Measured Line Strengths Research Articles

Effects of intercollisional interference on measured line strengths in the 3-0 quadrupole band of H 2

Recent observations of the 3-0 quadrupole band of H 2 by cavity ring-down spectroscopy confirm discrepancies with theoretical calculations of the quadrupole transition moment. They also supply enough data to suggest that the discrepancy comes from narrow intercollisional interference dips in the collision-induced absorption.

Terahertz spectroscopy applied to the measurement of strengths and self-broadening coefficients for high- J lines of OCS

A spectrometer operating in the 100–2000 GHz range and allowing for absolute line strength measurements has been developed. The continuous wave terahertz radiation is generated by mixing two Ti:Sapphire laser beams in a vertically integrated low temperature grown GaAs (LTG-GaAs) photomixer. Pure rotational lines of 16O 12C 32S in the ground vibrational state have been considered for J values up to 90. Observed self-broadening parameters are in agreement with those deduced from infrared experiments. For the first time in the submillimeter range, absolute line strengths have been determined, allowing for a determination of the electric dipole moment in good agreement with the value previously obtained from Stark effect measurements.

Line strength measurements for near-infrared intersystem transitions of NI

Intensities of 15 intersystem transitions and 5 LS allowed multiplets of neutral nitrogen (NI) from infrared part of the spectrum were measured by emission spectroscopy method. All allowed as well as LS-forbidden spectral lines belong to the 3p-3d transition array. The nitrogen spectra were excited in a wall-stabilized high-current arc ran in helium with small admixture of nitrogen. On the basis of these line (multiplet) intensity measurements, transition probabilities of 15 intersystem lines were determined relative to transition probabilities of appropriately chosen allowed multiplets. Finally the relative data for intersystem transitions were normalized to an absolute scale by applying reference multiplet strength values recommended by the Atomic Spectroscopy Group of NIST. The determined line strengths are compared with available calculated and — in the case of 5 transitions — also with experimental data.

Abundance Gradients in the Galaxy

Six H II regions at galactocentric distances of R = 10-15 kpc have been observed in the far-IR emission lines of [O III] (52 μm, 88 μm), [N III] (57 μm), and [S III] (19 μm) using the Kuiper Airborne Observatory. These observations have been combined with Very Large Array radio continuum observations of these sources to determine the abundances of O++, N++, and S++ relative to hydrogen. In addition, eight of the most recent sets of measurements of ionic line strengths in H II regions have been reanalyzed in order to attempt to reconcile differences in optical versus far-IR abundance determinations. We have in total 168 sets of observations of 117 H II regions in our analysis. The new analysis included updating the atomic constants (transition probabilities and collision cross sections), recalculation of some of the physical conditions in the H II regions (ne and Te), and the use of new photoionization models to determine stellar effective temperatures of the exciting stars. We also use the most recent data available for the distances for these objects, although for most we still rely on kinematic distance determinations. Our analysis finds little indication of differences between optical and infrared observations of the nitrogen abundances, but some differences are seen in the oxygen and sulfur abundances. A very significant offset continues to be seen between optical and infrared measurements of the N/O abundance ratio.

Line positions and line strengths for the 3← electric quadrupole band of H2Σg+1

Several rotational lines in the S and Q branches [including the previously unobserved Q(2) and Q(3) lines] of the 3-0 electric quadrupole band of H2 have been detected by cavity ring-down spectroscopy. Line strengths were measured at densities between 2.7x10(18) and 7.5x10(19) molecules cm-3 at room temperature. The observed line strengths in the S branch are consistent with earlier measurements, and systematically below theoretical calculations [relative differences of approximately 10% for the S(1),S(2), and S(3) lines, and nearly 30% for the S(0) line]. Line strength measurements for the Q branch range from 25% to 33% below theoretical calculations.

Measurements of line positions and strengths of HD 18O and D 218O in the 2500–4280 cm −1 region

Measurements of line positions and strengths of D 2 18O and HD 18O were obtained with a Fourier transform spectrometer. The data were analyzed to obtain energy levels of the (100), (020), and (001) vibrational states of HD 18O and the (001) and (011) states of D 2 18O and the vibrational bands of these states connected to the ground state covered the spectral region from 2500 to 4278 cm −1. 456 absorption lines of D 2 18O and 856 lines of HD 18O were assigned from the spectra. The measurements were of oxygen-18 enriched samples of deuterated water vapor and the spectra also contained features of HD 16O, D 2 16O, H 2 16O, H 2 17O and H 2 18O of which several were used as frequency calibration standards.

The Iron Line Background

We investigate the presence of iron line emission among faint X-ray sources identified in the 1Ms Chandra Deep Field South and in the 2Ms Chandra Deep Field North. Individual source spectra are stacked in seven redshift bins over the range z=0.5-4. We find that iron line emission is an ubiquitous property of X-ray sources up to z~3. The measured line strengths are in good agreement with those expected by simple pre-Chandra estimates based on X-ray background synthesis models. The average rest frame equivalent width of the iron line does not show significant changes with redshift.

Diode laser absorption spectroscopy measurement of linestrengths and pressure broadening coefficients of the methane 2 ν3 band at elevated temperatures

A diode laser sensor based on absorption spectroscopy has been developed for the measurement of spectroscopic parameters in the R (3) and R (4) manifolds of 2 ν 3 band of CH 4. Individual linestrengths of each transition are determined for a range of temperatures. In addition, collision-broadened half-widths for CO 2, N 2, H 2O, CH 4, and CO collision partners are measured as a function of temperature and pressure for these strongly overlapped transitions. From this, temperature dependence of the collision half-width for each collision partner is determined. Using a new method for calculation of collisional broadening at high temperatures for strongly overlapped transitions makes these transitions accessible for spectroscopy.

Star formation activity of intermediate redshift cluster galaxies out to the infall regions

We present a spectroscopic analysis of two galaxy clusters at z 0.2, out to ∼4 Mpc. The two clusters VMF73 and VMF74 as identified by Vikhlinin et al. (1998) were observed with multiple object spectroscopy using MOSCA at the Calar Alto 3.5 m telescope. Both clusters lie in the ROSAT Position Sensitive Proportional Counter field R285 and were selected from the X-ray Dark Cluster Survey (Gilbank et al. 2004) that provides optical V- and I-band data. VMF73 and VMF74 are located at respective redshifts of z = 0.25 and z = 0.18 with velocity dispersions of 671 km s -1 and 442 km s -1 , respectively. Both cluster velocity dispersions are consistent with Gaussians. The spectroscopic observations reach out to ∼2.5 virial radii. Line strength measurements of the emission lines H α and [O II]λ3727 are used to assess the star formation activity of cluster galaxies which show radial and density dependences. The mean and median of both line strength distributions as well as the fraction of star forming galaxies increase with increasing clustercentric distance and decreasing local galaxy density. Except for two galaxies with strong H α and [O II] emission, all of the cluster galaxies are normal star forming or passive galaxies. Our results are consistent with other studies that show the truncation in star formation occurs far from the cluster centre.

The stellar populations of low-redshift clusters

We present some preliminary results from an on-going study of the evolution of stellar populations in rich clusters of galaxies. Our baseline sample contains core line-strength measurements from 183 galaxies with . This result implies that the stellar populations in larger galaxies are older than in smaller galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Measurements of the line strengths, N2-, and O2-broadened half-widths in the 2.NU.2+.NU.3 band of 14N216O at room temperature

The line strengths, N2-, and O2-broadened half-widths in the 2ν2+ν3 band of 14N216O were determined from spectra obtained by a high-resolution Fourier transform spectrometer at room temperature. The squared vibrational transition dipole moment and the coefficients of the Herman-Wallis factor were also determined for this band. The measured line strengths agreed well with the values of HITRAN2K. The N2- and O2-broadened halfwidths were in agreement with the results of recent high-resolution experiments within the experimental errors. The air-broadened half-widths were calculated using the smoothed N2- and O2-broadened half-widths and compared with the values of HITRAN2K.

UV/optical properties of z∼2.5 radio galaxies

Keck LRISp optical spectropolarimetry and VLT ISAAC NIR spectroscopy of an overlapping sample of z∼2.5 radio galaxies has provided a set of uniquely high quality spectra stretching from Ly α to H α. The measurement of emission and absorption line strengths, continuum polarization and SED allow us to quantify the various emission and scattering mechanisms that comprise the observed spectra. We identify this epoch as critical in the chemical evolution of massive spheroids and show that, while star formation must be very active, most of the UV/optical radiation we see from these luminous sources derives from the AGN.

Combined interferometric and absorption-spectroscopic technique for determining molecular line strengths: Applications toCO2

A diode-laser-based technique has been developed for absolute line strength measurements with high precision and accuracy, combining a spectroscopic determination of the integrated absorbance with an optical measurement of the absorption path length by means of a Michelson interferometer. This method has been applied to several ${}^{12}{\mathrm{C}}^{16}{\mathrm{O}}_{2}$ vibrorotational transitions belonging to the ${\ensuremath{\nu}}_{1}+2{\ensuremath{\nu}}_{2}^{0}+{\ensuremath{\nu}}_{3}$ combination band, in the spectral region around 2 \ensuremath{\mu}m. The 1\ensuremath{\sigma} overall accuracy in line strength determination ranges between $0.4%$ and $0.7%,$ while the experimental reproducibility is estimated to be around $0.1%.$ To our knowledge, these levels are the highest ever reached before. The pressure-broadening coefficients for the same transitions are also reported.

Analysis of skin line pattern for lesion classification.

It has been observed that skin patterning tends to be disrupted by malignant but not by benign skin lesions. This suggests that measurements of skin pattern disruption on simply captured white light optical skin images could be a useful contribution to a diagnostic feature set. Previous work using a measurement of line strength by a consistent high-value profiling technique followed by local variance measurement or a region agglomerative classifier to measure skin line pattern disruption was extremely promising but computationally intensive, suggesting that the idea of measuring skin pattern disruption was useful but a simpler method was required. The skin pattern was extracted by high-pass filtration and enhanced by adaptive anisotropic (spatial variant) filtering which smoothes along skin lines but not across them. The skin line main direction and direction variance were estimated using a local image gradient matrix and the difference of these measures across the lesion image boundary was used as a lesion classifier. A set of images of malignant melanoma and benign naevi were processed as above and the scatter plot of results in a two-dimensional feature (line direction and line variation difference) space showed excellent separation of benign and malignant lesions. An ROC plot enclosed an area of 0.88. The experimental results showed that the local line direction and the local line variation were promising features for distinguishing malignant melanoma from benign lesion and the methods used were effective and computationally low-cost.

Remote determination of oxygen and water at millimetre wave frequencies using a fibre optic communications network

This paper describes the development of a remote millimetre wave (MMW) spectrometer capable of operation in the 57–66, 114–128 and 171–189 GHz bands. A 9.5–10.5 GHz signal from a yttrium iron garnet (YIG) source is carried via an infrared (IR) laser down a 1 km fibre-optic cable using a high-speed communications modulator. The 6th harmonic of the transmitted microwave signal is generated directly with an active sextrupler, which permits working in the 57–66 GHz band. For operation at 114–128 and 171–189 GHz, the 57–66 GHz output from the sextrupler is doubled or tripled by a further harmonic generator. Absorption line strength measurements and hence sample concentration determinations are undertaken using a Fabry–Perot cavity absorption cell. The spectroscopic data are recovered from the remote spectrometer by transmitting the rectified signal back over a further fibre-optic cable. Also described are the methods of cavity stabilisation and control across this fibre optic network. Oxygen determinations in the 57–66 and 114–128 GHz bands are performed to evaluate the performance of the spectrometer. A determination of water vapour in air at atmospheric pressure, at 183 GHz, is also presented, over a range of ∼5×10 −5 to ∼0.025 volume fraction in air.

VLT spectroscopy of NGC 3115 globular clusters

We present results derived from VLT–FORS2 spectra of 24 different globular clusters associated with the lenticular galaxy NGC 3115. A subsample of 17 globular clusters have sufficiently high signal–to–noise to allow precision measurements of absorption line-strengths. Comparing these indices to new stellar population models by Thomas et al. we determine ages, metallicities and element abundance ratios. For the first time these stellar population models explicitly take abundance ratio biases in the Lick/IDS stellar library into account. Our data are also compared with the Lick/IDS observations of Milky Way and M 31 globular clusters. Unpublished higher order Balmer lines (H and H) from the Lick/IDS observations are given in the Appendix. Our best age estimates show that the observed clusters which sample the bimodal colour distribution of NGC 3115 are coeval within our observational errors (2–3 Gyr). Our best calibrated age/metallicity diagnostic diagram (Hβ vs. [MgFe]) indicates an absolute age of 11–12 Gyr consistent with the luminosity weighted age for the central part of NGC 3115. We confirm with our accurate line-strength measurements that the colour is a good metallicity indicator within the probed metallicity range (). The abundance ratios for globular clusters in NGC 3115 give an inhomogeneous picture. We find a range from solar to super-solar ratios for both blue and red clusters. This is similar to the data for M 31 while the Milky Way seems to harbour clusters which are mainly consistent with . From our accurate recession velocities we detect, independent of metallicity, clear rotation in the sample of globular clusters. In order to explain the metallicity and abundance ratio pattern, particularly the range in abundance ratios for the metal rich globular clusters in NGC 3115, we favour a formation picture with more than two distinct formation episodes.

The SAURON project - I. The panoramic integral-field spectrograph

A new integral-field spectrograph, SAURON, is described. It is based on the TIGER principle, and uses a lenslet array. SAURON has a large field of view and high throughput, and allows simultaneous sky subtraction. Its design is optimized for studies of the stellar kinematics, gas kinematics, and line-strength distributions of nearby early-type galaxies. The instrument design and specifications are described, as well as the extensive analysis software which was developed to obtain fully calibrated spectra, and the associated kinematic and line-strength measurements. A companion paper will report on the first results obtained with SAURON on the William Herschel Telescope.

The First Hour of Extragalactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster

On 1999 May 26, one of the Sloan Digital Sky Survey (SDSS) fiber-fed spectrographs saw astronomical first light. This was followed by the first spectroscopic commissioning run during the dark period of 1999 June. We present here the first hour of extragalactic spectroscopy taken during these early commissioning stages: an observation of the Coma cluster of galaxies. Our data samples the southern part of this cluster, out to a radius of 15 (1.8 h-1 Mpc, approximately to the virial radius) and thus fully covers the NGC 4839 group. We outline in this paper the main characteristics of the SDSS spectroscopic systems and provide redshifts and spectral classifications for 196 Coma galaxies, of which 45 redshifts are new. For the 151 galaxies in common with the literature, we find excellent agreement between our redshift determinations and the published values, e.g., for the largest homogeneous sample of galaxies in common (63 galaxies observed by Colless & Dunn) we find a mean offset of 3 km s -1 and an rms scatter of only 24 km s -1. As part of our analysis, we have investigated four different spectral classification algorithms: measurements of the spectral line strengths, a principal component decomposition, a wavelet analysis and the fitting of spectral synthesis models to the data. We find that these classification schemes are in broad agreement and can provide physical insight into the evolutionary histories of our cluster galaxies. We find that a significant fraction (25%) of our observed Coma galaxies show signs of recent star formation activity and that the velocity dispersion of these active galaxies (emission-line and poststarburst galaxies) is 30% larger than the absorption-line galaxies. We also find no active galaxies within the central (projected) 200 h-1 kpc of the cluster. The spatial distribution of our Coma active galaxies is consistent with that found at higher redshift for the CNOC1 cluster survey. Beyond the core region, the fraction of bright active galaxies appears to rise slowly out to the virial radius and are randomly distributed within the cluster with no apparent correlation with the potential merger or postmerger of the NGC 4839 group. We briefly discuss possible origins of this recent galaxy star formation.

Electric dipole moment function of H 35Cl

The radial Schrödinger wave equation was solved numerically using an anharmonic potential function with 11 parameters to generate wavefunctions and vibration–rotation energy levels of the hydrogen chloride molecule H 35Cl. Measured line strengths available in the literature cover transitions up to v=7. Using the measured values of the line strengths along with the computed wavefunctions, a set of 135 dipole moment matrix elements M 0 v′(m) were calculated. Finally, the dipole moment coefficients, M 0, M 1,…, M 7, were evaluated from the matrix elements.

Pressure broadening and shift of transitions of the first overtone of HCl

High-resolution spectroscopic measurements were made using distributed feedback diode lasers. We measured line strength and pressure-induced broadening and shift for two lines, R(3) and P(4), of the first overtone (2?0) ro-vibrational band, for the two isotopomers H35Cl and H37Cl, according to their natural abundances; measurements were also made in the presence of foreign gases. Comparison was made with available data when possible.