Science Highlight




Science Verification: Water Masers

Description / Details of the target

Sources (all Oxygen-rich giant or super-giant stars) 
R Hor 02 53 52.76 -49 53 22.6 
IK Tau 03 53 28.84 +11 24 22.6 
R Dor 04 36 45.59 -62 04 37.8 
U Dor 05 10 08.84 -64 19 04.3 
VY CMa 07 22 58.33 -25 46 03.2

v = 0, 10(2,9)-9(2,6) 321.226 GHz 
v = 0, 5(1,5)-4(2,2) 325.153 GHz and 
v = 1, 1(1,0)-1(0,1) 658.0065 GHz

Example references: Menten & Melnick, 1991, ApJ, 377, 647; Menten & Young 1995, ApJ, 450, 67; Hunter et al., 2007, IAUS, 242,481

Capabilities to be verified

With these targets we will demonstrate Cycle 1 high-angular resolution capabilities. Observations will use the 12-m array. Correlator modes to be demonstrated are: mixed and 1 spw per baseband modes. Additional functionalities to be demonstrated are: spectral averaging, survey mode (non-multi-field). There are also some special issues to be worked out for obtaining satisfactory band-pass calibration for very bright lines, particularly in the presence of strong atmospheric absorption by water, e.g. at 325 GHz.


We need objects with high brightness temperature and an important aspect is to demonstrate that full coherence is obtained over the long baselines which means comparing the intensities in total power with the cross-correlations. This is much easier to do with spectral sources. These masers are lines are obvious choice. The objects are relatively simple but are expected to show structure at around the 0.1" scale which is what is to be demonstrated here. The specific list was chosen to be available at night at around the end of the year when the longer baselines should become available.


The VY CMa data was released on 7 September 2014 and can be obtained via the ALMA Science Portal.