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Title: The JCMT Transient Survey: Data Reduction and Calibration Methods

Abstract

Though there has been a significant amount of work investigating the early stages of low-mass star formation in recent years, the evolution of the mass assembly rate onto the central protostar remains largely unconstrained. Examining in depth the variation in this rate is critical to understanding the physics of star formation. Instabilities in the outer and inner circumstellar disk can lead to episodic outbursts. Observing these brightness variations at infrared or submillimeter wavelengths constrains the current accretion models. The JCMT Transient Survey is a three-year project dedicated to studying the continuum variability of deeply embedded protostars in eight nearby star-forming regions at a one-month cadence. We use the SCUBA-2 instrument to simultaneously observe these regions at wavelengths of 450 and 850 μ m. In this paper, we present the data reduction techniques, image alignment procedures, and relative flux calibration methods for 850 μ m data. We compare the properties and locations of bright, compact emission sources fitted with Gaussians over time. Doing so, we achieve a spatial alignment of better than 1″ between the repeated observations and an uncertainty of 2%–3% in the relative peak brightness of significant, localized emission. This combination of imaging performance is unprecedented in ground-based, single-dishmore » submillimeter observations. Finally, we identify a few sources that show possible and confirmed brightness variations. These sources will be closely monitored and presented in further detail in additional studies throughout the duration of the survey.« less

Authors:
;  [1]; ;  [2]; ;  [3];  [4]; ;  [5];
  1. Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada)
  2. NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada)
  3. Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2 (Canada)
  4. Academia Sinica Institute of Astronomy and Astrophysics, 645 N. A‘ohōkū Place, Hilo, HI 96720 (United States)
  5. East Asian Observatory, 660 North A‘ohōkū Place, University Park, Hilo, Hawaii 96720 (United States)
Publication Date:
OSTI Identifier:
22663431
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 843; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALIGNMENT; BRIGHTNESS; CALIBRATION; COMPACTS; COMPARATIVE EVALUATIONS; DATA ANALYSIS; EMISSION; EVOLUTION; IMAGE PROCESSING; INSTABILITY; MASS; PERFORMANCE; PROTOSTARS; REDUCTION; STARS; TRANSIENTS; WAVELENGTHS

Citation Formats

Mairs, Steve, Lane, James, Johnstone, Doug, Kirk, Helen, Lacaille, Kevin, Chapman, Scott, Bower, Geoffrey C., Bell, Graham S., Graves, Sarah, E-mail: smairs@uvic.ca, and Collaboration: JCMT Transient Team. The JCMT Transient Survey: Data Reduction and Calibration Methods. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA7844.
Mairs, Steve, Lane, James, Johnstone, Doug, Kirk, Helen, Lacaille, Kevin, Chapman, Scott, Bower, Geoffrey C., Bell, Graham S., Graves, Sarah, E-mail: smairs@uvic.ca, & Collaboration: JCMT Transient Team. The JCMT Transient Survey: Data Reduction and Calibration Methods. United States. doi:10.3847/1538-4357/AA7844.
Mairs, Steve, Lane, James, Johnstone, Doug, Kirk, Helen, Lacaille, Kevin, Chapman, Scott, Bower, Geoffrey C., Bell, Graham S., Graves, Sarah, E-mail: smairs@uvic.ca, and Collaboration: JCMT Transient Team. Sat . "The JCMT Transient Survey: Data Reduction and Calibration Methods". United States. doi:10.3847/1538-4357/AA7844.
@article{osti_22663431,
title = {The JCMT Transient Survey: Data Reduction and Calibration Methods},
author = {Mairs, Steve and Lane, James and Johnstone, Doug and Kirk, Helen and Lacaille, Kevin and Chapman, Scott and Bower, Geoffrey C. and Bell, Graham S. and Graves, Sarah, E-mail: smairs@uvic.ca and Collaboration: JCMT Transient Team},
abstractNote = {Though there has been a significant amount of work investigating the early stages of low-mass star formation in recent years, the evolution of the mass assembly rate onto the central protostar remains largely unconstrained. Examining in depth the variation in this rate is critical to understanding the physics of star formation. Instabilities in the outer and inner circumstellar disk can lead to episodic outbursts. Observing these brightness variations at infrared or submillimeter wavelengths constrains the current accretion models. The JCMT Transient Survey is a three-year project dedicated to studying the continuum variability of deeply embedded protostars in eight nearby star-forming regions at a one-month cadence. We use the SCUBA-2 instrument to simultaneously observe these regions at wavelengths of 450 and 850 μ m. In this paper, we present the data reduction techniques, image alignment procedures, and relative flux calibration methods for 850 μ m data. We compare the properties and locations of bright, compact emission sources fitted with Gaussians over time. Doing so, we achieve a spatial alignment of better than 1″ between the repeated observations and an uncertainty of 2%–3% in the relative peak brightness of significant, localized emission. This combination of imaging performance is unprecedented in ground-based, single-dish submillimeter observations. Finally, we identify a few sources that show possible and confirmed brightness variations. These sources will be closely monitored and presented in further detail in additional studies throughout the duration of the survey.},
doi = {10.3847/1538-4357/AA7844},
journal = {Astrophysical Journal},
number = 1,
volume = 843,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}
}
  • During the protostellar phase of stellar evolution, accretion onto the star is expected to be variable, but this suspected variability has been difficult to detect because protostars are deeply embedded. In this paper, we describe a submillimeter luminosity burst of the Class I protostar EC 53 in Serpens Main, the first variable found during our dedicated JCMT/SCUBA-2 monitoring program of eight nearby star-forming regions. EC 53 remained quiescent for the first six months of our survey, from 2016 February to August. The submillimeter emission began to brighten in 2016 September, reached a peak brightness of 1.5 times the faint state,more » and has been decaying slowly since 2017 February. The change in submillimeter brightness is interpreted as dust heating in the envelope, generated by a luminosity increase of the protostar of a factor of ≥4. The 850 μ m light curve resembles the historical K -band light curve, which varies by a factor of ∼6 with a 543 period and is interpreted as accretion variability excited by interactions between the accretion disk and a close binary system. The predictable detections of accretion variability observed at both near-infrared and submillimeter wavelengths make the system a unique test-bed, enabling us to capture the moment of the accretion burst and to study the consequences of the outburst on the protostellar disk and envelope.« less
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