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First spectral line detections with the 4 WAPPs
Project a1653
T. Ghosh, K. O'Neil, C. Salter
Figure 16: Detection of two Damped Ly­# (DLA) absorption systems in HI absorption against the quasar,
J074110.6+311200 (OI363). The data were taken on Saturday, 31­Jan­04, using 4 WAPP sub­correlators, each with
4096 channels over 100 MHz, recording both linear polarization which were subsequently added. The observations
were taken in ``Double Position Switched'' (DPS) mode, with ON­OFF measurements for two bright continuum
sources. The plot above represents the ratio of the flux densities of the sources --- i.e. (ON1- OFF1)/(ON2-
OFF2 ). This e#ectively removes bandpass ripples due to standing waves caused by the continuum emissions.
The quasi­linear slope on the resulting baseline is as OI363 has an inverted spectrum, while its DPS companion,
4C31.30, has a normal spectrum. RFI spikes and bands occuring in the OFF spectra during the experiment are
marked in orange, with the DPS spectrum in black. The two blow­ups show two features appearing outside the
RFI bands and which are consistent with DLA systems in OI363. These are in fact the already­known DLAs in
that object at z = 0.0912 & 0.2212.
16