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Fw: SkyGX + larger VSX FOV + GCPD

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  • Wolfgang Renz
    ... It is strictly true. I just said that its possible (you can try it by sticking an U band filter in front of a blue sensitive CCD) and not claimed how
    Message 1 of 6 , Sep 24 11:04 AM
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      > ----- Original Message -----
      > From: "multiple.stars" <multiple.stars@...>
      > To: "Wolfgang Renz" <w_renz@...>
      > Sent: Sunday, September 24, 2006 12:38 PM
      > Subject: Re: SkyGX + larger VSX FOV + GCPD
      >
      > --- In vsx-dis@yahoogroups.com, "Wolfgang Renz" <w_renz@...>
      > wrote:
      >
      >> U band measurements of bright vars are possible for PMT
      >> and CCD PEP.
      >
      > That is not strictly true.

      It is strictly true.

      I just said that its possible (you can try it by sticking an U band filter
      in front of a blue sensitive CCD) and not claimed how good/bad the
      results will be (depending on the location and the state of the
      atmosphere). But even at high altitude sites it will also depend on
      the zenith distance of the stars.


      > U band measurements depend upon being stuck on top of certain
      > geographic locations of mountains amongst dry air.
      >
      > The width of the passband is affected by overlap with water (can't
      > remember if it's emission and/or absorption) affecting measured flux.

      Not even close. Rayleigh scattering and Ozone absorbtion.

      Take a look at e.g.:
      UFL, AST3722 Techniques of Observational Astronomy, John P. Oliver
      The Effect of the Earth's Atmosphere
      http://www.astro.ufl.edu/~oliver/ast3722/lectures/EffectOfAtmosphere/EffectAtmos.htm
      http://www.astro.ufl.edu/~oliver/ast3722/lectures/EffectOfAtmosphere/absCoeff.GIF
      http://www.astro.ufl.edu/~oliver/ast3722/lectures/EffectOfAtmosphere/ZenithExt.jpg
      Bruce L. Gary
      ATMOSPHERIC SEEING DEGRADATION, FOCAL REDUCERS
      AND UNDERLYING METEOROLOGY
      http://brucegary.net/ASD/x.htm
      ALL-SKY PHOTOMETRY: AN ITERATIVE PROCEDURE
      http://reductionism.net.seanic.net/CCD_TE/AllSkyPhotometry.html
      http://reductionism.net.seanic.net/CCD_TE/atmos_trans.gif
      Photometry for Smarties - PHOTOMETRY USING SIMPLIFIED
      MAGNITUDE EQUATIONS: CONCEPTS AND DERIVATIONS
      http://brucegary.net/photometry/x.htm
      http://brucegary.net/photometry/Ext%20vs%20Altitude.png

      > These passbands were originally a compromise between need and
      > available photoreceptor response. U could likely have been narrower
      > to avoid this, but flux would likely have been too low for this to be
      > measurable in reasonable exposure times, originally.
      >
      > For instance Stromgren (that's o umlaut) u I believe suffers this not,
      > however it will readily be noticed that next to no one (amateur) tries
      > to use this narrower passband photometric system of Stromgren, which
      > can give amazingly useful astrophysical information re interstellar
      > extinction, the Balmer discontinuity, estimatable metallicity, and
      > direct inference of spectral type. Stromgren is on the edge of being
      > a spectrophotometric system. Wings four colour photometry subset has
      > always gone to waste too, and is far more useful for LPVs than J etc,
      > but again, narrow passbands.
      >
      >
      > However, I'm talking from memory here, so we'll do it by example in
      > case I get pulled up on minor inaccuracies of generally correct
      > statements :-
      >
      > Uncle Arne rarely does U work, even sat on top of a mountain in
      > Flagstaff, unless he has to, or it is expressly warranted. This may
      > at times be reflected by the difficulty inherent in doing U band work,
      > but it will mostly be consequent upon him usually not having the
      > proper atmospheric conditions to reliably do the work, and with U you
      > _must_ have two or three nights to give a bit of standard deviation to
      > keep it tight. In the other bands Arne can often get away with single
      > night stuff and declare it usable, all things being equal.

      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.


      > Otherwise, given no complications, his BVRcIc sequences would
      > automatically be UBVRcIc everytime (or UBVIc sequences if his filter
      > wheel has only so many orificices).

      If you complain about U band, you must complain about Ic band too.
      Due to the Ozone (~770nm) and increased H2O (~930nm) absorb-
      tions 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.


      > Outlinkage to GCPD wouldn't be unreasonable besides all that, it's
      > just a mule to access, if there's some global HTTP GET access point
      > that returns a summary page listing all available photometry in the
      > database, with further jump off links, yes, if not, don't bother I'd say.

      Its a major source of photometric data. So its important for at least
      bright vars.

      You can search individual stars by name or by coordinates:
      http://obswww.unige.ch/gcpd/indexform.html
      e.g. for Algol
      http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=0100019356
      http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=Algol
      http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=HD%20019356
      Presently recognised acronyms:
      http://obswww.unige.ch/gcpd/acrolist.html
      For different photometric systems:
      01 = Johnson UBV, 08 = UBVRI, ...

      But you are right, the name and coordinates Search Results index
      pages can currently not be created by a URL. But if someone with
      a name asks Jean-Claude.Mermilliod to change it, I'm sure he will
      consider it.


      > Further, I know damn well folk will take everything in it as gospel
      > truth just coz it is the GCPD, rather than using it critically, as say
      > Sebastian does (ie he uses it critically), and wouldn't encourage
      > most of todays amateur photometrists to go anywhere near
      > anything Arne doesn't regularly use himself and thus experienced
      > enough with its nature to advise upon it as VSX's resident
      > photometrist.
      >
      > John Greaves


      Clear skies
      Wolfgang

      --
      Wolfgang Renz, Karlsruhe, Germany
      Rz.BAV = WRe.vsnet = RWG.AAVSO
    • Wolfgang Renz
      Hello Jeff I ve researched a bit on U band obs. But I fear that we will reach in most cases just the red half of the actual U band due to low elevation obs,
      Message 2 of 6 , Sep 24 11:26 AM
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        Hello Jeff

        I've researched a bit on U band obs. But I fear that we will reach
        in most cases just the red half of the actual U band due to low
        elevation obs, absorbtions in glas and visually optimized AR
        coatings.
        Therefore the results will partially be biased (comparing to obs
        without such restrictions) depending on the color of the stars.

        Clear skies
        Wolfgang

        --
        Wolfgang Renz, Karlsruhe, Germany
        Rz.BAV = WRe.vsnet = RWG.AAVSO




        ----- Original Message -----
        From: "Jeff Hopkins" <phxjeff@...>
        To: "Wolfgang Renz" <w_renz@...>; <vsx-dis@yahoogroups.com>
        Sent: Sunday, September 24, 2006 8:14 PM
        Subject: Re: Fw: SkyGX + larger VSX FOV + GCPD


        > Hello Wolfgang,
        >
        > As you know I do almost exclusive UNV PMT photometry. I have been
        > experimenting with BVRI CCD photometry and JH singe channel
        > photometry.
        >
        > I get very good U data at my backyard observatory with a C-8 at
        > 1,200' ASL. There are many naysayers who will tell you we cannot
        > do U band work with a SCT due to the corrector plate or due close
        > to sea level work, but they are wrong.
        >
        > Check my U band data of zeta Aurigae. This is an extreme, but shows a
        > large U band eclipse compared to BV.
        >
        > http://www.hposoft.com/Astro/PEP/ZetaAurigaeData.html
        >
        > Jeff
        >
        >
        >
        > At 11:04 -0700 9/24/06, Wolfgang Renz wrote:
        >>> ----- Original Message -----
        >>> From: "multiple.stars" <multiple.stars@...>
        >>> To: "Wolfgang Renz" <w_renz@...>
        >>> Sent: Sunday, September 24, 2006 12:38 PM
        >>> Subject: Re: SkyGX + larger VSX FOV + GCPD
        >>>
        >>> --- In vsx-dis@yahoogroups.com, "Wolfgang Renz" <w_renz@...>
        >>> wrote:
        >>>
        >>>> U band measurements of bright vars are possible for PMT
        >>>> and CCD PEP.
        >>>
        >>> That is not strictly true.
        >>
        >>It is strictly true.
        >>
        >>I just said that its possible (you can try it by sticking an U band filter
        >>in front of a blue sensitive CCD) and not claimed how good/bad the
        >>results will be (depending on the location and the state of the
        >>atmosphere). But even at high altitude sites it will also depend on
        >>the zenith distance of the stars.
        >>
        >>> U band measurements depend upon being stuck on top of certain
        >>> geographic locations of mountains amongst dry air.
        >>>
        >>> The width of the passband is affected by overlap with water (can't
        >>> remember if it's emission and/or absorption) affecting measured flux.
        >>
        >>Not even close. Rayleigh scattering and Ozone absorbtion.
        >>
        >>Take a look at e.g.:
        >>UFL, AST3722 Techniques of Observational Astronomy, John P. Oliver
        >>The Effect of the Earth's Atmosphere
        >>
        >>http://www.astro.ufl.edu/~oliver/ast3722/lectures/EffectOfAtmosphere/EffectAtmos.htm
        >>
        >>http://www.astro.ufl.edu/~oliver/ast3722/lectures/EffectOfAtmosphere/absCoeff.GIF
        >>
        >>http://www.astro.ufl.edu/~oliver/ast3722/lectures/EffectOfAtmosphere/ZenithExt.jpg
        >>Bruce L. Gary
        >>ATMOSPHERIC SEEING DEGRADATION, FOCAL REDUCERS
        >>AND UNDERLYING METEOROLOGY
        >> http://brucegary.net/ASD/x.htm
        >>ALL-SKY PHOTOMETRY: AN ITERATIVE PROCEDURE
        >> http://reductionism.net.seanic.net/CCD_TE/AllSkyPhotometry.html
        >> http://reductionism.net.seanic.net/CCD_TE/atmos_trans.gif
        >>Photometry for Smarties - PHOTOMETRY USING SIMPLIFIED
        >>MAGNITUDE EQUATIONS: CONCEPTS AND DERIVATIONS
        >> http://brucegary.net/photometry/x.htm
        >> http://brucegary.net/photometry/Ext%20vs%20Altitude.png
        >>
        >>> These passbands were originally a compromise between need and
        >>> available photoreceptor response. U could likely have been narrower
        >>> to avoid this, but flux would likely have been too low for this to be
        >>> measurable in reasonable exposure times, originally.
        >>>
        >>> For instance Stromgren (that's o umlaut) u I believe suffers this not,
        >>> however it will readily be noticed that next to no one (amateur) tries
        >>> to use this narrower passband photometric system of Stromgren, which
        >>> can give amazingly useful astrophysical information re interstellar
        >>> extinction, the Balmer discontinuity, estimatable metallicity, and
        >>> direct inference of spectral type. Stromgren is on the edge of being
        >>> a spectrophotometric system. Wings four colour photometry subset has
        >>> always gone to waste too, and is far more useful for LPVs than J etc,
        >>> but again, narrow passbands.
        >>>
        >>>
        >>> However, I'm talking from memory here, so we'll do it by example in
        >>> case I get pulled up on minor inaccuracies of generally correct
        >>> statements :-
        >>>
        >>> Uncle Arne rarely does U work, even sat on top of a mountain in
        >>> Flagstaff, unless he has to, or it is expressly warranted. This may
        >>> at times be reflected by the difficulty inherent in doing U band work,
        >>> but it will mostly be consequent upon him usually not having the
        >>> proper atmospheric conditions to reliably do the work, and with U you
        >>> _must_ have two or three nights to give a bit of standard deviation to
        >>> keep it tight. In the other bands Arne can often get away with single
        >>> night stuff and declare it usable, all things being equal.
        >>
        >>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.
        >>
        >>> Otherwise, given no complications, his BVRcIc sequences would
        >>> automatically be UBVRcIc everytime (or UBVIc sequences if his filter
        >>> wheel has only so many orificices).
        >>
        >>If you complain about U band, you must complain about Ic band too.
        >>Due to the Ozone (~770nm) and increased H2O (~930nm) absorb-
        >>tions 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.
        >>
        >>> Outlinkage to GCPD wouldn't be unreasonable besides all that, it's
        >>> just a mule to access, if there's some global HTTP GET access point
        >>> that returns a summary page listing all available photometry in the
        >>> database, with further jump off links, yes, if not, don't bother I'd say.
        >>
        >>Its a major source of photometric data. So its important for at least
        >>bright vars.
        >>
        >>You can search individual stars by name or by coordinates:
        >> http://obswww.unige.ch/gcpd/indexform.html
        >> e.g. for Algol
        >>
        >>http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=0100019356
        >>
        >>http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=Algol
        >>
        >>http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=HD%20019356
        >>Presently recognised acronyms:
        >> http://obswww.unige.ch/gcpd/acrolist.html
        >>For different photometric systems:
        >> 01 = Johnson UBV, 08 = UBVRI, ...
        >>
        >>But you are right, the name and coordinates Search Results index
        >>pages can currently not be created by a URL. But if someone with
        >>a name asks Jean-Claude.Mermilliod to change it, I'm sure he will
        >>consider it.
        >>
        >>> Further, I know damn well folk will take everything in it as gospel
        >>> truth just coz it is the GCPD, rather than using it critically, as say
        >>> Sebastian does (ie he uses it critically), and wouldn't encourage
        >>> most of todays amateur photometrists to go anywhere near
        >>> anything Arne doesn't regularly use himself and thus experienced
        >>> enough with its nature to advise upon it as VSX's resident
        >>> photometrist.
        >>>
        >>> John Greaves
        >>
        >>Clear skies
        >> Wolfgang
        >>
        >>--
        >>Wolfgang Renz, Karlsruhe, Germany
        >>Rz.BAV = WRe.vsnet = RWG.AAVSO
        >
        >
        >
        > --
        > Jeff Hopkins
        > HPO SOFT
        > Counting Photons
        > http://www.hposoft.com/Astro/astro.html
        > Hopkins Phoenix Observatory
        > 7812 West Clayton Drive
        > Phoenix, Arizona 85033-2439 U.S.A.
        > www.hposoft.com
      • multiple star
        ... So it might be strictly true, but it might not be strictly true ;) ... Are you sure there s no water problem? My memory. Rayleigh scattering by what? If
        Message 3 of 6 , Sep 24 12:03 PM
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          --- Wolfgang Renz <w_renz@...> wrote:

          > >> U band measurements of bright vars are possible for PMT
          > >> and CCD PEP.
          > >
          > > That is not strictly true.
          >
          > It is strictly true.
          >
          > I just said that its possible (you can try it by sticking an U band
          > filter
          > in front of a blue sensitive CCD) and not claimed how good/bad the
          > results will be (depending on the location and the state of the
          > atmosphere).

          So it might be strictly true, but it might not be strictly true ;)

          > > U band measurements depend upon being stuck on top of certain
          > > geographic locations of mountains amongst dry air.
          > >
          > > The width of the passband is affected by overlap with water
          > (can't
          > > remember if it's emission and/or absorption) affecting measured
          > flux.
          >
          > Not even close. Rayleigh scattering and Ozone absorbtion.

          Are you sure there's no water problem? My memory.

          Rayleigh scattering by what? If atmospheric it wouldn't matter
          where.

          Ozone absorption, well, I believe Ozone is a somewhat sizeable part
          of manmade pollutants at low attitudes, so I can see that.

          > 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? U is incredibly
          more useful than doing Rc and Ic if you've already got B and V coming
          in too. Well, for some things, shouldn't make global assertions, I
          shouldn't. You've already got thermal stuff with B and V, Rc and Ic
          become redundant. U-B measures the Balmer discontinuity.

          I've just looked the stuff up in the books, yep, altitude dependent
          is U, but nothing said about it being due to moisture, just being due
          to the atmosphere, so I've wrongly remembered it being water,
          especially as it says night to night dependent even at altitude, and
          I couldn't think of much else but altocirrus.

          > > Otherwise, given no complications, his BVRcIc sequences would
          > > automatically be UBVRcIc everytime (or UBVIc sequences if his
          > filter
          > > wheel has only so many orificices).
          >
          > If you complain about U band, you must complain about Ic band too.
          > Due to the Ozone (~770nm) and increased H2O (~930nm) absorb-
          > tions 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 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.

          >
          >
          > > Outlinkage to GCPD wouldn't be unreasonable besides all that,
          > it's
          > > just a mule to access, if there's some global HTTP GET access
          > point
          > > that returns a summary page listing all available photometry in
          > the
          > > database, with further jump off links, yes, if not, don't bother
          > I'd say.
          >
          > Its a major source of photometric data. So its important for at
          > least
          > bright vars.
          >
          > You can search individual stars by name or by coordinates:
          > http://obswww.unige.ch/gcpd/indexform.html
          > e.g. for Algol
          >
          >
          http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=0100019356
          >
          >
          http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=Algol
          >
          >
          http://obswww.unige.ch/gcpd/cgi-bin/photoSys.cgi?phot=08&type=original&refer=with&mode=starno&ident=HD%20019356
          > Presently recognised acronyms:
          > http://obswww.unige.ch/gcpd/acrolist.html
          > For different photometric systems:
          > 01 = Johnson UBV, 08 = UBVRI, ...
          >
          > But you are right, the name and coordinates Search Results index
          > pages can currently not be created by a URL. But if someone with
          > a name asks Jean-Claude.Mermilliod to change it, I'm sure he will
          > consider it.
          >
          I think I investigated linkage to it early on in VSX, amongst
          checking http linkage to several sources Chris hadn't used. I didn't
          mention many things I looked at, and he'd outlinked to most of the
          relevant sources anyway, on his own initiative, and with prior advice
          and the like.

          Cheers

          John


          __________________________________________________
          Do You Yahoo!?
          Tired of spam? Yahoo! Mail has the best spam protection around
          http://mail.yahoo.com
        • Wolfgang Renz
          Hello Jeff ... The interesting part of the U band is the part below the Balmer jump. And thats the part you won t get much photons from with an usual amateur
          Message 4 of 6 , Sep 24 2:50 PM
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            Hello Jeff

            > If I had read all the negative comments about U band work before I
            > started PEP I would have never bothered with the U band.
            >
            > I have a great deal of U band data taken with my 1P21 and C-8 at
            > a relatively low elevation. Any "bias" should be removed via the
            > transformation coefficients and differential photometry.

            The interesting part of the U band is the part below the Balmer jump.
            And thats the part you won't get much photons from with an usual
            amateur (CCD) setup. You might transfom the data to the standard
            U band, but that doesn't necessaryly mean that it will also reflect the
            reality well (especially if you just use a lower-order linear transfor-
            mation). The result cann't be better than the stars you used to deduce
            the coefficients from. If your target is different than these, the trans-
            formation cann't incorporate it.


            > I think the zeta Aurigae data shows what can be done in the U band
            > with a PMT and SCT at low elevations. The eclipse is shallow in B
            > and V bands (and probably more so in longer wavelengths) yet very
            > pronounced in the U band. There has been concern about red leak
            > for the U band, but the 1P21 sensitivity falls off to near zero in the
            > red and longer wavelengths. The fact that the U band depth of the
            > eclipse is much greater than the B and even more so relative to V
            > indicates to me it is indeed U wavelengths that are being observed
            > not red as the eclipse would be extremely shallow, if at all, in the
            > longer wavelengths.

            I don't doubt that one can measure something in the U band (I started
            to try it myself on beta Lyr, R CrB and V2281 Oph with my ST-10XME),
            but the (amateur CCD) results should be verified by a comparison with
            the results of a system at a high elevation site that is optimized for U
            band work.
            I'll be able to compare my U band CCD tesults of epsilon Aur results
            at least with your PMT results that should be much closer to the true U
            band.

            If one catches (with a CCD) just the red half of the U band transmis-
            sion, the amplitude will be still much larger than in B band. E.g. the
            V2291 Oph eclipse at end of July was very obvious and much deeper
            in the U band than in the B and redder band images, but thats still
            no proof that I was also able to catch all the photons that would be
            required to represent the U band well.

            The red leak of my U band filter is just 1/100 of the max transmission
            in the NUV (80% vs. 0.8%). But that probably is still too much to get
            good results with red stars without applying a special red leak cor-
            rection.


            > Now the case of CCD U band is very different. Most CCDs are not
            > very sensitive in the U band yet very sensitive in the longer wave-
            > lengths. This is one reason I don't even bother with a U filter for
            > CCD work. I probably should experiment with it, however. It's a
            > matter of time and energy for me.

            IMO the situation with blue and NUV sensitive PMTs and PDs is
            different than with CCDs (see my other email). CCDs that are
            optimized for NUV are very rare. I don't know an amateur that owns
            one. Even most of the pros don't have access to one.
            And the ones that are common with amateurs (the Kodak KAF ME
            chips) are still a borderline case. If these chips have an ordinary
            chip cover glas (like in all SBIG cameras), the NUV transmission is
            lowered considerably.


            > BTW, I've stared my UBV photometry of epsilon Aurigae (start mid-
            > August, but have had poor weather so only a few observations so
            > far).
            > Did you ever come to any conclusions on short focal length CCD
            > photometry?
            > Gene Lucas is still planning to try it, but is slow getting started.

            As I just have the west half of the sky it will take me a few more
            month before I can observe epsilon Aur again.
            I'm still experimenting with my photometry pipeline and waiting
            to derive my transformation coefficients (finding something bright
            for U band isn't easy).


            Clear skies
            Wolfgang

            --
            Wolfgang Renz, Karlsruhe, Germany
            Rz.BAV = WRe.vsnet = RWG.AAVSO



            > At 11:26 -0700 9/24/06, Wolfgang Renz wrote:
            >>Hello Jeff
            >>
            >>I've researched a bit on U band obs. But I fear that we will reach
            >>in most cases just the red half of the actual U band due to low
            >>elevation obs, absorbtions in glas and visually optimized AR
            >>coatings.
            >>Therefore the results will partially be biased (comparing to obs
            >>without such restrictions) depending on the color of the stars.
            >>
            >>Clear skies
            >> Wolfgang
            >>
            >>--
            >>Wolfgang Renz, Karlsruhe, Germany
            >>Rz.BAV = WRe.vsnet = RWG.AAVSO
            >>
            >>----- Original Message -----
            >>From: "Jeff Hopkins" <phxjeff@...>
            >>To: "Wolfgang Renz" <w_renz@...>; <vsx-dis@yahoogroups.com>
            >>Sent: Sunday, September 24, 2006 8:14 PM
            >>Subject: Re: Fw: SkyGX + larger VSX FOV + GCPD
            >>
            >>> Hello Wolfgang,
            >>>
            >>> As you know I do almost exclusive UNV PMT photometry. I have been
            >>> experimenting with BVRI CCD photometry and JH singe channel
            >>> photometry.
            >>>
            >>> I get very good U data at my backyard observatory with a C-8 at
            >>> 1,200' ASL. There are many naysayers who will tell you we cannot
            >>> do U band work with a SCT due to the corrector plate or due close
            >>> to sea level work, but they are wrong.
            >>>
            >>> Check my U band data of zeta Aurigae. This is an extreme, but shows a
            >>> large U band eclipse compared to BV.
            >>>
            >>> http://www.hposoft.com/Astro/PEP/ZetaAurigaeData.html
            >>>
            >>> Jeff
          • Wolfgang Renz
            ... 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. ... I
            Message 5 of 6 , Sep 24 3:06 PM
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              >> 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.


              >> 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.


              >> But you are right, the name and coordinates Search Results index
              >> pages can currently not be created by a URL. But if someone with
              >> a name asks Jean-Claude.Mermilliod to change it, I'm sure he will
              >> consider it.
              >>
              > I think I investigated linkage to it early on in VSX, amongst
              > checking http linkage to several sources Chris hadn't used. I didn't
              > mention many things I looked at, and he'd outlinked to most of the
              > relevant sources anyway, on his own initiative, and with prior advice
              > and the like.


              Clear skies
              Wolfgang

              --
              Wolfgang Renz, Karlsruhe, Germany
              Rz.BAV = WRe.vsnet = RWG.AAVSO
            • Arne Henden
              ... It is a combination of factors: lower QE of the CCD, higher extinction, lower transmission of the filter, less flux from the star. Typically, at nofs a
              Message 6 of 6 , Sep 24 4:46 PM
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                On 9/24/06, Wolfgang Renz <w_renz@...> wrote:
                >
                > >> 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.
                >
                It is a combination of factors: lower QE of the CCD, higher extinction,
                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.
                >
                > >> 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.
                >
                The nofs Ic is an interference filter that closely matches Cousins Ic when
                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.
                Arne
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