Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
A study of gas-phase element abundances reported in the literature for17 different elements sampled over 243 sight lines in the local part ofour Galaxy reveals that the depletions into solid form (dust grains) areextremely well characterized by trends that employ only three kinds ofparameters. One is an index that describes the overall level ofdepletion applicable to the gas in any particular sight line, and theother two represent linear coefficients that describe how to derive eachelement's depletion from this sight-line parameter. The information fromthis study reveals the relative proportions of different elements thatare incorporated into dust at different stages of grain growth. Anextremely simple scheme is proposed for deriving the dust contents andmetallicities of absorption-line systems that are seen in the spectra ofdistant quasars or the optical afterglows of gamma-ray bursts. Contraryto presently accepted thinking, the elements sulfur and krypton appearto show measurable changes in their depletions as the general levels ofdepletions of other elements increase, although more data are needed toascertain whether or not these findings are truly compelling. Nitrogenappears to show no such increase. The incorporation of oxygen into solidform in the densest gas regions far exceeds the amounts that can takethe form of silicates or metallic oxides; this conclusion is based ondifferential measurements of depletion and thus is unaffected byuncertainties in the solar abundance reference scale.Based in large part on published observations from (1) the NASA/ESAHubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555, (2) theFar Ultraviolet Spectroscopic Explorer (FUSE) mission operated by JohnsHopkins University, supported by NASA contract NAS5-32985, and (3) TheCopernicus satellite, supported by NASA grant NAGW-77 to PrincetonUniversity.
| Faint recombination lines in Galactic PNe with a [WC] nucleus
Aims. We present spatially resolved high-resolution spectrophotometricdata for the planetary nebulae PB 8, NGC 2867, and PB 6. We haveanalyzed two knots in NGC 2867 and PB 6 and one in PB 8. The threenebulae are ionized by [WC] type nuclei: early [WO] for PB 6 and NGC2867 and [WC 5-6] in the case of PB 8. Our aim is to study the behaviorof the abundance discrepancy problem (ADF) in this type of planetarynebula. Methods: We measured a large number of optical recombination(ORL) and collisionally excited lines (CEL), from different ionizationstages (many more than in any previous work), thus, we were able toderive physical conditions from many different diagnostic procedures. Wedetermined ionic abundances from the available collisionally excited andrecombination lines. Based on both sets of ionic abundances, we derivedtotal chemical abundances in the nebulae using suitable ionizationcorrection factors. Results: From CELs, we have found abundancestypical of Galactic disk planetary nebulae. Moderate ADF(O++)were found for PB 8 (2.57) and NGC 2867 (1.63). For NGC 2867, abundancesfrom ORLs are higher but still consistent with Galactic disk planetarynebulae. On the contrary, PB 8 presents a very high O/H ratio from ORLs.A high C/O was obtained from ORLs for NGC 2867; this ratio is similar toC/O obtained from CELs and with the chemical composition of the wind ofthe central star, indicating that there was no further C-enrichment inthe star, relative to O, after the nebular material ejection. On thecontrary, we found C/O<1 in PB 8. Interestingly, we obtain(C/O)ORLs/(C/O)CELs < 1 in PB 8 and NGC 2867; this added to thesimilarity between the heliocentric velocities measured in [O iii] and Oii lines for our three objects argue against the presence of H-deficientmetal-rich knots coming from a late thermal pulse event.Based on data obtained at Las Campanas Observatory, CarnegieInstitution.Table 3 is only available in electronic form at http://www.aanda.org
| A slitless spectroscopic survey for quasars near quasars
We present the results of the “Quasars near Quasars” (QNQ)survey, a CCD-based slitless spectroscopic survey for faint V⪉ 22quasars at 1.7⪉ z⪉ 3.6 on 18 26.2 arcmin× 33.5 arcminfields centred on bright quasars at 2.761.7 wewere able to confirm 80 new quasars at 0.580≤ z≤ 3.586 on 16 ofour fields. 64 of the newly discovered quasars are located at z>1.7.The overall high success rate implies that most of the remaining 88candidates are quasars as well, although the majority of them likelyresides at z<1.7 on the basis of the observed line shapes andstrengths. Due to the insufficient depth of the input source cataloguesneeded for extraction of the slitless spectra our survey is not welldefined in terms of limiting magnitude for faint 2.5⪉ z⪉ 3.6quasars whose Lyα emission is detectable well beyond V=22, albeitat a continuum S/N⪉ 1. While not useful for characterising theevolving space density of quasars, our sample provides many new closelyspaced quasar sightlines around intensely studied quasars for furtherinvestigations on the three-dimensional distribution of theintergalactic medium.Based on observations collected at the European Southern Observatory,Chile (Proposals 70.A-0425, 074.A-0273 and 075.A-0141). Data takenunder proposals 68.A-0330 and 70.A-0384 were obtained from the ESOScience Archive.Table 2 and Appendices A-C are only available in electronic form athttp://www.aanda.org
| Bimodality in low-luminosity E and S0 galaxies
Stellar population characteristics are presented for a sample oflow-luminosity early-type galaxies (LLEs) in order to compare them withtheir more luminous counterparts. Long-slit spectra of a sample of 10LLEs were taken with the ESO New Technology Telescope, selected fortheir low luminosities. Line strengths were measured on the Lickstandard system. Lick indices for these LLEs were correlated withvelocity dispersion (σ), alongside published data for a variety ofHubble types. The LLEs were found to fall below an extrapolation of thecorrelation for luminous ellipticals and were consistent with thelocations of spiral bulges in plots of line strengths versus σ.Luminosity weighted average ages, metallicities and abundance ratioswere estimated from χ2 fitting of 19 Lick indices topredictions from simple stellar population models. The LLEs appearyounger than luminous ellipticals and of comparable ages to spiralbulges. These LLEs show a bimodal metallicity distribution, consistingof a low-metallicity group (possibly misclassified dwarf spheroidalgalaxies) and a high-metallicity group (similar to spiral bulges).Finally, they have low α-element to iron peak abundance ratiosindicative of slow, extended star formation.
| New active galactic nuclei detected in ROSAT All Sky Survey galaxies. II. The complete dataset
Aims. The ROSAT ALL Sky Survey Bright Source Catalogue (RASS-BSC) hasbeen correlated with the Catalogue of Principal Galaxies (PGC) toidentify new extragalactic counterparts. 550 reliable opticalcounterparts have been detected. However there existed no opticalspectra for about 200 Active Galactic Nuclei (AGN) candidates before theROSAT ALL Sky Survey (RASS) was completed. Methods: We took opticalspectra of 176 X-ray candidates and companions at ESO, Calar Altoobservatory and McDonald observatory. When necessary we used a lineprofile decomposition to measure line fluxes, widths and centers toclassify their type of activity. Results: We discuss the redshift-,linewidth-, as well as optical and X-ray luminosity distribution of ourROSAT selected sample. 139 galaxies of our 166 X-ray counterparts havebeen identified as AGN with 93 being Seyfert 1 galaxies (61%). Eighteenof them (20%) are Narrow Line Seyfert 1 galaxies. 34 X-ray candidates(21%) are LINERs and only eight candidates (5%) are Seyfert 2. The ratioof the number of Seyfert 1 galaxies to Seyfert 2 galaxies is about 11/1.Optical surveys result in ratios of 1/1.4. The high fraction of detectedSeyfert 1 galaxies is explained by the sensitivity of the ROSAT to softX-rays which are heavily absorbed in type 2 AGN. Two X-ray candidatesare HII-galaxies and 25 candidates (15%) show no signs of spectralactivity. The AGN in our RASS selected sample exhibit slightly higheroptical luminosities (MB = (-20.71 ± 1.75) mag) andsimilar X-ray luminosities (log(LX [ erg s-1] ) =42.9 ± 1.7) compared to other AGN surveys. The Hα linewidth distribution (FWHM) of our newly identified ROSAT AGN sample issimilar to the line widths distribution based on SDSS AGN. However, ournewly identified RASS AGN have rather reddish colors explaining why theyhave not been detected before in ultraviolet or blue excess surveys.
| Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 ≡ the Einstein Cross . I. Spectrophotometric monitoring with the VLT
We present the results of the first long-term (2.2 years) spectroscopicmonitoring of a gravitationally lensed quasar, namely the Einstein CrossQSO 2237+0305. The goal of this paper is to present the observationalfacts to be compared in follow-up papers with theoretical models toconstrain the inner structure of the source quasar. We spatiallydeconvolve deep VLT/FORS1 spectra to accurately separate the spectrum ofthe lensing galaxy from the spectra of the quasar images. Accuratecross-calibration of the 58 observations at 31-epoch from October 2004to December 2006 is carried out with non-variable foreground starsobserved simultaneously with the quasar. The quasar spectra are furtherdecomposed into a continuum component and several broad emission linesto infer the variations of these spectral components. We find prominentmicrolensing events in the quasar images A and B, while images C and Dare almost quiescent on a timescale of a few months. The strongestvariations are observed in the continuum of image A. Their amplitude islarger in the blue (0.7 mag) than in the red (0.5 mag), consistent withmicrolensing of an accretion disk. Variations in the intensity andprofile of the broad emission lines are also reported, most prominentlyin the wings of the C III and center of the C IV emission lines. Duringa strong microlensing episode observed in June 2006 in quasar image A,the broad component of the C III is more highly magnified than thenarrow component. In addition, the emission lines with higher ionizationpotentials are more magnified than the lines with lower ionizationpotentials, consistent with the results obtained with reverberationmapping. Finally, we find that the V-band differential extinction by thelens, between the quasar images, is in the range 0.1-0.3 mag.Based on observations madewith the ESO-VLT Unit Telescope # 2 Kueyen(Cerro Paranal, Chile; Proposals073.B-0243(A&B),074.B-0270(A),075.B-0350(A),076.B-0197(A),177.B-0615(A&B), PI: F. Courbin).
| Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest
Precision astrometry at microarcsecond accuracy has applications for awide range of astrophysical problems. This paper is a study of thescience questions that can be addressed using an instrument withflexible scheduling that delivers parallaxes at about 4 μas ontargets as faint as V=20, and differential accuracy of 0.6 μas onbright targets. The science topics are drawn primarily from the team keyprojects, selected in 2000, for the Space Interferometry MissionPlanetQuest (SIM PlanetQuest). We use the capabilities of this missionto illustrate the importance of the next level of astrometric precisionin modern astrophysics. SIM PlanetQuest is currently in the detaileddesign phase, having completed in 2005 all of the enabling technologiesneeded for the flight instrument. It will be the first space-basedlong-baseline Michelson interferometer designed for precisionastrometry. SIM PlanetQuest will contribute strongly to manyastronomical fields, including stellar and galactic astrophysics,planetary systems around nearby stars, and the study of quasar and AGNnuclei. Using differential astrometry SIM PlanetQuest will search forplanets with masses as small as Earth orbiting in the "habitable zone"around the nearest stars, and could discover many dozen if Earth-likeplanets are common. It will characterize the multiple-planet systemsthat are now known to exist, and it will be able to search forterrestrial planets around all of the candidate target stars in theTerrestrial Planet Finder and Darwin mission lists. It will be capableof detecting planets around young stars, thereby providing insights intohow planetary systems are born and how they evolve with time. Precisionastrometry allows the measurement of accurate dynamical masses for starsin binary systems. SIM PlanetQuest will observe significant numbers ofvery high- and low-mass stars, providing stellar masses to 1%, theaccuracy needed to challenge physical models. Using precisionproper-motion measurements, SIM PlanetQuest will probe the Galactic massdistribution, and, through studies of tidal tails, the formation andevolution of the Galactic halo. SIM PlanetQuest will contribute tocosmology through improved accuracy of the Hubble constant. Withrepeated astrometric measurements of the nuclei of active galaxies, SIMPlanetQuest will probe the dynamics of accretion disks aroundsupermassive black holes, and the relativistic jets that emerge fromthem.
| Spectropolarimetry of the Type IIb Supernova 2001ig
We present spectropolarimetric observations of the Type IIb SN 2001ig inNGC 7424; conducted with the ESO VLT FORS1 on 2001 December 16, 2002January 3, and 2002 August 16, or 13, 31, and 256 days postexplosion.These observations are at three different stages of the SN evolution:(1) the hydrogen-rich photospheric phase, (2) the Type II to Type Ibtransitional phase, and (3) the nebular phase. At each of these stages,the observations show remarkably different polarization properties as afunction of wavelength. We show that the degree of interstellarpolarization is 0.17%. The low intrinsic polarization (~0.2%) at thefirst epoch is consistent with an almost spherical (<10% deviationfrom spherical symmetry) hydrogen-dominated ejecta. Similar to SN 1987Aand to Type IIP SNe, a sharp increase in the degree of the polarization(~1%) is observed when the outer hydrogen layer becomes optically thinby day 31; only at this epoch is the polarization well described by a``dominant axis.'' The polarization angle of the data shows a rotationthrough ~40° between the first and second epochs, indicating thatthe asymmetries of the first epoch were not directly coupled with thoseobserved at the second epoch. For the most polarized lines, we observewavelength-dependent loop structures in addition to the dominant axis onthe Q-U plane. We show that the polarization properties of Type IIb SNeare roughly similar to one another, but with significant differencesarising due to line blending effects especially with the high velocitiesobserved for SN 2001ig. This suggests that the geometry of SN 2001ig isrelated to SN 1993J and that these events may have arisen from a similarbinary progenitor system.Based on observations made with ESO Telescopes at the ParanalObservatory, under programs 68.D-0571 and 69.D-0438.
| The chemical composition of planetary nebulae and HII regions in NGC 3109
Aims.We present deep spectrophotometry for a sample of 8 planetarynebulae (PNe) and 12 HII regions distributed throughout the dwarfirregular galaxy NGC 3109, in order to analyze the chemical compositionof both types of nebulae. Methods: We describe the observations anddata reduction, and present line intensities for the nebular emissionlines detected. The physical conditions and the abundances of He, O, Ne,N, S and Ar are derived, using the classical T_e-based method. Weconfirm our previous identification of PNe and HII regions based onphotometry, except for one object, which we argue is a compact HIIregion rather than a planetary nebula. Results: We find that thechemical composition of the interstellar medium in NGC 3109, as sampledby its HII regions, is remarkably uniform. The oxygen abundance is logO/H + 12 = 7.77 ± 0.07 in this galaxy, as compared to 8.05± 0.09 for the Small Magellanic Cloud (for which we rederived themetallicity in a homogeneous way). PNe show significantly higher oxygenabundances in NGC 3109: log O/H + 12 = 8.16 ± 0.19. Similarly towhat has been suggested for some of the PNe in the Magellanic Clouds andother metal-poor galaxies, we argue that oxygen in the PNe in NGC 3109is affected by dredge up in their progenitors. This could also be thecase for neon, although the uncertainties for this element are bigger. Conclusions: From our analysis, we conclude that oxygen and neon are notalways a safe indicator of the chemical composition of the interstellarmedium at low metallicities. An alternative to the O and Ne enrichmentin PNe is that the low metallicity in HII regions has been caused bydilution of the interstellar medium due to an interaction with aneighboring galaxy about a Gyr ago. The excitation patterns of the PNein NGC 3109 are very different from the excitation patterns of PNe inother galaxies. This issue needs to be investigated further, as itimplies that the evolution of PNe depends upon the properties of theirprogenitor stellar populations, which vary from galaxy to galaxy. Thisshould affect the planetary nebula luminosity function and its use as adistance indicator. Regarding individual objects, we find that theplanetary nebula named PN 14 shows clear Wolf-Rayet features, very lowexcitation and high density. Thus, it is similar to some of the galacticPNe ionized by late [WC] stars.Based on observations collected at the European Southern Observatory,VLT, Paranal, Chile, program ID 076.B-0166.This paper includes data obtained with the 6.5-m Magellan Telescopeslocated at Las Campanas Observatory, Chile.
| Radiative Column and Light Curve of X-Ray Binary Pulsars
We examine the published light curves (LCs) of 117 X-ray binary pulsars,while focusing on the dependence of their light curves on the observedenergy bands. It is found that the energy dependence of the LCs appearsonly when the X-ray luminosity is larger than ˜ 5 ×1036 erg s-1. Assuming that the behavior of lightcurve is related to the radiative accretion column on the neutron-starsurface, this energy threshold can be considered as observational proofof the accretion column formation proposed by Basko and Sunyaev. Once wecan grasp the existence of a radiative column, we can also obtainseveral useful pieces of information about the neutron-star properties.As an instance, we performed a statistical analysis of the orientationangle of the magnetic axis, and we found that the inclination angle ofthe magnetic axis should be small in order to explain the observedstatistics.
| On the orbital periods of the AM CVn stars HP Librae and V803 Centauri
We analyse high time resolution spectroscopy of the AM CVn stars HPLibrae and V803 Centauri, taken with the New Technology Telescope (NTT)and the Very Large Telescope (VLT) of the European Southern Observatory,Chile.We present evidence that the literature value for V803 Cen's orbitalperiod is incorrect, based on an observed `S-wave' in the binary'sspectrogram. We measure a spectroscopic period PV803Cen =1596.4 +/- 1.2s of the S-wave feature, which is significantly shorterthan the 1611-s periods found in previous photometric studies. Weconclude that the latter period likely represents a `superhump'. If oneassumes that our S-wave period is the orbital period, V803 Cen's massratio can be expected to be much less extreme than previously thought,at q ~ 0.07 rather than q ~ 0.016. This relaxes the constraints on themasses of the components considerably: the donor star then does not needto be fully degenerate, and the mass of the accreting white dwarf nolonger has to be very close to the Chandrasekhar limit.For HP Lib, we similarly measure a spectroscopic periodPHPLib = 1102.8 +/- 0.2s. This supports the identification ofHP Lib's photometric periods found in the literature, and theconstraints upon the masses derived from them.
| COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses. VI. Redshift of the lensing galaxy in seven gravitationally lensed quasars
Aims.The knowledge of the redshift of a lensing galaxy that producesmultiple images of a background quasar is essential to any subsequentmodeling, whether related to the determination of the Hubble constantH0 or to the mass profile of the lensing galaxy. We presentthe results of our ongoing spectroscopic observations of gravitationallylensed quasars in order to measure the redshift of their lensinggalaxies. We report on the determination of the lens redshift in sevengravitationally lensed systems. Methods: Our deep VLT/FORS1 spectraare spatially deconvolved in order to separate the spectrum of thelensing galaxies from the glare of the much brighter quasar images. Ourobserving strategy involves observations in Multi-Object-Spectroscopy(MOS) mode which allows the simultaneous observation of the target andof several crucial PSF and flux calibration stars. The advantage of thismethod over traditional long-slit observations is that it allows a muchmore reliable extraction and flux calibration of the spectra. Results:We obtain the first reliable spectra of the lensing galaxies in sixlensed quasars: FBQ 0951+2635 (z_lens~=0.260), BRI 0952-0115(z_lens~=0.632), HE 2149-2745 (z_lens~=0.603), Q 0142-100(z_lens~=0.491), SDSS J0246-0825 (z_lens~=0.723), and SDSS J0806+2006(z_lens~=0.573). The last three redshifts also correspond to the Mg IIdoublet seen in absorption in the quasar spectra at the lens redshift.Our spectroscopic redshifts of HE 2149-2745 and FBQ 0951+2635 are higherthan previously reported, which means that H0 estimates fromthese two systems must be revised to higher values. Finally, wereanalyse the blue side of our previously published spectra of Q1355-2257 and find Mg II in absorption at z =0.702, confirming ourprevious redshift estimate. The spectra of all lenses are typical ofearly-type galaxies.Based onobservations made with the ESO-VLT Unit Telescope 2 Kueyen (CerroParanal, Chile; Programs 077.A-0155, PI: G. Meylan).
| 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.
| The Localized Chemical Pollution in NGC 5253 Revisited: Results from Deep Echelle Spectrophotometry
We present echelle spectrophotometry of the blue compact dwarf galaxyNGC 5253 obtained with the VLT UVES. We have measured the intensities ofa large number of permitted and forbidden emission lines in four zonesof the central part of the galaxy. We detect faint C II and O IIrecombination lines, the first time that these are unambiguouslydetected in a dwarf starburst galaxy. The physical conditions of theionized gas have been derived using a large number of different lineintensity ratios. Chemical abundances of He, N, O, Ne, S, Cl, Ar, and Fehave been determined following standard methods. C++ andO++ abundances have been derived from pure recombinationlines and are larger than those obtained from collisionally excitedlines (from 0.30 to 0.40 dex for C++ and from 0.19 to 0.28dex for O++). This result is consistent with a temperaturefluctuation parameter (t2) between 0.050 and 0.072. Weconfirm previous results that indicate the presence of a localized Nenrichment in certain zones of NGC 5253 and detect a possible slight Heoverabundance in the same zones. The enrichment pattern agrees with thatexpected for the pollution by the ejecta of Wolf-Rayet (W-R) stars. Theamount of enriched material needed to produce the observed overabundanceis consistent with the mass lost by the number of W-R stars estimated inthe starbursts. We discuss the possible origin of the difference betweenabundances derived from recombination and collisionally excited lines(the so-called abundance discrepancy problem) in H II regions, findingthat a recent hypothesis based on the delayed enrichment by SN ejectainclusions seems not to explain the observed features.Based on observations collected at the European Southern Observatory,Chile, proposal ESO 70.C-0008(A).
| A radio continuum and neutral hydrogen counterpart to the IRAS Vela shell
Aims.We look for radio-continuum and atomic neutral hydrogen (Hi)counterparts of the IRAS Vela shell (IVS). Methods: .Neutralhydrogen (Hi) and 1410 MHz radio continuum surveys carried out with theInstituto Argentino de Radioastronomía (IAR) dishes are the maindatabases used in this investigation. Results: .A goodmorphological correlation was found between arc-shaped structures atradio wavelengths and in the 100 μm IR emission. This correlation isobserved at velocities of the Hi between -17.5 and -2.1 kms-1, in agreement with the velocities of the molecular gasdetected in the region. The radial distribution of the differentcomponents is consistent with the presence of an expanding shell that isbeing ionized from inside. Assuming a distance of 400 pc, the amount ofionized and atomic gas associated with the IVS is 2.3 ×104 and 6.8 × 104 solar masses,respectively. The origin of the expansion of the IVS could not beidentified.
| The wide field imager Lyman-alpha search (WFILAS) for galaxies at redshift ~5.7. II. Survey design and sample analysis
Context: .Wide-field narrowband surveys are an efficient way ofsearching large volumes of high-redshift space for distant galaxies. Aims: .We describe the Wide Field Imager Lyman-Alpha Search (WFILAS)over 0.74 sq. degree for bright emission-line galaxies at z ˜5.7. Methods: .WFILAS uses deep images taken with the Wide FieldImager (WFI) on the ESO/MPI 2.2 m telescope in three narrowband (70Å), one encompassing intermediate band (220 Å) and twobroadband filters, B and R. We use the novel technique of anencompassing intermediate band filter to exclude false detections.Images taken with broadband B and R filters are used to remove lowredshift galaxies from our sample. Results: .We present a sampleof seven Lyα emitting galaxy candidates, two of which arespectroscopically confirmed. Compared to other surveys all ourcandidates are bright, the results of this survey complements othernarrowband surveys at this redshift. Most of our candidates are in theregime of bright luminosities, beyond the reach of less voluminoussurveys. Adding our candidates to those of another survey increases thederived luminosity density by ~30%. We also find potential clustering inthe Chandra Deep Field South, supporting overdensities discovered byother surveys. Based on a FORS2/VLT spectrum we additionally present theanalysis of the second confirmed Lyα emitting galaxy in oursample. We find that it is the brightest Lyα emitting galaxy (1× 10-16 erg s-1 cm-2) at thisredshift to date and the second confirmed candidate of our survey. Bothobjects exhibit the presence of a possible second Lyα componentredward of the line.
| Faint emission lines in the Galactic HII regions M16, M20 and NGC 3603*
We present deep echelle spectrophotometry of the Galactic HII regionsM16, M20 and NGC 3603. The data have been taken with the Very LargeTelescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10400Å range. We have detected more than 200 emission lines in eachregion. Physical conditions have been derived using different continuumand line intensity ratios. We have derived He+,C++ and O++ abundances from pure recombinationlines as well as collisionally excited lines (CELs) for a large numberof ions of different elements. We have obtained consistent estimationsof the temperature fluctuation parameter, t2, using differentmethods. We also report the detection of deuterium Balmer lines up toDδ (M16) and to Dγ (M20) in the blue wings of the hydrogenlines, which excitation mechanism seems to be continuum fluorescence.The temperature fluctuation paradigm agrees with the results obtainedfrom optical CELs, and the more uncertain ones from far-infraredfine-structure CELs in NGC 3603, although, more observations coveringthe same volume of the nebula are necessary to obtain solid conclusions.
| Low-resolution VLT spectroscopy of GRBs 991216, 011211 and 021211
We present low-resolution VLT spectroscopy of the afterglow of thegamma-ray bursts (GRBs) 991216, 011211 and 021211. Our spectrum of GRB991216 is the only optical spectrum for this afterglow. It shows twoprobable absorption systems at z=0.80 and z=1.02, where the highestredshift most likely reflects the distance to the host galaxy. A thirdsystem may be detected at z=0.77. HST imaging of the field, obtained 4months after the burst, has resulted in the detection of two amorphousregions of emission, one at the projected afterglow position, and theother 0.primeprime6 away. The spectrum shows a depression influx in between 4000 Å and 5500 Å. This could be the resultof a 2175 Å-type extinction feature in the host of GRB 991216, butat a rather red wavelength of 2360 Å. If this interpretation iscorrect, it is the first time the extinction feature is seen in a GRBafterglow spectrum. It is centered at a wavelength similar to that ofthe ultra-violet (UV) bumps inferred from observations of a fewUV-strong, hydrogen-poor stars in the Galaxy. All significant absorptionlines (except for one) detected in the spectrum of GRB 011211 areidentified with lines originating in a single absorption system atz=2.142±0.002, the redshift of the GRB 011211 host galaxy. Wealso detect the Lyα absorption line in the host, to which we fit aneutral hydrogen column density of log N(ion{H}{i}) = 20.4±0.2,which indicates that it is a damped Lyα system. Using acurve-of-growth analysis, we estimate the Si, Fe and Al metallicity atthe GRB 011211 redshift to be [Si/H] =-0.9+0.6-0.4, [Fe/H]=-1.3±0.3, and [Al/H] =-1.0+0.5-0.3. For GRB 021211, we detect a singleemission line in a spectrum obtained tens of days after the burst, whichwe identify as [ion{O}{ii}] λ3727 at z=1.006. The correspondingunobscured [ion{O}{ii}] star-formation rate is 1.4 Mȯyr-1.
| Precatalysmic binary systems.
Not Available
| The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Deep echelle spectrophotometry of S 311, a Galactic HII region located outside the solar circle
We present echelle spectrophotometry of the Galactic HII region S 311.The data have been taken with the Very Large TelescopeUltraviolet-Visual Echelle Spectrograph in the 3100-10400 Årange.We have measured the intensities of 263 emission lines; 178 arepermitted lines of H0, D0 (deuterium),He0, C0, C+, N0,N+, O0, O+, S+,Si0, Si+, Ar0 and Fe0; someof them are produced by recombination and others mainly by fluorescence.Physical conditions have been derived using different continuum- andline-intensity ratios. We have derived He+, C++and O++ ionic abundances from pure recombination lines aswell as abundances from collisionally excited lines for a large numberof ions of different elements. We have obtained consistent estimationsof t2 applying different methods. We have found that thetemperature fluctuations paradigm is consistent with theTe(HeI) versus Te(HI) relation for HII regions, incontrast with what has been found for planetary nebulae. We report thedetection of deuterium Balmer lines up to Dδ in the blue wings ofthe hydrogen lines, whose excitation mechanism seems to be continuumfluorescence.
| Carbon and Oxygen Galactic Gradients: Observational Values from H II Region Recombination Lines
We present results of deep echelle spectrophotometry of eight Galactic HII regions located at Galactocentric distances between 6.3 and 10.4 kpc.The data have been taken with the Very Large Telescope UltravioletEchelle Spectrograph in the 3100-10360 Å range. We have derivedC++ and O++ abundances from recombination linesfor all the objects as well as O+ abundances from this kindof line for three of the nebulae. The intensity of recombination linesis almost independent of the assumed electron temperature as well as ofthe possible presence of spatial temperature variations or fluctuationsinside the nebulae. These data allow the determination of the gas-phaseC and O abundance gradients of the Galactic disk, of paramountimportance for chemical evolution models. This is the first time the Cgradient is derived from such a large number of H II regions distributedin such a wide range of Galactocentric distances. Abundance gradientsare found of the form Δlog(O/H)=-0.044+/-0.010 dexkpc-1, Δlog(C/H)=-0.103+/-0.018 dex kpc-1,and Δlog(C/O)=-0.058+/-0.018 dex kpc-1.Based on observations collected at the European Southern Observatory,Chile; proposals ESO 68.C-0149(A) and ESO 70.C-0008(A).
| The Chandra Deep Field-South: Optical Spectroscopy. I.
We present the results of our spectroscopic follow-up program of theX-ray sources detected in the 942 ks exposure of the Chandra DeepField-South (CDFS). A total of 288 possible counterparts were observedat the VLT with the FORS1/FORS2 spectrographs for 251 of the 349 Chandrasources (including three additional faint X-ray sources). Spectra andR-band images are shown for all the observed sources and R-K colors aregiven for most of them. Spectroscopic redshifts were obtained for 168X-ray sources, of which 137 have both reliable optical identificationand redshift estimate (including 16 external identifications). TheR<24 observed sample comprises 161 X-ray objects (181 opticalcounterparts), and 126 of them have unambiguous spectroscopicidentification. There are two spikes in the redshift distribution,predominantly populated by type 2 active galactic nuclei (AGNs) but alsotype 1 AGN and X-ray normal galaxies: the one at z=0.734 is fairlynarrow (in redshift space) and comprises two clusters/groups of galaxiescentered on extended X-ray sources, the second one at z=0.674 is broaderand should trace a sheetlike structure. The type 1 and type 2populations are clearly separated in X-ray/optical diagnostics involvingparameters sensitive to absorption/reddening: X-ray hardness ratio (HR),optical/near-IR color, soft X-ray flux, and optical brightness.Nevertheless, these two populations cover similar ranges of hard X-rayluminosity and absolute K magnitude, thus trace similar levels ofgravitational accretion. Consequently, we introduce a new classificationbased solely on X-ray properties, HR, and X-ray luminosity, consistentwith the unified AGN model. This X-ray classification uncovers a largefraction of optically obscured, X-ray-luminous AGNs missed by theclassical optical classification. We find a similar number of X-ray type1 and type 2 QSOs [LX(0.5-10keV)>1044 ergss-1] at z>2 (13 sources with unambiguous spectroscopicidentification); most X-ray type 1 QSOs are bright, R<~24, whereasmost X-ray type 2 QSOs have R>~24, which may explain the differencewith the CDFN results as few spectroscopic redshifts were obtained forR>24 CDFN X-ray counterparts. There are X-ray type 1 QSOs down toz~0.5, but a strong decrease at z<2 in the fraction of luminous X-raytype 2 QSOs may indicate a cosmic evolution of the X-ray luminosityfunction of the type 2 population. An X-ray spectral analysis isrequired to confirm this possible evolution. The red color of most X-raytype 2 AGNs could be due to dust associated with the X-ray absorbingmaterial and/or a substantial contribution of the host galaxy light. Thelatter can also be important for some redder X-ray type 1 AGNs. There isa large population of EROs (R-K>5) as X-ray counterparts, and theirfraction strongly increases with decreasing optical flux, up to 25% forthe R>=24 sample. They cover the whole range of X-ray hardnessratios, comprise objects of various classes (in particular a highfraction of z>~1 X-ray absorbed AGNs, but also elliptical andstarburst galaxies) and more than half of them should be fairly brightX-ray sources [LX(0.5-10keV)>1042 ergss-1]. Photometric redshifts will be necessary to derive theproperties and evolution of the X-ray selected EROs.Based on observations collected at the European Southern Observatory,Chile [ESO no. 66.A-0270(A) and 67.A-0418(A)].
| Interpretation of the variability of the β Cephei star λ Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binaryβ Cephei star λ Scorpii. Moreover, we present the firstdetermination of the properties of the triple system to which λScorpii belongs. Our analysis is based on a time series of 815high-resolution spectra, covering a timespan of 14 years. We find aclose orbit of 5.9525 d days (e=0.26) and a wide orbit of approximately1082d days (e=0.23). The orbital parameters of the triplestar and a spectrum synthesis lead us to conclude that the system iscomposed of two early-type B stars and a low-mass pre-main-sequence starrather than containing an ultra-massive white dwarf as claimed before.Our proposed configuration is compatible with population synthesis. Theradial velocity variations of the primary allow us to confirm thepresence of at least one pulsation mode with frequency 4.679410 cd-1 which is subject to the light-time effect in the triplesystem. A detailed analysis of the complex line-profile variations isdescribed in a subsequent paper.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, ChileTable \ref{observations} is only available in electronic form athttp://www.edpsciences.org
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Detection and high-resolution spectroscopy of a huge flare on the old M 9 dwarf DENIS 104814.7-395606.1
We report a flare on the M 9 dwarf DENIS 104814.7-395606.1, whose massplaces it directly at the hydrogen burning limit. The event was observedin a spectral sequence during 1.3 h. Line shifts to bluer wavelengthswere detected in Hα, Hβ, and in the NaI D lines, indicating mass motions. In addition we detect a fluxenhancement on the blue side of the two Balmer lines in the lastspectrum of our series. We interpret this as rising gas cloud with aprojected velocity of about 100 km s-1 which may lead to massejection. The higher Balmer lines Hγ to H8are not seen due to our instrumental setup, but in the last spectrumthere is strong evidence for H9 being in emission.Based on observations collected at the European Southern Observatory,Paranal, 68.D-0166A, Chile.
| The Impact of Space Experiments on our Knowledge of the Physics of the Universe
With the advent of space experiments it was demonstrated that cosmicsources emit energy practically across all the electromagnetic spectrumvia different physical processes. Several physical quantities givewitness to these processes which usually are not stationary; thosephysical observable quantities are then generally variable. Thereforesimultaneous multifrequency observations are strictly necessary in orderto understand the actual behaviour of cosmic sources. Space experimentshave opened practically all the electromagnetic windows on the Universe.A discussion of the most important results coming from multifrequencyphotonic astrophysics experiments will provide new inputs for theadvance of the knowledge of the physics, very often in its more extremeconditions. A multitude of high quality data across practically thewhole electromagnetic spectrum came at the scientific community'sdisposal a few years after the beginning of the Space Era. With thesedata we are attempting to explain the physics governing the Universeand, moreover, its origin, which has been and still is a matter of thegreatest curiosity for humanity. In this paper we will try to describethe last steps of the investigation born with the advent of spaceexperiments, to note upon the most important results and open problemsstill existing, and to comment upon the perspectives we can reasonablyexpect. Once the idea of this paper was well accepted by ourselves, wehad the problem of how to plan the exposition. Indeed, the exposition ofthe results can be made in different ways, following several points ofview, according to: - a division in diffuse and discrete sources; -different classes of cosmic sources; - different spectral ranges, whichimplies in turn a sub-classification in accordance with differenttechniques of observations; - different physical emission mechanisms ofelectromagnetic radiation; - different vehicles used for launching theexperiments (aircraft, balloons, rockets, satellites, observatories). Inorder to exhaustively present The Impact of Space Experiments on ourKnowledge of the Physics of the Universe it would then have beennecessary to write a kind of Encyclopaedia of the Astronomical SpaceResearch, which is not our desire. On the contrary, since our goal is toprovide an useful tool for the reader who has not specialized in spaceastrophysics and for the students, we decided to write this paper in theform of a review, the length of which can be still consideredreasonable, taking into account the complexity of the argumentsdiscussed. Because of the impossibility of realizing a complete pictureof the physics governing the Universe, we were obliged to select how toproceed, the subjects to be discussed the more or the less, or those tobe rejected. Because this work was born in the Ph.D. thesis of one of us(LSG) (Sabau-Graziati, 1990) we decided to follow the `astronomicaltradition' used there, namely: the spectral energy ranges. Although suchenergy ranges do not determine physical objects (even if in many casessuch ranges are used to define the sources as: radio, infrared, optical,ultraviolet, X-ray, γ-ray emitters), they do determine themethods of study, and from the technical point of view they define thetechnology employed in the relative experiments. However, since then wehave decided to avoid a deep description of the experiments, satellites,and observatories, simply to grant a preference to the physical results,rather than to technologies, however fundamental for obtaining thoseresults. The exposition, after an introduction (Section 1) and somecrucial results from space astronomy (Section 2), has been focussed intothree parts: the physics of the diffuse cosmic sources deduced fromspace experiments (Section 3), the physics of cosmic rays from ground-and space-based experiments (Section 4), and the physics of discretecosmic sources deduced from space experiments (Section 5). In this firstpart of the paper we have used the logic of describing the main resultsobtained in different energy ranges, which in turn characterize theexperiments on board space vehicles. Within each energy range we havediscussed the contributions to the knowledge of various kind of cosmicsources coming from different experiments. And this part is mainlyderived by the bulk of the introductory part of LSG's Ph.D. thesis. Inthe second part of the paper, starting from Section 6, we have preferredto discuss several classes of cosmic sources independently of the energyranges, mainly focussing the results from a multifrequency point ofview, making a preference for the knowledge of the physics governing thewhole class. This was decided also because of the multitude of new spaceexperiments launched in the last fifteen years, which would haverendered almost impossible a discussion of the results divided intoenergy ranges without weakening the construction of the entire puzzle.We do not pretend to cover every aspect of every subject consideredunder the heading of the physics of the universe. Instead a crosssection of essays on historical, modern, and philosophical topics areoffered and combined with personal views into tricks of the spaceastrophysics trade. The reader is, then, invited to accept this papereven though it obviously lacks completeness and the arguments discussedare certainly biased by a selection effect owed essentially to ourknowledge, and to it being of a reasonable length. Some parts of itcould seem, in certain sense, to belong to an older paper, in which the`news' is not reported. But this is owed to our own choice, just in fullaccord with the goals of the text: we want to present those resultswhich have, in our opinion, been really important, in the development ofthe science. These impacting results do not necessarily constitute thelast news. This text was formally closed just on the day of the launchof the INTEGRAL satellite: October 17, 2002. After that date onlyfinishing touches have been added.
| Luminous supersoft X-ray sources
We discuss possible evolution channels that lead to the formation ofluminous supersoft X-ray sources, subclasses of which may be progenitorsof type Ia supernovae. We carry out full evolution calculations from thezero-age main sequence to the supersoft source. A novel feature of ourcalculations is the inclusion of thermohaline mixing after mass transferduring binary evolution. The main effect of this is to producesecondaries of non-solar composition. Candidate initial progenitors areintermediate-mass donors of about 7 Mȯ with companionsin the range 1.5-3.0 Mȯ. We concentrate on earlycase-C evolution, which means that the primary fills its Roche lobe whenit ascends the Early Asymptotic Giant Branch while its core is highlyevolved and massive enough to form a CO white dwarf. A crucial role,established by observations in this part of HR diagram, is played bymass loss in winds and we treat winds with a new approach. Sincecommon-envelope evolution (CE) is generally invoked to explain theformation of close binaries with one or two degenerate components, weassume that the progenitors undergo severe mass and angular momentumloss through such a phase. We further study how the configurations ofthe post-CE systems, composed of a massive white dwarf and a 1.5-3.0Mȯ companion, depend on the parameters of CE-evolutionand mass-loss rates in various phases of evolution. Under these generalassumptions a new path for the formation of SSSs is found which differsfrom that of the, usually assumed, solar composition donors. Our resultsmay explain supersoft systems with enhanced helium abundances such as USco and very luminous extragalactic supersoft sources such as CAL 83 inthe LMC and possibly the CHANDRA source (N1) in M 81.
| High-energy sources before INTEGRAL. INTEGRAL reference catalog
We describe the INTEGRAL reference catalog which classifies previouslyknown bright X-ray and gamma-ray sources before the launch of INTEGRAL.These sources are, or have been at least once, brighter than ~ 1 mCrababove 3 keV, and are expected to be detected by INTEGRAL. This catalogis being used in the INTEGRAL Quick Look Analysis to discover newsources or significantly variable sources. We compiled several publishedX-ray and gamma-ray catalogs, and surveyed recent publications for newsources. Consequently, there are 1122 sources in our INTEGRAL referencecatalog. In addition to the source positions, we show an approximatespectral model and expected flux for each source, based on which wederive expected INTEGRAL counting rates. Assuming the default instrumentperformances and at least ~ 105 s exposure time for anypart of the sky, we expect that INTEGRAL will detect at least ~ 700sources below 10 keV and ~ 400 sources above 20 keV over the missionlife.The Catalog is available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/411/L59
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Крма |
| Ректацензија: | 06h48m04.70s |
| Deклинација: | -44°18'58.4" |
| Apparent магнитуда: | 8.246 |
| Даљина: | 862.069 parsecs |
| Proper motion RA: | -4.8 |
| Proper motion Dec: | 7.3 |
| B-T magnitude: | 7.922 |
| V-T magnitude: | 8.22 |
Каталог и designations:
|
