Browsing by Author "Feng, S."

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    FAUST - V. Hot methanol in the [BHB2007] 11 protobinary system; hot corino versus shock origin
    (EDP Sciences, 2022) Vastel, C.; Alves, F.; Ceccarelli, C.; Bouvier, M.; Jiménez-Serra, I.; Sakai, T.; Caselli, P.; Evans, L.; Fontani, F.; Gal, R. Le; Chandler, C.J.; Svoboda, B.; Maud, L.; Codella, C.; Sakai, N.; Lόpez-Sepulcre, A.; Moellenbrock, G.; Aikawa, Y.; Balucani, N.; Bianchi, E.; Busquet, G.; Caux, E.; Charnley, S.; Cuello, N.; Simone, M. De; Dulieu, F.; Durân, A.; Fedele, D.; Feng, S.; Francis, L.; Hama, T.; Hanawa, T.; Herbst, E.; Hirota, T.; Imai, M.; Isella, A.; Johnstone, D.; Lefloch, B.; Loinard, L.; Maureira, M.; Murillo, N.M.; Mercimek, S.; Mori, S.; Menard, F.; Miotello, A.; Nakatani, R.; Nomura, H.; Oba, Y.; Ohashi, S.; Okoda, Y.; Ospina-Zamudio, J.; Oya, Y.; Pineda, J.E.; Podio, L.; Rimola, A.; Cox, D. Segura; Shirley, Y.; Testi, L.; Viti, S.; Watanabe, N.; Watanabe, Y.; Witzel, A.; Xue, C.; Zhang, Y.; Zhao, B.; Yamamoto, S.
    Aims.Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the build-up of chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance.Methods. We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disc has previously been detected.Results. Twelve methanol lines have been detected with upper energies in the [45–537] K range along with one 13CH3OH transition and one methyl formate (CH3OCHO) line blended with one of the methanol transitions. The methanol emission is compact (FWHM ~ 0.5″) and encompasses both protostars, which are separated by only 0.2″ (28 au). In addition, the overall methanol line emission presents three velocity components, which are not spatially resolved by our observations. Nonetheless, a detailed analysis of the spatial origin of these three components suggests that they are associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A radiative transfer analysis of the methanol lines gives a kinetic temperature of [100–140] K, an H2 volume density of 106–107 cm−3 and column density of a few 1018 cm−2 in all three components with a source size of ~0.15″. Thus, this hot and dense gas is highly enriched in methanol with an abundance as high as 10−5. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects.Conclusions. Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis.
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    FAUST - XIII. Dusty cavity and molecular shock driven by IRS7B in the Corona Australis cluster
    (EDP Sciences, 2024) Sabatini, G.; Podio, L.; Codella, C.; Watanabe, Y.; Simone, M. De; Bianchi, E.; Ceccarelli, C.; Chandler, C. J.; Sakai, N.; Svoboda, B.; Testi, L.; Aikawa, Y.; Balucani, N.; Bouvier, M.; Caselli, P.; Caux, E.; Chahine, L.; Charnley, S.; Cuello, N.; Dulieu, F.; Evans, L.; Fedele, D.; Feng, S.; Fontani, F.; Hama, T.; Hanawa, T.; Herbst, E.; Hirota, T.; Isella, A.; Jímenez-Serra, I.; Johnstone, D.; Lefloch, B.; Gal, R. Le; Loinard, L.; Liu, H. B.; López-Sepulcre, A.; Maud, L. T.; Maureira, M. J.; Menard, F.; Miotello, A.; Moellenbrock, G.; Nomura, H.; Oba, Y.; Ohashi, S.; Okoda, Y.; Oya, Y.; Pineda, J.; Rimola, A.; Sakai, T.; Segura-Cox, D.; Shirley, Y.; Vastel, C.; Viti, S.; Watanabe, N.; Zhang, Y.; Zhang, Z. E.; Yamamoto, S.
    Context.The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems.Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster.Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H2CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H 2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4.Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.
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    FAUST - XVII. Super deuteration in the planet-forming system IRS 63 where the streamer strikes the disk
    (EDP Sciences, 2024) Podio, L.; Ceccarelli, C.; Codella, C.; Sabatini, G.; Segura-Cox, D.; Balucani, N.; Rimola, A.; Ugliengo, P.; Chandler, C. J.; Sakai, N.; Svoboda, B.; Pineda, J.; Simone, M. De; Bianchi, E.; Caselli, P.; Isella, A.; Aikawa, Y.; Bouvier, M.; Caux, E.; Chahine, L.; Charnley, S. B.; Cuello, N.; Dulieu, F.; Evans, L.; Fedele, D.; Feng, S.; Fontani, F.; Hama, T.; Hanawa, T.; Herbst, E.; Hirota, T.; Jiménez-Serra, I.; Johnstone, D.; Lefloch, B.; Gal, R. Le; Loinard, L.; Liu, H. Baobab; López-Sepulcre, A.; Maud, L. T.; Maureira, M. J.; Menard, F.; Miotello, A.; Moellenbrock, G.; Nomura, H.; Oba, Y.; Ohashi, S.; Okoda, Y.; Oya, Y.; Sakai, T.; Shirley, Y.; Testi, L.; Vastel, C.; Viti, S.; Watanabe, N.; Watanabe, Y.; Zhang, Y.; Zhang, Z. E.; Yamamoto, S.
    Context. Recent observations suggest that planet formation starts early, in protostellar disks of ≤105 yr, which are characterized by strong interactions with the environment, such as through accretion streamers and molecular outflows.Aims. To investigate the impact of such phenomena on the physical and chemical properties of a disk, it is key to understand what chemistry planets inherit from their natal environment. Methods. In the context of the ALMA large program Fifty AU Study of the chemistry in the disk/envelope system of solar-like protostars (FAUST), we present observations on scales from ∼1500 au to ∼60 au of H2CO, HDCO, and D2CO toward the young planet-forming disk IRS 63. Results. The H2CO probes the gas in the disk as well as in a large scale streamer (∼1500 au) impacting onto the southeast disk side. We detected for the first time deuterated formaldehyde, HDCO and D2CO, in a planet-forming disk and HDCO in the streamer that is feeding it. These detections allowed us to estimate the deuterium fractionation of H2CO in the disk: [HDCO]/[H2CO] ∼ 0.1 − 0.3 and [D2CO]/[H2CO] ∼ 0.1. Interestingly, while HDCO follows the H2CO distribution in the disk and in the streamer, the distribution of D2CO is highly asymmetric, with a peak of the emission (and [D]/[H] ratio) in the southeast disk side, where the streamer crashes onto the disk. In addition, D2CO was detected in two spots along the blue- and redshifted outflow. This suggests that (i) in the disk, HDCO formation is dominated by gas-phase reactions in a manner similar to H2CO, while (ii) D2CO is mainly formed on the grain mantles during the prestellar phase and/or in the disk itself and is at present released in the gas phase in the shocks driven by the streamer and the outflow. Conclusions. These findings testify to the key role of streamers in the buildup of the disk concerning both the final mass available for planet formation and its chemical composition.
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    Hall and field-effect mobilities in few layeredﾠp-WSe2ﾠfield-effect transistors
    (Macmillan Publishers Limited, 2015) Pradhan, N.R.; Rhodes, D.; Memaran, S.; Poumirol, J.M.; Smirnov, D.; Talapatra, S.; Feng, S.; Perea-Lopez, N.; Elias, A.L.; Terrones, M.; Ajayan, P.M.; Balicas, L.
    Here, we present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2. Without dielectric engineering and beyond a T-dependent threshold gate-voltage, we observe maximum hole mobilities approaching 350 cm(2)/Vs at T = 300 K. The hole Hall mobility reaches a maximum value of 650 cm(2)/Vs as T is lowered below ~150 K, indicating that insofar WSe2-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. The gate capacitance, as extracted from the Hall-effect, reveals the presence of spurious charges in the channel, while the two-terminal sheet resistivity displays two-dimensional variable-range hopping behavior, indicating carrier localization induced by disorder at the interface between WSe2 and SiO2. We argue that improvements in the fabrication protocols as, for example, the use of a substrate free of dangling bonds are likely to produce WSe2-based FETs displaying higher room temperature mobilities, i.e. approaching those of p-doped Si, which would make it a suitable candidate for high performance opto-electronics.