Context: Hyper-velocity stars (HVS) are moving so fast that they are unbound to the Galaxy. Dynamical ejection by a supermassive black hole is favoured to explain their origin. Aims: Locating the place of birth of an individual HVS is of utmost importance to understanding the ejection mechanism. Methods: SDSS J013655.91+242546.0 (J0136+2425 for short) ...

The HYPER-MUCHFUSS (HYPER-velocity stars or Massive Unseen Companions of Hot Faint Underluminous Stars from SDSS) project targets a population of high-velocity subluminous B stars to discover either close binaries with massive unseen companions or hyper-velocity stars. We re-observed ...

We report the discovery of an unbound hyper-velocity star, US 708, in the Milky Way halo, with a heliocentric radial velocity of +708�15 {km s-1}. A quantitative NLTE model atmosphere analysis of optical spectra obtained with LRIS at the Keck I telescope shows that US 708 is an extremely helium-rich (N_He/N_H=10) subluminous O type ...

We report the discovery of an unbound hyper-velocity star, US 708, in the Milky Way halo, with a heliocentric radial velocity of +708+-15km/s. A quantitative NLTE model atmosphere analysis of optical spectra obtained with LRIS at the Keck I telescope shows that US 708 is an extremely helium-rich (N(He)/N(H)=10) subluminous O type star ...

Jun 6, 2007 ... Artist's rendering of the planet orbiting the star Gliese 436 (Lynette ... "A" type stars - ones that have nearly completed their life cycle ...

Context: Hyper-velocity stars are suggested to originate from the dynamical interaction of binary stars with the supermassive black hole in the Galactic centre (GC), which accelerates one component of the binary to beyond the Galactic escape velocity. Aims: The evolutionary status and GC origin of the hyper-velocity ...

The ability to experimentally study scaled aspects of the explosion dynamics of core- collapse supernovae (massive stars that explode from the inside out) or the radiation kinetics of accreting neutron stars or black holes on high energy density (HED) facilities, such as the new National Ignition Facility (NIF), is an exciting scientific development. ...

A review is presented on the properties, origin and evolutionary links of hot subluminous stars which are generally believed to be extreme Horizontal Branch stars or closely related objects. They exist both in the disk and halo populations (globular clusters) of the Galaxy. Amongst the field stars a large fraction of sdBs are found to ...

... _ - IN LOW-DENSITY, HYPER VELOCITY, ARGON FLOW By A. B. Bailey and WH Sims ... IN LOW-DENSITY, HYPERVELOCITY, ARGON FLOW By ...

... Corporate Author : EMBRY-RIDDLE AERONAUTICAL UNIV DAYTONA BEACH FL. Personal Author(s) : Erdman, Peter. Handle / proxy Url : ...

We investigate in detail the probability distribution function (pdf) of the proper-motion measurement errors in the SDSS+USNO-B proper-motion catalog of Munn et al. using clean quasar samples. The pdf of the errors is well represented by a Gaussian core with extended wings, plus a very small fraction (<0.1%) of "outliers." We find that while formally the pdf could be well fit by a ...

A search for Lambda Bootis stars in two OB associations, Orion OB1 and Lacerta OB1, has been carried out. One Lambda Bootis star has been discovered in the Orion OB1 association. In addition, nine A-type stars which appear to be slightly metal weak have been found in the two associations. The Lambda Bootis ...

Four-color (uvby) photoelectric observations have yielded provisional periods for three peculiar A-type stars. For 108 Aquarii, the period is 3.73d. For HD 184905, the period is either 1.84d or 2.17d, and for theta 1 Microscopii the most probable periods ...

In this paper we introduce an extension to the MK system of spectral classification that allows the precise classification of pre-main-sequence (PMS) A-type stars, including most Herbig Ae stars. This classification scheme characterizes the star by a standard MK type, the presence and strength of emission and/or ...

-Newton observation of Altair and study the coronal X-ray properties of a late A-type star for the first time that resembles those of low activity stars of later spectral type. Cool plasma at low density produces weak X-ray, Stars: activity, Stars: coronae, X-rays: stars ...

Context. High-velocity stars in the Galactic halo, e.g. the so-called hyper-velocity stars (HVS), are important tracers of the properties of the dark matter halo, in particular its mass. Aims: A search for the fastest stars among hot subdwarfs (sdB) in the halo is carried out to identify HVS, unbound to the ...

As part of our continuing search for peculiar A-type stars, especially ? Bootis stars, in open clusters of all ages, we have obtained classification spectra of 130 late B, A, and early F-type stars in 12 intermediate-age open clusters, including NGC 1039, 2281, 2548, 6633, 7039, 7063, 7092, and 7209, IC 4665, IC ...

Among the twenty A-type stars within a distance of 20 pc from the Sun there are several pairs and a triple composed in each case of stars having similar space motions. The probability of the occurrence of so many such moving systems in this sample is extr...

The ? Bootis stars are a spectroscopic subgroup of chemically peculiar Population I A-type stars. They show significant underabundances of Fe-peak elements and solar abundances of lighter elements. Theoretical explanations include surface phenomena and binarity. We compared the pulsating ? Bootis star HD 210111 ...

Cameron, A.G.W., 1971: Nuclear processes associated with peculiar A-type stars. Publ. Astron. Soc. Pacific , 83, 495-591, doi:10.1086/129175. ...

Aims: We investigate the magnetic dichotomy between Ap/Bp and other A-type stars by carrying out a deep spectropolarimetric study of Am and HgMn stars. Methods: Using the NARVAL spectropolarimeter at the T�lescope Bernard Lyot (Observatoire du Pic du Midi, France), we obtained high-resolution circular polarisation spectroscopy of 12 ...

ABS>A number of A-type stars suspected to have weak metallic lines were selected on Curtis Schmidt objective-prism plates, and four-color photometry was obtained for seven of these objects. The photometry confirms that the majority of the stars are in fact metal deficient, and it appears that such stars can be selected with ...

Very high driving pressures (tens or hundreds of GPa), are required to accelerate flier plates to hypervelocities. This loading pressure pulse on the fiber plates must be nearly shockless to prevent the plate from melting or vaporizing. This is accomplish...

A systematic study is described that has led to the successful launch of thin flier-plates to velocities of 16 km/s. In this paper, the authors describe a novel technique that has been implemented to enhance the performance of the Sandia Hyper Velocity La...

Electric guns have severe corrosion and erosion problems due to the high temperature and pressures produced by the plasma and gun hyper-velocities. The mechanisms of corrosion and erosion in gun-tube launchers are very complex. The overcoming of erosion a...

... Personal Author(s) : McMillan, AR ; Clough, Nestor ; Lieblein, Seymour. Handle / proxy Url : Report Date : APR 1969. Pagination or Media Count : 30 ...

The possibility of applying the principle of magnetic levitation to the acceleration of condensed matter to obtain hyper-velocities is examined. Condensed matter is adopted to avoid space-charge effects at high particle densities and consequently necessit...

The 1.25 Inch Diameter Actuator is intended to control air vanes of a hyper velocity missile containing no warhead but designed to penetrate armored vehicles vehicles (tanks, etc.). A solenoid sec was written and presented to Orshansky. They manufactured ...

Since the IRAS discovery of Vega's large thermal infrared excess over the expected photospheric flux, dust disks have been found around a large fraction of main-sequence A-type stars. With the detection of gas giant planets orbiting Alpha PsA, Beta Pic, and HR 8799, we now have evidence that A-type stars can host planetary systems. ...

We have identified 17 A-type stars in the Galactic Plane that have mid-infrared (mid-IR) excesses at 8 {mu}m. From observed colors in the (r' - H{alpha}) - (r' - i') plane, we first identified 23,050 early A-type main-sequence (MS) star candidates in the Isaac Newton Photometric H-Alpha ...

In the search of extraterrestrial life it was speculated about the existence of a Circumstellar Habitable Zone (CHZ) around stars at which inside planets are suitable for life. Different researches show that the stars types at which CHZ support life are the stars K, G, and F with the type G as the more probable. However in a recent ...

We analyse the light curves of over 9000 A-F stars in the first public release of Kepler data and examine the noise properties in constant or nearly constant stars. For the A stars, we find a correlation between the excess power in certain frequency regions and the effective temperature which may be due to granulation. The majority of ...

The study of detached eclipsing binaries is one of the most powerful ways to investigate the properties of individual stars and stellar systems. We present preliminary masses, radii and effective temperatures for the eclipsing binary WW Aurigae, which is composed of two metallic-lined A-type stars. We also reanalyse the data on HD ...

We have decided to address the problem of how abundances and peculiarities change during main sequence evolution. We have setup a program to measure the atmospheric abundance patterns from tens of A-type star members of clusters of different ages, and compare the results with theory predictions. In this paper we present the overall project and we focus on the results obtained ...

As the chemical abundance values of normal A stars overlap those of incipient and moderate Am stars, we examine the abundance anomalies of the Am and superficially normal A stars together. We study the results of 17 consistently performed studies by Adelman and his associates who used Dominion Astrophysical Observatory long camera ...

Aims:We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak magnetic field. Methods: We have obtained high resolution, high signal-to-noise ratio spectra of eight previously-classified ...

We report the detection of N V 1239 A transition region emission in HST/Goddard High Resolution Spectrograph spectra of the A7 V stars, alpha Aql and alpha Cep. Our observations provide the first direct evidence of 1--3 x 105 K material in the atmospheres of normal A-type stars. For both stars, and for the mid ...

We present 24 ?m Spitzer MIPS photometric observations of the ~50 Myr open cluster IC 2391. Thirty-four cluster members ranging in spectral type from B3 to M5 were observed in the central square degree of the cluster. Excesses indicative of debris disks were discovered around one A star, six FGK stars, and possibly one M dwarf. For the cluster members ...

We present Spitzer MIPS observations at 24 {mu}m of 37 solar-type stars in the Pleiades and combine them with previous observations to obtain a sample of 71 stars. We report that 23 stars, or 32% +- 6.8%, have excesses at 24 {mu}m at least 10% above their photospheric emission. We compare our results with studies of debris disks in ...

Several ? Sct stars were photometrically monitored with the satellite CoRoT and observed in high-resolution spectroscopy from ground. We present here the preliminary results of the abundance analysis of several potential CoRoT targets. Moreover, new insights are given about the problem of the huge number of detected frequencies by comparing ? Sct stars ...

I wondered why there are still slowly rotating (V < 120 km s{sup -1}) normal A0-A9 field stars when such stars should have become Ap or Am stars by a diffusion mechanism. My first guess was that this was related to an unusually high binary frequency, but the frequency turned out to be normal, as shown in a paper in preparation. ...

We report on UBVRI CCD photometry that has been obtained over the course of the past seven years for a sample of over 1600 metal-poor (MP), field horizontal-branch (FHB), and other A-type candidates selected from two large objective-prism surveys, the HK survey of Beers and collaborators and the Hamburg/ESO stellar survey of Christlieb and colleagues. These ...

A-type stars have both a shallow near-surface zone of fast convection that can excite acoustic modes and a deep zone of core convection whose properties may be studied through asteroseismology. Many A stars also exhibit large magnetic spots as they rotate. We have explored the properties of core convection in rotating ...

We present an analysis of ?5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ? M?/M ? ? 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of ...

We have used the recently developed electron force field (eFF) and ReaxFF reactive force field to simulate the hypervelocity impacts experienced by the Cassini ion and neutral mass spectrometer during the Enceladus and Titian encounters.

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An experimental approach for the captive flight ground-testing of a prototypical exoatmospheric kinetic kill vehicle is described. The primary objective of these tests is to evaluate target tracking and intercept guidance control algorithms. Test hardware is described, including the vehicle, hyper-velocity target simulator and diagnostics systems. Initial test results are ...

In order to reveal the star-forming history of the molecular cloud complex we studied the intermediate mass stellar population in the Cepheus Flare region. (Paper I dealt with the distance and the young stellar object candidates of the region.) Correlating the IRAS Point Source Catalogue and Faint Source Catalogue positions with those of 1214 B8-A8 and 1760 F0-F5 type ...

We present the results of 3--D simulations of core convection dynamos within A-type stars of 2 solar masses, at a range of rotation rates. The inner 30% by radius of such stars are considered in our calculations, with the spherical domain thereby encompassing the convective core and some of the surrounding radiative envelope. We ...

We present the results of 3-D nonlinear simulations of magnetic dynamo action by core convection within A-type stars of 2 M? with a range of rotation rates. We consider the inner 30% by radius of such stars, with the spherical domain thereby encompassing the convective core and a portion of the surrounding radiative envelope. The ...

We have carried out 3-D simulations of core convection and dynamo activity within A-type stars of two solar masses at a range of rotation rates. Our models consider the inner 30% by radius of such stars, thus capturing the entire convective core and a portion of the surrounding radiative envelope within the spherical computational ...

Star-forming events in starbursts and normal galaxies have a direct impact on the global stellar content of galaxies. These events create numerous compact clusters where stars are produced in great number. These stars eventually end up in the star field background where they are smoothly distributed. However, ...

A common explanation for the observed X-ray emission of A-type stars is the presence of a hidden late-type companion. While this assumption can be shown to be correct in some cases, a number of lines of evidence suggests that low-mass companions cannot be the correct cause for the observed activity in all cases. A model explains the X-ray emission for magnetic Ap/Bp ...

We have completed an extensive search for stars hosting terrestrial planet zone dust by cross-correlating the Tycho-2 and IRAS catalogs. Near-infrared to far-infrared excess emission has been discovered towards a 10-20 Myr old, A-type member of the Upper-Centaurus-Lupus association. The hot dust component ( 750 K) in combination with the high fractional ...

We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 lsim M */M sunlsim 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to ...

We present an analysis of approx5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 approx< M{sub *}/M{sub sun}approx< 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital ...

We have identified a star in the Wide Angle Search for Planets (WASP) archive photometry with an unusual light curve due to the total eclipse of a small, hot star by an apparently normal A-type star and with an orbital period of only 0.668 d. From an analysis of the WASP light curve together with V-band and IC-band ...

We have searched for interstellar or circumstellar absorption lines in the center of Ca II K towards bright A-type stars that are mostly within 80 pc of the Sun. Narrow absorption features are found in about 30 % of the 28 normal main-sequence A stars and 18 metal-deficient lambda Bootis stars studied. We have ...

Aims:A sample of v sin i of B9 to F2-type main sequence single stars has been built from highly homogeneous {v sin i} parameters determined for a large sample cleansed of objects presenting the Am and Ap phenomenon as well as of all known binaries. The aim is to study the distributions of rotational velocities in the mass range of A-type stars for normal ...

We have performed abundance analysis of two slowly rotating, late A-type stars, HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtained echelle spectra covering the spectral range 4000-9850 �. These spectra allowed us to identify an extensive line list for 31 chemical elements, the most complete to date for A-type stars. Two ...

Massive stars are crucial building blocks of galaxies and the universe, as production sites of heavy elements and as stirring agents and energy providers through stellar winds and supernovae. The field of magnetic massive stars has seen tremendous progress in recent years. Different perspectives�ranging from direct field measurements over dynamo theory ...

Massive stars are crucial building blocks of galaxies and the universe, as production sites of heavy elements and as stirring agents and energy providers through stellar winds and supernovae. The field of magnetic massive stars has seen tremendous progress in recent years. Different perspectives - ranging from direct field measurements over dynamo theory ...

The pseudoluminosity effect in the metallic line A-type stars found by Abt and Morgan (1976) is confirmed in a random sample of 27 Am stars. From a morphological study of their spectra in the wavelength interval 3850-4400 A at a reciprocal dispersion of 66 A/mm, revised spectral types are given on the MK system for their K-line and ...

In an attempt of clarifying the connection between the photospheric abundance anomalies and the stellar rotation as well as of exploring the nature of ``normal A'' stars, the abundances of seven elements (C, O, Si, Ca, Ti, Fe, and Ba) and the projected rotational velocity for 46 A-type field stars were determined by applying the ...

In 2009, the rapidly oscillating peculiar A-type (roAp) star 33 Lib was the target of an intense observing campaign, combining ground-based spectroscopy with space photometry obtained with the Microvariability and Oscillation of STars (MOST) satellite. We collected 780 spectra using the Echelle Spectro Polarimetric Device for the ...

In 2009, the rapidly oscillating peculiar A-type (roAp) star 33 Lib was the target of an intense observing campaign, combining ground-based spectroscopy with space photometry obtained with the Microvariability and Oscillation of STars (MOST) satellite. We collected 780 spectra using the Echelle Spectro Polarimetric Device for the ...

We present the results of a medium-resolution spectroscopic survey of 43 field horizontal-branch (FHB) candidates carried out near the south galactic pole, selected from the original list of FHB candidates compiled by Beers et al. (2007). The observation list includes only stars classified as �high-probability� candidates, according to their 2MASS infrared colours. ...

We present the results of three-dimensional simulations of core convection within A-type stars of 2 Msolar, at a range of rotation rates. We consider the inner 30% by radius of such stars, thereby encompassing the convective core and some of the surrounding radiative envelope. We utilize our anelastic spherical harmonic code, which ...

A common explanation for the observed X-ray emission of A-type stars is the presence of a hidden late-type companion. While this hypothesis can be shown to be correct in some cases, there is also evidence suggesting that low-mass companions cannot be the proper cause for the observed X-ray activity in all cases. Babel and Montmerle (1997) presented a theoretical framework to ...

Effects of high speed impacts on radiation-induced defects were investigated with a plasma rail-gun. Vitreous quartz targets irradiated by ?-ray were shocked with polycarbonate projectiles at a speed of 7 km/s, then the remaining destroyed pieces were examined by ESR spectroscopy to investigate the degree of ``impact-annealing''. The white substance from the impact point showed a trace of melting ...

Spectral data, atmospheric parameters, and LTE metal abundances are presented for 22 massive (about 5 to 20 Msun), Galactic, A-type supergiants. The atmospheric analysis of each star is performed using the most recent Kurucz LTE model atmospheres. Atmospheric parameters (Teff, log g, ?) are determined from Mg I/II equilibrium and fitting theoretical H? ...

The search for substellar companions around stars with different masses along the main sequence is critical to understanding the different processes leading to the formation of low-mass stars, brown dwarfs, and planets. In particular, the existence of a large population of low-mass stars and brown dwarfs physically bound to early-type ...

In this poster, we present results from a program whose goals are to (1) examine the degree to which current LTE atmosphere models can reproduce the complex UV spectra (1200-3200 A) of the A-type stars; in order to (2) develop better estimates of the physical properties, including composition, for specific target stars with available archival UV data; and ...

Although photometric and spectroscopic surveys with the Spitzer Space Telescope increased remarkably the number of well studied debris disks around A-type and Sun-like stars, detailed analyzes of debris disks around F-type stars remained less frequent. Using the MIPS camera and the IRS spectrograph we searched for debris dust around 82 ...

Although photometric and spectroscopic surveys with the Spitzer Space Telescope remarkably increased the number of well-studied debris disks around A-type and Sun-like stars, detailed analyses of debris disks around F-type stars remained less frequent. Using the MIPS camera and the Infrared Spectrograph (IRS) spectrograph, we searched ...

In the past decade, increasing larger samples of field stars in the Milky Way have been used to constrain the shape and dynamics of the halo and thick-disk populations, to estimate the mass of the Milky Way, and to search for the presence of coherent streams of stars likely arising from shredded dwarf galaxies such as Sagittarius and Canis Major. ...

We present FEROS high-resolution (R ~ 45 000) optical spectroscopy of 34 Herbig Ae/Be star candidates with previously unknown or poorly constrained spectral types. Within the sample, 16 sources are positionally coincident with nearby (d < 250 pc) star-forming regions (SFRs). All the candidates have reported infrared excess. We determine the spectral ...

We report precise Doppler measurements of seven subgiants from Keck Observatory. All seven stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. The host stars have masses ranging from 1.1 ? M*/M&sun; ? 1.9, radii 3.4 ? R*/R&sun; ? 6.1, and metallicities -0.21 ? [Fe/H] ? +0.26. The planets are ...

Stars with spectral types earlier than about F0 on (or close) to the main sequence have long been believed to lack observable surface convection, although evolutionary models of A-type stars do predict very thin surface convective zones. We present evidence for granulation in two {delta} Scuti stars of spectral type A2: HD 174936 and ...

Near-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star ? Cas (F2IV) and a hotter one ? Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting ...

In this work we analysed recently obtained spectroscopic observations of the early A-type spectroscopic binary gamma Gem. The research is based on spectroscopic observations made with the 2 m telescope at the Th�ringer Landessternwarte Tautenburg, Germany. On the basis of 30 TLS spectrograms we derived abundances of C, O, Na (NLTE) and Mg, Si, Sc, Ti, Cr and Fe (LTE). We ...

We present the results of nonlinear 3--D simulations of magnetic dynamo action by core convection within A-type stars of 2 solar masses, at a range of rotation rates. We consider the inner 30% by radius of such stars, with the spherical domain thereby encompassing the convective core and a portion of the surrounding radiative envelope. ...