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Ýlgili Makaleler
New results on the massive star-forming region S106 by BEAR spectro-imagery
As a typical example of interaction of a massive star with its parentcloud, the close environment of S106 IR in thestar-forming region S106 was observed at highspectral resolution (~16 km s-1). Integral field spectroscopywith BEAR, an imaging Fourier Transform Spectrometer (FTS), on a fieldof ~40´´in diameter, in the H2 1-0 S(1), 2-1 S(1),Brγ, He I and [Fe III] lines. From the data several maps wereobtained: intensity, velocity and linewidth in the Brγ and the H21-0 S(1) line, 1-0 S(1)/2-1 S(1) line ratio, and continuum emission at2.1 μm. From the latter, about twenty low-mass stars were detectedwith photometry in this band, and an estimate of their mass was madeleading to the conclusion that S106 is a site of formation of mainlysub-solar mass stars. The intensity structure of the excited moleculargas H2 was found to be clumpy while the velocity is almost uniformely atvLSR ≃ 1.5 km s-1 except to the south wherethe velocity reaches up to 15 km s-1 in a zone limited by thelong edge of a rectangular hole in the emission. The H2 line ratio mapwith values from 1 to 9 implies that UV-absorption and shocks areparticipating in the excitation process. A PDR model with a temperatureof 3700 K for S106 IR was used to retrieve the H2 gas density andtemperature. The density was found to vary between 1 and 3.5 ×105 cm-3 with corresponding temperatures between660 and 1240 K. The study of the linewidth distribution indicates formost of the gas a supersonic turbulence with a mean contribution to theobserved profiles of ≥6 km s-1. Turbulence is likely tobe responsible for the observed clumpy structure of the excited gas.Point-like spots with a linewidth as high as 30 km s-1 in oneposition are detected, which may be vortices in the molecular gas. The HII region probed by Brγ shows a broad range of velocity, from -45to +80 km s-1, organized in velocity structures thatcorrespond to two pairs of large, bipolar outflows originating from themassive source, not directed along the axis of the H II region. Emissionlines of He I and [Fe III] are detected in a bright area to thesouthwest of S106 IR, with point-like structures suggestingphotoevaporating clumps. From the velocity data, a 3-D model of theenvironment of S106 IR is proposed. S106 is an example of an evolved HII region seen face-on. The central source located at the edge of itsparent molecular cloud has carved an expanding cylinder of turbulent,atomic gas of ≃0.1 pc in radius. This massive object was formed byan accretion disk process. The disk is still present and the bipolaroutflows are remnants of the massive star activity. A time scale of 1400yr is estimated for the most recent event. A thin and quiescent clumpylayer of warm H2 marks the transition of the H II region to themolecular cloud. From the data, there are locally no signs of ongoingstar formation.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| The Compact H II Region S88B: Excitation and Extinction
We have undertaken an investigation into the excitation of, and dustextinction to, the massive star formation region S88B. Studying stellarproperties of the wide-field Two Micron All Sky Survey (2MASS) J (1.23μm), H (1.65 μm), and Ks (2.16 μm) images, we havedetermined the extent of, and extinction to, the molecular cloudassociated with the ultracompact H II regions S88B-1 and S88B-2 and witha newly described infrared H II region. Infrared observations ofBrγ and Brα hydrogen recombination lines provide extinctionmaps to the infrared H II region, and 3.3 and 3.4 μm images show thepolycyclic aromatic hydrocarbon (PAH) emission distribution. We alsoreport the detection of an infrared counterpart to S88B-2.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| JHK Standard Stars on the CIT Photometric System
We present a set of 58 stars with JHK standard values on the CIT systemand with a suitable magnitude range for use with array detectors onsmall- to moderate-size telescopes. Each final value is based on six to47 measures (with a mean of 17) obtained on separate nights with the USNaval Observatory (USNO) NICMOS3 (HgCdTe) camera. The objects include 20primary CIT standards from Elias et al. and 38 secondary sourcesselected from the SAAO and UKIRT standards lists, cover a K-magnituderange between 6.0 and 10.8, and lie north of declination -20°. Thestars were reduced to the CIT system as defined by Elias et al.,producing a USNO system that is identical to the near-infrared CITsystem. This work densifies the original CIT system by nearly a factorof 3 and extends its range by about 3 mag. The SAAO and UKIRT standardsare also compared with the CIT system.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| Near-Infrared Photometric Survey of Proto-planetary Nebula Candidates
We present JHK' photometric measurements of 78 objects mostly consistingof proto-planetary nebula candidates. Photometric magnitudes aredetermined by means of imaging and aperture photometry. Unlike theobservations with a photometer with a fixed-sized beam, the method ofimaging photometry permits accurate derivation of photometric values,because the target sources can be correctly identified and confusionwith neighboring sources can be easily avoided. Of the 78 sourcesobserved, we report nearly 10 cases in which the source seems to havebeen misidentified or confused by nearby bright sources. We also presentnearly two dozen cases in which the source seems to have indicated avariability that prompts a follow-up monitoring. There are also a fewsources that show previously unreported extendedness. In addition, wepresent H-band finding charts of the target sources.
| Multiple Molecular H2 Outflows in AFGL 618
We report high spatial (0.5") and high spectral (9 km s-1)resolution spectro-imaging of the 2.12 μm H2 1-->0 S(1)line in the proto-planetary nebula AFGL 618 using BEAR at theCanada-France-Hawaii Telescope. The observations reveal the presence ofmultiple, high-velocity, molecular outflows that align with theremarkable optical jets seen in Hubble Space Telescope images. Thestructure and kinematics of the outflows show how jets interact withcircumstellar gas and shape the environment in which planetary nebulaeform.Based on observations collected at the Canada-France-Hawaii Telescope,operated by the National Research Council of Canada, the Centre Nationalde la Recherche Scientifique de France, and the University of Hawaii.
| H II Emission from a Complete Spectroscopic Survey of Be Stars in h and χ Persei
We describe data for emission-line B stars observed in a spectroscopicsurvey of h and χ Persei. The survey is complete to V=12.5 andcovers an area of ~1100 arcmin2 roughly centered on the twoclusters. We detect 32 Be stars; some have low Hα emissionstrength. Seven of these are new identifications; seven others areconfirmations of Be stars previously identified using photometry. Fiveof the observed Be stars show significant Hα profile variationsfrom epoch to epoch. We show that spectral indices yield physicalcharacteristics of the H II emission region. This automatic method isrobust and easily applied to large spectroscopic samples. We inferHα:Hβ flux ratios of 2-5 and observe a linear relationshipbetween Hα emission and J-K color for these stars. We include aHertzsprung-Russell diagram for the B-type stars in the clusters.
| The radio galaxy 3C 356 and clues to the trigger mechanisms for powerful radio sources
We present deep near-infrared images, taken with the Subaru Telescope,of the region around the z=1.08 radio source 3C 356 which show it to beassociated with a poor cluster of galaxies. We discuss evidence thatthis cluster comprises two subclusters traced by the two galaxiespreviously proposed as identifications for 3C 356, which both seem toharbour active galactic nuclei, and which have the disturbedmorphologies expected if they underwent an interpenetrating collision atthe time the radio jets were triggered. We explain the high luminosityand temperature of the diffuse X-ray emission from this system as theresult of shock heating of intracluster gas by the merger of two galaxygroups. Taken together with the results on other well-studied powerfulradio sources, we suggest that the key ingredient for triggering apowerful radio source, at least at epochs corresponding to z~1, is agalaxy-galaxy interaction which can be orchestrated by the merger oftheir parent subclusters. This provides an explanation for the rapiddecline in the number density of powerful radio sources since z~1. Weargue that attempts to use distant radio-selected clusters to trace theformation and evolution of the general cluster population must addressways in which X-ray properties can be influenced by the radio source,both directly, by mechanisms such as inverse Compton scattering, andindirectly, by the fact that the radio source may be preferentiallytriggered at a specific time during the formation of the cluster.
| High resolution near-infrared spectro-imaging of NGC 7027
We present near-infrared spectro-imaging of the young planetary nebulaNGC 7027 between 2.10 and 2.20 mu m with high spatial (0.5'')and high spectral (8.7 km s-1) resolution. The observations,made using BEAR at the CFHT, reveal the detailed morphology andkinematics of the ionized nebula (in the Brgamma line and 16 otheratomic lines) and the surrounding molecular envelope (in the 1-0 S(1)line of H2). The observations show that the ionized gas formsan elongated ( ~ 6 arcsec x 12 arcsec , PA = 32degr ), limb-brightenedshell with an expansion velocity of 19.5 km s-1 along theline of sight. The shell is composed of numerous small condensations andhas nearly parallel sides with flattened ends that are not well matchedby a uniform ellipsoidal model. Low level Brgamma emission is detectedat high red- and blue-shifted velocities (+/- 55 km s-1)along a bipolar axis at PA = 60degr that deviates significantly fromthat of the main nebula. The H2 emission is distributed atthe periphery of the ionized gas, in a limb-brightened, bi-conical shell(~ 10arcsec x 13arcsec , PA = 28degr ) with enhanced emission at theequator and complex structure at the ends of the major axis. TheH2 emission traces the inner edge of the extended molecularenvelope seen in CO, and its distribution and intensity are well matchedby model predictions of a high-density (nH ~106-105 cm-3) photo-dissociationregion. The kinematic structure of the H2 emission reveals aremarkable series of lobes and openings in the molecular shell. Thesefeatures are point symmetric about the center, and the most prominentpair aligns with the high velocity, bipolar emission seen in Brgamma.These observations demonstrate recent activity by collimated outflows inNGC 7027, with a multiple, bipolar geometry. The interaction of theoutflows with the surrounding envelope has significantly affected themorphology of the developing nebula and its environment, and theirpresence in this well-studied archetype underscores the generalimportance of outflows in the early shaping history of planetarynebulae. Based on observations collected at the Canada-France-HawaiiTelescope, operated by the National Research Council of Canada, theCentre National de la Recherche Scientifique de France, and theUniversity of Hawaii.
| Large-Scale Extended Emission around the Helix Nebula: Dust, Molecules, Atoms, and Ions
We present new observations of the ionized gas, molecular gas, and cooldust in the Helix Nebula (NGC 7293). The ionized gas is observed in theform of an Hα image, which is constructed using images from theSouthern Hα Sky Survey Atlas. The molecular emission was mappedusing the H2 v=1-->0 S(1) line at 2.122 μm. Thefar-infrared (FIR) observations were obtained using ISOPHOT on theInfrared Space Observatory. The Hα observations are more sensitivethan previous measurements and show the huge extent of the Helix,confirming it as a density-bounded nebula and showing previously unseenpoint-symmetric structures. The H2 observations show that themolecular gas follows the distribution of molecular material shown inprevious work. The molecular emission is confined to that part of thenebula seen in the classic optical image. Furthermore, comparison of theH2 emission strength with time-dependent models forphotodissociation regions (PDRs) shows that the emission arises fromthermal excitation of the hydrogen molecules in PDRs and not fromshocks. The FIR observations, at 90 and 160 μm, represent mostlycontributions from thermal dust emission from cool dust grains butinclude a small contribution from ionized atomic lines. Comparison ofthe FIR emission with the Hα observation shows that the dust andionized gas are coincident and extend to ~1100" radius. This equates toa spatial radial extent of more than 1 pc (assuming a distance to theHelix of ~200 pc). Assuming that the outer layers of the circumstellarshell have spherical symmetry, radiative transfer modeling of theemission in Hα gives a shell mass of ~1.5 Msolar.However, the modeling does not cover the outermost part of the shell(beyond ~600" radius), and therefore this is a lower limit for the shellmass. Moreover, the models suggest the need for very large dust grains,with ~80% of the dust mass in grains larger than 3.5 μm. Comparisonof these new observations with previous observations shows thelarge-scale stratification of the Helix in terms of ionized gas anddust, as well as the coexistence of molecular species inside the ionizedzones, where molecules survive in dense condensations and cometaryknots.
| Large Proper-Motion Infrared [Fe II] Emission-Line Features in GGD 37
We report the detection of proper motions in [Fe II] 1.644 μmemission among the southeasternmost features in the Herbig-Haro objectcomplex GGD 37. Imaging observations were made over a period of 5 yr, atepochs 1993.67, 1996.71, and 1998.68, that reveal proper-motionvelocities of 400+/-200 km s-1 at GGD 37:W2 and 850+/-200 kms-1 at a newly identified object, designated GGD 37:RWPF 1.We believe the proper-motion velocity of GGD 37:RWPF 1 is the highestfound to date for a Herbig-Haro object. The direction of GGD 37:RWPF 1'sproper motion is almost due west, away from the nearby young stellarobject complex in Cep A East. GGD 37:W2's direction of proper motion isnorth/northwest, which does not lead back to any of the compact objectsin Cep A East.
| Do galaxy mergers form elliptical galaxies? A comparison of kinematic and photometric properties
We present near-infrared K-band imaging and spectroscopy of a sample ofgalaxy mergers, which we use to derive light profile indices, absolutemagnitudes and central velocity dispersions. We find that the lightdistributions of mergers more nearly resemble those of ellipticals thanthose of bulges, but that the mergers lie well away from the FundamentalPlane defined by the ellipticals. We interpret this as being due toenhancement of the K-band surface brightness of the mergers by asignificant population of supergiant stars, and independent evidence forsuch a population is inferred from measurements of the depth of the2.3-μm CO absorption feature.
| A complete sample of radio sources in the North Ecliptic Cap, selected at 38MHz - III. Further imaging observations and the photometric properties of the sample
Further imaging observations of a sample of radio sources in the NorthEcliptic Cap are presented and a number of new identifications are made.Using redshifts from spectroscopic data presented in a companion paperby Lacy et al., the photometric properties of the galaxies in the sampleare discussed. It is shown that: (1) out to at least z~0.6 radiogalaxies are good standard candles irrespective of radio luminosity; (2)for 0.6<~z<~1 a large fraction of the sample has magnitudes andcolours consistent with a non-evolving giant elliptical, and (3) athigher redshifts, where the R-band samples the rest-frame UV flux, mostobjects have less UV luminosity than expected if they form their stellarpopulations at a constant rate from a high redshift to z~1 in unobscuredstar-forming regions (assuming an Einstein-de Sitter cosmology). Theconsequences of these observations are briefly discussed.
| Optical and Near-Infrared Spectroscopy of Cygnus A
We present optical and near-infrared spectroscopy of the luminous radiogalaxy Cygnus A (3C 405). Optical (~6700-9300 Å) observations wereobtained of the central region, including the region where most emissionlines are strongest, about 1.5" northwest of the nucleus. However,high-ionization lines ([Ar XI] and [Fe XI]), as well as an unidentifiedfeature at ~7608 Å, are stronger in the continuum-dominatedsoutheast component. We detect the near-infrared Ca triplet inabsorption, and we use it to obtain a new determination of the redshiftand velocity dispersion of the stellar component of Cygnus A. Theinfrared (~1.9-2.5 μm) spectrum of the nucleus shows emission from[Si VI], [S XI], and possibly [Si XI]. A number of molecular hydrogentransitions were also detected; their ratios favor X-ray heating fromthe nuclear source over other possible origins (e.g., shocks) as themost likely excitation mechanism. We see no evidence for broad-linewings on the Paα line profile, confirming that the broad-lineregion in Cygnus A remains heavily obscured at 2 μm.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| Near-Infrared Spectroscopy and a Search for CO Emission in Three Extremely Luminous IRAS Sources: IRAS F09105+4108, IRAS F15307+3252, and PG 1634+706
Rest-frame 0.48-1.1 μm emission-line strengths and molecular gas mass(H_2) upper limits for three luminous infrared sources-the hyperluminousinfrared galaxies IRAS F09105+4108 (z = 0.4417), IRAS F15307+3252 (z =0.926), and the optically selected QSO PG 1634+706 (z = 1.338)-arepresented. Diagnostic emission-line ratios ([O III] lambda5007/Hβ,[S II] lambdalambda6716, 6731/Hα, [N II] lambda6583/Hα, and[S III] lambdalambda9069, 9532/Hα) indicate a Seyfert 2-likespectrum for both infrared galaxies, consistent with previouslypublished work. The upper limits of molecular gas mass for all threesources are M(H_2) < (1-3) x 10^10 h^-2 M_ȯ (q_0 = 0.5, H_0 =100 h km s^-1 Mpc^-1), less than that of the most gas-rich infraredgalaxies in the local universe. All three sources haveL_ir/L^'_CO~1300-2000 and thus are the extragalactic sources with themost extreme L_ir/L^'_CO values measured to date. Given the relativelywarm far-infrared colors for all three objects, much of their infraredluminosity may emanate from a relatively modest amount of warm dust(e.g., M_d ~ 10^5-10^7 h^-2 M_ȯ, T_d = 200-100 K) near the AGN. ForF09105+4108 and F15307+3252, the implied circumnuclear covering factorof this dust is ~90%, while for PG 1634+706 the covering factor is only~35%.
| The near-infrared extinction law and limits on the pre-main-sequence population of the Rho Ophiuchi dark cloud
We describe new techniques to measure the NIR extinction law and toplace limits on the premain-sequence stellar population of a dark cloud.We analyze JHK imaging data for the central 1 sq deg of the Rho Ophiuchicloud core and show that nearly all stars projected onto regions of lowCS intensity, ICS 10 K km/s, are background stars. Most sources atlarger CS intensities lie within cloud material. We use the backgroundstars to derive the slope of the NIR extinction law, E(J-H)/E(H-K) =1.57 +/- 0.03. This result is consistent with previous extinction lawsbut has a factor of two to three smaller uncertainty. The new Rho Ophextinction law yields strong constraints on the number of previouslyundiscovered premain-sequence stars in the cloud, 46 +/- 11, and thenumber of previously undiscovered young stars with near-IR excesses, 15+/- 4. Neither limit exceeds the number of known premain-sequence starsin the cloud about 100. Thus, current samples of premain-sequence starsare reasonably complete for K = 14 or less.
| The Most Distant [OIII]-Emitting Quasar PKS 1937-101 at Redshift 3.8
We report on the discovery of a high-z quasar with unambiguous[OIII]lambda 5007 emission: PKS 1937-101 at redshift 3.8. This quasar,however, shows little evidence for rest-frame ultraviolet and opticalFeII emission. It is thus shown that PKS 1937-101 does not belong to aclass of super-iron-rich high-z quasars reported by Elston, Thompson,and Hill (1994, AAA61.159.045). The epoch of major star formation in thehost galaxy is briefly discussed.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Cygnus X-3 in outburst: quenched radio emission, radiation losses and variable local opacity
We present multiwavelength observations of Cygnus X-3 during an extendedoutburst in 1994 February-March. Intensive radio monitoring at 13.3, 3.6and 2.0cm is complemented by observations at (sub)millimetre andinfrared wavelengths, which find Cyg X-3 to be unusually bright andvariable, and include the first reported detection of the source at 0.45mm. We report the first confirmation of quenched radio emission prior toradio flaring independently of observations at Green Bank. Theobservations reveal evidence for wavelength-dependent radiation lossesand gradually decreasing opacity in the environment of the radio jet. Wefind that the radiation losses are likely to be predominantly inverseCompton losses experienced by the radio-emitting electrons in the strongradiation field of a luminous companion to the compact object. Weinterpret the decreasing opacity during the flare sequence as resultingfrom a decreasing proportion of thermal electrons entrained in the jet,reflecting a decreasing density in the region of jet formation. Wepresent, drawing in part on the work of other authors, a model basedupon mass transfer rate instability predicting gamma-ray, X-ray,infrared and radio trends during a radio flaring sequence.
| Multiwavelength Observations of Collisional Ring Galaxies.I.Broad-Band Images, Global Properties, and Radial Colors of the Sample Galaxies
This is one of a series of papers discussing the optical, infrared andradio continuum properties of a sample of collisional ring galaxies. Thepresent paper concentrates on the global broad-band optical (B, V and R)and near-IR (J, H and K) images of the galaxies and describe theirglobal properties. An analysis of the colors of the galaxies over avariety of wavelength baselines is described. In the B and V bands, thebluest colors are found in the outer bright ring. The B-V colors of thesample of galaxies are blue, the median value for the sample is B-V =0.60, and V-K= 2.33 mag. The IR morphology of the galaxies is, in mostcases, very similar to that of the B-band data, suggesting that theclumpy appearance of the star formation in the outer rings is real, andnot a result of patchy dust obscuration. Only in one ring (WN1, aSeyfert ring galaxy) was the IR morphology different from the optical,suggesting the presence of significant dust in the disk. In II Hz 4,faint spiral arms are seen within the ring. There is a suggestion thatthe larger rings have redder V-K colors, which may be due to anincreased incidence of nuclear bulges in larger ring galaxies. Radialprofiles of surface brightness and color are presented for fourgalaxies. In all cases, the colors becomes bluer as one proceedsradially outwards, but in two galaxies, the rings redden again outsidethe main ring, suggesting the existence of a red stellar population thatmay have pre-dated the collisions.
| Flaring and quiescent infrared behaviour of Cygnus X-3
We present new infrared observations of the exotic X-ray binary systemCygnus X-3, including high-time-resolution simultaneous H- and K-bandphotometry over ~1.5 orbital periods and 1-5mum photometry during bothperiods of apparent infrared quiescence and flaring activity. Thesimultaneous H- and K-band observations reveal the 4.8-h orbitalmodulation of the source, superimposed upon which are a number ofextremely rapid flare events. We find rise times for these events of<=15 s, and find that the source becomes redder in (H-K) during theflares. This latter effect is confirmed by 1-5 μm photometry during aperiod of prolonged quasi-stable flaring. We model this reddening incolour during flaring in terms of optically thin free-free emission froma hot dense plasma, possibly associated with a thermal gas in thehigh-velocity radio jets revealed by radio VLBI. Size, luminosity andlack of self-absorption considerations allow us to place strongconstraints on possible values of N_e and T for this plasma, and we findthat the dominant cooling mechanism is likely to be bremsstrahlungcooling. Dereddening of new 1-5mum data combined with 0.7-1.0mum resultsfrom the literature is consistent with an estimated infrared extinctionto the source of 4.5<=A_J<=7.5 mag, and an infrared excess above ablackbody stellar continuum which is inherent to the source.
| The empirical scale of temperatures of the low main sequence (F0V-K5V).
We have calibrated the effective temperatures of the low main sequencestars ranging spectral types from F0 to K5 versus [Fe/H] and colours(B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and ubvy-β, using alarge sample of dwarfs and subdwarfs. The effective temperatures, scaledto direct T_eff_ determinations via reliable angular diametermeasurements, were derived applying the InfraRed Flux Method with thenew grid of atmosphere models developed by Kurucz (1993). We have fittedpolynomial functions of the form θ_eff_=P(colour,[Fe/H]) usingthe least squares method. The precision of the fits ranges from 30K for(V-K) to 154K for (J-H). The new relations have been compared toprevious calibrations. We also provide the empirical intrinsic colours(U-B), (B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and β, inthe ranges: 4000K[Fe/H]>-2.5.
| Water Ice in the Disk around the Protostar AFGL 2136 IRS 1
The protostar AFGL 2136 IRS 1 illuminates the Juggler nebula and drivesa massive molecular outflow. The line of sight toward AFGL 2136 alsodisplays a rich spectrum of solid state absorption features. Toinvestigate the distribution of ice-coated grains in the environment ofIRS 1, we obtained narrowband images at six near-infrared wavelengthssurrounding and including the 3.08 mu m water ice feature. These images(specifically, a color map constructed from 2.14 and 3.60 mu m images)provide vivid evidence for the presence of a disk around IRS 1 andappear to reveal, for the first time, the detailed distribution of waterice in the local environment of a protostar. Models of the 2--4 mu mspectral energy distributions (SEDs) toward IRS 1 and the Juggler nebulasuggest that the abundance of icy grains is larger along lines of sightthrough the disk than along lines of sight away from the equatorialplane of IRS 1. Thus, while we find evidence that icy grains existthroughout the cloud core containing AFGL 2136, it appears that thephysical conditions in the circumstellar disk around IRS 1 are moreconducive to ice mantle survival and/or growth than are physicalconditions in its rarefied polar regions.
| Photometry of the post-common-envelope binary PG 0308+096
We present R- and H-band photometry of PG 0308+096. We demonstrate thatthe orbital modulation is consistent with that of a dwarf M star heatedby a DA white dwarf within the constraints given by the kinematicparameters. By fitting the photometry with an irradiation model wedetermine that the radius of the white dwarf is 0.019<=R_wd<=0.026R_ (90 per cent confidence). In order to derive these limits, we havedeveloped a fitting procedure that takes account of the externalconstraints derived from the spectroscopic analysis by Saffer et al. Wedetermine that the period of the system is 0.286654+/-0.00000078d, whichis one of the cycle count aliases considered by Saffer et al. We showthat the Hα emission from the surface of the red star can bemodelled as either optically thick or thin, but in the latter case thered dwarf must have intrinsic emission.
| Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5).
We have applied the InfraRed Flux Method (IRFM) to a sample of 475dwarfs and subdwarfs in order to derive their effective temperatureswith a mean accuracy of about 1.5%. We have used the new homogeneousgrid of theoretical model atmosphere flux distributions developed byKurucz (1991, 1993) for the application of the IRFM. The atmosphericparameters of the stars cover, roughly, the ranges:3500K<=T_eff_<=8000K -3.5<=[Fe/H]<=+0.53.5<=log(g)<=5. The monocromatic infrared fluxes at the continuum,and the bolometric fluxes are derived using recent results, whichsatisfy the accuracy requeriments of the work. Photometric calibrationshave been revised and applied to estimate metallicities, although directspectroscopic determinations were preferred when available. The adoptedinfrared absolute flux calibration, based on direct optical measurementsof angular stellar diameters, sets the effective temperatures determinedusing the IRFM on the same scale than those obtained by direct methods.We derive three temperatures, T_J_, T_H_ and T_K_, for each star usingthe monochromatic fluxes at different infrared wavelengths in thephotometric bands J, H, and K. They show good consistency over 4000 K,and no trend with wavelength may be appreciated. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of the errors associated to the different inputs ofthe method, and their transmission into the final temperatures. We alsoprovide comparison with previous works.
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| Takýmyýldýz: | Herkul |
| Sað Açýklýk: | 17h47m58.56s |
| Yükselim: | +39°58'50.9" |
| Görünürdeki Parlaklýk: | 7.601 |
| Uzaklýk: | 171.233 parsek |
| özdevim Sað Açýklýk: | -8.3 |
| özdevim Yükselim: | 129.8 |
| B-T magnitude: | 7.84 |
| V-T magnitude: | 7.621 |
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