Molecular gas toward G18.8+1.8

Abstract

Aims. This work aims at investigating the characteristics of the molecular gas associated with the nebula G18.8+1.8, which is linked to the Wolf-Rayet star HD 168206 (WR 113), and its relation to other components of its local interstellar medium. Methods. We carried out molecular observations of the 12 CO(J = 1−0) and (J = 2−1) lines with an angular resolution of 44 and 22 using the SEST telescope. Complementary NANTEN data of the 12 CO(1−0) line were also used. The dust emission was analyzed using Spitzer-IRAC images at 8.0 μm, and WISE data at 3.4 μm, 4.6 μm, and 12.0 μm. Results. The SEST data allowed us to identify a molecular component (Cloud 3) that has velocities in the interval from ∼+30 to +36 km s −1 and is most probably linked to the nebula. Morphological and kinematical properties suggest that Cloud 3 consists of a wind-blown molecular half-shell, which expands around WR 113. The ratio R 2−1/1−0 and excitation temperatures indicate that the molecular gas is being irradiated by strong UV radiation. The location of the inner optical ring in the outer edge of Cloud 3 suggests that the stars SerOB2-1, -2, -3, -63, and -64 are responsables for the ionization of Cloud 3 and the inner ring nebula. A comparison between the spatial distribution of the molecular gas and the PAH emission at 8 μm indicates the existence of a photodissociation region between the ionized and the molecular gas. A search for candidate young stellar objects (YSOs) in the region around G18.8+1.8 based on available 2MASS, MSX, IRAS, and Spitzer-IRAC catalogs resulted in the detection of about sixty sources, some of them projected onto Cloud 3. Two small spots of clustered candidate YSOs are projected near the outer border of Cloud 3, although a triggered stellar formation scenario is doubtful.

870μm continuum observations of the bubble-shaped nebula Gum 31

“…Dense molecular condensations (or clumps) lying at the border of Galactic Hii regions are therefore among the most likely sites for stellar births, and hence, where to look for early stages of star formation (e.g. Cappa et al 2009;Vasquez et al 2012;Deharveng et al 2012;Duronea et al 2014). In recent years, the triggered star formation process, especially the C&C mechanism, has been studied extensively at the edges of many bubble-shaped Hii regions such as RCW 79,RCW 120, The LABOCA map (data corresponding to Fig.…”

“…Dense molecular condensations (or clumps) lying at the border of Galactic Hii regions are then among the most likely sites for stellar births, and hence, to look for early stages of star formation (e.g. Cappa et al 2009;Vasquez et al 2012;Deharveng et al 2012;Duronea et al 2014). In recent years, the triggered star formation process, especially the C&C mechanism, has been studied extensively on the edges of many bubble-shaped Hii regions such as Sh2-104, RCW 79, Sh2-212, RCW 120, Sh2-217, Sh2-90 (Deharveng et al 2003, 2008Zavagno et al 2006Zavagno et al , 2010Brand et al 2011;Samal et al 2014), as well as in several surveys (e.g Thompson et al 2012;Simpson et al 2012) Gum 31 is one of the many southern Galactic Hii regions that appear as a ring at infrared (IR) wavelengths (see the upper panel of Fig.…”

Molecules, dust, and protostars in NGC 3503

“…Therefore, when massive stars form inside a molecular cloud it is expected that they dominate the state of the parental cloud and consequently the stellar formation process within. It has been shown that a large fraction of stars originate at the peripheries of Hii regions (Pomarès et al 2009;Cappa et al 2009;Deharveng et al 2010Deharveng et al , 2012Vasquez et al 2012). Tables 5 and 6 are available in electronic form at http://www.aanda.org…”

“…Therefore, when massive stars form inside a molecular cloud it is expected that they dominate the state of the parental cloud and consequently the further stellar formation process within. Indeed, it has been shown that a large fraction of stars originates at the peripheries of Hii regions (Pomarès et al 2009;Romero & Cappa 2009;Cappa et al 2009;Deharveng et al 2010;Vasquez et al 2012;Deharveng et al 2012). Having this in mind, it is instructive to study the molecular gas adjacent to Hii regions since it can provide important information on the interaction between massive stars and their natal environments.…”

Estudio multiespectral de nebulosas anillo alrededor de estrellas Wolf-Rayet

“…Concluyeron que la nebulosa está en una etapa intermedia entre las fases de conservación de la energía y de conservación de momento. Los resultados fueron reunidos en el trabajo Vasquez et al (2008).…”