IRAS16293Band9

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Contents

Science Target Overview

IRAS 16293-2422 (d=160 pc; Chini 1981) is a well studied nearby Class 0 proto-binary system (consists of sources A and B) located in L1689 (i.e., Ophiuchus star forming cloud). The projected separation between sources A and B is roughly 5" (Mundy et al. 1992; Chandler et al. 2005; Figure 1 left panel). Sub-arcsecond VLA and SMA centimeter and millimeter/submillimeter continuum images have spatially resolved source A as several components associated with protostars and jets (Chandler et al. 2005; Pech et al. 2010). IRAS 16293-2422 hosts a large-scale quadrupolar outflow (Walker et al. 1988; Mizuno et al. 1990; Castets et al. 2001; Hirano et al. 2001; Garay et al. 2002; Stark et al. 2004; Yeh et al. 2008). The outflow aligned in the east-west direction is currently active and likely originated from source A (Figure 1 right panel). The origin of the other large-scale outflow aligned in the northeast-southwest direction is not clear. Previous molecular line studies with the SMA have revealed detailed structure and kinematics in the circumbinary envelope for each component. These imply gas infall and outflow motions (Chandler et al. 2005; Takakuwa et al. 2007; Yeh et al. 2008). In addition, IRAS 16293-2422 exhibits strong emission from a number of complex organic molecules and other species usually associated with hot cores in massive star-forming regions, especially towards source A (e.g., Blake et al. 1994; van Dishoeck et al. 1995; Bottinelli et al. 2004; Kuan et a. 2004; Schoier et al. 2004; Chandler et al. 2005; Huang et al. 2005; Bisschop et al. 2008; Jorgensen et al. 2011; Caux et al. 2011). Finally, source B shows a narrow line width (Bisschop et al. 2008; Jorgensen et al. 2011) and no clear signature of outflow (Chandler et al. 2005). This suggests that the source may be at the very young evolutionary stage; likely even before the mass accretion/loss processes start.

Fig. 1. Left: Sub-arcsecond continuum image obtained with SMA at 310 GHz by Chandler et al. (2005). Right: Integrated blueshifted and redshifted CO (2-1) image tracing molecular outflow originated from source A. The data were obtained with SMA by Yeh et al. (2008). The emission is integrated over the velocity channels from V_lsr=-7.2 to 3.3 km/s on the blueshifted side and from V_lsr=5.5 to 31.9 km/s on the redshifted side.

ALMA Data Overview

ALMA Science Verification data at Band 9 (602-720 GHz) was taken for IRAS 16293-2422 on April 16 and 17, 2012. The observations have been performed with a seven pointing mosaic centered at RA=16h 32m 22.7s, Dec=-24d28’32.5’’ as shown in Figure 1. The complete 7 pointing mosaic can be seen in Figure 2, superposed on archival SMA data for better visualization.

A scheduling block about 2.3 hours long was run four times for a total of about 9.2 hours of observing time. The integration time of each visibility is 6.048 sec, and the total on-source time of of each pointing is between 16 to 20 min. Three data sets were obtained post-transit, while the other one was obtained pre-transit. The name of the four ASDMs are as follows (with the median value of zenithal precipitable water vapor given in parentheses):

  • uid___A002_X3d4118_X39b (0.31 mm)
  • uid___A002_X3d55cb_X575 (0.65 mm)
  • uid___A002_X3d55cb_Xb50 (0.43 mm)
  • uid___A002_X3d55cb_X90c (0.41 mm)

Data were obtained with the Double Sideband (DSB) Band 9 receivers. Four basebands were used for obtaining data with Frequency Division Mode (FDM). The baseband centers are located at approximately: 704.249, 691.299, 689.499, and 687.499 GHz. The CO (6-5) line at a rest frequency of 691.473 GHz is strongly detected (though extremely resolved out), along with numerous other weaker (but more compact) organic species throughout all four basebands. Each spectral window is 1.875 GHz in width, and contains 3840 channels. The channel separation is 0.488 MHz (0.2 km/s), but the spectral resolution is factor of 2 poorer (0.4 km/s) due to online Hanning smoothing. The image cubes were made with 0.4 km/s channels.

These data were obtained using the Cycle 0 Early Science extended configuration which resulted in an angular resolution of about 0.22"

Fig. 2.Pointings (crosses) and field of view (circles with 9”) for the ALMA band 9 SV observations toward IRAS 16293-2422 overlaid on SMA continuum image at 310 GHz obtained with the extended configuration (angular resolution of 0.97”x0.76”). The SMA data were retrieved from archive. The positions of source Aa, Ab, and B reported in Chandler et al. (2005) are denoted by the black dots.

Using the data for publication: The following statement should be included in the acknowledgment of papers using the datasets listed above: “The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. This paper makes use of the following ALMA Science Verification data: ADS/JAO.ALMA#2011.0.00007.SV"

We thank the following people for suggesting IRAS16293 for ALMA Science Verification: Jes Jorgensen, Suzanne Bisschop, Ewine van Dishoeck, Tyler Bourke, Johan Lindberg, Michiel Hogerheijde, Bill Dent, Martin Zwaan, Al Wootten.

Obtaining the Data

To download all the data, follow one of the next links:

North America

Europe

East Asia

The links provide you with the option to download the following gzipped tar files:

IRAS16293_Band9_UnCalibratedMS - The file contains the raw data files in ALMA Science Data Model (ASDM) format already converted into CASA Measurement Sets (MS) using importasdm inside CASA.

IRAS16293_Band9_CalibratedMS - The fully-calibrated u-v data, ready for imaging.

IRAS16293_Band9_ReferenceImages - The final continuum and spectral line images.

You can work with these data products at any of the three stages: the UnCalibratedMS, the Calibrated MS (ready for imaging, or the ReferenceImages. Warning: the UnCalibrated data is large.

Caveat: Before using the ReferenceImages for scientific purposes, please note that only a few of the very strongest lines have been excluded from the continuum subtraction or continuum imaging - you may wish to do a more careful job if your science application is strongly dependent on the flux density or morphology of source B, in particular which shows both strong absorption and emission at the 0.2" resolution of these data. Additionally, there was a glitch in the System Temperature (Tsys) measurements for the absolute flux calibrator, Juno, necessitating the application of Tsys from another source at different elevation. Together with the inherent uncertainties in the Juno flux density model (it has a large crater), the overall absolute flux density uncertainty is at least 20%.

IRAS16293 Band 9 Data Reduction Tutorial

The tutorial (called a casaguide) for reducing these data using CASA version 3.4 has been split into calibration and imaging pages:

1) IRAS16293_Band9_-_Calibration_for_CASA_3.4 : This section of the tutorial steps you through inspection and calibration of the basic visibility (u-v) data. To complete this part, you will need the data in the first directory: IRAS16293_Band9_UnCalibratedMS.

WARNING: On June 14, 2012 this guide was changed to correct for a 1.2" position error in the 
phase calibrator (1625-254). Without correction, the science images will suffer from a similar 
offset. The final data products (calibrated science data and images) will soon be updated in 
the ALMA science portal. 

2) IRAS16293_Band9_-_Imaging_for_CASA_3.4 : This part of the tutorial focuses on constructing images from the fully calibrated visibility data. If you wish to skip calibration and proceed directly to this part of the tutorial, you will need the fully-calibrated visibility data in the IRAS16293_Band9_CalibratedMS directory.

We also provide the final continuum and spectral line images in the IRAS16293_Band9_ReferenceImages directory.

NOTE: CASA 3.4 (≥ r19874) is required to process the data using the guides above see http://casa.nrao.edu/casa_obtaining.shtml.

How to Use A CASA Guide

For tips on using CASA and ways CASA can be run, see EVLA_Spectral_Line_Calibration_IRC+10216#How_to_Use_This_casaguide page.

To learn how to extract executable Python scripts from the tutorial, see Extracting_scripts_from_these_tutorials.

Within the guides:

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Last checked on CASA Version 3.4.0.

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