Echelle Data Research Articles

A Self‐consistent Optical, Ultraviolet, and Extreme‐Ultraviolet Model for the Spectrum of the Hot White Dwarf G191‐B2B

The star G191-B2B is one of a number of hot DA white dwarfs whose atmospheres have been found to contain significant quantities of heavy elements, including C, N, O, Si, Fe, and Ni. Several earlier studies have measured their abundances using IUE echelle data in conjunction with synthetic spectra derived from theoretical model atmosphere calculations of varying degrees of sophistication. However, predictions of the EUV spectrum based on these observations failed completely to match either its shape or absolute flux level. We present here the results of new non-LTE model calculations including the effects of line blanketing from more than 9 million (mainly Fe and Ni) transitions. For the first time, we are able to find an effective temperature and composition that can consistently match the optical, FUV and EUV data. However, to maintain this agreement below the He ii Λ228 Lyman limit, it is necessary to incorporate additional He ii opacity in the form of photospheric, circumstellar or interstellar material.

Making the Figaro Data Reduction System Portable

AbstractThe Figaro data reduction system was originally written for DEC VAXes running VMS, and little attention was paid to making it portable. Recently, however, a cooperative effort between the AAO, MSSSO, UNSW, the UK Starlink network and Caltech has resulted in a version for UNIX. This new version has been run under VMS and three different versions of UNIX. The files produced by any version may be read directly by any other version, although Figaro has a particularly complex file format which contains an extensible, self-defining, hierarchical structure of data items. This complexity has allowed the addition of error and quality data, as well as specific structures used, for example, for echelle data. Figaro is written mainly in Fortran (with numerous DEC extensions) but there is also a significant use of C. While C and Fortran are reasonably portable, the way one is called from the other is less portable and needs careful handling. Ports to other systems are possible, with effort; a Macintosh version is being considered.

Internal motions of HII regions and giant HII regions

We report new echelle observations of the kinematics of 30 HII regions in the LMC, including the 30 Doradus giant HII region. All of the HII regions possess supersonic velocity dispersions, which can be attributed to a combination of turbulent motions and discrete velocity splitting produced by stellar winds and/or embedded supernova remnants (SNRs). The core of 30 Dor is unique, with a complex velocity structure that parallels its chaotic optical morphology. We use our calibrated echelle data to measure the physical properties and energetic requirements of these velocity structures. The most spectacular structures in 30 Dor are several fast expanding shells, which appear to be produced at least partially by SNRs.

THE REDUCTION OF FIBER-FED ECHELLE SPECTROGRAPH DATA: METHODS AND AN IDL-BASED SOLUTION PROCEDURE

ABSTRACT Echelle spectrograph data present several challenges in data reduction. In this paper we address the general problem of accurately extracting spectra from a night's worth of raw CCD fiber-fed echelle data frames. We first briefly review echelle spectroscopy: properties of the basic echelle spectrograph, how the orders are arranged on the CCD, and what demands and constraints this data format places on reduction algorithms. We then discuss solutions to the various problems for fiber-fed data, with particular emphasison the removal of the scattered light background. Finally, we discuss our implementation of these solutions. We have written a package using the Interactive Data Language (IDL) that uses the methods described in this paper to give accurate extractions of spectra from fiber-fed echelle frames with any number of spectral orders of arbitrary tilt and curvature. We describe how interested persons may obtain the package through anonymous FTP.

ABUNDANCE PATTERNS IN RED-GIANT CH STARS

ABSTRACT A detailed abundance analysis of seven red-giant CH stars has been conducted. Using high resolution echelle and coude spectrographic data and modern analysis techniques involving model stellar atmospheres and computer codes which model LTE radiative transfer, the abundances of carbon, nitrogen and oxygen, the carbon isotope ratios and the abundances of the s-process elements have been determined. The red-giant CH stars are a class of metal-poor giants with equivalent spectral types of G and K which show enhanced abundances of s-process elements. Studies of their kinematics indicate that the red-giant CH stars are members of the halo of our galaxy (Hartwick & Cowley 1985). Therefore, the CH stars provide valuable information about the early chemical evolution of our galaxy. In addition, it is known that the red-giant CH stars are members of binary systems like the barium stars (McClure 1984), so they are also valuable in the study of mass transfer. The carbon isotope ratios are found to break the red-giant CH stars into two groups--those with 12C 13C >/= 20 and those with 12C 13C ~4 (a value associated with equilibrium burning of the CN cycle) and carbon and nitrogen abundances are found to be greatly enhanced, [C+N/Fe] ~+1.0. In addition, it is found that the red-giant CH stars show large enhancements of the s-process elements with the enhancements of the heavy s-process peak elements (Ba through Sm) being larger than the light s-process peak elements (Sr, Y and Zr) by a factor of approximately six. Taken with the orbital data available for the red-giant CH stars, the carbon, nitrogen and oxygen abundances and the carbon isotope ratios are consistent with a picture in which carbon and s-process elements were dumped onto the incipient red-giant CH star from an AGB star. The accreted material is mixed deep enough into the star's interior to be subjected to CN burning. In addition, the greatly enhanced s-process abundances stars strongly suggest that the 13C (alpha ,n)16O reaction is the source of neutrons for the s-process. In addition, the abundance patterns in the globular-cluster CH star, M22 III-106, have been analyzed. It is found to have an abnormally large carbon abundance, but the C/O ratio is much less than unity and the star shows no evidence for enhanced abundances of the s-process elements. Therefore, M22 III-106 is most likely not a CH star in the sense that term is applied to galactic CH stars. The most probable explanation for the carbon overabundance in M22 III-106 is that CN processing has not been as complete in this star as in other giants of similar composition in M22.

Observations of potassium in the tenuous lunar atmosphere

Spectra showing the potassium D1 emission line above the Moon's bright limb (subsolar point) were obtained at first quarter the night of 29 April 1989. The number density at the surface is 9.5 ± 1 atoms cm−3. Linear regression analyses find equally good fits to a one term model with a scale height of 80 km and corresponding temperature of 600 K, or a two term model with a thermal component accommodated to the sub‐solar surface temperature (T=395 K, scale height = 52 km; nt=9.6 K atoms cm−2 sec−1) and with a nonthermal component (represented as T=2500 K, scale height = 329 km; nnt= 1.1 K atoms cm−2 sec−1). In either case there is a large nonthermal component and a deficiency of atoms equilibrated to the surface temperature. The calculated thermalization rate of the nonthermal component through encounters with the lunar surface gives a source strength for the thermal component a factor of 7 greater than loss by photoionization. A possible explanation for the low thermalized population is the existence of a fast and efficient way of depleting the thermal component and supplying the nonthermal by momentary adsorption on the surface and subsequent photo‐desorption by the considerable visible solar irradiance. Also important, this plausible mechanism for the redistribution of thermal and nonthermal components may completely mask the original velocity distribution of the source population.

Relative abundance determinations in extremely metal poor giants. I - Photometry and equivalent width measurements

view Abstract Citations (21) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relative Abundance Determinations in Extremely Metal-poor Giants. I. Photometry and Equivalent Width Measurements Peterson, Ruth C. ; Carney, Bruce W. Abstract Photometry and measurements of equivalent widths are presented for nine extremely metal-poor stars, including two in the globular cluster M92. Reddening estimates are evaluated in depth. An extensive intercomparison is presented of equivalent widths derived here and by various other authors for the same stars. With the echelle spectrograph, long-focus camera, and TEK CCD data, widths from 2 to 20 mA are measured to + or - 2 mA for a star with V = 6, and widths from 12 to 50 mA are measured to + or - 10 mA for a star with V = 12. Photographic image-tube echelle data produced widths good to + or - 10 mA over 10-100 mA from two plates. It is shown that the nickel overabundance deduced for the most extremely metal poor stars by Luck and Bond (1985) may arise from their overestimate of equivalent widths of weak lines at the limit of detectability. Publication: The Astrophysical Journal Pub Date: December 1989 DOI: 10.1086/168115 Bibcode: 1989ApJ...347..266P Keywords: Abundance; Astronomical Photometry; Giant Stars; Stellar Spectra; Stellar Spectrophotometry; Echelle Gratings; Globular Clusters; Interstellar Extinction; Metallicity; Astrophysics; CLUSTERS: GLOBULAR; STARS: ABUNDANCES; STARS: LATE-TYPE; STARS: POPULATION II full text sources ADS | data products SIMBAD (9) Related Materials (1) Part 2: 1990ApJ...350..173P

Interstellar molecular lines in the direction of the young star TY CrA

view Abstract Citations (32) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Molecular Lines in the Direction of the Young Star TY CrA Cardelli, Jason A. ; Wallerstein, George Abstract Echelle data for the CN, CH, and CH(+) lines along the line of sight to TY CrA, a young star in a very young star forming region, are discussed. The molecular abundances of CN and CH are low in comparison to those of HD 29647. The results suggest that CH(+) is formed in a weak shock that may be associated with the local cloud collapse. The large abundances of CH(+) and CH imply a shock with a velocity of about 10 km/s (seen at an angle from the normal to the shock front of about 70 deg) and a radiation-field-enhancement factor of about 3-5. Publication: The Astronomical Journal Pub Date: April 1989 DOI: 10.1086/115052 Bibcode: 1989AJ.....97.1099C Keywords: Absorption Spectra; Early Stars; Interstellar Matter; Line Spectra; Molecular Spectra; Echelle Gratings; H Ii Regions; Interstellar Extinction; Photochemical Reactions; Astrophysics; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (12)

SMALL-SCALE KINEMATIC STRUCTURES IN RING NEBULAE AROUND WOLF-RAYET STARS

ABSTRACT Four ring nebulas around galactic Wolf-Rayet stars have been observed with echelle spectrographs in the long-slit mode: NGC 2359, NGC 3199, NGC 6888, and RCW 58. The spatial resolution of these observations is seeing limited at about 1-3 arcsec, which is almost a two orders of magnitude improvement from the previous Fabry-Perot scanner observations. To avoid large geometric corrections, the slit positions were placed as close to the central stars as possible. The results show that the ejecta-type nebula RCW 58 is a clumpy shell expanding regularly at about 110 km/s, as opposed to the chaotic expansion concluded from the earlier Fabry-Perot observations. For the three windblown bubbles, NGC 2359, NGC 3199, and NGC 6888, the small-scale structures revealed in the echelle data can explain the apparently discrepant expansion velocities derived from the previous large-aperture Fabry-Perot observations.

Kinematics of H II regions in the blue irregulars NGC 4214 and NGC 4449

view Abstract Citations (33) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematics of H II regions in the blue irregulars NGC 4214 and NGC 4449. Hartmann, Lee W. ; Geller, Margaret J. ; Huchra, John P. Abstract The authors have measured emission-line radial velocities for 22 and 35 H II regions in the actively star-forming irregular galaxies NGC 4214 and NGC 4449, respectively. The echelle data show that in both galaxies the velocity dispersion is comparable with any systematic motions. Both galaxies have velocity gradients ⪆20 km s-1 on scales of several hundred parcsecs. Because these systems contain large amount of gas, the velocity discontinuities can probably be maintained for only about a rotation time, or for ≡108yr. The gas compression which must from the non-equilibrium velocity fields in these two systems probably triggered the bursts of star formation. The authors suggest that the chaotic velocity fields result from a recent merger or collision with another small system or gas cloud(s). The close, small, gas-rich companions of both NGC 4214 and NGC 4449 lend support to this hypothesis. Publication: The Astronomical Journal Pub Date: December 1986 DOI: 10.1086/114262 Bibcode: 1986AJ.....92.1278H Keywords: Astronomical Spectroscopy; Galactic Structure; Gas Dynamics; H Ii Regions; Irregular Galaxies; Radial Velocity; Compressed Gas; Emission Spectra; Line Spectra; Star Formation; Velocity Distribution; Astrophysics; H II Regions:Irregular Galaxies; Irregular Galaxies:H II Regions; Irregular Galaxies:Kinematics; Irregular Galaxies:Star Formation; Star Formation:Irregular Galaxies full text sources ADS | data products SIMBAD (59) NED (2)

Supergiants and the galactic metallicity gradient. I - 27 late-type supergiants in the inner-arm regions

From an analysis of high-dispersion Kitt Peak echelle data, atmospheric parameters and chemical abundances have been derived for 27 supergiants of spectral type F through M. Since the star studied lie within about 1 kpc of the Sun, their abundances will form the local reference point for extensions of this study to larger distances. The derived (Fe/H) ratios range from -0.6 to +0.1 dex, show a mean value of -0.15 dex, and have an internal uncertainty of +- 0.2 dex.