The characteristics of the IR emission features in the spectra of Herbig Ae stars: evidence for chemical evolution

Boersma, C.; Bouwman, J.; Lahuis, F.; Kerckhoven, C. van; Tielens, A. G. G. M.; Waters, L. B. F. M.; Henning, Thomas

doi:10.1051/0004-6361:20078001

Cited by 51 publications

(59 citation statements)

References 35 publications

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“…Silicates and PAHs are seen in the mid-IR (e.g. Boersma et al 2008). Eisner et al (2004) showed that interferometric visibilities are consistent with a disk close to face-on, although a significant nonzero inclination cannot be ruled out.…”

Section: Herbig Ae/be Stars With Detected Magnetic Fieldsmentioning

confidence: 99%

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

100

149

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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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Section: Herbig Ae/be Stars With Detected Magnetic Fieldsmentioning

confidence: 99%

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

100

149

View full text Add to dashboard Cite

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“…Tielens (2008) pointed out that this relationship can also be interpreted as a step function instead of a continuous dependence. In this respect, the deviation from class A seems to be connected to the presence of circumstellar material Boersma et al 2008). However, the underlying cause of these variations in the 11.2 μm band is not well understood (see e.g., van Diedenhoven et al 2004).…”

Section: Pahmentioning

confidence: 99%

Mid-IR observations of circumstellar disks

Schuetz¹,

Meeus

Sterzik³

et al. 2009

A&A

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We present new mid-infrared spectra of 15 targets (1 FU Orionis object, 4 Herbig Ae stars, 5 T Tauri stars, and 5 Vega-type stars), obtained with the TIMMI2 camera at La Silla Observatory (ESO). Three targets are members of the β Pic moving group (HD 155 555, HD 181 296, and HD 319 139). PAH bands are observed towards the T Tauri star HD 34 700 and the Herbig Ae star PDS 144 N. For HD 34 700, the band profiles indicate processed PAHs. The spectrum of the Vega-type object η Corvi (HD 109 085), for which a resolved disk at sub-mm wavelengths is known, appears stellar between 8-13 μm, but a small excess emission was reported by Spitzer observations. Similarly, no indication of circumstellar matter at mid-infrared wavelengths is found towards the Vega-like stars HD 3003, HD 80 951, HD 181 296, and, surprisingly, the T Tauri system HD 155 555. The silicate emission features of the remaining eight sources are modelled with a mixture of silicates of different grain sizes and composition. Unprocessed dust dominates FU Ori, HD 143 006, and CD-43 344. Large amorphous grains are the main dust component around HD 190 073, HD 319 139, KK Oph, and PDS 144 S. Both small grains and crystalline dust is found for the Vega-type HD 123 356, with a dominance of small amorphous grains. We show that the infrared emission of the binary HD 123 356 is dominated by its late-type secondary, but optical spectroscopy is still required to confirm the age of the system and the spectral class of the companion. For most targets, this is their first mid-infrared spectroscopic observation. We investigate trends between stellar, disk, and silicate properties and confirm correlations identified in previous studies. Several objects present an exciting potential for follow-up high-resolution disk studies.

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“…These data are part of the Spitzer program with PID 3470. Both spectra have been studied earlier by Boersma et al (2008), where the profile variations of the "7.7" μm feature were investigated. The spectrum of HD 36917 is our representative spectrum for this type of object and it is presented in Fig.…”

Section: Astronomical Spectra From 15-20 μMmentioning

confidence: 99%

The 15–20 μm PAH emission features: probes of individual PAHs?

Boersma¹,

Bauschlicher

Allamandola

et al. 2010

A&A

Self Cite

124

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Context. Spectral features between about 15−20 μm are commonly associated with polycyclic aromatic hydrocarbons (PAHs). With the NASA Spitzer Space Telescope these features are reported routinely, and as such, warrant a deeper molecular explanation. Aims. We aim to determine the characteristics of the group of carriers of the plateau and the distinct sub-features at 15.8, 16.4, 17.4, 17.8 and 18.9 μm and to draw astronomical implications from these spectra. Methods. We analyse and interpret the spectra of 15 different sources using the NASA Ames PAH IR spectroscopic database. Results. The bands within the 15−20 μm region show large variations. Except for the 16.4 μm band, there is also no connection, both in band strength and feature classification, with the mid-IR PAH bands. Of the PAH spectra considered, only those from species containing pendent rings show one "common" characteristic: a band near the astronomical 16.4 μm position. However, coupling with the carbon skeleton's core influences its precise position in the spectrum. Compact PAHs in the size range 50−130 carbon atoms, consistently show a strong band near the astronomical 17.4 μm band position. Conclusions. The 15−20 μm region is the transition zone from PAH nearest neighbour modes to full-skeleton modes. We conclude that a few individual PAHs dominate the astronomical PAH family when clear features are prominent. In the few cases of a broad plateau, the PAH family would be far richer. Although PAHs containing pendent rings showed promise explaining the astronomical 16.4 μm band, coupling with the skeleton core and the inherent strong quartet mode expected around 13.5 μm, make it a less viable candidate. The number of large PAHs in the database becomes a limitation in studying the emission between 15−20 μm and longward. Computation of larger PAH spectra should therefore be stimulated, especially for understanding the forthcoming far-IR data expected from Herschel, SOFIA and ALMA.

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The characteristics of the IR emission features in the spectra of Herbig Ae stars: evidence for chemical evolution

Cited by 51 publications

References 35 publications

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

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

Mid-IR observations of circumstellar disks

The 15–20 μm PAH emission features: probes of individual PAHs?

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