Karen O'Neil

Set-up

• K-band
• 800Hz Bandwidth
  
• 2048 channels
  
• 4 Quad
  
• 1 samplers (total)
  
• 3-level
  
• Linear Polarization
• Observing using beam-switching technique

Summary

• Pointing corrections was less than 1'.
• All of the data has poor baselines, with 40-60 MHz ripples overlying 200-300MHz ripples. This could cause serious problems for observers.
• The bandpass shapes and rms levels for the IFs/samplers for each bank were virtually identical.
• It was impossible to determine how well the measured flux compared to published values, as no calibrators were observed. Approximately comparing the measured peaks with those in the literature show the values to be approximately correct.
• The measured rms of the data was about 2x the theoretical value, and it did not go down as 1/sqrt(time). This is presumably due to the poor baselines.
• This mode is not recommended for general use until the baseline issues are dealt with.

Observations

• Data taken on 08/09 May, 2003
  
• Data file is T_KBAND_09MAY03
  

  Scan	Source	Comments
  84	VY CMa	300s
  85	VY CMa	300s
  86	VY CMa	300s
  87	VY CMa	300s
  88	VY CMa	300s
  89	VY CMa	300s
  90	VY CMa	300s
  91	VY CMa	300s
  92	VY CMa	300s
  93	VY CMa	300s

Analysis

I. VY CMa

Ten 300s beam-switched observations were made of the 22GHz line in VY CMa. In all cases, the baseline showed considerable structure, as exemplified below:

Fig 1.VY CMa in Bank A for scan 84.

Fig 2.VY CMa in Bank A for scan 84.

Fig 3. VY CMa in Bank A for average of all scans with 200-300 MHz ripple removed.

Other images available:

• VY CMa in Bank B for scan 84.
• VY CMa in Bank B for scan 84, blowup on baseline
• VY CMa in Bank C for scan 84.
• VY CMa in Bank C for scan 84, blowup on baseline
• VY CMa in Bank D for scan 84.
• VY CMa in Bank A for average of all scans.
• VY CMa in Bank A for average of all scans, blowup on baseline
• VY CMa in Bank A for average of all scans, blowup on baseline with 200-300 MHz ripple removed.
• VY CMa in Bank B for average of all scans.
• VY CMa in Bank C for average of all scans.
• VY CMa in Bank C for average of all scans, blowup on baseline
• VY CMa in Bank C for average of all scans, blowup on baseline with 200-300 MHz ripple removed.
• VY CMa in Bank D for average of all scans.
• VY CMa in Bank D for average of all scans, blowup on baseline

The measured flux, peak, and velocity widths of VY CMa ranged from 1456 K to 5753 K, showing that the problems with the baseline dominate the science. The average of all 10 scans is below:

Fig 4. Average of all scans for Bank A, blown up on the line of interest.

Fig 5. Average of all scans for Bank B, blown up on the line of interest.

Fig 6. Average of all scans for Bank C, blown up on the line of interest.

Fig 7. Average of all scans for Bank D, blown up on the line of interest.

III. Central Velocity

The data was taken in topocentric mode, which aips++ does not deeal with. However, applying accurate corrections to the data show that the velocities do in fact match that in the literature, as shown below:

Fig 8. Scan 84, Bank A, corrected to true LSR velocities.

Fig 9. Spectra from Moran, et.al (1973 ApJ 185, 535)

III. RMS

The rms noise ranged from 30-50 mK after removing a 6th order baseline from the 200 channels of interest. The RMS of the ten averaged scans was approximatel half the value for the individual scans, for all banks and all polarizations, Assuming a Tsys of 116K for the two polarizations (taken from the average values) gives a theoretical value of 19 mK for one 300s scan and 6 mK for the average of the ten scans. This is considerably lower than was measured.