Line Strenghts Research Articles

Age, metallicity, and star formation history of spheroidal galaxies in cluster atz∼ 1.2

We present the analysis, based on spectra collected at the Large Binocular Telescope, of the stellar populations in seven spheroidal galaxies in the cluster XLSSJ0223 at $z$$\sim$1.22. The aim is to constrain the epoch of their formation and their star formation history. Using absorption line strenghts and full spectral fitting, we derive for the stellar populations of the seven spheroids a median age <Age>=2.4$\pm$0.6 Gyr, corresponding to a median formation redshift $<$$z_f$$>$$\sim2.6_{-0.5}^{+0.7}$ (lookback time = 11$_{-1.0}^{+0.6}$ Gyr). We find a significant scatter in age, showing that massive spheroids, at least in our targeted cluster, are not coeval. The median metallicity is [Z/H]=0.09$\pm$0.16, as for early-types in clusters at 0$<$$z$<0.9. This lack of evolution of [Z/H] over the range 0$<$$z$$<$1.3, corresponding to the last 9 billions years, suggests that no significant additional star formation and chemical enrichment are required for cluster spheroids to reach the present-day population. We do not detect significant correlation between age and velocity dispersion $\sigma_e$, or dynamical mass M$_{dyn}$, or effective stellar mass density $\Sigma_e$. On the contrary, the metallicity [Z/H] of the seven spheroids is correlated to their dynamical mass M$_{dyn}$, according to a relation similar to the one for local spheroids. [Z/H] is also anticorrelated to stellar mass density $\Sigma_e$ because of the anticorrelation between M$_{dyn}$ and $\Sigma_e$. Therefore, the basic trends observed in the local universe were already established at $z\sim1.3$, i.e. more massive spheroids are more metal rich, have lower stellar mass density and tend to be older than lower-mass galaxies.

Integrated spectral study of small angular diameter galactic open clusters

This paper presents flux-calibrated integrated spectra obtained at Complejo Astronómico El Leoncito (CASLEO, Argentina) for a sample of 9 Galactic open clusters of small angular diameter. The spectra cover the optical range (3800–6800 Å), with a resolution of ∼14 Å. With one exception (Ruprecht 158), the selected clusters are projected into the fourth Galactic quadrant (282o < l < 345o) near the Galactic plane (∣b∣ ≤ 9o). We performed simultaneous estimates of foreground interstellar reddening and age by comparing the continuum distribution and line strenghts of the cluster spectra with those of template cluster spectra with known parameters. We thus provide spectroscopic information independent from that derived through color-magnitude diagram studies. We found three clusters (Collinder 249, NGC 4463 and Ruprecht 122) younger than ∼40 Myr, four moderately young ones (BH 92, Harvard 5, Hogg 14 and Pismis 23) with ages within 200–400 Myr, and two intermediate-age ones (Ruprecht 158 and ESO 065-SC07) with ages within 1.0–2.2 Gyr. The derived foreground E(B−V) color excesses vary from around 0.0 in Ruprecht 158 to ∼1.1 in Pismis 23. In general terms, the results obtained show good agreement with previous photometric results. In Ruprecht 158 and BH 92, however, some differences are found between the parameters here obtained and previous values in the literature. Individual spectra of some comparatively bright stars located in the fields of 5 out of the 9 clusters here studied, allowed us to evaluate their membership status. The current cluster sample complements that of 46 open clusters previously studied by our group in an effort to gather a spectral library with several clusters per age bin. The cluster spectral library that we have been building is an important tool to tie studies of resolved and unresolved stellar content.

The molecular gas content of the advanced S+E merger NGC 4441

<i>Context. <i/>Despite their importance to galaxy evolution, mergers between a spiral and an elliptical (S+E mergers) have been poorly studied so far. NGC 4441 is a nearby candidate of an advanced remnant of such a merger, showing typical tidal structures such as an optical tail and two shells as well as two H i tails. <i>Aims. <i/>Studying the molecular gas content provides clues about the impact of a recent merger event on the star formation. Simulations of S+E mergers yield conflicting predictions about both the strength and the extent of an induced starburst. Thus, observations of the amount and the distribution of the molecular gas, the raw material of star formation, are needed to understand the influence of the merger on the star formation history.<i>Methods. <i/><sup>12<sup/>CO and <sup>13<sup/>CO (1-0) and (2-1) observations were obtained using the Onsala Space Observatory 20 m and IRAM 30 m telescope as well as the Plateau de Bure interferometer. These data allow us to carry out a basic analysis of the molecular gas properties, such as estimates of the molecular gas mass, temperature, and density and the star formation efficiency.<i>Results. <i/>The CO observations detect an extended molecular gas reservoir out to ~4 kpc, with a total molecular gas mass of . Furthermore, high resolution imaging shows a central molecular gas feature, which is probably a rotating disc hosting most of the molecular gas ( ). This nuclear disc has a different sense of rotation to the large-scale H i structure, indicating a kinematically decoupled core. We modeled the state of the interstellar medium with the radiative transfer code RADEX, using the ratios of the <sup>12<sup/>CO to <sup>13<sup/>CO line strenghts. The results are consistent with a diffuse ( cm<sup>-3<sup/>) molecular medium with no significant indications of cold, dense cores of ongoing star formation. This is in agreement with the moderate star formation rate of measured for NGC 4441. Assuming a constant star formation rate, the gas depletion time is 10<sup>8<sup/> yr. NGC 4441 might be a nearby candidate early-type galaxy with a dominant A-star population, a so-called E+A galaxy, which is in a post-starburst phase several 10<sup>8<sup/> yr after a merger event.

Properties of the δ Scorpii Circumstellar Disk from Continuum Modeling

We present optical $WBVR$ and infrared $JHKL$ photometric observations of the Be binary system $\delta$ Sco, obtained in 2000--2005, mid-infrared (10 and $18 \mu$m) photometry and optical ($\lambda\lambda$ 3200--10500 \AA) spectropolarimetry obtained in 2001. Our optical photometry confirms the results of much more frequent visual monitoring of $\delta$ Sco. In 2005, we detected a significant decrease in the object's brightness, both in optical and near-infrared brightness, which is associated with a continuous rise in the hydrogen line strenghts. We discuss possible causes for this phenomenon, which is difficult to explain in view of current models of Be star disks. The 2001 spectral energy distribution and polarization are succesfully modeled with a three-dimensional non-LTE Monte Carlo code which produces a self-consistent determination of the hydrogen level populations, electron temperature, and gas density for hot star disks. Our disk model is hydrostatically supported in the vertical direction and radially controlled by viscosity. Such a disk model has, essentially, only two free parameters, viz., the equatorial mass loss rate and the disk outer radius. We find that the primary companion is surrounded by a small (7 $R_\star$), geometrically-thin disk, which is highly non-isothermal and fully ionized. Our model requires an average equatorial mass loss rate of $1.5\times 10^{-9} M_{\sun}$ yr$^{-1}$.

Diode laser measurements of temperature-dependent line parameters for water vapor near 820 nm

Air- and self-broadening coefficients and relative line strenghts for 8–10 low-J lines in the (2 1 1) vibrational band of water vapor have been accurately measured over the T = 330–540 K range using an 817–824 nm GaAlAs diode laser. The technique of wavelength modulation with third-harmonic line locking and second-harmonic detection was used to derive the line parameters with accuracies of several percent from measurements with absorptivities as low as 2 x 10 -3. The linewidths and temperature coefficients are in good agreement with theoretical calculations and with recent measurements in the (2 2 1) and (3 0 1) bands. Absolute line strenghts have been derived from measurements on two of the lines and are found to be 21 ±4% higher than the values listed in the 1991 HITRAN compilation.

Density dependence of the 5 μm infrared spectrum of NH 3

Measurements of dilute mixtures of NH 3 in H 2 were made in the window region 1900–2100 cm -1 of the NH 3 spectrum to determine its behavior with increasing pressure of H 2. The spectra of pure H 2, pure NH 3, and mixtures of the two, in the total pressure range from 2.38 to 8.17 atm at 309 K, were obtained with a 975 cm White cell. Synthetic spectra were calculated using precise line strenghts, line positions, and a Lorentz profile. The experimental and calculated spectra are in reasonably good agreement, except that the former is super-imposed on a rather flat background not given by the calculation. A possible mechanism for this background is suggested.

Benchmark calculations of first principles rotational and ro-vibrational line strenghts

Benchmark first principles calculations of the pure rotational and ro-vibrational transition frequencies and line strengths are presented, using two independent program suites. Both sets of calculations were performed using the same potential energy and dipole surfaces. Our example calculations use recently calculated surfaces for H 2S which have been shown to give good agreement with experimental data. The results, which show perfect agreement for the energy levels, transition frequencies and line strengths, are used as an external check on the two program suites. It is suggested they could provide a standard with which other groups working in this field can compare their calculations.

Water vapor line strengths in the 1-μm region

The line strenghts of H 2O bands ν 1 + ν 2 + ν 3 and ν 2 + 2 ν 3 have been measured using a high-resolution Nd-glass single-mode laser spectrophotometer. The parameters of 33 lines were found by fitting a Voigt contour to experimental line profile. The vibration-rotation interaction affecting the line strength was taken into account by using the F factor in the three-parametric form, and its constants for ν 1 + ν 2 + ν 3 and ν 2 + 2 ν 3 bands were found. There is a good agreement between line intensities calculated using these constants and the experimental values.

Photon emission from suprathermal helium ions in a partially ionized hydrogen gas

The relative intensity and profiles of He i lambda5876, He ii lambda4686, and He ii lambda3203 have been calculated using a suprathermal-ion model for broad emission lines in Seyfert galaxies and quasars. With the results of this calculation it may be possible to explain the observed helium line strenghts in 3C 120, NGC 4151, NGC 7469, and I4329A.

Band model formulation for inhomogeneous optical paths

The band-model formulation developed by Lindquist and Simmons to handle radiance calculations for highly inhomogeneous and nonisothermal optical paths is discussed and extended. The original formulation was based on the statistical band model for a random array of equal-intensity pressure-broadened Lorentz lines. Here, the formulation is extended to include bands of constant-intensity Doppler lines and bands of Lorentz or Doppler lines with an exponential distribution of line strenghts. Results are presented for the equivalent width derivative functions y( x,ϱ) for the constant-intensity Lorentz, constant-intensity Doppler, and exponential-intensity Doppler cases. Various approximations to these functions for extreme x and ϱ conditions are also presented. A closed-form solution for y( x,ϱ ) is given for the exponentially distributed Lorentz line case.

Filter Transmission Effects on Photoelectric Measures of Rotationally Broadened Hβ Line Strenghts.

Filter Transmission Effects on Photoelectric Measures of Rotationally Broadened Hβ Line Strenghts.