Strong Absorption Lines Research Articles

The 2dF Galaxy Redshift Survey: the local E+A galaxy population

We select a sample of low-redshift (z ~ 0.1) E+A galaxies from the 2dF Galaxy Redshift Survey (2dFGRS). The spectra of these objects are defined by strong hydrogen Balmer absorption lines (H-delta, H-gamma, H-beta) combined with a lack of [OII] 3727A emission, together implying a recently-truncated burst of star formation. The E+A spectrum is thus a signpost to galaxies in the process of evolution. We quantify the local environments, clustering properties and luminosity function of the E+A galaxies. We find that the environments are consistent with the ensemble of 2dFGRS galaxies: low-redshift E+A systems are located predominantly in the field, existing as isolated objects or in poor groups. However, the luminosity distribution of galaxies selected using three Balmer absorption lines H-delta-gamma-beta appears more typical of ellipticals. Indeed, morphologically these galaxies are preferentially spheroidal (E/S0) systems. In a small but significant number we find evidence for recent major mergers, such as tidal tails. We infer that major mergers are one important formation mechanism for E+A galaxies, as suggested by previous studies. At low redshift the merger probability is high in the field and low in clusters, thus these recently-formed spheroidal systems do not follow the usual morphology-density relation for ellipticals. Regarding the selection of E+A galaxies: we find that basing the Balmer-line criterion solely on H-delta absorption leads to a significant sub-population of disk systems with detectable H-alpha emission. In these objects the [OII] emission is presumably either obscured by dust or present with a low signal-to-noise ratio, whilst the (H-gamma, H-beta) absorption features are subject to emission-filling.

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.

Jahn–Teller effect in van der Waals complexes; Ar–C6H6+ and Ar–C6D6+

The two asymptotically degenerate potential energy surfaces of argon interacting with the X (2)E(1g) ground state benzene(+) cation were calculated ab initio from the interaction energy of the neutral Ar-benzene complex given by Koch et al. [J. Chem. Phys. 111, 198 (1999)] and the difference of the geometry-dependent ionization energies of the complex and the benzene monomer computed by the outer valence Green's function method. Coinciding minima in the two potential surfaces of the ionic complex occur for Ar on the C(6v) symmetry axis of benzene(+) (the z axis) at z(e)=3.506 A. The binding energy D(e) of 520 cm(-1) is only 34% larger than the value for the neutral Ar-benzene complex. The higher one of the two surfaces is similar in shape to the neutral Ar-benzene potential, the lower potential is much flatter in the (x,y) bend direction. Nonadiabatic (Jahn-Teller) coupling was taken into account by transformation of the two adiabatic potentials to a two-by-two matrix of diabatic potentials. This transformation is based on the assumption that the adiabatic states of the Ar-benzene(+) complex geometrically follow the Ar atom. Ab initio calculations of the nonadiabatic coupling matrix element between the adiabatic states with the two-state-averaged CAS-SCF(5,6) method confirmed the validity of this assumption. The bound vibronic states of both Ar-C(6)H(6) (+) and Ar-C(6)D(6) (+) were computed with this two-state diabatic model in a basis of three-dimensional harmonic oscillator functions for the van der Waals modes. The binding energy D(0)=480 cm(-1) of the perdeuterated complex agrees well with the experimental upper bound of 485 cm(-1). The ground and excited vibronic levels and wave functions were used, with a simple model dipole function, to generate a theoretical far-infrared spectrum. Strong absorption lines were found at 10.1 cm(-1) (bend) and 47.9 cm(-1) (stretch) that agree well with measurements. The unusually low bend frequency is related to the flatness of the lower adiabatic potential in the (x,y) direction. The van der Waals bend mode of e(1) symmetry is quadratically Jahn-Teller active and shows a large splitting, with vibronic levels of A(1), E(2), and A(2) symmetry at 1.3, 10.1, and 50.2 cm(-1). The level at 1.3 cm(-1) leads to a strong absorption line as well, which could not be measured because it is too close to the monomer line. The level at 50.2 cm(-1) gives rise to weaker absorption. Several other weak lines in the frequency range of 10 to 60 cm(-1) were found.

Metal Enrichment in Near-Infrared Luminous Galaxies at z ~ 2: Signatures of Proto-elliptical Galaxies?

We present the analysis of the co-added rest-frame UV spectrum (1200 A < z < 2000 A) of five K-luminous galaxies at z ~2 from the K20 survey. The composite spectrum is characterized by strong absorption lines over the UV continuum from C, N, O, Al, Si, and Fe in various ionization stages. While some of these lines are interstellar, several among the strongest absorptions are identified with stellar photospheric lines. Most of the photospheric and interstellar features are stronger in the K-luminous composite spectrum than in Lyman break galaxies at z ~3. This suggests higher metallicity and possibly also larger interstellar velocity dispersion caused by macroscopic motions. The absorption lines and the slope of the UV continuum are well matched by the spectrum of the nearby luminous infrared galaxy NGC 6090, which is in the process of merging. A metallicity higher than solar is suggested by comparing the pure photospheric lines (Si III, C III, and Fe V) with starburst models. The evidence of high metallicity, together with the high masses, high star formation rates, and possibly strong clustering, well qualify these galaxies as progenitors of local massive elliptical galaxies.

Keck Spectroscopy of Two Young Globular Clusters in the Merger Remnant NGC 3921

Low-resolution, ultraviolet-to-visual spectra of two candidate globular clusters in the merger remnant NGC 3921 (czLG = 6021 km s-1) are presented. These two clusters of apparent magnitude V ≈ 22.2 (MV ≈ -12.5) lie at projected distances of about 5 kpc (0.9 Reff) from the center and move with halo-type radial velocities relative to the local galaxy background. Their spectra show strong Balmer absorption lines [EW(Hβ–Hδ) = 11–13 A] indicative of main-sequence turnoffs dominated by A-type stars. Comparisons with model-cluster spectra computed by Bruzual & Charlot and others yield cluster ages in the range of 200–530 Myr, and metallicities about solar to within a factor of three. Given their small half-light radii (Reff 5 pc) and ages corresponding to ~102 core-crossing times, these clusters are gravitationally bound and hence indeed young globulars. Assuming that they had Chabrier-type initial mass functions, their estimated current masses are (2.3 ± 0.1) × 106 ⊙ and (1.5 ± 0.1) × 106 ⊙, respectively, or roughly half the mass of ω Cen. Since NGC 3921 itself shows many signs of being a 0.7 ± 0.3 Gyr old protoelliptical, these two young globulars of roughly solar metallicity and their many counterparts observed with the Hubble Space Telescope provide supporting evidence that, in the process of forming elliptical-like remnants, major mergers of gas-rich disks can also increase the number of metal-rich globular clusters.

TheXMM‐NewtonIron Line Profile of NGC 3783

We report on observations of the iron K line in the nearby Seyfert 1 galaxy, NGC 3783, obtained in a long, 2 orbit (approx. 240 ks) XMM-Newton observation. The line profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV, with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV emission is the K(alpha) line from near neutral Fe, whilst the 7.0 keV feature probably originates from a blend of the neutral Fe K(beta) line and the Hydrogen-like line of Fe at 6.97 keV. The relatively narrow velocity width of the K(alpha) line (approx. less than 5000 km/s), its lack of response to the continuum emission on short timescales and the detection of a neutral Compton reflection component are all consistent with a distant origin in Compton-thick matter such as the putative molecular torus. A strong absorption line from highly ionized iron (at 6.67 keV) is detected in the time-averaged iron line profile, whilst the depth of the feature appears to vary with time, being strongest when the continuum flux is higher. The iron absorption line probably arises from the highest ionization component of the known warm absorber in NGC 3783, with an ionization of log xi approx 3 and column density of N(sub H) approx. 5 x 10(exp 22)/sq cm and may originate from within 0.1 pc of the nucleus. A weak red-wing to the iron K line profile is also detected below 6.4 keV. However when the effect of the highly ionized warm absorber on the underlying continuum is taken into account, the requirement for a relativistic iron line component from the inner disk is reduced.

Integral field observations of damped Lyman‐α galaxies

AbstractWe report preliminary results from a targeted investigation on quasars containing damped Lyman‐α absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line‐emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (zabs = 3.15) and Q0151+045 (zabs=0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyα emission from an area of 3″ ×5″. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

PSR J1909-3744: A Binary Millisecond Pulsar with a Very Small Duty Cycle

We report the discovery of PSR J1909-3744, a 2.95 ms pulsar in a nearly circular 1.53 day orbit. Its narrow pulse width of 43 μs allows pulse arrival times to be determined with great accuracy. We have spectroscopically identified the companion as a moderately hot (T ≈ 8500 K) white dwarf with strong absorption lines. Radial velocity measurements of the companion will yield the mass ratio of the system. Our timing data suggest the presence of Shapiro delay; we expect that further timing observations, combined with the mass ratio, will allow the first accurate determination of a millisecond pulsar mass. We have measured the timing parallax and proper motion for this pulsar, which indicate a transverse velocity of 140 km s-1. This pulsar's stunningly narrow pulse profile makes it an excellent candidate for precision timing experiments that attempt to detect low-frequency gravitational waves from coalescing supermassive black hole binaries.

Probing the Inflow/Outflow and Accretion Disk of Cygnus X‐1 in the High State with theChandraHigh Energy Transmission Grating

Cygnus X-1 was observed in the high state at the conjunction orbital phase (0) with Chandra High Energy Transmission Grating (HETG). Strong and asymmetric absorption lines of highly ionized species were detected, such as Fe xxv, Fe xxiv, Fe xxiii, Si xiv, S xvi, Ne x, etc. In the high state the profile of the absorption lines is composed of an extended red wing and a less extended blue wing. The red wings of higher ionized species are more extended than those of lower ionized species. The detection of these lines provides a way to probe the properties of the flow around the companion and the black hole in Cyg X-1 during the high state. A broad emission feature around 6.5 keV was significantly detected from the spectra of both the Chandra/HETG and the RXTE/Proportional Counter Array. This feature appears to be symmetric and can be fitted with a Gaussian function rather than the Laor disk line model of the fluorescent Fe K(alpha) line from an accretion disk. The implications of these results on the structure of the accretion flow of Cyg X-1 in the high state are discussed.

First diode-pumped Yb-doped solid-state laser continuously tunable between 1000 and 1010�nm

We demonstrate that the ytterbium-doped medium Yb:YSO can provide laser oscillation in the 1000–1010 nm wavelength range under diode pumping around 980 nm. Ytterbium-doped Y2SiO5 crystal has been chosen for its high emission cross section around 1 μm combined with a strong absorption line at 978 nm. We have developed an original pumping architecture that permits us to overcome problems due to the small difference between pump and laser wavelengths. In this way, laser emission continuously tunable in the 1000–1010 nm wavelength range has been obtained with more than 100 mW of output power. This kind of laser is the first step toward a metrological source around 500 nm stabilized on an I2 absorption line. Furthermore, 100 mW of laser light has been obtained at 998.5 nm, leading to a remarkably low quantum defect of 2.1%.

The Kinematics and Physical Conditions of the Ionized Gas in NGC 4593 fromChandraHigh‐Energy Grating Spectroscopy

We observed the Seyfert 1 galaxy NGC 4593 with the Chandra high energy transmission gratings and present a detailed analysis of the soft X-ray spectrum. We measure strong absorption lines from He-like O, Ne, Mg, Si, H-like N, O, Ne, Mg, Si and highly ionized Fe XIX-XXV. Only the NLya, OLya and MgLya lines appear to be marginally resolved. We identify a spectral feature at $\sim 0.707$ keV with a neutral Fe L edge, which might suggest that there is dust along the line-of-sight to \ngc. Neutral Si absorption, which might also be expected from absorption due to dust is present (though not significantly) in the form of a weak neutral Si edge. We also detect, at marginal signficance, NLya and O VII (r) 1s-2p ($\lambda 21.602 $) absorption at $z \sim 0$, due to a hot medium in our Local Group. The soft X-ray spectrum of NGC 4593 is adequately described by a simple, single-zone photoionized absorber with an equivalent Hydrogen column density of $5.37^{+1.45}_{-0.79} \times 10^{21} \rm{cm}^{-2}$ and an ionization parameter of $\log \xi= 2.52^{+0.06}_{-0.04}$ ergs cm $\rm{s}^{-1}$ although there remain some features which are not identified. Although the photoionized gas almost certainly is comprised of matter in more than one ionization state and may consist of several kinematic components, data with better signal-to-noise ratio and better spectral resolution are required to justify a more complex model.

The Fundamental Plane atz = 1.27: First Calibration of the Mass Scale of Red Galaxies at Redshiftsz &gt; 1

We present results on the Fundamental Plane (FP) of early-type galaxies in the cluster RDCS J0848+4453 at z=1.27. Internal velocity dispersions of three K-selected early-type galaxies are determined from deep Keck spectra. Structural parameters are determined from HST NICMOS images. The galaxies show substantial offsets from the FP of the nearby Coma cluster, as expected from passive evolution of their stellar populations. The offsets from the FP can be expressed as offsets in M/L ratio. The M/L ratios of the two most massive galaxies are consistent with an extrapolation of results obtained at z=0.02-0.83. The evolution of early-type galaxies with masses >10^11 M_sun is well described by ln M/L(B) = (-1.06 +- 0.09) z, corresponding to passive evolution of -1.50 +- 0.13 mag at z=1.3. Ignoring selection effects, the best fitting stellar formation redshift is z*=2.6, corresponding to a luminosity weighted age at the epoch of observation of ~2 Gyr. The M/L ratios of these two galaxies are also in excellent agreement with predictions from models that include progenitor bias. The third galaxy is a factor ~10 less massive than the other two, shows strong Balmer absorption lines in its spectrum, and is offset from the Coma Fundamental Plane by 2.9 mag in rest-frame B. Despite their large range in M/L ratios, all three galaxies fall in the ``Extremely Red Object'' (ERO) class with I-H>3 and R-K>5, and our results show that it is hazardous to use simple models for converting luminosity to mass for these objects. Measurements of M/L ratios at high redshift can be considered first steps to empirically disentangle luminosity and mass evolution at the high mass end of the galaxy population, lifting an important degeneracy in the interpretation of evolution of the luminosity function. [SHORTENED]

Imaging spectropolarimetry of Ti I 2231 nm in a sunspot

Spectro-polarimetric observations at 2231 nm were made of NOAA 10008 near the west solar limb on 29 June 2002 using the National Solar Observatory McMath-Pierce Telescope at Kitt Peak and the California State University Northridge - National Solar Observatory infrared camera. Scans of spectra in both Stokes I and Stokes V were collected; the intensity spectra were processed to remove strong telluric absorption lines, and the Stokes V umbral spectra were corrected for instrumental polarization. The sunspot temperature is computed using the continuum contrast and umbral temperatures down to about 3700 K are observed. A strong Ti I line at 2231.0 nm is used to probe the magnetic and velocity fields in the spot umbra and penumbra. Measurements of the Ti I equivalent width versus plasma temperature in the sunspot agree with model predictions. Zeeman splitting measurements of the Stokes I and Stokes V profiles show magnetic fields up to 3300 G in the umbra, and a dependence of the magnetic field on the plasma temperature similar to that which was seen using Fe I 1565 nm observations of the same spot two days earlier. The umbral Doppler velocity measurements are averaged in 16 azimuthal bins, and no radial flows are revealed to a limit of +/- 200 m s(-1). A Stokes V magnetogram shows a reversal of the line-of-sight magnetic component between the limb and disk center sides of the penumbra. Because the Ti I line is weak in the penumbra, individual spectra are averaged in azimuthal bins over the entire penumbral radial extent. The averaged Stokes V spectra show a magnetic reversal as a function of sunspot azimuthal angle. The mean penumbral magnetic field as measured with the Stokes V Zeeman component splitting is 1400 G. Several weak spectral lines are observed in the sunspot and the variation of the equivalent width versus temperature for four lines is examined. If these lines are from molecules, it is possible that lines at 2230.67, 2230.77, and 2231.70 nm originate from OH, while the line at 2232.21 nm may originate from CN.

The Kinematics and Physical Conditions of the Ionized Gas in Markarian 509. I.ChandraHigh Energy Grating Spectroscopy

We observed the Seyfert 1 galaxy Mrk 509 for ~59 ks with the Chandra high-energy transmission gratings, simultaneously with HST/STIS and RXTE. Here we present a detailed analysis of the soft X-ray spectrum observed with Chandra. We measure strong absorption lines from He-like Ne and Mg and from H-like N, O, and Ne. Weaker absorption lines may also be present. The lines are unresolved except for Ne X Lyα (λ12.134) and Ne IX 1s2-1s2p (λ13.447), which appear to be marginally resolved. The profiles are blueshifted with respect to the systemic velocity of Mrk 509, indicating an outflow of ~-200 km s-1. There is also a hint that the profiles may have a velocity component near systemic. The soft X-ray spectrum can be described in remarkable detail with a simple, single-zone photoionized absorber having an equivalent neutral hydrogen column density of 2.06 × 1021cm-2 and an ionization parameter of log ξ = 1.76 (or log U = 0.27). Although the photoionized gas almost certainly is comprised of matter in more than one ionization state and may consist of several kinematic components, data with better spectral resolution and signal-to-noise ratio would be required to justify a more complex model. The UV data, on the other hand, have a velocity resolution of ~10 km s-1 and can easily detect eight kinematic components, covering roughly the same velocities as the X-ray absorption profiles. Even though the X-ray and UV absorbers share the same velocity space, the UV absorbers have a much smaller column density and ionization state. We show that models of the X-ray data do not predict significant UV absorption and are therefore consistent with the UV data. Finally, we do not detect any soft X-ray emission lines.

Infrared and NMR Spectra of Arylsulphonamides, 4-X-C6H4SO2NH2 and i-X, j-YC6H3SO2NH2 (X=H; CH3; C2H5; F; Cl; Br; I or NO2 and i-X, j-Y=2,3-(CH3)2; 2,4-(CH3)2; 2,5- (CH3)2; 2-CH3, 4-Cl; 2-CH3, 5-Cl; 3-CH3, 4-Cl; 2,4-Cl2 or 3,4-Cl2)

Several arylsulphonamides of the configuration, 4-X-C6H4SO2NH2 (where X= H; CH3; C2H5; F; Cl; Br; I or NO2) and i-X, j-YC6H3SO2NH2 (where i-X, j-Y=2,3-(CH3)2; 2,4-(CH3)2; 2,5-(CH3)2; 2-CH3,4-Cl; 2-CH3,5-Cl; 3-CH3,4-Cl; 2,4-Cl2 or 3,4-Cl2) were prepared, and their infrared spectra were measured in the solid state. The NMR spectra were recorded in solution. N-H asymmetric and symmetric stretching vibrations absorb in the ranges, 3390 - 3323 cm-1 and 3279 - 3229 cm-1, respectively. Asymmetric and symmetric SO2 stretching vibrations appear as strong absorption lines in the ranges, 1344 - 1317 cm-1 and 1187 - 1147 cm-1, respectively. Sulphonamides exhibit S-N stretching vibrational absorptions in the range, 924 - 906 cm-1. The effect of substitution in the phenyl ring in terms of electron withdrawing and electron donating groups could not be generalised, as the effect is non-systematic. The chemical shift is highly dependent on the electron density around the nucleus or associated with the atom to which it is bonded. Hence empirical correlations relating the chemical shifts to the structures have been discussed. The chemical shifts of aromatic protons and carbons in all the arylsulphonamides have been calculated by adding substituent contributions to the shift of benzene, the principle of substituent addition. Considering the approximation made, the agreement between the calculated and experimental chemical shift values is reasonably good. Generally, electron-withdrawing groups shows high chemical shifts compared to electron-donating groups.

The Matrix Isolation Spectrum of the CH 2+ Ion

For CH 2 + molecular ions at 5 K we simulate the infrared absorption spectrum, and tabulate all strong absorption lines from 0 to 16 000 cm −1. We use ab initio potential energy, dipole moment, and transition moment surfaces in conjunction with our program system RENNER, which allows for the Renner–Teller effect and spin–orbit coupling in a full-dimensions calculation. This is done for the purpose of guiding our search for the matrix isolation spectrum; our attempts at finding this spectrum are also described.

The Effects of Inhomogeneous Absorbers on the Formation of Intrinsic Quasar Absorption Lines

We investigate the formation of absorption lines in an inhomogeneous medium covering an extended source, in the context of intrinsic quasar (QSO) absorption lines. We first describe a simple formalism to model the effect of having a range of column densities in front of the source. It is shown that if the probability distribution of column densities is a power law with index p, the remaining flux in a line in which the medium is very optically thick scales as τ-(p+1), where τ is the maximum optical depth in front of the source. This power-law behavior appears to give a better description of the observed relation between optical depth and flux near the bottom of strong intrinsic QSO absorption lines than the standard exponential behavior. The formalism provides an alternative to the model that assumes partial homogeneous covering, which is the current standard in the interpretation of intrinsic QSO absorption lines that do not show exponential behavior, and in some respects provides a better fit to the observed line strengths. We show that inhomogeneous covering can lead to an apparent velocity-dependent covering factor if the partial homogeneous covering model is applied to doublet lines. The covering factor derived from a partial homogeneous covering analysis does, however, yield information on the characteristics of the column density distribution, such as the sharpness of the edges and peaks. We apply the inhomogeneous covering formalism to two observed QSO absorption-line systems to demonstrate these effects.

Oscillations in the solar atmosphere: some diagnostic aspects

Oscillations in velocity and intensity are detectable over a range of height in the solar atmosphere. Properties of the atmosphere can be deduced from the stratification revealed by the corresponding power and phase-difference spectra, potentially in a manner independent of optical spectroscopy. In this paper, published acoustic power spectra and phase-difference spectra, mainly derived from observations in the NaD2 line, are interpreted through a simple model of the oscillations in an exploratory investigation along these lines. The difference between the ‘heights of formation’ at two positions in the line profile is deduced from the ratio of oscillatory power. The corresponding phase difference between oscillations in velocity at the two heights is compared with the phase spectrum derived from observations. Deduced acoustically, the ‘height of formation’ of the core of the D2 line is about 700 km above that of the pressure-broadened wing. The indicated acoustic cut-off frequency is about 4.5 mHz, a value significantly lower than that usually quoted. A variety of observational evidence is consistent with this value. The low value is probably a consequence of radiative damping, with a relaxation time of about 55 s. The phase relations between the vertical and horizontal components of motion, the temperature and the pressure are considered. At low frequencies the velocity/intensity phase difference, for oscillations of moderate to high degree, is significantly affected by the horizontal motion, even if observations are restricted to a relatively small window at disc centre. There is evidence that at the edge of the Doppler cores of strong absorption lines, fluctuations in intensity are in anti-phase with fluctuations in temperature.

New technique for in-situ measurement of ammonia distribution in industrial combustion systems.

A new technique of a laser gas monitoring system with a linear Charge-Coupled Device (CCD) has been developed to measure in-situ distribution of ammonia concentrations at various temperatures. The concentration is determined by measuring absorption with a tunable 13CO2 waveguide laser that is frequency modulated between two adjacent emission lines. One line coincides with a strong ammonia absorption line, while the other is used as a reference. By its referencing the system is auto-calibrated continuously. The high spectral resolution of the laser suppresses interference by other species. Multi-light path is used to achieve distribution of ammonia concentration in the flue gas channel, which is inhomogeneous. The linear CCD is used to replace detectors, which can avoid errors caused by parameter inconsistency of multi-detector and enable lower cost, fast and exact data acquisition and processing with computer by video interface. The measuring technique presented in this paper can be used to protect industrial environment against pollution in the chemical industry, several power plants and waste incinerators.

Exploring the Full Stellar Population of the Upper Scorpius OB Association

We investigate the stellar population and star formation history of the Upper Scorpius OB association, the most nearby region of recent massive star formation, over the full stellar mass range from 0.1 to 20 M?. The first part of this paper describes an extension of our large spectroscopic survey (Preibisch et al., published in 2001) for low-mass pre?main-sequence (PMS) stars in Upper Scorpius. Using the multiobject spectrograph 2dF at the Anglo-Australian Telescope, we obtained spectra of 469 stars with magnitudes R = 12.5?18.0 in a 6 deg2 area. Among these, we find 68 new PMS stars, nearly all of them M-type stars, by their strong lithium absorption lines. The total area covered by our 2dF survey is now 9 deg2 and contains 166 new PMS stars. Combining these results with our earlier investigation (Preibisch & Zinnecker) yields a sample of 250 PMS stars in the mass range ~0.1 to ~2 M?. The location of these stars in the HR diagram suggests a mean age of 5 Myr without a significant age spread. In the second part of this paper, we also consider the population of 114 high-mass members identified in detailed Hipparcos studies. We construct a combined HR diagram for the 364 high- and low-mass members and find that the whole stellar population is very well characterized by a very narrow age distribution around 5 Myr. We estimate individual masses for all members and construct an empirical mass function covering the mass range from 0.1 up to 20 M?. A power-law fit to the mass function gives a slope of ? ~ -2.6 above ~2 M? and a much flatter slope (? ~ -0.9) below ~0.6 M?. The initial mass function of Upper Sco is not identical, but within the errors consistent with recent determinations of the field initial mass function. There is certainly no deficit of low-mass stars in the Upper Sco OB association, but rather a small excess of low-mass stars. Our results on the stellar age distribution confirm earlier indications that the star formation process in Upper Sco was triggered and support previous conjectures that the triggering event was a supernova shock wave originating from the nearby Upper Centaurus?Lupus association.