Aply600 questions

[Keith Graham]

I have read Christian’s online description at http://www.astrosurf.com/~buil/alpy600/performances.htm. I have also read the product description on the Shelyak web site, but I still have some questions regarding the Aply 600.

I currently own the LhiresIII which I use at f/10 on a 30 cm scope at my principle home. I have been using it to submit high resolution (13000) spectra to BeSS. My plan would be to mount the ALPY600 on either a 20cm or 25 cm SCT at my summer home. I can use a 6.3 telecompressor to reduce the f ratio from f/10 to f/6.3.

My questions:

1. With such a setup, would the spectra I could obtain with the ALPY600 be acceptable for BeSS? Would the resolution be too low?
2. Do you know of any other repositories where spectra using the ALPY600 would be useable?
3. I see from the description that one use would be to compare spectral changes with photometric changes in variable stars. This would be ideal for me as I do use one scope for CV photometry another for spectroscopy. But would this data be of any scientific use, and is there a repository for such data?
4. If I am understanding correctly, f/6.3 is the better focal ratio to use than f/10 with the Alpy600. I would be using an SBIG ST7 camera on this setup. By interpolating the chart on the website, it would appear that I could get a range of 3700A-6800A. Is this chart designed for an f/5 system? If so, what would the spectral range on the ST7 frame at f/10 and f/6.3? What would be other advantage(s) and disadvantage(s) of either focal ratio?

Cheers,

Keith Graham

[Francois Teyssier]

Hello Keith,

1. Low resolution spectra (Alpy, Lisa, Lhires 150 l/mm ...) are accepted by Bess
For low resolution spectroscopy the axes are :
- detection of outbursts
- spectroscopy of faint stars : of a total of 2078 stars in the catalog, 1233 have not yet any spectrum. Many of them are easy or almost easy targets for a low resolution spectrograph

Another subject is search for new be stars. Amoung bright B-type stars, about 15 to 20% have been détected as Be stars.
For higher magnitudes 7 to 10, only a few percents are indexed.
So, observing B star of luminosity class V or IV fromBright Star Catalog or Tycho Catalog, you can spot a new Be star.

2. Unfortunaltly, the only amateur repository for amateurs, up to now, is Bess.
The idea of an international database remains an idea.
However, the spectra of some campaigns are gathered in ARAS web pages,
such, for instance :

Nova Mon 2012 :http://www.astrosurf.com/aras/novae/TableauSpectres.htm

The spectra of a campaign upon the request of a professional : T Tauri stars ; http://www.astrosurf.com/aras/Aras_TTau ... paign.html

3. You can also developpe your own programs :

See for instance long term survey of CI Cygni :http://www.astronomie-amateur.fr/feuill ... Cyg_2.htmlwhose results are followed and regularly commented by one the specialists of symbiotic stars

Spectroscopy is a new area of amateur astronomy. We have to build toghether the framework and resources.

Best regards

François Teyssier

[Robin Leadbeater]

Hi Keith,

François has answered 1-3 so I will try to answer 4. The wavelength range only depends on the camera sensor size and the ALPY 600 optics so the wavelength range will be the same with the different focal ratios. The advantage of running lower focal ratios (down to f5) is that with extended objects you can fit more photons through the slit so it is more sensitive. Depending on your aperture and seeing, you may also get more sensitivity on stars if the star size at f10 is significantly bigger than the slit. You can also see more of the surrounding area in the guider image and guiding accuracy is less critical at lower FR. I am not sure of any downsides, though perhaps in common with most optics, the spectrum may not be quite so sharp at the edges at f5 compared with f10 giving some loss of resolution. Olivier or Christian would be better placed to answer that though.

Cheers
Robin

[Keith Graham]

Thank you Francois and Robin. This is a great help. It is good to know that there is a use for low res spectroscopy. I also see that the new RR Lyr campaign would have a need for low res spectroscopy.

Cheers,

Keith

[Christian Buil]

Hi Keith,

Below a faint Be star spectrum (StHA 143) at V=12.0 for the BeSS database taken with Alpy 600. It is a typical faint object, only easly accessible with
LISA/Alpy class spectrograph, for low resolution survey (note, the Halpha line profile can not be detailled, of course). I use here a modest diameter telescope, D=200 mm, but with a fast f-ratio, f/4 (CN-212 Newton telescope). The configuration is easy to use because the short focal length (sharp stellar image and easy to guide). The setup is ultraluminous for extended objet spectroscopy.

Alpy 600 can be used at f/10 but the tyoical magnitude lost relative to a f/5-f/6 configuration is 0,5 to 1 magnitude (the exact value is very dependant of seeing and the actual telescope diameter).

Christian