Contents
Images
Upload your image
DSS Images Other Images
Related articles
Axisymmetric and stationary structures of magnetized barotropic stars with extremely strong magnetic fields deep inside
We have succeeded in obtaining magnetized star models that haveextremely strong magnetic fields in the interior of the star. In ourformulation, arbitrary functions of the magnetic flux function appear inthe expression for the current density. By appropriately choosing thefunctional form for one of the arbitrary functions that corresponds tothe distribution of the toroidal current density, we have obtainedconfigurations with magnetic field distributions that are highlylocalized within the central part and near the magnetic axis region. Theabsolute values of the central magnetic fields are stronger than thoseof the surface region by two orders of magnitude. By applying ourresults to magnetars, the internal magnetic poloidal fields could be1017 G, although the surface magnetic fields are about1015 G in the case of magnetars. For white dwarfs, theinternal magnetic poloidal fields could be 1012 G, when thesurface magnetic fields are 109-1010 G .
| Recent Star Formation in Clusters of Galaxies: Extremely Compact Starbursts in A539 and A634
We report on the detection of two Hα-emitting extremely compactobjects from deep images of the A634 and A539 clusters of galaxies atz~0.03. Follow-up long-slit spectroscopy of these two unresolved sourcesrevealed that they are members of their respective clusters, showing HII-type spectra. The luminosity and the extreme equivalent width ofHα + [N II] measured for these sources, together with their verycompact appearance, has raised a question about the origin of theseintense starbursts in the cluster environment. We propose that thecompact starburst in A539 resulted from the compression of theinterstellar gas of a dwarf galaxy when entering the cluster core, whilethe starburst galaxy in A634 is likely to be the result of agalaxy-galaxy interaction, illustrating the preprocessing of galaxiesduring their infall toward the central regions of clusters. Thecontribution of these compact star-forming dwarf galaxies to the starformation history of galaxy clusters is discussed, as well as a possiblelink with the recently discovered early-type ultracompact dwarfgalaxies. We note that these extreme objects will rarely be detected innormal magnitude-limited optical or NIR surveys, mainly due to their lowstellar masses (on the order of 106 Msolar),whereas they will easily show up in dedicated Hα surveys given thehigh equivalent width of their emission lines.
| Old Globular Clusters Masquerading as Young in NGC 4365?
High signal-to-noise ratio, low-resolution spectra have been obtainedfor 22 globular clusters (GCs) in NGC 4365. Some of these were selectedas probable representatives of an intermediate-age (2-5 Gyr), extremelymetal-rich GC subpopulation. The presence of such a subpopulation hadbeen inferred from the unusual optical and near-infrared colordistributions of GCs in this otherwise typical Virgo elliptical galaxy.However, ages derived from Lick indices are consistent with uniformlyold mean ages for all GCs in our sample. The metallicities of theclusters show some evidence of a trimodal distribution. The mostmetal-poor and metal-rich peaks are consistent with the values expectedfor an elliptical galaxy of this luminosity, but there appears to be anadditional, intermediate-metallicity peak lying between them. New HubbleSpace Telescope photometry is consistent with this result. A plausiblescenario is that in earlier data these three peaks merged into a singlebroad distribution. Our results suggest that it is difficult to identifyintermediate-age GC subpopulations solely with photometry, even whenboth optical and near-infrared colors are used.
| The Second Byurakan Survey. General Catalogue
The Second Byurakan Survey (SBS) General Catalogue is presented. TheSBS, a continuation of the Markarian survey reaching fainter limitingmagnitudes, is the first survey which combines the search of galaxiesand QSOs. A total area of 991OS#square;degrees of the Northern sky wascovered with the use of three objective prisms in combination withSchott filters. The limited magnitude on the best plates reached B ~19.5.The General Catalogue consists of 3563 objects presented in two parts: aCatalogue of galaxies (1863 objects) and one of stellar objects (1700objects). The Catalogue of SBS AGN consists of 761 objects (155 SyG, 596QSOs, and 10 BLLac). Multi-wavelength data are presented for 1438 SBSobjects identified with X-ray, IRAS and FIRST sources.Spectrophotometric observations obtained over 26 years are available for3132 objects. Redshifts were measured for ~ 2100 extragalactic objects.Spectral classification is presented for ~ 2970 objects. The majority ofthe data is presented here for the first time. The Catalogue presentsnew large homogeneous deep representative complete samples of brightQSOs, AGNs, and faint UVX galaxies in the Northern sky. The SBS sampleis found to be complete at 70% for galaxies and ~ 85% for AGN/QSOs withB ≤ 17.5.
| Evidence for an Intermediate-Age, Metal-rich Population of Globular Clusters in NGC 4365
We present spectroscopy for globular clusters (GCs) in the ellipticalgalaxy NGC 4365, obtained with the Low-Resolution Imaging Spectrographon the Keck I telescope. Previous studies have shown that the opticalcolor distribution of GCs in NGC 4365 lacks the bimodal structure thatis common in globular cluster systems, showing only a single broad peak.Measurements of Balmer line indices (Hβ, Hγ, and Hδ) onthe GC spectra support recent suggestions by Puzia et al. on the basisof optical and near-infrared photometry that some of the clusters in NGC4365 are intermediate-age (2-5 Gyr) and metal-rich(-0.4<~[Z/H]<~0) rather than old (~10-15 Gyr) and metal-poor. Wealso find some genuinely metal-poor, old clusters, suggesting that theages and metallicities of the two populations conspire to produce thesingle broad distribution observed in optical colors.Based on data obtained at the W. M. Keck Observatory, which is operatedas a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration.
| A Search for Binary Hot Subdwarfs. II. Infrared Photometry of Palomar-Green Survey sdO Stars
Eight sdO binary candidates have been identified through IR photometryof 25 type O hot subdwarfs. Five of the eight binary candidates areidentified for the first time. These new binary candidates complement alist of nine optically identified sdO binary candidates discovered in anearlier portion of this project. The new candidates are identified onthe basis of IR color excesses in two-color plots ofextinction-corrected data. We estimate that at least 64% of thePalomar-Green Survey sdOC hot subdwarfs are binary.
| A Search for Binary Hot Subdwarfs. I. BVRI Photometry of Palomar-Green Survey sdO Stars
Nine binary candidates have been identified from a sample of 64 hotsubdwarf sdO/OB/OC stars selected from the Palomar-Green Survey. Threeof the binary candidates had been identified previously. The binarycandidates emerged from BVRI photometric observations and wereidentified by their intrinsic color excesses in two-color plots and bycomparison to synthetic binary system colors. The data presented hereare the initial results of a larger program aimed at identifyinghelium-rich hot subdwarf binary systems suitable for more detailedinvestigation of their fundamental stellar parameters and evolutionarystatus.
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| Infrared flux excesses from hot subdwarfs. II. 72 more objects
In our search, started in February, 1994, for JHK excess fluxes amongthe hot subdwarf population as an indicator for the presence of binarycompanions, results for 72 more hot objects (=63 hot subdwarfs + 1Horizontal Branch B star + 7 white dwarfs + 1 non-subdwarf object)observed with the Carlos Sanchez CVF IR photometer (in June and October,1994), are presented. The exact number of binary hot subdwarfs hasgained renewed importance after the recent discovery of pulsators withG-F companions. The total number of candidates we propose may help toset some constraints; for example, out of 41 objects with excesses, 13may have G-type binary companions. From our new sample, 14 discoveriesof binary candidates have been found: BD+25 4655, Feige 108, HD 4539, HD149382, HD 216135, KPD 2109+440, LSI+63 198, LSIV+10 9, LSV+22 38, PG0011+221, PG 0116+242, PG 0314+103, PG 2151+100 and TON 139. Besides, 2more from reanalysis of February, 1994, data - BD+37 1977 and BD+481777, may now be found to be IR excess candidates. Two suspectedbinaries, PB 8555 and SB 7, are also confirmed. By fitting \cite[Kurucz(1993)]{kur93} model spectra and assuming zero-age main sequencecompanions, we find upper limits on the subdwarf gravities. Thedistributions of upper limits on log(g), mostly between about 5.25 and6.5, are nearly identical for both sdBs and sdOs. Figure~1 is onlyavailable in the electronic version of the paper(http://www.edpsciences.com)
| Spectral classification of stars in the Second Byurakan Sky Survey. I.
Results are given on a spectral classification of 316 stars and objectshaving a continuous spectrum, selected in the course of the SecondByurakan Spectral Sky Survey. Slit spectra are used, obtained from 1978to 1994, predominantly on the 6-m telescope of the Special AstrophysicalObservatory, Russian Academy of Sciences, with a resolution of 5-15Å. The sample contains objects in the range of stellar magnitudes10.12 ? m(pg) ? 19.5. We found 114 DA, 13 DB, 4 DC, and 1 DQ whitedwarfs, 57 sdB and 13 sdO subdwarfs, 12 NHB, 10 cataclysmic variables,76 stars of late spectral types, 3 spectroscopic binary systems, and 13objects with a continuous spectrum. Several recordings are given foreach of these spectral types.
| Proper motions of the hot subdwarfs. The kinematic population membership of the sdB.
We report on first results from an ongoing program to measure andanalyze proper motions for hot subdwarf and white dwarf stars, with theaim of determining to which stellar population sdB stars (in the Vmagnitude range 10.5 to 14.5) belong. Ours is the largest sample of hotsubdwarf proper motions measured to date. Our kinematic analysissuggests that the parent population of these hydrogen-rich sdB stars isas old or older than the old disk. We measure the absolute magnitude ofthe sdB in the field as M_V_=4.5, providing independent confirmation ofabsolute V magnitude estimates for these stars from clusters andspectroscopic analyses. Provided it can be shown that the sdO starsevolve from the sdB, then the sdO absolute V magnitude distribution isabout 1 magnitude brighter than for the sdB, and 1 magnitude wider.
| The Distance to Two Neutral Hydrogen Clouds: The High-Velocity Complex A and the Low-Latitude Intermediate-Velocity Cloud
A lower limit to the distance of the high-velocity cloud (HVC) complex Aof 4 kpc (z > 3 kpc) is derived. The HVC is detected toward theSeyfert galaxy Mrk 106 in Mg II ??2796, 2803 absorptionspectra taken with Hubble Space Telescope (HST) proving that Mg^+^ ispresent in the cloud. It is not detected in the Mg II spectra of twostars, PG 0859+593 (distance 4 kpc) and PG 0906+597 (distance 0.7 kpc).The distances to the stars are derived by matching Stromgren photometryand intermediate-resolution spectroscopy with model stellar atmospheres;they are estimated to be accurate to within 1 kpc. From a combination ofEffelsberg data and Westerbork maps with 2' or 3' resolution, we showthat the H I column density and thus the Mg^+^ abundance in thedirection of the two stars is sufficiently high for the nondetections toimply that the HVC is behind the stars. This distance limit can be usedto eliminate several recent models for complex A that placed it nearby.We also derive a distance bracket of 1.7 < d < 4 kpc (1.1 < z< 3 kpc) for an intermediate-velocity cloud (IVC) at velocities ofabout -50 km s^-1^. This IVC was named the Low-LatitudeIntermediate-Velocity Arch by Kuntz & Danly and is seen between l =120^deg^-160^deg^ and b = 30^deg^- 45^deg^.
| Infrared flux excesses from hot subdwarfs.
Observations of 27 hot subdwarf stars and white dwarfs have beenperformed with an IR photometer in a search for excess fluxes in the JHKbands. 22 of the objects are observed for the first time in theinfrared. In 11 of the stars a significant excess flux was found, 2 ofwhich are new discoveries: GD 274 and GD 299. We confirm the suspicionof Moehler et al. (1990) that PG0232+095 is a composite system, and wereinforce the suggestion of Thejll et al. (1991, 1994a) that Feige 34 isa composite system. The excesses are most likely due to companion stars,mainly of spectral types A - K. We estimate the subdwarf gravities,assuming zero-age main sequence companions, and thus find upper limitson log(g). For the hot sdO Feige 34 we estimate from the publishedtrigonometric parallaxes an absolute magnitude M_v_^F34^=5.6^+0.9^_-1.6_and surface gravity log(gpi_)=6.8^+0.3^_-0.7_.
| UBVRI photometry of G, K, M HIPPARCOS stars. II
As indicated by Grenon (1989), the data of the present series of reportson the UBVRI photometry of late-type stars in the Hipparcos InputCatalog are to be employed in computations of Hipparcos observing time,as well as in evaluating the observability of faint stars by thesatellite. Attention is here given to late type stars in the V = 8-12range, including distant red giants in the Galactic plane (Hipparcosproposal 189), as well as high proper motion stars included in the G,LTT, LP, and MCC catalogs.
| Accurate optical positions for 110 Byurakan objects and 24 blue stars from the 'Second Byurakan Spectral Sky Survey (II)'
Abstract image available at:http://adsabs.harvard.edu/abs/1990AJ....100.1028S
| High-redshift radio galaxies from the Molonglo Catalogue
Radio and optical observations of a sample of southern hemisphere radiogalaxies, selected from the 408 MHz Molonglo Reference Catalogue, arediscussed. The sample is defined by means of two criteria: fluxdensities greater than 0.9 Jy and low-frequency spectral indices steeperthan -0.9. From the initial sample of 700 sources, 150 combine the bestcharacteristics of the 1 Jy and ultrasteep samples. It is suggested thatthese sources can be used to find galaxies at large redshift and explorethe properties of galaxies at extreme luminosities and early epochs. VLA6 cm maps and optical identifications of 13 sources are presented.Eleven of the sources have extended optical structures with morphologiescharacteristic of high-redshift (z greater than 0.8) radio galaxies.
| Spectrophotometric standards
Spectrophotometry for 25 stars intended to be used as standards ispresented. These stars were mainly selected for having nearlyfeatureless spectra, making them suitable for use at variousresolutions. Sixteen of these have not had previous spectrophotometrypublished, and eight are fainter than V = 14. Also presented areimproved data for nine of the stars observed by Stone (1974, 1977) andOke (1974). The wavelength coverage is from 3200 to 8100 A, and themagnitudes are on the Hayes-Latham system. On the average, thenight-to-night photometric precision of the data is better than 0.01mag. The external agreement with stars in common with Stone is typicallybetter than 0.03 within 50 A bandpasses. Magnitudes are presented usingthe same bandpasses employed by Stone, as well as at more frequentwavelengths in order to facilitate the flux calibration of data obtainedwith high resolution or small detectors (e.g., CCDs). Other bandpassescan be constructed from the data, which are made available via theAstronomical Data Center.
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| The Palomar-Green catalog of ultraviolet-excess stellar objects
The Palomar-Green Catalog of Ultraviolet Excess Stellar Objects ispresented, with data consisting of positions on the sky accurate toabout 8 arcsec in each coordinate, photographic B-magnitudes accurate to0.29 mag, spectral types, some cross references, and photoelectricbroadband, multichannel, and Stromgren colors when available. Extensivediscussion is given on magnitude calibration using a combination ofphotoelectric measurements and star count modeling, and on thestatistical completeness of the sample based on internal and externaltests. Of the 1874 objects in the catalog, 1715 comprise a statisticallycomplete sample covering 10,714 square degrees from 266 fields taken onthe Palomar 18-inch (46-cm) Schmidt telescope. Limiting magnitudes varyfrom field to field, distributed around B = 16.1 mag, ranging from 15.49to 16.67. The dominant population is that of the hot, hydrogenatmosphere subdwarfs, the sdB stars, which comprise nearly 40 percent ofthe sample. At 16th magnitude, the hot subdwarf (sdB, sdO) number countsare increasing by about a factor of 2 per mag, the hot white dwarfs by 4per mag, and quasars by 8 per mag. The result is a very different mix ofspectral types expected at 18th mag than is found at 16th mag. Thesuggestion is made that the sdB stars are part of the old disk ratherthan a halo population.
| Second Byurakan spectral sky survey. II - Results for region centered on alpha = 09h50m, delta = +55 deg 00 arcmin
The second list of objects in the Second Biurakan Spectral Sky Survey ofthe region centered on alpha = 09h50m, delta = +55 deg 00 arcmin isgiven. The list contains data on 110 objects and galaxies of a peculiarphysical nature and 24 blue stars. The observations were made with the40-52 arcsec Schmidt telescope of the Biurakan Astrophysical Observatorywith a set of three objective prisms using Kodak IIIaJ and IIIaFemulsions sensitized in nitrogen. The area is found to contain 20 quasarcandidates and four Seyfert galaxies, 27 blue stellar objects, 24galaxies with an appreciable ultraviolet continuum, and 39 emissiongalaxies without appreciable ultraviolet radiation. The surfacebrightness of the quasars and Seyferts on the considered area down tothe limiting magnitude 19.5 M is more than 1.5 per square degree withallowance for the already known quasars. The surface density of emissiongalaxies is about four per square degree.
| Polarimetric observations of white dwarf stars
Observations of the linear polarization of radiation from 85 white dwarfand subdwarf stars were made in the UBVOR bands with the 2.6-m telescopeof the Crimean Astrophysical Observatory during 1971-1979. An intrinsicpolarization twice as large as the rms measurement error was found formore than 50 percent of the objects. In a number of cases (e.g., GD 299,EG 191, Feige 110, and EG 159) there is evidence for variability of thelinear polarization.
| Lowell Proper Motion Survey - Summary Catalogue of GD and GR Stars
Not Available
| Polarized radiation in magnetic white dwarfs.
Abstract image available at:http://adsabs.harvard.edu/abs/1976ApJ...209..868R
| Spectrophotometry of five magnetic white dwarfs.
Abstract image available at:http://adsabs.harvard.edu/abs/1976MNRAS.174..191W
| The Nature of Faint Blue Stars in the Halo. II
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJS...28..157G&db_key=AST
| The Evolutionary Status of the Blue Halo Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJS...26...37N&db_key=AST
| A list of white dwarf suspects II : special objects of small proper motion from the Lowell survey
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Großer Bär |
| Right ascension: | 09h38m20.34s |
| Declination: | +55°05'50.1" |
| Apparent magnitude: | 12.378 |
| Proper motion RA: | 2.4 |
| Proper motion Dec: | -71.2 |
| B-T magnitude: | 11.795 |
| V-T magnitude: | 12.33 |
Catalogs and designations:
|
