelson, ED 2005, 'X-ray emission from early-type stars in the Orion Nebula Cluster', Astrophysical Journal, Supplement Series, vol. 160, no. 2, pp. 557-581. https://doi.org/10.1086/432375

X-ray emission from early-type stars in the Orion Nebula Cluster. / Stelzer, B.; Flaccomio, E.; Montmerle, T.; Micela, G.; Sciortino, S.; Favata, F.; Preibisch, T.; Feigelson, E. D.

In: Astrophysical Journal, Supplement Series, Vol. 160, No. 2, 01.10.2005, p. 557-581.

Research output: Contribution to journalArticle

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T1 - X-ray emission from early-type stars in the Orion Nebula Cluster

AU - Stelzer, B.

AU - Flaccomio, E.

AU - Montmerle, T.

AU - Micela, G.

AU - Sciortino, S.

AU - Favata, F.

AU - Preibisch, T.

AU - Feigelson, E. D.

PY - 2005/10/1

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N2 - The X-ray properties of twenty ∼1 Myr old O, B, and A stars of the Orion Trapezium are examined with data from the Chandra Orion Ultradeep Project (COUP). On the basis of simple theories for X-ray emission, we define two classes separated at spectral type B4: hotter stars have strong winds that may give rise to X-ray emission in small- or large-scale wind shocks, and cooler stars that should be X-ray dark due to their weaker winds and absence of outer convection zones where dynamos can generate magnetic fields. Emission by late-type magnetically active companions may be present in either class. Sixteen of the 20 stars are detected with a wide range of X-ray luminosities, log L X (ergs s -1) ∼ 29-33, and X-ray efficiencies, log (L X/L bol) ∼ -4 to -8. Only two stars, θ 1 Ori D (B0.5) and NU Ori (B1), show exclusively the constant soft-spectrum emission at log(L X/L bol) ∼ -7 expected from the standard model involving many small shocks in an unmagnetized radiatively accelerated wind. Most of the other massive O7-B3 stars exhibit some combination of soft-spectrum wind emission, hard-spectrum flaring, and/or rotational modulation indicating large-scale inhomogeneity. Magnetic confinement of winds with large-scale shocks can be invoked to explain these phenomena. This is supported in some cases by nonthermal radio emission and/or chemical peculiarities, or direct detection of the magnetic field (θ 1 Ori C). Most of the stars in the weak-wind class exhibit X-ray flares and log L X < 31 ergs s -1, consistent with magnetic activity from known or unseen low-mass companions. In most cases, the X-ray spectra can be interpreted in terms of a two-temperature plasma model with a soft component of 3-10 MK and a hard component up to 40 MK. All nondetections belong to the weak-wind class. A group of stars exhibit hybrid properties - flarelike behavior superimposed on a constant component with log L X ∼ 32 ergs s -1 - which suggest both magnetic activity and wind emission.

AB - The X-ray properties of twenty ∼1 Myr old O, B, and A stars of the Orion Trapezium are examined with data from the Chandra Orion Ultradeep Project (COUP). On the basis of simple theories for X-ray emission, we define two classes separated at spectral type B4: hotter stars have strong winds that may give rise to X-ray emission in small- or large-scale wind shocks, and cooler stars that should be X-ray dark due to their weaker winds and absence of outer convection zones where dynamos can generate magnetic fields. Emission by late-type magnetically active companions may be present in either class. Sixteen of the 20 stars are detected with a wide range of X-ray luminosities, log L X (ergs s -1) ∼ 29-33, and X-ray efficiencies, log (L X/L bol) ∼ -4 to -8. Only two stars, θ 1 Ori D (B0.5) and NU Ori (B1), show exclusively the constant soft-spectrum emission at log(L X/L bol) ∼ -7 expected from the standard model involving many small shocks in an unmagnetized radiatively accelerated wind. Most of the other massive O7-B3 stars exhibit some combination of soft-spectrum wind emission, hard-spectrum flaring, and/or rotational modulation indicating large-scale inhomogeneity. Magnetic confinement of winds with large-scale shocks can be invoked to explain these phenomena. This is supported in some cases by nonthermal radio emission and/or chemical peculiarities, or direct detection of the magnetic field (θ 1 Ori C). Most of the stars in the weak-wind class exhibit X-ray flares and log L X < 31 ergs s -1, consistent with magnetic activity from known or unseen low-mass companions. In most cases, the X-ray spectra can be interpreted in terms of a two-temperature plasma model with a soft component of 3-10 MK and a hard component up to 40 MK. All nondetections belong to the weak-wind class. A group of stars exhibit hybrid properties - flarelike behavior superimposed on a constant component with log L X ∼ 32 ergs s -1 - which suggest both magnetic activity and wind emission.

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Stelzer B, Flaccomio E, Montmerle T, Micela G, Sciortino S, Favata F et al. X-ray emission from early-type stars in the Orion Nebula Cluster. Astrophysical Journal, Supplement Series. 2005 Oct 1;160(2):557-581. https://doi.org/10.1086/432375