Search

We employed the SERENDIP III system with the Arecibo radio telescope to search for possible artificial extraterrestrial signals. Over the four years of this search we covered 93% of the sky observable at Arecibo at least once and 44% of the sky five times or more with a sensitivity of ~3E-25 W/m2. The data were sent to a 4 million channel spectrum analyzer. Information was obtained from over 1E+14 independent data points and the results were then analyzed via a suite of pattern detection algorithms to identify narrow band spectral power peaks that were not readily identifiable as the product of human activity. We separately selected data coincident with interesting nearby G dwarf stars that were encountered by chance in our sky survey for suggestions of excess power peaks. The peak power distributions in both these data sets were consistent with random noise. We report upper limits on possible signals from the stars investigated and provide examples of the most interesting candidates identified in the sky survey. This paper was intended for publication in 2000 and is presented here without change from the version submitted to ApJS in 2000., Comment: 9 pages. 5 figures. 2 tables. emulateapj 5/12/14 or later required

The idea that credible searches for Extra-Terrestrial Intelligence (ETI) could be carried out were laid out in detail in the (now classic) paper by Morrison and Cocconi (1959). They suggested using the radio band for these searches. Since then radio searches have been carried out by over sixty different groups. No signals from ETI's have been identified. Most searches did not have high sensitivity and it is not surprising that ETI signals were not detected. It is important to note, however, that these efforts were instrumental in developing new technical capabilities and they helped generate wide interest in this field. In this paper I will briefly discuss the more sensitive searches that have been carried out and some of the other searches that are arguably quite innovative or have been influential in some other manner., Comment: 5 pages including one table. Presented at SPIE Conf. 8152, San Diego, CA, Aug 24, 2011 (v1 was missing a section and section headings)

Observations with the Extreme Ultraviolet Explorer (EUVE) have shown the Coma Cluster to be a source of EUV emission in excess of that produced by X-ray gas in the cluster. We have re-examined the EUVE data on this cluster in an attempt to obtain clues as to the origin of this emission. We find two important new results. First, the ratio between the azimuthally averaged EUV excess emission and the ROSAT hard X-ray flux is constant as a function of distance from the cluster center outward. Second, a correlation analysis between the EUV excess emission and the X-ray emission shows that on a detailed level the EUV excess is spatially closely related to the X-ray emission. These findings contradict previous suggestions as to the underlying source of the diffuse EUV emission in Coma and provide important information in regards to the true source of this emission. We propose a new explanation for the source of this emission: inverse Compton scattering of microwave background photons by secondary electrons and positrons. We explore this possibility in some detail and show that it is consistent with all of the available observational evidence. The parent cosmic ray protons may have been produced by any of a number of sources, including supernovae, active galaxies, galactic winds, and cluster formation shocks, but we believe that the most likely source is cluster formation shocks. If the EUV emission in the Coma Cluster is, in fact, the result of secondary electrons, this may be the only direct evidence for secondary electrons in the intracluster medium of a cluster of galaxies, since recent work suggests that secondary electrons may not be the cause of radio halos., Comment: 17 pages, 7 eps figures inline, submitted to ApJ

A variety of models have been explored in regard to the origin of the excess extreme ultraviolet (~ 0.1 keV) emission in the Coma cluster. It is now established that the flux is non-thermal and the only non-thermal source mechanism that appears viable is inverse Compton emission produced by ~ 100 MeV electrons interacting with the cosmic microwave background photons. All but one of the models that have been proposed require a cluster magnetic field < 1 micro G. However, recent observations strongly suggest the magnetic field in the Coma cluster is ~ 5 micro G. We investigate the constraints on models imposed by a 5 micro G cluster field and find a limited class of models that are compatible with this constraint. We also investigate the possibility that the excess hard (40-60 keV) X-ray emission in the cluster is produced by inverse Compton emission with the same electron population that produces the EUV excess. We find no scenarios that are compatible with a large cluster magnetic field, and consequently in this case these two components must be unrelated., Comment: 21 pages, 10 figures, Accepted for publication in ApJ

We present studies of the Extreme Ultraviolet (EUV) emission in the Fornax cluster of galaxies; a relatively nearby well-studied cluster with X-ray emitting cluster gas and a very large radio source. We examine both the large-scale (~size of the X-ray emitting cluster gas), and the small-scale (

We present the results of a search for Extreme Ultraviolet emission in A4059, a cluster with an X-ray emitting cluster gas. Our analysis of Extreme Ultraviolet Explorer (EUVE) Deep Survey observations of this cluster shows that it is associated with diffuse EUV emission. Outside the central 2 arcmin radius the entire EUV emission detected is explained by the low energy tail of the X-ray emitting gas. Within the central 2 arcmin region of the cluster we find a deficit of EUV emission compared to that expected from the X-ray gas. This flux deficit is discussed in the context of the cluster's cooling flow. The results derived for A4059 are compared to EUVE results obtained for other clusters such as Coma, Virgo, A1795, and A2199. As part of the study we have carried out a detailed investigation of the stability of the EUVE Deep Survey detector background. Based on long integrations of blank sky over 27 months we disprove claims of substantial time dependent changes in the detector background by R. Lieu and coworkers. We also show, contrary to the claim of R. Lieu and coworkers, that the images obtained with the detector are independent of the pulse height threshold of the detector over a substantial range of threshold settings., Comment: 8 pages, 4 figures, accepted for publication in ApJ

We re-examine {\em Voyager} Ultraviolet Spectrograph data used to establish upper limits to the $\lambda$ 500-900 \AA and $\lambda$ 900-1100 \AA cosmic diffuse background. The measurement of diffuse flux with the {\em Voyager} UVS data requires complex corrections for noise sources which are far larger than the astronomical signal. In the analyses carried out to date, the upper limits obtained on the diffuse background show statistical anomalies which indicate that substantial systematic errors are present. We detail these anomalies and identify specific problems with the analysis. We derive statistically robust 2~$\sigma$ upper limits for continuum flux of 570~photons~s$^{-1}$ cm$^{-2}$~ster$^{-1}$~\AA$^{-1}$ and for the 1000 \AA~ diffuse line flux of 11,790~photons~s$^{-1}$ cm$^{-2}$~ster$^{-1}$. The true limits may be substantially higher because of unknown systematic uncertainties. The new statistical limits alone are insufficient to support previous conclusions based on the {\em Voyager} data including work on the character of interstellar dust and estimates of the diffuse extragalactic far UV background as absorbed by intergalactic dust., Comment: To be published in the Astrophysical Journal

We present results of a re-analysis of archival EUVE data of the central region of the Virgo cluster. We employ the new analysis method developed by Bowyer, Bergh\"ofer & Korpela (1999) and find diffuse emission reaching out to a distance of $\approx 13\arcmin$. The spatial distribution of this flux is incompatible with a thermal plasma origin. We investigate whether this emission is due to inverse Compton scattering of relativistic electrons against the 3$^{\circ}$ K black-body background. We show that this emission cannot be produced by an extrapolation to lower energies of the observed synchrotron radio emitting electrons and an additional component of low energy relativistic electrons is required. In addition to discussing the diffuse EUV emission, we present an analysis of the EUV emission originating from the jet in M87., Comment: 9 pages, 8 figures, accepted for publication in the Astrophysical Journal

We report new EUV data on the cluster of galaxies Abell 1795. These data were taken well away from a detector defect which could have compromised earlier results on this cluster. Our new observations confirm the validity of the original data set. However, we find our results are strongly influenced by the variation of the telescope sensitivity over the field of view and upon the details of the subtraction of the EUV emission from the X-ray plasma. We investigate these effects using our new data and archival data on Abell 1795, Abell 2199 and the Coma cluster. When we use the appropriate correction factors, we find there is no evidence for any excess EUV emission in Abell 1795 or Abell 2199. However, we do find excess EUV emission in the Coma Cluster using our new analysis procedures, confirming that in at least this cluster some as yet unidentified process is operative., Comment: 20 pages, LaTeX (aasms4.sty, 10 eps figures), accepted to ApJ for 1 Dec 1999 volume

We present the far ultraviolet spectrum of alpha Virginis taken with EURD spectrograph on-board MINISAT-01. The spectral range covered is from ~900 to 1080 A with 5 A spectral resolution. We have fitted Kurucz models to IUE spectra of alpha Vir and compared the extension of the model to our wavelengths with EURD data. This comparison shows that EURD fluxes are consistent with the prediction of the model within 20-30%, depending on the reddening assumed. EURD fluxes are consistent with Voyager observations but are ~60% higher than most previous rocket observations of alpha Vir., Comment: 13 pages, 4 figures. Submitted to The Astrophysical Journal

We report a new analysis of diffuse EUV emission in clusters of galaxies. We find the cluster emission is strongly influenced by the variation of the telescope sensitivity over the field of view and upon the details of the subtraction of the EUV emission for the X-ray plasma. We investigate these effects on Abell 1795, Abell 2199, and the Coma cluster. When we use the appropriate correction factors, we find there is no evidence for any excess EUV emission in Abell 1795 or Abell 2199, However, we do find extended EUV emission in the Coma cluster and in the Virgo cluster using our new analysis proceedures, confirming that in these clusters some as yet unidentified process is operative., Comment: 7 pages, presented at Ringberg Workshop on Diffuse Thermal and Relativistic Plasma in Galaxy Clusters

Lieu, Mittaz, Bonamente, Durret and Kaastra have provided a document which claims to rebut the finding by Bowyer, Berghoefer and Korpela presented at the Ringburg Workshop (April 1999) that excess EUV emission detected in some clusters of galaxies is an artifact of the background subtraction employed. We provide here a response to their claims., Comment: 4 pages

We report on spectral observations of the night sky in the band around 900 angstroms where the emission line in the Sciama model of radiatively decaying massive neutrinos would be present. The data were obtained with a high resolution, high sensitivity spectrometer flown on the Spanish MINISAT satellite. The observed emission is far less intense than that expected in the Sciama model., Comment: 9 pages, accepted to ApJ

We have used the Deep Survey telescope of EUVE to investigate shadows in the diffuse EUV/Soft X-Ray background cast by clouds in the interstellar medium. We confirm the existence of a shadow previously reported, and provide evidence for two new shadows. We used IRAS data to identify the clouds producing these shadows and to determine their optical depth to EUV radiation. The EUV-absorbing clouds are optically thick in the EUV, and all EUV emission detected in the direction of these shadows must be produced from material in front of the clouds. We obtained new optical data to determine the distance to these clouds. We use a new differential cloud technique to obtain the pressure of the interstellar medium. These results do not depend on any zero level calibration of the data. Our results provide evidence that the pressure of the hot interstellar gas is the same in three different directions in the local interstellar medium, and is at least 8 times higher than derived for the local cloud surrounding our Sun. This provides new evidence for large thermal pressure imbalances in the local ISM, and directly contradicts the basic assumption of thermal pressure equilibrium used in almost all present models of the interstellar medium., Comment: 13 pages, 13 figures

We have examined the hypothesis that the majority of the diffuse EUV flux in the Coma cluster is due to inverse Compton scattering of low energy cosmic ray electrons (0.16 < epsilon < 0.31 GeV) against the 3K black-body background. We present data on the two-dimensional spatial distribution of the EUV flux and show that these data provide strong support for a non-thermal origin for the EUV flux. However, we show that this emission cannot be produced by an extrapolation to lower energies of the observed synchrotron radio emitting electrons and an additional component of low energy cosmic ray electrons is required., Comment: 11 pages, 5 figures

The Berkeley spectrograph aboard the ORFEUS telescope made its second flight on the 14-day ORFEUS-SPAS II mission of the Space Shuttle Columbia in November/December 1996. Approximately half of the available observing time was dedicated to the Berkeley spectrograph, which was used by both Principal and Guest Investigators. The spectrograph's full bandpass is 390-1218 A; here we discuss its in-flight performance at far-ultraviolet (FUV) wavelengths, where most of the observations were performed. The instrument's effective area peaks at 8.9 +/- 0.5 cm^2 near 1020 A, and the mean spectral resolution is 95 km/s FWHM for point sources. Over most of the spectral range, the typical night-time background event rate in each spectral resolution element was about 0.003/s. Simultaneous background observations of an adjacent blank field were provided through a secondary, off-axis aperture. The Berkeley spectrograph's unique combination of sensitivity and resolution provided valuable observations of approximately 105 distinct astronomical targets, ranging in distance from the earth's own moon to some of the brightest AGN., Comment: LaTeX file, 12 pages, 2 encapsulated PostScript figures. Uses aaspp4.sty. To appear in The Astrophysical Journal (Letters). The ORFEUS telescope is described at http://sag-www.ssl.berkeley.edu/orfeus/

We present the first intermediate-resolution (lambda / 3000) spectrum of the bright quasi-stellar object 3C273 at wavelengths between 900 and 1200 A. Observations were performed with the Berkeley spectrograph aboard the ORFEUS-SPAS II mission. We detect Lyman beta counterparts to previously-identified intergalactic Lyman-alpha features at cz = 19900, 1600, and 1000 km/s; counterparts to other putative Lyman-alpha clouds along the sight line are below our detection limit. The strengths of the two very low redshift Lyman-beta features, which are believed to arise in Virgo intracluster gas, exceed preflight expectations, suggesting that the previous determination of the cloud parameters may underestimate the true column densities. A curve-of-growth analysis sets a minimum H I column density of 4 E14/cm^2 for the 1600 km/s cloud. We find marginally significant evidence for Galactic H_2 along the sight line, with a total column density of about 1 E15/cm^2. We detect the stronger interstellar O VI doublet member unambiguously; the weaker member is blended with other features. If the Doppler b value for O VI is comparable to that determined for N V then the O VI column density is 7 +/- 2 E14/cm^2, significantly above the only previous estimate. The O VI / N V ratio is about 10, consistent with the low end of the range observed in the disk. Additional interstellar species detected for the first time toward 3C273 (at modest statistical significance) include P II, Fe III, Ar I, and S III., Comment: LaTeX file, 11 pages, 4 encapsulated PostScript figures. Uses aaspp4.sty and astrobib.sty. (Astrobib is available from http://www.stsci.edu/software/TeX.html .) The ORFEUS telescope is described at http://sag-www.ssl.berkeley.edu/orfeus/ . To appear in ApJ (Letters)

We present the results of searches for EUV emission from neutron stars conducted with the EUVE Deep Survey and Scanner Telescopes. To date, 21 fields containing known neutron stars have been observed in the Lexan/Boron (40--190 angstrom) band. Of these, 11 fields were simultaneously observed in the Aluminum/Carbon (160-385 angstrom) band. Five neutron stars which have been detected in the EUV have been reported previously; no new detections have been made in the studies reported here. For those sources not detected, we have used the observations to obtain limits on the spectral flux from the neutron stars in these bands. We provide means to convert these fluxes into intrinsic source fluxes for black-body and power law spectra for varying levels of absorption by the interstellar medium., Comment: 11 pages; 5 encapsulated postscript files; requires aastex macros and psfig 1.2; Accepted for publication in AJ. Adds one object, fixes typos

We report on extreme-ultraviolet (EUV) spectroscopic observations of the B bright giant epsilon Canis Majoris made during the ORFEUS-SPAS II mission. We assess the performance of the instrument in the EUV and find that the effective area is roughly 3 times that of the Extreme-Ultraviolet Explorer (EUVE) long-wavelength spectrometer and that the spectral resolution is lambda/Delta(lambda) = 1250. We identify most of the features, qualitatively compare different models, and examine the wind-broadened O V and Si IV lines, which display blue edge velocities up to 800 km/s., Comment: 10 pages LaTeX, 5 figures, accepted by ApJ Letters, replacement includes just a few editorial changes

One of the keys to interpreting the character and evolution of interstellar matter in the galaxy is understanding the distribution of the low density hot (10^5 K -10^6 K) phase of the interstellar medium (ISM). This phase is much more difficult to observe than the cooler high density components of the ISM because of its low density and lack of easily observable tracers. Because gas of this temperature emits mainly in the far ultraviolet (912 angstrom - 1800 angstroms) and extreme ultraviolet (80 angstrom - 912 angstrom), and (for gas hotter than 10^6 K) X-rays, observations in these bands can provide important constraints to the distribution of this gas. Because of interstellar opacity at EUV wavelengths, only FUV and X-ray observations can provide clues to the properties of hot gas from distant regions. We present results from a search for FUV emission from the diffuse ISM conducted with an orbital FUV spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer, which covers the band from 950 angstrom to 1080 angstrom with 3.2 angstrom resolution, observed a region of low neutral hydrogen column density near the south galactic pole for a total effective integration time of 1583 seconds. The only emission line detected was a geocoronal hydrogen line at 1025 angstrom. We are able to place upper limits to several expected emission features that provide constraints on interstellar plasma parameters. We are also able to place limits on the continuum emission throughout the bandpass. We compare these limits and other diffuse observations with several models of the structure of the interstellar medium and discuss the ramifications., Comment: 23 pages, LaTeX, 10 eps figures, uses aaspp4.sty and Psfig/TeX Release 1.2, Minor editorial changes

We present measurements of interstellar H_2 absorption lines in the continuum spectra of seven early-type stars in the Galactic disk at distances between 1 and 4 kpc. Five of these stars provide lines of sight through the Sagittarius spiral arm. The spectra, obtained with the Berkeley EUV/FUV spectrometer on the ORFEUS telescope in 1993 September, have a resolution of 3000 and statistical signal-to-noise ratios between 20 and 80. We determine column densities for each observed rotational level and derive excitation temperatures and densities for the H_2 clouds along each line of sight. Our data continue the relationships among H_2 column density, fractional molecular abundance, and reddening apparent in Copernicus observations of nearby stars, indicating a common mechanism for H_2 production. Estimates of cloud temperatures and densities are consistent with those derived from Copernicus data. We find that the molecular fraction of hydrogen is nearly constant over a wide range of distances and mean reddenings, consistent with a model in which a significant fraction of the neutral ISM is associated with H_2-bearing molecular clouds, even along low-density lines of sight., Comment: LaTeX file, 19 pages, 6 encapsulated PostScript figures. Uses aaspp4.sty and astrobib.sty. (Astrobib is available from http://www.stsci.edu/software/TeX.html .) To be published in The Astrophysical Journal, Vol. 492, January 1998