[daip] [Fwd: Re: VLA-AB465-data]

[Eric Greisen]

Data Analysts wrote:
> 
> 
> ------------------------------------------------------------------------
> 
> Subject:
> Re: VLA-AB465-data
> From:
> trevino <trevino at iram.es>
> Date:
> Tue, 24 Jan 2012 17:55:32 +0100
> To:
> Data Analysts <analysts at aoc.nrao.edu>
> 
> To:
> Data Analysts <analysts at aoc.nrao.edu>
> 
> 
> 
> Thanks for your rapid answer!
> 
> Is there any way to calculate this dates?
> 
> REgarding the strange velocity (340 km/s) in the LISTR, I would like to 
> know if there is a way to confirm if this was the velocity really used? 
> I mean, the line appears well detected, and it should be around 10 km/s. 
> I would like to know if there is a way to check the real observed 
> frequency, and confirm which is the correct velocity scale.
> 
> Furthermore, in the header of the image, the channel of reference for 
> frequency is number 1 (out of 31). Typically the reference channel 
> should be number 16, isn't it? For the velocity axis, the 340km/s is 
> located in the reference channel 128! All this make me think that there 
> could be a problem with the labelling of the hird axis.
> 
> Thanks in advance, and best regards.

The velocities indicated are just plain wrong and I am uncertain about 
the reference pixels as well.  I loaded each segment separately and the
ones with narrow channels seemed to be quite strange.  I suspect that 
they are modes 8 or 9 and there seems to be significant discussion in 
the comments inside FILLM for how to determine correct values.  In one 
data set there are 31 channels it says but reference pixel 128!  That 
cannot be.

The frequencies are presumably correct although for what channel I 
cannot say.  A velocity of 350 km/s is a 1750 kHz shift +- 30 km/s max 
for the Earth's motion so 1420.405752 - 1.75 = 1418.65 Mhz and it says 
things like 1420.4 for the frequency.  So the velocities lie.

One of the segments has a reference day of 19871205 but all the data 
contained therein is at day 49 wrt to that date or after the next 
segment on 1988 1/25.  All this makes me wonder what is going on.

The reference channel for a 31 channel data set is normally channel 16. 
  After processing say with DBCON it may become 1 (not 128).  I do note 
that the offset of pixel 128 from say 16 is the equivalent of 273 km/s 
more or less.  But the 340 is supposed to apply to the reference pixel 
so this data set does not make sense.

I guess I can take a little more time to try to look at it but I am due 
to go on vacation Monday.

Eric Greisen


> On Tue, 24 Jan 2012 09:05:56 -0700, Data Analysts <analysts at aoc.nrao.edu>
> wrote:
>> Hi Sandra,
>>
>> The LST day number is 53884 for January 23, 1988 for this project. 
>> Is that all you need?
>>
>> Best regards,
>> Meri Stanley
>> NRAO Data Analyst
>>
>>
>> trevino wrote:
>>>  Dear VLA staff
>>>
>>>  My name is Sandra Trevino-Morales. I'm PhD student of IRAM-spain, and,
>>> I'm writing to you because I have a problem in VLA data that I am
>>> reducing,
>>>  and I would like to ask for your help on this.
>>>
>>>  The data are HI observation on MONR2 under the project AB465, the PI
> is
>>> John Bally, and the project was observed in January 23th 1988.
>>>
>>>  The problem in this observation is that we expected the HI line at
>>> 10km/s, but I it is at 630 km/s. Also there is something strange in the
> 
>>> LISTR, it is that the velocity of the source is 340 km/s. Can you tell
>>> me,
>>> how cain I fit it? 
>>>
>>> Now I'm trying to check:
>>>
>>>  http://www.vla.nrao.edu/astro/guides/dopset/
>>>
>>> But, I don know how to find the correct LST date. Can you help me with
> my
>>> problem?.
>>>
>>> Best regards, Sandra.
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
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