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FUSE Observations of Germanium, Zirconium and Lead in Sdb Stars
We report the detection of the Ge III, Zr IV, Pb III and Pb IV resonancelines in Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of hotsubdwarf B stars (sdB). We analyze 18 stars that cover the effectivetemperature domain for this class of stars. We carry out an abundanceanalysis and demonstrate that Ge, Zr and Pb abundances are higher thanthe ones observed in the Sun's photosphere in almost every star. Weperform radiative levitation calculations on Ge, Zr and Pb, and showthat the theory predicts higher Ge and Zr abundances than theobservations. Moreover, the large scatter of observed abundances cannotbe explained by the radiative levitation alone. This suggests that othermechanisms must be taken into account for explaining the abundances ofGe, Zr and Pb in the atmospheres of sdB stars.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| The detection of binary companions to subdwarf B stars
Intermediate dispersion spectroscopy of a sample of 40 hot subdwarf Bstars between 5500 and 9000Angstroms has been obtained. The sampleincludes a large fraction of targets which have been studiedphotometrically. Seven targets show strong lines arising from theinfrared Caii triplet, the unequivocal signature of a cool companion.The positiveCaii identifications include known photometric binaries andnew targets; all are associated with a photometric red excess. Assuminga canonical value for the subdwarf luminosity, all of the detectedcompanions are overluminous compared with the main sequence. Thedetection procedure indicates an improved and more secure method for themeasurement of the binary frequency of hot subdwarfs.
| A search for magnetic stars in late stages of stellar evolution
No abstract submitted
| 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.
| A search for stars with strong magnetic fields among horizontal-branch stars and hot subdwarfs
Observations obtained with the 6-m BTA telescope for a few A, Bhorizontal-branch stars and hot subdwarfs have been used to measuretheir effective magnetic fields. No magnetic fields similar to those ofAp, Bp main-sequence stars were found.
| Distance and metallicity limits of high-velocity clouds.
This paper presents results of a program to derive distances ofhigh-velocity clouds (HVCs) through measurement of absorption in theCaIIH and K lines. The problems of the method and their solutions arediscussed in detail. A probable detection of absorption toward theSeyfert galaxy Mark106 is reported, which gives a Ca^+^ abundance of(17+/-6)x10^-9^ in HVC complex A. The non-detection of CaII absorptionagainst a stellar probe sets a tentative lower limit of 1.6kpc to thedistance of complex A. Non-detections of HVC CaII lines in 9 starsprojected on complexes M, C and H may give distance limits, if theCa^+^/HI ratio in those HVCs can be derived from absorptions againstextra-galactic probes. High-resolution HI observations are required toget reliable Ca^+^ abundances. Westerbork HI synthesis observations arereported for several directions together with profiles obtained at theEffelsberg 100-meter dish. From results on several HVCs, we concludethat the Ca^+^/HI ratio may vary strongly between different HVCcomplexes.
| Studies of hot B subdwarfs. 9: Cousins BVRI photometry and the binary fraction of hot, hydrogen-rich subdwarfs in the Palomar-Green survey
Cousins BVRI photometry is presented for a sample of 100 hot,hydrogen-rich subdwarf candidates selected principally from thePalomar-Green (PG) and Kitt Peak-Downes colorimetric surveys. Thecombination of these data with existing Stroemgren photometry permitsthe construction of energy distributions in the range lambda lambda3500-7900. With the help of flux-ratio diagrams, we have isolated 31objects with flat energy distributions indicative of a composite nature.Approximate effective temperatures and spectral types are derived forthe primary and secondary stars, respectively. We present evidence,based on the absolute visual magnitudes determined for the primarycomponents, that the secondary stars in most systems are likely to beoverluminous compared to normal main-sequence stars. Because ofselection effects, the spectral types of the secondary stars arerestricted to the range late G to early M. When allowance is made forthese selection effects, the fraction of hot hydrogen-rich subdwarfswith main-sequence companions in the PG survey can be inferred, and isestimated to be approximately 54%-66%.
| 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.
| Studies of hot B subdwarfs. I - Stromgren photometry of the Greenstein-Sargent-sample
Stromgren colors for a sample of 25 hot B subdwarfs are presented. Thesestars form a well-defined sequence in a two-color diagram, the existenceof which is shown to be consistent with the evolutionary scenario forsdB stars proposed by Wesemael et al. (1982). A comparison of thephotometric data with appropriate model atmosphere calculations suggeststhat hot B subdwarfs have effective temperatures ranging from 25,000 Kto upward of 40,000 K, and surface gravities generally above log g =5.0.
| 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
| A Photometric Classification of the Feige Blue Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1970PASP...82.1305G
| An Atlas of Indentification Charts for 113 Blue Stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1959ApJ...129..600F
| A Search for Underluminous Hot Stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1958ApJ...128..267F
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Наблюдательные данные и астрометрия
| Созвездие: | Большая Медведица |
| Прямое восхождение: | 13h40m14.70s |
| Склонение: | +60°52'47.6" |
| Видимая звёздная величина: | 11.738 |
| Собственное движение RA: | 16.9 |
| Собственное движение Dec: | -60 |
| B-T magnitude: | 11.485 |
| V-T magnitude: | 11.718 |
Каталоги и обозначения:
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