Forum der Vereinigung der Sternfreunde :: High resolution spectra of Vega and Sirius wanted

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?

Autor:	Nando Romeo [ 13. Juni 2010, 14:24:16 PM ]
Betreff des Beitrags:	High resolution spectra of Vega and Sirius wanted
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)?

Autor:	Robin Leadbeater [ 14. Juni 2010, 00:46:21 AM ]
Betreff des Beitrags:	Re: High resolution spectra of Vega and Sirius wanted
ELODIE archive 3895-6815 Å R=42000 http://atlas.obs-hp.fr/elodie/ Robin

Autor:	Nando Romeo [ 14. Juni 2010, 11:54:53 AM ]
Betreff des Beitrags:
Is it true that Vega is spectroscopically variable and therefore not suitable for being used as reference star? What about Sirius?

Autor:	Otmar Stahl [ 14. Juni 2010, 12:16:18 PM ]
Betreff des Beitrags:	High resolution spectra of Vega and Sirius wanted
Hello, On 06/14/2010 11:54 AM, Nando Romeo wrote: Zitat: Is it true that Vega is spectroscopically variable and therefore not suitable for being used as reference star? 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. Zitat: What about Sirius? Sirius is far south, which is not favorable for northern hemisphere observers. Best regards, Otmar

Autor:	Robin Leadbeater [ 14. Juni 2010, 19:06:10 PM ]
Betreff des Beitrags:
I usually use Altair if I want a bright A star at this time of year Robin

Forum der Vereinigung der Sternfreunde https://forum.vdsastro.de/

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Autor:	Nando Romeo [ 14. Juni 2010, 21:48:22 PM ]
Betreff des Beitrags:
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?

Autor:	Robin Leadbeater [ 15. Juni 2010, 00:19:28 AM ]
Betreff des Beitrags:
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

Autor:	Otmar Stahl [ 15. Juni 2010, 11:09:22 AM ]
Betreff des Beitrags:	High resolution spectra of Vega and Sirius wanted
Hello, On 06/14/2010 09:48 PM, Nando Romeo wrote: Zitat: Why does the fact that Vega is a fast rotator, seen almost pole-on, make it somewhat problematic as a standard star? 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. Zitat: 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 still a good standard star. It is only more problematic as the primary flux standard than originally thought. Best regards, Otmar

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