scholarly journals Peter Pan discs: finding Neverland’s parameters

2020 ◽  
Vol 496 (1) ◽  
pp. L111-L115
Author(s):  
Gavin A L Coleman ◽  
Thomas J Haworth
Keyword(s):  
Initial Conditions ◽  
Mass Star ◽  
Evolutionary Models ◽  
Peter Pan ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Accretion Rates ◽  
Order Of Magnitude ◽  
Low Mass

ABSTRACT Peter Pan discs are a recently discovered class of long-lived discs around low-mass stars that survive for an order of magnitude longer than typical discs. In this paper, we use disc evolutionary models to determine the required balance between initial conditions and the magnitude of dispersal processes for Peter Pan discs to be primordial. We find that we require low transport (α ∼ 10−4), extremely low external photoevaporation (${\le}10^{-9}\, {\rm M}_{\odot }\, {\rm yr^{-1}}$), and relatively high disc masses (>0.25M*) to produce discs with ages and accretion rates consistent with Peter Pan discs. Higher transport (α = 10−3) results in disc lifetimes that are too short and even lower transport (α = 10−5) leads to accretion rates smaller than those observed. The required external photoevaporation rates are so low that primordial Peter Pan discs will have formed in rare environments on the periphery of low-mass star-forming regions, or deeply embedded, and as such have never subsequently been exposed to higher amounts of UV radiation. Given that such an external photoevaporation scenario is rare, the required disc parameters and accretion properties may reflect the initial conditions and accretion rates of a much larger fraction of the discs around low-mass stars.

scholarly journals Quiescent high mass cores in Orion region

2006 ◽  
Vol 2 (S237) ◽  
pp. 488-488
Author(s):  
T. Velusamy ◽  
D. Li ◽  
P. F. Goldsmith ◽  
W. D. Langer
Keyword(s):  
Initial Conditions ◽  
High Mass ◽  
Mass Star ◽  
Core Mass ◽  
Star Forming ◽  
Star Forming Regions ◽  
Starting Point ◽  
Order Of Magnitude ◽  
Mass Size ◽  
Low Mass

Our goal is to study relatively quiescent dense gas cores, isolated from disruptive stars, to understand the initial conditions of massive star formation. Determining their mass, size, dynamical status, and core mass distribution is a starting point to understand the mechanisms for formation, collapse, and the origin of their IMF. We obtained CSO 350 μm, images of quiescent regions in Orion and detected 51 resolved or nearly resolved molecular cores with masses ranging from 0.1 M to 46 M (Li et al. 2006). The mean mass is 9.8 M, which is one order of magnitude higher than that of the resolved cores in low mass star forming regions, such as Taurus. Our sample includes largely thermally unstable cores, which implies that the cores are supported neither by thermal pressure nor by turbulence, and are probably supercritical. They are likely precursors of protostars.

scholarly journals Search for radio jets from massive young stellar objects

2020 ◽  
Vol 645 ◽  
pp. A29
Author(s):  
Ü. Kavak ◽  
Á. Sánchez-Monge ◽  
A. López-Sepulcre ◽  
R. Cesaroni ◽  
F. F. S. van der Tak ◽  
...  
Keyword(s):  
Field Of View ◽  
Radio Continuum ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Radio Jets ◽  
Star Forming Regions ◽  
Nonthermal Emission ◽  
Low Mass

Context. Recent theoretical and observational studies debate the similarities of the formation process of high- (>8 M⊙) and low-mass stars. The formation of low-mass stars is directly associated with the presence of disks and jets. Theoretical models predict that stars with masses up to 140 M⊙ can be formed through disk-mediated accretion in disk-jet systems. According to this scenario, radio jets are expected to be common in high-mass star-forming regions. Aims. We aim to increase the number of known radio jets in high-mass star-forming regions by searching for radio-jet candidates at radio continuum wavelengths. Methods. We used the Karl G. Jansky Very Large Array (VLA) to observe 18 high-mass star-forming regions in the C band (6 cm, ≈1′′.0 resolution) and K band (1.3 cm, ≈0′′.3 resolution). We searched for radio-jet candidates by studying the association of radio continuum sources with shock activity signs (e.g., molecular outflows, extended green objects, and maser emission). Our VLA observations also targeted the 22 GHz H2O and 6.7 GHz CH3OH maser lines. Results. We have identified 146 radio continuum sources, 40 of which are located within the field of view of both images (C and K band maps). We derived the spectral index, which is consistent with thermal emission (between − 0.1 and + 2.0) for 73% of these sources. Based on the association with shock-activity signs, we identified 28 radio-jet candidates. Out of these, we identified 7 as the most probable radio jets. The radio luminosity of the radio-jet candidates is correlated with the bolometric luminosity and the outflow momentum rate. About 7–36% of the radio-jet candidates are associated with nonthermal emission. The radio-jet candidates associated with 6.7 GHz CH3OH maser emission are preferentially thermal winds and jets, while a considerable fraction of radio-jet candidates associated with H2O masers show nonthermal emission that is likely due to strong shocks. Conclusions. About 60% of the radio continuum sources detected within the field of view of our VLA images are potential radio jets. The remaining sources could be compact H II regions in their early stages of development, or radio jets for which we currently lack further evidence of shock activity. Our sample of 18 regions is divided into 8 less evolved infrared-dark regions and 10 more evolved infrared-bright regions. We found that ≈71% of the identified radio-jet candidates are located in the more evolved regions. Similarly, 25% of the less evolved regions harbor one of the most probable radio jets, while up to 50% of the more evolved regions contain one of these radio-jet candidates. This suggests that the detection of radio jets in high-mass star-forming regions is more likely in slightly more evolved regions.

scholarly journals A centrally concentrated sub-solar-mass starless core in the Taurus L1495 filamentary complex

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Kazuki Tokuda ◽  
Kengo Tachihara ◽  
Kazuya Saigo ◽  
Phillipe André ◽  
Yosuke Miyamoto ◽  
...  
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
Volume Density ◽  
Mass Star ◽  
Brown Dwarf ◽  
Solar Mass ◽  
Star Forming ◽  
The Core ◽  
Order Of Magnitude ◽  
Low Mass

Abstract The formation scenario of brown dwarfs is still unclear because observational studies to investigate its initial condition are quite limited. Our systematic survey of nearby low-mass star-forming regions using the Atacama Compact Array (aka the Morita array) and the IRAM 30-m telescope in 1.2 mm continuum has identified a centrally concentrated starless condensation with a central H2 volume density of ∼106 cm−3, MC5-N, connected to a narrow (width ∼0.03 pc) filamentary cloud in the Taurus L1495 region. The mass of the core is $\sim {0.2\!-\!0.4}\, M_{\odot }$, which is an order of magnitude smaller than typical low-mass pre-stellar cores. Taking into account a typical core to star formation efficiency for pre-stellar cores (∼20%–40%) in nearby molecular clouds, brown dwarf(s) or very low-mass star(s) may be going to be formed in this core. We have found possible substructures at the high-density portion of the core, although much higher angular resolution observation is needed to clearly confirm them. The subsequent N2H+ and N2D+ observations using the Nobeyama 45-m telescope have confirmed the high-deuterium fractionation (∼30%). These dynamically and chemically evolved features indicate that this core is on the verge of proto-brown dwarf or very low-mass star formation and is an ideal source to investigate the initial conditions of such low-mass objects via gravitational collapse and/or fragmentation of the filamentary cloud complex.

scholarly journals X-shooter observations of low-mass stars in the η Chamaeleontis association

2018 ◽  
Vol 609 ◽  
pp. A70 ◽  
Author(s):  
Michael Rugel ◽  
Davide Fedele ◽  
Gregory Herczeg
Keyword(s):  
Young Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Plane Parallel ◽  
Star Forming Regions ◽  
Uv Emission ◽  
Accretion Rates ◽  
Low Mass

The nearby η Chamaeleontis association is a collection of 4–10 Myr old stars with a disk fraction of 35–45%. In this study, the broad wavelength coverage of VLT/X-shooter is used to measure the stellar and mass accretion properties of 15 low-mass stars in the η Chamaeleontis association. For each star, the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab. Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The accretion rates measured here are similar to those obtained from previous measurements of excess UV emission, but tend to be higher than past measurements from Hα modeling. The mass accretion rates are consistent with those of other young star forming regions.

scholarly journals Low-Mass Versus High-Mass Star Formation

1997 ◽  
Vol 182 ◽  
pp. 537-549
Author(s):  
T. W. Hartquist ◽  
J. E. Dyson
Keyword(s):  
Star Formation ◽  
Young Stars ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Global Properties ◽  
Low Mass

Structures like the clumps identified in the CO maps of the Rosette Molecular Cloud and the dense cores such as those in B5, a cluster of cores and young low-mass stars, are key to considerations of star formation. Whether star formation is a self-inducing process or one that causes itself to turn off depends greatly on whether the responses of the interclump and intercore media to young stars cause the collapse of clumps or cores to be faster than their ablation. We present a naive introduction to the lengthscales over which such responses are significant, mention ways in which the responses might induce collapse, review some of the little that is known of how flows of media around clumps and cores ablate them, and then return to the issue of the lengthscales over which such responses are significant by considering the global properties of mass-loaded flows in clumpy star forming regions.

scholarly journals Processed and Unprocessed Ices in Circumstellar Disks

2005 ◽  
Vol 13 ◽  
pp. 479-481
Author(s):  
Klaus Pontoppidan ◽  
Ewine van Dishoeck ◽  
Emmanuel Dartois ◽  
Wing-Fai Thi
Keyword(s):  
Circumstellar Disks ◽  
High Mass ◽  
Formation Mechanisms ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Solar Type ◽  
Low Mass ◽  
Circumstellar Environments

AbstractWe present 3-5 µm VLT-ISAAC spectroscopy showing the presence of methanol ices in edge-on disks of young embedded stars. Examples include the disks of L1489 IRS in Taurus and CRBR 2422.8-3423 in Ophiuchus, the last of which has the highest column density of solid CO known toward a YSO. Several additional low-mass sources in the Serpens and Chameleon molecular clouds exhibit abundant solid methanol although it is not clear if the ice is associated with a disk or with the envelope. These are the first detections of solid methanol in the disks and circumstellar environments of embedded young low-mass stars providing evidence that complex molecular species previously observed only in the solid state toward high-mass star forming regions are also present near solar-type young stars. The constraints on the formation mechanisms of methanol and the chemical evolution of ices as the material is incorporated into circumstellar disks are discussed.

scholarly journals The Circumstellar Environment of Embedded Massive Stars

2002 ◽  
Vol 12 ◽  
pp. 143-145 ◽  
Author(s):  
Lee G. Mundy ◽  
Friedrich Wyrowski ◽  
Sarah Watt
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Submillimeter Wavelength ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Circumstellar Environments ◽  
Near Future

Millimeter and submillimeter wavelength images of massive star-forming regions are uncovering the natal material distribution and revealing the complexities of their circumstellar environments on size scales from parsecs to 100’s of AU. Progress in these areas has been slower than for low-mass stars because massive stars are more distant, and because they are gregarious siblings with different evolutionary stages that can co-exist even within a core. Nevertheless, observational goals for the near future include the characterization of an early evolutionary sequence for massive stars, determination if the accretion process and formation sequence for massive stars is similar to that of low-mass stars, and understanding of the role of triggering events in massive star formation.

scholarly journals ATLASGAL – Ammonia observations towards the southern Galactic plane

2018 ◽  
Vol 609 ◽  
pp. A125 ◽  
Author(s):  
M. Wienen ◽  
F. Wyrowski ◽  
K. M. Menten ◽  
J. S. Urquhart ◽  
C. M. Walmsley ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Hyperfine Structure ◽  
Optical Depth ◽  
Line Width ◽  
Rotational Temperature ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subsample of 289 sources, the N2H+ (1–0) line was measured with the Mopra telescope. Results. We measured a median NH3 (1, 1) line width of ~ 2 km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 × 10-6 to 10-8. For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1.

scholarly journals Submillimeter Array Observations of Magnetic Fields in Star Forming Regions

2010 ◽  
Vol 6 (S270) ◽  
pp. 103-106
Author(s):  
R. Rao ◽  
J.-M. Girart ◽  
D. P. Marrone
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Computational Models ◽  
Dominant Role ◽  
Theoretical Models ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

AbstractThere have been a number of theoretical and computational models which state that magnetic fields play an important role in the process of star formation. Competing theories instead postulate that it is turbulence which is dominant and magnetic fields are weak. The recent installation of a polarimetry system at the Submillimeter Array (SMA) has enabled us to conduct observations that could potentially distinguish between the two theories. Some of the nearby low mass star forming regions show hour-glass shaped magnetic field structures that are consistent with theoretical models in which the magnetic field plays a dominant role. However, there are other similar regions where no significant polarization is detected. Future polarimetry observations made by the Submillimeter Array should be able to increase the sample of observed regions. These measurements will allow us to address observationally the important question of the role of magnetic fields and/or turbulence in the process of star formation.

scholarly journals Physical Properties of Molecular Envelopes in Low-Mass Star-Forming Regions

2000 ◽  
Vol 197 ◽  
pp. 61-70
Author(s):  
Nagayoshi Ohashi
Keyword(s):  
Physical Properties ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Narrow Line ◽  
Stellar Objects ◽  
Velocity Pattern ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Line Widths

We have carried out interferometric observations of pre-protostellar and protostellar envelopes in Taurus. Protostellar envelopes are dense gaseous condensations with young stellar objects or protostars, while pre-protostellar envelopes are those without any known young stellar objects. Five pre-protostellar envelopes have been observed in CCS JN=32–21, showing flattened and clumpy structures of the envelopes. The observed CCS spectra show moderately narrow line widths, ~0.1 to ~0.35 km s–1. One pre-protostellar envelope, L1544, shows a remarkable velocity pattern, which can be explained in terms of infall and rotation. Our C18O J=1–0 observations of 8 protostellar envelopes show that they have also flattened structures like pre-protostellar envelopes but no clumpy structures. Four out the eight envelopes show velocity patterns that can be explained by motions of infall (and rotation). Physical properties of pre-protostellar and protostellar envelopes are discussed in detail.

Sign in / Sign up

Export Citation Format

Share Document