X‐Ray Study of Herbig Ae/Be Stars

Hamaguchi, Kenji; Yamauchi, Shigeo; Koyama, K.

doi:10.1086/423192

Cited by 93 publications

(142 citation statements)

References 69 publications

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“…These data were presented previously by Hamaguchi et al (2000Hamaguchi et al ( , 2005. Here we only discuss the ∼6 h observing sequence 21007010, during which the decay phase of an X-ray flare was observed.…”

Section: Coronographic Adaptive Opticsmentioning

confidence: 69%

On the origin of the X-ray emission towards the early Herbig Be star MWC 297

Drew²

2005

A&A

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Abstract. We present high resolution ( 0.2 ) AO-corrected coronographic near-infrared imaging on the early-type Herbig Be star MWC 297. X-ray flaring has been reported towards this young object, however this has been difficult to reconcile with its early spectral type (B1.5) and relatively high mass (∼10 M ). Our infrared and X-ray analysis shows that the X-ray flaring is likely due to a late-type star in the same field. The case of MWC 297 emphasizes the need for coronographic imaging to address the reality of X-ray emission towards Herbig Ae/Be stars, which is needed to understand the differences between low and high-mass star formation.

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Section: Coronographic Adaptive Opticsmentioning

confidence: 69%

On the origin of the X-ray emission towards the early Herbig Be star MWC 297

Drew²

2005

A&A

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“…Siebenmorgen et al (1998) reported the presence of a large circumstellar elliptical ring of PAH emission with thousands of AU in diameter and an indication for the possible existence of a candidate companion. It was also detected as an X-ray source in ROSAT and Chandra observations (Hamaguchi et al 2005;Stelzer et al 2006) HD 139614: Our previous measurements of HD 139614 revealed the presence of a weak magnetic field in the range from −116 G to −450 G. (Hubrig et al 2004b;. The current diagnosis of magnetic fields in this star yielded no detection at a 3σ level, neither in Balmer nor in metal lines, with error bars as low as 25 G. In analogy with our previous detections, the measured magnetic field is of negative polarity and Ca ii H&K lines in HD 139614 show distinct Zeeman features.…”

Section: Stars With Measurements Suggestivementioning

confidence: 96%

Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars and stars with debris disks

Hubrig

Stelzer

Schöller

et al. 2009

A&A

101

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Context. Recently, evidence for the presence of weak magnetic fields in Herbig Ae/Be stars has been found in several studies. Aims. We seek to expand the sample of intermediate-mass pre-main sequence stars with circular polarization data to measure their magnetic fields, and to determine whether magnetic field properties in these stars are correlated with mass-accretion rate, disk inclination, companions, silicates, PAHs, or show a correlation with age and X-ray emission as expected for the decay of a remnant dynamo. Methods. Spectropolarimetric observations of 21 Herbig Ae/Be stars and six debris disk stars have been obtained at the European Southern Observatory with FORS 1 mounted on the 8 m Kueyen telescope of the VLT. With the GRISM 600B in the wavelength range 3250-6215 Å we were able to cover all hydrogen Balmer lines from Hβ to the Balmer jump. In all observations a slit width of 0. 4 was used to obtain a spectral resolving power of R ≈ 2000. Results. Among the 21 Herbig Ae/Be stars studied, new detections of a magnetic field were achieved in six stars. For three Herbig Ae/Be stars, we confirm previous magnetic field detections. The largest longitudinal magnetic field, B z = −454 ± 42 G, was detected in the Herbig Ae/Be star HD 101412 using hydrogen lines. No field detection at a significance level of 3σ was achieved in stars with debris disks. Our study does not indicate any correlation of the strength of the longitudinal magnetic field with disk orientation, disk geometry, or the presence of a companion. We also do not see any simple dependence on the mass-accretion rate. However, it is likely that the range of observed field values qualitatively supports the expectations from magnetospheric accretion models giving support for dipole-like field geometries. Both the magnetic field strength and the X-ray emission show hints of a decline with age in the range of ∼2-14 Myr probed by our sample, supporting a dynamo mechanism that decays with age. However, our study of rotation does not show any obvious trend of the strength of the longitudinal magnetic field with rotation period. Furthermore, the stars seem to obey the universal power-law relation between magnetic flux and X-ray luminosity established for the Sun and main-sequence active dwarf stars.

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“…Damiani et al 1994;Zinnecker & Preibisch 1994;Hamaguchi et al 2005;Stelzer et al 2009). Then, to further restrict the range of masses, and that of absorptions, we excluded stars with I c > 16, corresponding to M > 0.1−0.2 M for COUP sources with low optical absorption 4 (A V < 2.0).…”

Section: Sample Definitions and Selection Criteriamentioning

confidence: 99%

X-ray variability of pre-main-sequence stars

Flaccomio

Micela

Sciortino

2012

A&A

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Context. The first million years of the pre-main-sequence (PMS) evolution of low-mass stars are characterized by magnetospheric accretion, a circumstellar proto-planetary disk, and the processes leading to its dispersal. Among these, photo-evaporation caused by strong X-ray emission from the central star is probably significant. Several aspects of the X-ray emission from coronae and accretion shocks remain mysterious, e.g., whether and how much accretion affects coronal emission. Aims. We studied the X-ray variability of ∼1 Myr old low-mass PMS stars as a function of timescale, stellar rotation, and stellar characteristics to gain insights into the working of PMS coronae, their X-ray emission, and the circumstellar environment in which they are immersed. Methods. We have exploited the ∼850 ks long Chandra observation of the Orion Nebula Cluster obtained by the COUP collaboration in January 2003, and statistically analyzed the X-ray lightcurves of low-mass stars in several subsamples. Our main focus was to characterize the different X-ray behavior of stars with and without circumstellar accretion disks, and to infer the physical mechanism responsible for the observed variability. Results. Accreting stars (classical T Tauri stars, CTTSs) are found to be more variable than non-accreting stars (weak-line T Tauri stars, WTTSs) at all timescales and in all X-ray energy bands considered. Variability is seen to increase with timescale, up to the longest probed, ∼10 days. Signatures of rotational modulation are observed for both CTTSs and WTTSs, and most clearly for CTTSs in the soft X-ray band. Lower mass stars are more variable than higher mass stars. Conclusions. We propose that the difference in variability between CTTSs and WTTSs may be explained assuming that the X-ray emission of CTTS is affected by time-variable absorption due to circumstellar structures, such as warps in the inner disk and/or accretion streams. This suggestion is appealing because, in the hypothesis that the coronae of CTTSs and WTTSs are similar, it may also explain why CTTSs have lower and more scattered X-ray emission levels compared to WTTSs.

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X‐Ray Study of Herbig Ae/Be Stars

Cited by 93 publications

References 69 publications

On the origin of the X-ray emission towards the early Herbig Be star MWC 297

On the origin of the X-ray emission towards the early Herbig Be star MWC 297

Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars and stars with debris disks

X-ray variability of pre-main-sequence stars

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