A survey of emission-line stars in the CMa star formation region

A survey of emission-line stars was carried out in the CMa star formation region, based on spectral observations with the Kiso Schmidt telescope. In total, 128 emission-line stars were detected, ranging fromV=6 to 15, and the majority are found withV between 11 and 14. A comparison with the existing catalogues shows that some emission-line stars are common with ours, while some exhibit no detectable emission line on our plates, suggesting the variability of emission-line strength. The two-colour (U–B, B–V) diagram is also shown for the detected stars.Paper presented at the IAU Third-Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.On leave from the Bosscha Observatory, Institute of Technology Bandung, Indonesia.     

High sensitivity SiO maser survey for mira variables

Simultaneous observations of the six transitions of SiO for 106 late-type stars were made. The SiO maser emission was detected in 83 stars. Thev=3 maser emission was detected in eight stars, and the²⁹SiOv=0 emission in six stars. The²⁹SiOv=0 emission is stronger and narrower than that of²⁸SiO, suggesting that the²⁹SiO emission is masing.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Searching for Runaway OB Stars in Supernova Remnants

Searching for runaway stars in Supernova remnants gives us the possibility to estimate the mass ratio in binary systems in which there occur Supernova explosion. Such a method also gives information on portions of spectroscopic and close binaries among the stars on the main sequence with mass > 7–8 M⊙. More importantly, we can learn more about space velocities and spin periods of pulsars by this way. We have searched for runaway OB stars in central parts of 48 Supernova remnants with distances less than about 3 kpc. In 16 of the remnants in our sample, there is no candidate O or B type star and we have shown that pulsars (point sources) might be born not only in spectroscopic and close binaries. We have represented a list of stars which are candidates for runaway B type stars located in Supernova remnants. Spectroscopic investigations on these candidates could provide solutions for the problems mentioned above.__________Published in Astrofizika, Vol. 48, No. 3, pp. 393–408 (August 2005).     

New Hα objects in dark nebulae. I.

Results of a search for new H objects in the Cepheus region are presented. The observations on which the search was based were made in 1979 and 1985 at the 40 Schmidt telescope of the Byurakan Astrophysical Observatory with a 4° objective prism. Of the 80 emission stars detected, 68 are new. Most of them are fainter than the sun in absolute magnitude. A large fraction of the emission stars discovered may be flare stars as well as T Tau and Herbig Ae/Be stars.Translated fromAstrofizika, Vol. 39, No. 1, pp. 57–65, January–March, 1996.     

The location and X-ray emission of shocks around isolated be stars

All hot stars are observed to have X-ray emission: O stars haveL _X /L _bol 10^–7, whilst B stars' emission drops off with spectral subtype. Dynamical instability of OB star radiatively driven winds generates shocked regions which may be responsible for the bulk of the X-rays observed. The wind-compressed disc model of Bjorkman & Cassinelli (1993) presents another site for X-ray emission. The disc formed in the equatorial plane of a fast rotating Be star from equatorward drift of wind streamlines is confined on both sides by a shock which may also generate X-rays. As the X-ray emission originating from the wind shocking is ubiquitous amongst B and Be stars then the wind-compressed disc model näively predicts that Be stars should generate more X-rays than B stars of equivalent spectral subtype.The X-ray emission from the shocks confining compression discs has been calculated and compared to a limited set of observations. The excess X-ray emission from the Be star disc shocks is found to be undetectable over the inherent wind shocking emission.     

Gas—Dust Shells around Some Early-Type Stars with an IR Excess (of Emission)

The results of an investigation of IR (IRAS) observations of 58 O—B—A—F stars of different luminosity classes, which are mainly members of various associations, are presented. The color indices of these stars are determined and two-color diagrams are constructed. The emission excesses at 12 and 25 mm (E ₁₂ and E ₂₅) are also compared with the absorption A₁₆₄₀ of UV radiation. It is concluded that 24 stars (of the 58 investigated) are disk systems of the Vega type, to which Vega = N 53 also belongs. Eight known stars of the Vega type are also given in the figures for comparison. The remaining 34 stars may have gas—dust shells and/or shell—disks. The IR emission excesses of the 34 investigated stars and 11 comparison stars (eight of them are Be-Ae stars) are evidently due both to thermal emission from grains and to the emission from free—free transitions of electrons in the gas—dust shells of these stars.     

Multiplex approach to the photometric detection of planets

If the hypothesis is correct that most solar-like stars have planetary systems and have planets in inner orbits, then approximately 1% of these stars should have planets with orbital planes close enough to our line of sight to show transits. To get a statistically significant estimate of the fraction of stars that have planets in inner orbits, it is necessary to monitor thousands of stars continuously for a period of several years. To accomplish this requires the use of a multi-channel photometer system. We present here several multi-channel methods that have been used for ground-based observations and a concept for applying multi-channel photometry to the detection of numerous Earth-sized planets.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Frequency of Be and Ae stars in spectroscopic binaries

The frequency of Be and Ae stars in spectroscopic binaries and Algol binaries is examined based on the available catalogue data, and compared with that of stars in theBright Star Catalogue. It is shown that in binary systems Be and Ae stars reveal different statistical behaviours. The frequency of Be stars in spectroscopic binaries shows a notable peak in its orbital-period distribution in the range of 100–300 days, suggesting a statistical group separated from Algol systems. In contrast, most of Ae stars in spectroscopic binaries belong to the Algol systems.     

Observational support for radiative pumping of SiO masers in evolved stars

SiO maser emission in AGB stars is found to be systematically distributed in ring structures, displaying tangential linear polarization. Using the VLBA, we have performed observations of such SiO maser emission at 43 GHz in the circumstellar envelopes of several late-type stars. We simultaneously mapped the v=1 and v=2, J=1–0 transitions. Our new maps show, for most spots, a systematic spatial shift between both maser lines. We discuss the implication of these results on the possible pumping mechanisms, concluding that the existing data favour radiative pumping schemes.     

A survey of emission-line stars in the perseus dark cloud

The results of an objective prism survey of H_α emission-line stars in a 5° × 5° region around NGC 1333 are presented. We have identified 25 stars as having H_α -line in emission, of which 11 have been discovered in the Lick H_α-survey. The limiting magnitude of the present survey is about 16.7 mag. in blue. These are suspected to be mainly T Tauri stars. Based on the UGR(Kiso) multiexposure plates, we have found that, on the [(G - U), (R - G)]-diagram, the domain of H_α emission line stars is fairly well delineated and separate from other stars. Some interesting features in their space distribution are also discussed briefly.     

Cold dust around chamaeleon stars

Here we present the results of 1.3 millimetre continuum measurements for intermediatemass stars in the Chamaeleon system of dark clouds. The detected millimetre radiation is most probably thermal emission from cold circumstellar dust grains. The measured millimetre fluxes are combined with infrared observations to model the broad-band spectral energy distribution (SED). In this way the parameters of the emission regions are determined.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

High excitation emission lines in binary systems with roundchroms

An unexpected empirical fact, a dependence of the observed luminosities inhigh excitation emission lines – 1240 NV, 1400 SiIV, 1550 CIV, 1640 HeII– on the intercomponent distance a of RS CVn type close binary systems,is revealed. It is assumed that those high excitation emission lines aregenerated most probably in a cone-like region between the Lagrangian pointL ₁ and the surface of the primary component of the system. Thebehavior of high excitation emission lines at various phases of theeclipse in the case of two binary systems, SX Cas and 22 Vul, indicatesthe possibility of existence of such a `Lagrangian cone' in the structureof common chromospheres – roundchroms – of close binary systems as amain source of generation of high excitation emission lines.     

Detection of accreting circumstellar gas around weak emission-line Herbig Ae/Be stars

We present archival and recent IUE high dispersion spectra of late B stars which reveal the presence of accreting gas with velocities as high as 350 km s^–1, collisional ionization of the accreting gas to temperatures above the stellar T_eff, and column densities intermediate between those observed toward classical Herbig Ae/Be stars and the nearby proto-planetary system Pictoris. One of the stars, HD 176386, while lacking obvious optical signatures of youth, is a member of the R CrA star formation region, and with an inferred age of 2.8 Myr has not yet arrived on the zero-age main sequence (ZAMS). The other object, an isolated, field B star with pronounced IR excess due to warm, circumstellar dust, 51 Oph, exhibits only modest h emission. The combination of high velocity, accreting gas in systems with IR excesses due to circumstellar dust suggests that not only are these objects candidate proto-planetary systems, but that they may represent an extension to higher stellar masses of the weak-emission pre-main sequence (PMS) stars.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Joint Spectrophotometric Catalogue of the Sternberg State Astronomical Institute and Fessenkov Astrophysical Institute: The analysis of common stars

TheSpectrophotometric Catalogue of the Sternberg State Astronomical Institute contains 875 stars; 8 of them are standards.TheCatalogue of the Fessenkov Astrophysical Institute consists of 1123 stars. The data on the spectral energy distribution for about a half of these stars are published.A comparison of energy distribution data for 473 common stars in the range 3200–7600 Å was made. Calibration of Alpha Lyr from Hayes (1985) was used for all the stars of both catalogues.In difference of the previous publications the comparison includes much more stars and energy distribution data were corrected where necessary. The agreement between the corrected data is better than in the case of the earlier comparison. Reductional factors due to the instrumental effects were taken into account for 275 stars from theSternberg Institute Catalogue. These factors are in the limits 1.01–1.04 and their mean value is 1.03.The reductional factors for the stars from theFessenkov Institute Catalague are much larger: 1.06–1.12 with the mean 1.06–1.07. In this case the reduction factors were taken into account for all the stars of the catalogue except the brightest ones withV<2.0.The values of the differences between spectral energy distribution data for common stars in dependence of magnitude, spectral type, and wavelength are presented.     

Effective temperatures,radii, and luminosities of O emission,Be and Ae stars

Our de-reddened fluxes, together with the ultraviolet measurements of Thompsonet al. (1978), have been compared with those of Kurucz's (1979) model atmospheres to derive effective temperatures of some O emission, Be and Ae stars. With the measured monochromatic fluxes we determined their angular diameters and luminosities. It is found that the majority of the stars are cooler than the Zero-Age Main Sequence (ZAMS), suggesting that they are slightly more evolved than ZAMS stars.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. The observations were made at the Observatoire de Haute Provence (France) and La Silla (E.S.O., Chile).     

High energy gamma-ray emission from binaries

The current Cherenkov telescopes together with GLAST are opening up a new window into the physics at work close to black holes and rapidly rotating neutron stars with great breakthrough potential. Very high energy gamma-ray emission up to 10 TeV is now established in several binaries. The radiative output of gamma-ray binaries is in fact dominated by emission above 1–10 MeV. Most are likely powered by the rotational spindown of a young neutron star that generates a highly relativistic wind. The interaction of this pulsar wind with the companion’s stellar wind is responsible for the high energy gamma-ray emission. There are hints that microquasars, accretion-powered binaries emitting relativistic jets, also emit gamma-ray flares that may be linked to the accretion–ejection process. Studying high energy gamma-ray emission from binaries offers good prospects for the study of pulsar winds physics and may bring new insights into the link between accretion and ejection close to black holes.     

Spectrophotometric study of Be stars

A large sample of Be stars has been studied spectrophotometrically in the visible region. The continuum energy distribution data for 23 Be stars included in the list of Harmanecet al. (1983) are presented and discussed in the wavelength range 3200 Å–8000 Å. For 15 Be stars the observations reported in the present work are new. By comparing the observed continua with models, the effective temperatures of these stars have been estimated. It is found that, in general, Be stars have lower effective temperature than the corresponding normal B stars. The present study shows that the early-Be stars (B0–B5) possess near-ultraviolet and near-infrared excess emissions more frequently than the late-Be stars (B5–B9). The seven new Be stars are detected to show pole-on characteristics.     

Analysis of the plasma laser star model of QSOs

The investigations on the Plasma Laser Star Model of QSOs reported in our previous paper are continued. Here we assume that QSOs are early type stars with temperatures in the range 10⁴–10⁵ K. It is pointed out that the spectral lines of such stars may have asymmetric shapes and large broadening leading to errors in measurement up to 20 Å. The conventional red-shift theory, however, allows fitting errors much more than this amount for many QSO emission lines. By taking the abundances of elements in QSO atmsopheres identical with the average cosmic abundance we analyze and compare the interpretations of the emission lines of 330 QSOs (263 QSOs are from Burbidgeet al.'s list and the rest are more recently discovered (QSOs) according to the new and the conventional theories.     

10-µm images and spectra of T Tauri stars

T Tauri stars are young stars usually surrounded by dusty disks similar to the one from which we believe our own Solar System formed. Most T Tauri stars exhibit a broad emission or absorption band between 7.5 and 13.5µm which is attributed to silicate grains in the circumstellar environment. We imaged three spatially resolved T Tauri binaries through a set of broadband filters which include the spectral region occupied by the silicate band. Two of these objects (T Tauri and Haro 6–10) are infrared companion systems in which one component is optically much fainter but contributes strongly in the infrared. Both infrared companions exhibit a deep silicate absorption which is not present in their primaries, indicating that they suffer very strong local extinction which may be due to an edge-on circumstellar disk or to a dense shell. We also took low resolution spectra of the silicate feature of two unresolved T Tauris to look for narrow features in the silicate band which would indicate the presence of specific minerals such as olivine. We observed GK Tau, for which Cohen and Witteborn (1985) reported a narrow emission feature at 9.7µm, but do not find evidence for this feature, and conclude that it is either time-dependent or an artifact of absorption by telluric ozone.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

X-ray Observations of Binary and Single Wolf-Rayet Stars with XMM-Newton and Chandra

We present an overview of recent X-ray observations of Wolf-Rayet (WR) stars with XMM-Newton and Chandra. These observations are aimed at determining the differences in X-ray properties between massive WR + OB binary systems and putatively single WR stars. A new XMM spectrum of the nearby WN8 + OB binary WR 147 shows hard absorbed X-ray emission (including the Fe Kα line complex), characteristic of colliding wind shock sources. In contrast, sensitive observations of four of the closest known single WC (carbon-rich) WR stars have yielded only non-detections. These results tentatively suggest that single WC stars are X-ray quiet. The presence of a companion may thus be an essential factor in elevating the X-ray emission of WC + OB stars to detectable levels.