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A principal component analysis approach to the star formation history of elliptical galaxies in compact groups
Environmental differences in the stellar populations of early-typegalaxies are explored using principal component analysis (PCA), focusingon differences between elliptical galaxies in Hickson Compact Groups(HCGs) and in the field. The method is model-independent and purelyrelies on variations between the observed spectra. The projections (PC1,PC2) of the observed spectra on the first and second principalcomponents reveal a difference with respect to environment, with a widerrange in PC1 and PC2 in the group sample. We define a spectral parameter(ζ ≡ 0.36PC1-PC2) which simplifies this result to a singlenumber: field galaxies have a very similar value of ζ, whereas HCGgalaxies span a wide range in this parameter. The segregation is foundregardless of the way the input spectral energy distributions (SEDs) arepresented to PCA (i.e. changing the spectral range; using uncalibrateddata; subtracting the continuum or masking the SED to include only theLick spectral regions). Simple models are applied to give physicalmeaning to the PCs. We obtain a strong correlation between the values ofζ and the mass fraction in younger stars, so that some groupgalaxies present a higher fraction of them, implying a more complex starformation history in groups. Regarding `dynamically related' observablessuch as a4 or velocity dispersion, we find a correlation withPC3, but not with either PC1 or PC2. PCA is more sensitive than othermethods based on a direct analysis of observables such as the structureof the surface brightness profile or the equivalent width of absorptionlines. The latter do not reveal any significant variation between fieldand compact group galaxies. Our results imply that the presence of youngstars only amounts to a fraction of a per cent in its contribution tothe total variance, reflecting the power of PCA as a tool to extractsmall variations in the spectra from unresolved stellar populations.
| NGC 7419: a young open cluster with a number of very young intermediate mass pre-MS stars
We present a photometric and spectroscopic study of the young opencluster NGC 7419, which is known to host a large number of classical Bestars for reasons not well understood. Based on CCD photometricobservations of 327 stars in UBV passbands, we estimated the clusterparameters as, reddening [E(B - V)] = 1.65 +/- 0.15 mag and distance =2900 +/- 400 pc. The turn-off age of the cluster was estimated as 25 +/-5 Myr using isochrone fits. UBV data of the stars were combined with theJHK data from Two-Micron All-Sky Survey (2MASS) and were used to createthe near-infrared (NIR) (J - H) versus (H - K) colour-colour diagram. Alarge fraction of stars (42 per cent) was found to have NIR excess andtheir location in the diagram was used to identify them as intermediatemass pre-main-sequence (MS) stars. The isochrone fits to pre-MS stars inthe optical colour-magnitude diagram showed that the turn-on age of thecluster is 0.3-3 Myr. This indicates that there has been a recentepisode of star formation in the vicinity of the cluster.Slitless spectra were used to identify 27 stars which showed Hα inemission in the field of the cluster, of which six are newidentifications. All these stars were found to show NIR excess and arelocated closer to the region populated by Herbig Ae/Be stars in the (J -H) versus (H - K) diagram. Slit spectra of 25 stars were obtained in theregion 3700-9000 Å. The spectral features were found to be verysimilar to those of Herbig Be stars. These stars were found to be morereddened than the main-sequence stars by 0.4 mag, on an average. Thus,the emission-line stars found in this cluster are more similar to theHerbig Be-type stars where the circumstellar material is the remnant ofthe accretion disc. We conclude that the second episode of starformation has led to the formation of a large number of Herbig Be starsas well as intermediate mass pre-MS stars in the field of NGC 7419, thusexplaining the presence of emission-line stars in this cluster. Thiscould be one of the young open clusters with the largest number ofHerbig Be stars.
| Post-outburst phase of McNeil's nebula (V1647 Orionis)
We present a detailed study of the post-outburst phase of McNeil'snebula (V1647 Orionis) using optical B, V, R, I and near-infrared (NIR)J, H, K photometric and low-resolution optical spectroscopicobservations. The observations were carried out with the Himalaya FaintObject Spectrograph Camera (HFOSC), NIR camera (NIRCAM), the TataInstitute of Fundamental Research (TIFR) Near-Infrared Camera (TIRCAM)and NICMOS cameras on the 2-m Himalayan Chandra Telescope (HCT) and1.2-m Physical Research Laboratory (PRL) telescopes during the period2004 February-2005 December. The optical and NIR observations show ageneral decline in the brightness of the exciting source of McNeil'snebula (V1647 Ori). Our recent optical images show that V1647 Ori hasfaded by more than 3 mag since February 2004. McNeil's nebula has alsofaded considerably. The optical/NIR photometric data also show asignificant variation in the magnitudes (ΔV= 0.78, ΔR= 0.44,ΔI= 0.21, ΔJ= 0.24 and ΔH= 0.20 mag) of V1647 Oriwithin a period of one month, which is possibly undergoing a phasesimilar to eruptive variables, like EXors or FUors. The optical spectrashow a few features such as strong Hα emission with blue-shiftedabsorption and the CaII IR triplet (8498, 8542 and 8662 Å) inemission. As compared to the period just after outburst, there is adecrease in the depth and extent of the blue-shifted absorptioncomponent, indicating a weakening in the powerful stellar wind. Thepresence of the CaII IR triplet in emission confirms that V1647 Ori is apre-main-sequence star. The long-term, post-outburst photometricobservations of V1647 Ori suggest an EXor rather than an FUor event. Anoptical/IR comparison of the region surrounding McNeil's nebula showsthat the optical nebula is more widely and predominantly extended to thenorth, whereas the IR nebula is relatively confined (diameter ~60arcsec), but definitely extended, to the south, too. The large colourgradient from north to south and the sudden absence of an optical nebulato the south are suggestive of a large-scale disc-like structure (orenvelope) surrounding the central source that hides the southern nebula.
| Neon and Oxygen Abundances in M33
We present new spectroscopic observations of 13 H II regions in theLocal Group spiral galaxy M33. The regions observed range from 1 to 7kpc in distance from the nucleus. Of the 13 H II regions observed, the[O III] λ4363 line was detected in six regions. Electrontemperatures were thus able to be determined directly from the spectrausing the [O III] λλ4959, 5007/λ4363 line ratio.Based on these temperature measurements, oxygen and neon abundances andtheir radial gradients were calculated. For neon, a gradient of-0.016+/-0.017 dex kpc-1 was computed, which agrees with theNe/H gradient derived previously from ISO spectra. A gradient of-0.012+/-0.011 dex kpc-1 was computed for O/H, much shallowerthan was derived in previous studies. The newly calculated O/H and Ne/Hgradients are in much better agreement with each other, as expected frompredictions of stellar nucleosynthesis. We examine the correlationbetween the WC/WN ratio and metallicity, and find that the new M33abundances do not impact the observed correlation significantly. We alsoidentify two new He II-emitting H II regions in M33, the first to bediscovered in a spiral galaxy other than the Milky Way. In both casesthe nebular He II emission is not associated with Wolf-Rayet stars.Therefore, caution is warranted in interpreting the relationship betweennebular He II emission and Wolf-Rayet stars when both are observed inthe integrated spectrum of an H II region.
| Are isolated planetary-mass objects really isolated?. A brown dwarf-exoplanet system candidate in the σ Orionis cluster
Context: .Free-floating planetary-mass objects have masses below thedeuterium burning mass limit at about 13 Jupiter masses, and have mostlybeen found in very young open clusters. Their origin and relationship tostars and brown dwarfs are still a mystery. Aims: .The recentdetection by direct imaging of three giant planets at wide separation(50-250 AU) from their primaries has raised the question about the true"isolation" of planetary-mass objects in clusters. Our goal was to testthe possibility that some free-floating planetary-mass objects could infact be part of wide planetary systems. Methods: .We searched inthe literature for stellar and brown-dwarf candidates members of theσ Orionis cluster (~3 Ma, ~360 pc) at small angular separationsfrom published candidate planetary-mass objects. We found one candidateplanetary system composed of an X-ray source, SE 70, and aplanetary-mass object, S Ori 68, separated by only 4.6 arcsec. In orderto assess the cluster membership of the X-ray source, we obtainedmid-resolution optical spectroscopy using ISIS on the William HerschelTelescope. We also compiled additional data on the target from availableastronomical catalogues. Results: .We have found that SE 70follows the spectrophotometric sequence of the cluster and displaysspectroscopic features of youth, such as lithium in absorption andchromospheric Hα emission. The radial velocity is consistent withcluster membership. Hence, SE 70 is very probably a member of theσ Orionis cluster. The projected physical separation between SE 70and S Ori 68 is 1700~± 300 AU at the distance of the cluster. Ifa common proper motion is confirmed in the near future, the system wouldbe composed of an M5-6 brown dwarf with an estimated mass of ~45 M_Jupand an L5 ± 2 giant planet with an estimated mass of ~5 M_Jup. Itwould be the widest and one of the lowest-mass planetary systems knownso far.
| Spectroscopic observations of the rapid rotating post-AGB star IRAS 05381+1012
We report on the high-resolution stellar parameters and abundanceanalysis of the rapidly rotating post-AGB star IRAS 05381+1012. Analysisof high-resolution spectra shows that IRAS 05381+1012 has an effectivetemperature of T_eff=5200± 100 K and a surface gravity of logg=1.0± 0.5 corresponding to a spectral type G(2-3)I. Theseparameters result in an estimated luminosity of 970 Lȯand a distance of 2700 pc. We also show that IRAS 05381+1012 has aprojected rotational velocity vsin i=40± 10 km s-1.The abundance analysis based on a few available lines reveals that thisstar is an iron-deficient object with [Fe/H]=-0.8. We also analyze theabundance pattern and compare it to other classes of stars with similarstellar parameters.
| The afterglow of GRB 050709 and the nature of the short-hard γ-ray bursts
The final chapter in the long-standing mystery of the γ-ray bursts(GRBs) centres on the origin of the short-hard class of bursts, whichare suspected on theoretical grounds to result from the coalescence ofneutron-star or black-hole binary systems. Numerous searches for theafterglows of short-hard bursts have been made, galvanized by therevolution in our understanding of long-duration GRBs that followed thediscovery in 1997 of their broadband (X-ray, optical and radio)afterglow emission. Here we present the discovery of the X-ray afterglowof a short-hard burst, GRB 050709, whose accurate position allows us toassociate it unambiguously with a star-forming galaxy at redshift z =0.160, and whose optical lightcurve definitively excludes a supernovaassociation. Together with results from three other recent short-hardbursts, this suggests that short-hard bursts release much less energythan the long-duration GRBs. Models requiring young stellar populations,such as magnetars and collapsars, are ruled out, while coalescingdegenerate binaries remain the most promising progenitor candidates.
| An atlas of calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering theregion around the λλ8498, 8542, 8662 calcium triplet(CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26Seyfert 1s, three starburst and six normal galaxies. The spectra pertainto the inner ~300 pc in radius, and thus sample the central kinematicsand stellar populations of active galaxies. The data are used to measurestellar velocity dispersions (σ*) with bothcross-correlation and direct fitting methods. These measurements arefound to be in good agreement with each other and with those in previousstudies for objects in common. The CaT equivalent width is alsomeasured. We find average values and sample dispersions ofWCaT of 4.6 +/- 2.0, 7.0 +/- 1.0 and 7.7 +/- 1.0 Å forSeyfert 1s, Seyfert 2s and normal galaxies, respectively. We furtherpresent an atlas of [SIII]λ9069 emission-line profiles for asubset of 40 galaxies. These data are analysed in a companion paperwhich addresses the connection between stellar and narrow-line regionkinematics, the behaviour of the CaT equivalent width as a function ofσ*, activity type and stellar population properties.
| The Distance and Metallicity of the Newly Discovered, Nearby Irregular Galaxy HIZSS 3
HIZSS 3 is an H I source in the Zone of Avoidance. Its radiocharacteristics are consistent with it being a previously unknown,nearby (~1.8 Mpc), low-mass dwarf irregular (dIrr) galaxy. Opticalobservations have shown that it contains a modest H II region, but theyfailed to reveal a resolved stellar population. New spectroscopicobservations of the H II region obtained at the MMT Observatory arepresented here. They are used to derive the line-of-sight extinction[E(B-V)=1.41+/-0.04] and gas metallicity (logO/H+12~7.8) of the H IIregion. New near-IR imaging observations obtained at the ESO Very LargeTelescope are also presented here. These images clearly reveal theresolved stellar population of HIZSS 3 for the first time. NarrowbandPaβ images of the H II region are used in combination withpreviously published Hα data to obtain an independentline-of-sight extinction estimate: E(B-V)=1.32+/-0.04. The adoptedforeground extinction is E(B-V)=1.36+/-0.06. Using the K-band luminosityfunction and K,J-K color-magnitude diagram, the apparent magnitude andcolor of the tip of the red giant branch are derived. In turn, theseparameters are combined with the adopted foreground extinction toestimate the distance (1.69+/-0.07 Mpc) and mean red giant branchmetallicity ([Fe/H]=-0.5+/-0.1). As an ensemble, these new observationssignificantly strengthen the conclusion that HIZSS 3 is a newlydiscovered low-mass dIrr galaxy lurking behind the Milky Way in theoutskirts of the Local Group.The optical spectroscopic observations reported here were obtained atthe MMT Observatory, a joint facility of the Smithsonian Institution andthe University of Arizona. The near-IR imaging observations reportedhere were collected at the European Southern Observatory, Cerro Paranal,Chile, within observing program 271.B-5047.
| Studying the Variation of the Fine-Structure Constant Using Emission-Line Multiplets
As an extension of the method by Bahcall and coworkers to investigatethe time dependence of the fine-structure constant, we describe anapproach based on new observations of forbidden-line multiplets fromdifferent ionic species. We obtain optical spectra of fine-structuretransitions in [Ne III], [Ne V], [O III], [O I], and [S II] multipletsfrom a sample of 14 Seyfert 1.5 galaxies in the low-z range0.035
| Old Globular Clusters Masquerading as Young in NGC 4365?
High signal-to-noise ratio, low-resolution spectra have been obtainedfor 22 globular clusters (GCs) in NGC 4365. Some of these were selectedas probable representatives of an intermediate-age (2-5 Gyr), extremelymetal-rich GC subpopulation. The presence of such a subpopulation hadbeen inferred from the unusual optical and near-infrared colordistributions of GCs in this otherwise typical Virgo elliptical galaxy.However, ages derived from Lick indices are consistent with uniformlyold mean ages for all GCs in our sample. The metallicities of theclusters show some evidence of a trimodal distribution. The mostmetal-poor and metal-rich peaks are consistent with the values expectedfor an elliptical galaxy of this luminosity, but there appears to be anadditional, intermediate-metallicity peak lying between them. New HubbleSpace Telescope photometry is consistent with this result. A plausiblescenario is that in earlier data these three peaks merged into a singlebroad distribution. Our results suggest that it is difficult to identifyintermediate-age GC subpopulations solely with photometry, even whenboth optical and near-infrared colors are used.
| Signature of Electron Capture in Iron-rich Ejecta of SN 2003du
Late-time near-infrared and optical spectra of the normal-bright Type Iasupernova 2003du about 300 days after the explosion are presented. Atthis late epoch, the emission profiles of well-isolated [Fe II] lines(in particular that of the strong 1.644 μm feature) trace out theglobal kinematic distribution of radioactive material in the expandingsupernova ejecta. In SN 2003du, the 1.644 μm [Fe II] line seems toshow a flat-topped profile, indicative of a thick but hollow-centeredexpanding shell, rather than a strongly peaked profile that would beexpected from a ``center-filled'' distribution. Based on detailed modelsfor exploding Chandrasekhar-mass white dwarfs, we show that the featureis consistent with spherical explosion models. Our model predicts acentral region of nonradioactive electron capture elements up to2500-3000 km s-1 as a consequence of burning under highdensity and an extended region of radioactive 56Ni up to9000-10,000 km s-1. Furthermore, our analysis indicates thatthe 1.644 μm [Fe II] line profile is not consistent with strongmixing between the regions of electron-capture isotopes and the56Ni layers, as is predicted by detailed three-dimensionalmodels for nuclear deflagration fronts. We discuss the possibility thatthe flat-topped profile could be produced as a result of an infraredcatastrophe and conclude that such an explanation is unlikely. Wediscuss the limitations of our analysis and place our results intocontext by comparison with constraints on the distribution ofradioactive 56Ni in other SNe Ia and briefly discuss thepotential implications of our result for the use of SNe Ia ascosmological standard candles.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan, and at McDonald Observatoryof the University of Texas at Austin.
| The Space Density of Redshift 5.7 Lyα Emitters: First Constraints from a Multislit Windows Search
We present results from a blind, spectroscopic search for redshift 5.7Lyα emission-line galaxies at Keck I. Using a band-limiting filterand custom slit mask, we cover the LRIS detector with low-resolutionspectra in the 8100-8250 Å atmospheric window, which contains nobright night-sky emission lines. We find nine objects with line fluxesgreater than our flux limit of 6×10-18 ergss-1 cm-2 in our ~5.1 arcmin2 field. Werule out a Lyα identification for six of these based on theabsence of the continuum break, expected at rest 1215 Å for high-zgalaxies and/or the identification of additional emission lines in ourfollow-up spectra. We find that extremely metal-poor, foregroundemission-line galaxies are the most difficult type of interloper torecognize. For the three remaining emission-line objects, we identify aplausible counterpart for each object in a deep V-band image of thefield, suggesting that none of them has a continuum break in the i band.Our preliminary conclusion is that our field contains no z=5.7 Lyαemitters brighter than 0.6L*Lyα, whereL*Lyα≡3.26×1042 ergss-1. Selecting a field with zero Lyα emitters ismarginally consistent with the no-evolution hypothesis-i.e., we expectedto recover 2-3 Lyα emitters, assuming that the Lyαluminosity function at redshift 5.7 is the same as it is at redshift 3.Our null result rules out a brightening ofL*Lyα by more than a factor of 1.7 fromredshift 3 to 5.7, or, over the same redshift interval, an increase ofmore than a factor of 2.2 in the number density of Lyα emitters.The paucity of z=5.7 Lyα emitters raises the question of whetherthe Lyα-selected population plays a significant role inmaintaining the ionization of the intergalactic medium (IGM) at z=5.7.We find that if the escape fraction of Lyα radiation is less than0.4fLyc, where fLyc is the escape fraction ofLyman continuum photons, then the star formation rate in theLyα-emitting population is high enough in the no-evolution model(our upper limit) to maintain the ionization of the IGM at z=5.7.Data presented here were obtained at the W. M. Keck Observatory, whichis operated as a scientific partnership among the California Instituteof Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| The tidally disturbed luminous compact blue galaxy Mkn 1087 and its surroundings
We present new broad-band optical and near-infrared CCD imaging togetherwith deep optical intermediate-resolution spectroscopy of Mkn 1087 andits surrounding objects. We analyze the morphology and colors of thestellar populations of the brightest objects, some of themstar-formation areas, as well as the kinematics, physical conditions andchemical composition of the ionized gas associated with them. Mkn 1087does not host an Active Galactic Nucleus, but it could be a LuminousCompact Blue Galaxy. Although it was classified as a suspectedWolf-Rayet galaxy, we do not detect the spectral features of these sortof massive stars. Mkn 1087 shows morphological and kinematical featuresthat can be explained assuming that it is in interaction with two nearbygalaxies: the bright KPG 103a and a dwarf (MB-18)star-forming companion. We argue that this dwarf companion is not atidal object but an external galaxy because of its low metallicity[12+log(O/H) = 8.24] with respect to the one derived for Mkn 1087[12+log(O/H) = 8.57] and its kinematics. Some of the non-stellar objectssurrounding Mkn 1087 are connected by bridges of matter with the mainbody, host star-formation events and show similar abundances despitetheir different angular distances. These facts, together theirkinematics, suggest that they are tidal dwarf galaxies formed frommaterial stripped from Mkn 1087. A bright star-forming region at thesouth of Mkn 1087 (knot #7) does not show indications of being a tidalgalaxy or the product of a merging process as suggested in previousworks. We argue that Mkn 1087 and its surroundings should be considereda group of galaxies.Based on observations made with several telescopes operated on theislands of La Palma and Tenerife by the Isaac Newton Group of Telescopesand Instituto de Astrofísica de Canarias in the SpanishObservatories of Roque de Los Muchachos and Teide of the Instituto deAstrofísica de Canarias.
| Nuclear Starburst Activity in the Seyfert 2 Galaxy NGC 2273
We present spectrophotometric results of the Seyfert 2 galaxy NGC 2273.The presence of high-order Balmer absorption lines (H8, H9, H10) andweak equivalent widths of CaII K λ3933, CN λ4200, G-bandλ4300 and MgIb λ5173 clearly indicate recent star-formingactivity in the nuclear region. Using a simple stellar populationsynthesis model, we find that for the best fit, the contributions of apower-law featureless continuum, an intermediate-age (108 yr) and an old (>109 yr) stellar populationto the total light at the reference normalization wavelength are 10.0%,33.4% and 56.6%, respectively. The existence of recent starburstactivity is also consistent with its high far-infrared luminosity (logLFIR/ Lȯ = 9.9), its infrared color indexes [α(25,60) = -1.81 and α(60, 100)= -0.79, typical values for Seyfertgalaxies with circumnuclear starburst], and its q-value (2.23, ratio ofinfrared to radio flux, very similar to that of normal spirals andstarburst galaxies). Byrd et al. have suggested that NGC 2273 might haveinteracted with NGC 2273B in less than 109 yr ago, so thestarburst activity in this galaxy could have been triggered by tidalinteraction, as indicated in recent numerical simulations.
| The Metallicities of Star-forming Galaxies at Intermediate Redshifts 0.47 < z < 0.92
Estimates of the [O/H] metallicity of the star-forming gas in a sampleof 66 Canada-France Redshift Survey galaxies in the range0.4775%) have the[O/H]~8.9 metallicities that are seen locally in galaxies of similarluminosities. However, a minority (<25%) appear to have significantlylower metallicities [O/H]<8.6, as indicated by high values of thePagel R23 parameter. The fraction of the sample at theselower [O/H] values would be reduced if the reddening in these objectswere lower than the EB-V~0.3 assumed. The high metallicitiesof the majority of the galaxies suggest that they do not fade to below-metallicity dwarf galaxies today. Only one of the 66 galaxies has anoptical emission-line spectrum similar to the few Lyman break galaxiesrecently observed at z~3, emphasizing the differences from thatpopulation. The inferred emission-line gas [O/H] metallicity broadlycorrelates with luminosity in both the rest B and J bands but withconsiderable scatter introduced, especially at lower luminosities, bythe range in [O/H] observed. The metallicity does not appear tocorrelate well with galaxy size, Hβ strength, or, with the verylimited data available, kinematics. The metallicity does correlate wellwith the continuum optical and optical to infrared colors in a way thatcould be explained as a combination of photospheric effects, differingages of the stellar population, and/or different amounts of reddening.None of these should produce large variations in the M/L ratio. Theseresults support a ``downsizing'' picture of galaxy evolution, in whichthe manifestations of star-forming evolutionary activity appear inprogressively more massive galaxies at earlier epochs, rather than a``fading dwarf'' picture in which the luminous active galaxies at highredshift are highly brightened dwarf galaxies. The overall change inmetallicity of star-forming galaxies over the last half of the age ofthe universe appears to have been modest, Δ[O/H]=0.08+/-0.06. Thisis consistent with the age-metallicity relation in the Galactic disk andis broadly consistent with models for the chemical evolution of theuniverse, especially those that consider different environments.
| Evidence for an Intermediate-Age, Metal-rich Population of Globular Clusters in NGC 4365
We present spectroscopy for globular clusters (GCs) in the ellipticalgalaxy NGC 4365, obtained with the Low-Resolution Imaging Spectrographon the Keck I telescope. Previous studies have shown that the opticalcolor distribution of GCs in NGC 4365 lacks the bimodal structure thatis common in globular cluster systems, showing only a single broad peak.Measurements of Balmer line indices (Hβ, Hγ, and Hδ) onthe GC spectra support recent suggestions by Puzia et al. on the basisof optical and near-infrared photometry that some of the clusters in NGC4365 are intermediate-age (2-5 Gyr) and metal-rich(-0.4<~[Z/H]<~0) rather than old (~10-15 Gyr) and metal-poor. Wealso find some genuinely metal-poor, old clusters, suggesting that theages and metallicities of the two populations conspire to produce thesingle broad distribution observed in optical colors.Based on data obtained at the W. M. Keck Observatory, which is operatedas a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration.
| Chemical Abundances in Broad Emission Line Regions: The ``Nitrogen-loud'' Quasi-Stellar Object Q0353-383
The intensity of the strong N V λ1240 line relative to C IVλ1549 or to He II λ1640 has been proposed as an indicatorof the metallicity of quasi-stellar object (QSO) broad emission lineregions, allowing abundance measurements in a large number of QSOs outto the highest redshifts. Previously, it had been shown that the(normally) much weaker lines N III] λ1750 and N IV] λ1486could be used in the same way. The redshift 1.96 QSO 0353-383 has longbeen known to have N III] and N IV] lines that are far stronger relativeto Lyα or C IV than in any other QSO. Because in this particularcase these intercombination lines can be easily measured, this unusualobject provides an ideal opportunity for testing whether the N V line isa valid abundance indicator. Using new observations of Q0353-383 madeboth with the Hubble Space Telescope in the ultraviolet and from theground in the visible passband, we have carefully remeasured theemission lines and reanalyzed their strengths using the latest models ofthe QSO broad emission line region. We find that intensity ratiosinvolving the strengths of N V, N IV], and N III] relative to lines ofHe, C, and O all indicate that nitrogen is overabundant relative tooxygen in Q0353-383 by a factor of ~15 compared to solar ratios. Thisagreement among the diagnostics supports the use of these lines formeasuring broad emission line region chemical abundances. If nitrogenbehaves like a secondary element, such that N/O~O/H, then the extremenitrogen enhancement in Q0353-383 implies a metallicity of ~15 times thesolar value. Even if Q0353-383 represents an extreme outlier in theN/O~O/H relation, the overall metallicity should still be at least 5times solar. Unusually high metallicities in Q0353-383 might imply thatwe caught this object just as the gas-phase metallicity in the centralpart of its host galaxy has peaked, at a time when the interstellar gassupply is nearly exhausted and hence the fuel source for the central QSOis ready to shut off.
| Spectroscopy of Low Surface Brightness Galaxies with the Hobby-Eberly Telescope
We have obtained low-resolution spectra of 19 red and blue low surfacebrightness (LSB) galaxies, using the Marcario Low-ResolutionSpectrograph on the 9.2 m Hobby-Eberly Telescope. These galaxies form avery heterogeneous class, whose spectra qualitatively resemble those ofhigh surface brightness galaxies covering the full range of spectra seenin galaxies of Hubble types from E to Irr. We use a combination ofemission-line (EW(Hα), [N II] λ6584/Hα) andabsorption-line (Mg b, Hβ, ) based diagnostics toinvestigate the star formation and chemical enrichment histories ofthese galaxies. These are diverse, with some galaxies having lowmetallicity and very young mean stellar ages and other galaxies showingold, supersolar-metallicity stellar populations. In contrast with someprevious studies, which found a strong trend of decreasing metallicitywith decreasing central surface brightness, we find a population ofgalaxies with low surface brightness and near-solar metallicity.Correlations between several of the gas-phase and stellar population ageand metallicity indicators are used to place constraints on plausibleevolutionary scenarios for LSB galaxies. The redshift range spanned bythese galaxies is broad, with radial velocities from 3400 kms-1 to more than 65,000 km s-1. A subset of thesample galaxies have published H I redshifts and gas masses based onobservations with the Arecibo 305 m single-dish radio telescope, whichplace these galaxies far off of the mean Tully-Fisher relation. Our newoptical redshifts do not agree with the published H I redshifts forthese galaxies. Most of the discrepancies can be explained by beamconfusion in the Arecibo observations, causing erroneous H I detectionsfor some of the galaxies.
| Narrow band survey for intragroup light in the Leo HI cloud. Constraints on the galaxy background contamination in imaging surveys for intracluster planetary nebulae
We have observed emission line objects located in a 0.26 deg2field in the M 96 (Leo) group, coincident with the intergalactic HIcloud. The emission line objects were selected using the same procedureas used for the search for intracluster planetary nebulae in the Virgocluster. 29 emission line objects were identified, with [OIII] filtermagnitudes brighter than m5007=28. Their m5007luminosity function has a bright cut-off =~ 1.2 mag fainter than forthe luminosity function of the planetary nebulae (PN) associated withthe elliptical galaxies in the M 96 group. Therefore the vast majorityof these emission line objects are compatible with not being intragroupplanetary nebulae at the Leo group distance of 10 Mpc. Spectroscopicfollow-up of two emission line objects in this Leo field showed thatindeed these do not have the [OIII] lambda 4959, lambda 5007 Ådoublet expected for a real PN. The brighter source is identified as anAGN at redshift z = 3.128, because of a second emission in the nearinfrared, identified as FeII (lambda 2220 Å).From these data we derive three main results: (i) from the absence of PNwe can determine a more stringent upper limit to the surface brightnessin any old stellar population associated with the Leo HI cloud at thesurveyed position, mu B,*<32.8 mag arcsec-2.(ii) This translates to an upper limit of 1.6% for the fraction ofluminosity in a diffuse intragroup component in the densest3ox 2o area of the Leo group, relative to thelight in galaxies. (iii) Using this Leo field as a blank field, wederive an average fraction of 13.6% background emission line objectsthat enter in surveys of Virgo intracluster PN. This is in agreementwith an earlier estimate (15%) obtained from the Ly break galaxypopulation at z = 3.13. The small fraction confirms the validity of theselection criteria for intracluster PN candidates in Virgo.Based on observations carried out at the ESO MPI 2.2 m telescope, LaSilla, and at the VLT - UT4, Paranal, Chile.
| A Multi-Wavelength Study of the H II Region Sharpless 217
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| Time-dependent Optical Spectroscopy of GRB 010222: Clues to the Gamma-Ray Burst Environment
We present sequential optical spectra of the afterglow of GRB 010222obtained 1 day apart using the Low-Resolution Imaging Spectrometer(LRIS) and the Echellette Spectrograph and Imager (ESI) on the KeckTelescopes. Three low-ionization absorption systems arespectroscopically identified at z1=1.47688,z2=1.15628, and z3=0.92747. The higher resolutionESI spectrum reveals two distinct components in the highest redshiftsystem at z1a=1.47590 and z1b=1.47688. Weinterpret the z1b=1.47688 system as an absorption feature ofthe disk of the host galaxy of GRB 010222. The best-fitted power-lawoptical continuum and [Zn/Cr] ratio imply low dust content or a localgray dust component near the burst site. In addition, we do not detectstrong signatures of vibrationally excited states of H2. Ifthe gamma-ray burst took place in a superbubble or young stellarcluster, there are no outstanding signatures of an ionized absorbereither. Analysis of the spectral time dependence at low resolution showsno significant evidence for absorption-line variability. This lack ofvariability is confronted with time-dependent photoionizationsimulations designed to apply the observed flux from GRB 010222 to avariety of assumed atomic gas densities and cloud radii. The absence oftime dependence in the absorption lines implies that high-densityenvironments are disfavored. In particular, if the GRB environment wasdust free, its density was unlikely to exceednHI=102 cm-3. If depletion of metalsonto dust is similar to Galactic values or less than solar abundancesare present, then nHI>=2×104cm-3 is probably ruled out in the immediate vicinity of theburst. Based on data obtained at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and NASA and was made possiblewith the generous financial support of the W. M. Keck Foundation.
| Multiwavelength Observations of the Peculiar Planetary Nebula IC 2149
We report high- and low-dispersion spectroscopy, optical imaging, andhigh-resolution Very Large Array-A λ3.6 cm continuum observationsof the peculiar planetary nebula IC 2149. These observations show that``bipolar'' is a suitable morphological classification for IC 2149. Mostnebular material is concentrated in a knotty, bright ring seen edge-on,embedded in an apparently oblate ellipsoidal shell from which remnant orincipient bipolar lobes emerge. We confirm the previously reporteddepletion in heavy elements and deduce a very low ejected nebular mass<~0.03 Msolar. All this information indicates that theformation of IC 2149 is the result of the evolution of a low-masscentral star.
| Optical Spectral Monitoring of XTE J1118+480 in Outburst: Evidence for a Precessing Accretion Disk?
We present spectroscopic observations of the X-ray transient XTEJ1118+480 acquired during different epochs following the 2000 Marchoutburst. We find that the emission line profiles show variations intheir double-peak structure on timescales longer than the 4.1 hr orbitalperiod. We suggest that these changes are due to a tidally drivenprecessing disk. Doppler imaging of the more intense Balmer lines andthe He II λ4686 line shows evidence of a persistent region ofenhanced intensity superposed on the disk which is probably associatedwith the gas stream, the hot spot, or both. We discuss the possibleorigins of the optical flux in the system and conclude that it may bedue to a viscously heated disk.
| Intracluster Planetary Nebulae in Virgo: Photometric Selection, Spectroscopic Validation, and Cluster Depth
We have imaged an empty area of 34×34 arcmin2 1.5dnorth of the Virgo Cluster core to survey for intracluster planetarynebula (PN) candidates. We have implemented and tested a fully automaticprocedure for the selection of emission-line objects in wide-fieldimages, based on the on-off technique from Ciardullo and Jacoby. Freemanet al. have spectroscopically confirmed a sample of intraclusterplanetary nebulae in one Virgo field. We use the photometric andmorphological properties of this sample to test our selection procedure.In our newly surveyed Virgo field, 75 objects were identified as bestcandidates for intracluster PNe. The luminosity function of thespectroscopically confirmed PNe shows a brighter cutoff than theplanetary nebula luminosity function for the inner regions of M87. Sucha brighter cutoff is also observed in the newly surveyed field andindicates a smaller distance modulus, implying that the front end of theVirgo Cluster is closer to us by a significant amount: 14% closer (2.1Mpc) than M87 for the spectroscopic field, using the PN luminosityfunction distance of 14.9 Mpc to M87, and 18% closer (2.8 Mpc) than M87for the newly surveyed field. Independent distance indicators(Tully-Fisher relation for Virgo spirals and surface brightnessfluctuations for Virgo ellipticals) agree with these findings. Fromthese two Virgo Cluster fields there is no evidence that the surfaceluminosity density for the diffuse stellar component in the clusterdecreases with radius. The luminosity surface density of the diffusestellar population is comparable to that of the galaxies. This paper isbased on observations carried out at the ESO telescopes at La Silla andat the Anglo Australian Observatory.
| Nebular Spectra of the Type Ic Supernovae 1997B and 1997X
New spectra of the Type Ic supernovae 1997B and 1997X at nebular phaseare shown. Although one of them, SN 1997X, was studied with some detailaround its maximum and its properties compared with other well-known SNeIb/c, both of these events were later followed within its nebular phase.Our aim is to explore the behavior of these supernovae when they reachedthe nebular phase. Comparisons with data of other SNe Ic at similarnebular phases, mainly by using spectra from the Canarias Database, arealso performed. The results derived from these comparisons reinforce thequite heterogeneous behavior found in SNe Ic nebular spectra. Inparticular, the widths of the [O I] and [Ca II] emissions found in SN1997B are wider than the average for Type Ic events, while the [O I]width of SN 1997X is narrower than the average and is nearly comparableto typical [O I] widths found in SNe Ib. Based on observations made withthe 2.5 m Isaac Newton Telescope and the 4.2 m William HerschelTelescope operated on La Palma by the Isaac Newton Group of Telescopesat Observatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.
| A Survey for Very Faint Planetary Nebulae in the SMC. I. Identification, Confirmation, and Preliminary Analysis
Using the ESO 2.2 m telescope with the 8K×8K mosaic CCD, we havesurveyed 2.8 deg2 (~1.6d×1.7d) of the Small MagellanicCloud (SMC) to search for faint planetary nebulae (PNs); 34 PNs werepreviously known in this central region. We identified 25 new PNs, allfaint and spectroscopically confirmed. Most of these are spatiallyextended with typical diameters of ~1 pc, but a few are as large as ~3pc. Based on the total number of PNs previously known (~80), we can nowestimate that there should be ~139 PNs in the SMC to the limits of asurvey such as this one, which is complete to 6 mag down the planetarynebulae luminosity function (PNLF). For a complete survey (8 mag downthe PNLF), there should be about 216 PNs. Because no new bright PNs werefound in this survey, the bright end of the PNLF remains unchanged fromthat reported by Jacoby, Walker, & Ciardullo. Consequently, thedistance modulus to the SMC, derived using the PNLF technique, is still~19.1. However, a strong new feature is now evident in the PN brightnessdistribution that may be attributed to central stars evolving from arelatively young population. This feature may serve as an indicator ofthe ages of the PN progenitors. The survey spectra that were used toconfirm the candidates as PNs also provide a clue to the nature of thevery faint PNs. Statistically, the fainter PNs of our survey exhibit ahigh incidence (~28%) of strong [N II] emission [where I([NII])/I(Hα)>1] relative to the bright Sanduleak et al. sample (~6%)reported by Meatheringham & Dopita, and comparable to theintermediate-brightness Jacoby sample (~26%) reported by Boroson &Liebert. This incidence of strong [N II] is higher than in theKingsburgh & Barlow sample (~17%) of Galactic PNs, despite the ~3times higher abundance of nitrogen in the Galaxy. We propose that thevery faint SMC PNs are selectively biased toward the chemically enrichedType I objects derived from younger, more massive progenitors and arepartially obscured by their own dust. This brightness-dependentpopulation change is also seen in the Large Magellanic Cloud. Based onobservations collected at the European Southern Observatory, Chile, ESOproposal number 63.I-0235
| Spectroscopic analyses of the ``blue hook'' stars in omega Centauri: A test of the late hot flasher scenario
omega Cen contains the largest population of very hot horizontal branch(HB) stars known in a globular cluster. Recent UV observations (Whitneyet al. \cite{whro98}; D'Cruz et al. \cite{dcoc00}) show a significantpopulation of hot stars below the zero-age horizontal branch (``bluehook'' stars), which cannot be explained by canonical stellar evolution.Stars which suffer unusually large mass loss on the red giant branch andthus experience the helium core flash while descending the white dwarfcooling curve could populate this region. Theory predicts that these``late hot flashers'' should show higher temperatures than the hottestcanonical HB stars and should have helium- and carbon-rich atmospheres.We obtained and analysed medium resolution spectra of a sample of bluehook stars to derive their atmospheric parameters. The blue hook starsare indeed both hotter (Teff >=35 000 K) and morehelium-rich than classical extreme HB stars. In addition we findindications for a large enhancement of the carbon abundance relative tothe cluster abundance.
| MWC 560: An SS 433 type object with a white dwarf
Spectral variations of the peculiar symbiotic object MWC 560 (V694 Mon)have been monitored for 10 years since 1991. The radial velocity of theblue edge of the broad absorption components of H I lines is measured toevaluate the outflow velocity of the jet. The variation of the outflowvelocity suggests that there are active and stable stages in thissystem. The outflow velocity in the stable stage seems to vary accordingto the long-term light variation with a period of 1930 days. Thisvariation of the outflow velocity could be explained with a model of gasoutflow from an accretion disk precessing with a period of 1930 days. Ifthe observed amplitude of the light variation, Delta mpg =~0.72 mag, was purely due to the precession, the maximum inclination ofthe disk to the line of sight should be about 59 degrees. Since theoutflow is observed always as absorption, the open angle of the outflowshould be larger than 59 degrees. However, the amplitude of the lightvariation due to the precession of the disk seems to be still ratheruncertain. In the active stage the outflow velocity was much higher (inthe negative sense) than in the stable stage, and rapid variations ofthe outflow velocity were observed. During the outburst in 1990, thisobject was in the active stage, while no significant brightening wasobserved in the active stages in 1993 and 1999 at least in the V band.The durations of the active stages were several months.
| Spectroscopic study of blue compact galaxies. I. The spectra
Blue compact galaxies are compact objects that are dominated by intensestar formation. Most of them have dramatically different propertiescompared to the Milky Way and many other nearby galaxies. Using theIRAS, H I data, and optical spectra, we wanted to measure the currentstar formation rates, stellar components, metallicities, and starformation histories and evolution of a large blue compact galaxy sample.We anticipate that our study will be useful as a benchmark for studiesof emission line galaxies at high redshift. In the first paper of thisseries, we describe the selection, spectroscopic observation, datareduction and calibration, and spectrophotometric accuracy of a sampleof 97 luminous blue compact galaxies. We present a spectrophotometricatlas of rest-frame spectra, as well as tables of the recessionvelocities and the signal-to-noise ratios. The recession velocities ofthese galaxies are measured with an accuracy of delta V< 67 kms-1. The average signal-to-noise ratio of sample spectra is ~51. The spectral line strengths, equivalent widths and continuum fluxesare also measured for the same galaxies and will be analyzed in the nextpaper of this series. The atlas and tables of measurements will be madeavailable electronically. Table 3 and Fig. 4 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/389/845
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Observation and Astrometry data
| Constellation: | Monoceros |
| Right ascension: | 06h45m13.37s |
| Declination: | +02°08'14.7" |
| Apparent magnitude: | 10.404 |
| Proper motion RA: | -0.6 |
| Proper motion Dec: | -0.9 |
| B-T magnitude: | 10.587 |
| V-T magnitude: | 10.42 |
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