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Thread: New SN alert - SN 2018ivc in Messier 77

  1. #41
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    Default Re: New SN alert - SN 2018ivc in Messier 77



    Quote Originally Posted by not_Fritz_Argelander View Post
    There's photometry in this link https://wis-tns.weizmann.ac.il/object/2018ivc stating magnitude 15 and fading.
    Yeah, I am aware of that, however, can you clarify for me what "type" of magnitude does this refer to as it doesn't specify as far as I could see? That certainly doesn't track with the visual appearance I got three nights ago. Unless my perception of its brightness as compared to the mag 13.2 star north of the galaxy is way off track.
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  2. #42
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    Default Re: New SN alert - SN 2018ivc in Messier 77

    Quote Originally Posted by KT4HX View Post
    Yeah, I am aware of that, however, can you clarify for me what "type" of magnitude does this refer to as it doesn't specify as far as I could see? That certainly doesn't track with the visual appearance I got three nights ago. Unless my perception of its brightness as compared to the mag 13.2 star north of the galaxy is way off track.
    I think your perception of brightness may need adjustment. Visual estimates against a high background are notoriously unreliable.

    The largest photometry set says r-ZTF is the filter. So this is the R band filter of the Zwicky Transient Facility. A picture of the filter is on p17, fig 12 of this document:

    http://www.oir.caltech.edu/twiki_oir...8_combined.pdf

    Since comparing the flux at visual (5500) to R band (6500) about a magnitude difference is reasonable (thus allowing for greater blue sensitivity in the eye). The flus is higher in the blue as shown in the spectrum in the link cited. So that accounts for 1 of the 2 magnitudes difference. The other magnitude of difference is due to systematic error from having a bright background. The eye tends to add brightness from the background to the star.
    Last edited by not_Fritz_Argelander; 12-05-2018 at 09:17 PM.
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    Default Re: New SN alert - SN 2018ivc in Messier 77

    Quote Originally Posted by not_Fritz_Argelander View Post
    I think your perception of brightness may need adjustment. Visual estimates against a high background are notoriously unreliable.

    The largest photometry set says r-ZTF is the filter. So this is the R band filter of the Zwicky Transient Facility. A picture of the filter is on p17, fig 12 of this document:

    http://www.oir.caltech.edu/twiki_oir...8_combined.pdf

    Since comparing the flux at visual (5500) to R band (6500) about a magnitude difference is reasonable (thus allowing for greater blue sensitivity in the eye). The flus is higher in the blue as shown in the spectrum in the link cited. So that accounts for 1 of the 2 magnitudes difference. The other magnitude of difference is due to systematic error from having a bright background. The eye tends to add brightness from the background to the star.
    Thanks for the clarification. Indeed the brightness of the central region of M77 is problematic. I also considered that the bright knot (H-II region) east of the SN could possibly be influencing my perception of the star's brightness. Visual appearances are always subject to illusory affect. Regardless, it is in the log with both the 12 and 17.5 so am satisfied with that.
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  5. #44
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    Default Re: New SN alert - SN 2018ivc in Messier 77

    Quote Originally Posted by KT4HX View Post
    Thanks for the clarification. Indeed the brightness of the central region of M77 is problematic. I also considered that the bright knot (H-II region) east of the SN could possibly be influencing my perception of the star's brightness. Visual appearances are always subject to illusory affect. Regardless, it is in the log with both the 12 and 17.5 so am satisfied with that.
    Hello Alan, and on a side line,

    I can remember to have seen, and to have reported here, the last bright supernova in M101 through the binoculars, even if it should not have been visible through the binoculars, as the Ursa Major has been low above the NE horizon.
    I have also made a sketch, even if I am otherwise not sketching,
    and I even remember that the SN has been at "7 o'clock" off the M101 core.
    It sounds like as if the galaxy glow would "amplify" the brightness of a proxy SN, otherwise hardly visible if far away.

    Thank you very much for your description of the SN in M77, I have lerned a lot from you how to observe such events,

    JG
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  7. #45
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    Default Re: New SN alert - SN 2018ivc in Messier 77

    I think the usual rule for limiting stellar magnitude is pessimistic anyway. It is also magnification dependent. See figure 11 in the following link for a more realistic (IMO) appraisal that includes the dependency on exit pupil:

    https://www.telescope-optics.net/functions.htm
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    Default Re: New SN alert - SN 2018ivc in Messier 77

    Quote Originally Posted by not_Fritz_Argelander View Post
    I think the usual rule for limiting stellar magnitude is pessimistic anyway. It is also magnification dependent. See figure 11 in the following link for a more realistic (IMO) appraisal that includes the dependency on exit pupil:

    https://www.telescope-optics.net/functions.htm
    Hello not_Fritz,

    I agree!
    It is also the nonlinear response to the brightness, and the integration time which pulls out the faint stars.
    Thank you for the link,

    JG
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    Default Re: New SN alert - SN 2018ivc in Messier 77

    Quote Originally Posted by j.gardavsky View Post
    Hello Alan, and on a side line,

    I can remember to have seen, and to have reported here, the last bright supernova in M101 through the binoculars, even if it should not have been visible through the binoculars, as the Ursa Major has been low above the NE horizon.
    I have also made a sketch, even if I am otherwise not sketching,
    and I even remember that the SN has been at "7 o'clock" off the M101 core.
    It sounds like as if the galaxy glow would "amplify" the brightness of a proxy SN, otherwise hardly visible if far away.

    Thank you very much for your description of the SN in M77, I have learned a lot from you how to observe such events,

    JG
    Thank you JG. I also recall that one as well. I believe it was SN 2011fe. I too saw it with binoculars, but very, very faintly as I was at a more southern location at the time.

    I have seen time and time again while observing galaxies over the decades that seemingly bright (by magnitude) foreground stars imposed upon a galaxy can be lost within the overall glow of the galaxy. Either they are reduced in apparent brightness or simply not seen. That is not true in every case obviously, but I've seen it more often than some may think.

    Quote Originally Posted by not_Fritz_Argelander View Post
    I think the usual rule for limiting stellar magnitude is pessimistic anyway. It is also magnification dependent. See figure 11 in the following link for a more realistic (IMO) appraisal that includes the dependency on exit pupil:

    https://www.telescope-optics.net/functions.htm
    Thanks for the link nFA. As we all know, limiting stellar magnitude is full of variables, particularly from one observer to the next. I would also add that sky conditions will noticeably impact it as well. My limiting magnitude with the same scope using the same magnitude is quite different from our typically Bortle 5 backyard as compared to our normally Bortle 3 dark site house.
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