ARO 12M
my home upper gernal Observation ARO HHT ARO 12M ASTE CSO DeLingHa13 IRAM 30M KOSMA LSST Nobeyama 45M YNAO40m SESHAN25 Herschel

Caution!! Although I am happy to share my research notes below with all visitors to my webpages, these pages are mainly designed for my own use and subject to change without warning. I do not guarantee the correctness of all contents as well.

ARO 12M telescope (see more details at ARO 12M telescope's homepage)

Table of contents:

1. basic information
2. mainbeam temperatrue (T_mb)
3. beam size and telescope efficiencies (BWHM,eta_l, eta_fss, eta*_m, eta_mb)
4. flux density convertion
5. Data File Formats (astro/horizon, Xremote)

　

Basic information of the 12M telescope

Name: Astronomy Radio Observatory (ARO) 12M Telescope
Location:  Monte Wilson
           East longitude: -111d 36m 53.00475s
           North latitude: +31d  57m 12.000s 
           Elevation: 1894.5 meters (6215.8 feets)
 Diameter = 12m.
Surface accuracy: 75 um rms
Wavelength range: ??
Pointing accuracy: 5" rms
Mount: elevation over azimuth
Elevation and azimuth limits: 80 deg > EL > 15 deg, rewind at AZ = 66.8 deg
Default beam switch: throw of +- 2 arcmin for 3 mm and +- 1 arcmin for 1 mm at 1.25 Hz.
Default data format: sdd (single dish data format). Line data can be converted to CLASS format using command uni2class.
Tuning ranges of receivers: SiS receivers that reject the unwanted sideband by tuning the backshots. An hamonic generator is switched into the optical path of the receiver to allow precise measurement of the sideband rejection ratio. At most frequencies, the rejection ratio is >=20 dB.

Receiver

Tuning Range (GHz)

Approximate Tsys(SSB) (K)

3mmlo

68-90

170-225

3mmhi

90-116

160-350

2mm

130-170

180-400

Millimeter Autocorrelation (MAC) confingurations:

　

Bandwidth and Channels

Useable Bandwidth

and Channels1

?ν2

Resolution

(MHz)

Channels

(MHz)

Channels

(kHz)

(kHz)

2 IF Modes

800

2048

600*

1536

390.6

781.2

800

4096

600

3072

195.3

390.6

400

4096

300*

3072

97.6

195.3

400

8192

300

6144

48.8

97.6

200

8192

150*

6144

24.4

48.8

200

16384

150

12288

12.2

24.4

100

16384

75*

12288

6.1

12.2

100

32768

75

24576

3

6.1

4 IF Modes

800

1024

600*

768

781.2

1562

800

2048

600

1536

390.6

781.2

400

2048

300*

1536

195.3

390.6

400

4096

300

3072

97.6

195.3

200

4096

150*

3072

48.8

97.6

200

8192

150

6144

24.4

48.8

100

8192

75*

6144

12.2

24.4

100

16384

75

12288

6.1

12.2

1 The useable bandwidth takes account of the 75% efficiency of the analog filters.
2 NOTE: This is the frequency sampling interval, not the FWHM channel width, for a given channel. The FWHM channel width is 2.0 times this value.
See Appendix D for details.
All values in this table refer to each IF.
Modes tagged with a * are produced by dropping the last half of the lags

The temperature given in observation data file is TR*, the observed source antenna temperature corrected for atmospheric attenuation, radiative loss and rearward scattering and spillover. The main beam temperature can be calculated as

Tmb = TR* / etam* 

Here etam* is corrected main beam efficiency. (see more details on efficiencies below)

BWHM beam sizes and efficiencies: (as a function of frequency)           [go to top]

(caution!! These paramters are valid only for observations after the reconstruction of the current 12M telescope from a old 35 feet (11 meter) telescope in 1982!)

Parameters of the 12M telescope from chapter 3, Table 3.2 of the 12M telescope document: (eta_mb is calculated by I)

Frequency (GHz) Beamwidth (arcsec) eta_A eta_l eta_fss eta*_m 　 eta_mb
70 90 0.52 0.94 0.68 0.98 　 0.63
90 70 0.51 0.94 0.68 0.95 　 0.61
115 55 0.48 0.94 0.68 0.85 　 0.54
145 43 0.45 0.94 0.68 0.8 　 0.51
　eta_A is the aperture efficiency
  eta_l is the radiative and rearward scattering and spillover efficiency
  eta_fss is the foreward scattering and spillover efficiency
  eta*_m is the corrected mainbeam efficiency used to convert T*_R into mainbeam temperature T_mb (T*_R is the temperature recorded in the 12M telescope data)

    T_mb = T*_R / eta*_m

The usually defined mainbeam efficiency eta_mb that converts atmospheric-opacity corrected antenna temperature T'_A into T_mb is related to these efficiencies through

    eta_mb = eta_l x eta_fss x eta*_m

The corresponding values of eta_mb is also calculated and listed in the right most column of above table.

The angular beam width is a linear function of wavelength and telesocope physical diameter. Therefore, we can fit a relationship

    FWHM = const * lambda/D

Here, FWHM is in unit of radian, lambda is the wavelength in m, D is the physic telescope diameter in m, "const" is a constant that is determined by the fitting the formula to the frequencies and beamwidths in above table. It's found to be: 
    const = 1.23 +- 0.01

The beamwidth can be calculated from the physical diameter (12m) and these efficiencies as well. (click here to see how)
------------------------------------------------------------------
According to the well known relationship between effective antenna area Ae and beam solid angle Omega_A: Ae = lambda2/Omega_A, and the definition of aperture efficiency with geometrical antenna area Ap: eta_A = Ae/Ap, we have
    Omega_A = lambda2/Ae = lambda2/eta_A/Ap = lambda2/eta_A/(pi*D2/4)
For a two-dimensional gaussian beam pattern
    P(x,y) = exp[-(x2+y2)/2sig2], 
the Gaussian beam solid angule is
    Omega_G = int{P(x,y)}dxdy = 2pi*sig2.
The FWHM of the gaussian beam is BWHM = 2sqrt(2ln2)sig. Therefore,
    Omega_G = (pi/4ln2) * BWHM2
The Gaussian beam is related to the actual beam though main beam efficiency eta_mb, assuming the Gaussian beam is a proper fit of the actual main beam, say
    Omega_A = Omega_G / eta_mb = (pi/4ln2) * BWHM2 / eta_mb
Therefore,
    BWHM = 4*sqrt(ln2)*lambda / ( pi*D) * sqrt(eta_mb/eta_A)    [rad] 
Then we can make a corresponding list of the calculated BWHMs for represent frequencies:
     70 GHz -- BWHM = 86 arcsec
     90 GHz -- BWHM = 66 arcsec
    115 GHz -- BWHM = 50 arcsec
    145 GHz -- BWHM = 40 arcsec
One can see that these calculated values agree well with the measured values in above table.
------------------------------------------------------------------

For 12M telescope, etam* can be found in the 12M telescope manual(Fig C.1 in Appendix C.3.2 and Table 3.2 in Chapter 3) as well. Here I give several representative values for broader range of frequencies through interpolation from the Fig C.1:

     70 GHz -- etam* = 0.98
     90 GHz -- etam* = 0.95
    100 GHz -- etam* = 0.88
    150 GHz -- etam* = 0.74
    200 GHz -- etam* = 0.60
    250 GHz -- etam* = 0.46
    300 GHz -- etam* = 0.34

Flux density can be derived from the mainbeam temperature as     [go to top]

Snu = BWHM(")2 / lambda(cm)2 Tmb 5.097 X 10-4    [Jy]

Here  phi is angular diameter of the Gaussian main beam in arcsec (BWHM, determined below from aperture efficiencies), lambda is observing wavelength in cm, Tmb is the main beam temperature derived above. 

Data File Formats            [back to top]

Input data file for ASTRO/horizon:            [back to top]

# List of some Extended Green Objects:
G10.29-0.13 EQ 2000.0 18:08:49.3 -20:05:57 LS +13.4  # EGO
G10.34-0.14 EQ 2000.0 18:09:00.0 -20:03:35 LS +13.3  # EGO
G11.11-0.11 EQ 2000.0 18:10:28.3 -19:22:31 LS +27.8  # EGO
G12.42+0.50 EQ 2000.0 18:10:51.1 -17:55:50 LS +16.7  # EGO
G12.20-0.03 EQ 2000.0 18:12:23.6 -18:22:54 LS +51.1  # EGO

Data file for Xremote:            [back to top]
# Spectral line pointing Catalogue
# Positions Obtained from Simbad unless otherwise noted, 
# * adjusted for PM
00:23:14.26  +55:47:33.9  J2000 TCas    -7.0   LSR  RAD # 1.0  
01:06:25.96  +12:35:53.5  J2000 WXPsc    8.5   LSR  RAD # 1.4 
01:26:58.07  -32:32:34.0  J2000 RScl   -18.4   LSR  RAD # 1.5  2.2
01:33:51.21  +62:26:53.5  J2000 GL230  -54.0   LSR  RAD # 0.9  
02:19:20.80  -02:58:40.7  J2000 Mira    46.5   LSR  RAD # 6.8  *J2005
[back to top]

　

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