BETA LYRAE (15-30 july 2005)
From french amateurs astronomers a call for spectroscopic observations
French amateur astronomers launched the idea of a multisite spectroscopic observation of the famous variable beta Lyrae during the period
15 July-30July. Mainly the observations were done by Olivier Thizy with MUSICOS at the St. Veran observatory.
Many spectra come also from Buil, Desnoux, Rondi, Delmas at Pic du Midi.
Here on we collect our poor contribution. For us is a first occasion to treat our spectra and compare them with other observers.
Our Spectra
We were successul in collecting spectra of Beta Lyrae on 17th July (Paolo Valisa) and 30th July (Giorgio Cardarelli).
Giorgio observed also on 16th but it was his first spectrum (we are growing!) and was a little out of focus so we do
not present it here.
Our spectrograph on a 60 cm telescope is equipped with 1800 and 600 l/mm gratings, a 50 mm camera lens and a new ST10-XME CCD
(almost the first light for this camera).
First we collected a low resolution (1.7 Å/pix) spectrum of Vega and obtained the spectral response curve of our instrument.
We applied this correction to a low resolution spectrum of beta Lyrae to obtain a corrected spectrum. On this spectrum we the adjusted
the baseline of the high resolution(0.35 Å/pix) spectra. Of course, the flat and dark were first subtracted from the original CCD images.
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Picture 1: Spectrum of Vega, recorded with 1.7 Å/pixel dispersion and a 10 sec exposure compared with the reference from the atlas of
Pickels. Note the ripple in the spectral response between 5200 and 5800 Å that we found also in HR spectra, probably due to the CCD.
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Picture 2: Spectrum of Beta Lyrae, recorded with 1.7 Å/pixel dispersion and a 100 sec exposure, as recorded (blue) and corrected (red)
for spectral response of spectrograph and atmosphere. Correction file was obtained by Vega spectrum (Picture 1).
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The high resolution spectra were calibrated using a Ne lamp on a terrestrial reference frame and are at this stage ready for subtraction
of telluric lines due to atmospheric H2O absorption.
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Picture 3: Spectrum of Beta Lyrae around Halfa, recorded with 0.32 Å/pixel dispersion and a 300 sec exposure, is being calibrated with
a Ne lamp spectrum recorded few seconds later.
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Hbeta region
17.854 UT july 2005
300 sec exposure
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He I 5875 Å region
17.89 UT july 2005
300 sec exposure
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Halfa - He I 6678 Å
17.99 UT july 2005
300 sec exposure
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H beta region
30.898 UT july 2005
300 sec exposure
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He I 5875 Å region
30.922 UT july 2005
300 sec exposure
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Halfa and He I 6678 Å
30.929 UT july 2005
300 sec exposure
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He I 7066 Å
30.936 UT july 2005
300 sec exposure
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Subtraction of atmospheric Water Vapour lines was performed only in the region 6400-6700 Å, because we do not have
at moment a wider list of lines (this we used was supplied by Valerie Desnoux). From line positions and intensities
we calculated a sinthetic spectrum. The best fit with experimental data was obtained with 0.8 Å FWHM (for spectrum
of 17 july) and 1.2 Å FWHM (for spectrum of 30 july that is slightly defocused). The VW spectrum was multiplied with
baseline of the Halfa spectrum and then added. Fitting was better with gaussian shape, worse with
Lorentzian.
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Picture 4: The sinthetic spectrum of atmospheric Water vapour ready to be added to the Beta Lyr spectrum.
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Picture 5: The final result. Now two spectra can be compared. Y axis are arbitrary units and 1000 counts were subtracted to the spectrum of 30 july to avoid overlapping.
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Halfa region
17.88 UT july 2005
WV subtracted
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Halfa region
30.929 UT july 2005
WV subtracted
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The values calculated from these two spectra of the equivalent width and FWHM of the Halfa line are:
on 2005/07/17.88 UT EW=16.6 Å FWHM=10.8 Å
on 2005/07/30.929 UT EW= 17.7 Å FWHM= 10.7 Å
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