spectro-aras.com

Hello.

I wonder if the Excel LHIRES exposure calculator (http://astrosurf.com/thizy/lhires3/e_etcl.html) can be applied to LISA. I know there is an application as a LISA exposure calculator but i am interested in getting all the values obtained in the Excel one.

I guess for that the entries for the spectroscope have to be changed, but i do not know some of them.

Objective focal length : 130 mm
Grooves per mm : 300
Total angle : ?
Lens to grating distance : ?
Elements transmissions : ?
Efficiency of gratting : ?

Or maybe this spreadsheet is not usable with a LISA?

Thanks.

David Cejudo.

Hi David,

This version of Christian Buil's etcl.xls spreadsheet is designed for the LHIRES which is a littrow design so will not work with the LISA which is a classical design with separate collimator and camera lens. What you need is the version for a classical spectrograph with the LISA parameters from here
http://www.astrosurf.com/buil/us/compute/compute.htm
(or perhaps better Ken Harrison's improved modified version with the LISA parameters entered)

Cheers
Robin

There's already a SimSpec V4.3 set up for the LISA.

Hi Robin and Ken,

Interesting. What star temperture do you input for a Nova like the Nova Per 2020 ?

or in general ...

Rainer

Rainer,
What do you want to do with the star temperature??

Ken Harrison wrote:Rainer,
What do you want to do with the star temperature??

Interesting question. It is an input into the simspec 4.3 version of the spreadsheet along with other stellar parameters (currently 10800 K) Presumably these are used to estimate the flux and therefore SNR at the chosen wavelength relative to the magnitude in the V passband (though the filter used for magnitude measurement is not explicitly stated in the spreadsheet.)

Note that these spreadsheets are useful for design purposes only. Actual exposures are best be determined on the night as they depend on the type of object, the observing conditions on the night and the correct setting of many other variables specific to the wavelength in question, eg camera QE, grating efficiency, atmospheric absorption (which is wavelength, air mass and seasonally dependent), interstellar extinction, etc, etc.


Cheer
Robin

Hi Ken and Robin,

Thanks. I have seen that many beginners, I got to know two recently, are trying to calculate everything instead of empirically get experience as I did 9 years ago and nowadays again.

I have seen this is not only here in Spectroscopy. They loose hours and hours calculating if the pixel size of their camera fits into their telescope, as if they would ahve a choice afterwards when they already own it

That is why I posted my question

I guess also they use as calculator their " Smart Phone "

Thanks and regards Rainer