Molecular emission from GG Carinae’s circumbinary disk

Abstract

Context. The appearance of the B[e] phenomenon in evolved massive stars such as B [e] supergiants is still a mystery. While these stars are generally found to have disks that are cool and dense enough for efficient molecule and dust condensation, the origin of the disk material is still unclear. Aims. We aim at studying the kinematics and origin of the disk in the eccentric binary system GG Car, whose primary component is proposed to be a B[e] supergiant. Methods. Based on medium-and high-resolution near-infrared spectra we analyzed the CO-band emission detected from GG Car. The complete CO-band structure delivers information on the density and temperature of the emitting region, and the detectable 13 CO bands allow us to constrain the evolutionary phase. In addition, the kinematics of the CO gas can be extracted from the shape of the first 12 CO band head. Results. We find that the CO gas is located in a ring surrounding the eccentric binary system, and its kinematics agrees with Keplerian rotation with a velocity, projected to the line of sight, of 80 ± 1 km s −1 . The CO ring has a column density of (5 ± 3) × 10 21 cm −2 and a temperature of 3200 ± 500 K. In addition, the material is chemically enriched in 13 C, which agrees with the primary component being slightly evolved off the main sequence. We discuss two possible scenarios for the origin of the circumbinary disk: (i) nonconservative Roche lobe overflow; and (ii) the possibility that the progenitor of the primary component could have been a classical Be star. Neither can be firmly excluded, but for Roche lobe overflow to occur, a combination of stellar and orbital parameter extrema would be required.

Probing the ejecta of evolved massive stars in transition

“…From the investigation by Kraus (2009), it is clear that pre-main sequence levels of 13 C should not produce visible molecular band head emission. We therefore conclude that each of the objects in this study with detected CO emission is in fact an evolved, post-main sequence Kraus et al (2013) . object. This point is especially poignant in the case of MWC 137 which has been frequently cited as a possible Herbig B[e] star (Hillenbrand et al 1992).…”

“…Since several of the objects with CO emission appeared rotationally broadened (beyond the SINFONI velocity resolution of 60 km s −1 ), but with significant 13 CO emission, we used the codes of Kraus et al (2000Kraus et al ( , 2009 as the base for a hybrid model that computes both the 12 CO and 13 CO emission spectra assuming that the emitting material is located in a thin, rotating ring within the circumstellar environment. The assumption that the material is located in a relatively narrow ring around the star with constant temperature, column density, and rotational velocity is supported by both theory (see e.g., Kraus 2009) and observations (see e.g., Kraus et al 2000Kraus et al , 2013Liermann et al 2010). It may be possible that the material is distributed in a much different configuration, such as a shell or bipolar LBV type ejecta.…”

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

“…of the molecular disk (Kraus et al , 2013bKraus 2009;Liermann et al 2010;Cidale et al 2012;Muratore et al 2015). In addition, the involved column densities in these rings are high, justifying the LTE assumption.…”

“…Investigations of the kinematics within the gaseous (atomic and molecular) disk regions often revealed that it is consistent with Keplerian rotation (Millour et al 2011;Aret et al 2012;Cidale et al 2012;Wheelwright et al 2012b;Kraus et al 2010Kraus et al , 2013bKraus et al , 2014Kraus et al , 2015bMuratore et al 2015). In some cases, observations support evidence of disk variability as seen in LHA 115-S 18 (Torres et al 2012) and HD 327083 (Kraus et al 2013a), sudden disk formation as in LHA 115-S 65 (Oksala et al 2012), and disk dissipation as in CI Cam (Liermann et al 2014).…”

The circumstellar environment and evolutionary state of the supergiant B[e] star Wd1-9

“…4) have been resolved interferometrically around the sgB[e] stars HD327083 (Wheelwright et al 2012) and MWC300 (Wang et al 2012), with the former of considerable interest since it comprises a binary within the torus. Although less massive and with larger orbital separation than expected for Wd1-9, GG Car and VFTS 698 are both spectroscopic sgB[e] binaries (Gosset et al 1985;Dunstall et al 2012), with the former associated with a circumbinary molecular disc/torus (Kraus et al 2013). While not formally classified as a sgB[e] star, HDE 326823 is a likely ∼6.123 day binary (Richardson et al 2011), comprising a proto-WN8 primary (Marcolino et al 2007) and a more massive secondary hidden by an accretion disc, with both stars in turn surrounded by a circumbinary disc with a dusty component (Ardila et al 2010).…”