scholarly journals Bipolar H II regions

2018 ◽  
Vol 617 ◽  
pp. A67 ◽  
Author(s):  
M. R. Samal ◽  
L. Deharveng ◽  
A. Zavagno ◽  
L. D. Anderson ◽  
S. Molinari ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Galactic Plane ◽  
Three Dimensional ◽  
Young Stellar Objects ◽  
Formation Processes ◽  
Two Dimensional ◽  
Stellar Objects ◽  
Flat Structures ◽  
Exciting Star

Aims. We aim to identify bipolar Galactic H II regions and to understand their parental cloud structures, morphologies, evolution, and impact on the formation of new generations of stars. Methods. We use the Spitzer-GLIMPSE, Spitzer-MIPSGAL, and Herschel-Hi-GAL surveys to identify bipolar H II regions and to examine their morphologies. We search for their exciting star(s) using NIR data from the 2MASS, UKIDSS, and VISTA surveys. Massive molecular clumps are detected near these bipolar nebulae, and we estimate their temperatures, column densities, masses, and densities. We locate Class 0/I young stellar objects (YSOs) in their vicinities using the Spitzer and Herschel-PACS emission. Results. Numerical simulations suggest bipolar H II regions form and evolve in a two-dimensional flat- or sheet-like molecular cloud. We identified 16 bipolar nebulae in a zone of the Galactic plane between ℓ ± 60° and |b| < 1°. This small number, when compared with the 1377 bubble H II regions in the same area, suggests that most H II regions form and evolve in a three-dimensional medium. We present the catalogue of the 16 bipolar nebulae and a detailed investigation for six of these. Our results suggest that these regions formed in dense and flat structures that contain filaments. We find that bipolar H II regions have massive clumps in their surroundings. The most compact and massive clumps are always located at the waist of the bipolar nebula, adjacent to the ionised gas. These massive clumps are dense, with a mean density in the range of 105 cm−3 to several 106 cm−3 in their centres. Luminous Class 0/I sources of several thousand solar luminosities, many of which have associated maser emission, are embedded inside these clumps. We suggest that most, if not all, massive 0/I YSO formation has probably been triggered by the expansion of the central bipolar nebula, but the processes involved are still unknown. Modelling of such nebula is needed to understand the star formation processes at play.

scholarly journals Triggered star formation in a cometary atomic/molecular cloud in the Cep OB3 association

2019 ◽  
Vol 489 (4) ◽  
pp. 4809-4816 ◽  
Author(s):  
Brandon Marshall ◽  
C R Kerton
Keyword(s):  
Star Formation ◽  
Galactic Plane ◽  
Initial Conditions ◽  
Young Stellar Objects ◽  
Wide Field ◽  
Infrared Source ◽  
Stellar Objects ◽  
Iras Source ◽  
Infrared Observations ◽  
Infrared Survey

ABSTRACT We present a study of a small atomic/molecular cometary cloud associated with the infrared source IRAS 23153+6938. The cloud is located 70 pc from the massive O-type stars in the Cepheus OB3 association, and is very likely an excellent example of triggered star formation via radiation-driven implosion (RDI). The cloud was studied using $\rm{H\,\small{I}}$ and 12CO data from the Canadian Galactic Plane Survey (CGPS) and infrared observations from the Wide-field Infrared Survey Explorer (WISE) telescope. The molecular mass is approximately MH2 = 350 ± 45 M$\odot$, and we find that the single IRAS source is actually the centre of a small cluster of class I and class II young stellar objects (YSOs). To compare with theory, we make reasonable estimates for the cometary cloud’s initial conditions and find that the cloud is located within the correct theoretical phase space for RDI to occur. In addition, both the morphology of the cloud and the location of different YSO classes relative to the cloud match what would be expected for RDI. We conclude that RDI is the most likely explanation for star formation within the cloud, and we suggest that similar studies of molecular clouds associated with nearby OB associations may be able to identify comparable examples.

scholarly journals Cloud fragmentation cascades and feedback: on reconciling an unfettered inertial range with a low star formation rate

2020 ◽  
Vol 493 (1) ◽  
pp. 815-820
Author(s):  
Eric G Blackman
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Dynamic Range ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Cloud Complex

ABSTRACT Molecular cloud complexes exhibit both (i) an unfettered Larson-type spectrum over much of their dynamic range, whilst (ii) still producing a much lower star formation rate than were this cascade to remain unfettered all the way down to star-forming scales. Here we explain the compatibility of these attributes with minimalist considerations of a mass-conserving fragmentation cascade, combined with estimates of stellar feedback. Of importance is that the amount of feedback needed to abate fragmentation and truncate the complex decreases with decreasing scale. The scale at which the feedback momentum matches the free-fall momentum marks a transition scale below most of the cascade is truncated and the molecular cloud complex dissipated. For a 106 M⊙ giant molecular cloud (GMC) complex starting with radius of ∼50 pc, the combined feedback from young stellar objects, supernovae, radiation, and stellar winds for a GMC cloud complex can truncate the cascade within an outer free-fall time but only after the cascade reaches parsec scales.

scholarly journals 3D shape of Orion A from Gaia DR2

2018 ◽  
Vol 619 ◽  
pp. A106 ◽  
Author(s):  
Josefa E. Großschedl ◽  
João Alves ◽  
Stefan Meingast ◽  
Christine Ackerl ◽  
Joana Ascenso ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Large Scale ◽  
Galactic Plane ◽  
Young Stellar Objects ◽  
Long Tail ◽  
Stellar Objects ◽  
Star Forming ◽  
3D Shape ◽  
Order Of Magnitude ◽  
High Column

We use the Gaia DR2 distances of about 700 mid-infrared selected young stellar objects in the benchmark giant molecular cloud Orion A to infer its 3D shape and orientation. We find that Orion A is not the fairly straight filamentary cloud that we see in (2D) projection, but instead a cometary-like cloud oriented toward the Galactic plane, with two distinct components: a denser and enhanced star-forming (bent) Head, and a lower density and star-formation quieter ∼75 pc long Tail. The true extent of Orion A is not the projected ∼40 pc but ∼90 pc, making it by far the largest molecular cloud in the local neighborhood. Its aspect ratio (∼30:1) and high column-density fraction (∼45%) make it similar to large-scale Milky Way filaments (“bones”), despite its distance to the galactic mid-plane being an order of magnitude larger than typically found for these structures.

scholarly journals Spatial distribution of star formation related to ionized regions throughout the inner Galactic plane

2017 ◽  
Vol 605 ◽  
pp. A35 ◽  
Author(s):  
P. Palmeirim ◽  
A. Zavagno ◽  
D. Elia ◽  
T. J. T. Moore ◽  
A. Whitworth ◽  
...  
Keyword(s):  
Star Formation ◽  
Galactic Plane ◽  
Formation Rate ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
Evolutionary Trend ◽  
Stellar Objects ◽  
Star Forming ◽  
Early Stages ◽  
Local Environments

We present a comprehensive statistical analysis of star-forming objects located in the vicinities of 1360 bubble structures throughout the Galactic plane and their local environments. The compilation of ~70 000 star-forming sources, found in the proximity of the ionized (Hii) regions and detected in both Hi-GAL and GLIMPSE surveys, provided a broad overview of the different evolutionary stages of star-formation in bubbles, from prestellar objects to more evolved young stellar objects (YSOs). Surface density maps of star-forming objects clearly reveal an evolutionary trend where more evolved star-forming objects (Class II YSO candidates) are found spatially located near the center, while younger star-forming objects are found at the edge of the bubbles. We derived dynamic ages for a subsample of 182 H ii regions for which kinematic distances and radio continuum flux measurements were available. We detect approximately 80% more star-forming sources per unit area in the direction of bubbles than in the surrounding fields. We estimate the clump formation efficiency (CFE) of Hi-GAL clumps in the direction of the shell of the bubbles to be ~15%, around twice the value of the CFE in fields that are not affected by feedback effects. We find that the higher values of CFE are mostly due to the higher CFE of protostellar clumps, in particular in younger bubbles, whose density of the bubble shells is higher. We argue that the formation rate from prestellar to protostellar phase is probably higher during the early stages of the (H ii ) bubble expansion. Furthermore, we also find a higher fraction of massive YSOs (MYSOs) in bubbles at the early stages of expansion (<2 Myr) than older bubbles. Evaluation of the fragmentation time inside the shell of bubbles advocates the preexistence of clumps in the medium before the bubble expansion in order to explain the formation of MYSOs in the youngest H ii regions (<1 Myr), as supported by numerical simulations. Approximately 23% of the Hi-GAL clumps are found located in the direction of a bubble, with 15% for prestellar clumps and 41% for protostellar clumps. We argue that the high fraction of protostellar clumps may be due to the acceleration of the star-formation process cause by the feedback of the (Hii) bubbles.

scholarly journals Billions of stars: the near infrared view of the Plane with UKIDSS and VISTA

2009 ◽  
Vol 5 (H15) ◽  
pp. 779-779 ◽  
Author(s):  
Philip W. Lucas ◽  
David Samuel
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Visual Inspection ◽  
Near Infrared ◽  
Galactic Plane ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Formation Regions ◽  
Initial Results ◽  
Cross Match

AbstractThe UKIDSS Galactic Plane Survey (GPS) is surveying the northern and equatorial plane in the J, H and K bands. Here we report initial results from searches for new clusters and star formation regions. 248 clusters have been detected by our Bayesian search, of which 127 are new. A visual inspection of the images is also proving successful. A cross match with Spitzer-GLIMPSE to find clusters of Young Stellar Objects is being attempted. No new globular clusters are detected except for two likely candidates already detected by Mercer et al. in GLIMPSE.

scholarly journals Massive Star Formation Throughout the Galactic Disk

2009 ◽  
Vol 5 (H15) ◽  
pp. 798-798
Author(s):  
Stan Kurtz
Keyword(s):  
Star Formation ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Young Stellar Objects ◽  
High Mass ◽  
Molecular Gas ◽  
Mass Star ◽  
Ionized Gas ◽  
Stellar Objects ◽  
Infrared Spectral

AbstractHigh-mass star formation is manifestly a phenomenon of the Galactic Plane. The process begins with pre-stellar cores, evolves to proto-stellar objects, and culminates in massive main-sequence stars. Because massive young stellar objects are deeply embedded, the radio, sub-mm, and far/mid-infrared spectral windows are the most revealing. Galactic plane surveys at these wavelengths trace hot and cold molecular gas, interstellar masers, warm dust, and ionized gas that are present during star formation.

scholarly journals Three generations of stars: a possible case of triggered star formation

2020 ◽  
Vol 496 (1) ◽  
pp. 870-874
Author(s):  
M B Areal ◽  
A Buccino ◽  
S Paron ◽  
C Fariña ◽  
M E Ortega
Keyword(s):  
Star Formation ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Three Generations ◽  
The North ◽  
Western Border ◽  
H Ii Region ◽  
New Generation ◽  
North Western

ABSTRACT Evidence for triggered star formation linking three generations of stars is difficult to assemble, as it requires convincingly associating evolved massive stars with H ii regions that, in turn, would need to present signs of active star formation. We present observational evidence for triggered star formation relating three generations of stars in the neighbourhood of the star LS II +26 8. We carried out new spectroscopic observations of LS II +26 8, revealing that it is a B0 III-type star. We note that LS II +26 8 is located exactly at the geometric centre of a semi-shell-like H ii region complex. The most conspicuous component of this complex is the H ii region Sh2-90, which is probably triggering a new generation of stars. The distances to LS II +26 8 and to Sh2-90 are in agreement (between 2.6 and 3 kpc). Analysis of the interstellar medium on a larger spatial scale shows that the H ii region complex lies on the north-western border of an extended H2 shell. The radius of this molecular shell is about 13 pc, which is in agreement with what an O9 V star (the probable initial spectral type of LS II +26 8 as inferred from evolutive tracks) can generate through its winds in the molecular environment. In conclusion, the spatial and temporal correspondences derived in our analysis enable us to propose a probable triggered star formation scenario initiated by the evolved massive star LS II +26 8 during its main-sequence stage, followed by stars exciting the H ii region complex formed in the molecular shell, and culminating in the birth of young stellar objects around Sh2-90.

SiO as a chemical signature of outflows from bright, compact sources in MSX IR-dark clouds

2004 ◽  
Vol 82 (6) ◽  
pp. 740-743 ◽  
Author(s):  
P A Feldman ◽  
R O Redman ◽  
L W Avery ◽  
J Di Francesco ◽  
J D Fiege ◽  
...  
Keyword(s):  
Star Formation ◽  
Young Stellar Objects ◽  
Line Profiles ◽  
Bipolar Outflows ◽  
Dark Cloud ◽  
Stellar Objects ◽  
Dark Clouds ◽  
Dense Cores ◽  
Infrared Dark Clouds ◽  
Compact Sources

The line profiles of dense cores in infrared-dark clouds indicate the presence of young stellar objects (YSOs), but the youth of the YSOs and the large distances to the clouds make it difficult to distinguish the outflows that normally accompany star formation from turbulence within the cloud. We report here the first unambiguous identification of a bipolar outflow from a young stellar object (YSO) in an infrared-dark cloud, using observations of SiO to distinguish the relatively small amounts of gas in the outflow from the rest of the ambient cloud. Key words: infrared-dark clouds, star formation, bipolar outflows, SiO, G81.56+0.10.

First Near-infrared Imaging Polarimetry of Young Stellar Objects in the Circinus Molecular Cloud

2018 ◽  
Vol 234 (2) ◽  
pp. 42 ◽  
Author(s):  
Jungmi Kwon ◽  
Takao Nakagawa ◽  
Motohide Tamura ◽  
James H. Hough ◽  
Minho Choi ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Young Stellar Objects ◽  
Near Infrared Imaging ◽  
Stellar Objects ◽  
Imaging Polarimetry
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