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Hi John,
Glad you found the source of your flexure. If screwed down tight I have found the ALPY to be remarkably stable. I could not detect any flexure on mine in tests moving at around the sky.
If you have not come across it before, Christian Buil has some information on the effect of combining lamp and stellar lines which you might find interesting.
http://www.astrosurf.com/buil/isis/guide_alpy/resume_calibration.htm (method 3)
Though not necessary for most applications, if you are looking for the highest accuracy using stellar spectra dont forget to take account of the earth’s motion and the radial velocity of the star which can add up to a few tens of km/s. The effects are small but can be an Angstrom or two, detectable even with the ALPY.
Cheers
Hello Jack,
It is over years ago since I built my LHIRES but just checked and I see I actually just moved both washers to the same side. Take care to tighten the screws evenly and not to tighten too much as it brings the lens into direct contact with the metal holder. I would only do it if you are seeing significant shifts in the lines backwards and forwards as the lens is rotated. Presumably the problem in my case was uneven thickness of the washers. I did it to prove what was going on. It worked so I left it rather than trying different washers.
I suppose you could use the double line for calibration if you can identify the wavelengths. You could check Richard Walker’s Atlas to see if they are identified
Cheers
Robin
The host galaxy brightness from Vizier would be the integrated brightness over the whole galaxy rather than just the core. Perhaps this explains why your measured core brightness is not higher than the Vizier magnitude ? (At a rough estimate, I would expect the SN to have increased the brightness by ~0.5 mag)
Cheers
Robin
Hi David,
From the sharp H alpha emission line in the spectrum (from the host galaxy) the redshift = ~0.04 which corresponds to ~170MPc distance. The spectrum is clearly a type 1a. At this distance a type 1a SN would reach ~16.9 at maximum, not allowing for any redenning. The ASAS-SN mag 17.2 does seem rather bright for 9-12 days before maximum but ages estimated from the spectra can be notoriously unreliable so it could be closer to maximum than this
Robin
4200.67A looks to be a blend in my lamp spectrum and H alpha has completely disappeared from my lamp now
Cheers
Robin
Attached is the wavelength calibrated spectrum of my ALPY lamp used to produce the calibration fit above (1D fits file, you may need to change the extension to fit. for some reason the forum allows .fits file extension but not .fit)
Cheers
Robin
Hi John,
I dont use BASS but below are the lines used by ISIS from a typical run. (Given the pixel size and the postion of one strong line it finds them automatically and produces a 4th order fit with RMS 0.25A typically.) The fit deteriorates slightly beyond 3900A but ISIS can also include Balmer lines in the violet to improve the fit there
If your lines are blurred at the violet end it could be worthwhile trying a tweak of the focus. The ALPY optics are designed to give excellent performance into the UV but with some compromise at the IR end beyond ~7000A
If you have not come across this already Richard Walker’s list is also a good one for identifying lines to use in the lamp spectrum (not all lines may be present or may differ in intensity though from lamp to lamp, for example H leaks out through the glass over time. Also watch out for blends at lower resolutions)
http://www.ursusmajor.ch/downloads/sques-relco-sc480-eichlinien-5.0.pdf
Cheers
Robin
Wavelength fit deviation
point #1 x = 338.470 lambda = 3946.250 dlambda = -0.150
point #2 x = 423.993 lambda = 4158.408 dlambda = 0.182
point #3 x = 565.202 lambda = 4510.823 dlambda = -0.093
point #4 x = 578.791 lambda = 4544.813 dlambda = 0.237
point #5 x = 623.978 lambda = 4657.878 dlambda = 0.022
point #6 x = 666.777 lambda = 4764.983 dlambda = -0.113
point #7 x = 746.795 lambda = 4965.095 dlambda = -0.015
point #8 x = 921.725 lambda = 5400.811 dlambda = -0.251
point #9 x = 1104.901 lambda = 5852.418 dlambda = 0.072
point #10 x = 1275.212 lambda = 6266.399 dlambda = 0.091
point #11 x = 1375.164 lambda = 6506.326 dlambda = 0.204
point #12 x = 1647.149 lambda = 7147.469 dlambda = -0.429
point #13 x = 1749.146 lambda = 7383.738 dlambda = 0.242
————————————————————————–
Coefficient a4 : 3.302033E-11
Coefficient a3 : -1.853850E-07
Coefficient a2 : 2.729276E-04
Coefficient a1 : 2.34638
Coefficient a0 : 3127.559
————————————————————————–
RMS : 0.248411
————————————————————————–
Hi Gary,
Indeed. I had not come across the name before and googled him after I posted. I wonder if his name had any influence on his choice of career ? I decided at an early age that my traditional family occupation was not for me 😉
Robin
The spacing of the lines is different in the two images and there are several extra weak lines in the one with the close double. There has been a big wavelength shift to the left of about half a field between the two images and we are looking at a different part of the spectrum. (The line on the right in the first spectrum corresponds to the line on the left in the second spectrum. The doubled line is outside the right hand edge of the field in the first spectrum)
See attached
Robin
I see there is a paper published on this already
https://arxiv.org/abs/1805.00994
Note the second author’s name. Unless it is a pseudonym, he/she just had to be an astronomer !
Robin
Just seen this paper where they suggest that there was indeed a dip in the light curve around maximum indicating a “super earth” exoplanet
https://arxiv.org/abs/1802.06659
Robin
Hi Hugh,
OK so I assume your two spectra are scaled relative to the continuum over some common wavelength range? From the AAVSO data however, the V band total flux has reduced by ~0.4 mag between the two dates (I assumed values of 8.3 and 8.7) which means the amount of flux in the emission lines in the later relative flux calibrated spectrum is exaggerated. To calibrate in absolute flux I used a tool in ISIS (“Tools”, “Spectra 3” , “Flux density conversion” ) which integrates the flux in the spectrum over the standard (Bessel) V filter passband and uses the photometric V magnitude (from AAVSO) to rescale the spectrum in physical flux values. (Using the relationship between V mag and physical flux established for the standard star Vega). There are some approximations/assumptions in this method I believe and I think David Boyd has published a more rigorous method somewhere where he uses his own photometric brightness measurements but I think it should be good enough to show the trends.
Cheers
Robin
Yes, astronomers in particular seem to be a pocket of resistance against the forces of SI.
In my other life in the paper industry, the US measure the weight per surface area of paper in pounds per ream (now generally 500 sheets) where the specified sheet size depends on the type of paper you are taking about. So 20lb newsprint (36×24 inches) is much lighter than 20lb bond paper (22×17 inches) for example !
Tonight’s spectrum (in absolute flux) compared with previous spectra. Although the H alpha line remains strong in the spectrum relative to the continuum, when expressed in absolute flux the line intensity has fallen significantly over the past 4 days.
Robin
I suspected as much. It looked noticeably brighter in the spectrograph guider but the moment I moved it onto the slit, the mist rolled in so no spectrum last night.
Robin
EDIT: No sign of rebrightening in later data in the AAVSO database though. I am now kicking myself for not grabbing the guider image
EDIT: I see the 7.3mag in VSS was in I. My guider camera is unfiltered and the nova is very interstellar reddened so probably explains why it looked so much brighter to me than the nearby Vmag 9.3 star
The ARAS spectroscopy group have a symbiotic relationship with Prof Steve Shore at the University of Pisa. (We take spectra and he explains what they mean). Today he puts this event into an astrophysical context.
http://www.spectro-aras.com/forum/viewtopic.php?f=5&t=2015&start=30#p10615
Cheers
Robin
Here are my three spectra calibrated in absolute flux (using V mag values from the AAVSO database) rather than relative to the continuum. It is interesting to see how the peak flux at H alpha remains constant as the continuum falls away.
Here is tonight’s spectrum. H alpha is really dominating the spectrum now as the continuum drops away. About 1/3 of the total flux in the visible range is now from H alpha.
Robin
Simbad comes up with LSPM J0443+4722 a high proper motion star for these coordinates – good spot !
