J/A+A/713/A13ivo://CDS.VizieR/J/A+A/713/A13CDSSchmidt M.R.2026-09-01T07:15:31Z2026-09-01T08:15:06ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fratomic-physicsTitanium monoxide plays an important role in determining the atmospheric structure of M-type stars and in shaping the visible part of their spectra. The precision of synthetic spectra when confronted with high-resolution observations depends on the completeness of the included transitions and on the accuracy of line positions and line intensities. We aim to systematically assess the quality of synthetic spectra computed with up-to-date TiO line lists by comparing them with high-resolution, high signal-to-noise spectra of cool stars calibrated in absolute or relative flux. We compute synthetic spectra for late-type M giants and identify systematic discrepancies in the wavelength range 5810-5850{AA}. To investigate the origin of these discrepancies, we analyse experimental TiO absorption cross-sections. We report the detection of a molecular band of the singlet system ^1^{Pi^-a^1^{Delta} of the TiO, with an R-head located at 5814.8{AA}, overlapping the 1-3 band of the {alpha} (C^3^{Delta}-X^3^{Delta}) system. The lower state of the band is identified as the a^1^{Delta} v"=0 state, while the upper state is most likely the ^1^{Pi} in its ground vibrational state. The empirical band intensity is derived by comparing the relative strengths of neighbouring bands from the C^3^{Delta}-X^3^{Delta} and B^3^{Pi}^-X^3^{Delta} systems in the experimental cross-section. The band intensity is further validated by synthetic spectrum calculations for the late-type giant 30 Her (M6 III) and comparison with its observed spectrum from the MELCHIORS library. The i^1^{Pi} (optionally 2^1^{Pi}) electronic state has been predicted by theoretical calculations. While energies of two vibrationally excited states were previously inferred from de-perturbation analyses of the {alpha} system, accurate spectroscopic constants for this electronic state were lacking. The newly identified band is sufficiently strong to affect the flux distribution in the spectra of cool stars.2026A&A...713A..13Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/713/A13CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/713/A13https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/713/A13http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/713/A13https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/713/A13https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/713/A13http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/713/A13GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/713/A13/table1Lines and residuals for the TiO i^1^{Pi} - a^1^{Delta} transitionrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Total angular momentum of upper statephys.angMomentumintP'Upper state e/f parityphys.atmol.paritycharJ''Total angular momentum of lower statephys.mol.qnintP''Lower state e/f parityphys.atmol.paritycharObsObserved line position, cm^-1^cm**-1em.wldoubleCalcCalculated line position, cm^-1^cm**-1em.wldoubleO-CObserved - calculated value, cm^-1^cm**-1stat.fit.residualfloatLineLine assignment (1)meta.id;spect.linecharJ/A+A/713/A13/table3PGOPHER line list for TiO i^1^{Pi} - a^1^{Delta} transitionrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Total angular momentum of upper statephys.angMomentumintP'Upper state e/f parityphys.atmol.paritycharJ''Total angular momentum of lower statephys.mol.qnintP''Lower state e/f parityphys.atmol.paritycharPosCalculated line position, cm^-1^cm**-1em.wldoubleEupUpper state energy level, cm^-1^cm**-1phys.energy;phys.atmol.leveldoubleEloLower state energy level, cm^-1^cm**-1phys.energy;phys.atmol.leveldoubleAEinstein A value, s^-1^s**-1phys.atmol.transProbdoublefOscillator strengthphys.atmol.oscStrengthfloatLineLine assignment (1)meta.id;spect.linechar