Contents
Images
Upload your image
DSS Images Other Images
Related articles
The Iron Abundance in Galactic Planetary Nebulae
We constrain the iron abundance in a sample of 33 low-ionizationGalactic planetary nebulae (PNe) using [Fe III] lines andcorrecting for the contribution of higher ionization states withionization correction factors that take into account uncertainties inthe atomic data. We find very low iron abundances in all the objects,suggesting that more than 90% of their iron atoms are condensed ontodust grains. This number is based on the solar iron abundance andimplies a lower limit on the dust-to-gas mass ratio, solely due to iron,of M dust/M gas >= 1.3 ×10–3 for our sample. The depletion factors of differentPNe cover about two orders of magnitude, probably reflecting differencesin the formation, growth, or destruction of their dust grains. However,we do not find any systematic difference between the gaseous ironabundances calculated for C-rich and O-rich PNe, suggesting similar irondepletion efficiencies in both environments. The iron abundances of oursample PNe are similar to those derived following the same procedure fora group of 10 Galactic H II regions. These high depletion factorsargue for high depletion efficiencies of refractory elements onto dustgrains both in molecular clouds and asymptotic giant branch stars, andlow dust destruction efficiencies both in interstellar and circumstellarionized gas.Partly based on observations made with the 2.1 m telescope atObservatorio Astronómico Nacional, San Pedro Mártir,Mexico.
| Spiral Density Wave Triggering of Star Formation in SA and SAB Galaxies
Azimuthal color (age) gradients across spiral arms are one of the mainpredictions of density wave theory; gradients are the result of starformation triggered by the spiral waves. In a sample of 13 spiralgalaxies of types A and AB, we find that ten of them present regionsthat match the theoretical predictions. By comparing the observedgradients with stellar population synthesis models, the pattern speedand the location of major resonances have been determined. The resonancepositions inferred from this analysis indicate that nine of the objectshave spiral arms that extend to the outer Lindblad resonance; for one ofthe galaxies, the spiral arms reach the corotation radius. The effectsof dust, and of stellar densities, velocities, and metallicities on thecolor gradients are also discussed.
| Optical and Infrared Observations of Two Magnetic Interacting Binaries: Tau 4 (RXJ0502.8+1624) & SDSS J121209.31+013627.7
We present new optical photometric and spectroscopic observations andK-band spectroscopy of two magnetic interacting binaries: Tau 4(RXJ0502.8+1624) and SDSS J121209.31+013627.7. Tau 4 shows short-term,highly modulated optical light but no orbital period is firmly detected.K-band spectroscopy shows H and He I emission and reveals a remarkablephase-resolved dataset. We detect clear evidence for cyclotron humps inthe K-band implying a magnetic white dwarf with B ~ 7-11 MG andconfirming Tau 4 as a magnetic binary. A short self eclipse by the gasstream is evident as the spectrum changes from emission to absorptionand back within a few minutes. None of our K-band spectra of Tau 4appear similar to the previously reported observation. Opticalspectroscopy of SDSS J121209.31+013627.7 in 2007 May and June showsZeeman-split Balmer absorption lines as previously noted in theliterature but only weak, sporadic Hα emission compared to pastdata. However, stronger Hα emission returned in 2008 February,looking similar to that previously detected in 2006. The variable natureof this emission line makes irradiation from the white dwarf an unlikelycause of the Hα emission in J1212. The nature of J1212 isreminiscent of that observed in its near twin, EF Eri.
| Echelle Long-Slit Optical Spectroscopy of Evolved Stars
We present echelle long-slit optical spectra of a sample of objectsevolving off the asymptotic giant branch (AGB), most of them in thepreplanetary nebula (PPN) phase, obtained with the ESI and MIKEspectrographs at the 10 m Keck II and 6.5 m Magellan-I telescopes,respectively. The total wavelength range covered with ESI (MIKE) is~3900-10900 Å (~3600-7200 Å). In this paper, we focus ouranalysis mainly on the Hα profiles. Prominent Hα emission isdetected in half of the objects, most of which show broad Hα wings(with total widths of up to ~4000 km s-1). In the majority ofthe Hα-emission sources, fast, post-AGB winds are revealed byP-Cygni profiles. In ~37% of the objects Hα is observed inabsorption. In almost all cases, the absorption profile is partiallyfilled with emission, leading to complex, structured profiles that areinterpreted as an indication of incipient post-AGB mass loss. The restof the objects (~13%) are Hα nondetections. We investigatecorrelations between the Hα profile and different stellar andenvelope parameters. All sources in which Hα is seen mainly inabsorption have F-G type central stars, whereas sources with intenseHα emission span a larger range of spectral types from O to G,with a relative maximum around B, and also including very late C types.Shocks may be an important excitation/ionization agent of the closestellar surroundings for objects with late type central stars. Sourceswith pure emission or P Cygni Hα profiles have larger J-K colorexcess than objects with Hα mainly in absorption, which suggeststhe presence of warm dust near the star in the former. The two classesof profile sources also segregate in the IRAS color-color diagram in away that intense Hα-emitters have dust grains with a larger rangeof temperatures. Spectral classification of the central stars in oursample is presented. For a subsample (13 objects), the stellarluminosity has been derived from the analysis of the O I 7771-7775Å infrared triplet. The location in the HR diagram of most ofthese targets, which represent ~30% of the whole sample, is consistentwith relatively high final (and, presumably, initial) masses in therange Mf~0.6-0.9 Msolar (Mi~3-8Msolar).
| Meeting the Cool Neighbors. X. Ultracool Dwarfs from the 2MASS All-Sky Data Release
Using data from the 2 Micron All Sky Survey All-Sky Point SourceCatalogue, we have extended our census of nearby ultracool dwarfs tocover the full celestial sphere above Galactic latitude of 15°.Starting with an initial catalog of 2,139,484 sources, we have winnowedthe sample to 467 candidate late-type M or L dwarfs within 20 pc of theSun. Fifty-four of those sources already have spectroscopic observationsconfirming them as late-type dwarfs. We present optical spectroscopy of376 of the remaining 413 sources, and identify 44 as ultracool dwarfswith spectroscopic distances less than 20 pc. Twenty-five of the 37sources that lack optical data have near-infrared spectroscopy.Combining the present sample with our previous results and data from theliterature, we catalog 94 L dwarf systems within 20 pc. We discuss thedistribution of activity, as measured by Hα emission, in thisvolume-limited sample. We have coupled the present ultracool catalogwith data for stars in the northern 8 pc sample and recent (incomplete)statistics for T dwarfs to provide a snapshot of the current 20 pccensus as a function of spectral type.
| A Combined EIS-NVSS Survey Of Radio Sources (CENSORS) - III. Spectroscopic observations
The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4-GHzradio survey selected from the NRAO VLA Sky Survey (NVSS) and completeto a flux density of 7.2mJy. It targets the ESO Imaging Survey (EIS)Patch D, which is a 3 × 2-deg2 field centred on(J2000). This paper presents the results of spectroscopic observationsof 143 of the 150 CENSORS sources. The primary motivation for theseobservations is to achieve sufficient spectroscopic completeness so thatthe sample may be used to investigate the evolution of radio sources.The observations result in secure spectroscopic redshifts for 63 percent of the sample and likely redshifts (based on a single emissionline, for example) for a further 8 per cent. Following theidentification of the quasars and star-forming galaxies in the CENSORSsample, estimated redshifts are calculated for the remainder of thesample via the K - z relation for radio galaxies.Comparison of the redshift distribution of the CENSORS radio sources todistributions predicted by the various radio luminosity functionevolution models of Dunlop & Peacock, results in no good match. Thisdemonstrates that this sample can be used to expand upon previous workin that field.
| Optical Spectroscopy of Type ia Supernovae
We present 432 low-dispersion optical spectra of 32 Type Ia supernovae(SNe Ia) that also have well-calibrated light curves. The coverageranges from 6 epochs to 36 epochs of spectroscopy. Most of the data wereobtained with the 1.5 m Tillinghast telescope at the F. L. WhippleObservatory with typical wavelength coverage of 3700-7400 Å and aresolution of ~7 Å. The earliest spectra are 13 days before B-bandmaximum; two-thirds of the SNe were observed before maximum brightness.Coverage for some SNe continues almost to the nebular phase. Theconsistency of the method of observation and the technique of reductionmakes this an ideal data set for studying the spectroscopic diversity ofSNe Ia.Based in part on observations obtained at the F. L. Whipple Observatory,which is operated by the Smithsonian Astrophysical Observatory, and theMMT Observatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona.
| The underluminous Type Ia supernova 2005bl and the class of objects similar to SN 1991bg
Optical observations of the Type Ia supernova (SN Ia) 2005bl in NGC4070, obtained from -6 to +66d with respect to the B-band maximum, arepresented. The photometric evolution is characterized by rapidlydeclining light curves [Δm15(B)true = 1.93]and red colours at peak and soon thereafter. With MB,max =-17.24 the SN is an underluminous SN Ia, similar to the peculiar SNe1991bg and 1999by. This similarity also holds for the spectroscopicappearance, the only remarkable difference being the likely presence ofcarbon in pre-maximum spectra of SN 2005bl. A comparison study amongunderluminous SNe Ia is performed, based on a number ofspectrophotometric parameters. Previously reported correlations of thelight-curve decline rate with peak luminosity and (Si) are confirmed,and a large range of post-maximum SiII λ6355 velocity gradientsis encountered. 1D synthetic spectra for SN 2005bl are presented, whichconfirm the presence of carbon and suggest an overall low burningefficiency with a significant amount of leftover unburned material.Also, the Fe content in pre-maximum spectra is very low, which may pointto a low metallicity of the precursor. Implications for possibleprogenitor scenarios of underluminous SNe Ia are briefly discussed.Based on observations at ESO-Paranal, Programme 075.D-0662(B).E-mail: tauben@mpa-garching.mpg.de
| Deep optical observations of the interaction of the SS 433 microquasar jet with the W50 radio continuum shell
Four mosaics of deep, continuum-subtracted, CCD images have beenobtained over the extensive Galactic radio continuum shell, W50, whichsurrounds the remarkable stellar system SS 433. Two of these mosaics inthe and [O III] 5007 Å emission lines, respectively, cover a fieldof which contains all of W50 but at a low angular resolution of 5arcsec. The third and fourth mosaics cover the eastern (in [O III] 5007Å) and western (in 6548, 6584 Å) filamentary nebulosity,respectively, but at an angular resolution of 1 arcsec. Theseobservations are supplemented by new low-dispersion spectra andlong-slit, spatially resolved echelle spectra. The [O III] 5007 Åimages show for the first time the distribution of this emission in boththe eastern and western filaments while new emission features are alsofound in both of these regions. Approaching flows of faintly emittingmaterial from the bright eastern filaments of up 100 km s-1in radial velocity are detected. The present observations also suggestthat the heliocentric systemic radial velocity of the whole system is 56+/- 2 km s-1. Furthermore, very deep imagery andhigh-resolution spectroscopy of a small part of the northern radio ridgeof W50 has revealed for the first time the very faint optical nebulosityassociated with this edge. It is suggested that patchy foreground dustalong the ~5 kpc sightline is inhibiting the detection of all of theoptical nebulosity associated with W50. The interaction of themicroquasar jets of SS 433 with the W50 shell is discussed.
| The optical spectrum of the Vela pulsar
Context: Our knowledge of the optical spectra of Isolated Neutron Stars(INSs) is limited by their intrinsic faintness. Among the fourteenoptically identified INSs, medium resolution spectra have been obtainedonly for a handful of objects. No spectrum has been published yet forthe Vela pulsar (PSR B0833-45), the third brightest (V=23.6) INS with anoptical counterpart. Optical multi-band photometry underlines a flatcontinuum. Aims: In this work we present the first opticalspectroscopy observations of the Vela pulsar, performed in the 4000-11000 Å spectral range. Methods: Our observations have beenperformed at the ESO Very Large Telescope (VLT) using the FORS2instrument. Results: The spectrum of the Vela pulsar ischaracterized by a flat power-law Fν ∝ν-α with α = -0.04 ±0.04 (4000-8000Å), which compares well with the values obtained from broad-bandphotometry. This confirms, once more, that the optical emission of Velais entirely of magnetospheric origin. Conclusions: Thecomparison between the optical spectral indeces of rotation-powered INSsdoes not show evidence for a spectral evolution, suggesting that, as inthe X-rays, the INS aging does not affect the spectral properties of themagnetospheric emission. At the same time, the optical spectral indecesare found to be nearly always flatter then the X-rays ones, clearlysuggesting a general spectral turnover at lower energies.Based on observations collected at the European Southern Observatory,Paranal, Chile under programme ID 66.D-0261(A).
| Lyα Emission-Line Galaxies at z = 3.1 in the Extended Chandra Deep Field-South
We describe the results of an extremely deep, 0.28 deg2survey for z=3.1 Lyα emission-line galaxies in the ExtendedChandra Deep Field-South. By using a narrowband 5000 Å filter andcomplementary broadband photometry from the MUSYC survey, we identify astatistically complete sample of 162 galaxies with monochromatic fluxesbrighter than 1.5×10-17 ergs cm-2s-1 and observer's frame equivalent widths greater than 80Å. We show that the equivalent width distribution of these objectsfollows an exponential with a rest-frame scale length ofw0=76+11-8 Å. In addition, weshow that in the emission line, the luminosity function of Lyαgalaxies has a faint-end power-law slope ofα=-1.49+0.45-0.34, a bright-end cutoff oflogL*=42.64+0.26-0.15, and a spacedensity above our detection thresholds of(1.46+/-0.12)×10-3 h370 galaxiesMpc-3. Finally, by comparing the emission-line and continuumproperties of the Lyα emitters, we show that the star formationrates derived from Lyα are ~3 times lower than those inferred fromthe rest-frame UV continuum. We use this offset to deduce the existenceof a small amount of internal extinction within the host galaxies. Thisextinction, coupled with the lack of extremely high equivalent widthemitters, argues that these galaxies are not primordial Population IIIobjects, although they are young and relatively chemically unevolved.
| Discovery of a single faint AGN in a large sample of z > 5 Lyman break galaxies
As part of a large spectroscopic survey of z > 5 Lyman break galaxies(LBGs), we have identified a single source which is clearly hosting anactive galactic nucleus (AGN). Out of a sample of more than 50spectroscopically confirmed R-band dropout galaxies at z ~ 5 and above,only J104048.6-115550.2 at z = 5.44 shows evidence for a high ionizationpotential emission line indicating the presence of a hard ionizingcontinuum from an AGN. Like most objects in our sample the rest-frame-UVspectrum shows the UV continuum breaking across a Lyα line.Uniquely within this sample of LBGs, emission from NV is also detected,a clear signature of AGN photoionization. The object is spatiallyresolved in Hubble Space Telescope (HST) imaging. This, and thecomparatively high Lyα/NV flux ratio indicates that the majorityof the Lyα (and the UV continuum longward of it) originates fromstellar photoionization, a product of the ongoing starburst in the LBG.Even without the AGN emission, this object would have beenphotometrically selected and spectroscopically confirmed as a Lymanbreak in our survey. The measured optical flux (IAB = 26.1)is therefore an upper limit to that from the AGN and is of order 100times fainter than the majority of known quasars at these redshifts. Thedetection of a single object in our survey volume is consistent with thebest current models of high redshift AGN luminosity function, providinga substantial fraction of such AGN is found within luminous starburstinggalaxies. We discuss the cosmological implications of this discovery.
| Kinematics and stellar populations of the dwarf elliptical galaxy IC 3653
We present the first 3D observations of a diffuse elliptical galaxy(dE). The good quality data (S/N up to 40) reveal the kinematicalsignature of an embedded stellar disc, reminiscent of what is commonlyobserved in elliptical galaxies, though similarity of their origins isquestionable. Colour map built from Hubble Space Telescope AdvancedCamera for Surveys (ACS) images confirms the presence of this disc. Itscharacteristic scale (about 3 arcsec =250 pc) is about a half ofgalaxy's effective radius, and its metallicity is 0.1-0.2 dex largerthan the underlying population. Fitting the spectra with syntheticsingle stellar populations (SSP), we found an SSP-equivalent age of 5Gyr and nearly solar metallicity [Fe/H] = -0.06 dex. We checked thatthese determinations are consistent with those based on Lick indices,but have smaller error bars. The kinematical discovery of a stellar discin dE gives additional support to an evolutionary link from dwarfirregular galaxies due to stripping of the gas against the intraclustermedium.
| Interstellar medium oxygen abundances of dwarf irregular galaxies in Centaurus A and nearby groups
We present results of optical spectroscopy of 35 HII regions from eightdwarf galaxies in the Centaurus A (Cen A) group. [OIII] λ4363 isdetected in ESO272-G025 and ESO324-G024, and direct oxygen abundances of12 + log(O/H) = 7.76 +/- 0.09 and 7.94 +/- 0.11 are derived,respectively. For the remaining galaxies, abundances are derived usingcommon bright-line methods. To compare the influence of groupenvironments on dwarf galaxies, we have also gathered data foradditional dwarf irregular galaxies from the Cen A and the Sculptorgroups from the literature. We have examined possible relationshipsbetween oxygen abundance, gas fraction, effective chemical yield andtidal indices. Despite large positive tidal indices for a number of CenA dwarfs in the present sample, there is no clear separation betweengalaxies with positive tidal indices and galaxies with negative tidalindices in the luminosity-metallicity, metallicity-gas fraction andmetallicity-tidal index diagrams. The HI surface mass density decreaseswith increasing positive tidal index, which is expected in strong tidalencounters. There are no strong trends between oxygen abundances oryields and projected distances of galaxies within their respectivegroups. We also present spectra for 13 HII regions in three nearby dwarfirregular galaxies: DDO 47, NGC 3109 and Sextans B. For DDO 47, the[OIII] λ4363 oxygen abundance (7.92 +/- 0.06) for the HII regionSHK91 No. 18 agrees with recently published values. For Sextans B, the[OIII] λ4363 oxygen abundance (7.80 +/- 0.13) for HII regionSHK91 No. 5 agrees with published work in which O+ abundanceswere determined entirely from [OII] λλ7320, 7330 fluxes.Based on EFOSC2 observations collected at the European SouthernObservatory, Chile: proposal #70.B-0180(B).E-mail: hlee@gemini.edu
| Calibrating Type Ia Supernovae Using the Planetary Nebula Luminosity Function. I. Initial Results
We report the results of an [O III] λ5007 survey for PNe in fivegalaxies that were hosts of well-observed SNe Ia: NGC 524, NGC 1316, NGC1380, NGC 1448, and NGC 4526. The goals of this survey are to betterquantify the zero point of the maximum magnitude-decline rate relationfor SNe Ia and to validate the insensitivity of Type Ia luminosity toparent stellar population using the host galaxy Hubble type as asurrogate. We detected a total of 45 PN candidates in NGC 1316, 44candidates in NGC 1380, and 94 candidates in NGC 4526. From these dataand the empirical planetary nebula luminosity function (PNLF), we derivedistances of 17.9+0.8-0.9,16.1+0.8-1.1, and13.6+1.3-1.2 Mpc, respectively. Our deriveddistance to NGC 4526 has a lower precision due to the likely presence ofVirgo intracluster PNe in the foreground of this galaxy. In NGC 524 andNGC 1448 we detected no PN candidates down to the limiting magnitudes ofour observations. We present a formalism for setting realistic distancelimits in these two cases and derive robust lower limits of 20.9 and15.8 Mpc, respectively. After combining these results with otherdistances from the PNLF, Cepheid, and surface brightness fluctuationdistance indicators, we calibrate the optical and NIR relations for SNeIa and find that the Hubble constants derived from each of the threemethods are broadly consistent, implying that the properties of SNe Iado not vary drastically as a function of stellar population. Wedetermine a preliminary Hubble constant of H0=77+/-3(random)+/-5 (systematic) km s-1 Mpc-1 for thePNLF, although more nearby galaxies with high-quality observations areclearly needed.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory. This paper includes data gathered withthe 6.5 m Magellan Telescopes located at Las Campanas Observatory,Chile.
| Recent Star Formation in Clusters of Galaxies: Extremely Compact Starbursts in A539 and A634
We report on the detection of two Hα-emitting extremely compactobjects from deep images of the A634 and A539 clusters of galaxies atz~0.03. Follow-up long-slit spectroscopy of these two unresolved sourcesrevealed that they are members of their respective clusters, showing HII-type spectra. The luminosity and the extreme equivalent width ofHα + [N II] measured for these sources, together with their verycompact appearance, has raised a question about the origin of theseintense starbursts in the cluster environment. We propose that thecompact starburst in A539 resulted from the compression of theinterstellar gas of a dwarf galaxy when entering the cluster core, whilethe starburst galaxy in A634 is likely to be the result of agalaxy-galaxy interaction, illustrating the preprocessing of galaxiesduring their infall toward the central regions of clusters. Thecontribution of these compact star-forming dwarf galaxies to the starformation history of galaxy clusters is discussed, as well as a possiblelink with the recently discovered early-type ultracompact dwarfgalaxies. We note that these extreme objects will rarely be detected innormal magnitude-limited optical or NIR surveys, mainly due to their lowstellar masses (on the order of 106 Msolar),whereas they will easily show up in dedicated Hα surveys given thehigh equivalent width of their emission lines.
| Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud. II. The extended sample
Context: .All galaxies that have been adequately examined so far haveshown an extended stellar halo. Aims: .To search for such a haloin the LMC we have obtained low-resolution spectra for 100 LMC RR Lyraestars, of which 87 are in the field and 13 in the clusters NGC 1835 andNGC 2019. Methods: .We measured radial velocities for 87 LMC RRLyrae stars, and metallicities for 78 RR Lyrae stars, nearly triplingthe previous sample. These targets are located in 10 fields covering awide range of distances, out to 2.5 degrees from the center of the LMC. Results: .Our main result is that the mean velocity dispersionfor the LMC RR Lyrae stars is σRV = 50 ± 2 kms-1. This quantity does not appear to vary with distance fromthe LMC center. The metallicity shows a Gaussian distribution, with mean[Fe/H] = -1.53 ± 0.02 dex, and dispersion σ_[Fe/H] =0.20± 0.02 dex in the Harris metallicity scale, confirming thatthey represent a very homogeneous metal-poor population. There is nodependence between the kinematics and metallicity of the field RR Lyraestar population. Conclusions: .Using good quality low-resolutionspectra from FORS1, FORS2 and GEMINI-GMOS we have found that field RRLyrae stars in the LMC show a large velocity dispersion and that thisindicate the presence of old and metal-poor stellar halo. All theevidence so far for the halo, however, is from the spectroscopy of theinner LMC regions, similar to the inner flattened halo in our Galaxy.Further study is necessary to confirm this important result.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. II. Kinematics and Full Sample Analysis
This paper continues the analysis of faint high-latitude B stars fromMartin. Here we analyze the kinematics of the stars and combine themwith the abundance information from the first paper to classify eachone. The sample contains 31 Population I runaways, 15 old evolved stars(including 5 blue horizontal-branch [BHB] stars, 3 post-HB stars, 1pulsating helium dwarf, and 6 stars of ambiguous classification), 1 Fdwarf, and 2 stars that do not easily fit in one of the othercategories. No star in the sample unambiguously shows thecharacteristics of a young massive star formed in situ in the halo. Thetwo unclassified stars are probably extreme Population I runaways. Thelow binary frequency and rotational velocity distribution of thePopulation I runaways imply that most were ejected from dense starclusters by the dynamic ejection scenario. However, we remain puzzled bythe lack of runaway Be stars. We also confirm that PB 166 and HIP 41979are both nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory, operated by the University of Texas at Austin.
| Nearby early-type galaxies with ionized gas. II. Line-strength indices for 18 additional galaxies
We previously presented a data-set of line-strength indices for 50early-type galaxies in the nearby Universe. The galaxy sample is biasedtoward galaxies showing emission lines, located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. The present addendum enlargesthe above data-set of line-strength indices by analyzing 18 additionalearly-type galaxies (three galaxies, NGC 3607, NGC 5077 and NGC 5898were presented in the previous set). We measured 25 line-strengthindices, defined by the Lick IDS "standard" system (Trager et al. 1998,ApJS, 116, 1; Worthey & Ottaviani 1997, ApJS, 111, 377), for 7luminosity weighted apertures and 4 gradients of each galaxy. Thisaddendum presents the line-strength data-set and compares it with theavailable data in the literature.
| Spectrophotometry of Sextans A and B: Chemical Abundances of H II Regions and Planetary Nebulae
We present the results of high-quality long-slit spectroscopy ofplanetary nebulae (PNe) and H II regions in the two dwarf irregular(dIrr) galaxies Sextans A and B, which belong to a small group ofgalaxies just outside the Local Group. The observations were obtainedwith the New Technology Telescope ESO Multi-Mode Instrument. In SextansA we obtained the element abundances in its only known PN and in three HII regions with the classical Te method. The oxygenabundances in these three H II regions of Sextans A are all consistentwithin the individual rms uncertainties, with an average12+log(O/H)=7.54+/-0.06. The oxygen abundance of the PN in Sextans A is,however, significantly higher: 12+log(O/H)=8.02+/-0.05. This PN is evenmore enriched in nitrogen and helium, suggesting a classification as aPN of type I. The PN abundances of S and Ar, which are presumablyunaffected by nucleosynthesis in the progenitor star, are well belowthose in the H II regions, indicating lower metallicity at the epoch ofthe PN progenitor formation (~1.5 Gyr ago, according to our estimatesbased on the PN parameters). In Sextans B we obtained spectra of one PNand six H II regions. Element abundances with the Te methodcould be derived for the PN and three of the H II regions. For two ofthese H II regions, which have a separation of only ~70 pc inprojection, the oxygen abundances do not differ within the rmsuncertainties, with a mean of 12+log(O/H)=7.53+/-0.05. The third H IIregion, which is about 0.6 kpc northeast of the first two, is twice asmetal-rich, with 12+log(O/H)=7.84+/-0.05. This suggests considerableinhomogeneity in the present-day metallicity distribution in Sextans B.Whether this implies a general chemical inhomogeneity among populationsof comparable age in Sextans B, and thus a metallicity spread at a givenage, or whether we happen to see the short-lived effects of freshlyejected nucleosynthesis products prior to their dispersal and mixingwith the ambient interstellar medium will require further study. For thePN we measured an O/H ratio of 12+log(O/H)=7.47+/-0.16, consistent withthat of the low-metallicity H II regions. We discuss the new metallicitydata for the H II regions and PNe in the context of the published starformation histories and published abundances of the two dIrr galaxies.Both dIrrs show generally similar star formation histories in the senseof continuous star formation with amplitude variations but differ intheir detailed enrichment timescales and star formation rates as afunction of time. If we combine the photometrically derived estimatesfor the mean metallicity of the old red giant branch population in bothdIrrs with the present-day metallicity of the H II regions, both dIrrshave experienced chemical enrichment by at least 0.8 dex (lower limit)throughout their history.Based on observations obtained at the European Southern Observatory, LaSilla, Chile [072.A-0087(B)].
| Stellar velocity dispersion in narrow-line Seyfert 1 galaxies
Several authors have recently explored, for narrow-line Seyfert 1galaxies (NLS1s), the relationship between black hole mass(MBH) and stellar velocity dispersion (σ*).Their results are more or less in agreement and seem to indicate thatNLS1s fill the region below the fit obtained by Tremaine et al., showinga range of σ* similar to that of Seyfert 1 galaxies,and a lower MBH. Until now, the [OIII] width has been used inplace of the stellar velocity dispersion, but some indications havebegun to arise against the effectiveness of the gaseous kinematics inrepresenting the bulge potential, at least in NLS1s. Bian & Zhaohave stressed the urgency of producing true σ*measurements. Here, we present new stellar velocity dispersions obtainedthrough direct measurements of the CaII absorption triplet (~8550Å) in the nuclei of eight NLS1 galaxies. The resultingσ* values and a comparison withσ[OIII] confirm our suspicion that [OIII] typicallyoverestimates the stellar velocity dispersion. We demonstrate that NLS1sfollow the MBH-σ* relation as Seyfert 1,quasars and non-active galaxies.
| VLT Spectroscopy of RR Lyrae Stars in the Sagittarius Tidal Stream
Sixteen RR Lyrae variables from the QUEST survey that lie in the leadingarm of the tidal stream from the Sagittarius dSph galaxy have beenobserved spectroscopically to measure their radial velocities and metalabundances. The systemic velocities of 14 stars, which were determinedby fitting a standard velocity curve to the individual measurements,have a sharply peaked distribution with a mean of 33 km s-1and a standard deviation of only 25 km s-1. The [Fe/H]distribution of these stars has a mean of -1.76 and a standard deviationof 0.22. These measurements are in good agreement with previous onesfrom smaller samples of stars. The mean metallicity is consistent withthe age-metallicity relation that is observed in the main body of theSgr dSph galaxy. The radial velocities and the distances from the Sun ofthese stars are compared with recent numerical simulations of the Sgrstreams that assume different shapes for the dark matter halo. Modelsthat assume a oblate halo do not fit the data as well as ones thatassume a spherical or a prolate distribution. However, none of the fitsare completely satisfactory. Every model fails to reproduce the longextent of the stream in right ascension (36°) that is seen in theregion covered by the QUEST survey. Further modeling is required to seeif this and the other mismatches between theory and observation can beremoved by judicial choices for the model parameters or instead rule outa class of models.
| 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.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
| Young Stars far from the Galactic Plane: Runaways from Clusters
Quite recently, a significant number of OB stars far from the galacticplane have been found, situated at z-distances ranging from severalhundreds of pc to several kpc. The short lifetimes of these stars poseproblems for their interpretation in terms of the standard picture ofstar formation. Different mechanisms have been put forward to explainthe existence of these stars, either within the conventional view, orpostulating star formation in the galactic halo itself. These mechanismsrange from arguing that they are misidentified evolved or abnormalstars, to postulating powerful ejection mechanisms for young disk stars;in situ formation also admits several variants. We have collected fromthe literature a list of young stars far from the plane, for which theevidence of youth seems convincing. We discuss two possible formationmechanisms for these stars: ejection from the plane as the result ofdynamical evolution of small clusters (Poveda et al. 1967) and in situformation, via induced shocks created by spiral density waves (Martos etal. 1999). We compute galactic orbits for these stars, and identify thestars that could be explained by one or the other mechanism. We findthat about 90 percent of the stars can be accounted for by the clusterejection mechanism, that is, they can be regarded as runaway stars inthe galactic halo.
| VLT spectroscopy of globular cluster systems. I. The photometric and spectroscopic data set
We present Lick line-index measurements of extragalactic globularclusters in seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585,5846, and 7192) with different morphological types (E-S0) located infield and group/cluster environments. High-quality spectra were takenwith the FORS2 instrument at ESO's Very Large Telescope. 50% of ourdata allows an age resolution Δ t/t≈0.3 and a metallicityresolution 0.25-0.4 dex, depending on the absolute metallicity.Globular cluster candidates are selected from deep B, V, R, I, KFORS2/ISAAC photometry with 80-100% success rate inside one effectiveradius. Using combined optical/near-infrared colour-colour diagrams wepresent a method to efficiently reduce fore-/background contaminationdown to 10%. We find clear signs for bi-modality in the globularcluster colour distributions of NGC 1380, 3115, and 3585. The colourdistributions of globular clusters in NGC 2434, 3379, 5846, and 7192 areconsistent with a broad single-peak distribution. For the analysedglobular cluster systems the slopes of projected radial surface densityprofiles, of the form Σ(R) R -Γ, varybetween 0.8 and 2.6. Blue and red globular cluster sub-populationsshow similar slopes in the clearly bi-modal systems. For galaxies withsingle-peak globular cluster colour distributions, there is a hint thatthe blue cluster system seems to have a more extended radialdistribution than the red one. Using globular clusters as a tracerpopulation we determine total dynamical masses of host galaxies out tolarge radii (1.6-4.8 R_eff). For the sample we find masses in therange 8.8×1010 M_ȯ up to1.2×1012 M_ȯ. The line index data presentedhere will be used in accompanying papers of this series to derive ages,metallicities and abundance ratios. A compilation of currently availablehigh-quality Lick index measurements for globular clusters inelliptical, lenticular, and late-type galaxies is provided and willserve to augment the current data set.Based on observations collected at the European Southern Observatory,Cerro Paranal, Chile under programme ID P65.N-0281, P66.B-0068, andP67.B-0034.Appendix A is only available in electronic form athttp://www.edpsciences.orgAppendices B and C are 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/415/123
| Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
We present measurements of the projected stellar rotation velocities(vsini) of a sample of 45 candidate field horizontal-branch (HB) starsspanning a wide range of effective temperatures, from red HB stars withTeff~=5000K to blue HB stars with Teff of 17,000K.Among the cooler blue HB stars (Teff=7500-11500 K), weconfirm prior studies showing that, although a majority of stars rotateat vsini<15kms-1, there exists a subset of ``fastrotators'' with vsini as high as 30-35 km s-1. All but one ofthe red HB stars in our sample have vsini<10kms-1, and noanalogous rotation bimodality is evident. We also identify anarrow-lined hot star (Teff~=16,000K) with enhancedphotospheric metal abundances and helium depletion, similar to theabundance patterns found among hot BHB stars in globular clusters, andfour other stars that may also belong in this category. We discussdetails of the spectral line fitting procedure that we use to deducevsini and explore how measurements of field HB star rotation may shedlight on the issue of HB star rotation in globular clusters.
| Analysis of the Interaction Effects in the Southern Galaxy Pair Tol 1238-364 and ESO 381-G009
In the context of the connection among galaxy-galaxy interaction,starbursts, and nuclear activity, we present and discuss a quantitativemorphological analysis based on BVR images and a detailed spectroscopicinvestigation of two interacting galaxies, the Seyfert 2 Tol 1238-364(IC 3639) and its companion ESO 381-G009, forming a triple system withESO 381-G006. Broadband optical photometry is complemented by Hαimaging, which provides information about the distribution ofstar-forming regions across the galaxies. Long-slit spectroscopic dataobtained at different position angles of the slit are employed todetermine the physical conditions of circumnuclear and extranuclearregions. A mixture of thermal and nonthermal ionizing radiation is foundin the surroundings of the nucleus of Tol 1238-364, and the energybudget supports the presence of a circumnuclear starburst. Severalregions in both the galaxies show anomalous line ratios: additionalionization by shock heating and low ionization of some extranuclear H IIregions are suggested as possible explanations. An analysis of theemission-line profiles reveals the presence of a broad Hαcomponent in the nuclear region of Tol 1238-364. Independent estimatesof the star formation rates (SFRs) were obtained through flux-calibratedHα images and far-infrared (FIR) emission in the four IRAS bands.Overall, SFR densities have been compared with the SFR densities derivedfrom Hα emission in the individual regions of the galaxies sampledby long-slit spectra. In both the galaxies an enhancement of the starformation activity with respect to isolated galaxies is revealed. Theprevalence of starburst or nuclear activity has been examined throughFIR color indices. The interaction scenario is discussed on the basis ofthe observed galaxy properties.Based on data collected at the ESO-MPIA 2.2 m telescope in La Silla,Chile.
| Hα+[N II] Observations of the H II Regions in M81
In a first of a series of studies of the Hα+[N II] emission fromnearby spiral galaxies, we present measurements of Hα+[N II]emission from H II regions in M81. Our method uses large-field CCDimages and long-slit spectra and is part of the ongoingBeijing-Arizona-Taipei-Connecticut Sky Survey (the BATC survey). The CCDimages are taken with the National Astronomical Observatories of China(NAOC) 0.6/0.9 m f/3 Schmidt telescope at the Xinglong ObservingStation, using a multicolor filter set. Spectra of 10 of the brightest HII regions are obtained using the NAOC 2.16 m telescope with a Tek1024×1024 CCD. The continua of the spectra are calibrated byflux-calibrated images taken from the Schmidt observations. We determinethe continuum component of our Hα+[N II] image via interpolationfrom the more accurately measured backgrounds (M81 starlight) obtainedfrom the two neighboring (in wavelength) BATC filter images. We use thecalibrated fluxes of Hα+[N II] emission from the spectra tonormalize this interpolated, continuum-subtracted Hα+[N II] image.We estimate the zero-point uncertainty of the measured Hα+[N II]emission flux to be ~8%. A catalog of Hα+[N II] fluxes for 456 HII regions is provided, with those fluxes being on a more consistentlinear scale than previously available. The logarithmically binnedHα+[N II] luminosity function of H II regions is found to haveslope α=-0.70, consistent with previous results (which allowedα=-0.5 to -0.8). From the overall Hα+[N II] luminosity ofthe H II regions, the star formation rate of M81 is found to be ~0.68Msolar yr-1, modulo uncertainty with extinctioncorrections.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Παρθένος |
| Right ascension: | 12h06m47.23s |
| Declination: | +11°40'12.7" |
| Apparent magnitude: | 11.004 |
| Proper motion RA: | -8.2 |
| Proper motion Dec: | -5.3 |
| B-T magnitude: | 10.786 |
| V-T magnitude: | 10.986 |
Catalogs and designations:
|
