As part of the BeSS monitoring program (Be, Herbig Ae/Be and B[e] stars), it seemed important to highlight notion such as flux and overall system efficiency. This efficiency has a direct impact on signal to noise ratio (SNR) on our spectra and we are all looking to optimize it.
Efficiency depends on several parameters, including seeing and transparency of the observing site, instrument performances (telescope and spectrograph), and the adjustment of the equipment as well as the observing protocol.
It is easy to loose photons in this instrumental chain... so how to estimate if your flux throughput is "normal" or not?
One of the best way to know is to compare between each others. Such diagnostic is then precious to judge the efficiency of your observation system and, if needed, to optimize it.
This is what we propose to do by using a bright, not too variable, well positionned northern hemisphere star at the moment; our choice is on the Be star psi Persei (37 Per).
The following protocol is proposed to anyone interested to join this effort and know more about their own efficiency: take spectra of psi Per if possible when it is high in the sky (to reduce atmospheric uncertainty) using your standard acquisition and data reduction process. Then send:
1/ reduced spectrum in BeSS database
3/ email the same reduced profile to
christian.buil@wanadoo.fr so SNR can be calculated. Please precise the specifications of your telescope, spectrograph, sensor, individual exposure time and number of exposures; add any comments you may find useful: estimation of seeing, transparency and how it compare with your usual conditions...
2/ email the "raw" profile in ADU units to
christian.buil@wanadoo.fr
Note on obtaining such "raw" profile in ADU when using ISIS:
-If you use an echelle spectrograph, just submit the OBJECT0_34.DAT file which is created in your working directory
-If you use another spectrograph: enter a NULL value in Lamnda1 and Lambda2 in the Configuration tab and leave empty the "Instrumental Response" field in the General tab (remember to put back the usual values when reducing your pther spectra).
Note that the goal of this study is to cross-compare our signal to noise ratio; wavelength calibration quality won't be analyzed for exemple.
Results will be published publicly. It will help to better target future pro/am campaigns and it will help all of use to progress together.
Do not hesitate to take spectra on different nights in order to average seeing and sky transparency conditions... and of course to observe other BeSS stars!
You can see partial results here :
http://www.spectro-aras.com/forum/viewt ... f=8&t=1916
The BeSS team
Site:
http://basebe.obspm.fr/basebe/Accueil.php?flag_lang=en
See also ArasBeAm :
http://arasbeam.free.fr/?lang=en
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