bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absolute Parameter Determination in Low-Mass Eclipsing Binaries. Radiative Parameters for BH VIR, ZZ UMa and CR Cas
Authors: Clement R. , Reglero V. , Garcia M. , Fabregat J. , Bravo A. , Suso J. 
Published: July 2016

AbstractA new uvby and Hβ monitoring program of low mass eclipsing binaries is currently being carried out in the framework of a 5 year observational program which also involves radial velocity determinations. The scope of this work is to provide very accurate absolute astrophysical parameters: mass, radius and effective temperatures, for main sequence late-type stars. One of the main goals is to improve the mass-luminosity relation in the low and intermediate mass range. A second objective is to perform accurate tests of the most recent grids of evolutionary models. This program is complementary to that currently being in progresss by the Copenhagen group.In this contribution we present the photometric preliminary results obtained for three of the systems included in our long term survey: BH Vir, ZZ UMa and CR Cas for which, primary eclipses have been observed. Particular attention is paid to the determination of reddening, distances and radiative properties. A more detailed study will be carried out when the light curves and radial velocity measurements are completed
Let Us Begin by Modelling Two Observed Delta Scuti Stars Simultaneously
Authors: Michel E. , Goupil M.J. , Lebreton Y. 
Published: July 2016

AbstractWe consider here two Delta Scuti stars GX Pegasi and V650 Tauri, which show very close masses and evolution stages as infered from photometrical calibration. The se two stars have been observed by the STEPHI team (Michel et al. 1990, Belmonte et al. this procedings) and they appear to be multiperiodic pulsators. For both these stars, an identification of the observed frequencies is proposed, from comparison with adiabatic eigenfrequencies computed for well suited stellar mode ls. This interpretation reveals very different pulsational behaviors despite the sta rs are expected to present very similar internal structures. We report here a first step toward constraining models by improving the fit between the observed and the calculated eigenfrequencies. The effect of overshooting and of the recent enhancement of the opacities are i nvestigated.
Asteroseismological Models with Rotation
Authors: Suran Doru Marian , Oprescu Gabriela 
Published: July 2016

AbstractThe low frequency NRP oscillations are considered in the case of differential rotation. Partial differential equations for adiabatic oscillations are reduced to a system of ordinary equations by means of a truncated spherical-harmonic expansion. The numerical method for solving the system is described. The final model also includes line profile variations (lpv) and posttheoretical mass (pth) calculations for the complete determinations of the physical, chemical, rotational and seismological properties of the stars.
Is It Possible to Determine Whether a Star is Rotating About a Unique Axis?
Authors: Gough D.O. , Kosovichev A.G. 
Published: July 2016

Rotating stars are normally presumed to rotate about a unique axis. Would it be possible to determine whether or not that presumption is correct? This is a natural question to raise, particularly after the suggestion by T. Bai & P. Sturrock that the core of the sun rotates about an axis that is inclined to the axis of rotation of the envelope.A variation with radius of the direction of the rotation axis would modify the form of rotational splitting of oscillation eigenfrequencies. But so too does a variation with depth and latitude in the magnitude of the angular velocity. One type of variation can mimic the other, and so frequency information alone cannot differentiate between them. What is different, however, is the structure of the eigenfunctions. Therefore, in principle, one might hope to untangle the two phenomena using information about both the frequencies and the amplitudes of the oscillations.We consider a simple model of a star which is divided into two regions, each of which is rotating about a different fixed axis. We enquire whether there are any circumstances under which it might be possible to determine seismologically the separate orientations of the axes.
Short-Term Spectral Variability in the Herbig Ae Star Ab Aur: Preliminary Analysis of Chromospheric Lines
Authors: Böhm Torsten , Catala Claude 
Published: July 2016

The Herbig Ae stars are PMS objects of intermediate mass. Their location in the H-R diagram indicates that they are in the radiative phase of their quasi-static contraction toward the main sequence, i.e. that they do not possess outer convective zones, according to the standard stellar evolution theory (Iben, 1965; Gilliland, 1986). In spite of the expected absence of subphotospheric convective envelopes, these stars show remarkable signs of activity: emission in the Mg II h and k lines, presence of the CIV resonance lines at 1550 A and He I 5875.7 A line, Ca II IR triplet in emission, etc... Considering that stellar activity, witnessed by the same type of indicators in other parts of the H-R diagram, is generally attributed to dynamo magnetic fields and/or acoustic waves generated in the convection zone, these active phenomena are quite paradoxical in the Herbig Ae stars.The main question concerns the origin of their activity: is this activity linked to phenomena occurring within the stars, like e.g. dynamo-generated magnetic fields, or to an external agent, like e.g. a boundary layer between an accretion disk and the stellar surface? We already have some indirect clues that the activity of the Herbig Ae stars might be of magnetic origin (Praderie et al., 1986; Catala et al. 1986) observed a rotational modulation of lines formed in the wind of AB Aur, prototype of the Herbig Ae stars. By analogy with the solar wind, they proposed that the modulation might be due to the corotation of azimuthal structures in the wind, controlled by a surface magnetic field.
Photometric Detection of Low-Order Nrp in Be Stars
Authors: Pavlovski K. , Ružić Ž. , Vujnović V. 
Published: July 2016

AbstractPeriod analysis of Be stars 28 Cyg and EW Lac has shown that their photometric variations are multiperiodic. Dominant periods have counterpart in low-order NRP modes identified in the independent line profile studies.
E.V.R.I.S. on Board Mars 94: The First Space Experiment Devoted to Stellar Seismology
Authors: Baglin A. , Weissg W. , Bisnovatyi-Kogan G. 
Published: July 2016

AbstractThe EVRIS experiment is an exploratory mission devoted to stellar seismology. It will observe approximately ten bright stars, for 20 days each, during the cruise of the Russian “MARS 94” mission. The photometer will be able to detect amplitudes of modes as small as a few 10−6 magnitude.
VLBI Observations of H2O and SiO Masers in Late Type Stars
Authors: Takaba H. , Iwata T. , Miyoshi M. , Ukita N. , Kameno S. , Matumoto K. 
Published: July 2016

AbstractThe results of a VLBI observation between Kashima 34 m and Nobeyama 45 m are presented. Water maser at 22.235 GHz and SiO masers at 43 GHz in some late type stars are mapped almost simultaneously. Data reduction is still on the way, then we report mainly for the blocking model of H2O maser.
The Nobeyama Millimeter Array Survey for Protoplanetary Disks Around Protostar Candidates and T Tauri Stars in Taurus
Authors: Ohashi Nagayoshi , Kawabe Ryohei , Hayashi Masahiko , Ishiguro Masato 
Published: July 2016

AbstractThe Nobeyama Millimeter Array Survey for protoplanetary disks has been made for 19 protostellar IRAS sources in Taurus; 13 were invisible protostars and 6 were youngest T Tauri stars. We observed the 98 GHz continuum and CS(J=2-1) line emissions simultaneously with spatial resolutions of 2.8”- 8.8” (360 AU-1,200 AU). Unresolved continuum emission was detected from 5 of 6 T Tauri stars and 2 of 13 protostar candidates. The continuum emission arose from compact circumstellar disks. Extended CS emission was detected around 2 T Tauri stars and 11 protostar candidates. There is a remarkable tendency for the detectability for the 98 GHz continuum emission to be small for protostar candidates. This tendency is explained if the mass of protoplanetary disks around protostars is not as large as that around T Tauri stars; the disk mass may increase with the increase of central stellar mass by dynamical accretion in the course of evolution from protostars to T Tauri stars.
A Vertical Structure of the Edge-On Galaxy, NGC 891
Authors: Handa Toshihiro , Sofue Yoshiaki , Ikeuchi Satoru , Ishizuki Sumio , Kawabe Ryohei 
Published: July 2016

Most of observational researches on molecular gas in galaxies have focused on the two-dimensional distributions in galactic disks so far. In order to investigate vertical structure of the galactic disk and the disk-halo interaction we need high-resolution observations of edge-on galaxies.So we observed the nearest edge-on galaxy, NGC 891, using the Nobeyama Millimeter Array (NMA). Its distance is estimated to be 8.9 Mpc using the Tully-Fisher relation and H-band photometric data. The synthesized beamsize was 4.5” x 4.4” and the field of view due to attenuation of the element antenna (Handa et al. 1992). The field center is 90”-offset from the center of the galaxy along the major axis toward the northern side, where the CO intensity has a local maximum (Sofue et al. 1987). After the standard data reduction procedure in AIPS, including CLEAN, we obtained 10 channel-maps with a 19.5 km s−1 velocity width from 289.8 km s−1 to 465.2 km s−1 with respect to the local standard of rest.In the integrated intensity map a narrow CO emission ridge is seen (Figure 1). It is an edge-on view of molecular gas disk of the galaxy. The confinement of the CO emission in the thin disk suggests that most of the molecular gas is belonging to the population-I objects like in our Galaxy. The apparent thickness of the ridge is about 7”, which means that the deconvolved width is about 6” or 270 pc (FWHM). The position-velocity diagram averaged along the major axis over the field of view shows no systematic velocity gradient along the minor axis (Figure 2). It means that the deconvolved thickness of the CO disk is intrinsic. This width is broader than that of our Galaxy by factor 2. The geometrically thick CO disk of NGC 891 may be due to active star formation in the disk.
Abundances in Magnetic Ap Stars
Authors: Cowley Charles R. 
Published: July 2016

AbstractThe spatial inhomogeneities, Zeeman broadening, and extreme abundance anomalies have thus far prevented definitive analyses of magnetic CP stars. Nevertheless, the abundance anomalies are so large that many of them have been known for decades. Abundance excesses of iron-peak elements of factors of 10 to 100 are common. Relative abundances on the iron peak are not constant. The lines of vanadium and nickel are often weak, and these elements may even be deficient in some stars. In spitè of the large variations, the odd-even effect persists; there is only minor evidence that chemical separation has perturbed the nuclear pattern. The lanthanide rare earths can have excesses of 100 to 1000 or even more in extreme cases. For these elements there is some evidence of fractionation. The actinide rare earth elements uranium and thorium are weakly (but surely!) present in a few of the magnetic CP stars: the best case is HR 465.
Abundances of Heavy Elements in CP Stars
Authors: Sadakane K. 
Published: July 2016

AbstractRecent determinations of abundances of heavy elements in CP stars are examined. An emphasis is placed on those elements which are found in a group of CP Stars but not in others. Fragmentary data are available for most of heavy elements. Systematic surveys (especially in the UV region) using a large sample of stars are needed before we understand the physics of the apparently erratic behavior of heavy elements in CP stars.
A New Opacity-Sampling Model Atmosphere Program for Arbitrary Abundances
Authors: Kurucz Robert L. 
Published: July 2016

AbstractI have developed a new version of my model atmosphere program called ATLAS12. It recognizes more than 1000 species, each in up to 10 isotopic forms, including all ions of the elements up through Zn and the first 5 ions of heavier elements up through Es. The elemental abundances are treated as variable with depth. ATLAS12 has 6 input files of line data containing 58,000,000 atomic and molecular lines. For each line the wavelength, identification, lower energy level, gf, radiative, Stark, and van der Waals damping constants are packed into 16 bytes. At each wavelength point in a frequency integration the profiles of all the significant nearby lines are computed and summed. The program and line files will be distributed in the fall of 1992.There are no significant differences at A0 between an opacity-sampled model computed with ATLAS12 and opacity-distribution-function model computed with ATLAS9. ATLAS12 allows arbitrary abundances but is slower. The new program can be used to produce improved models for Am and Ap stars that include the effects of millions of lines.
Zeeman Doppler Imaging
Authors: Wehlau William , Rice John 
Published: July 2016

AbstractThe mapping of stellar surfaces using the observed profiles of spectral lines is described. The problem is expressed in terms of an integral equation to be solved, using Tikhonov’s method. The local line profiles may be given either by an analytic approximation or by the solution of the equation of transfer with a model atmosphere. The model atmospheres commonly used may not correctly represent the stellar atmosphere which may lead to errors in the derived surface maps. Tests of mapping programs and applications to real stars show the capabilities and limitations of surface mapping. Mapping stellar magnetic fields places more severe demands on the data and computational programs than mapping the abundance distributions.
Mapping the Surface Distribution of Elements on Ap Stars Using the Maximum Entropy Method
Authors: Hatzes Artie P. 
Published: July 2016

AbstractA technique for deriving the distribution of elements on the surface of Ap stars using maximum entropy reconstruction principles is described. The technique is applied to deriving the silicon distribution on 56 Ari, CU Vir, 11 Ori and the chromium distribution onϒ2Ari. Silicon on these stars is depleted at the magnetic poles and is enhanced in regions between the magnetic equator and poles. The chromium distribution onϒ2Ari is markedly different than the chromium distribution seen on other Ap stars. It shows depletions at one of the magnetic poles (as do other Ap stars) but it does not show the depleted band at the equator as has been seen onθAur, 45 Her, andωHer. The silicon distribution on 11 Ori also differs from that found on other stars in that it shows evidence for a depleted band, similar to what has been seen in the chromium distribution is some stars. Characteristic features in the abundance maps such as spots or bands appear to mark the location of the magnetic poles or equator so that these maps can be used to infer the magnetic field geometries on these stars. Dipole decentering parameters derived from the abundance maps yield decentering parameters of about 0.2 stellar radii. The amount of decentering seems to be correlated with rotation period (longer period Ap stars have less decentering). Horizontal diffusion can complicate the use of abundance maps to determine the field geometry. The effects of horizontal diffusion can only be understood by a proper theoretical study of its effects or by mapping the elemental distribution on Ap stars of known age.
Determination of Stellar Magnetism Based on the Computerized Evaluation of Zeeman-Spectra
Authors: Gerth Ewald 
Published: July 2016

AbstractA package of computer-programs is presented, which is suited for the evaluation of stellar spectra in regard of line positions in order to determine the magnetic field strength and the radial velocity. The programs have been developed for the calculation of the measuring data obtained from photographic spectrograms but could be generalized for the online observation in a spectrograph at the telescope using an electronic detector.The network of programs may be amplified deliberately as required for any special application. For the exchange of data among cooperating institutes we propose the standardization of programs and data-files as outlined below.
Search for Magnetic Fields in Vega, Gamma Geminorum, and Sirius
Authors: Takada-Hidai Masahide , Jugaku Jun 
Published: July 2016

AbstractMagnetic fields in Vega, ϒ Geminorum, and Sirius are searched by using empirical and theoretical relations of magnetic-field strength to the relative differences between the equivalent widths of each pair of the two Fe II lines near 6150 and 4400 Å. We estimated the possible strengths of their magnetic fields as follows: 0.0 kG or 2.5 – 3.5 kG for Vega, 0 – 2 kG or 2.8 – 3.0 kG for ϒ Gem, and 0.0 kG or ∼ 2(?) – 2.5 kG for Sirius. The empirical relation yields the former value in each star, which is consistent with those determined through polarization measurements, while the theoretical relation the latter with systematically large values.
Variability Among Magnetic and Nonmagnetic Stars
Authors: Schöneich Werner , Želwanowa Elia 
Published: July 2016

AbstractThe present paper concentrates on several seemingly nonstandard cases of variability related to CP stars. Variability of magnetic CP stars with time scales different from rotational period, variability among the HgMn stars, variability of normal stars with variations similar to CP stars, and a relation between Be and CP stars are shortly discussed.
Carbon and Silicon in Normal a Stars and in Lambda Bootis Stars
Authors: Holweger Hartmut , Stürenburg Sven 
Published: July 2016

AbstractThe anticorrelation of C and Si previously inferred from high-resolution spectroscopy of sharp-lined A stars classified as normal or mild Am is also found among the metal-deficient, more rapidly rotating λ Boo stars. The entire sample of program stars covers the range [C/Si] = − 1.14 (Sirius, mild Am star) to + 1.35 (HR 7400, λ Boo-type). Iron varies parallel with silicon. With respect to surface chemistry the λ Boo stars do not form a distinct group but rather represent the lower end in a continuous sequence of ‘metal’ abundance extending over more than 1.5 dex.We argue that differential accretion of gas and dust in late stages of star formation or during the main-sequence phase is responsible for most of the abundance variations of the lighter elements up to the iron group. Enhanced or impeded accretion of dust leads to a metal-rich or metal-poor surface composition, respectively. The heavy trace elements Sr and Ba show additional anomalies indicating that other processes like gravitational and radiative separation are also involved.
A Search for λ Bootis Stars in OB Associations
Authors: Gray R.O. , Corbally C.J. 
Published: July 2016

AbstractA search for λ Bootis stars in two OB associations (Orion and Lacerta OB1) has been carried out. One clear example of a ZAMS λ Bootis star has been discovered in Orion OB1. Both Orion OB1 and Lacerta OB1 contain, as well, a number of mildly metal-weak A-stars which may be λ Bootis stars in-the-making.
Long Term Variability in CP Stars
Authors: Hensberge Herman 
Published: July 2016

AbstractA search for CP2 stars with long photometric periods during more than one decade has led to the detection of the long period variables HD 94660 and HD 116458. Furthermore, in the case of ϒ Equ, the CP star with the longest magnetic period, a monotonic change of the light output has been measured. Light curves are presented for the known long period variables HD 187474 and HD 188041. The results on the other stars in the programme are shortly discussed.
Chemically Peculiar Stars in Clusters: Upper and Lower Age Limits of CP Stars
Authors: North P. 
Published: July 2016

AbstractThe evolutionary state of CP Stars is defined using members of open clusters. It is confirmed that all CP stars belong to the main sequence, if the case of Horizontal-Branch Stars is omitted. The frequency of CP Stars as a function of age has been reconsidered: it is found constant for the CP2 stars, but significantly increasing with age for the CP1 (Am) stars.
Photometric Properties of CP Stars in the Infrared
Authors: Catalano Francesco A. , Leone Francesco , Kroll Reinhold 
Published: July 2016

AbstractEightysix chemically peculiar stars have been observed in the near infrared with the aim to extend the comprehension of the differences between normal and peculiar stars. These stars have been checked for variability. Most of the stars are previously known light variables, although their periods were not accurate enough to phase together different kinds of observations carried out several years apart. For about 20 stars the period has been refined by combining our own uvby observations with the ones available in the literature.
Age Determination for Am Stars
Authors: Figueras F. , Torra J. , Jordi C. , Asiain R. 
Published: July 2016

AbstractFrom uvby and Hβ photometry, individual stellar ages for A type stars have been derived using three different evolutionary models. In this paper we evaluate the corrections for metallicity and rotation to be applied to the physical parameters of Am and their influence on the determined ages. A test based on the Hyades open cluster is also presented.
Atomic Opacities
Authors: Seaton M. J. 
Published: July 2016

LetIv(r, θ) be the intensity of radiation of frequencyv, at a distancerfrom the centre of a star and in a direction making an angleθto the outward normal. In a plane-parallel approximation the equation of radiative transfer iswhere𝛋vis the opacity andjvthe emissivity. The net outward flux of radiant energy isand the flux integrated over all frequencies is
Proper Motions from Schmidt Plate Scans at STScI
Authors: MacConnell D. Jack , Roberts Wm. James , Williamson Ramon L. 
Published: July 2016

AbstractWe describe a program of determining proper motions from digitized scans of Palomar Oschin Schmidt telescope plates at the Space Telescope Science Institute. Our method is most useful over 11 ≲ V ≲ 18 and .
The Stellar Space Distributions of dA and gK Stars
Authors: Dawanas D. N. , Hidayat B. 
Published: July 2016

AbstractWe present a case study on the stellar space distribution of stars with MK spectral types B8 to A2 (dA) and gG8 to gK2 (gK) in a sky region of 25 square degrees, centred at the galactic coordinate l = 4° and b = +12°. Two hundred and forty-eight (248) stars with MK type of B8–A2 and gG8–gK2 were identified in this field. The space density distributions of these stars were obtained by employing the Matrix and Malmquist methods. The relative density of B8–A2 stars tends to be similar to that of gG8–gK2 stars, which implies that the two groups of stars occupy the same space volume in the galaxy. The comparison with those of Field-3 (l = 0.8°, b = –10°) show that the space density distribution of the two groups of stars above and below the galactic plane is not the same. Above the galactic plane, the space density of the gK stars is higher than those of dA stars, whereas below the galactic plane the density of dA stars is higher than for the gK stars. For both groups, the maximum space density occurs at around 30–40 pc from the galactic plane.
A Survey of Emission-line Stars in the Outer Part of the Orion Star-forming Region
Authors: Wiramihardja Suhardja D. , Nakano Makoto , Kogure Tomokazu 
Published: July 2016

AbstractWe report the result of our survey observations in the outer part of the Orion star-forming region which consists of six Kiso sky areas (150 square degrees). In total, we detected only 48 emission line stars. The low surface density suggests that the Orion star-forming region probably terminates around these areas.