Argus is a 16-pixel W-band focal plane array for millimeter
spectroscopy that has been deployed on the Green Bank Telescope
(GBT). The array is designed to operate in the 85-116 GHz range (Sieth
et al. 2014, SPIE 9153;
doi:10.1117/12.2055655 (pdf)).
Argus is a collaboration between Stanford U. (PI Sarah Church),
Caltech, JPL, Univ. Maryland, Univ. Miami, and the Green Bank
Observatory (GBO).
Figure: The test map of
13CO in DR21 shown at the right was taken with an opacity of 0.42
(marginal conditions) in about 40 minutes of mapping using all 16
beams of Argus. The map is the result of the default data processing
without any data editing. The small beam of the GBT is shown in white
to the lower-right of the image for comparison.
Key Information for GBO call for proposals
Good frequency range: 74--116 GHz
Receiver noise: 40--80 K
Spatial resolution ~1.2 * Lambda/100m (resolutions of 6-7arcsec have been
measured at 110GHz)
4x4 element focal plane array with beam separation of 30.4 arcsec
on the sky in both the elevation and cross-elevation directions.
Single linear polarization per feed
Instananous instrument bandwidth is 1.5 GHz (which is similar to
the VEGAS spectrometer bandwidth)
All 16 beams of ARGUS can be connected to the 16 VEGAS channels
(VEGAS has 8 dual polarization banks [16 spectrometer channels])
Single-side band instrument with IQ-mixer scheme to separate the
USB and LSB. The user can select one of the side-bands to connect
with VEGAS. Sideband isolation is about 10-20 dB.
Instructions estimating the observing time needed for Argus using
the GBT sensitivity and mapping calculators
(example of time estimation).
Argus has successfully completed its commissioning and has been
carrying out science observations on the GBT since 2017. The normal
DSS scheduling system applies, and priority for observations will be
given to teams that visit Green Bank to carry out the observations.
Example Argus observing scripts are located at:
/home/astro-util/projects/Argus/OBS while example Argus GBTIDL
reduction scripts are located at: /home/astro-util/projects/Argus/PRO.
All Argus data collected before 2018.10.22 19:30 UT will need to swap
the positional information between Beam-2 and Beam-3 to be consistent
with the actual positions on the sky for these beams. This was due to
a cable mis-match for these beams in the equipment
room. (link for more information)
Note: Beam2 and Beam3 are for the instrument beam numbering system
(1-16). This corresponding to fdnum1 and fdnum2 using GBTIDL
numbering system (0-15).
Figures: (Noise Temperature as a function of
frequency measured for Argus during good weather conditions during a
maintenance day (zenith tau(90GHz)=0.057). The small "+" are
individual Tsys measurements for each of the 16 beams, where Tsys
corresponds to the total system temperature applicable for Ta. The
median over all the beams of these values is shown by the squares.
The median of the effective Tsys* corresponding to the system
temperature associated with the measured Ta* is shown by the
triangles, while the median values for the implied receiver noise
temperature is shown by the diamonds. The First and 2nd Light
spectra are the first time the GBT has observed above 100 GHz.
Commissioning and First Light
Argus finished its intial commissioning 2016.12.04 and is now
carrying out shared-risk science observations on the GBT.
2016.03.30 TGBT15A_901_06: First Light with intitial VEGAS setups
with beams 9-16 (1st light
spectrum)
2016.04.06 TGBT15A_901_08: 2nd Light fixed software/hardware
USB/LSB inconsistency 12CO, 13CO-C18O, and HCN-HCO+ setups, beams
9-16 (12co spectrum) Small test map
taken of Orion-KL with HCN and HCO+.
2016.04.09 TGBT15A_901_09: Initial observations with the DCR.
Array orientation flipped with respect to the beam-offset data
file. We need to update the array EL Beam offsets in Joe's database
(simply multiply by -1.).
The pointing LPC and focus LPC derived agree with expectations
using the standard GBT model, i.e., there are no significant offsets
from the current model.
Data collected on the other 8 beams not connected through the
IFRack. Some work is needed in updating levels on J13, J6, J15, and
J16 {not enough power getting to VEGAS} with these data.
A map of IRC10216 was taken in 13CO. Note, the map will have a
-1.4' offset in EL (a leftover offset from the pointing tests which
was not removed before starting the map). We will need to map each
beam separately and then combine.
2016.09.07: All 16 channels balanced with VEGAS successfully with yig power
from 75 to 115 GHz. IF levels ok across full Argus range.
TGBT15A_901_25: AutoOOF test data collected for Melinda
2016.09.15 TGBT15A_901_27
13CO + C18O mapping of DR21, tau_zenith(110GHz)=0.42
Verified Argus works on low end of the band. Can configure Argus
down to 74 GHz with current GB software and Argus appears it will
work down to about 72 GHz before the LO power goes below threshold.
Cannot observe sources with velocities yet. Need to observe at
the redshifted velocity. The GB software needs to be updated to
apply the yig-freq command after applying a velocity shift to the
LO1a input signal when observing a source.
Carried out RAlongMap and DecLatMap of NGC1068 in HCN and HCO+.
Carried out DecLatMap of MonR2 in 13CO and C18O.
Carried out mapping observations of bright source 3c84 (Ra/Dec
mapping) for all 16 beams. The co-added data showed a Gaussian
beam at 86GHz of 10.4arcsec, which is a bit worse than expected.
Carried out additional calibration observations with 3c84.
2016.12.20 TGBT16A_901_35
Tsys measurements from 74--116 GHz for all beams (scans 5-90)
Waterfall stability data for scans 93,94,95,96.. with vancal91+92
at 89GHz.
(plots of Noise Measurements)
Tsys* is effective system temperature associated with measured Ta*
temperature scale. Tsys is system temperature associated with Ta
temperature scale which is used for the other GBT bands. Trx is
the estimated receiver temperature subtracting by subtracting off
the contribution from the sky and spill-over.
Tsys*=Tsys*exp(tau_o*A)/eta_l; Trx = Tsys-Tsky-Tspillover-Tbg
2017.06.27 TGBT15A_901_49: USB vs LSB Tsys measurements. USB and LSB has
similar performance except at the high end of the band where USB is
better on average. Much of the improved performance in USB at
high-frequency is due to beam-8 which does not have any side-band
rejection so that the LSB Tsys values are doubled in compared to USB
at 115 GHz. Below 100 GHz, users will get slightly better
performance in LSB. At 100-110 GHz the performance is similar and
above 110 GHz, USB should be used.
VEGAS Bandpass with Argus
VEGAS is the new GBT spectrometer and supports several modes. Here we
show the VEGAS bandpass performance as a function of bandwidth/mode
for Argus. The bandpass shapes shown here are similar to those seen
with other GBT receivers. The narrow-bandwidth modes (11-24 MHz) have
a smoother bandpass and are good for frequency switching, while the
larger bandwidth modes (100-1500 MHz) show signficant
ripples/structure across the bandpass.
Figure: The test map of
13CO in DR21 shown at the right was taken with an opacity of 0.42
(marginal conditions) in about 40 minutes of mapping using all 16
beams of Argus. The map is the result of the default data processing
without any data editing. The small beam of the GBT is shown in white
to the lower-right of the image for comparison.
