AZ Cas 3700-4000A

[Robin Leadbeater]

Cezary est intéressé par les spectres de AZ Cas couvrant 3700-4000A. Je ne peux obtenir SNR ~ 15 à 3 heures à la résolution 1.5A. Quelqu'un peut-il faire mieux?


The 3700-4000A range is of interest in AZ Cas as the B star dominates in the region and it show large changes as the B star passes through eclipse and periastron (See fig 5 in Cowley 1977 referenced on Cezary Galan's website)
I contacted Cezary to ask if it was of interest for amateurs to attempt to measure this region. This was his reply:
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----- Original Message -----
From: "Cezary Galan" <Cezary.Galan@astri.uni.torun.pl>
To: "Robin Leadbeater" <robin@leadbeaterhome.fsnet.co.uk>
Sent: Friday, September 07, 2012 10:03 PM
Subject: Re: AZ Cas campaign - spectroscopy


.......... It could be perhaps especially interesting to cover range around Ca H and K. I encourage you to try it. It would be worth, I think, to cover simultaneously Balmer (eg. H8 - H11) lines. Looking on the Fig. 5 Cowley et al. 1977 (PASP, 89, 882) there are large changes occuring around the eclipses. We are going to use our CCS spectrograph to obtain the spectra in this region with a resolution R ~ 4000 (maybe 6000). We will see whether we can obtain good enough spectra. However because of some problems with software we will be able to start with this at the beginning of October.We are very interested in your results with H and K lines.

Kind regards,
Cezary

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This is a very difficult region for me. The AZCas flux is much lower than at H alpha, the camera and grating response reduces rapidly and the LHIRES achromat cannot keep focus over the full region. I was able to take a spectrum but even in 3 hours I could only get SNR of ~15. (On average I was only recording a photon in each bin every 12 seconds ) It does however show the main features expected at this phase (see attached)

If anyone can do better then Cezary would be very grateful

Cheers
Robin

[Robin Leadbeater]

The same region using a 600 l/mm grating. The total exposure time was 220 min. The resolution is lower of course but the SNR is better. This may be the only possibility to record spectra when the brightness drops during eclipse.

Cheers
Robin

[Robin Leadbeater]

My third spectrum in this region, again using the 600 l/mm grating, compared with the previous spectra. (The first spectrum taken using the 1200 l/mm grating has been gaussian filtered to match the resolution of the 600 grating spectra)
Total exposure was increased further to 4hr 20min (a record for me) giving an SNR of ~60
As well as low sensitivity and poor focus, wavelength calibration is also a problem as there are only 2 unblended lines in this region which I have been able to identify in the internal neon spectrum (from Ar) and the Filly Dot lamp is just is a mass of blended lines at this resolution so I am using a 2 line linear calibration. This seems quite good though (~+-0.3A based on comparing spectrum of Altair with a UVES spectrum)

Cezary Galan's team hope to get thier spectrograph working again in early October and start measuring in this region. I will be glad to move to an easier region of the spectrum

Cheers
Robin

[Robin Leadbeater]

Here is another spectrum of this region for 6th October. (note the decimal date on the graphic is incorrect. It should read 20121006.915) Exposure was 11x1200 but conditions were poor for a time so the SNR is only ~40. There is no obvious change since 12th September.

Cheers
Robin

[Robin Leadbeater]

I was hoping to follow the changes in this region of the spectrum during ingress but the weather here is bad and there are no clear skies forecast for the next week. Is there anyone else able to measure this important part of the spectrum using a LHIRES 600 l/mm or a LISA?

J'espérais de suivre les changements dans cette région du spectre lors de l'entrée mais le temps ici est mauvais et il n'y a pas un ciel clair prévues pour la semaine prochaine. Y at-il quelqu'un d'autre capable de mesurer cette partie importante du spectre en utilisant un LHIRES 600 l / mm ou un LISA?

Thanks,
Robin

[Robin Leadbeater]

The AAVSO data U B brightness started to drop on ~19th Nov so we appear to be at ingress

After several weeks poor weather, I was finally able to get another spectrum in the violet on 17 Nov. It shows a dramatic change with many new lines appearing and the Ca H K lines are deeper and broader. (see raw spectrum image compared with a month earlier) The reduced spectra overlay well on spectra from previous eclipses at the same phase, allowing for my lower resolution. (Cowley 1977 fig 5)

Cheers
Robin

AZCas_20121021_1117_annot.jpg (48.73 KiB) Viewed 6783 times

cowley_tho20121021_20121117.png (59.65 KiB) Viewed 6783 times