A spectroscopic survey of Herbig Ae/Be stars with X-Shooter – II. Accretion diagnostic lines

Abstract

The Herbig Ae/Be stars (HAeBes) allow an exploration of the properties of PreMain Sequence(PMS) stars above the low-mass range (< 2 M ⊙ ) and those bordering the high-mass range (> 8 M ⊙ ). This paper is the second in a series exploring accretion in 91 HAeBes with Very Large Telescope/X-shooter spectra. Equivalent width measurements are carried out on 32 different lines, spanning the UV to NIR, in order to obtain their line luminosities. The line luminosities were compared to accretion luminosities, which were determined directly from measurements of an UV-excess. When detected, emission lines always demonstrate a correlation with the accretion luminosity, regardless of detection frequency. The average relationship between accretion luminosity and line luminosity is found to be L acc ∝ L line 1.16±0.15 . This is in agreement with the findings in Classical T Tauri stars, although the HAeBe relationship is generally steeper, particularly towards the Herbig Be mass range. Since all observed lines display a correlation with the accretion luminosity, all of them can be used as accretion tracers. This has increased the number of accretion diagnostic lines in HAeBes tenfold. However, questions still remain on the physical origin of each line, which may not be due to accretion.

Spiral Arms in Disks: Planets or Gravitational Instability?

“…To address this challenge, several groups have calibrated the veiling of the Balmer jump against various emission-line diagnostics for stars with the greatest ultraviolet contrast. In an X-Shooter survey of 91 Herbig Ae/Be stars, Fairlamb et al (2015Fairlamb et al ( , 2017 have calibrated the luminosity of 32 emission lines against the accretion luminosity as inferred from the veiling of the Balmer jump.…”

“…The equivalent widths of the photospheric features were taken from Fairlamb et al (2017) when available. For stars not included in their study, stars with matching temperatures and gravities were used to infer the photospheric equivalent width.…”

Variability of Disk Emission in Pre-main-sequence and Related Stars. IV. Investigating the Structural Changes in the Inner Disk Region of MWC 480

“…These were converted to line luminosities using a distance of 142 pc. The line luminosities were transformed to mass accretion luminosities using the calibrations of Fairlamb et al (2017) for Paβ and Brγ, respectively. These were then converted to mass accretion rates usinġ M=L acc R * /GM * , with adopted values of R * =1.96 R e , and the stellar mass M * =2.15 M e .…”

“…These were then converted to mass accretion rates usinġ M=L acc R * /GM * , with adopted values of R * =1.96 R e , and the stellar mass M * =2.15 M e . While there are many different calibrations of the mass accretion rates based on these line, we selected that of Fairlamb et al (2017), as it was derived specifically for Herbig AeBe stars and has among the smallest calibration uncertainties in the literature. The mass accretion rates for MWC 480 were time-dependent, being (1.4-2.01)× 10 −7 M e yr −1 and (1.26-2.30)×10 −7 M e yr −1 derived from Brγ and Paβ lines, respectively (see Table 3).…”

“…a The line luminosities are based on a distance of 142 pc. The conversion of line luminosities to accretion luminosities uses the relationships derived by Fairlamb et al (2017) for Pa β and Br γ. These are derived for lower accretion rates and may suffer from systematic uncertainties.…”