Ammonia observations in the LBV nebula G79.29+0.46

Abstract

Context. The surroundings of luminous blue variable (LBV) stars are excellent laboratories to study the effects of their high UV radiation, powerful winds, and strong ejection events onto the surrounding gas and dust. Aims. We aim at determining the physical parameters of the dense gas near G79.29+0.46, an LBV-candidate located at the centre of two concentric infrared rings, which may interact with the infrared dark cloud (IRDC) G79.3+0.3. Methods. The Effelsberg 100 m telescope was used to observe the NH 3 (1, 1) and (2, 2) emission in a field of view of 7 × 7 including the infrared rings and a part of the IRDC. In addition, we observed particular positions in the NH 3 (3,3) transition toward the strongest region of the IRDC, which is also closest to the ring nebula. Results. We report here the first coherent ring-like structure of dense NH 3 gas associated with an evolved massive star. It is well traced in both ammonia lines, surrounding an already known infrared ring nebula; its column density is two orders of magnitude lower than the IRDC. The NH 3 emission in the IRDC is characterized by a low and uniform rotational temperature (T rot ∼10 K) and moderately high opacities in the (1, 1) line. The rest of the observed field is spotted by warm or hot zones (T rot >30 K) and characterized by optically thin emission of the (1, 1) line. The NH 3 abundances are about 10 −8 in the IRDC, and 10 −10 -10 −9 elsewhere. The warm temperatures and low abundances of NH 3 in the ring suggest that the gas is being heated and photo-dissociated by the intense UV field of the LBV star. An outstanding region is found to the south-west (SW) of the LBV star within the IRDC. The NH 3 (3, 3) emission at the centre of the SW region reveals two velocity components tracing gas at temperatures >30 K. Of particular interest is the northern edge of the SW region, which coincides with the border of the ring nebula and a region of strong 6 cm continuum emission; here, the opacity of the (1, 1) line and the NH 3 abundance do not decrease as expected in a typical clump of an isolated cold dark cloud. This strongly suggests some kind of interaction between the ring nebula (powered by the LBV star) and the IRDC. We finally discuss the possibility of NH 3 evaporation from the dust grain mantles due to the already known presence of low-velocity shocks in the area. Conclusions. The detection of the NH 3 associated with this LBV ring nebula, as well as the special characteristics of the northern border of the SW region, confirm that the surroundings of G79.29+0.46 constitute an exemplary scenario, which merits to be studied in detail by other molecular tracers and higher angular resolutions.

NIKA2 observations around LBV stars Emission from stars and circumstellar material

“…It is noteworthy the layered structure seen around the (100", −20") position, where it is clearly noted the bubble in blue, the shell affected by a mass-loss process in red and the unaffected IRDC in red. The lowest values of α are consistent with non-thermal emission probably produced by the shocks already discovered [9,10]. On the other hand, most of the IRDC (related to DR15) depicts values of α compatible with a cold cloud [28].…”

“…Important efforts have been made in the study of the molecular structures around LBVs. The best studied object is probably G79.29+0.46, where we discovered a number of concentric, shocked shells associated with mass-loss events developed in the last 10 3 − 10 4 yr [7][8][9][10]. In MGE042.0787+00.5084 (hereafter MGE042), we also found a molecular torus in slow expansion, with similar dynamical ages [11].…”

“…The G79.29+0.46 field is dominated by bright and intense emission running from southeast to west. This emission corresponds to an infrared dark cloud (IRDC) linked to DR15, which is known to host active star formation [21], probably induced by the close LBV [9,10]. The star is detected at both bands, more clearly at 2mm.…”

A High-Resolution Study of Near-Infrared Diffuse Interstellar Bands

“…StRS 368 is also identified with G79.29+0.46, a Luminous Blue Variable (LBV) candidate. This star exhibits local nebulosity seen in both the radio and mid-IR that has been attributed to circumstellar material ejected during earlier phases of greater LBV activity (Rizzo et al 2014, Umana et al 2011). This circumstellar material may be responsible for some fraction of the extinction seen toward this object, although the angular size of the nebulosity suggests it is unlikely to be responsible for ∼ 8 m of additional extinction, the approximate horizontal displacement of this object from the general trend in Figure 4.…”

The Young Stellar Population of the Cygnus-X Dr15 Region

“…Recently, the western segment of the IRDC, has been shown to host a young stellar cluster in interaction with the Luminous Blue Variable (LBV) source G79.29+0.46 (Rizzo et al 2008;Jiménez-Esteban et al 2010). Distance to G79.29+0.46 has been also estimated to be 1.4 kpc (Rizzo et al 2014;Palau et al 2014).…”