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Strange magnification pattern in the large separation lens SDSS J1004+4112 from optical to X-rays
We present simultaneous XMM-Newton UV and X-ray observations of thequadruply lensed quasar SDSS J1004+4112 (RBS825). Simultaneously with the XMM-Newton observations we alsoperformed integral field spectroscopy on the two closest lens images Aand B using the Calar Alto PMAS spectrograph. In X-rays the widelyspaced components C and D are clearly resolved, while the closer pair ofimages A and B is marginally resolved in the XMM-EPIC images. Theintegrated X-ray flux of the system has decreased by a factor of 6 sinceit was observed in the ROSAT All Sky Survey in 1990, while the X-rayspectrum became much harder with the power law index evolving fromΓ=-2.3 to Γ=-1.86. By deblending the X-ray images of thelensed QSO we find that the X-ray flux ratios between the lens images Aand B are significantly different from the simultaneously obtained UVratios and previously measured optical flux ratios. Our optical spectrumof lens image A shows an enhancement in the blue emission line wings,which has been observed in previous epochs as a transient feature. Wepropose a scenario where intrinsic UV and X-ray variability gives riseto line variations which are selectively magnified in image A bymicrolensing. The extended emission of the lensing cluster of galaxiesis clearly detected in the EPIC images, we measure a 0.5-2.0 keVluminosity of 1.4 × 1044~erg/s. Based on the clusterX-ray properties, we estimate a mass of 2-6 ×1014~Mȯ.
| An Atlas of Spectrophotometric Landolt Standard Stars
We present CCD observations of 102 Landolt standard stars obtained withthe Ritchey-Chrétien spectrograph on the Cerro TololoInter-American Observatory 1.5 m telescope. Using stellar atmospheremodels, we have extended the flux points to our six spectrophotometricsecondary standards, in both the blue and the red, allowing us toproduce flux-calibrated spectra that span a wavelength range from 3050Å to 1.1 μm. Mean differences between UBVRI spectrophotometrycomputed using Bessell's standard passbands and Landolt's publishedphotometry were determined to be 1% or less. Observers in bothhemispheres will find these spectra useful for flux-calibrating spectra,and through the use of accurately constructed instrumental passbands,will be able to compute accurate corrections to bring instrumentalmagnitudes to any desired standard photometric system (S-corrections).In addition, by combining empirical and modeled spectra of the Sun,Sirius, and Vega, we calculate and compare synthetic photometry toobserved photometry taken from the literature for these three stars.
| The Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating the Ages of Bars
In order to perform a detailed study of the stellar kinematics in thevertical axis of bars, we obtained high signal-to-noise spectra alongthe major and minor axes of the bars in a sample of 14 face-on galaxiesand used them to determine the line-of-sight stellar velocitydistribution, parameterized as a Gauss-Hermite series. With these data,we developed a diagnostic tool that allows one to distinguish betweenrecently formed and evolved bars, as well as to estimate their ages,assuming that bars form in vertically thin disks that are recognizableby low values for the vertical velocity dispersion σz.Through N-body realizations of bar unstable disk galaxies we were alsoable to check the timescales involved in the processes that give bars animportant vertical structure. We show that σz inevolved bars is roughly 100 km s-1, which translates to aheight scale of about 1.4 kpc, giving support to scenarios in whichbulges form through disk material. Furthermore, the bars in ournumerical simulations have values for σz generallysmaller than 50 km s-1, even after evolving for 2 Gyr,suggesting that a slow process is responsible for making bars asvertically thick as we observe. We verify theoretically that theSpitzer-Schwarzschild mechanism is quantitatively able to explain theseobservations if we assume that giant molecular clouds are twice asconcentrated along the bar as in the rest of the disk.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| CHORIZOS: A χ2 Code for Parameterized Modeling and Characterization of Photometry and Spectrophotometry
We have developed CHi-square cOde for parameterRized modeling andcharacterIZation of phOtometry and Spectrophotmetry (CHORIZOS). CHORIZOScan use up to two intrinsic free parameters (e.g., temperature andgravity for stars, type and redshift for galaxies, or age andmetallicity for stellar clusters) and two extrinsic parameters (amountand type of extinction). The code uses χ2 minimization tofind all models compatible with the observed data in the modelN-dimensional (N=1, 2, 3, 4) parameter space. CHORIZOS can use eithercorrelated or uncorrelated colors as input and is specially designed toidentify possible parameter degeneracies and multiple solutions. Thecode is written in IDL and is available to the astronomical community.Here we present the techniques used, test the code, apply it to a fewwell-known astronomical problems, and suggest possible applications. Asa first scientific result from CHORIZOS, we confirm from photometry theneed for a revised temperature-spectral type scale for OB starspreviously derived from spectroscopy.
| Spectroscopic classification of a suspected SU UMa Star in Libra
We present optical spectroscopy of the suspected SUUMa type variableASAS 153616-0839.1, recently discovered in Libra (Pojmanski, G. 2004,VSNET alert 7982). The object shows a very blue continuum, with hydrogenand HeI lines in absorption, only H showing an emission core. HeII andhigher ionised lines are present in emission. The spectrum is typicalfor a SUUMa type system in early outburst phase and thus confirms thephotometric classification.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Library of flux-calibrated echelle spectra of southern late-type dwarfs with different activity levels
We present Echelle spectra of 91 late-type dwarfs, of spectral typesfrom F to M and of different levels of chromospheric activity, obtainedwith the 2.15 m telescope of the CASLEO Observatory located in theArgentinean Andes. Our observations range from 3890 to 6690 Å, ata spectral resolution from 0.141 to 0.249 Å per pixel(R=λ/δ λ ≈ 26 400). The observations were fluxcalibrated with the aid of long slit spectra. A version of thecalibrated spectra is available via the World Wide Web.Table 2 is 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/A+A/414/699The spectra are available as FITS and ascii-files at the URL:http://www.iafe.uba.ar/cincunegui/spectra/Table2.html. They are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/699. When convertingthe fits to ascii, the spectra were oversampled to a constant δλ ≈ 0.15 Å.Table 2 is also available in electronic form at the CDS via anonymous
| Statistics of the Instability Strip of β Cephei Stars
We present a study of the β Cephei instability strip based on asample of 49 stars of this type. After deriving their effectivetemperatures and luminosities from their observed (B-V), (U-B) colorsand parallaxes we find their positions in the HR diagram to be mostlyconfined to the main sequence, and their masses to lie between 7Mȯ and 30 Mȯ. Their distribution on theHR diagram matches well with our previous theoretical instability stripwhich has an upper bound in the luminosity and rather tight boundariesin the effective temperature.
| Weak Emission-Line Central Stars of Planetary Nebulae
We present new spectroscopic data of 14 candidates for the weakemission-line type of central stars of planetary nebulae ([WELS]). Witha medium resolution of about 2 Å, we confirmed the main spectralcharacteristics of these stars but found that two objects of our sampleare in fact early-type [WC] ([WCE]) stars. The λ4650 and C IVλλ 5801, 5812 features are resolved, and they were used ina tentative classification. Based on the C IV lines the [WELS] stars ofour sample can be divided qualitatively into two main groups: clearemission and very weak or no emission. We compared mean equivalentwidths of carbon and oxygen lines of the [WELS] stars with those of the[WCE] and [WCL] types. The results are not conclusive but point in favorof an increase in temperature from [WCL] to [WCE], followed perhaps by adecrease from [WCE] to [WELS].Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under agreement with theObservatório Nacional, Brazil.
| Metallicities of the SPB stars from the IUE ultraviolet spectra
We derived the stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddenings for 20 SPB and34 reference stars observed during the IUE satellite mission. Theparameters were derived by means of an algorithmic procedure of fittingtheoretical flux distributions to the low-resolution IUE spectra andoptical spectrophotometric observations. Since the metallicity [m/H] hasa special importance for pulsating B type stars, we focused ourattention on that parameter. We found that the mean value of themetallicity of the considered SPB and reference stars amounts to [m/H] ~-0.20. The results only slightly depend on the reduction procedure usedfor the IUE images (NEWSIPS and INES). The metal abundances obtained inthis paper are in accordance with the average value of -0.2 dex forstars in the solar neighborhood recently reported by otherinvestigators.Tables 3-7 are 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/404/689
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| New Spectroscopic Data and Classification of Southern [WC] Stars
New spectroscopic data of a sample of 10 southern [WC] stars arepresented and described. Equivalent widths of carbon line transitions (CII λ4267, C III λ5696, and C IV λλ5801,5812) are used to revise the classification of the seven late-type [WCL]stars of the sample. For them, our spectra allowed us to employ aquantitative system. We have confirmed the previous classification forthree of the objects, but for three others, we have encountereddifferent subtypes. Because of the weakness of the oxygen lines, it wasnot possible to suggest subtypes for the three [WCE] stars. Based onobservations made with the 1.52 m telescope at the European SouthernObservatory (La Silla, Chile) under agreement with theObservatório Nacional, Brazil.
| Electron temperature fluctuations in 30 Doradus
We present an observational study of the spatial variation of theelectron temperature in the 30 Doradus Nebula. Weused the [ion {O}{iii}] (lambda 4959 + lambda 5007)/lambda 4363 ratio toestimate the electron temperature at 135 positions in the nebula acrossthree different directions. We analysed long-slit spectrophotometricdata of high signal-to-noise in the range of 4100 to 5030 Åobtained with the Cassegrain spectrograph attached to the 1.60 mtelescope of the Laboratório Nacional de Astrofísica,Brazil. No large-scale electron temperature gradient was detected in 30Doradus. The electron temperature estimates obtained are fairlyhomogeneous with a mean value of 10 270 +/- 140 (3sigma ) K. Thecompatibility between the present estimates with optical and radiotemperature determinations found in the literature for other positionsor for the entire nebula corroborates this conclusion. Temperaturefluctuations of small amplitude were observed with a variance relativeto the mean of ts2= 0.0025 or equivalently with adispersion of only 5%. The areas with lower surface brightness seem topresent slightly higher electron temperatures. This would indicate thatthe bright arcs of 30 Doradus, which correspond to the densest regions,would have lower electron temperatures than the most diffuse areas.
| The Constant-Velocity Highly Collimated Outflows of the Planetary Nebula He 2-90
We present high-dispersion echelle spectroscopic observations and anarrowband [N II] image of the remarkable jetlike features of He 2-90.They are detected in the echelle spectra in the Hα and [N II]lines but not in other nebular lines. The [N II]/Hα ratio isuniformly high, ~=1. The observed kinematics reveals bipolar collimatedoutflows in the jetlike features and shows that the southeast(northwest) component expands toward (away from) the observer at aremarkably constant line-of-sight velocity, 26.0+/-0.5 kms-1. The observed expansion velocity and the opening angle ofthe jetlike features are used to estimate an inclination angle of~=5° with respect to the sky plane and a space expansion velocity of~=290 km s-1. The spectrum of the bright central nebulareveals a profusion of Fe lines and extended wings of the Hα line,similar to those seen in symbiotic stars and some young planetarynebulae that are presumed to host a mass-exchanging binary system. Ifthis is the case for He 2-90, the constant velocity and direction of thejets require a very stable dynamic system against precession andwarping.
| Variable Hα Line Emission from the Central Star of the Helix Nebula
The central star of the Helix Nebula is a hot white dwarf withunexpected hard X-ray emission. With an effective temperature of~100,000 K, the star is a powerful source of H-ionizing radiation; theatmosphere of a stellar or planetary companion, if present, will beionized and emit recombination lines. To probe the origin of hard X-rayemission from the Helix Nebula's central star, we have obtainedmultiepoch, high-dispersion spectra of the star and have found temporalvariation in the Hα line profile over a time span of 1 week. Theobserved width and strength of the variable Hα emission componentare consistent with the hypothesized dMe companion proposed to explainthe hard X-ray emission. A dMe companion, however, cannot explain thepossible detection of variable He II and [N II] emission. Follow-upspectroscopic monitoring of the Helix Nebula central star is needed tobetter establish the identification of the spectral lines and theirtemporal behavior in order to determine the origin of the opticalvariability and hard X-ray emission.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| The HB Narrowband Comet Filters: Standard Stars and Calibrations
We present results concerning the development and calibration of a newset of narrowband comet filters, designated the HB filter set, which wasdesigned and manufactured to replace aging IHW filters. Information isalso presented about the design and manufacturing of the filters,including the reasoning that was used for deciding the final wavelengthsand bandpasses. The new filters are designed to measure five differentgas species (OH, NH, CN, C2, C3), two ions(CO+, H2O+), and four continuum points.An improved understanding of extended wings from emission bands in cometspectra, gained since the development of the IHW filters, wasincorporated into the new design, so that contamination from undesiredspecies is significantly reduced compared to previous filters. Inaddition, advances in manufacturing techniques lead to squarertransmission profiles, higher peak transmission and UV filters withlonger lifetimes. We performed the necessary calibrations so that dataobtained with the filters can be converted to absolute fluxes, allowingfor, among other things, accurate subtraction of the continuum from thegas species. Flux standards and solar analogs were selected andobserved, and the data were used to establish a magnitude system for theHB filters. The star measurements were also used to evaluate which solaranalogs were best representatives of the Sun and to explore how the fluxstandards differed in the UV with respect to their spectral type. Newprocedures were developed to account for the non-linear extinction inthe OH filter, so that proper extrapolations to zero airmass can beperformed, and a new formalism, which can account for mutualcontaminations in two (or more) filters, was developed for reducingcomet observations. The relevant equations and reduction coefficientsare given, along with detailed instructions on how to apply them. Wealso performed a series of tests involving factors that can affecteither the filter transmission profiles or the distribution of theemission lines in the gas species to determine how these effectspropagate through to the calibration coefficients. The results indicatethat there are only two factors that are a concern at a level of morethan a few percent: f-ratios smaller than f/4, and a few individualfilters whose transmission profiles are significantly different from thefilters used in the calibrations.
| B Stars as a Diagnostic of Star Formation at Low and High Redshift
We have extended the evolutionary synthesis models by Leitherer et al.by including a new library of B stars generated from the IUEhigh-dispersion spectra archive. We present the library and show how thestellar spectral properties vary according to luminosity classes andspectral types. We have generated synthetic UV spectra for prototypicalyoung stellar populations varying the IMF and the star formation law.Clear signs of age effects are seen in all models. The contribution of Bstars in the UV line spectrum is clearly detected, in particular forgreater ages when O stars have evolved. With the addition of the newlibrary we are able to investigate the fraction of stellar andinterstellar contributions and the variation in the spectral shapes ofintense lines. We have used our models to date the spectrum of the localsuper-star cluster NGC 1705-1. Photospheric lines of C III λ1247,Si III λ1417, and S V λ1502 were used as diagnostics todate the burst of NGC 1705-1 at 10 Myr. Interstellar lines are clearlyseen in the NGC 1705-1 spectrum. Broadening and blueshifts of severalresonance lines are stronger in the galaxy spectrum than in our modelsand are confirmed to be intrinsic of the galaxy. Si II λ1261 andAl II λ1671 were found to be pure interstellar lines with anaverage blueshift of 78 km s-1 owing to a directed outflow ofthe interstellar medium. We have selected the star-forming galaxy1512-cB58 as a first application of the new models to high-z galaxies.This galaxy is at z=2.723, it is gravitationally lensed, and its highsignal-to-noise ratio Keck spectrum shows features typical of localstarburst galaxies, such as NGC 1705-1. Models with continuous starformation were found to be more adequate for 1512-cB58 since there arespectral features typical of a composite stellar population of O and Bstars. A model with Z=0.4 Zsolar and an IMF with α=2.8reproduces the stellar features of the 1512-cB58 spectrum.
| Integrated photometry of galactic H Ii regions
Integrated photoelectric measurements of the equivalent width W_Hβ, the [O Iii]/Hβ ratio and the Hβ emission line flux arepresented for 31 southern hemisphere galactic H Ii regions. The Lymancontinuum photon fluxes are obtained for some of these objects. Theintegrated [O Iii]/Hβ ratios have not shown any statisticallysignificant deviation from non-integrated measurements found in theliterature.
| The eclipsing binary V578 Mon in the Rosette nebula: age and distance to NGC 2244 using Fourier disentangled component spectra
V578 Mon is a member of the young stellar cluster NGC 2244 which isembedded in the Rosette nebula. It is a double-lined binary, consistingof two early-B type components which eclipse each other partially duringtheir 2.40848-day orbit. A novel technique of Fourier disentangling isapplied to disentangle the spectrum of the binary into the spectra ofits components, allowing a direct spectroscopic temperaturedetermination for each component. Together with an analysis of the lightcurve, the spectral disentangling process allows us to derive theorbital and fundamental stellar parameters. The hotter star (T_eff = 30000 K) has a mass of 14.5 Msun and a radius of 5.2 Rsun. The cooler one (T_eff = 26 400 K) has a mass of 10.3 Msun and a radius of 4.3 Rsun . Both stars are well insidetheir critical Roche lobe and move in an eccentric orbit (e=0.087) whichhas a semi-major axis of 22 Rsun and is seen at aninclination of 72.6degr . The rotation of both stars is synchronizedwith the orbital motion. The systemic velocity of 34.9 km s-1,confirms that the binary belongs to NGC 2244. The age of the binary,and hence of NGC 2244, is (2.3±0.2) 106 years. Fromthe fundamental stellar parameters and the interstellar absorption, thedistance to the cluster is derived to be 1.39 ±0.1 kpc, i.e.slightly lower than that found from photometric studies. Its age andspace velocity indicate that NGC 2244 is formed in the galactic plane.The high accuracy obtained (e.g. probable errors of 0.5% for the masses,1m -1.5% for the radii, despite the lack of total eclipses,and 1.5% for the temperatures) is a direct consequence of the spectraldisentangling technique, which as a by-product delivers very accurateradial velocities for all orbital phases. Based on observations obtainedat the European Southern Observatory (ESO), La Silla, Chile Table 5 isonly available in electronic form at the CDS via anonymous ftp to130.79.128.5 or at http://cdsweb.u-strasbg.fr
| Optical long-slit spectroscopy and imaging of OH 231.8+4.2
We present optical long-slit spectra and complementary broad and narrowband images of the bipolar proto-planetary nebula OH231.8+4.2. Absolute J2000 coordinates have been calculated forour maps from the position of nearby stars. Our maps of the opticalcontinuum show the spatial distribution of the starlight scattered bydust grains. This component is found to be highly elongated along thenebular axis, with a structure very similar to that of the molecularemission. Flux variations with time of the red continuum emission aredetected. Our long-slit spectroscopy of Hα and other atomic linesreveals wide spectral profiles and, in general, a complex spatial andspectral emission distribution. The emission arises from two broad lobesand is shifted toward shorter (north lobe) and longer wavelengths (southlobe), indicating that the gas is flowing outwards at high velocity. Theclumpiness of the emission nebula is remarkable. A simple model has beenused to describe the complex structure and kinematics of this source.Our model suggests that, in addition to the two extended, hollow lobesidentified in the Hα images, a smaller, bubble-like expandingstructure should lie inside the south lobe. A comparison of the emissionline spectrum with predictions of theoretical shock models confirms thatthe optical lines have been shock excited. We have estimated theelectron density of the lobes and deduced the total ionized mass of thenebula, obtaining a low value of ~5\times10-4M\odot. We interpret the shaping and evolution of OH231.8+4.2 in the wind interaction scenario for planetarynebulae formation. The peculiar structure and kinematics of themolecular outflow and the ionized envelope are explained in terms of ashock regime transition: the well collimated molecular outflow and thedifferent components of the optical nebula would consist ofcircumstellar material swept-up by a unique shock in a radiative, andnon-radiative regime, respectively. Finally, we briefly discuss thecontroversial evolutionary status of OH 231.8+4.2.
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| Two new planetary nebulae and an AGN in the Galactic Plane
A search for planetary nebulae was carried out using candidates selectedby their infrared colours and 5 GHz radio emission. One new planetarynebula was identified on the basis of its small angular size, strong[OIII] emission and infrared colours. Another object, known as thepossible planetary nebula Wray 16-28, is similarly identified as aplanetary nebula. An undiscovered AGN was also found, and is classed asa Seyfert 2 Galaxy on the basis of its strong OIII emission, linewidthsof approx. 500 km/s, and 5 GHz radio flux. Low-resolution opticalspectra are presented and distance estimates discussed.
| An analysis of the Johnson et al. Catalina UBVRI photometry for second order extinction effects.
Not Available
| GAIA Spectroscopy: Proposing the 8500--8750 Angstroms Region and Evaluating the Performances
We propose the Gaia spectroscopic observations to be performed over thewavelength interval 8500--8750 Angstroms, with an optimal dispersion of0.25 Angstroms/pix (or 1000 pixels budget per spectrum) and a 2 pixelPSF. In this paper, on the base of extensive observations as well assynthetic spectra and simulations, we review the spectroscopicperformances expected for Gaia: radial and rotational velocities,spectral classification, detection of mass-loss and spectralpeculiarities, chemical abundance analysis and reddening estimates fromthe 8620 Angstroms diffuse interstellar band. Lower dispersion spectra(corresponding to smaller pixel budgets) are considered too.
| Galactic-Scale Outflow and Supersonic Ram-Pressure Stripping in the Virgo Cluster Galaxy NGC 4388
The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the Universityof Hawaii 2.2 m telescope was used to map the Hα and [O III]lambda5007 emission-line profiles across the entire disk of the edge-onSb galaxy NGC 4388. We confirm a rich complex of highly ionized gas thatextends ~4 kpc above the disk of this galaxy. Low-ionization gasassociated with star formation is also present in the disk. Evidence forbar streaming is detected in the disk component and is discussed in acompanion paper. Nonrotational blueshifted velocities of 50-250 km s^-1are measured in the extraplanar gas northeast of the nucleus. Thebrighter features in this complex tend to have more blueshiftedvelocities. A redshifted cloud is also detected 2 kpc southwest of thenucleus. The velocity field of the extraplanar gas of NGC 4388 appearsto be unaffected by the inferred supersonic (Mach number M~3) motion ofthis galaxy through the ICM of the Virgo cluster. We argue that this isbecause the galaxy and the high-|z| gas lie behind a Mach cone withopening angle ~80 deg. The shocked ICM that flows near the galaxy has avelocity of ~500 km s^-1 and exerts insufficient ram pressure on theextraplanar gas to perturb its kinematics. We consider severalexplanations of the velocity field of the extraplanar gas. Velocities,especially blueshifted velocities on the north of the galaxy, are bestexplained as a bipolar outflow that is tilted by >12 deg from thenormal to the disk. The observed offset between the extraplanar gas andthe radio structure may be due to buoyancy or refractive bending bydensity gradients in the halo gas. Velocity substructure in theoutflowing gas also suggests an interaction with ambient halo gas.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נחש מים |
| התרוממות ימנית: | 08h43m13.50s |
| סירוב: | +03°23'55.0" |
| גודל גלוי: | 4.3 |
| מרחק: | 143.062 פארסק |
| תנועה נכונה: | -19.3 |
| תנועה נכונה: | -1.8 |
| B-T magnitude: | 4.037 |
| V-T magnitude: | 4.248 |
קטלוגים וכינוים:
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