תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Disk Evolution in the Orion OB1 Association
We analyze multiband photometry of a subsample of low-mass stars in theassociations Ori OB1a and 1b discovered during the Centro deInvestigaciones de Astronomía (CIDA) Orion Variability Survey,which have ages of 7-10 and 3-5 Myr, respectively. We obtainedUBVRCIC photometry at Mount Hopkins for sixclassical T Tauri stars (CTTSs) and 26 weak T Tauri stars (WTTSs) in OriOB1a and for 21 CTTSs and two WTTSs in Ori OB1b. We also obtained L-bandphotometry for 14 CTTSs at Mount Hopkins and 10 and 18 μm photometrywith OSCIR at Gemini for six CTTSs; of these, all six were detected at10 μm, whereas only one was detected at 18 μm. We estimate massaccretion rates from the excess luminosity at U and find that they areconsistent with determinations for a number of other associations, withor without high-mass star formation. The observed decrease of massaccretion rate with age is qualitatively consistent with predictions ofviscous evolution of accretion disks, although other factors can alsoplay a role in slowing accretion rates. We compare the excesses overphotospheric fluxes in H-K, K-L, and K-N with the younger sample ofTaurus and find an overall decrease of disk emission from Taurus to OriOB1b to Ori OB1a. This decrease implies that significant grain growthand settling toward the midplane has taken place in the inner disks ofOri OB1. We compare the spectral energy distribution of the stardetected at both 10 and 18 μm with disk models for similar stellarand accretion parameters. We find that the low fluxes shortward of 18μm of this Ori OB1b star cannot be due to the smaller disk radiusexpected from viscous evolution in the presence of the far-ultravioletradiation fields from the OB stars in the association. Instead, we findthat the disk of this star is essentially a flat disk, with little ifany flaring, indicating a significant degree of dust settling toward themidplane, as expected from dust evolution in protoplanetary disks.
| 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.
| A Multiwavelength Scattered Light Analysis of the Dust Grain Population in the GG Tauri Circumbinary Ring
We present the first 3.8 μm image of the dusty ring surrounding theyoung binary system GG Tau, obtained with the W. M. Keck II 10 mtelescope's adaptive optics system. This is the longest wavelength atwhich the ring has been detected in scattered light so far, allowing amultiwavelength analysis of the scattering properties of the dust grainspresent in this protoplanetary disk in combination with previous,shorter wavelength, Hubble Space Telescope images. We find that thescattering phase function of the dust grains in the disk is only weaklydependent on the wavelength. This is inconsistent with dust modelsinferred from observations of the interstellar medium or dense molecularclouds. In particular, the strongly forward-throwing scattering phasefunction observed at 3.8 μm implies a significant increase in thepopulation of large (>~1 μm) grains, which provides directevidence for grain growth in the ring. However, the grain sizedistribution required to match the 3.8 μm image of the ring isincompatible with its published 1 μm polarization map, implying thatthe dust population is not uniform throughout the ring. We also showthat our 3.8 μm scattered light image probes a deeper layer of thering than previous shorter wavelength images, as demonstrated by a shiftin the location of the inner edge of the disk's scattered lightdistribution between 1 and 3.8 μm. We therefore propose a stratifiedstructure for the ring in which the surface layers, located ~50 AU abovethe ring midplane, contain dust grains that are very similar to thosefound in dense molecular clouds, while the region of the ring located~25 AU from the midplane contains significantly larger grains. Thisstratified structure is likely the result of vertical dust settlingand/or preferred grain growth in the densest parts of the ring.
| 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.
| No Fossil Disk in the T Tauri Multiple System V773 Tauri
We present new multiepoch near-infrared (NIR) and optical high angularresolution images of the V773 Tau pre-main-sequence triple system, aweak-line T Tauri star (WTTS) system in which the presence of anevolved, ``fossil'' protoplanetary disk has been inferred on the basisof a significant IR excess. Our images reveal a fourth object bound tothe system, V773 Tau D. While it is much fainter than all othercomponents at 2 μm, it is the brightest source in the system at 4.7μm. We also present medium-resolution K-band adaptive opticsspectroscopy of this object, which is featureless with the exception ofa weak Brγ emission line. Based on this spectrum and on thespectral energy distribution (SED) of the system, we show that V773 TauD is another member of the small class of ``infrared companions'' (IRCs)to T Tauri stars (TTSs). It is the least luminous, and probably theleast massive, component of the system, as opposed to most other IRCs,which suggests that numerous low-luminosity IRCs such as V773 Tau D maystill remain to be discovered. Furthermore, it is the source of thestrong IR excess in the system. We therefore reject the interpretationof this excess as the signature of a fossil (or ``passive'') disk andfurther suggest that these systems may be much less frequent thanpreviously thought. We further show that V773 Tau C is a variableclassical TTS (CTTS) and that its motion provides a well-constrainedorbital model. We show that V773 Tau D can be dynamically stable withinthis quadruple system if its orbit is highly inclined. Finally, V773 Tauis the first multiple system to display such a variety of evolutionarystates (WTTS, CTTS, IRC), which may be the consequence of the strongstar-star interactions in this compact quadruple system.
| 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.
| 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.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Near-infrared line imaging of the circumnuclear starburst rings in the active galaxies NGC 1097 and NGC 6574
We present high spatial resolution near-infrared broad-band JHK andBrgaussmma 2.166 mum and H_2 1-0 S(1) 2.121 mum emission line images ofthe circumnuclear star formation rings in the LINER/Seyfert 1 galaxy NGC1097 and in the Seyfert 2 galaxy NGC 6574. We investigate themorphology, extinction, and the star formation properties and history ofthe rings, by comparing the observed properties with an evolutionarypopulation synthesis model. The clumpy morphology in both galaxiesvaries strongly with wavelength, due to a combination of extinction,emission from hot dust and red supergiants, and the age of the stellarpopulations in the rings. The near-infrared and radio morphologies arein general agreement, although there are differences in the detailedmorphology. From the comparison of Brgaussmma and Hα fluxes, wederive average extinctions toward the hot spots A_V = 1.3 for NGC 1097and A_V = 2.1 for NGC 6574. The observed H_2/Brgaussmma ratios indicatethat in both rings the main excitation mechanism of the molecular gas isUV radiation from hot young stars, while shocks can contribute only in afew regions. The starburst rings in both galaxies exhibit smallBrgaussmma equivalent widths. Assuming a constant star formation ratewith M_u = 100 M_sun results in extremely long ages (up to 1 Gyr), indisagreement with the morphology and the radio spectral index of thegalaxies. This situation is only slightly remedied by a reduced uppermass cutoff (M_u = 30 M_sun). We prefer a model of an instantaneousburst of star formation with M_u = 100 M_sun occurring sim6-7 Myr ago.Gaseous nuclear bars parallel to the stellar nuclear bar were detectedin both galaxies, and we derive M sim100 M_sun for the mass of theexcited nuclear H_2 emission. Finally, we briefly discuss the connectionbetween the rings, bars and the fuelling of nuclear activity.
| Cepheus A East: Unraveling the Mysteries
New infrared images of Cep A East are presented that show two regions ofshock-excited line emission from separate bipolar flows. We identify thedominant sources powering the outflows and argue that the resultssupport a multiple outflow model (Narayanan & Walker) as opposed toa quadrupolar outflow scenario. The images include near-infraredbroadband (K [2.158 mu m], L" [3.81 mu m], and M' [4.67 mu m]) andspectral line ([Fe II] emission line at 1.644 mu m and H2 1-0 S[1] lineat 2.122 mu m) observations, as well as continuum emission, at 1.644 mum and 2.122 mu m. Considering our data and other results, we present aunified, self-consistent picture of the disk and shock structure. Thenorthern emission region appears to be the result of the ablation of adense molecular clump (coincident with HW 6) in the path of a divertingjet from YSO HW 2 and subsequent multiple bow shocks with promptentrainment arising from the interaction of the jet with the molecularcloud Cep A-2. The southern line emission region near HW 7 resembles the"artillery shell" bow shocks found in Orion and is most likely a J-typeshock caused by a jet from another YSO, possibly HW 3(d)ii.
| 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.
| 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.
| Imaging the host galaxies of high-redshift radio-quiet QSOs
We present new deep K-band and optical images of four radio-quiet QSOsat z approximately = 1 and six radio-quiet QSOs at z approximately =2.5, as well as optical images only of six more at z approximately =2.5. We have examined the images carefully for evidence of extended'fuzz' from any putative QSO host galaxy. None of the z approximately =2.5 QSOs shows any extended emission, and only two of the zapproximately = 1 QSOs show marginal evidence for extended emission. Our3 sigma detection limits in the K images, mK approximately =21 for an isolated source, would correspond approximately to anunevolved Lstar elliptical galaxy at z = 2.5 or 2-3 magfainter than an Lstar elliptical at z = 1, although ourlimits on host galaxy light are weaker than this due to the difficultyof separating galaxy light from QSO light. We simulate simple models ofdisk and elliptical host galaxies, and find that the marginal emissionaround the two z approximately = 1 QSOs can be explained by disks orbulges that are approximately 1-2 mag brighter than an unevolvedLstar galaxy in one case and approximately 1.5-2.5 magbrighter than Lstar in the other. For two other zapproximately = 1 QSOs, we have only upper limits (L approximately =Lstar). The hosts of the high-redshift sample must be nobrighter than about 3 mag above an unevolved Lstar galaxy,and are at least 1 magnitude fainter than the hosts of radio-loud QSOsat the same redshift. If the easily detected K-band light surrounding aprevious sample of otherwise similar but radio-loud QSOs is starlight,then it must evolve on timescales of greater than or approximately equalto 108 yr (e.g., Chambers & Charlot 1990); therefore ournon-detection of host galaxy fuzz around radio-quiet QSOs supports theview that high-redshift radio-quiet and radio-loud QSOs inhabitdifferent host objects, rather than being single types of objects thatturn their radio emission on and off over short timescales. This isconsistent with the general trend at low redshifts that radio-loud QSOsare found in giant elliptical galaxies while radio-quiet QSOs are foundin less luminous disk galaxies. It also suggests that the processesresponsible for the spectacular properties of radio-loud AGNs at highredshifts might not be generally relevent to the (far more numerous)radio-quiet population.
| Multiwavelength observations of ring galaxies. 2: Global star formation in ring galaxies
We present optical H-alpha emission-line images and K band near-infraredimages of a sample of collisionally formed ring galaxies. These are usedto determine the distribution of star formation and the distribution ofthe old stellar population, respectively, in the galaxies. Our resultsshow ring galaxies to have similar Hcx luminosities to starburstgalaxies, with star formation being contained almost exclusively in thering. In the larger ring galaxies we observe the ionized hydrogen to lieon the outer edge of the underlying, broader, K band ring. No conclusiveevidence is found in our sample for a true underlying stellar densitywave. Rather, the evidence suggests that either the density waves havepassed into the outer, mainly H I disk of the galaxies or that theprogenitor galaxies were mainly gas-rich low surface brightness objectsand that most of the optical/IR light we now observe has resulted fromrecent star formation in the expanding ring.
| Interstellar medium and star formation in the nearby QSO I ZW 1
We report the first detection of the millimeter (13)CO(1-0) and thenear-infrared H2 v = 1-0 S(1) line from the QSO I Zw 1. We also presentupper limits on the 1.6435 micrometer (Fe II) and 1.9615 micrometer (SiVI) line as well as high-resolution near-infrared continuum data on itsnucleus. We interpret the results in light of previously published(12)CO data on this source and common properties of the far-infrared andmolecular line emission of external, luminous infrared galaxies. Wepropose a two-component model for the molecular line emission in which acore and disk component have similar contributions. In this model thenucleus is dominated by emission from warm, (mostly) optically thickmolecular gas, whereas the line emission in the disk is mostly due tocold, probably subthermally excited molecular gas. We also confirm theneed for a two-component model for I Zw 1 in which about 2/3 of thefar-infrared luminosity originates in the disk and 1/3 originates in thenucleus. We estimate star-forming rate and efficiency for the disk andthe nucleus of the I Zw 1 host galaxy and find that the values for bothare comparable to those of luminous IRAS galaxies. Over the whole diskthe star formation efficiency is close to the maximum value of approx. =30 solar luminosity/solar mass found in Galactic star-forming regionslike M17 or W51. Analysis of the nuclear near-infrared colors suggests amixture of a QSO nucleus and an extincted stellar component contributingabout 10%-20% of the flux density at 2.2 micrometer. This results in anestimate of the molecular bulge size of the order of 1 sec to 2 sec(1.2-2.4 kpc). However, the presence of the QSO nucleus in I Zw 1 isclearly related to the nucleus would be blocked by obscuring material, IZw 1 would be seen as a luminous IRAS galaxy.
| Molecular hydrogen and excitation in the HH 1-2 system
We present a series of molecular hydrogen images of the Herbig-Haro 1-2system in the 1-0 S(1) transition at 2.121 microns, with a spatialresolution of approximately 2 sec. The distribution of H2 is thencompared with that of the excitation, given by the (S II) 6717+6731 toH-alpha line ratio. We find that most optical condensations in the HH1-2 system, including the VLA 1 jet, have H2 counterparts. H2 emissionis detected in most low excitation knots, as expected for low velocityshocks (50 km/s less than), but also in high excitation regions, like inHH 1F and HH 2A min. For these latter objects, the H2 emission could bedue to the interaction of the preionizing flux, produced by 150-200 km/sshocks, with the surrounding interstellar matter, i.e., fluorescence.The lack fluorescent lines in the ultraviolet (UV), however, suggest adifferent mechanism. H2 is detected at the tip of the VLA 1 jet, wherethe knot morphology suggests the presence of a second bow shock. H2 isdetected also SE of HH 2E and SW of HH 1F, in regions with known NH3emission.
| The faintest stars - Infrared photometry, spectra, and bolometric magnitude
Infrared JHKLL-prime photometry, and low resolution IF spectra arepresented for the faintest stars. The stellar H2O bands which dominatethe atmospheres of these stars were studied. L band fluxes of thesestars are considerably depressed relative to L prime fluxes by thepresence of stellar H2O absorption. Strong H2O absorption is observed inthese infrared spectra. The amount of flux which is 'overcounted' whenH2O absorption bands are ignored is examined. Bolometric fluxes arecalculated using broadband photometry alone, requiring a correction ofonly approximately 5 percent to 10 percent. Photometric and spectraldata is used to evaluate bolometric corrections and magnitudes of asample of late type M dwarfs.
| A filter for deep near-infrared imaging
The K passband (central wavelength 2.2 microns, FWHM 0.4 micron) is thelongest wavelength standard near-IR passband through which deepground-based imaging is possible. Thermal emission from telescope,instrument, and sky limits the depth to which such imaging can reach byproducing strongly temperature-dependent backgrounds in the range11-13.5 mag/sq arcsec. This paper describes how a passband, which isdenoted as K-prime, located slightly shortward of the standard Kpassband (central wavelength 2.1 microns), yet still within the sameatmospheric window, leads to a significantly lower thermal component ofthe background, reducing the background surface brightness by up to 0.9mag sq arcsec, and thereby allowing deeper imaging to be obtained in thesame integration time. The photometric differences between the K-primefilter and the standard K filter are discussed.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| Two protostar candidates in the bright-rimmed dark cloud LDN 1206
The discovery of several near IR objects associated with two IRAS pointsources in the LDN 1206 region is reported. IRAS 22272 + 6358A isprobably a 'protostar' which is seen only in scattered light at near-IRwavelengths because of heavy obscuration by an almost edge-oncircumstellar disk. In contrast, IRAS 22272 + 6358B is directly visibleat these wavelengths and is perhaps an object which lies betweenprotostars and T-Tauri stars in its evolution. Both direct andpolarimetric K-band images of the region are presented, as well asspectral energy distributions constructed from J, H, K, L, L-prime, andM data and published far-IR and mm data.
| JHKLM standard stars in the ESO system
A list of 199 standard stars suitable for the ESO standard photometricsystem at JHKLM is given. Faint stars (although brighter than K = 7.7)to be used on larger telescopes are included. This list is based on ananalysis of all infrared photometric observations carried out at LaSilla from 1979 until 1989 inclusive. The accuracy of the data (about0.02 mag. at J, H, K, L, and M) is similar to the one achieved at SAAOand CTIO. Comparisons with these systems, as well as with the AAO andMSSO systems, are made: it is shown that the ESO system is very close tothe other ones, with the exception of CTIOs.
| Molecular hydrogen and optical images of HH 7-11
Flux-calibrated H2 images of HH 7-11 with H-alpha and forbidden S IIimages taken nearly simultaneously are compared. The brightest objectsin H2 also radiate optically. A bow shock with a magnetic precursorexplains most of the existing observations of HH 7.
| High-resolution H and K mapping of W51
The H-II region W51 has been mapped in the near-infrared H and Kwavebands with a resolution of about 6 arcsec over an area of about 14sq arcsec. The W51 IRS 1 source has been resolved into six components,and an arc-like extension of small H-II regions is found that seems toparallel the edge of the molecular cloud. Measurements of the fluxes andextinctions of these sources are presented. A close correspondence isnoted between the present K maps and the radio maps of Scott (1978).
| The cool components of symbiotic stars. II - Infrared photometry
This paper reports IR photometry for a sample of symbiotic binaries andK-M comparison stars. Measured CO absorption-band strengths of the coolcomponents in symbiotic stars generally are comparable to those ofsingle red giant and bright giant stars, but it is difficult todetermine the luminosity classes of these objects from their photometricCO indices. The 12-micron excesses observed in symbiotics require theircool components to lose mass more rapidly than do single red giantstars. Thus, mass-loss rates derived for red giants in close binarysystems may not be accurate estimates for mass loss in single redgiants.
| Infrared and optical observations of low-activity comets, P/Arend-Rigaux (1984k) and P/Neujmin 1 (1984c)
Optical observations obtained with the 1.2-m UK Schmidt telescope, andIR observations obtained with the 2.8-m United Kingdom InfraredTelescope on Mauna Kea, Hawaii in 1984, of Comets P/Arend-Rigaux 1984kand P/Neujmin 1 1984c are presented. Data indicate that Arend-Rigaux isan active comet with an appreciable dust coma and anisotropic dustemission. An effective radius of about 4.5 and an albedo of 0.06 + or0.03 are found at 1.25 microns. Comet Neujmin 1 showed only minoractivity and is suggested to be a transitional object. Some data onComet Shoemaker 1984s are also presented, and all three cometsinvestigated have colors similar to C-type or RD-type asteroidssuggesting dark carbonaceous material.
| Color evolution in high-redshift galaxies
The Simultaneous Photometer for Infrared and Visual Light has been usedto observe 40 radio- and 39 optically-selected giant elliptical galaxiesof known redshift in the 0.019-1.6 range. There is no indication in theresults obtained of differences between the colors of radio and nonradiogalaxies, with the exception of H-K in the z=0.2-0.4 range; the H-Kcolor is best fitted by a passively evolving model with little residualstar formation. Some galaxies exhibit strong blueward deviations. Thisbehavior is most easily explained by star formation episodes involvingsmall fractions of the total number of stars.
| Recent star formation in interacting galaxies. I - Evidence from JHKL photometry
A survey has been carried out using JHKL photometry to investigaterecent star formation in interacting galaxies. The objective was to lookfor a K-L excess produced by 'warm' dust heated by a putative burst ofstar formation. K-L excesses are found suggesting that interactionsinduce starbursts with an efficiency approaching 100 percent. Theappearance of these inferred starbursts in interacting systems ofdifferent morphological types is qualitatively consistent with dynamicalstudies of galaxy interactions. However, the common occurrence of suchstarbursts shows that interactions have implications for theastrophysics of galaxies well beyond purely morphological effects.
| Infrared spectroscopy of symbiotic stars and the nature of their cool components
Low-resolution 2-4 micron spectroscopy of a small sample of symbioticstars is presented, in an effort to determine if the giant components ofthese systems fill their Roche Lobes. A (2.35)-(2.2) color indexmeasures the strength of the CO absorption band and provides a usefuldiscriminant of luminosity class among single M-type giants whichseparates normal giants from supergiants at the same spectral type.Although interpretation of symbiotic spectra is complicated somewhat bytheir binary nature, the results suggest the late-type components inthese systems range from normal red giants to bright asymptotic giants.The possible presence of non-Roche Lobe filling, low-luminosity giantsin some symbiotic stars cannot be understood within the framework ofexisting theories for these interesting objects, and thus may provideimportant information for understanding mass transfer in binary systems.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דגים |
| התרוממות ימנית: | 00h15m57.30s |
| סירוב: | +04°15'04.0" |
| גודל גלוי: | 7.119 |
| מרחק: | 136.612 פארסק |
| תנועה נכונה: | 20 |
| תנועה נכונה: | -13.7 |
| B-T magnitude: | 7.174 |
| V-T magnitude: | 7.124 |
קטלוגים וכינוים:
|
