Weak Emission Lines Research Articles

The spectral response of superconducting tunnel junction X-ray detectors

The Advanced Detector Group at LLNL is developing superconducting Nb–Al–AlOx–Al–Nb tunnel junction detector arrays for high-resolution soft X-ray spectrometry. We have characterized the detector response function in the energy range between 50 and 2000 eV with monochromatic X-rays, in collaboration with the Physikalisch-Technische Bundesanstalt Laboratory at the BESSY II electron storage ring. The detectors have an energy resolution between 7 and 15 eV FWHM in that energy range, and a count rate capability of ∼10,000 counts/s per detector pixel. In addition, the detector response function exhibits several spectral artifacts, and although their magnitude is only on the order of 1% of the main line, they can reduce the sensitivity for X-ray analysis of dilute specimens if they overlap with the correspondingly weak emission lines. We have characterized these artifacts by scanning a collimated synchrotron radiation beam across the detector area. We identify their origin due to X-ray absorption at locations other than the main Nb absorber film, and outline future detector designs to reduce the artifacts and thereby extend the spectrometer sensitivity.

High‐Resolution X‐Ray Spectrum of the Accreting Binary X‐Ray Pulsar GX 1+4

We present here high resolution X-ray spectrum of the accreting binary X-ray pulsar GX 1+4 obtained with the High Energy Transmission Grating (HETG) instrument of the Chandra X-ray Observatory. This was supplemented by a simultaneous observation with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE). During this observation, the source was in a somewhat low intensity state and the pulse profile with both Chandra and RXTE shows a narrow dip, characteristic of GX 1+4 in medium and low intensity states. The continuum X-ray spectrum obtained with the HETG and PCA can be fitted well with a high energy cutoff power-law model with line of sight absorption. Interestingly, we find that this low state is accompanied by a relatively small absorption column density. A 6.4 keV narrow emission line with an equivalent width of 70 eV is clearly detected in the HETG spectrum. The fluorescence iron line, or at least part of it is produced in the neutral or lowly ionized iron in the circumstellar material that also causes most of the line of sight absorption. In the HETG spectrum, we have found evidence for a weak (equivalent width ~30 eV) emission line at 6.95 keV. This line is identified as Ly_alpha emission line from hydrogen-like iron and the spectrum does not show emission lines from helium-like iron. We discuss various emission regions for the hydrogen-like iron emission line, like gas diffused into the Alfven sphere or an accretion curtain flowing from the inner accretion disk to the magnetic poles.

Two Extreme Double-peaked Line Emitters in the Sloan Digital Sky Survey

Double-peaked Balmer lines have been observed in about 150 active galactic nuclei and were interpreted preferentially as emission from relativistic accretion disks. We report the discovery of extreme double-peaked lines in SDSS J0942+0900 and SDSS J1417+6141. The FWHM of the Hα line, 40,600 km s-1, in the first object is almost twice as large as the broadest previously known. By comparing the line profile with accretion disk models, we find that most of the line flux is emitted from a narrow annulus around 100rg in SDSS J0942+0900, and from a disk with radii between 100rg and 400rg in SDSS J1417+6141. This is the first time that an accretion disk at radii below 100rg has been directly probed through optical emission lines. A certain asymmetry in the disk is required for both objects. Another, much weaker, broad Hα component (Wλ ~ 20 A and FWHM ~ 4000 km s-1) is also detected in both objects. Both objects show weak radio emission and strong high-ionization narrow lines.

HE 0141-3932: A bright QSO with an unusual emission line spectrum and associated absorption

HE 0141−3932 (zem = 1.80) is a bright blue radio-quite quasar with an unusually weak Lyα emission line. Large redshift differences (∆z = 0.05) are observed between high ionization and low ionization emission lines. Absorption systems identified at zabs = 1.78, 1.71, and 1.68 show mild oversolar metallicities (Z ≈ 1−2 Z� ) and can be attributed to the associated gas clouds ejected from the circumnuclear region. The joint analysis of the emission and absorption lines leads to the conclusion that this quasar is seen almost pole-on. Its apparent luminosity may be Doppler boosted by ∼10 times. The absorbing gas shows a high abundance of Fe, Mg and Al ((Fe, Mg, Al/C) � 0.15 ± 0.10) along with underabundance of N ((N/C) ≤− 0.5). This abundance pattern is at variance with current chemical evolution models of QSOs predicting (N/C) > ∼ 0a nd (Fe/C) < 0a t Z ∼ Z� .

Reanalysis of the spectrum of the z = 10 galaxy

In a recent paper Pello et al. reported observations of a faint galaxy, gravitationally lensed by the galaxy cluster Abell 1835. Deep J-band spectroscopy revealed a weak emission line near 1.34 microns, detected in two spectra with different central wavelengths. The line was interpreted as Lyman-alpha at redshift z=10.0. This interpretation is supported by the broad-band photometric spectral energy distribution, and by the location of the galaxy close to the lens critical line for this redshift. We have reanalysed the two spectra, just released from the data archive. Our analysis includes allowance for wavelength shifts due to transverse drift of the object in the slit. We do not detect a significant emission line at the reported location, or nearby, at either grating setting, nor in the combined spectrum. We provide a possible explanation for the reported detection as due to spurious positive flux introduced in the sky-subtraction stage as a result of variable hot pixels. We provide our final reduced 2D frame, and corresponding error array.

The populations of planetary nebulae in the direction of the Galactic bulge

We have observed 44 planetary nebulae (PNe) in the direction of the Galactic bulge, and merged our data with published ones. We have distinguished, in the merged sample of 164 PNe, those PNe most likely to prtain physically to the Galactic bulge and those most likely to belong to the Galactic disk. We have determined the chemical composition of all the 164 objects in a coherent way. We looked for stellar emission features and discovered 14 new [WR] stars and 15 new weak emission line central stars. The analyzed data led us to the following conclusions: (1) the spectral type distribution of [WR] stars is very different in the bulge and in the disk of the Galaxy. However, the observed distributions are strongly dependent on selection effects. (2) The proportion of [WR] PNe is significantly larger in the bulge than in the disk. (3) The oxygen abundances in [WR] stars do no appear to be significantly affected by nucleosynthesis and mixing in the progenitors. (4) The O/H gradient of the Galactic disk PNe population flattens in the most internal parts of the Galaxy. (5) The median oxygen abundance in the bulge PN population is larger by 0.2 dex than in the disk population seen in the direction of the bulge. (6) Bulge PNe with smaller O/H tend to have smaller radial velocities. (7) The oxygen abundance distribution of bulge PNe is similar in shape to that of the metallicity distribution of bulge giants, but significantly narrower. (8) The location of SB 32 (PN G 349.7-09.1) in the (, ) diagram and its low oxygen abundance argues that it probably belongs to the halo population.

Identification of Three Weak Lines and Their Influences onDiagnostics of Electron Temperature and Density in Astrophysical Plasmas

By comparing of the spectra from the Chandra LETGs observation with thesynthetic spectra of argon, we identify two weak emission lines, thatis, the Ar XV 27.470 A line with transition2s3p 1P1−2s2 1S0 and the Ar XVI 27.872 A line withtransition 3d 2D3/2−2p 2P1/2, which blend with the NVII Lyα emission line. Severalsecond-order spectral lines are also identified, one of which isthe second-order Fe XVIII 14.534 A line withtransition 2p4(3P)3d 2F5/2−2p5 2P3/2, whichblends with theinter-combination line of He-like N VI. In order to study the effects ofthese new identified weak lines on the electron temperature anddensity, we diagnose the two parameters using the intensity ratioof triplets of the He-like N VI and that of resonance lines of H-and He-like N. In the literature, there is a discrepancy of thetemperatures deduced from N VI from other He-like ions, suchas C V and O VII. The discrepancy disappears after thecontribution of these weak lines is taken into account.

A spectroscopic atlas of the HgMn star HD 175640 (B9 V) $\lambda\lambda$ 3040–10 000 Å

We present a high resolution spectral atlas of the HgMn star HD 175640 covering the 3040-10 000 Å region. UVES spectra observed with 90 000-110 000 resolving power and signal to noise ratio ranging from 200 to 400 are compared with a synthetic spectrum computed with the SYNTHE code (Kurucz [CITE]). The model atmosphere is an ATLAS12 model (Kurucz [CITE]) with parameters = 12 000 K, = 3.95, ξ = 0 km s-1. The stellar individual abundances in ATLAS12 were derived from an iterative procedure. The starting atomic line lists downloaded from the Kurucz website have been improved and extended by examining different sources in the literature and by comparing the computed profiles with the observed spectrum. The high quality of the data allowed us to study the isotopic and hyperfine structure for several lines of , , , , , and . Numerous weak emission lines from and have been identified in the red part of the spectrum, starting at ≈λ 5847 Å. Two emission lines of (mult. 10, mult. 9) have been observed for the first time. All and emission lines originate from the high excitation states ( 89 000 cm-1 for and 62 000 cm-1 for ) with large transition probabilities (1.00). The synthetic spectrum superimposed on the observed spectrum as well as the adopted improved atomic line lists are available at the CDS and http://wwwuser.oat.ts.astro.it/castelli/stars.html. An extended discussion on each identified ion and related atomic data is available both on the quoted website and in an electronic Appendix to the paper.

Vertical Bridgman growth and annealing effect of Bi doped ZnSe single crystal

In order to prepare p-type ZnSe, bismuth (Bi) as an acceptor dopant was doped into ZnSe single crystal by vertical Bridgman method. Photoluminescence (PL) spectra measured at 4.2 K on as-grown crystal showed the strong shallow donor–acceptor pair (DsAP) emission, deep donor–acceptor pair (DdAP) emission and weak I1Bi emission line. To enhance the activation ratio of Bi in ZnSe single crystals, ZnSe:Bi was annealed in saturated zinc and selenium atmosphere at different temperatures. In the case of annealing in the range of 700–800 °C, DdAP emission disappeared and the intensities of DsAP and I1Bi emission relatively increased. From the dependence of PL spectra on excitation light intensity and the temperature, the acceptor activation energy and deep donor level were estimated about 103 meV and 34 meV, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Lyman Break Galaxies atz ∼ 5: Rest‐Frame Ultraviolet Spectra

We report initial results for spectroscopic observations of candidates of Lyman break galaxies (LBGs) at z ~ 5 in a region centered on the Hubble Deep Field-North by using the Faint Object Camera and Spectrograph attached to the Subaru Telescope. Eight objects with IC ≤ 25.0 mag, including one active galactic nucleus, are confirmed to be at 4.5 < z < 5.2. The rest-frame UV spectra of seven LBGs commonly show no or weak Lyα emission lines (rest-frame equivalent width of 0-10 A) and relatively strong low-ionization interstellar metal absorption lines of Si II λ1260, O I+Si II λ1303, and C II λ1334 (mean rest-frame equivalent widths of them are -1.2 to -5.1 A). These properties are significantly different from those of the mean rest-frame UV spectrum of LBGs at z ~ 3 but are quite similar to those of subgroups of LBGs at z ~ 3 with no or weak Lyα emission. The weakness of Lyα emission and strong low-ionization interstellar metal absorption lines may indicate that these LBGs at z ~ 5 are chemically evolved to some degree and have a dusty environment. Since the fraction of such LBGs at z ~ 5 in our sample is larger than that at z ~ 3, we may witness some sign of evolution of LBGs from z ~ 5 to z ~ 3, although the present sample size is very small. It is also possible, however, that the brighter LBGs tend to show no or weak Lyα emission, because our spectroscopic sample is bright (brighter than L*) among LBGs at z ~ 5. More observations are required to establish spectroscopic nature of LBGs at z ~ 5.

XMM – Newton observations of the Seyfert 1 galaxy ESO 141-G55

We report on an observation of the Seyfert 1 galaxy ESO 141–G55 performed in October 2001 with the EPIC MOS cameras and Reflection Grating Spectrometers (RGS) on board the XMM – Newton observatory. We find the hard (3–10 keV) continuum slope, including reflection, to be somewhat flatter (Γ=1.72±0.06) than that of a typical broad-line Seyfert 1 galaxy. The spectrum shows a weak emission line at 6.45 ± 0.04 keV with a measured equivalent width of ≈ 40 eV. A broad spectral feature is observed around 7 keV that can be fitted by an absorption edge at 7.6 ± 0.1 keV. The extrapolation of the primary power law continuum to energies lower than 2 keV indicates the presence of a soft excess component contributing 45± 3% of the overall flux in the 0.3–2.0 keV energy range. This soft-excess cannot be explained solely by enhanced reflection from a highly ionized disk.

0.8–13 Micron Spectroscopy of V838 Monocerotis and a Model for Its Emission

Abstract : We report on the results of a number of infrared spectra (0.8-2.5, 2.1-4.6, and 3-14 microns) of V838 Monocerotis, taken from a short time after discovery in 2002 January to about 14 months later, in early 2003. The spectrum evolved dramatically, changing from a quasi-photospheric stellar spectrum with weak atomic emission lines (some with P Cygni profiles) to one showing a wide range of deep absorption features indicative of a cool, extended atmosphere with a circumstellar dust shell. The early spectra showed lines of s-process elements, such as Sr II and Ba I. The later spectra showed absorption by gaseous H2O, CO, AlO, TiO, SiO, SO2, OH, VO, and SH, as well as a complex of emission near 10 microns reminiscent of silicate emission, with a central absorbing feature at 10:3 microns. Thus, V838 Mon appears to be oxygen-rich. A simple, spherically symmetric model of the system involving a central star with a two-component expanding circumstellar shell is presented that is able to explain the major molecular features and spectral energy distribution in the object's late stages. The derived shell mass and distance are 0.04 M(circle dot solar) and 9.2 kpc, respectively.

Emission lines in the optical spectrum of 3 Cen A

Previously, weak emission lines had been detected at red wavelengths in the spectra of a limited sample of mid to late B type main sequence stars. A fuller description of the occurrence and origins of these lines has yet to be forwarded, in part due to the lack of observations detailing the spectral transitions involved. To address this deficiency, we present a line list of weak emission features found in the optical and near infrared spectral region of the chemically peculiar He-weak star 3 Cen A (HD 120709). Nearly 350 features, mostly associated with allowed transitions from high-excitation states of first ions, are catalogued along with identifications. Prominent among the emission lines are the spectra P II, Mn II, Fe II, Ni II and Cu II. Emission lines from Ca II, Si II and Hg II are also evident. Abundances are determined for several elements from synthetic spectrum fitting, with anomalies detected for the ions O I/II, P II/III and Si II/III. The LTE synthetic spectrum fitting also revealed that the low excitation 4s−4p transitions of Fe II predict an abundance that is greater than that determined from higher excitation 4d−4f transitions. Several of these latter transitions have upper energy levels that are found to be associated with emission lines. We also present empirical considerations for the excitation processes leading to the weak emission lines.

BeppoSAXobservations of the accretion-powered X-ray pulsar SMC X-1

We present here results obtained from three BeppoSAX observations of the accretion-powered X-ray pulsar SMC X-1 carried out during the declining phases of its 40--60 days long super-orbital period. Timing analysis of the data clearly shows a continuing spin-up of the neutron star. Energy-resolved timing analysis shows that the pulse-profile of SMC X-1 is single peaked at energies less than 1.0 keV whereas an additional peak, the amplitude of which increases with energy within the MECS range, is present at higher energies. Broad-band pulse-phase-averaged spectroscopy of the BeppoSAX data, which is done for the first time since its discovery, shows that the energy spectrum in the 0.1--80 keV energy band has three components, a soft excess that can be modeled as a thermal black-body, a hard power-law component with a high-energy exponential cutoff and a narrow and weak iron emission line at 6.4 keV. Pulse-phase resolved spectroscopy indicates a pulsating nature of the soft spectral component, as seen in a few other binary X-ray pulsars, with a certain phase offset with respect to the hard power-law component. Dissimilar shape and phase of the soft and hard X-ray pulse profiles suggest a different origin of the soft and hard components.

Timing and Spectral Studies of the Transient X‐Ray Pulsar EXO 053109−6609.2 withASCAandBeppoSAX

We report timing and spectral properties of the transient Be X-ray pulsar EXO 053109--6609.2 studied using observations made with the ASCA and BeppoSAX observatories. Though there must have been at least one spin-down episode of the pulsar since its discovery, the new pulse period measurements show a monotonic spin-up trend since 1996. The pulse profile is found to have marginal energy dependence. There is also evidence for strong luminosity dependence of the pulse profile, a single peaked profile at low luminosity that changes to a double peaked profile at high luminosity. This suggests a change in the accretion pattern at certain luminosity level. The X-ray spectrum is found to consist of a simple power-law with photon index in the range of 0.4--0.8. At high intensity level the spectrum also shows presence of weak iron emission line.

A joint mid-infrared spectroscopic and X-ray imaging investigation of LINER galaxies

We present a comprehensive comparative high resolution mid-IR spectroscopic and X-ray imaging investigation of LINERs using archival observations from the ISO-SWS and the Chandra Advanced CCD Imaging Spectrometer. Although the sample is heterogenous and incomplete, this is the first comprehensive study of the mid-infrared fine structure line emission of LINERs. These results have been compared with similar observations of starburst galaxies and AGN. We find that LINERs very clearly fall between starbursts and AGN in their mid-IR fine structure line spectra, showing /LFIR and / ratios, both measures of the dominant nuclear energy source in dust-enshrouded galaxies, intermediate between those of AGN and starbursts. Chandra imaging observations of the LINERs reveal hard nuclear point sources morphologically consistent with AGN in most (67%) of the sample, with a clear trend with IR-brightness. Most LINERs that show a single dominant hard compact X-ray core are IR-faint (LFIR/), whereas most LINERs that show scattered X-ray sources are IR-bright. A comparative X-ray/mid-IR spectroscopic investigation of LINERs reveals some puzzling results. Objects that display strong hard nuclear X-ray cores should also display high excitation lines in the IR. However, we find two LINERs disagree with this expectation. The galaxy NGC 404 shows weak soft X-ray emission consistent with a starburst but has the most prominent highest excitation mid-IR spectrum of our entire sample. Using IR emission line diagnostics alone, this galaxy would be classified as hosting a dominant AGN. Conversely, the IR luminous LINER NGC 6240 has an extremely luminous binary AGN as revealed by the X-rays but shows weak IR emission lines. With the advent of SIRTF, and future IR missions such as Herschel and JWST, it is increasingly critical to determine the origin of these multiwavelength anomalies.

The nuclear region of low luminosity flat radio spectrum sources

We report on the spectroscopic study of 19 low luminosity Flat Radio Spectrum (LL FRS) sources selected from Marchã's et al. ([CITE]) 200 mJy sample. In the optical, these objects are mainly dominated by the host galaxy starlight. After correcting the data for this effect, we obtain a new set of spectra clearly displaying weak emission lines; such features carry valuable information concerning the excitation mechanisms at work in the nuclear regions of LL FRS sources. We have used a special routine to model the spectra and assess the intensities and velocities of the emission lines; we have analyzed the results in terms of diagnostic diagrams. Our analysis shows that 79% of the studied objects harbour a Low Ionization Nuclear Emission-line Region (or LINER) whose contribution was swamped by the host galaxy starlight. The remaining objects display a higher ionization spectrum, more typical of Seyferts; due to the poor quality of the spectra, it was not possible to identify any possible large Balmer components. The fact that we observe a LINER-type spectrum in LL FRS sources supports the idea that some of these objects could be undergoing an ADAF phase; in addition, such a low ionization emission-line spectrum is in agreement with the black hole mass values and sub-Eddington accretion rates published for some FRS sources.

Mapping of Mars O 2 1.27 μm dayglow at four seasonal points

The O 2 dayglow at 1.27 μm is formed by high-altitude ozone on Mars and is a sensitive tracer of Mars photochemistry. Mapping of this dayglow using the IRTF/CSHELL long-slit spectrograph requires the extraction of weak emission lines against a strong continuum of the reflected solar light. Some new tools are suggested to improve the data processing. The observed O 2 dayglow intensities at L S=67°, 112°, 148°, and 173° show a decrease from late spring (aphelion) to fall equinox by a factor of ≈5 at low latitudes (±30°). This decrease agrees with that predicted by a model of Clancy and Nair (1996, J. Geophys. Res. 101 (12) 12785–12790), although the dayglow intensities are weaker than those based on that model. The measured dayglow variations with latitude are rather low at L S=67°, 112°, and 148° and unexpectedly high at 173°. The dayglow intensity peaks near noon and is smaller at 9:00 and 16:30 LT by a factor of 2. Some data on the ozone profile near aphelion are obtained from a combination of the dayglow and ozone observations. It is hardly possible to detect the O 2 night airglow at 1.27 μm on Mars using the existing ground-based and on-orbit instruments. The O 2 dayglow intensity as a function of latitude and season from aphelion to fall equinox has been obtained. Our goal is to extend this distribution to the full martian year and get a database for Mars photochemistry to complement the MGS/TES observations of water vapor, atmospheric temperature, and dust and ice aerosol.

Hubble Space TelescopeObservations of the Nova-like Cataclysmic Variable V348 Puppis

We present time series UV and optical (1150 -- 8000 A) spectrophotometry of the novalike (NL) cataclysmic variable V348 Pup through and after eclipse. Outside of eclipse, the spectrum is characterized by a blue continuum, strong line emission, and a broad dip from 2000 -- 3000 A. The continuum eclipse depth is roughly the same over the entire wavelength range covered and there are no signatures of the WD eclipse in the light curves. Model steady-state accretion disk spectra provide a poor fit to the shape of the UV-optical spectrum outside of eclipse. All of these properties are consistent with a disk that is self-shielding, hiding the inner disk and the white dwarf. In eclipse, the emission lines and the broad dip are occulted less than the continuum, indicating vertical extension in these components. The dip is consistent with the presence of a vertical ``Fe II'' absorbing curtain in the system. Archival UV-optical spectra of the lower-inclination NL UX UMa show a bluer continuum and weaker line emission than in V348 Pup and no broad dip. There is strong flickering in V348 Pup. The flickering spectrum shows that the flickering occurs only in the continuum. We did not detect any periodicities associated with the rapid variability. The properties of V348 Pup are consistent with its previous identification as a member of the SW Sex sub-class of NLs.

Diffuse Hard X‐Ray Sources Discovered with theASCAGalactic Plane Survey

We found diffuse hard X-ray sources G11.0+0.0, G25.5+0.0, and G26.6-0.1 in the ASCA Galactic plane survey data. The X-ray spectra are featureless with no emission line and are fitted with both models of a thin thermal plasma in nonequilibrium ionization and a power-law function. The source distances are estimated to be 1-8 kpc, using the best-fit NH values under the assumption that the mean density in the line of sight is 1 H cm-3. The source sizes and luminosities are then 4.5-27 pc and (0.8-23) × 1033 ergs s-1. Although the source sizes are typical for supernova remnants (SNR) with young-to-intermediate ages, the X-ray luminosity, plasma temperature, and weak emission lines in the spectra are all unusual. This suggests that these objects are either shell-like SNRs dominated by X-ray synchrotron emission, like SN 1006 or, alternatively, plerionic SNRs. The total number of these classes of SNRs in our Galaxy is also estimated.