John Coffin

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Viewing 20 posts - 21 through 40 (of 63 total)
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  • in reply to: UV Aurigae, where can I find out more? #580808
    John Coffin
    Participant

    Thank you Andy, that’s very helpful. John.

    in reply to: List of campaigns? #580415
    John Coffin
    Participant

    Another idea would be to put an agreed key word or phrase in posts about spectroscopy campaigns so that they were searchable, and also a way of ordering search results by date. An alternative, though maybe messy idea, would be to have a forum just for campaigns. Thanks everyone for all the ideas, maybe it’s something to discuss at the forthcoming spectroscopy workshops. 

    in reply to: Scintillation and ALPY spectra #580411
    John Coffin
    Participant

    Does scintillation shift the wavelength of spectra? What would be a reasonable minimum exposure time to avoid problems due to scintillation? 

    in reply to: Spectrum of Comet 46P/Wirtanen #580379
    John Coffin
    Participant

    That’s helpful, thanks, John

    in reply to: Spectrum of Comet 46P/Wirtanen #580375
    John Coffin
    Participant

    Nice spectra. I tried to collect a spectrum of 38P/Stephan-Oterma last week. The  spectrum of the nucleus was basically a straight line and the coma indistinguishable from the sky background spectrum from a part of the sky a few degrees away, (total exposure 4200 secs). On reflection I think I was a bit optimistic, the nucleus is mag 14.5 and the total mag is 10. I wondered if a a short focal length telescope is better for spectra of faint comets. What magnitude does a comet need to reach before it’s reasonable to expect to capture a spectrum with amateur equipment?

    in reply to: Windows 7 upgrade #580328
    John Coffin
    Participant

    Dear Jack, there is a guide to processing hot pixels (bad pixels in PHD2) here https://openphdguiding.org/man-dev/Darks_BadPixel_Maps.htm

    I hope that is what you are looking for.

    Best wishes, John

    in reply to: Request for monitoring of X Per #580273
    John Coffin
    Participant

    Here is one from the 18th November with an Alpy. 

    What changes are we looking for, and how often should we monitor with low resolution spectra? 

    in reply to: Software for guiding on a slit #580260
    John Coffin
    Participant

    I’ve used PHD2. I don’t guide on the target star but on a different one. I then adjust the lock position to move the target star onto the slit. Seems to work well.

    There is a step by step guide on how to do this here.   https://github.com/OpenPHDGuiding/phd2/wiki/PHD2-Guiding-for-Spectroscopy

    in reply to: What wavelength error is acceptable with an Alpy? #580231
    John Coffin
    Participant

    I took your advice and compared the lamp images from the evening where I had calibration problems. There was a shift of minus 3 A between the first and second lamp image. The meridian flip was between the first and second images. Thereafter the lamp image shifted plus 0.4 A and stayed there.

    I thought I had checked everything was tightened, but today I’ve discovered the two Allen head bolts holding the slit in place had worked loose. No idea how! 

     I don’t think this explains everything though. The star spectra have a different amount of shift at different wavelengths, while the lamp spectra have the same shift all the way along. I can only think that the different light paths of the lamp and the stars are at the root of the problem as you have been saying.  

    in reply to: What wavelength error is acceptable with an Alpy? #580238
    John Coffin
    Participant

    The best fit for Z And was when the only frame taken after the meridian flip was used, and it was calibrated using the mixed Balmer and lamp method. The Balmer lines were found from Pi And (also taken after the flip).

    The lamp was the one taken for Z And, after the flip. No heliocentric or corrections for radial velocity were made.

    The errors were 

    H alpha                 -0.4

    H beta                   +0.65

    H gamma             +1.2

    H delta                  +1.0

     H epsilon             -1.0

    When the same frame was calibrated using its lamp lines only and not the Balmer lines from Pi And

    Errors are:

    H alpha                 -0.4

    H beta                   -1.45

    H gamma             -1.8

    H delta                  -2.5

    H epsilon             -3.5

    So for me it seems the mixed method gave the best results 

    in reply to: What wavelength error is acceptable with an Alpy? #580196
    John Coffin
    Participant

    I’ll do as you say. Thanks.

    John

    in reply to: What wavelength error is acceptable with an Alpy? #580193
    John Coffin
    Participant

    Dear fellow Alpy users, please see my post #41

    Everything In my Alpy is screwed down tight as far as I can tell. Yet I am getting these large disparities in the calibration of H alpha.

    It suggests something does change when the instrument moves from one star to another, i thought of checking the Relco bulb isn’t loose, presumably the grism  is unlikely to move as it’s held in place by a spring.

    The best calibration using the lamp lines occurred when there was a meridian flip between the target and the acquisition of the lamp lines.

    in reply to: What wavelength error is acceptable with an Alpy? #580183
    John Coffin
    Participant

    Method

    Spectra of Zeta Cas and Z And were collected, the latter was exposed for 240s to avoid saturating the H alpha emission line and then a further set of exposures for 600s were taken in order to show more detail in the continuum and other emission lines.  Towards the end of the series taken for 600s the telescope reached the meridian and the lamp image for that set was not taken until after the meridian flip. On the other occasions the lamp image was taken immediately after the end of a capture sequence.

    Results

    The spectra were processed in ISIS in three different ways.

    Balmer lines only

    This couldn’t calibrate Zeta Cas so was not suitable for Z And either

    Mixed Balmer and lamp lines calibration

    Each time the lamp lines for the particular target were used.

    Zeta Cas               H alpha blue shift 1 A, accurate from H beta onwards towards the UV end.

    Z And (600s)       H alpha red shift 2 A, gradually increasing so at H delta the red shift was 3.4 A.

    Z And (240s)       H alpha blue shift 6 A, reducing so at H delta the blue shift was 4.0 A.

    In all targets using the mixed method the wavelength errors become more shifted towards the red at shorter wavelengths.

    Lamp lines only calibration

    Zeta Cas               H alpha blue shift 1 A, increasing so at H delta the blue shift was 4.5 A.

    Z And (600s)       H alpha red shift 0.7, accurate calibration from H beta to H delta. H epsilon was blue                        shifted by 1.5 A.

    Z And (240s)       H alpha blue shift 6.0 A, increasing so that at H delta the blue shift was 7.7 A.

    So in all the targets calibrated by the lamp lines alone, the wavelength error shifts towards the blue at shorter wavelengths. 

    I will be very interested to see the result of your Filly Dot experiment. I may have to throw away my calibration module. (I’ll keep it for the flat fields actually).

    Cheers, John

    in reply to: What wavelength error is acceptable with an Alpy? #580159
    John Coffin
    Participant

    Thanks for all your advice. Much appreciated!

    John

    in reply to: What wavelength error is acceptable with an Alpy? #580157
    John Coffin
    Participant

    No, I didn’t tick that box. Here is the new improved lamp spectrum which looks accurate. I noticed that the intensity of the lines that ISIS uses for calibration are much weaker than those above 7000 A. Perhaps I should not worry about saturating those brighter lines and try using a longer exposure in order to make the ones used by ISIS brighter. 

    What do you think is the way forward now? I was hoping to submit spectra to our database. Should I put a comment in the FITs header about the calibration method and its (?) inherent problems, ie mixed method with accuracy upto H beta, 3A blueshift near H alpha.

    What would be the best way to calibrate now? Would it depend on the nature of the target? 

    in reply to: What wavelength error is acceptable with an Alpy? #580154
    John Coffin
    Participant

    Hi Andrew, I’ve processed the calibration image as is if were a star, of course I had to use the same image to calibrate it. The result was odd, but the neon 6965 line was incorrectly calibrated.

    The lines are broad and fuzzy in this area, so perhaps I need to focus it better there?

    I understand that if I do this I will lose definition at the blue end of the spectrum. Thank you for your thoughts on this issue. I am very grateful for everyone’s input into this. 

    I’ve attached the files of these images.

    Regards, John

    in reply to: What wavelength error is acceptable with an Alpy? #580152
    John Coffin
    Participant

    Last night’s specrum of Pi Andromeda (HD 00369) was still about 3 A out at H alpha but very accurate from H beta to epsilon. 

    If this is an error due to undersampling why would it only affect H alpha?

    If undersampling is the issue, can I calibrate the dispersion of a spectrum collected binned x 2 using a reference star that was not binned? 

    in reply to: What wavelength error is acceptable with an Alpy? #580135
    John Coffin
    Participant

    The reflector isn’t perfectly straight and the bulb emits light from one side of itself.

    in reply to: What wavelength error is acceptable with an Alpy? #580127
    John Coffin
    Participant

    I took these lamp lines indoors. The one I took last night was saturated towards the red end of the spectrum and gave me a similar result and were taken at the end of the evening after the calibration star. The ambient temperature was 2 C last night.   Next time I will take some in the middle of the target exposures, and again with the reference star and see if that makes any difference. 

    in reply to: What wavelength error is acceptable with an Alpy? #580126
    John Coffin
    Participant

    Dear Robin, all the Balmer lines were blue shifted by about 2 A, though H zeta and H epsilon were shifted by 3 and 2.5 A respectively. 

    I’ll check all the connectors, though I thought they were tight really. 

    Here’s the report

    Load the image : c:spectra20181028zeta_draconis-1.fit

    Load the image : c:spectra20181028zeta_draconis-2.fit

    Load the image : c:spectra20181028zeta_draconis-3.fit

    Load the image : c:spectra20181028zeta_draconis-4.fit

    Load the image : c:spectra20181028zeta_draconis-5.fit

    Load the image : c:spectra20181028zeta_draconis-6.fit

    Substract the offset : c:spectra20181028caliboffset.fit

    Substract the dark : c:spectra20181028calibdark600_b2_minus10-.fit

    Dark coefficient (1) : 0.0333

    Dark coefficient (2) : 0.0333

    Dark coefficient (3) : 0.0333

    Dark coefficient (4) : 0.0333

    Dark coefficient (5) : 0.0333

    Dark coefficient (6) : 0.0333

    Divide by the flat-field : c:spectra20181028flat.fit

    Flat-field level : 38096

    Cosmetic correction : c:spectra20181028calibcosme.lst

    Smile correction – Y0 = 658  Radius = 11056

    Transverse registration at intermediate Y coordinate = 533.00

    Spectrum Y coordinate Y 1 = 533.31

    Spectrum Y coordinate Y 2 = 533.47

    Spectrum Y coordinate Y 3 = 533.53

    Spectrum Y coordinate Y 4 = 533.73

    Spectrum Y coordinate Y 5 = 533.76

    Spectrum Y coordinate Y 6 = 533.58

    Remove sky background

    Save image : c:spectra20181028@s.fit (sky not removed)

    Save 0b product : c:spectra20181028_Zeta Dra.fit (2D image)

    Adopted Y coordinate : 532.51

    Tilt correction (second pass)

    Remove sky background (second pass)

    Write 2D image : c:spectra20181028@1.fit

    Write 2D image : c:spectra20181028@2.fit

    Write 2D image : c:spectra20181028@3.fit

    Write 2D image : c:spectra20181028@4.fit

    Write 2D image : c:spectra20181028@5.fit

    Write 2D image : c:spectra20181028@6.fit

    Optimal binning

    Write raw profile : c:spectra20181028@raw1.dat

    Write raw profile : c:spectra20181028@raw2.dat

    Write raw profile : c:spectra20181028@raw3.dat

    Write raw profile : c:spectra20181028@raw4.dat

    Write raw profile : c:spectra20181028@raw5.dat

    Write raw profile : c:spectra20181028@raw6.dat

    Intensity of individual profiles (ADU)…

    Mean (median) for profile #1 : 278613 (48845)

    Mean (median) for profile #2 : 267945 (46851)

    Mean (median) for profile #3 : 274931 (46238)

    Mean (median) for profile #4 : 283742 (47380)

    Mean (median) for profile #5 : 261979 (48189)

    Mean (median) for profile #6 : 248222 (44512)

    Standard summation of individual profiles

    Save uncalibrated spectral profile : c:spectra20181028@star.dat

    Processing of calibration image : c:spectra20181028neon5.fit

    Dark coefficient (calibration) : 0.0083

    Save image : c:spectra20181028@calib.fit (2D image)

    Save spectral profile : c:spectra20181028@calib.dat

    Spectral calibration

    ————————————————————————–

    Primary dispersion : 

    Coefficient a4 : -1.941613E-13

    Coefficient a3 : 5.199794E-09

    Coefficient a2 : -4.783460E-05

    Coefficient a1 : 0.39175

    Coefficient a0 : -710.014

    ————————————————————————–

    RMS : 0.091500 (en pixels)

    ————————————————————————–

    Primary wavelength fit deviation

    point #1  Lambda = 3770.630  px = 326.562  dx = -0.067

    point #2  Lambda = 3797.300  px = 332.190  dx = 0.154

    point #3  Lambda = 3835.390  px = 340.215  dx = -0.078

    point #4  Lambda = 3889.050  px = 351.495  dx = -0.013

    point #5  Lambda = 3970.080  px = 368.476  dx = 0.043

    point #6  Lambda = 4101.750  px = 395.954  dx = -0.049

    point #7  Lambda = 4340.480  px = 445.487  dx = -0.017

    point #8  Lambda = 4861.340  px = 552.926  dx = 0.039

    point #9  Lambda = 6562.850  px = 910.356  dx = -0.070

    point #10  Lambda = 6869.000  px = 976.968  dx = 0.067

    point #11  Lambda = 7605.000  px = 1140.339  dx = -0.009

    ————————————————————————–

    Inverse dispersion equation  

    Coefficient a4 : 2.999117E-10

    Coefficient a3 : -1.336891E-06

    Coefficient a2 : 1.632851E-03

    Coefficient a1 : 4.09469

    Coefficient a0 : 2135.790

    ————————————————————————–

    RMS : 0.311249 (in angstroms)

    ————————————————————————–

    Wavelength fit deviation

    point #1  x = 397.713  lambda = 3945.982  dlambda = 0.118

    point #2  x = 441.652  lambda = 4158.959  dlambda = -0.369

    point #3  x = 513.877  lambda = 4510.640  dlambda = 0.090

    point #4  x = 520.824  lambda = 4544.520  dlambda = 0.530

    point #5  x = 544.099  lambda = 4658.045  dlambda = -0.145

    point #6  x = 565.974  lambda = 4764.726  dlambda = 0.144

    point #7  x = 607.204  lambda = 4965.603  dlambda = -0.523

    point #8  x = 696.858  lambda = 5400.458  dlambda = 0.102

    point #9  x = 791.067  lambda = 5852.415  dlambda = 0.075

    point #10  x = 878.731  lambda = 6266.457  dlambda = 0.033

    point #11  x = 930.316  lambda = 6506.578  dlambda = -0.048

    point #12  x = 1071.150  lambda = 7147.069  dlambda = -0.029

    point #13  x = 1124.583  lambda = 7383.958  dlambda = 0.022

    ————————————————————————–

    Coefficient a4 : 2.999117E-10

    Coefficient a3 : -1.336891E-06

    Coefficient a2 : 1.632851E-03

    Coefficient a1 : 4.09469

    Coefficient a0 : 2135.790

    ————————————————————————–

    RMS : 0.311249

    ————————————————————————–

    —————————————————————————-

    Normalization spectral range : [6650  –  6750]

    Normalization value (final profile) : 42355639.7

    Normalization value (individulal profile #1) : 7359979.4

    Normalization value (individulal profile #2) : 7024372.2

    Normalization value (individulal profile #3) : 7031455.9

    Normalization value (individulal profile #4) : 7078341.5

    Normalization value (individulal profile #5) : 7177964.8

    Normalization value (individulal profile #6) : 6683525.9

    —————————————————————————-

    Spectrum #1   ( b ) – ( v ) intensity = ( 0.836 ) – ( 0.996 )

    Spectrum #2   ( b ) – ( v ) intensity = ( 0.860 ) – ( 0.994 )

    Spectrum #3   ( b ) – ( v ) intensity = ( 0.910 ) – ( 0.997 )

    Spectrum #4   ( b ) – ( v ) intensity = ( 0.948 ) – ( 0.998 )

    Spectrum #5   ( b ) – ( v ) intensity = ( 0.784 ) – ( 0.996 )

    Spectrum #6   ( b ) – ( v ) intensity = ( 0.796 ) – ( 0.997 )

    ( b ) – ( v ) mean intensity = ( 0.856 ) – ( 0.996 )

    ( b ) – ( v ) median intensity = ( 0.860 ) – ( 0.997 )

    —————————————————————————-

    Write individual DAT processed profile : c:spectra20181028@pro1.dat

    Write individual DAT processed profile : c:spectra20181028@pro2.dat

    Write individual DAT processed profile : c:spectra20181028@pro3.dat

    Write individual DAT processed profile : c:spectra20181028@pro4.dat

    Write individual DAT processed profile : c:spectra20181028@pro5.dat

    Write individual DAT processed profile : c:spectra20181028@pro6.dat

    Write individual FITS processed profile : c:spectra20181028@pro1.fit

    Write individual FITS processed profile : c:spectra20181028@pro2.fit

    Write individual FITS processed profile : c:spectra20181028@pro3.fit

    Write individual FITS processed profile : c:spectra20181028@pro4.fit

    Write individual FITS processed profile : c:spectra20181028@pro5.fit

    Write individual FITS processed profile : c:spectra20181028@pro6.fit

    —————————————————————————-

    Write final profile : c:spectra20181028_zetadra_20181028_970_J_Coffin.fit

    Write final profile : c:spectra20181028_zetadra_20181028_970_J_Coffin.dat

    Intermediate files removed

    —————————————————————————-

    Acquisition starting date : 28/10/2018 23:16:27

    Duration : 42.0 secondes

    Mid-exposure date : 28.970/10/2018

    Mid-exposure Julian day : 2458420.4700

    Resolution power : 507.6

    Ok. 

Viewing 20 posts - 21 through 40 (of 63 total)