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  • 1
    Online Resource
    Online Resource
    Studying Magnetic Fields and Dust in M17 Using Polarized Thermal Dust Emission Observed by SOFIA/HAWC+
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 929, No. 1 ( 2022-04-01), p. 27-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 929, No. 1 ( 2022-04-01), p. 27-
    Abstract: We report on the highest spatial resolution measurement to date of magnetic fields (B-fields) in M17 using thermal dust polarization measurements taken by SOFIA/HAWC+ centered at a wavelength of 154 μ m. Using the Davis–Chandrasekhar–Fermi method, in which the polarization angle dispersion calculated using the structure function technique is the quantity directly observed by SOFIA/HAWC+, we found the presence of strong B-fields of 980 ± 230 and 1665 ± 885 μ G in the lower-density M17-N and higher-density M17-S regions, respectively. The B-field morphology in M17-N possibly mimics the fields in gravitationally collapsing molecular cores, while in M17-S the fields run perpendicular to the density structure. M17-S also displays a pillar feature and an asymmetric large-scale hourglass-shaped field. We use the mean B-field strengths to determine Alfvénic Mach numbers for both regions, finding that B-fields dominate over turbulence. We calculate the mass-to-flux ratio, λ , finding λ = 0.07 for M17-N and 0.28 for M17-S. These subcritical λ values are consistent with the lack of massive stars formed in M17. To study dust physics, we analyze the relationship between dust polarization fraction, p , emission intensity, I , gas column density, N (H 2 ), polarization angle dispersion function, S , and dust temperature, T d . p decreases with intensity as I − α with α = 0.51. p tends to first increase with T d , but then decreases at higher T d . The latter feature, seen in M17-N at high T d when N (H 2 ) and S decrease, is evidence of the radiative torque disruption effect.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac5abf
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 2
    Online Resource
    Online Resource
    The JCMT BISTRO-2 Survey: Magnetic Fields of the Massive DR21 Filament
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 941, No. 2 ( 2022-12-01), p. 122-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 941, No. 2 ( 2022-12-01), p. 122-
    Abstract: We present 850 μ m dust polarization observations of the massive DR21 filament from the B -fields In STar-forming Region Observations (BISTRO) survey, using the POL-2 polarimeter and the SCUBA-2 camera on the James Clerk Maxwell Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale ridge of the DR21 main filament. In the subfilaments, the magnetic fields are mainly parallel to the filamentary structures and smoothly connect to the magnetic fields of the main filament. We compare the POL-2 and Planck dust polarization observations to study the magnetic field structures of the DR21 filament on 0.1–10 pc scales. The magnetic fields revealed in the Planck data are well-aligned with those of the POL-2 data, indicating a smooth variation of magnetic fields from large to small scales. The plane-of-sky magnetic field strengths derived from angular dispersion functions of dust polarization are 0.6–1.0 mG in the DR21 filament and ∼0.1 mG in the surrounding ambient gas. The mass-to-flux ratios are found to be magnetically supercritical in the filament and slightly subcritical to nearly critical in the ambient gas. The alignment between column density structures and magnetic fields changes from random alignment in the low-density ambient gas probed by Planck to mostly perpendicular in the high-density main filament probed by James Clerk Maxwell Telescope. The magnetic field structures of the DR21 filament are in agreement with MHD simulations of a strongly magnetized medium, suggesting that magnetic fields play an important role in shaping the DR21 main filament and subfilaments.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac9dfb
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 3
    Online Resource
    Online Resource
    The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 941, No. 1 ( 2022-12-01), p. 51-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 941, No. 1 ( 2022-12-01), p. 51-
    Abstract: We present and analyze observations of polarized dust emission at 850 μ m toward the central 1 × 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis–Chandrasekhar–Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C 18 O ( J = 3 − 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 ± 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 ± 0.02. Additionally, the mean Alfvén Mach number is 0.35 ± 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac99e0
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). I. The Massive Filament G11.11–0.12 Observed by SOFIA/HAWC+
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 953, No. 1 ( 2023-08-01), p. 66-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 953, No. 1 ( 2023-08-01), p. 66-
    Abstract: We report the first measurement of polarized thermal dust emission toward the entire infrared dark cloud G11.11−0.12 taken by the polarimeter SOFIA/HAWC+ at 214 μ m. The obtained magnetic fields ( B -fields) from the polarized emission of the early-stage and massive filament tend to be perpendicular to its spine. We produce a map of B -field strengths for the center region of the filament. The strengths vary in the range of 100–600 μ G and are strongest along the filament's spine. The central region is sub-Alfvénic and mostly subcritical, meaning that B -fields dominate over turbulence and are strong enough to resist gravitational collapse. The alignment and properties of dust grains in the filament are studied using radiative torque (RAT) theory. We find the decrease of polarization degree P with emission intensity I , i.e., depolarization effect, of the form P ∝ I − α with α ∼ 0.8–0.9, implying a significant loss of grain alignment in the filament's spine. The depolarization can be explained by the decrease in RAT alignment efficiency toward the denser regions with weaker radiation field, which cannot be explained by B -field tangling. We study the effect of the enhanced magnetic relaxation by embedded iron inclusions on RAT alignment and find that the high polarization fraction P ∼ 20%–30% in the outer layer of the filament is potential evidence for the magnetically enhanced RAT alignment mechanism. This is the first time this effect is evaluated in a filament. Based on the polarization fraction and RAT alignment theory, we also find evidence for grain growth in the filament.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acdb6e
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 5
    Online Resource
    Online Resource
    The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 952, No. 1 ( 2023-07-01), p. 29-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 952, No. 1 ( 2023-07-01), p. 29-
    Abstract: We present observations of polarized dust emission at 850 μ m from the L43 molecular cloud, which sits in the Ophiuchus cloud complex. The data were taken using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the BISTRO large program. L43 is a dense ( N H 2 ∼ 10 22 –10 23 cm −2 ) complex molecular cloud with a submillimeter-bright starless core and two protostellar sources. There appears to be an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity to the southeast. We see a magnetic field that appears to be aligned with the cavity walls of the outflow, suggesting interaction with the outflow. We also find a magnetic field strength of up to ∼160 ± 30 μ G in the main starless core and up to ∼90 ± 40 μ G in the more diffuse, extended region. These field strengths give magnetically super- and subcritical values, respectively, and both are found to be roughly trans-Alfvénic. We also present a new method of data reduction for these denser but fainter objects like starless cores.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acd6f2
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 6
    Online Resource
    Online Resource
    B-fields in Star-forming Region Observations (BISTRO): Magnetic Fields in the Filamentary Structures of Serpens Main
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 926, No. 2 ( 2022-02-01), p. 163-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 926, No. 2 ( 2022-02-01), p. 163-
    Abstract: We present 850 μ m polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where N H 2 〈 0.93 × 10 22 cm −2 (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at N H 2 ≈ 4.6 × 10 22 cm −2 . This can be interpreted as a signature of core formation. At N H 2 ≈ 16 × 10 22 cm −2 , magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments ( B POS = 60–300 μ G)) using the Davis–Chandrasekhar–Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac4bbe
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 7
    Online Resource
    Online Resource
    First BISTRO Observations of the Dark Cloud Taurus L1495A-B10: The Role of the Magnetic Field in the Earliest Stages of Low-mass Star Formation
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 946, No. 2 ( 2023-04-01), p. 62-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 946, No. 2 ( 2023-04-01), p. 62-
    Abstract: We present BISTRO Survey 850 μ m dust emission polarization observations of the L1495A-B10 region of the Taurus molecular cloud, taken at the James Clerk Maxwell Telescope (JCMT). We observe a roughly triangular network of dense filaments. We detect nine of the dense starless cores embedded within these filaments in polarization, finding that the plane-of-sky orientation of the core-scale magnetic field lies roughly perpendicular to the filaments in almost all cases. We also find that the large-scale magnetic field orientation measured by Planck is not correlated with any of the core or filament structures, except in the case of the lowest-density core. We propose a scenario for early prestellar evolution that is both an extension to, and consistent with, previous models, introducing an additional evolutionary transitional stage between field-dominated and matter-dominated evolution, observed here for the first time. In this scenario, the cloud collapses first to a sheet-like structure. Uniquely, we appear to be seeing this sheet almost face on. The sheet fragments into filaments, which in turn form cores. However, the material must reach a certain critical density before the evolution changes from being field dominated to being matter dominated. We measure the sheet surface density and the magnetic field strength at that transition for the first time and show consistency with an analytical prediction that had previously gone untested for over 50 yr.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acbea4
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 8
    Online Resource
    Online Resource
    Grain Alignment and Disruption by Radiative Torques in Dense Molecular Clouds and Implication for Polarization Holes
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Vol. 908, No. 2 ( 2021-02-01), p. 218-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 908, No. 2 ( 2021-02-01), p. 218-
    Abstract: Dust polarization induced by aligned grains is widely used to study magnetic fields in various astrophysical environments. However, the question of to what optical depth grain alignment still exists in a dense molecular cloud (MC) is unclear. In this paper, we derive analytical formulae for the minimum size of aligned grains ( a align ) and rotational disruption ( a disr ) by RAdiative Torques (RATs) as a function of the local physical parameters within MCs. We first find the analytical approximations for the radiation strength and mean wavelength of the attenuated radiation field in a dense MC with and without embedded stars, and then derive analytical formulae for a align and a disr as functions of the visual extinction A V and gas density. We find that, within a starless core of density , grains of size can be aligned at A V  ∼ 5 by RATs, whereas micron-sized grains can still be aligned at . The increase in a align with A V can explain the presence of polarization holes observed toward starless cores. For MCs with an embedded protostar, the efficiency of both alignment and rotational disruption increases toward the protostar due to the increasing radiation strength. Such a disruption effect results in the decrease of the polarization degree with A V or emission intensity, reproducing the popular polarization holes observed toward the location of protostars. Finally, we derive the formula for the maximum A V where grain alignment still exists in a starless core, and we discuss its potential for constraining grain growth.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/abd54f
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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  • 9
    Online Resource
    Online Resource
    Modeling Extinction and Reddening Effects by Circumstellar Dust in the Betelgeuse Envelope in the Presence of Radiative Torque Disruption
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 936, No. 2 ( 2022-09-01), p. 101-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 936, No. 2 ( 2022-09-01), p. 101-
    Abstract: Circumstellar dust forms and evolves within the envelope of evolved stars, including asymptotic giant branch (AGB) and red supergiant (RSG) stars. The extinction of stellar light by circumstellar dust is vital for interpreting RSG/AGB observations and determining high-mass RSG progenitors of core-collapse supernovae. However, circumstellar dust properties are not well understood. Modern understanding of dust evolution suggests that intense stellar radiation can radically change dust properties across the circumstellar envelope through the RAdiative Torque Disruption (RAT-D) mechanism. In this paper, we study the impacts of RAT-D on the grain size distribution (GSD) of circumstellar dust and model its effects on photometric observations of α Orionis (Betelgeuse). Due to the RAT-D effects, large grains formed in the dust formation zone are disrupted into smaller species of size a 〈 0.5 μ m. Using the GSD constrained by the RAT-D effects, we model the visual extinction of background stars and Betelgeuse. We find that the extinction decreases at near-UV, optical, and IR wavelengths while increasing at far-UV wavelengths. The resulting flux potentially reproduces the observation from the near-UV to the near-IR range. Our results can be used to explain dust extinction and photometric observations of other RSG/AGB stars.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac86d9
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 10
    Online Resource
    Online Resource
    Observations of Magnetic Fields Surrounding LkH α 101 Taken by the BISTRO Survey with JCMT-POL-2
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Vol. 908, No. 1 ( 2021-02-08), p. 10-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 908, No. 1 ( 2021-02-08), p. 10-
    Type of Medium: Online Resource
    ISSN: 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/abd0fc
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
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