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Redshift and Narrowband Filters

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  • nakbrooks
    Bit of a newbie question this. Taking an H-a narrowband filter as an example, this passes light at 656nm +/- 2.5nm (for a 5nm filter). However for objects
    Message 1 of 15 , Sep 2, 2013
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      Bit of a newbie question this.

      Taking an H-a narrowband filter as an example, this passes light at 656nm +/- 2.5nm (for a 5nm filter).

      However for objects outside the home group of galaxies light will generally be redshifted, meaning that hydrogen emissions will appear at a lower frequency, outside the 5nm range if they are sufficiently distant, and will not be transmitted by the H-a filter.

      Am I missing something obvious here, or do narrowband filters only work for objects that are relatively close?

      Nigel
    • stan_ccd
      ... > ... objects outside the home group of galaxies light will generally be redshifted, meaning that > hydrogen emissions will appear at a
      Message 2 of 15 , Sep 2, 2013
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        --- In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:
        > ... objects outside the home group of galaxies light will generally be redshifted, meaning that > hydrogen emissions will appear at a lower frequency... not be transmitted by the H-a filter.



        It is most unlikely that your equipment is capable of discriminating H-a regions in galaxies that far away so it's largely a moot point.    Have you calculated the cosmic distance necessary to shift off the filter?   >   Note that many narrow H-a filters are off-centered from H-a in order to minimize the effects of faster f-ratio light cones, which shift the filter's pass-band by increasing the effective thickness of the interference layers.  This filter shift towards the red should benefit red-shifted galaxies in a slow f-ratio system.   >   Stan
      • stan_ccd
        -- <ccd-newastro@yahoogroups.com> wrote: > ... objects outside the home group of galaxies light will generally be redshifted, meaning
        Message 3 of 15 , Sep 2, 2013
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          -- <ccd-newastro@yahoogroups.com> wrote:
          > ... objects outside the home group of galaxies light will generally be redshifted, meaning that
          > hydrogen emissions will appear at a lower frequency... not be transmitted by the H-a filter.


          It is most unlikely that your equipment is capable of discriminating H-a regions in galaxies that far away so it's largely a moot point.    Have you calculated the cosmic distance necessary to shift off the filter?   

          Note that many narrow H-a filters are off-centered from H-a in order to minimize the effects of faster f-ratio light cones, which shift the filter's pass-band by increasing the effective thickness of the interference layers.  This filter shift towards the red should benefit red-shifted galaxies in a slow f-ratio system.   

           Stan

          P.S. the new Yahoo web UI has been released prematurely with too many bugs, annoyances and stupidities. I am particularly irked by the stripping of all formatting (multiple paragraphs get collapsed into a single garbled msg).   
        • stan_ccd
          > many narrow H-a filters are off-centered from H-a...   Opps. I had that backwards.   Such filters are tuned towards the blue (so
          Message 4 of 15 , Sep 2, 2013
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            > many narrow H-a filters are off-centered from H-a...   Opps. I had that backwards.   Such filters are tuned towards the blue (so that the longer slanted rays are within the pass-band) and that would work against red-shifted objects.   Stan
          • stan_ccd
            "many narrow H-a filters are off-centered from H-a..."   Opps. I had that backwards.   Such filters are tuned towards the blue
            Message 5 of 15 , Sep 2, 2013
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              "many narrow H-a filters are off-centered from H-a..."   Opps. I had that backwards.   Such filters are tuned towards the blue (so that the longer slanted rays are within the pass-band) and that would work against red-shifted objects.     Stan   P.S. Sorry for the repeated and un-viewable msgs, due to this crappy Yahoo UI <arghh>
            • Rich Fabbri
              Hi Nigel, Resolving gas clouds at cosmological distances isn t something we amateurs can do, while we use narrowband filters to collect light (of specific
              Message 6 of 15 , Sep 2, 2013
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                Hi Nigel,

                Resolving gas clouds at cosmological distances isn't something we amateurs can do, while we use narrowband filters to collect light (of specific elements) across those gas cloud regions we CAN resolve.

                AFAIK the gas cloud Messier objects are all in our galaxy while the Messier galaxies were (in his time) thought-to-be IN our galaxy!

                Even Einstein wasn't aware of other galaxies until Edwin Hubble (March, 1929) used Henrietta Leavitt's Cepheid Variable work to discover M31 was well outside our galaxy... that M31 was also a galaxy!

                Imaging galaxies can of course be done with with (broadband) RGB and Luminance filters.

                Rich


                Sent from my Galaxy SIII

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              • Scott Schafer
                zzzzzr ________________________________ From: stan_ccd@yahoo.com To: ccd-newastro@yahoogroups.com Sent: Monday, September 2, 2013 11:28
                Message 7 of 15 , Sep 2, 2013
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                  zzzzzr


                  ________________________________
                  From: "stan_ccd@..." <stan_ccd@...>
                  To: ccd-newastro@yahoogroups.com
                  Sent: Monday, September 2, 2013 11:28 AM
                  Subject: [ccd-newastro] RE: Redshift and Narrowband Filters



                   
                  --- In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:
                  > ... objects outside the home group of galaxies light will generally be redshifted, meaning that > hydrogen emissions will appear at a lower frequency... not be transmitted by the H-a filter.

                  It is most unlikely that your equipment is capable of discriminating H-a regions in galaxies that far away so it's largely a moot point.    Have you calculated the cosmic distance necessary to shift off the filter?   >   Note that many narrow H-a filters are off-centered from H-a in order to minimize the effects of faster f-ratio light cones, which shift the filter's pass-band by increasing the effective thickness of the interference layers.  This filter shift towards the red should benefit red-shifted galaxies in a slow f-ratio system.   >   Stan


                  [Non-text portions of this message have been removed]
                • nakbrooks
                  I worked out that it would only become an issue with objects over about 10 mega parsecs away so agreed, not an issue for me. How do professionals handle it
                  Message 8 of 15 , Sep 2, 2013
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                    I worked out that it would only become an issue with objects over about 10 mega parsecs away so agreed, not an issue for me.

                    How do professionals handle it though - do they have different filter sets for different distances?

                    Totally agree with you on Yahoo Neo interface - absolute rubbish and particularly tee'd off that you can't select the classic interface.
                  • Ron Wodaski
                    Professionals have huge numbers of filters for all kinds of specific purposes. So, yes, they would have the exact bandpass filter they required, should they
                    Message 9 of 15 , Sep 2, 2013
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                      Professionals have huge numbers of filters for all kinds of specific purposes. So, yes, they would have the exact bandpass filter they required, should they need to do that work.

                      Ron Wodaski



                      On Sep 3, 2013, at 3:08 AM, ukzxcvb@... wrote:

                      > I worked out that it would only become an issue with objects over about 10 mega parsecs away so agreed, not an issue for me.
                      >
                      > How do professionals handle it though - do they have different filter sets for different distances?
                      >
                      > Totally agree with you on Yahoo Neo interface - absolute rubbish and particularly tee'd off that you can't select the classic interface.
                      >
                      >



                      [Non-text portions of this message have been removed]
                    • Neil Holmes
                      Ron is correct. If you would like to read a nice article about the results of using narrowband filters to choose a particular redshift (or distance), you might
                      Message 10 of 15 , Sep 3, 2013
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                        Ron is correct.
                        If you would like to read a nice article about the results of using narrowband filters to choose a particular redshift (or distance), you might want to take a look at Cantalupo, et al. in the Monthly Notices of the Royal Astronomical Society: Detection of dark galaxies and circum-galactic filaments fluorescently illuminated by a quasar at z=2.4, published last year.
                        - neil holmes

                        Neil Holmes
                        ncholmes@...




                        [Non-text portions of this message have been removed]
                      • jtheios
                        And even that is not enough. My daughter is a senior at a major university in California majoring in Astrophysics. For the past year or so she's be helping
                        Message 11 of 15 , Sep 3, 2013
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                          And even that is not enough. My daughter is a senior at a major university in California majoring in Astrophysics. For the past year or so she's be helping one of her professors on a research project to model star forming regions in galaxies-- some of the them fairly significantly redshifted. What they do is select a set of Ha filters on the instrument that matches as much as possible the redshift of a target galaxy-- one on either side of the redshifted value. They take sets of images with these filters, and then after calibration and stacking (using basically the same techniques we use) my daughter does some interesting stuff in IRAF to extract a final image with a very specific and narrow Ha value (much narrower than any of the filters). It's all very interesting.


                          --- In ccd-newastro@yahoogroups.com, <yahoo@...> wrote:

                          Professionals have huge numbers of filters for all kinds of specific purposes. So, yes, they would have the exact bandpass filter they required, should they need to do that work.



                          Ron Wodaski







                          On Sep 3, 2013, at 3:08 AM, ukzxcvb@... wrote:



                          > I worked out that it would only become an issue with objects over about 10 mega parsecs away so agreed, not an issue for me.

                          >

                          > How do professionals handle it though - do they have different filter sets for different distances?

                          >

                          > Totally agree with you on Yahoo Neo interface - absolute rubbish and particularly tee'd off that you can't select the classic interface.

                          >

                          >







                          [Non-text portions of this message have been removed]
                        • Mike Dodd
                          ... To the group.... I apologize for allowing this posting to go through. Yahoo s new Web interface Javascript _appeared_ to be non-responsive when I tried to
                          Message 12 of 15 , Sep 7, 2013
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                            Scott Schafer wrote:
                            > zzzzzr

                            To the group.... I apologize for allowing this posting to go through.
                            Yahoo's new Web interface Javascript _appeared_ to be non-responsive
                            when I tried to reject it, but somehow it became approved. Yahoo has
                            really messed-up the Web interface.

                            Scott: Please refrain from posting useless messages such as this. It
                            contains nothing helpful to other list members. Thank you.

                            Mike Dodd, Co-moderator
                          • swschafer1953
                            ... To the group.... I apologize for allowing this posting to go through. Yahoo s new Web interface Javascript _appeared_ to be non-responsive when I tried to
                            Message 13 of 15 , Sep 7, 2013
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                              Mike,


                              I just saw your post and would like to clear MY name.  Either there are two "Scott Schafer"s in this Group or else it is some sort of bizarre error.  I have not knowingly posted a message recently in this Group.  I would never post such a rude message.  In fact, I was enjoying this particular thread because much of my work is with NB.


                              Best regards,


                              Scott       (scott W.schafer) 




                              --- In ccd-newastro@yahoogroups.com, <mike@...> wrote:

                              Scott Schafer wrote:
                              > zzzzzr

                              To the group.... I apologize for allowing this posting to go through.
                              Yahoo's new Web interface Javascript _appeared_ to be non-responsive
                              when I tried to reject it, but somehow it became approved. Yahoo has
                              really messed-up the Web interface.

                              Scott: Please refrain from posting useless messages such as this. It
                              contains nothing helpful to other list members. Thank you.

                              Mike Dodd, Co-moderator
                            • Mike Dodd
                              ... Thank you for your prompt reply, Scott. All I know is what I saw in the message that appeared on the list with your name on it. Perhaps your account has
                              Message 14 of 15 , Sep 7, 2013
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                                swschafer1953@... wrote:
                                > Mike,
                                >
                                > I just saw your post and would like to clear MY name. Either there are
                                > two "Scott Schafer"s in this Group or else it is some sort of bizarre
                                > error. I have not knowingly posted a message recently in this Group. I
                                > would never post such a rude message. In fact, I was enjoying this
                                > particular thread because much of my work is with NB.
                                >
                                > Best regards,
                                >
                                > Scott (scott W.schafer)

                                Thank you for your prompt reply, Scott. All I know is what I saw in the
                                message that appeared on the list with your name on it.

                                Perhaps your account has been hacked.

                                I was as surprised as you. I don't know what's going on with Yahoo since
                                they changed their website.

                                I will keep my eyes open and contact you off-list if another suspicious
                                posting with your name on it comes along.

                                Thanks again. Sorry for the false alarm.

                                --- Mike
                              • swschafer1953
                                ... Thank you for your prompt reply, Scott. All I know is what I saw in the message that appeared on the list with your name on it. Perhaps your account has
                                Message 15 of 15 , Sep 7, 2013
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                                  Thanks, Mike


                                  ---Scott 



                                  --- In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                                  swschafer1953@... wrote:
                                  > Mike,
                                  >
                                  > I just saw your post and would like to clear MY name. Either there are
                                  > two "Scott Schafer"s in this Group or else it is some sort of bizarre
                                  > error. I have not knowingly posted a message recently in this Group. I
                                  > would never post such a rude message. In fact, I was enjoying this
                                  > particular thread because much of my work is with NB.
                                  >
                                  > Best regards,
                                  >
                                  > Scott (scott W.schafer)

                                  Thank you for your prompt reply, Scott. All I know is what I saw in the
                                  message that appeared on the list with your name on it.

                                  Perhaps your account has been hacked.

                                  I was as surprised as you. I don't know what's going on with Yahoo since
                                  they changed their website.

                                  I will keep my eyes open and contact you off-list if another suspicious
                                  posting with your name on it comes along.

                                  Thanks again. Sorry for the false alarm.

                                  --- Mike
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