Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
An Online Catalog of Cataclysmic Variable Spectra from the Far-Ultraviolet Spectroscopic Explorer
We present an online catalog containing spectra and supportinginformation for cataclysmic variables that have been observed with theFar-Ultraviolet Spectroscopic Explorer (FUSE). For each object in thecatalog we list some of the basic system parameters such as (R.A.,decl.), period, inclination, and white dwarf mass, as well asinformation on the available FUSE spectra: data ID, observation date andtime, and exposure time. In addition, we provide parameters needed forthe analysis of the FUSE spectra such as the reddening E(B - V),distance, and state (high, low, intermediate) of the system at the timeit was observed. For some of these spectra we have carried out modelfits to the continuum with synthetic stellar and/or disk spectra usingthe codes TLUSTY and SYNSPEC. We provide the parameters obtained fromthese model fits; this includes the white dwarf temperature, gravity,projected rotational velocity, and elemental abundances of C, Si, S, andN, together with the disk mass accretion rate, the resultinginclination, and model-derived distance (when unknown). For each objectone or more figures are provided (as gif files) with line identificationand model fit(s) when available. The FUSE spectra and the syntheticspectra are directly available for download as ASCII tables. Referencesare provided for each object, as well as for the model fits. In thisarticle we present 36 objects, and additional ones will be added to theonline catalog in the future. In addition to cataclysmic variables, wealso include a few related objects, such as a wind-accreting whitedwarf, a pre-cataclysmic variable, and some symbiotics.
| A Compilation of Interstellar Column Densities
We have collated absorption line data toward 3008 stars in order tocreate a unified database of interstellar column densities. These datahave been taken from a number of different published sources and includemany different species and ionizations. The preliminary results from ouranalysis show a tight relation [N(H)/E(B - V) = 6.12 ×1021] between N(H) and E(B - V). Similar plots havebeen obtained with many different species, and their correlations alongwith the correlation coefficients are presented.
| A Survey of Far Ultraviolet Spectroscopic Explorer Observations of Cataclysmic Variables
During its lifetime, the Far Ultraviolet Spectroscopic Explorer (FUSE)was used to observe 99 cataclysmic variables (CVs) in 211 separateobservations. Here, we present a survey of the moderate-resolution (R ~=10, 000), far-ultraviolet (905-1188 Å), time-averaged FUSE spectraof CVs. The FUSE spectra are morphologically diverse. They showcontributions from the accretion disk, the disk chromosphere, diskoutflows, and the white dwarf (WD), but the relative contribution ofeach component varies widely as a function of CV subtype, orbital periodand evolutionary state, inclination, mass accretion rate, and magneticfield strength of the WD. The data reveal information about thestructure, temperature, density and mass flow rates of the disk and diskwinds, the temperature of the WD and the effects of ongoing accretion onits structure, and the long-term response of the systems to diskoutbursts. The complete atlas of time-averaged FUSE spectra of CVs isavailable at the Multimission Archive at Space Telescope ScienceInstitute as a High Level Science Product.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE was operated for NASA by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| A critical analysis of three near-infrared photometric methods of estimating distances to cataclysmic variables
A critical analysis of three methods of estimating distances tocataclysmic variables (CVs) is performed. These methods, by Ak et al.,Beuermann, and Knigge, all use near-infrared (JHK or Ks)magnitudes and the Barnes-Evans relation. We compare all threemethods to distances measured by trigonometric parallax by Thorstensen,with Hubble Space Telescope, and with the HIPPARCOS spacecraft.We findthat the method of Ak et al. works best overall for all CVs, predictingdistances on the average 4% less than those measured by trigonometricparallaxes. The method of Beuermann overestimates distances by 52%. Themethod of Knigge underestimates distances by 26%, although this was onlyever meant as a lower limit, since it assumes all light comes from thesecondary star.
| A Method for the Study of Accretion Disk Emission in Cataclysmic Variables. I. The Model
We have developed a spectrum synthesis method for modeling theultraviolet (UV) emission from the accretion disk from cataclysmicvariables (CVs). The disk is separated into concentric rings, with aninternal structure from the Wade & Hubeny disk-atmosphere models.For each ring, a wind atmosphere is calculated in the comoving framewith a vertical velocity structure obtained from a solution of the Eulerequation. Using simple assumptions, regarding rotation and the windstreamlines, these one-dimensional models are combined into a single2.5-dimensional model for which we compute synthetic spectra. We findthat the resulting line and continuum behavior as a function of theorbital inclination is consistent with the observations, and verify thatthe accretion rate affects the wind temperature, leading tocorresponding trends in the intensity of UV lines. In general, we alsofind that the primary mass has a strong effect on the P Cygni absorptionprofiles, the synthetic emission line profiles are strongly sensitive tothe wind temperature structure, and an increase in the mass-loss rateenhances the resonance line intensities. Synthetic spectra were comparedwith UV data for two high orbital inclination nova-like CVs—RW Triand V347 Pup. We needed to include disk regions with arbitrary enhancedmass loss to reproduce reasonably well widths and line profiles. Thisfact and a lack of flux in some high ionization lines may be thesignature of the presence of density-enhanced regions in the wind, oralternatively, may result from inadequacies in some of our simplifyingassumptions.
| The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars
We present an attempt to reconstruct the complete evolutionary pathfollowed by cataclysmic variables (CVs), based on the observedmass-radius relationship of their donor stars. Along the way, we updatethe semi-empirical CV donor sequence presented previously by one of us,present a comprehensive review of the connection between CV evolutionand the secondary stars in these systems, and reexamine most of thecommonly used magnetic braking (MB) recipes, finding that evenconceptually similar ones can differ greatly in both magnitude andfunctional form. The great advantage of using donor radii to infermass-transfer and angular-momentum-loss (AML) rates is that they samplethe longest accessible timescales and are most likely to represent thetrue secular (evolutionary average) rates. We show explicitly that ifCVs exhibit long-term mass-transfer-rate fluctuations, as is oftenassumed, the expected variability timescales are so long that othertracers of the mass-transfer rate—including white dwarf (WD)temperatures—become unreliable. We carefully explore how much ofthe radius difference between CV donors and models of isolatedmain-sequence stars may be due to mechanisms other than mass loss. Thetidal and rotational deformation of Roche-lobe-filling stars produces ~=4.5% radius inflation below the period gap and ~= 7.9% above. Acomparison of stellar models to mass-radius data for non-interactingstars suggests a real offset of ~= 1.5% for fully convective stars(i.e., donors below the gap) and ~= 4.9% for partially radiative ones(donors above the gap). We also show that donor bloating due toirradiation is probably smaller than, and at most comparable to, theseeffects. After calibrating our models to account for these issues, wefit self-consistent evolution sequences to our compilation of donormasses and radii. In the standard model of CV evolution, AMLs below theperiod gap are assumed to be driven solely by gravitational radiation(GR), while AMLs above the gap are usually described by an MB law firstsuggested by Rappaport et al. We adopt simple scaled versions of theseAML recipes and find that these are able to match the data quite well.The optimal scaling factors turn out to be f GR = 2.47± 0.22 below the gap and f MB = 0.66 ± 0.05above (the errors here are purely statistical, and the standard modelcorresponds to f GR = f MB = 1). This revisedmodel describes the mass-radius data significantly better than thestandard model. Some of the most important implications and applicationsof our results are as follows. (1) The revised evolution sequence yieldscorrect locations for the minimum period and the upper edge of theperiod gap; the standard sequence does not. (2) The observed spectraltypes of CV donors are compatible with both standard and revised models.(3) A direct comparison of predicted and observed WD temperaturessuggests an even higher value for f GR, but this comparisonis sensitive to the assumed mean WD mass and the possible existence ofmass-transfer-rate fluctuations. (4) The predicted absolute magnitudesof donor stars in the near-infrared form a lower envelope around theobserved absolute magnitudes for systems with parallax distances. Thisis true for all of our sequences, so any of them can be used to set firmlower limits on (or obtain rough estimates of) the distances toward CVsbased only on P orb and single epoch near-IR measurements.(5) Both standard and revised sequences predict that short-period CVsshould be susceptible to dwarf nova (DN) eruptions, consistent withobservations. However, both sequences also predict that the fraction ofDNe among long-period CVs should decline with P orb above theperiod gap. Observations suggest the opposite behavior, and we discussthe possible explanations for this discrepancy. (6) Approximate orbitalperiod distributions constructed from our evolution sequences suggestthat the ratio of long-period CVs to short-period, pre-bounce CVs isabout 3 × higher for the revised sequence than the standard one.This may resolve a long-standing problem in CV evolution. Tablesdescribing our donor and evolution sequences are provided inelectronically readable form.
| The age of cataclysmic variables: A kinematical study
Using available astrometric and radial velocity data, the spacevelocities of cataclysmic variables (CVs) with respect to Sun werecomputed and kinematical properties of various sub-groups of CVs wereinvestigated. Although observational errors of systemic velocities(?) are high, propagated errors are usually less than computeddispersions. According to the analysis of propagated uncertainties ofthe computed space velocities, available sample was refined by removingthe systems with the largest propagated uncertainties so that thereliability of the space velocity dispersions was improved. Having adispersion of 51±7kms-1 for the space velocities, CVsin the current refined sample (159 systems) are found to have 5 ±1 Gyr mean kinematical age. After removing magnetic systems from thesample, it is found that non-magnetic CVs (134 systems) have a meankinematical age of 4 ± 1 Gyr. According to 5 ± 1 and 4± 1 Gyr kinematical ages implied by 52 ± 8 and 45 ±7 km s-1 dispersions for non-magnetic systems below andabove the period gap, CVs below the period gap are older than systemsabove the gap, which is a result in agreement with the standardevolution theory of CVs. Age difference between the systems below andabove the gap is smaller than that expected from the standard theory,indicating a similarity of the angular momentum loss time scales insystems with low-mass and high-mass secondary stars. Assuming anisotropic distribution, ? velocity dispersions of non-magnetic CVsbelow and above the period gap are calculated??=30±5kms-1 and??=26±4kms-1. The smalldifference of ? velocity dispersions between the systems below andabove the gap may imply that magnetic braking does not operate in thedetached phase, during which the system evolves from the post-commonenvelope orbit into contact.
| The Geometry and Ionization Structure of the Wind in the Eclipsing Nova-like Variables RW Tri and UX UMa
The UV spectra of nova-like variables are dominated by emission from theaccretion disk, modified by scattering in a wind emanating from thedisk. Here, we model the spectra of RW Tri and UX UMa, the only twoeclipsing nova-like variables which have been observed with the HubbleSpace Telescope in the far-ultraviolet, in an attempt to constrain thegeometry and the ionization structure of their winds. Using our MonteCarlo radiative transfer code, we computed spectra for simplyparameterized axisymmetric biconical outflow models and were able tofind plausible models for both systems. These reproduce the primary UVresonance lines—N V, Si IV, and C IV—in the observed spectrain and out of eclipse. The distribution of these ions in the wind modelsis similar in both cases as is the extent of the primary scatteringregions in which these lines are formed. The inferred mass-loss ratesare 6%-8% of the mass accretion rates for the systems. We discuss theimplication of our point models for our understanding of accretion diskwinds in cataclysmic variables.
| The Anomalous Accretion Disk of the Cataclysmic Variable RW Sextantis
Synthetic spectra covering the wavelength range 900-3000 Å providean accurate fit, established by a ?2 ?analysis, to a combined observed spectrum of RW Sextantis. Twoseparately calibrated distances to the system establish the syntheticspectrum comparison on an absolute flux basis but with two alternativescaling factors, requiring alternative values of \dot{M} for finalmodels. Based on comparisons for a range of \dot{M} values, the observedspectrum does not follow the standard model. Rather than the exponent0.25 in the expression for the radial temperature profile, a value closeto 0.125 produces a synthetic spectrum with an accurate fit to thecombined spectrum. A study of time-series Far Ultraviolet SpectroscopicExplorer spectra shows that a proposed warped or tilted disk is notsupported by the data; an alternative proposal is that an observednon-axisymmetric wind results from an interaction with the mass transferstream debris.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc. underNASA contract NAS5-26555, and the NASA-CNES-CSA Far UltravioletExplorer, which is operated for NASA by the Johns Hopkins Universityunder NASA contract NAS5-32985.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| On the Accretion Rates of SW Sextantis Nova-like Variables
We present accretion rates for selected samples of nova-like variableshaving IUE archival spectra and distances uniformly determined using aninfrared method by Knigge. A comparison with accretion rates derivedindependently with a multiparametric optimization modeling approach byPuebla et al. is carried out. The accretion rates of SW Sextantisnova-like systems are compared with the accretion rates of non-SWSextantis systems in the Puebla et al. sample and in our sample, whichwas selected in the orbital period range of three to four and a halfhours, with all systems having distances using the method of Knigge.Based upon the two independent modeling approaches, we find nosignificant difference between the accretion rates of SW Sextantissystems and non-SW Sextantis nova-like systems insofar as opticallythick disk models are appropriate. We find little evidence to suggestthat the SW Sex stars have higher accretion rates than other nova-likecataclysmic variables (CVs) above the period gap within the same rangeof orbital periods.
| Cluster AgeS Experiment (CASE): deficiency of observed dwarf novae in globular clusters
We present the results of a search for dwarf novae (DNe) in globularclusters (GCs). It is based on the largest available homogeneous sampleof observations, in terms of the time-span, number of observations andnumber of clusters. It includes 16 Galactic GCs and yielded two newcertain DNe: M55-CV1 and M22-CV2. All previously known systems locatedin our fields were recovered, too. We surveyed M4, M5, M10, M12, M22,M30, M55, NGC 288, NGC 362, NGC 2808, NGC 3201, NGC 4372, NGC 6362, NGC6752, ? Centauri (NGC 5139) and 47 Tucanae (NGC 104). Thediscovery of two DNe, namely M55-CV1 and M22-CV2, was already reportedby Kaluzny et al. and Pietrukowicz et al., respectively. In theremaining 14 GCs, we found no certain new DNe. Our result raises thetotal number of known DNe in the Galactic GCs to 12 DNe, distributedamong seven clusters. Our survey recovered all three already knownerupting cataclysmic variables (CVs) located in our fields, namelyM5-V101, M22-CV1, and V4 in the foreground of M30. To assess theefficiency of the survey, we analysed images with inserted artificialstars mimicking outbursts of the prototype DNe SS Cygni and U Geminorum.Depending on the conditions, we recovered between 16-100 per cent ofthese artificial stars. The efficiency seems to be predominantlyaffected by duty cycle/time-sampling and much less bydistance/magnitude. Except for saturated tiny collapsed cores of M30,NGC 362 and NGC 6752 (and also the dense core of NGC 2808), crowdingeffects in the V band were avoided by our image subtraction techniqueaugmented with auxiliary unsaturated B-band images. Our results clearlydemonstrate that in GCs common types of DNe are very rare indeed.However, great care must be taken before these conclusions can beextended to the CV population in GCs.
| Spatial distribution and galactic model parameters of cataclysmic variables
The spatial distribution, galactic model parameters and luminosityfunction of cataclysmic variables (CVs) in the solar neighbourhood havebeen determined from a carefully established sample of 459 CVs. Thesample contains all of the CVs with distances computed from theperiod-luminosity-colours (PLCs) relation of CVs which has been recentlyderived and calibrated with 2MASS photometric data. It has been foundthat an exponential function fits best to the observationalz-distributions of all of the CVs in the sample, non-magnetic CVs anddwarf novae, while the sech2 function is more appropriate fornova-like stars and polars. The vertical scaleheight of CVs is 158± 14 pc for the 2MASS J-band limiting apparent magnitude of 15.8.On the other hand, the vertical scaleheights are 128 ± 20 and 160± 5 pc for dwarf novae and nova-like stars, respectively. Thelocal space density of CVs is found to be ˜3 ×10-5 pc-3 which is in agreement withthe lower limit of the theoretical predictions. The luminosity functionof CVs shows an increasing trend toward higher space densities at lowluminosities, implying that the number of short-period systems should behigh. The discrepancies between the theoretical and observationalpopulation studies of CVs will almost disappear if for the z-dependenceof the space density the sech2 density function is used.
| A New, Bright, Short-Period, Emission Line Binary in Ophiuchus
The 11th magnitude star LS IV-08°3 has been classified previously asan OB star in the Luminous Stars survey, or alternatively as a hotsubdwarf. It is actually a binary star. We present spectroscopy,spectroscopic orbital elements, and time-series photometry fromobservations made at the Kitt Peak National Observatory 2.1 m, StewardObservatory 2.3 m, MDM Observatory 1.3 m and 2.4 m, Hobby-Eberly 9.2 m,and Michigan State University 0.6 m telescopes. The star exhibitsemission of varying strength in the cores of H and He I absorptionlines. Emission is also present at 4686 Å (He II) and near4640/4650 Å (N III/C III). Time-series spectroscopy collected from2005 July to 2007 June shows coherent, periodic radial velocityvariations of the H? line, which we interpret as orbital motionwith a period of 0.1952894(10) days. High-resolution spectra show thatthere are two emission components, one broad and one narrow, moving inantiphase, as might arise from an accretion disk and the irradiated faceof the mass donor star. Less coherent, low-amplitude photometricvariability is also present on a timescale similar to the orbitalperiod. Diffuse interstellar bands indicate considerable reddening,which however is consistent with a distance of ~100-200 pc. The star isthe likely counterpart of a weak ROSAT X-ray source, whose propertiesare consistent with accretion in a cataclysmic variable (CV) binarysystem. We classify LS IV-08°3 as a new member of the UX UMasubclass of CV stars.Based in part on observations obtained with the Hobby-Eberly Telescope,which is a joint project of the University of Texas at Austin, thePennsylvania State University, Stanford University,Ludwig-Maximillians-Universität München, andGeorg-August-Universität Göttingen.
| A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables
We have performed a statistical test of the currently used accretiondisk models for cataclysmic variables (CVs) using a set of 33 CVs withsteady disks (10 old novae and 23 nova-like systems). The mass transferrate () for each system was also calculated. Ultraviolet (UV) data werefitted by model spectra using a multiparametric optimization method,aiming to constrain the values. It was verified that these accretiondisk models fail to fit both color and flux simultaneously, aspreviously noted when composite stellar atmosphere models were fitted tothe UV spectra of CVs by Wade. By applying such models to a sample ofnovae and nova-like CVs, we confirm that the limb-darkening effect mustbe taken into account when estimating mass transfer rates, especiallyfor high-inclination systems. Important fitting degeneracies of thebasic disk parameters are analyzed. Our simulations suggest that toreproduce the observations a revision of the temperature profile, atleast in the innermost parts of the disk, seems to be required, andpossibly the vertical distribution of the viscosity should be revised.In addition, an optically thin layer or an extended disk componentshould be considered. This component may be physically represented by adisk wind and/or a chromosphere. A physical description of theemission-line profiles may help to break the degeneracies that appearwhen only the continuum is analyzed. The average value of found fornova-like systems is ~9.3 × 10-9 Modotyr-1, while ~1.3 × 10-8 Modotyr-1 is found for old classical novae. No clear evidence isfound for either the presence or absence of a correlation between andthe orbital period. Such correlation analysis was performed for highaccretion rate systems (15 nova-like systems and 10 old novae), but wewere not able to find a well-defined correlation as found by Patterson.By measuring the equivalent width of the emission lines (C IV?1550 and He II ?1640) we found a lack of systems with lowand strong UV emission lines. A correlation between the equivalent widthof such lines and the orbital inclination (i) was also confirmed.
| New Ultraviolet Observations of AM CVn
We have obtained observations of the ultraviolet spectrum of AM CVn, anultrashort-period helium cataclysmic variable, using the Space TelescopeImaging Spectrograph aboard the Hubble Space Telescope (HST). Weobtained data in time-tag mode during two consecutive orbits of HST,covering 1600-3150 and 1140-1710 Å, respectively. The meanspectrum is approximately flat in f?. The absorptionprofiles of the strong lines of N V, Si IV, C IV, He II, and N IV areblueshifted and in some cases asymmetric, evidencing a wind that ispartly occulted by the accretion disk. There is weak redshifted emissionfrom N V and He II. The profiles of these lines vary mildly with time.The light curve shows a decline of ~20% over the span of theobservations. There is also flickering and a 27 s (or 54 s) "dwarf novaoscillation," revealed in a power-spectrum analysis. The amplitude ofthis oscillation is larger at shorter wavelengths. We assemble andillustrate the spectral energy distribution of AM CVn from theultraviolet to the near-infrared. Modeling the accretion phenomenon inthis binary system can in principle lead to a robust estimate of themass accretion rate on to the central white dwarf, which is of greatinterest in characterizing the evolutionary history of the binarysystem. Inferences about the mass accretion rate depend strongly on thelocal radiative properties of the disk, as we illustrate. Uncertainty inthe distance of AM CVn and other parameters of the binary systemcurrently limit the ability to confidently infer the mass accretionrate.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555. These observations are associated with program8159.
| A new absolute magnitude calibration with 2MASS for cataclysmic variables
Using reliable trigonometric measurements, we find that the absolutemagnitude of cataclysmic variables depends on the orbital period andde-reddened (J ‑ H)0 and (H ‑Ks)0 colours of 2MASS (Two Micron All Sky Survey)photometric system. The calibration equation covers the ranges0.032d < Porb ⩽ 0.454d,‑0.08 < (J ‑ H)0 ⩽ 1.54, ‑0.03 <(H ‑ Ks)0 ⩽ 0.56 and 2.0
| Broadband UBVRCIC Photometry of Horizontal-Branch and Metal-poor Candidates from the HK and Hamburg/ESO Surveys. I.
We report broadband UBV and/or BVRCIC CCDphotometry for a total of 1857 stars in the thick-disk and halopopulations of the Galaxy. The majority of our targets were selected ascandidate field horizontal-branch or other A-type stars (FHB/A, N=576),or candidate low-metallicity stars (N=1221), from the HK and Hamburg/ESOobjective-prism surveys. Similar data for a small number of additionalstars from other samples are also reported. These data are being usedfor several purposes. In the case of the FHB/A candidates they are usedto accurately separate the lower gravity FHB stars from various highergravity A-type stars, a subsample that includes the so-called blue metalpoor stars, halo and thick-disk blue stragglers, main-sequence A-typedwarfs, and Am and Ap stars. These data are also being used to derivephotometric distance estimates to high-velocity hydrogen clouds in theGalaxy and for improved measurements of the mass of the Galaxy.Photometric data for the metal-poor candidates are being used to refineestimates of stellar metallicity for objects with availablemedium-resolution spectroscopy, to obtain distance estimates forkinematic analyses, and to establish initial estimates of effectivetemperature for analysis of high-resolution spectroscopy of the starsfor which this information now exists.
| Bright Metal-poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
We present a sample of 1777 bright (91.0) metal-poor([Fe/H]<-2.0) giants of 9%+/-2%, which is lower than previouslyreported. However, the frequency rises to similar (>20%) and highervalues with increasing distance from the Galactic plane. Although thenumbers of stars at low metallicity are falling rapidly at the lowestmetallicities, there is evidence that the fraction of carbon-enhancedmetal-poor stars is increasing rapidly as a function of decliningmetallicity. For ~60 objects, high-resolution data have already beenobtained; one of these, HE 1327-2326, is the new record holder for themost iron-deficient star known.
| Rapid Hα Variability in T Coronae Borealis
We report on a search conducted for variability in the Hα emissionline of the recurrent nova T CrB with a time resolution of 10-15minutes. This is comparable to the timescale of the photometricflickering observed in this object. This is the first time thatobservations of the short-timescale emission-line variation have beenmade for this system. On two nights (1999 January 6 and 7), we detectedstatistically significant variability (at the 99% confidence level) inthe Hα line profile. This variability is confined to the centralpart of the emission line (+/-100 km s-1), althoughFWZI(Hα)~800 km s-1. The variability in the lineprofile is accompanied by variability of the total equivalent width,EW(Hα): +/-8% for 1999 January 6 and +/-6% for 1999 January 7(calculated from the mean EW value). Assuming Keplerian motion, thevariability is generated at a distance of ~20-30 Rsolar fromthe white dwarf, which is approximately the radius of the ring that thestream of gas forms as it flows away from the L1 Lagrangian point. Forthree other nights we are only able to put upper limits on thevariability, ΔEW(Hα): +/-2% for 1998 April 15, +/-4% for1998 August 2, and +/-3% for 1998 August 3.Based on observations obtained at the National Astronomical ObservatoryRozhen, Bulgaria.
| FUSE observations of V592 Cas: the continuing enigma of orbitally modulated spectral signatures of accretion disc winds
By exploiting Far Ultraviolet Spectroscopic Explorer (FUSE) satellitetime-series data, we have probed the relation between accretion discgeometry and bipolar outflow in the low-inclination, nova-likecataclysmic variable (CV) V592 Cas. Our results show that the outflow isstrictly modulated on the orbital period and not on the (negative orpositive) superhump periods of this system. This implies that theprecession of either the disc eccentricity or its tilt is not directlyaffecting the structure and global dynamics of the outflow. Theprincipal variability in the ultraviolet resonance lines ischaracterized by Doppler shifts of the entire blueward absorptiontroughs, in concert for a range of low- and high-ionization cases. Therepetitive behaviour is asymmetric and highly non-sinusoidal over theorbital cycle of the system. The disc wind characteristics derived hereallow V592 Cas to be added to a growing number of non-magnetic CVs whichexhibit orbitally modulated wind variability. The origin of thedeparture in axisymmetry, which has to be fixed in the binary starframe, remains to be established.
| 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.
| A FUSE Survey of Disk-Accreting Cataclysmic Variables
We present initial results of a survey of the FUV spectra ofdisk-accreting cataclysmic variables obtained with the Far UltravioletSpectroscopic Explorer (FUSE).
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Sextante |
| Ascensión Recta: | 10h19m56.62s |
| Declinación: | -08°41'56.1" |
| Magnitud Aparente: | 10.641 |
| Movimiento Propio en Ascensión Recta: | -20.5 |
| Movimiento Propio en Declinación: | -17.1 |
| B-T magnitude: | 10.628 |
| V-T magnitude: | 10.64 |
Catálogos y designaciones:
|
