Triggered Star Formation in Nearby High Galactic Latitude Clouds: Preliminary Overview (original) (raw)
Related papers
Triggered Star Formation in the Orion Bright‐rimmed Clouds
The Astrophysical Journal, 2005
We have developed an empirical and effective set of criteria, based on the Two Micron All Sky Survey (2MASS) colors, to select candidate classical T Tauri stars (CTTSs). This provides a useful tool to study the young stellar population in star-forming regions. Here we present our analysis of the bright-rimmed clouds (BRCs) B35, B30, IC 2118, LDN 1616, LDN 1634, and Ori East to show how massive stars interact with molecular clouds to trigger star formation. Our results support the radiation-driven implosion model, in which the ionization fronts from OB stars compress a nearby cloud until the local density exceeds the critical value, thereby inducing the cloud to collapse to form stars. We find that only BRCs associated with strong IRAS 100 m emission (a tracer of high density) and H emission (a tracer of ionization fronts) show signs of ongoing star formation. Relevant timescales, including the ages of O stars, expanding H ii regions, and the ages of CTTSs, are consistent with sequential star formation. We also find that CTTSs are only seen between the OB stars and the BRCs, with those closer to the BRCs being progressively younger. There are no CTTSs leading the ionization fronts, i.e., within the molecular clouds. All of these findings provide strong evidence of triggered star formation and show the major roles massive stars play in sustaining the starforming activities in the region.
Triggered star formation in Orion cometary clouds?
Astronomy and Astrophysics, 2002
We present new 1.2 mm continuum maps and near-and mid-infrared images of the cometary cloud L1616 located to the west of the Orion OB associations and apparently shaped by the winds and radiation coming from the massive, hot stars in the OB association. The new data reveal evidence for ongoing star formation in the cloud in addition to the known cluster of somewhat more evolved stars illuminating the NGC 1788 reflection nebula in the head of the cometary cloud. The 1.2 mm survey reveals a tight group of dust continuum sources, the brightest of which is seen to drive a powerful near-infrared H 2 jet, apparently a very young protostar of Class 0 type. The location of the newly discovered protostar with respect to the older cluster and the direction towards the OB association suggests an age sequence due to a wave of star formation driven through the cloud and triggered by the impact of the nearby OB association: the older generation of stars is located on the side of the cloud directly facing the OB association, whereas a new generation of star formation takes place deeper within the cloud.
The VISTA Orion mini-survey: star formation in the Lynds 1630 North cloud
Astronomy & Astrophysics, 2015
The Orion cloud complex presents a variety of star formation mechanisms and properties and is still one of the most intriguing targets for star formation studies. We present VISTA/VIRCAM near-infrared observations of the L1630N star-forming region, including the stellar clusters NGC 2068 and NGC 2071 in the Orion molecular cloud B, and discuss them in combination with Spitzer data. We select 186 young stellar object (YSO) candidates in the region on the basis of multi-color criteria, confirm the YSO nature of the majority of them using published spectroscopy from the literature, and use this sample to investigate the overall star formation properties in L1630N. The K-band luminosity function of L1630N is remarkably similar to that of the Trapezium cluster, i.e., it presents a broad peak in the range 0.3-0.7 M ⊙ and a fraction of substellar objects of ∼20%. The fraction of YSOs still surrounded by disk/envelopes is very high (∼85%) compared to other star-forming regions of similar age (1-2 Myr), but includes some uncertain corrections for diskless YSOs. Yet, a possibly high disk fraction, together with the fact that 1/3 of the cloud mass has a gas surface density above the threshold for star formation (∼129 M ⊙ pc −2), points toward a still ongoing star formation activity in L1630N. The star formation efficiency (SFE), star formation rate (SFR), and density of star formation of L1630N are within the ranges estimated for Galactic star-forming regions by the Spitzer core to disk and Gould's Belt surveys. However, the SFE and SFR are lower than the average value measured in the Orion A cloud and, in particular, lower than that in the southern regions of L1630. This might suggest different star formation mechanisms within the L1630 cloud complex.
Astronomy & Astrophysics, 2017
Context. The nature of turbulence in molecular clouds is one of the key parameters that control star formation efficiency: compressive motions, as opposed to solenoidal motions, can trigger the collapse of cores, or mark the expansion of Hii regions. Aims. We try to observationally derive the fractions of momentum density (ρv) contained in the solenoidal and compressive modes of turbulence in the Orion B molecular cloud and relate these fractions to the star formation efficiency in the cloud. Methods. The implementation of a statistical method applied to a 13 CO(J = 1−0) datacube obtained with the IRAM-30 m telescope, enables us to retrieve 3-dimensional quantities from the projected quantities provided by the observations, which yields an estimate of the compressive versus solenoidal ratio in various regions of the cloud. Results. Despite the Orion B molecular cloud being highly supersonic (mean Mach number ∼6), the fractions of motion in each mode diverge significantly from equipartition. The cloud's motions are, on average, mostly solenoidal (excess >8% with respect to equipartition), which is consistent with its low star formation rate. On the other hand, the motions around the main star forming regions (NGC 2023 and NGC 2024) prove to be strongly compressive. Conclusions. We have successfully applied to observational data a method that has so far only been tested on simulations, and we have shown that there can be a strong intra-cloud variability of the compressive and solenoidal fractions, these fractions being in turn related to the star formation efficiency. This opens a new possibility for star formation diagnostics in galactic molecular clouds.
Triggered Star Formation on the Border of the Orion-Eridanus Superbubble
The Astrophysical Journal, 2009
A census of classical T Tauri stars and Herbig Ae/Be stars has been performed around the Orion-Eridanus Superbubble which is ionized and created by the Ori OB1 association. This sample is used to study the spatial distribution of newborn stars, hence the recent star formation sequence, in the region that includes two giant molecular clouds (Orion A and B) and additional smaller clouds (
The COMPLETE Survey of Star-Forming Regions on its Second Birthday
2004
At age two, humans are just learning to speak, and they see the world in an unbiased way. At age two, the COMPLETE (COordinated Molecular Probe Line Extinction Thermal Emission) Survey of Star-Forming Regions is just beginning to hint at what it will do for our world view, and it is unbiased as well. The coordinated observations that comprise COMPLETE have already shown us: 1) that large (∼ 10 pc) scale bubbles created by winds from evolved stars dominate maps of extended dust emission even in relatively low-mass star-forming regions (e.g. Perseus and Ophiuchus); 2) that "giant" (> 1 pc-scale) outflows from young stars can be easily detected by applying statistical tools to an unbiased CO survey (e.g. we have doubled the number of known outflows in Perseus using the Spectral Correlation Function); and 3) that many apparent high column-density "clouds" seen in projection are actually the superposition of many velocity features (likely at different distances) along the line of sight. The upcoming detailed analysis of these new observations will quantify the degree to which the apparently ubiquitous spherical and collimated outflows can sculpt and stir molecular clouds. Taken together with recent numerical simulations' results and measurements of high velocities for some young stars, the COMPLETE Survey also raises, and should soon answer, questions about how, when, and how far stars move away from their birthplaces as functions of time.
2019
Using the NANTEN2 Observatory, we carried out a molecular line study of high-mass star forming regions with reflection nebulae, NGC 2068 and NGC 2071, in Orion in the 13CO(J=2-1) transition. The 13CO distribution shows that there are two velocity components at 9.0 and 10.5 km/s . The blue-shifted component is in the northeast associated with NGC 2071, whereas the red-shifted component is in the southwest associated with NGC 2068. The total intensity distribution of the two clouds shows a gap of ~1 pc, suggesting that they are detached at present. A detailed spatial comparison indicates that the two show complementary distributions. The blue-shifted component lies toward an intensity depression to the northwest of the red-shifted component, where we find that a displacement of 0.8 pc makes the two clouds fit well with each other. Furthermore, a new simulation of non-frontal collisions shows that observations from 60 degrees off the collisional axis agreed well with the velocity struc...
Observational study of sites of triggered star formation: CO and mid-infrared observations
Arxiv preprint arXiv:0902.4751, 2009
Context. Bright-rimmed clouds (BRCs) are isolated molecular clouds located on the edges of evolved HII regions. Star formation within these clouds may have been triggered through the propagation of photoionisation-induced shocks driven by the expansion of the HII region. Aims. The main focus of this paper is to investigate the current level of star formation within a sample of southern hemisphere BRCs and evaluate to what extent, if any, star formation may have been triggered. Methods. In this paper we present the results of a programme of position-switched CO observations towards 45 southern BRCs. The 12 CO, 13 CO and C 18 O J=1-0 rotational transitions were simultaneously observed using the 22-m Mopra telescope. We complement these observations with archival mid-infrared data obtained from the MSX and Spitzer, as well as submillimetre and radio data previously reported in the literature. Combining all of the available data with the observations presented here allows us to build up a comprehensive picture of the current level of star formation activity within a significant number of BRCs. Results. Analysis of the CO, mid-infrared and radio data result in the clouds being divided into three distinct groups: a) clouds that appear to be relatively unaffected by the photoionisation from the nearby OB star(s); b) clouds that show evidence of significant interaction between the molecular material and the HII regions; c) clouds towards which no CO emission is detected, but are associated with strong ionisation fronts; these are thought to be examples of clouds undergoing an ionisation flash. We refer to these groups as spontaneous, triggered, and zapped clouds, respectively. Comparing the physical parameters of spontaneous and triggered samples we find striking differences in luminosity, surface temperature and column density with all three quantities significantly enhanced for the clouds considered to have been triggered. Furthermore, we find strong evidence for star formation within the triggered sample by way of methanol and H 2 O masers, embedded midinfrared point sources and CO wings, however, we find evidence of ongoing star formation within only two of the spontaneous sample. Conclusions. We have used CO, mid-infrared and radio data to identify 24 of the 45 southern BRCs that are undergoing a strong interaction with their HII region. We can therefore exclude the other 21 sources (∼50%) from future studies of triggered star formation. Fourteen of the 24 interacting BRCs are found to be associated with embedded mid-infrared point sources and we find strong evidence of that these clouds are forming stars. The absence of mid-infrared sources towards the remaining ten clouds and the lack of any other evidence of star formation within these clouds leads us to conclude that these represent an earlier evolutionary stage of star formation.
Observational Evidence for Triggered Star Formation on Scales of 1 to 300 pc
2003
We present evidence for triggered star formation on two different spatial scales in the NGC 281 molecular cloud complex. This remarkable complex is situated 300 pc above the Galactic plane, and appears to be part of a 270 pc diameter ring of atomic and molecular clouds expanding at 22 km /s. We suggest that the ring has formed in a
Lynds 1622: a nearby star-forming cloud projected on Orion B?
Monthly Notices of the Royal Astronomical Society, 2008
We present results of optical spectroscopic and photometric observation of the premain sequence stars associated with the cometary shaped dark cloud Lynds 1622, and 12 CO and 13 CO observations of the cloud. We determined the effective temperatures and luminosities of 14 pre-main sequence stars associated with the cloud from their positions in the Hertzsprung-Russell diagram, as well as constructed their spectral energy distributions using optical, 2MASS and Spitzer IRAC and MIPS data. We derived physical parameters of L 1622 from the molecular observations. Our results are not compatible with the assumption that L 1622 lies on the near side of the Orion-Eridanus loop, but suggest that L 1622 is as distant as Orion B. At a distance of 400 pc the mass of the cloud, derived from our 12 CO data, is 1100 M ⊙ , its star formation efficiency is ∼ 1.8%, and the average age of its low-mass pre-main sequence star population is about 1 million years.