Forum der Vereinigung der Sternfreunde

Hello experts!

The DADOS spectrograph has a 90 degree angle between the incident and diffracted beam but most other designs (eg LISA) have a much smaller angle ~35 deg. 90 deg makes the design simpler but are there any disadvantages to using a 90 degree angle?

Thanks
Robin

Hi Robin,

behind the arguments of Ken there is a further disadvantage of a high total angel: you cannot use gratings of high dispersion. In the Dados the 900 g/mm grating is the end.

_________________
Herzliche Grüße / best regards

Lothar

https://lotharschanne.wordpress.com/

Hi together! I do not know Ken's Argument but I guess DADOS has a large Anamorphosis factor. That means an enlarged slit image in the focal plane reduces the achievable spectral resolution.

Cheers, Thomas

Ah, now I've seen Ken's contribution. Yes, shading is an issue but I do not consider it as a major disadvantage. It doesn't matter if I loose some percent of light. If I loose 60%, yes, then I would loose a magnitude. But that will not happen.

Thomas

Thanks to everyone,

I am thinking about the best spectrograph design for identifying supernovae. It is possible to do this with the Star Analyser using only R~100 but the sky background limits the magnitude to ~15. The LISA with a slit is already reaching mag 16 at R~600 with a 280mm aperture so a low dispersion slit design with say a 400mm aperture could perhaps reach mag 17-18 which would make it useful for confirming amateur supernovae discoveries.

Cheers
Robin

Hi Robin, the topic of sn identification is what eventually led me to purchase a star analyser. Do you have further details on this you could share.

Thanks Steven

_________________
Apache-Sitgreaves Center for Astrophysics
http://darkskyobserving.com

Hi Steven,
You can see a few supernovae spectra taken with the Star Analyser (or the grating it was developed from) on my website here
http://www.threehillsobservatory.co.uk/ ... esults.htm
but ultimately with a slitless system the various problems of sky background, interference from the parent galaxy or stars in the same field limit how faint you can practically go, hence the interest in a low resolution slit based system. (The main lines are so doppler broadened in sn spectra that I reckon it should be possible to do a basic classification with R <200)

You might also be interested in these recent examples of amateur sn spectra
http://www.astrosurf.com/aras/surveys/s ... dh/obs.htm
http://www.astrosurf.com/aras/surveys/s ... e/obs.html
taken with Star Analyser, LHIRES (150l/mm grating) or LISA

Cheers
Robin