High-resolution Doppler Spectroscopy Research Articles

Doppler tomography as a tool for characterising exoplanet atmospheres II: an analysis of HD 179949 b

Abstract High-resolution Doppler spectroscopy provides an avenue to study the atmosphere of both transiting and non-transiting planets. This powerful method has also yielded some of the most robust atmospheric detections to date. Currently, high-resolution Doppler spectroscopy detects atmospheric signals by cross-correlating observed data with a model atmospheric spectrum. This technique has been successful in detecting various molecules such as H2O, CO, HCN and TiO, as well as several atomic species. Here we present an alternative method of performing high-resolution Doppler spectroscopy, using a technique known as Doppler tomography. We present an analysis of HD 179949 b using Doppler tomography and provide Doppler tomograms confirming previous detections of CO at 2.3 μm and H2O at both 2.3 μm and 3.5 μmwithin the atmosphere of HD 179949 b, showing significantly lower background noise levels when compared to cross-correlation methods applied to the same data. We also present a novel detection of H2O at 2.1 μm as well as a tentative detection of CO on the night side of the planet at 2.3 μm. This represents the first observational evidence for molecular absorption in the night-side emission spectrum of an exoplanet using Doppler spectroscopy.

Dayside Fe i Emission, Day–Night Brightness Contrast and Phase Offset of the Exoplanet WASP-33b

We report on Fe i in the dayside atmosphere of the ultra-hot-Jupiter WASP-33b, providing evidence for a thermal inversion in the presence of an atomic species. We also introduce a new way to constrain the planet’s brightness variation throughout its orbit, including its day–night contrast and peak phase offset, using high-resolution Doppler spectroscopy alone. We do so by analyzing high-resolution optical spectra of six arcs of the planet’s phase curve, using Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) on the Canada–France–Hawaii telescope and High Dispersion Spectrograph on the Subaru telescope. By employing a likelihood mapping technique, we explore the marginalized distributions of parameterized atmospheric models, and detect Fe i emission at high significance (>10.4σ) in our combined data sets, located at K p = 222.1 ± 0.4 km s−1 and v sys = −6.5 ± 0.3 km s−1. Our values agree with previous reports. By accounting for WASP-33b’s brightness variation, we find evidence that its nightside flux is <10% of the dayside flux and the emission peak is shifted westward of the substellar point, assuming the spectrum is dominated by Fe i. Our ESPaDOnS data, which cover phases before and after the secondary eclipse more evenly, weakly constrain the phase offset to +22 ± 12 degrees. We caution that the derived volume-mixing ratio depends on our choice of temperature-pressure profile, but note it does not significantly influence our constraints on day–night contrast or phase offset. Finally, we use simulations to illustrate how observations with increased phase coverage and higher signal-to-noise ratios can improve these constraints, showcasing the expanding capabilities of high-resolution Doppler spectroscopy.

Silicon in the dayside atmospheres of two ultra-hot Jupiters

Atmospheres of highly irradiated gas giant planets host a large variety of atomic and ionic species. Here we observe the thermal emission spectra of the two ultra-hot Jupiters WASP-33b and KELT-20b/MASCARA-2b in the near-infrared wavelength range with CARMENES. Via high-resolution Doppler spectroscopy, we searched for neutral silicon (Si) in their dayside atmospheres. We detect the Si spectral signature of both planets via cross-correlation with model spectra. Detection levels of 4.8σ and 5.4σ, respectively, are observed when assuming a solar atmospheric composition. This is the first detection of Si in exoplanet atmospheres. The presence of Si is an important finding due to its fundamental role in cloud formation and, hence, for the planetary energy balance. Since the spectral lines are detected in emission, our results also confirm the presence of an inverted temperature profile in the dayside atmospheres of both planets.

Evidence for TiO in the Atmosphere of the Hot Jupiter HAT-P-65 b

Abstract We present the low-resolution transmission spectra of the puffy hot Jupiter HAT-P-65b (0.53 MJup, 1.89 RJup, T eq = 1930 K), based on two transits observed using the OSIRIS spectrograph on the 10.4 m Gran Telescopio CANARIAS. The transmission spectra of the two nights are consistent, covering the wavelength range 517–938 nm and consisting of mostly 5 nm spectral bins. We perform equilibrium-chemistry spectral retrieval analyses on the jointly fitted transmission spectrum and obtain an equilibrium temperature of K and a cloud coverage of %, revealing a relatively clear planetary atmosphere. Based on free-chemistry retrieval, we report strong evidence for titanium oxide (TiO). Additional individual analyses in each night reveal weak-to-moderate evidence for TiO in both nights, but moderate evidence for Na or VO only in one of the nights. Future high-resolution Doppler spectroscopy as well as emission observations will help confirm the presence of TiO and constrain its role in shaping the vertical thermal structure of HAT-P-65b’s atmosphere.

Measurements of the energy distribution of W atoms sputtered by low energy Ar ions using high-resolution Doppler spectroscopy

Emission spectra of neural tungsten (W) sputtered by impact of argon (Ar) ions in a weakly magnetized (<0.1 T) Ar plasma were measured using a high resolution spectrometer at normal incidence angle to the surface. The measurements were performed for the mono-energetic impact energies between 70 and 150 eV using the neutral tungsten (W I) line at 4982.593 Å. The line shape of this line was simulated using a Doppler-shifted emission model to determine the energy distribution. Additional broadening mechanisms were taken into account: instrumental broadening, Zeeman effect and finally the photon or light reflectance at the W surface.The obtained energy distribution was found in a very good agreement with the Thompson distribution, even though deviations for lower impact energies are observed, e.g. the high-energy tail of sputtered particles demonstrates a faster drop compared to 1/E 2 at energies below 100 eV. Moreover, the standard cosine (Knudsen cosine law) distribution provides a rather good description of emission spectra in the energy range of study. Finally, the energy distribution was also compared with simulations carried out with the binary collision approximation (BCA) based Monte-Carlo code SDTrimSP. It shows a marginally worse description at low energies and better description of the high energy tail compared to the Thompson one. Furthermore, the model was used to determine in-situ the degree of light reflection at the W surface. The results are in excellent agreement with the literature data.

Seeing above the clouds with high-resolution spectroscopy

ABSTRACT In the last decade, ground-based high-resolution Doppler spectroscopy (HRS) has detected numerous species in transiting and non-transiting hot Jupiters, and is ideally placed for atmospheric characterization of warm Neptunes and super Earths. Many of these cooler and smaller exoplanets have shown cloudy atmospheres from low-resolution near-infrared observations, making constraints on chemical species difficult. We investigate how HRS can improve on these given its sensitivity to spectral line cores which probe higher altitudes above the clouds. We model transmission spectra for the warm Neptune GJ 3470b and determine the detectability of H2O with the CARMENES, GIANO, and SPIRou spectrographs. We also model a grid of spectra for another warm Neptune, GJ 436b, over a range of cloud-top pressure and H2O abundance. We show H2O is detectable for both planets with modest observational time and that the high H2O abundance-high cloud deck degeneracy is broken with HRS. However, meaningful constraints on abundance and cloud-top pressure are only possible in the high-metallicity scenario. We also show that detections of CH4 and NH3 are possible from cloudy models of GJ 436b. Lastly, we show how the presence of the Earth’s transmission spectrum hinders the detection of H2O for the most cloudy scenarios given that telluric absorption overlaps with the strongest H2O features. The constraints possible with HRS on the molecular species can be used for compositional analysis and to study the chemical diversity of such planets in the future.

Measurement and parameterization of sub-1 eV ion temperatures in a helium plasma confined by a magnetic mirror

Using a magnetic mirror plasma device, helium ion temperatures were investigated using high resolution Doppler spectroscopy of the He II line at 468.6 nm. The objective was to improve the quality of fits to Langmuir probe data. Measured temperatures, which represent an average value over a line of sight, ranged from 0.07 eV to 0.32 eV with higher values reached in stronger magnetic fields. An analytic expression for the line of sight integral of a variable width Gaussian signal is presented, and it is demonstrated that the integrated signal can, in practice, be accurately fitted by a single Gaussian line shape. A large number of spectra was acquired using a randomized experimental design with four independently controllable engineering variables and three discrete magnetic fields. Separate parameterizations of the results for each magnetic field in terms of the engineering variables showed that the data could already be well fitted using only the plasma current as a predictor. The fit to the ion temperature data was significantly improved when both the plasma current and filament bias voltage were used as predictors. The helium gas fill pressure had negligible predictive value for the ion temperature. (figures in this article are in colour only in the electronic version).

On the robustness of analysis techniques for molecular detections using high-resolution exoplanet spectroscopy

High-resolution doppler spectroscopy provides a powerful means for chemical detections in exoplanetary atmospheres. This approach involves monitoring hundreds of molecular lines in the planetary spectrum doppler shifted by the orbital motion of the planet. The molecules are detected by cross-correlating the observed spectrum of the system with a model planetary spectrum. The method has led to molecular detections of H2O, CO, and TiO in hot Jupiters using large ground-based telescopes. Critical to this method, however, is the accurate removal of the stellar and telluric features from the observed spectrum, also known as detrending. Previous molecular detections have relied on specific choices of detrending methods and parameters. However, the robustness of molecular detections across the different choices has not been investigated in detail. We conduct a systematic investigation of the effect of detrending algorithms, parameters, and optimizations on chemical detections using high-resolution spectroscopy. As a case study, we consider the hot Jupiter HD 189733 b. Using multiple methods, we confirm high-significance detections of H2O (4.8$\sigma$) and CO (4.7$\sigma$). Additionally, we report evidence for HCN at high significance (5.0$\sigma$). On the other hand, our results highlight the need for improved metrics and extended observations for robust confirmations of such detections. In particular, we show that detection significances of $\gtrsim$ 4$\sigma$ can be obtained by optimizing detrending at incorrect locations in the planetary velocity space; such false positives can occur in nearly 30\% of cases. We discuss approaches to help distinguish molecular detections from spurious noise.

Evidence for Multiple Molecular Species in the Hot Jupiter HD 209458b

Abstract Molecular species in planetary atmospheres provide key insights into their atmospheric processes and formation conditions. In recent years, high-resolution Doppler spectroscopy in the near-infrared has allowed detections of H2O and CO in the atmospheres of several hot Jupiters. This method involves monitoring the spectral lines of the planetary thermal emission Doppler-shifted due to the radial velocity of the planet over its orbit. However, aside from CO and H2O, which are the primary oxygen- and carbon-bearing species in hot H2-rich atmospheres, little else is known about the molecular compositions of hot Jupiters. Several recent studies have suggested the importance and detectability of nitrogen-bearing species in such atmospheres. In this Letter, we confirm potential detections of CO and H2O in the hot Jupiter HD 209458b using high-resolution spectroscopy. We also report a cross-correlation peak with a signal-to-noise ratio of 4.7 from a search for HCN. The results are obtained using high-resolution phase-resolved spectroscopy with the Very Large Telescope CRyogenic high-resolution InfraRed Echelle Spectrograph (VLT CRIRES) and standard analysis methods reported in the literature. A more robust treatment of telluric contamination and other residuals would improve confidence and enable unambiguous molecular detections. The presence of HCN could provide constraints on the C/O ratio of HD 209458b and its potential origins.

High-speed multi-THz-range mode-hop-free tunable mid-IR laser spectrometer

We report on a widely (2.25 THz or 75 cm(-1)) and rapidly (4.5 THz/s) mode-hop-free (MHF) tunable mid-IR laser source at ~3.3 μm, consisting of a 5%-MgO:LiNbO(3) singly resonant optical parametric oscillator (SRO) pumped by an automated broadly MHF tunable extended-cavity diode laser (ECDL). The broad and rapid MHF tuning capability of the ECDL is readily transferred to the SRO idler wave owing to the quasi-noncritical pump spectral acceptance bandwidth of the quasi-phase-matching. Fast and broadband high-resolution Doppler spectroscopy measurements of the ν(3) band of CH(4) are presented to illustrate the performance of the mid-IR optical parametric oscillator spectrometer.

Anomalous Diffusion in a Linear Plasma Generator

AbstractPlasma production and particle transport of the magnetized plasma in the linear device PSI‐2 are investigated by analyzing the radial density and electron temperature pro.les obtained from Langmuir probe measurements. Additional information on the atomic (H) and proton temperatures is obtained from high resolution Doppler spectroscopy. The density profiles are found to be hollow, but do extend radially far beyond the visible rim with an exponential decay length of 3 cm. They can be explained by parallel and perpendicular diffusion in combination with a cylindrical source extending along the magnetic field all over the device. A large perpendicular diffusion coefficient in the range of 5 m2/s is inferred from the experimental results. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

New wind measurements in Venus’ lower mesosphere from visible spectroscopy

The dynamics of Venus’ mesosphere (70–110 km) is characterized by the superposition of two different wind regimes: (1) Venus’ retrograde superrotation; (2) a sub-solar to anti-solar (SS–AS) flow pattern, driven by solar EUV heating on the sunlit hemisphere. Here, we report on new ground-based velocity measurements in the lower part of the mesosphere. We took advantage of two essentially symmetric Venus elongations in 2001 and 2002 to perform high-resolution Doppler spectroscopy ( R=120,000) in 12C 16O 2 visible lines of the 5 ν 3 band and in a few solar Fraunhofer lines near 8700 Å. These measurements, mapped over several points on Venus’ illuminated hemisphere, probe the region of cloud tops. More precisely, the solar Fraunhofer lines sample levels a few kilometers below the UV features (i.e. near ∼67 km), while the CO 2 lines probe an altitude higher by about 7 km. The wind field over Venus’ disk is retrieved with an rms uncertainty of 15–25 m s −1 on individual measurements. Kinematical fit to a one- or two-component circulation model indicates the dominance of the zonal retrograde flow with a mean equatorial velocity of ∼75 m s −1, exhibiting very strong day-to-day variations (±65 m s −1). Results are very consistent for the two kinds of lines, suggesting a negligible vertical wind shear over 67–74 km. The SS–AS flow is not detected in single-day observations, but combining the results from all data suggests that this component may invade the lower mesosphere with a ∼40 m s −1 velocity.

Plasma rotation in a plasma generator

The plasma rotation in a linear magnetic configuration has been investigated by means of high-resolution Doppler-spectroscopy. The effects of external device parameters and ion mass as well as the radial profiles have been studied. A simple model, based on the conservation of the total angular momentum, explains the main empirically determined dependences of the average angular velocity. The results are compared with the common multifluid description developed for hollow cathode discharges.

Vertical winds: a tutorial

Vertical winds in the thermosphere exist at far greater speeds than expected from a first-principles modelling approach. Early observations by ground-based high resolution Doppler spectroscopy and tracking of vapor trails indentified the phenomenon but there was little understanding of how the thermosphere could be stably stratified and yet sustain upward and downward winds of up to 100 m s−1. It is clear that such strong vertical motions must have important dynamic and thermodynamic coupling effects as well as inevitable disruption of diffusive equilibrium. Up to the present, little has been done to study such activity in thermospheric models. More recent observations show that regions of large vertical winds tend to be restricted in time and space and some can be qualitatively understood in terms of adjacent upward and downward moving air columns driven directly by localized heating or indirectly by gravity waves emanating from some distant disturbance. The horizontal scale of these motions is thought to be tens to a few hundred kilometers and the time scale tens of minutes to a few hours. They are not well represented in global-scale models because they are small compared to the grid size. Some attempts have been made to describe vertical winds in local and in nested-grid models. However, a full description of the nature of vertical winds and their comprehensive and self-consistent inclusion in thermospheric models remains to be done.

Vector correlations in the photofragmentation of HN3

Hydrazoic acid was excited to its lowest electronic excited state à 1A″ and the fragments were analyzed by high resolution Doppler spectroscopy. The NH fragment is rotationally cold, while N2 is strongly internally excited fint(N2)=0.48. The Λ doublets are populated statistically. The alignment of NH rotation vs the transition dipole moment of the parent is low (βμJ≤0.14). The vector correlation between the translational (vNH) and rotational (JNH) motion of the NH fragments is positive and increases with increasing JNH, indicating a preferential parallel alignment of vNH and JNH(βvJ≂0.40). The observed correlation between the transition dipole moment of the parent and the NH(1Δ) recoil velocity is negative at low NH rotations [βμv(JNH=2)=−0.4] and increases to positive values with increasing JNH. The HN3 distorts from a nonplanar configuration after excitation of a linear-bent electronic transition in the NNN framework, resulting in a strong N2 rotation and relatively weak NH rotation. The upper potential surface must be dependent on the torsional angle of the NN–NH system.

Joint product state distribution of coincidently generated photofragment pairs

The joint product state distribution of coincident fragment pairs formed in the same elementary photodissociation process has been determined. This correlation between quantum state populations of two molecular products has been measured by high resolution Doppler spectroscopy in conjunction with level-specific detection of the ejected photofragments. One product molecule, formed in a specific quantum state, is excited by laser induced fluorescence and the wing of the corresponding Doppler profile is analyzed to determine the product state distribution of the partner fragment. In the photodissociation of jet-cooled hydrogen peroxide at 193 nm two OH partner radicals are formed with comparable angular momenta. For a specific rotation of one hydroxyl radical the product state distribution of the partner fragment is centered at about the same rotation with a width of only a few rotational quanta. The orbital angular momentum is of the order of 1 ℏ and the impact parameter is extremely small. Experimentally observed joint product state distribution and trajectory calculations on ab initio potential energy surfaces are in excellent agreement.

Photofragment energy distribution and rotational anisotropy from excitation of HN 3 at 266 nm

The photodissociation dynamics of hydrazoic acid at 266 nm has been analyzed by high-resolution Doppler spectroscopy. The NH fragment carries most of the available energy as translation, f T(NH) = 0.32, and only 3% as rotation; N 2 is mainly internally excited, f int(N 2) = 0.48 with fairly low translational motion, f T(N 2) = 0.17. The rotational distribution is Gaussian-like, peaking at J NH≈5–6. Previously published rotational state distributions are perturbed by rotational relaxation. The Λ doublets are populated statistically. The alignment of NH rotation versus the transition dipole moment of the parent is low ( A 0 (2) ⩽ 0.19). The vector correlation between the translational (ν NH) and rotational ( J NH) motion of the NH fragment is positive, indicating a preferential parallel alignment of ν NH and J NH.