16 research outputs found
NANTEN 12CO (J=1-0) observations around the star WR 55
Context: A complete study of the molecular and ionized gas in the environs of
the nebula RCW 78 around WR 55 is presented. Aims: The aim of this work is to
investigate the spatial distribution, physical characteristics, and kinematical
properties of the molecular gas linked to the galactic nebula RCW 78 to achieve
a better understanding of its interaction with the star and with the ionized
gas. Methods: This study was based on 12CO(1-0) fully sampled observations of a
region of ~0.45{\deg} 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 SGPS and PMNRAO Southern Radio Survey,
respectively, and available infrared MIPSGAL images at 24 microns. Results: A
molecular gas component in the velocity range from ~ -58 to -45 km s-1,
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 x 10^4 Msun. The analysis of the molecular
data revealed the presence of a velocity gradient, in agreement with the Halpha
line. New radiocontinuum flux density determinations confirm the thermal nature
of RCW 78. This indicates that the ionized gas in RCW 78 arises from
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 very likely associated with the star HD 117797 and with a
collection of candidate YSOs, lying at a distance of 3.9 kpc, while the rest of
the molecular gas at velocities between -56 and -46 km s-1 constitute an
incomplete ring-like structure which expands 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.Comment: 14 pages, 10 figures.Accepted for publication in A&
Molecular gas towards G18.8+1.8
This work aims at investigating the characteristics of the molecular gas
associated with the nebula G18.8+1.8, linked to the Wolf-Rayet star HD168206
(WR 113), and its relation to other components of its local interstellar
medium.
We carried out molecular observations of the 12CO(J=1-0) and (J=2-1) lines
with angular resolution of 44 arcsec and 22 arcsec 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 microns, and WISE data
at 3.4, 4.6, and 12.0 microns.
The SEST data allowed us to identify a molecular component (Cloud 3) having
velocities in the interval from ~ +30 to +36 km/s which is most probably linked
to the nebula. Morphological and kinematical properties suggest that Cloud 3
constitute a wind-blown molecular half-shell, which expands around WR113. 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 m indicates the existence of a PDR 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 candidates YSOs are projected near the
outer border of Cloud 3, although a triggered stellar formation scenario is
doubtful.Comment: 12 pages, 9 figures, accepted for publication in A&
870 micron continuum observations of the bubble-shaped nebula Gum 31
We are presenting here a study of the cold dust in the infrared ring nebula
Gum 31. We aim at deriving the physical properties of the molecular gas and
dust associated with the nebula, and investigating its correlation with the
star formation in the region, that was probably triggered by the expansion of
the ionization front. We use 870 micron data obtained with LABOCA to map the
dust emission. The obtained LABOCA image was compared to archival IR,radio
continuum, and optical images. The 870 micron emission follows the 8 micron
(Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing
the classical morphology of a spherical shell. We use the 870 micron and 250
micron images to identify 60 dust clumps in the collected layers of molecular
gas using the Gaussclumps algorithm. The clumps have effective deconvolved
radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume
densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the
clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21
K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass
distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to
M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for
the stellar IMF in the solar neighborhood, suggesting that the clumps are not
direct progenitors of single stars/protostars. The mass-radius relationship for
the 41 clumps detected in the 870 microns emission shows that only 37% of them
lie in or above the high-mass star formation threshold, most of them having
candidate YSOs projected inside. A comparison of the dynamical age of the HII
region with the fragmentation time, allowed us to conclude that the collect and
collapse mechanism may be important for the star formation at the edge of Gum
31, although other processes may also be acting.Comment: 15 pages, 10 figures. Accepted for publication in A&
Molecular gas and star formation towards the IR dust bubble S24 and its environs
We present a multi-wavelength analysis of the infrared dust bubble S24, and
its environs, with the aim of investigating the characteristics of the
molecular gas and the interstellar dust linked to them, and analyzing the
evolutionary status of the young stellar objects (YSOs) identified there. Using
APEX data, we mapped the molecular emission in the CO(2-1), CO(2-1),
CO(2-1), and CO(3-2) lines in a region of about 5'x 5' in size
around the bubble. The cold dust distribution was analyzed using ATLASGAL and
Herschel images. Complementary IR and radio data were also used.The molecular
gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities
between -48.0 km sec and -40.0 km sec. The gas distribution
reveals a shell-like molecular structure of 0.8 pc in radius bordering
the bubble. A cold dust counterpart of the shell is detected in the LABOCA and
Herschel images.The presence of extended emission at 24 m and radio
continuum emission inside the bubble indicates that the bubble is a compact HII
region. Part of the molecular gas bordering S24 coincides with the extended
infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the
interface between S24 and G341.217-0.237. As regards G341.220-0.213, the
presence of an arc-like molecular structure at the northern and eastern
sections of this IR source indicates that G341.220-0.213 is interacting with
the molecular gas. Several YSO candidates are found to be linked to the IR
extended sources, thus confirming their nature as active star-forming regions.
The total gas mass in the region and the H ambient density amount to 10300
M and 5900 cm, indicating that G341.220-0.213, G341.217-0.237,
and the S24 HII region are evolving in a high density medium. A triggering star
formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the
referee repor
Triggered massive star formation associated with the bubble HII region Sh2-39 (N5)
Aims. Aiming at studying the physical properties of Galactic IR bubbles and to explore their impact in triggering massive star formation, we perform a multiwavelength analysis of the bubble Hii region Sh2-39 (N5) and its environs. Methods. To analyze the molecular gas we use CO(3-2) and HCO+ (4-3) line data obtained with the on-the-fly technique from the ASTE telescope. To study the distribution and physical characteristics of the dust, we make use of archival data from ATLASGAL, Herschel, and MSX, while the ionized gas was studied making use of an NVSS image. We use public WISE, Spitzer, and MSX point source catalogs to search for infrared candidate YSOs in the region. To investigate the stellar cluster [BDS2003]6 we use IR spectroscopic data obtained with the ARCoIRIS spectrograph, mounted on Blanco 4-m Telescope at CTIO, and new available IR Ks band observations from the VVVeXtended ESO Public Survey (VVVX). Results. The new ASTE observations allowed the molecular gas component in the velocity range from 30 km s−1 to 46 km s−1 , associated with Sh2-39, to be studied in detail. The morphology of the molecular gas suggests that the ionized gas is expanding against its parental cloud. We have identified four molecular clumps, that were likely formed by the expansion of the ionization front, and determined some of their physical and dynamical properties. Clumps having HCO+ and 870 µm counterparts show evidence of gravitational collapse. We identified several candidate YSOs across the molecular component. Their spatial distribution, as well as the fragmentation time derived for the collected layers of the molecular gas, suggest that massive star formation might have been triggered by the expansion of the nebula via the collect and collapse mechanism. The spectroscopical distance obtained for the stellar cluster [BDS2003]6, placed over one of the collapsing clumps in the border of the Hii region, reveals that this cluster is physically associated with the neabula and gives more support to the triggered massive star formation scenario. A radio continuum data analysis indicates that the nebula is older and expands at lower velocity than typical IR Galactic bubblesFil: Duronea, Nicolas Urbano. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Cappa, Cristina Elisabeth. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Bronfman, L.. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; ChileFil: Borissova, J.. Universidad de Valparaiso; ChileFil: Gromadzki, M.. Universidad de Valparaiso; Chil
Physical characterization of S169: A prototypical IR bubble associated with the massive star-forming region IRAS12326-6245
With the aim of studying the properties of Galactic IR bubbles and their
impact in massive star formation, we present a study of the IR bubble S169,
associated with the massive star forming region IRAS12326-6245. We used
CO(2-1),CO(2-1), CO(2-1), HCN(3-2), and HCO+(3-2) line data
obtained with the APEX telescope to study the properties of the molecular gas
in the nebula and the IRAS source . To analyze the properties and distribution
of the dust, we used IRAC-GLIMPSE, Herschel, and ATLASGAL data. The properties
of the ionized gas were studied using images obtained from the SUMSS survey and
SuperCOSMOS database. In our search for stellar and protostellar objects in the
region, we used IR and optical point source calalogs. The new APEX observations
allowed us to identify three molecular components associated with the nebula,
namely: at 39 km/s (component A), 25 km/s (component B), and 17 km/s
(component C). Six molecular condensations (MC1 to MC6) were identified in
component A, with MC3 (the densest and more massive one) being the molecular
counterpart of IRAS12326-6245. For this source, we estimated an H column
density up to 810 cm. To explain the morphology and
velocity of components A, B, and C, we propose a simple model consisting of a
partially complete semisphere-like structure expanding at ~ 12 km/s. The
introduction of this model has led to a discussion about the distance to both
S169 and IRAS12326-6245, which was estimated to be ~ 2 kpc. Several candidate
YSOs were identified, projected mostly onto the molecular condensations MC3,
MC4, and MC5, which indicates that the star-formation process is very active at
the borders of the nebula. A comparison between observable and modeled
parameters was not enough to discern whether the collect-and-collapse mechanism
is acting at the edge of S169.Comment: 17 pages, 12 figures. Accepted for publication in A&
A multifrequency study of the active star forming complex NGC6357. I. Interstellar structures linked to the open cluster Pis24
We investigate the distribution of the gas (ionized, neutral atomic and
molecular), and interstellar dust in the complex star forming region NGC6357
with the goal of studying the interplay between the massive stars in the open
cluster Pis24 and the surrounding interstellar matter. Our study of the
distribution of the ionized gas is based on narrow-band Hhalfa, [SII], and
[OIII] images obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on
radio continuum observations at 1465 MHz taken with the VLA with a synthesized
beam of 40 arcsec. The distribution of the molecular gas is analyzed using
12CO(1-0) data obtained with the Nanten radiotelescope, Chile (angular
resolution = 2.7 arcmin). The interstellar dust distribution was studied using
mid-infrared data from the GLIMPSE survey and far-infrared observations from
IRAS. NGC6357 consists of a large ionized shell and a number of smaller optical
nebulosities. The optical, radio continuum, and near- and mid-IR images
delineate the distributions of the ionized gas and interstellar dust in the HII
regions and in previously unknown wind blown bubbles linked to the massive
stars in Pis24 revealing surrounding photodissociation regions. The CO line
observations allowed us to identify the molecular counterparts of the ionized
structures in the complex and to confirm the presence of photodissociation
regions. The action of the WR star HD157504 on the surrounding gas was also
investigated. The molecular mass in the complex is estimated to be (4+/-2)X10^5
Mo. Mean electron densities derived from the radio data suggest electron
densities > 200 cm^-3, indicating that NGC6357 is a complex formed in a region
of high ambient density. The known massive stars in Pis24 and a number of newly
inferred massive stars are mainly responsible for the excitation and
photodissociation of the parental molecular cloud.Comment: 16 pages, 9 figures. Accepted for publication in MNRA
Ionized gas, molecules, and dust in Sh2-132
We analyze the various interstellar components of the HII region Sh2-132. The
main stellar source is the double binary system that includes the Wolf-Rayet
star WR153ab. We use radio continuum images at 408 and 1420 MHz, and HI 21cm
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 IR 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 n_e = 20 cm^{-3} and M_HII = 1500
Mo. 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, similar to the velocity of the ionized gas. The
emission at 8.3 mic. reveals a ring like feature of about 15' that encircles
the bright optical regions. This emission is due to the PAHs 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 UV photon flux.Comment: 11 figures and 5 tables, accepted in MNRA
NGC 3503 and its molecular environment
We present a study of the molecular gas and interstellar dust distribution in
the environs of the HII region NGC 3503 associated with the open cluster Pis 17
with the aim of investigating the spatial distribution of the molecular gas
linked to the nebula and achieving a better understanding of the interaction of
the nebula and Pis 17 with their molecular environment.
We based our study in ^{12}CO(1-0) observations of a region of ~0.6 deg. in
size obtained with the 4-m NANTEN telescope, unpublished radio continuum data
at 4800 and 8640 MHz obtained with the ATCA telescope, radio continuum data at
843 MHz obtained from SUMSS, and available IRAS, MSX, IRAC-GLIMPSE, and MIPSGAL
images.
We found a molecular cloud (Component 1) having a mean velocity of -24.7 km
s^{-1}, compatible with the velocity of the ionized gas, which is associated
with the nebula and its surroundings. Adopting a distance of 2.9 +/- 0.4 kpc
the total molecular mass and density yield (7.6 +/- 2.1) x 10^3 Msun and 400
+/- 240 cm^{-3}, respectively.
The radio continuum data confirm the existence of an electron density
gradient in NGC 3503. The IR emission shows the presence of a PDR bordering the
higher density regions of the nebula. The spatial distribution of the CO
emission shows that the nebula coincides with a molecular clump, with the
strongest CO emission peak located close to the higher electron density region.
The more negative velocities of the molecular gas (about -27 km s^{-1}), is
coincident with NGC 3503. Candidate YSOs were detected towards the HII region,
suggesting that embedded star formation may be occurring in the neighbourhood
of the nebula. The presence of a clear electron density gradient, along with
the spatial distribution of the molecular gas and PAHs in the region indicates
that NGC 3503 is a blister-type HII region that probably has undergone a
champagne phase
Molecular gas associated with RCW 121 and RCW 122
Aims. We analyse the distribution of the molecular gas towards the
region containing
the open cluster Havlen-Moffat 1 (HM 1) the Wolf-Rayet stars WR 87,
WR 89, and WR 91, and the star forming regions
RCW 121 and RCW 122, with the aim of looking
for a possible physical relationship among these objects.
Methods. We used the carbon monoxide observations carried out at λ ~ 2.6 mm with
the 4 m NANTEN radiotelescope; new flux density determinations
derived from already existing radio continuum surveys at 2.417, 5,
8.35, and 14.35 GHz; continuum flux density determinations available
in the literature; and the Midcourse Space Experiment (MSX) and
the Improved Reprocessing of the IRAS Survey (IRIS)
databases.
Results. Adopting a distance of 5 kpc for RCW 121 and RCW 122, we found
a giant molecular cloud (GMC) with a linear extent of
~100 20 pc to be associated with galactic
star-forming regions. The total mass of this GMC is of the
order of 1.2 106 solar masses and its mean radial velocity
is about -15 km s-1. Within the GMC there are individual
molecular gas concentrations, having total molecular masses in the
range from 4.6 104 (RCW 122 C)
to 2.2 105 (RCW 122). The CO
profiles observed toward the peak of the molecular concentrations
are broad, with typical full-width half-maximum around 6 to 7 km s-1, and show line asymmetries and/or double-peaked shape that
change with the observed position within a given CO
concentration. An analysis of the MSX and IRAS
databases show that each CO concentration has a strong
IR counterpart. The dust temperature of these concentrations
range from 46 K (RCW 121) to 76 K (RCW 122 C).
Their infrared luminosity are a few times 105 . The new
radio continuum flux density determinations are in good
agreement with previous determinations at other frequencies, and
confirm the thermal nature of RCW 121 and RCW 122.
Based on the newly-determined 5 GHz flux density, we found that
to power these Hi