Near-infrared Lines Research Articles

Optical and near-infrared recombination lines of oxygen ions from Cassiopeia A knots

Context. Fast-moving knots (FMK) in the Galactic supernova remnant Cassiopeia A consist mainly of metals and allow us to study element production in supernovae and to investigate shock physics in great detail.Aims. We discuss and suggest observations of a previously unexplored class of spectral lines, the metal recombination lines in optical and near-infrared bands, emitted by the cold ionized and cooling plasma in fast-moving knots.Methods. By tracing ion radiative and dielectronic recombination, collisional l -redistribution and radiative cascade processes, we compute resulting oxygen, silicon and sulphur recombination line emissivities. This allows us to determine the oxygen recombination line fluxes, based on a fast-moving knot model that predicts the existence of highly-ionized ions from moderate to very low plasma temperatures.Results. The calculations predict oxygen ion recombination line fluxes detectable with modern optical telescopes in the wavelength range from 0.5 to 3 μ m. Recombination line flux ratios to collisionally-excited lines will allow us to probe in detail the process of rapid cloud cooling after the passage of a shock front, to test high abundances of O4+ , O5+ and O6+ ions at low temperatures and measure them, to test existing theoretical models of FMK and to build more precise ones.

Novel oxychloroborate glasses containing neodymium ions: Synthesis, structure and luminescent properties

Novel oxychloroborate glasses containing Nd 3+ ions in the B 2O 3–PbCl 2–PbO–Al 2O 3–WO 3 system were investigated. The results on synthesis, short-range order structure and luminescent properties are reported. The influence of the PbCl 2 content on the glass properties was analyzed. The near-infrared luminescence lines at 0.91, 1.06 and 1.33 μm were registered in oxychloride lead borate glasses, which correspond to the transitions from the 4F 3/2 state to the 4I 9/2, 4I 11/2 and 4I 13/2 low-lying states of the Nd 3+ ions. Luminescence decays from the 4F 3/2 state were analyzed, in details. The effect of OH − content on the 4F 3/2 lifetime of Nd 3+ is much stronger than decreasing of phonon energy of the host. Consequently, the measured 4F 3/2 lifetime of Nd 3+ slightly decreases with the increasing of PbCl 2 concentration.

Probing the Central Regions of Nearby Compact Elliptical Galaxies

K-band spectroscopic observations recorded with NIFS+ALTAIR on Gemini North are used to probe the central arcsec of the compact elliptical galaxies NGC 4486B, NGC 5846A, and M32. The angular resolution of these data is ~0.1 arcsec FWHM. The central stellar contents of NGC 4486B and NGC 5846A are similar, in the sense that they occupy the same regions of the (Ca I, 12CO), (Na I, 12CO) and (13CO, 12CO) diagrams. The NGC 4486B and NGC 5846A observations depart from the sequence defined by solar neighborhood giants in the (Na I, 12CO) diagram, in a sense that is consistent with both galaxies having non-solar chemical mixtures. For comparison, the M32 data is consistent with a chemical enrichment history like that in the Galactic disk; M32 could not have formed from the stripping of a larger elliptical galaxy. The behaviour of the near-infrared line indices as a function of radius is also investigated. The radial gradients that are present in NGC 4486B and NGC 5846A at large radii break down or reverse within the central few tenths of an arcsec. Evidence is presented that the nuclear regions of NGC 4486B and NGC 5846A harbour intermediate age populations.

M1–78: a nitrogen-rich Galactic compact H II region beyond the Perseus arm

Context. There is considerable controversy surrounding the nature of M1−78, a compact nebula located beyond the Perseus arm. It was first classified as a planetary nebula and is nowadays generally considered to be a compact H ii region. Aims. To investigate the nature of M1−78 further, we present a detailed spectroscopic study of M1−78 in the optical and near-infrared. Methods. We obtained long-slit, intermediate-resolution, optical spectroscopy with the ISIS spectrograph mounted on the William Herschel Telescope (WHT) at Roque de los Muchachos Observatory (La Palma, Spain). As a complement, we obtained long-slit, intermediate-resolution, near-infrared spectra using LIRIS, the near-infrared imager/spectrographer also installed at the WHT. Results. M1−78 is a high-density nebula with substantial physical differences between its two main morphological zones: a bright arc in the SW and a blob of emission in the NE. Specifically, the blob in the NE has a higher electron temperature (13 400 K) and visual extinction (about 9 mag) than the SW arc. The most important result, however, is the confirmation of a nitrogen enrichment in M1−78. This enrichment is stronger at the location of the NE blob and is correlated with a defficiency in the O abundance and a (dubious) He enrichment. Such an abundance pattern is typical of ejecta nebulae around evolved massive stars such as Wolf-Rayet and Luminous Blue Variable stars. The spatial variations in the physical conditions and chemical abundances and the presence of more than one possible ionizing source indicate, however, that M1−78 is better described as a combination of a compact H ii region + ejecta. This is confirmed by the He i 2.112 µm/Brγ line ratio, which indicates a hot (Teff > 40 000 K) O star in the SW arc. Finally, we detect H2 emission that extends over a large (∼30 �� ) area around the ionized nebula. Analysis of the near-infrared H2 lines indicates

Tracing the origins of permitted emission lines in RU Lupi down to AU scales

Context. Most of the observed emission lines and continuum excess from young accreting low mass stars (Classical T Tauri stars – CTTSs) take place in the star-disk or inner disk region. These regions have a complex emission topology that is still largely unknown. Aims. In this paper the magnetospheric accretion and inner wind contributions to the observed permitted He and H near infrared (NIR) lines of the bright southern CTTS RU Lupi are investigated for the first time. Methods. Previous optical observations of RU Lupi have shown a strong Hα profile, due to the emission from a wind in the line wings, and a micro-jet detected in forbidden lines. We extend this analysis to NIR lines through the seeing-limited, high spectral-resolution spectra taken with VLT/ISAAC, and narrow-band imaging and low spectral-resolution spectroscopy acquired with the adaptive optics (AO) aided telescope VLT/NACO. Using spectro-astrometric analysis we investigate the presence of extended emission down to very low spatial scales (a few AU). Results. The HeI λ10830 line presents a P Cygni profile whose absorption feature indicates the presence of an inner stellar wind. Moreover, the spectro-astrometric analysis proves the presence of an extended emission superimposed on the absorption feature and likely coming from the micro-jet detected in the optical. In contrast, the origin of the hydrogen Paschen and Brackett lines is difficult to address. We tried to explain the observed line profiles and flux ratios with both accretion and wind models showing the limits of both approaches. The lack of a spectro-astrometric signal indicates that the HI emission is either compact or symmetric. Our analysis confirms the sensitivity of the HeI line to the faint extended emission regions in the close proximity of the star.

PARP1-dependent Kinetics of Recruitment of MRE11 and NBS1 Proteins to Multiple DNA Damage Sites

Poly(ADP-ribose) polymerase 1 (PARP1) is a nuclear enzyme that is rapidly activated by DNA strand breaks and signals the presence of DNA lesions by attaching ADP-ribose units to chromatin-associated proteins. The therapeutic applications of PARP inhibitors in potentiating the killing action of ionizing radiation have been well documented and are attracting increasing interest as a cancer treatment. However, the initial kinetics underlying the recognition of multiple DNA lesions by PARP1 and how inhibition of PARP potentiates the activity of DNA-damaging agents are unknown. Here we report the spatiotemporal dynamics of PARP1 recruitment to DNA damage induced by laser microirradiation in single living cells. We provide direct evidence that PARP1 is able to accumulate at a locally induced DNA double strand break. Most importantly, we observed that the rapid accumulation of MRE11 and NBS1 at sites of DNA damage requires PARP1. By determining the kinetics of protein assembly following DNA damage, our study reveals the cooperation between PARP1 and the double strand break sensors MRE11 and NBS1 in the close vicinity of a DNA lesion. This may explain the sensitivity of cancer cells to PARP inhibitors.

Quiet-Sun Internetwork Magnetic Fields from the Inversion of Hinode Measurements

We analyze Fe I 630 nm observations of the quiet Sun at disk center taken with the spectropolarimeter of the Solar Optical Telescope aboard the Hinode satellite. A significant fraction of the scanned area, including granules, turns out to be covered by magnetic fields. We derive field strength and inclination probability density functions from a Milne-Eddington inversion of the observed Stokes profiles. They show that the internetwork consists of very inclined, hG fields. As expected, network areas exhibit a predominance of kG field concentrations. The high spatial resolution of Hinode's spectropolarimetric measurements brings to an agreement the results obtained from the analysis of visible and near-infrared lines.

Near-infrared spectra of Seyfert galaxies and line production mechanisms

New observations are reported of J-band spectra (1.04micron -- 1.4 micron) of three Seyfert 2 galaxies, Mkn 34, Mkn 78 and NGC 5929. In each case the spectral range includes the near-infrared lines of [FeII], [PII], HeI and Pa beta. Each Seyfert galaxy has a known radio jet, and we investigate the infrared line ratios of the nuclear and extended regions of each galaxy compared to the radio structure. In Mkn 34 there is a clear indication of an extranuclear region, probably coincident with a shock induced by the radio jet, in which [FeII] is considerably enhanced, although the nuclear emission is almost certainly the result of photoionization by the continuum of the active nucleus. Similar effects in extranuclear regions are seen in the other objects, in the case of Mkn 78 confirming recent studies by Ramos Almeida et al. A possible detection of extranuclear [PII] emission suggests, if real, that photoionization by the active nucleus is the dominant line excitation mechanism over the whole source, including the regions coincident with the radio jet.

The Abundances of Light Neutron‐Capture Elements in Planetary Nebulae. I. Photoionization Modeling and Ionization Corrections

We have conducted a large-scale survey of 120 planetary nebulae (PNe) to search for the near-infrared emission lines [Kr III] 2.199 μm and [Se IV] 2.287 μm. The neutron (n)-capture elements Se and Kr may be enriched in a PN if its progenitor star experienced s-process nucleosynthesis and third dredge-up. In order to determine Se and Kr abundances, we have added these elements to the atomic databases of the photoionization codes Cloudy and XSTAR, which we use to derive ionization correction factors (ICFs) to account for the abundances of unobserved Se and Kr ions. However, much of the atomic data governing the ionization balance of these two elements are unknown, and have been approximated from general principles. We find that uncertainties in the atomic data can lead to errors approaching 0.3 dex in the derived Se abundances and up to 0.2-0.25 dex for Kr. To reduce the uncertainties in the Kr ionization balance stemming from the approximate atomic data, we have modeled 10 bright PNe in our sample, selected because they exhibit emission lines from multiple Kr ions in their optical and near-infrared spectra. We have empirically adjusted the uncertain Kr atomic data until the observed line intensities of the various Kr ions are adequately reproduced by our models. Using the adjusted Kr atomic data, we have computed a grid of models over a wide range of physical parameters (central star temperature, nebular density, and ionization parameter) and derived formulae that can be used to compute Se and Kr ICFs. In the second paper of this series, we will apply these ICFs to our full sample of 120 PNe, which comprises the first large-scale survey of n-capture elements in PNe.

A Spectroscopic Study of Nuclear Processing and the Production of Anomalously Strong Lines in the Crab Nebula

We present and discuss correlations for optical and near-infrared (5500-10030 Å) line intensity measurements at many positions in the Crab Nebula. These correlations suggest the existence of gas produced by a range of nuclear processing, from material in which synthesis ended with the CNO cycle, to some helium burning and nitrogen depletion, to regions containing enriched products of oxygen burning. The latter exhibit a gradual, linear rise of [Ni II] emission with increasing argon enrichment, whereas gas with less nuclear processing shows markedly different [Ni II] emission characteristics, including the highest derived abundances. This suggests two origins for stable, neutron-rich nickel in the nebula: a type of "alpha-rich freeze out" in the more highly processed material and possibly removal of ions from the neutron star in other regions. In addition, the data indicate that anomalously strong observed [C I] emission comes from broad, low-ionization H+ to H0 transition zones. Although the strongest He I emission could also be enhanced in similar low-ionization gas, correlations between relevant line ratios argue against that interpretation, strengthening the case for an exceptionally high helium mass fraction in some locations.

Near-IR bromine Laser Induced Breakdown Spectroscopy detection and ambient gas effects on emission line asymmetric Stark broadening and shift

Investigation via Laser-Induced Breakdown Spectroscopy of a near-infrared bromine emission line (827.2 nm) with an UltraViolet ablation laser and a gated detector is reported. The effects of ambient pressure and gas species (air, O 2, N 2 and He) on the atomic emission line strength and spectral profile were systematically investigated. Substantially improved signal strength and reduced background radiation are demonstrated near 100 mbar ambient pressure with all gases. Optimal results were achieved when helium was used. Asymmetric broadening and shift of the 827.2 nm bromine line, attributed to pressure-dependent Stark effect has been revealed. This effect is prominent when air, oxygen or nitrogen are present and is much less manifested when helium is used. Possible interpretations of this effect are presented.

On the signatures of gravitational redshift: the onset of relativistic emission lines

Aims. We quantify the effect of gravitational redshift on emission lines to explore the transition region from the Newtonian to the Einsteinian regime. With the emitting region closer to the Kerr black hole, lines are successively subjected to a stronger gravitationally induced shift and distortion. Simulated lines are compared to broad, optical emission lines observed in Mrk 110. Methods. We simulate relativistic emission line profiles by using Kerr ray tracing techniques. Emitting regions are assumed to be thin equatorial rings in stationary Keplerian rotation. The emission lines are characterised by a generalized Doppler factor or redshift associated with the line core. Results. With decreasing distance from the black hole, the gravitational redshift starts to smoothly deviate from the Newtonian Doppler factor: Shifts of the line cores reveal an effect at levels of 0.0015 to 60% at gravitational radii ranging from 10^{5} to 2. This corresponds to fully relativistic Doppler factors of 0.999985 to 0.4048. The intrinsic line shape distortion by strong gravity i.e. very asymmetric lines occur at radii smaller than roughly ten gravitational radii. Conclusions. Due to the asymptotical flatness of black hole space-time, GR effects are ubiquitous and their onset can be tested observationally with sufficient spectral resolution. With a resolving power of ~100000, yielding a resolution of ~0.1 Angstroems for optical and near-infrared broad emission lines like H\beta, HeII and Pa\alpha, the gravitational redshift can be probed out to approximately 75000 gravitational radii. [abridged]

Evershed Clouds as Precursors of Moving Magnetic Features around Sunspots

The relation between the Evershed flow and moving magnetic features (MMFs) is studied using high-cadence, simultaneous spectropolarimetric measurements of a sunspot in visible (630.2 nm) and near-infrared (1565 nm) lines. Doppler velocities, magnetograms, and total linear polarization maps are calculated from the observed Stokes profiles. We follow the temporal evolution of two Evershed clouds that move radially outward along the same penumbral filament. Eventually, the clouds cross the visible border of the spot and enter the moat region, where they become MMFs. The flux patch farther from the sunspot has the same polarity of the spot, while the MMF closer to it has opposite polarity and exhibits abnormal circular polarization profiles. Our results provide strong evidence that at least some MMFs are the continuation of the penumbral Evershed flow into the moat. This, in turn, suggests that MMFs are magnetically connected to sunspots.

U Geminorum: a Test Case for Orbital Parameters Determination

AbstractHigh-resolution spectroscopy of U Gem was obtained during quiescence. We did not find a hot spot or gas stream around the outer boundaries of the accretion disk. Instead, we detected a strong narrow emission near the location of the secondary star. We measured the radial velocity curve from the wings of the double-peaked Hα emission line, and obtained a semi-amplitude value in excellent agreement with the ultraviolet results by Long & Gilliland (1999). We present also a new method to obtain K2, which enhances the detection of absorption or emission features arising in the late-type companion. Our results are compared with published values derived from the near-infrared NaI line doublet. From a comparison of the TiO band with those of late type M stars, we find that a best fit is obtained for a M6 V star, contributing 5% of the total light at that spectral region. Assuming that the radial velocity semi-amplitudes reflect accurately the motion of the binary components, then from our results: Kem = 108 ± 2 km s−1; Kabs = 310 ± 5 km s−1, and using the inclination angle by Zhang & Robinson (1987); i = 69°.7 ± 0.7, the system parameters become: MWD = 1.20 ± 0.05 M⊙; MRD = 0.42 ± 0.04 M⊙; and a = 1.55 ± 0.02 R⊙. Based on the separation of the double emission peaks, we calculate an outer disk radius of Rout/a ∼ 0.63, close to the distance of the inner Lagrangian point L1/a ∼ 0.63. Therefore we suggest that, at the time of observations, the accretion disk was filling the Roche-Lobe of the primary, and that the matter leaving the L1 point was colliding with the disc directly, producing the hot spot at this location. Specific details not included in the printed version can be found in the Electronic Poster (EP).

Passive optical diagnostic of Xe-propelled Hall thrusters. I. Emission cross sections

This paper presents a set of xenon apparent emission excitation cross sections for emission lines that have diagnostic value in the analysis of Xe-propelled Hall thruster plasmas. Emission cross sections are presented for three excitation processes involving ground-state xenon atoms: e−+Xe, Xe++Xe, and Xe2++Xe. The cross sections are derived from luminescence spectra produced at single-collision conditions. Apparent emission excitation cross sections are tabulated for 12 visible and 8 near-infrared lines for electron energies ranging from 10to70eV. In case of the near-infrared lines, radiation trapping effects are accounted for by measuring the detailed pressure dependence of the apparent emission cross sections and extrapolating to zero pressure. A semiempirical expression for the pressure dependence is derived that allows zero-pressure extrapolation from threshold to 70eV. Ion-induced cross sections are reported for the same emission lines at an energy per unit charge E∕q of 300eV, chosen for typical Hall thruster operating voltages. Radiation trapping effects are negligible for the ion emission excitation cross sections between 0.1 and 2.0mTorr in the present luminescence experiment.

Radio and infrared recombination studies of the southern massive star forming region G333.6-0.2

We present high spatial resolution radio and near-infrared hydrogen recombination line observations of the southern massive star-forming region G333.6 0.2. The 3.4-cm continuum peak is found slightly offset from the infrared source. The H90α spectra show for the first time a double peak profile at some positions. The complex velocity s tructure may be accounted for by champagne outflows, which may also explain the offset betw een the radio and infrared sources. The 2.17-µm Brγ image and H90α map are combined to construct an extinction map which shows a trend probably set by the blister nature of the H II region. The total number of Lyman continuum photons in the central 50-arcsec is estimated to be equivalent to that emitted by up to 19 O7V stars.

Passive optical diagnostic of Xe propelled Hall thrusters. II. Collisional-radiative model

A collisional radiative model is presented for analyzing the xenon-propelled Hall thruster optical radiation based on apparent electron and ion-impact emission cross sections associated with lines in the visible and near-infrared region of the spectrum. The emission cross sections of selected near-infrared emission lines are incorporated in a collisional-radiative model. The effect of stepwise excitation via metastable states on the derived line intensities for emissions from XeI 5p56p(6p′) levels is evaluated. Meanwhile, visible XeII emissions are shown to provide plasma densities at high electron temperature conditions. The electron temperature and spatial ion number density distribution were determined from the luminescence spectra measured in the discharge and plume near-field plasma of the Hall thruster, the TSNIIMASH D-55 anode layer thruster. The results are in good agreement with the probe measurement data and simulations reported in the literature for the same thruster. The analysis of the Hall thruster XeI near-infrared spectra demonstrates that the neglect of ion-atom collisions results in an erroneous electron temperature determination at electron temperatures below 10eV.

Measuring Magnetic Fields in Ultracool Stars and Brown Dwarfs

We present a new method for direct measurement of magnetic fields on ultracool stars and brown dwarfs. It takes advantage of the Wing-Ford band of FeH, which are seen throughout the M and L spectral types. These molecular features are not as blended as other optical molecular bands, are reasonably strong through most of the spectral range, and exhibit a response to magnetic fields which is easier to detect than other magnetic diagnostics, including the usual optical and near-infrared atomic spectral lines that have heretofore been employed. The FeH bands show a systematic growth as the star gets cooler. We do not find any contamination by CrH in the relevant spectral region. We are able to model cool and rapidly-rotating spectra from warmer, slowly-rotating spectra utilizing an interpolation scheme based on optical depth scaling. We show that the FeH features can distinguish between negligible, moderate, and high magnetic fluxes on low-mass dwarfs, with a current accuracy of about one kilogauss. Two different approaches to extracting the information from the spectra are developed and compared. Which one is superior depends on a number of factors. We demostrate the validity of our new procedures by comparing the spectra of three M stars whose magnetic fluxes are already known from atomic line analysis. The low and high field stars are used to produce interpolated moderate-strength spectra which closely resemble the moderate-field star. The assumption of linear behavior for the magnetic effects appears to be reasonable, but until the molecular constants are better understood the method is subject to that assumption, and rather approximate. Nonetheless, it opens a new regime of very low-mass objects to direct confirmation and testing of their magnetic dynamos.

Oscillator Strengths of Near‐Infrared Lines of Feii

We present extensive configuration interaction calculations of oscillator strengths and transition rates of certain near-infrared emission lines of Fe II observed in the BD Weigelt blobs of η Carinae. Comparison is made between our work and results available in existing databases. We offer arguments in favor of our results being the most accurate, where differences occur.

Near-infrared line spectropolarimetry of hot massive stars

In order to study the inner parts of the circumstellar materi al around optically faint, infrared bright objects, we present the first medium-resolution spec tropolarimetric data taken in the near-infrared. In this paper we discuss Paline data of GL 490, a well-known embedded massive young stellar object, and of MWC 349A and MWC 342, twooptically faint stars that are proposed to be in the pre-main sequence phase of evolution. As a check on the method, the classical Be starTau, known to display polarization changes at optical wavelengths, was observed as well. Three of our targets show a line across Pa�. ForTau and MWC 349A this effect is due to depolarisation by a circumstellar electron-scattering disk. In both cases, the position angle of the polarisation i s consistent with that of the larger scale disks imaged at other wavelengths, validating infrar ed spectropolarimetry as a means to detect flattening on small scales. The tentative detectio n of a rotation in the polarization position angle at Pain the embedded massive young stellar object GL 490 suggests the presence of a small scale rotating accretion disk with an inner hole - similar to those recently discovered at optical wavelengths in Herbig Ae and T Tauri stars.