J/A+A/713/A13 TiO i1Π-a1Δ system in stellar spectra (Schmidt, 2026)
First identification of the TiO i1Π - a1Δ system in stellar
spectra and its spectroscopic characterization.
Schmidt M.R.
<Astron. Astrophys. 713, A13 (2026)>
=2026A&A...713A..13S 2026A&A...713A..13S (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: line: identification - molecular data - opacity - stars: atmospheres -
stars: late-type
Abstract:
Titanium 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 5810-5850Å. 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-a1^Δ of the TiO, with an R-head located at 5814.8Å,
overlapping the 1-3 band of the α (C3Δ-X3Δ)
system. The lower state of the band is identified as the a1Δ
v"=0 state, while the upper state is most likely the 1Π in its
ground vibrational state. The empirical band intensity is derived by
comparing the relative strengths of neighbouring bands from the
C3Δ-X3Δ and B3Π-X3^Δ 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 i1Π (optionally 21Π) electronic state has been predicted
by theoretical calculations. While energies of two vibrationally
excited states were previously inferred from de-perturbation analyses
of the α 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.
Description:
Two tables are available:
Table1: Lines and Residuals for the TiO i1Π-a1Δ
Transition from PGOPHER Log File which contains the full list of
identified and analysed transitions for the TiO i1Π-a1Δ
0-0 band is given. The table contains observed, calculated line
positions and residuals of the fit as printed by PGOPHER in its Log
file.
Table3: PGOPHER line list for TiO i1Π - a1Δ Transition
contains the empirical line list for the 0-0 band of the main
isotopologue 48Ti16O, based on the derived spectroscopic constants
and empirical intensities extrapolated up to J=200.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 94 161 Lines and residuals for the
TiO i1Π - a1Δ transition
table3.dat 117 1192 PGOPHER line list for
TiO i1Π - a1Δ transition
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- J' Total angular momentum of upper state
5 A1 --- P' Upper state e/f parity
7- 9 I3 --- J'' Total angular momentum of lower state
11 A1 --- P'' Lower state e/f parity
13- 22 F10.4 cm-1 Obs Observed line position, cm-1
24- 33 F10.4 cm-1 Calc Calculated line position, cm-1
35- 41 F7.4 cm-1 O-C Observed - calculated value, cm-1
43- 94 A52 --- Line Line assignment (1)
--------------------------------------------------------------------------------
Note (1): The line assignment is
^{Delta N}^Δ J{p''}(J'') i1Π v' J' N' F1p
- a1Δ v'' J'' N'' F1p
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- J' Total angular momentum of upper state
5 A1 --- P' Upper state e/f parity
7- 9 I3 --- J'' Total angular momentum of lower state
11 A1 --- P'' Lower state e/f parity
13- 21 F9.3 cm-1 Pos Calculated line position, cm-1
23- 31 F9.3 cm-1 Eup Upper state energy level, cm-1
33- 41 F9.3 cm-1 Elo Lower state energy level, cm-1
43- 52 F10.1 s-1 A Einstein A value, s-1
54- 59 F6.4 --- f Oscillator strength
61-117 A57 --- Line Line assignment (1)
--------------------------------------------------------------------------------
Note (1): The line assignment is
^{Delta N}^Δ J{p''}(J'') i1Π v' J' N' F1p
- a1Δ v'' J'' N'' F1p
--------------------------------------------------------------------------------
Acknowledgements:
Mirek R. Schmidt, schmidt(at)ncac.torun.pl
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 17-Jul-2026