LBT/LUCIFER near-infrared spectroscopy of PV Cephei

Abstract

Context. Young stellar objects (YSOs) occasionally experience enhanced accretion events, the nature of which is still poorly understood. The discovery of various embedded outbursting YSOs has recently questioned the classical definition of EXors and FUors. Aims. We present a detailed spectroscopic investigation of the young eruptive star PV Cep, to improve our understanding of its nature and characterise its circumstellar environment after its last outburst in 2004. Methods. The analysis of our medium-resolution spectroscopy in the near-infrared (NIR, 0.9-2.35 μm), collected in 2012 at the Large Binocular Telescope with the IR spectrograph LUCIFER, allows us to infer the main stellar parameters (visual extinction, accretion luminosity, mass accretion and ejection rates), and model the inner disc, jet, and wind. Results. The NIR spectrum displays several strong emission lines associated with accretion/ejection activity and circumstellar environment. Our analysis shows that the brightness of PV Cep is fading, as well as the mass accretion rate (2 × 10 −7 M yr −1 in 2012 vs. ∼5 × 10 −6 M yr −1 in 2004), which is more than one order of magnitude lower than in the outburst phase.Among the several emission lines, only the [Fe ii] intensity increased after the outburst. The observed [Fe ii] emission delineates blue-and red-shifted lobes, both with high-and low-velocity components, which trace an asymmetric jet and wind, respectively. The observed emission in the jet has a dynamical age of 7-8 years, indicating that it was produced during the last outburst. The visual extinction decreases moving from the red-shifted (A V (red) = 10.1 ± 0.7 mag) to the blue-shifted lobe (A V (blue) = 6.5 ± 0.4 mag). We measure an average electron temperature of 17 500 K and electron densities of 30 000 cm −3 and 15 000 cm −3 for the blue and the red lobe, respectively. The mass ejection rate in both lobes is ∼1.5 × 10 −7 M yr −1 , approximately matching the high accretion rate observed during and immediately after the outburst (Ṁ out /Ṁ acc ∼ 0.05-0.1). The observed jet/outflow asymmetries are consistent with an inhomogeneous medium. Our modelling of the CO emission hints at a small-scale gaseous disc ring, extending from ∼0.2-0.4 AU to ∼3 AU from the source, with an inner temperature of ∼3000 K. Our H i lines modelling indicates that most of the observed emission comes from an expanding disc wind at T e = 10 000 K. The line profiles are strongly affected by scattering, disc screening, and outflow self-absorption. Conclusions. According to the classical definition, PV Cep is not an EXor object, because it is more massive and younger than typical EXors. Nevertheless, its spectrum shows the signature of an "EXor-like" outburst, suggesting a common origin.

Radio outburst from a massive (proto)star

“…This suggests that any ejection episode might be highly asymmetric, as also discussed by other authors (e.g. Melnikov et al 2008Melnikov et al , 2009Caratti o Garatti et al 2013;Cesaroni et al 2013).…”

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

“…Because the absorption in the disk wind and the ratio R con are different for optically thick and thin hydrogen lines, the lines of different series can have different shapes or shifts. For example, in the star PV Cep (A5), the ratio R con for Brγ is higher than that for Paβ by about a factor of 7 (Caratti o Garatti et al 2013). Figure 20 illustrates a case when R con for the Brγ line is equal to R 5 (Table 3), and for the Paβ line it is seven times lower.…”

“…The gas electron temperature T e is assumed to be constant and equal to 10 000 K in all models except B5 and B6; in the latter models T e = 8000 K. The choice of the disk wind parameters is conditioned by the results of the magneto-centrifugal disk wind model for TTSs with some changes in the launching region because of the difference in the inner accretion disk structure (e.g., Natta et al 2001;Dullemond et al 2001). The range of the mass-loss values is based on the estimates of mass loss and accretion rates from the literature (e.g., Hillenbrand et al 1992;Lada & Adams 1992;Hartmann et al 1993;Tambovtseva et al 2001;Muzerolle et al 2004;Garcia Lopez et al 2006;Donehew & Brittain 2011;Klaassen et al 2013;Mendigutía et al 2013).…”

“…High atomic series lines, in particular, the Brackett series, can be used for these studies (e.g., Garcia Lopez et al 2006;Weigelt et al 2007;Kraus et al 2008;Donehew & Brittain 2010;Caratti o Garatti 2013;Lumsden et al 2012). A comparison of these lines with the Hα lines shows that the latter are often substantially wider than the infrared lines (see, e.g., Hamann & Person 1992;Reipurth et al 1996;Drew et al 1997).…”

Turbulent mixing layers in supersonic protostellar outflows, with application to DG Tauri

“…Hirth et al 1997;Woitas et al 2002;Pyo et al 2003;Coffey et al 2008;Rodríguez-González et al 2012;Caratti o Garatti et al 2013). The nature of the high-velocity jets in many sources has been studied extensively, including searches for signs of jet rotation c 0000 The Authors arXiv:1510.01394v1 [astro-ph.SR] 5 Oct 2015 (Bacciotti et al 2000;Coffey et al 2004Coffey et al , 2007White et al 2014a, hereafter Paper I), recollimation shocks (Paper I; Güdel et al 2005Güdel et al , 2008Günther et al 2009;Bonito et al 2011;Schneider et al 2013) and studies of the propagation of shock-excited moving knots (Paper I; Burrows et al 1996;Reipurth et al 2002;Pyo et al 2003;Agra-Amboage et al 2011).…”