Contents
Images
Upload your image
DSS Images Other Images
Related articles
E-BOSS: an Extensive stellar BOw Shock Survey. I. Methods and first catalogue
Context. Bow shocks are produced by many astrophysical objects whereshock waves are present. Stellar bow shocks, generated by runaway stars,have been previously detected in small numbers and well-studied. Alongwith progress in model development and improvements in observinginstruments, our knowledge of the emission produced by these objects andits origin can now be more clearly understood. Aims: We produce astellar bow-shock catalogue by applying uniform search criteria and asystematic search process. This catalogue is a starting point forstatistical studies, to help us address fundamental questions such as,for instance, the conditions under wich a stellar bow shock isdetectable. Methods: By using the newest infrared data releases,we carried out a search for bow shocks produced by early-type runawaystars. We first explored whether a set of known IRAS bow shockcandidates are visible in the most recently available IR data, which hasmuch higher resolution and sensitivity. We then carried out a selectionof runaway stars from the latest, large runaway catalogue available. Inthis first release, we focused on OB stars and searched for bow-shapedfeatures in the vicinity of these stars. Results: We provide abow-shock candidate survey that gathers a total of 28 members, which wecall the Extensive stellar BOw Shock Survey (E-BOSS). We derive the mainbow-shock parameters, and present some preliminary statistical resultson the detected objects. Conclusions: Our analysis of the initialsample and the newly detected objects yields a bow-shock detectabilityaround OB stars of ~10 per cent. The detections do not seem to dependparticularly on either stellar mass, age or position. The extension ofthe E-BOSS sample, with upcoming IR data, and by considering, forexample, other spectral types as well, will allow us to perform a moredetailed study of the findings.
| Ejection velocities of high Galactic latitude runaway stars
We estimate the distribution of ejection velocities for the knownpopulation of high Galactic latitude runaway stars. The initial sampleis a collection of 174 early-type stars selected from the literature.The stars are first classified according to their evolutionary status inorder to obtain a homogeneous sample of 96 genuine main-sequence stars.Their present velocities and flight times are then estimated usingproper motion data from various astrometric catalogues (includingTycho-2, UCAC2 and USNO-B) and the ejection velocities are computed bytracing their orbits back in time, based on a Galactic potential. Thepotential used is constructed from a mass density model chosen to fitthe most recent observational constraints.We find evidence for two different populations of runaway stars: a'high' velocity population, with a maximum ejection velocity of about400-500 km s-1, and a 'low' velocity population, with amaximum ejection velocity of about 300 km s-1. We argue thatthe observed limit of 500 km s-1 and the bimodality of theobserved ejection velocity distribution are natural consequences of theso-called Binary Ejection Mechanism. We discuss the connection betweenthe 'high' velocity population and the so-called hypervelocity stars,showing how previously studied hypervelocity stars are consistent withthe results obtained.We also find that some stars that were once thought to be best explainedas being formed in the halo are compatible with a runaway hypothesisonce proper motions are included in the analysis. However, three starsin the selected sample appear to be inconsistent with ejection from theGalactic disc. Possible scenarios are discussed, including a possibleformation in the Galactic halo.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| A survey for pulsating subdwarf B stars with the Nordic Optical Telescope
Context. A search programme for pulsating subdwarf B stars was conductedwith the Nordic Optical Telescope on La Palma over 59 nights between1999 and 2009. Aims: The purpose of the programme was tosignificantly extend the number of rapidly pulsating sdB stars to betterunderstand the properties of this new group of variable compact stars. Methods: Candidates were selected initially from the HS and HEsurveys, but were supplemented with additional objects from othersurveys. Short sequences of time-series photometry were made on thecandidates to determine the presence of rapid pulsations. Results: In total twenty new pulsators were found in this survey, mostof which have already been published and some extensively studied. Wepresent four new short period pulsators, bringing the total of suchpulsators up to 49. We also give limits on pulsation amplitudes for 285objects with no obvious periodic variations, summarise the results ofthe survey, and provide improved physical parameters on the compositepulsators for which only preliminary estimates were published earlier.Full Table 5 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/513/A6
| The Century Survey Galactic Halo Project III: A Complete 4300 DEG2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo
We present a complete spectroscopic survey of 2414 2MASS-selected bluehorizontal branch (BHB) candidates selected over 4300 deg2 ofthe sky. We identify 655 BHB stars in this non-kinematically selectedsample. We calculate the luminosity function of field BHB stars, andfind evidence for very few hot BHB stars in the field. The BHB starslocated at a distance from the Galactic plane |Z| < 4 kpc trace whatis clearly a metal-weak thick disk population, with a mean metallicityof [Fe/H] = -1.7, a rotation velocity gradient of dvrot/d|Z|= -28 ± 3.4 km s-1 in the region |Z| < 6 kpc, and adensity scale height of hZ = 1.26 ± 0.1 kpc. The BHBstars located at 5 < |Z| < 9 kpc are a predominantly inner-halopopulation, with a mean metallicity of [Fe/H] = -2.0 and a mean Galacticrotation of -4 ± 31 km s-1. We infer the density ofhalo and thick disk BHB stars is 104 ± 37 kpc-3 nearthe Sun, and the relative normalization of halo to thick-disk BHB starsis 4 ± 1% near the Sun.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. II. Kinematics and Full Sample Analysis
This paper continues the analysis of faint high-latitude B stars fromMartin. Here we analyze the kinematics of the stars and combine themwith the abundance information from the first paper to classify eachone. The sample contains 31 Population I runaways, 15 old evolved stars(including 5 blue horizontal-branch [BHB] stars, 3 post-HB stars, 1pulsating helium dwarf, and 6 stars of ambiguous classification), 1 Fdwarf, and 2 stars that do not easily fit in one of the othercategories. No star in the sample unambiguously shows thecharacteristics of a young massive star formed in situ in the halo. Thetwo unclassified stars are probably extreme Population I runaways. Thelow binary frequency and rotational velocity distribution of thePopulation I runaways imply that most were ejected from dense starclusters by the dynamic ejection scenario. However, we remain puzzled bythe lack of runaway Be stars. We also confirm that PB 166 and HIP 41979are both nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory, operated by the University of Texas at Austin.
| 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.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
| Accurate optical positions for 2978 objects from the Second Byurakan Survey (SBS) with the Digitized Sky Survey
Optical positions of 2978 objects listed in the Second Byurakan Survey(SBS) were obtained using the Digitized Sky Survey (DSS), and are givenwith an rms uncertainty ~ 1 arcsec in each coordinate. Tables 1 and 2are only available in electronic form at the CDS via anonymous ftp130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Spectral classification of stars in the Second Byurakan Sky Survey. II.
The results of the spectra/classification of 310 stars and objectshaving a continuous spectrum, selected in the course of the SecondByurakan Spectral Sky Survey, are given. Slit spectra were used in thework, which were obtained from 1978 to 1994, mainly on the 6-m telescopeof the Special Astrophysical Observatory, Russian Academy of Sciences;some of the spectra were obtained on the 2.6-m telescope of the ByurakanAstrophysical Observatory, National Academy of Sciences of Armenia, andthe 4.5-m Multiple-Mirror Telescope (USA), with 5-15 Å resolution.The sample contains objects in the range of stellar magnitudes 11.0 ?m(pg) ? 19.5. We found 93 DA, 2 DO, 12 DB, and 1 DC white dwarfs, 83sdB and 20 sdO subdwarfs, 34 NHB variables, 2 cataclysmic variables, 48stars of late spectral types, 8 spectroscopic binary systems, and 7objects having a continuous spectrum. Several recordings are given foreach of these spectral types.
| A high galactic latitude survey of far-ultraviolet excess objects
This study presents optical spectra obtained for a selection of objectsincluded in a catalog of far UV-bright, high-galactic-latitude objectsdetected with a balloon-borne survey telescope. The observed objectsprovide a sample of subdwarf O and B stars, white dwarfs, and binarysystems including a hot subluminous member. Model-atmospheres analysisof the subdwarf sample is used to determine the temperature, gravity,and helium-to-hydrogen ratio of the individual objects. A smoothdistribution of objects is found on the gravity-versus-temperaturediagram near the theoretical location of the extended horizontal branch.A break between the helium-rich and helium-poor objects is found tooccur at 40,000 K. Suspected binary objects were identified and analyzedto determine the temperature and gravity of the hot subluminous memberin each system. The number of subdwarf stars contained in the binariesis determined at 65 to 100 percent. The proportion of white dwarfs thatexperience the subdwarf phase of evolution is found to be 0.94 percent.
| Peculiar and normal early-type stars in the galactic halo
High resolution optical spectra of eight high latitude blue stars havebeen obtained. Three of the sample are identified as subdwarfs. Theremaining five are analyzed for atmospheric parameters and metal and Heabundances using model atmosphere techniques. Four of the sample appearto be normal B type stars 2 kpc or more from the plane. With alogarithmic surface gravity estimated to be 4.6 + or - 0.3 dex, PB 166could be either a main sequence, horizontal branch or cool subdwarf. Thenature of this star is discussed in view of its approximately normalPopulation I chemical composition.
| Investigations of young stars in the galactic halo
High resolution optical spectra of fifteen intermediate and highlatitude blue stars have been obtained using the 2.5 m Isaac Newton andthe 3.9 m Anglo-Australian Telescopes. Three of the sample areidentified as subdwarfs. The remaining twelve are analyzed foratmospheric parameters and metal and helium abundances using modelatmosphere techniques, and appear to be normal B-type stars 1 kpc ormore from the plane. Their origin is discussed in terms of theiravailable kinematics. Eight of the stars could have been formed in thegalactic plane and reached their present z-positions in their lifetimes.From the stellar kinematics, cluster ejection seems the most likelymechanism for their presence in the halo, although close binary ejectionmay have been responsible for a small number of these stars. Four starscould not have traveled from the disk to their current halo z-distancesin their lifetimes, and the idea of star formation in the halo isbriefly discussed.
| 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.
| The nature of the four blue halo stars of Tobin
Model atmosphere techniques presently used to analyze visual spectra ofTobin's (1986) four blue halo star IUE spectra have yielded resultsconfirming the population I character of Feige 40. H.O.+23 deg B, andH.O.+41 deg B. A 2-3 kpc distance from the galactic plane corresponds tothese results. The fourth star, PB 166, is likely to be a little-evolvedhorizontal-branch star with a distance of only 1 kpc. Radial velocitiesdetermined from coude spectra are consistent with the evolutionary statederived.
| Interstellar absorption lines in the spectra of the high-latitude blue stars PB 166, H.O. +41°B, H.O. +23°B, and Feige 40.
Not Available
| Low-resolution IUE observations of four unreddened, 11th magnitude B stars at high galactic latitudes
Low-resolution IUE spectra are presented for the four faint, unreddened,high-latitude, mid-B stars Feige 40 (≡FB 72), H.O. +23°B, H.O.+41°B (≡SS II 135) and PB 166. By comparison with stars in theHeck et al. atlas, the spectra are like those of normal disc stars ofPopulation I metallicity. This suggests that the programme stars aremassive, luminous objects, which, if true, means that they are situatedseveral kiloparsecs outside the galactic plane. Effective temperaturesand upper limits on the Population I ages are derived. Radial velocitiesare known for two of the stars: they are consistent with stellar birthin the galactic plane followed by ejection, at high speed, to thepresent locations within the evolutionary lifetimes. Predictions aremade for the radial velocities of the other two stars.
| Four-colour and H-beta photometry of blue stars selected from a balloon-ultraviolet survey and other sources
New uvby and/or H-beta photometry is obtained at the Chiranhigh-altitude outstation for 105 stars. Certain of the program stars areselected from a comparison of the SCAP 2000 balloon-ultraviolet skysurvey of the Laboratoire d'Astronomie Spatiale with the correspondingblue and red prints of the Palomar Observatory sky survey. Only a smallportion of these stars turn out to be B stars, whereas, the rest of thestars, which are selected from a variety of other sources, are mostly Bstars and if of normal luminosity are in many cases many Population Iscale heights from the galactic plane. It is shown that theidentification of B stars is practicable only at a good observing siteand that if H-beta photometry is also obtained, sdOB, sdB, and hothorizontal branch B stars can be distinguished from normal stars bytheir position in the beta/c(0) diagram.
| Low-resolution IUE observations of four unreddened, 11th magnitude Bstars at high galactic latitudes.
Not Available
| A survey of high-latitude regions at balloon ultraviolet wavelengths
The results of approximately a 200 square degree relatively deep surveyof high-latitude regions at balloon ultraviolet wavelengths arepresented. Ultraviolet photometry is combined with ground-basedspectrography to improve or extend knowledge on specific cases. Theobserved local space densities of hot stars are compared with thosederived by other studies; the data suggest that the density of SdO's isnot significantly higher than what can be expected from ground-basedstudies. In addition, three stars near F0 which show an ultravioletexcess are briefly discussed.
| A search for faint blue stars in high galactic latitudes. I. Nine PSS fields near the north galactic pole.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28..123B&db_key=AST
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
