Seminarium Optyczne

Spectroscopy – in whatever form – is still our only probe for distant objects where direct investigation is impossible.Molecular spectra have been identified in cool stellar objects (where cool implies temperatures around 3000 K). Sometransition metal monohydrides have been identified in sunspots and in the spectra of cool stars [1], FeH and CrH raisingspecial interest because they are good probes of magnetic field [2]. Laboratory spectra are required to supply reliableparameters for spectropolarimetric analysis of such remote objects, and this is the focus of my talk. One obvious hurdlearises from the equilibrium temperatures of 'cool' stellar objects, far higher than the range of temperatures typicallyaccessible in the laboratory, particularly when high spectral resolution is required. Another is the difficulty in modellingthe electronic structure of these species, characterised by non-zero spin and orbital angular momentum, and large spinorbitcouplings between them. The lowest-lying electronic states of NiH illustrate this very well [3-5]. Resolvedfluorescence probes multiple vibronic levels very efficiently in this context.We have also used cw laser excitation and Fourier-transform resolved fluorescence to study Zeeman patterns,working at magnetic fields typically 0.3-0.5 T provided by permanent magnets. Investigating the profiles of FeH linesobserved in sunspot spectra, recorded in Stokes V polarisation at the solar Telescope THEMIS in Tenerife[6], we findthat the field deduced from atomic lines (Ti,Fe) is around ~10 % higher than that found from FeHn suggesting thatmolecules form at higher altitudes in the solar atmosphere.References[1] L. Wallace, W. Livingston, P. Bernath, and R.S. Ram, N.S.O. Technical Report N° 1998-002, Available online :ftp://nsokp.nso.edu/pub/atlas/spot3alt (1998).[2] N. Afram, S.V. Berdyugina, D.M. Fluri, S.K. Solanki , and A. Lagg, Astron. & Astrophys. 482 (2), 387 (2008).[3] A.J. Ross, P. Crozet, C. Richard, H. Harker, S.H. Ashworth, and D.W. Tokaryk, Mol. Phys. 110 (17), 2019 (2012).[4] M. Abbasi, A. Shayesteh, P. Crozet, and A.J. Ross, J. Mol. Spectrosc. 349, 49 (2018).[5] I. Havalyova, I. Bozhinova, A.J. Ross, P. Crozet, and A.E. Pashov, Bilbao Poster P2-61 (2018). , 25th Int Conf. on High Res;Molecular Spectroscopy, Bilbao, poster P2, 61 (2018). Also, I. Havalyova, PhD thesis in progress, Univ. Sofia.[6] P. Crozet, G. Tourasse, A. Ross, F. Paletou, and A.L. Ariste, EAS Publications Series European Conference on LaboratoryAstrophysics 58, 63 (2013).

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