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Wavefront outer scale deduced from interferometric dispersed fringes
In addition to site characterization, measurements of criticalatmospheric parameters are required to design and to optimize futureadaptive optic systems and long-baseline interferometers. It is possibleto estimate seeing conditions by processing data obtained with existingHigh Angular Resolution instruments. We report the results of jointobservations with the GI2T interferometer and the GSM site-testingmonitor performed over a period of several nights.We compared estimates of the wavefront outer scale done at variousbaselines as well as the seeing (Fried's parameter). We processedinterferometric data by calculating power spectra of dispersed fringeimages. Deduced measurements of the optical path difference lead to theestimates of the outer scale. We found that the outer scale valuesobtained from the GI2T data are mostly in the 5-30m range, in goodagreement with GSM measurements.
| Shapes of Spectral Line Bisectors for Cool Stars
The shape of the line bisector for the prototype spectral line Fe Iλ6253 was measured for an array of 54 stars on the cool half ofthe HR diagram. These bisectors are given in tables along with theirerrors. The classic C shape is shown by only a rather restricted rangein effective temperature and luminosity. The detailed change in bisectorshape with effective temperature and luminosity is documented moreprecisely than in previous work. The most blueward point on the bisectorchanges its height systematically with luminosity and can be used as aluminosity or gravity discriminant. The wide range of bisector shapescontains significant information about the velocity fields in theatmospheres of these stars, but extracting that information may requireextensive modeling.
| An Improved Infrared Passband System for Ground-based Photometry: Realization
We describe new simulations and field trials of the new infraredpassband system developed and discussed by Young, Milone, & Stagg,who discussed and illustrated the state of infrared photometry andsuggested ways in which it could be improved. In particular, theypresented a new set of passbands that minimize the dependence of thephotometry on the water vapor bands of the atmospheric windows, whichdefined the edges of many previous infrared passbands, especially whenused at sites and under conditions for which they were not designed. Inthis paper, we present numerical simulations for three atmosphericmodels, demonstrate a measure of the signal-to-noise ratio in the newpassbands for these models, and present observational data obtained at arelatively low-elevation site. The latter demonstrate the utility ofthis system for most astronomical sites where photometry can beperformed, and permit the transformation of observations to this system.Publications of the Rothney Astrophysical Observatory, No. 74.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 180: zeta Aurigae
Not Available
| Analysis of the Na, Mg, Al, and Si Abundances in the Atmospheres of Red Giants of Different Spectral Subgroups
We analyze the Na, Mg, Al, and Si abundances in the atmospheres of morethan 40 stars, includingred giants of different spectral subgroups(normal red giants, mild and classical barium stars) and severalsupergiants. All these elements exhibit abundance excesses, with theoverabundance increasing with the star’s luminosity. Thedependence of the overabundances for each of these elements on theluminosity (or log g) is the same for all the spectral subgroups,testifying to a common origin: they are all products of hydrogen burningin the NeNa and MgAl cycles that have been dredged up from the stellarinteriors to the outer atmospheric layers by convection that graduallydevelops during the star’s evolution from the main sequence to thered-giant stage. The sodium abundances derived for several stars arelower than for other stars with similar atmospheric parameters. The agesand kinematic characteristics of these two groups of stars suggest thatthey probably belong to different stellar generations.
| Thermal emission at radio frequencies from supernova remnants and a modified theoretical Σ D relation
In this paper, we discuss known discrepancies between theoreticallyderived and empirically measured relations between the radio surfacebrightness Σ and the diameter D of supernova remnants (SNRs):these relations are commonly known as the Σ D relations. We arguethat these discrepancies may be at least partially explained by takinginto account thermal emission at radio frequencies from SNRs atparticular evolutionary stages and located in particular environments.The major contributions of this paper may be summarized as follows: (i)we consider thermal emission at radio frequencies from SNRs in thefollowing scenarios: a relatively young SNR evolving in a densemolecular cloud environment (n 100 1000 cm‑3) andan extremely evolved SNR expanding in a dense warm medium (n 1 10cm‑3). Both of these SNRs are assumed to be in theadiabatic phase of evolution. We develop models of the radio emissionfrom both of these types of SNRs and each of these models demonstratethat through the thermal bremsstrahlung process significant thermalemission at radio frequencies is expected from both types of SNR. Basedon a literature search, we claim that thermal absorption or emission atradio frequencies has been detected for one evolved Galactic SNR andfour young Galactic SNRs with similar properties to our modelled evolvedand young SNRs. (ii) We construct artificial radio spectra for both ofthese two types of SNRs: in particular, we discuss our simulatedspectrum for the evolved Galactic SNR OA 184. By including thermalemission in our simulated spectra, we obtain different slopes in ΣD relations: these new slopes are in closer agreement to empiricallyobtained relations than the theoretically derived relations which do nottake thermal emission into account. (iii) Lastly, we present anadditional modification to the theoretical Σ D relation for SNRsin the adiabatic expansion phase. This modification is based on theconvolution of the synchrotron emissivity with the emissivity derived inthis paper for thermal bremsstrahlung emission from an ionized gas cloud(that is, a theoretical construct of an SNR).
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| A catalog of stellar magnetic rotational phase curves
Magnetized stars usually exhibit periodic variations of the effective(longitudinal) magnetic field Be caused by their rotation. Wepresent a catalog of magnetic rotational phase curves, Be vs.the rotational phase φ, and tables of their parameters for 136stars on the main sequence and above it. Phase curves were obtained bythe least squares fitting of sine wave or double wave functions to theavailable Be measurements, which were compiled from theexisting literature. Most of the catalogued objects are chemicallypeculiar A and B type stars (127 stars). For some stars we also improvedor determined periods of their rotation. We discuss the distribution ofparameters describing magnetic rotational phase curves in our sample.All tables and Appendix A are only available in electronic form athttp://www.edpsciences.org
| A high-resolution spectral analysis of the suspected spectroscopic binary HD 165553
Not Available
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| The R Coronae Borealis stars: carbon abundances from forbidden carbon lines
Spectra of several R Coronae Borealis (RCB) stars at maximum light havebeen examined for the [CI] 9850- and 8727-Åabsorption lines. The9850-Åline is variously blended with an FeII and CN lines, butpositive identifications of the [CI] line are made for RCrB and SUTau.The 8727-Åline is detected in the spectrum of the five starsobserved in this wavelength region. Carbon abundances are derived fromthe [CI] lines using the model atmospheres and atmospheric parametersused by Asplund et al.Although the observed strength of a CI line is constant from cool to hotRCB stars, the strength is lower than predicted by an amount equivalentto a factor of 4 reduction of the gf-value of a line. Asplund et al.dubbed this `the carbon problem' and discussed possible solutions.The [CI] 9850-Åline seen clearly in RCrB and SUTau confirms themagnitude of the carbon problem revealed by the CI lines. The [CI]8727-Åline measured in five stars shows an enhanced carbonproblem. The gf-value required to fit the observed [CI] 8727-Ålineis a factor of 15 less than the well-determined theoretical gf-value. Wesuggest that the carbon problem for all lines may be alleviated to someextent by a chromospheric-like temperature rise in these stars. The risefar exceeds that predicted by our non-local thermodynamic equilibriumcalculations, and requires a substantial deposition of mechanicalenergy.
| 10-μm absorption spectra of silicates for two new diffuse interstellar medium sightlines
We present low resolution 10-μm spectra of the newly identifieddiffuse interstellar medium (ISM) sightlines towards StRS 217 and StRS371 and a new spectrum of Cyg OB2 no. 12 obtained at the UK InfraredTelescope (UKIRT) with the Michelle imager/spectrometer. As previously,the μ Cephei emissivity better represents the profile of diffusemedium silicates than does the broader Trapezium emissivity which ischaracteristic of dust in molecular clouds. These spectra together withseven spectra published by Roche & Aitken comprise the majority ofthe silicates data set for the diffuse ISM. The observed sample includessources in the first galactic quadrant at heliocentric distances ofabout 1.0-4.2 kpc. We find the silicate optical depth,csil=AV/(19.2 +/- 0.6) and the ratio ofcsil to heliocentric distance, d, is in the range 0.1<~csil/d<~ 0.7 kpc-1 for StRS 217 the ratiocould be as high as csil/d<~ 1.2 kpc-1.However, this ratio is dominated by uncertainties in the distanceestimates and does not indicate the degree of clumping in the diffuseinterstellar medium.
| Determination of fundamental characteristics for stars of the F, G, and K spectral types. The surface gravities and metallicity parameters.
Not Available
| A Spectral Atlas of F and G Stars
We present an atlas of a group of bright stars in the range of spectralclasses F--G and luminosity classes I--V. The spectra were obtainedwith spectral resolution R 15,000 within spectral region4500--6620 Å. Typical spectra of stars with different metallicity[Fe/H] are included. We also show the digital version of the spectraldata in FITS format.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| A Multiwavelength Search for a Counterpart of the Brightest Unidentified Gamma-Ray Source 3EG J2020+4017 (2CG 078+2)
In search of the counterpart to the brightest unidentified gamma-raysource, 3EG J2020+4017 (2CG 078+2), we report on new X-ray and radioobservations of the γ Cygni field with the Chandra X-RayObservatory and with the Green Bank Telescope (GBT). We also report onreanalysis of archival ROSAT data. With Chandra it became possible forthe first time to measure the position of the putative gamma-raycounterpart, RX J2020.2+4026, with subarcsecond accuracy and to deduceits X-ray spectral characteristics. These observations demonstrate thatRX J2020.2+4026 is associated with a K field star and therefore isunlikely to be the counterpart of the bright gamma-ray source 2CG 078+2in the SNR G78.2+2.1 as had been previously suggested. The Chandraobservation detected 37 additional X-ray sources, which were correlatedwith catalogs of optical and infrared data. Subsequent GBT radioobservations covered the complete 99% EGRET likelihood contour of 3EGJ2020+4017 with a sensitivity limit of L820~0.1 mJykpc2, which is lower than most of the recent deep radiosearch limits. If there is a pulsar operating in 3EG J2020+4017, thissensitivity limit suggests that either the pulsar does not producesignificant amounts of radio emission or that its geometry is such thatthe radio beam does not intersect with the line of sight. Finally,reanalysis of archival ROSAT data leads to a flux upper limit offX(0.1-2.4keV)<1.8×10-13 ergss-1 cm-2 for a putative pointlike X-ray sourcelocated within the 68% confidence contour of 3EG J2020+4017. Adoptingthe supernova remnant age of 5400 yr and assuming a spin-down to X-rayenergy conversion factor of 10-4, this upper limit constrainsthe parameters of a putative neutron star as a counterpart for 3EGJ2020+4017 to be P >~ 160 (d 1.5 kpc)-1 ms,P>~5×10-13 (d 1.5 kpc-1)-1 ss-1, and B⊥>~9×1012 (d1.5 kpc)-1 G.
| A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. VI. NGC 6910
We present results of variability search in the field of the young opencluster NGC 6910. We found four beta Cep-type stars in the cluster,which makes it rather exceptional among the northern clusters observedin our project. Two of these beta Cep stars show three modes withamplitudes above the detection level, in the remaining two we detectsingle modes. We discuss the possibility that the large number of betaCep stars in NGC 6910 is due to higher metallicity of the cluster. Inaddition, we found four other variables, one ellipsoidal or eclipsingbinary and three that show irregular variations. The latter three starshave H alpha in emission.We also provide VI_C photometry for 139 stars down to V=16.6 mag and Halpha photometry for 73 stars. Using this photometry we estimate thecluster age to be equal to 6+/-2 Myr, and the distance modulus,11.0+/-0.3 mag. The reddening is high and variable across the cluster.In terms of the E(V-I_C) color-excess it amounts to 1.25-1.7 mag,corresponding to E(B-V) between 1.0 mag and 1.4 mag. The averagereddening in the central field is E(V-I_ C=1.47+/-0.04 mag.
| A Revised Calibration of the MV-W(O I 7774) Relationship using Hipparcos Data: Its Application to Cepheids and Evolved Stars
A new calibration of the MV-W(O I 7774) relationship hasbeen calculated using better reddening and distance estimates for asample of 27 calibrator stars of spectral types A to G, based onaccurate parallaxes and proper motions from the Hipparcos and Tychocatalogues. The present calibration predicts absolute magnitude withaccuracies of +/-0.38mag for a sample covering a large range ofMV, from -9.5 to +0.35 mag. The color term included in aprevious paper has been dropped since its inclusion does not lead to anysignificant improvement in the calibration. The variation of the O I7774 feature in the classical cepheid SS Sct has been studied. Wecalculated a phase-dependent correction to random phase OI featurestrengths in Cepheids, such that it predicts mean absolute magnitudesusing the above calibration. After applying such a correction, we couldincrease the list of calibrators to 58 by adding MV and O Itriplet strength data for 31 classical Cepheids. The standard error ofthe calibration using the composite sample was comparable to thatobtained from the primary 27 calibrators, showing that it is possible tocalculate mean Cepheid luminosities from random phase observations ofthe O I 7774 feature. We use our derived calibrations to estimateMV for a set of evolved objects to be able to locate theirpositions in the HR diagram.
| A two color pupil imaging method to detect stellar oscillations
Observations of stellar intensity oscillations from the ground arestrongly affected by intensity fluctuations caused by the atmosphere(scintillation). However, by using a differential observational methodthat images the pupil of the telescope in two colors at the same time ona single CCD, we can partially compensate for this source of atmosphericnoise (which is color dependant) as well as other problems, such asguiding and saturation. Moreover, by placing instruments at differentlocations (eg. Dome C and South Pole) we can further reduce theatmospheric noise contribution by using cross-spectral methods, such asRandom Lag Singular Cross-Spectrum Analysis (RLSCA). (We also decreasethe likelihood of gaps in the data string due to bad weather). The RLSCAmethod is well suited for extracting common oscillatory components fromtwo or more observations, including their relative phases. We haveevaluated the performance of our method using real data from SOHO. Wefind that our differential algorithm can recover the absolute amplitudesof the solar intensity oscillations with an efficiency of 70%. We arecurrently carrying out tests using a number of telescopes, including BigBear, Mt. Wilson, Teramo and Milano, while waiting for the South Poleand Dome C sites to become available.
| My researches at the infrared doors
As a historical and biographical introduction to this Conference, I givehere a brief review about my studies in infrared astronomy. I begunmaking regular observations in this unexplored (at that time) fieldmoving from the wavelengths just beyond the visible, where I discovered,for example, the galaxies then named Maffei 1 and Maffei 2, located inthe Zone of Avoidance. The analysis of the material thus collected,mainly aimed at studies on long period variables (LPVs), produced aseries of new and hardly predicted results. Further importantdevelopments of my researches in infrared are now expected from theongoing development of an Antarctica telescope for the mid-infraredbands. These bands were an almost unexplored range of the spectrum onlya few years ago: now the researches discussed in this meeting show howmany new fields of study have become active in them.
| A Spectral Analysis of HD 165553
High resolution spectra of HD 165553, a star reported to be aspectroscopic binary of spectral type F8 Ib are analysed. The stellarparameters - effective temperature, surface gravity and microturbulenceare determined using model atmospheres. A detail chemical compositionstudy indicates a near-solar composition for HD 165553. Comparison ofits spectrum with that of Cyg, a normal supergiant of spectral type F8Iab indicates that the star is of a later spectral type; a spectral typeG Iab seems more likely for HD 165553.
| Angular Diameters of Stars from the Mark III Optical Interferometer
Observations of 85 stars were obtained at wavelengths between 451 and800 nm with the Mark III Stellar Interferometer on Mount Wilson, nearPasadena, California. Angular diameters were determined by fitting auniform-disk model to the visibility amplitude versus projected baselinelength. Half the angular diameters determined at 800 nm have formalerrors smaller than 1%. Limb-darkened angular diameters, effectivetemperatures, and surface brightnesses were determined for these stars,and relationships between these parameters are presented. Scatter inthese relationships is larger than would be expected from themeasurement uncertainties. We argue that this scatter is not due to anunderestimate of the angular diameter errors; whether it is due tophotometric errors or is intrinsic to the relationship is unresolved.The agreement with other observations of the same stars at the samewavelengths is good; the width of the difference distribution iscomparable to that estimated from the error bars, but the wings of thedistribution are larger than Gaussian. Comparison with infraredmeasurements is more problematic; in disagreement with models, coolerstars appear systematically smaller in the near-infrared than expected,warmer stars larger.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| High-resolution spectroscopy of QY Sge: an obscured RV Tauri variable?
The first high-resolution optical spectra of QY Sge are presented anddiscussed. Menzies & Whitelock, on the basis of photometry andlow-resolution spectra, suggested that this G0I supergiant was obscuredby dust and seen only by scattered light from a circumstellar reflectionnebula. The new spectra confirm and extend this picture. Photosphericlines are unusually broad indicating scattering of photons from dust inthe stellar wind. The presence of very broad, NaD emission lines isconfirmed. Sharp emission lines from low levels of abundant neutralmetal atoms are reported for the first time. An abundance analysis ofphotospheric lines shows that the stellar atmosphere is of approximatelysolar composition but with highly condensable (e.g. Sc and Ti) elementsdepleted by factors of 5-10.
| High resolution spectroscopy of QY Sge.
Not Available
| Non-imaging Gamma Ray Telescopes
Despite continual improvement of the Atmospheric Cherenkov Technique,the number of astrophysical gamma ray sources that have been wellstudied from the ground remains small (less than a half-dozen), duemainly to the nature of the cosmic accelerators themselves. For mostActive Galactic Nuclei of the blazar class, the energy range in whichimagers are sensitive lies beyond the inverse Compton peak, where theflux falls rapidly with increasing energy. A few galactic sources arevery bright in EGRET but the spectra roll over (e.g. Geminga), whilemany have no break in the EGRET data but are intrinsically weak. TheCrab nebula is an exception, along with a some others. Increasing thedata sample thus requires a lower energy threshold, increased fluxsensitivity, or a combination of the two. Long term progress will comewith the imager arrays (HESS & VERITAS, beginning in 2002), the verylarge imagers (MAGIC & MACE) and with GLAST (2006). This paperreviews work-in-progress aimed at reaching the 50 GeV range using solarplants.
| Cosmic rays from SNRs and TeV gamma-ray astronomy
The origin of Galactic cosmic rays is still a burning question thatforms a major motivation for developments in ground-based gamma-rayastronomy. SNRs are long-thought to be sites for the acceleration ofGalactic cosmic rays, and evidence for gamma-ray be capable ofaccelerating particles to multi-TeV energies. Yet, along with this, andin the same overall model framework (diffusive shock acceleration), isthe need to accommodate upper limits at TeV energies imposed on otherexamples. This review will present an update on the status of SNRobservations at TeV energies, their interpretation, and discuss therelevant parameters and issues of next generation ground-basedinstruments relating to their ability to confirm SNRs as Galactic cosmicray sources.
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