Stellar Mass Accretion Research Articles

A C(18)O (J = 1 goes to 0) survey of protostellar candidates embedded in the Taurus molecular cloud

view Abstract Citations (15) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A C 18O (J = 1--0) Survey of Protostellar Candidates Embedded in the Taurus Molecular Cloud Hayashi, Masahiko ; Hasegawa, Tetsuo ; Ohashi, Nagayoshi ; Sunada, Kazuyoshi Abstract C(18)O (J = 1 goes to 0) observations were made toward a sample of 32 protostellar sources associated with the Taurus molecular cloud complex. The sources were selected from the IRAS Point Source Catalog with criteria to pick up solar-type protostar candidates. The C(18)O intensity for the optically invisible objects is correlated with the IRAS flux at 25, 60, and 100 micrometers, while at 12 micrometers the correlation is rather ambiguous. The correlation between the C(18)O intensity and the IRAS flux for the invisible objects suggests that both the C(18)O intensity and the IRAS flux at 25, 60, and 100 micrometers well represent the amount of gas and dust, respectively, in the extended envelopes (radius approximately 400-4000 AU) around these objects, while the worse correlation seen at 12 micrometers is consistent with the 12 micrometers emission arising from compact circumstellar disks. The visible objects show wide scatter in the C(18)O intensity with no clear correlation with the IRAS flux at all four wavelength bands, consistent with the IRAS emission originating from circumstellar disks at any infrared wavelengths. The difference in the correlation between the invisible and visible sources means that protostellar envelopes around invisible sources are dissipated away in the course of evolution from invisible sources into visible ones, probably due to accretion onto the central star or due to being blown off by molecular outflows. The observed smooth decrease of the C(18)O intensity from the invisible to visible sources implies the mass dissipation timescale of approximately 105 yr at a rate of greater than or approximately equal to 6 x 10-7 solar masses/yr. Publication: The Astrophysical Journal Pub Date: May 1994 DOI: 10.1086/174057 Bibcode: 1994ApJ...426..234H Keywords: Carbon Monoxide; Infrared Astronomy; Molecular Clouds; Protostars; Radio Astronomy; Stellar Envelopes; Stellar Evolution; Stellar Mass Accretion; Taurus Constellation; Astronomical Catalogs; Infrared Astronomy Satellite; Radio Telescopes; Spectral Energy Distribution; Astronomy; ISM: CLOUDS; ISM: MOLECULES; RADIO LINES: ISM; STARS: CIRCUMSTELLAR MATTER; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (34)

On the new theory of ultra-high-energy gamma-ray production in Cygnus X-3

view Abstract Citations (4) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the New Theory of Ultra--High-Energy Gamma-Ray Production in Cygnus X-3 Mitra, Abhas Abstract We develope here a model for ultra-high-energy gamma-ray production in Cygnus X-3 based on our earlier suggestion that in the presence of a strong soft X-ray field around the putative neutron star, the most dominant mechanism for cooling of the ultra-high-energy (UHE) protons should be the photomeson process which, in turn, should give rise to Very-High-Energy (VHE) - UHE gamma-rays. We envisage the spherical accretion shock around the neutron star to be specially conducive to acceleration of protons following supposed minor enhanced mass accretion and concomitant recession of the magnetopause due to enhanced radiation pressure at suitable orbital phases. It is also assumed that the accretion shock is quasi-perpendicular to enable fastest possible acceleration of protons. Relatively lower energy protons remain trapped in the magnetosphere yielding relatively lower energy pi0s and then photons. On the other hand, the highest energy protons stream out of the magnetopause (to reach a region of much lower magnetic field) and give rise to UHE gamma-rays. However, in most of the realistic cases, there may be a significant reduction of the high-energy photon luminosity because of magnetic degradation of the photons. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/174022 Bibcode: 1994ApJ...425..782M Keywords: Gamma Rays; High Energy Interactions; Neutron Stars; Particle Acceleration; Particle Production; Gamma Ray Observatory; Hadrons; Magnetopause; Pions; Shock Wave Propagation; Stellar Mass Accretion; X Ray Binaries; Astrophysics; ACCELERATION OF PARTICLES; GAMMA RAYS: THEORY; RADIATION MECHANISMS: NONTHERMAL; STARS: INDIVIDUAL CONSTELLATION NAME: CYGNUS X-3 full text sources ADS | data products SIMBAD (1)

Advection-dominated accretion: A self-similar solution

view Abstract Citations (1929) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Advection-dominated Accretion: A Self-similar Solution Narayan, Ramesh ; Yi, Insu Abstract We consider viscous rotating accretion flows in which most of the viscously dissipated energy is stored as entropy rather than being radiated. Such advection-dominated flows may occur when the optical depth is either very small or very large. We obtain a family of self-similar solutions where the temperature of the accreting gas is nearly virial and the flow is quasi-spherical. The gas rotates at much less than the Keplerian angular velocity; therefore, the central stars in such flows will cease to spin up long before they reach the break-up limit. Further, the Bernoulli parameter is positive, implying that advection-dominated flows are susceptible to producing outflows. Convection is likely in many of these flows and, if present, will tend to enhance the above effects. We suggest that advection-dominated accretion may provide an explanation for the slow spin rates of accreting stars and the widespread occurrence of outflows and jets in accreting systems. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/187381 arXiv: arXiv:astro-ph/9403052 Bibcode: 1994ApJ...428L..13N Keywords: Accretion Disks; Advection; Astronomical Models; Black Holes (Astronomy); Cooling Flows (Astrophysics); Stellar Mass Accretion; Viscous Flow; Hydrodynamics; Rotating Disks; Two Dimensional Flow; Astrophysics; ACCRETION; ACCRETION DISKS; BLACK HOLE PHYSICS; HYDRODYNAMICS; Astrophysics E-Print: 7 pages of text, 1 postscript figure, plain TeX, Harvard-Smithsonian Center for Astrophysics Preprint Series No. 3809 full text sources arXiv | ADS |

A polar-nucleus dark lane in the barred spiral M83: Three dimensional accretion in the nucleus

view Abstract Citations (22) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Polar-Nucleus Dark Lane in the Barred Spiral M83: Three-Dimensional Accretion in the Nucleus Sofue, Yoshiaki ; Wakamatsu, Ken-Ichi Abstract The central region of the barred spiral galaxy M83 reveals a polar- nucleus dust lane, which extends from the northeast molecular bar and crosses the central bulge. Its southwest counterpart is not visible, being hidden behind the bulge. This asymmetry, in spite of the galaxy's face-on orientation and the symmetric bar structure in the CO line emission, indicates that the dark lane is an off-plane structure. Such a "polar-nucleus" structure can be formed by a noncoplanar, three- dimensional accretion in a warped disk. Publication: The Astronomical Journal Pub Date: March 1994 DOI: 10.1086/116914 arXiv: arXiv:astro-ph/9308037 Bibcode: 1994AJ....107.1018S Keywords: Cosmic Dust; Galactic Nuclei; Interstellar Gas; Polar Regions; Spiral Galaxies; Stellar Mass Accretion; Three Dimensional Models; Velocity Distribution; Astronomical Observatories; Cameras; Cassegrain Optics; Optical Filters; Photographic Plates; Telescopes; Astrophysics; GALAXIES: INDIVIDUAL: M83; ACCRETION; GALAXIES: NUCLEI; Astrophysics E-Print: (to appear in AJ), 5 pages, plainTeX, U-Tokyo Astro. No.93-25 full text sources arXiv | ADS | data products SIMBAD (27) NED (15)

Capture and induced disk accretion in young star encounters

view Abstract Citations (91) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Capture and Induced Disk Accretion in Young Star Encounters Ostriker, Eve C. Abstract Young stars display evidence of moderately massive, centrifugally supported, gaseous, and dusty circumstellar disks. These disks are highly susceptible to compressional and transverse disturbances. Such density and bending waves may be excited by tidal forces from external gravitational perturbers, including passing, initially unbound stars. The energy and angular momentum exchange between the two-body orbit and the disk permits capture of passing stars on near-parabolic orbits, and can cause disk accretion. We compute energy and angular momentum transfer for near-parabolic orbits with periastron xmin beyond two disk radii rD, as a function of relative disk-orbit angles, using linear perturbation theory. We present both numerical evaluation of the integrations and asymptotic analytic results. These are used to compute capture rates and induced accretion rates in stellar clusters. We find that for encounters with xmin near 2rD, the disk angular momentum is reduced by a few to several percent (angle-averaged), with prograde, coplanar orientations yielding reductions by more than 10%. For typical open cluster parameters, the capture probability is less than 0.1% at xmin approximately 2rD; for most orientations energy is actually given to the perturber, rather than the reverse. Capture is permitted only for polar and retrograde encounters, and even then is unlikely. In particular, the asymptotic analytic results (large xmin/rD limit) for resonant transfer predict that the disk's energy change will be positive for inclinations greater than 101.5 deg, with the maximum, positive value at inclination 117 deg only 1% of the (negative) disk energy change at zero inclination. Both the angular momentum transfer and the capture probability drop off with increasing xmin/rD, first as an exponential and then as a power law. We explain this behavior in terms of the ratio of perturbed angular velocity to disk angular velocities, and the spectrum of allowed resonances. We compare our results on star/disk-star encounters with other capture calculations, and find that many of the same considerations also apply to star-star encounters and galaxy-galaxy encounters. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173890 Bibcode: 1994ApJ...424..292O Keywords: Accretion Disks; Binary Stars; Interstellar Matter; Perturbation Theory; Pre-Main Sequence Stars; Stellar Envelopes; Angular Momentum; Celestial Mechanics; Stellar Mass Accretion; Stellar Orbits; Astrophysics; ACCRETION; ACCRETION DISKS; CELESTIAL MECHANICS; STELLAR DYNAMICS; STARS: BINARIES: GENERAL; STARS: CIRCUMSTELLAR MATTER; STARS: PRE--MAIN-SEQUENCE full text sources ADS |

Accretion onto a 1.4 solar mass white dwarf: Classical nova, recurrent nova, or supernova?

view Abstract Citations (63) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Accretion onto a 1.4 Msun White Dwarf: Classical Nova, Recurrent Nova, or Supernova? Kovetz, Attay ; Prialnik, Dina Abstract We have computed successive outbursts on a carbon-oxygen 1.4 solar mass white dwarf, accreting hydrogen-rich material at rates of 10-10 to 10-6 solar mass/yr. Mass accretion, diffusion, nuclear burning -- using a network of 36 isotopes -- and hydrodynamic mass loss are included in these calculations. We find the outburst characteristics to vary considerably with the accretion rate. For the highest accretion rate, the outbursts diminish in strength and should eventually lead to steady burning; no mass is ejected and hence such a scenario should result in a Type I supernova explosion. For an accretion rate of 10-7 solar mass/yr, the eruptions occur at intervals of almost a year and some mass is ejected, but still less than the mass accreted prior to outburst. An accretion rate of 10-8 solar mass/yr results in outbursts typical of recurrent novae: the recurrence time is less than 20 yr, velocities are approximately 500 km/s, and the ejected mass -- larger than the accreted mass -- is approximately 2 x 10-7 solar mass; it is significantly enriched in helium, but also to a lesser extent, in CNO elements. The lowest accretion rates considered lead to outbursts characteristic of very fast novae, with decline times of a few days, velocities up to 3000 km/s, amplitudes up to 14 mag and ejected masses of approximately 10-6 solar mass, moderately enriched in CNO. We conclude that accretion onto a very massive white dwarf may lead, depending on the accretion rate, either to recurrent novae, to very fast classical novae, or to mass accumulation that may eventually lead to a supernova. We emphasize that, in all cases, several outbursts should be calculated in order to obtain the correct composition and mass of the ejected material. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173891 Bibcode: 1994ApJ...424..319K Keywords: Accretion Disks; Novae; Supernovae; White Dwarf Stars; Stellar Luminosity; Stellar Mass Accretion; Astrophysics; ACCRETION; ACCRETION DISKS; DIFFUSION; STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: INTERIORS; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (4)

The multiplicity of T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius: A 2.2 micron speckle imaging survey

view Abstract Citations (584) References (61) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Multiplicity of T Tauri Stars in the Star Forming Regions Taurus-Auriga and Ophiuchus-Scorpius: A 2.2 Micron Speckle Imaging Survey Ghez, A. M. ; Neugebauer, G. ; Matthews, K. Abstract We present the results of a magnitude limited (K less than = 8.5 mag) speckle imaging survey of 69 T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius. Thirty-three companion stars were found with separations ranging from 0.07 sec to 2.5 sec, nine are new detections. This survey reveals a distinction between the classical T Tauri stars (CTTS) and the weak-lined T Tauri stars (WTTS) based on the binary star frequency as a function of separation: the WTTS binary star distribution is enhanced at the closer separations (less than 50 AU) relative to the CTTS binary star distribution. We suggest that the nearby companion stars shorten the accretion time scale in multiple star systems, thereby accounting for the presence of WTTS that are coeval with many CTTS. The binary star frequency in the projected linear separation range 16 to 252 AU for T Tauri stars (60 (+/- 17)%) is a factor of 4 greater than that of the solar-type main-sequence stars (16(+/- 3)%). Given the limited separation range of this survey, the rate at which binaries are detected suggests that most, if not all, T Tauri stars have companions. We propose that the observed overabundance of companions of T Tauri stars is an evolutionary effect, in which triple and higher order T Tauri stars are disrupted by close encounters with another star or system of stars. Publication: The Astronomical Journal Pub Date: November 1993 DOI: 10.1086/116782 Bibcode: 1993AJ....106.2005G Keywords: Companion Stars; Speckle Patterns; Star Formation; Stellar Evolution; T Tauri Stars; Astronomical Photometry; Image Analysis; Stellar Mass Accretion; Telescopes; Astronomy; STARS: EVOLUTION; STARS: PRE-MAIN SEQUENCE full text sources ADS | data products SIMBAD (76)

New six-color intermediate-band photometry and photometric solutions for U Cephei

view Abstract Citations (11) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New Six-Color Intermediate-Band Photometry and Photometric Solutions for U Cephei Burnett, Brian J. ; Etzel, Paul B. ; Olson, Edward C. Abstract We describe new six-color intermediate-band photometric observations of U Cephei, obtained during an interval of consistently low mass-transfer activity. We use the new Wilson eclipsing binary computer program to obtain several photometric solutions, which incorporate the rapid rotation of the hot star. Residual trends for solutions using all observations show the absorbing effect of the stream between phases 0.7 and 0.96. A second set of solutions, omitting data in this phase range, leads to more satisfactory results. Our photometric mass ratio is somewhat smaller than the spectroscopic values found by both Batten (1974) and Tomkin (1981). Differences between our solutions and those of Rafert and Markworth (1991) are probably due to residual contamination of light curves by circumstellar matter. Publication: The Astronomical Journal Pub Date: October 1993 DOI: 10.1086/116752 Bibcode: 1993AJ....106.1627B Keywords: Cepheid Variables; Stellar Mass Accretion; Stellar Rotation; Stellar Spectra; Astronomical Photometry; Light Curve; Stellar Magnitude; Stellar Temperature; Astrophysics; STARS: INDIVIUAL: U CEPHEI; BINARIES: ECLIPSING full text sources ADS | data products SIMBAD (7)

A study of metal abundance patterns in cool white dwarfs. III - Comparison of the predictions of the two-phase accretion model with the observations

view Abstract Citations (105) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of Metal Abundance Patterns in Cool White Dwarfs. III. Comparison of the Predictions of the Two-Phase Accretion Model with the Observations Dupuis, J. ; Fontaine, G. ; Wesemael, F. Abstract The predictions of a two-phase accretion model is compared with all the observations currently available on the metal-line phenomenon in cool white dwarfs. The model is based on a simplified picture of the interstellar medium, but makes specific predictions as to the presence of metals in the photospheres of these stars. The gross observed metal abundance patterns are found to be very well accounted for within the framework of the model. For many individual stars, it is also possible to infer directly the accretion rates necessary to maintain photospheric metal abundances. The question of traces of hydrogen in these stars is discussed. It is found that hydrogen, like the metals, must be accreted. However, hydrogen accretion must be reduced by factors of 10 exp 2 to 10 exp 7 with respect to metal accretion to account for the observations. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1993 DOI: 10.1086/191808 Bibcode: 1993ApJS...87..345D Keywords: Abundance; Cool Stars; Metallicity; Stellar Mass Accretion; Stellar Models; White Dwarf Stars; Helium; Hydrogen; Photosphere; Stellar Atmospheres; Stellar Composition; Stellar Temperature; Astrophysics; STARS: ABUNDANCES; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (34) MAST (1) Related Materials (2) Part 1: 1992ApJS...82..505D Part 2: 1993ApJS...84...73D

The atmospheres of T Tauri stars. II - Chromospheric line fluxes and veiling

view Abstract Citations (30) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Atmospheres of T Tauri Stars. II. Chromospheric Line Fluxes and Veiling Batalha, C. C. ; Basri, Gibor Abstract A set of high-resolution calibrated spectra of southern T Tauri Stars (TTS), comprising objects with H-alpha equivalent widths ranging from 3 to 40 A are used to derive one-component plane-parallel chromospheric models. Our motivation is to discover how much emission activity can truly be ascribed to stellar activity, using real calibrated stellar data. We find that simple models can reproduce the Ca II line at 8542 A for most of the stars. The chromospheric enhancements are comparable to the ones found among active main-sequence stars of similar spectral type. These models cannot account for the veiling observed in TTS. Likewise, realistic TTS chromospheres are unable to create the observed Balmer jumps. The targets have a range of H-alpha strength that allow us to study possible correlations among narrow symmetric emission lines, and H-alpha which probes nonstellar regions. On the basis of their stellar vs systemic luminosities, Sz 77, Sz 82, and Sz 19 present signatures of disk accretion, in addition to the previously reported case of Sz 98. By correlating the fluxes of the Ca II IR line, H-alpha and the near-IR excess, we conclude that disk accretion may enhance the luminosity of typical chromospheric emission lines. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172926 Bibcode: 1993ApJ...412..363B Keywords: Chromosphere; Stellar Atmospheres; Stellar Spectra; T Tauri Stars; Emission Spectra; H Alpha Line; Spectral Line Width; Stellar Activity; Stellar Luminosity; Stellar Mass Accretion; Stellar Models; Astrophysics; STARS: PRE--MAIN-SEQUENCE; STARS: CHROMOSPHERES; LINE: FORMATION; RADIATIVE TRANSFER full text sources ADS | data products SIMBAD (6) Related Materials (1) Part 1: 1987ApJ...318..823F

Subarcsecond images of CW Tauri - Constraints on disk size and jet formation

view Abstract Citations (17) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Subarcsecond Images of CW Tauri: Constraints on Disk Size and Jet Formation Gomez de Castro, Ana I. Abstract Subarcsecond spatial resolution images in the forbidden S II and forbidden N II + H-alpha emission lines of the T Tauri star (TTS) CW Tau are presented. It is shown that CW Tau has a jet that extends up to 2.2 arcsec (300 AU) from the star in the direction P.A. = 144 deg. The jet emits strongly in forbidden S II, and it is already collimated at 1.3 arcsec (176 AU) from the star. The images also indicate that CW Tau is extended in the east-west direction and that the jet is slightly shifted to the east. This suggests that CW Tau may be a binary with the two components separated 0.20 arcsec (28 AU). The observations are compared with the theoretical models proposed for the production of forbidden line emission regions and protostellar jets. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/186936 Bibcode: 1993ApJ...412L..43G Keywords: Binary Stars; Emission Spectra; H Alpha Line; Plasma Jets; Accretion Disks; Nebulae; Space Observations (From Earth); Stellar Mass Accretion; Astrophysics; STARS: FORMATION; STARS: INDIVIDUAL CONSTELLATION NAME: CW TAURI; STARS: INDIVIDUAL CONSTELLATION NAME: FM TAURI; STARS: INDIVIDUAL CONSTELLATION NAME: V773 TAURI; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (5)

SN 1987A - an empirical and analytic approach

view Abstract Citations (50) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SN 1987A: an Empirical and Analytic Approach Bethe, Hans A. Abstract Starting from Wilson's idea that the supernova gets its energy from neutrinos heating the mantle of the star, I use the neutrino observations to find the available neutrino flux. This agrees well with recent computations by Wilson and Mayle, using "neutron fingers." In the mantle of the star, one can define a "gain radius:" outside this radius, the energy gain from neutrino absorption is greater than the energy loss by electron capture. The temperature and density are calculated from simple arguments for r 100 km: In the region where free nucleons dominate, the entropy is assumed to be constant; in the region where nucleons and α-particles are mixed, the fraction of nucleons is determined from the internal energy. One can then calculate the fraction of neutrino energy which can be transferred to the region outside the gain radius; this turns out to be 1%-2%. With the observed neutrino flux, this gives a supernova energy of 0.8 foe (1 foe = 10^51^ ergs); nucleosynthesis adds about 0.4 foe, for a total of 1.2 foe, compared with the observed energy of 1.4 +/- 0.4 foe. In this paper, I shall try to go as directly as possible to the calculation of the supernova energy. Other problems are discussed in Sections 11-14. In particular, it is shown that, and why, the shock wave starts only after some delay. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172911 Bibcode: 1993ApJ...412..192B Keywords: Computational Astrophysics; Neutrinos; Nuclear Astrophysics; Stellar Interiors; Supernova 1987a; Electron Capture; Shock Fronts; Shock Waves; Stellar Convection; Stellar Mass Accretion; Stellar Structure; Temperature Distribution; Astrophysics full text sources ADS | data products NED (2) SIMBAD (1)

Near-infrared observations of the HH 111 region

view Abstract Citations (69) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Observations of the HH 111 Region Gredel, Roland ; Reipurth, Bo Abstract Deep near-infrared images and long-slit spectra of the HH 111 jet region are presented. Two bipolar jets were detected; the HH 111 jet, and a new optically invisible jet, HH 121, from the same source. Near-infrared long-slit spectra confirmed the emission-line nature of the jets. The HH 121 bipolar jet emanates from the source at a large angle to the HH 111 jet and it is suggested that the source is a pre-main sequence-binary. Near-infrared lines were used to derive electron densities and extinction in parts of the HH 111 jet and an excitation temperature was derived from H2 lines. Publication: The Astrophysical Journal Pub Date: April 1993 DOI: 10.1086/186798 Bibcode: 1993ApJ...407L..29G Keywords: Binary Stars; Interstellar Matter; Plasma Jets; Stellar Evolution; Stellar Mass Accretion; Astronomical Spectroscopy; Hydrogen; Infrared Astronomy; Line Spectra; Reflection Nebulae; Astrophysics; ISM: INDIVIDUAL ALPHANUMERIC: HH 111; ISM: JETS AND OUTFLOWS; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (2)

Binary structure and accretion flow of the new intermediate polar H0253 + 193

view Abstract Citations (13) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Binary Structure and Accretion Flow of the New Intermediate Polar H0253+193 Kamata, Yuichi ; Koyama, Katsuji Abstract This paper describes X-ray spectral variations of H0253 + 193 during its 6 hr binary orbit and 206 s pulsation. The orbital-phase-resolved X-ray spectra were well fitted by a thermal bremsstrahlung model with a temperature ranging from 16 to 33 keV and an iron emission line at about 6.7 keV. No systematic change of the temperature with orbital phase was found, but a clear orbital modulation of the hydrogen column density (NH) was discovered. H0253 + 193 shows total eclipses and double-peaked pulse profiles. During the ingress and egress of the eclipse, no significant spectral change was observed. The fractional pulse amplitude decreases as the X-ray energy increases. A possible geometry of the binary system and the structure of the accretion flow are discussed. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/172363 Bibcode: 1993ApJ...405..307K Keywords: Eclipsing Binary Stars; Stellar Mass Accretion; X Ray Sources; White Dwarf Stars; X Ray Spectra; Astrophysics; STARS: BINARIES: CLOSE; STARS: INDIVIDUAL ALPHANUMERIC: H0253; 193; X-RAYS: STARS full text sources ADS | data products SIMBAD (1)

Multiple hydrogen flashes on accreting low-mass white dwarfs - Novae and DAO stars

view Abstract Citations (45) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiple Hydrogen Flashes on Accreting Low-Mass White Dwarfs: Novae and DAO Stars Shara, Michael M. ; Prialnik, Dina ; Kovetz, Attay Abstract The evolution of two low-mass white dwarfs, accreting hydrogen-rich matter at a rate of 10 exp -9 solar mass/yr was calculated by means of a hydrodynamic code. A 0.6 solar mass white dwarf, composed of carbon and oxygen, and a 0.4 solar mass helium white dwarf are considered, both of low intrinsic luminosity. They are found to undergo periodic eruptions, which, for the CO white dwarf become regular only after about five cycles. The outbursts are similar in appearance to those of classical novae, although on a largely stretched time scale. The high-luminosity phase lasts for about 200 yr for both stars. The accretion continues for 4 x 10 exp 5 yr and 9 x 10 exp 5 yr, for the 0.6 and 0.4 solar mass WDs, respectively. Both stars lose mass following the outburst. While the more massive white dwarf ejects the entire accreted mass, the smaller, He WD retains some of the accreted material which is added to the core after being burnt into helium. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/172433 Bibcode: 1993ApJ...406..220S Keywords: Cataclysmic Variables; Dwarf Novae; Stellar Evolution; Stellar Mass Accretion; White Dwarf Stars; Binary Stars; Stellar Luminosity; Stellar Mass Ejection; Astrophysics; ACCRETION; ACCRETION DISKS; DIFFUSION; STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: BINARIES: CLOSE; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (5)

Gamma-ray bursts from stellar mass accretion disks around black holes

A cosmological model for gamma-ray bursts is explored in which the radiation is produced as a broadly beamed pair fireball along the rotation axis of an accreting black hole. The black hole may be a consequence of neutron star merger or neutron star-black hole merger, but for long complex bursts, it is more likely to come from the collapse of a single Wolf-Rayet star endowed with rotation ('failed' Type Ib supernova). The disk is geometrically thick and typically has a mass inside 100 km of several tenths of a solar mass. In the failed supernova case, the disk is fed for a longer period of time by the collapsing star. At its inner edge the disk is thick to its own neutrino emission and evolves on a viscous time scale of several seconds. In a region roughly 30 km across, interior to the accretion disk and along its axis of rotation, a pair fireball is generated by neutrino annihilation and electron-neutrino scattering which deposit approximately 10 exp 50 ergs/s.

Can we observe accreting, isolated neutron stars?

view Abstract Citations (126) References (69) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Can We Observe Accreting, Isolated Neutron Stars? Blaes, Omer ; Madau, Piero Abstract The present evaluation of the observability of isolated neutron stars (NSs) that accrete interstellar material, as sources of quiescent and transient UV and X-radiation gives attention to the solar neighborhood spatial and kinematic properties indicated by Monte Carlo simulations of 100,000 orbits in the Galactic potential. A semianalytic method which can swiftly reproduce the full kinematic properties of the local NS population is shown to yield excellent agreement with Monte Carlo results. An investigation is conducted of the emission properties of accreting NSs moving supersonically in dense atomic and molecular clouds. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/172240 Bibcode: 1993ApJ...403..690B Keywords: Neutron Stars; Stellar Mass Accretion; X Ray Sources; Computational Astrophysics; H Ii Regions; Interstellar Magnetic Fields; Molecular Clouds; Monte Carlo Method; Solar Neighborhood; Ultraviolet Radiation; Astrophysics; ACCRETION; ACCRETION DISKS; STARS: NEUTRON; STARS: STATISTICS; X-RAYS: BURSTS; X-RAYS: STARS full text sources ADS | data products SIMBAD (17)

An X-ray excited wind in Centaurus X-3

view Abstract Citations (33) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An X-Ray Excited Wind in Centaurus X-3 Day, C. S. R. ; Stevens, Ian R. Abstract We propose a new interpretation of the behavior of the notable X-ray binary source Centaurus X-3. Based on both theoretical and observational arguments (using EXOSAT data), we suggest that an X-ray excited wind emanating from the O star is present in this system. Further, we suggest that this wind is responsible for the mass transfer in the system rather than Roche-lobe overflow or a normal radiatively driven stellar wind. We show that the ionization conditions in Cen X-3 are too extreme to permit a normal radiatively driven wind to emanate from portions of the stellar surface facing toward the neutron star. In addition, the flux of X-rays from the neutron star is strong enough to drive a thermal wind from the O star with sufficient mass-flux to power the X-ray source. We find that this model can reasonably account for the long duration of the eclipse transitions and other observed features of Cen X-3. If confirmed, this will be the first example of an X-ray excited wind in a massive binary. We also discuss the relationship between the excited wind in Cen X-3 to the situation in eclipsing millisecond pulsars, where an excited wind is also believed to be present. Publication: The Astrophysical Journal Pub Date: January 1993 DOI: 10.1086/172205 Bibcode: 1993ApJ...403..322D Keywords: Neutron Stars; O Stars; Stellar Winds; X Ray Binaries; Exosat Satellite; Light Curve; Massive Stars; Stellar Mass Accretion; Stellar Systems; Astrophysics; STARS: BINARIES: CLOSE; STARS: PULSARS: GENERAL; STARS: INDIVIDUAL CONSTELLATION NAME: CENTAURUS X-3; STARS: MASS LOSS; X-RAYS: STARS full text sources ADS | data products SIMBAD (7)

Noise-driven radiative shocks. II - Further implications for the quasi-periodic oscillations of the AM Herculis objects

view Abstract Citations (22) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Noise-driven Radiative Shocks. II. Further Implications for the Quasi-periodic Oscillations of the AM Herculis Objects Wood, Kent S. ; Imamura, James N. ; Wolff, Michael T. Abstract The driven-shock model by Wolff et al. (1992) is extended and used to model the low-amplitude quasiperiodic oscillations (QPOs) driven by accretion noise in AM Her objects. The driven-shock model is discussed qualitatively with calculational details of the revised version. QPO-like features in the optical and X-ray are shown to be produced by bremsstrahlung-dominated shocks from accretion onto white dwarfs. These features are found to be consistent with the range of properties associated with the AM Her QPO sources. The bremsstrahlung-dominated shocks are shown to have linear responses for the conditions associated with QPO sources, and a luminosity expression for QPO sources is derived. The present analysis supports the shock-oscillation model for describing the optical QPOs from these objects. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171884 Bibcode: 1992ApJ...398..593W Keywords: Shock Wave Propagation; Stellar Mass Accretion; Stellar Oscillations; Stellar Radiation; White Dwarf Stars; Bremsstrahlung; Cyclotron Radiation; Stellar Luminosity; Stellar Models; X Ray Spectra; Astrophysics; RADIATION MECHANISMS: BREMSSTRAHLUNG; SHOCK WAVES; STARS: OSCILLATIONS; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (4) Related Materials (1) Part 1: 1958ApJ...127..194C

Properties of quasi-periodic oscillations in accreting magnetic white dwarfs

view Abstract Citations (29) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Properties of Quasi-periodic Oscillations in Accreting Magnetic White Dwarfs Wu, Kinwah ; Chanmugam, G. ; Shaviv, G. Abstract Previous studies of time-dependent accretion onto magnetic white dwarfs, in which the cooling was assumed to be due to bremsstrahlung emission, have shown that the accretion shock undergoes oscillations. However, when cyclotron cooling is also included, the oscillations are damped for sufficiently strong magnetic fields. Here we demonstrate that the oscillations can be sustained by accretion-fluctuation-induced excitations. The frequency of the QPOs are shown to increase quadratically with the magnetic field strength. We interpret the oscillations as a two-phase process in which bremsstrahlung cooling dominates in one half-cycle and cyclotron cooling in the other. Such a process may have very different consequences compared to a single-phase process where the functional form of the cooling is essentially the same throughout the cycle. If in the two-phase process damping occurs mainly in the cyclotron cooling half-cycle, there will be a universal effective damping factor which tends to suppress all oscillation modes indiscriminately. The oscillations of the accretion shock also could be a limit cycle process in which the system vacillates between two branches. Publication: The Astrophysical Journal Pub Date: September 1992 DOI: 10.1086/171782 Bibcode: 1992ApJ...397..232W Keywords: Accretion Disks; Bremsstrahlung; Stellar Magnetic Fields; Stellar Oscillations; White Dwarf Stars; Cyclotron Radiation; Harmonics; Luminosity; Stellar Mass Accretion; Astrophysics; ACCRETION; ACCRETION DISKS; HYDRODYNAMICS; STARS: MAGNETIC FIELDS; STARS: OSCILLATIONS; STARS: WHITE DWARFS full text sources ADS |