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Identification of blue high proper motion objects in the Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for newbright blue high proper motion objects in the entire sky: white dwarfs,hot subdwarfs, runaway OB stars, and early-type stars in nearby youngmoving groups. Methods: We performed an all-sky cross-matchbetween the optical Tycho-2 and near-infrared 2MASS catalogues withAladin, and selected objects with proper motions ? > 50 masyr-1 and colours VT - Ks < -0.5 magwith TOPCAT. We also collected multi-wavelength photometry, constructedthe spectral energy distributions and estimated effective temperaturesfrom fits to atmospheric models with VOSA for the most interestingtargets. Results: We assembled a sample of 32 bright blue highproper motion objects, including ten sdO/B subdwarfs, nine DA whitedwarfs, five young early-type stars (two of which are runaway stars),two blue horizontal branch stars, one star with poor information, andfive objects reported for the first time in this work. These last fiveobjects have magnitudes BT ? 11.0-11.6 mag, effectivetemperatures Teff ? 24 000-30 000 K, and are located inthe region of known white dwarfs and hot subdwarfs in a reduced propermotion-colour diagram. We confirmed the hot subdwarf nature of one ofthe new objects, Albus 5, with public far-ultraviolet spectroscopic dataobtained with FUSE.
| 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)
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| 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_.
| The kinematics of Milky Way halo gas. I - Observations of low-ionization species
Ultraviolet interstellar line day observed with the IUE toward 70 halostars and four extragalactic sight lines are analyzed in a study of thelarge-scale kinematic properties of the Milky Way halo gas. The motionsof the low-ionization gas is focused on. Large systematic velocities arefound, and a pronounced asymmetry in the absorption characteristics ofhalo gas toward the Galactic poles is indicated. In the north,substantial amounts of material are falling toward the disk atvelocities up to about 120 km/s in the most extreme case. Toward thesouth, low-ionization material shows no extreme or systematic motions.
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| A comparative study of the ultraviolet spectrum of hot subdwarfs
The high and low resolution IUE spectra of four O subdwarfs (BD+75°325, BD +48°1777, BD +37°1977, BD +37°442) areanalyzed. Line identification is given for the most abundant ions in thefar ultraviolet. Fe V is by far the ion with the largest number oflines. Broad P Cygni profiles of the N V and C IV resonance doublets areobserved in BD +37°442 and BD +37°1977, with terminal velocitiesof 2200 and 2300 km s-1 respectively. The N IV 1718 Åline presents an extended blue wing also arising in the winds of thesestars. A low interstellar extinction (E(B-V) ? 0.05) is derived fromthe weakness of the 2200 Å i.s. band, and from theLyα profile. Mean radial velocities are given forthe photospheric and interstellar atomic species, and a high stellarvelocity is found for the four stars, in agreement with the PopulationII nature of these objects.
| Highly-evolved stars
The ways in which the IUE has proved useful in studying highly evolvedstars are reviewed. The importance of high dispersion spectra forabundance analyses of the sd0 stars and for studies of the wind from thecentral star of NGC 6543 and the wind from the 0 type component of VelaX-1 is shown. Low dispersion spectra are used for absolutespectrophotometry of the dwarf nova, Ex Hya. Angular resolution isimportant for detecting and locating UV sources in globular clusters.
| 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.
| Spectral atlas of helium-rich stars
An atlas of coude spectra of 33 helium-rich O- and B-stars and 11comparison stars in the 3700-4600 A spectral range is presented. Theatlas comprises stars with temperatures from 10,000 to 60,000 deg K inwhich He lines are visible in the spectra, and includes variable Hestars; stars with spectral types O8 to B5 and magnitudes (m(v)) lessthan or equal to 11.0 are considered. The purpose of the atlas is togive a sample of spectra in which, from the observational point of view,the differences caused by certain physical parameters includingeffective temperature, logarithm of the gravity and observed rotationalvelocity, can be judged by eye. Mechanisms for He enrichment in theatmosphere are also discussed.
| SB 21, an extremely helium-rich subdwarf O-star
Spectral observations of the subdwarf O star SB 21 are reported. Theobservations were made at a dispersion of 29 A/mm in the spectral range4250-4800 A using a 3.6-m telescope and an image dissector scanner. TheH gamma line is found to be absent in SB 21, while the He I lines at4388, 4471 and 4713 A and the He II lines at 4686 and possibly 4542 aredetected. A detailed nonlocal thermodynamic equilibrium model analysisof the data indicates an effective temperature of 35,000 K, log g of 5.5and a He/H density ratio greater than 10. Differences between theextremely helium rich objects SB 21, CPD-31 1701 and BD + 48 177 andother extremely helium-rich objects such as BD +37 1877 and BD +37 442are pointed out.
| A sample of new hot subluminous stars taken from the list of ultraviolet objects detected by the S2/68 Sky Survey Experiment
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85..367B&db_key=AST
| Analysis of the UV spectrum of three hot subdwarfs
International Ultraviolet Explorer high resolution observations of threeO subdwarfs (BD + 37 deg 442, BD + 32 deg 1977, and BD + 48 deg 1777)were taken. The spectra are characterized by very high excitationphotospheric lines. Intense interstellar lines are present, whosepossible circumstellar origin is suggested in view of the absence of the2200 A interstellar band.
| Lowell Proper Motion Survey - Summary Catalogue of GD and GR Stars
Not Available
| Spectral classification of ultraviolet objects.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&A....66L...9B&db_key=AST
| Three new hot subdwarfs: AGK2 +81 266, BD +39 3226, BD +34 1543.
Abstract image available at:http://adsabs.harvard.edu/abs/1978A&A....64L...9B
| 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 list of white dwarf suspects II : special objects of small proper motion from the Lowell survey
Not Available
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