Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAre molecular outflows around high-mass stars driven by ionization feedback?
93
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The formation of massive stars exceeding 10 solar masses usually results in large-scale molecular outflows. Numerical simulations, including ionization, of the formation of such stars show evidence for ionization-driven molecular outflows. We here examine whether the outflows seen in these models reproduce the observations. We compute synthetic ALMA and CARMA maps of CO emission lines of the outflows, and compare their signatures to existing single-dish and interferometric data. We find that the ionization-driven models can only reproduce weak outflows around high-mass star-forming regions. We argue that expanding H II regions probably do not represent the dominant mechanism for driving observed outflows. We suggest instead that observed outflows are driven by the collective action of the outflows from the many lower-mass stars that inevitably form around young massive stars in a cluster.
rate research
Read More
Numerous spherical ``shells have been observed in young star-forming environments that host low- and intermediate-mass stars. These observations suggest that these shells may be produced by isotropic stellar wind feedback from young main-sequence stars. However, the driving mechanism for these shells remains uncertain because the momentum injected by winds is too low to explain their sizes and dynamics due to their low mass-loss rates. However, these studies neglect how the wind kinetic energy is transferred to the ISM and instead assume it is instantly lost via radiation, suggesting that these shells are momentum-driven. Intermediate-mass stars have fast ($v_w gtrsim 1000$ km/s) stellar winds and therefore the energy injected by winds should produce energy-driven adiabatic wind bubbles that are larger than momentum-driven wind bubbles. Here, we explore if energy-driven wind feedback can produce the observed shells by performing a series of 3D magneto-hydrodynamic simulations of wind feedback from intermediate-mass and high-mass stars that are placed in a magnetized, turbulent molecular cloud. We find that, for the high-mass stars modeled, energy-driven wind feedback produces $sim$pc scale wind bubbles in molecular clouds that agree with the observed shell sizes but winds from intermediate-mass stars can not produce similar shells because of their lower mass-loss rates and velocities. Therefore, such shells must be driven by other feedback processes inherent to low- and intermediate-mass star formation.
Large scale spectral maps of star forming regions enable the comparative study of the gas excitation around an ensemble of sources at a common frame of reference, providing direct insights in the multitude of processes involved. In this paper we employ spectral-line maps to decipher the excitation, the kinematical and dynamical processes in NGC 1333 as revealed by a number of different emission lines, aiming to set a reference for the applicability of tracers in constraining diverse physical processes. We reconstruct line maps for H$_2$ , CO, H$_2$O and C$^+$ using data obtained with the Spitzer-IRS and Herschel HIFI-SPIRE. We compare the morphological features of the maps and derive the gas excitation for regions of interest employing LTE and non-LTE methods. We also calculate the kinematical and dynamical properties for each outflow tracer consistently for all outflows in NGC 1333. We finally measure the water abundance in outflows with respect to carbon monoxide and molecular hydrogen. CO and H$_2$ are highly excited around B-stars and at lower levels trace protostellar outflows. H$_2$O emission is dominated by a moderately fast component associated with outflows. Intermediate J CO lines appear brightest at the locations traced by a narrow H$_2$O component, indicating that beyond the dominating collisional processes, a secondary, radiative excitation component can also be active. The morphology, kinematics, excitation and abundance variations of water are consistent with its excitation and partial dissociation in shocks. Water abundance ranges between 5 x 10$^{-7}$ and 10$^{-5}$, with the lower values being more representative. Water is brightest and most abundant around IRAS 4A which is consistent with the latter hosting a hot corino source. Finally, the outflow mass flux is found highest for CO and decreases by one and two orders of magnitude for H$_2$ and H$_2$O, respectively.
We use a suite of SPH simulations to investigate the susceptibility of protoplanetary discs to the effects of self-gravity as a function of star-disc properties. We also include passive irradiation from the host star using different models for the stellar luminosities. The critical disc-to-star mass ratio for axisymmetry (for which we produce criteria) increases significantly for low-mass stars. This could have important consequences for increasing the potential mass reservoir in a proto Trappist-1 system, since even the efficient Ormel et al. (2017) formation model will be influenced by processes like external photoevaporation, which can rapidly and dramatically deplete the dust reservoir. The aforementioned scaling of the critical $M_d/M_*$ for axisymmetry occurs in part because the Toomre $Q$ parameter has a linear dependence on surface density (which promotes instability) and only an $M_*^{1/2}$ dependence on shear (which reduces instability), but also occurs because, for a given $M_d/M_*$, the thermal evolution depends on the host star mass. The early phase stellar irradiation of the disc (for which the luminosity is much higher than at the zero age main sequence, particularly at low stellar masses) can also play a key role in significantly reducing the role of self-gravity, meaning that even Solar mass stars could support axisymmetric discs a factor two higher in mass than usually considered possible. We apply our criteria to the DSHARP discs with spirals, finding that self-gravity can explain the observed spirals so long as the discs are optically thick to the host star irradiation.
We present the detection and follow-up observations of planetary candidates around low-mass stars observed by the K2 mission. Based on light-curve analysis, adaptive-optics imaging, and optical spectroscopy at low and high resolution (including radial velocity measurements), we validate 16 planets around 12 low-mass stars observed during K2 campaigns 5-10. Among the 16 planets, 12 are newly validated, with orbital periods ranging from 0.96-33 days. For one of the planets (K2-151b) we present ground-based transit photometry, allowing us to refine the ephemerides. Combining our K2 M-dwarf planets together with the validated or confirmed planets found previously, we investigate the dependence of planet radius $R_p$ on stellar insolation and metallicity [Fe/H]. We confirm that for periods $Plesssim 2$ days, planets with a radius $R_pgtrsim 2,R_oplus$ are less common than planets with a radius between 1-2$,R_oplus$. We also see a hint of the radius valley between 1.5 and 2$,R_oplus$ that has been seen for close-in planets around FGK stars. These features in the radius/period distribution could be attributed to photoevaporation of planetary envelopes by high-energy photons from the host star, as they have for FGK stars. For the M dwarfs, though, the features are not as well defined, and we cannot rule out other explanations such as atmospheric loss from internal planetary heat sources, or truncation of the protoplanetary disk. There also appears to be a relation between planet size and metallicity: those few planets larger than about 3 $R_oplus$ are found around the most metal-rich M dwarfs.
Whether high mass stars continue to accrete material beyond the formation of an HII region is still an open question. Ionized infall and outflow have been seen in some sources, but their ties to the surrounding molecular gas are not well constrained. We aim to quantify the ionized and molecular gas dynamics in a high mass star forming region (K3-50A) and their interaction. We present CARMA observations of the 3mm continuum, H41alpha, and HCO+ emission, and VLA continuum observations at 23 GHz and 14.7 GHz to quantify the gas and its dynamics in K3-50A. We find large scale dynamics consistent with previous observations. On small scales, we find evidence for interaction between the ionized and molecular gas which suggests the ionized outflow is entraining the molecular one. This is the first time such an outflow entrained by photo ionized gas has been observed. Accretion may be ongoing in K3-50A because an ionized bipolar outflow is still being powered, which is in turn entraining part of the surrounding molecular gas. This outflow scenario is similar to that predicted by ionization feedback models.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
