Reference Star Question

[Francois Teyssier]

Dear Keith,
Pickles is a synthetic data (theorical profile), for each (or almost) type of star.
The resolution is low, but ggod enough for alpy or lisa (remember we use A type star, the best are early type) so there's almost no lines 'except Balmer li,es of course)
The only problem using this method with Pickles : is the type of the star choose as refence (for instance from Simbad) correct ? If yes, the method is almost perfect. If no ...
But generally speaking, the spectral type of bright stars (< mag 6) are well known. This is not the case in Tycho !

François

[Robin Leadbeater]

Hi Keith

Are Pickles spectra corrected above the atmosphere as are the Miles spectra? Then again, why not use a Miles star of the same spectral/luminosity class as the reference star to get the correction profile instead of Pickles? We know that the Miles have been corrected for above the atmosphere, so would not the Miles stars create a potentially more accurate correction profile?

Yes Pickles are as at top of the atmosphere and with no interstellar extinction. As Francois said, they are not actual star spectra but synthetic ones typical of that type of star. Miles spectra are real measurements of stars which may or may not be typical of the spectral type and may have interstellar extinction. This does not matter though as we have the actual spectrum. (If you compare a Miles spectrum with the same spectral type in Pickles you will see differences, sometimes quite large) What we need to know for a reference star is what the actual spectrum should look like regardless of what spectral type has been assigned to it. That is why Miles, NOAO stars etc are the preferred choice. If however all you have is a star with an assigned spectral type but no actual spectrum, then the best you can do is assume it is typical and has an insignificant interstellar extinction and use a typical spectrum of that type eg from Pickles.

Along the same line, I noticed that the NOAO Indo-us library contains a number of OV,BV, and AV stars. Are these reliable stars to used for correction purposes?

I believe so. (On the suggestion of Martin Dubbs, I am using Zet Aql from NOAO for example for correcting medium resolution spectra for the current WR campaign.) As they are actual spectra they have the same advantage over Pickles etc that Miles spectra have

Cheers
Robin

[Martin Dubs]

Hi Robin,

zet Aql was one of the calibration stars suggested by the PI of the WR campaign. I suggested it because I wanted to use the same reference throughout the campaign and it was better for that purpose than Regulus which disappears now in the twilight and is far from the observed stars. Apart from that I have no special preference for that star but use it also for my own calibration of WR stars and other stars in that area. Normally I do not worry too much about differential absorption between target and reference star as I am more interested in individual lines. I fully agree with you to preferentially use Miles and NOAO references, my preference is Miles if available.
How are you progressing with the WR stars? I did not hear much of the campaign lately (no news is good news).

Regards, Martin

[Robin Leadbeater]

Hi Martin,

Yes I meant that the suggestion of using the NOAO as a good source of Zet Aql spectrum was yours. The zet Aql spectrum suggested by the PI proved not to be suitable. In this campaign all reduction will ultimately be done by the pro team, so what reference spectrum of Zet Aql they use will be up to them but I like to reduce my own spectra too
With my variable weather I cannot get anywhere near the coverage they can get on Teide but I have taken quite a few good quality spectra which hopefully will fill in some gaps (a good run in the last half of July but only two part nights in August so far) I see they are clouded out tonight on Teide but so am I


Cheers
Robin

[Keith Graham]

Robin, Francois, and Martin,

Thanks so much for your replies. I think I I now have a much better understanding regarding the use of Miles, NOAO, and Pickles libraries. It appears that Miles is the first choice. If a MIles star is not available NOAO is the second choice. The beauty of Francois' list is that there are many more reference star choices from which to choose, but they may not be on either the Miles or NOAO libraries. In that case, the Pickles library is used. Sound reasonable?

Cheers,

Keith