Collisional and infrared radiative pumping of molecular vibrational states - The carbon monoxide infrared bands

Scoville, N. Z.; Krotkov, R.; Wang, D.

doi:10.1086/158306

Cited by 41 publications

(35 citation statements)

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“…Elitzur (1983) argued for a different formulation For Δv = 1 (v = v − 1), this last formula reduces to Scoville et al (1980) argued that the probabilities of collisioninduced vibrational transitions are proportional to the corresponding radiative transition matrix elements (Born-Coulomb long range interaction). Therefore, the vibrational de-excitation rate coefficients from v to v can be derived from the v = 1 → 0 rate coefficients:…”

Section: Extrapolating Vibrational Transition Ratesmentioning

confidence: 99%

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Radiation thermo-chemical models of protoplanetary discs

Thi

Kamp²,

Woitke

et al. 2013

A&A

110

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Context. The carbon monoxide (CO) ro-vibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X 1 Σ + to the electronic A 1 Π state of CO should be taken into account in disc models. Aims. We wish to understand the excitation mechanism of CO ro-vibrational emission seen in Herbig Ae discs, in particular in transitions involving highly excited rotational and vibrational levels. Methods. We implemented a CO model molecule that includes up to 50 rotational levels within nine vibrational levels for the ground and A-excited states in the radiative-photochemical code ProDiMo. We took CO collisions with hydrogen molecules (H 2 ), hydrogen atoms (H), helium (He), and electrons into account. We estimated the missing collision rates using standard scaling laws and discussed their limitations. We tested the effectiveness of ultraviolet (UV) fluorescence pumping for the population of high-vibrational levels (v = 1-9, J = 1-50) for four Herbig Ae disc models (disc mass M disc = 10 −2 , 10 −4 and inner radius R disc = 1, 20 AU). We tested the effect of infrared (IR) pumping on the CO vibrational temperature and the rotational population in the ground vibrational level. Results. UV fluorescence and IR pumping impact on the population of ro-vibrational v > 1 levels. The v = 1 rotational levels are populated at rotational temperatures between the radiation temperature around 4.6 μm and the gas kinetic temperature. The UV pumping efficiency increases with decreasing disc mass. The consequence is that the vibrational temperatures T vib , which measure the relative populations between the vibrational levels, are higher than the disc gas kinetic temperatures (suprathermal population of the vibrational levels). The effect is more important for low-density gases because of lower collisional de-excitations.The UV pumping is more efficient for low-mass (M disc < 10 −3 M ) than high-mass (M disc > 10 −3 M ) discs. Rotational temperatures from fundamental transitions derived using optically thick 12 CO v = 1−0 lines do not reflect the gas kinetic temperature. Uncertainties in the rate coefficients within an order of magnitude result in variations in the CO line fluxes up to 20%. CO pure rotational levels with energies lower than 1000 K are populated in local thermodynamic equilibrium but are sensitive to a number of vibrational levels included in the model. The 12 CO pure rotational lines are highly optically thick for transition from levels up to E upper = 2000 K. The model line fluxes are comparable with the observed line fluxes from typical Herbig Ae low-and high-mass discs.

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Section: Extrapolating Vibrational Transition Ratesmentioning

confidence: 99%

“…Completeness in the rate coefficients can be attained only by using approximate extrapolation rules derived from physical considerations. Krotkov et al (1980) and Scoville et al (1980) studied the efficiency of UV and IR pumping but considered only purevibrational levels.…”

Section: Introductionmentioning

confidence: 99%

Radiation thermo-chemical models of protoplanetary discs

Thi

Kamp²,

Woitke

et al. 2013

A&A

110

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“…CO first-overtone band emission is a well known feature arising especially from the rotating accretion disks around young stellar objects (YSO), and the physics of CO band formation in such rotating pre-main sequence disks has already been discussed widely in the literature (see, e.g., Scoville et al 1980;Carr 1989;Najita et al 1996;Kraus 2000;Kraus et al 2000). The main focus in YSO research is therefore especially the structure of the 2 −→ 0 band head, which contains the complete velocity information, and from which the rotation velocity, disk inclination, as well as some information concerning the density and temperature within the CO forming disk region can be derived (e.g., Carr et al 1993;Chandler et al 1993;Carr 1995;Najita et al 1996;Kraus 2000;Kraus et al 2000;Bik & Thi 2004;Berthoud et al 2007).…”

Section: Co Band Formationmentioning

confidence: 99%

The pre- versus post-main sequence evolutionary phase of B[e] stars

Kraus¹

2008

A&A

109

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Context. Many galactic B[e] stars suffer from improper distance determinations, which make it difficult to distinguish between a preand post-main sequence evolutionary phase on the basis of luminosity arguments. In addition, these stars have opaque circumstellar material, obscuring the central star, so that no detailed surface abundance studies can be performed. Aims. Instead of studying the surface abundances as a tracer of the evolutionary phase, we propose a different indicator for the supergiant status of a B[e] star, based on the enrichment of its circumstellar matter by 13 C, and detectable via its 13 CO band emission in the K band spectra. Methods. Based on stellar evolution models, we calculate the variation of the 12 C/ 13 C isotopic surface abundance ratio during the evolution of non-rotating stars with different initial masses. For different values of the 12 C/ 13 C ratio we then compute synthetic firstovertone vibration-rotational band spectra from both the 12 CO and 13 CO molecule at different spectral resolutions. We further discuss the influence of stellar rotation on the variation of the surface 12 C/ 13 C ratio and on the possibility of 13 CO band detection. Results. The surface 12 C/ 13 C isotope ratio is found to decrease strongly during the post-main sequence evolution of non-rotating stars, from its interstellar value of about 70 to a value of about 15-20 for stars with initial masses higher than 7 M , and to a value of less than 5 for stars with initial masses higher than 25 M . We find that detectable 13 CO band head emission is produced for isotope ratios 12 C/ 13 C < ∼ 20, and can most easily be detected with a spectral resolution of R ∼ 1500 . . . 3000. For the rotating stellar models, the drop in 12 C/ 13 C already occurs for all stars with M in > ∼ 9 M during the main-sequence evolution. The detection of 13 CO band head emission in such mid-resolution K band spectra of a B[e] star thus favours an evolved rather than a young nature of the object.

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“…In all cases, CO emission is seen together with Brγ line emission, but these two features probably come from different volumes of gas. At temperatures of about 4000 K, CO is dissociated and molecular hydrogen is dissociated by collisions for values higher than 3000 K. However, for density values higher than 10 7 cm −3 and in the presence of H 2 , CO dominates the cooling (Scoville et al 1980). Therefore the CO bands are specific probes of the circumstellar portions where the gas is relatively warm at high densities.…”

Section: Near-ir Spectroscopymentioning

confidence: 99%

Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data

Lorenzetti

Giannini

Calzoletti

et al. 2006

A&A

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Aims. We present a near-IR study of the EXor variable V1118 Ori, performed by following a slightly declining phase after a recent outburst. In particular, the near-IR (0.8-2.3 µm) spectrum, obtained for the first time, shows a wide variety of emission features of the H i (Paschen and Brackett series), He i recombination, and CO overtone.Methods. By comparing the observed spectrum with a wind model, a mass loss rate of 4 × 10 −8 M yr −1 can be derived along with other parameters whose values are typical of an accreting T Tauri star. In addition, we have used X-ray data from the XMM archive, taken in two different epochs during the declining phase monitored in IR. The X-ray emission (in the range 0.5-10 keV) permits us to derive several parameters (as plasma temperatures and L X luminosity) that confirm the T Tauri nature of the source. Results. In the near-IR, the object maintains a low extinction (A V < ∼ 2) during all the activity phases, confirming that variable extinction does not contribute to brightness variations. The lack of both a significant amount of circumstellar material and any evidence of IR cooling from collimated jet/outflow driven by the source indicates that at least this member of the EXor class is in a late stage of the pre-main sequence evolution. When going from inactive to active phases, the luminosity increases considerably (from 1.4 L to more than 25 L ) and the observed spectral energy distribution assumes different shapes, all typical of a T Tauri star. In the X-ray regime, an evident fading is present, detected in the post-outburst phase, which cannot be reconciled with the presence of any absorbing material. This circumstance, combined with the persistence (in the pre-and post-outburst phases) of a temperature component at about 10 MK, suggests that accretion has some influence in regulating the coronal activity.

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Collisional and infrared radiative pumping of molecular vibrational states - The carbon monoxide infrared bands

Cited by 41 publications

References 0 publications

Radiation thermo-chemical models of protoplanetary discs

Radiation thermo-chemical models of protoplanetary discs

The pre- versus post-main sequence evolutionary phase of B[e] stars

Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data

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