How Do Stars Gain Their Mass? A JCMT/SCUBA-2 Transient Survey of Protostars in Nearby Star-forming Regions

Creators: Herczeg, Gregory J.; Hillenbrand, Lynne A.

Abstract

Most protostars have luminosities that are fainter than expected from steady accretion over the protostellar lifetime. The solution to this problem may lie in episodic mass accretion—prolonged periods of very low accretion punctuated by short bursts of rapid accretion. However, the timescale and amplitude for variability at the protostellar phase is almost entirely unconstrained. In A James Clerk Maxwell Telescope/SCUBA-2 Transient Survey of Protostars in Nearby Star-forming Regions, we are monitoring monthly with SCUBA-2 the submillimeter emission in eight fields within nearby (<500 pc) star-forming regions to measure the accretion variability of protostars. The total survey area of ~1.6 deg^2 includes ~105 peaks with peaks brighter than 0.5 Jy/beam (43 associated with embedded protostars or disks) and 237 peaks of 0.125–0.5 Jy/beam (50 with embedded protostars or disks). Each field has enough bright peaks for flux calibration relative to other peaks in the same field, which improves upon the nominal flux calibration uncertainties of submillimeter observations to reach a precision of ~2%–3% rms, and also provides quantified confidence in any measured variability. The timescales and amplitudes of any submillimeter variation will then be converted into variations in accretion rate and subsequently used to infer the physical causes of the variability. This survey is the first dedicated survey for submillimeter variability and complements other transient surveys at optical and near-IR wavelengths, which are not sensitive to accretion variability of deeply embedded protostars.

Additional Information

© 2017 The American Astronomical Society. Received 2017 June 9; revised 2017 September 5; accepted 2017 September 6; published 2017 October 27. We thank the JCMT staff for their care and attention in implementing these time-sensitive observations and for help in the reduction and distribution of the data. We also thank the anonymous referee for their careful read of and comments on the manuscript. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. G.H. is supported by general grant 11473005 awarded by the National Science Foundation of China. S.M. was partially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada graduate scholarship program. D.J. is supported by the National Research Council of Canada and by an NSERC Discovery Grant. J.-E.L. was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF; grant No. NRF-2015R1A2A2A01004769) and the Korea Astronomy and Space Science Institute under the R&D program (Project No. 2015-1-320-18) supervised by the Ministry of Science, ICT and Future Planning. Partial salary support for A.P. was provided by a Canadian Institute for Theoretical Astrophysics (CITA) National Fellowship. M.K. was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT & Future Planning (No. NRF-2015R1C1A1A01052160). W.K. was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2016R1C1B2013642). C.-W.L. was supported by the Basic Science Research Program though the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (NRF-2016R1A2B4012593). E.V. acknowledges support by the Austrian Science Fund (FWF) under research grant I2549-N27. S.-P.L. is thankful for the support of the Ministry of Science and Technology (MoST) of Taiwan through Grants 102-2119-M-007-004-MY3 and 105-2119-M-007-024. The JCMT is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan, Academia Sinica Institute of Astronomy and Astrophysics, the Korea Astronomy and Space Science Institute, the National Astronomical Observatories of China and the Chinese Academy of Sciences (Grant No. XDB09000000), with additional funding support from the Science and Technology Facilities Council of the United Kingdom and participating universities in the United Kingdom and Canada. The identification number for the JCMT Transient Survey under which the SCUBA-2 data used in this paper is M16AL001. The authors thank the JCMT staff for their support of the data collection and reduction efforts. The starlink software is supported by the East Asian Observatory. This research has made use of the NASA Astrophysics Data System and the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency. This research used the services of the Canadian Advanced Network for Astronomy Research (CANFAR) which in turn is supported by CANARIE, Compute Canada, University of Victoria, the National Research Council of Canada, and the Canadian Space Agency. This research made use of APLpy, an open-source plotting package for Python hosted at http://aplpy.github.com, and matplotlib, a 2D plotting library for Python (Hunter 2007).

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