CIT6 : fault report as at 08 Nov 2001

 Fault 2001_11_04_s5_t5_rrp.fault 

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    Report by     :  RRP
                                         date: 11/04 2001
    System is     :  Other/Unknown
                                         time:  08:24
    Fault type is :  Other/Unknown
                                         loss:  0 hrs

    Notice will be sent to: jcmt_faults

                     Briefly describe fault condition:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                     Actual time (HST) of failure:  08:20
When transiting in the north we had a completely unacceptable pointing
shift of over 13" - I repeated the post transit pointing 3 times to
confirm this, the fits were good in each case and had also been good
the previous pointing prior to transit. I think I remembered to log all
of these - if not the relevant scans are 33, 40,41,42 in m01buhflex.
Note that at the same time (after the pointings) we did a spectral line
focus which worked beautifully. This is an excellent new feature that
saves considerable amounts of time (in this case we would have had to slew
half way round the sky to get to a suitable continuum focusing source).



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    RESPONSE by   : IMC
                                    date:  11/06 2001

The pointing on this source the following night were equally disturbing :

 HST 04 Nov 2001
   az      el      uaz    uel  hh mm ss.s source
  426.14  38.50    0.6   -9.6  03 57 26.2 CIT6 
  423.68  57.94    1.9   -9.9  05 27 58.4 CIT6 
  402.73  74.78   -1.6   -7.4  06 54 08.9 CIT6
  320.77  75.74   -1.2    7.1  08 23 22.5 CIT6 
  296.72  59.16    0.4    5.7  09 49 58.3 CIT6

 HST 05 Nov 2001
  426.16  39.02    1.2   -8.4  03 55 55.7 CIT6
  424.06  56.91    3.4   -8.3  05 19 12.3 CIT6 
  411.49  71.34    2.9   -6.0  06 30 28.1 CIT6
  337.59  78.31    2.4    5.3  07 58 23.2 CIT6 
  299.56  64.04    0.6    8.0  09 22 37.2 CIT6

A consistent elevation shift of ~12" between the NE and The NW.

A transit inclinometry experiment was done on UT 05 Nov, but gave a
full amplitude at the horizon of 3" (now installed) - it's not a transit
effect problem.

The source was observed in the dawn - which might have invoked an
'atmospheric' problem of some sort.

But I think the answer is that the coordinates of this object are
insufficiently accurate.

CIT6 is aka RWLMi, IRC+30219, AFGL1403 - and it's also a double.  In its
various guises it's coordinates are given by SIMBAD as 10 16 02.0 ( RJ )
+30 34 19.0  or
             10 13 10.7 (1950) +30 49 17
   Gezari as 10 13 11   (1950) +30 49 17
             10 13 12   (1950) +30 49 24  as IRC+30219 10 13 19   (1950)
             +30 49 07  as RWLMi

It doesn't appear in the SAO or Hipparchus catalogs - being too faint
(mv>10 or so) .

The Digitized Sky Survey also shows the brighter of the double source
offset from its quoted position by ~4" to the NE - I'm not sure that
this completely explains the specific error pattern we see . . .

We could possibly derive better submm coordinates from our own data,
but not necessarily these recent small datasets.

Please beware of this source until its coordinates are improved.


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    RESPONSE by   : RRP
                                    date:  11/07 2001
This is rather serious given that this is one of the most commonly
used spectral line pointing sources (due to its location in the sky
it is very convenient for many projects that have no continuum source
nearby). We should try and sort this out as soon as possible. I don't
really understand why not knowing it co-ords properly should cause this
shift at transit though (two days in a row)?


 
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    RESPONSE by   : NJESSOP
                                         date:  11/07 2001
 
This source rapidly rotates through about 180 degrees while transiting.
The telescope offsets are in Az, El not RA, dec so a fixed error in
the source position (in this case it looks like an error in the RA 
position of about 8 arcseconds - although I cant work out wether its East 
or West) would lead to the source offset rapidly rotating/flipping in the 
Az, El frame. This would repeat. A transit tracking experiment would
be useful, because we might catch the rotation in action, we could
also bin in RA/DEC - is this source visible with SCUBA?

 
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    RESPONSE by   : NJESSOP
                                         date:  11/07 2001
 
Note by the way that this isnt the only source in the spectral line list 
which has a large offset, Ive noticed one more (cant remember which it is 
and its only marked in the paper version at the summit). Large offsets 
should ring alarm bells when using this list.



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    RESPONSE by   : HEM
                                    date:  11/07 2001

CIT6 has been mapped quite a number of times with SCUBA, beginning with a 
program of my own (M97BC30), which never saw the light of day. I will 
endeavour to re-reduce my data later today.


 
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    RESPONSE by   : NJESSOP
                                         date:  11/07 2001
 
Robin and I have looked at the log for both Het and SCUBA data on the 
nights of the 5th. We'd argue that there is evidence that this problem
was not just associated with a single object, Uaz seems to have been 
consistently switching between +8 and -5 depending on what side of 
transit you were on. I would respectfully suggest all data for the night 
may be worth looking at again.
 
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    RESPONSE by   : IMC
                                         date:  11/07 2001
 
On UT Nov 04 & 05 pointings on w3(oh) in the 4th quadrant,
were followed by the pointings on CIT6 in the 5th and then 
the 4th quadrants. The pointing changes incurred when going from 
w3(oh)/q4 to CIT6/q5 indeed tend to confirm the later CIT6 q5/q4
changes. However, w3(oh) is not the simplest of sources, structurally, 
and likely is contributing its own intrinsic, frequency-dependent
centroid errors to this problem. 

The 2 other heterodyne datasets from these two nights that includes pairs
either side of transit also involve w3(oh), while the one SCUBA dataset
with such pairs involves sources at elevations at or above 80 degs -where
model errors are likely. The largest elevation pointing changes recorded
at these elevations is only (?!) 3", but would correspond to something
truly horrendous at the horizon if a 'transit-error' explanation was to
be sought.

It is not possible to relate the pointings on CIT6 to any absolute frame
from these recent data.

However : it was observed amongst many other sources since Henry's 
Jan 1998 data, including, most recently, the nights of UT May 05 & 06.
The (daz,del) 'errors' of CIT6 on those 2 nights convert
to 'errors' in (RA,Dec) of approx (0.17s +- 0.07s, -0.2" +- 0.2") :
so maybe 2" in RA. There were other strong systematic model errors
during these nights, but CIT6 was not any further deviant.
This would tend to indicate that the coordinates are OK at the
level of a couple of arcseconds : certainly not enough to explain
the recent ~12" changes through transit. (Hmm)

I shall next dig out the earlier data (from 1998 & 2000) and
process them similarly.

Meanwhile I am grateful to Jonathan for the graphical display
of the several versions of the coordinates for CIT6 now available
here.


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    RESPONSE by   : IMC
                                    date:  11/08 2001

 at ESO use (or determine) 
            10 16 02.34 (RJ2000) +30 34 16.3
               +-  0.03                  0.6
    cf our  10 16 02.0           +30 34 19.0

This gives a difference of (4.4", -2.7") in the sense (ESO-JCMT). 

See
their CO:1-0 & 2-1 maps and spectra.

I suggest that further discussion of this topic leave the forum of the
jcmt fault system ; I shall establish a webpage
and welcome input via email

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