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A 0.2-solar-mass protostar with a Keplerian disk in the very young L1527 IRS system



In their earliest stages, protostars accrete mass from their surrounding envelopes through circumstellar disks. Until now, the smallest observed protostar-to-envelope mass ratio was about 2.1 (ref. 1). The protostar L1527 IRS is thought to be in the earliest stages of star formation2. Its envelope contains about one solar mass of material within a radius of about 0.05 parsecs (refs 3, 4), and earlier observations suggested the presence of an edge-on disk5. Here we report observations of dust continuum emission and 13CO (rotational quantum number J = 2 → 1) line emission from the disk around L1527 IRS, from which we determine a protostellar mass of 0.19 ± 0.04 solar masses and a protostar-to-envelope mass ratio of about 0.2. We conclude that most of the luminosity is generated through the accretion process, with an accretion rate of about 6.6 × 10−7 solar masses per year. If it has been accreting at that rate through much of its life, its age is approximately 300,000 years, although theory suggests larger accretion rates earlier6, so it may be younger. The presence of a rotationally supported disk is confirmed, and significantly more mass may be added to its planet-forming region as well as to the protostar itself in the future.

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Figure 1: Cartoon of a protostellar system rotated to match the orientation of L1527.
Figure 2: Images of the edge-on disk around the protostar L1527.
Figure 3: 13 CO emission from the disk around L1527 exhibiting a Keplerian rotation signature.
Figure 4: Plots of radius versus velocity, showing the rotation curve derived from the 13 CO emission.


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We thank E. Bergin for comments on the manuscript and W. Kwon for discussing improvements to the data reduction. J.J.T. was supported by NASA through Hubble Fellowship grant HSTHF-51300.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. L.H. and J.J.T. acknowledge partial support from the University of Michigan. H.-F.C. was supported by NASA through the NASA Astrobiology Institute under cooperative agreement NNA09DA77A issued through the Office of Space Science. L.W.L. and H.-F.C. acknowledge support from the Laboratory for Astronomical Imaging at the University of Illinois and the NSF under grant AST-07-09206. P.D. acknowledges a grant from PAPIIT-UNAM. L.L. was supported by DGAPA, UNAM, CONACyT (México) and the Alexander von Humboldt Stiftung. Support for CARMA construction was derived from the states of Illinois, California and Maryland, the James S. McDonnell Foundation, the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the University of Chicago, the Associates of the California Institute of Technology, and the NSF. Continuing CARMA development and operations are supported by the NSF under a cooperative agreement, and by the CARMA partner universities. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The National Radio Astronomy Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc.

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J.J.T., H.-F.C., D.J.W. and L.W.L. participated in data acquisition and reduction. All authors contributed to the data analysis, discussed the results and commented on the manuscript.

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Correspondence to John J. Tobin.

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The authors declare no competing financial interests.

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This file contains Supplementary Text and Data 1-4, Supplementary Figures 1-3. Supplementary Tables 1-2 and additional references. (PDF 491 kb)

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Tobin, J., Hartmann, L., Chiang, HF. et al. A 0.2-solar-mass protostar with a Keplerian disk in the very young L1527 IRS system. Nature 492, 83–85 (2012).

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