Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Rotational Velocity Determinations for 118 δ Scuti Variables
A calibration method is presented for the determination of projectedrotational velocities of 118 δ Scuti variables from FWHMmeasurements of metal lines near 4500 Å. The calibration relationused was derived from measurements of 29 stars. Of the 44 stars brighterthan 8th magnitude and north of –1° declination which did nothave values in the Rodríguez catalog (Rodríguez, E.,López González, M. J., & López de Coca, P.2000, A&AS, 144, 469) we present values for 38. In addition, wepresent new projected rotational velocity, vsin i, values for 10 starssouth of –1° or fainter than 8th magnitude for a total of 48vsin i values for stars with no previously published values.
| 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.
| A Multi-Band Photometric Study of Tidal Debris in a Compact Group of Galaxies: Seyfert's Sextet
In order to investigate the properties of the prominent tidal debrisfeature extending to the northeast of a compact group of galaxies,Seyfert's Sextet, we analyzed multi-band (U, B, V, VR, R, I, J, H, andK') photometric imaging data and obtained the following results: 1) Theradial surface brightness distribution of this tidal debris in Seyfert'sSextet (TDSS) in each band appears to be well approximated by anexponential profile. 2) The observed B-V color of TDSS is similar tothose of dwarf elliptical galaxies in nearby clusters. 3) Comparing thespectral energy distribution (SED) of TDSS with theoretical photometricevolution models and with the SED of the stars in the outer part of HCG79b, we find that its SED is comparable to that of a ~10Gyr-old stellarpopulation with solar metallicity, similar to the stellar population inthe outer part of HCG 79b. This suggests that TDSS consists of starsthat may have been liberated from HCG 79b by strong ga laxyinteractions, not a pre-existing dwarf galaxy as previously thought.
| Optical and infrared spectroscopy of the type IIn SN 1998S: days 3-127
We present contemporary optical and infrared spectroscopic observationsof the type IIn SN 1998S covering the period between 3 and 127 daysafter discovery. During the first week the spectra are characterized byprominent broad H, He and Ciii/Niii emission lines with narrow peaks,superimposed on a very blue continuum (T~24000K). In the following twoweeks the Ciii/Niii emission vanished, together with the broad emissioncomponents of the H and He lines. Broad, blueshifted absorptioncomponents appeared in the spectra. The temperature of the continuumalso dropped to ~14000K. By the end of the first month the spectrumcomprised broad, blueshifted absorptions in H, He, Siii, Feii and Scii.By day 44, broad emission components in H and He reappeared in thespectra. These persisted to as late as days ~100-130, becomingincreasingly asymmetric. We agree with Leonard et al. that the broademission lines indicate interaction between the ejecta and circumstellarmaterial (CSM) emitted by the progenitor. We also agree that theprogenitor of SN 1998S appears to have gone through at least two phasesof mass-loss, giving rise to two CSM zones. Examination of the spectraindicates that the inner zone extended to <=90au, while the outer CSMextended from 185au to over 1800au. We also present high-resolutionspectra obtained at days 17 and 36. These spectra exhibit narrow P CygniHi and Hei lines superimposed on shallower, broader absorptioncomponents. Narrow lines of [Nii], [Oiii], [Neiii] and [Feiii] are alsoseen. We attribute the narrow lines to recombination and heatingfollowing ionization of the outer CSM shell by the UV/X-ray flash atshock breakout. Using these lines, we show that the outer CSM had avelocity of 40-50kms-1. Assuming a constant velocity, we caninfer that the outer CSM wind commenced more than 170 years ago, andceased about 20 years ago, while the inner CSM wind may have commencedless than 9 years ago. During the era of the outer CSM wind the outflowfrom the progenitor was high - at least~2×10-5Msolaryr-1. Thiscorresponds to a mass-loss of at least ~0.003Msolar,suggesting a massive progenitor. The shallower, broader absorption is ofwidth ~350kms-1, and may have arisen from a component of theouter CSM shell produced when the progenitor was going through a laterblue supergiant phase. Alternatively, it may have been produced by theacceleration of the outer CSM by the radiation pressure of the UVprecursor. We also describe and model first-overtone emission in carbonmonoxide observed in SN 1998S. We deduce a CO mass of~10-3Msolar moving at ~2200kms-1, andinfer a mixed metal/He core of about 4Msolar, againindicating a massive progenitor. Only three core-collapse supernovaehave been observed in the K band at post-100 days, and all three haveexhibited emission from CO.
| Infrared L-Band Observations of the Trapezium Cluster: A Census of Circumstellar Disks and Candidate Protostars
We report the results of a sensitive near-infrared JHKL imaging surveyof the Trapezium cluster in Orion. We use the JHKL colors to obtain acensus of infrared excess stars in the cluster. Of (391) stars brighterthan 12th magnitude in the K and L bands, 80%+/-7% are found to exhibitdetectable infrared excess on the J-H, K-L color-color diagram.Examination of a subsample of 285 of these stars with published spectraltypes yields a slightly higher infrared excess fraction of 85%. We findthat 97% of the optical proplyds in the cluster exhibit excess in theJHKL color-color diagram indicating that the most likely origin of theobserved infrared excesses is from circumstellar disks. We interpretthese results to indicate that the fraction of stars in the cluster withcircumstellar disks is between 80%-85%, confirming earlier publishedsuggestions of a high disk fraction for this young cluster. Moreover, wefind that the probability of finding an infrared excess around a star isindependent of stellar mass over essentially the entire range of thestellar mass function down to the hydrogen burning limit. Consequently,the vast majority of stars in the Trapezium cluster appear to have beenborn with circumstellar disks and the potential to subsequently formplanetary systems, despite formation within the environment of a richand dense stellar cluster. We identify 78 stars in our samplecharacterized by K-L colors suggestive of deeply embedded objects. Thespatial distribution of these objects differs from that of the rest ofthe cluster members and is similar to that of the dense molecular cloudridge behind the cluster. About half of these objects are detected inthe short wavelength (J and H) bands, and these are found to becharacterized by extreme infrared excess. This suggests that many ofthese sources could be protostellar in nature. If even a modest fraction(i.e., ~50%) of these objects are protostars, then star formation couldbe continuing in the molecular ridge at a rate comparable to that whichproduced the foreground Trapezium cluster.
| An early-time infrared and optical study of the Type Ia Supernova 1998bu in M96
We present first-season infrared (IR) and optical photometry andspectroscopy of the Type Ia Supernova 1998bu in M96. We also reportoptical polarimetry of this event. SN 1998bu is one of the closest typeIa supernovae of modern times, and the distance of its host galaxy iswell determined. We find that SN 1998bu is both photometrically andspectroscopically normal. However, the extinction to this event isunusually high, with AV = 1.0 ± 0.11. We find that SN1998bu peaked at an intrinsic MV = -19.37 ± 0.23.Adopting a distance modulus of 30.25 (Tanvir et al.) and using Phillipset al.'s relations for the Hubble constant, we obtain H0 =70.4 ± 4.3 km s-1 Mpc-1. Combination of ourIR photometry with those of Jha et al. provides one of the most completeearly-phase IR light curves for a SN Ia published so far. In particular,SN 1998bu is the first normal SN Ia for which good pre-tBmaxIR coverage has been obtained. It reveals that the J, H and K lightcurves peak about 5 days earlier than the flux in the B-band curve.
| Evidence for a Supernova in Reanalyzed Optical and Near-Infrared Images of GRB 970228
We present B-, V-, RC-, IC-, J-, H-, K-, andK'-band observations of the optical transient (OT) associated with GRB970228, based on a reanalysis of previously used images and unpublisheddata. In order to minimize calibration differences, we have collectedand analyzed most of the photometry and consistently determined themagnitude of the OT relative to a set of secondary field stars. Weconfirm our earlier finding that the early decay of the light curves(before 1997 March 6) was faster than that at intermediate times(between 1997 March 6 and April 7). At late times the light curvesresume a fast decay (after 1997 April 7). The early-time observations ofGRB 970228 are consistent with relativistic blast-wave models, but theintermediate- and late-time observations are hard to understand in thisframework. The observations are well explained by an initial power-lawdecay with ?=-1.51+/-0.06 modified at later times by a Type Icsupernova light curve. Together with the evidence for GRB 980326 and GRB980425, this gives further support for the idea that at least some?-ray bursts are associated with a possibly rare type ofsupernova.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Near-Infrared Observations of Type 2 QSO at z=0.9
Results of near-infrared (NIR) observations of a type 2 QSO, AXJ08494+4454, at z=0.9, which was identified in our optical follow-upobservations of the ASCA Lynx deep survey, are presented. NIR J-bandspectroscopic observations show presence of a narrow (FWHM=470 kms-1) Hα emission line and no strong broad component,which confirms that this object is type 2, as suggested in the previousoptical spectroscopy (no broad Hβ emission). IC andK-band imaging observations reveal that this object has a significantlyredder color (IC-K=3.4 mag) than normal type 1 QSOs but has asimilar color to those of nearby type 2 Seyfert galaxies and starburstgalaxies. The absolute magnitude of this object in B band is muchfainter than M*B for the type 1 QSO luminosityfunction at z~0.9, but about 1.5 mag brighter thanM*B of the luminosity function for field galaxiesat z~0.9. The red color and the faint optical magnitude may be a resultof dust extinction, or we may be seeing the host galaxy with a hiddenactive nucleus. Based on observations with the United Kingdom InfraredTelescope (UKIRT), which is operated by the Joint Astronomy Centre onbehalf of the Particle Physics and Astronomy Research Council U.K., andthe University of Hawaii 2.2 m Telescope, HI.
| The 75th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 916 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| 1.65 μm (H-band) surface photometry of galaxies. III. observations of 558 galaxies with the TIRGO 1.5 m telescope
We present near-infrared H-band (1.65 μm ) surface photometry of 558galaxies in the Coma Supercluster and in the Virgo cluster. This dataset, obtained with the Arcetri NICMOS3 camera ARNICA mounted on theGornergrat Infrared Telescope, is aimed at complementing, withobservations of mostly early-type objects, our NIR survey of spiralgalaxies in these regions, presented in previous papers of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derived. We confirm the existence of apositive correlation between the near-infrared concentration index andthe galaxy H-band luminosity Based on observations taken at TIRGO(Gornergrat, Switzerland). TIRGO is operated by CAISMI-CNR, Arcetri,Firenze, Italy. Tables 1 and 2 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| An Infrared Search for Extinguished Supernovae in Starburst Galaxies
IR and radio-band observations of heavily extinguished regions instarburst galaxies suggest a high supernova (SN) rate associated withsuch regions. Optically measured SN rates may therefore underestimatethe total SN rate by factors of up to 10, as a result of the very highextinction (A_B~10-20 mag) to core-collapse SNe in starburst regions.The IR/radio SN rates come from a variety of indirect means, however,which suffer from model dependence and other problems. We describe adirect measurement of the SN rate from a regular patrol of starburstgalaxies done with K'-band imaging to minimize the effects ofextinction. A collection of K'-band measurements of core-collapse SNenear maximum light is presented. Such measurements (excluding 1987A) arenot well reported in the literature. Results of a preliminary K'-bandsearch, using the MIRC camera at the Wyoming Infrared Observatory and animproved search strategy using the new ORCA optics, are described. Amonthly patrol of a sample of IRAS bright (mostly starburst) galaxieswithin 25 Mpc should yield 1-6 SNe yr^-1, corresponding to the range ofestimated SN rates. Our initial MIRC search with low resolution (2.2"pixels) failed to find extinguished SNe in the IRAS galaxies, limitingthe SN rate outside the nucleus (at greater than 15" radius) to lessthan 3.8 far-IR SN rate units (SNe per century per 10^10 L_solarmeasured at 60 and 100 mum, or FIRSRU) at 90% confidence. The MIRCcamera had insufficient resolution to search nuclear starburst regions,where starburst and SN activity is concentrated; therefore, we wereunable to rigorously test the hypothesis of high SN rates in heavilyobscured star-forming regions. We conclude that high-resolution nuclearSN searches in starburst galaxies with small fields are more productivethan low-resolution, large-field searches, even for our sample of large(often several arcminutes) galaxies. With our ORCA high-resolutionoptics, we could limit the total SN rate to less than 1.3 FIRSRU at 90%confidence in 3 years of observations, lower than most estimates.
| Excited molecular hydrogen around the Seyfert nuclei of NGC 3227 and 4151
High-resolution images of the nuclear regions of the Seyfert galaxiesNGC 3227 and 4151 have been obtained in the H_2 1-0 S(1) emission line(rest lambda = 2.1218 mu m) with the IRCAM3 camera on the 3.8-m UKIRTtelescope. A 2" elongation of the photoexcited H_2 is observed in NGC3227 that is coincident with the optical nucleus. Combined with otherobservations, this indicates the presence of a molecular discsurrounding the active nucleus with the interior being photoexcited. A 2x 2.5 arcsec^2 ring of excited H_2 centred on the nucleus is partiallyobserved in NGC 4151. This is believed to be part of a circumnucleartorus that contains ionized, atomic and molecular gas in an onion-skinstructure.
| Infrared Spectroscopy of Faint High Galactic Latitude Carbon Stars
Carbon stars at high Galactic latitudes used to study the kinematics ofthe Galactic halo are difficult to distinguish from nearby dwarf carbon(dC) stars at intermediate spectral resolution. This paper presentsnear-infrared spectra of a sample of carbon stars that show that the COfirst-overtone bands are far weaker in the known dC stars than in giantsfor a given H-K color. This finding, along with the unusual location ofdC stars in the JHK color-color diagram, may be explained by the effectsof collision-induced absorption, which is predicted, in stars of lowmetallicity and high surface gravity, to greatly suppress molecularabsorption features in the near-infrared.
| A disc of shocked molecular hydrogen around the active nucleus of NGC 3079
A high-resolution image of the nuclear regions of the active galaxy NGC3079 has been obtained in the H_2 1-0 S(1) emission line (rest lambda =2.1218 μm) with the IRCAM3 camera on the 3.8-m UKIRT telescope. An ~35 pc diameter elongated core within a more diffuse, 300 pc long, regionof most likely shock-excited H_2 is shown to surround the active nucleusand be embedded within what could be an extended region of enhanced starformation. A disc of molecular gas could be present that shapes theemission of relativistic gas away from the plane of the galaxy. Thisnuclear H_2 1-0 S(1) emitting gas (of total mass ~ 10^3 M_solar) iswithin a central dip in the distribution of cool, CO emitting, moleculargas (of total mass ~ 10^10 M_solar) which extends much further from thenucleus. The distributions of both the hot and the cool molecular gasesare likely to be clumpy.
| HD 84800: A new delta Scuti variable
Not Available
| 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.
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| Infrared and optical spectroscopy of Type IA supernovae in the nebular phase
We present near-infrared (NIR) spectra for Type Ia supernovae at epochsof 13 to 338d after maximum blue light. Some contemporary opticalspectra are also shown. All the NIR spectra exhibit considerablestructure throughout the J, H and K bands. In particular, they exhibit aflux `deficit' in the J band which persists as late as 175d. This isresponsible for the well-known red J-H colour. To identify the emissionfeatures and test the ^56Ni hypothesis for the explosion and subsequentlight curve, we compare the NIR and optical nebular-phase data with asimple non-LTE nebular spectral model. We find that many of the spectralfeatures are due to iron-group elements, and that the J-band deficit isdue to a lack of emission lines from species that dominate the rest ofthe IR/optical spectrum. Nevertheless, some emission is unaccounted for,possibly due to inaccuracies in the cobalt atomic data. For somesupernovae, blueshifts of 1000-3000 km s^-1 are seen in infrared andoptical features at 3 months. We suggest that this is due to clumping inthe ejecta. The evolution of the cobalt/iron mass ratio indicates that^56Co-decay dominates the abundances of these elements. The absolutemasses of iron-group elements which we derive support the basicthermonuclear explosion scenario for Type Ia supernovae. A core-collapseorigin is less consistent with our data.
| Near infrared surface photometry of late-type Virgo cluster galaxies
Near Infrared (K' band) surface photometry has been obtained for 102 (88late-type) Virgo cluster galaxies. A subset of 20 galaxies was alsoimaged in the H band. Magnitudes and diameters within the 21.5 and 22.0mag arcsec$^{-2}$ isophote, concentration indices and total H and K'magnitudes are derived. Basic statistical properties of a completesample of spiral galaxies spanning the range 6.3 < K'_T < 13.5 aregiven. Tables 3, 5 and 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html} Based on observations taken atthe Calar Alto Observatory, operated by the Max-Planck-Institut furAstronomie (Heidelberg) jointly with the Spanish National Commission forAstronomy.
| 1.65μm (H-band) surface photometry of galaxies. II. Observations of 297 galaxies with the TIRGO 1.5m telescope.
We present near-infrared H-band (1.65μm) surface photometry of 297galaxies (mostly) in the Coma Supercluster obtained with the ArcetriNICMOS3 camera, ARNICA, mounted on the Gornergrat Infrared Telescope.Magnitudes and diameters within the 21.5mag/arcsec^2^ isophote,concentration indices, and total H magnitudes are derived. Combiningthese observations with those obtained similarly using the Calar Altotelescopes (Paper I, 1996A&AS..120..489G) we find a strong positivecorrelation between the near-infrared concentration index and the galaxyH-band luminosity, and we analyze the consequent dependence ofnear-infrared growth-curves on H-band luminosity.
| 1.65 μm (H-band) surface photometry of disk galaxies. I. Observations of 158 galaxies with the Calar Alto 2.2 M telescope.
Near Infrared (H-band) surface photometry of 158 (mostly) disk galaxiesbelonging to the Coma Supercluster and to the A262 and Cancer clusterswas obtained using the 256^2^ NICMOS3 array MAGIC attached to the 2.2mCalar Alto telescope. Magnitudes and diameters within the21.5mag/arcsec^2^ isophote, concentration indices and total H magnitudesare derived.
| Starburst Galaxies. II. Imaging and Spectroscopy of a Radio-selected Sample
We present J-, H-, and K-band images and low-resolution K-band spectraof the 20 most luminous starburst galaxies from the survey of Condon,Frayer, & Broderick. Optical rotation curves are also shown for 10of these galaxies. Near-infrared colors, optical depths, CO indices, anddynamical masses are calculated. The near-infrared colors of thestarburst nuclei are significantly redder than those observed in"normal" galaxies. Together, the Brγ and radio fluxes availablefor five of the galaxies imply that the starbursts are heavily obscured;an average extinction of A_V_~ 25 is derived. Strong CO absorptionfeatures indicate that late-type evolved stars are present in many ofthe starbursts. The average dynamical mass of the starburst region isfound to be (1.0 +/- 0.4) x 10^9^ M_sun_.
| Near-infrared imaging in H_2_ of molecular (CO) outflows from young stars.
In an attempt to identify the molecular shocks associated with theacceleration of ambient gas by collimated outflows from young stars, wehave imaged a number of known molecular (CO) outflows in H_2_ v=1-0 S(1)and wide-band K. H_2_ line emission is detected in all six sources: (o)In the L 1157, VLA 1623 and NGC 6334I outflows, bow-shaped H_2_ featuresare observed coincident with or just ahead of (downwind of) peaks in theCO outflow maps. (o) In NGC 2264G, as well as a compact group of H_2_knots coincident with the blue-shifted CO peak, we see an extended H_2_filament that traces the northern edge of the red-shifted CO flow. (o)In the L 1641N and Haro 4-255 molecular outflows we see a closecorrelation between H_2_ line emission features and peaks in the COoutflow maps. In each outflow system, the H_2_ probably results fromshocks associated with the interaction of the flow with the ambient,molecular gas. A comparison of the H_2_ data with CO outflow mapsstrongly suggests that "prompt entrainment" near the head of a jet isthe dominant mechanism for producing the CO outflows in at least some ofthese sources. We are also able to account for the ratios of observedradiated energy (derived from H_2_ v=1-0 S(1) flux measurements) tomechanical power in the CO outflows in at least half of the outflowswith a very simple, strong, radiative shock model.
| 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.
| Near Infrared Imaging of Dwarf Ellipticals Irregulars and Blue Compact Galaxies in the Virgo Cluster
New near-IR images are presented for 13 dwarf galaxies in the Virgocluster. Together with previous data these provide a data base of JHKimaging for 26 dwarf ellipticals (dEs), dwarf irregulars (dIs) and bluecompact dwarfs (BCDs). These images show the dIs to be highly asymmetricand unrelaxed, implying that they are dynamically young and unevolved.This is consistent with their blue near-IR and optical-IR colours whichare most easily explained by young stellar populations. The dEs aresymmetrical and apparently relaxed, with very uniform colours indicatingthat they are dominated by old stars. They generally have exponentiallight profiles, but the brighter galaxies tend to exhibit more cuspedlight distributions, similar to the de Vaucouleurs profiles of brightellipticals. The BCDs have moderately asymmetric light profiles, andparadoxically red colours, possibly indicating an intermediate-agestellar population. They are probably dEs which have undergone bursts ofstar formation in the last few X 10^9^ years, whilst the dIs are afundamentally distinct population. Colour gradients are present in manyof the galaxies, invariably in the sense that the nuclei are redder thanthe surrounding galaxy light.
| Multifrequency windows on spiral galaxies. 3.Internal extinction at optical and near-infrared wavelengths
We present aperture photometry data in the H, V, Band U bands of about100 spiral galaxies belonging to 8 nearby clusters and to the ComaSupercluster. The data are used in conjunction with other measurementsavailable in the literature to study, for the first time on the same setof approximately 500 galaxies, the internal extinction in spiral disksin the H, V, B and U bands. We study the color(V-H, B-H, U-H)inclination relation to determine the color-extinction coefficients. Wederive the lower limits to the internal extinction coefficients atoptical wavelengths assuming that galaxies are fully transparent in theH band. In the opposite assumption that galaxies are optically thick inthe blue we use the surface brightness--inclination relation to derivethe upper limits to the above parameters. Assuming a sandwich model forthe distribution of stars and of the absorbing dust, we find that bothsets of parameters are consistent with tau greater than 1 in theoptical. The ratio of the dust to star z-scales decreases withincreasing wavelength, indicating that the thickness of the distributionof the young stars is narrower than that of the old stars. We also findthat the face-on extinction correction is not negligible.
| Classification of Population II supergiants and related stars in the Vilnius system
The results of photometric classification in the Vilnius system of 117Population II supergiants, suspected supergiants, and related stars aregiven. Their photometric spectral types, intrinsic color indices (Y-V)0,color excesses E(Y-V), metallicities Fe/H, and absolute magnitudes MVare determined. It is shown that the system allows us to detect the UUHerculis-type supergiants photometrically. The analyzed SRd star samplefalls into two groups of metallicity and luminosity. Our photometricclassification assigns luminosity classes from III to V to 37 F-K starswith /b/ greater than 16 deg classified by Bartaya (1979) from objectiveprism spectra as supergiants.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Большая Медведица |
| Прямое восхождение: | 09h48m44.65s |
| Склонение: | +43°39'55.6" |
| Видимая звёздная величина: | 7.782 |
| Расстояние: | 150.15 парсек |
| Собственное движение RA: | -26.5 |
| Собственное движение Dec: | -30.1 |
| B-T magnitude: | 7.96 |
| V-T magnitude: | 7.797 |
Каталоги и обозначения:
|
