Protostellar CCS Project Results and Discussion


TIP Last Modified: JeffMangum - 19 Oct 2006

Table of Contents:


To Do List

  • Flux calibration.
  • Opacity correction calculation.
  • C13CCS RMS calculations.
  • Search for HC7N 21-20 in IF3.


Observation Summary

Session Log
Session Date Tau0 Sources Comments
1 2006/09/07 ?.??? Per5, B5, L1527 Weather reasonably good. Test source DR21OH confirmed correlator setup. Pointing checked every 2-3 hours and found to be good to ?? arcsec or so.
2 2006/09/21 ?.??? L260, L483 Weather not great. Test source DR21OH confirmed correlator setup. Pointing checked every 2-3 hours and found to be good to ?? arcsec or so.
3 2006/06/25 ?.??? L1251E, L483 Weather pretty good. Pointing checked every 1-2 hours and found to be good to ?? arcsec or so.
4 2006/06/26 ?.??? L1251E, L483 Weather not great. Pointing checked every 1-2 hours and found to be good to ?? arcsec or so.


Receiver and Correlator Setups:

  • K-Band:
    • Receiver 'Rcvr22_26'
    • Dual Feed
    • Frequency Switching (+4.11 MHz offset)
    • BW = 50 MHz per IF
    • Nchan = 16384 per IF
    • Channel Width = 3.052 kHz (0.2 km/s at 4.8 GHz)
    • Dual Circular Polarization per IF
    • IF1 = 22254.493 MHz (C13CCS 2(1)-1(0))
    • IF2 = 22344.033 MHz (CCS 2(1)-1(0))
    • IF3 = 23703.546 MHz (NH3 (1,1),(2,2), and HC7N 21-20)
    • IF4 = 23963.901 MHz (HC5N 9-8)


Flux Calibration

Several things to note about GBT flux calibration:
  • The K-to-Jy conversion factors listed and used by the GBT exposure calculator are out-of-date.
  • Standard K-to-Jy or opacity information is not written to the gbtidl data headers (this is a project currently in development).
  • To get historical opacity estimates from Ron Madellena's weather calculations, use the "cleo forecasts" command from any GB computer. This will start a gui which allows one to select dates, frequencies, etc for any observation that happened after May 2004. You can write the results to a file or just get a graph. These plots are linked to the Observation Summary above (the Tau0 column).
  • The current aperture efficiency measurements are well-fit by the following: \eta_A = 0.71 \exp\left(-\left(0.0163 \nu(GHz)\right)^2\right). At 4.8 and 14.5 GHz this yields \eta_A = 0.71 and 0.67, respectively. For EL = 90 and zero atmospheric opacity, Ta/S = 2.846*\eta_A = 2.0 and 1.9 for 4.8 and 14.5 GHz, respectively.
  • Using the Madellena weather calculations to derive average Tau0 at 22.5 GHz for each of our observation sessions (see Observation Summary table above) I calculate, for elevation >~ 30 degrees, K/Jy = ?.??+-?.?? at 22.5 GHz. These are the K/Jy calibration factors that we should use.
  • The absolute amplitude calibration is reported to be no better than 10-15%, due mainly to temporal drifts in the noise diodes used as absolute amplitude calibration standards. For more accurate calibration one should do a spectral line measurement of a standard flux calibration source (like 3C286) and directly derive the K-to-Jy conversion.


Data Reduction Summary

  • Inspected all scans for bad baselines, correlator lag problems (rare), and band suckouts (even rarer). See comments in results table below.
  • Summed spectra for each source/IF into the following files:
    • CCSGBT.fits: Dual-polarization average of all central position spectra for each IF.
    • CCSGBTpolave.fits: Dual-polarization average of all spectra for each IF.
    • CCSGBTmaps.fits: Dual-polarization average of all spectra per position, source, and IF.
    • CCSGBTbase.fits: Baseline-fitted (1st order baseline) version of CCSGBT.fits.
    • CCSGBTmapsbase.fits: Baseline-fitted (1st order baseline) version of CCSGBTmaps.fits.
  • Temperature scale is Ta.


CCS/C13CS/NH3/HC5N Observation Summary

Observation Summary
Source Position (J2000;km/s) Session Scan Numbers
Per5 03:29:51.6, +31:39:04, 8.21 1 13-34
B5 03:47:42.4, +32:52:01, 10.20 1 40-49,67-115,121-169,180-228
L1527 04:39:53.6, +26:03:05, 5.95 1 234-235,236-284,285-286
L260 16:47:06.7, -09:35:21, 3.47 2 17-22,23-120,126-135,141-147
L483 18:17:29.7, -04:39:38, 5.31 2,3,4 148-151,30-37,44-92,99-173,124,172,178-226,237-238
L1251E 22:38:50.9, +75:11:04, -3.66 3,4 6-24,6-64,70-118


Results

In the following I list the summed and baselined results for both central positions and maps. Note that files named "HC3N*" are actually HC5N measurements (error in naming).

Results Summary
Source CCS 2(1)-1(0) C13CCS 2(1)-1(0) NH3(1,1) NH3(2,2) HC5N 9-8
Per5 Peak ~ 0.15 K RMS = ?.??? Peak ~ 3.0 K Peak ~ 0.6 K Peak ~ 0.15 K
B5 Peak ~ 0.30 K RMS = ?.??? Peak ~ 2.3 K Peak ~ 0.45 K Peak ~ 0.22 K
CCS Map NH3(1,1) Map NH3(2,2) Map HC5N 9-8 Map
L1527 Peak ~ 0.32 K RMS = ?.??? Peak ~ 2.3 K Peak ~ 0.40 K Peak ~ 0.60 K
CCS Map NH3(1,1) Map NH3(2,2) Map HC5N 9-8 Map
L260 Peak ~ 0.22 K RMS = ?.??? Peak ~ 2.9 K Peak ~ 0.70 K Peak ~ 0.28 K
CCS Map NH3(1,1) Map NH3(2,2) Map HC5N 9-8 Map
L483 Peak ~ 1.0 K RMS = ?.??? Peak ~ 4.0 K Peak ~ 2.1 K Peak ~ 1.1 K
CCS Map NH3(1,1) Map NH3(2,2) Map HC5N 9-8 Map
L1251E Peak ~ 0.10 K RMS = ?.??? Peak ~ 2.2 K Peak ~ 0.6 K Peak ~ 0.1 K
CCS Map NH3(1,1) Map NH3(2,2) Map HC5N 9-8 Map


Data Files and Analysis Notes(Restricted Access)

Get the reduced (CCSGBT*.fits.gz) files from the restricted access data file location.


GBTIDL Reduction Scripts Used

  • keepfs.pro: Used to sum dual-polarization scans.
  • cave.pro: Used average all spectra for a given position.
  • cfs.pro: Used to average all central position spectra.
  • mapfind.pro: Used final all spectra for a given position, source, and IF and average them (useful for map data, obviously).
  • postage.pro: Used to make a "postage stamp" plot of map data.


Motivation for these CCS Measurements


Topic revision: r6 - 2010-02-02, JeffMangum
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback