397 research outputs found
Triggered massive-star formation on the borders of Galactic HII regions. II. Evidence for the collect and collapse process around RCW 79
We present SEST-SIMBA 1.2-mm continuum maps and ESO-NTT SOFI JHK images of
the Galactic HII region RCW 79. The millimetre continuum data reveal the
presence of massive fragments located in a dust emission ring surrounding the
ionized gas. The two most massive fragments are diametrically opposite each
other in the ring. The near-IR data, centred on the compact HII region located
at the south-eastern border of RCW 79, show the presence of an IR-bright
cluster containing massive stars along with young stellar objects with near-IR
excesses. A bright near- and mid-IR source is detected towards maser emissions,
1.2 pc north-east of the compact HII region centre. Additional information,
extracted from the Spitzer GLIMPSE survey, are used to discuss the nature of
the bright IR sources observed towards RCW 79. Twelve luminous Class I sources
are identified towards the most massive millimetre fragments. All these facts
strongly indicate that the massive-star formation observed at the border of the
HII region RCW 79 has been triggered by its expansion, most probably by the
collect and collapse process.Comment: 14 pages, 15 figures. Accepted for publication in A&A. The images
have been highly compressed for astro-ph. A version of this paper with
higher-resolution figures is available at
http://www.oamp.fr/matiere/rcw79.pd
The molecular complex associated with the Galactic HII region Sh2-90: a possible site of triggered star formation
We investigate the star formation activity in the molecular complex
associated with the Galactic HII region Sh2-90, using radio-continuum maps
obtained at 1280 MHz and 610 MHz, Herschel Hi-GAL observations at 70 -- 500
microns, and deep near-infrared observation at JHK bands, along with Spitzer
observations. Sh2-90 presents a bubble morphology in the mid-IR (size ~ 0.9 pc
x 1.6 pc). Radio observations suggest it is an evolved HII region with an
electron density ~ 144 cm^-3, emission measure ~ 6.7 x 10^4 cm^-6 pc and a
ionized mass ~ 55 Msun. From Hi-GAL observations it is found that the HII
region is part of an elongated extended molecular cloud (size ~ 5.6 pc x 9.7
pc, H_2 column density >= 3 x 10^21 cm^-2 and dust temperature 18 -- 27 K) of
total mass >= 1 x 10^4 Msun. We identify the ionizing cluster of Sh2-90, the
main exciting star being an O8--O9 V star. Five cold dust clumps (mass ~ 8 --
95 Msun), four mid-IR blobs around B stars, and a compact HII region are found
at the edge of the bubble.The velocity information derived from CO (J=3-2) data
cubes suggests that most of them are associated with the Sh2-90 region. 129
YSOs are identified (Class I, Class II, and near-IR excess sources). The
majority of the YSOs are low mass (<= 3 Msun) sources and they are distributed
mostly in the regions of high column density. Four candidate Class 0/I MYSOs
have been found; they will possibly evolve to stars of mass >= 15 Msun. We
suggest multi-generation star formation is present in the complex. From the
evidences of interaction, the time scales involved and the evolutionary status
of stellar/protostellar sources, we argue that the star formation at the
immediate border/edges of Sh2-90 might have been triggered by the expanding HII
region. However, several young sources in this complex are probably formed by
some other processes.Comment: 22 pages, 22 figures, accepted for publication in Astronomy and
Astrophysic
Star Formation Towards The Galactic H Ii Region Rcw 120 - Herschel Observations Of Compact Sources
The expansion of H ii regions can trigger the formation of stars. An overdensity of young stellar objects is observed at the edges of H ii regions but the mechanisms that give rise to this phenomenon are not clearly identified. Moreover, it is difficult to establish a causal link between H ii -region expansion and the star formation observed at the edges of these regions. A clear age gradient observed in the spatial distribution of young sources in the surrounding might be a strong argument in favor of triggering
Herschel Observations Of The Galactic H Ii Region Rcw 79
Triggered star formation around H II regions could be an important process. The Galactic H II region RCW79 is a prototypical object for triggered high‐mass star formation. Aims. We aim to obtain a census of the young stellar population observed at the edges of the H II region and to determine the properties of the young sources in order to characterize the star formation processes that take place at the edges of this ionized region. Methods. We take advantage of Herschel data from the surveys HOBYS, `` Evolution of Interstellar Dust\u27\u27, and Hi‐Gal to extract compact sources. We use the algorithm getsources. We complement the Herschel data with archival 2MASS, Spitzer, and WISE data to determine the physical parameters of the sources (e. g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution. Results. We created the dust temperature and column density maps along with the column density probability distribution function (PDF) for the entire RCW79 region. We obtained a sample of 50 compact sources in this region, 96% of which are situated in the ionization‐compressed layer of cold and dense gas that is characterized by the column density PDF with a double‐peaked lognormal distribution. The 50 sources have sizes of similar to 0.1‐0.4 pc with a typical value of similar to 0 : 2 pc, temperatures of similar to 11‐26 K, envelope masses of similar to 6 760 M‐circle dot, densities of similar to 0.1 44 +/‐ 10(5) cm(3), and luminosities of similar to 19‐12712 L‐circle dot. The sources are classified into 16 class 0, 19 intermediate, and 15 class I objects. Their distribution follows the evolutionary tracks in the diagram of bolometric luminosity versus envelope mass (L‐bol‐M‐env) well. A mass threshold of 140 M fi, determined from the L‐bol‐M‐env diagram, yields 12 candidate massive dense cores that may form high‐mass stars. The core formation efficiency (CFE) for the 8 massive condensations shows an increasing trend of the CFE with density. This suggests that the denser the condensation, the higher the fraction of its mass transformation into dense cores, as previously observed in other high‐mass star‐forming regions
Mopra CO Observations of the Bubble HII Region RCW120
We use the Mopra radio telescope to test for expansion of the molecular gas
associated with the bubble HII region RCW120. A ring, or bubble, morphology is
common for Galactic HII regions, but the three-dimensional geometry of such
objects is still unclear. Detected near- and far-side expansion of the
associated molecular material would be consistent with a three-dimensional
spherical object. We map the transitions of CO,
CO, CO, and CO, and detect emission from all
isotopologues. We do not detect the masing lines of
CHOH at 108.8939 GHz. The strongest CO emission is from the
photodissociation region (PDR), and there is a deficit of emission toward the
bubble interior. We find no evidence for expansion of the molecular material
associated with RCW120 and therefore can make no claims about its geometry. The
lack of detected expansion is roughly in agreement with models for the
time-evolution of an HII region like RCW120, and is consistent with an
expansion speed of . Single-position CO spectra show
signatures of expansion, which underscores the importance of mapped spectra for
such work. Dust temperature enhancements outside the PDR of RCW120 coincide
with a deficit of emission in CO, confirming that these temperature
enhancements are due to holes in the RCW120 PDR. H emission shows that
RCW120 is leaking of the ionizing photons into the interstellar
medium (ISM) through PDR holes at the locations of the temperature
enhancements. H-alpha emission also shows a diffuse "halo" from leaked photons
not associated with discrete holes in the PDR. Overall of all
ionizing photons are leaking into the nearby ISM.Comment: 35 pages, 14 figures. Accepted to Ap
Can music be figurative? Exploring the possibility of crossmodal similarities between music and visual arts
According to both experimental research and common sense, classical music is a better fit for figurative art than jazz. We hypothesize that similar fits may reflect underlying crossmodal structural similarities between music and painting genres. We present two preliminary studies aimed at addressing our hypothesis. Experiment 1 tested the goodness of the fit between two music genres (classical and jazz) and two painting genres (figurative and abstract). Participants were presented with twenty sets of six paintings (three figurative, three abstract) viewed in combination with three sound conditions: 1) silence, 2) classical music, or 3) jazz. While figurative paintings scored higher aesthetic appreciation than abstract ones, a gender effect was also found: the aesthetic appreciation of paintings in male participants was modulated by music genre, whilst music genre did not affect the aesthetic appreciation in female participants. Our results support only in part the notion that classical music enhances the aesthetic appreciation of figurative art. Experiment 2 aimed at testing whether the conceptual categories ‘figurative’ and ‘abstract’ can be extended also to music. In session 1, participants were first asked to classify 30 paintings (10 abstract, 10 figurative, 10 ambiguous that could fit either category) as abstract or figurative and the to rate them for pleasantness; in session 2 participants were asked to classify 40 excerpts of music (20 classical, 20 jazz) as abstract or figurative and to rate them for pleasantness. Paintings which were clearly abstract or figurative were all classified accordingly, while the majority of ambiguous paintings were classified as abstract. Results also show a gender effect for painting’s pleasantness: female participants rated higher ambiguous and abstract paintings. More interestingly, results show an effect of music genre on classification, showing that it is possible to classify music as figurative or abstract, thus supporting the hypothesis of cross-modal similarities between the two sensory-different artistic expressions
Bipolar HII regions - Morphology and star formation in their vicinity - I - G319.8800.79 and G010.3200.15
Our goal is to identify bipolar HII regions and to understand their
morphology, their evolution, and the role they play in the formation of new
generations of stars. We use the Spitzer and Herschel Hi-GAL surveys to
identify bipolar HII regions. We search for their exciting star(s) and estimate
their distances using near-IR data. Dense clumps are detected using
Herschel-SPIRE data. MALT90 observations allow us to ascertain their
association with the central HII region. We identify Class 0/I YSOs using their
Spitzer and Herschel-PACS emissions. These methods will be applied to the
entire sample of candidate bipolar HII regions. This paper focuses on two
bipolar HII regions, one interesting in terms of its morphology,
G319.8800.79, and one in terms of its star formation, G010.3200.15. Their
exciting clusters are identified and their photometric distances estimated to
be 2.6 kpc and 1.75 kpc, respectively. We suggest that these regions formed in
dense and flat structures that contain filaments. They have a central ionized
region and ionized lobes perpendicular to the parental cloud. The remains of
the parental cloud appear as dense (more than 10^4 per cm^3) and cold (14-17 K)
condensations. The dust in the PDR is warm (19-25 K). Dense massive clumps are
present around the central ionized region. G010.32-00.14 is especially
remarkable because five clumps of several hundred solar masses surround the
central HII region; their peak column density is a few 10^23 per cm^2, and the
mean density in their central regions reaches several 10^5 per cm^3. Four of
them contain at least one massive YSO; these clumps also contain extended green
objects and Class II methanol masers. This morphology suggests that the
formation of a second generation of massive stars has been triggered by the
central bipolar HII region. It occurs in the compressed material of the
parental cloud.Comment: 32 pages, 28 figures, to be published in A&
Star formation triggered by the Galactic HII region RCW 120: First results from the Herschel Space Observatory
By means of different physical mechanisms, the expansion of HII regions can
promote the formation of new stars of all masses. RCW 120 is a nearby Galactic
HII region where triggered star formation occurs. This region is well-studied -
there being a wealth of existing data - and is nearby. However, it is
surrounded by dense regions for which far infrared data is essential to obtain
an unbiased view of the star formation process and in particular to establish
whether very young protostars are present. We attempt to identify all Young
Stellar Objects (YSOs), especially those previously undetected at shorter
wavelengths, to derive their physical properties and obtain insight into the
star formation history in this region. We use Herschel-PACS and -SPIRE images
to determine the distribution of YSOs observed in the field. We use a spectral
energy distribution fitting tool to derive the YSOs physical properties.
Herschel-PACS and -SPIRE images confirm the existence of a young source and
allow us to determine its nature as a high-mass (8-10 MSun) Class 0 object
(whose emission is dominated by a massive envelope) towards the massive
condensation 1 observed at (sub)-millimeter wavelengths. This source was not
detected at 24 micron and only barely seen in the MISPGAL 70 micron data.
Several other red sources are detected at Herschel wavelengths and coincide
with the peaks of the millimeter condensations. SED fitting results for the
brightest Herschel sources indicate that, apart from the massive Class 0 that
forms in condensation 1, young low mass stars are forming around RCW 120. The
YSOs observed on the borders of RCW 120 are younger than its ionizing star,
which has an age of about 2.5 Myr.Comment: 5 pqges, 3 figures, accepted by A&A (Special issue on the Herschel
first results
Spatial distribution of emission in Unidentified Infrared Bands from Midcourse Space Experiment Survey
Recently the Midcourse Space Experiment (MSX) has surveyed the Galactic plane
in mainly four infrared bands between 6 and 25 micron. Two of these bands cover
several Unidentified Infrared emission Bands (UIBs). With the aim of extracting
the spatial distribution of the UIB emission on a large scale, a scheme has
been developed to model the MSX data with emission in the UIBs alongwith the
underlying thermal continuum from the interstellar dust. In order to test this
scheme, a sample of five Galactic compact H II regions (Sh-61, Sh-138, Sh-152,
Sh-156, Sh-186; Zavagno & Ducci 2001) for which imaging study in some
individual UIBs is available from ISOCAM measurements, has been studied. The
results of this comparative study on small angular scale are as follows : (i)
the morphological details extracted from our scheme agree very well with those
from the superior ISOCAM measurements; (ii) the integrated strength of UIBs
extracted from the MSX database correlates extremely well with the sum of the
strengths of individual UIBs measured from ISOCAM. This tight correlation is
very encouraging and promises the potential of MSX database for study of large
scale spatial distribution of UIB emission (and the carriers of UIBs) in the
entire Galactic plane.Comment: to be published in Astronomy & Astrophysics; (9 pages including 2
tables & 11 figures
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