Focus Meeting 4 - Poster Abstracts

Seeking for magnetic fields in rotating disks/jets around young stars

Bacciotti, Francesca

We have started a project with ALMA for a combined study of rotation and magnetic properties in disks and jets around low mass young stars. _x000D_ The motivation is to test the models of magneto-centrifugal launch of jets along the magnetic field lines that thread the disk. This mechanism is relevant for star formation, as the associated magnetic braking of the disk allows the extration of angular momentum from teh system and the accretion of disk material onto the central star._x000D_ Our plan is to use the polarimetric capabilities of ALMA to determine the magnetic configuration _x000D_ in systems with rotating jets and disks. In these cases, in fact, we expect to find strong ordered magnetization in the first ten of AU from the source._x000D_ We have recently obtained ALMA Band 7 polarimetric data for the young systems DG Tau and CW Tau, two T Tauri stars for which the rotation properties of jet and disk are well known. _x000D_ The analysis of these data reveals, however, that dust self-scattering concurs strongly with the magnetic configuration to the determination of the polarization patterns._x000D_ We present here the first results of the project, illustrating the different interpretations. Even in the case in which magnetic alignement is weak, the polarization configuration can be a powerful tool for the diagnostics of the dust properties in disks.

Gas dynamics and NH$_2$D chemistry in high-mass pre/protocluster clumps

Zhang, Chuanpeng

The initial stage of star formation is very difficult to study due to its high density ($n_{\rm H_2} >$ 10$^6$\,cm$^{-3}$) and low temperature ($T_{\rm dust} <$ 18\,K), which lead to many molecules depleted from the gas phase by freezing out onto dust grains. However, the deuterium species like NH$_2$D could survive in the extreme condition. In this work, we present NH$_2$D, NH$_3$ (1,\,1) and (2,\,2) observations using PdBI and VLA, respectively, towards eight massive precluster clumps (G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71). We use 3D \textit{Gaussclumps} to extract NH$_2$D cores and provide a statistical view of their deuterium chemistry. The NH$_2$D cores are gravitationally bound, and have potential to form intermediate- or high-mass stars in future. We find that NH$_2$D emissions are not associated with either a dust continuum or NH$_3$ peak position or infrared source, but just surrounding the central continuum cores, suggesting they are prestellar or starless cores. We detect extreme high deuterium fractionation of $0.03 \leqslant D_{\rm frac} \leqslant 1.41$ with a median value of 0.45$\pm$0.01. We find that the correlation between $D_{\rm frac}$ and $T_{\rm kin}$ is a positive-correlation from 13 to 16.5\,K, but anti-correlation from 16.5 to 22\,K. The most suitable habitat for NH$_2$D reaction may be at the temperature of around 16.5\,K. The detected NH$_2$D lines are very narrow with a median value of around 0.94$\pm$0.09\,$\kms$. The line widths are still dominated by both thermal motions and turbulence. Using NH$_3$ (1,\,1) as a dynamical tracer, we find a very complicated dynamical movement towards all the eight clumps, either outflow and rotation, or convergent flow and collision, or large velocity gradient. The sample generally present obvious characteristic of Keplerian disk, suggesting that accretion is keep going and increasing gradually from prestellar core to evolved source stages.

Magnetic fields and polarimetry in planet-forming disks

Bertrang, Gesa H.-M.

Understanding the physical processes in planet-forming disks is vital for the understanding of planet formation. It has been predicted that magnetic fields are an important factor on a wide range of these mechanisms, such as the migration of planet(esimals) and the mere evolution of disks. Yet, observational constraints are still pending. In the classical picture, (sub-)mm continuum polarization is the tracer for magnetic fields in disks. Aspherical dust grains, whose thermal emission is intrinsically polarized, get aligned by the magnetic field due to radiative torques. In recent years, however, this picture has been challenged. New theoretical studies show that (sub-)mm continuum polarization can also be created by scattering of the thermal dust emission or arise from aspherical grains which are aligned by the radiation field rather than the magnetic field. These three mechanisms trace fundamentally different physics in protoplanetary disks, yet, their polarization predictions are not clearly distinguishable. I will give an outlook on how to disentangle the sources of continuum polarimetry with ALMA by applying spectro-polarimetry, and present the first predictions for linear line polarization in disks.

Twinkle little stars: Massive stars are quenched in strong magnetic fields

Tabatabaei, Fatemeh

I present a recent discovery of the role of the magnetic fields and cosmic rays in decelerating the formation of massive stars in the center of NGC1097. Full polarization VLA/radio continuum observations combined with the SMA/CO and the HST/H-alpha and Paschen-alpha data, allowed us to separate the thermal and synchrotron emission, map the ordered & turbulent magnetic field strength, and investigate the energy balance on scales of giant molecular clouds. The strong magnetic field in the central kpc region of NGC1097 is mainly turbulent on observed scales. A comparison of the mass-to-magnetic flux ratio of the molecular clouds shows that most of them are magnetically supported against gravitational collapse needed to form cores of massive stars. Moreover, the star formation efficiency of the clouds drops with the equipartition magnetic field strength. Such an anti-correlation holds with neither the turbulent gas nor the thermal gas pressure. Magnetic fields supporting the molecular clouds prevent collapse of gas to densities needed to form massive stars. Instead,  cloud fragmentation will continue to reach the regime for the low density gas to form many low-mass stars.

Abundance Patterns in Herbig Ae/Be Stars

Cowley, Charles

The peculiar chemistry of some HAeBe stars is usually described as resembling the photospheric composition of the Lambda Boo stars, where the lighter CNO elements have normal or solar composition while the heavier elements are depleted. In Lambda Boo stars, this abundance pattern is closely related to the volatility of the elements, essentially to the condensation temperatures (Tc). The "Lambda Boo" abundance pattern is much too simplistic to describe modern results. The simplest abundance pattern in HAeBe stars shows a high correlation with Tc. However, unlike the canonical Lambda Boo pattern, the volatile elements may be significantly overabundant. Within the CNO elements themselves, large abundance anomalies can occur. Most puzzling is the behavior of intermediate volatiles, such as sodium and especially zinc. Simple mechanisms based only on Tc canot explain these anomalies.The magnetic fields of HAeBe stars are weaker and less common than in their low-mass congeners, the T Tauri stars. An understanding their magnetism combined with their chemistry should help to constrain theories of their formation and magnetospheric accretion histories.We remark on the difficulties and uncertainties in analyzing spectra often replete with emissions, and significant rotational broadening. Use of the Ca II K-line to determine spectral type, and thence E(B-V) is questionable. However, most HAeBe stars show diffuse interstellar bands, whose strengths can be related to E(B-V).

Characterization of methanol as a magnetic field tracer in massive star-forming regions

Lankhaar, Boy

Magnetic fields play an important role during star formation. Direct magnetic field strength observations have proven specifically challenging in the dynamic protostellar phase. Because of their occurrence in the densest parts of star forming regions, masers, through polarization observations, are the main source of magnetic field strength and morphology measurements around protostars. Of all maser species, methanol is one of the strongest and most abundant tracers of gas around high-mass protostellar disks and in outflows. However, because experimental determination of the magnetic characteristics of methanol has remained unsuccessful, a magnetic field strength analysis of these regions could hitherto not be performed. In this talk, we present quantum-chemical calculations of the Zeeman-parameters of methanol. We use these parameters in re-analyzing methanol maser polarization observations. With these calculations, we can confirm the presence of dynamically important magnetic fields around protostars. 

On the origin of density filaments in the magnetized and turbulent interstellar medium

Xu, Siyao

This study is motivated by recent observations on ubiquitous interstellar density filaments and guided by modern theories of compressible magnetohydrodynamic (MHD) turbulence. As the fundamental dynamics of compressible MHD turbulence, perpendicular turbulent mixing entails elongated density structures aligned with the local magnetic field, accounting for low-density parallel filaments seen in both diffuse media and diffuse regions of molecular clouds (MCs), e.g., HI filaments, striations and subfilaments in MCs. Differently, in highly supersonic MHD turbulence in MCs, shocks driven by supersonic flows result in dense filaments. Simple shock physics involving magnetic effects can well explain the preference on observing dense filaments perpendicular to magnetic fields in MCs as shown by Planck, which set up the necessary condition for the self-gravity to take over the gas dynamics and initiate the subsequent star formation.

Zeeman Effect Observations in Class I Methanol Masers

Momjian, Emmanuel

We report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the star forming region DR21W. The 44 GHz methanol masers in this source occur in a ~3 arcsec linear structure that runs from northwest to southeast, with the two dominant components at each end, and several weaker components in between. Toward a 93 Jy maser in the dominant northwestern component, we find a significant Zeeman detection of -23.4 ± 3.2 Hz. If we use the recently published result of Lankhaar et al. (2018) that the F=5→4 hyperfine transition is responsible for the 44 GHz methanol maser line, then their value of z=-0.920 Hz/mG yields a line-of-sight magnetic field of 25.4 ± 3.5 mG. If Class I methanol masers are pumped in high density regions with n ~ 107-8 cm-3, then magnetic fields in these maser regions should be a few to several tens of mG. Therefore, our result in DR21W is certainly consistent with the expected values. We also give a brief overview of past Zeeman effect detections in Class I methanol masers (e.g., Sarma & Momjian 2011; Momjian & Sarma 2017) in light of the recently measured Zeeman splitting factors.

Fragmentation of Filamentary Cloud Permeated by Perpendicular Magnetic Field

Hanawa, Tomoyuki

We examine the linear stability of a filamentary cloud permeated by a perpendicular magnetic field._x000D_ The model cloud is assumed to have a Plummer-like profile and to be supported against the self gravity_x000D_ by turbulence. The effects of turbulence is taken into account by enhancing effective pressure_x000D_ of a low density gas. We derive the effective pressure as a function of the density from the condition of the hydrostatic balance. When the radial density profile is broader, i.e., the index is smaller, the model cloud is more unstable against radial collapse. When the magnetic field is mildly strong, the radial collapse is suppressed. If the displacement vanishes in the region very far from_x000D_ the cloud axis, the model cloud is stabilized completely by mildly strong magnetic field. _x000D_ If the rearrangement of the magnetic flux tubes is permitted, the model cloud is unstable even_x000D_ when the magnetic field is extremely strong. The stability depends on the outer boundary condition. _x000D_ The growth rate of the rearrangement mode is smaller for a lower index. We also discuss the case when the initial magnetic field is oblique to the cloud axis.

Kinematics of neutral and ionized gas in the candidate protostar with efficient magnetic braking B335

Yen, Hsi-Wei

The magnetic field in collapsing dense cores is expected to slow down the gas motions and transfer the angular momentum of the collapsing material outward, and thus suppress the formation of large-scale Keplerian disks, the so-called "magnetic braking". However, this effect of the magnetic field is observationally not well understood. In this presentation, I will introduce our observational results of the kinematics of neutral and ionized gas in the Class 0 protostar B335. With the single-dish, SMA, and ALMA observations in the neutral molecular line, C18O (2-1), we found that the specific angular momentum in B335 decreases with decreasing radii from 0.1 pc to 100 au scales, and on a 100 au scale the specific angular momentum is a factor of two lower than the expectation from the collapse model where the angular momentum is conserved. In addition, no Keplerian disk with a size larger than 10 au was observed with ALMA. Thus, B335 is a promising candidate with efficient magnetic braking. We have also observed B335 in the ionized molecular line, H13CO+ (3-2), with ALMA. The infalling velocity in the protostellar envelope on a 100 au scale around B335 measured from the H13CO+ emission is consistent with that from the C18O emission within the uncertainty, and our observations put an upper limit of the ion-neutral velocity drift to be 0.3 km/s on a 100 au scale. These results suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope. However, due to our limited angular resolution, we cannot rule out that there is a significant velocity drift only in the midplane of the infalling envelope. Future observations with higher angular resolutions are needed to establish the definite presence of ambipolar diffusion in B335.

Millimetre polarization in a disk around a massive protostar

Girart, Josep M.

Here we present deep, 40 milliarcsecond agular resolution, 1.14 mm, polarimetric, ALMA observations towards, the massive protostar driving the HH 80-81 radio jet. The observations resolves the disk oriented perpendicular to the radio jet, with a radius of the ~290 au at 1.7 kpc distance. The continuum brightness temperature, the intensity profile and the polarization properties clearly indicates that the disk is optically thick for a radius of R>170 au. The linear polarization pattern indicates that is dominated by self-scattering. We discuss the effects of self-scattering and radiaton alignment of elongated grains for dust continuum polarimetrics observations aimed to study magnetic fields.

Dust emission and polarisation in the massive star-forming filament G35.39-0.33

Juvela, Mika

G35.39-0.33 is a massive (~5000 MSun) filamentary cloud at a distance of 2.9 kpc. It has a number of low-luminosity infrared sources and potentially prestellar massive cores but still appears to be in an early stage of its star formation activity. We have used JCMT POL-2 850 µm observations and Planck 353 GHz measurements to study dust emission and polarisation in the G35.39-0.33 field. The relationships between the magnetic field geometry, grain alignment, and polarisation fraction were examined with radiative transfer modelling.The G35.39-0.33 cloud exhibits large values of submillimetre dust opacity and opacity spectral index, both typical of very dense clouds. Planck data reveal an almost uniform polarisation fraction and a field direction that is at an oblique angle relative to the main cloud. In SCUBA-2 observations, the magnetic field is mostly perpendicular to the filament but at one end turns parallel to it. There is no contradiction because the SCUBA-2 measurements are not sensitive to the large scale field. The polarisation fraction in the filament is of the order of p=1-2%. The decrease of p as a function of column density is partly caused by noise, with a possible contribution from the filtering of the extended emission. The data are in agreement with models where grain alignment is lost at densities above ~104 cm-3. The agreement with simulations employing radiative torques alignment is only approximate but strong conclusions are precluded by the uncertainty of the 3D field geometry and the spatial filtering of the ground-based observations.The presentation is given on behalf of the JCMT Large Program SCOPE (PI T. Liu).

Non-Zeeman Circular Polarization of Molecular Spectral Lines in the ISM

Chamma, Mohammed

We searched archival data of the Submillimeter Array (SMA) for evidence of circular polarization in common molecular tracers, most notably CO. This circular polarization possibly arises from anisotropic resonant scattering (ARS) whereby background linear polarization signals are converted to circular polarization, as indicated by observations of Orion KL taken with the Caltech Submillimeter Observatory and of the supernova remnant IC443 taken with the IRAM 30m. We find circular polarization in NGC7538, IRC+10216 and Orion KL for transitions of CO, SiO and SiS to levels high enough to suggest that the presence of circular polarization in these spectral lines is widespread for such objects, and that the conversion of linear-to-circular polarization is common. This implies that measuring circular polarization is an important step when studying magnetic fields through the linear polarization of molecular spectral lines in the interstellar medium.

Statistics of the relative orientation between magnetic fields in clumps and filaments

Alina, Dana

Star formation seems to be more efficient inside filamentary structures of molecular clouds. The role that the magnetic field plays in this process can be revealed using polarimetric data. We have performed a statistical analysis of the relative orientation between the plane-of-sky magnetic field and the filaments associated with the Galactic Cold Clumps - the very cold condensations of ISM that could host regions of star formation. We have separated polarization parameters components of the filaments and their background using thin optical medium assumption, and the filaments have been detected in the Planck data using the Rolling Hough Transform algorithm. Alignment properties depend on the density of the filaments but also on the density of the filaments’ environment. We find both parallel and perpendicular alignment between the matter structures and the magnetic field inside the Planck Cold Clumps situated in high density environments while there is mostly parallel alignment inside the filaments if the clumps contribution is omitted.

Circumstellar Disks and Outflows in Turbulent Molecular Cloud Cores: Possible Formation Mechanism for Misaligned Systems

Matsumoto, Tomoaki

We investigate the formation of circumstellar disks and outflows subsequent to the collapse of molecular cloud cores with the magnetic field and turbulence. The ohmic dissipation is also considered, showing a high resistivity in the high-density regime. Numerical simulations are performed by using an adaptive mesh refinement (AMR) to follow the evolution up to ~1000 years after the formation of a protostar.In the simulations, circumstellar disks are formed around the protostars; those in magnetized models are considerably smaller than those in nonmagnetized models, but their size increases with time. The models with stronger magnetic fields tend to produce smaller disks. During evolution in the magnetized models, the mass ratios of a disk to a protostar is approximately constant at ~1%-10%.The circumstellar disks are aligned according to their angular momentum, and the outflows accelerate along the magnetic field on the 10-100 au scale; this produces a disk that is misaligned with the outflow. The magnetic field has an internal structure in the cloud cores, which causes misalignment between the outflows and the magnetic field on the scale of the cloud core. The distribution of the angular momentum vectors in a core also has a non-monotonic internal structure. This should create a time-dependent accretion of angular momenta onto the circumstellar disk. Therefore, the circumstellar disks are expected to change their orientation as well as their sizes in the long-term evolutions.The models with strong magnetic field tend to exhibit cavities in the flat, infalling envelopes. The radius of the cavity increases with time, and it increases up to ~50 au by the end of the simulation. The cavities are caused by the magnetic pressure. Such cavities probably correspond to the complex circumstellar structures, which have been revealed by the recent high-resolution observations. 

Magnetic massive stars in star forming regions

Hubrig, Swetlana

One idea for the origin of magnetic fields in massive stars suggests that themagnetic field is the fossil remnant of the Galactic ISM magnetic field,amplified during the collapse of the magnetised gas cloud. A search for thepresence of magnetic fields in massive stars located in active sites of starformation led to the detection of rather strong magnetic fields in a few youngstars. Future spectropolarimetric observations are urgently needed to obtaininsights into the mechanisms that drive the generation of kG magnetic fieldsduring high-mass star formation.

An abundance analysis of AK Sco, a Herbig Ae SB2 system with a magnetic component

Hubrig, Swetlana

AK Sco is an SB2 system formed by two nearly identical Herbig Ae stars, withT_eff = 6500 K and log g = 4.5, surrounded by a circumbinary disk. This activelyaccreting system is of special interest among the pre-main-sequence binariesbecause of its prominent ultraviolet excess and the high eccentricity of itsorbit. Moreover, recent spectropolarimetric observations using HARPSpol indicatethe presence of a weak magnetic field in the secondary component. An abundanceanalysis of both components has shown that all elements have a solar abundancein the two stars, except for Li and Ba. These elements are enhanced by 2.2 and0.5 dex, respectively, in the A component and by 2.4 and 0.5 dex, respectively,in the B component.

Measuring Magnetic Fields from Water Masers in the Synchrotron Protostellar Jet in W3(H2O)

Goddi, Ciriaco

Magnetic fields are invoked to launch, drive, and shape jets in both low- and high-mass protostars, but observational data on the spatial scales required to assess their role in the protostellar mass-loss process is still scarce.We report full polarimetric VLBA observations of water masers towardsthe Turner-Welch Object in the W3(OH) high-mass star formingcomplex. This object drives a synchrotron jet, which is quiteexceptional for a high-mass protostar, and is associated with astrongly polarized water maser source, W3(H2O),making it an optimal target to investigate the role of magnetic fieldson the innermost scales of protostellar disk-jet systems.The linearly  polarized emission from water masers provides clues on the orientationof the local magnetic field, while the measurement of the Zeemansplitting from circular polarization provides its strength.The water masers trace a bipolar, biconical outflow at the center of the synchrotron jet.Although  on scales of a few thousand AU the magnetic field inferredfrom the masers is on average orientated along the flow axis, onsmaller scales (10s to 100s of AU), we have revealed a misalignmentbetween the magnetic field and the velocity vectors, which arises fromthe compression of the field component along  the shock front.Our measurements support a scenario where the magnetic field would evolve fromhaving a dominant  component parallel to the outflow velocity in thepre-shock gas, with field strengths of the order of a few tens of mG(at densities of 107 cm-3), to being mainly dominated by  theperpendicular component of order of a few hundred of mG in the post-shock gaswhere the water masers are excited (at densities of 109 cm-3).The general implication is that in the undisturbed (i.e. not-shocked)circumstellar gas, the flow velocities would follow closely themagnetic field lines, while in the gas shocked by the prostostellarjet the magnetic field would be re-configured to be parallel to the shock front. 

Magnetically regulated collapse in the B335 protostar ? ALMA observations of the polarized dust continuum emission

Maury, Anaëlle

The role of the magnetic field during protostellar collapse is poorly constrained from an observational point of view, although it could be significant if we believe state-of-the-art models of protostellar formation. We present polarimetric observations of the 233 GHz thermal dust continuum emission obtained with ALMA in the B335 Class~0 protostar. Linearly polarized dust emission arising from the circumstellar material in the envelope of B335 is detected at all scales probed by our observations, from radii of 50 to 1000 au._x000D_ The magnetic field structure producing the dust polarization has a very ordered topology in the inner envelope, with a transition from a large-scale poloidal magnetic field, in the outflow direction, to strongly pinched in the equatorial direction. This is probably due to magnetic field lines being dragged along the dominating infall direction since B335 does not exhibit prominent rotation._x000D_ Our data and their qualitative comparison to a family of magnetized protostellar collapse models show that, during the magnetized collapse in B335, the magnetic field is maintaining a high level of organization from scales 1000 au to 50 au: this suggests the field is dynamically relevant and capable of influencing the typical outcome of protostellar collapse, such as regulating the disk size in B335.

POLICAN first results: Infrared Polarization of the Molecular Cloud Associated to IRAS18236-1205

Luna, Abraham

Using the new infrared image polarimeter POLICAN (Devaraj, R., Luna, A., Carrasco, L., et al. PASP 2018), at the Guillermo Haro Astrophysical Observatory in Cananea Sonora Mexico, we investigate the role of the magnetic fields in the process of star formation observed at the molecular cloud associated to the source IRAS18236-1205 (Retes, R., Mayya, Y.D., Luna, A., and Carrasco, L. Apj, 2017). Using the polarization field measured in H band in the molecular cloud, we obtained a strong correlation in the projected orientation with the observed molecular outflow at the IRAS central densest molecular region. Comparing the mean field projected polarization orientation in the cloud with the Milky Way Galactic plane field, there is a 20deg of deviation and the long axis for the filamentary molecular cloud is perpendicular to the outflow (Luna, A., Retes, R., Devaraj, R., et al. RMxAASC 2017). Using the Chandrasekhar-Fermi (CF) method we investigated the energy balance of the complete cloud. Column densities were estimated with the molecular component and confirmed with an approaching model using Herschel photometric data. Following these approach and using POLICAN instrument we are observing nearest molecular clouds like MonR2 and other regions at the Milky Way galactic plane (< 3kpc) to analyze their stability using the CF approximation. Results will be compared against theoretical models with strong and weak magnetic fields in molecular clouds with ongoing star formation (Zamora-Aviles, M., Vazquez-Semadeni. E., et al 2018).

Evolving Models of Stellar Photospheric and Coronal Magnetic Fields

Cheung, Mark

We present results from an ongoing effort to model the evolving photospheric and coronal magnetic fields of cool stars. In this project, we run a series of surface flux transport (SFT) models of starspot evolution. SFT models are used as lower boundary conditions to drive evolving models of stellar coronal magnetic fields. The coronal magnetic fields are modeled by magnetofriction (MF), which allows us to construct force-free coronal fields evolving in response to starspot evolution. The combined SFT/MF simulations are used to synthesize dynamic Stokes spectra to serve as inputs for Zeeman Doppler Imaging (ZDI) inversions. Photometric light curves modulated by starspot evolution and stellar rotation are also synthesized. We report on tests of the validity of ZDI inversions for such models, and examine the correspondence between inferred stellar magnetic properties with the input SFT parameters governing flux emergence, differential rotation and turbulent dispersal. This project is part the Solar-Stellar Connection Focus Science Team funded by NASA's Living With A Star program.

MHD turbulence, self-gravity and radiative cooling effects on star formation regions

Barreto M. dos Santos, Lucas

In spite of being the focus of intense investigation for several decades, the comprehension on how star formation (SF) occurs is still a great challenge. In our galaxy, it is well known that stars are formed in dense regions within giant molecular clouds. The total internal pressure (thermal plus magnetic) in the clouds is, in general, large enough to prevent its gravitational collapse and an external agent, like turbulence driven by supernova shocks, spiral waves or stellar winds may be necessary to provoke the formation of high density, supersonic regions that may in turn collapse to form stars or an entire group of them. In this work we present three-dimensional MHD simulations of star formation regions considering the effects of radiative cooling and self-gravity in the overall process of ISM turbulence evolution and clouds collapse. Several models involving different regimes of super to sub-Alfvenic turbulence have been considered. In general lines, the results reveal the formation of elongated filaments with a few star-forming cores mainly at the confluence of the filaments, resembling, e.g., the recently observed features of the ISM by Hershel and CCAT at mm wavelengths. A detailed statistical analysis aiming at the characterization of several observable quantities, like the probability density function (PDF), the core mass function (CMF), the density power spectrum, and the overall magnetic field orientation in the filaments as a function of their size and scales will be also presented. In particular, we find that at large scale, more diffuse regions, the overall magnetic field orientation is parallel to the filaments while at smaller, denser regions, where self-gravity confinement prevails, the magnetic fields are in general perpendicular to the filaments, in consistency with observations. Finally, we will present direct comparisons of the simulations with selected regions of Hershel, CCAT and PLANCK foreground.

Doppler images of V1358 Ori

Kriskovics, Levente

We present Doppler images of the active dwarf V1358 Ori. The maps are derived with our new Doppler imaging code iMap applied on TBL-NARVAL data, covering two consecutive rotations. The maps show polar spottedness, as well as cooler features on lower latitudes. Solar-type surface differential rotational pattern is also detected by cross-correlating the consecutive maps.

Changing the Landscape: New Ways of Tracing and Probing Magnetic fields with Velocity and Synchrotron Gradients


Modern understanding of MHD turbulence suggests that this type of turbulence is strongly anisotropic at small scales. This entails a conclusion that gradients of velocity and magnetic field are perpendicular to the local direction of the magnetic field. Guided by this fact we proposed, developed and successfully tested with observational data a set of new techniques for studying interstellar magnetic fields. I shall demonstrate how the velocity gradients can be measured using either velocity centroids of thin channel spectroscopic maps, while magnetic field gradients can be measured using synchrotron intensity or synchrotron polarization. I shall present 3D maps of galactic magnetic fields obtained with the new technique, demonstrate that gradients can provide both magnetic field tracing and identify the regions of graviational collapse. I shall discuss new ways of obtaining magnetic field strength using the gradients. I shall show how to use different types of gradients to map the structure of the magnetic web within the multiphase interstellar media. 

The SOUTH POL Survey: Status and First Results

Magalhaes, Antonio Mario

SOUTH POL is a survey of the Southern sky in optical linearly polarized light. It uses a newly built, wide field polarimeter for T80-S, an 84 cm robotic telescope installed at Cerro Tololo (CTIO), Chile. It will initially cover the sky South of declination -15 deg aiming at a polarimetric accuracy < 0.1% at V~14-15. The telescope-camera combination covers a field of about 2.0 square degrees.SOUTH POL will impact areas such as Cosmology, Extragalactic Astronomy, Interstellar Medium of the Galaxy and Magellanic Clouds, Star Formation, Stellar Envelopes, Stellar Explosions and Solar System. Both catalog data and raw images will be made available. The polarimeter has been successfully commissioned in mid-November, 2017. We will describe the instrument, data reduction and its challenges, as well as a sample of the first results.

B-fields and dust grains in the L1689 stream region: an interpretation of Planck polarization data

Matsumura, Masafumi

We investigate the polarization properties around the L1689 stream in rho Oph star forming region. We have found that the observed polarization with Planck makes a nearly closed curve in the Stokes QU plane, as a function of position in a direction perpendicular to the stream. Possible interpretations of this pattern will be presented.

The role of the magnetic field in a translucent molecular cloud

Panopoulou, Georgia

Translucent molecular clouds represent a vastly underexploredregime of cloud evolution in terms of the effect of the magnetic field. Theirpristine nature renders them ideal for investigating the initialproperties of the magnetic field, prior to the onset of star formation.Using starlight polarimetry, we map the plane-of-sky magnetic field orientationthroughout ~10 sq. degrees of the Polaris Flare translucent molecular cloud.We provide the first quantitative estimate of the magnetic field strength in thistype of system. By combining our measurements with the high-resolution Herscheldust emission map, we find a preferred alignment between filaments and theobserved magnetic field. Our results support the presence of a strong magneticfield in this system.

Three-dimensional simulations of accretion onto a star from a magnetized accretion disk: Fast funnel-wall accretion

Takasao, Shinsuke

We show the results of global three-dimensional magnetohydrodynamics simulations of an accretion disk with a rotating, weakly magnetized central star. The disk is threaded by a weak large-scale poloidal magnetic field. The central star has no strong stellar magnetosphere initially and is only weakly magnetized. We investigate the structure of the accretion flows from a turbulent accretion disk onto the star. Our simulations reveal that fast accretion onto the star at high latitudes is established even without a stellar magnetosphere. We find that the failed disk wind becomes the fast, high-latitude accretion as a result of angular momentum exchange mediated by magnetic fields. The rapid angular momentum exchange occurs well above the disk, where the Lorentz force that decelerates the rotational motion of gas can be comparable to the centrifugal force. Unlike the classical magnetospheric accretion model, fast accretion streams are not guided by magnetic fields of the stellar magnetosphere. Nevertheless, the accretion velocity reaches the free-fall velocity at the stellar surface owing to the efficient angular momentum loss at a distant place from the star. Our model can be applied to Herbig Ae/Be stars whose magnetic fields are generally not strong enough to form magnetospheres, and also provides a possible explanation why Herbig Ae/Be stars show indications of fast accretion. A magnetically-driven jet does not blow from the disk in our weak field model. The differential rotation cannot generate sufficiently strong magnetic fields for the jet acceleration, because the Parker instability, which only occurs in 3D, interrupts the field amplification.

Magnetic fields along the pre-main sequence: new magnetic field measurements of Herbig Ae stars using high resolution HARPS spectropolarimetry

Jaervinen, Silva

Herbig Ae/Be-type stars are analogs of T Tauri stars at higher masses. Since the confirmation of magnetospheric accretion using Balmer and sodium line profiles in the Herbig Ae star UX Ori, a number of magnetic studies have been attempted, indicating that about 20 Herbig Ae/Be stars likely have globally organized magnetic fields. The low detection rate of magnetic fields in Herbig Ae stars can be explained by the weakness of these fields and rather large measurement uncertainties. The obtained density distribution of the root mean square longitudinal magnetic field values revealed that only a few stars have magnetic fields stronger than 200G, and half of the sample possesses magnetic fields of about 100G or less. These results call into question our current understanding of the magnetospheric accretion process in intermediate-mass pre-main sequence stars, as they indicate that the magnetic fields of Herbig Ae/Be stars are by far weaker than those measured in their lower mass classical T Tauri star counterparts, usually possessing kG magnetic fields. We report on the results of our analysis of a sample of presumably single Herbig Ae/Be stars based on recent observations obtained with HARPSpol attached to ESO's 3.6m telescope. Knowledge of the magnetic field structure combined with the determination of the chemical composition are indispensable to constrain theories on star formation and magnetospheric accretion in intermediate-mass stars. As of today, magnetic phase curves have been obtained only for two Herbig Ae/Be stars, HD101412 and V380 Ori.

Magnetic field difference in young-embedded massive protoclusters and evolved massive protoclusters in M17

Nguyen-Luong, Quang

Magnetic fields play an important role in star formation. They affect how the molecular gas assembles mass to form denser filamentary structures and eventually fragments to form stars. It is only recently that observations of magnetic fields via dust polarization have become efficient with the emergence of new sensitive submm polarimetric cameras such as SCUBA2-POL on JCMT and infrared polarimetric camera SIRPOL. We present the submm and infrared polarimetric maps of  that map the B-field inside the massive star-forming filaments M17SWex which host young-embedded massive protoclusters and the M17 giant HII region which host an evolved massive protocluster.  We will disscuss the structures of the B- fields in the two similar regions but at different evolutionary stages to answer the questions: 1) What is the relative contribution of B-field to the energy budget in different phases?2) what is the role of B-fields in mass assembly from the filamentary network onto individual cores?3) Similarity or Difference between young-embedded and evolved massive protocluster environments?This leads to the understanding how mass is transferred, assembled and collapsed from the cloud scales to core scales and then evolve to star clusters.

Magnetic Field Alignment in Massive Protoclusters

Chen, Vivien

The influence of magnetic fields on dynamics and timescales of star formation remains an open question. The alignment of magnetic field with respect to mass accretion flow renders greatly different expectation for gas kinematics. Polarized emission arising from magnetically aligned dust grains in the mm/sub-mm wavebands is often used to map the 2D morphology of the 3D magnetic fields on the plane of sky. Although a pinched field morphology aligned with the outflow axis has been reported in a few massive porto-clusters, it remains unclear whether these cases well represent the rich diversity of forming clusters. As part of the SMA polarization legacy project, we have observed the polarized dust emission at 882um in the nearby (1.83 kpc) massive protocluster W3 IRS5 with an angular resolution of 2.7” (~5000 AU). W3 IRS 5 is a luminous proto-cluster with at least eight hyper-compact HII regions and makes a much younger analogue to the Trapezium system. Our polarization maps show a pinched morphology while the CO emission suggests two pairs of bipolar outflows. We have developed radiative transfer models to interpret the observed polarized dust emission. We are able to reproduce observed polarization pattern with a misaligned hourglass geometry of magnetic field. This suggests that the magnetic field does not necessarily remain well-aligned at scales of cluster formation. Comparison with the case of G240.31+0.07, which displays a well-aligned field morphology, will also be discussed. 

The peculiarity of the accretion process in the magnetic Ae star HD104237

Schoeller, Markus

We have studied the magnetospheric accretion in the Herbig Ae binary system HD104237 using spectroscopic parameters of the He I 10830, Pa gamma, and He I 5876 lines, formed in the accretion region. Employing 21 spectra obtained with ISAAC and X-shooter, we found that the temporal behavior of the diagnostic lines can be explained by a variable amount of matter being accreted in the region between the star and the observer. Using a periodogram analysis of the diagnostic line parameters, we examined the possible origin of the accretion flow in HD104237 and considered the following four scenarios: matter flows from the circumbinary envelope, mass exchange between the system's components, magnetospheric accretion (MA) from the disk onto the star, and fast high-latitude accretion from a disk wind onto a weakly magnetized star. Based on a correlation analysis, we were able to show that the primary component is responsible for the observed emission line spectrum of the system. Since we do not find any correlation of the spectroscopic parameters with the phase of the orbital period (P ~ 20d), we can reject the first two scenarios. However, we found a variation period of P = 5.37+-0.04d of the diagnostic line parameters, which likely represents the stellar rotation period of the primary and favors the MA scenario. An estimation of the radius of the magnetosphere (Rm ~ 2Rstar) also supports the MA scenario for HD104237. Yet, we cannot exclude that fast high-latitude accretion from a disk wind takes place in HD104237.

The Role of Turbulence, Gravity and Magnetic Fields in High-Mass Star Formation from HOPS Clumps

de Gouveia Dal Pino, Elisabete

We used ‘the H2O Southern Galactic Plane Survey’ (HOPS) to study dense regions of gas in the southern Galactic plane that are likely to form stars. We used HOPS NH3(1,1) data to define the positions of dense cores/ clumps of gas. Other tracers we studied from HOPS are NH3(2,2), NH3(3,3), H2O maser, H69a and HC3N. By analysing spectra of all the clumps, we measured and derived physical parameters to understand these clumps. We investigated how different physical parameters are correlated to shed some light on the physical events the clumps have experienced. Further, we performed virial analysis, investigated Larson’s relationships among HOPS clumps and mass-size distribution. We discussed the role of turbulence, gravity and magnetic fields in high-mass star formation from HOPS Clumps. The results from our current study suggest that the gravitationally bound clumps are an effect of global or Galactic scale turbulence according to Larson’s laws. Using mass-size plane we found that most of our clumps are high-mass star forming. We also observed two streams of clump-clusters in the mass-size plane - one lies in the virialised and high-mass star forming zone, the other one lies in the non-virialised low mass star forming zone.

ALMA polarization studies of Nearby galaxies

Paladino, Rosita

Magnetic fields are an essential ingredient of star formation in galaxies, at various spatial scales.They affect directly the mean gas density, which impacts significantly the star formation rate, but they also regulate the collapse and fragmentation of molecular clouds.Nearby galaxies offer the unique opportunity to study magnetic fields in different environments on large scales, while still being close enough to allow detailed studies of small scale structures.The large scale magnetic fields in galaxies are investigated through observations of synchrotron polarized emission. On giant molecular clouds scales, so far only in the Milky Way, dust polarization measurements have been obtained. Relating these different tracers at different scales is fundamental to clearly understand the role of magnetic fields.With current data for the Milky Way, it is difficult to reconcile magnetic field models with both synchrotron and dust polarization observed. More sophysticated models are needed, and observational constraints on the observed dust polarization in different location of nearby galaxies are crucial.ALMA, with its incomparable combination of resolution and sensitivity, offers a new tool to observe dust continuum at giant molecular clouds scales in nearby galaxies and detect its polarization.With these unprecedented observations it will be possible to combine dust polarization and synchrotron information  to build a coherent picture of magnetic fields in galactic interstellar medium.

On the Role of Magnetic Fields in Cloud Dynamics in Serpens South/Aquila Rift

Kusune, Takayoshi

We made NIR polarimetric observations toward 1x0.5 square degree area of Serpens South/Aquila Rift (e.g., Sugitani et al. 2011). We also conducted mapping observations in 12CO/13CO/C18O/N2H+ with the Nobeyama 45-m telescope and found that this region contains several filaments with different velocities, which are roughly parallel to each other. Using the Histogram of Relative Orientations (Soler et al. 2015), the filaments are found to be roughly perpendicular to the magnetic field. Applying the Davis-Chandrasekhar-Fermi method, the plane-of-sky magnetic field strength is estimated to be 30-100 µG. The morphology of the field and molecular gas suggests that the magnetic field plays an important role in the filament evolution. We also found that the global field is somewhat curved in the southern part, suggesting that the expanding shell by the nearby HII region, W40, dynamically affects the filaments. The C18O velocity structure along the filament also indicates the dynamical interaction with W40 (Shimoikura et al. 2018 in prep.). The dense filaments are magnetically supercritical as a whole, and thus the magnetic field is not so strong to fully support the filaments against gravitational contraction. As a result, the gravitational fragmentation appears to promote the formation of dense cores where protostars form. This is consistent with the fact that the active cluster formation, which we call Serpens South cluster, is ongoing in the southern part of the densest filament (e.g., Könyves et al. 2015). We propose that the global motion of the filaments is regulated by the magnetic field and the collision of the filaments along the global magnetic field triggered the protocluster formation in Serpens South (Nakamura et al. 2014). Furthermore, we will report the results of the CCS Zeeman measurement toward the Serpens South cluster using Z45 on the Nobeyama 45-m telescope (Mizuno et al. 2015; Nakamura et al. 2015) to constrain the 3D magnetic structure in this region.

The role of magnetic field in star formation

Tessema, Solomon Belay

In  this  paper  we  present  the  role  of  magnetic  field  in  star  formation.  Star  formation  in  magnetized molecular cloud (MC) needs clear understanding of how the magnetic pressure counteracts gravity and prevent gravitational collapse. In other hand, magnetic field transports excess angular momentum from the central core. Thus the outflow of angular momentum causes the mass to fall onto the central core. Therefore,  magnetic  fields  are  important  at  every  scale  in  the  star  formation  process.  We  focus  on questions regarding the role of magnetic fields in star formation such as: What is the effect of magnetic fields on MC core collapse? Do magnetic fields tend to suppress collapse or enhance the core collapse? In case of the weak field the cloud core collapses in a freefall time. But if the field is strong the cloud may not collapse unless external pressure dominates this field. Therefore, in this work we need to show theoretically how the strong magnetic field is dragged inward by the external pressure during the core collapse and formulate the critical mass of the core in the presence of magnetic pressure and external pressure as well as show the interplay among gravity, magnetic pressure and external pressure.  

Statistical analysis of polarized dust emission in the environment of Planck Galactic cold clumps

Ristorcelli, Isabelle

Magnetic fields are considered one of the key physical agents that regulate star formation, but their actual role in the formation and evolution of dense cores remains an open question. Polarized dust continuum emission is particularly well-suited to probe the magnetic field structure in the dense, cold interstellar medium. Such observations also provide tight constraints on the efficiency of dust alignment along magnetic field lines, which are needed to properly infer the magnetic field properties from observations. With the Planck all-sky survey of dust submillimetre emission in intensity and polarization, we can investigate intermediate spatial scales in the hierarchy of star formation, between global molecular cloud measurements and studies of individual prestellar cores. Planck further enables a statistical analysis of the polarization properties of clumps. We have recently built the first all-sky catalogue of Galactic Cold Clumps (PGCC, Planck collaboration XXVIII 2016), a fraction of which we have studied in detail with our Herschel Key Programme ‘Galactic Cold Cores’. The sources cover a broad range in physical properties and correspond to different evolutionary stages in the star formation process, from quiescent starless clumps and nearby cores to young protostellar objects. We present new results from our statistical analysis of the polarized 353GHz Planck data for the PGCC sources. We have in particular studied the variation of the polarization fraction as a function of the column density and of the polarization angle dispersion function. We have also analysed the magnetic field morphology and compared it to structures (filaments, striations) traced at higher resolution with Herschel in the environment of PGCC sources, searching for evolutionary signatures. Finally, we will discuss our results in the context of MHD simulations that include radiative transfer and the dust radiative torque alignment mechanism.

Far Beyond the Sun: Mapping the Magnetic Cycle of the Young Solar-Analog iota Horologii

Alvarado Gomez, Julian David

A former member of the Hyades cluster, iota Horologii (? Hor) is a ~625 Myr old Sun-like star which displays the shortest coronal activity cycle known to date (PCYC ? 1.6 yr). Apart from the Sun, this X-ray activity cycle is also the only one identified on a single star so far. The link between the activity cycles and the characteristics of the surface magnetic field is a fundamental piece of information to understand the origin of stellar magnetism in late-type stars. Here we present the initial results of a long-term observing campaign aimed at studying the evolution of the magnetic cycle of ? Hor, using ground-based high-resolution spectropolarimetry. Using the technique of Zeeman Doppler Imaging (ZDI), we have successfully detected non-simultaneous large-scale polarity reversals associated with the azimuthal and the radial components of the magnetic field, over the course of the activity cycle of the star. Moreover, using state-of-the-art 3D Magneto-Hydrodynamics (MHD) simulations, each recovered ZDI radial field map help us to self-consistently model the coronal structure, stellar wind, and astrospheric conditions around the star. These models will be compared with simultaneous X-ray monitoring of the corona using XMM-Newton (AO-16), and with stellar wind diagnostics from HST (Cycles 25 & 26).

Exploring the 3D properites behind dust polarization maps of star forming filaments

Küffmeier, Michael

To trigger a hot debate among astronomers, it is often enough to ask about the importance of magnetic fields. In the field of star formation, this is mainly because of ambiguities both in models with and observations of magnetic fields. In models, on the one hand magnetic fields help in transporting angular momentum, on the other hand if they are too strong they suppress the formation of disks altogether. To constrain the orientation of magnetic fields, polarization of dust grains have been considered as a useful tracer. However, polarization of dust is not only affected by magnetic fields, and therefore it is a very sensitive tracer. Our aim is to demonstrate the different polarization features in different regions of molecular clouds by producing synthetic observations with the radiative transfer code polaris. Based on magnetohydrodynamical simulations with the adaptive mesh refinement code ramses of a molecular cloud region of (4 pc)^3 in volume, we produce synthetic dust polarization maps. The MHD simulations successfully reproduce the IMF and apply a maximum resolution of 50 AU in the vicinity of the stars. The stars -- modeled as sink particles in the original MHD simulations – are used as sources of radiation by adopting stellar properties obtained with the stellar evolution code MESA at given snapshots. Besides showing the dependencies of the polarization signal on the underlying physical properties, we also discuss issues when considering the ratio of polarization signal and surface density against the background of the three dimensional nature in Giant Molecular Cloud.

Observational signposts of shock-induced magnetic field compression in star-forming environments

Wiesemeyer, Helmut

This contribution summarizes the observational signposts for the shock compression of magnetic fields in star-forming environments. The evidence stems from the polarimetry of cloud-cloud collisions, and of PDRs exposed to the UV radiation and winds from young stellar clusters. Besides their dynamical role, compressed magnetic fields increase the cosmic ray flux above the Galactic average. The trapped cosmic ray particles contribute to the heating budget of the shocked gas. This mechanism is assumed to account for the anomalously high excitation in the Orion bar, a scenario which is also suggested by the submm dust polarization presented in this contribution. The observational findings are compared with studies of shock-compressed molecular gas exposed to expanding supernova remnants.

Two Different Grain Distributions within the Protoplanetary Disk around HD 142527 Revealed by ALMA Polarization Observation

Satoshi, Ohashi

We present ALMA polarization observations of the 0.87-millimeter dust continuum emission toward the circumstellar disk around HD 142527 with high spatial resolution to identify the polarization mechanisms. There have been proposed three mechanisms for the polarized emission: grain alignment with magnetic fields, grain alignment with radiation gradient, and self-scattering of thermal dust emission.We confirm that the polarization vectors in the northern region are consistent with the self-scattering theory. Furthermore, we find that the polarization vectors in the southern region are likely explained by the grain alignment with the magnetic fields.To understand the difference in the polarization mechanisms, we propose a simple grain size segregation model: small dust grains ($\lesssim$ 100 micron) are dominant and aligned with the magnetic fields in the southern region, while middle-sized ($\sim100$ micron) grains in the upper layers emit the self-scattered polarized emission in the northern region because the grain size is $\sim\lambda/2\pi$, where $\lambda$ is the observing wavelength in the self-scattering theory.The grain size near the middle plane in the northern region cannot be measured because the emission at 0.87 mm is optically thick. However, larger dust grains ($\gtrsim$ cm) may be accumulated due to the gas pressure bump.This is consistent with the previous analysis of the disk in the senses that large grain accumulation and optically thick emission from the northern region. This model is also consistent with the theories where the smaller dust grains are aligned with magnetic fields. The magnetic fields are toroidal at least in the southern regions.

Near-IR imaging polarimetry of the RCW 106 cloud complex

Tamaoki, Shohei

We have carried out near-IR imaging polarimetry toward RCW 106 with the JHKs-simultaneous imaging polarimeter SIRPOL mounted on the IRSF 1.4m telescope at SAAO, in March and May, 2017 and January, 2018.  We have observed 29 fields and covered mostly the southern part of the giant molecular cloud complex associated with the HII region RCW 106, which is located at a distance of 3.5 kpc and is elongated approximately in the north-south direction with a size of ~70x15 pc.  Our preliminary analysis indicates that the magnetic field seems to globally run along the complex elongation, unlike many other elongated clouds that are often reported to have their global elongations perpendicular to the magnetic fields.  The RCW 106 complex consists of many small filaments or clumps.  Some of such filaments seem to parallel to the magnetic fields, but some others perpendicular.  Around the central part of the HII region RCW 106, the magnetic field appears to be influenced by the expansion of this HII region.Here, we present our preliminary results by comparing with the archival molecular line and far- to mid-IR data.

Magnetic Braking of Circumstellar Disks may not be so Catastrophic

Kwon, Woojin

Magnetic fields affect star formation over a broad range of scales from ~1 pc to ~100 au. In particular, interferometric observations and ideal magneto-hydrodynamic (MHD) simulations have reported that formation of a rotation-supported disk around the earliest young stellar objects (YSOs) is largely suppressed by magnetic fields aligned with the rotational axis of the YSOs, which is known as the magnetic braking catastrophe. We present ALMA observations toward the protostar L1448 IRS 2, where rotation is detected and magnetic fields are aligned with the rotation axis (poloidal fields) on ~500 au scales. Our data show that on ~100 au scales, the field morphology changes to toroidal, which implies strong evidence for a circumstellar disk.  On the other hand, the magnetic field strength, as estimated by the Davis-Chandrasekhar-Fermi method, is strong enough to hinder the formation of a rotationally supported disk, which is inconsistent with the central toroidal field.  This result suggests that magnetic braking may not be so catastrophic for early disk formation, even in YSOs with magnetic fields aligned to the rotational axis and that non-ideal MHD effects should be considered for understanding early disk formation around YSOs.

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