The β Cephei instability strip     

L. Deng  D.R. Xiong 《Monthly notices of the Royal Astronomical Society》2001,327(3):881-887

We carried out a series of linear stability analyses of the radial and low-degree non-radial p modes for stellar models with initial masses of     . The stellar models were computed by using convective overshoot distance     , 0.25 and 0.40  H _P. Our numerical results show that the β Cephei instability strip forms a horn-shaped region pointing upwards near the main sequence on the Hertzsprung–Russell diagram (HRD). The lower part of the instability strip for the radial modes join the zero-age main-sequence (ZAMS) at     , while the top of the instability strip extends up to     . The instability strip for the non-radial modes is even wider. The overall instability strip is dominated by the radial and non-radial fundamental modes. The first overtone (the radial-order index     is also pulsationally unstable. We have shown that the β Cephei stability is almost independent of the overshoot parameter d _over used for the stellar models, while it depends critically on the metal abundance. With decreasing metal abundance, the instability region shrinks and eventually disappears for     .  相似文献   

Starburst activity in a ROSAT narrow emission-line galaxy     

Katherine F. Gunn  I. M. MHardy  O. Almaini  T. Shanks  T. J. Sumner  T. W. B. Muxlow  A. Efstathiou  L. R. Jones  S. M. Croom  J. C. Manners  A. M. Newsam  K. O. Mason  S. B. G. Serjeant  M. Rowan-Robinson 《Monthly notices of the Royal Astronomical Society》2001,324(2):305-312

We present multiwaveband photometric and optical spectropolarimetric observations of the R =15.9 narrow emission-line galaxy R117_A which lies on the edge of the error circle of the ROSAT X-ray source R117. The overall spectral energy distribution of the galaxy is well modelled by a combination of a normal spiral galaxy and a moderate-strength burst of star formation. The far-infrared and radio emission is extended along the major axis of the galaxy, indicating an extended starburst.
On positional grounds, the galaxy is a good candidate for the identification of R117, and the observed X-ray flux is very close to what would be expected from a starburst of the observed far-infrared and radio fluxes. Although an obscured high-redshift QSO cannot be entirely ruled out as contributing some fraction of the X-ray flux, we find no candidates to K =20.8 within the X-ray error box, and so conclude that R117_A is responsible for a large fraction, if not all, of the X-ray emission from R117.
Searches for indicators of an obscured AGN in R117_A have so far proven negative; deep spectropolarimetric observations show no signs of broad lines to a limit of 1 per cent and, for the observed far-infrared and radio emission, we would expect 10 times greater X-ray flux if the overall emission were powered by an AGN. We therefore conclude that the X-ray emission from R117 is dominated by starburst emission from the galaxy R117_A.  相似文献   

Authors' Reply     

Kaare L. Rasmussen  Hans J. F. Olsen  Raymond Gwozdz  Evgeniy M. Kolesnikov 《Meteoritics & planetary science》2001,36(7):1001-1006

Abstract— Jull et al. propose an alternative interpretation of our depth vs. ¹⁴C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable.  相似文献   

High-temperature geothermal reservoir possibilities in Hungary     

L. Stegena  F. Horváth  K. Landy  Z. Nagy  J. Rumpler 《地学学报》1994,6(3):282-288

Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations.  相似文献   

Exposure age,terrestrial age and pre‐atmospheric radius of the Chinguetti mesosiderite: Not part of a much larger mass     

K. C. WELTEN  P. A. BLAND  S. S. RUSSELL  M. M. GRADY  M. W. CAFFEE  J. MASARIK  A. J. T. JULL  H. W. WEBER  L. SCHULTZ 《Meteoritics & planetary science》2001,36(7):939-946

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Noble gases in interplanetary dust particles,II: Excess helium‐3 in cluster particles and modeling constraints on interplanetary dust particle exposures to cosmic‐ray irradiation     

R. O. Pepin  R. L. Palma  D. J. Schlutter 《Meteoritics & planetary science》2001,36(11):1515-1534

Abstract— Measurements of He isotopes in cluster interplanetary dust particles (IDPs) from stratospheric dust collector L2009 reveal anomalous ³He/⁴He ratios comparable to those seen earlier, up to ～40x the solar wind ratio, in particles from the companion collector L2011. These overabundances of ³He in the L2009 samples are masked by much higher ⁴He contents compared to the L2011 particles, and are visible only in minor gas fractions evolved by stepwise heating at high temperatures. Cosmic‐ray induced spallogenic reactions are efficient producers of ³He. The majority of this paper is devoted to a detailed assessment of the possible role of spallation in generating the ³He excesses in these and other cluster IDPs. A model of collisional erosion and fragmentation during inward transit through the interplanetary dust environment is used to estimate space lifetimes of particles from asteroidal and Edgeworth–Kuiper Belt sources. Results of the modeling indicate that Poynting–Robertson orbital evolution timescales of IDPs small enough to elude destruction on their way to Earth from either location are far shorter than the cosmic‐ray exposure ages required to account for observed ³He overabundances. Grains large enough to have sufficiently long space residence times are fragmented close to their sources. An alternative to long in‐space exposure could be prolonged irradiation of particles buried in parent body regoliths prior to their ejection as IDPs. A qualitative calculation suggests, however, that collisional erosion of asteroidal upper‐regolith materials is likely to occur on timescales shorter than the > 1 Ga burial times needed for accumulation of spallogenic ³He to the levels seen in several cluster particles. In contrast, regoliths on Edgeworth–Kuiper Belt objects may be stable enough to account for the ³He excesses, and delivery of heavily pre‐irradiated IDPs to the inner solar system by short‐period Edgeworth–Kuiper Belt comets remains a possibility. A potential problem is that the expected associated abundances of spallation‐produced ²¹Ne appear to be absent, although here the present IDP data base is too sparse and for the most part too imprecise to rule out a spallogenic origin. Relatively short periods of pre‐ejection residence in asteroidal regoliths may be responsible for the curiously broad exposure age distributions reported for micrometeorites extracted from Greenland and sea‐floor sediments.  相似文献   

A detailed abundance analysis of the hot post-AGB star ZNG-1 in M10     

C.J. Mooney  W.R.J. Rolleston  F.P. Keenan  P.L. Dufton  D.L. Pollacco  H.R. Magee 《Monthly notices of the Royal Astronomical Society》2001,326(3):1101-1109

We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T _eff=26 500±1000 K and log  g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity.  相似文献   

The EVN-MarkIV VLBI Data Processor     

R. T. Schilizzi  W. Aldrich  B. Anderson  A. Bos  R. M. Campbell  J. Canaris  R. Cappallo  J. L. Casse  A. Cattani  J. Goodman  H. J. van Langevelde  A. Maccafferri  R. Millenaar  R. G. Noble  F. Olnon  S. M. Parsley  C. Phillips  S. V. Pogrebenko  D. Smythe  A. Szomoru  H. Verkouter  A. R. Whitney 《Experimental Astronomy》2001,12(1):49-67

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The Gulf of Maine boundary: Dropping anchor or setting a course?     

Ted L. McDorman  Phillip M. Saunders  David L. VanderZwaag 《Marine Policy》1985,9(2):90-107

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Profiles of spectral lines of an accretion ring around a Kerr black hole     

J. L. Zhang  S. P. Xiang  J. F. Lu 《Astrophysics and Space Science》1985,113(1):181-187

Profiles of spectral lines emitted from an accretion ring around an object with strong gravitational field should be affected by Doppler shift, gravitational redshift, and deflection of light. Taking these effects into account, precise line profile of a Keplerian ring around a Kerr black hole for a distant observer is obtained by solving the kinetic equation of photons.  相似文献