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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.
| The Lick AGN Monitoring Project: Broad-line Region Radii and Black Hole Masses from Reverberation Mapping of Hβ
We have recently completed a 64-night spectroscopic monitoring campaignat the Lick Observatory 3-m Shane telescope with the aim of measuringthe masses of the black holes in 12 nearby (z < 0.05) Seyfert 1galaxies with expected masses in the range~106-107 M sun and also thewell-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of theobjects in the sample (including NGC 5548) showed optical variability ofsufficient strength during the monitoring campaign to allow for a timelag to be measured between the continuum fluctuations and the responseto these fluctuations in the broad Hβ emission. We present here thelight curves for all the objects in this sample and the subsequentHβ time lags for the nine objects where these measurements werepossible. The Hβ lag time is directly related to the size of thebroad-line region (BLR) in AGNs, and by combining the Hβ lag timewith the measured width of the Hβ emission line in the variablepart of the spectrum, we determine the virial mass of the centralsupermassive black hole in these nine AGNs. The absolute calibration ofthe black hole masses is based on the normalization derived by Onken etal., which brings the masses determined by reverberation mapping intoagreement with the local MBH-σsstarfrelationship for quiescentgalaxies. We also examine the time lag response as a function ofvelocity across the Hβ line profile for six of the AGNs. Theanalysis of four leads to rather ambiguous results with relatively flattime lags as a function of velocity. However, SBS 1116+583A exhibits asymmetric time lag response around the line center reminiscent of simplemodels for circularly orbiting BLR clouds, and Arp 151 shows anasymmetric profile that is most easily explained by a simplegravitational infall model. Further investigation will be necessary tofully understand the constraints placed on the physical models of theBLR by the velocity-resolved response in these objects.
| Structure of the Accretion Flow in Broad-Line Radio Galaxies: The Case of 3C 390.3
We present XMM-Newton and Suzaku observations of the broad-line radiogalaxy 3C 390.3 acquired in 2004 October and 2006 December,respectively. An archival Swift BAT spectrum from the 9 month survey isalso analyzed, as well as an optical spectrum simultaneous toXMM-Newton. At soft X-rays, no absorption features are detected in theReflection Grating Spectrometer spectrum of 3C 390.3 a narrowemission line is found at 0.564 keV, most likely originating in thenarrow-line region. Both the EPIC and XIS data sets confirm the presenceof an Fe Kα emission line at 6.4 keV with equivalentwidth (EW) = 40 eV. The Fe Kα line has a width FWHM ~8800 km s-1, consistent within a factor of2 with the width of the double-peaked Hα line, suggesting anorigin from the broad-line region. The data show for the first time aweak, broad bump extending from 5 to 7 keV. When fitted with aGaussian, its centroid energy is 6.6 keV in the source's rest framewith FWHM of 43,000 km s-1 and EW of 50 eVits most likely interpretation is emission from He-likeFe (Fe XXV), suggesting the presence of an ionized medium inthe inner regions of 3C 390.3. The broadband 0.5-100 keVcontinuum is well described by a single power law with photon indexΓ = 1.6 and cutoff energy 157 keV, plus cold reflection withstrength R = 0.5. In addition, ionized reflection is required to accountfor the 6.6 keV bump in the broadband continuum, yielding anionization parameter ξ ~ 2700 erg cm s-1 the innerradius of the ionized reflector is constrained to be larger than20rG , although this result depends on the assumed emissivityprofile of the disk. If true, we argue that the lack of broad Fe Kemission from within 20rG indicates that the innermostregions of the disk in 3C 390.3 are obscured and/or poorlyilluminated. While the spectral energy distribution (SED) of3C 390.3 is generally dominated by accretion-related continuum,during accretion low states the jet can significantly contribute in theoptical to X-ray bands via synchrotron self-Compton emission. TheCompton component is expected to extend to and peak at GeV gamma rayswhere it will be detected with the Fermi Gamma-Ray Space Telescopeduring its first few years of operation.
| Keck HIRES Spectroscopy of Extragalactic H II Regions: C and O Abundances from Recombination Lines
We present very deep spectrophotometry of 14 bright extragalacticH II regions belonging to spiral, irregular, and blue compactgalaxies. The data for 13 objects were taken with the High ResolutionEchelle Spectrometer on the Keck I telescope. We have measured C IIrecombination lines in 10 of the objects and O II recombinationlines in eight of them. We have determined electron temperatures fromline ratios of several ions, especially those of low ionizationpotential. We have found a rather tight linear empirical relationbetween T e([N II]) and T e([O III]). Wehave found that O II lines give always larger abundances than[O III] lines. Moreover, the difference of both O++abundance determinations—the so-called abundance discrepancyfactor—is very similar in all the objects, with a mean value of0.26 ± 0.09 dex, independent of the properties of the H IIregion and of the parent galaxy. Using the observed recombination lines,we have determined the O, C, and C/O radial abundance gradients forthree spiral galaxies: M33, M101, and NGC 2403, finding that C abundancegradients are always steeper than those of O, producing negative C/Ogradients across the galactic disks. This result is similar to thatfound in the Milky Way and has important implications for chemicalevolution models and the nucleosynthesis of C.Most of the data presented herein were obtained at the W.M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California and theNational Aeronautics and Space Administration. The Observatory was madepossible by the generous financial support of the W.M. Keck Foundation.Part of the observations were made with the 4.2 m William HerschelTelescope (WHT), operated on the island of La Palma by the Isaac NewtonGroup in the Spanish Observatorio del Roque de los Muchachos of theInstituto de Astrofísica de Canarias.
| CN Variations in High-Metallicity Globular and Open Clusters
We present a comparison of CN band strength variations in thehigh-metallicity globular clusters NGC 6356 and NGC 6528 with thosemeasured in the old open clusters NGC 188, NCG 2158 and NGC 7789.Star-to-star abundance variations, of which CN differences are a readilyobservable sign, are commonplace in moderate-metallicity halo globularclusters but are unseen in the field or in open clusters. We find thatthe open clusters have narrow, unimodal distributions of CN bandstrength, as expected from the literature, while the globular clustershave broad, bimodal distributions of CN band strength, similar tomoderate-metallicity halo globular clusters. This result has interestingimplications for the various mechanisms proposed to explain the originof globular cluster abundance inhomogeneities, and suggests that thelocal environment at the epoch of cluster formation plays a vital rolein regulating intracluster enrichment processes.
| Evidence of a link between the evolution of clusters and their AGN fraction
We discuss the optical properties, X-ray detections and active galacticnucleus (AGN) populations of four clusters at z ~ 1 in the Subaru-XMMDeep Field (SXDF). The velocity distribution and plausible extendedX-ray detections are examined, as well as the number of X-ray pointsources and radio sources associated with the clusters. We find that thetwo clusters that appear virialized and have an extended X-ray detectioncontain few, if any, AGN, whereas the two pre-virialized clusters have alarge AGN population. This constitutes evidence that the AGN fraction inclusters is linked to the clusters' evolutionary stage. The number ofX-ray AGN in the pre-virialized clusters is consistent with anoverdensity of a factor of ~200 the radio AGN appear to be clusteredwith a factor of 3 to 6 higher. The median K-band luminosities ofLK = 1.7 +/- 0.7 L* for the X-ray sources and LK =2.3 +/- 0.1 L* for the radio sources support the theory that these AGNare triggered by galaxy interaction and merging events in sub-groupswith low internal velocity distributions, which make up the clusterenvironment in a pre-virialization evolutionary stage.
| Extremely Luminous Supernova 2006gy at Late Phase: Detection of Optical Emission from Supernova
Supernova (SN) 2006gy is an extremely luminous Type IIn SN characterizedby the bright peak magnitude MR ~-22 mag and itslong duration. The mechanism giving rise to its huge luminosity is stillunclear. We performed optical spectroscopy and photometry of SN 2006gyat late time, ~400 days after the explosion, with the Subaru/FOCAS in agood seeing condition. We carefully extracted the SN component, althoughthere is an ambiguity because of the contamination by bright nucleus ofthe host galaxy. We found that the SN faded by ~3 mag from ~200 to~400 days after the explosion (i.e., by ~5 mag from peak to ~400days) in R band. The overall light curve is marginally consistent withthe 56Ni heating model, although the flattening around 200days suggests the optical flux declined more steeply between ~200 and~400 days. The late time spectrum was quite peculiar among all types ofSNe. It showed many intermediate width (~2000 km s-1FWHM) emission lines, e.g., [Fe II], [Ca II], and Ca II. The absence ofthe broad [O I] 6300, 6364 line and weakness of [Fe II] and [Ca II]lines compared with Ca II IR triplet would be explained by a moderatelyhigh electron density in the line emitting region. This high-densityassumption seems to be consistent with the large amount of ejecta andlow expansion velocity of SN 2006gy. The Hα line luminosity was assmall as ~1× 1039 erg s-1, beingcomparable with those of normal Type II SNe at similar epochs. Ourobservation indicates that the strong circumstellar medium interactionhad almost finished by ~400 days. If the late time optical flux ispurely powered by radioactive decay, at least M(56Ni) ~ 3 Msun should be produced at the SN explosion. In the late phasespectrum, there were several unusual emission lines at7400 Å-8800 Å and some of them might be due to Tior Ni synthesized at the explosion.Based on data collected at Subaru telescope, which is operated by theNational Astronomical Observatory of Japan (NAOJ).
| The Polarimetric and Photometric Variability of HH 30
We have obtained ground-based photopolarimetry of the young stellarobject HH 30 over the course of one year. Our observations reveal thepresence of a dominant periodic modulation of the polarization with aperiod of 7.49 ± 0.04 days or one of the aliases of this periodclose to 1 day. There are also suggestions of a weak periodic modulationin the photometry with the same period but a phase displaced by onequarter of a period. These results are in agreement with the lighthousemodel for HH 30, in which a beam or shadow from a central source sweepsacross the disk. Our observations by themselves appear to be consistentwith both of the mechanisms that have been proposed for thelighthouse—asymmetric accretion hot spots on the star or orbitingclumps or voids in the disk—and provide strong quantitativeconstraints for future models.
| Iphas A-Type Stars with Mid-Infrared Excesses in Spitzer Surveys
We have identified 17 A-type stars in the Galactic Plane that havemid-infrared (mid-IR) excesses at 8 μm. From observed colors in the(r' - Hα) - (r' - i') plane, we first identified23,050 early A-type main-sequence (MS) star candidates in the IsaacNewton Photometric H-Alpha Survey (IPHAS) point source database that arelocated in Spitzer Galactic Legacy Mid-Plane Survey ExtraordinaireGalactic plane fields. Imposing the requirement that they be detected inall seven Two Micron All Sky Survey and Infrared Astronomical Satellitebands led to a sample of 2692 candidate A-type stars with fully sampled0.6 to 8 μm spectral energy distributions (SEDs). Opticalclassification spectra of 18 of the IPHAS candidate A-type MS starsshowed that all but one could be well fitted using MS A-type templates,with the other being an A-type supergiant. Out of the 2692 A-typecandidates 17 (0.6%) were found to have 8 μm excesses above theexpected photospheric values. Taking into account non-A-Typecontamination estimates, the 8 μm excess fraction is adjusted to~0.7%. The distances to these sources range from 0.7 to 2.5 kpc. Only 10out of the 17 excess stars had been covered by Spitzer MIPSGAL surveyfields, of which five had detectable excesses at 24 μm. Forsources with excesses detected in at least two mid-IR wavelength bands,blackbody fits to the excess SEDs yielded temperatures ranging from 270to 650 K, and bolometric luminosity ratios L IR/Lsstarf from 2.2 × 10-3 - 1.9× 10-2, with a mean value of 7.9 ×10-3 (these bolometric luminosities are lower limits ascold dust is not detectable by this survey). Both the presence of mid-IRexcesses and the derived bolometric luminosity ratios are consistentwith many of these systems being in the planet-building transition phasebetween the early protoplanetary disk phase and the later debris diskphase.
| The Dual-Axis Circumstellar Environment of the Type IIn Supernova 1997eg
We present multi-epoch spectral and spectropolarimetric observations ofthe Type IIn supernova (SN) 1997eg that indicate the presence of aflattened disklike concentration of circumstellar material surroundingaspherical ejecta, with which the disk is misaligned. The polarizationacross the broad Hα, Hβ, and He I λ5876 lines of SN1997eg forms closed loops when viewed in the Stokes q-u plane. Suchloops occur when the geometrical symmetry of one or both of the Stokesparameters across spectral lines is broken, in this case most likely byoccultation of the ejecta by the equatorial circumstellar matterconcentration. The polarization of the narrow Balmer lines possesses anintrinsic axis that differs by 12° from that of the elongated ejectaand probably indicates the orientation of the disklike circumstellarmaterial. The existence of two different axes of symmetry in SN 1997egsuggests that neither rotation of the progenitor nor the influence of acompanion star can be the sole mechanism creating a preferred axiswithin the supernova system. Our model supports the emerging hypothesisthat the progenitors of some Type IIn supernovae are luminous bluevariable stars, whose presupernova mass eruptions form the circumstellarshells that physically characterize the SN IIn subclass. Theseconclusions, which are independent of interstellar polarization effects,would have been unobservable with only a single epoch ofspectropolarimetry.
| Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants
We present the results of an observational study of the efficiency ofdeep mixing in globular cluster red giants as a function of stellarmetallicity. We determine [C/Fe] abundances based on low-resolutionspectra taken with the Kast spectrograph on the 3 m Shane telescope atLick Observatory. Spectra centered on the 4300 Å CH absorptionband were taken for 42 bright red giants in 11 Galactic globularclusters ranging in metallicity from M92 ([Fe/H] = 2.29) to NGC 6712([Fe/H] = 1.01). Carbon abundances were derived by comparing values ofthe CH-band strength index S 2(CH) measured from the datawith values measured from a large grid of SSG synthetic spectra.Present-day abundances are combined with theoretical calculations of thetime since the onset of mixing, which is also a function of stellarmetallicity, to calculate the carbon depletion rate across ourmetallicity range. We find that the carbon depletion rate is twice ashigh at a metallicity of [Fe/H] = 2.3 than at [Fe/H] = 1.3, which is aresult qualitatively predicted by some theoretical explanations of thedeep mixing process.
| Post-common envelope binaries from SDSS - III. Seven new orbital periods
We present follow-up spectroscopy and photometry of 11 post-commonenvelope binary (PCEB) candidates identified from multiple Sloan DigitalSky Survey (SDSS) spectroscopy in an earlier paper. Radial velocitymeasurements using the NaIλλ8183.27, 8194.81 absorptiondoublet were performed for nine of these systems and providedmeasurements of six orbital periods in the range Porb = 2.7-17.4h. Three PCEB candidates did not show significant radial velocityvariations in the follow-up data, and we discuss the implications forthe use of SDSS spectroscopy alone to identify PCEBs. Differentialphotometry confirmed one of our spectroscopic orbital periods andprovided one additional Porb measurement. Binary parametersare estimated for the seven objects for which we have measured theorbital period and the radial velocity amplitude of the low-masscompanion star, Ksec. So far, we have published nine SDSSPCEBs orbital periods, all of them Porb < 1d. We performMonte Carlo simulations and show that 3σ SDSS radial velocityvariations should still be detectable for systems in the orbital periodrange of Porb ~ 1- 10d. Consequently, our results suggestthat the number of PCEBs decreases considerably for Porb >1d, and that during the CE phase the orbital energy of the binary staris may be less efficiently used to expel the envelope than frequentlyassumed.
| Echelle Long-Slit Optical Spectroscopy of Evolved Stars
We present echelle long-slit optical spectra of a sample of objectsevolving off the asymptotic giant branch (AGB), most of them in thepreplanetary nebula (PPN) phase, obtained with the ESI and MIKEspectrographs at the 10 m Keck II and 6.5 m Magellan-I telescopes,respectively. The total wavelength range covered with ESI (MIKE) is~3900-10900 Å (~3600-7200 Å). In this paper, we focus ouranalysis mainly on the Hα profiles. Prominent Hα emission isdetected in half of the objects, most of which show broad Hα wings(with total widths of up to ~4000 km s-1). In the majority ofthe Hα-emission sources, fast, post-AGB winds are revealed byP-Cygni profiles. In ~37% of the objects Hα is observed inabsorption. In almost all cases, the absorption profile is partiallyfilled with emission, leading to complex, structured profiles that areinterpreted as an indication of incipient post-AGB mass loss. The restof the objects (~13%) are Hα nondetections. We investigatecorrelations between the Hα profile and different stellar andenvelope parameters. All sources in which Hα is seen mainly inabsorption have F-G type central stars, whereas sources with intenseHα emission span a larger range of spectral types from O to G,with a relative maximum around B, and also including very late C types.Shocks may be an important excitation/ionization agent of the closestellar surroundings for objects with late type central stars. Sourceswith pure emission or P Cygni Hα profiles have larger J-K colorexcess than objects with Hα mainly in absorption, which suggeststhe presence of warm dust near the star in the former. The two classesof profile sources also segregate in the IRAS color-color diagram in away that intense Hα-emitters have dust grains with a larger rangeof temperatures. Spectral classification of the central stars in oursample is presented. For a subsample (13 objects), the stellarluminosity has been derived from the analysis of the O I 7771-7775Å infrared triplet. The location in the HR diagram of most ofthese targets, which represent ~30% of the whole sample, is consistentwith relatively high final (and, presumably, initial) masses in therange Mf~0.6-0.9 Msolar (Mi~3-8Msolar).
| Two new intermediate polars with a soft X-ray component
Aims. We analyze the first X-ray observations with XMM-Newton of 1RXSJ070407.9+262501 and 1RXS 180340.0+401214, in order to characterizetheir broad-band temporal and spectral properties, also in theUV/optical domain, and to confirm them as intermediate polars. Methods:For both objects, we performed a timing analysis of the X-ray andUV/optical light curves to detect the white dwarf spin pulsations andstudy their energy dependence. For 1RXS 180340.0+401214 we also analyzedoptical spectroscopic data to determine the orbital period. X-rayspectra were analyzed in the 0.2-10.0 keV range to characterize theemission properties of both sources. Results: We find that the X-raylight curves of both systems are energy dependent and are dominated,below 3-5 keV, by strong pulsations at the white dwarf rotationalperiods (480 s for 1RXS J070407.9+262501 and 1520.5 s for 1RXS180340.0+401214). In 1RXS 180340.0+401214 we also detect an X-ray beatvariability at 1697 s which, together with our new optical spectroscopy,favours an orbital period of 4.4 h that is longer than previouslyestimated. Both systems show complex spectra with a hard (temperature upto 40 keV) optically thin and a soft (kT ~ 85-100 eV) optically thickcomponents heavily absorbed by material partially covering the X-raysources. Conclusions: Our observations confirm the two systems asintermediate polars and also add them as new members of the growinggroup of “soft” systems which show the presence of a softX-ray blackbody component. Differences in the temperatures of theblackbodies are qualitatively explained in terms of reprocessing overdifferent sizes of the white dwarf spot. We suggest that systems showingcooler soft X-ray blackbody components also possess white dwarfsirradiated by cyclotron radiation.Based on observations obtained with XMM-Newton, an ESA science missionwith instruments and contributions directly funded by ESA Member Statesand NASA, and with the Observatoire de Haute Provence (CNRS), France.
| Metallicity and Alpha-Element Abundance Measurement in Red Giant Stars from Medium-Resolution Spectra
We present a technique that applies spectral synthesis tomedium-resolution spectroscopy (MRS; R~6000) in the red (6300Å<λ<9100 Å) to measure [Fe/H] and [α/Fe]of individual red giant stars over a wide metallicity range. We applyour technique to 264 red giant stars in seven Galactic globular clustersand demonstrate that it reproduces the metallicities andα-enhancements derived from high-resolution spectroscopy (HRS).The MRS technique excludes the three Ca II triplet lines and insteadrelies on a plethora of weaker lines. Unlike empirical metallicityestimators, such as the equivalent width of the Ca II triplet, thesynthetic method presented here is applicable over an arbitrarily widemetallicity range and is independent of assumptions about theα-enhancement. Estimates of cluster mean [Fe/H] from different HRSstudies show typical scatter of ~0.1 dex but can be larger than 0.2 dexfor metal-rich clusters. The scatter in HRS abundance estimates amongindividual stars in a given cluster is also comparable to 0.1 dex. Bycomparison, the scatter among MRS [Fe/H] estimates of individual starsin a given cluster is ~0.1 dex for most clusters but 0.17 dex for themost metal-rich cluster, M71 (<[Fe/H]>=-0.8). A star-by-starcomparison of HRS versus MRS [α/Fe] estimates indicates that theprecision in [α/Fe]MRS is 0.05 dex. The errors in[Fe/H]MRS and [α/Fe]MRS increase beyond 0.25dex only below signal-to-noise ratios of 20 Å-1, whichis typical for existing MRS of the red giant stars in Leo I, one of themost distant Milky Way satellites (250 kpc).
| Radiative levitation: a likely explanation for pulsations in the unique hot O subdwarf star SDSS J160043.6+074802.9
Context: SDSS J160043.6+074802.9 (J1600+0748 for short) is the only hotsdO star for which unambiguous multiperiodic luminosity variations havebeen reported so far. These rapid variations, with periods in the rangefrom ~60 s to ~120 s, are best qualitatively explained in terms ofpulsational instabilities, but the exact nature of the driving mechanismhas remained a puzzle. Aims: Our primary goal is to examinequantitatively how pulsation modes can be excited in an object such asJ1600+0748. Given the failure of uniform-metallicity models as welldocumented in the recent Ph.D. thesis of C.Rodríguez-López, we consider the effects of radiativelevitation on iron as a means to boost the efficiency of theopacity-driving mechanism in models of J1600+0748. Methods: We combinehigh sensitivity time-averaged optical spectroscopy and fullnonadiabatic calculations to carry out our study. In the first instance,this is used to estimate the location of J1600+0748 in the log g-T_effplane. Given this essential input, we pulsate stellar models consistentwith these atmospheric parameters. We construct both uniform-metallicitymodels and structures in which the iron abundance is specified by thecondition of diffusive equilibrium between gravitational settling andradiative levitation. Results: On the basis of NTLE H/He syntheticspectra, we find that the target star has the following atmosphericparameters: log g = 5.93 ± 0.11, T_eff = 71 070 ± 2725 K,and log N(He)/N(H) = -0.85 ± 0.08. This takes into account ourdeconvolution of the spectrum of J1600+0748 as it is polluted by thelight of a main sequence companion. We confirm that uniform-metallicitystellar models with Z in the range from 0.02 to 0.10 cannot excitepulsation modes of the kind observed. On the other hand, we find thatthe inclusion of radiative levitation, as we implemented it, leads topulsational instabilities in a period range that overlaps with, althoughit is narrower than, the observed range in J1600+0748. The excited modescorrespond to low-order, low-degree p-modes. Conclusions: We infer thatradiative levitation is a likely essential ingredient in the excitationphysics at work in J1600+0748.
| The Peculiar Globular Cluster System of the s0 Galaxy NGC 7457
We present Hubble Space Telescope photometry and Keck spectroscopy ofglobular clusters (GCs) in the nearby S0 galaxy NGC 7457. The V -I color-magnitude diagram of GCs lacks the clear bimodality present inmost early-type galaxies; there may be a significant population ofintermediate-color objects. Of 13 spectroscopically observed GCs, twoare unusually metal-rich and feature bright [O III] emission lines. Weconclude that one probably hosts a planetary nebula and the other asupernova remnant. Such emission-line objects should be more common inan intermediate-age stellar population than in an old one. We thereforesuggest that, in addition to the typical old metal-rich and oldmetal-poor GC subpopulations, there may be a third subpopulation of anintermediate age. Such a subpopulation may have been formed ~2-3 Gyrago, in the same star-forming event that dominates the stellarpopulation of the center of the galaxy.
| a Large-Scale Optical-Near Survey for Brown Dwarfs and Very Low Mass Stars in the Orion OB1 Association
We report the initial results of a large-scale optical-near-infrared(IR) survey to extend the known young population of the entire Orionstar-forming region down to the substellar domain. Using deep opticalI-band photometry and data from the Two Micron All Sky Survey (2MASS),we selected candidates across ~14.8 deg2 in the ~8 Myr oldOri OB1a subassociation and over ~6.7 deg2 in the ~3 Myr oldOri OB1b subassociation, with completeness down to 0.05 M sunand 0.072 M sun respectively. We obtained low-resolutionoptical spectra for a subsample of four candidates in Ori OB1a and 26 inOri OB1b; as a result we confirmed three new members in Ori OB1a, one ofwhich is substellar, and 19 new members in Ori OB1b, out of which sevenare at the substellar limit and five are substellar. We looked into thepresence of accretion signatures by measuring the strength of theHα emission line. Accordingly, we classified the new members ashaving Classical T-Tauri star-like (CTTS) or Weak Lined T Tauristar-like (WTTS) nature. We found that all the new members confirmed inOri OB1a are WTTSs, while 39+25 -22% of thenew members in Ori OB1b exhibit CTTS-like behavior, suggestive ofongoing accretion from a circum(sub)stellar disk. Additionally we foundthat none of the members confirmed in OB1a shows near-IR color excesswhile 38+26 -21% of OB1b members show H- K color excess. These results are consistent with recentfindings for low-mass young stars in Orion OB1. The similarity inCTTS-like properties and near-IR excess across the substellar boundarygives support to the idea of a common formation mechanism for low-massstars and at least the most massive brown dwarfs. Finally, we comment onthe discovery of two new members classified as CTTSs, both exhibitingW(Hα) lsim -140 Å, suggesting significant ongoingaccretion.
| The Evolution of the Peculiar Type Ia Supernova SN 2005hk over 400 Days
UBVRI photometry and medium-resolution optical spectroscopy of thepeculiar Type Ia supernova SN 2005hk are presented and analyzed,covering the premaximum phase to around 400 days after explosion. Thesupernova is found to be underluminous compared to ``normal'' Type Iasupernovae. The photometric and spectroscopic evolution of SN 2005hk isremarkably similar to the peculiar Type Ia event SN 2002cx. Theexpansion velocity of the supernova ejecta is found to be lower thannormal Type Ia events. The spectra obtained >~200 days sinceexplosion do not show the presence of forbidden [Fe II], [Fe III], and[Co III] lines, but are dominated by narrow, permitted Fe II, NIR Ca II,and Na I lines with P Cygni profiles. The thermonuclear explosion modelwith Chandrasekhar mass ejecta and a kinetic energy smaller(EK=0.3×1051 ergs) than that of canonicalType Ia supernovae is found to well explain the observed bolometriclight curve. The mass of 56Ni synthesized in this explosionis 0.18 Msolar. The early spectra are successfully modeledwith this less energetic model, with some modifications of the abundancedistribution. The late spectrum is explained as a combination of aphotospheric component and a nebular component.
| Integrated field spectroscopy of E+A (post-starburst) galaxies with the Kyoto tridimensional spectrograph II
We have performed two-dimensional spectroscopy of three nearby E+A(post-starburst) galaxies with the Kyoto tridimensional spectrograph II(Kyoto3DII) integral field spectrograph. In all the cases, Hδabsorption is stronger at the centre of the galaxies, but significantlyextended at the scale of a few kiloparsec. For one galaxy (J1656), wefound a close companion galaxy at the same redshift. The galaxy turnedout to be a star-forming galaxy with a strong emission in Hγ. Forthe other two galaxies, we have found that the central post-starburstregions possibly extend toward the direction of the tidal tails. Ourresults are consistent with the merger/interaction origin of E+Agalaxies, where the infalling-gas possibly caused by galaxy-galaxymerging creates a central starburst, succeeded by a post-starburst (E+A)phase once the gas is depleted.
| Reionization and Galaxy Evolution Probed by z = 7 Lyα Emitters
We have performed narrowband NB973 (bandwidth 200 Å centered at9755 Å) imaging of the Subaru Deep Field (SDF) and found two z=7Lyα emitter (LAE) candidates down to NB973 =24.9. Carrying outdeep follow-up spectroscopy, we identified one of them as a real z=6.96LAE. This has established a new redshift record, showing that galaxyformation was in progress just 750 Myr after the big bang. Meanwhile,the Lyα line luminosity function of LAEs is known to decline fromz=5.7 to 6.6 in the SDF; L* at z=6.6 is 40%-60% that atz=5.7. We also confirm that the number density of z=7 LAEs is only 17%of the density at z=6.6 comparing the latest SDF LAE samples. Thisseries of significant decreases in LAE density with increasing redshiftcould be the result of galaxy evolution during these epochs. However,using the UV continuum luminosity functions of LAEs and Lyman breakgalaxies, and a LAE evolution model based on hierarchical clustering, wefind that galaxy evolution alone cannot entirely explain the decrease indensity. This extra density deficit might reflect the attenuation of theLyα photons from LAEs by the neutral hydrogen possibly left at thelast stage of cosmic reionization at z~6-7.Based on data collected at Subaru Telescope, which is operated byNational Astronomical Observatory of Japan.
| Spectral observations of FBS blue stellar objects in the zone δ = + 35°
The next list of spectral data on blue stellar objects (BSOs) ispresented. 58 FBS objects in a zone with a central declination δ =+ 35° were observed with the 2.6-m telescope at the ByurakanObservatory during 1990 1991. In addition, 3 objects were observed (3CCD spectra were obtained) with the BAO 2.6-m and OHP 1.93-m telescopesin 1997 2000 using modern instrumentation. 9 white dwarfs, 47 hotsubdwarfs, and 2 HBB stars have been discovered. Spectra of the 10 mostinteresting objects are given.
| Optical Spectroscopy of Type ia Supernovae
We present 432 low-dispersion optical spectra of 32 Type Ia supernovae(SNe Ia) that also have well-calibrated light curves. The coverageranges from 6 epochs to 36 epochs of spectroscopy. Most of the data wereobtained with the 1.5 m Tillinghast telescope at the F. L. WhippleObservatory with typical wavelength coverage of 3700-7400 Å and aresolution of ~7 Å. The earliest spectra are 13 days before B-bandmaximum; two-thirds of the SNe were observed before maximum brightness.Coverage for some SNe continues almost to the nebular phase. Theconsistency of the method of observation and the technique of reductionmakes this an ideal data set for studying the spectroscopic diversity ofSNe Ia.Based in part on observations obtained at the F. L. Whipple Observatory,which is operated by the Smithsonian Astrophysical Observatory, and theMMT Observatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona.
| M1-78: a nitrogen-rich Galactic compact H II region beyond the Perseus arm
Context: There is considerable controversy surrounding the nature ofM1-78, a compact nebula located beyond the Perseus arm. It was firstclassified as a planetary nebula and is nowadays generally considered tobe a compact H II region. Aims: To investigate the nature of M1-78further, we present a detailed spectroscopic study of M1-78 in theoptical and near-infrared. Methods: We obtained long-slit,intermediate-resolution, optical spectroscopy with the ISIS spectrographmounted on the William Herschel Telescope (WHT) at Roque de losMuchachos Observatory (La Palma, Spain). As a complement, we obtainedlong-slit, intermediate-resolution, near-infrared spectra using LIRIS,the near-infrared imager/spectrographer also installed at the WHT.Results: M1-78 is a high-density nebula with substantial physicaldifferences between its two main morphological zones: a bright arc inthe SW and a blob of emission in the NE. Specifically, the blob in theNE has a higher electron temperature (13 400 K) and visual extinction(about 9 mag) than the SW arc. The most important result, however, isthe confirmation of a nitrogen enrichment in M1-78. This enrichment isstronger at the location of the NE blob and is correlated with adefficiency in the O abundance and a (dubious) He enrichment. Such anabundance pattern is typical of ejecta nebulae around evolved massivestars such as Wolf-Rayet and Luminous Blue Variable stars. The spatialvariations in the physical conditions and chemical abundances and thepresence of more than one possible ionizing source indicate, however,that M1-78 is better described as a combination of a compact H II region+ ejecta. This is confirmed by the He I 2.112 μm/Brγ lineratio, which indicates a hot (T_eff ⪆ 40 000 K) O star in the SWarc. Finally, we detect H2 emission that extends over a large(~30´´) area around the ionized nebula. Analysis of thenear-infrared H2 lines indicates that the excitation mechanism is UVfluorescence.
| Exploring interstellar titanium and deuterium abundances and other correlations
Aims. The origin of the observed variability of the gas-phase D/H ratioin the local interstellar medium is still debated, and in particular therole of deuterium depletion onto dust grains. Here we extend the studyof the relationship between deuterium and titanium, a refractory speciesand tracer of elemental depletion, and explore other relationships. Methods: We have acquired high resolution spectra for nine early-typestars using the VLT/UVES spectrograph, and detected the absorption linesof interstellar TiII. Using a weighted orthogonal distance regression(ODR) code and a special method to treat non symmetric errors, wecompare the TiII columns with the corresponding HI, DI and also OIcolumns. In parallel we perform the same comparisons for available FeIIdata. Results: We find a significant correlation between TiII/HI andD/H in our data set, and, when combined with published results, weconfirm and better constrain the previously established trends andextend the trends to low HI columns. We exclude uncertainties in HI andOI columns as the main contributor to the derived metals-deuteriumcorrelations by showing that the TiII/HI ratio is positively correlatedwith DI/OI. We find a similar correlation between FeII/HI and DI/OI. TheTiII gradients are similar or slightly smaller than for FeII, while onewould expect larger variations on the basis of the higher condensationtemperature of titanium. However we argue that ionisation effectsintroduce biases that affect iron and not titanium and may explain thegradient similarity. We find a less significant negative correlationbetween the TiII/DI ratio and the hydrogen column, possibly a sign ofdifferent evaporation of D and metals according to the cloud properties.More TiII absorption data along very low H column lines-of-sight wouldbe useful to improve the correlation statistics.Based on observations taken with the Ultraviolet and Visual EchelleSpectrograph (UVES) on the Very Large Telescope (VLT) Unit 2 (Kueyen) atParanal, Chile, operated by ESO.
| Using Quantitative Spectroscopic Analysis to Determine the Properties and Distances of Type II Plateau Supernovae: SN 2005cs and SN 2006bp
We analyze the Type II plateau supernovae (SNe IIP) SN 2005cs and SN2006bp with the non-LTE model atmosphere code CMFGEN. We fit 13 spectrain the first month for SN 2005cs and 18 for SN 2006bp. Swift ultravioletphotometry and ground-based optical photometry calibrate each spectrum.Our analysis shows that both objects were discovered less than 3 daysafter they exploded, making these the earliest SN IIP spectra everstudied. They reveal broad and very weak lines from highly ionized fastejecta with an extremely steep density profile. We identify He IIλ4686 emission in the SN 2006bp ejecta. Days later, the spectraresemble the prototypical Type IIP SN 1999em, which had asupergiant-like photospheric composition. Despite the association of SN2005cs with possible X-ray emission, the emergent UV and optical lightcomes from the photosphere, not from circumstellar emission. We surmisethat the very steep density falloff we infer at early times may be afossil of the combined actions of the shock wave passage and radiationdriving at shock breakout. Based on tailored CMFGEN models, the directfitting technique and the expanding photosphere method both yielddistances and explosion times that agree within a few percent. We derivea distance to NGC 5194, the host of SN 2005cs, of 8.9+/-0.5 Mpc and17.5+/-0.8 Mpc for SN 2006bp in NGC 3953. The luminosity of SN 2006bp is1.5 times that of SN 1999em and 6 times that of SN 2005cs. Reliabledistances to SNe IIP that do not depend on a small range in luminosityprovide an independent route to the Hubble constant and improvedconstraints on other cosmological parameters.
| The Neon Abundance in the Ejecta of QU Vulpeculae from Late-Epoch Infrared Spectra
We present ground-based SpectroCam-10 mid-infrared, MMT optical, andSpitzer Space Telescope IRS mid-infrared spectra taken 7.62, 18.75, and19.38 yr, respectively, after the outburst of the old classical nova QUVulpeculae (Nova Vul 1984#2). The spectra of the ejecta are dominated byforbidden line emission from neon and oxygen. Our analysis shows thatneon was, at the first and last epochs respectively, more than 76 and168 times overabundant by number with respect to hydrogen compared tothe solar value. These high lower limits to the neon abundance confirmthat QU Vul involved a thermonuclear runaway on an ONeMg white dwarf,and approach the yields predicted by models of the nucleosynthesis insuch events.
| The interplay between ionized gas and massive stars in the HII galaxy IIZw70: integral field spectroscopy with PMAS
Aims.We performed an integral field spectroscopic study for the HIIgalaxy IIZw70 to investigate the interplay between its ionizedinterstellar medium (ISM) and the massive star formation. Methods:Observations were taken in the optical spectral range from λ3700Å-6800 Å with the Potsdam Multi-Aperture Spectrophotometer(PMAS) attached to the 3.5 m telescope at Calar Alto Observatory. Wecreated and analyzed maps of spatially distributed emission-lines (atdifferent stages of excitation), continuum emission, and properties ofthe ionized ISM (ionization structure indicators, physical-chemicalconditions, dust extinction, kinematics). We investigated the relationof these properties to the spatial distribution and evolutionary stageof the massive stars. Results: For the first time we have detectedWolf-Rayet (WR) stars in this galaxy. The peak of the ionized gasemission coincides with both the location of the maximum of the stellarcontinuum emission and the WR bump. The region of the galaxy with lowerdust extinction corresponds to the region that shows the lowest valuesof velocity dispersion and radial velocity. The overall picture suggeststhat the ISM of this region is being disrupted via photoionization andstellar winds, leading to a spatial decoupling between gas+stars anddust clouds. The bulk of dust appears to be located at the boundaries ofthe region occupied by the probable ionizing cluster. We also found thatthis region is associated to the nebular emission in HeIIλ4686and to the intensity maximum of most emission lines. This indicates thatthe hard ionizing radiation responsible for the HeIIλ4686 nebularemission can be related to the youngest stars. Within ~0.4 × 0.3kpc2 in the central burst, we derived oxygen abundances usingdirect determinations of T_e[OIII]. We found abundances in the range 12+ log(O/H) = 7.65-8.05, yielding an error-weighted mean of 12 + log(O/H)= 7.86 ± 0.05 that has been taken as the representative oxygenabundance for IIZw70.
| The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey
We use the ROSAT North Ecliptic Pole (NEP) survey to construct a small,but purely X-ray flux-limited sample of cataclysmic variable stars(CVs). The sample includes only four systems, two of which (RXJ1715.6+6856 and RX J1831.7+6511) are new discoveries. We presenttime-resolved spectroscopy of the new CVs and measure orbital periods of1.64 +/- 0.02 and 4.01 +/- 0.03h for RX J1715.6+6856 and RXJ1831.7+6511, respectively. We also estimate distances for all the CVsin our sample, based mainly on their apparent brightness in theinfrared. The space density of the CV population represented by oursmall sample is 1.1+2.3-0.7 ×10-5pc-3. We can also place upper limits on thespace density of any subpopulation of CVs too faint to be included inthe NEP survey. In particular, we show that if the overall space densityof CVs is as high as 2 × 10-4pc-3 (as hasbeen predicted theoretically), the vast majority of CVs must be fainterthan LX ~= 2 × 1029ergs-1.
| Discovery of polarized emission from the long period intermediate polar RX J2133.7+5107
Aims.We intended to investigate the magnetic field properties of therecently identified intermediate polar RX J2133.7+5107. Methods: Wecarried out UBVRI photopolarimetric observations of the target usingTURPOL on the Nordic Optical Telescope over 2 nights in July/August2006. Results: We found that RX J2133.7+5107 emitscircularly polarized light in all UBVRI bands (up to 3%). This is thefirst detection of circular polarization in this object. The circularpolarization modulations and flux variations give hints of cyclotronbeaming effects and suggest that the field strength in RXJ2133.7+5107 is possibly one of the highest found amongst theIPs. Conclusions: The highly asynchronous rotation of RXJ2133.7+5107 (the spin to orbital period ratio is ˜0.022), suggests that it has only recently come into contact andalthough it is likely to evolve into a polar, it is currently a long wayfrom doing so. We suggest a possible link between the detection of asoft X-ray blackbody component and polarized optical emission inintermediate polars.Based on observations obtained at the Nordic Optical Telescope at theRoque de los Muchachos Observatory in La Palma.
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Dades d'Observació i Astrometria
| Constel·lació: | Pegasus |
| Ascensió Recta: | 21h51m11.02s |
| Declinació: | +28°51'50.4" |
| Magnitud Aparent: | 10.563 |
| Moviment propi RA: | -36.9 |
| Moviment propi Dec: | -56.6 |
| B-T magnitude: | 10.147 |
| V-T magnitude: | 10.529 |
Catàlegs i designacions:
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