Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Ultraviolet Properties of Galactic Globular Clusters with GALEX. I. The Color-Magnitude Diagrams
We present Galaxy Evolution Explorer (GALEX) data for 44 Galacticglobular clusters (GCs) obtained during three GALEX observing cyclesbetween 2004 and 2008. This is the largest homogeneous data set on theUV photometric properties of Galactic GCs ever collected. The sampleselection and photometric analysis are discussed, and color-magnitudediagrams (CMDs) are presented. The blue and intermediate-blue horizontalbranch is the dominant feature of the UV CMDs of old Galactic GCs. Oursample is large enough to display the remarkable variety of horizontalbranch shapes found in old stellar populations. Other stellar types thatare obviously detected are blue stragglers and post-core-He burningstars. The main features of UV CMDs of Galactic GCs are brieflydiscussed. We establish the locus of post-core-He burning stars in theUV CMD and present a catalog of candidate asymptotic giant branch (AGB),AGB-manqué, post early-AGB, and post-AGB stars within our clustersample.The authors dedicate this paper to the memory of co-author Bob Rood, apioneer in the theory of the evolution of low-mass stars, and a friend,who sadly passed away on 2011 November 2.
| Average Metallicity and Star Formation Rate of Ly? Emitters Probed by a Triple Narrowband Survey
We present the average metallicity and star formation rate (SFR) ofLy? emitters (LAEs) measured from our large-area survey with threenarrowband (NB) filters covering the Ly?, [O II]?3727, andH?+[N II] lines of LAEs at z = 2.2. We select 919 z = 2.2 LAEsfrom Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACSspectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRMnear-infrared NB filters whose central wavelengths are matched toredshifted [O II] and H? nebular lines, respectively. By stackingthe near-infrared images of the LAEs, we successfully obtain averagenebular-line fluxes of LAEs, the majority of which are too faint to beidentified individually by NB imaging or deep spectroscopy. The stackedobject has an H? luminosity of 1.7 × 1042 ergs-1 corresponding to an SFR of 14 M &sun;yr-1. We place, for the first time, a firm lower limitto the average metallicity of LAEs of Z >~ 0.09 Z &sun;(2?) based on the [O II]/(H?+[N II]) index together withphotoionization models and empirical relations. This lower limit ofmetallicity rules out the hypothesis that LAEs, so far observed at z ~2, are extremely metal-poor (Z < 2 × 10-2 Z&sun;) galaxies at the 4? level. This limit is higherthan a simple extrapolation of the observed mass-metallicity relation ofz ~ 2 UV-selected galaxies toward lower masses (5 × 108M &sun;), but roughly consistent with a recently proposedfundamental mass-metallicity relation when the LAEs' relatively low SFRis taken into account. The H? and Ly? luminosities of ourNB-selected LAEs indicate that the escape fraction of Ly? photonsis ~12%-30%, much higher than the values derived for other galaxypopulations at z ~ 2.Based in part on data collected at Subaru Telescope, which is operatedby the National Astronomical Observatory of Japan.
| Central powering of the largest Lyman-? nebula is revealed by polarized radiation
High-redshift Lyman-? (Ly?) blobs are extended, luminous butrare structures that seem to be associated with the highest peaks in thematter density of the Universe. Their energy output and morphology aresimilar to those of powerful radio galaxies, but the source of theluminosity is unclear. Some blobs are associated with ultraviolet orinfrared bright galaxies, suggesting an extreme starburst event oraccretion onto a central black hole. Another possibility is gas that isshock-excited by supernovae. But not all blobs are associated withgalaxies, and these ones may instead be heated by gas falling into adark-matter halo. The polarization of the Ly? emission can inprinciple distinguish between these options, but a previous attempt todetect this signature returned a null detection. Here we reportobservations of polarized Ly? from the blob LAB1 (ref. 2).Although the central region shows no measurable polarization, thepolarized fraction (P) increases to ~20 per cent at a radius of45kiloparsecs, forming an almost complete polarized ring. The detectionof polarized radiation is inconsistent with the in situ production ofLy? photons, and we conclude that they must have been produced inthe galaxies hosted within the nebula, and re-scattered by neutralhydrogen.
| Cataclysmic variables below the period gap: mass determinations of 14 eclipsing systems
We present high-speed, three-colour photometry of the eclipsingcataclysmic variables CTCV J1300-3052, CTCV J2354-4700 and SDSSJ115207.00+404947.8. These systems have orbital periods of 128.07, 94.39and 97.52 min, respectively, placing all three systems below theobserved 'period gap' for cataclysmic variables. For each system wedetermine the system parameters by fitting a parametrized model to theobserved eclipse light curve by ?2 minimization.We also present an updated analysis of all other eclipsing systemspreviously analysed by our group. The updated analysis utilizes Markovchain Monte Carlo techniques which enable us to arrive confidently atthe best fits for each system with more robust determinations of ourerrors. A new bright-spot model is also adopted, that allows bettermodelling of bright-spot dominated systems. In addition, we correct abug in the old code which resulted in the white dwarf radius beingunderestimated, and consequently both the white dwarf and donor massbeing overestimated. New donor masses are generally between 1? and2? of those originally published, with the exception of SDSS 1502(-2.9?, ?Mr=-0.012 M&sun;) and DV UMa(+6.1?, ?Mr=+0.039 M&sun;). We notethat the donor mass of SDSS 1501 has been revised upwards by 0.024M&sun; (+1.9?). This system was previously identifiedas having evolved past the minimum orbital period for cataclysmicvariables, but the new mass determination suggests otherwise. Our newanalysis confirms that SDSS 1035 and SDSS 1433 have evolved past theperiod minimum for cataclysmic variables, corroborating our earlierstudies.We find that the radii of donor stars are oversized when compared totheoretical models, by approximately 10 per cent. We show that this canbe explained by invoking either enhanced angular momentum loss, or bytaking into account the effects of star spots. We are unable to favourone cause over the other, as we lack enough precise mass determinationsfor systems with orbital periods between 100 and 130 min, whereevolutionary tracks begin to diverge significantly.We also find a strong tendency towards high white dwarf masses withinour sample, and no evidence for any He-core white dwarfs. The dominanceof high-mass white dwarfs implies that erosion of the white dwarf duringthe nova outburst must be negligible, or that not all of the massaccreted is ejected during nova cycles, resulting in the white dwarfgrowing in mass.
| The inverse problem of the theory of degenerate dwarfs
Based on the radii and masses of degenerate dwarfs derived fromHIPPARCOS and other observations, we estimate the microscopic parametersof a Chandrasekhar model (the relativistic parameter at the stellarcenter x 0, and the chemical-composition parameterµ e = A/Z, where A is the mass number and Z is thenuclear charge). We have obtained analytical expressions for themacroscopic characteristics (mass, radius, energy) as functions of x0 and µ e . From the calculated dependenceof the energy on these parameters, we have found constraints on therange of variability of x 0, which are in good agreement withthe observed radius distribution of dwarfs. The critical value of x0 at which stability breaks down due to general-relativisitceffects is found more accurately than previously. We propose ageneralized model with an inhomogeneous (coordinate-dependent) chemicalcomposition, with µ e = µ e ( r).
| Ly? emitters at z= 6.5 in the SSA22 field: an area more neutral or void at the end of the re-ionization epoch
We present results of a survey of Ly? emitters (LAEs) at z= 6.5which is thought to be the final epoch of the cosmic re-ionization. In a?530 arcmin2 deep image of the SSA22 field taken through anarrow-band filter NB912 installed in the Subaru/Suprime-Cam, we havefound only 14 LAE candidates with LLy?? 3 ×1042 erg s-1. Even applying the same colourselection criteria, the number density of the LAE candidates is a factorof 3 smaller than that found at the same redshift in the Subaru DeepField (SDF). Assuming the number density in the SDF is a cosmic average,the probability to have a number density equal to or smaller than thatfound in the SSA22 field is only 7 per cent if we consider fluctuationby the large-scale structure (i.e. cosmic variance) and Poisson error.Therefore, the SSA22 field may be a rare void at z= 6.5. On the otherhand, we have found that the number density of i'-drop galaxies with25.5 < z' < 26.0 in the SSA22 field agrees well with that in theSDF. If we consider a scenario that a larger neutral fraction ofintergalactic hydrogen, xH I, in the SSA22 field obscures apart of Ly? emission, xH I in the SSA22 field should beabout two times larger than that in the SDF. This can be translated intoxH I < 0.9 at z= 6.5 in the SSA22 field. A much largersurvey area than previous ones is required to overcome a largefluctuation reported here and to obtain a robust constraint on xHI at the end of the re-ionization from LAEs. This work is based ondata collected at Subaru Telescope and obtained from theSubaru-Mitaka-Okayama-Kiso Archive System (SMOKA), which is operated bythe Astronomy Data Center, National Astronomical Observatory of Japan.
| A selection of hot subluminous stars in the GALEX survey - I. Correlation with the Guide Star Catalog
We assembled a catalogue of bright, hot subdwarf and white dwarf starsextracted from a joint ultraviolet, optical and infrared source list.The selection is secured using colour criteria that correlate well witheffective temperatures Teff? 12 000 K. We built aNUV- V versus V - J diagram for ?60 000 bright sourcesusing the Galaxy Evolution Explorer (GALEX) NUV magnitude(NUV < 14), the associated Guide Star Catalog (GSC2.3.2)photographic quick-V magnitude and the Two-Micron All-Sky Survey J and Hmagnitudes. This distillation process delivered a catalogue of ?700sources with NUV- V < 0.5 comprising ˜160 known hotsubdwarf stars and another ˜60 known white dwarf stars. A reducedproper-motion diagram built using the proper-motion measurementsextracted from the Naval Observatory Merged Astrometric Dataset allowedus to identify an additional ˜120 new hot subdwarf candidates and˜10 hot white dwarf candidates. We present a spectroscopic studyof a subset of 52 subdwarfs, 48 of them analysed here for the firsttime, and with nine objects brighter than V ˜ 12. Our sample ofspectroscopically confirmed hot subdwarfs comprises 10 sdO-type starsand 42 sdB-type stars suitable for pulsation and binary studies. We alsopresent a study of 50 known white dwarfs selected in the GALEX surveyand six new white dwarfs from our catalogue of subluminous candidates.Ultraviolet, optical and infrared synthetic magnitudes employed in theselection and analysis of white dwarf stars are listed in appendix.Based on observations made with ESO telescopes at the La Silla ParanalObservatory under programmes 82.D-0750, 83.D-0540 and085.D-0866.Visiting Astronomer, Kitt Peak National Observatory, NationalOptical Astronomy Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA) under cooperativeagreement with the National Science Foundation.
| The dust coma environment of the short period comets 32P/Comas Solá, 56P/Slaughter-Burnham, and 78P/Gehrels 2 from ground-based observations
Aims: The aim of this paper is to contribute to thecharacterisation of the general properties, differences, andcommonalities of the short period comet family and, more in particular,to characterise the dust environment of three poorly studied members ofthe family: 32P/Comas Solá, 56P/Slaughter-Burnham, and78P/Gehrels 2. Methods: Multicolour broad-band photometry of thecomets observed around their perihelion in October 2004 from the Loianotelescope has been used to characterise their dust coma morphology andproperties and to model the dust production rate Results:32P/Comas Solá shows no remarkable dust coma features, while both56P/Slaughter-Burnham and 78P/Gehrels 2 show departures from regularbrightness distribution, with a north/south asymmetry and axysimmetriclobes, respectively, probably indicating emission features on thenucleus surface. For comet 78P, it has been possible to compute a 1-Dsurface brightness profile with slope m = -1.54 ± 0.05. In anaperture of radius ? = 7.2 × 103 km, the measuredAf? is 127 ± 10 cm, 102 ± 8 cm (weighted averagebetween two observing nights) and 846 ± 55 cm for comets 32P, 56Pand 78P, respectively. All comets have a redder dust coma than the Sun.Comets 32P (dust production rate Qd from 2 to 46 kg/s) and56P (Qd from 1 to 24 kg/s) are quite standard dust emittersamong the short-period comet family, while comet 78P (Qd from14 to 345 kg/s) is more active than the average at that heliocentricdistance.
| 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.
| Hard X-ray Emission Associated with White Dwarfs. III.
Hard X-ray emission associated with white dwarfs (WDs) can be used todiagnose the presence of late-type binary companions, mass accretionfrom companions, or physical processes with unknown origins. Since ourprevious systematic searches for hard X-ray emission associated withWDs, the Galactic WD catalog has been augmented by >10,000 new WDsfrom the Sloan Digital Sky Survey and new X-ray point-source catalogsfrom XMM-Newton and ROSAT have become available. Therefore, we haveextended the search using the updated catalogs, and found 17 new casesof WDs associated with hard X-ray emission. The 32 WDs associated withhard X-ray emission, from the current and previous searches, can bedivided into five categories: (1) binary WD with a coronal companion,(2) binary WD with mass transfer from a companion, (3) single hot WDwith a hard X-ray component peaking near 1 keV in addition to a softphotospheric component, (4) two PG 1159 stars with very faint X-rayemission in the 0.9-2.0 keV band, and (5) two DA WDs whose photosphericemission component has a hard shoulder extending to 0.5-0.9 keV. Theorigin of the hard X-ray emission in the latter three categories is notyet known. Deeper X-ray observations with higher angular and spectralresolutions are needed to help us understand these WDs' hard X-rayemission.
| Discoveries from a Near-infrared Proper Motion Survey Using Multi-epoch Two Micron All-Sky Survey Data
We have conducted a 4030 deg2 near-infrared proper motionsurvey using multi-epoch data from the Two Micron All-Sky Survey(2MASS). We find 2778 proper motion candidates, 647 of which are notlisted in SIMBAD. After comparison to Digitized Sky Survey images, wefind that 107 of our proper motion candidates lack counterparts at B, R,and I bands and are thus 2MASS-only detections. We present results ofspectroscopic follow-up of 188 targets that include the infrared-onlysources along with selected optical-counterpart sources with faintreduced proper motions or interesting colors. We also establish a set ofnear-infrared spectroscopic standards with which to anchor near-infraredclassifications for our objects. Among the discoveries are six youngfield brown dwarfs, five "red L" dwarfs, three L-type subdwarfs, twelveM-type subdwarfs, eight "blue L" dwarfs, and several T dwarfs. Wefurther refine the definitions of these exotic classes to aid futureidentification of similar objects. We examine their kinematics and findthat both the "blue L" and "red L" dwarfs appear to be drawn from arelatively old population. This survey provides a glimpse of the kindsof research that will be possible through time-domain infrared projectssuch as the UKIDSS Large Area Survey, various VISTA surveys, and WISE,and also through z- or y-band enabled, multi-epoch surveys such asPan-STARRS and LSST.Some of the spectroscopic data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership amongthe California Institute of Technology, the University of California,and the National Aeronautics and Space Administration. The Observatorywas made possible by the generous financial support of the W. M. KeckFoundation. Other spectroscopic data were collected at the SubaruTelescope, which is operated by the National Astronomical Observatory ofJapan.
| The Kyoto Tridimensional Spectrograph II on Subaru and the University of Hawaii 88 in Telescopes
In order to investigate physical conditions of ionized gas in galaxies,as well as its kinematics, we have developed the Kyoto tridimensionalspectrograph II. It is a multimode optical instrument, includingintegral field spectrograph (IFS) and Fabry-Perot imager modes. We havedesigned it compact so that we can mount it on 2 m class telescopes aswell as on the 8.2 m Subaru telescope. Special care was taken to obtainhigh-quality calibrations in the IFS mode. In order to remove thechromatic aberration of micropupil images produced by a lenslet array,we have introduced a corrector lens system behind the lenslet array. Theinternal calibration system simulates the telescope optics so that thesystem provides micropupil images identical to those produced by thetelescope. The rigidness of the instrument provides the positionalstability of micropupil images. We have succeeded in test observationsof all the modes on Subaru and the University of Hawaii 88 in (UH88)telescopes and have verified the performance of the instrument. Thisincludes the instrument efficiencies as well as the effective skybackground subtraction and the minimization of crosstalk effects in theIFS mode. In the IFS mode a spatial resolution of 0.4? wasobtained in good seeing conditions. Each of 37×37 lensletssubtends 0.1? in Subaru's case. This samples the image size well.A wider field of view is emphasized in the case of UH88.
| High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey. III. DA white dwarfs
Context: The ESO Supernova Ia Progenitor Survey (SPY) tookhigh-resolution spectra of more than 1000 white dwarfs and pre-whitedwarfs. About two thirds of the stars observed are hydrogen-dominated DAwhite dwarfs. Here we present a catalog and detailed spectroscopicanalysis of the DA stars in the SPY. Aims: Atmospheric parameterseffective temperature and surface gravity are determined for normal DAs.Double-degenerate binaries, DAs with magnetic fields or dM companions,are classified and discussed. Methods: The spectra are comparedwith theoretical model atmospheres using a ?2 fittingtechnique. Results: Our final sample contains 615 DAs, which showonly hydrogen features in their spectra, although some aredouble-degenerate binaries. 187 are new detections or classifications.We also find 10 magnetic DAs (4 new) and 46 DA+dM pairs (10 new).Based on data obtained at the Paranal Observatory ofthe European Southern Observatory for programmes 165.H-0588 and167.D-0407.
| Discovery of the first symbiotic star in NGC6822
We report the discovery of the first symbiotic star (V = 21.6,KS = 15.8mag) in the Local Group dwarf irregular galaxyNGC6822. This star was identified during a spectral survey of H?emission-line objects using the Southern African Large Telescope duringits performance-verification phase. The observed strong emission linesof HI and HeII suggest a high electron density and T* < 130000K forthe hot companion. The infrared colours allow us to classify this objectas an S-type symbiotic star, comprising a red giant losing mass to acompact companion. The red giant is an asymptotic giant branch (AGB)carbon star, and a semiregular variable, pulsating in the first overtonewith a period of 142 d. Its bolometric magnitude is Mbol =-4.4mag.We review what is known about the luminosities of extragalacticsymbiotic stars, showing that most, possibly all, contain AGB stars. Wesuggest that a much larger fraction of Galactic symbiotic stars maycontain AGB stars than was previously realized.Based on observations made with the Southern African Large Telescope(SALT) and the Infrared Survey Facility (IRSF). E-mail: akniazev@saao.ac.za
| UBVRI Photometric Standard Stars Around the Celestial Equator: Updates and Additions
New broadband UBVRI photoelectric observations on theJohnson-Kron-Cousins photometric system have been made of 202 starsaround the sky, and centered at the celestial equator. These starsconstitute both an update of and additions to a previously publishedlist of equatorial photometric standard stars. The list is capable ofproviding, for both celestial hemispheres, an internally consistenthomogeneous broadband standard photometric system around the sky. Whenthese new measurements are included with those previously published byLandolt (1992), the entire list of standard stars in this paperencompasses the magnitude range 8.90 < V < 16.30, and the colorindex range -0.35 < (B - V) < +2.30.
| Infrared Signatures of Disrupted Minor Planets at White Dwarfs
Spitzer Space Observatory IRAC and MIPS photometric observations arepresented for 20 white dwarfs with T eff lsim 20, 000 K andmetal-contaminated photospheres. A warm circumstellar disk is detectedat GD 16 and likely at PG 1457-086, while the remaining targets fail toreveal mid-infrared excess typical of dust disks, including a number ofheavily polluted stars. Extending previous studies, over 50% of allsingle white dwarfs with implied metal-accretion rates dM/dtgsim 3× 108 g s-1 display a warm infrared excessfrom orbiting dust; the likely result of a tidally destroyed minorplanet. This benchmark accretion rate lies between the dust productionrates of 106 g s-1 in the solar system zodiacalcloud and 1010 g s-1 often inferred for debrisdisks at main-sequence A-type stars. It is estimated that between 1% and3% of all single white dwarfs with cooling ages less than around 0.5 Gyrpossess circumstellar dust, signifying an underlying population of minorplanets.
| TAUVEX flight calibrations: Plans and challenges
The operational tasks for the Performance Verification (PV) andcalibration phase in the first year of TAUVEX operation are presented.The new challenges regarding the possible reduction in sensitivity areoutlined and are reflected in the specialized plan for first few monthsof the mission. The calibration operations will be extended into thefirst year, in parallel to an unprecedented deep exposure of thecelestial poles. The preliminary zero-points of the instrumentalphotometric system, in AB and Vega-based magnitude systems, arecalculated for pre-ground calibrations data as well as for the updatedresults. For flux calibration, the effective wavelengths, bandwidths andconversion factors are calculated for both pre-ground and updatedvalues. These conversion factors are to be used for converting theTAUVEX count rates to flux and UV luminosity of the sources.
| The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe
In this work we present the first spectroscopic results obtained withthe Southern African Large Telescope (SALT) during itsperformance-verification phase. We find that the Sagittarius dwarfspheroidal galaxy (Sgr) contains a youngest stellar population with[O/H] ~ -0.2 and age t > 1Gyr, and an oldest population with [O/H]=-2.0. The values are based on spectra of two planetary nebulae (PNe),using empirical abundance determinations. We calculated abundances forO, N, Ne, Ar, S, Cl, Fe, C and He. We confirm the high abundances of PNStWr2-21 with 12 + log(O/H) = 8.57 +/- 0.02 dex. The other PN studied,BoBn1, is an extraordinary object in that the neon abundance exceedsthat of oxygen. The abundances of S, Ar and Cl in BoBn1 yield theoriginal stellar metallicity, corresponding to 12 + log(O/H) = 6.72 +/-0.16 dex which is 1/110 of the solar value. The actual [O/H] is muchhigher: third dredge-up enriched the material by a factor of ~12 inoxygen, ~240 in nitrogen and ~70 in neon. Neon as well as nitrogen andoxygen content may have been produced in the intershell of low-massasymptotic giant branch (AGB) stars. Well defined broad WR lines arepresent in the spectrum of StWr2-21 and absent in the spectrum of BoBn1.This puts the fraction of [WR]-type central PNe stars to 67 per cent fordSph galaxies.Based on observations obtained with Southern African Large Telescope(SALT).E-mail: akniazev@saao.ac.za (AYK); a.zijlstra@manchester.ac.uk (AAZ)
| The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Ly? Emitters from z=3.1 to 5.7 in the 1 deg2 Field: Luminosity Functions and AGN
We present luminosity functions (LFs) and various properties ofLy? emitters (LAEs) at z=3.1, 3.7, and 5.7, in a 1 deg2sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field. We obtain aphotometric sample of 858 LAE candidates based on deep SubaruSuprime-Cam imaging data and a spectroscopic sample of 84 confirmed LAEsfrom Subaru FOCAS and VLT VIMOS spectroscopy in a survey volume of~106 Mpc3 with a limiting Ly? luminosity of~3×1042 ergs s-1. We derive the LFs of theLy? and UV continuum (~=1500 Å) for each redshift, takinginto account the statistical error and the field-to-field variation. Wefind that the apparent Ly? LF shows no significant evolutionbetween z=3.1 and 5.7 within factors of 1.8 and 2.7 in L* and?*, respectively. On the other hand, the UV LF of LAEs increasesfrom z=3.1 to 5.7, indicating that galaxies with Ly? emission aremore common at earlier epochs. We identify six LAEs with AGN activitiesfrom our spectra combined with VLA, Spitzer, and XMM-Newton data. Amongthe photometrically selected LAEs at z=3.1 and 3.7, only ~=1% show AGNactivities, while the brightest LAEs with logL(Ly?)>~43.4-43.6ergs s-1 appear to always host AGNs. Our LAEs are bluer inUV-continuum color than dropout galaxies, suggesting lower extinctionand/or younger stellar populations. Our stacking analyses provide upperlimits to the radio luminosity and thefHeII/fLy? line fraction and constrain thehidden star formation (+low-luminosity AGN) and the primordialpopulation in LAEs.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.
| A Photometric Survey for Lyα-He II Dual Emitters: Searching for Population III Stars in High-Redshift Galaxies
We present a new photometric search for high-z galaxies hostingPopulation III (Pop III) stars based on deep intermediate-band imagingobservations obtained in the Subaru Deep Field (SDF), using Suprime-Camon the Subaru Telescope. By combining our new data with the existingbroadband and narrowband data, we searched for galaxies that emitstrongly in both Lyα and He II λ1640 (dual emitters) andare promising candidates for Pop III-hosting galaxies at3.93<~z<~4.01 and 4.57<~z<~4.65. Although we found 10 dualemitters, most of them turn out to be [O II]-[O III] dual emitters orHβ-(Hα+[N II]) dual emitters at z<1, as inferred fromtheir broadband colors and from the ratio of the equivalent widths. Noconvincing candidate Lyα-He II dual emitter ofSFRPopIII>~2 Msolar yr-1 was foundby our photometric search in 4.03×105 Mpc3in the SDF. This result disfavors low-feedback models for Pop III starclusters and implies an upper limit on the Pop III SFR density ofSFRDPopIII<5×10-6 Msolaryr-1 Mpc-3. This new selection method to searchfor Pop III-hosting galaxies should be useful in future narrowbandsurveys to achieve the first observational detection of Pop III-hostinggalaxies at high redshifts.
| The Calibration and Data Products of GALEX
We describe the calibration status and data products pertaining to theGR2 and GR3 data releases of the Galaxy Evolution Explorer (GALEX).These releases have identical pipeline calibrations that aresignificantly improved over the GR1 data release. GALEX continues tosurvey the sky in the far-ultraviolet (FUV, ~154 nm) andnear-ultraviolet (NUV, ~232 nm) bands, providing simultaneous imagingwith a pair of photon-counting, microchannel plate, delay line readoutdetectors. These 1.25° field of view detectors are well suited toultraviolet observations because of their excellent red rejection andnegligible background. A dithered mode of observing and photon listoutput pose complex requirements on the data processing pipeline,entangling detector calibrations, and aspect reconstruction algorithms.Recent improvements have achieved photometric repeatability of 0.05 and0.03 mAB in the FUV and NUV, respectively. We have detected along-term drift of order 1% FUV and 6% NUV over the mission. Astrometricprecision is of order 0.5" rms in both bands. In this paper we providethe GALEX user with a broad overview of the calibration issues likely tobe confronted in the current release. Improvements are likely as theGALEX mission continues into an extended phase with a healthyinstrument, no consumables, and increased opportunities for guestinvestigations.
| A Comparative Study of Optical and Ultraviolet Effective Temperatures for DA White Dwarfs from the IUE Archive
We present a comparative study of effective temperatures determined fromthe hydrogen Balmer lines and from the UV energy distribution for 140 DAwhite dwarfs drawn from the International Ultraviolet Explorer (IUE)archive. Our results indicate that the optical and UV temperatures ofthe majority of stars below Teff~40,000 K and within ~75 pcare in fairly good agreement given the uncertainties. At highertemperatures and/or larger distances, however, significant discrepanciesare observed. Several mechanisms are investigated to account for thesediscrepancies, including the effect of interstellar reddening, thepresence of metals in the photosphere, and the existence of unresolvedbinary white dwarfs. The results of our analysis reveal thatwavelength-dependent extinction is the most natural explanation for theobserved temperature differences. We also attempt to predict thedifferences in optical and UV temperatures expected from unresolveddegenerate binaries by performing an exhaustive simulation of compositemodel spectra. In light of these simulations, we then discuss some knowndouble degenerates and identify new binary candidates by restricting ouranalysis to stars located within 75 pc, where the effect of interstellarreddening is significantly reduced.
| Albus 1: A Very Bright White Dwarf Candidate
We have serendipitously discovered a previously unknown, bright source(BT=11.75+/-0.07 mag) with a very blueVT-Ks color, which we have named Albus 1. Aphotometric and astrometric study using Virtual Observatory tools hasshown that it possesses an appreciable proper motion and magnitudes andcolors very similar to those of the well-known white dwarf G191-B2B. Weconsider Albus 1 as a DA-type white dwarf located at about 40 pc. If itsnature is confirmed, Albus 1 would be the sixth brightest isolated whitedwarf in the sky, which would make it an excellent spectrophotometricstandard.
| A Spitzer White Dwarf Infrared Survey
We present mid-infrared photometry of 124 white dwarf stars with theSpitzer Space Telescope. Objects were observed simultaneously at 4.5 and8.0 ?m with sensitivities better than 0.1 mJy. This data set can beused to test models of white dwarf atmospheres in a new wavelengthregime, as well as to search for planetary companions and debris disks.
| Externally Polluted White Dwarfs with Dust Disks
We report Spitzer Space Telescope photometry of 11 externally pollutedwhite dwarfs. Of the nine stars for which we have IRAC photometry, wefind that GD 40, GD 133, and PG 1015+161 each has an infrared excessthat can be understood as arising from a flat, opaque, dusty disk. GD 56also has an infrared excess characteristic of circumstellar dust, but aflat-disk model cannot reproduce the data unless there are grains aswarm as 1700 K and perhaps not even then. Our data support the previoussuggestion that the metals in the atmosphere of GD 40 are the result ofaccretion of a tidally disrupted asteroid with a chondritic composition.
| Calibrating TAUVEX: turning space hardware into a scientific instrument
This article explains the basic philosophy of calibrating TAUVEX on theground at the El-Op facilities in Israel, and in space after launch. Werefer the reader to historical articles describing TAUVEX, its designand calibration, and update the knowledge base as to the modern testingand calibration procedures. We explicitly point out the productsexpected to result from the calibration process.
| A Dusty Disk around WD 1150-153: Explaining the Metals in White Dwarfs by Accretion from the Interstellar Medium versus Debris Disks
We report the discovery of excess K-band radiation from a metal-rich DAVwhite dwarf star, WD 1150-153. Our near-infrared spectroscopicobservations show that the excess radiation cannot be explained by a(sub)stellar companion, and is likely to be caused by a debris disksimilar to the other DAZ white dwarfs with circumstellar debris disks.We find that the fraction of DAZ white dwarfs with detectable debrisdisks is at least 14%. We also revisit the problem of explaining themetals in white dwarf photospheres by accretion from the interstellarmedium (ISM). We use the observed interstellar column densities towardstars in close angular proximity and similar distance as DAZ whitedwarfs to constrain the contribution of accretion from the ISM. We findno correlation between the accretion density required to supply metalsobserved in DAZs with the densities observed in their interstellarenvironment, indicating that ISM accretion alone cannot explain thepresence of metals in nearby DAZ white dwarfs. Although ISM accretionwill certainly contribute, our analysis indicates that it is not thedominant source of metals for most DAZ white dwarfs. Instead, thegrowing number of circumstellar debris disks around DAZs suggests thatcircumstellar material may play a more dominant role in polluting thewhite dwarf atmospheres.
| The mass and luminosity functions and the formation rate of DA white dwarfs in the Sloan Digital Sky Survey
Aims.The SDSS Data Release 1 includes 1833 DA white dwarfs (WDs) andforms the largest homogeneous sample of WDs. This sample provides thebest opportunity to study the statistical properties of WDs. Methods:We adopt a recently established theoretical model to calculate the massand distance of each WD using the observational data. Then we adopt abin-correction method to correct for selection effects and use the 1/Vweight-factor method to calculate the luminosity function, thecontinuous mass function and the formation rate of these WDs. Results:The SDSS DA WD sample is incomplete and suffers seriously from selectioneffects. After corrections for the selection effects, only 531 WDsremain. From this final sample we derive the most up-to-date luminosityfunction and mass function, in which we find a broad peak of WD massescentered around 0.58 Mȯ. The DA WD space density iscalculated as 8.81×10-5 pc-3 and theformation rate is 2.579×10-13 pc-3yr-1. Conclusions: The statistical properties of the SDSS DAWD sample are generally in good agreement with previous observationaland theoretical studies, and provide us information on the formation andevolution of WDs. However, a larger and more complete all-sky WD sampleis still needed to explain some subtle disagreements and unresolvedissues.Full Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/627
| The fraction of DA white dwarfs with kilo-Gauss magnetic fields
Context: Weak magnetic fields have been searched for on only a smallnumber of white dwarfs. Current estimates find that about 10% of allwhite dwarfs have fields in excess of 1 MG; according to previousstudies this number increases up to about 25% in the kG regime. Aims:Our aim is to improve on these statistics by a new sample of ten whitedwarfs in order to determine the ratio of magnetic to field-free whitedwarfs. Methods: Mean longitudinal magnetic fields strengths weredetermined by means of high-precision circular polarimetry of Hβand Hγ with the FORS1 spectrograph of the VLT "Kueyen" 8 mtelescope. Results: In one of our objects (LTT 7987), we detected astatistically significant (97% confidence level) longitudinal magneticfield varying between (-1± 0.5) kG and (+1± 0.5) kG. Thiswould be the weakest magnetic field ever found in a white dwarf, butsystematic errors cannot completely be ruled out at this level ofaccuracy. We also observed the sdO star EC 11481-2303 but could notdetect a magnetic field. Conclusions: . VLT observations withuncertainties typically of 1000 G or less suggest that 15-20% of WDshave kG fields. Together with previous investigations, the fraction ofkG magnetic fields in white dwarfs amounts to about 11-15%, which isclose to the current estimations for highly magnetic white dwarfs (>1MG).Based on observations made with ESO Telescopes at the La Silla orParanal Observatories under programme ID 073.D-0356. Figures A.1 and A.2are only available in electronic form at http://www.aanda.org
| Calibration of Synthetic Photometry Using DA White Dwarfs
We have calibrated four major ground-based photometric systems withrespect to the Hubble Space Telescope (HST) absolute flux scale, whichis defined by Vega and four fundamental DA white dwarfs. Thesephotometric systems include the Johnson-Kron-Cousins UBVRI, theStrömgren uvby filters, the Two Micron All Sky SurveyJHKs, and the Sloan Digital Sky Survey ugriz filters.Synthetic magnitudes are calculated from model white dwarf spectrafolded through the published filter response functions; these magnitudesin turn are absolutely calibrated with respect to the HST flux scale.Effective zero-magnitude fluxes and zero-point offsets of each systemare determined. In order to verify the external observationalconsistency, as well as to demonstrate the applicability of thesedefinitions, the synthetic magnitudes are compared with the respectiveobserved magnitudes of larger sets of DA white dwarfs that havewell-determined effective temperatures and surface gravities and span awide range in both of these parameters.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Pegasus |
| Ascensió Recta: | 21h52m25.38s |
| Declinació: | +02°23'19.6" |
| Magnitud Aparent: | 13.283 |
| Distancia: | 25.1 parsecs |
| Moviment propi RA: | 14.1 |
| Moviment propi Dec: | -300.4 |
| B-T magnitude: | 12.243 |
| V-T magnitude: | 13.198 |
Catàlegs i designacions:
|
INHABITED SKY
