Line Identifications Research Articles

Automated Selection and Characterization of Emission-Line Sources in Advanced Camera for Surveys Wide Field Camera Grism Data

We present complementary techniques to find emission-line targets and measure their properties in a semi-automated fashion from grism observations obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope (HST). The first technique is to find all likely sources in a direct image, extract their spectra, and search them for emission lines. The second method is to look for emission-line sources as compact structures in an unsharp masked version of the grism image. Using these methods we identify 46 emission-line targets in the Hubble Deep Field-North using a modest (three-orbit) expenditure of HST observing time. Grism spectroscopy is a powerful tool for efficiently identifying interesting low-luminosity, moderate-redshift emission-line field galaxies. The sources found here have a median i-band (F775W) flux 1.5 mag fainter than the spectroscopic redshift catalog of Cohen et al. They have redshift z ≤ 1.42, and high equivalent widths (typically >100 A) and are usually less luminous than the characteristic luminosity at the same redshift. The chief obstacle in interpreting the results is line identification, since the majority of sources have a single emission line and the spectral resolution is low. Photometric redshifts are useful for providing a first-guess redshift. However, even at the depth of the state-of-the-art ground-based and HST data used here, photometric errors can result in uncertainties in line identifications, especially for sources with i magnitudes fainter than 24.5 ABmag. Reliable line identification for the faintest emission-line galaxies requires additional ground-based spectroscopy for confirmation. Of particular concern are the faint high-EW [O II] emitters, which could represent a strongly evolving galaxy population if the possibility that they are misidentified lower redshift interlopers can be ruled out.

Core Atomic Physics Studies in Alcator C-Mod

The Rydberg series (1s2 to 1snp) up to n = 14 of helium-like argon (Z = 18) has been observed from Alcator C-Mod plasmas using a high-resolution X-ray spectrometer array. High-n satellites to these lines of the form 1s22s to 1s2snp and 1s22p to 1s2pnp with 3 ≤ n ≤ 12 have been recorded. X-ray spectra of 2l - nl’ transitions with 3 ≤ n ≤ 18 in molybdenum (Z = 42) and 3 ≤ n ≤ 12 in krypton (Z = 36) and niobium (Z = 41) from charge states around neon-like have also been measured. Numerous examples of the configuration interaction, which alters the line intensities in some transitions of neon-like ions with nearly degenerate upper levels, have been observed. Accurate wavelengths of all of these transitions (±0.5 mÅ) have been determined by comparison to neighboring reference lines from H- and He-like charge states. Line identifications have been made by comparison to ab initio atomic structure calculations, using a fully relativistic, parametric potential code. Measured line intensities have been compared with collisional radiative modeling that includes the contributions from dielectronic recombination and inner shell excitation rates, with good agreement.

Eta Carinae across the 2003.5 Minimum: Deciphering the Spectrum toward Weigelt D

Hubble Space Telescope Space Telescope Imaging Spectrograph (HST STIS) near-ultraviolet (NUV) echelle spectra reveal complex structure in the sight line toward the Weigelt D condensation located 0.25'' north-northwest of ? Car. In previous studies, the Weigelt condensations have been described to exhibit pure emission line spectra dominated by transitions in mainly singly and doubly ionized iron-group elements. However, high spectral (R ~ 100,000) and angular (<0.060'' FWHM) resolutions show that the spectra are modified by circumstellar (CS) absorption and stellar wind lines formed as far as 1500 AU from the central source. This analysis uses data recorded between 2000 October and 2004 March to monitor changes in emission and absorption as the UV photoexciting fluxes from ? Car drop and later reappear. We compare changes in the wind profiles seen against the star and the CS absorptions to gain knowledge of the properties of the extended wind and the ejecta. Complete spectra, in the wavelength region 2424-2706 ?, with line identifications are available in the electronic edition of this paper.

Spectral atlas of massive stars around $\ion{He}{i}$ 10 830 Å

We present a digital atlas of peculiar, high-luminosity massive stars in the near-infrared region (10470-11000 A) at medium resolution (R~7000). The spectra are centered around He I 10830 A, which is formed in the wind of those stars, and is a crucial line to obtain their physical parameters. The instrumental configuration also sampled a rich variety of emission lines of Fe II, Mg II, C I, N I and Pa gamma. Secure identifications for most spectral lines are given, based on synthetic atmosphere models calculated by our group. We also propose that two unidentified absorption features have interstellar and/or circumstellar origin. For the strongest one (10780 A) an empirical calibration between E(B-V) and equivalent width is provided. The atlas displays the spectra of massive stars organized in four categories, namely Be stars, OBA Iape (or luminous blue variables, LBV candidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars. For comparison, the photospheric spectra of non emission-line stars are presented. Selected LBVs were observed in different epochs from 2001 to 2004, and their spectral variability reveals that some stars, such as Eta Car, AG Car and HR Car, suffered dramatic spectroscopic changes during this time interval.

Metal Absorption Profiles from the Central Star of the Planetary Nebula M27 (NGC 6853, PN G060.8−03.6, the Dumbbell): Photospheric and Nebular Line Identifications

High resolution spectra of the hot central star of the planetary nebula (CSPN) M27, acquired with the Far Ultraviolet Spectroscopic Explorer (\FUSE), have revealed an unusually rich set of narrow molecular hydrogen absorption features. This object is also unique in that the velocity of nebular absorption features are cleanly separated from the velocity of the intervening interstellar medium. These features blend with and in many cases obscure atomic features. We have developed a continuum model of the CSPN including atomic and molecular hydrogen absorption. Using this model we have identified and tabulated the metal lines as arising from either photospheric, nebular and/or non-nebular velocity systems. We find the nebular outflow and ionization balance to be stratified with high ionization states favored at low velocity and low ionization states favored at high velocity. Neutrals and molecules are found at a velocity that marks the transistion between these two regimes. These observations are a challenge to the interacting wind model of PN evolution. Mappings at high resolution of the line profiles for \ion{C}{1} \ion{-}{4}, \ion{N}{1} \ion{-}{3}, \ion{O}{1}, \ion{O}{6}, \ion{Si}{2} \ion{-}{4}, \ion{P}{2} \ion{-}{5}, \ion{S}{2} \ion{-}{4}, \ion{Ar}{1} \ion{-}{2} and \ion{Fe}{2} \ion{-}{3} within the \FUSE and STIS bandpasses are presented. The digitial spectra of the stars and the model are freely available on the H$_2$ools website. They will be useful for photospheric analyses seeking to determine the metallicity of the central star and for absorption line based atomic and molecular abundance determination of the nebular outflow.

The James Clerk Maxwell Telescope Spectral Legacy Survey

ABSTRACTStars form in the densest, coldest, most quiescent regions of molecular clouds. Molecules provide the only probes that can reveal the dynamics, physics, chemistry, and evolution of these regions, but our understanding of the molecular inventory of sources and how this is related to their physical state and evolution is rudimentary and incomplete. The Spectral Legacy Survey (SLS) is one of seven surveys recently approved by the James Clerk Maxwell Telescope (JCMT) Board of Directors. Beginning in 2007, the SLS will produce a spectral imaging survey of the content and distribution of all the molecules detected in the 345 GHz atmospheric window (between 332 and 373 GHz) toward a sample of five sources. Our intended targets are a low‐mass core (NGC 1333 IRAS 4), three high‐mass cores spanning a range of star‐forming environments and evolutionary states (W49, AFGL 2591, and IRAS 20126), and a photodissociation region (the Orion Bar). The SLS will use the unique spectral imaging capabilities of HARP‐B/ACSIS (Heterodyne Array Receiver Programme B/Auto‐Correlation Spectrometer and Imaging System) to study the molecular inventory and the physical structure of these objects, which span different evolutionary stages and physical environments and to probe their evolution during the star formation process. As its name suggests, the SLS will provide a lasting data legacy from the JCMT that is intended to benefit the entire astronomical community. As such, the entire data set (including calibrated spectral data cubes, maps of molecular emission, line identifications, and calculations of the gas temperature and column density) will be publicly available.

Metallicity and age of M31 globulars from automated fits to theoretical spectra

We are calculating stellar spectra for types A through K using Kurucz codes, Castelli models, and Kurucz laboratory lines plus guessed identifications for other lines in the spectra. Weighted coadditions of these spectra are being constructed to match spectra observed in integrated light of old stellar systems such as elliptical galaxies and globular clusters. Grids of theoretical spectra, both stellar and composite, that include an enhancement of light elements and span a wide metallicity range will be calculated over 2200Å–9000Å, and will be archived on MAST at the Hubble Space Telescope website. Here we summarize our results and describe how we automate the fit to our grid of an observed high-resolution stellar or globular-cluster spectrum, to determine the stellar parameters or to break the age-metallicity degeneracy.

High Resolution Spectroscopy of Halo Stars in the Near UV and Blue Region I. Spectra in the Wavelength Region 3550–5000Å

An atlas of high resolution (R = 60 000) CCD-spectra in the wavelength range 3500–5000 A is presented for four objects in metallicity range −3.0<[Fe/H]<−0.6, temperature range 4750<Teff<5900 K, and surface gravity range 1.6<lg g<5.0. We describe the calibration of the stellar atmospheric parameters using Alonso's formula based on the method of infrared flux and outline the determination of the abundances of a total number of 25 chemical elements. An analysis of the abundance determination errors for different chemical elements is carried out, and a method is provided for the observations and reduction of spectral material. Properties of the method of producing an atlas of spectra and line identifications are described.

Benchmarking atomic data for astrophysics: Fe xviii

Fe xviii produces, in the X-ray and extreme ultraviolet, L-shell () spectral lines which are among the brightest ones in e.g. solar flares and in Chandra, XMM-Newton spectra of active stars. Recent R-matrix scattering calculations of Witthoeft et al. (2006, A&A, 446, 361) produce theoretical intensities for some of the brightest transitions increased by large factors (2–3), so it is timely to use these calculations to review and assess all previous line identifications on a quantitative basis. This paper discusses only the most important lines for laboratory and astrophysical applications. Many previous identifications are revised and some tentative ones finally confirmed. Many lines are found to be significantly blended. A considerable number of new identifications are proposed. Excellent agreeement between observed and predicted intensities is found in the majority of cases for the first time. It is therefore now possible to use Fe xviii L-shell lines to measure electron densities in laboratory plasmas and temperatures for a wide range of astrophysical sources.

Hydrogen and helium traces in type Ib-c supernovae

The spectroscopic properties of a selected optical photospheric spectra of core collapse supernovae (CCSNe) are investigated.Special attention is devoted to traces of hydrogen at early phases. The generated spectra are found to match the observed ones reasonably well, including a list of only 23 candidate ions. Guided by SN Ib 1990I, the observed trough near 6300\AA is attributed to H$\alpha$ in almost all Type Ib events, although in some objects it becomes too weak to be discernible, especially at later phases. Alternative line identifications are discussed. Differences in the way hydrogen manifests its presence within CCSNe are highlighted. In Type Ib SNe, the H$\alpha$ contrast velocity (i.e. line velocity minus the photospheric velocity) seems to increase with time at early epochs, reaching values as high as 8000 km s$^{-1}$ around 15-20 days after maximum and then remains almost constant. The derived photospheric velocities, indicate a lower velocity for Type II SNe 1987A and 1999em as compared to SN Ic 1994I and SN IIb 1993J, while Type Ib events display a somewhat larger variation. The scatter, around day 20, is measured to be $\sim$5000 km s$^{-1}$. Following two simple approaches, rough estimates of ejecta and hydrogen masses are given. A mass of hydrogen of approximately 0.02 $M_\odot$ is obtained for SN 1990I, while SNe 1983N and 2000H ejected $\sim$0.008 $M_\odot$ and $\sim$0.08 $M_\odot$ of hydrogen, respectively. SN 1993J has a higher hydrogen mass, $\sim 0.7$ $M_\odot$ with a large uncertainty. A low mass and thin hydrogen layer with very high ejection velocities above the helium shell, is thus the most likely scenario for Type Ib SNe. Some interesting and curious issues relating to oxygen lines suggest future investigations.

Comparative Direct Analysis of Type Ia Supernova Spectra. II. Maximum Light

ABSTRACTA comparative study of near–maximum‐light optical spectra of 24 Type Ia supernovae (SNe Ia) is presented. The spectra are assigned to four groups. Seven “core‐normal” SNe Ia have very similar spectra, except for strong, high‐velocity Ca ii absorption in SN 2001el. Seven SNe Ia are assigned to a “broad‐line” group, the most extreme of which is SN 1984A. Five SNe Ia, including SN 1991bg, are assigned to a “cool” group. Five SNe Ia, including SN 1991T, are assigned to a “shallow‐silicon” group. Comparisons with SYNOW synthetic spectra provide a basis for discussion of line identifications and an internally consistent quantification of the maximum‐light spectroscopic diversity among SNe Ia. The extent to which SN Ia maximum‐light spectra appear to have a continuous distribution of properties, rather than consist of discrete subtypes, is discussed.

Eta Carinae across the 2003.5 Minimum: The Character and Variability of the Ejecta Absorption in the Near‐Ultraviolet

We present Hubble Space Telescope (HST ) Space Telescope Imaging Spectrograph (STIS) high-resolution near- ultraviolet (NUV) spectra ofCar's central source recorded before, during and after the 2003.5 spectroscopic minimum. Our focus is on the narrow absorption lines formed in multiple circumstellar shells, superimposed on the broad P Cygni stellar wind features, and how they respond to the flux variations ofCar across the minimum. Over 30 separate narrow-line velocity components are identified: three around � 146 km s � 1 , many between � 323 and � 587kms � 1 ,andafewexceeding � 1000kms � 1 .Ingeneral,excitationdecreaseswithincreasingvelocityindicating that the primary excitation is by UV stellar photons and that the slower shells are located closer to the central source. Twowell-isolatedvelocitysystemsat � 146and � 513kms � 1 displayverydifferentspectralcharacteristicsregarding ionization/excitation and respond differently toCar's spectroscopic minimum. The � 146 km s � 1 shell, associated with the (internal) Little Homunculus, is ionized across the broad spectroscopic maximum but relaxes during the few months long minimum. The � 146 km s � 1 component is joined by adjacent velocity components in lines of singly ionized iron-group elements. Ti ii and V ii absorptions appear during the minimum, most likely caused by a decrease in Lyman-ionizing flux. The � 513 km s � 1 component, part of the (outer) Homunculus, does not show significant changes in atomic absorptions, but intermediate-velocity components between � 369 and � 503 km s � 1 vary during the minimum. We present the NUV spectrum and describe its general characteristics, but we focus on identifications of thenebularabsorptionlinesandtheirvariationsacrossthe2003.5minimum.Thecompletespectrumbetween2380 and 3160 8 with line identifications is available in the electronic edition of this paper.

CHIANTI—An Atomic Database for Emission Lines. VII. New Data for X‐Rays and Other Improvements

The CHIANTI atomic database contains atomic energy levels, wavelengths, radiative transition probabilities, and collisional excitation data for a large number of ions of astrophysical interest. CHIANTI also includes a suite of IDL routines to calculate synthetic spectra and carry out plasma diagnostics. Version 5 has been released, which includes several new features, as well as new data for many ions. The new features in CHIANTI are as follows: the inclusion of ionization and recombination rates to individual excited levels as a means to populate atomic levels; data for Kα and Kβ emission from Fe II to Fe XXIV; new data for high-energy configurations in Fe XVII to Fe XXIII; and a complete reassessment of level energies and line identifications in the X-ray range, multitemperature particle distributions, and photoexcitation from any user-defined radiation field. New data for ions already in the database, as well as data for ions not present in earlier versions of the database, are also included. Version 5 of CHIANTI represents a major improvement in the calculation of line emissivities and synthetic spectra in the X-ray range and expands and improves theoretical spectra calculations in all other wavelength ranges.

Line Imaging of Orion KL at 865 μm with the Submillimeter Array

We present the first submillimeter (865 μm) imaging spectral survey at 1'' resolution conducted with the Submillimeter Array toward Orion KL. Within the 2 × 2 GHz bandpasses (lower and upper sidebands, 337.2-339.2 and 347.2-349.2 GHz), we find about 145 spectral lines from 13 species, six isotopologues, and five vibrational excited states. Most nitrogen-bearing molecules are strong toward the hot core, whereas the oxygen-bearing molecules peak toward the southwest in the so-called compact ridge. Imaging of spectral lines is shown to be an additional tool to improve the identifications of molecular lines. Arcsecond spatial resolution allows us to distinguish the molecular emission of the sources I and n from that of the hot core. The only molecular species detected strongly toward source I is SiO, delineating mainly the collimated northeast-southwest low-velocity outflow. The two positions close to source I, which have previously been reported to show maser emission in the v = 0 28SiO (1-0) and (2-1) lines, show no detectable maser emission in the v = 0 28SiO (8-7) at our spatial resolution. SiO is weak toward source n, and thus source n may not currently be driving a molecular outflow. CH3OH is the molecule with the highest number of identified lines (46) in this spectral window. This line forest allows us to estimate temperatures in the region, and we find temperatures between 50 and 350 K, with the peak temperatures occurring toward the hot core. The detection of strong vibrational excited emission from the submillimeter continuum peak SMA1 supports the interpretation that the source SMA1 is likely of protostellar nature.

Spectral Atlas of X‐Ray Lines Emitted during Solar Flares Based on CHIANTI

A spectral atlas of X-ray lines in the wavelength range 7.47-18.97 Angstroms is presented, based on high-resolution spectra obtained during two M-class solar flares (on 1980 August 25 and 1985 July 2) with the Flat Crystal Spectrometer on board the Solar Maximum Mission. The physical properties of the flaring plasmas are derived as a function of time using strong, isolated lines. From these properties predicted spectra using the CHIANTI database have been obtained which were then compared with wavelengths and fluxes of lines in the observed spectra to establish line identifications. identifications for nearly all the observed lines in the resulting atlas are given, with some significant corrections to previous analysis of these flare spectra.

Quantitative spectroscopy of photospheric-phase type II supernovae

We present first results on the quantitative spectroscopic analysis of the photospheric-phase of Type II supernovae (SN). The analyses are based on the non-LTE model atmosphere code, CMFGEN, of Hillier & Miller (1998). A key asset of CMFGEN is its thorough treatment of line-blanketing due to metal species. From its applicability to hot star environments, the main modifications to the source code were to allow a linear velocity law, a power-law density distribution, an adaptive grid to handle the steep H recombination/ionization front occurring in cooler SN models, and a routine to compute the gray temperature structure in the presence of large velocities. In this first paper we demonstrate the ability of CMFGEN to reproduce, with a high level of accuracy, the UV and optical observations of a sample of well observed Type II SN, i.e. SN1987A and SN1999em, at representative stages of their photospheric evolution. Two principal stages of SN are modeled - that where hydrogen is fully ionized, and that in which H is only partially ionized. We provide detailed and accurate line identifications for our sample of epochs. We discuss the impact on the SED of varying the density exponent, the spatial scale of the SN, the value of Rmax and the metallicity; we illustrate the formation sites for selected lines. Both Hydrogen Balmer and Helium lines (when present) are very well reproduced, even for our adopted CNO-equilibrium abundance values adequate for a massive supergiant progenitor star. NII lines are also predicted in the blue-wing of both Hbeta and HeI 5875A, and thus not associated with peculiar absorption/emission far above the photosphere. We finally present a pedagogical discussion of P-Cygni profile formation and explain, e.g., the noticeable blue-shift of Halpha in early time spectra (much abridged abstract).

Benchmarking atomic data for astrophysics: $\ion{Fe}{xxiii}$

Recent scattering calculations for are benchmarked against laboratory and astrophysical observations. The collisional data are supplemented by radiative data obtained with empirical adjustments that take into account observed wavelengths. All previous line identifications and energy levels are reviewed and assessed in light of these new calculations. Most of the previous identifications, in particular of the astrophysically-important spectral lines are confirmed. However, some identification are rejected or questioned, and new ones proposed. The agreement between theoretical and experimental data in terms of wavelengths, line intensities and level lifetimes is very good. Observations of L-shell emission lines provide a great opportunity to directly measure electron temperatures for a wide range of astrophysical sources. Examples from solar (SMM, SOLEX) and stellar (Chandra, EUVE) observations are provided.

The Ultraviolet Spectrum of η Carinae: Investigation of the Ejecta Absorption

We have investigated the far- through mid-UV (1150-2360 A) spectrum of η Carinae during the late stages of its broad maximum using the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) moderate dispersion echelle modes. The η Car spectrum is a mixture of absorption and emission lines from the surrounding nebula superimposed on broad stellar wind features. This paper provides a description of the observed spectrum including the wind features, the interstellar absorption, and the emission spectrum from the surrounding nebula, but with the emphasis on the absorption spectrum formed in the foreground ejecta. The ejecta absorption spectrum has a complicated velocity structure in which two velocity structures, at -146 and -513 km s-1, are easily distinguished. These two velocity components, formed in different regions of the η Car nebula, have in an earlier analysis been identified and demonstrated to have very different spectral characteristics. The slower velocity component is time variable over the spectroscopic period and is characterized by spectral lines from mainly singly ionized iron-peak elements, while the faster one shows transitions from neutral and singly ionized elements in addition to molecular lines from the hydrogen Lyman bands. The high-velocity H2 lines dominate great parts of the spectrum with over 800 identified transitions from energy levels up to 30,000 cm-1. The STIS MAMA data provide the tool for spatial investigations of the central parts of η Car. H I Lyα pumped and semiforbidden emission lines are observed to be formed east of the central source toward Weigelt blobs B and C, located up to 02 from the central source. The complete spectrum, with nebular and interstellar line identifications, is available in the electronic edition of the paper.

EUV Line Identifications and Lifetime Measurements in Highly Charged Iron Ions

When beam-foil experiments on ions of the iron group were done at the Bochum Dynamitron tandem accelerator, line identifications of intercombination lines in Mg- and Al-like Fe matched previously unclassified lines that appear in the EUV spectrum of the solar corona. Beam-foil work continued on Si- to Cl-like Fe ions, identifying in particular decays of high-J levels with nanosecond lifetimes. Millisecond lifetimes in the same ions were then measured at a heavy-ion storage ring and at an electron beam ion trap. Remaining problems and prospects for solutions are discussed.

MGGPOD: a Monte Carlo Suite for Modeling Instrumental Line and Continuum Backgrounds in Gamma‐Ray Astronomy

Intense and complex instrumental backgrounds, against which the much smaller signals from celestial sources have to be discerned, are a notorious problem for low and intermediate energy gamma-ray astronomy (~50 keV - 10 MeV). Therefore a detailed qualitative and quantitative understanding of instrumental line and continuum backgrounds is crucial for most stages of gamma-ray astronomy missions, ranging from the design and development of new instrumentation through performance prediction to data reduction. We have developed MGGPOD, a user-friendly suite of Monte Carlo codes built around the widely used GEANT (Version 3.21) package, to simulate ab initio the physical processes relevant for the production of instrumental backgrounds. These include the build-up and delayed decay of radioactive isotopes as well as the prompt de-excitation of excited nuclei, both of which give rise to a plethora of instrumental gamma-ray background lines in addition to continuum backgrounds. The MGGPOD package and documentation are publicly available for download from this http URL We demonstrate the capabilities of the MGGPOD suite by modeling high resolution gamma-ray spectra recorded by the Transient Gamma-Ray Spectrometer (TGRS) on board Wind during 1995. The TGRS is a Ge spectrometer operating in the 40 keV to 8 MeV range. Due to its fine energy resolution, these spectra reveal the complex instrumental background in formidable detail, particularly the many prompt and delayed gamma-ray lines. We evaluate the successes and failures of the MGGPOD package in reproducing TGRS data, and provide identifications for the numerous instrumental lines.