Optical spectroscopic variability of Herbig Ae/Be stars

Abstract

Aims. In order to gain insights into the variability behaviour of the circumstellar (CS) atomic gas, we have analysed 337 multi-epoch optical spectra of 38 Herbig Ae/Be (HAeBe) stars. Methods. Equivalent widths (EWs) and line fluxes of the Hα, [O i]6300, He i5876 and Na iD lines were obtained for each spectrum; the Hα line width at 10% of peak intensity (W 10 ) and profile shapes were also measured and classified. The mean line strengths and relative variabilities were quantified for each star. Simultaneous optical photometry was used to estimate the line fluxes.Results. We present a homogeneous spectroscopic database of HAeBe stars. The lines are variable in practically all stars and timescales, although 30% of the objects show a constant EW in [O i]6300, which is also the only line that shows no variability on timescales of hours. The He i5876 and Na iD EW relative variabilities are typically the largest, followed by those in [O i]6300 and Hα. The EW changes can be larger than one order of magnitude for the He i5876 line, and up to a factor 4 for Hα. The [O i]6300 and Hα EW relative variabilities are correlated for most stars in the sample. The Hα mean EW and W 10 are uncorrelated, as are their relative variabilities. The Hα profile changes in ∼70% of the objects. The massive stars in the sample (M * > 3 M ) usually show more stable Hα profiles with blueshifted self-absorptions and less variable 10% widths. Conclusions. Our data suggest multiple causes for the different line variations, but the [O i]6300 and Hα variability must share a similar origin in many objects. The physical mechanism responsible for the Hα line broadening does not depend on the amount of emission; unlike in lower-mass stars, physical properties based on the Hα luminosity and W 10 would significantly differ. Our results provide additional support to previous works that reported different physical mechanisms in Herbig Ae and Herbig Be stars. The multi-epoch observations we present are a useful tool for understanding the origin of the CS lines and their variability, and to establish distinctions in the physical processes operating in pre-main sequence stars.

POISSON project

“…has been observed in several young objects: variations affect in particular the line profiles, but the line flux changes at maximum by a factor of a few, which is much less than variations observed on longer timescales (e.g. Scholz et al 2005;Stelzer et al 2007;Mendigutía et al 2011). Apart from this limitation, the accretion luminosities derived from the five tracers should therefore be consistent with each other.…”

Hydrogen lines as a diagnostic tool for studying multicomponent emitting regions in hot young stars: magnetosphere, X-wind, and disk wind

“…All kinds of shapes from the classification by Reipurth et al are observed: P Cygni, single-and doublepeaked (see, e.g., Böhm & Catala 1995;Grinin et al 2001;Mora et al 2001;Feigelson et al 2003;Beskrovnaya & Pogodin 2004;Movsessian et al 2008;Grady et al 2011;Montesinos 2009;Mendigutía 2012). Such a vast sample of profile shapes suggests that this line originates in a very complex environment possibly including the accretion disk, disk wind, jet, and magnetosphere.…”

Probing the wind-launching regions of the Herbig Be star HD 58647 with high spectral resolution interferometry

“…There are at least three possible types of outflows around young stellar objects: (1) a disc wind launched from the accretion disc (e.g. Blandford & Payne 1982;Ustyugova et al 1995;Romanova et al 1997;Ouyed & Pudritz 1997; Ustyugova Grady et al (1996), h Mendigutía et al (2011), i van Leeuwen (2007), j Perryman et al (1997), k Cutri et al (2003).…”