Observational perspective of the youngest phases of intermediate-mass stars

Beltrán, M. T.

doi:10.1007/s10509-014-2151-0

Cited by 9 publications

(9 citation statements)

References 77 publications

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“…Importantly and similar to what has been demonstrated for the solar-type stars, the existence of circumstellar disks in the embedded protostellar phase has been established unambiguously by observations (Zapata et al, 2007;Sánchez-Monge et al, 2010;van Kempen et al, 2012;Takahashi et al, 2012). The properties of these IM star disks are similar to those of their lower-mass counterparts (Beltrán, 2015). However, whether they are in Keplerian rotation is still a matter of debate .…”

Section: Disks In Intermediate-mass Ysosmentioning

confidence: 84%

“…Complex organic molecules, such as CH 3 OH, CH 3 CN, and HCOOCH 3 , including isotopomers and vibrationally excited transitions, with excitation energies >1000 K and pre-biotic molecules, such as CH 2 OHCHO, are abundant in HM star-forming regions and also in a few IM star-forming regions (see Beltrán, 2015, and references therein). The large bandwidth of current radio/mm interferometers allows us to study the physical properties and velocity field of these embedded (proto)stars in many different species, covering a broad range of excitation conditions, as recently demonstrated by ALMA observations at 850 µm of B-type (proto)stars: G35.20+0.74N A and B (Sánchez-Monge et al, 2014) and G35.03+0.35 A .…”

Section: Disk Tracersmentioning

confidence: 99%

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Accretion disks in luminous young stellar objects

Beltrán

Wit

2016

Astron Astrophys Rev

193

189

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An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate-and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and therefore predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.

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Section: Disks In Intermediate-mass Ysosmentioning

confidence: 84%

Section: Disk Tracersmentioning

confidence: 99%

Accretion disks in luminous young stellar objects

Beltrán

Wit

2016

Astron Astrophys Rev

193

189

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“…7 We do not treat the topic of intermediate-mass star formation separately in this review. As many of the characteristics of the early stages of intermediate-and low-mass star formation are thought to be similar (Beltrán, 2015), we include references to several intermediate-mass objects and regions in this section. Many of these intermediate-mass sources are in Orion (e.g., Takahashi et al, 2006Takahashi et al, , 2018Hull et al, 2014), but there are also objects in other regions, such as Serpens SMM1 in the Serpens Main molecular cloud (van Kempen et al, 2016;Hull et al, 2017b).…”

Section: The Role Of the Magnetic Field In Protostellar Collapsementioning

confidence: 99%

Interferometric Observations of Magnetic Fields in Forming Stars

Hull

Zhang

2019

Front. Astron. Space Sci.

114

103

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The magnetic field is a key ingredient in the recipe of star formation. However, the importance of the magnetic field in the early stages of the formation of low-and high-mass stars is still far from certain. Over the past two decades, the millimeter and submillimeter interferometers BIMA, OVRO, CARMA, SMA, and most recently ALMA have made major strides in unveiling the role of the magnetic field in star formation at progressively smaller spatial scales; ALMA observations have recently achieved spatial resolutions of up to ∼ 100 au and ∼ 1,000 au in nearby low-and high-mass star-forming regions, respectively. From the kiloparsec scale of molecular clouds down to the inner few hundred au immediately surrounding forming stars, the polarization at millimeter and submillimeter wavelengths is dominated by polarized thermal dust emission, where the dust grains are aligned relative to the magnetic field. Interferometric studies have focused on this dust polarization and occasionally on the polarization of spectral-line emission. We review the current state of the field of magnetized star formation, from the first BIMA results through the latest ALMA observations, in the context of several questions that continue to motivate the studies of highand low-mass star formation. By aggregating and analyzing the results from individual studies, we come to several conclusions: (1) Magnetic fields and outflows from low-mass protostellar cores are randomly aligned, suggesting that the magnetic field at ∼ 1000 au scales is not the dominant factor in setting the angular momentum of embedded disks and outflows. (2) Recent measurements of the thermal and dynamic properties in high-mass star-forming regions reveal small virial parameters, challenging the assumption of equilibrium star formation. However, we estimate that a magnetic field strength of a fraction of a mG to several mG in these objects could bring the dense gas close to a state of equilibrium. Finally, (3) We find that the small number of sources with hourglass-shaped magnetic field morphologies at 0.01-0.1 pc scales cannot be explained purely by projection effects, suggesting that while it does occur occasionally, magnetically dominated core collapse is not the predominant mode of low-or high-mass star formation. Magnetic fields in forming stars Polarized molecular-line emissionPolarization of molecular-line emission is another tracer of the magnetic field in star-forming regions. Molecular and atomic lines are sensitive to magnetic fields, which cause their spectral levels to split into magnetic sub-levels. For some molecules, linear polarization can arise when an anisotropy in the radiation and/or velocity field yields a population of magnetic sub-levels that are not in local thermodynamic equilibrium (LTE); this is known as the Goldreich-Kylafis (G-K) effect. Polarization from the G-K effect is most easily detected where the spectral line emission has an optical depth τ ≈ 1, when the ratio of the collision rate to the radiative transition rate (i.e., the spontaneous emi...

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“…APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. conducted in recent years (e.g., Beltrán 2015;Takahashi et al 2009Takahashi et al , 2006van Kempen et al 2012;Crimier et al 2010;Beltrán et al 2008;Fuente et al 2007Fuente et al , 2001; Zapata et al 2004Zapata et al , 2005, little information is available, in particular about outflows from class 0-type sources.…”

Section: Introductionmentioning

confidence: 99%

Warm gas in protostellar outflows

Gómez-Ruiz

Leurini

Menten

et al. 2019

A&A

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Context. OMC-2/3 is one of the nearest embedded cluster-forming regions that includes intermediate-mass protostars at early stages of evolution. A previous CO (3–2) mapping survey towards this region revealed outflow activity related to sources at different evolutionary phases. Aims. The present work presents a study of the warm gas in the high-velocity emission from several outflows found in CO (3–2) emission by previous observations, determines their physical conditions, and makes a comparison with previous results in low-mass star-forming regions. Methods. We used the CHAMP+ heterodyne array on the APEX telescope to map the CO (6–5) and CO (7–6) emission in the OMC-2 FIR 6 and OMC-3 MMS 1-6 regions, and to observe 13CO (6–5) at selected positions. We analyzed these data together with previous CO (3–2) observations. In addition, we mapped the SiO (5–4) emission in OMC-2 FIR 6. Results. The CO (6–5) emission was detected in most of the outflow lobes in the mapped regions, while the CO (7–6) was found mostly in the OMC-3 outflows. In the OMC-3 MMS 5 outflow, a previously undetected extremely high-velocity gas was found in CO (6–5). This extremely high-velocity emission arises from the regions close to the central object MMS 5. Radiative transfer models revealed that the high-velocity gas from MMS 5 outflow consists of gas with nH2 = 104–105 cm−3 and T > 200 K, similar to what is observed in young Class 0 low-mass protostars. For the other outflows, values of nH2 > 104 cm−3 were found. Conclusions. The physical conditions and kinematic properties of the young intermediate-mass outflows presented here are similar to those found in outflows from Class 0 low-mass objects. Due to their excitation requirements, mid − J CO lines are good tracers of extremely high-velocity gas in young outflows likely related to jets.

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Observational perspective of the youngest phases of intermediate-mass stars

Cited by 9 publications

References 77 publications

Accretion disks in luminous young stellar objects

Accretion disks in luminous young stellar objects

Interferometric Observations of Magnetic Fields in Forming Stars

Warm gas in protostellar outflows

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