Stellar Spectroscopy Research Articles

STELLAR KINEMATICS AND STRUCTURAL PROPERTIES OF VIRGO CLUSTER DWARF EARLY-TYPE GALAXIES FROM THE SMAKCED PROJECT. II. THE SURVEY AND A SYSTEMATIC ANALYSIS OF KINEMATIC ANOMALIES AND ASYMMETRIES

We present spatially resolved kinematics and global stellar populations and mass-to-light ratios for a sample of 39 dwarf early-type (dE) galaxies in the Virgo cluster studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. This sample is representative of the early-type population in the absolute magnitude range -19.0 < M_r < -16.0. For each dE, we measure the rotation curve and velocity dispersion profile and fit an analytic function to the rotation curve. We study the significance of the departure of the rotation curve from the best fit analytic function (poorly fit) and of the difference between the approaching and receding sides of the rotation curve (asymmetry). We find that 62 +/- 8 % (23 out of the 39) of the dEs have a significant anomaly in their rotation curve. Analysis of the images reveals photometric anomalies for most galaxies. However, there is no clear correlation between the significance of the photometric and kinematic anomalies. We measure age-sensitive and metallicity-sensitive Lick spectral indices and find a wide range of ages and metallicities. We also find that 4 dEs have emission partially filling in the Balmer absorption lines. Finally, we estimate the total masses and dark matter fractions of the dEs. They have a median total mass and dark matter fraction within the Re of log Me = 9.1 +/- 0.2 and f_DM = 46 +/- 18 %. We plot several scaling relations and show that dEs seem to be the bridge between massive early-type and dwarf spheroidal galaxies.

Extreme ultraviolet (EUV) solar spectral irradiance (SSI) for ionospheric application – history and contemporary state-of-art

Abstract. After a historical survey of space related EUV measurements in Germany and the role of Karl Rawer in pursuing this work, we describe present developments in EUV spectroscopy and provide a brief outlook on future activities. The group of Karl Rawer has performed the first scientific space project in Western Europe on 19th October 1954. Then it was decided to include the field of solar EUV spectroscopy in ionospheric investigations. Starting in 1957 an intensified development of instrumentation was going on to explore solar EUV radiation, atmospheric airglow and auroral emissions until the institute had to stop space activities in the early nineteen-eighties. EUV spectroscopy was continued outside of the institute during eight years. This area of work was supported again by the institute developing the Auto-Calibrating Spectrometers (SolACES) for a mission on the International Space Station (ISS). After more than six years in space the instrument is still in operation. Meanwhile the work on the primary task also to validate EUV data available from other space missions has made good progress. The first results of validating those data and combine them into one set of EUV solar spectral irradiance are very promising. It will be recommended for using it by the science and application community. Moreover, a new low-cost type of an EUV spectrometer is presented for monitoring the solar EUV radiation. It shall be further developed for providing EUV-TEC data to be applied in ionospheric models replacing the Covington index F10.7. Applying these data for example in the GNSS signal evaluation a more accurate determination of GNSS receiver positions is expected for correcting the propagation delays of navigation signals traveling through the ionosphere from space to earth. – Latest results in the field of solar EUV spectroscopy are discussed, too.

Atomic data for stellar spectroscopy: recent successes and remaining needs

Stellar chemical composition analyses provide vital insights into galactic nucleosynthesis. Atomic line data are critical inputs to stellar abundance computations. Recent lab studies have made significant progress in refining and extending knowledge of transition probabilities, isotopic wavelength shifts, and hyperfine substructure patterns for the absorption lines that are of most interest to stellar spectroscopists. The observable neutron-capture (n-capture) element species (Z 30) have been scrutinized in lab studies by several groups. For many species the uncertainties in experimental oscillator strengths are 10%, which permits detailed assessment of rapid and slow n-capture nucleosynthesis contributions. In this review, extreme examples of r-process-enriched stars in the galactic halo will be shown, which suggest that the description of observable n-capture abundances in these stars is nearly complete. Unfortunately, there are serious remaining concerns about the reliability of observed abundances of lighter elements. In particular, it is not clear that line formation in real stellar atmospheres is being modeled correctly. But for many elements with Z 30 the atomic transition data are not yet settled. Highlights will be given of some recent large improvements, with suggestions for the most important needs for the near future.

The analysis of starlight: two centuries of astronomical spectroscopy

First published in 1986, this is the story of the analysis of starlight by astronomical spectroscopy. Beginning with Joseph Fraunhofer's discovery of spectral lines in the early nineteenth century, this new edition continues the story through to the year 2000. In addition to the key discoveries, it presents the cultural and social history of stellar astrophysics by introducing the leading astronomers and their struggles, triumphs and disagreements. Basic concepts in spectroscopy and spectral analysis are included, so both observational and theoretical aspects are described, in a non-mathematical framework. This new edition covers the final decades of the twentieth century, with its major advances in stellar astrophysics: the discovery of extrasolar planets, new classes of stars and the observation of the ultraviolet spectra of stars from satellites. The in-depth coverage makes it essential reading for graduate students working in stellar spectroscopy, professional and amateur astronomers, and historians of science.

THE SLUGGS SURVEY: WIDE-FIELD STELLAR KINEMATICS OF EARLY-TYPE GALAXIES

We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ~2-4 R_e (effective radii), as part of the ongoing SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (sigma_inst ~ 25 km/s) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, sigma, h_3, and h_4) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R_e often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS^3D survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.

Cosmic Gamma-Ray Spectroscopy

AbstractPenetrating gamma-rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. Multiple-interaction detectors in space combined with sophisticated post-processing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Spectral signatures in the MeV regime originate from transitions in the nuclei of atoms (rather than in their electron shell). Nuclear transitions are stimulated by either radioactive decays or high-energy nuclear collisions such as with cosmic rays. Gamma-ray lines have been detected from radioactive isotopes produced in nuclear burning inside stars and supernovae, and from energetic-particle interactions in solar flares. Radioactive-decay gamma-rays from 56Ni directly reflect the source of supernova light. 44Ti is produced in core-collapse supernova interiors, and the paucity of corresponding 44Ti gamma-ray line sources reflects the variety of dynamical co...

Solar space research by imaging X-ray spectroscopy

X-ray spectroscopy is the main method of solar research today. The core of the method is the construction of images of the solar disk in narrow spectral bands. The main advantage of this method is the ability to detect plasma radiation in a given temperature range, which allows study of specific layers of the solar atmosphere or classes of phenomena. The results of solar X-ray spectroscopy onboard CORONAS-Photon spacecraft are discussed, providing an understanding of the current state of solar research in Russia.

STELLAR KINEMATICS AND STRUCTURAL PROPERTIES OF VIRGO CLUSTER DWARF EARLY-TYPE GALAXIES FROM THE SMAKCED PROJECT. I. KINEMATICALLY DECOUPLED CORES AND IMPLICATIONS FOR INFALLEN GROUPS IN CLUSTERS

We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.8'' (0.14 kpc) and 4.2'' (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation; and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC.The frequency of occurence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

The power of principled bayesian methods in the study of stellar evolution

It takes years of effort employing the best telescopes and instruments to obtain high-quality stellar photometry, astrometry, and spectroscopy. Stellar evolution models contain the experience of lifetimes of theoretical calculations and testing. Yet most astronomers fit these valuable models to these precious datasets by eye. We show that a principled Bayesian approach to fitting models to stellar data yields substantially more information over a range of stellar astrophysics. We highlight advances in determining the ages of star clusters, mass ratios of binary stars, limitations in the accuracy of stellar models, post-main-sequence mass loss, and the ages of individual white dwarfs. We also outline a number of unsolved problems that would benefit from principled Bayesian analyses.

Photonic lanterns

AbstractMultimode optical fibers have been primarily (and almost solely) used as “light pipes” in short distance telecommunications and in remote and astronomical spectroscopy. The modal properties of the multimode waveguides are rarely exploited and mostly discussed in the context of guiding light. Until recently, most photonic applications in the applied sciences have arisen from developments in telecommunications. However, the photonic lantern is one of several devices that arose to solve problems in astrophotonics and space photonics. Interestingly, these devices are now being explored for use in telecommunications and are likely to find commercial use in the next few years, particularly in the development of compact spectrographs. Photonic lanterns allow for a low-loss transformation of a multimode waveguide into a discrete number of single-mode waveguides and vice versa, thus enabling the use of single-mode photonic technologies in multimode systems. In this review, we will discuss the theory and function of the photonic lantern, along with several different variants of the technology. We will also discuss some of its applications in more detail. Furthermore, we foreshadow future applications of this technology to the field of nanophotonics.

Optical characterization of two-dimensional array of 2048 tilting micromirrors for astronomical spectroscopy

A micromirror array composed of 2048 silicon micromirrors measuring 200 × 100 μm² and tilting by 25° was developed as a reconfigurable slit mask for multi-object spectroscopy (MOS) in astronomy. The fill factor, contrast, and mirror deformation at both room and cryogenic temperatures were investigated. Contrast was measured using an optical setup that mimics a MOS instrument, and mirror deformation was characterized using a Twyman-Green interferometer. The results indicate that the array exhibited a fill factor of 82%, a contrast ratio of 1000:1, and surface mirror deformations of 8 nm and 27 nm for mirrors tilted at 298 K and 162 K, respectively.

The Stagger-grid: A grid of 3D stellar atmosphere models

We present the Stagger-grid, a comprehensive grid of time-dependent, 3D hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications like stellar spectroscopy, asteroseismology and the study of stellar convection. In this introductory paper, we describe the methods used for the computation of the grid and discuss the general properties of the 3D models as well as their temporal and spatial averages (<3D>). All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~220 grid models range in Teff from 4000 to 7000K in steps of 500K, in log g from 1.5 to 5.0 in steps of 0.5 dex, and [Fe/H] from -4.0 to +0.5 in steps of 0.5 and 1.0 dex. We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy value of the adiabatic convection zone. The range in intensity contrast is enhanced at lower metallicity. The granule size correlates closely with the pressure scale height sampled at the depth of maximum velocity. We compare the <3D> models with widely applied 1D models, as well as with theoretical 1D hydrostatic models generated with the same EOS and opacity tables as the 3D models, in order to isolate the effects of using self-consistent and hydrodynamic modeling of convection, rather than the classical mixing length theory approach. For the first time, we are able to quantify systematically over a broad range of stellar parameters the uncertainties of 1D models arising from the simplified treatment of physics, in particular convective energy transport. In agreement with previous findings, we find that the differences can be significant, especially for metal-poor stars.

Grazing-incidence spectrometer for soft X-ray solar imaging spectroscopy

The design and realization of a stigmatic grazing-incidence instrument for space applications to solar imaging spectroscopy is presented. We propose an optical layout in which imaging and spectral capabilities are decoupled by the use of crossed cylindrical mirrors. The design consists of a double telescope and a spectrograph: telescope I consists of a single cylindrical mirror with parabolic section, focusing the radiation on the entrance slit of the spectrograph in the spectral dispersion plane; telescope II consists of two cylindrical mirrors with aspherical section in Wolter configuration focusing the radiation on the spectrograph focal plane in the direction perpendicular to the spectral dispersion plane; the spectrograph consists of a grazing-incidence spherical variable-line-spaced grating with flat-field properties. Telescope II is crossed with respect to the grating and telescope I, i.e., is mounted with its tangential planes coincident with the grating equatorial plane, to decouple spectral and spatial focusing properties. The spectral resolution is preserved also for off-axis angles. The instrument that has been realized operates in the 4-26 nm spectral range and has a field of view of 0.5 deg to image the full Sun disk.

Cosmic Gamma-Ray Spectroscopy

Penetrating gamma- rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. A combination of multiple-interaction detectors in space and post-processing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Spectral signatures in the MeV regime originate from transitions in atomic nuclei, stimulated by either radioactive decays or high-energy nuclear collisions such as with cosmic rays. Lines have been detected from radioactive isotopes produced in stellar and supernova nuclear burning, and from energetic-particle interactions in solar flares. Radioactive-decay gamma-rays from 56Ni directly reflect the power source of supernova light. 44Ti is produced in core-collapse supernova interiors and the largely unknown and dynamical conditions herein. From 26Al and 60Fe which are distributed in interstellar space from massive-star nucleosynthesis over millions of years. Additionally, nuclear de-excitation lines have been measured in solar-flare events, and convey information a b out energetic particle production in these outbursts, and t heir interaction in the solar atmosphere. Annihilating posit rons add another very special astrophysical source, which has been puzzling so far, with its characteristic gamma-rays at 511 keV; it has been measured both in such solar flares, and throughout the interstellar medium of our Milky Way galaxy. - We discuss instrumentation and data processing for cosmic gamma-ray spectroscopy, and the astrophysical issues and insights from these measurements.

Astronomical imaging Fourier spectroscopy at far-infrared wavelengths

The principles and practice of astronomical imaging Fourier transform spectroscopy (FTS) at far-infrared wavelengths are described. The Mach–Zehnder (MZ) interferometer design has been widely adopted for current and future imaging FTS instruments; we compare this design with two other common interferometer formats. Examples of three instruments based on the MZ design are presented. The techniques for retrieving astrophysical parameters from the measured spectra are discussed using calibration data obtained with the Herschel–SPIRE instrument. The paper concludes with an example of imaging spectroscopy obtained with the SPIRE FTS instrument.

The Promise of Recent and Future Observatories and Instruments

AbstractThe identification of the carrier(s) of diffuse interstellar bands (DIBs) is one of the oldest mysteries in stellar spectroscopy. With the advent of 8-10m-class telescopes substantial progress has been made in measuring the properties of DIBs in the optical and near-infrared wavelength domain, not only in the Galaxy, but also in different environments encountered in Local Group galaxies and beyond. Still, the DIB carriers have remained unidentified. The coming decade will witness the development of extremely large telescopes (GMT, TMT and E-ELT) and their instrumentation. In this overview I will highlight the current instrumentation plan of these future observatories, emphasizing their potential role in solving the enigma of the DIBs.

What Microwave Astronomical Spectroscopy can tell you about the Carriers of the DIBs

AbstractAstronomical microwave spectroscopy has greatly broadened the inventory of identifiable chemical species in diffuse molecular gas and is an increasingly effective way to measure the abundances of polar molecules that may be candidate diffuse interstellar band carriers. Here we review some recent developments that hold new promise for chemical abundance determinations. We summarize and categorize the molecular inventory that has accrued in the past twenty years from microwave observations of diffuse clouds and we present summary tables of the molecular abundances within various chemical families in both dark and diffuse molecular gas.

Integral wide-field spectroscopy in astronomy: the Imaging FTS solution

Long-slit grating spectrometers in scanning mode and Fabry–Perot interferometers as tunable filters are commonly used to perform integral wide-field spectroscopy on extended astrophysical objects as HII regions and nearby galaxies. The goal of this paper is to demonstrate, by comparison, through a thorough review of the imaging Fourier transform spectrometer (IFTS) properties, that this instrument represents another interesting solution. After a brief recall of the performances, regarding FOV and spectral resolution, of the grating spectrometer, without and with integral field units (IFU), and of the imaging Fabry–Perot, it is demonstrated that for an IFTS the product of the maximum resolution R by the entrance beam etendue U is equal to $2.6\,N\times S_I$ with $N\,\times \,N$ the number of pixels of the detector array and S $_I$ the area of the interferometer beamsplitter. As a consequence, the IFTS offers the most flexible choice of field size and spectral resolution, up to high values for both parameters. It also presents on a wide field an important multichannel advantage in comparison to integral field grating spectrometers, even with multiple IFUs. To complete, the few astronomical IFTSs, built behind ground-based telescopes and in space, for the visible range up to the sub-millimetric domain, are presented. Through two wide-field IFTS projects, one in the visible, the other one in the mid-infrared, the question is addressed of the practical FOV and resolution limits, set by the optical design of the instrument, which can be achieved. Within the 0.3 to $\sim $ 2.5 $\upmu$ m domain, a Michelson interferometer with wide-field diopric collimators provides the easiest solution. This design is illustrated by a $11^{\prime}\times 11^{\prime}$ -field IFTS in the 0.35–0.90 $\upmu$ m range around an off-axis interferometer, called SITELLE, proposed for the 3.6-m CFH Telescope. At longer wavelengths, an all-mirror optics is required, as studied for a spaceborne IFTS, H2EX, for the 8–29 $\upmu$ m range, a $20^{\prime} \times 20^{\prime}$ field, and a high resolution of $\simeq 3\times 10^4$ at 10 $\upmu$ m. To comply with these characteristics, the interferometer is designed with cat’s eye retroreflectors. In the same domain and up to the far infrared, if the instrument aims only at a low spectral resolution (few thousands) and a smaller field (few arcmins $^2$ ), roof-top or corner cube mirrors, as for the IFTS SPIRE on the Herschel space telescope, are usable. At last, perspectives are opened, behind an ELT in the visible and the near infrared with the SITELLE optical combination, in the 2–5 $\upmu$ m on the Antarctic plateau or in space up to longer wavelengths, with the H2EX design, to provide the missing capability of global high spectral resolution studies of extended sources, from comets to distant galaxy clusters.

Structure of carbon monoxide time variations in the atmospheric thickness over Central Eurasia (Issyk Kul Monitoring Station)

The results of measurements of the CO content in the atmospheric thickness by the method of solar molecular-absorption spectroscopy are presented. Over 87 months of observations, the annual mean CO content decreased by ∼19% at a mean rate of changes equal to −(0.14 ± 0.02) atm cm per year. Maxima and minima of seasonal variations most often fall on February and September, respectively. The mean overall amplitude of changes in the CO content during the annual cycle is about 50% of the mean value. The Fourier analysis revealed variations in the CO composition with periods from 3 to 84 months. A simple statistical model satisfactorily describes time changes in the CO content in the atmospheric thickness. The results of measurements of the CO content in the atmospheric thickness are compared with the data of CO measurements in samples of surface air at stations of the Global Atmospheric Watch.

INTERNAL STELLAR KINEMATICS OF M32 FROM THE SPLASH SURVEY: DARK HALO CONSTRAINTS

As part of the SPLASH survey of the Andromeda (M31) system, we have obtained Keck/DEIMOS spectra of the compact elliptical (cE) satellite M32. This is the first resolved-star kinematical study of any cE galaxy. In contrast to most previous kinematical studies that extended out to r≾30 ~ 1 r^(eff) I ~ 100 pc, we measure the rotation curve and velocity dispersion profile out to r ~ 250 and higher order Gauss-Hermite moments out to r ~ 70. We achieve this by combining integrated-light spectroscopy at small radii (where crowding/blending are severe) with resolved stellar spectroscopy at larger radii, using spatial and kinematical information to account statistically for M31 contamination. The rotation curve and velocity dispersion profile extend well beyond the radius (r ~ 150) where the isophotes are distorted. Unlike NGC 205, another close dwarf companion of M31, M32's kinematics appear regular and symmetric and do not show obvious sharp gradients across the region of isophotal elongation and twists. We interpret M31's kinematics using three-integral axisymmetric dynamical equilibrium models constructed using Schwarzschild's orbit superposition technique. Models with a constant mass-to-light ratio can fit the data remarkably well. However, since such a model requires an increasing tangential anisotropy with radius, invoking the presence of an extended dark halo may be more plausible. Such an extended dark halo is definitely required to bind a half-dozen fast-moving stars observed at the largest radii, but these stars may not be an equilibrium component of M32.