Forum der Vereinigung der Sternfreunde

Dear all,

In order to obtain the instrumental response by using the spectrum of a reference star of class A with softwares like Rlhires and SpcAudace, I need a standard high resolution spectrum of Vega and Sirius in the region from 6000 to 7000 A.
As unfortunately in the UVES database these spectra are not available, could anybody send me a link to a database where they are (preferably in *.fit)?

ELODIE archive
3895-6815 Å
R=42000
http://atlas.obs-hp.fr/elodie/

Robin

Is it true that Vega is spectroscopically variable and therefore not suitable for being used as reference star?

What about Sirius?

Hello,

On 06/14/2010 11:54 AM, Nando Romeo wrote: It has been discovered that Vega is a fast rotator, seen almost pole-on.
This makes it somewhat problematic as a standard stars. I am not aware,
however, that it is spectroscopically variable. If at all, these are
probably very small variations.
Sirius is far south, which is not favorable for northern hemisphere
observers.

Best regards,
Otmar

I usually use Altair if I want a bright A star at this time of year

Robin

Why does the fact that Vega is a fast rotator, seen almost pole-on,
make it somewhat problematic as a standard star?
It would be a pity if I couldn't use it, because in summer it's better positioned than Altair for longer periods for nothern observers with partly obstructed sky, and in autumn in the early evening it would be the only one...
Is Sirius a good reference star on its own, latitude problems aside?
Can you suggest other good high declination reference stars well positioned in summer and in autumn for northern observers?

Vega is fine, just use an example from the ELODIE archive with high S/N and taken at a reasonable elevation. (Unlike the UVES archive, the ELODIE archive includes all sorts of spectra of varying quality so you need to tak a bit of care to make sure you have chosen a good one)

Robin

Hello,

On 06/14/2010 09:48 PM, Nando Romeo wrote: Fast rotators are more difficult to model, because the surface
temperature and gravity depend on stellar latitude. The observed
spectrum therefore is a mixture of spectra of different temperature and
gravity.
Vega is still a good standard star. It is only more problematic as *the*
primary flux standard than originally thought.

Best regards,
Otmar