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Call for Proposals: 40-m Thai National Radio Telescope, Cycle 1

17 December 2024 to 7 February 2025
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Science Commissioning

Contents

     1. H I (1.42 GHz) observation

     2. The main and satellite lines of OH masers

     3. References

1. H I (1.42 GHz) observation

For H I (1.42 GHz) commissioning of 40-m TNRT, we observed an H I standard region S8 (l = 207 deg, b = –15 deg) listed in Williams, D. R. W. 1973 with 40-m TNRT on October, 2024. The frequency resolution of the observation was 1.9 kHz corresponding to a velocity resolution of 0.4 km s-1.  The on source time was 30 sec. Dual linear polarization (Vertical & Horizontal) data were recorded.

TNRT output file (MBFITS; Multi-Beam FITS; Muders, et al. 2006) was analyzed by standard procedures as

  1. Sky subtraction
  2. The determination of Tsys* (opacity corrected system noise temperature)
  3. The determination of Ta* (opacity corrected antenna temperature)
  4. Unit conversion from Kelvin (K) to Jansky (Jy)
  5. Conversion to the brightness temperature (TB; Kelvin)
  6. The correction of the Doppler effect.

The detail of the TNRT data reduction is summarized in the "Data reduction" section of this web page. Since 40-m TNRT observation at L-band cannot support the frequency switching, we employed the position switching for step 1. Even though we observed relatively H I free region at (l = 63 deg, b = +78 deg) for obtaining the sky data, H I emission is detected anywhere in the Milky Way and thus the sky data may degrade the absolute value of brightness temperature in the target data. For step 5, we referred to "Useful equations for radio astronomy"

We compared S8's spectrum obtained with 40-m TNRT with those obtained with other telescopes (see Figure 1-1; Table 1-2). Given a typical amplitude calibration error of single-dish data (~10 %) and different velocity resolutions, individual spectra are consistent with each other. However, the amplitude value of TNRT result may be underestimated due to the sky data which have small amount of H I emission. Although further investigation of H I observation with 40-m TNRT will be required, we accept H I observation with 40-m TNRT in this semester. Also, H I mapping observation with raster scanning is also accepted in this semester even though the H I mapping is under science commissioning

Figure 1-1: H I spectra for S8 (l = 207 deg, b = –15 deg), which are obtained with 40-m TNRT (Top), Effelsberg 100-m (Middle top; The Effelsberg-Bonn Hi Survey), Dwingeloo 25-m (Middle bottom; LAB survey) and Parkes 64-m (Bottom; GASS survey). Horizontal dotted lines show maximum brightness temperatures of individual spectra while vertical ones represent LSR velocities at which maximum temperatures of individual spectra are obtained.
 
Table 1-1: Comparison of S8's spectra obtained with 40-m TNRT and other telescopes.
Telescope

Maximum brightness

temperature, TB, max [K]

VLSR at

TB, max [km s-1]

Velocity

resolution [km s-1]
40-m TNRT 67.9 6.5 0.4
Effelsberg 100-m 72.9 6.5 1.3
Dwingeloo 25-m 70.7 6.2 1.0
Parkes 64-m 72.9 5.8 0.8

 

 

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2. The main and satellite lines of OH masers

Example spectra of the main and satellite lines of OH masers obtained with 40-m TNRT are shown in Figures 2-1 and 2-2. We confirmed only small fluctuations in the spectra of VY CMa for about 70 days (Figure 2-2 (bottom)), which are lower than 8 %, 13 % and 5 % for 1612, 1665 and 1667-MHz transitions, respectively. The results are consistent with that of SiO maser where Alcolea et al. (1999) reported a low contrast of 1.3 for ~1 year. Note that Yudaeva 1986 reported the OH maser burst of VY CMa in Feb–March 1985.

Figure 2-1: OH maser spectra of W49N obtained with 40-m TNRT on 27th November, 2024. Spectra at different transitions of 1612.231 (top),  1665.4018 (top middle), 1667.359 MHz (bottom middle), and 1720.530 (bottom) MHz are shown. For visualization purpose, these spectra are vertically shifted. Note that these spectra include continuum emission (~30 Jy).

Figure 2-2: (Top) OH maser spectra of VY CMa obtained with 40-m TNRT on 30th May, 2024. Spectra at different transitions of 1612.231 (top),  1665.4018 (middle) and 1667.359 MHz (bottom) are displayed. These figures are vertically shifted for visualization. (Bottom) The maximum flux density of each transition is shown as a function of time.

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3. References

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