18 Dec
2012
18 Dec
'12
9:50 a.m.
Hi Justus and Jeff,
Justus, this is the last day to consider the questions in my email
below. What I am hoping to hear from you is a well-reasoned
confirmation that the transfer function data we have in the can is all
we are likely to ever need to support BICEP2's B-mode science analysis.
From your previous reply, it sounds like we have complete GCP-acquired
data with the 2011/12 biases, and some MCE-acquired data for the
original 2010 biases, presumably both under sky loading. I don't know
of a posting that shows the limitations of GCP vs MCE data for
constraining transfer functions in our science band. I'm operating
under the assumption that the GCP-acquired data is sufficient for our
science analysis, which seems likely to me, but I really don't have the
information to be sure so I'd like to hear from you.
Jeff, can you help shed any light here?
If there is a need to retake sky-loading transfer function data with the
MCE on the DSL balcony it will be a lot of effort for folks at Pole in
the next several days, but in principle there is still time if we decide
today. Let's try to get a firm decision at the telecon in 3 hours.
John
On 12/13/12 4:00 PM, John Kovac wrote:
Hi Justus,
I'm afraid it is really too late now to take additional data on the
mount--the team at Pole is taking BICEP2 off the mount within the next
2 hours. We can beg them to point BICEP2 at the sky off the DSL
balcony, but if so we have to really understand why we're doing this.
Why do you want to see the raw detector transfer functions, without
the GCP and MCE filters?
What is the value of the MCE-acquired data to our science analysis,
compared to the GCP data? All that matters for our ultimate analysis
is whether we understand the transfer function well enough in the
science band, right? Does your old MCE-acquired data show evidence
that some detectors have raw transfer functions we may need to correct
for even at < 5 Hz?
Or is the GCP-acquired data taken with 2012 biases/tunings on the sky
good enough to exclude the possibility of A-B transfer function
mismatch in the science band for our RGL detectors at the level that
would introduce significant T->P contamination? What spec on this have
you been targeting? Roughly speaking I would expect it to be similar
to relgain mismatch--that was the argument we made in Takahashi et
al. I'd like to see what analysis you've done--have you got
GCP-acquired measured transfer functions for all the RGL's?
John
On 12/12/12 12:23 PM, Brevik, Justus A. wrote:
--
___________________________________________________________________
John Kovac jmkovac(a)cfa.harvard.edu
Assistant Professor, Astronomy and Physics, Harvard University
160 Concord Ave rm 310, Cambridge MA 02138, 617-496-0611
Hey John,
I've been looking through the transfer function data that I acquired
through GCP, and the data quality looks very good and I believe I
have a complete set of all the bias and tuning settings we used.
Well, at least what we used up until Feb 2012. I'm not sure if we
have used any new tuning (possibly) or bias (unlikely) setting since
then. If we have, then perhaps we should run a schedule for that
data. I should hope that different tunings (and their effect on the
flux feedback servo) should have a minimal impact on the transfer
functions.
In addition to looking through the GCP acquired data, I have been
searching for transfer function data acquired directly through the
MCE. I had planned on taking this data last Feb but it doesn't
appear that I did. Some of this data exists from the previous year,
but not at the new bias / tuning settings. It would be useful to
have this data in the can in order to see the raw detector transfer
functions, without the additional filters added by the MCE and GCP.
If there is still time to take this data, I think it would be prudent
to spend some time on it. I can write a note on how to take this
data for Jon (or whomever else), as well as get on the phone or gchat
to work with him real-time, and do spot checks of whatever data I can
get my hands on. Do you think there is time and motivation to do
this? Sorry this data doesn't already exist in a complete form.
Justus