TY - JOUR
T1 - Constraints on the surface magnetic fields and age of a cool hypergiant
T2 - XMM-Newton X-ray observations of VY CMa
AU - Montez, Rodolfo
AU - Kastner, Joel H.
AU - Humphreys, Roberta M.
AU - Turok, Rebecca L.
AU - Davidson, Kris
N1 - Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved..
PY - 2015/2/10
Y1 - 2015/2/10
N2 - The complex circumstellar ejecta of highly evolved, cool hypergiants are indicative of multiple, asymmetric mass-loss events. To explore whether such episodic, non-isotropic mass loss may be driven by surface magnetic activity, we have observed the archetypical cool hypergiant VY CMa with the XMM-Newton X-ray satellite observatory. The hypergiant itself is not detected in these observations. From the upper limit on the X-ray flux from VY CMa at the time of our observations (FX,UL ≈ 8 × 10-14 erg cm-2 s-1, corresponding to log LX/Lbol ≤ -8), we estimate an average surface magnetic field strength fB ≤ 2 × 10-3 G (where f is the filling factor of magnetically active surface regions). These X-ray results for VY CMa represent the most stringent constraints to date on the magnetic field strength near the surface of a hypergiant. VY CMa's mass loss is episodic, however, and the hypergiant may have been in a state of low surface magnetic activity during the XMM observations. The XMM observations also yield detections of more than 100 X-ray sources within ∼15′ of VY CMa, roughly 50 of which have near-infrared counterparts. Analysis of X-ray hardness ratios and IR colors indicates that some of these field sources may be young, late-type stars associated with VY CMa, its adjacent molecular cloud complex, and the young cluster NGC 2362. Further study of the VY CMa field is warranted, given the potential to ascertain the evolutionary timescale of this enigmatic, massive star.
AB - The complex circumstellar ejecta of highly evolved, cool hypergiants are indicative of multiple, asymmetric mass-loss events. To explore whether such episodic, non-isotropic mass loss may be driven by surface magnetic activity, we have observed the archetypical cool hypergiant VY CMa with the XMM-Newton X-ray satellite observatory. The hypergiant itself is not detected in these observations. From the upper limit on the X-ray flux from VY CMa at the time of our observations (FX,UL ≈ 8 × 10-14 erg cm-2 s-1, corresponding to log LX/Lbol ≤ -8), we estimate an average surface magnetic field strength fB ≤ 2 × 10-3 G (where f is the filling factor of magnetically active surface regions). These X-ray results for VY CMa represent the most stringent constraints to date on the magnetic field strength near the surface of a hypergiant. VY CMa's mass loss is episodic, however, and the hypergiant may have been in a state of low surface magnetic activity during the XMM observations. The XMM observations also yield detections of more than 100 X-ray sources within ∼15′ of VY CMa, roughly 50 of which have near-infrared counterparts. Analysis of X-ray hardness ratios and IR colors indicates that some of these field sources may be young, late-type stars associated with VY CMa, its adjacent molecular cloud complex, and the young cluster NGC 2362. Further study of the VY CMa field is warranted, given the potential to ascertain the evolutionary timescale of this enigmatic, massive star.
KW - X-rays: stars
KW - stars: early-type
KW - stars: individual (VY CMa, HD 58061)
KW - stars: magnetic field
KW - stars: pre-main sequence
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U2 - 10.1088/0004-637X/800/1/4
DO - 10.1088/0004-637X/800/1/4
M3 - Article
AN - SCOPUS:84922567079
VL - 800
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
SN - 2041-8205
IS - 1
M1 - 4
ER -