Re: [vsx-dis] Fw: SkyGX + larger VSX FOV + GCPD
- On 9/24/06, Wolfgang Renz <w_renz@...> wrote:
>It is a combination of factors: lower QE of the CCD, higher extinction,
> >> A major "difficulty inherent" (no matter the site they are done
> >> from) is that the U band measurements alone takes about
> >> as much time as the BVRcIc measurements take together.
> > Is that really a problem when he's doing a sequence?
> > ...
> > I was thinking he didn't do U because the nights rarely let him,
> > and as he was already at altitude, I assumed high altitude
> > cirrus was the only problem left there.
> If one can calibrate twice as many fields in the same time,
> then the decision is easy if the the U band is of no special
> interest for the traget.
lower transmission of the filter, less flux from the star. Typically, at
nofs a U-band exposure is 6x the length of a V-band exposure. This
means for both the target field and all of the Landolt/extinction fields,
you have to spend 2x longer on each field if you want U-band calibration.
So, in general, you get something less than half of the number of fields
calibrated per night if you include U-band. While I can do it at nofs, and
the results are good, I don't do it unless I know the requester can make
effective use of U-band.
>The nofs Ic is an interference filter that closely matches Cousins Ic when
> >> If you complain about U band, you must complain about Ic
> >> band too. Due to the Ozone (~770nm) and increased H2O
> >> (~930nm) absorbtions at low altitude sites and the wide
> >> spread usage of pure Bessell prescription Ic band filters
> >> that don't have the required 880-900 nm short cut to match
> >> the actual standard Cousins PMT PEP Ic band.
> > Err, I was talking about Uncle Arne using Ic in Flagstaff, not
> > general Ic work: I always say Rc is preferable, despite (actually,
> > because of) the problems inherent with that intrinsic to stellar
> > absorption and emission lines.
> I haven't seen a transmission plot of the filters Arne uses at Flag.
> Maybe he can say if the Ic one is with or without short-cut.
used with a CCD. The Sonoita (SRO) Ic is a Bessell filter that has the
red tail and gives poorer results on red stars. We're going to be replacing
that filter this year.