Engineering topics

Sonneborn, George

Publications and source records attributed to Sonneborn, George.

At least 55 records · Page 3

NASA NTRS2004

The Mass of the Classical Cepheid S Mus

A FUSE spectrum of the hot companion of the Cepheid S Mus has been obtained, reduced and analysed. Since the determination of the temperature of S Mus B is the prime goal of this program, we have identified two regions in the spectrum which are temperature sensitive in the temperature range of the companion, but which are not overly affected by molecular hydrogen absorption. From comparison of the spectrum with spectra of stars of known temperature, we have determined the temperature of the companion to be 17,000 K. From this a mass has been inferred. Combining this mass with the orbital velocity ratio of the Cepheid and the companion (from the ground-based Cepheid orbit, and HST GHRS echelle observations), the mass of the Cepheid is determined to be 6.0 =/- 0.4 solar masses. The results have been presented at a conference (conference proceedings in press--see attachment).

Sonneborn, George↗

NASA NTRS2004

Particle Acceleration in SN1006 Shock Waves

The FUSE data have been reduced, and a paper on the results is in progress. The main results have been presented in a poster at the January 2004 AAS meeting and an ApJ paper in press. The primary result is that the widths of the 0 VI lines in the NW filament are a bit less than the width expected if the oxygen kinetic temperature is 16 times the proton temperature (mass proportional heating). This is at variance with measurements of shocks in the heliosphere, where preferential heating of oxygen and other heavy species is observed. The paper discusses the theoretical implications for collisionless shock wave physics. A secondary result is that no O VI emission was observed from the NE filament. While the very different particle distribution in that region can partially account for the weakness of the O VI lines, the simplest interpretation is that the pre-shock density in the NE is less than 0.22 times the density in the NW.

Sonneborn, George↗

NASA NTRS2004

Probing me Reverse Shock in an Oxygen-Rich Supernova Remnant

The aim of this project is to examine the O VI emission at three positions around the X- ray bright ring of the remnant in order to investigate the relation between the O VI emission, the X-ray O VII and O VIII emission, and the optical [OIII} emission, and how these vary around the rim of the remnant. All three pointings and the background pointing have now been observed; the archive notification for the most recent dataset was Oct 30, 2003. After reprocessing and screening, the net exposure time for the SE exposure is only 54 percent of the approved time (15 kilosec). for the SE exposure, the available statistics are not good enough for analysis. A request for reobservation to make up for the lost time in the SE pointing has been approved. Broad O VI 1032 and O VI 1038 emission is detected with velocity width of at least 800 km/s, and possibly exceeding 1000 km/s. The Flanagan et al. analysis of the Chandra grating data show bulk velocities in the X-ray gas of order +/- 1000 km/s. In the region of the FUSE E0lO2-SE pointing, the Chandra data indicate both blue-shifted and red-shifted emission. Analysis of the velocity structure of the O VI emission will provide additional constraints on the kinematics of the gas: is it emission from a tilted expanding barrel, or a more symmetric expansion? The O VI fluxes are also needed to assess whether the O VI is radiation from recombining O VII or instead fiom cooler gas ionizing toward O VII. The emission is faint, however, which complicates the analysis. Because the lines are so broad, absorption by intervening H2, CII, and foreground OVI must be considered. A number of stars in the SMC have been observed which provide information on foreground OVI absorption. The initial analyses have concentrated on the Li1F channel since the guidance is based on that channel. The Li2F channel is being examined exposure by exposure to see if any of the data can be used to improve the signal to noise in the Li1F data.

Gaetz, Terrance↗

NASA NTRS2004

Outbursts in Symbiotic Binaries

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

Sonneborn, George↗

NASA NTRS2004

Molecular Hydrogen in the Quiescent Disk of SW UMA

The FUSE observation has been reduced and a paper is in progress. The analysis has been slow because of the very noisy quality of the data. We anticipate submitting a paper in 2 or 3 months. The primary result is that there is no H_2 fluorescent emission. However, there seems to be no accretion disk. The upper limit to the continuum level is well below that observed by IUE, and while O VI lines are present, they are extremely faint and much narrower that the published and archival H alpha profiles. It appears that the accretion has essentially shut off entirely, leaving only very faint O VI and C III emission from the white dwarf. We are considering a magnetic model analogous to that for AE Aqr.

Raymond, John C.↗

NASA NTRS2003

Doppler Imaging with FUSE: The Partially Eclipsing Binary VW Cep

This report covers the FUSE Guest Observer program. This project involves the study of emission line profiles for the partially eclipsing, rapidly rotating binary system VW Cep. Active regions on the surface of the star(s) produce observable line shifts as the stars move with respect to the observer. By studying the time-dependence of the line profile changes and centroid shifts, one can determine the location of the activity. FUSE spectra were obtained by the P.I. 27 Sept 2002 and data reduction is in progress. Since we are interested in line profile analysis, we are now investigating the wavelength scale calibration in some detail. We have also obtained and are analyzing Chandra data in order to compare the X-ray velocities with the FUV velocities. A complementary project comparing X-ray and Far UltraViolet (FUV) emission for the similar system 44i Boo is also underway. Postdoctoral fellow Ronnie Hoogerwerf has joined the investigation team and will perform the data analysis, once the calibration is optimized.

Sonneborn, George↗

NASA NTRS2003

Probing the Reverse Shock in an Oxygen-Rich Supernova Remnant

The aim of this proposal was to examine the O VI emission at three positions around the X-ray bright ring of the remnant in order to investigate the relation between the O VI emission, the X-ray O VII and O VIII emission, and the optical [O III] emission, and how these vary around the rim of the remnant. So far, only one Far Ultraviolet Spectroscopic Explorer (FUSE) pointing at the remnant has been performed, together with the background pointing needed to subtract the diffuse scattered light from nearby O stars. The data were recalibrated using the CalFUSE calibration pipeline, but the emission is faint enough that hand processing will be needed for this pointing to optimize the extraction. Rereduction of the data is underway. A postdoctoral fellow has also been hired, and in part she will assist with the analysis.

Sonneborn, George↗

NASA NTRS2003

Small-Scale Interstellar Structure Toward the Open Cluster CHI Persei-Fuse II

The purpose of this study was to measure the physical conditions of gas along sight lines toward 6 stars in the core Chi Persei open cluster. These sight lines traverse gas in both the Orion and Perseus spiral arms of the Galaxy, at distances of 500 and 2000 pc, respectively. The stars have angular separations ranging from 45 to 280 arcsec; 60 arcsec corresponds to linear distances of 0.15 and 0.6 pc in the two arms. Thus, abundance variations in these observations would constitute evidence for small-scale variations in the properties of the interstellar medium. Ground-based Na I observations at high resolution (approx. 15 km/sec) toward 172 stars (including the 6 in this study) in the double open cluster h and Chi Persei have revealed complex spatial variation. These variations are especially evident in the gas at velocities of -40 and -55 km/sec, corresponding to the Perseus spiral arm. 21 cm observations of HI emission using the Low Resolution DRAO Survey, with a 12-arcmin beam, also show variations. Averaging the Na I apparent optical depth profiles of neighboring sight lines in order to mimic such a beam size reduces the variation, as compared to the individual Na I measurements, but still show variations larger than seen in the 21 cm profiles. Na I is not the dominant ionization state of Na in the interstellar medium. Thus, it is possible that the variations seen really trace physical structures in the interstellar medium, or they may simply result from variations in the radiation field seen by the gas, or be due to some other environmental circumstance. To distinguish among these possibilities in the present study we obtained FUSE spectra toward the 6 targets in order to measure the molecular hydrogen absorption profiles along these sight lines. The higher J states of H2 are populated by the ambient W radiation field, and thus can provide insight into the environment affecting the gas. If both the high and low J states reveal absorption line profiles with variations similar to that observed in Na I, this would indicate that the variations are due to real structures in the interstellar medium. On the other hand, if the only the high J profiles mimicked the Na I profiles, then the variations may be attributable to environmental effects. We found that the H2 profiles showed considerable variation over the 6 sight lines, and that the profiles, despite having somewhat lower velocity resolution, resemble the Na I profiles. Thus, it appears that the gas really does exhibit variations in physical structures along these sight lines. Useful follow-up work would be to obtain higher signal-to-noise FUSE observations of H2, since the present data are of only moderate quality, and to obtain data on additional targets in this double cluster, in order to map out in more detail the extent and magnitude of the small-scale variations.

Sonneborn, George↗

NASA NTRS2003

Particle Acceleration in SN1006 Shock Waves

This grant is for the analysis of FUSE observations of particle acceleration in supernova remnant SN1006 shock waves. We have performed quick look analysis of the data, but because the source is faint and because the O VI emission lines on SN1006 are extremely broad, extreme care is needed for background subtraction and profile fitting. Moreover, the bulk of the analysis in will consist of model calculations. The Ly beta and O VI lines are clearly detected at the position in the NW filament of SN1006, but not in the NE position where non-thermal X-rays are strong. The lack of O VI emission in the NE places an upper limit on the pre-shock density there.

Raymond, John C.↗

NASA NTRS2003

Molecular Hydrogen in the Quiescent Disk of SW UMA

The data have been acquired and re-reduced by Alex Lobel. We do not detect the molecular hydrogen transitions expected from models of a molecular disk illuminated by Ly alpha photons. We are currently working on an interpretation of the O VI emission lines to determine whether they arise in the disk or the boundary layer. The upper limit on continuum flux will provide an important constraint on models of white dwarf heating in cataclysmic variables.

Raymond, John C.↗

NASA NTRS2003

The Mass of the Classical Cepheid S Mus

This program was to obtain a FUSE satellite spectrum of the classical Cepheid S Mus. The aim was to determine the temperature of the hot companion. Combining this with orbital velocity data, the mass of the Cepheid can be obtained. The spectrum was obtained in spring, 2002. Preliminary reductions have been done, which confirm the results from the lower resolution Voyager spectrum. Final reductions are in progress.

Evans, Nancy↗

NASA NTRS2003

Non-Radiative Shocks in The Cygnus Loop: H2 in HH2 Fluorescence or Collisions?

The FUSE observations of a non-radiative shock wave in the Cygnus Loop were obtained in June and October 2000. The two main results were near equilibration of the kinetic temperature of oxygen with protons and electrons and inferred 3D structure and pre-shock density for the shock including resonance scattering. The 3D structure in turn implies density fluctuations in keeping with the level expected for interstellar turbulence. Major results are contained in an ApJ paper in press and some extensions are contained in a conference proceedings paper in Rev. Mex. A&A in press. Very early results were given in the Ghavamian et al. paper in 2000. The observations of HH2 have not yet been obtained due to the pointing constraints of FUSE. They were scheduled for early January 2003, but we have not yet received the processed data. We are hoping to get the data shortly.

Raymond, John C.↗

NASA NTRS2003

The FUSE Survey of 0 VI in the Galactic Halo

This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

Sonneborn, George↗

NASA NTRS2002

Outbursts In Symbiotic Binaries (FUSE 2000)

During the past year, we made good progress on analysis of FUSE observations of the symbiotic binary Z And. For background, Z And is a binary system composed of a red giant and a hot component of unknown status. The orbital period is roughly 750 days. The hot component undergoes large-scale eruptions every 10-20 yr. An outburst began several years ago, triggering this FUSE opportunity. First, we obtained an excellent set of ground-based optical data in support, of the FUSE observations. We used FAST, a high throughput low resolution spectrograph on the 1.5-m telescope at Mt. Hopkins, Arizona. A 300 g/ mm grating blazed at 4750 A, a 3 in. slit, and a thinned Loral 512 x 2688 CCD gave us spectra covering 3800-7500 A at a resolution of 6 A. The wavelength solution for each spectrum has a probable error of +/- 0.5 A or better. Most of the resulting spectra have moderate signal-to-noise, S/.N approx. greater than 30 per pixel. The time coverage for these spectra is excellent. Typically, we acquired spectra every 1-2 nights during dark runs at Mt. Hopkins. These data cover most of the rise and all of the decline of the recent outburst. The spectra show a wealth of emission lines, including H I, He I, He II, [Fe V11], and the Raman scattering bands at 6830 A and 7088 A. The Raman bands and other high ionization features vary considerably throughout the outburst. These features will enable us to correlate variations in the FUSE spectra with variations in the optical spectra. Second, we began an analysis of FUSE spectra of Z And. We have carefully examined the spectra, identifying real features and defects. We have identified and measured fluxes for all strong emission lines, including the O VI doublet at 1032 A and 1038 A. These and several other strong emission lines display pronounced P Cygni absorption components indicative of outgrowing gas. We will attempt to correlate these velocities with similar profiles observed on optical spectra. The line velocities - together with line variations - will yield physical parameters for the expanding shell of gas in the outer atmosphere of the hot component. We also worked on several diagnostic tools, including upgrades to photoionization programs developed by the PI and others. We plan to use these tools to derive electron densities and temperatures front intercombination and forbidden lines observed on optical and FUSE spectra. Preliminary results indicate a large electron density, n(sub e) is greater than or = 10(exp 10)/cc and a modest electron temperature, T(sub e) approx. 20,000 K. We see no evidence for shocked gas as observed in some other symbiotics. However, we have yet to include several important lines of [Fe VII] and [Ne V] in the analysis. Inclusion of these lines will yield an improved estimate of the electron temperature in the gas. Finally, we have one additional FUSE spectrum planned for acquisition during this cycle. These data will provide important information concerning the state of the system farther along in its decline. Once we have this spectrum in hand, we plan to complete our analysis and publish our results.

Kenyon, Scott J.↗

NASA NTRS2002

Shocks in Dense Clouds in the Vela Supernova Remnant: FUSE

We have obtained 8 LWRS FUSE spectra to study a recently identified interaction of the Vela supernova remnant with a dense cloud region along its western edge. The goal is to quantify the temperature, ionization, density, and abundance characteristics associated with this shock/dense cloud interface by means of UV absorption line studies. Our detection of high-velocity absorption line C I at +90 to +130 km/s with IUE toward a narrow region interior to the Vela SNR strongly suggests the Vela supernova remnant is interacting with a dense ISM or molecular cloud. The shock/dense cloud interface is suggested by (1) the rarity of detection of high-velocity C I seen in IUE spectra, (2) its very limited spatial distribution in the remnant, and (3) a marked decrease in X-ray emission in the region immediately west of the position of these stars where one also finds a 100 micron emission ridge in IRAS images. We have investigated the shock physics and general properties of this interaction region through a focussed UV absorption line study using FUSE spectra. We have FUSE data on OVI absorption lines observed toward 8 stars behind the Vela supernova remnant (SNR). We compare the OVI observations with IUE observations of CIV absorption toward the same stars. Most of the stars, which are all B stars, have complex continua making the extraction of absorption lines difficult. Three of the stars, HD 72088, HD 72089 and HD 72350, however, are rapid rotators (v sin i less than 100 km/s) making the derivation of absorption column densities much easier. We have measured OVI and CIV column densities for the "main component" (i.e. the low velocity component) for these stars. In addition, by removing the H2 line at 1032.35A (121.6 km/s relative to OVI), we find high velocity components of OVI at approximately 150 km/s that we attribute to the shock in the Vela SNR. The column density ratios and magnitudes are compared to both steady shock models and results of hydrodynamical SNR modeling. We find that the models require the shock to be relatively slow (approximately 100 - 170 km/s) to match the FUSE data. We discuss the implications of our results for models of the evolution of the Vela SNR.

Nichols, Joy↗

NASA NTRS2002

Non-Radiative Shocks in the Cygnus Loop: H2 in HH2 Fluorescence or Collisions?

Far Ultraviolet Spectroscopic Explorer (FUSE) observations at four positions across a faint H-alpha filament in the northern Cygnus Loop were carried out successfully. The O(VI) profiles were measured in the four spectra, and we are in the process of fitting them. We have constructed models for a rippled sheet of emission seen almost edge-on based on non-radiative shock wave models for the time-dependent ionization state of the gas behind the shock. The function that describes the rippled sheet geometry predicts the line-of sight velocity component, and we add thermal broadening for various assumed values of ion-ion and ion-electron equilibration. We then compute the radiative transfer in each of the O(VI) lines along the line of sight. Finally, we multiply by the transmission of the ISM using average O(VI) column densities. So far, it appears that partial thermal equilibration is required. Neither full equilibration nor total lack of equilibration seems to provide a workable model. The HH2 observations have not yet been obtained. FUSE has many targets in this region of the sky. We are hoping to get the observations in the spring if FUSE pointing stability allows.

Raymond, John C.↗

NASA NTRS2002

Interstellar Deuterium, Nitrogen and Oxygen Abundances Toward BD+28(deg) 4211: Results from the Far Ultraviolet Spectroscopic Explorer

High resolution far-ultraviolet spectra of the O-type subdwarf BD+28(deg)4211 were obtained with the Far Ultraviolet Spectroscopic Explorer to measure the interstellar deuterium, nitrogen, and oxygen abundances in this direction. The interstellar D(I) transitions are analyzed down to Ly(ioat) at 920.7 A. The star was observed several times at different target offsets in the direction of spectral dispersion. The aligned and coedited spectra have high signal-to-noise ratios (S/N=50-100). D(I), N(I), and O(I) transitions were analyzed with curve-of-growth and profile fitting techniques. A model of interstellar molecular hydrogen on the line of sight was derived from H(II) lines in the FUSE spectra and used to help analyze some features where blending with H(II) was significant. The H(I) column density was determined from high resolution HST/STIS spectra of Ly(alpha) to be log N(H(I))= 19.846+/-0.035(2sigma), which is higher than is typical for sight lines in the local ISM studied for D/H. We found that D/H=(1.39+/-0.21)x 10(exp -5)(2sigma) and O/H=(2.37+/-0.55)x10(exp -4)(2sigma). O/H toward BD+28(deg)4211 appears to be significantly below the mean O/H ratio for the ISM and the Local Bubble.

Sonneborn, George↗

NASA NTRS2002

Far Ultraviolet Astronomy

The Far Ultraviolet Spectroscopic Explorer (FUSE) is studying a wide range of astronomical problems in the 905-1187 Angstrom wavelength region through the use of high resolution spectroscopy. The FUSE bandpass forms a nearly optimal complement to the spectral coverage provided by the Hubble Space Telescope (HST), which extends down to approximately 1170 Angstroms. The photoionization threshold of atomic hydrogen (911 Angstroms) sets a natural short-wavelength limit for the FUV. FUSE was launched in June 1999 from Cape Canaveral, Florida, on a Delta II rocket into a 768 km circular orbit. Scientific observations started later that year. This spectral region is extremely rich in spectral diagnostics of astrophysical gases over a wide range of temperatures (100 K to over 10 million K). Important strong spectral lines in this wavelength range include those of neutral hydrogen, deuterium, nitrogen, oxygen, and argon (H I, D I, N I, O I, and Ar I), molecular hydrogen (H2), five-times ionized oxygen (O VI), and several ionization states of sulfur (S III - S VI). These elements are essential for understanding the origin and evolution of the chemical elements, the formation of stars and our Solar System, and the structure of galaxies, including our Milky Way. FUSE is one of NASA's Explorer missions and a cooperative project of NASA and the space agencies of Canada and France. These missions are smaller, more scientifically focused missions than the larger observatories, like Hubble and Chandra. FUSE was designed, built and operated for NASA by the Department of Physics and Astronomy at Johns Hopkins University. Hundreds of astronomers world-wide are using FUSE for a wide range of scientific research. Some of the important scientific discoveries from the first two years of the mission are described.

Sonneborn, George↗