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Ýlgili Makaleler
The Spectroscopic Diversity of Type Ia Supernovae
We present 2603 spectra of 462 nearby Type Ia supernovae (SNe Ia),including 2065 previously unpublished spectra, obtained during 1993-2008through the Center for Astrophysics Supernova Program. There are onaverage eight spectra for each of the 313 SNe Ia with at least twospectra. Most of the spectra were obtained with the FAST spectrograph atthe Fred Lawrence Whipple Observatory 1.5 m telescope and reduced in aconsistent manner, making this data set well suited for studies of SN Iaspectroscopic diversity. Using additional data from the literature, westudy the spectroscopic and photometric properties of SNe Ia as afunction of spectroscopic class using the classification schemes ofBranch et al. and Wang et al. The width-luminosity relation appears tobe steeper for SNe Ia with broader lines, although the result is notstatistically significant with the present sample. Based on theevolution of the characteristic Si II ?6355 line, we proposeimproved methods for measuring velocity gradients, revealing a largerrange than previously suspected, from ~0 to ~400 km s-1day-1 considering the instantaneous velocity declinerate at maximum light. We find a weaker and less significant correlationbetween Si II velocity and intrinsic B - V color at maximum lightthan reported by Foley et al., owing to a more comprehensive treatmentof uncertainties and host galaxy dust. We study the extent of nuclearburning and the presence of unburnt carbon in the outermost layers ofthe ejecta and report new detections of C II ?6580 in 23early-time SN Ia spectra. The frequency of C II detections is not higherin SNe Ia with bluer colors or narrower light curves, in conflict withthe recent results of Thomas et al. Based on nebular spectra of 27 SNeIa, we find no relation between the FWHM of the iron emission feature at~4700 Å and ?m 15(B) after removing the twolow-luminosity SN 1986G and SN 1991bg, suggesting that the peakluminosity is not strongly dependent on the kinetic energy of theexplosion for most SNe Ia. Finally, we confirm the correlation ofvelocity shifts in some nebular lines with the intrinsic B - Vcolor of SNe Ia at maximum light, although several outliers suggest apossible non-monotonic behavior for the largest blueshifts.Based in part on observations obtained at the F. L. Whipple Observatory,which is operated by the Smithsonian Astrophysical Observatory, the MMTObservatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona, and with the 6.5 m Magellan Telescopeslocated at Las Campanas Observatory, Chile.
| Ultraviolet Properties of Galactic Globular Clusters with GALEX. I. The Color-Magnitude Diagrams
We present Galaxy Evolution Explorer (GALEX) data for 44 Galacticglobular clusters (GCs) obtained during three GALEX observing cyclesbetween 2004 and 2008. This is the largest homogeneous data set on theUV photometric properties of Galactic GCs ever collected. The sampleselection and photometric analysis are discussed, and color-magnitudediagrams (CMDs) are presented. The blue and intermediate-blue horizontalbranch is the dominant feature of the UV CMDs of old Galactic GCs. Oursample is large enough to display the remarkable variety of horizontalbranch shapes found in old stellar populations. Other stellar types thatare obviously detected are blue stragglers and post-core-He burningstars. The main features of UV CMDs of Galactic GCs are brieflydiscussed. We establish the locus of post-core-He burning stars in theUV CMD and present a catalog of candidate asymptotic giant branch (AGB),AGB-manqué, post early-AGB, and post-AGB stars within our clustersample.The authors dedicate this paper to the memory of co-author Bob Rood, apioneer in the theory of the evolution of low-mass stars, and a friend,who sadly passed away on 2011 November 2.
| Characteristics of Star-forming Regions in the Advanced Minor-merger, Luminous Infrared Galaxy NGC 4194
We report the results of long-slit spectroscopy at position angles68°, 131°, and 164° for the minor-merger NGC 4194, aluminous infrared starburst galaxy. The mass within 1.2 kpc of thedynamical center is estimated to be 4.8 × 109 to 1.7× 1010 M &sun;, depending on the assumedinclination to the plane of the sky. The star formation rate (SFR) inthe areas sampled is 8 M &sun; yr-1. Themetallicity, log(O/H) + 12, ranges from ~8.8 to >9.0 in regions ofsignificant star formation, suggesting that the metallicity has beenenhanced by the current star formation. The star-forming regions rangein age from 5 to 9 Myr, with the youngest ages occurring in the regionsof high SFR. Electron temperatures and the location of the spectra inemission line diagnostic diagrams suggest the presence of shock waves,presumably due to the presence of supernovae, winds from massive stars,and/or collisions of clouds due to the merger. The presence of massivestars and supernovae is consistent with the ages determined for thestar-forming regions. The ages of the continua produced by the stellarpopulation are estimated to range from 10 Myr to 5 Gyr. Much of thestellar population represented in the continua was probably formedbefore the merger and represents the progenitor galaxies.
| Quantitative Spectroscopy of Blue Supergiant Stars in the Disk of M81: Metallicity, Metallicity Gradient, and Distance
The quantitative spectral analysis of low-resolution (~5 Å) KeckLRIS spectra of blue supergiants in the disk of the giant spiral galaxyM81 is used to determine stellar effective temperatures, gravities,metallicities, luminosities, interstellar reddening, and a new distanceusing the flux-weighted gravity-luminosity relationship. Substantialreddening and extinction are found with E(B - V) ranging between0.13 and 0.38 mag and an average value of 0.26 mag. The distance modulusobtained after individual reddening corrections is 27.7 ± 0.1mag. The result is discussed with regard to recently measured tip of thered giant branch and Cepheid distances. The metallicities (based onelements such as iron, titanium, magnesium) are supersolar (?0.2 dex)in the inner disk (R lsim 5 kpc) and slightly subsolar (? -0.05 dex) in the outer disk (R gsim 10 kpc) with a shallow metallicitygradient of 0.034 dex kpc-1. The comparison withpublished oxygen abundances of planetary nebulae and metallicitiesdetermined through fits of Hubble Space Telescope color-magnitudediagrams indicates a late metal enrichment and a flattening of theabundance gradient over the last 5 Gyr. This might be the result of gasinfall from metal-rich satellite galaxies. Combining these M81metallicities with published blue supergiant abundance studies in theLocal Group and the Sculptor Group, a galaxy mass-metallicityrelationship based solely on stellar spectroscopic studies is presentedand compared with recent studies of Sloan Digital Sky Surveystar-forming galaxies.
| New insights on Stephan's Quintet: exploring the shock in three dimensions
Aims: We study the ionized gas emission from the large scaleshock region of Stephan's Quintet (SQ). Methods: We carried outintegral field unit (IFU) optical spectroscopy on three pointings in andnear the SQ shock. We used Potsdam MultiAperture Spectrometer (PMAS) onthe 3.5 m Calar Alto telescope to obtain measures of emission lines thatprovide insight into physical properties of the gas. Severe blending ofH? and [Nii]?6548, 6583 Å emission lines in manyspaxels required the assumption of at least two kinematical componentsto extract fluxes for the individual lines. Results: The mainresults from our study include (a) detection of discrete emissionfeatures in the new intruder velocity range 5400-6000 km s-1showing properties consistent with Hii regions, (b) detection of alow-velocity component spanning the range 5800-6300 km s-1with properties resembling a solar-metallicity shocked gas and (c)detection of a high-velocity component at ?6600 km s-1with properties consistent with those of a low-metallicity shocked gas. Conclusions: The two shocked components are interpreted asproducts of a collision between NGC 7318b new intruder and a debrisfield in its path. This has given rise to a complex structure of ionizedgas where several components with different kinematical and physicalproperties coexist, although part of the original interstellar medium(ISM) associated with NGC 7318b is still present and remains unaltered.Our observations suggest that the low-velocity ionized component mighthave existed before the new intruder collision and could be associatedwith the NW-LV Hi component. The high-velocity ionized component mightfill the gap between the Hi complexes observed in SQ-A and NGC 7319'stidal filament (NW-HV, Arc-N and Arc-S in Williams et al. 2002, AJ, 123,2417).Based on observations taken at the 3.5 m telescope at Calar AltoObservatory.Tables 1-5, Figs. 12-19 and Appendix A are available inelectronic form at http://www.aanda.org
| CALIFA, the Calar Alto Legacy Integral Field Area survey. I. Survey presentation
The final product of galaxy evolution through cosmic time is thepopulation of galaxies in the local universe. These galaxies are alsothose that can be studied in most detail, thus providing a stringentbenchmark for our understanding of galaxy evolution. Through the hugesuccess of spectroscopic single-fiber, statistical surveys of the LocalUniverse in the last decade, it has become clear, however, that anauthoritative observational description of galaxies will involvemeasuring their spatially resolved properties over their full opticalextent for a statistically significant sample. We present here the CalarAlto Legacy Integral Field Area (CALIFA) survey, which has been designedto provide a first step in this direction. We summarize the survey goalsand design, including sample selection and observational strategy. Wealso showcase the data taken during the first observing runs (June/July2010) and outline the reduction pipeline, quality control schemes andgeneral characteristics of the reduced data. This survey is obtainingspatially resolved spectroscopic information of a diameter selectedsample of ~600 galaxies in the Local Universe (0.005 < z < 0.03).CALIFA has been designed to allow the building of two-dimensional mapsof the following quantities: (a) stellar populations: ages andmetallicities; (b) ionized gas: distribution, excitation mechanism andchemical abundances; and (c) kinematic properties: both from stellar andionized gas components. CALIFA uses the PPAK integral field unit (IFU),with a hexagonal field-of-view of ~1.3⎕', with a 100% coveringfactor by adopting a three-pointing dithering scheme. The opticalwavelength range is covered from 3700 to 7000 Å, using twooverlapping setups (V500 and V1200), with different resolutions: R ~ 850and R ~ 1650, respectively. CALIFA is a legacy survey, intended for thecommunity. The reduced data will be released, once the quality has beenguaranteed. The analyzed data fulfillthe expectations of the originalobserving proposal, on the basis of a set of quality checks andexploratory analysis: (i) the final datacubes reach a 3? limitingsurface brightness depth of ~23.0 mag/arcsec2 for the V500grating data (~22.8 mag/arcsec2 for V1200); (ii) about ~70%of the covered field-of-view is above this 3? limit; (iii) thedata have a blue-to-red relative flux calibration within a few percentin most of the wavelength range; (iv) the absolute flux calibration isaccurate within ~8%with respect to SDSS; (v) the measured spectralresolution is ~85 km s-1 for V1200 (~150 km s-1for V500); (vi) the estimated accuracy of the wavelength calibration is~5 km s-1 for the V1200 data (~10 km s-1 for theV500 data); (vii) the aperture matched CALIFA and SDSS spectra arequalitatively and quantitatively similar. Finally, we show that we areable to carry out all measurements indicated above, recovering theproperties of the stellar populations, the ionized gas andthe kinematicsof both components. The associated maps illustrate the spatial variationof these parameters across the field, reemphasizing the redshiftdependence of single aperture spectroscopic measurements. We concludefrom this first look at the data that CALIFA will be an importantresource for archaeological studies of galaxies in the Local Universe.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by theMax-Planck-Institut für Astronomie and the Instituto deAstrofísica de Andalucía (CSIC).
| The GALEX Arecibo SDSS Survey. V. The Relation between the H I Content of Galaxies and Metal Enrichment at Their Outskirts
We have obtained long-slit spectra of 174 star-forming galaxies withstellar masses greater than 1010 M &sun; fromthe GALEX Arecibo Sloan Digital Sky Survey (GASS) survey. These galaxieshave both H I and H2 mass measurements. The averagemetallicity profile is strikingly flat out to R 90, theradius enclosing 90% of the r-band light. Metallicity profiles whichdecline steadily with radius are found primarily for galaxies in oursample with low stellar mass (log(M *) < 10.2),concentration, and/or mean stellar mass density. Beyond ~R90, however, around 10% of the galaxies in our sample exhibita sharp downturn in metallicity. Remarkably, we find that the magnitudeof the outer metallicity drop is well correlated with the total H Icontent of the galaxy (measured as f H I = M H I/M *). We examine the radial profiles of stellarpopulation ages and star formation rate densities, and conclude that thegalaxies with largest outer metallicity drops are actively growing theirstellar disks, with mass-doubling times across the whole disk onlyone-third as long as a typical GASS galaxy. We also describe acorrelation between local stellar mass density and metallicity, which isvalid across all galaxies in our sample. We argue that much of therecent stellar mass growth at the edges of these galaxies can be linkedto the accretion or radial transport of relatively pristine gas frombeyond the galaxies' stellar disks.
| Hoag's Object: evidence for cold accretion on to an elliptical galaxy
We present new photometric and spectroscopic observations of the famousHoag's Object, a peculiar ring galaxy with a central roundish core. Thenature of Hoag's Object is still under controversy. Previous studiesdemonstrated that a major accretion event that took place at least 2-3Gyr ago can account for the observational evidence. However, the role ofinternal non-linear mechanisms in forming the outer ring was not yetcompletely ruled out.The observations reported here consist of WFPC2 optical data retrievedfrom the Hubble Space Telescope archive as well as long-slit and 3Dspectroscopic data obtained at the Russian BTA 6-m telescope. These newdata, together with H I and optical information from the literature, areused to demonstrate that Hoag's Object is a relatively isolated systemsurrounded by a luminous quasi-spiral pattern and a massive, low-densityH I disc. The main stellar body is an old, mildly triaxial ellipticalgalaxy with very high angular momentum.We review previous formation scenarios of Hoag's Object in light of thenew data and conclude that the peculiar morphology could not represent alate phase in barred early-type galaxies evolution. In addition, noobservational evidence supports late merging events in the evolution ofthe galaxy, although further tests are required before safely dismissingthis idea. Combining all the information, we propose a new scenariowhere the elliptical core formed in the early Universe with the H I discforming shortly after the core by prolonged 'cold' accretion ofprimordial gas from the intergalactic medium.The low gas density does not allow intense star formation to occureverywhere in the disc, but only along a tightly wound spiral pattern ofenhanced density induced by the triaxial gravitational potential.According to this view, the physical mechanism that forms rings inHoag-like galaxies is closely linked with that in some non-barred discgalaxies, although the formation and evolution of both classes ofgalaxies are clearly distinct. Whether or not this unique evolutionarytrack is related to the galaxy residing in an underdensed environmentremains to be solved. A detailed H I mapping of Hoag's Object and itsenvironment is required to test our hypothesis and to examine the natureof the H I disc.
| Galactic S Stars: Investigations of Color, Motion, and Spectral Features
Known bright S stars, recognized as such by their enhanced s-processabundances and C/O ratio, are typically members of the asymptotic giantbranch (AGB) or the red giant branch. Few modern digital spectra forthese objects have been published, from which intermediate resolutionspectral indices and classifications could be derived. For published Sstars, we find accurate positions using the Two-Micron All Sky Survey(2MASS), and use the FAST spectrograph of the Tillinghast reflector onMt. Hopkins to obtain the spectra of 57 objects. We make available adigital S star spectral atlas consisting of 14 spectra of S stars withdiverse spectral features. We define and derive basic spectral indicesthat can help distinguish S stars from late-type (M) giants and carbonstars. We convolve all our spectra with the Sloan Digital Sky Surveybandpasses, and employ the resulting gri magnitudes together with 2MASSJHKs mags to investigate S star colors. These objects havecolors similar to carbon and M stars, and are therefore difficult todistinguish by color alone. Using near- and mid-infrared colors fromIRAS and Akari, we identify some of the stars as intrinsic (AGB) orextrinsic (with abundances enhanced by past mass transfer). We also useV band and 2MASS magnitudes to calculate a temperature index for starsin the sample. We analyze the proper motions and parallaxes of oursample stars to determine upper and lower limit absolute magnitudes anddistances, and confirm that most are probably giants.
| A new planetary nebula in the outer reaches of the Galaxy
Aims: A proper determination of the abundance gradient in theMilky Way requires the observation of objects at large galactiocentricdistances. With this aim, we are exploring the planetary nebulapopulation towards the Galactic anticentre. In this article, thediscovery and physico-chemical study of a new planetary nebula towardsthe anticentre direction, IPHASX J052531.19+281945.1 (PNG 178.1-04.0),is presented. Methods: The planetary nebula was discovered fromthe IPHAS survey. Long-slit follow-up spectroscopy was carried out toconfirm its planetary nebula nature and to calculate its physical andchemical characteristics. Results: The newly discovered planetarynebula turned out to be located at a very large galactocentric distance(DGC = 20.8 ± 3.8 kpc), larger than any previouslyknown planetary nebula with measured abundances. Its relatively highoxygen abundance (12+log(O/H) = 8.36 ± 0.03) supports aflattening of the Galactic abundance gradient at large galactocentricdistances rather than a linearly decreasing gradient.
| On the nature of the H II regions in the extended ultraviolet disc of NGC 4625
Using deep Subaru/Faint Object Camera And Spectrograph (FOCAS) spectraof 34 H II regions in both the inner and outer parts of the extendedultraviolet (XUV) disc galaxy NGC 4625 we have measured an abundancegradient out to almost 2.5 times the optical isophotal radius. Weapplied several strong line abundance calibrations to determine the H IIregion abundances, including R23, [N II]/[O II], [NII]/H? as well as the [O III] ?4363 auroral line, which wedetected in three of the H II regions. We find that at the transitionbetween the inner and outer disc the abundance gradient becomes flatter.In addition, there appears to be an abundance discontinuity in proximityof this transition. Several of our target H II regions appear to deviatefrom the ionization sequence defined in the [N II]/H? versus [OIII]/H? diagnostic diagram by bright extragalactic H II regions.Using theoretical models we conclude that the most likely explanationsfor these deviations are either related to the time evolution of the HII regions or stochastic variations in the ionizing stellar populationsof these low-mass H II regions, although we are unable to distinguishbetween these two effects. Such effects can also impact on thereliability of the strong line abundance determinations.
| The Line Polarization within a Giant Ly? Nebula
Recent theoretical work has suggested that Ly? nebulae could besubstantially polarized in the Ly? emission line, depending on thegeometry, kinematics, and powering mechanism at work. Polarizationobservations can therefore provide a useful constraint on the source ofionization in these systems. In this Letter, we present the firstLy? polarization measurements for a giant Ly? nebula atz? 2.656. We do not detect any significant linear polarization of theLy? emission: P Ly? = 2.6% ± 2.8%(corrected for statistical bias) within a single large aperture. Thecurrent data also do not show evidence for the radial polarizationgradient predicted by some theoretical models. These results rule outsingly scattered Ly? (e.g., from the nearby active galacticnucleus, AGN) and may be inconsistent with some models of backscatteringin a spherical outflow. However, the effects of seeing, diminishedsignal-to-noise ratio, and angle averaging within radial bins make itdifficult to put strong constraints on the radial polarization profile.The current constraints may be consistent with higher density outflowmodels, spherically symmetric infall models, photoionization by starformation within the nebula or the nearby AGN, resonant scattering, ornon-spherically symmetric cold accretion (i.e., along filaments). Highersignal-to-noise ratio data probing to higher spatial resolution willallow us to harness the full diagnostic power of polarizationobservations in distinguishing between theoretical models of giantLy? nebulae.
| Ejection velocities of high Galactic latitude runaway stars
We estimate the distribution of ejection velocities for the knownpopulation of high Galactic latitude runaway stars. The initial sampleis a collection of 174 early-type stars selected from the literature.The stars are first classified according to their evolutionary status inorder to obtain a homogeneous sample of 96 genuine main-sequence stars.Their present velocities and flight times are then estimated usingproper motion data from various astrometric catalogues (includingTycho-2, UCAC2 and USNO-B) and the ejection velocities are computed bytracing their orbits back in time, based on a Galactic potential. Thepotential used is constructed from a mass density model chosen to fitthe most recent observational constraints.We find evidence for two different populations of runaway stars: a'high' velocity population, with a maximum ejection velocity of about400-500 km s-1, and a 'low' velocity population, with amaximum ejection velocity of about 300 km s-1. We argue thatthe observed limit of 500 km s-1 and the bimodality of theobserved ejection velocity distribution are natural consequences of theso-called Binary Ejection Mechanism. We discuss the connection betweenthe 'high' velocity population and the so-called hypervelocity stars,showing how previously studied hypervelocity stars are consistent withthe results obtained.We also find that some stars that were once thought to be best explainedas being formed in the halo are compatible with a runaway hypothesisonce proper motions are included in the analysis. However, three starsin the selected sample appear to be inconsistent with ejection from theGalactic disc. Possible scenarios are discussed, including a possibleformation in the Galactic halo.
| The Subaru Ly? blob survey: a sample of 100-kpc Ly? blobs at z= 3
We present results of a survey for giant Ly? blobs (LABs) at z= 3with Subaru/Suprime-Cam. We obtained Ly? imaging at z= 3.09± 0.03 around the SSA22 protocluster and in several blank fields.The total survey area is 2.1 deg2, corresponding to acomoving volume of 1.6 × 106 Mpc3. Using auniform detection threshold of 1.4 × 10-18 ergs-1 cm-2 arcsec-2 for the Ly?images, we construct a sample of 14 LAB candidates with major-axisdiameters larger than 100 kpc, including five previously known blobs andtwo known quasars. This survey triples the number of known LABs over 100kpc. The giant LAB sample shows a possible `morphology-densityrelation': filamentary LABs reside in average density environments asderived from compact Ly? emitters, while circular LABs reside inboth average density and overdense environments. Although it is hard toexamine the formation mechanisms of LABs only from the Ly?morphologies, more filamentary LABs may relate to cold gas accretionfrom the surrounding intergalactic medium (IGM) and more circular LABsmay relate to large-scale gas outflows, which are driven by intensestarbursts and/or by active galactic nucleus activities. Our surveyhighlights the potential usefulness of giant LABs to investigate theinteractions between galaxies and the surrounding IGM from the field tooverdense environments at high redshift. a The 1?surface brightness limit (10-18 erg s-1cm-2 arcsec-2). b The 5?limiting magnitude calculated with 2-arcsec-diameter aperturephotometry.
| Dark spot, spiral waves and the SW Sextantis behaviour: it is all about UX Ursae Majoris
We present an analysis of time-resolved, medium-resolution opticalspectroscopic observations of UX Ursae Majoris (UX UMa) in the blue(3920-5250 Å) and red (6100-7200 Å) wavelength ranges thatwere obtained in 1999 April and 2008 March, respectively. The observedcharacteristics of our spectra indicate that UX UMa has been indifferent states during those observations. The blue spectra are verycomplex. They are dominated by strong and broad single-peaked emissionlines of hydrogen. The high-excitation lines of He II ?4686 andthe Bowen blend are quite strong as well. All the lines consist of amixture of absorption and emission components. Using Doppler tomography,we have identified four distinct components of the system: the accretiondisc, the secondary star, the bright spot from the gas stream/discimpact region and the unique compact area of absorption in the accretiondisc seen as a dark spot in the lower left-hand quadrant of thetomograms. In the red wavelength range, both the hydrogen (H?) andneutral helium (He I ?6678 and He I ?7065) lines wereobserved in emission and both exhibited double-peaked profiles. Dopplertomography of these lines reveals spiral structure in the accretiondisc, but in contrast to the blue wavelength range, there is no evidencefor either the dark spot or the gas stream/disc impact region emission,while the emission from the secondary star is weak. During theobservations in 1999, UX UMa showed many of the defining properties ofthe SW Sextantis stars. However, all these features almost completelydisappeared in 2008. We have also estimated the radial velocitysemi-amplitudes K1 and K2 and evaluated the systemparameters of UX UMa. These estimates are inconsistent with previousvalues derived by means of analysis of white dwarf eclipse features inthe light curve in different wavelength ranges.
| Spectral Variability of Romano's Star
We combine archival spectral observations of the LBV star V532 (Romano'sstar) together with existing photometric data in the B band.Spectroscopic data cover 15 years of observations (from 1992 to 2007).We show that the object in maximum of brightness behaves as an emissionline supergiant while in minimum V532 moves along the sequence of lateWN stars. In this sense, the object behaves similarly to the well-knownLuminous Blue Variable (LBV) stars AG Car and R127, but is somewhathotter at the minima. We identify about 100 spectral lines in the3700-7300Å range. As of today, our spectroscopy is the mostcomprehensive for this object. The velocity of the wind is derived usingthe He I triplet lines (360±30 km s(-1) ). Physical parameters ofthe nebula around V532 are estimated.
| Mapping the properties of blue compact dwarf galaxies: integral field spectroscopy with PMAS
Context. Blue compact dwarf (BCD) galaxies are low-luminosity, low-metalcontent dwarf systems undergoing violent bursts of star formation. Theypresent a unique opportunity to probe galaxy formation and evolution andto investigate the process of star formation in a relatively simplescenario. Spectrophotometric studies of BCDs are essential todisentangle and characterize their stellar populations. Aims: Weperform integral field spectroscopy of a sample of BCDs with the aim ofanalyzing their morphology, the spatial distribution of some of theirphysical properties (excitation, extinction, and electron density) andtheir relationship with the distribution and evolutionary state of thestellar populations. Methods: Integral field spectroscopyobservations of the sample galaxies were carried out with the PotsdamMulti-Aperture Spectrophotometer (PMAS) at the 3.5 m telescope at CalarAlto Observatory. An area 16 arcsec × 16 arcsec in size was mappedwith a spatial sampling of 1 arcsec × 1 arcsec. We obtained datain the 3590-6996 Å spectral range, with a linear dispersion of 3.2Å per pixel. From these data we built two-dimensional maps of theflux of the most prominent emission lines, of two continuum bands, ofthe most relevant line ratios, and of the gas velocity field. Integratedspectra of the most prominent star-forming regions and of whole objectswithin the FOV were used to derive their physical parameters and the gasmetal abundances. Results: Six galaxies display the samemorphology both in emission line and in continuum maps; only in twoobjects, Mrk 32 and Tololo 1434+032, the distributions of the ionizedgas and of the stars differ considerably. In general the differentexcitation maps for a same object display the same pattern and trace thestar-forming regions, as expected for objects ionized by hot stars; onlythe outer regions of Mrk 32, I Zw 123 and I Zw 159 display higher [SII]/H? values, suggestive of shocks. Six galaxies display aninhomogeneous dust distribution. Regarding the kinematics, Mrk 750, Mrk206 and I Zw 159 display a clear rotation pattern, while in Mrk 32, Mrk475 and I Zw 123 the velocity fields are flat.Tables 3-6 and Figs. 3-9 are only available in electronic form at http://www.aanda.org
| Small-spatial-scale variations of nebular properties and the abundance discrepancy in three Galactic HII regions
We present the results of long-slit spectroscopy in several slitpositions that cover different morphological structures of the centralparts of three bright Galactic HII regions: M8, M17 and NGC 7635. Westudy the spatial distributions of a large number of nebular parameters,such as the extinction coefficient, line fluxes, physical conditions andionic abundances at the maximum spatial resolution attainable with ourinstrumentation. Particularly, our goal is to study the behaviour of theabundance discrepancy factor of O2+ [ADF(O2+)],defined as the logarithmic difference of the O2+ abundancesderived from collisionally excited and recombination lines. We find thatADF(O2+) remains fairly constant along the slit positions ofM8 and M17. For NGC 7635, we only detect the OII recombination lines inthe integrated spectrum along the whole slit, where ADF(O2+)reaches a remarkably high value of about 0.59 dex. We compare ourresults with previous results obtained for the Orion Nebula. We findmuch evidence to suggest the presence of a candidate Herbig-Haro objectin M8.Based on observations made with the 4.2-m William Herschel Telescope(WHT) operated on the island of La Palma by the Isaac Newton Group inthe Spanish Observatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.E-mail: amd@iac.es
| Integral Field Unit Spectroscopy of the Stellar Disk Truncation Region of NGC 6155
Like the majority of spiral galaxies, NGC 6155 exhibits an exponentialsurface brightness profile that steepens significantly at large radii.Using the VIRUS-P integral field unit spectrograph, we have gatheredspatially resolved spectra of the system. Modifying the GANDALF spectralfitting routine for use on the complex stellar populations found inspirals, we find that the average stellar ages increase significantlybeyond the profile break radius. This result is in good agreement withrecent simulations that predict the outskirts of disk galaxies arepopulated through stellar migration. With the ability to bin multiplefibers, we are able to measure stellar population ages down to ?V ~ 24 mag arcsec-2.This Letter includes data taken at The McDonald Observatory of TheUniversity of Texas at Austin.
| LoCuSS: first results from strong-lensing analysis of 20 massive galaxy clusters at z = 0.2
We present a statistical analysis of a sample of 20 strong lensingclusters drawn from the Local Cluster Substructure Survey, based onhigh-resolution Hubble Space Telescope imaging of the cluster cores andfollow-up spectroscopic observations using the Keck-I telescope. We usedetailed parametrized models of the mass distribution in the clustercores, to measure the total cluster mass and fraction of that massassociated with substructures within R <= 250kpc. These measurementsare compared with the distribution of baryons in the cores, as traced bythe old stellar populations and the X-ray emitting intracluster medium.Our main results include: (i) the distribution of Einstein radii islognormal, with a peak and 1? width of = 1.16 +/- 0.28;(ii) we detect an X-ray/lensing mass discrepancy of = 1.3 at 3? significance -clusters with larger substructure fractions displaying greater massdiscrepancies, and thus greater departures from hydrostatic equilibriumand (iii) cluster substructure fraction is also correlated with theslope of the gas density profile on small scales, implying a connectionbetween cluster-cluster mergers and gas cooling. Overall our results areconsistent with the view that cluster-cluster mergers play a prominentrole in shaping the properties of cluster cores, in particular causingdepartures from hydrostatic equilibrium, and possibly disturbing coolcores. Our results do not support recent claims that large Einsteinradius clusters present a challenge to the cold dark matter paradigm.
| A new Wolf-Rayet star and its circumstellar nebula in Aquila
We report the discovery of a new Wolf-Rayet star in Aquila via detectionof its circumstellar nebula (reminiscent of ring nebulae associated withlate WN stars) using the Spitzer Space Telescope archival data. Ourspectroscopic follow-up of the central point source associated with thenebula showed that it is a WN7h star (we named it WR121b). We analysedthe spectrum of WR121b by using the Potsdam Wolf-Rayet modelatmospheres, obtaining a stellar temperature of ~=50kK. The stellar windcomposition is dominated by helium with ~20 per cent of hydrogen. Thestellar spectrum is highly reddened [E(B - V) = 2.85mag]. Adopting anabsolute magnitude of Mv = -5.7, the star has a luminosity oflogL/Lsolar = 5.75 and a mass-loss rate of10-4.7Msolaryr-1, and resides at adistance of 6.3kpc. We searched for a possible parent cluster of WR121band found that this star is located at ~=1° from the young starcluster embedded in the giant HII region W43 (containing a WN7+a/OB?star - WR121a). We also discovered a bow shock around the O9.5III starALS9956, located at from the cluster. We discuss the possibility thatWR121b and ALS9956 are runaway stars ejected from the cluster in W43.Based on observations collected at the German-Spanish AstronomicalCenter, Calar Alto, jointly operated by the Max-Planck-Institut fürAstronomie Heidelberg and the Instituto de Astrofísica deAndalucía (CSIC).E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK);wrh@astro.physik.uni-potsdam.de (WRH); berdnik@sai.msu.ru (LNB);fabrika@sao.ru (SF); azamat@sao.ru (AFV)
| StarCAT: A Catalog of Space Telescope Imaging Spectrograph Ultraviolet Echelle Spectra of Stars
StarCAT is a catalog of high resolution ultraviolet spectra of objectsclassified as "stars," recorded by Space Telescope Imaging Spectrograph(STIS) during its initial seven years of operations (1997-2004). StarCATis based on 3184 echelle observations of 545 distinct targets, with atotal exposure duration of 5.2 Ms. For many of the objects, broadultraviolet coverage has been achieved by splicing echellegrams taken intwo or more FUV (1150-1700 Å) and/or NUV (1600-3100 Å)settings. In cases of multiple pointings on conspicuously variablesources, spectra were separated into independent epochs. Otherwise,different epochs were combined to enhance the signal-to-noise ratio(S/N). A post-facto correction to the {\sf calstis} pipeline data setscompensated for subtle wavelength distortions identified in a previousstudy of the STIS calibration lamps. An internal "fluxing" procedureyielded coherent spectral energy distributions (SEDs) for objects withbroadly overlapping wavelength coverage. The best StarCAT materialachieves 300 m s-1 internal velocity precision;absolute accuracy at the 1 km s-1 level; photometricaccuracy of order 4%; and relative flux precision several times better(limited mainly by knowledge of SEDs of UV standard stars). WhileStarCAT represents a milestone in the large-scale post-processing ofSTIS echellegrams, a number of potential improvements in the underlying"final" pipeline are identified.
| The Globular Cluster System of the Virgo Giant Elliptical Galaxy NGC 4636. I. Subaru/Faint Object Camera and Spectrograph Spectroscopy and Database
We present a spectroscopic study of the globular clusters (GCs) in thegiant elliptical galaxy NGC 4636 in the Virgo Cluster. We selectedtarget GC candidates using the Washington photometry derived from thedeep CCD images taken at the KPNO 4 m Telescope. Then we obtained thespectra of 164 target objects in the field of NGC 4636 using theMulti-Object Spectroscopy mode of Faint Object Camera and Spectrographon the Subaru 8.2 m Telescope. We have measured the velocities for 122objects: 105 GCs in NGC 4636, the nucleus of NGC 4636, 11 foregroundstars, two background galaxies, and three probable intracluster GCs inthe Virgo Cluster. The GCs in NGC 4636 are located in the projectedgalactocentric radius within 10' (corresponding to 43 kpc). The measuredvelocities for the GCs range from ~300 km s-1 to ~1600 kms-1, with a mean value of 932+25 -22 kms-1, which is in good agreement with the velocity for thenucleus of NGC 4636, 928 ± 45 km s-1. The velocitydispersion of the GCs in NGC 4636 is derived to be 231+15-17 km s-1, and the velocity dispersion of theblue GCs is slightly larger than that of the red GCs. Combining ourresults with data in the literature, we produce a master catalog ofradial velocities for 238 GCs in NGC 4636. The velocity dispersion ofthe GCs in the master catalog is found to be 225+12-9 km s-1 for the entire sample, 251+18-12 km s-1 for 108 blue GCs, and 205+11-13 km s-1 for 130 red GCs.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.
| 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.
| Low-ionization pairs of knots in planetary nebulae: physical properties and excitation
We obtained optical long-slit spectra of four planetary nebulae (PNe)with low-ionization pair of knots, namely He 1-1, IC 2149, KjPn 8 andNGC 7662.These data allow us to derive the physical parameters and excitation ofthe pairs of knots, and those of higher ionization inner components ofthe nebulae, separately.Our results are as follows. (1) The electron temperatures of the knotsare within the range 9500-14500 K, similar to the temperatures of thehigher ionization rims/shells. (2) Typical knots' densities are 500-2000cm-3. (3) Empirical densities of the inner rims/shells arehigher than those of the pairs of knots, by up to a factor of 10.Theoretical predictions, at variance with the empirical results, suggestthat knots should be denser than the inner regions, by at least a factorof 10. (4) Empirical and theoretical density contrasts can be reconciledif we assume that at least 90 per cent of the knots' gas is neutral(likely composed of dust and molecules). (5) By using the new Raga etal. shock modelling and diagnostic diagrams appropriated for spatiallyresolved PNe, we suggest that high-velocity shocked knots travelling inthe photoionized outer regions of PNe can explain the emission of thepairs of knots analysed in this paper.
| The Discovery of a Large Ly?+He II Nebula at z ? 1.67: A Candidate Low Metallicity Region?
We have discovered a ?45 kpc Ly? nebula (or Ly? "blob")at z ? 1.67 which exhibits strong, spatially extended He II emissionand very weak C IV and C III] emission. This is the first spatiallyextended Ly?+He II emitter observed and the lowest redshiftLy? blob yet found. Strong Ly? and He II?1640emission in the absence of metal lines has been proposed as a uniqueobservational signature of primordial galaxy formation (e.g., fromgravitational cooling radiation or Population III star formation), butno convincing examples of spatially extended Ly?+He II emittershave surfaced either in Ly?-emitting galaxy surveys at highredshifts (z > 4) or in studies of Ly? nebulae at lowerredshifts. From comparisons with photoionization models, we find thatthe observed line ratios in this nebula are consistent with lowmetallicity gas (Z lsim 10-2-10-3 Zsun), but that this conclusion depends on the unknownionization parameter of the system. The large He II equivalent width(?37 ± 10 Å) and the large He II/Ly? ratio (0.12± 0.04) suggest that the cloud is being illuminated by a hardionizing continuum, either an active galactic nucleus (AGN) or very lowmetallicity stars, or perhaps powered by gravitational coolingradiation. Thus far there is no obvious sign of a powerful AGN in ornear the system, so in order to power the nebula while remaining hiddenfrom view even in the mid-infrared, the AGN would need to be heavilyobscured. Despite the strong Ly?+He II emission, it is not yetclear what is the dominant power source for this nebula. The systemtherefore serves as an instructive example of how the complexities oftrue astrophysical sources will complicate matters when attempting touse a strong Ly?+He II signature as a unique tracer of primordialgalaxy formation.
| An Imaging and Spectroscopic Study of Four Strong Mg II Absorbers Revealed by GRB 060418
We present results from an imaging and spectroscopic study of fourstrong Mg II absorbers of W(2796) gsim 1 Å revealed by theafterglow of GRB 060418 at z GRB = 1.491. These absorbers, atz = 0.603, 0.656, 1.107, and z GRB, exhibit large ionabundances that suggest neutral gas columns characteristic of dampedLy? systems. The imaging data include optical images obtainedusing Low-Resolution Imaging Spectrometer (LRIS) on the Keck I telescopeand using Advanced Camera for Surveys on board Hubble Space Telescope,and near-infrared H-band images obtained using Persson's AuxiliaryNasmyth Infrared Camera on the Magellan Baade Telescope and K'-bandimages obtained using NIRC2 with laser guide star adaptive optics on theKeck II telescope. These images reveal six distinct objects at ?? lsim 3farcs5 of the afterglow's position, two of which exhibitwell-resolved mature disk morphology, one shows red colors, and threeare blue compact sources. Follow-up spectroscopic observations usingLRIS confirm that one of the disk galaxies coincides with the Mg IIabsorber at z = 0.656. The observed broadband spectral energydistributions of the second disk galaxy and the red source indicate thatthey are associated with the absorbers at z = 0.603 and z = 1.107,respectively. These results show that strong Mg II absorbers identifiedin gamma-ray burst (GRB) afterglow spectra are associated with typicalgalaxies of luminosity ?0.1 - 1 L * at impact parameter of? lsim 10 h -1 kpc. The close angular separation wouldpreclude easy detections toward a bright quasar. Finally, we associatethe remaining three blue compact sources with the GRB host galaxy,noting that they are likely star-forming knots located at projecteddistances of ? = 2 - 12 h -1 kpc from the afterglow. Atthe afterglow's position, we derive a 2? upper limit to theunderlying star-formation rate intensity of 0.0074 M sunyr-1 kpc-2.Based in part on observations made 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.
| 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.
| Identifications of Five INTEGRAL Sources via Optical Spectroscopy
The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) isdiscovering hundreds of new hard X-ray sources, many of which remainunidentified. We report on optical spectroscopy of five such sources forwhich X-ray observations at lower energies (~0.5-10 keV) and higherangular resolutions than INTEGRAL have allowed for unique opticalcounterparts to be located. We find that INTEGRAL Gamma-Ray (IGR)J16426+6536 and IGR J22292+6647 are Type 1 Seyfert active galacticnuclei (with IGR J16426+6536 further classified as a Seyfert 1.5) whichhave redshifts of z = 0.323 and z = 0.113, respectively. IGR J18308-1232is identified as a cataclysmic variable (CV), and we confirm a previousidentification of IGR J19267+1325 as a magnetic CV. IGR J18214-1318 isidentified as an obscured high-mass X-ray binary (HMXB), which aresystems thought to have a compact object embedded in the stellar wind ofa massive star. We combine Chandra fluxes with distances based on theoptical observations to calculate X-ray luminosities of the HMXB andCVs, finding L 0.3-10 keV = 5 × 1036 ergs-1 for IGR J18214-1318, L 0.3-10 keV = 1.3× 1032 erg s-1 for IGR J18308-1232, and L0.3-10 keV = 6.7 × 1032 erg s-1for IGR J19267+1325.
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| Takýmyýldýz: | Kuzey Taci |
| Sað Açýklýk: | 15h51m59.89s |
| Yükselim: | +32°56'54.4" |
| Görünürdeki Parlaklýk: | 10.721 |
| özdevim Sað Açýklýk: | -10.1 |
| özdevim Yükselim: | 3.7 |
| B-T magnitude: | 10.584 |
| V-T magnitude: | 10.71 |
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