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.

scholarly journals Molecular environs and triggered star formation around the large Galactic infrared bubble N 24

2019 ◽  
Vol 487 (2) ◽  
pp. 1517-1528 ◽  
Author(s):  
Xu Li ◽  
Jarken Esimbek ◽  
Jianjun Zhou ◽  
W A Baan ◽  
Weiguang Ji ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Young Stellar Objects ◽  
Collapse Mechanism ◽  
Kinetic Temperature ◽  
H Ii Regions ◽  
Dark Cloud ◽  
Stellar Objects ◽  
Multi Wavelength ◽  
Mass Size

Abstract A multi-wavelength analysis of the large Galactic infrared bubble N 24 is presented in this paper in order to investigate the molecular and star-formation environment around expanding H ii regions. Using archival data from Herschel and ATLASGAL, the distribution and physical properties of the dust over the entire bubble are studied. Using the Clumpfind2d algorithm, 23 dense clumps are identified, with sizes and masses in the range 0.65–1.73 pc and 600–16 300 M⊙, respectively. To analyse the molecular environment in N 24, observations of NH3 (1,1) and (2,2) were carried out using the Nanshan 26-m radio telescope. Analysis of the kinetic temperature and gravitational stability of these clumps suggests gravitational collapse in several of them. The mass–size distributions of the clumps and the presence of massive young protostars indicate that the shell of N 24 is a region of ongoing massive-star formation. The compatibility of the dynamical and fragmentation timescales and the overabundance of young stellar objects and clumps on the rim suggest that the ‘collect-and-collapse’ mechanism is in play at the boundary of the bubble, but the existence of the infrared dark cloud at the edge of bubble indicates that a ‘radiation-driven implosion’ mechanism may also have played a role there.

Molecular Clouds and Star Formation in the Southern H II Regions

1999 ◽  
Vol 51 (6) ◽  
pp. 791-818 ◽  
Author(s):  
Reiko Yamaguchi ◽  
Hiro Saito ◽  
Norikazu Mizuno ◽  
Yoshihiro Mine ◽  
Akira Mizuno ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Formation Rate ◽  
Point Sources ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Order Of Magnitude ◽  
Formation Efficiency ◽  
Active Formation

Abstract We have carried out extensive 13CO(J = 1−0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is ≳103L⊙. In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2−0.4 M⊙ yr-1, corresponding to a few 10% by mass.

scholarly journals 3D shape of Orion A with Gaia DR2 An informed view on Star Formation Rates and Efficiencies

2018 ◽  
Vol 14 (S345) ◽  
pp. 27-33
Author(s):  
Josefa E. Großschedl ◽  
João Alves ◽  
Stefan Meingast ◽  
Birgit Hasenberger
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Orion Nebula ◽  
Stellar Objects ◽  
Star Forming ◽  
The North ◽  
Low Mass ◽  
The Rich

AbstractThe giant molecular cloud Orion A is the closest massive star-forming region to earth (d ∼ 400 pc). It contains the rich Orion Nebula Cluster (ONC) in the North, and low-mass star-forming regions (L1641, L1647) to the South. To get a better understanding of the differences in star formation activity, we perform an analysis of the gas mass distribution and star formation rate across the cloud. We find that the gas is roughly uniformly distributed, while, oddly, the ONC region produced about a factor of ten more stars compared to the rest of the cloud. For a better interpretation of this phenomenon, we use Gaia DR2 parallaxes, to analyse distances of young stellar objects, using them as proxy for cloud distances. We find that the ONC region indeed lies at about 400 pc while the low-mass star-forming parts are inclined about 70∘ from the plane of the sky reaching until ∼470 pc. With this we estimate that Orion A is an about 90 pc long filamentary cloud (about twice as long as previously assumed), with its “Head” (the ONC region) being “bent” and oriented towards the galactic mid-plane. This striking new view allows us to perform a more robust analysis of this important star-forming region in the future.

scholarly journals Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium

2020 ◽  
Vol 493 (3) ◽  
pp. 4463-4517 ◽  
Author(s):  
Tho Do-Duy ◽  
Christopher M Wright ◽  
Takuya Fujiyoshi ◽  
Alistair Glasse ◽  
Ralf Siebenmorgen ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Mass Fraction ◽  
Cosmic Ray ◽  
Young Stellar Objects ◽  
Absorption Feature ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Stellar Outflows ◽  
T Tauri

ABSTRACT Utilizing several instruments on 4–8 m telescopes, we have observed a large sample of objects in the mid-infrared (8–13 μm). These comprise a few evolved stars, multiple envelopes of embedded young stellar objects (YSOs) or compact H-II regions, and several sightlines through the interstellar medium (ISM). The latter is where dust resides – and is potentially modified – between its formation in evolved stellar outflows and deposition in molecular clouds. In most objects, we detect not only the well-known 9.7 μm absorption feature of amorphous silicates but also a second absorption band around 11.1 μm whose carrier is attributed to crystalline forsterite. We propose that crystalline silicates are essentially ubiquitous in the ISM and earliest phases of star formation, and are evolutionary precursors to T-Tauri and Herbig stars where such silicates have been commonly found. Modelling shows that in most YSOs, H-II regions and ISM cases, the forsterite mass fraction is between 1 and 2 per cent, suggesting that the younger phases inherit their abundance from the ISM. However, several sources show much stronger features (abundances ≥3 per cent). This suggests that significant processing, perhaps crystallization by thermal annealing, occurs early on in star formation. Most intriguing is the first detection of crystalline silicate in the diffuse ISM. We propose that our observed abundance is consistent with a mass fraction of crystalline silicates of 10–20 per cent injected into the ISM, along with commonly accepted lifetimes against their destruction, but only if cosmic ray-induced amorphization is insignificant over a few Giga years.

scholarly journals Reproductive health among Venezuelan migrant women at the north western border of Brazil: A qualitative study

2021 ◽  
pp. 100060
Author(s):  
Maria Y. Makuch ◽  
Maria Jose D. Osis ◽  
Cinthia Brasil ◽  
Helder S.F. de Amorim ◽  
Luis Bahamondes
Keyword(s):  
Reproductive Health ◽  
Qualitative Study ◽  
Migrant Women ◽  
The North ◽  
Western Border ◽  
North Western

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.

scholarly journals Long-Term Multicolour Photometry of the Young Stellar Objects FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cygni

2015 ◽  
Vol 32 ◽  
Author(s):  
S. I. Ibryamov ◽  
E. H. Semkov ◽  
S. P. Peneva
Keyword(s):  
Gulf Of Mexico ◽  
Young Stellar Objects ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Photometric Variability ◽  
The North ◽  
Dense Molecular Cloud ◽  
Photometric Observations ◽  
All Optical

AbstractResults from long-term multicolour optical photometric observations of the pre-main-sequence stars FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cyg collected during the period from 1997 June to 2014 December are presented. The objects are located in the dense molecular cloud L935, named ‘Gulf of Mexico’, in the field between the North America and Pelican nebulae. All stars from our study exhibit strong photometric variability in all optical passbands. Using our BVRI observations and data published by other authors, we tried to define the reasons for the observed brightness variations. The presented paper is a part of our long-term photometric study of the young stellar objects in the region of ‘Gulf of Mexico’.

Aeolian Environments

2005 ◽  
Author(s):  
Eduard Koster
Keyword(s):  
Sand Dunes ◽  
Ural Mountain ◽  
Aeolian Processes ◽  
The North ◽  
Aeolian Deposits ◽  
The World ◽  
Western Border ◽  
Late Weichselian ◽  
The Baltic ◽  
North Western

The literature on aeolian processes and on aeolian morphological and sedimentological features has shown a dramatic increase during the last decade. A variety of textbooks, extensive reviews, and special issues of journal volumes devoted to aeolian research have been published (Nordstrom et al. 1990; Pye and Tsoar 1990; Kozarski 1991; Pye 1993; Pye and Lancaster 1993; Cooke et al. 1993; Lancaster 1995; Tchakerian 1995; Livingstone and Warren 1996; Goudie et al. 1999). However, not surprisingly the majority of these studies discuss aeolian processes and phenomena in the extensive warm arid regions of the world. The results of aeolian research in the less extensive, but still impressive, cold arid environments of the world are only available in a diversity of articles. At best they are only briefly mentioned in textbooks on aeolian geomorphology (Koster 1988, 1995; McKenna-Neuman 1993). Likewise, the literature with respect to wind-driven deposits in western Europe is scattered and not easily accessible. The aeolian geological record for Europe, as reflected in the ‘European sand belt’ in the north-western and central European Lowlands, which extends from Britain to the Polish–Russian border, is known in great detail (Koster 1988; van Geel et al. 1989; Böse 1991). Zeeberg (1998) showed that extensive aeolian deposits progress with two separate arms into the Baltic Region, and into Belorussia and northernmost Ukraine. Recently, Mangerud et al. (1999) concluded that the sand belt extends even to the Pechora lowlands close to the north-western border of the Ural mountain range in Russia. Sand dunes and cover sands are widespread and well developed in this easternmost extension of the European sand belt. The northerly edges of this sand belt more or less coincide with the maximal position of the Late Weichselian (Devensian, Vistulian) ice sheet, while the southern edges grade into coverloams or sandy loess and loess (Mücher 1986; Siebertz 1988; Antoine et al. 1999). However, along these southern edges the dune fields and sand sheets regionally are derived from different sources, such as the sands of the Keuper Formation or the floodplains of the Rhine and Main rivers.

scholarly journals The Star Formation Region Associated with the Cometary Nebula GM24

1987 ◽  
Vol 115 ◽  
pp. 188-188
Author(s):  
M. Tapia ◽  
M. Roth ◽  
L.F. Rodríguez ◽  
J. Cantó ◽  
P. Persi ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Near Infrared ◽  
Broad Band ◽  
Large Temperature ◽  
Stellar Objects ◽  
Star Formation Region ◽  
The Past ◽  
Visible Part ◽  
H Ii Region

GM24 is a small visible nebulosity in the vicinity of a molecular cloud. In this contribution we present the results of continuum (6-cm) and CO line (J = 1 → 0) radio observations, infrared maps, broad-band photometry and low-resolution spectroscopy as well as long-slit Echelle Ha spectroscopy. We found evidence that the GM24 = PP85 nebula is part of a larger region where star formation occurred in the past 104 years; the region is embedded in a typical molecular cloud with a dimension of ∼ 10 pc and mass of ∼104 M⊙. A compact radio H II region seems to be associated with GM24 and with one of the mid-infrared peaks detected. The nebula is most probably the visible part of an embedded H II region that is starting to emerge from the cloud. The other infrared peaks found in its vicinity (∼ 1 pc) are probably associated with less evolved stellar objects. The complex also shows an extended near-infrared flux which we believe to arise in a reflection nebula. From energy arguments, we found that the luminosity required to power the H II region and keep the cloud at the observed large temperature (TK ≅33 K), is ∼105 L⊙ which is consistent with the infrared total flux from the present measurements and those from IRAS of 4x104 L⊙; this corresponds to the flux of ∼3 BO ZAMS stars. The details of the present work have appeared in the Revista Mexicana de Astronomía y Astrofísica, Volume 11, 83, 1985.

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