Spiral arms and instability within the AFGL 4176 mm1 disc

Johnston, Kevin; Hoare, M. G.; Beuther, H.; Kuiper, Rolf; Kee, N. D.; Linz, H.; Boley, Paul A.; Maud, L. T.; Ahmadi, A.; Robitaille, Thomas

doi:10.1051/0004-6361/201937154

Cited by 52 publications

(41 citation statements)

References 36 publications

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“…Interestingly, recent high-resolution radio imaging of MM1 suggests the presence of two spiral-arm accretion flows, winding toward the protostar as traced by methanol masers (Brogan et al 2019;Chen et al 2020b). This is in line with very high-resolution ALMA imaging of high-mass protostars that provided evidence for filamentary streamers pointing onto the central sources (Goddi et al 2018;Johnston et al 2020). These might represent multidirectional accretion channels which possibly inhibit the formation of a large, steady disk at the very early stages of massive star formation.…”

Section: Accretion Burst Driverssupporting

confidence: 54%

Infrared observations of the flaring maser source G358.93−0.03

Stecklum

Wolf

Linz

et al. 2021

A&A

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Context. Class II methanol masers are signposts of massive young stellar objects (MYSOs). Recent evidence shows that flares of these masers are driven by MYSO accretion bursts. Thus, maser monitoring can be used to identify such bursts which are hard to discover otherwise. Infrared observations reveal burst-induced changes in the spectral energy distribution (first and foremost a luminosity increase), which provide valuable information on a very intense phase of high-mass star formation. Aims. In mid-January 2019, flaring of the 6.7 GHz CH3OH maser (hereafter maser) of the MYSO G358.93-0.03 (hereafter G358) was reported. The international maser community initiated an extensive observational campaign which revealed extraordinary maser activity and yielded the detection of numerous new masering transitions. Interferometric imaging with the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array resolved the maser emitting core of the star forming region and proved the association of the masers with the brightest continuum source (MM1), which hosts a hot molecular core. These observations, however, failed to detect a significant rise in the (sub)millimeter dust continuum emission. Therefore, we performed near-infrared (NIR) and far-infrared (FIR) observations to prove or disprove whether the CH3OH flare was driven by an accretion burst. Methods. NIR imaging with the Gamma-Ray Burst Optical/Near-infrared Detector has been acquired and integral-field spectroscopy with the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) was carried out on two occasions to detect possible counterparts to the (sub)millimeter sources and compare their photometry to archival measurements. The comparison of pre-burst and burst spectral energy distributions is of crucial importance to judge whether a substantial luminosity increase, caused by an accretion burst, is present and if it triggered the maser flare. Radiative transfer modeling of the spectral energy distribution (SED) of the dust continuum emission at multiple epochs provides valuable information on the bursting MYSO. Results. The FIR fluxes of MM1 measured with FIFI-LS exceed those from Herschel significantly, which clearly confirms the presence of an accretion burst. The second epoch data, taken about 16 months later, still show increased fluxes. Our radiative transfer modeling yielded major burst parameters and suggests that the MYSO features a circumstellar disk which might be transient. From the pre-burst, burst, and post-burst SEDs, conclusions on heating and cooling time-scales could be drawn. Circumstances of the burst-induced maser relocation have been explored. Conclusions. The verification of the accretion burst from G358 is another confirmation that Class II methanol maser flares represent an alert for such events. Thus, monitoring of these masers greatly enhances the chances of identifying MYSOs during periods of intense growth. The few events known to date already indicate that there is a broad range in burst strength and duration as well as environmental characteristics. The G358 event is the shortest and least luminous accretion burst known to date. According to models, bursts of this kind occur most often.

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Section: Accretion Burst Driverssupporting

confidence: 54%

Infrared observations of the flaring maser source G358.93−0.03

Stecklum

Wolf

Linz

et al. 2021

A&A

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“…A similar observational example of a fragmenting, 1000 AU disk is AFGL 4176 (Johnston et al 2020a). In their earlier, low resolution study (Johnston et al 2015), the authors report an unresolved, large structure in Keplerian rotation.…”

Section: Disk Fragmentation and Kinematicsmentioning

confidence: 97%

“…In their earlier, low resolution study (Johnston et al 2015), the authors report an unresolved, large structure in Keplerian rotation. Their higher resolution (30 mas, Johnston et al (2020a)) observations, however, show that the disk is fragmented into a spiral and is Toomre unstable. The eastern spiral arm also shows a condensation separated by ∼700 AU from the central peak (see their Figure 2), comparable to the core separations that we see towards VLA 3.…”

Section: Disk Fragmentation and Kinematicsmentioning

confidence: 98%

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Disk fragmentation in high-mass star formation

Suri

Beuther

Gieser

et al. 2021

A&A

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Context. Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentation. Aims. We study the kinematics and fragmentation of the disk around the high-mass star forming region AFGL 2591-VLA 3 which was hypothesized to be fragmenting based on the observations that show multiple outflow directions. Methods. We use a new set of high-resolution (0 . 19) IRAM/NOEMA observations at 843 µm towards VLA 3 which allow us to resolve its disk, characterize the fragmentation, and study its kinematics. In addition to the 843 µm continuum emission, our spectral setup targets warm dense gas and outflow tracers such as HCN, HC 3 N and SO 2 , as well as vibrationally excited HCN lines. Results. The high resolution continuum and line emission maps reveal multiple fragments with subsolar masses within the inner ∼1000 AU of VLA 3. Furthermore, the velocity field of the inner disk observed at 843 µm shows a similar behavior to that of the larger scale velocity field studied in the CORE project at 1.37 mm. Conclusions. We present the first observational evidence for disk fragmentation towards AFGL 2591-VLA 3, a source that was thought to be a single high-mass core. While the fragments themselves are low-mass, the rotation of the disk is dominated by the protostar with a mass of 10.3±1.8 M . These data also show that NOEMA Band 4 can obtain the highest currently achievable spatial resolution at (sub-)mm wavelengths in observations of strong northern sources.

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“…Four annular structures have been found by ALMA in a protostellar disk less than 0.5 Myr old (Segura-Cox et al 2020), again implying rapid formation of protoplanets at large distances, presumably implicating disk gravitational instability. ALMA has also been used to study the spiral arms surrounding the AFGL 4176 O-type star, finding that the outer disk is cool enough to be gravitationally unstable and is likely to fragment into a companion object (Johnston et al 2020). In fact, outer disk temperatures for the HD 163296 protoplanetary disk drop to ∼ 18 K in the midplane beyond 100 au (Dullemond et al 2020).…”

Section: Introductionmentioning

confidence: 99%

The Effect of the Approach to Gas Disk Gravitational Instability on the Rapid Formation of Gas Giant Planets

Boss¹

2019

ApJ

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Observational evidence suggests that gas disk instability may be responsible for the formation of at least some gas giant exoplanets, particularly massive or distant gas giants. With regard to close-in gas giants, Boss (2017) used the β cooling approximation to calculate hydrodynamical models of inner gas disk instability, finding that provided disks with low values of the initial minimum Toomre stability parameter (i.e., Q i < 2 inside 20 au) form, fragmentation into self-gravitating clumps could occur even for β as high as 100 (i.e., extremely slow cooling). Those results implied that the evolution of disks toward low Q i must be taken into account. This paper presents such models: initial disk masses of 0.091 M ⊙ extending from 4 to 20 au around a 1 M ⊙ protostar, with a range (1 to 100) of β cooling parameters, the same as in Boss (2017), but with all the disks starting with Q i = 2.7, i.e., gravitationally stable, and allowed to cool from their initial outer disk temperature of 180 K to as low as 40 K. All the disks eventually fragment into at least one dense clump. The clumps were again replaced by virtual protoplanets (VPs) and the masses and orbits of the resulting ensemble of VPs compare favorably with those of Boss (2017), supporting the claim that disk instability can form gas giants rapidly inside 20 au, provided that sufficiently massive protoplanetary disks exist.

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Spiral arms and instability within the AFGL 4176 mm1 disc

Cited by 52 publications

References 36 publications

Infrared observations of the flaring maser source G358.93−0.03

Infrared observations of the flaring maser source G358.93−0.03

Disk fragmentation in high-mass star formation

The Effect of the Approach to Gas Disk Gravitational Instability on the Rapid Formation of Gas Giant Planets

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