Rotational spectra of vibrationally excited AlO and TiO in oxygen rich stars

Abstract

Rotational transitions in vibrationally excited AlO and TiO -- two possible precursors of dust -- were observed in the 300 GHz range (1 mm wavelength) towards the oxygen rich AGB stars R Dor and IK Tau with ALMA, and vibrationally excited AlO was observed towards the red supergiant VY CMa with the SMA. The $J=11\to 10$ transition of TiO in the $v=1\mathrm{and}2$ levels, and the $N=9\to 8$ transition in the $v=2$ level of AlO were identified towards R Dor; the $J=11\to 10$ line of TiO was identified in the $v=1$ level towards IK Tau; and two transitions in the $v=1\mathrm{and}2$ levels of AlO were identified towards VY CMa. The newly-derived high vibrational temperature of TiO and AlO in R Dor of $1800\pm 200$ K, and prior measurements of the angular extent confirm that the majority of the emission is from a region within $\lesssim 2R_{\star }$ of the central star. A full radiative transfer analysis of AlO in R Dor yielded a fractional abundance of $\sim$3% of the solar abundance of Al. From a similar analysis of TiO a fractional abundance of $\sim 78$% of the solar abundance of Ti was found. The observations provide indirect evidence that TiO is present in a rotating disk close to the star. Further observations in the ground and excited vibrational levels are needed to determine whether AlO, TiO, and TiO${}_2$ are seeds of the Al${}_2$O${}_3$ dust in R Dor, and perhaps in the gravitationally bound dust shells in other AGB stars with low mass loss rates.

Accepted for publication in ApJ

References in corpus (11)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• A close halo of large transparent grains around extreme red giant stars
• Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• ExoMol molecular line lists: IX The spectrum of AlO
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• An observational study of dust nucleation in Mira ($o$ Ceti): II. Titanium oxides are negligible for nucleation at high temperatures
• An ALMA view of SO and SO${}_2$ around oxygen-rich AGB stars
• Mass-independent analysis of the stable isotopologues of gas-phase titanium monoxide -- TiO
• Dusty wind of W Hya. Multi-wavelength modelling of the present-day and recent mass-loss
• Detection of highly excited OH towards AGB stars: A new probe of shocked gas in the extended atmospheres

Cited by in corpus (10)

• Evolution and Mass Loss of Cool Ageing Stars: a Daedalean Story
• Bottom-up dust nucleation theory in oxygen-rich evolved stars I. Aluminium oxide clusters
• A high-resolution line list for AlO
• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA
• ATOMIUM: Halide molecules around the S-type AGB star W Aquilae
• The Rotationally Resolved Infrared Spectrum of TiO and Its Isotopologues
• The unusual 3D distribution of NaCl around the AGB star IK Tau
• Molecules and Chemistry in Red Supergiants
• Condensation sequence of circumstellar cluster seeds (CSCCS)