VV Cep: Fe absorptions increase around Ca II doublet

[Peter Somogyi]

Hello,

After some observation gap, I've tried my new ATIK 428 EXm camera in the UV with LHIres III 2400/mm grating in order to continue my serie at the same resolution like I have had in 2015 and 2016 autumn:

viewtopic.php?f=19&t=1233&start=20

Now I can clearly identify a non-shortterm big increase of many Fe absorptions:

(I regret not always including the complex 3859.911 Fe feature fully.)
I don't know for sure, but possibly the Fe notions in VSpec should be Fe I.
Based on 11 spectra - one from 2015 -, not seen any variance before on these lines.
Currently I hope it's not only an exceptional shortterm variation. To make sure, continuing my serie monthly if possible.

To see all my serie in the same range, here my all the relevant .fits, attaching "spectra_vhel_norm.zip" (helocentric correction was necessary) - at this moment I can't see anyone picking these up.

Cheers,
Peter

PS.: had to use a "black light bulb" as a flat for the 428 EXm (this camera flat requires special treatment), removing 3 emissions. But, I've checked and it doesn't have any correlation with the Fe lines.

[James Foster]

To: Peter,

Your LHlresIII 2400 l/mm grating spectra of VV Cep on 4Jun17 had good agreement with my L-200 with 1800 l/mm grating of this object on 08Jul17:

I had to shift my spectra -1.6A in Isis to line up the two; I didn't correct for heliocentric & VV Cep rotational motion. Since I use a lower resolution grating
and a wider CCD (Atik460ex) I get more of the spectrum, abiet, at lower resolution.

James

[Peter Somogyi]

Hello James,

Yes, your spectrum looks to me matching somewhat, however your wider and lower resolution spectrum has many spikes where I don't have any (e.g. in the 3915-3921A region where apart from the 3-4 Fe absorptions, nothing should change).
How much ADU did you have in a RAW image at what exposure time and bining, and which slit? At what FHWM? (ISIS => 3. Calibration => Line PSF: I get FHWM=2.87 in the middle)
I've had 1860 ADU (at good times, poor times: half) of a 10 minute exposre (30 cm scope, 35 micron slit, ATIK 428 EXm, bin2x2). Final sum of exposures are always above 1 hour (or 1.5-2 hour at faint times).
I also suggest comparing with the same resolution and f-ratio, otherwise we'd need to extract EWs that is hard to calculate here because the continuum is very hard to define.

On the other hand, these Fe I spikes looks to be pulling back - luckily shot one more between clouds yesterday:

So this event might only be temporary, or due to an advenure with resolution (on 20170604.002 had the highest).

asdb_vvcep_20170708_894.zip

(7.51 KiB) Downloaded 226 times

Peter

[James Foster]

To: Peter,

I just switched Isis back to LISA processing so I cant answer all your questions; I enclose a link to the Isis processed spectrum, just save & rename it from .tif to .fit
http://astroimage.info/spectra/_vvcepcah_20170708_428SHFRT-1.6aCROPPED.tif

Here is a "smoothed" low-pass gaussian filtered version of the spectrum missing alot of those anomalous spikes:


Here are my imaging specifications:
Telescope: CDK17 (43 cm aperture reflector) working at F/6.8
Spectroscope: JTW L-200 utilizing 1800 l/mm grating (Lithrow type) Slit used is 43 micron wide, using Alpy Calibration module for flats (Master flat= 57.6K adu)
Imaging CCD: Atik 460ex
Guiding CCD: Atik Titan
Exposure info: 10x600sec exposures at 2x2 binning with three (20 sec exp) Ar-Ne calibration images before and after exposure sequence, processed in
Isis V5.9.0 using the star HD188512 for IR correction.

Let me know if you want any more info. I've been doing spectroscopy for a much shorter time than yourself seeing all the excellent spectra you've gathered the last
several years, so mistakes on my part are inevitable. Btw, I plan to purchase the LHIres III before the prices go up next week (15Jul17), with the 1800 grat. at well
as the included 24oo grat.

Sincerely Yours,

James

[Peter Somogyi]

Interesting James, yours asdb_vvcep_20161001_292 was confirming my asdb_vvcep_20161004_952 (publicly available both) of that time.
Which is a good sign, because you just need to fix a problem for today, and you can also have a longterm data when you manage to shoot a similar quality result.
But, your current spectrum you just linked I suspect having an SNR problem.
Typical fault is guiding (e.g. PHD2 easily takes up the ghost image when you're careless) or focusing (in the UV always problemmatic), your wide coverage requires very high care (so as mine..).
I also easily make such mistakes, using a ref.star (e.g. 7 Cep at beginning and end) and determining its ADU on histogram tells you early if something is wrong.
Of course, the LHires does the best around H-alpha, but in the UV I think you will find your ATIK 460 EX chip to be oversized.
Based on asdb_vvcep_20161001_292, my insight that L200 may work here better on that resolution, and it is worth to continue e.g. monthly at least.

Peter

[James Foster]

To: Peter,

Thanks for the kind advice......
RE" yours asdb_vvcep_20161001_292 was confirming my asdb_vvcep_20161004_952 (publicly available both) of that time."
I would be suspect of any of my spectra work prior to processing in Isis (before April 2017) and the non-usage of flats before acquiring the Alpy calibration module.

Regarding focus, I usually focus on a 2nd magnitude F or B star in the CaK region before stating a long run in Cak, so I don't think that's my problem. Guiding could be an issue, since the OTA is pretty heavy compared with the mount (AP1200) I'm using. It doesn't help that I start my exposures before the object (VV Cep) crosses meridian in the east, otherwise I could not go over 60min total exposure time because of dawn's approach; this will get better after July.

My typical guide error is +/- 0.6 pixels in Dec. (RA is usually 1/2 that). No telecompressor is used so I'm guiding at 3,000mm F/6.8. The slit runs parallel to the long axis of the
chip (left-to-right) and the guiding directions are X=Dec, Y=RA.

James

[Ken Harrison]

James,
Why are you "suspect" of your pre ISIS spectra?
Have you processes the same spectra and seen differences??
Ken

[Peter Somogyi]

James,

Can you please upload a raw image in 2D scaling linearily to conitnuum with telling the max ADU level (e.g. histogram), or link a raw .fits?

What binning zone (reticule => binning zone) did you specify in ISIS?
See: http://www.astrosurf.com/buil/isis/guid ... to1_en.htm => "binning zone adjusting" - this must be exceptionally large with your scope!

Then we could confirm it's really SNR (=> treat guiding / focus / anything else) or come from processing (have you forgotten increasing binning zone, eventually signal leaks into the background zone and gets removed?? have you tried processing without flats/darks/bias? - just empty the field to exclude).

The AP1200 by factory page tells the CDK17 as an example, so I wouldn't expect any trouble.
But, guiding on ghost/reflection image is an easy and typical mistake when star is so bright, I also easily mistaken this (hence always check, check, check... ).

I am speaking here about factor of 5-10x of signal loss, not the quality of your setup, must be something obvious.

Peter

[James Foster]

To: Ken,

RE:Why are you "suspect" of your pre ISIS spectra?"
No flats were used and and average set of Ar-Ne calibration images were used before and after the "lights" spectra were taken.

Have you processes the same spectra and seen differences??
Can't really since I have no flats from this era and my optical set-up (spacers) is different.

James

[James Foster]

To: Peter,
RE:"But, guiding on ghost/reflection image is an easy and typical mistake when star is so bright, I also easily mistaken this (hence always check, check, check... )."

Actually I usually do guide on the "Ghost" image when the magnitude is under 5th. However I do this after I carefully align the subject target on the
position of the slit with a given bin. I actually have this x,y position written in a notebook for 1x1 and 2x2 bin guiding. If I need to guide on an overly bright
target, I usually do a very short exposure (0.2sec) and add a guide delay of 4-5 seconds; I never guide at less than 2 sec exposure because this is just "chasing the seeing."
Give me your email and I'll send you the raws and master dark, flat, & offset or email me at jrfcometAThotmail.com (AT=@)

James