Strength Of Absorption Features Research Articles

Earth as an Exoplanet. II. Earth’s Time-variable Thermal Emission and Its Atmospheric Seasonality of Bioindicators

We assess the dependence of Earth’s disk-integrated mid-infrared thermal emission spectrum on observation geometries and investigate which and how spectral features are impacted by seasonality on Earth. We compiled an exclusive data set containing 2690 disk-integrated thermal emission spectra for four different full-disk observing geometries (North and South Pole-centered and Africa and Pacific-centered equatorial views) over four consecutive years. The spectra were derived from 2378 spectral channels in the wavelength range from 3.75–15.4 μm (nominal resolution ≈1200) and were recorded by the Atmospheric Infrared Sounder on board the Aqua satellite. We learned that there is significant seasonal variability in Earth’s thermal emission spectrum, and the strength of spectral features of bioindicators, such as N2O, CH4, O3, and CO2 depends strongly on both season and viewing geometry. In addition, we found a strong spectral degeneracy with respect to the latter two indicating that multi-epoch measurements and time-dependent signals may be required in order to fully characterize planetary environments. Even for Earth and especially for equatorial views, the variations in flux and strength of absorption features in the disk-integrated data are small and typically ≤ 10%. Disentangling these variations from the noise in future exoplanet observations will be a challenge. However, irrespectively of when the planet will be measured (i.e., day or night or season) the results from mid-infrared observations will remain the same to the zeroth order, which is an advantage over reflected light observations.

Longitudinal Variation of H2O Ice Absorption on Miranda

Many tidally locked icy satellites in the outer solar system show leading/trailing hemispherical asymmetries in the strength of near-infrared (NIR) H2O ice absorption bands, in which the absorption bands are stronger on the leading hemisphere. This is often attributed to a combination of magnetospheric irradiation effects and impact gardening, which can modify grain size, expose fresh ice, and produce dark contaminating compounds that reduce the strength of absorption features. Previous research identified this leading/trailing asymmetry on the four largest classical Uranian satellites but did not find a clear leading/trailing asymmetry on Miranda, the smallest and innermost classical moon. We undertook an extensive observational campaign to investigate variations of the NIR spectral signature of H2O ice with longitude on Miranda’s northern hemisphere. We acquired 22 new spectra with the TripleSpec spectrograph on the ARC 3.5 m telescope and four new spectra with GNIRS on Gemini North. Our analysis also includes three unpublished and seven previously published spectra taken with SpeX on the 3 m IRTF. We confirm that Miranda has no substantial leading/trailing hemispherical asymmetry in the strength of its H2O ice absorption features. We additionally find evidence for an anti-Uranus/sub-Uranus asymmetry in the strength of the 1.5 μm H2O ice band that is not seen on the other Uranian satellites, suggesting that additional endogenic or exogenic processes influence the longitudinal distribution of H2O ice band strengths on Miranda.

Challenges to Constraining Exoplanet Masses via Transmission Spectroscopy

Abstract MassSpec, a method for determining the mass of a transiting exoplanet from its transmission spectrum alone, was proposed by de Wit & Seager. The premise of this method relies on the planet’s surface gravity being extracted from the transmission spectrum via its effect on the atmospheric scale height, which in turn determines the strength of absorption features. Here, we further explore the applicability of MassSpec to low-mass exoplanets—specifically those in the super-Earth size range for which radial velocity determinations of the planetary mass can be extremely challenging and resource intensive. Determining the masses of these planets is of the utmost importance because their nature is otherwise highly unconstrained. Without knowledge of the mass, these planets could be rocky, icy, or gas-dominated. To investigate the effects of planetary mass on transmission spectra, we present simulated observations of super-Earths with atmospheres made up of mixtures of H2O and H2, both with and without clouds. We model their transmission spectra and run simulations of each planet as it would be observed with James Webb Space Telescope using the NIRISS, NIRSpec, and MIRI instruments. We find that significant degeneracies exist between transmission spectra of planets with different masses and compositions, making it impossible to unambiguously determine the planet’s mass in many cases.

RADIAL TRENDS IN IMF-SENSITIVE ABSORPTION FEATURES IN TWO EARLY-TYPE GALAXIES: EVIDENCE FOR ABUNDANCE-DRIVEN GRADIENTS

ABSTRACT Samples of early-type galaxies show a correlation between stellar velocity dispersion and the stellar initial mass function (IMF) as inferred from gravity-sensitive absorption lines in the galaxies’ central regions. To search for spatial variations in the IMF, we have observed two early-type galaxies with Keck/LRIS and measured radial gradients in the strengths of absorption features from 4000–5500 Å and 8000–10000 Å. We present spatially resolved measurements of the dwarf-sensitive spectral indices Na I (8190 Å) and Wing-Ford FeH (9915 Å), as well as indices for species of H, C2, CN, Mg, Ca, TiO , and Fe. Our measurements show a metallicity gradient in both objects, and Mg/Fe consistent with a shallow gradient in α-enhancement, matching widely observed trends for massive early-type galaxies. The Na I index and the CN1 index at 4160 Å exhibit significantly steeper gradients, with a break at r ∼ 0.1 r eff ( r ∼ 300 pc). Inside this radius, Na I strength increases sharply toward the galaxy center, consistent with a rapid central rise in [Na/Fe]. In contrast, the ratio of the FeH to Fe index strength decreases toward the galaxy center. This behavior cannot be reproduced by a steepening IMF inside of 0.1 r eff if the IMF is a single power law. While gradients in the mass function above ∼ 0.4 M ⊙ may occur, exceptional care is required to disentangle these IMF variations from the extreme variations in individual element abundances near the galaxies’ centers.

EARLY OBSERVATIONS AND ANALYSIS OF THE TYPE Ia SN 2014J IN M82

We present optical and near infrared (NIR) observations of the nearby Type Ia SN 2014J. Seventeen optical and twenty-three NIR spectra were obtained from 10 days before ($-$10d) to 10 days after (+10d) the time of maximum $B$-band brightness. The relative strengths of absorption features and their patterns of development can be compared at one day intervals throughout most of this period. Carbon is not detected in the optical spectra, but we identify CI $\lambda$ 1.0693 in the NIR spectra. We find that MgII lines with high oscillator strengths have higher initial velocities than other MgII lines. We show that the velocity differences can be explained by differences in optical depths due to oscillator strengths. The spectra of SN 2014J show it is a normal SN Ia, but many parameters are near the boundaries between normal and high-velocity subclasses. The velocities for OI, MgII, SiII, SII, CaII and FeII suggest that SN 2014J has a layered structure with little or no mixing. That result is consistent with the delayed detonation explosion models. We also report photometric observations, obtained from $-$10d to +29d, in the $UBVRIJH$ and $K_s$ bands. SN 2014J is about 3 magnitudes fainter than a normal SN Ia at the distance of M82, which we attribute to extinction in the host. The template fitting package SNooPy is used to interpret the light curves and to derive photometric parameters. Using $R_V$ = 1.46, which is consistent with previous studies, SNooPy finds that $A_V = 1.80$ for $E(B-V)_{host}=1.23 \pm 0.01$ mag. The maximum $B$-band brightness of $-19.19 \pm 0.10$ mag was reached on February 1.74 UT $ \pm 0.13$ days and the supernova had a decline parameter of $\Delta m_{15}=1.11 \pm 0.02$ mag.

GALAXIES M32 AND NGC 5102 CONFIRM A NEAR-INFRARED SPECTROSCOPIC CHRONOMETER

We present near infrared (NIR) IRTF/SpeX spectra of the intermediate-age galaxy M32 and the post-starburst galaxy NGC 5102. We show that features from thermally-pulsing asymptotic giant branch (TP-AGB) and main sequence turn-off (MSTO) stars yield similar ages to those derived from optical spectra. The TP-AGB can dominate the NIR flux of a coeval stellar population between ~0.1 and ~2 Gyr, and the strong features of (especially C-rich) TP-AGB stars are useful chronometers in integrated light studies. Likewise, the Paschen series in MSTO stars is stongly dependent on age and is an indicator of a young stellar component in integrated spectra. We define four NIR spectroscopic indices to measure the strength of absorption features from both C-rich TP-AGB stars and hydrogen features in main sequence stars, in a preliminary effort to construct a robust chronometer that probes the contributions from stars in different evolutionary phases. By comparing the values of the indices measured in M32 and NGC 5102 to those in the Maraston (2005) stellar population synthesis models for various ages and metallicities, we show that model predictions for the ages of the nuclei of M32 and NGC 5102 agree with previous results obtained from integrated optical spectroscopy and CMD analysis of the giant branches. The indices discriminate between an intermediate age population of ~3-4 Gyr, a younger population of <1 Gyr, and can also detect the signatures of very young (<100 Myr) populations.

Field-based remote-sensing for experimental intertidal ecology: Case studies using hyperspatial and hyperspectral data for New South Wales (Australia)

Many ecological processes in intertidal areas act at very small (mm to cm) spatial scales so manipulative ecological experiments are done at scales at which these processes are proposed to occur. Remote-sensing using field-based sensors enable ecologists to capture variability that must be measured to test hypotheses about small-scale processes. We present two case studies where remote-sensing from field-based platforms has been used to acquire data for manipulative ecological experiments in intertidal areas. The first study, from a rock platform, investigates the spatial scales of variability in chlorophyll (as an index of algal biomass) in experimental plots prior to and after the removal of encrusting macro-algae. Digital colour-infrared (CIR) imagery of the rock platform was obtained before the removal of the encrusting macro-algae and on 1, 44, 75, 117 and 160 days after removal. Amount of chlorophyll was derived from the CIR data using a simple ratio of reflectances at near-infrared (NIR) and red wavelengths. Block Mean Square (BMS) analysis showed that there was little variability in amounts of chlorophyll at very small (≤ 2.26 cm 2) scales, prior to and after removal of encrusting macro-algae. The greatest variability occurred at the largest block-size analysed (36.19 cm 2). This identifies the spatial scale at which micro-algal food resources are variably scattered on the shore. Results discriminate variability at about 60–80 mm distances. Distributions of micro-algae are caused by a complicated interplay of scale-dependent ecological processes, including grazing. These findings provide a basis for the design of manipulative experiments at appropriate scales to unravel these processes. The second study used field reflectance spectra (350–1050 nm) to: i) determine whether the amount of algae in soft sediments could be changed by manipulating the amounts of light reaching the sediment surface and ii) test the hypothesis that the strength of in vivo absorption features, as indices of the amount of chlorophyll and other pigments, was correlated with measures of sediment-stability (erosion threshold and erosion rate). Several different measures of the strength of absorption features were investigated to determine the best predictor of stability of the sediment. Reflectance spectra showed that amounts of algae had been successfully manipulated. Derivative reflectance at individual wavelengths, indicative of absorption by chlorophyll- a and chlorophyll- c, were the best predictors of sediment-stability. These case studies demonstrate some novel uses of field-based remote-sensing to provide information at the spatial scales relevant to many intertidal ecologists. Such techniques should have an increasingly important role in ecological field experimentation where non-destructive sampling of photosynthetic pigments is desired.

X-ray Spectroscopy of Thermally Emitting Neutron Stars

I describe recent high-resolution X-ray spectroscopy of surface emission from nearby, thermally emitting neutron stars. I focus on RX J0720.4−3125, RX J1308.6+2127 and RX J1605.3+3249, all of which have similar temperature, but differ in the presence and strength of absorption features in their spectrA. I discuss possible causes for the absorption we see in two sources, and conclude that it may be proton cyclotron line absorption, but weakened due to the strong-field quantum electrodynamics effect of vacuum resonance mode conversion.

Strengths of absorption features in vibration-rotational band v=6← v=0 of 14N 16O X 2Πr in the near infrared region

The strengths or integrated absorption intensities of individual features in band v=6← v=0 of gaseous 14N 16O X 2 Π r are measured at (297.35 ± 0.4) K with spectral resolution 6 m −1. For unresolved features near band heads in R branches, partition of total intensity enables estimates for each transition, apart from spin-rotation doubling and hyperfine effects. As a sum of these strengths of lines, the strength of the entire band centred near 1 083 606 m −1, including sub-bands for both 2 Π 1/2 and 2 Π 3/2, is (5.63±0.28)×10 −27 m. We compare measured strengths with those calculated from deduced values of transition moment for electric dipolar moment and Herman–Wallis coefficient.

Evidence for a Sizable Age Spread among Galaxies from the UV Upturn Phenomenon in Early-Type Systems

The suggestion of Lee (1994, ApJ, 430, L113) that the age spread among galaxies is responsible for the systematic variation of ultraviolet (UV) upturn among the early-type systems is confirmed here with the detailed population synthesis models. Our models suggest that the far-UV spectra of these systems are composite of hot metal-poor horizontal-branch (HB) stars (and their post-HB progeny) and metal-rich post-asymptotic giant-branch (PAGB) stars. The systematic variation of UV upturn, however, depends on the contribution from hot metal-poor HB stars and their progeny, which in turn depends on the ages of oldest stellar populations in galaxies. Consequently, our models predict that the strength of absorption features, such as C IV and Si IV, is anticorrelated with the strength of UV upturn. This is consistent with the far-UV spectra for NGC1399 and M31 obtained by the Hopkins Ultraviolet Telescope aboard the Astro-1 space shuttle mission. We note that the opposite trend is expected in other's models that favor metal-rich solution for the UV upturn phenomenon without age spread among galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. With the assumption that the UV upturn phenomenon is solely due to the age variations among galaxies, we tentatively estimate the difference in age between the giant ellipticals and our Galaxy to be 4 billion years or more. This suggests that the best estimate for the lower limit of the age of the Universe is close to 20 Gyrs, which of course would be in conflict with the current estimate of the Ho together with the standard cosmological models with zero cosmological constant. The reader is referred to Park &amp; Lee (1995, ApJL, in press) for details of this work.

QUANTITATIVE SPECTRAL TYPES FOR 19 ALGOL SECONDARIES

ABSTRACT Time-resolved spectra of 19 short-period Algol-type binary star systems obtained during total eclipse used to derive the temperature spectral class of the mass-losing secondary component. The spectral classifications employed a quantitative comparison of the strengths of absorption features in stars of known spectral class with those of the program stars. The luminosity spectral class cannot be determined from these data, so both main sequence and giant stars were used for the comparison. Our spectral types are compared with published types and found to be generally in good agreement, unless the published types are derived from the light curves. The photometrically-detemrined types are systematically later than our directly-determined types. This effect is shown to also exist in catalogs of Algol parameters.

Strength of mineral absorption features in the transmitted component of near‐infrared reflected light: First results from RELAB

Bidirectional reflectance measurements are the only type of reflectance data available to the remote observer. For compositional interpretations, data are desired not only for identification of possible mineral components but also for modal abundance. The latter requires detailed information about the strength of absorption features. Using a new laboratory facility, the RELAB, laboratory data in the near infrared are presented that document effects of particle size, mineral mixtures, and viewing geometry for selected materials with well‐developed absorption bands. The commonly observed increase in reflectance with decrease in particle size is also observed for absorption bands as well as a related decrease in absorption strength. For small particles in parts of the spectrum of maximum reflectance, however, a minor decrease in reflectance with a decrease in particle size is sometimes observed. Small particles dominate the observed characteristics of particulate surfaces, which contain a range of particle sizes. The mean optical path length (transmission through particles) of reflected radiation measured for a variety of particle sizes has an apparent upper limit of about 2 mm for particles &lt;250 μm. The typical number of particles involved in the optical path is less than 50.

Frost grain size metamorphism: Implications for remote sensing of planetary surfaces

The effective grain size of a material on a planetary surface affects the strength of absorption features observed in the reflectance of a particulate surface. In the case of a planetary surface containing volatile ices, the absorption characteristics can change in connection with processes leading to a change in the grain size of the material. The present investigation is concerned with an evaluation regarding the occurrence of such processes and the implications for remote sensing applications. It is found that quantitative modeling of the kinetics of grain growth and destruction by thermal and nonthermal processes can provide a means to reconcile apparent optical paths in the volatile portions of planetary surfaces with the physical history of those surfaces. Attention is also given to conditions in the case of the Pluto/Triton system, Uranus and Saturnian satellites, and the Galilean system.

Radial Variations in the Strengths of Absorption Features in the Spectra of Two Early-Type Galaxies

view Abstract Citations (20) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radial Variations in the Strengths of Absorption Features in the Spectra of Two Early-Type Galaxies Welch, Gary A. ; Forrester, William T. Abstract A spectrophotometric study based on image-tube spectrograms has been conducted of selected absorption features in the galaxies NGC 3115 (E7/SO) and NGC 4472 (E2). Significant radial variation-in the sense of decreasing strength with distance occurs in the violet cyanogen bands at X3883 and X42l6, the C band, the Mg i$MgH blend at XS175, and the "D" line of neutral sodium at X5892. A qualitatively consistent interpretation is that the relative abundance of metallic elements and of late dwarf stars is high in the nuclei of these galaxies. In relation to the size of the system the strengths decline much more rapidly in NGC 4472 which may reflect a difference in the stellar velocity distributions within the galaxies. Publication: The Astronomical Journal Pub Date: June 1972 DOI: 10.1086/111288 Bibcode: 1972AJ.....77..333W full text sources ADS | data products NED (2)

The composition of planetary atmospheres

The present status of research on the composition of planetary atmospheres is reviewed. It is shown that CO 2 is the major constituent in the atmospheres of Venus and Mars, and that H 2 is almost certainly the dominant constituent for the outer planets Jupiter, Saturn, Uranus, and Neptune. Ground based i.r. spectroscopy is the largest single source of information on atmospheric composition and much of the paper is concerned with difficulties involved in the interpretation of i.r. spectra. The mechanisms for line formation are examined carefully and it is concluded that multiple scattering by cloud materials must play a dominant role for Jupiter, Saturn, and Venus. There is no evidence for visible cloud layers on either Uranus or Neptune. Both planets, however, exhibit deep molecular atmospheres and Rayleigh scattering will affect the strength of absorption features. Considerable attention is given to the techniques available for the line formation problem in a scattering medium, and the usefulness of similarity relations is emphasized. The dependence of equivalent width on abundance and pressure is obscure for a scattering atmosphere. The principal characteristics of the scattering curve of growth are reviewed from an intuitive rather than mathematical viewpoint.