A LOFAR DETECTION OF THE LOW-MASS YOUNG STAR T TAU AT 149 MHz

Coughlan, Colm P.; Ainsworth, Rachael; Eislöffel, J.; Hoeft, M.; Drabent, A.; Scaife, Anna M. M.; Ray, T. P.; Bell, M. E.; Broderick, J. W.; Corbel, S.; Grießmeier, Jean-Mathias; Horst, A. J. van der; Leeuwen, J. van; Markoff, Sera; Pietka, M.; Stewart, A.; Wijers, R. A. M. J.; Zarka, Philippe

doi:10.3847/1538-4357/834/2/206

Cited by 9 publications

(6 citation statements)

References 40 publications

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“…While Galactic cold cores are showing very low levels of AME that may be indicative of very small dust grains depletion, still nothing is known about the level of AME associated to YSOs. Radio observations obtained with the Giant Metre Radio Telescope (GMRT; Ainsworth et al 2016;Coughlan et al 2017) are probing the free-free emission associated with the outflow of T Tau. Any detection of AME associated with such objects in the frequency range 10-60 GHz would be indicative of dust grain evolution and possibly could be used as a star-formation evolution tracer.…”

Section: Future Directions For Galactic Ame Studiesmentioning

confidence: 99%

The State-of-Play of Anomalous Microwave Emission (AME) research

Dickinson

Ali-Haı̈moud

Barr

et al. 2018

New Astronomy Reviews

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Anomalous Microwave Emission (AME) is a component of diffuse Galactic radiation observed at frequencies in the range ≈ 10-60 GHz. AME was first detected in 1996 and recognised as an additional component of emission in 1997. Since then, AME has been observed by a range of experiments and in a variety of environments. AME is spatially correlated with far-IR thermal dust emission but cannot be explained by synchrotron or free-free emission mechanisms, and is far in excess of the emission contributed by thermal dust emission with the power-law opacity consistent with the observed emission at sub-mm wavelengths. Polarization observations have shown that AME is very weakly polarized ( 1 %). The most natural explanation for AME is rotational emission from ultra-small dust grains ("spinning dust"), first postulated in 1957.

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Section: Future Directions For Galactic Ame Studiesmentioning

confidence: 99%

The State-of-Play of Anomalous Microwave Emission (AME) research

Dickinson

Ali-Haı̈moud

Barr

et al. 2018

New Astronomy Reviews

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“…This is the second time that a YSO has been observed using LOFAR. The low-mass YSO T Tau was observed in the same observing campaign and reported on in Coughlan et al (2017). In section 2, we discuss how the observations were carried out and the data reduction process.…”

Section: Introductionmentioning

confidence: 99%

The First Detection of a Low-frequency Turnover in Nonthermal Emission from the Jet of a Young Star

Feeney-Johansson

Purser

Ray

et al. 2019

ApJL

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Radio emission in jets from young stellar objects (YSOs) in the form of nonthermal emission has been seen toward several YSOs. Thought to be synchrotron emission from strong shocks in the jet, it could provide valuable information about the magnetic field in the jet. Here we report on the detection of synchrotron emission in two emission knots in the jet of the low-mass YSO DG Tau A at 152 MHz using the Low-Frequency Array (LOFAR), the first time nonthermal emission has been observed in a YSO jet at such low frequencies. In one of the knots, a low-frequency turnover in its spectrum is clearly seen compared to higher frequencies. This is the first time such a turnover has been seen in nonthermal emission in a YSO jet. We consider several possible mechanisms for the turnover and fit models for each of these to the spectrum. Based on the physical parameters predicted by each model, the Razin effect appears to be the most likely explanation for the turnover. From the Razin effect fit, we can obtain an estimate for the magnetic field strength within the emission knot of ∼ 20 µG. If the Razin effect is the correct mechanism, this is the first time the magnetic field strength along a YSO jet has been measured based on a low-frequency turnover in nonthermal emission.

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“…Recently, the observation of the radio emission from jets has reached much lower frequencies, as in the recent Low Frequency ARray (LOFAR) observations at 149 GHz (2 m) of T Tau (Coughlan et al 2017). These observations have revealed the low-frequency turnover of the free-free spectrum, a result that has allowed the degeneracy between emission measure and electron density to be broken.…”

Section: Information From Radio Jetsmentioning

confidence: 99%

Radio jets from young stellar objects

Anglada

Rodrı́guez²,

Carrasco-González³

2018

Astron Astrophys Rev

133

151

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Jets and outflows are ubiquitous in the process of formation of stars since outflow is intimately associated with accretion. Free-free (thermal) radio continuum emission in the centimeter domain is associated with these jets. The emission is relatively weak and compact, and sensitive radio interferometers of high angular resolution are required to detect and study it. One of the key problems in the study of outflows is to determine how they are accelerated and collimated. Observations in the cm range are most useful to trace the base of the ionized jets, close to the young central object and the inner parts of its accretion disk, where optical or near-IR imaging is made difficult by the high extinction present. Radio recombination lines in jets (in combination with proper motions) should provide their 3D kinematics at very small scale (near their origin). Future instruments such as the Square Kilometre Array (SKA) and the Next Generation Very Large Array (ngVLA) will be crucial to perform this kind of sensitive observations. Thermal jets are associated with both high and low mass protostars and possibly even with objects in the substellar domain. The ionizing mechanism of these radio jets appears to be related to shocks in the associated outflows, as suggested by the observed correlation between the centimeter luminosity and the outflow momentum rate. From this correlation and that of the centimeter luminosity with the bolometric luminosity of the system it will be possible to discriminate between unresolved HII regions and jets, and to infer additional physical properties of the embedded objects. Some jets associated with young stellar objects (YSOs) show indications of nonthermal emission (negative spectral indices) in part of their lobes. Linearly polarized synchrotron emission has been found in the jet of HH 80-81, allowing one to measure the direction and intensity of the jet magnetic field, a key ingredient to determine the collimation and ejection mechanisms. As only a fraction of the emission is polarized, very sensitive observations such as those that will be feasible with the interferometers previously mentioned are required to perform studies in a large sample of sources. Jets are present in many kinds of astrophysical scenarios. Characterizing radio jets in YSOs, where thermal emission allows one to determine their physical conditions in a reliable way, would also be useful in understanding acceleration and collimation mechanisms in all kinds of astrophysical jets, such as those associated with stellar and supermassive black holes and planetary nebulae.

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A LOFAR DETECTION OF THE LOW-MASS YOUNG STAR T TAU AT 149 MHz

Cited by 9 publications

References 40 publications

The State-of-Play of Anomalous Microwave Emission (AME) research

The State-of-Play of Anomalous Microwave Emission (AME) research

The First Detection of a Low-frequency Turnover in Nonthermal Emission from the Jet of a Young Star

Radio jets from young stellar objects

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