Carbon monoxide in the environs of the star WR 16

Aims. We analyze the carbon monoxide emission around the star WR 16 aiming to study the physical characteristics of the molecular gas linked to the star and to achieve a better understanding of the interaction between massive stars with their surroundings. Methods. We study the molecular gas in a region in size using CO J = 1 → 0 and 13CO J = 1 → 0 line data obtained with the 4-m NANTEN telescope. Radio continuum archival data at 4.85 GHz, obtained from the Parkes-MIT-NRAO Southern Radio Survey, are also analyzed to account for the ionized gas. Available IRAS (HIRES) 60 μm and 100 μm images are used to study the characteristics of the dust around the star. Results. Our new CO and 13CO data allow the low/intermediate density molecular gas surrounding the WR nebula to be completely mapped. We report two molecular features at-5 km s-1 and-8.5 km s-1 (components 1 and 2, respectively) having a good morphological resemblance with the Hα emission of the ring nebula. Component 2 seems to be associated with the external ring, while component 1 is placed at the interface between component 2 and the Hα emission. We also report a third molecular feature ∼10′ in size (component 3) at a velocity of-9.5 km s-1 having a good morphological correspondence with the inner optical and IR emission, although high resolution observations are recommended to confirm its existence. The stratified morphology and kinematics of the molecular gas could be associated to shock fronts and high mass-loss events related to different evolutive phases of the WR star, which have acted upon the surrounding circumstellar molecular gas. An analysis of the mass of component 1 suggests that this feature is composed of swept-up interstellar gas and is probably enriched by molecular ejecta. The direction of the proper motion of WR 16 suggests that the morphology observed at infrared, optical, radio continuum, and probably molecular emission of the inner ring nebula is induced by the stellar motion.Facultad de Ciencias Astronómicas y Geofísica

Gas molecular en la nebulosa anillo alrededor de WR 16

Using NANTEN 12CO (J=1→ 0) observations, the distribution of the molecular gas towards the multiple ring nebula sorrounding the star WR 16 has been analysed. Two striking features associated with the star and the nebula, respectively, were identified. One of them, the external one, is interstellar molecular gas which has been wind shaped in an early stage of the star. The internal feature is only noticed in a very small velocity range and has probably a stellar origin. Physical parameters have been calculated and kinematical models have been constructed in order to explain the physical link between these features and the nebula.En este artículo se presenta un estudio del gas molecular llevado a cabo en la nebulosa anillo múltiple alrededor de la estrella WR 16, usando observaciones de la línea (J=1→ 0) del 12CO obtenidas con el radiotelescopio NANTEN. Se encontraron dos estructuras moleculares cuya morfología las asocia a la nebulosa. La estructura más externa podría haberse originado como resultado de la interacción con los vientos de la estrella en una etapa temprana de su evolución. La estructura interna parece estar formada por gas molecular originado en la atmósfera de la estrella en una etapa intermedia de su evolución y sólo es visible en un rango muy peque˜no de velocidad radial. Para estas estructuras, se calcularon algunos parámetros físicos y se construyó un modelo cinemático que podría explicar su morfología y su relación con la estrella y la nebulosa.Instituto Argentino de Radioastronomí

Molecular gas toward G18.8+1.8

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 12CO(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 12CO(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 R2-1/1-0 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.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Gas molecular en la nebulosa anillo alrededor de WR 16

Using NANTEN 12CO (J=1→ 0) observations, the distribution of the molecular gas towards the multiple ring nebula sorrounding the star WR 16 has been analysed. Two striking features associated with the star and the nebula, respectively, were identified. One of them, the external one, is interstellar molecular gas which has been wind shaped in an early stage of the star. The internal feature is only noticed in a very small velocity range and has probably a stellar origin. Physical parameters have been calculated and kinematical models have been constructed in order to explain the physical link between these features and the nebula.En este artículo se presenta un estudio del gas molecular llevado a cabo en la nebulosa anillo múltiple alrededor de la estrella WR 16, usando observaciones de la línea (J=1→ 0) del 12CO obtenidas con el radiotelescopio NANTEN. Se encontraron dos estructuras moleculares cuya morfología las asocia a la nebulosa. La estructura más externa podría haberse originado como resultado de la interacción con los vientos de la estrella en una etapa temprana de su evolución. La estructura interna parece estar formada por gas molecular originado en la atmósfera de la estrella en una etapa intermedia de su evolución y sólo es visible en un rango muy peque˜no de velocidad radial. Para estas estructuras, se calcularon algunos parámetros físicos y se construyó un modelo cinemático que podría explicar su morfología y su relación con la estrella y la nebulosa.Instituto Argentino de Radioastronomí

NANTEN 12CO (J = 1 → 0) observations around the star WR 55

Context. We present a complete study of the molecular and ionized gas in the environs of the nebula RCW 78 around WR 55. Aims. We investigate the spatial distribution, physical characteristics, and kinematical properties of the molecular gas linked to the galactic nebula RCW 78 to obtain a clearer understanding of its interaction with both the star and the ionized gas. Methods. Our study is based on 12CO(1-0) fully sampled observations of a region of ∼0°.45 in size around the star WR 55 and the nebula RCW 78 obtained with the 4-m NANTEN telescope, radio continuum archival data at 1.4 and 4.85 GHz, obtained from the SGPS and PMNRAO Southern Radio Survey, respectively, and available infrared MIPSGAL images at 24 μm. Results. A molecular gas component in the velocity range from ∼-58 km s-1 to-45 km s-1, which is compatible with the velocity of the ionized gas, was found to be associated with the optical nebula. Adopting a distance of ∼5 kpc, the mass of this molecular component is about 3.4 × 104 M⊙ . Our analysis of the molecular data reveals a velocity gradient that is consistent with that found for the Hα line. New radio-continuum flux-density determinations confirm the thermal nature of RCW 78. This indicates that the ionized gas in RCW 78 arises from the photoionization of the molecular gas component in the velocity range from-58 km s-1 to-45 km s-1. A molecular concentration at a velocity of-56.1 km s-1 (identified as C1) is likely associated with the star HD 117797 and with an ensemble of candidate YSOs, lying at a distance of 3.9 kpc, while the rest of the molecular gas at velocities between-56 km s-1 and-46 km s-1 constitute an incomplete ring-like structure expanding around WR 55 at a velocity of about ∼5 km s-1. Mechanical energy and time requirements indicate that WR 55 is very capable of sustaining the expansion of the nebula.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Ionized gas, molecules and dust in Sh2-132

We analyse the various interstellar components of the H II region Sh2-132. The main stellar source is the double binary system that includes the Wolf–Rayet star WR 153ab. We use radio continuum images at 408 and 1420 MHz, and H I 21-cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO(1–0) line at 115 GHz from the Five College Radio Astronomy Observatory, and available mid- and far-infrared observations obtained with the MSX and IRAS satellites, respectively. Sh2-132 is composed of two shells showing radio continuum counterparts at both frequencies. The emission is thermal in nature. The estimated rms electron density and ionized mass of the nebula are ne≃ 20 cm−3 and MH II ≃ 1500 M⊙. The distribution of the CO emission shows molecular gas bordering the ionized nebula and interacting with it. The velocities of the molecular gas is in the range −38 to −53 km s−1, similar to the velocity of the ionized gas. The emission at 8.3 μm reveals a ring-like feature of about 15 arcmin that encircles the bright optical regions. This emission is due to the polycyclic aromatic hydrocarbons and marks the location of photodissociation regions. The gas distribution in the environs of Sh2-132 can be explained in a scenario where the massive stars in the region photodissociated, ionized and swept up the dense molecular material from the parental cloud through their strong stellar winds and intense ultraviolet (UV) photon flux.Facultad de Ciencias Astronómicas y Geofísica

Molecular gas toward G18.8+1.8

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 12CO(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 12CO(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 R2-1/1-0 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.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

Ionized gas, molecules and dust in Sh2-132

We analyse the various interstellar components of the H II region Sh2-132. The main stellar source is the double binary system that includes the Wolf–Rayet star WR 153ab. We use radio continuum images at 408 and 1420 MHz, and H I 21-cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO(1–0) line at 115 GHz from the Five College Radio Astronomy Observatory, and available mid- and far-infrared observations obtained with the MSX and IRAS satellites, respectively. Sh2-132 is composed of two shells showing radio continuum counterparts at both frequencies. The emission is thermal in nature. The estimated rms electron density and ionized mass of the nebula are ne≃ 20 cm−3 and MH II ≃ 1500 M⊙. The distribution of the CO emission shows molecular gas bordering the ionized nebula and interacting with it. The velocities of the molecular gas is in the range −38 to −53 km s−1, similar to the velocity of the ionized gas. The emission at 8.3 μm reveals a ring-like feature of about 15 arcmin that encircles the bright optical regions. This emission is due to the polycyclic aromatic hydrocarbons and marks the location of photodissociation regions. The gas distribution in the environs of Sh2-132 can be explained in a scenario where the massive stars in the region photodissociated, ionized and swept up the dense molecular material from the parental cloud through their strong stellar winds and intense ultraviolet (UV) photon flux.Facultad de Ciencias Astronómicas y Geofísica

Carbon monoxide in the environs of the star WR 16

Aims. We analyze the carbon monoxide emission around the star WR 16 aiming to study the physical characteristics of the molecular gas linked to the star and to achieve a better understanding of the interaction between massive stars with their surroundings. Methods. We study the molecular gas in a region in size using CO J = 1 → 0 and 13CO J = 1 → 0 line data obtained with the 4-m NANTEN telescope. Radio continuum archival data at 4.85 GHz, obtained from the Parkes-MIT-NRAO Southern Radio Survey, are also analyzed to account for the ionized gas. Available IRAS (HIRES) 60 μm and 100 μm images are used to study the characteristics of the dust around the star. Results. Our new CO and 13CO data allow the low/intermediate density molecular gas surrounding the WR nebula to be completely mapped. We report two molecular features at-5 km s-1 and-8.5 km s-1 (components 1 and 2, respectively) having a good morphological resemblance with the Hα emission of the ring nebula. Component 2 seems to be associated with the external ring, while component 1 is placed at the interface between component 2 and the Hα emission. We also report a third molecular feature ∼10′ in size (component 3) at a velocity of-9.5 km s-1 having a good morphological correspondence with the inner optical and IR emission, although high resolution observations are recommended to confirm its existence. The stratified morphology and kinematics of the molecular gas could be associated to shock fronts and high mass-loss events related to different evolutive phases of the WR star, which have acted upon the surrounding circumstellar molecular gas. An analysis of the mass of component 1 suggests that this feature is composed of swept-up interstellar gas and is probably enriched by molecular ejecta. The direction of the proper motion of WR 16 suggests that the morphology observed at infrared, optical, radio continuum, and probably molecular emission of the inner ring nebula is induced by the stellar motion.Facultad de Ciencias Astronómicas y Geofísica

NANTEN 12CO (J = 1 → 0) observations around the star WR 55

Context. We present a complete study of the molecular and ionized gas in the environs of the nebula RCW 78 around WR 55. Aims. We investigate the spatial distribution, physical characteristics, and kinematical properties of the molecular gas linked to the galactic nebula RCW 78 to obtain a clearer understanding of its interaction with both the star and the ionized gas. Methods. Our study is based on 12CO(1-0) fully sampled observations of a region of ∼0°.45 in size around the star WR 55 and the nebula RCW 78 obtained with the 4-m NANTEN telescope, radio continuum archival data at 1.4 and 4.85 GHz, obtained from the SGPS and PMNRAO Southern Radio Survey, respectively, and available infrared MIPSGAL images at 24 μm. Results. A molecular gas component in the velocity range from ∼-58 km s-1 to-45 km s-1, which is compatible with the velocity of the ionized gas, was found to be associated with the optical nebula. Adopting a distance of ∼5 kpc, the mass of this molecular component is about 3.4 × 104 M⊙ . Our analysis of the molecular data reveals a velocity gradient that is consistent with that found for the Hα line. New radio-continuum flux-density determinations confirm the thermal nature of RCW 78. This indicates that the ionized gas in RCW 78 arises from the photoionization of the molecular gas component in the velocity range from-58 km s-1 to-45 km s-1. A molecular concentration at a velocity of-56.1 km s-1 (identified as C1) is likely associated with the star HD 117797 and with an ensemble of candidate YSOs, lying at a distance of 3.9 kpc, while the rest of the molecular gas at velocities between-56 km s-1 and-46 km s-1 constitute an incomplete ring-like structure expanding around WR 55 at a velocity of about ∼5 km s-1. Mechanical energy and time requirements indicate that WR 55 is very capable of sustaining the expansion of the nebula.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí