CO Fundamental Band Research Articles

FUNDAMENTAL VIBRATIONAL TRANSITION OF CO DURING THE OUTBURST OF EX LUPI IN 2008,

We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental band at 4.6-5.0 um. The observations were carried out at the VLT and the Subaru Telescope at six epochs from April to August 2008, covering the plateau of the outburst and the fading phase to a quiescent state. The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 um, but composed of two subcomponents that decay with different rates. The narrow line emission (50 km s-1 in FWHM) is near the systemic velocity of EX Lupi. These emission lines appear exclusively in v=1-0. The line widths translate to a characteristic orbiting radius of 0.4 AU. The broad line component (FWZI ~ 150 km s-1) is highly excited upto v<=6. The line flux of the component decreases faster than the narrow line emission. Simple modeling of the line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04-0.4 AU. The excitation state, the decay speed of the line flux, and the line profile, indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event.

AKARIOBSERVATIONS OF BROWN DWARFS. I. CO AND CO2BANDS IN THE NEAR-INFRARED SPECTRA

Near-infrared medium-resolution spectra of seven bright brown dwarfs are presented. The spectra were obtained with the Infrared Camera (IRC) on board the infrared astronomical satellite AKARI, covering 2.5--5.0 um with a spectral resolution of approximately 120. The spectral types of the objects range from L5 to T8, and enable us to study the spectral evolution of brown dwarfs. The observed spectra are in general consistent with the predictions from the previous observations and photospheric models. We find that the CO fundamental band around 4.6 um is clearly seen even in the T8 dwarf 2MASS J041519-0935, confirming the presence of non-equilibrium chemical state in the atmosphere. We also identify the CO_2 fundamental stretching-mode band at 4.2 um for the first time in the spectra of late-L and T-type brown dwarfs. We analyze the observed spectra by comparing with the predicted ones based on the Unified Cloudy Model (UCM). Although overall spectral energy distributions (SEDs) can be reasonably fitted with the UCM, observed CO and CO_2 bands in late-L and T-dwarfs are unexpectedly stronger than the model predictions assuming local thermodynamical equilibrium (LTE). We examine the vertical mixing model and find that this model explains the CO band at least partly in the T-dwarfs 2MASS J041519-0935 and 2MASS J055919-1404. The CO fundamental band also shows excess absorption against the predicted one in the L9 dwarf SDSS J083008+4828. Since CO is already highly abundant in the upper photospheres of late-L dwarfs, the extra CO by vertical mixing has little effect on the CO band strengths, and the vertical mixing model cannot be applied to this L-dwarf. A more serious problem is that the significant enhancement of the CO_2 4.2 um band in both the late-L and T dwarfs cannot be explained at all by the vertical mixing model. The enhancement of the CO_2 band remains puzzling.

A TENTATIVE IDENTIFICATION OF HCN ICE ON TRITON

Spectra of Triton between 1.8 and 5.5 μm, obtained in 2007 May and 2009 November, have been analyzed to determine the global surface composition. The spectra were acquired with the grism and the prism of the Infrared Camera on board AKARI with spectral resolutions of 135 and 22, respectively. The data from 4 to 5 μm are shown in this Letter and compared to the spectra of N2, CO, and CO2, i.e., all the known ices on this moon that have distinct bands in this previously unexplored wavelength range. We report the detection of a 4σ absorption band at 4.76 μm (2101 cm–1), which we attribute tentatively to the presence of solid HCN. This is the sixth ice to be identified on Triton and an expected component of its surface because it is a precipitating photochemical product of Triton's thin N2 and CH4 atmosphere. It is also formed directly by irradiation of mixtures of N2 and CH4 ices. Here we consider only pure HCN, although it might be dissolved in N2 on the surface of Triton because of the evaporation and recondensation of N2 over its seasonal cycle. The AKARI spectrum of Triton also covers the wavelengths of the fundamental (1-0) band of β-phase N2 ice (4.296 μm, 2328 cm–1), which has never been detected in an astronomical body before, and whose presence is consistent with the overtone (2-0) band previously reported. Fundamental bands of CO and CO2 ices are also present.

A mid-infrared scanned-wavelength laser absorption sensor for carbon monoxide and temperature measurements from 900 to 4000 K

Mid-infrared laser absorption sensors based on quantum cascade laser (QCL) technology offer the potential for high-sensitivity, selective, and high-speed measurements of temperature and concentration for species of interest in high-temperature environments, such as those found in combustion devices. A new mid-infrared QCL absorption sensor for carbon monoxide and temperature measurements has been developed near the intensity peak of the CO fundamental band at 4.6 μm, providing orders-of-magnitude greater sensitivity than the overtone bands accessible with telecommunications lasers. The sensor is capable of probing the R(9), R(10), R(17), and R(18) transitions of the CO fundamental ro-vibrational band which are located at frequencies where H2O and CO2 spectral interference is minimal. Temperature measurements are made via scanned-wavelength two-line ratio techniques using either the R(9) and R(17) or the R(10) and R(18) line pairs. The high-speed (1–2 kHz) scanned-wavelength sensor is demonstrated in room-temperature gas cell measurements of CO and, to demonstrate the potential of the sensor for high-temperature thermometry, in shock-heated gases containing CO for a very wide range of temperature (950–3500 K) near 1 atm. To our knowledge, these measurements represent the first use of QCL-based absorption sensor for thermometry at elevated combustion-like temperatures. The high-temperature measurements of CO mole fraction and temperature agree with the post-reflected-shock conditions within ±1.5% and ±1.2% (1σ deviation), respectively.

Probing the mass-loss history of the unusual Mira variable R Hydrae through its infrared CO wind

Context. The unusual Mira variable R Hya is well known for its declining period between ad 1770 and 1950, which is possibly attributed to a recent thermal pulse. Aims. The goal of this study is to probe the circumstellar envelope (CSE) around R Hya and to check for a correlation between the derived density structure and the declining period. Methods. We investigate the CSE around R Hya by performing an in-depth analysis of (1.) the photospheric light scattered by three vibration-rotation transitions in the fundamental band of CO at 4.6 mu m; and (2.) the pure rotational CO J = 1-0 through 6-5 emission lines excited in the CSE. The vibrational-rotational lines trace the inner CSE within 3.5 '', whereas the pure rotational CO lines are sensitive probes of the cooler gas further out in the CSE. Results. The combined analysis bear evidence of a change in mass-loss rate some 220 yr ago (at similar to 150 R-* or similar to 1.9 arcsec from the star). While the mass-loss rate before ad 1770 is estimated to be similar to 2 x 10(-7) M-circle dot/yr, the present day mass-loss rate is a factor of similar to 20 lower. The derived mass-loss history nicely agrees with the mass-loss rate estimates by Zijlstra et al. (2002) on the basis of the period decline. Moreover, the recent detection of an AGB-ISM bow shock around R Hya at 100 arcsec to the west by Wareing et al. (2006) shows that the detached shell seen in the 60 mu m IRAS images can be explained by a slowing-down of the stellar wind by surrounding matter and that no extra mass-loss modulation around 1-2 arcmin needs to be invoked. Conclusions. Our results give empirical evidence to the thermal-pulse model, which is capable of explaining both the period evolution and the mass-loss history of R Hya.

Infrared spectroscopy of carbon monoxide in V838 Monocerotis during 2002–2006

Aims. We report spectra of the overtone and fundamental bands of CO in the eruptive variable V838 Mon, which trace the recent evolution of the star and allow its ejecta to be characterized. Methods. The data were obtained at the United Kingdom Infrared Telescope on fourteen nights from 2002 January, shortly after the first outburst of the star, to 2006 April. Results. Although the near-infrared stellar spectrum superficially resembled a cool supergiant after both the first and third of its outbursts in 2002, its infrared “photosphere” at that time consisted of highly blueshifted gas that was moving outward from the original stellar surface. A spectrum obtained during the third outburst reveals a remarkable combination of emission and absorption in the CO first overtone bands. The most recent observations show a composite spectrum that includes a stellar-like photosphere at a temperature similar to that seen just after the initial outburst, but at a radial velocity redshifted by 15 km s -1 relative to the stellar velocity determined from SiO maser emission, suggesting that the atmosphere is now contracting. Three shell components, corresponding to expansion velocities of 15, 85, and 145 km s -1 , also are present, but absorption is seen at all expansion velocities out to 200 km s -1 . Weak absorption features of fundamental band lines of 13 CO have been detected. However, the large uncertainty in the value of 12 C/ 13 C does not constrain the evolutionary status of the progenitor.

Scientific goals for the observation of Venus by VIRTIS on ESA/Venus express mission

The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3–1 μm range), VIRTIS-M-IR (imaging spectrometer in the 1–5 μm range) and VIRTIS-H (aperture high-resolution spectrometer in the 2–5 μm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus's chemical cycles. In particular, CO, H 2O, OCS and SO 2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 μm fundamental band of CO 2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 μm, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation.

SpitzerIRAC Photometry of M, L, and T Dwarfs

We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M_(5.8) versus [5.8]-[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one-parameter family in T_(eff). Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of 5 (~70M_J to ~15M_J), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 μm fluxes to be lower than expected, from which we infer a stronger CO fundamental band at ~4.67 μm. This suggests that equilibrium CH_4/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of K_s, IRAC 3.6 μm, and 4.5 μm bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the M_k versus K_s-[4.5] relation, which shows a smooth progression over spectral type, and splits the M, L, and T types cleanly.

Collisional line shifting and broadening in the fundamental P-branch of CO in Ar between 214 and 324 K

The collisional shifts and widths of several P-branch spectral lines in the fundamental band of CO–Ar have been measured at temperatures between 214 and 324 K and pressures between 0.025 and 1 atm. The widths have been determined using a line shape model based on the solution of the transport/relaxation equation for the appropriate off-diagonal element of the density matrix. The model uses a realistic molecular potential energy surface to calculate the speed dependence of the collisional broadening, and a rigid sphere potential to calculate the translational motion. It is found that both the shifting and broadening coefficients follow a power law dependence on the temperature. Additionally, it is demonstrated that studies have tended to overestimate the accuracy of collisional widths when the line shape model used to obtain the widths involves multiple fitted line shape parameters or fails to fit the measured spectra within the experimental noise.

Early-Time Spitzer Observations of the Type II Plateau Supernova SN 2004dj

We present mid-infrared observations with the Spitzer Space Telescope of the nearby Type II-P supernova SN 2004dj at epochs of 89-129 days. We have obtained the first mid-IR spectra of any supernova apart from SN 1987A. A prominent [Ni II] 6.64 μm line is observed, from which we deduce that the mass of stable nickel must be at least 2.2 × 10-4 M☉. We also observe the red wing of the CO fundamental band. We relate our findings to possible progenitors and favor an evolved star, most likely a red supergiant, with a probable initial mass between ~10 and 15 M☉.

Laser diode photoacoustic detection in the infrared and near infrared spectral ranges

A new technique for high resolution photoacoustic detection based on application of laser diodes has been developed. This method was tested and compared using identical photoacoustic instrumentation (cell and microphone) to study gas absorption in three different spectral regions, namely: the infrared range near 2100 cm(-1), CO and OCS fundamental band absorption; the ranges near 4200 and 4350 cm(-1), CH4, NH3 and N2O overtone and combination band absorption; the near infrared range near 6500 cm(-1), CO, CO2 and NH3 overtone absorption. Several types of diode laser operating at room temperature or at liquid nitrogen temperature were compared. The optimum gas pressures for the maximum sensitivity of the photoacoustic signals were found and the detection limits were estimated for all of the gases studied. The best sensitivity was achieved for NH3 at 100 ppbv. The sensitivity of the developed system was tested on detection of traces of NH3 and CO2 gases from car exhaust.

Close coupling calculations for rotational relaxation of CO in argon: Accuracy of energy corrected sudden scaling procedures and comparison with experimental data

Fully quantal scattering calculations are carried out for CO in argon using both the close coupling (CC) and coupled states (CS) methods. CC and CS cross sections σ(j→j′) generally agree to within 15% or less with the exception of those corresponding to low Δj=|j′−j| values at low j where differences may reach 50%. The discrepancy arises mostly from efficient collisions with large orbital angular momentum, where the rotation of the quantization axis can no longer be neglected. Then, the CC calculations were used to test a scaling procedure based on the energy corrected sudden (ECS) approximation: given a set of basic cross-section σ(j→0), is it possible to predict the entire σo(j→j′) relaxation matrix? The ECS procedure yields reasonable agreement, on average, at the 13% level. However it fails at reproducing the Δj=1 cross sections in cases where the concept of a mean adiabaticity factor losses its physical meaning since the duration of the efficient collisions varies too much with the orbital angular momentum. On that basis, we have examined another question: the validity of an inversion procedure, based on the ECS scheme. Is it possible to determine the basic cross sections σ(j→0) starting from the knowledge of the easily measurable diagonal elements σo(j→j)? The ECS inverted basic rates agree with the CC ones to within about 20% up to j=15 and strongly diverge for higher j while the inversion leads to an overestimation of the mean duration of the efficient collisions. Then, using a high resolution Raman spectrometer, we recorded the Q-branch head of the fundamental band of CO in mixture with Ar at three temperatures, 87, 195, and 300 K, and total pressures up to 1.25 bar. Line-mixing effects in experimental Raman profiles are compared with CC theoretical predictions. Finally the close coupling results are also used to predict rotational relaxation times measured in free jets.

Theoretical absorption spectrum of the Ar–CO van der Waals complex

The three-dimensional intermolecular electric dipole moment surface of Ar–CO is calculated at the coupled cluster singles and doubles level of theory with the aug-cc-pVTZ basis set extended with a 3s3p2d1f1g set of midbond functions. Using the rovibrational energies and wave functions of our recent study [J. Chem. Phys. 117, 6562 (2002)], temperature-dependent spectral intensities are evaluated and compared to available experimental data. Based on the theoretical spectrum, alternative assignments of the experimentally observed lines in the fundamental band of CO around 2160 and 2166 cm−1 are suggested.

Infrared spectral classification of normal stars

Moderate resolution (400) 2.38-45.2m infrared spectra of stars without dust features were obtained with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). The observations are part of a larger program with the objective to extend and refine the current infrared classification schemes. In particular, our data provide the basis for a more detailed classification of the 1.N-1.NO sources (ordinary and oxygen rich naked stars) as defined by Kraemer et al. (2002) in a comprehensive classification of the ISO-SWS spectra. For our analysis, the continuum was determined by fitting Engelke's function (Engelke 1992) to the SWS data. The stellar angular diameters derived from these estimates of the continuum are in good agreement with values obtained by other methods. Analysis of the equivalent widths of the CO fundamental and first overtone molecular bands, the SiO fundamental and first overtone, as well as the H2O bending mode band as a function of MK class, reveals that there is sucient information in the SWS spectra to distinguish between hot (B, A, F) and cool stars. Furthermore, it is possible to determine the spectral type for the G, K and M giants, and subtype ranges in a sequence of K and M giants. The equivalent widths of the CO and SiO bands are found to be well correlated in K and M stars, such that the equivalent widths of the CO fundamental, the SiO first overtone and the SiO fundamental can be reasonably well extrapolated from the depth of the CO first overtone. We have identified two stars, HR 365 and V Nor, whose mid-infrared spectrum does not correspond to their respective optical classification. HR 365 may have a late M companion, which dominates the observed infrared spectrum while V Nor is a late type giant that was included because its spectrum was classified as featureless under the IRAS LRS scheme. According to Kraemer et al. (2002), V Nor has a thin dust shell, which distorts the analysis of its mid-infrared absorption bands.

5 Micron Photometry of Late-Type Dwarfs

We present narrowband M photometry of nine low-mass dwarfs with spectral types ranging from M2.5 to L0.5. Combining the (L'-M') colors derived from our observations with data from the literature, we find colors consistent with a Rayleigh-Jeans flux distribution for spectral types earlier than M5, but enhanced F3.8/F4.7 flux ratios (negative [L'-M'] colors) at later spectral types. This probably reflects increased absorption at M' due to the CO fundamental band. We compare our results against recent model predictions and briefly discuss the implications.

Shifting and broadening in the fundamental band of CO highly diluted in He and Ar: A comparison with theory

We present measurements of the shifts and widths of the rovibrational lines of the fundamental band of CO highly diluted in He and Ar at 296 K. The shifts are decomposed into parts odd and even in the line number, m. These are then compared with close coupled calculations carried out with the best known interaction potentials. There is general agreement between the calculated and measured values of the broadening and shifting. Furthermore, the results illustrate that the decomposition of the shifts into parts, odd and even in m, is a powerful tool for separating out the relative contributions of the isotropic and anisotropic part of the interaction to the shifts and which part needs to be corrected if there is a discrepancy. Thus, shift measurements can be added to the list of experiments that may be used to determine reliable interaction potentials. The results also show, given a potential, that close coupled calculations are accurate and could be used to confirm or establish empirical models of the temperature dependence of the broadening or shifting, etc. Such modeling is important at atmospheric physics.

Spectroscopic manifestation of molecular rotation dynamics in dense media: CO fundamental band in liquid and solid CO-Kr and CO-Xe solutions

Abstract The shape of the CO fundamental band has been studied in CO-Kr and CO-Xe mixtures in a wide temperature range from the critical temperature to values lower than the melting point of the solutions. The band shape transformation has been analyzed by means of a simple cell model, which takes into account the effect of the nearest environment on CO rotation dynamics of a molecule in dense media. The band shape observed in liquid solutions shows the constraint of CO rotational mobility; this effect has been described by introducing an effective potential barrier for rotational motion. The model analysis of the obtained experimental data results in an estimation of the rotational motion relaxation parameter and of the effective barrier values for CO dissolved in Kr and Xe. The CO rotational motion becomes more hindered when going to lower-temperature liquid solutions. The liquid-to-solid phase transition leads to an increase of the relaxation rate, the effective barrier values decrease, and the rotational motion tends to become rotational diffusion.

Stabilized Tunable Diode Laser Measurements of the P(2) Line in the 13CO Fundamental Band Broadened by Helium at Temperatures between 11.5 and 298.6 K

We determined accurate He-broadening parameters and collisional cross sections for the P(2) line in the fundamental band of CO at room temperature and at intermediate temperatures down to 11.5 K. We also determined a precise value for the temperature dependence of the line-broadening parameter on (T)−n with n equal to 0.548±0.010. Our results validate the microwave results for the J=1 to J=2 rotational transitions measured over the same range of temperatures which were reported previously by Beaky et al. (1996, J. Chem. Phys.105, 3994–4004).

Mira’s Wind Explored in Scattering Infrared CO Lines

We have observed the intermediate regions of the circumstellar envelope of Mira (o Ceti) in photospheric light scattered by three vibration-rotation transitions of the fundamental band of CO, from low-excited rotational levels of the ground vibrational state, at an angular distance of β ~ 2''-7'' away from the star. The data were obtained with the Phoenix spectrometer mounted on the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately 05 and seeing limited. Our observations provide absolute fluxes, leading to an independent new estimate of the mass-loss rate of approximately 3 × 10-7 M☉ yr-1, as derived from a simple analytic wind model. We find that the scattered intensity from the wind of Mira for 2'' β 7'' decreases as β-3, which suggests a time constant mass-loss rate, when averaged over 100 yr, over the past 1200 yr.

The weakly bound complex CO–orthoD2: Detection of millimeter-wave transitions

For the first time two rotational transitions of the CO–orthoD2 van der Waals molecular complex have been recorded in a supersonic jet and assigned to the two R-branch transitions, R(1) (J,j,l)=2,1,1←1,0,1 112 806.515(50) MHz, R(2)=3,1,2,←2,0,2 119 746.484(50) MHz. These transitions were detected with the highly sensitive intracavity spectrometer based on the millimeter wave generator, called OROTRON. Their measured frequencies are in close agreement with the frequency positions predicted from the infrared spectrum, which accompanies the fundamental band of CO in the 4.7 μm region, and which has been published recently by McKellar [J. Chem. Phys. 112, 9282 (2000)]. The millimeter wave transitions will allow a precise determination of the rotational levels with different parity in the vibrational vCO=0 ground state.