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Optical to Near-Infrared Spectrum of a Massive Evolved Galaxy at z = 1.26
We present the optical to near-infrared (IR) spectrum of the galaxy TSPSJ1329-0957, a red and bright member of the class of extremely redobjects (EROs) at z = 1.26. This galaxy was found in the course of theTokyo-Stromlo Photometry Survey (TSPS) which we are conducting in thesouthern sky. The spectroscopic observations were carried out with theGemini Multi-Object Spectrograph (GMOS) and the Gemini Near Infra-RedSpectrograph (GNIRS) mounted on the Gemini-South telescope. The widewavelength coverage of 0.6-2.3 μm provides useful clues as to thenature of EROs while most published spectra are limited to a narrowerspectral range which is dictated by the need for efficient redshiftdetermination in a large survey. We compare our spectrum with severaloptical composite spectra obtained in recent large surveys, and withstellar population synthesis models. The effectiveness of using near-IRbroadband data, instead of the spectral data, in deriving the galaxyproperties are also investigated. We find that TSPS J1329-0957 formedwhen the universe was 2-3 Gyr old, and subsequently evolved passively tobecome one of the most massive galaxies found in the z = 1-2 universe.Its early type and estimated stellar mass ofM*=1011.5 Msolar clearly point to thisgalaxy being a direct ancestor of the brightest elliptical andspheroidal galaxies in the local universe.
| Investigating ChaMPlane X-Ray Sources in the Galactic Bulge with Magellan LDSS2 Spectra
We have carried out optical and X-ray spectral analyses on a sample of136 candidate optical counterparts of X-ray sources found in fiveGalactic bulge fields included in our Chandra Multiwavelength PlaneSurvey. We use a combination of optical spectral fitting and quantileX-ray analysis to obtain the hydrogen column density toward each object,and a three-dimensional dust model of the Galaxy to estimate the mostprobable distance in each case. We present the discovery of a populationof stellar coronal emission sources, likely consisting ofpre-main-sequence, young main-sequence, and main-sequence stars, as wellas a component of active binaries of RS CVn or BY Dra type. We identifyone candidate quiescent low-mass X-ray binary with a subgiant companion;we note that this object may also be an RS CVn system. We report thediscovery of three new X-ray-detected cataclysmic variables (CVs) in thedirection of the Galactic center (at distances <~2 kpc). This numberis in excess of predictions made with a simple CV model based on a localCV space density of <~10-5 pc-3, and a scaleheight ~200 pc. We discuss several possible reasons for this observedexcess.
| Analysis of the FUSE Spectrum of the Hot, Evolved Star GD 605
We present an analysis of the atmospheric properties of the evolved,hydrogen-rich object GD 605 using FUSE, IUE, and optical spectra inconjunction with non-LTE (NLTE) model atmospheres and synthetic spectra.We also present an analysis of the interstellar medium along the line ofsight toward this star. Our effective temperature determination relieson the constraints on the ionization balance O IV/O V imposed by theFUSE data, while the surface gravity relies on a match to the Balmerlines in the optical spectrum. Our analysis yieldsTeff~85,000 K, logg~5.25, and a helium abundance close to thesolar value. These parameters suggest that GD 605 is in a post-AGBevolutionary phase and belongs to the class of hydrogen-rich centralstar of planetary nebulae, subclass O(H). Apart from lines of hydrogenand helium, about two dozen photospheric lines are observed in the FUSEdata, which are dominated by the O VI λλ1031.9 and 1037.6transitions. In addition, we detect lines associated with the followingions: N IV, O IV, O V, Si IV, S VI, Ar VII, as well as Fe VII. Syntheticspectra based on NLTE line-blanketed model atmospheres reproduce most ofthe line profiles observed in what appears to be an atmosphere deficientin heavy elements. Our calculations do not fully reproduce the strengthof the strongest ultraviolet lines seen, the O VI doublet, perhaps asign that some contribution to this structure may arise in theinterstellar medium or in a circumstellar environment. We discussvarious scenarios to account for the absence of a visible nebula and thedearth of heavy elements in the atmosphere of GD 605.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Precise Estimates of the Synthetic Spectral Distances to DA White Dwarfs
Using recent photometric calibrations, we develop greatly improveddistance estimates for DA white dwarfs using multi-band syntheticphotometry based on spectroscopic temperatures and gravities. Very goodcorrelations are shown to exist between our spectroscopically basedphotometric distance estimates and those derived from trigonometricparallaxes. We investigate the uncertainties involved in our distanceestimates, as well as discuss the circumstances where such techniquesare most likely to fail. We apply our techniques to the large sample ofSloan Digital Sky Survey DA white dwarfs where automated fitting of H IBalmer profiles yields spectrometric temperatures and gravities. Wedetermine simple empirical corrections to these temperatures andgravities with respect to published slit spectroscopy. After applyingthese T eff-log g corrections as well as appropriateinterstellar extinction corrections, where necessary, we derivespectroscopically based photometric distances for 7062 DA stars fromthis sample.
| a New Look at the Local White Dwarf Population
We have conducted a detailed new survey of the local population of whitedwarfs lying within 20 pc of the Sun. A new revised catalog of localwhite dwarfs containing 122 entries (126 individual degenerate stars) ispresented. This list contains 27 white dwarfs not included in a previouslist from 2002, as well as new and recently published trigonometricparallaxes. In several cases new members of the local white dwarfpopulation have come to light through accurate photometric distanceestimates. In addition, a suspected new double degenerate system (WD0423+120) has been identified. The 20 pc sample is currently estimatedto be 80% complete. Using a variety of recent spectroscopic,photometric, and trigonometric distance determinations, we re-compute aspace density of 4.8 ± 0.5 × 10 3 pc3 corresponding to a mass density of 3.2 ± 0.3 ×10 3 M sun pc 3 from the completeportion of the sample within 13 pc. We find an overall mean mass for thelocal white dwarfs of 0.665 M sun, a value larger than mostother non-volume-limited estimates. Although the sample is small, wefind no evidence of a correlation between mass and temperature in whichwhite dwarfs below 13,000 K are systematically more massive than thoseabove this temperature. Within 20 pc 25% of the white dwarfs are inbinary systems (including double degenerate systems). Approximately 6%are double degenerates and 6.5% are Sirius-like systems. The fraction ofmagnetic white dwarfs in the local population is found to be 13%.
| 174P/Echeclus: a strange case of outburst
Context: More than ten Centaurs are now known to have cometary activityat large heliocentric distance (i.e. ≃5-13 AU). Among theseobjects, 174P/Echeclus which showed cometary activity at 13 AU from theSun, is a unique case, because of: (i) the amplitude of its outburst,(ii) the source of cometary activity that appears distinct from Echeclusitself. Aims: This paper aims at investigating the physical conditionsthat have led to this unusual outburst. The purpose is also to quantifythis phenomenon and to provide observational constraints for itsmodeling. Methods: We use observations from different telescopes,performed before, during, and after the outburst. We performed the mainobservations on March 23 and 30, 2006, with the 8.2-m ESO Very LargeTelescope and FORS 1 instrument. They consist of visible images andspectra. Results: Our main results are: (i) a cometary source distinctfrom Echeclus itself that presents a brightness distribution compatiblewith a diffuse source; (ii) a total dust production rate Q_dust≃ 86kg s-1 and a parameter Afρ≃ 10 000 cm; (iii) noemission lines (CN and C2) can be detected in the visible range; (iv)the upper limits for the CN and C2 production rates are≃3.8×1025 and ≃1026 moleculess-1 respectively; (v) we detected no Echeclus' satellitebefore the outburst up to MR ≃ 26; (vi) the upper limitfor the object generating the coma is about 8 km in diameter; (vi) andwe detected no cometary activity one year later, in March 2007.Based on observations collected at the European Southern Observatory,Chile: ESO N° 71.C-0092(A), 276.C-5042(B) and 278.C-5046(A).
| The initial-final mass relationship from white dwarfs in common proper motion pairs
Context: The initial-final mass relationship of white dwarfs, which ispoorly constrained, is of paramount importance for different aspects ofmodern astrophysics. From an observational perspective, most of thestudies up to now have been done using white dwarfs in open clusters. Aims: In order to improve the initial-final mass relationship, weexplore the possibility of deriving a semi-empirical relation studyingwhite dwarfs in common proper motion pairs. If these systems arecomprised of a white dwarf and a FGK star, the total age and themetallicity of the progenitor of the white dwarf can be inferred fromthe detailed analysis of the companion. Methods: We have performed anexhaustive search for common proper motion pairs containing a DA whitedwarf and a FGK star using the available literature and crossing theSIMBAD database with the Villanova White Dwarf Catalog. We have acquiredlong-slit spectra of the white dwarf members of the selected commonproper motion pairs, as well as high resolution spectra of theircompanions. From these observations, a full analysis of the two membersof each common proper motion pair leads to the initial and final massesof the white dwarfs. Results: These observations have allowed us toprovide updated information for the white dwarfs, since some of themwere misclassified. In the case of the DA white dwarfs, theiratmospheric parameters, masses, and cooling times have been derivedusing appropriate white dwarf models and cooling sequences. From adetailed analysis of the FGK star spectra we have inferred themetallicity. Then, using either isochrones or X-ray luminosities we haveobtained the main-sequence lifetime of the progenitors, and subsequentlytheir initial masses. Conclusions: This work is the first one usingcommon proper motion pairs to improve the initial-final massrelationship, and has also allowed us to cover the poorly exploredlow-mass domain. As in the case of studies based on white dwarfs in openclusters, the distribution of the semi-empirical data presents a largescatter, which is higher than the expected uncertainties in the derivedvalues. This suggests that the initial-final mass relationship may notbe a single-valued function.Based on observations obtained at: Calar Alto Observatory,Almería, Spain, el Roque de los Muchachos, Canary Islands, Spain,McDonald Observatory, Texas, USA, and Las Campanas Observatory, Chile.Tables [see full textsee full textsee full text], [see full textsee fulltextsee full text] and [see full textsee full textsee full text] areonly available in electronic form at http://www.aanda.org
| Cluster and nebular properties of the central star-forming region of NGC 1140
We present new high spatial resolution Hubble Space Telescope/AdvancedCamera for Surveys (ACS) imaging of NGC 1140 and high spectralresolution Very Large Telescope/Ultraviolet and Visual EchelleSpectrograph spectroscopy of its central star-forming region. Thecentral region contains several clusters, the two brightest of which areclusters 1 and 6 from Hunter, O'Connell & Gallagher, located withinstar-forming knots A and B, respectively. A nebular analysis indicatesthat the knots have a Large Magellanic Cloud-like metallicity of 12 +logO/H = 8.29 +/-0.09. According to continuum-subtracted Hα ACSimaging, cluster 1 dominates the nebular emission of the brighter knotA. Conversely, negligible nebular emission in knot B originates fromcluster 6. Evolutionary synthesis modelling implies an age of 5 +/-1 Myrfor cluster 1, from which a photometric mass of (1.1 +/-0.3) ×106Msolar is obtained. For this age andphotometric mass, the modelling predicts the presence of ~5900 late Ostars within cluster 1. Wolf-Rayet (WR) features are observed in knot A,suggesting 550 late-type nitrogen-rich (WNL) and 200 early-typecarbon-rich (WCE) stars. Therefore, N(WR)/N(O) ~ 0.1, assuming that allthe WR stars are located within cluster 1. The velocity dispersions ofthe clusters were measured from constituent red supergiants as σ ~23 +/-1kms-1 for cluster 1 and σ ~ 26+/-1kms-1 for cluster 6. Combining σ with half-lightradii of 8 +/- 2 and 6.0 +/-0.2 pc measured from the F625W ACS imageimplies virial masses of (10 +/-3) × 106 and (9.1+/-0.8) × 106Msolar for clusters 1 and 6,respectively. The most likely reason for the difference between thedynamical and photometric masses of cluster 1 is that the velocitydispersion of knot A is not due solely to cluster 1, as assumed, but hasan additional component associated with cluster 2.E-mail: s.moll@sheffield.ac.ukBased on observations collected at the European Southern Observatory,Chile, under programme ESO 71.B-0058(A), and on observations obtainedwith the NASA/ESA Hubble Space Telescope, which is operated by theAssociation of Universities for Research in Astronomy, Incorporated,under NASA contract NAS 5-26555.
| Spectropolarimetry of the Type IIb Supernova 2001ig
We present spectropolarimetric observations of the Type IIb SN 2001ig inNGC 7424; conducted with the ESO VLT FORS1 on 2001 December 16, 2002January 3, and 2002 August 16, or 13, 31, and 256 days postexplosion.These observations are at three different stages of the SN evolution:(1) the hydrogen-rich photospheric phase, (2) the Type II to Type Ibtransitional phase, and (3) the nebular phase. At each of these stages,the observations show remarkably different polarization properties as afunction of wavelength. We show that the degree of interstellarpolarization is 0.17%. The low intrinsic polarization (~0.2%) at thefirst epoch is consistent with an almost spherical (<10% deviationfrom spherical symmetry) hydrogen-dominated ejecta. Similar to SN 1987Aand to Type IIP SNe, a sharp increase in the degree of the polarization(~1%) is observed when the outer hydrogen layer becomes optically thinby day 31; only at this epoch is the polarization well described by a``dominant axis.'' The polarization angle of the data shows a rotationthrough ~40° between the first and second epochs, indicating thatthe asymmetries of the first epoch were not directly coupled with thoseobserved at the second epoch. For the most polarized lines, we observewavelength-dependent loop structures in addition to the dominant axis onthe Q-U plane. We show that the polarization properties of Type IIb SNeare roughly similar to one another, but with significant differencesarising due to line blending effects especially with the high velocitiesobserved for SN 2001ig. This suggests that the geometry of SN 2001ig isrelated to SN 1993J and that these events may have arisen from a similarbinary progenitor system.Based on observations made with ESO Telescopes at the ParanalObservatory, under programs 68.D-0571 and 69.D-0438.
| Hα Tail, Intracluster H II Regions, and Star Formation: ESO 137-001 in Abell 3627
We present the discovery of a 40 kpc Hα tail and at least 29emission-line objects downstream of a star-forming galaxy, ESO 137-001,in the rich, nearby cluster A3627. The galaxy is known to possess adramatic 70 kpc X-ray tail. The detected Hα tail coincidespositionally with the X-ray tail. The Hα emission in the galaxy issharply truncated on the front and the sides near the nucleus,indicating significant ram pressure stripping. ESO 137-001 is thus thefirst cluster late-type galaxy known unambiguously to have both an X-raytail and an Hα tail. The emission-line objects are all distributeddownstream of the galaxy, with projected distances of up to 39 kpc fromthe galaxy. From the analysis on the Hαoff frame andthe estimate of the background emission-line objects, we conclude thatit is very likely that all 29 emission-line objects are H II regions inA3627. The high surface number density and luminosities of these H IIregions (up to 1040 ergs s-1) dwarf the previouslyknown examples of isolated H II regions in clusters. We suggest thatstar formation may proceed in the stripped ISM in both the galactic haloand intracluster space. The total mass of formed stars in the strippedISM of ESO 137-001 may approach several times 107Msolar. Therefore, stripping of the ISM not only contributesto the ICM, but also adds to the intracluster stellar light throughsubsequent star formation. The data also imply that ESO 137-001 is in anactive stage of transformation accompanied by the buildup of a centralbulge and depletion of the ISM.
| Spectroscopy of horizontal branch stars in NGC 6752. Anomalous results on atmospheric parameters and masses
Context: The determination of fundamental parameters for horizontalbranch stars in Galactic globular clusters frequently gives puzzlingresults, pointing to the lack of our understanding of their atmosphericstructure and the inadequate approximations by the models. Aims: Wewanted to measure effective temperatures, surface gravities, heliumabundances, and masses for hot horizontal branch stars in NGC6752 in order to compare the results with evolutionarypredictions. Methods: We used the ESO VLT-FORS2 facility to collectlow-resolution spectra of 51 targets distributed along the horizontalbranch. We determined atmospheric parameters, by comparison withtheoretical models through standard fitting routines, and masses bybasic equations. Results: Results generally agree with previous works,although not always with the theoretical expectations for cooler stars(T_eff≤ 15 000 K). The calculated color excess is systematicallylower than the literature values, pointing towards a possibleunderestimation of effective temperatures. Moreover, we find two groupsof stars at T_eff˜14 000 K and at T_eff˜27 000 K thatpresent anomalies with respect to the general trend and expectations. Wesuppose that the three peculiar bright stars at T_eff˜14 000 K areprobably affected by an enhanced stellar wind. For the eight extremehorizontal branch stars at T_eff˜27 000 K that show unusually highmasses, we find no plausible explanation. Conclusions: While most ofour results agree well with the predictions of standard horizontalbranch evolution, we still have problems with the low masses we derivein certain temperature ranges. We believe that Kurucz ATLAS9 LTE modelatmospheres with solar-scaled abundances are probably inadequate forthese temperature ranges. Concerning the group of anomalous stars atT_eff˜27 000 K, a Kolmogorov-Smirnov test indicates that there isonly an 8.4% probability that these stars are randomly drawn from thegeneral distribution in the color-magnitude diagram. This is notconclusive but indicates that these stars could be both (andindependently) spectroscopically and photometrically peculiar withrespect to the general extreme horizontal branch population.Based on observations with the ESO Very Large Telescope at ParanalObservatory, Chile (proposal ID 69.D-0682).
| A Comparative Study of Optical and Ultraviolet Effective Temperatures for DA White Dwarfs from the IUE Archive
We present a comparative study of effective temperatures determined fromthe hydrogen Balmer lines and from the UV energy distribution for 140 DAwhite dwarfs drawn from the International Ultraviolet Explorer (IUE)archive. Our results indicate that the optical and UV temperatures ofthe majority of stars below Teff~40,000 K and within ~75 pcare in fairly good agreement given the uncertainties. At highertemperatures and/or larger distances, however, significant discrepanciesare observed. Several mechanisms are investigated to account for thesediscrepancies, including the effect of interstellar reddening, thepresence of metals in the photosphere, and the existence of unresolvedbinary white dwarfs. The results of our analysis reveal thatwavelength-dependent extinction is the most natural explanation for theobserved temperature differences. We also attempt to predict thedifferences in optical and UV temperatures expected from unresolveddegenerate binaries by performing an exhaustive simulation of compositemodel spectra. In light of these simulations, we then discuss some knowndouble degenerates and identify new binary candidates by restricting ouranalysis to stars located within 75 pc, where the effect of interstellarreddening is significantly reduced.
| Cool Customers in the Stellar Graveyard. IV. Spitzer Search for Mid-IR excesses Around Five DAs
Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs,require external accretion of material to explain the presence of weakmetal-line absorption in their photospheres. The source of this materialis currently unknown, but could come from the interstellar medium,unseen companions, or relic planetesimals from asteroid belt or KuiperBelt analogs. Accurate mid-infrared photometry of these white dwarfsprovides additional information to solve the mystery of this accretionand to look for evidence of planetary systems that have survivedpost-main-sequence evolution. We present Spitzer Space Telescope IRACphotometry accurate to ~3% for four DAZs and one DA with circumstellarabsorption lines in the UV. We search for excesses due to unseencompanions or circumstellar dust disks. We use Hubble Space TelescopeNICMOS imaging of these white dwarfs to gauge the level of backgroundcontamination to our targets, as well as to rule out common propermotion companions to WD 1620-391. All of our targets show no excessesdue to companions >20 MJ, ruling out all but very low masscompanions to these white dwarfs at all separations. No excesses due tocircumstellar disks are observed, and we place limits on what types ofdisks may still be present.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. These observations are associatedwith program 10560.
| Integrated spectral properties of 22 small angular diameter galactic open clusters
Aims.Flux-calibrated integrated spectra of a sample of 22 Galactic openclusters of small angular diameter are presented. With one exception(ESO 429-SC2), all objects have Galactic longitudes in the range208° < l < 33°. The spectra cover the range ≈3600-6800Å, with a resolution of ≈14 Å. The properties of thepresent cluster sample are compared with those of well-studied clusterslocated in two 90° sectors, centred at l = 257° and l =347°. The dissolution rate of Galactic open clusters in these twosectors is examined. Methods: Using the equivalent widths of the Balmerlines and comparing line intensities and continuum distribution of thecluster spectra with those of template cluster spectra with knownproperties, we derive both foreground reddening values and ages. Thus,we provide information independent of that determined throughcolour-magnitude diagrams. Results: The derived E(B-V) values for thewhole sample vary from 0.0 in ESO 445-SC74 to 1.90 in Pismis 24, whilethe ages range from ~3 Myr (NGC 6604 and BH 151) to ~3.5 Gyr (Ruprecht2). For six clusters (Dolidze 34, ESO 429-SC2, ESO 445-SC74, Ruprecht 2,BH 151 and Hogg 9) the foreground E(B-V) colour excesses and ages aredetermined for the first time. The results obtained for the remainingclusters show, in general terms, good agreement with previousphotometric results. Conclusions: The age and reddening distributionsof the present sample match those of known clusters in the two selectedGalactic sectors. The present results would favour a major dissolutionrate of star clusters in these two sectors. Two new solar-metallicitytemplates are defined corresponding to the age groups of (4-5) Myr and30 Myr among those of Piatti et al. (2002, MNRAS, 335, 233). The Piattiet al. templates of 20 Myr and (3-4) Gyr are here redefined.Based on observations made at Complejo Astronómico El Leoncito,which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina (CONICET) and the National Universities of LaPlata, Córdoba and San Juan, Argentina. Tables [see full text]-[see full text] and Appendix are only availablein electronic form at http://www.aanda.org
| Albus 1: A Very Bright White Dwarf Candidate
We have serendipitously discovered a previously unknown, bright source(BT=11.75+/-0.07 mag) with a very blueVT-Ks color, which we have named Albus 1. Aphotometric and astrometric study using Virtual Observatory tools hasshown that it possesses an appreciable proper motion and magnitudes andcolors very similar to those of the well-known white dwarf G191-B2B. Weconsider Albus 1 as a DA-type white dwarf located at about 40 pc. If itsnature is confirmed, Albus 1 would be the sixth brightest isolated whitedwarf in the sky, which would make it an excellent spectrophotometricstandard.
| On the orbital periods of the AM CVn stars HP Librae and V803 Centauri
We analyse high time resolution spectroscopy of the AM CVn stars HPLibrae and V803 Centauri, taken with the New Technology Telescope (NTT)and the Very Large Telescope (VLT) of the European Southern Observatory,Chile.We present evidence that the literature value for V803 Cen's orbitalperiod is incorrect, based on an observed `S-wave' in the binary'sspectrogram. We measure a spectroscopic period PV803Cen =1596.4 +/- 1.2s of the S-wave feature, which is significantly shorterthan the 1611-s periods found in previous photometric studies. Weconclude that the latter period likely represents a `superhump'. If oneassumes that our S-wave period is the orbital period, V803 Cen's massratio can be expected to be much less extreme than previously thought,at q ~ 0.07 rather than q ~ 0.016. This relaxes the constraints on themasses of the components considerably: the donor star then does not needto be fully degenerate, and the mass of the accreting white dwarf nolonger has to be very close to the Chandrasekhar limit.For HP Lib, we similarly measure a spectroscopic periodPHPLib = 1102.8 +/- 0.2s. This supports the identification ofHP Lib's photometric periods found in the literature, and theconstraints upon the masses derived from them.
| A WFI survey in the Chamaeleon II dark cloud
Aims.We present the results of an optical multi-band survey for low-masspre-main sequence (PMS) stars and young brown dwarfs (BDs) in theChamaeleon II (Cha II) dark cloud. This surveyconstitutes the complementary optical data to the c2d Spitzer Legacysurvey in Cha II. Methods: Using the wide-fieldimager (WFI) at the ESO 2.2 m telescope, we surveyed a sky area of about1.75 square degrees in Cha II. The region wasobserved in the R_c, I_c, and z broad-bands, in Hα and in twomedium-band filters centred at 856 and 914 nm. We selected PMS star andyoung BD candidates using colour-magnitude diagrams (CMDs) andtheoretical isochrones reproduced ad-hoc for the WFI at the ESO2.2mtelescope system. We reinforced the selection criteria by using thepreviously known PMS stars in Cha II to define thePMS locus on the CMDs and by investigating the infrared (IR) colours ofthe candidates. By exploiting the WFI intermediate-band photometry wealso estimated the effective temperature and the level of Hαemission of the candidates. Results: Our survey, which is one of thelargest and deepest optical surveys conducted so far in ChaII, recovered the majority of the PMS stars and 10 membercandidates of the cloud from previous IR surveys. In addition, thesurvey revealed 10 new potential members. From our photometriccharacterisation, we estimate that some 50% of the 20 candidates willresult in true Cha II members. Based on ourtemperature estimates, we conclude that several of these objects areexpected to be sub-stellar and give a first estimate of the fraction ofsub-stellar objects.Based on observations carried out at the European Southern Observatory,La Silla, Chile under proposals numbers 67.C-0225 and 68.C-0311.Appendices and Fig. 14 are only available in electronic form athttp://www.aanda.org Table 7 is available in electronic form athttp://www.aanda.org and at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/470/281
| First detection of Zeeman absorption lines in the polar VV Puppis. Observations of low activity states
Aims.We investigated the low state of the polar VV Pup by collectinghigh S/N time series spectra. Methods: We monitored VV Pup withVLT+FORS1 and analyzed the evolution of its spectroscopic featuresacross two orbits. Results: We report the first detection ofphotospheric Zeeman lines in VV Puppis. We argue that the photosphericfield structure is inconsistent with the assumption that the accretionshocks are located close to the foot points of a closed field line in adipolar field distribution. A more complex field structure and couplingprocess is implied making VV Puppis similar to other well studied AMHerculis type systems.Based ondata collected on the ESO VLT within the program 272.D-5044(A).
| The mass and luminosity functions and the formation rate of DA white dwarfs in the Sloan Digital Sky Survey
Aims.The SDSS Data Release 1 includes 1833 DA white dwarfs (WDs) andforms the largest homogeneous sample of WDs. This sample provides thebest opportunity to study the statistical properties of WDs. Methods:We adopt a recently established theoretical model to calculate the massand distance of each WD using the observational data. Then we adopt abin-correction method to correct for selection effects and use the 1/Vweight-factor method to calculate the luminosity function, thecontinuous mass function and the formation rate of these WDs. Results:The SDSS DA WD sample is incomplete and suffers seriously from selectioneffects. After corrections for the selection effects, only 531 WDsremain. From this final sample we derive the most up-to-date luminosityfunction and mass function, in which we find a broad peak of WD massescentered around 0.58 Mȯ. The DA WD space density iscalculated as 8.81×10-5 pc-3 and theformation rate is 2.579×10-13 pc-3yr-1. Conclusions: The statistical properties of the SDSS DAWD sample are generally in good agreement with previous observationaland theoretical studies, and provide us information on the formation andevolution of WDs. However, a larger and more complete all-sky WD sampleis still needed to explain some subtle disagreements and unresolvedissues.Full Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/627
| Simultaneous Multiwavelength Observations of the Low/Hard State of the X-Ray Transient Source SWIFT J1753.5-0127
We report the results of simultaneous multiwavelength observations ofthe X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL,RXTE, NTT, REM, and VLA on 2005 August 10-12. The source, whichunderwent an X-ray outburst since 2005 May 30, was observed during theINTEGRAL Target of Opportunity program dedicated to new X-ray novaelocated in the Galactic halo. Broadband spectra and fast timingvariability properties of SWIFT J1753.5-0127 are analyzed together withthe optical, near-infrared, and radio data. We show that the source wassignificantly detected up to 600 keV with Comptonization parameters andtiming properties typical of the so-called low/hard state of black holecandidates. We build a spectral energy distribution and show that SWIFTJ1753.5-0127 does not follow the usual radio/X-ray correlation of X-raybinaries in the low/hard state. We give estimates of distance and mass.We conclude that SWIFT J1753.5-0127 belongs to the X-ray nova class andthat it is likely a black hole candidate transient source of theGalactic halo that remained in the low/hard state during its mainoutburst. We discuss our results in the context of Comptonization andjet models.
| Spectroscopy of Globular Clusters out to Large Radius in the Sombrero Galaxy
We present new velocities for 62 globular clusters in M104 (NGC 4594,the Sombrero Galaxy), 56 from 2dF on the AAT and 6 from Hydra on WIYN.Combined with previous data, we have a total sample of 108 M104 globularcluster velocities, extending to 20' radius (~60 kpc), alongwith BVR photometry for each of these. We use this wide-field data setto study the globular cluster kinematics and dark matter content of M104out to 10' radius (30 kpc). We find no rotation in theglobular cluster system. The edge-on nature of M104 makes it unlikelythat there is strong rotation which is face-on and hence unobserved;thus, the absence of rotation over our large radial range appears to bean intrinsic feature of the globular cluster system in M104. We discussways to explain this low rotation, including the possibility thatangular momentum has been transferred to even larger radii throughgalaxy mergers. The cluster velocity dispersion is ~230 kms-1 within several arcminutes of the galaxy center, and dropsto ~150 km s-1 at ~10' radius. We derive the massprofile of M104 using our velocity dispersion profile, together with theJeans equation under the assumptions of spherical symmetry and isotropy,and find excellent agreement with the mass inferred from the stellar andgas rotation curve within 3' radius. The M/LVincreases from ~4 near the galaxy center to ~17 at 7' radius(~20 kpc, or 4 Re), thus giving strong support for thepresence of a dark matter halo in M104. More globular cluster velocitiesat larger radii are needed to further study the low rotation in theglobular cluster system, and to see if the dark matter halo in M104extends beyond a radius of 30 kpc.
| An extreme rotation measure in the high-redshift radio galaxy PKS B0529-549
We present the results of a radio polarimetric study of thehigh-redshift radio galaxy PKS B0529-549 (z = 2.575), based onhigh-resolution 12-mm and 3-cm images obtained with the AustraliaTelescope Compact Array. The source is found to have a rest-frameFaraday rotation measure of -9600 rad m-2, the largest seenthus far in the environment of a z > 2 radio galaxy. In addition, therest-frame Faraday dispersion in the screen responsible for the rotationis calculated to be 5800 rad m-2, implying rotation measuresas large as -15400 rad m-2. Using supporting near-infrared(near-IR) imaging from the Very Large Telescope, we suggest that therotation measure originates in the Lyα halo surrounding the hostgalaxy, and estimate the magnetic field strength to be ~10μG. We alsopresent a new optical spectrum of PKS B0529-549 obtained with the NewTechnology Telescope, and propose that the emission-line ratios are bestdescribed by a photoionization model. Furthermore, the host galaxy isfound to exhibit both hot dust emission at 8.0 μm and significantinternal visual extinction (~1.6 mag), as inferred from Spitzer SpaceTelescope near/mid-IR imaging.Based on observations collected at the European Southern Observatory(ESO), La Silla, Chile (programme 077.A-0471), and on observations madewith the European Southern Observatory telescopes obtained from theESO/ST-ECF Science Archive Facility (programme 64.P-0500).E-mail: jess@physics.usyd.edu.au
| Spectral types of planetary host star candidates from OGLE III
Context: The Optical Gravitational Lensing Experiment project hasrecently provided the OGLE III list of low-luminosity object transitsfrom campaigns #3 and #4, reporting 40 new objects exhibiting thelow-amplitude photometric eclipses expected for exoplanets. Compared toprevious OGLE targets, these OGLE III candidates have been morerestrictively selected and may contain low-mass planets. Aims: We havesecured follow-up low-resolution spectroscopy for 28 candidates out ofthis list (and one from the OGLE Carina fields) to obtain an independentcharacterization of the primary stars by spectral classification andthus better constrain the parameters of their companions. Methods: Wefed the constraints from these results back into an improved light curvesolution. Together with the radius ratios from the transit measurements,we derived the radii of the low-luminosity companions. This allows us toexamine the possible sub-stellar nature of these objects. Results:Sixteen of the companions can be clearly identified as low-mass starsorbiting a main sequence primary, while 10 more objects are likely tohave red giant primaries and therefore also host a stellar companion; 3possibly have a sub-stellar nature (R≤ 0.15 R_ȯ). Conclusions:.The planetary nature of these objects should therefore be confirmed bydynamical mass determinations.
| The fraction of DA white dwarfs with kilo-Gauss magnetic fields
Context: Weak magnetic fields have been searched for on only a smallnumber of white dwarfs. Current estimates find that about 10% of allwhite dwarfs have fields in excess of 1 MG; according to previousstudies this number increases up to about 25% in the kG regime. Aims:Our aim is to improve on these statistics by a new sample of ten whitedwarfs in order to determine the ratio of magnetic to field-free whitedwarfs. Methods: Mean longitudinal magnetic fields strengths weredetermined by means of high-precision circular polarimetry of Hβand Hγ with the FORS1 spectrograph of the VLT "Kueyen" 8 mtelescope. Results: In one of our objects (LTT 7987), we detected astatistically significant (97% confidence level) longitudinal magneticfield varying between (-1± 0.5) kG and (+1± 0.5) kG. Thiswould be the weakest magnetic field ever found in a white dwarf, butsystematic errors cannot completely be ruled out at this level ofaccuracy. We also observed the sdO star EC 11481-2303 but could notdetect a magnetic field. Conclusions: . VLT observations withuncertainties typically of 1000 G or less suggest that 15-20% of WDshave kG fields. Together with previous investigations, the fraction ofkG magnetic fields in white dwarfs amounts to about 11-15%, which isclose to the current estimations for highly magnetic white dwarfs (>1MG).Based on observations made with ESO Telescopes at the La Silla orParanal Observatories under programme ID 073.D-0356. Figures A.1 and A.2are only available in electronic form at http://www.aanda.org
| Spectropolarimetric Survey of Hydrogen-rich White Dwarf Stars
We have conducted a survey of 61 southern white dwarfs searching formagnetic fields using Zeeman spectropolarimetry. Our objective is toobtain a magnetic field distribution for these objects and, inparticular, to find white dwarfs with weak fields. We found one possiblecandidate (WD 0310-688) that may have a weak magnetic field of-6.1+/-2.2 kG. Next, we determine the fraction and distribution ofmagnetic white dwarfs in the solar neighborhood and investigate theprobability of finding more of these objects based on the currentincidence of magnetism in white dwarfs within 20 pc of the Sun. We havealso analyzed the spectra of the white dwarfs to obtain effectivetemperatures and surface gravities.
| Properties of planets in binary systems. The role of binary separation
Aims.The statistical properties of planets in binaries wereinvestigated. Any difference to planets orbiting single stars can shedlight on the formation and evolution of planetary systems. As planetswere found around components of binaries with very different separationand mass ratio, it is particularly important to study thecharacteristics of planets as a function of the effective gravitationalinfluence of the companion. Methods: .A compilation of planets inbinary systems was made; a search for companions orbiting stars recentlyshown to host planets was performed, resulting in the addition of twofurther binary planet hosts (HD 20782 and HD 109749). The probableoriginal properties of the three binary planet hosts with white dwarfscompanions were also investigated. Using this updated sample of planetsin binaries we performed a statistical analysis of the distributions ofplanet mass, period, and eccentricity, fraction of multiplanet systems,and stellar metallicity for planets orbiting components of tight andwide binaries and single stars. Results: .The only highlysignificant difference revealed by our analysis concerns the massdistribution of short-period planets. Massive planets in short periodorbits are found in most cases around the components of rather tightbinaries. The properties of exoplanets orbiting the components of widebinaries are compatible with those of planets orbiting single stars,except for a possible greater abundance of high-eccentricity planets.The previously suggested lack of massive planets with P>100 days inbinaries is not confirmed. Conclusions: .We conclude that thepresence of a stellar companion with separation smaller than 100-300 AUis able to modify the formation and/or migration and/or the dynamicalevolution history of giant planets while wide companions play a morelimited role.Table 1 and Appendices A-C are only available in electronic form athttp://www.aanda.org
| Protoclusters associated with z > 2 radio galaxies . I. Characteristics of high redshift protoclusters
We present the results of a large program conducted with the Very LargeTelescope and augmented by observations with the Keck telescope tosearch for forming clusters of galaxies near powerful radio galaxies at2.0 < z < 5.2. Besides MRC 1138-262 at z = 2.16, the radio galaxyobserved in our pilot program, we obtained narrow- and broad-band imagesof eight radio galaxies and their surroundings. The imaging was used toselect candidate Lyα emitting galaxies in 3×3Mpc2 areas near the radio galaxies. A total of 300 candidateemitters were found with a rest-frame Lyα equivalent width of EW0> 15 Å and significance Σ ≡ {EW}_0/Δ{EW}0 > 3. Follow-up spectroscopy was performed on 152candidates in seven of the radio galaxy fields. Of these, 139 wereconfirmed to be Lyα emitters, four were low redshift interlopersand nine were non-detections. With the adopted criteria the success rateis 139/152 = 91%. In addition, 14 objects with EW0 < 15 and/orΣ < 3 were confirmed to be Lyα emitters. Combined withthe 15 Lyα emitters near MRC 1138-262, we have determinedLyα redshifts for 168 objects near eight radio galaxies. At leastsix of our eight fields are overdense in Lyα emitters by a factor3-5 as compared to the field density of Lyα emitters at similarredshifts, although the statistics in our highest redshift field (z =5.2) are poor. Also, the emitters show significant clustering invelocity space. In the overdense fields, the width of the velocitydistributions of the emitters is a factor 2-5 smaller than the width ofthe narrow-band filters. Taken together, we conclude that we havediscovered six forming clusters of galaxies (protoclusters). We estimatethat roughly 75% of powerful (L_2.7 GHz > 1033 ergs-1 Hz-1 sr-1) high redshift radiogalaxies reside in a protocluster. The protoclusters have sizes of atleast 1.75 Mpc, which is consistent with the structure sizes found byother groups. By using the volume occupied by the overdensities andassuming a bias parameter of b=3-6, we estimate that the protoclustershave masses in the range 2-9 × 1014 Mȯ.These protoclusters are likely to be progenitors of present-day(massive) clusters of galaxies. For the first time, we have been able toestimate the velocity dispersion of cluster progenitors from z˜5to 2. The velocity dispersion of the emitters increases with cosmictime, in agreement with the dark matter velocity dispersion in numericalsimulations of forming massive clusters.
| New members in the Upper Scorpius association from the UKIRT Infrared Deep Sky Survey Early Data Release†
We present the results of a 9.3-deg2 infrared (ZYJHK) surveyin the Upper Scorpius association extracted from the UKIRT Infrared DeepSky Survey (UKIDSS) Galactic Cluster Survey Early Data Release. We haveselected a total of 112 candidates from the (Z - J,Z) colour-magnitudediagram over the Z = 12.5-20.5 magnitude range, corresponding to M =0.25-0.01 Msolar at an age of 5 Myr and a distance of 145 pc.Additional photometry in J and K filters revealed most of them asreddened stars, leaving 32 possible members. Among them, 15 have propermotion consistent with higher-mass members from Hipparcos and opticalspectra with strong Hα in emission and weak gravity features. Wehave also extracted two lower-mass candidate members for which nooptical spectra are in hand. Three members exhibit strong Hαequivalent widths (>20 Å), suggesting that they could stillundergo accretion, whereas two other dwarfs show signs of chromosphericactivity. The likelihood of the binarity of a couple of new stellar andsubstellar members is discussed as well.Based on observations made with the United Kingdom Infrared Telescope,operated by the Joint Astronomy Centre on behalf of the UK ParticlePhysics and Astronomy Research Council.Based on observations collected with the European Southern Observatory(ESO) 3.6-m/EFOSC2 at ESO, La Silla, Chile (ESO programme 076C-0237).‡E-mail: nl41@star.le.ac.uk
| Constraining the environment of GRB 990712 through emission line fluxes
Aims.The energy output in the gamma-ray burst (GRB) prompt emission andafterglow phase is expected to photoionize the surrounding medium out tolarge radii. Cooling of this gas produces line emission that isparticularly strong in the optical, whose variability is a strongdiagnostics of the gas density and geometry in the close environment ofthe burst. Methods: .We present the results of a spectraltime-series analysis of the host galaxy of GRB 990712 observed up to ~6years after the burst. We analyze the emission line fluxes, togetherwith those of the previous observations of the same GRB, in search ofphotoionization signatures. Results: .We find that the emissionline fluxes show no variation within the uncertainties up to 6 yearsafter the burst, and we use the measured line intensities to set a limiton the density of the gas within a few parsecs of the burst location.This is the first time that emission from cooling GRB remnants is probedon time scales of years.
| Calibration of Synthetic Photometry Using DA White Dwarfs
We have calibrated four major ground-based photometric systems withrespect to the Hubble Space Telescope (HST) absolute flux scale, whichis defined by Vega and four fundamental DA white dwarfs. Thesephotometric systems include the Johnson-Kron-Cousins UBVRI, theStrömgren uvby filters, the Two Micron All Sky SurveyJHKs, and the Sloan Digital Sky Survey ugriz filters.Synthetic magnitudes are calculated from model white dwarf spectrafolded through the published filter response functions; these magnitudesin turn are absolutely calibrated with respect to the HST flux scale.Effective zero-magnitude fluxes and zero-point offsets of each systemare determined. In order to verify the external observationalconsistency, as well as to demonstrate the applicability of thesedefinitions, the synthetic magnitudes are compared with the respectiveobserved magnitudes of larger sets of DA white dwarfs that havewell-determined effective temperatures and surface gravities and span awide range in both of these parameters.
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