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Identification of blue high proper motion objects in the Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for newbright blue high proper motion objects in the entire sky: white dwarfs,hot subdwarfs, runaway OB stars, and early-type stars in nearby youngmoving groups. Methods: We performed an all-sky cross-matchbetween the optical Tycho-2 and near-infrared 2MASS catalogues withAladin, and selected objects with proper motions ? > 50 masyr-1 and colours VT - Ks < -0.5 magwith TOPCAT. We also collected multi-wavelength photometry, constructedthe spectral energy distributions and estimated effective temperaturesfrom fits to atmospheric models with VOSA for the most interestingtargets. Results: We assembled a sample of 32 bright blue highproper motion objects, including ten sdO/B subdwarfs, nine DA whitedwarfs, five young early-type stars (two of which are runaway stars),two blue horizontal branch stars, one star with poor information, andfive objects reported for the first time in this work. These last fiveobjects have magnitudes BT ? 11.0-11.6 mag, effectivetemperatures Teff ? 24 000-30 000 K, and are located inthe region of known white dwarfs and hot subdwarfs in a reduced propermotion-colour diagram. We confirmed the hot subdwarf nature of one ofthe new objects, Albus 5, with public far-ultraviolet spectroscopic dataobtained with FUSE.
| All-Sky Spectrally Matched UBVRI-ZY and u'g'r'i'z' Magnitudes for Stars in the Tycho2 Catalog
We present fitted UBVRI-ZY and u'g'r'i'z' magnitudes, spectral types,and distances for 2.4 million stars, derived from synthetic photometryof a library spectrum that best matches the Tycho2 BTVT , NOMAD RN , and 2MASS JHK2/Scatalog magnitudes. We present similarly synthesized multifiltermagnitudes, types, and distances for 4.8 million stars with 2MASS andSDSS photometry to g < 16 within the Sloan survey region, for Landoltand Sloan primary standards, and for Sloan northern (photometrictelescope) and southern secondary standards. The synthetic magnitudezero points for BT VT , UBVRI , ZVYV , JHK2/S , JHKMKO , Stromgren uvby,Sloan u'g'r'i'z', and ugirz are calibrated on 20 CALSPECspectrophotometric standards. The UBVRI and ugriz zero points havedispersions of 1-3%, for standards covering a range of color from - 0.3< V - I < 4.6 ; those for other filters are in the range of 2-5%.The spectrally matched fits to Tycho2 stars provide estimated 1?errors per star of ˜ 0.2 , 0.15, 0.12, 0.10, and 0.08 mag,respectively, in either UBVRI or u'g'r'i'z'; those for at least 70% ofthe SDSS survey region to g < 16 have estimated 1? errors perstar of ˜ 0.2 , 0.06, 0.04, 0.04, and 0.05 in u'g'r'i'z' or UBVRI.The density of Tycho2 stars, averaging about 60 stars per square degree,provides sufficient stars to enable automatic flux calibrations for mostdigital images with fields of view of 0.5° or more. Using severalsuch standards per field, automatic flux calibration can be achieved toa few percent in any filter, at any air mass, in most workable observingconditions, to facilitate intercomparison of data from different sites,telescopes, and instruments.
| Photometric calibration of the Supernova Legacy Survey fields
Aims: We present the photometric calibration of the Supernova LegacySurvey (SNLS) fields. The SNLS aims at measuring the distances to SNe Iaat (0.3 < z < 1) using MegaCam, the 1 deg2 imager onthe Canada-France-Hawaii Telescope (CFHT). The uncertainty affecting thephotometric calibration of the survey dominates the systematicuncertainty of the key measurement of the survey, namely the dark energyequation of state. The photometric calibration of the SNLS requiresobtaining a uniform response across the imager, calibrating the sciencefield stars in each survey band (SDSS-like ugriz bands) with respect tostandards with known flux in the same bands, and binding the calibrationto the UBVRI Landolt standards used to calibrate the nearby SNe from theliterature necessary to produce cosmological constraints. Methods: The spatial non-uniformities of the imager photometricresponse are mapped using dithered observations of dense stellar fields.Photometric zero-points against Landolt standards are obtained. Thelinearity of the instrument is studied. Results: We show that theimager filters and photometric response are not uniform and publishcorrection maps. We present models of the effective passbands of theinstrument as a function of the position on the focal plane. We define anatural magnitude system for MegaCam. We show that the systematicsaffecting the magnitude-to-flux relations can be reduced if we use thespectrophotometric standard star BD +17 4708 instead of Vega as afundamental flux standard. We publish ugriz catalogs of tertiarystandards for all the SNLS fields.Based on observations obtained with MegaPrime/MegaCam, a joint projectof CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT)which is operated by the National Research Council (NRC) of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique (CNRS) of France, and the University of Hawaii.This work is based in part on data products produced at the CanadianAstronomy Data Centre as part of the Canada-France-Hawaii TelescopeLegacy Survey, a collaborative project of NRC and CNRS. Tables 13-22 andD.1-D.3 are also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/506/999
| Revised and Updated Catalogue of the First Byurakan Survey Blue Stellar Objects
Eleven lists of blue stellar objects (BSOs) were published inAstrophysics in 1990-1996, found in the First Byurakan Survey (FBS)low-dispersion spectroscopic plates. The selection was carried out inthe region with +33° > ? > +45° and ? >+61° with a surface of 4000 deg2. As a result, thecatalogue of the FBS BSOs was compiled. Its preliminary version has beenavailable at Centre de Données Astronomiques de Strasbourg since1999. We revised and updated the FBS BSOs catalogue with new data fromrecently published optical and multiwavelength catalogs to give accessto all available data and make further comparative studies of theproperties of these objects possible. We made cross-correlations of theFBS BSOs catalogue with the Minnesota Automated Plate Scanner,USNO-B1.0, Sloan Digital Sky Survey, and Two Micron All Sky Survey, aswell as ROSAT, IRAS, NRAO VLA Sky Survey1The National RadioAstronomy Observatory is a facility of the National Science Foundationoperated under cooperative agreement by Associated Universities, Inc.,and Faint Images of the Radio Sky at Twenty cm catalogs, added updatedSIMBAD and NED data for the objects, and provided accurate DSS1 and DSS2positions and revised photometry. We also checked the objects for propermotion and variability. A refined classification for the low-dispersionspectra in the Digitized First Byurakan Survey was carried out. Therevised and updated catalogue of 1101 FBS BSOs is presented. The FBSBSOs catalogue can be used to study a complete sample of white dwarfs,hot subdwarfs, HBB stars, cataclysmic variables, bright active galacticnuclei, and to investigate individual interesting objects.
| Orbit of the Spectroscopic Binary HD 107346 Containing a Very Hot Component
The orbit of the spectroscopic binary system HD 107346 is calculatedfrom 50 CORAVEL-type radial velocity measurements. An orbit with aperiod P = 1024.2 days is obtained. The spectral type of the primary, G8IV, has been estimated from the spectrum analyzed by Straižys(1984). The spectral type and absolute magnitude of the secondary, sdO,is estimated by modeling the spectral energy distribution of the binaryconstructed from measurements in the FAUST, GALEX, UBV, Vilnius, ICousins and JHK photometric systems. The subdwarf component of thebinary system exhibits a very high temperature. We do not exclude thatthe hot component is a close interacting binary.
| Optical Multicolor Photometry of Spectrophotometric Standard Stars
Photoelectric data on the Johnson-Kron-Cousins UBVRI broadbandphotometric system are provided for a set of stars that have been usedas spectrophotometric standard stars for the Hubble Space Telescope.
| Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations
A variety of on-orbit imaging and spectroscopic observations are used tocharacterize the charge transfer efficiency (CTE) of the charge-coupleddevice (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboardthe Hubble Space Telescope. A set of formulae is presented to correctobservations of point sources for CTE-related loss of signal. For datataken in imaging mode, the CTE loss is parameterized in terms of thelocation of the source on the CCD, the source signal level within themeasurement aperture, the background level, and the time of observation.For spectroscopic data, it is found that one additional parameter isneeded in order to provide an adequate calibration of the CTE loss,namely, the signal in the point-spread function located between thesignal extraction box and the readout amplifier. The effect of thelatter parameter is significant for spectra taken using the G750L orG750M gratings of STIS. The algorithms presented here correct fluxcalibration inaccuracies due to CTE losses as large as 30% to within~1.5% rms throughout the wavelength range covered by the STIS CCD modes.This uncertainty is similar to the Poisson noise associated with asource detected at a signal level of about 2500 electrons per resolutionelement. Using bidirectional CCD readouts, centroid shifts incurred dueto CTE loss are also derived. A tight correlation is found between theCTE loss and the centroid shift (both for imaging and for spectroscopicmodes), thus enabling one to correct for both effects of imperfectcharge transfer to STIS CCD observations.Based on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated byAURA, Inc., under NASA contract NAS 5-26555.
| An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Structure and kinematics of the interstellar medium in the star-forming region in the BCD galaxy VII Zw 403 (UGC 6456)
The structure and kinematics of ionized supershells in the star-formingregion in the BCD galaxy VII Zw 403 (UGC 6456) are analyzed usingobservations with the SCORPIO focal reducer on the 6-m SpecialAstrophysical Observatory telescope in three modes: direct imaging (inthe H?, [O III], and [S II] lines), long-slit spectroscopy, andspectroscopy with a scanning Fabry-Perot interferometer. In addition tothe previously known bright H II regions and the faint giant ring thatsurrounds the entire starforming region, many new faint diffuse and arcstructures have been detected. A fine structure of the giant ring hasbeen revealed. We do not confirm the previously detected expansion ofthe bright shells around young stellar associations with a velocity of50-70 km s-1. We have estimated their expansion velocities to be nohigher than 15-20 km s-1; the corresponding kinematic age, no youngerthan 3-4 Myr, agrees well with the age of the compact OB associationsassociated with them. We correlate the faint extended filamentary anddiffuse regions of ionized gas identified almost in the entire centralregion of the galaxy and the giant H II ring with the older (10 Myr)stellar population of the most recent starburst. Weak high-velocity [OIII] and H? line wings (up to 300 km s-1 from the line center)have been detected in the brightest H II region. Such velocities havebeen observed in the galaxy for the first time. The previously publishedH? luminosity measurements for the galaxy are refined.
| The radio source Z0254+43: z = 4.067
In January 2005 spectral observations of the radio source Z0254+43 weremade on the BTA at the Special Astrophysical Observatory (SAO) of theRussian Academy of Sciences (RAN) and its red shift was found to bez=4.057. The BVRI magnitudes were found to be 22.68, 21.19, 19.94, and19.23, respectively. Photometric observations in December 2005 on theZeiss-1000 at the SAO revealed no significant variation in the opticalemission from this object over that year. We can discuss its variabilityon an hourly time scale with some caution. The variability of the fluxfrom Z0254+43 was observed from 1990 2005 on the RATAN-600 over a widerange of frequencies. It turns out that the amplitude of the variabilityis minimal at a frequency of ˜8 GHz. A model for the variabilityhas been constructed which yields an estimate of ˜28° for theorientation of the jet of Z0254+43 to the line of sight. The luminosityof Z0254+43 in the optical range is ˜2·1026 W/Hzand in the radio frequency range, ˜2·1027 W/Hz.
| A Cross-Calibration between Tycho-2 Photometry and Hubble Space Telescope Spectrophotometry
By analyzing a well-calibrated sample of 256 stars observed with bothHipparcos and HST, I show that Tycho-2 photometry and HSTspectrophotometry are accurate and stable enough to obtain a precisecross-calibration. Based on this analysis, I obtain the followingphotometric zero points with respect to Vega for Tycho-2: 0.020+/-0.001(BT-VT), 0.078+/-0.009 (BT), and0.058+/-0.009 (VT).
| DSS1/DSS2 astrometry for 1101 First Byurakan Survey blue stellar objects: Accurate positions and other results
Accurate measurements of the positions of 1101 First Byurakan Survey(FBS) blue stellar objects (the Second part of the FBS) have beencarried out on the DSS1 and DSS2 (red and blue images). To establish theaccuracy of the DSS1 and DSS2, measurements have been made for 153 AGNfor which absolute VLBI coordinates have been published. The rms errorsare: 0.45 arcsec for DSS1, 0.33 arcsec for DSS2 red, and 0.59 arcsec forDSS2 blue in each coordinate, the corresponding total positional errorsbeing 0.64 arcsec, 0.46 arcsec, and 0.83 arcsec, respectively. Thehighest accuracy (0.42 arcsec) is obtained by weighted averaging of theDSS1 and DSS2 red positions. It is shown that by using all three DSSimages accidental errors can be significantly reduced. The comparison ofDSS2 and DSS1 images made it possible to reveal positional differencesand proper motions for 78 objects (for 62 of these for the first time),including new high-probability candidate white dwarfs, and to findobjects showing strong variability, i.e. high-probability candidatecataclysmic variables.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/367
| Hubble Space Telescope Absolute Spectrophotometry of Vega from the Far-Ultraviolet to the Infrared
The Space Telescope Imaging Spectrograph (STIS) has measured theabsolute flux for Vega from 0.17-1.01 ?m on the Hubble SpaceTelescope white dwarf (WD) flux scale. These data are saturated by up toa factor of 80 overexposure but retain linearity to a precision of 0.2%because the charge bleeds along the columns and is recovered duringreadout of the CCD. The signal-to-noise ratio per pixel exceeds 1000,and the resolution R is about 500. A V magnitude of 0.026+/-0.008 isestablished for Vega, and the absolute flux level is3.46×10-9 ergs cm-2 s-1 at 5556Å. In the regions of Balmer and Paschen lines, the STIS equivalentwidths differ from the pioneering work of Hayes in 1985 but do agreewith predictions of a Kurucz model atmosphere, so that the STIS fluxdistribution is preferred to that of Hayes. Over the full wavelengthrange, the model atmosphere calculation shows excellent agreement withthe STIS flux distribution and is used to extrapolate predicted fluxesinto the IR region. However, the IR fluxes are 2% lower than thestandard Vega model of Cohen. IUE data provide the extension of themeasured STIS flux distribution from 0.17 down to 0.12 ?m. The STISrelative flux calibration is based on model atmosphere calculations ofpure hydrogen WDs, while the Hayes flux calibration is based on thephysics of laboratory lamps and blackbody ovens. The agreement to 1% ofthese two independent methods for determining the relative stellar fluxdistributions suggests that both methods may be correct from 0.5-0.8?m and adds confidence to claims that the fluxes relative to 5500Å are determined to better than 4% by the pure hydrogen WD modelsfrom 0.12 to 3 ?m.
| ? Carinae's Brightness Variations Since 1998: Hubble Space Telescope Observations of the Central Star
We have measured the brightness variations in ? Carinae for the past6 years using the Hubble Space Telescope (HST) Space Telescope ImagingSpectrograph and Advanced Camera for Surveys. Unlike ground-based data,observations by the HST allow direct measurement of the brightness ofthe central star by resolving it from the surrounding bright ejecta. Wefind interesting behavior during 2003 in the continuum and H?emission. The data show that the established long-term brightening trendof ? Car continues, including regular events that coincide with the5.5 yr spectroscopic cycle and other more rapid and unexpectedvariations. In addition to the HST data, we also present ground-baseddata obtained from the American Association of Variable Star Observersthat show many of the same features. The dip in the apparent brightnessof the central star at the time of the 2003.5 event is wavelengthdependent with no decrease in the continuum. These observations castdoubt on a simple eclipse or occultation as the explanation for the dipand place constraints on the models for the event.This research was conducted as part of the ? Carinae Hubble SpaceTelescope Treasury Project via grant GO-9420 from the Space TelescopeScience Institute. HST is operated by the Association of Universitiesfor Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.Some of the data presented in this paper were obtained from theMulti-mission Archive at the Space Telescope Science Institute (MAST).STScI is operated by AURA, Inc., under NASA contract NAS 5-26555.Support for MAST for non-HST data is provided by the NASA Office ofSpace Science via grant NAG 5-7584 and by other grants and contracts.Some of the data presented in this paper were obtained from the AmericanAssociation of Variable Star Observers International Database.
| Spectrophotometric Standards from the Far-Ultraviolet to the Near-Infrared: STIS and NICMOS Fluxes
With photometric repeatability in the 0.2%-0.4% range and wavelengthcoverage from 1150 to 10,200 Å, the Space Telescope ImagingSpectrograph (STIS) low-dispersion spectrophotometry provides excellentabsolute flux standards. STIS observations of 19 stars are used toupdate the database of Hubble Space Telescope standard stars withabsolute fluxes that are based on the white dwarf pure hydrogen scale.Uncertainties in the STIS absolute flux calibration range from 4% in thefar-UV to 2% at longer wavelengths. The relative and absolute fluxes ofour composite standards in the IR are verified by the Near InfraredCamera and Multi-Object Spectrograph (NICMOS) observations and byground-based IR photometry.
| Hubble Space Telescope Imaging of Central Stars of High-Excitation Planetary Nebulae with WFC and WFPC2
We present observations of four high excitation planetary nebulae (IC2165, Me 2-1, NGC 2440, NGC 7027) taken with the Wide Field Camera andthe Wide Field Planetary Camera 2 on board the Hubble Space Telescope.The high angular resolution of the instruments allows for theunambiguous identification of the central star, which was not found tobe the case in most previous studies. In addition, the panchromaticnature of the data, which include several ultraviolet bandpasses,permits us to directly determine the amount of dust extinction presentalong the sight line to the central star. The combination of these twocharacteristics make it possible to delineate the spectral energydistribution of the central stars. Assuming a Planck function spectrumand a standard interstellar extinction law with RV=3.1, theadopted EB-V values are 0.40 (IC 2165), 0.15 (Me 2-1), 0.15(NGC 2440), and 1.10 (NGC 7027). The wavelength coverage of ourmeasurements is not particularly sensitive to temperature values in therange 150,000-400,000 K. However, we do find that 200,000 K produces thebest fits. Again using a Planck function to represent the wavelengthdependence of the stellar flux, we determine V magnitudes of17.47+/-0.06 (IC 2165), 18.40+/-0.05 (Me 2-1), 17.63+/-0.16 (NGC 2440),and 16.04+/-0.04 (NGC 7027). Combining these results with literaturevalues for the emission-line fluxes and distances, we derive the Zanstratemperature, crossover magnitude, radius, and luminosities for eachobject. The implications of these measurements for the mass and theevolutionary state of each object is briefly discussed.
| The Surface Density of Extremely Red Objects
We present initial results from a field survey for extremely red objects[EROs, defined here as (R-K')>=6 mag] covering 154 arcmin^2 of sky,from the first of seven deep, wide-field K' images obtained as part ofthe Calar Alto Deep Imaging Survey (CADIS). The 5 sigma point sourcedetection limits are K^'=20.5 mag and R=25.0 mag, while extended-sourcelimits are up to 0.50-0.75 mag brighter. We identify a total of eightbright EROs with K^'<=19.0 mag. Six of these bright EROs are resolvedand are likely to be galaxies, while the remaining two are unresolved,with colors consistent with their being low-mass galactic stars. Wederive a surface density for the six bright, extragalactic EROs of0.039+/-0.016 arcmin^-2, which is higher by a factor of 4 than previousvalues. We estimate that the volume density of bright EROs to be as highas that of nearby Seyfert galaxies.
| First Byurakan Spectral Sky Survey. Blue stellar objects. XI. Region +80 ? ? ? +90°
The eleventh list of blue stellar objects in the second part of theFirst Byurakan Spectral Sky Survey (FBS) is presented. The list consistsof 64 objects located in the region +80 ? ? ? +90° and2h 08m ? a ? 20h 15m.The objects haveV magnitudes in the range 12.3 17.4 andB-V colorindices in the range -0.55-+0.55. Of the 98 objects, 56 are newlydiscovered. Tentative classifications are given for 28 objects, of whichthere is one planetary nebula, 6 possible quasars, 15 possible whitedwarfs, and 6 possible cataclysmic variables. Two of the latter arepossibly novae having erupted at the epoch of exposure of the FBS platesin this region.
| The Photometric Performance and Calibration of WFPC2
We discuss the photometric performance and calibration of the Wide FieldPlanetary Camera 2 (WFPC2) on the Hubble Space Telesopce (HST). Thestability and accuracy of WFPC2 photometric measurements is discussed,with particular attention given to charge transfer efficiency (CTE)effects, contamination effects in the ultraviolet (UV), and flat fieldaccuracy and normalization. Observational data are presented from bothWFPC2 observations and ground observations using a system similar tothat flown. WFPC2 photometric systems are defined both for the groundand flight systems. Transformations between these systems and theLandolt UBVRI system are presented. These transformations are sensitiveto details in the spectra being transformed, and these sensitivities arequantified and discussed. On-orbit observations are used to revise theprelaunch estimates of response curves to best match syntheticphotometry results with observations, and the accuracy of the resultingsynthetic photometry is discussed. Synthetic photometry is used todetermine zeropoints and transformations for all of the fight filters,and also to derive interstellar extinction values for the WFPC2 system.Using stellar interior and atmosphere models, isochrones in the WFPC2system are calculated and compared with several observations. (SECTION:Astronomical Instrumentation)
| A Search for Microflaring Activity on dMe Flare Stars. I. Observations of the dM8e Star CN Leonis
Microflares are frequent, short-duration, energetically weakdisturbances occurring in the nonradiatively heated regions of the Sunand other magnetically active stars. They are thought to be thelow-energy extension of flares commonly seen on active dMe stars and maybe a major source of heating the chromosphere and corona of cool starsin general. In this paper we describe rapid time sequence UV photometryof the dMe star CN Leo taken with the High Speed Photometer (HSP) aboardthe Hubble Space Telescope (HST). The filter was centered at 240 nm,near wavelengths at which flares are expected to have maximum intensityand the stellar background is small. During 2 hr of on-source observing,a total of 32 flarelike events were detected, with integrated countsranging from 12 to more than 14,000. In most cases the events hadintegrated energy ranging between 1027 and 1028ergs and can be classified as microflares. A considerable fine structurewas seen in these events, with substantial variations sometimesoccurring on timescales of less than 1 s. The occurrence rates for thesmaller events showed a power-law distribution, with a slope comparableto that seen for larger events observed from the ground. Extrapolatingthe occurrence rate relation to nanoflare energies indicates a predictedcount rate that is significantly smaller than that observed, suggestingthat the nanoflares have a different energy distribution than the largerevents.
| The performance and calibration of WFPC2 on the Huble Space Telescope
The Wide Field Planetary Camera 2 (WFPC2) was installed in the HubbleSpace Telescope (HST) in 1993 December. Since then, the instrument hasbeen providing high-quality images. A significant among of calibrationdata has been collected to aid in the understanding of the on-orbitperformance of the instrument. Generally, the behavior of the camera issimilar to its performance during the system-level thermal vacuum testat JPL in 1993 May. Surprises were a significantcharge-transfer-efficiency (CTE) problem and a significant growth ratein hot pixels at the original operating temperature of the CCDs (-76 degC). The operating temperature of the WFPC2 CCDs was changed to -88 deg Con 1994 April 23, and significant improvements in CTE and hot pixels areseen at this temperature. In this paper we describe the on-orbitperformance of the WFPC2. We discuss the optical and thermal history,the instrument throughput and stability, the Point Spread Function(PSF), the effects of undersampling on photometry, the properties ofcosmic rays observed on-orbit, and the geometric distortion in thecamera. We present the best techniques for the reduction of WFPC2 data,and describe the construction of calibration products includingsuperbiases, super-darks, and flat fields.
| Absolute flux calibration of optical spectrophotometric standard stars
A method based on Landolt photometry in B and V is developed to correctfor a wavelength independent offset of the absolute flux level ofoptical spectrophotometric standards. The method is based on syntheticphotometry techniques in B and V and is accurate to approximately 1%.The correction method is verified by Hubble Space Telescope Faint ObjectSpectrograph absolute fluxes for five calibration stars, which agreewith Landolt photometry to 0.5% in B and V.
| The ultraviolet calibration of the Hubble Space Telescope. IV - Absolute IUE fluxes of Hubble Space Telescope standard stars
UV fluxes are presented for 37 stars selected as calibration standardsfor the Hubble Space Telescope (HST). In order to provide data ofmaximum precision, new absolute calibrations have been derived for theIUE SWP and LWR cameras for point sources in the large apertures, whilethe sensitivities of the trail and small aperture observing modesrelative to the large apertures are updated for all three IUE cameras.More than 2700 individual spectra are used to define the absolute fluxdistributions of the 37 HST standard stars in the wavelength range1150-3300 A. A comparison with white dwarf model atmosphere calculationssuggests that the systematic external errors in the fluxes are less than15 percent, while comparison with ANS flux measurements demonstrates aninternal consistency of the IUE spectrophotometry of 2 percent, over adynamic range of 10,000, in bandpasses of 100 A or greater.
| An atlas of Hubble Space Telescope photometric, spectrophotometric, and polarimetric calibration objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99.1243T&db_key=AST
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| LWP absolute calibration : the SWP-LWP overlap discrepancy.
Not Available
| The degenerate stars with hydrogen atmospheres. I
Statistical results are presented for an analysis of 162 DA degeneratestars (those with hydrogen atmospheres). It is shown thatmultichannel-spectrometer colors for groups of similar stars lie closeto those predicted from pure hydrogen atmospheres for certain models andthat the temperatures obtained from fitting energy distributions tomodels agree with those from the G-R and U-V colors. Statisticallytreated equivalent widths are found to agree with theoreticalpredictions. These widths suggest that mean log g must exceed 7.0 andprobably lies above or near 8.0; the colors are consistent with log gnear or above 8.0. The space frequency of stars in the sample is derivedfrom the number of stars within limits of effective temperature.
| Three new hot subdwarfs: AGK2 +81 266, BD +39 3226, BD +34 1543.
Abstract image available at:http://adsabs.harvard.edu/abs/1978A&A....64L...9B
| The ultraviolet experiment onboard the astronomical Netherlands satellite - ANS
The ultraviolet experiment package on board the ANS consists of a 22 cmdiameter Cassegrain telescope, followed by a five channel intermediateband spectrophotometer. The instrument response function for eachbandpass is almost rectangular. The central wavelengths are 155, 180,220, 250 and 330 nm respectively. The in-orbit performance of theinstrument is according to expectations. Observational results of sometypical objects are summarized to illustrate the capabilities of theinstrument.
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Osservazione e dati astrometrici
| Costellazione: | Giraffa |
| Ascensione retta: | 09h21m19.16s |
| Declinazione: | +81°43'27.6" |
| Magnitudine apparente: | 11.926 |
| Moto proprio RA: | -12.9 |
| Moto proprio Dec: | -51.5 |
| B-T magnitude: | 11.482 |
| V-T magnitude: | 11.89 |
Cataloghi e designazioni:
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