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New Light in Star-Forming Dwarf Galaxies: The PMAS Integral Field View of the Blue Compact Dwarf Galaxy Mrk 409
We present an integral field spectroscopic study of the central 2× 2 kpc2 of the blue compact dwarf galaxy Mrk 409,observed with the Potsdam MultiAperture Spectrophotometer (PMAS). Thisstudy focuses on the morphology, two-dimensional chemical abundancepattern, excitation properties, and kinematics of the ionizedinterstellar medium in the starburst component. We also investigate thenature of the extended ring of ionized gas emission surrounding thebright nuclear starburst region of Mrk 409. PMAS spectra of selectedregions along the ring, interpreted with evolutionary and populationsynthesis models, indicate that their ionized emission is mainly due toa young stellar population with a total mass of ~1.5 ×106 M sun, which started forming almost coevally~10 Myr ago. This stellar component is likely confined to thecollisional interface of a spherically expanding, starburst-drivensuper-bubble with denser, swept-up ambient gas, ~600 pc away from thecentral starburst nucleus. The spectroscopic properties of the latterimply a large extinction (CH?>0.9), and the presenceof an additional non-thermal ionization source, most likely alow-luminosity active galactic nucleus. Mrk 409 shows a relatively largeoxygen abundance (12 + log(O/H) ~ 8.4) and no chemical abundancegradients out to R ~ 600 pc. The ionized gas kinematics displays anoverall regular rotation on a northwest-southeast axis, with a maximumvelocity of 60 km s-1 the total mass inside thestar-forming ring is about 1.4 × 109 M sun.Based on observations obtained at the German-Spanish AstronomicalCenter, Calar Alto, operated by the Max-Planck-Institut fürAstronomie Heidelberg jointly with the Spanish National Commission forAstronomy.
| Mapping the starburst in blue compact dwarf galaxies. PMAS integral field spectroscopy of Mrk 1418
Aims: By means of optical integral field spectroscopy observations, weaim to differentiate and characterize the starburst component in theblue compact dwarf (BCD) galaxy Mrk 1418. In particular we propose tostudy the stellar and ionized gas morphology, to investigate theionization mechanism(s) acting in the interstellar medium, and to derivethe physical parameters and abundances of the ionized gas. Methods: Integral field spectroscopy observations of Mrk 1418 werecarried out with the Potsdam multi-aperture spectrophotometer (PMAS) atthe 3.5 m telescope at Calar Alto Observatory. The central 16arcsec×16 arcsec (1.14 × 1.14 kpc2 at thedistance of Mrk 1418) were mapped with a spatial sampling of 1 arcsec;we took data in the 3590-6996 Å spectral range, with a lineardispersion of 3.2 Å per pixel. The seeing was about 1farcs5. Fromthese data we built maps of the most prominent emission lines, namely [Oii], H?, [O iii], H?, [N ii], and [S ii], as well as ofseveral continuum bands, plus maps of the main line ratios: [Oiii]/H?, [N ii]/H?, [S ii]/H?, and H?/H?,and derived the physical parameters and gaseous metal abundances of thedifferent star-forming regions detected in the field of view. Results: Mrk 1418 shows a distorted morphology both in the continuumand in the ionized gas maps; the current star- formation episode istaking place in five knots, distributed around the nucleus of thegalaxy. The interstellar medium surrounding these knots is photo-ionizedby stars, with no clear evidence for other excitation mechanisms. Thegalaxy displays an inhomogeneous dust distribution, with the highH?/H? ratio in the central areas indicating a large amount ofdust. The oxygen abundances derived for the individual star-formingknots are very similar, suggesting that the ionized interstellar mediumis chemically homogeneous in O/H over spatial scales of hundreds ofparsecs. This abundance (Z ? 0.4 Z? from theempirical calibrations) places Mrk 1418 among the high metallicity BCDgroup. Conclusions: These findings show the advantages ofIFS when investigating the properties of such complex objects as BCDs,with an asymmetric star-forming component. Only a bidimensional mappingof their central regions allows approaching such questions as the starformation processes in BCDs, the star-forming history of the individualstarburst knots, or the abundance gradients.Based on observations obtained at the German-Spanish AstronomicalCenter, Calar Alto, operated by the Max-Planck-Institut fur AstronomieHeidelberg jointly with the Spanish National Commission for Astronomy.
| First-Year Sloan Digital Sky Survey-II Supernova Results: Hubble Diagram and Cosmological Parameters
We present measurements of the Hubble diagram for 103 Type Ia supernovae(SNe) with redshifts 0.04 < z < 0.42, discovered during the firstseason (Fall 2005) of the Sloan Digital Sky Survey-II (SDSS-II)Supernova Survey. These data fill in the redshift "desert" between low-and high-redshift SN Ia surveys. Within the framework of the MLCS2K2light-curve fitting method, we use the SDSS-II SN sample to infer themean reddening parameter for host galaxies, RV = 2.18± 0.14stat ± 0.48syst, and find thatthe intrinsic distribution of host-galaxy extinction is well fitted byan exponential function, P(AV ) = exp(-AV/τV), with τV = 0.334 ± 0.088 mag.We combine the SDSS-II measurements with new distance estimates forpublished SN data from the ESSENCE survey, the Supernova Legacy Survey(SNLS), the Hubble Space Telescope (HST), and a compilation of Nearby SNIa measurements. A new feature in our analysis is the use of detailedMonte Carlo simulations of all surveys to account for selection biases,including those from spectroscopic targeting. Combining the SN Hubblediagram with measurements of baryon acoustic oscillations from the SDSSLuminous Red Galaxy sample and with cosmic microwave backgroundtemperature anisotropy measurements from the Wilkinson MicrowaveAnisotropy Probe, we estimate the cosmological parameters w andΩM, assuming a spatially flat cosmological model(FwCDM) with constant dark energy equation of state parameter, w. Wealso consider constraints upon ΩM andΩΛ for a cosmological constant model(ΛCDM) with w = -1 and non-zero spatial curvature. For theFwCDM model and the combined sample of 288 SNe Ia, we find w =-0.76 ± 0.07(stat) ± 0.11(syst), ΩM= 0.307 ± 0.019(stat) ± 0.023(syst) using MLCS2K2 and w =-0.96 ± 0.06(stat) ± 0.12(syst), ΩM= 0.265 ± 0.016(stat) ± 0.025(syst) using the SALT-IIfitter. We trace the discrepancy between these results to a differencein the rest-frame UV model combined with a different luminositycorrection from color variations; these differences mostly affect thedistance estimates for the SNLS and HST SNe. We present detaileddiscussions of systematic errors for both light-curve methods and findthat they both show data-model discrepancies in rest-frame U band. Forthe SALT-II approach, we also see strong evidence forredshift-dependence of the color-luminosity parameter (β).Restricting the analysis to the 136 SNe Ia in the Nearby+SDSS-IIsamples, we find much better agreement between the two analysis methodsbut with larger uncertainties: w = -0.92 ±0.13(stat)+0.10 -0.33(syst) for MLCS2K2 andw = -0.92 ± 0.11(stat)+0.07-0.15 (syst) for SALT-II.
| NGC 2770: A Supernova Ib Factory?
NGC 2770 has been the host of three supernovae (SNe) of Type Ib duringthe last ten years, SN 1999eh, SN 2007uy, and SN 2008D. SN 2008Dattracted special attention due to the serendipitous discovery of anassociated X-ray transient. In this paper, we study the properties ofNGC 2770 and specifically the three SN sites to investigate whether thisgalaxy is in any way peculiar to cause a high frequency of SNe Ib. Wemodel the global spectral energy distribution of the galaxy frombroadband data and derive a star formation and SN rate comparable to thevalues of the Milky Way. We further study the galaxy using longslitspectroscopy covering the major axis and the three SN sites. From thespectroscopic study we find subsolar metallicities for the SN sites, ahigh extinction and a moderate star formation rate. In a high-resolutionspectrum, we also detect diffuse interstellar bands in the line of sighttoward SN 2008D. A comparison of NGC 2770 to the global properties of agalaxy sample with high SN occurrence (>= 3 SN in the last 100 years)suggests that NGC 2770 is not particularly destined to produce such anenhancement of observed SNe. Its properties are also very different fromgamma-ray burst host galaxies. Statistical considerations on SN Ibdetection rates give a probability of ~1.5% to find a galaxy with threeIb SNe detected in ten years. The high number of rare Ib SNe in thisgalaxy is therefore likely to be a coincidence rather than specialproperties of the galaxy itself. NGC 2770 has a small irregularcompanion, NGC 2770B, which is highly star-forming, has a very low massand one of the lowest metallicities detected in the nearby universe asderived from longslit spectroscopy. In the most metal poor part, we evendetect Wolf-Rayet (WR) features, which is at odds with most currentmodels of WR stars which require high metallicities.Based on observations with the Nordic Optical Telescope, ESO proposal080.D-0526, the GALEX and NED databases.
| A spectroscopic study of the blue stragglers in M67
Based on spectrophotometric observations from the Guillermo HaroObservatory (Cananea, Mexico), a study of the spectral properties of thecomplete sample of 24 blue straggler stars (BSs) in the old Galacticopen cluster M67 (NGC 2682) is presented. All spectra, calibrated usingspectral standards, were recalibrated by means of photometric magnitudesin the Beijing-Arizona-Taipei-Connecticut system, which includes fluxesin 11 bands covering ~3500-10000 Å. The set of parameters wasobtained using two complementary approaches that rely on a comparison ofthe spectra with (i) an empirical sample of stars with well-establishedspectral types and (ii) a theoretical grid of optical spectra computedat both low and high resolution. The overall results indicate that theBSs in M67 span a wide range in Teff(~ 5600 -12600 K) andsurface gravities that are fully compatible with those expected formain-sequence objects (log g = 3.5 -5.0 dex).
| The serendipituous discovery of a short-period eclipsing polar in 2XMMp
We report the serendipituous discovery of the new eclipsing polar 2XMMpJ131223.4+173659. Its striking X-ray light curve attracted immediateinterest when we were visually inspecting the source products of the2XMMp catalogue. This light curve revealed its likely nature as amagnetic cataclysmic variable of AM Herculis (or polar) type with anorbital period of ~92 min, which was confirmed by follow-up opticalspectroscopy and photometry. 2XMMp J131223.4+173659? probably has aone-pole accretion geometry. It joins the group of now nine objects thatshow no evidence of a soft component in their X-ray spectra despitebeing in a high accretion state, thus escaping ROSAT/EUVE detection. Wediscuss the likely accretion scenario, the system parameters, and thespectral energy distribution.Based on observations obtained with XMM-Newton, an ESAscience mission with instruments and contributions directly funded byESAMember States and NASA.
| Propagating Star Formation in the Collisional Ring Galaxy Arp 10
Propagating star formation in a collisional ring galaxy Arp 10 isinvestigated by a complex approach, which includes the broadband andnarrowband photometry, long-slit spectroscopy, and scanning Fabry-Perotspectroscopy. The ionized gas velocity field obtained with best spatialresolution to date indicates a nonisotropic expansion of the outer ringwith a maximum velocity 110 km s-1. Strong vertical andnoncircular motions are also seen in the vicinity of the inner ring. Ourkinematic data suggest that Arp 10 has a small inclinationi=22deg and high total mass (1012Msolar within a 50 kpc radius). The abundance of oxygen12+log(O/H) in both star-forming rings is about 8.6. The analysis ofspectral indices provides an estimate on the propagation velocities ofboth rings and metallicity of the precollision stellar population. Asmall ``knot'' near the nucleus of Arp 10 is unambiguously identified asthe ``intruder.'' The intruder spectrum suggests that it was a spiralgalaxy before the collision, and its present mass amounts to at leastone-fourth of the total mass of Arp 10. We use a simplifiedtwo-dimensional hydrodynamic modeling of galaxy collisions to test acollisional origin of Arp 10. The sizes of the inner and outer rings,maximum expansion velocity of the outer ring, and radial profile of thegas circular velocity can be reproduced by a near-central collision withthe intruder galaxy, which occurred approximately 85 Myr ago. Weacknowledge that an apparent crescent-shaped distribution of Hαemission in the outer ring is caused by a star formation threshold inthe gas disk of Arp 10.
| 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.
| Cometary activity of distant object C/2002 VQ94 (LINEAR)
Aims.We have started a program of spectroscopic and photometricinvestigations of distant active comets in the optical domain. Thecomets with a significant level of activity-in particular, extendedtails-are the objects of our observations. Methods: .Theobservations were made at the 6-m telescope BTA (SAO RAS, Russia), withthe focal reducer SCORPIO attached to the prime focus of the telescope.Long-slit and photometry modes were turned to perform our firstobservations. The spectral resolution in the spectroscopy mode was 10Å. Results: .The result of the spectrum analysis of cometC/2002 VQ94 (LINEAR) is of particular interest. The comet observed atthe heliocentric distance of 6.8 AU clearly shows a rich molecularspectrum. We identified 14 vibrational bands of CO+ (CometTail system), emissions of C3, and some tentatively assigned toN2+ and CN. It should be emphasized that, for now,CO+ and tentatively assigned N2+ emissions aredetected at a record heliocentric distance.
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| Electron Density and Turbulence Gradients within the Extended Atmosphere of the M Supergiant Betelgeuse (α Orionis)
The extended atmosphere of the M supergiant Betelgeuse is complex withcool plasma dominating the structure by mass and small amounts ofembedded hotter chromospheric plasma. A major challenge is to understandthe interrelationship and juxtaposition of these different components,which in turn may provide clues to the nature of the process ofnonradiative heating and the mechanisms that drive mass loss. We examinethe chromospheric C II] λ2325 multiplet emission line electrondensity diagnostic using spatially scanned HST STIS echelle spectra.Escape probability models for the electron density-sensitive line ratiosreveal that the mean electron density decreases by 0.6 dex as the sightline goes from disk center to +/-75 mas. Radiative transfer simulationsusing spherical model atmospheres show that this trend can be explainedif the electron density declines with radius by nearly 2 dex acrossΔR~2R*. The emission profiles indicate that thechromospheric material corotates with the star and then becomesdecoupled by +/-75 mas from disk center. We find no evidence for radialoutflow in the chromospheric plasma. We find that the strongest C II]λ2325 emission lines are opacity broadened and that the gradientof atmospheric turbulence is surprisingly small. Using empiricalconstraints, we derive a relation between the relative C II columndensities in the cool and chromospheric atmospheric components and theexcitation temperature. These UV chromospheric results and previousradio analyses suggest that the chromosphere is pervasive but has asmall filling factor at ~3R*, suggestive of confinement andheating in magnetic structures.
| Star Formation in Satellite Galaxies
We present narrowband observations of the Hα emission in a sampleof 31 satellites orbiting isolated giant spiral galaxies. The samplestudied spans the range -19 mag
| Variable Unidentified Emission near 6307 Å in η Carinae
We have discovered a conspicuous unidentified variable feature near 6307Å in the spectrum of η Carinae that is spatially unresolvedfrom the central star and its wind (r<~200-300 AU). It is significantfor two reasons: first, such prominent unidentified lines are now rarein this object, and second, this feature varies strongly andsystematically. It exhibits a combination of characteristics that, sofar as we know, are unique in η Carinae's spectrum. It may provideinsights into the recurrent spectroscopic events and the star'slong-term brightening.This research is part of the Hubble Space Telescope Treasury Project forη Carinae, supported by grants GO-9420 and GO-9973 from the SpaceTelescope Science Institute (STScI), which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.Partially based on observations obtained with UVES at the ESO Very LargeTelescope, Paranal, Chile (proposals 70.D-0607[A], 71.D-0168[A], and72.D-0524[A]).
| PMAS: The Potsdam Multi-Aperture Spectrophotometer. II. The Wide Integral Field Unit PPak
PPak is a new fiber-based integral field unit (IFU) developed at theAstrophysical Institute of Potsdam and implemented as a module into theexisting Potsdam Multi-Aperture Spectrophotometer (PMAS) spectrograph.The purpose of PPak is to provide an extended field of view with a largelight-collecting power for each spatial element, as well as an adequatespectral resolution. The PPak system consists of a fiber bundle with 331object fibers, 36 sky fibers, and 15 calibration fibers. The object andsky fibers collect the light from the focal plane behind a focal reducerlens. The object fibers of PPak, each 2.7" in diameter, provide acontiguous hexagonal field of view of 74" × 64" on the sky, with afilling factor of 60%. The operational wavelength range is from 400 to900 nm. The PPak IFU, together with the PMAS spectrograph, are intendedfor the study of extended, low surface brightness objects, offering anoptimization of total light-collecting power and spectral resolution.This paper describes the instrument design, the assembly, integration,and tests, the commissioning and operational procedures, and presentsthe measured performance at the telescope.
| Subluminous O Stars
We report results of spectral analyses of sdO stars selected from theSupernova Ia Progenitor Survey, the Hamburg Quasar Survey and the SloanDigital Sky Survey and based on state-of-the-art NLTE model atmospheres.By combining the sdO with the sdB samples we discuss trends of theatmospheric parameters in order to search for evidence for possibleevolutionary linkage. The He-sdO stars are found to cluster near Teff =45 000 K, log g = 5.5, whereas the number of sdO stars in this area isvery small. The ``cooler'' sdO stars seem to form an extension to thesdB sequences. A couple of sdO stars are obviously evolved from theextended horizontal branch and reach temperatures as high as 80 000 K.We conjecture that the He-sdO stars and sdO/sdB stars have a differentevolutionary origin. This is corroborated by the much lower binaryfrequency of the former. Strong enrichments of iron group elements arediscovered for hydrogen-rich sdO stars as well as for sdB stars fromhigh resolution UV spectra and have severe implications for thetemperature scale. We finally highlight the discovery of ahyper-velocity He-sdO star with a radial velocity of 708 kms unbound tothe Galaxy.
| 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.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Discovery of magnetic fields in hot subdwarfs
We present polarisation measurements of sdB and sdO stars using FORS1 onthe VLT. The observations were made as part of a project to determinewhether magnetic fields in two super-metal-rich stars can explain theirextreme abundance peculiarities. Field strengths of up to ~1.5 kG rangehave been measured at varying levels of significance in each of our sixtargets, however no clear evidence was found between apparently normalsubdwarfs and the metal-rich objects. The origin of the magnetic fieldsis unknown. We also discuss the implications of our measurements formagnetic flux conservation in late stages of stellar evolution.
| A Cross-Calibration between Tycho-2 Photometry and Hubble Space Telescope Spectrophotometry
By analyzing a well-calibrated sample of 256 stars observed with bothHipparcos and HST, I show that Tycho-2 photometry and HSTspectrophotometry are accurate and stable enough to obtain a precisecross-calibration. Based on this analysis, I obtain the followingphotometric zero points with respect to Vega for Tycho-2: 0.020+/-0.001(BT-VT), 0.078+/-0.009 (BT), and0.058+/-0.009 (VT).
| Short time-scale optical variability of the dwarf Seyfert nucleus in NGC 4395
We present optical spectroscopic observations of the least-luminousknown Seyfert 1 galaxy, NGC 4395, which was monitored every half-hourover the course of three nights. The continuum emission varied by ~35per cent over the course of three nights and we find marginal evidencefor greater variability in the blue continuum than the red. A number ofdiagnostic checks were performed on the data in order to constrain anysystematic or aperture effects. No correlations were found thatadequately explained the observed variability, hence we conclude that wehave observed real intrinsic variability of the nuclear source. Nosimultaneous variability was measured in the broad H? line,although given the difficulty in deblending the broad and narrowcomponents it is difficult to comment on the significance of thisresult. The observed short time-scale continuum variability isconsistent with NGC 4395 having an intermediate-mass(~105Msolar) central supermassive black hole,rather than a very low accretion rate. Comparison with the Seyfert 1galaxy NGC 5548 shows that the observed variability seems to scale withblack hole mass in roughly the manner expected in accretion models.However, the absolute time-scale of variability differs by severalorders of magnitude from that expected in simple accretion disc modelsin both cases.
| A Study of the Near-Ultraviolet Spectrum of Vega
UV, optical, and near-IR spectra of Vega have been combined to test ourunderstanding of stellar atmospheric opacities and to examine thepossibility of constraining chemical abundances from low-resolution UVfluxes. We have carried out a detailed analysis assuming localthermodynamic equilibrium (LTE) to identify the most importantcontributors to the UV continuous opacity: H, H-, C I, and SiII. Our analysis also assumes that Vega is spherically symmetric andthat its atmosphere is well described with the plane-parallelapproximation. By comparing observations and computed fluxes, we havebeen able to discriminate between two different flux scales that havebeen proposed, the IUE-INES and the HST scales; we favor the latter. Theeffective temperature and angular diameter derived from the analysis ofobserved optical and near-UV spectra are in very good agreement withprevious determinations based on different techniques. The siliconabundance is poorly constrained by the UV observations of the continuumand strong lines, but the situation is more favorable for carbon, andthe abundances inferred from the UV continuum and optical absorptionlines are in good agreement. Some spectral intervals in the UV spectrumof Vega poorly reproduced by the calculations are likely affected bydeviations from LTE, but we conclude that our understanding of UVatmospheric opacities is fairly complete for early A-type stars.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| Rotationally Supported Virgo Cluster Dwarf Elliptical Galaxies: Stripped Dwarf Irregular Galaxies?
New observations of 16 dwarf elliptical galaxies (dEs) in the VirgoCluster indicate that at least seven dEs have significant velocitygradients along their optical major axis, with typical rotationamplitudes of 20-30 km s-1. Of the remaining nine galaxies inthis sample, six have velocity gradients of less than 20 kms-1 kpc-1, while the other three observations hadtoo low a signal-to-noise ratio to determine an accurate velocitygradient. Typical velocity dispersions for these galaxies are ~44+/-5 kms-1, indicating that rotation can be a significant componentof the stellar dynamics of Virgo dEs. When corrected for the limitedspatial extent of the spectral data, the rotation amplitudes of therotating dEs are comparable to those of similar-brightness dwarfirregular galaxies (dIs). Evidence of a relationship between therotation amplitude and galaxy luminosity is found and, in fact, agreeswell with the Tully-Fisher relation. The similarity in the scalingrelations of dIs and dEs implies that it is unlikely that dEs evolvefrom significantly more luminous galaxies. These observations reaffirmthe possibility that some cluster dEs may be formed when the neutralgaseous medium is stripped from dIs in the cluster environment. Wehypothesize that several different mechanisms are involved in thecreation of the overall population of dEs and that stripping ofinfalling dIs may be the dominant process in the creation of dEs inclusters like Virgo.
| Keck spectroscopy of Cosmic Lens All-Sky Survey gravitational lenses
We present the optical spectra of four newly discovered gravitationallenses from the Cosmic Lens All-Sky Survey (CLASS). These observationswere carried out using the Low-Resolution Imaging Spectrograph on the W.M. Keck-I Telescope as part of a programme to study galaxy-scalegravitational lenses. From our spectra, we found the redshift of thebackground source in CLASS B0128+437 (zs= 3.1240 +/- 0.0042)and the lensing galaxy redshifts in CLASS B0445+123 (z1=0.5583 +/- 0.0003) and CLASS B0850+054 (zl= 0.5883 +/-0.0006). Intriguingly, we also discovered that CLASS B0631+519 may havetwo lensing galaxies (zl,1= 0.0896 +/- 0.0001,zl,2= 0.6196 +/- 0.0004). We also found a single unidentifiedemission line from the lensing galaxy in CLASS B0128+437 and the lensedsource in CLASS B0850+054. We find the lensing galaxies in CLASSB0445+123 and CLASS B0631+519 (l, 2) to be early-type galaxies withEinstein radii of 2.8-3.0 h-1 kpc. The deflector in CLASSB0850+054 is a late-type galaxy with an Einstein radius of 1.6h-1 kpc.
| Terminal Velocities of Luminous, Early-Type Stars in the Small Magellanic Cloud
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS)are used to determine terminal velocities for 11 O and B-type giants andsupergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IVresonance lines. Using archival data from observations with the GoddardHigh-Resolution Spectrograph and the International Ultraviolet Explorertelescope, terminal velocities are obtained for a further five B-typesupergiants. We discuss the metallicity dependence of stellar terminalvelocities for supergiants, finding no evidence for a significantscaling between Galactic and SMC metallicities forTeff<30,000 K, consistent with the predictions ofradiation-driven wind theory. A comparison of thev&infy;/vesc ratio between the SMC and Galacticsamples, while consistent with the above statement, emphasizes that theuncertainties in the distances to galactic OB-type stars are a seriousobstacle to a detailed comparison with theory. For the SMC sample thereis considerable scatter in v&infy;/vesc at agiven effective temperature, perhaps indicative of uncertainties instellar masses.
| DW Cancri: a magnetic VY Scl star with an orbital period of 86 min
We present the first time-resolved spectroscopic study of thecataclysmic variable DW Cancri. We have determined an orbital period of86.10 +/- 0.05 min, which places the system very close to the observedminimum period of hydrogen-rich cataclysmic variables. This invalidatesprevious speculations of DW Cnc being either a permanent superhumperbelow the period minimum or a nova-like variable with an orbital periodlonger than 3 h showing quasi-periodic oscillations. The Balmer and HeIlines have double-peaked profiles and exhibit an intense S-wavecomponent moving with the orbital period. Remarkably, the Balmer and HeIradial velocity curves are modulated at two periods: 86.10 +/- 0.05(orbital) and 38.58 +/- 0.02 min. The same short period is found in theequivalent width variations of the single-peaked HeII 4686 line. We alsopresent time-resolved photometry of the system which shows a highlycoherent variation at 38.51 min, consistent with the short spectroscopicperiod. The large number of similarities with the short-periodintermediate polar V1025 Cen lead us to suggest that DW Cnc is anotherintermediate polar below the period gap, and we tentatively identify thephotometric and spectroscopic 38-min signals with the white dwarf spinperiod. DW Cnc has never been observed to undergo an outburst, but itoccasionally exhibits low states ~2 mag fainter than its typicalbrightness level of V~= 14.5, resembling the behaviour of the highmass-transfer VY Scl stars.
| The Rapidly Rotating, Hydrogen-deficient, Hot Post-Asymptotic Giant Branch Star ZNG 1 in the Globular Cluster M5
We report observations of the hot post-asymptotic giant branch star ZNG1 in the globular cluster M5 (NGC 5904) with the Far UltravioletSpectroscopic Explorer. From the resulting spectrum, we derive aneffective temperature Teff = 44300+/-300 K, a surface gravitylogg = 4.3+/-0.1, a rotational velocity vsini = 170+/-20 kms-1, and a luminosity log(L/Lsolar)=3.52+/-0.04.The atmosphere is helium-rich (Y=0.93), with enhanced carbon (2.6% bymass), nitrogen (0.51%), and oxygen (0.37%) abundances. The spectrumshows evidence of a wind with a terminal velocity near 1000 kms-1 and an expanding shell of carbon- and nitrogen-richmaterial around the star. The abundance pattern of ZNG 1 is suggestiveof the ``born-again'' scenario, whereby a star on the white dwarfcooling curve undergoes a very late shell flash and returns to theasymptotic giant branch, but the star's rapid rotation is more easilyexplained by a previous interaction with a binary companion.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer, which is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| INTEGRAL spectroscopy of three powerful radio galaxies: jet-cloud interactions seen in three dimensions
Integral-field spectroscopic observations are presented for threepowerful radio galaxies, namely 3C 277.3 (Coma A; z= 0.0857), 3C 171 (z=0.2384) and 3C 265 (z= 0.811), which are known to be undergoingjet-cloud interactions. The morphology, kinematics and ionization of thegas in the emission-line structure of these sources are mapped andanalysed. One-dimensional spectra are also extracted and integrated overthe different emission-line regions in each galaxy.In two of the galaxies (3C277.3 and 3C171) the radio sizes are ofsimilar extent to the emission-line structure. For these, enhancedemission-line regions are found associated with the radio structures, inaddition to complex kinematics and low ionization states close to theradio hotspots, indicating that jet-induced shocks disturb and ionizethe gas. Interestingly, the bright - presumably shock-ionized -emission-line region coincident with the radio jet knot in 3C277.3 showsquiescent kinematics and high ionization state. Possible explanationsfor this puzzling result are proposed.The images of 3C171 and 3C265 indicate that the lateral expansion of thecocoon has a significant effect on the kinematics and ionization of thegas, showing for the first time that the effects of the radio source arefelt far from the jet axis.In addition, the presence of a stellar-photoionized HII region isdetected in the extended emission-line nebula of the radio galaxy3C277.3.
| The Photospheric Absorption Lines in the Ultraviolet Spectrum of the Multiple System HD 5980
We search for radial velocity variations in the ultraviolet spectra ofthe erupting Wolf-Rayet/luminous blue variable system HD 5980, locatedin the Small Magellanic Cloud. We obtain an average radial velocity of22+/-22 km s-1 for five observations in 1999 at differentorbital phases, -39+/-24 km s-1 for one observation in 2001,and 20+/-45 km s-1 for one observation in 2002. Thesevelocities are with respect to the SMC O3 star MPG 355, which is used asone of the templates. Hence, radial velocity variations on the 19.265day (star A+star B) orbital timescale attributable to the erupting star(star A) of the system are not detected, thus confirming that thevisible absorption lines in the spectrum have their origin in a thirdstellar component (star C). We propose that star A has very broad(vsini~250 km s-1) absorption lines, which would escapedetection in the complicated emission-line spectrum of the system. Suchbroad lines, combined with the 128 km s-1 orbital motion,would lead to a lower amplitude fictitious radial velocity curve whenthe stationary set of absorption lines is measured. We conclude thatline profile variations at orbital phase 0.0 from one epoch ofobservations to another are associated with these broad underlyingabsorption lines, arising in the unstable photosphere of star A. Theanalysis is performed with the aid of synthetic UV spectra that arecalculated from LTE line-blanketed atmosphere models, and the HST SpaceTelescope Imaging Spectrograph spectra of four O-type stars in thecluster NGC 346, to which HD 5980 is believed to belong. We estimateTeff and obtain values of vsini and the mean radial velocityfor MPG 324 [O4 V((f))], MPG 368 [O4-5 V((f))], MPG 355 [O3 V(f*)], andMPG 113 (OC 6Vz). Based on observations with the NASA/ESA Hubble SpaceTelescope obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Zsiráf |
| Rektaszcenzió: | 08h10m49.50s |
| Deklináció: | +74°57'57.9" |
| Vizuális fényesség: | 9.481 |
| RA sajátmozgás: | 9.1 |
| Dec sajátmozgás: | 10.6 |
| B-T magnitude: | 9.139 |
| V-T magnitude: | 9.453 |
Katalógusok és elnevezések:
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