C.D.S. - SIMBAD4 rel 1.7 - 2020.07.08CEST15:59:09

2007A&A...468..541T - Astronomy and Astrophysics, volume 468, 541-556 (2007/6-3)

The first high-resolution X-ray spectrum of a Herbig star: AB Aurigae.


Abstract (from CDS):

The X-ray emission from Herbig Ae/Be stars remains to be explained. In later-type T Tauri stars, X-rays are thought to be produced by magnetically trapped coronal plasma, although accretion-shock induced X-rays have also been suggested. In earlier-type (OB) stars, shocks in unstable winds are thought to produce X-rays. We present the first high-resolution X-ray spectrum of a prototypical Herbig star AB Aurigae), measure and interpret various spectral features, and compare our results with model predictions. We use X-ray spectroscopy data from the XMM-Newton Reflection Grating Spectrometers and the EPIC instruments. The spectra are interpreted using thermal, optically thin emission models with variable element abundances and a photoelectric absorption component. We interpret line flux ratios in the He-like triplet of Ovii as a function of electron density and the UV radiation field. We use the nearby co-eval classical T Tauri star SU Aur as a comparison. AB Aurigae reveals a soft X-ray spectrum, most plasma being concentrated at 1-6MK. The He-like triplet reveals no signs of increased densities as reported for some accreting T Tau stars in the literature. There are also no clear indications of strong abundance anomalies in the emitting plasma. The light curve displays modulated variability, with a period of ≃42h. It is unlikely that a nearby, undetected lower-mass companion is the source of the X-rays. Accretion shocks close to the star would be expected to be irradiated by the photosphere, leading to alteration in the He-like triplet fluxes of Ovii, which we do not measure. Also, no indications for high densities are found, although the mass accretion rate is presently unknown. Emission from wind shocks is unlikely, given the weak radiation pressure. A possible explanation would be a solar-like magnetic corona. Magnetically confined winds are a very promising alternative. The X-ray period is indeed close to periods previously measured in optical lines from the wind.

Abstract Copyright:

Journal keyword(s): stars: coronae - stars: formation - stars: pre-main sequence - stars: magnetic fields - X-rays: stars - stars: individual: AB Aurigae

Simbad objects: 7

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Number of rows : 7

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
1 V* V892 Tau Ae* 04 18 40.6120892867 +28 19 15.641672501   16.6 14.69 14.35   A0Ve 266 0
2 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 3478 0
3 V* AB Aur Ae* 04 55 45.8459978418 +30 33 04.293281305 7.20 7.16 7.05 6.96 6.70 A0Ve 931 2
4 V* SU Aur Or* 04 55 59.3861369488 +30 34 01.499800471   10.33 9.30 9.17   G2IIIne 533 0
5 V* TW Hya TT* 11 01 51.9054298616 -34 42 17.031550898   11.94 10.50 10.626 9.18 K6Ve 1532 1
6 HD 163296 Ae* 17 56 21.2882188601 -21 57 21.872343282 7.00 6.93 6.85 6.86 6.67 A1Vep 802 0
7 EM* MWC 297 Ae* 18 27 39.5266257570 -03 49 52.136526892 15.57 14.34 12.31 11.34   B1.5Ve 266 0

    Equat.    Gal    SGal    Ecl

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