PACS and SPIRE spectroscopy of the red supergiant VY CMa

Abstract

With a luminosity >10 5 L and a mass-loss rate of ∼2 × 10 −4 M yr −1 , the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55-672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ∼1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.

Fundamental properties and atmospheric structure of the red supergiant VY Canis Majoris based on VLTI/AMBER spectro-interferometry

“…The decrease of the visibility indicates an increased contribution from extended intensity at these molecular bands. The presence of molecular layers in the extended atmospheres of red supergiants is consistent with earlier observations of red supergiants such as μ Cep and Betelgeuse (Perrin et al 2004(Perrin et al , 2005Tsuji 2006) and with the detection of warm water layers in the ISO and Herschel spectra of VY CMa (Polehampton et al 2010;Royer et al 2010).…”

“…Because of its brightness and importance, it has traditionally been extensively observed at many wavelengths. Currently, VY CMa experiences a renewed and increased interest because of observations at new facilities including, for instance, the Herschel Space Observatory (Royer et al 2010) and the submillimeter array (Fu et al 2012), as well as because of new results regarding the complexity of its molecular envelope (e.g., Ziurys et al 2007).…”

Pure rotational spectra of TiO and TiO2in VY Canis Majoris

“…As a result it is observed in regions with effective temperatures T eff < ∼ 4000 K, as well as in the cooler material just above the photosphere. TiO 2 is predicted to form in the reaction of TiO with H 2 O, which is abundant in these environments (Royer et al 2010). Owing to the lower bond dissociation energy of TiO 2 , it is predicted to be more abundant than TiO only at lower temperatures.…”

Silicon in the dust formation zone of IRC +10216

“…A description of the observing mode and of the data reduction process can be found in Royer et al (2010). The only difference with the data reduction of VY CMa as presented in Royer et al (2010) is that the ground-based calibration was used for IRC +10216. The estimated calibration uncertainty on the line fluxes is 50%.…”