ESPaDOnS
examples of spectra

This page presents examples of spectra collected with ESPaDOnS, either on the sky or during lab tests.

Zeeman signatures of magnetic stars

ESPaDOnS was designed to be very efficient at detecting Zeeman signatures induced by stellar magnetic fields (see science drivers). These signatures mostly show up as circular and linear polarisation features in line profiles. The figures below present such signatures in the particular case of the chemically peculiar star β CrB, both in circular polarisation (Stokes V, expanded by 5 and shown in red) and linear polarisation (Stokes Q and U, expanded by 10 and shown in red and blue respectively), within two selected wavelength domain.

The following two plots show the same information in the case of another chemically peculiar star 78 Vir. Note in particular that no linear polarisation signatures are detected in conjunction of the 614.9 FeII line (despite the strong circular polarisation signatures that are present), as expected if there is no crosstalk between polarisation states within the instrument. Click on either plots to enlarge. Note that these Stokes spectra are not produced with the cross-correlation type tool 'Least-Squares Deconvolution' (LSD), conversely to what the plot titles say.


The last plot on the right provides an example of Zeeman signatures in a cool active star, the giant primary star of the RS CVn system II Peg. Zeeman signatures are now computed using the cross-correlation tool Least-Squares Deconvolution (linear polarisation Zeeman signatures in the spectrum of cool stars are far too small to be detected in individual spectral lines). Note that Zeeman signatures are now expanded by factors of as much as 20 (for Stokes V) and 200 (for Stokes Q and U).

These plots demonstrate very clearly that ESPaDOnS is very efficient at detecting Zeeman signatures (in both circular and linear polarisation) in line profiles. More on the interpretation and modelling of these signatures can be found in the page presenting the most recent results obtained with ESPaDOnS.

Solar spectrum, Balmer lines

The full optical spectrum of the Sun was also recorded and processed with Libre-ESpRIT, to demonstrate that the spectroscopic properties of ESPaDOnS are nominal. A few portions of the reduced solar spectrum are presented below, starting with Balmer lines. Among the first five of the series (from Halpha to Hepsilon) present in the ESPaDOnS spectra, only the first two are included here for illustration purposes:

Solar spectrum @ Halpha	Solar spectrum @ Hbeta

Note that in both cases, the lines appear in the overlap regions of two consecutive orders. Rather than being concatenated, the orders are displayed on top of each other (the straight crossing segment being due to the plotting routines going back to the first wavelength of the following order). This illustrates in particular how well the two consecutive orders match throughout their overlap region, both in intensity and wavelength.

Solar spectrum, selected regions

Here, we show two close-up views of selected line profiles in the solar spectrum:

the first graph shows a spectrum portion very well known to solar physicists working on solar magnetism, including 2 close-by FeI lines with different magnetic sensitivities. ESPaDOnS observations (full line) are found to match perfectly with the reference Kitt Peak solar spectrum (dotted line) once the latter is broadened to a spectral resolution of 69,000 (dashed line). Only the two time variable telluric lines (@ 630.20 and 630.28nm) show (as expected) a significant difference with respect to the Kitt Peak spectrum;
the second graph shows a spectrum region in the near infrared (@ 760nm) heavily crowded with strong telluric bands having null core relative intensities; one can notice from this data that diffused light within the spectrograph is small and well corrected out by the reduction routines.

Solar spectrum @ 630.2 nm	Solar spectrum @ 763.5 nm

© Jean-François Donati, last update 2006 Jun 09