Variety Of Spectral Features Research Articles

SPIDER VIII – constraints on the stellar initial mass function of early-type galaxies from a variety of spectral features

We perform a spectroscopic study to constrain the stellar Initial Mass Function (IMF) by using a large sample of 24,781 early-type galaxies from the SDSS-based SPIDER survey. Clear evidence is found of a trend between IMF and central velocity dispersion, sigma0, evolving from a standard Kroupa/Chabrier IMF at 100km/s towards a more bottom-heavy IMF with increasing sigma0, becoming steeper than the Salpeter function at sigma0>220km/s. We analyze a variety of spectral indices, corrected to solar scale by means of semi-empirical correlations, and fitted simultaneously with extended MILES (MIUSCAT) stellar population models. Our analysis suggests that sigma0, rather than [alpha/Fe], drives the IMF variation. Although our analysis cannot discriminate between a single power-law (unimodal) and a low-mass (<0.5MSun) tapered (bimodal) IMF, we can robustly constrain the fraction in low-mass stars at birth, that is found to increase from 20% at sigma0~100km/s, up to 80% at sigma0~300km/s. Additional constraints can be provided with stellar mass-to-light (M/L) ratios: unimodal models predict M/L significantly larger than dynamical M/L, across the whole sigma0 range, whereas a bimodal IMF is compatible. Our results are robust against individual abundance variations. No significant variation is found in Na and Ca in addition to the expected change from the correlation between [alpha/Fe] and sigma0. [Abridged]

Principal component analysis and radiative transfer modelling ofSpitzerInfrared Spectrograph spectra of ultraluminous infrared galaxies

The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain a variety of spectral features that can be used as diagnostics to characterise the spectra. However, such diagnostics are biased by our prior prejudices on the origin of the features. Moreover, by using only part of the spectrum they do not utilise the full information content of the spectra. Blind statistical techniques such as principal component analysis (PCA) consider the whole spectrum, find correlated features and separate them out into distinct components. We further investigate the principal components (PCs) of ULIRGs derived in Wang et al.(2011). We quantitatively show that five PCs is optimal for describing the IRS spectra. These five components (PC1-PC5) and the mean spectrum provide a template basis set that reproduces spectra of all z<0.35 ULIRGs within the noise. For comparison, the spectra are also modelled with a combination of radiative transfer models of both starbursts and the dusty torus surrounding active galactic nuclei. The five PCs typically provide better fits than the models. We argue that the radiative transfer models require a colder dust component and have difficulty in modelling strong PAH features. Aided by the models we also interpret the physical processes that the principal components represent. The third principal component is shown to indicate the nature of the dominant power source, while PC1 is related to the inclination of the AGN torus. Finally, we use the 5 PCs to define a new classification scheme using 5D Gaussian mixtures modelling and trained on widely used optical classifications. The five PCs, average spectra for the four classifications and the code to classify objects are made available at: http://www.phys.susx.ac.uk/~pdh21/PCA/

SALT2: using distant supernovae to improve the use of type Ia supernovae as distance indicators

We present an empirical model of Type Ia supernovae spectro-photometric evolution with time. The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of Type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range 2500-8000 A with calculable uncertainties, including those arising from variability of spectral features. Thanks to the use of high-redshift SNe to model the rest-frame UV spectral energy distribution, we are able to derive improved distance estimates for SNe Ia in the redshift range 0.8<z<1.1. The model can also be used to improve spectroscopic identification algorithms, and derive photometric redshifts of distant Type Ia supernovae.

Burst‐To‐Burst Variability In Spectral Activity Underlying Diaphragm Electromyogram (EMG) Bursts In Anesthetized C57BL/6 Mice In Vivo

Previous work from our laboratory using time-frequency spectral analysis has suggested that the spectral characteristics of inspiratory motor output in mice are highly dynamic. In that work, burst-to-burst variability analysis was performed on 10-s segments of diaphragm EMG activity recorded from urethane-anesthetized adult C57BL/6 mice. Although short-term burst-to-burst variability was reported, the extent of long-term burst-to-burst variability in this model requires clarification. Here, we characterize the burst-to-burst variability of temporal and spectral features for basal diaphragm EMG bursts recorded from 6 mice using Poincaré plot analysis of breath n vs. n+1 on 5-min time segments, which contain ~750-1245 bursts. Analyses on temporal parameters (i.e., TI, TE, burst frequency, area) show a high degree of correlation between adjacent bursts, suggesting a small degree of both short- and long-term burst-to-burst variability. For spectral characteristics, power of medium frequency oscillations (MFO) appeared to be more deterministic than that seen in the high (HFO) or upper-high (UHFO) ranges, with low power MFO peaks being followed primarily by other low power MFO peaks. In contrast, power for the HFO and UHFO peaks were widely dispersed, indicating aperiodic behavior. Interestingly, however, there were some HFO peaks exhibiting low power that seemed to predict subsequent low power HFO peaks. These data are among the first to quantify short-term and long-term burst-to-burst variability of spectral features using mathematical fits to Poincaré plots, and demonstrate new insight into dynamic variability in the fast oscillatory rhythms inherent in inspiratory motor discharges. Supported by NS045321

Surface composition of TNOs and Centaurs: visible and near-infrared spectroscopy

Visible and near-infrared spectroscopy is the most effective technique to investigate the surface composition of atmosphereless bodies. However, the intrinsic faintness of Trans-Neptunian Objects (TNOs) and Centaurs imposes strong observational limits, and the sample of available information on these objects is still rather limited. Visible and near-infrared spectra, as well as models of the surface compositions, are today available only for about fifteen objects among TNOs and Centaurs. The most evident property is the huge variety of spectral features, physical characteristics, and compositions. This poses still unanswered questions about the origin and the early evolution of these small bodies. To cite this article: E. Dotto et al., C. R. Physique 4 (2003).

Molecular Features in ISO-SWS Spectra of O-Rich Long-Period Variables

The combination of ISO-SWS spectra from projects fkersch:orichsrv/ orichsrl and jhron:varlpv/varlpv2 allows us to cover a wide range of pulsational characteristics among AGB variables of type Mira, SRa, SRb and Lb and to follow selected objects through their pulsational cycle in order to probe for the interrelation of pulsation, stellar structure and mass loss. As expected we found features of CO, SiO, H2O, OH and probably CO2 in the ISO-SWS spectra of AGB variables. All bandheads predicted by spectra from CO and SiO linelists can be clearly seen. The features of CO, SiO and OH are very prominent in the spectra of relatively hot SR variables, whereas they are only weak or disappear completely in cool Mira stars. The spectra of cool Mira variables are dominated by absorption of H2O and maybe CO2. Synthetic CO and SiO spectra based on hydrostatic atmospheres predict very strong bands for the coolest stars, which is absolutely not in agreement with the observations. Also for hotter SR variables some of the features come out too strong (Figs. 1 and 2). However, we do not expect hydrostatic models to be able to reproduce the atmospheres of the coolest and most extended AGB variables (Miras). Exploratory spectra based on dynamical models predict a strong variability of spectral features, which has already been observed. Any interpretation of ISO-SWS spectra of cool giants has to take into account the molecular absorption caused by water.

Spectroscopic Study of Magnetic Behavior and Jahn-Teller Distortions in the Even-Electron System TbPO4

The high-resolution optical spectra of TbP${\mathrm{O}}_{4}$ show that there is antiferromagnetic ordering in the vicinity of 2.25 K, but that there must also be a Jahn-Teller distortion. Evidence that the distortion behavior couples strongly to the magnetic behavior is provided by optical experiments which show that (i) the distortion behavior must occur simultaneously with either magnetic ordering or the application of a large magnetic field and that (ii) the distortion is rotatable by an external magnetic field. It is possible to deduce from the distortion behavior the possible directions for the easy axis. A model is presented to explain the magnetic and distortion behavior. A variety of spectral features, including metamagnetic behavior, are observed but are not fully understood.

Filters for the Isolation of Narrow Regions in the Visible and Near-Visible Spectrum

Investigations of photochemical reactions in higher plants and other biological systems frequently require the irradiation of large areas with welldefined regions in the visible and near-visible spectrum. Large glass filters or dyed gelatin filters of the Wratten type are costly. Inexpensive theatrical gelatin filters, dyed cellophane, or other dyed plastics are available, but these are limited in variety of spectral characteristics and few of them have sharp absorption bands. The laboratory preparation of large dyed gelatin films is very inexpensive. These films are particularly useful for studies in plant photochemistry because the transmission bands can be adjusted to meet the special requirements of each problem. On the basis of laboratory experience and of various reports in the literature (?, 7, 10, 11, 13), the following information is presented on the technique of preparation of dyed gelatin films and the composition and transmission data for a few typical filters. In addition, data are presented on the transmission of water and solutions of copper sulphate and ferrous ammonium sulphate, which are useful as primary filters for the removal of the infrared and certain other regions of the visible and nearultraviolet spectrum. With water or aqueous solutions as primary filters and dyed gelatin films as secondary filters, it frequently is possible to isolate single lines of the mercury arc spectrum and fairly narrow regions from incandescent lamp sources. Since the gelatin films can be prepared conveniently in sizes up to at least one square meter, relatively high irradiances can be produced over areas of a square meter or more, making it possible to grow mature plants with spectral regions that are well defined and sufficiently narrow for many physiological studies. The dyed gelatin films to be described were prepared by the general method of casting hot solutions of dye and gelatin onto plate glass. After the layer has gelled, it is allowed to dry. If the glass has been treated previously with silicone, the film can be stripped from the casting plate and mounted between panes of window glass.