High Spectral Resolution Spectra Research Articles

X‐exoplanets coronal models and planet photoevaporation

AbstractHigh‐energy emission photons in the X‐ray and EUV bands ionize H and other atoms, posing a threat to the stability of the atmospheres of short‐period exoplanets orbiting late‐type stars. Effects such as planet atmospheric evaporation are being attributed in the last years to XUV stellar irradiation on the planets. Early theoretical works tried to model how the XUV emission would affect the planetary atmospheres, mainly by using the solar emission as a template. In X‐exoplanets, we reported for the first time coronal models based on actual data from the exoplanet host stars. The use of coronal models allows us to model the SED of the XUV emission of these stars, otherwise inaccessible to current telescopes. In this manuscript, I present the use of these models with datasets of different data quality, depending on the availability of low or high spectral resolution spectra in both X‐rays and UV. Comparison with actual data is shown for the exoplanet host star Proxima Cen and the Sun. The challenges for the future use of coronal models in exoplanet atmospheres are discussed, involving mainly the use of new EUV and X‐ray spectrographs, better atomic models, and more accurate planet atmosphere evolution models.

Area-ratio Fraunhofer line depth (aFLD) method approach to estimate solar-induced chlorophyll fluorescence in low spectral resolution spectra in a cool-temperate deciduous broadleaf forest.

Solar-induced chlorophyll fluorescence (SIF) emissions were estimated by the "area-ratio Fraunhofer line depth (aFLD) method", a new retrieval methodology in spectra from a low spectral resolution (SR) spectroradiometer (MS-700: full width half maximum (FWHM) of 10nm and spectral sampling interval of 3.3nm), assisted with a scaling to reference SIF detected from high SR spectrum. The sparse pixels of a spectrum of low SR misses detecting the minimum of the O2A absorption band around at 760nm, which makes the SIF detection by conventional FLD methods lose accuracy considerably. To overcome this, the aFLD method uses the definite integral of spectra over a wide interval between 750 and 780nm. The integration of the spectrum is insusceptible to the change in shape of the depression curve, leading to higher accuracy of the aFLD method. Daily SIF, calculated by the aFLD method using the spectra obtained with MS-700, was scaled to reference daily SIF calculated by the spectral fitting method using the spectra obtained from August to December 2019 with an ultrafine SR spectroradiometer (QE Pro, FWHM = 0.24nm). As a result, SIF calculated from MS-700 spectra by aFLD method was strongly correlated with the reference SIF from QE Pro spectra (r2 = 0.81) and was successfully scaled. Then, the scaled 11-year SIF from MS-700 at a deciduous broadleaf forest showed the correlation with GPP at multiple time steps: daily, monthly, and yearly, consistently during 2008-2018. The comparison of aFLD-derived SIF with the global Orbiting Carbon Observatory-2 (OCO-2) SIF data set (GOSIF) showed high correlation on monthly values during 2008-2017 (r2 = 0.85). The combining approach of the aFLD method with a scaling to reference SIF successfully detected long-term canopy SIF emissions, which has great potential to provide essential information on ecosystem-level photosynthesis.

Discriminating between hazy and clear hot-Jupiter atmospheres with CARMENES

Context. Relatively large radii of some hot Jupiters observed in the ultraviolet and blue-optical are generally interpreted to be due to Rayleigh scattering by high-altitude haze particles. However, the haze composition and its production mechanisms are not fully understood, and observational information is still limited. Aims. We aim to study the presence of hazes in the atmospheres of HD 209458 b and HD 189733 b with high spectral resolution spectra by analysing the strength of water vapour cross-correlation signals across the red optical and near-infrared wavelength ranges. Methods. A total of seven transits of the two planets were observed with the CARMENES spectrograph at the 3.5 m Calar Alto telescope. Their Doppler-shifted signals were disentangled from the telluric and stellar contributions using the detrending algorithm SYSREM. The residual spectra were subsequently cross-correlated with water vapour templates at 0.70–0.96 μm to measure the strength of the water vapour absorption bands. Results. The optical water vapour bands were detected at 5.2σ in HD 209458 b in one transit, whereas no evidence of them was found in four transits of HD 189733 b. Therefore, the relative strength of the optical water bands compared to those in the near-infrared were found to be larger in HD 209458 b than in HD 189733 b. Conclusions. We interpret the non-detection of optical water bands in the transmission spectra of HD 189733 b, compared to the detection in HD 209458 b, to be due to the presence of high-altitude hazes in the former planet, which are largely absent in the latter. This is consistent with previous measurements with the Hubble Space Telescope. We show that currently available CARMENES observations of hot Jupiters can be used to investigate the presence of haze extinction in their atmospheres.

Stability Assessment of OCO-2 Radiometric Calibration Using Aqua MODIS as a Reference

With three imaging grating spectrometers, the Orbiting Carbon Observatory-2 (OCO-2) measures high spectral resolution spectra ( λ / Δ λ ≈ 19,000) of reflected solar radiation within the molecular oxygen (O 2 ) A-band at 0.765 μ m and two carbon dioxide (CO 2 ) bands at 1.61 and 2.06 μ m. OCO-2 uses onboard lamps with a reflective diffuser, solar observations through a transmissive diffuser, lunar measurements, and surface targets for radiometric calibration and validation. Separating calibrator aging from instrument degradation poses a challenge to OCO-2. Here we present a methodology for trending the OCO-2 Build 8R radiometric calibration using OCO-2 nadir observations over eight desert sites and nearly simultaneous observations from Moderate Resolution Imaging Spectroradiometer (MODIS) with sensor viewing zenith angles of 15 ± 0.5 ∘ . For the O 2 A-band, this methodology is able to quantify a drift of −0.8 ± 0.1% per year and capture a small error in correcting the aging of the solar calibrator. For the other two OCO-2 bands, no measurable changes were seen, indicating less than 0.1% and less than 0.3% per year drift in the radiometric calibration of Band 2 and Band 3, respectively.

Observational estimate of the partial covering probability of quasar emission regions by distant H2 absorption clouds

ABSTRACT We have searched high spectral resolution spectra of quasars known to exhibit high redshift (z > 1.7) intervening H2-bearing damped Lyman-α (DLA) systems for partial coverage of the quasar emission by intervening H2 clouds. Partial coverage manifests itself by the presence of non-zero residual flux in the core of saturated H2 absorption lines. The residual flux can be observed either only at the bottom of absorption lines redshifted on top of quasar emission lines, in which case part of the broad line region (BLR) is not covered, or in all absorption lines, in case some continuum source is not covered. Among 35 H2 absorption clouds in 14 quasar spectra obtained with the VLT-UVES or Keck-HIRES spectrographs, we detect partial coverage of the BLR for 13 clouds. This result suggests that the probability of partial coverage of the QSO BLR by a distant H2 absorption cloud is about 40 per cent. For four systems towards Q 0013−0029, Q 0405−4418, Q 0812+3208, and J 2100−0641, partial coverage is detected for the first time. We determine the theoretical probability of partial coverage of the BLR by a distant H2 cloud as a function of the ratio between the cloud and the BLR sizes. Using this model, we obtain an estimate of the characteristic BLR radius of $50^{+19}_{-23}\,\rm{light \,days}$. This is similar to the estimate of the BLR size obtained by reverberation-mapping analysis $({\sim}100\,\rm{light\, days})$.

The Mean Magnetic Field Strength of CI Tau

Abstract We present a blind comparison of two methods to measure the mean surface magnetic field strength of the classical T Tauri star CI Tau based on Zeeman broadening of sensitive spectral lines. Our approach takes advantage of the greater Zeeman broadening at near-infrared compared to optical wavelengths. We analyze a high signal-to-noise, high spectral resolution spectrum from 1.5 to 2.5 μm observed with IGRINS (Immersion GRating INfrared Spectrometer) on the Discovery Channel Telescope. Both stellar parameterization with MoogStokes (which assumes a uniform magnetic field) and modeling with SYNTHMAG (which includes a distribution of magnetic field strengths) yield consistent measurements for the mean magnetic field strength of CI Tau is B of ∼2.2 kG. This value is typical compared with measurements for other young T Tauri stars and provides an important contribution to the existing sample given that it is the only known developed planetary system hosted by a young classical T Tauri star. Moreover, we potentially identify an interesting and suggestive trend when plotting the effective temperature and the mean magnetic field strength of T Tauri stars. While a larger sample is needed for confirmation, this trend only appears for a subset of the sample, which may have implications regarding the magnetic field generation.

The Structure of the Orion Nebula in the Direction of θ1 Ori C

Abstract We have used existing optical emission and absorption lines, [C ii] emission lines, and H i absorption lines to create a new model for a central column of material near the Trapezium region of the Orion Nebula. This was necessary because recent high spectral resolution spectra of optical emission lines and imaging spectra in the [C ii] 158 μm line have shown that there are new velocity systems associated with the foreground Veil and the material lying between θ 1 Ori C and the main ionization front of the nebula. When a family of models generated with the spectral synthesis code Cloudy were compared with the surface brightness of the emission lines and strengths of the Veil absorption lines seen in the Trapezium stars, distances from θ 1 Ori C were derived, with the closest, highest ionization layer being 1.3 pc. The line-of-sight distance of this layer is comparable with the size of the inner Huygens region in the plane of the sky. These layers are all blueshifted with respect to the Orion Nebula Cluster of stars, probably because of the pressure of a hot central bubble created by θ 1 Ori C's stellar wind. We find velocity components that are ascribed to both sides of this bubble. Our analysis shows that the foreground [C ii] 158 μm emission is part of a previously identified layer that forms a portion of a recently discovered expanding shell of material covering most of the larger Extended Orion Nebula.

Analysis of Two Dimensionality Reduction Techniques for Fast Simulation of the Spectral Radiances in the Hartley-Huggins Band

The new generation of atmospheric composition sensors such as TROPOMI is capable of providing spectra of high spatial and spectral resolution. To process this vast amount of spectral information, fast radiative transfer models (RTMs) are required. In this regard, we analyzed the efficiency of two acceleration techniques based on the principal component analysis (PCA) for simulating the Hartley-Huggins band spectra. In the first one, the PCA is used to map the data set of optical properties of the atmosphere to a lower-dimensional subspace, in which the correction function for an approximate but fast RTM is derived. The second technique is based on the dimensionality reduction of the data set of spectral radiances. Once the empirical orthogonal functions are found, the whole spectrum can be reconstructed by performing radiative transfer computations only for a specific subset of spectral points. We considered a clear-sky atmosphere where the optical properties are defined by Rayleigh scattering and trace gas absorption. Clouds can be integrated into the model as Lambertian reflectors. High computational performance is achieved by combining both techniques without losing accuracy. We found that for the Hartley-Huggins band, the combined use of these techniques yields an accuracy better than 0.05% while the speedup factor is about 20. This innovative combination of both PCA-based techniques can be applied in future works as an efficient approach for simulating the spectral radiances in other spectral regions.

Replay spoofing countermeasures using high spectro-temporal resolution features

The easy implementation of replay attacks by a fraudster poses a severe threat to automatic speaker verification (ASV) technology than the other spoofing attacks like speech synthesis and voice conversion. Replay attacks refer to an attack by a fraudster to get illegitimate access to an ASV system by playing back the speech sample collected from genuine target speaker. The significant cues that can differentiate between genuine and replay recordings are channel characteristics. To capture these characteristics, one need to extract features from the spectrum, which should have high spectral and temporal resolutions. Zero time windowing (ZTW) analysis of speech is one such time-frequency analysis technique, which results in high spectral and temporal resolution spectrum at each sampling instant. In this study, new features are proposed by applying cepstral analysis to ZTW spectrum. Experiments are performed on two publicly available replay attack databases namely BTAS 2016 and ASVspoof 2017. The first set of experiments are conducted using Gaussian mixture models to evaluate the potential of proposed features. Performance of the proposed system in terms of half total error rate is 0.75% and in terms of equal error rate is 14.75% on BTAS 2016 and ASVspoof 2017 evaluation sets respectively. A score level fusion is performed by using proposed features with previously proposed single frequency filtering cepstral coefficients. This fused result outperformed the previously reported best results on these two datasets.

High Spectral Resolution Spectroscopy of Sprites: A Natural Probe of the Mesosphere

AbstractWe present the first high spectral resolution (0.24 nm) spectra of sprites. These spectra were recorded in Europe in the summers and falls of 2015 and 2016 and during January 2017. The use of high spectral resolution has allowed us to resolve for the first time the internal (vibrorotational) structure of the sprite molecular N2 first positive system and to quantify the local gas (rotational) temperature of the mesosphere under the influence of sprites revealing that there is no measurable heating of the atmosphere associated to sprites at the altitudes explored. The temperatures of the explored region of the mesosphere range between 149 K ± 10 K and 226 K ± 20 K. The recorded spectroscopic data also provide valuable quantitative information on the concentrations of some of the vibrational levels of molecular nitrogen involved in transient red‐near‐infrared optical emissions from sprites. The regions of the transient luminous events recorded with our spectrograph (equipped with a horizontally oriented slit) correspond to altitudes in the 66 km to 74 km ± 5 km range.

Measurement of the lifetimes of vibrational states of DNA molecules in functionalized complexes of semiconductor quantum dots

Complexes of self-organized isolated semiconductor crystalline nc-Si/SiO2 quantum dots functionalized with short oligonucleotides are unique objects for revealing the manifestation of new quantum-size effects. It is shown that the observation of narrow spectral lines in micro-Raman scattering spectra of high spectral resolution makes it possible to determine the characteristic time scale of vibrational excitations of nucleotide molecules. The possibility of quantitative investigation into the structural-dynamic properties of fast vibrational processes in biomacromolecules is established.

High‐resolution X‐ray spectroscopy: The coming‐of‐age

Since the launch of Chandra and XMM‐Newton, high‐resolution X‐ray spectra of cosmic sources of all kinds have become available. These spectra have resulted in major scientific breakthroughs. However, because of the techniques used, in general, high‐quality spectra can be obtained only for the brightest few sources of each class. Moreover, except for the most compact extended sources, such as cool core clusters, grating spectra are limited to point sources. Hitomi made another major step forward, providing for the first time a high‐quality spectrum of an extended source and improved spectral sensitivity in the Fe‐K band. For point sources with the proposed Arcus mission, and for all sources with the launch of Athena, X‐ray spectroscopy will become mature. It will allow us to extend the investigations from the few handful of brightest sources of each category to a large number of sources far away in space and time, or to get high time resolution and high spectral resolution spectra of bright time‐variable sources.

Lines and continuum sky emission in the near infrared: observational constraints from deep high spectral resolution spectra with GIANO-TNG

Aims Determining the intensity of lines and continuum airglow emission in the H-band is important for the design of faint-object infrared spectrographs. Existing spectra at low/medium resolution cannot disentangle the true sky-continuum from instrumental effects (e.g. diffuse light in the wings of strong lines). We aim to obtain, for the first time, a high resolution infrared spectrum deep enough to set significant constraints on the continuum emission between the lines in the H-band. Methods During the second commissioning run of the GIANO high-resolution infrared spectrograph at La Palma Observatory, we pointed the instrument directly to the sky and obtained a deep spectrum that extends from 0.97 to 2.4 micron. Results The spectrum shows about 1500 emission lines, a factor of two more than in previous works. Of these, 80% are identified as OH transitions; half of these are from highly excited molecules (hot-OH component) that are not included in the OH airglow emission models normally used for astronomical applications. The other lines are attributable to O2 or unidentified. Several of the faint lines are in spectral regions that were previously believed to be free of line emission. The continuum in the H-band is marginally detected at a level of about 300 photons/m^2/s/arcsec^2/micron, equivalent to 20.1 AB-mag/arcsec^2. The observed spectrum and the list of observed sky-lines are published in electronic format. Conclusions Our measurements indicate that the sky continuum in the H-band could be even darker than previously believed. However, the myriad of airglow emission lines severely limits the spectral ranges where very low background can be effectively achieved with low/medium resolution spectrographs. We identify a few spectral bands that could still remain quite dark at the resolving power foreseen for VLT-MOONS (R ~6,600).

C II] absorption and emission in the diffuse interstellar medium across the Galactic plane

Ionized carbon is the main gas-phase reservoir of carbon in the neutral diffuse interstellar medium and its 158 micron fine structure transition [CII] is the most important cooling line of the diffuse interstellar medium (ISM). We combine [CII] absorption and emission spectroscopy to gain an improved understanding of physical conditions in the different phases of the ISM. We present high resolution [CII] spectra obtained with the Herschel/HIFI instrument towards bright dust continuum sources regions in the Galactic plane, probing simultaneously the diffuse gas along the line of sight and the background high-mass star forming regions. These data are complemented by observations of the 492 and 809 GHz fine structure lines of atomic carbon and by medium spectral resolution spectral maps of the fine structure lines of atomic oxygen at 63 and 145 microns with Herschel/PACS. We show that the presence of foreground absorption may completely cancel the emission from the background source in medium spectral resolution data and that high spectral resolution spectra are needed to interpret the [CII] and [OI] emission and the [CII]/FIR ratio. This phenomenon may explain part of the [CII]/FIR deficit seen in external luminous infrared galaxies. The C+ and C excitation in the diffuse gas is consistent with a median pressure of 5900 Kcm-3 for a mean TK ~100 K. The knowledge of the gas density allows us to determine the filling factor of the absorbing gas along the selected lines of sight: the median value is 2.4 %, in good agreement with the CNM properties. The mean excitation temperature is used to derive the average cooling due to C+ in the Galactic plane : 9.5 x 10^{-26} erg/s/H. Along the observed lines of sight, the gas phase carbon abundance does not exhibit a strong gradient as a function of Galacto-centric radius and has a weighted average of C/H = 1.5 +/- 0.4 x 10^{-4}.

Investigating the inner discs of Herbig Ae/Be stars with CO bandhead and Brγ emission★

Herbig Ae/Be stars lie in the mass range between low and high mass young stars, and therefore offer a unique opportunity to observe any changes in the formation processes that may occur across this boundary. This paper presents medium resolution VLT/X-Shooter spectra of six Herbig Ae/Be stars, drawn from a sample of 91 targets, and high resolution VLT/CRIRES spectra of five Herbig Ae/Be stars, chosen based on the presence of CO first overtone bandhead emission in their spectra. The X-Shooter survey reveals a low detection rate of CO first overtone emission (7 per cent), consisting of objects mainly of spectral type B. A positive correlation is found between the strength of the CO v=2-0 and Br {\gamma} emission lines, despite their intrinsic linewidths suggesting a separate kinematic origin. The high resolution CRIRES spectra are modelled, and are well fitted under the assumption that the emission originates from small scale Keplerian discs, interior to the dust sublimation radius, but outside the co-rotation radius of the central stars. In addition, our findings are in very good agreement for the one object where spatially resolved near-infrared interferometric studies have also been performed. These results suggest that the Herbig Ae/Be stars in question are in the process of gaining mass via disc accretion, and that modelling of high spectral resolution spectra is able to provide a reliable probe into the process of stellar accretion in young stars of intermediate to high masses.

Temperature stratification of the atmosphere of Arcturus

A brief overview of the results of the investigations of the red giant star Arcturus is given. One-dimensional LTE modeling of the atmospheres of Arcturus and the Sun as a star is carried out on the basis of synthesis of the extended wings of the H and K Ca II lines. It is found that the local continuum in this spectral region is underestimated by an average of 12% in the atlases of Arcturus. The average deficit in UV absorption amounts to 43% for Arcturus whereas it is 9% for the Sun. For Arcturus the correction factor to the continuum opacity at the wavelengths of 390.0, 392.5, 395.0, 398.0, and 400.0 nm equals 2.20, 1.90, 1.70, 1.55, and 1.45. The model atmosphere of Arcturus obtained from the best-fit of the wings of the H and K Ca II lines corresponds to the model atmosphere with the fundamental parameters T_eff = 4286 K, log g = 1.66, and [Fe/H]=-0.52 derived by Ramirez and Allende Prieto (2011). The temperature stratification of Arcturus' atmosphere is presented in tabular form. To obtain more accurate temperature stratification in the future, we need a high spectral resolution spectrum calibrated to absolute fluxes with high accuracy.

STUDIES OF NGC 6720 WITH CALIBRATED HST/WFC3 EMISSION-LINE FILTER IMAGES. I. STRUCTURE AND EVOLUTION* ,†

ABSTRACT We have performed a detailed analysis of the Ring Nebula (NGC 6720) using Hubble Space Telescope WFC3 images and derived a new three-dimensional model. Existing high spectral resolution spectra played an important supplementary role in our modeling. It is shown that the Main Ring of the nebula is an ionization-bounded irregular non-symmetric disk with a central cavity and perpendicular extended lobes pointed almost toward the observer. The faint outer halos are determined to be fossil radiation, i.e., radiation from gas ionized in an earlier stage of the nebula when it was not ionization bounded. The narrowband WFC3 filters that isolate some of the emission lines are affected by broadening on their short wavelength side and all the filters were calibrated using ground-based spectra. The filter calibration results are presented in an appendix.

Deuterium at high redshift

The detection of neutral deuterium in the low-metallicity damped Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported. Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04, as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming uniform metallicity throughout the system, our measurement translates to (D/H) = (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed to be broader than the OI absorption lines. From a consistent fit of the profiles we derive the turbulent broadening to be 5.2 km/s and the temperature of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.

IMAGING SPECTROMETER REMOTE SENSING METHODOLOGICAL TECHNOLOGY AND IT'S APPLICATION BASED ON SPECTROSCOPY

In 1980s early, remote sensing technique of imaging spectrometer began to be developed as a new remote sensing technique. Recently, this technique has developed very fast, and has become one of the three development trends of remote sensing technique (imaging spectrometer, microwave and 3S system). Because of these features of its high spectral resolution, hyperbands,and space image and spectra in one, developing the imaging spectrometer is not only able to more offectively and directly recognize the surface material of earth, but also it can more deeply research the component of making up material and it's structure. In this paper, the imaging spectrometer remote sensing technological development, the theoretical foundation, method and application are summarized.

THE ABUNDANCES OF POLYACETYLENES TOWARD CRL618

We present a mid-infrared high spectral resolution spectrum of CRL618 in the frequency ranges 778-784 and 1227-1249 cm^-1 (8.01-8.15 and 12.75-12.85 um) taken with the Texas Echelon-cross-Echelle Spectrograph (TEXES) and the Infrared Telescope Facility (IRTF). We have identified more than 170 ro-vibrational lines arising from C2H2, HCN, C4H2, and C6H2. We have found no unmistakable trace of C8H2. The line profiles display a complex structure suggesting the presence of polyacetylenes in several components of the circumstellar envelope (CSE). We derive total column densities of 2.5 10^17, 3.1 10^17, 2.1 10^17, 9.3 10^16 cm^-2, and < 5 10^16 cm^-2 for HCN, C2H2, C4H2, C6H2, and C8H2, respectively. The observations indicate that both the rotational and vibrational temperatures in the innermost CSE depend on the molecule, varying from 100 to 350 K for the rotational temperatures and 100 to 500 K for the vibrational temperatures. Our results support a chemistry in the innermost CSE based on radical-neutral reactions triggered by the intense UV radiation field.