45 research outputs found
The environment of the infrared dust bubble N65: a mutiwavelength study
AIMS: We investigate the environment of the infrared dust bubble N65 and
search for evidence of triggered star formation in its surroundings. METHODS:
We performed a multiwavelength study of the region around N65 with data taken
from large-scale surveys: Two Micron All Sky Survey, GLIMPSE, MIPSGAL, SCUBA,
and GRS. We analyzed the distribution of the molecular gas and dust in the
environment of N65 and performed infrared photometry and spectral analysis of
point sources to search for young stellar objects and identify the ionizing
star candidates. RESULTS: We found a molecular cloud that appears to be
fragmented into smaller clumps along the N65 PDR. This indicates that the
so-called collect and collapse process may be occurring. Several young stellar
objects are distributed among the molecular clumps. They may represent a second
generation of stars whose formation was triggered by the bubble expanding into
the molecular gas. We dentified O-type stars inside N65, which are the most
reliable ionizing star candidates.Comment: 15 pages, 10 figures, accepted for publication in A&A. Figures
degraded to reduce file siz
The HII region G35.673-00.847: another case of triggered star formation?
As part of a systematic study that we are performing with the aim to increase
the observational evidence of triggered star formation in the surroundings of
HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly
studied source. Using data from large-scale surveys: Two Micron All Sky Survey,
Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL,
Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky
Survey (NVSS) we performed a multiwavelength study of G35.673-00.847 and its
surroundings. The mid IR emission, shows that G35.673-00.847 has an almost
semi-ring like shape with a cut towards the galactic west. The radius of this
semi-ring is about 1.5' (~1.6 pc, at the distance of ~3.7 kpc). The distance
was estimated from an HI absorption study and from the analysis of the
molecular gas. Indeed, we find a molecular shell composed by several clumps
distributed around the HII region, suggesting that its expansion is collecting
the surrounding material. We find several YSO candidates over the molecular
shell. Finally, comparing the HII region dynamical age and the fragmentation
time of the molecular shell, we discard the collect and collapse as the
mechanism responsible for the YSOs formation, suggesting other processes such
as radiative driven implosion and/or small-scale Jeans gravitational
instabilities.Comment: Accepted for publication in A&A, 18 October 2010. Some figures were
degraded to reduce file siz
Star formation around RCW 120, the perfect bubble
We take advantage of the very simple morphology of RCW 120 -- a perfect
bubble -- to understand the mechanisms triggering star formation around an HII
region and to establish what kind of stars are formed there. We present 870
microns observations of RCW 120, obtained with the APEX-LABOCA camera. These
show the distribution of cold dust, and thus of neutral material. We use
Spitzer-MIPS observations at 24 and 70 microns to detect the young stellar
objects (YSOs) present in this region and to estimate their evolutionary
stages.
A layer of dense neutral material surrounds the HII region, having been swept
up during the region's expansion. This layer has a mass greater than 2000 solar
masses and is fragmented, with massive fragments elongated along the ionization
front (IF). We measured the 24 microns flux of 138 sources. Of these, 39 are
Class I or flat-spectrum YSOs observed in the direction of the collected layer.
We show that several triggering mechanisms are acting simultaneously in the
swept-up shell, where they form a second generation of stars. No massive YSOs
are detected. However, a massive, compact 870 microns core lies adjacent to the
IF. A 70 microns source with no 24 microns counterpart is detected at the same
position. This source is a likely candidate for a Class 0 YSO. Also at 24
microns, we detect a chain of about ten regularly spaced Class I or flat
spectrum sources, parallel to the IF, in the direction of the most massive
fragment. We suggest that the formation of these YSOs is the result of Jeans
gravitational instabilities in the collected layer. Finally, the 870 microns
emission, the 24 microns emission, and the Halpha emission show the existence
of an extended and partially ionized photodissociation region around RCW 120.Comment: 14 pages, 17 figure
Triggered massive-star formation on the borders of Galactic HII regions. IV- Star formation at the periphery of Sh2-212
Aims: We wish to establish whether sequential star formation is taking place
at the periphery of the Galactic HII region Sh2-212.
Methods: We present CO millimetre observations of this region obtained at the
IRAM 30-m telescope to investigate the distribution of associated molecular
material. We also use deep JHK observations obtained at the CFHT to study the
stellar content of the region, and radio observations obtained at the VLA to
look for the presence of an ultra-compact (UC) HII region and for maser
emission.
Results: In the optical, Sh2-212 is spherically symmetric around its central
exciting cluster. This HII region is located along a molecular filament. A
thin, well-defined half ring of molecular material surrounds the brightest part
of the HII region at the rear and is fragmented. The most massive fragment
(~200 solar masses) contains a massive young stellar object displaying a
near-IR excess; its spectral energy distribution indicates a high-mass
(~14solar masses), high-temperature (~30000K), and high-luminosity (~17000
solar luminosities) source. This object ionizes a UC HII region.
Conclusions: Sh2-212 is a good example of massive-star formation triggered
via the collect and collapse process. The massive YSO observed at its periphery
is a good candidate for a massive star formed in isolation.Comment: 12 pages, 14 figures. To be published in A&
The infrared dust bubble N22: an expanding HII region and the star formation around it
Aims. To increase the observational samples of star formation around
expanding Hii regions, we analyzed the interstellar medium and star formation
around N22.
Methods. We used data extracted from the seven large-scale surveys from
infrared to radio wavelengths. In addition we used the JCMT observations of the
J = 3-2 line of 12CO emission data released on CADC and the 12CO J = 2-1 and J
=3-2 lines observed by the KOSMA 3 m telescope. We performed a multiwavelength
study of bubble N22.
Results. A molecular shell composed of several clumps agrees very well with
the border of N22, suggesting that its expansion is collecting the surrounding
material. The high integrated 12CO line intensity ratio (ranging from 0.7 to
1.14) implies that shocks have driven into the molecular clouds. We identify
eleven possible O-type stars inside the Hii region, five of which are located
in projection inside the cavity of the 20 cm radio continuum emission and are
probably the exciting-star candidates of N22. Twenty-nine YSOs (young stellar
objects) are distributed close to the dense cores of N22. We conclude that star
formation is indeed active around N22; the formation of most of YSOs may have
been triggered by the expanding of the Hii region. After comparing the
dynamical age of N22 and the fragmentation time of the molecular shell, we
suggest that radiation-driven compression of pre-existing dense clumps may be
ongoing.Comment: accepted in A&A 30/05/2012. arXiv admin note: text overlap with
arXiv:1010.5430 by other author
A multiwavelength study of the star forming region IRAS 18544+0112
This work aims at investigating the molecular and infrared components in the
massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is
to determine the nature and the origin of this infrared source. To analyze the
molecular gas towards IRAS 18544+0112, we have carried out observations in a
90" x 90" region around l = 34.69, b = -0.65, using the Atacama Submillimeter
Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS
J=7-6 lines with an angular resolution of 22". The infrared emission in the
area has been analyzed using 2MASS and Spitzer public data. From the molecular
analysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star
forming regions, but we do not find any evidence of outflow activity. Moreover,
we do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species
normally enhanced in molecular outflows and high density envelopes. The 12CO
J=3-2 emission profile suggests the presence of expanding gas in the region.
The Spitzer images reveal that the infrared source has a conspicuous extended
emission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin
in size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um
emission. The non-detection of ionized gas related to IRAS 18544+0112, together
with the fact that it is still embedded in a molecular clump suggest that IRAS
18544+0112, has not reached the UCHII region stage yet. Based on near infrared
photometry we search for YSO candidates in the region and propos that 2MASS
18565878+0116233 is the infrared point source associated with IRAS 18544+0112.
Finally, we suggest that the expansion of a larger nearby HII region,
G034.8-0.7, might be related to the formation of IRAS 18544+0112.Comment: 14 pages, accepted for publication in A&A. Figures degraded to reduce
file siz
Star formation triggered by HII regions in our Galaxy: First results for N49 from the Herschel infrared survey of the Galactic plane
It has been shown that by means of different physical mechanisms the
expansion of HII regions can trigger the formation of new stars of all masses.
This process may be important to the formation of massive stars but has never
been quantified in the Galaxy. We use Herschel-PACS and -SPIRE images from the
Herschel Infrared survey of the Galactic plane, Hi-GAL, to perform this study.
We combine the Spitzer-GLIMPSE and -MIPSGAL, radio-continuum and sub-millimeter
surveys such as ATLASGAL with Hi-GAL to study Young Stellar Objects (YSOs)
observed towards Galactic HII regions. We select a representative HII region,
N49, located in the field centered on l=30 degr observed as part of the Hi-GAL
Science Demonstration Phase, to demonstrate the importance Hi-GAL will have to
this field of research. Hi-GAL PACS and SPIRE images reveal a new population of
embedded young stars, coincident with bright ATLASGAL condensations. The Hi-GAL
images also allow us, for the first time, to constrain the physical properties
of the newly formed stars by means of fits to their spectral energy
distribution. Massive young stellar objects are observed at the borders of the
N49 region and represent second generation massive stars whose formation has
been triggered by the expansion of the ionized region. Hi-GAL enables us to
detect a population of young stars at different evolutionary stages, cold
condensations only being detected in the SPIRE wavelength range. The far IR
coverage of Hi-GAL strongly constrains the physical properties of the YSOs. The
large and unbiased spatial coverage of this survey offers us a unique
opportunity to lead, for the first time, a global study of star formation
triggered by HII regions in our Galaxy.Comment: 4 pages, 2 figures, accepted by A&A (Special issue on Herschel first
results
Spitzer/IRAC view of Sh 2-284: Searching for evidence of triggered star formation in an isolated region in the outer Milky Way
Using Spitzer/IRAC observations of a region to be observed by the CoRoT
satellite, we have unraveled a new complex star-forming region at low
metallicity in the outer Galaxy. We perform a study of S284 in order to outline
the chain of events in this star-forming region. We used four-band Spitzer/IRAC
photometry as well as Halpha imaging obtained with INT/WFC. Combining these
data with the optical photometry obtained in the frame of CoRoTs preparation
and the 2MASS catalog we analysed the properties and distribution of young
stellar objects (YSOs) associated with point-like sources. We also studied the
SEDs of regions of extended emission, complementing our dataset with IRAS and
MSX data. We find that S284 is unique in several ways: it is very isolated at
the end of a spiral arm and both the diffuse dust and ionized emission are
remarkably symmetric. We have partially resolved the central clusters of the
three bubbles present in this region. Despite the different scales present in
its multiple-bubble morphology, our study points to a very narrow spread of
ages among the powering high-mass clusters. In contrast, the particular
sawtooth structure of the extended emission at the rim of each ionized bubble
harbours either small lower-mass clusters with a younger stellar population or
individual young reddened protostars. In particular, triggered star formation
is considered to be at work in these regions.Comment: Accepted by A&A. 13 pages, 10 figures, 2 Table
A multi-wavelength census of stellar contents in the young cluster NGC 1624
We present a comprehensive multi-wavelength analysis of the young cluster NGC
1624 associated with the H II region Sh2-212 using optical UBVRI photometry,
optical spectroscopy and GMRT radio continuum mapping along with the
near-infrared (NIR) JHK archival data. Reddening E(B-V) and distance to the
cluster are estimated to be 0.76 - 1.00 mag and 6.0 +/- 0.8 kpc, respectively.
Present analysis yields a spectral class of O6.5V for the main ionizing source
of the region. The distribution of YSOs in (J-H)/ (H-K) NIR colour-colour
diagram shows that a majority of them have A_V 4 mag. Based on the NIR
excess characteristics, we identified 120 probable candidate YSOs in this
region which yield a disk frequency of ~ 20%. These YSOs are found to have an
age spread of ~ 5 Myr with a median age of ~ 2-3 Myr and a mass range of ~ 0.1
- 3.0 . A significant number of YSOs are located close to the cluster
centre and we detect an enhanced density of reddened YSOs located/projected
close to the molecular clumps at the periphery of NGC 1624. This indicates that
the YSOs located within the cluster core are relatively older in comparison to
those located/projected near the clumps. From the radio continuum flux,
spectral class of the ionizing source of the ultra-compact H II region at the
periphery of Sh2-212 is estimated to be ~ B0.5V. From optical data, slope of
the mass function (MF) , in the mass range can
be represented by a single power law with a slope -1.18 +/- 0.10, whereas the
NIR data in the mass range yields = -1.31
+/- 0.15. The slope of the K-band luminosity function (KLF) for the cluster is
found to be 0.30 +/- 0.06 which is in agreement with the values obtained for
other young clusters.Comment: Accepted for publication in MNRA
The Ap 2-1 nebula and the surrounding molecular cloud G35.2-0.74: an active star forming region
Using data from large-scale surveys: 2MASS, GLIMPSE, MIPSGAL, VGPS, GRS, and
IPHAS, we performed a multiwavelength study of the ISM in a region of about 20'
x 20' towards the molecular cloud G35.2-0.74. Additionally, the Ap 2-1 nebula,
that is seen in projection over the molecular cloud, was studied using optical
data obtained with the 2.15 m telescope at CASLEO, Argentina. From the HI
absorption study we estimate a distance of ~2 kpc for Ap 2-1 confirming that
the nebula is embedded in the south portion of the molecular cloud G35.2-0.74.
Performing a photometric study and analysing the spectral energy distributions
of the sources likely embedded in the cloud, we confirm that this region is
very active in star formation, mainly towards the north, where we discover a
cluster of young stellar objects. From the H_alpha and [NII] lines we obtain a
radial velocity of v_LSR ~ 31 km/s for the Ap 2-1 nebula, in coincidence with
the velocity of the molecular cloud. Finally, we conclude that Ap 2-1 is an HII
region probably excited by an early B-type star.Comment: 9 pages, 10 figures, accepted to be published in MNRAS (July 5, 2010