ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP). II. Survey Overview: A First Look at 1.3 mm Continuum Maps and Molecular Outflows

Johnstone

et al. 2021

ApJ

Self Cite

We present the four-year survey results of monthly submillimeter monitoring of eight nearby (<500 pc) starforming regions by the JCMT Transient Survey. We apply the Lomb-Scargle Periodogram technique to search for and characterize variability on 295 submillimeter peaks brighter than 0.14 Jy beam −1 , including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starless sources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and no inherently stochastic sources are observed. We classify the secular variables by their timescales into three groups: Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect to mean peak brightness, is ∼4% for sources brighter than ∼0.5 Jy beam −1 . Limiting our sample to only these bright sources, the observed variable fraction is 37% (16 out of 43). Considering source evolution, we find a similar fraction of bright variables for both Class 0 and Class I. Using an empirically motivated conversion from submillimeter variability to variation in mass accretion rate, six sources (7% of our full sample) are predicted to have years-long accretion events during which the excess mass accreted reaches more than 40% above the total quiescently accreted mass: two previously known eruptive Class I sources, V1647 Ori and EC 53 (V371 Ser), and four Class 0 sources, HOPS 356, HOPS 373, HOPS 383, and West 40. Considering the full protostellar ensemble, the importance of episodic accretion on few years timescale is

Section: B16 Serpens South Carma 7: Linear Groupmentioning

confidence: 95%

“…Kounkel et al (2016) found no companions within 100-1000au of HOPS 315 using near-IR observations. ALMA observations of the source and outflow are also presented by Dutta et al (2020).…”

Section: B9 Orion Ngc 2068 Hops 315: Curved Groupmentioning

confidence: 99%

The JCMT Transient Survey: Four-year Summary of Monitoring the Submillimeter Variability of Protostars

Johnstone

et al. 2021

ApJ

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“…The ALMA observations of G205S2 and G206W2 were performed as part of the ALMASOP project (Project ID:2018.1.00302.S; PI: Tie Liu) in Band 6 during Cycle 6, from 2018 October to 2019 January, toward 72 fields (see Dutta et al 2020, for more details on the ALMASOP). This paper utilizes the low/high-velocity outflow tracer CO J=2-1 (230.53800 GHz), the high-velocity jet tracer SiO J=5-4 (217.10498 GHz), the envelope tracer C 18 O J=2-1 (219.56035 GHz), and 1.3 mm dust continuum emission.…”

Section: Observationsmentioning

confidence: 99%

“…4±2.4 L (HOPS 315;Furlan et al 2016;Dutta et al 2020). We compare this system with ALMA observations of a representative Class 0 protostar, G206.93-16.61W2 (hereafter, G206W2), with T bol = 31±10 K and L bol = 6.3±3.0 L (HOPS 399: Furlan et al 2016;Dutta et al 2020). Both sources exhibit very high mass-loss rates; however, the SiO jets present very different inclination angles.…”

Section: Introductionmentioning

confidence: 97%

“…The system G205.46-14.56S3 (hereafter, G205S3) has T bol = 180±33 K and L bol = 6. 4±2.4 L (HOPS 315;Furlan et al 2016;Dutta et al 2020). We compare this system with ALMA observations of a representative Class 0 protostar, G206.93-16.61W2 (hereafter, G206W2), with T bol = 31±10 K and L bol = 6.3±3.0 L (HOPS 399: Furlan et al 2016;Dutta et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Detection of a dense SiO jet in the evolved protostellar phase

Dutta,

Lee,

Johnstone

et al. 2021

Preprint

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Jets and outflows trace the accretion history of protostars. High-velocity molecular jets have been observed from several protostars in the early Class 0 phase of star formation, detected with the highdensity tracer SiO. Until now, no clear jet has been detected with SiO emission from isolated evolved Class I protostellar systems. We report a prominent dense SiO jet from a Class I source G205S3 (HOPS 315: T bol ∼ 180 K, spectral index ∼ 0.417), with a moderately high mass-loss rate (∼ 0.59 × 10 −6 M yr −1 ) estimated from CO emission. Together, these features suggest that G205S3 is still in a high accretion phase, similar to that expected of Class 0 objects. We compare G205S3 to a representative Class 0 system G206W2 (HOPS 399) and literature Class 0/I sources to explore the possible explanations behind the SiO emission seen at the later phase. We estimate a high inclination angle (∼ 40 • ) for G205S3 from CO emission, which may expose the infrared emission from the central core and mislead the spectral classification. However, the compact 1.3 mm continuum, C 18 O emission, location in the bolometric luminosity to sub-millimeter fluxes diagram, outflow force (∼ 3.26 × 10 −5 M km s −1 /yr) are also analogous to that of Class I systems. We thus consider G205S3 to be at the very early phase of Class I, and in the late phase of "high-accretion". The episodic ejection could be

Wide-angle protostellar outflows driven by narrow jets in stratified cores

Rabenanahary

Cabrit

Méliani

et al. 2022

A&A

Most simulations of outflow feedback on star formation are based on the assumption that outflows are driven by a wide angle "Xwind," rather than a narrow jet. However, the arguments initially raised against pure jet-driven flows were based on steady ejection in a uniform medium, a notion that is no longer supported based on recent observations. We aim to determine whether a pulsed narrow jet launched in a density-stratified, self-gravitating core could reproduce typical molecular outflow properties, without the help of a wide-angle wind component. We performed axisymmetric hydrodynamic simulations using the MPI-AMRVAC code with optically thin radiative cooling and grid refinement down to 5 au, on timescales up to 10 000 yrs. Then we computed the predicted properties for the purposes of a comparison with observational data. First, the jet-driven shell expands much faster and wider through a core with steeply decreasing density than through an uniform core. Second, when blown into the same singular flattened core, a jet-driven shell shows a similar width as a wide-angle wind-driven shell in the first few hundred years, but a decelerating expansion on long timescales. The flow adopts a conical shape, with a sheared velocity field along the shell walls and a base opening angle reaching up to α 90 • . Third, at realistic ages of ∼10 000 yrs, a pulsed jet-driven shell shows fitting features along with a qualitative resemblance with recent observations of protostellar outflows with the Atacama Large Millimeter Array, such as HH46-47 and CARMA-7. In particular, similarities can be seen in the shell widths, opening angles, position-velocity diagrams, and mass-velocity distribution, with some showing a closer resemblance than in simulations based on a wide-angle "X-wind" model. Therefore, taking into account a realistic ambient density stratification in addition to millenia-long integration times is equally essential to reliably predict the properties of outflows driven by a pulsed jet and to confront them with the observations.