Suchergebnisse

We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of similar to 0.'' (40au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of similar to 0.'' 08 (32 au) This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are 44.9(-3.4)(+5.8), 37.0(-3.0)(+4.9), and 28.5(-2.3)(+3.7) au, respectively, and the mean protostellar dust disk masses are 25.9(-4.0)(+7.7), 14.9(-2.2)(+3.8), 1.6(-1.9)(+3.5) M-circle plus, respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase. ; National Science Foundation (NSF): AST-1814762, AST-1716259, 1815784, 1910106 Homer L. Dodge Endowed Chair National Aeronautics & Space Administration (NASA): 80NSSC18K1095 European Union (EU): AYA2017-84390-C2-1-R State Agency for Research of the Spanish MCIU through "Center of Excellence Severo Ochoa" award: SEV-20170709 Huygens fellowship from Leiden University

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (HCCO), propyne (CHCCH), formamide (NHCHO), methoxy (CHO), methanol (CHOH), dimethyl ether (CHOCH), and methyl formate (HCOOCH). Results. Only two transitions of methanol (A, E) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E) in a very compact emission blob (∼7″ corresponding to ∼1000 au) toward the northeast of the L1521F protostar. The CS 2-1 transition is also detected within theWideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ∼1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H) ≥ 10 cm). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infalling gas or (ii) a cold and dense fragment that may just have been formed as a result of the intense gas dynamics within the L1521F VeLLO system. ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)