The 2dF QSO Redshift Survey – VI. Measuring Λ and β from redshift-space distortions in the power spectrum     

P.J. Outram  Fiona Hoyle  T. Shanks  B.J. Boyle  S.M. Croom  N.S. Loaring  L. Miller  R.J. Smith 《Monthly notices of the Royal Astronomical Society》2001,328(1):174-184

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BRIGHTNESS VARIATIONS OF Mg Ib BRIGHT FEATURES     

Dara  H.C.  Koutchmy  S.  Zachariadis  Th.G.  Alissandrakis  C.E. 《Solar physics》2001,198(2):313-324

We study the temporal intensity variations of Mgib bright features and investigate the corresponding Hα velocity pattern. The network bright features are well visible in the continuum, in images averaged over the duration of the observations (130 min). We detected `flashing' bright features, which appear and disappear within two to five minutes, while the rest of the bright features undergo small variations of either their shape and/or their intensity. A power spectrum analysis reveals a 10-min oscillation for approximately half of the stable bright features. The 5-min oscillations are detected mainly at the network boundaries, where stable bright features are located, while 3-min oscillations coincide with few bright features, but are also quite intense inside the network cells. The majority of bright features are associated with Hα downflows. The downflow is very intense at the location of `flashing' bright features.  相似文献   

Obscured AGB Stars in the LMC     

Jacco Th. Van Loon  Albert A. Zijlstra  Patricia A. Whitelock  M.A.T. Groenewegen  Cecile Loup  Peter Te Lintel Hekkert  Norman R. Trams  L.B.F.M. Waters 《Astrophysics and Space Science》1997,255(1-2):403-404

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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   

A high speed near infrared photometer for lunar occultation studies     

Ashok  N. M.  Chandrasekhar  T.  Ragland  Sam  Bhatt  H. C. 《Experimental Astronomy》1994,4(3-4):177-188

A recently developed near infrared high speed photometer intended for lunar oc-cultation studies is described. The primary scientific objective is to reach milli arc second levels of angular resolution so that circumstellar structure of the occulted sources can be resolved. Near infrared sky brightness close to the lunar limb is also studied. Angular diameter derived from the observed occultation of IRC +20169 is presented and system performance discussed.  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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Prediction in Real Time of the 2000 July 14 Heliospheric Shock Wave and its Companions During the `Bastille' Epoch*     

Dryer  M.  Fry  C.D.  Sun  W.  Deehr  C.  Smith  Z.  Akasofu  S.-I.  Andrews  M.D. 《Solar physics》2001,204(1-2):265-284

Prediction of solar-generated disturbances and their three-dimensional propagation through interplanetary space continues to present a vitally important operational space weather forecasting objective. This paper presents the first successful real-time prediction of a series of major heliospheric shock waves at Earth, including the one from the 14 July 2000 (`Bastille Day') flare. An ensemble of three models and their predictions were distributed to a world-wide group of interested scientists as part of an informal Internet space weather forecast research program. Two of the models, STOA (Shock Time of Arrival) and ISPM (Interplanetary Shock Propagation Model), presently in operation by the US Air Force Weather Agency, provided predictions of shock arrival time (SAT) that were, respectively, 0.5 hours after and 3.7 hours before the observed arrival. The third model, HAFv.2 (Hakamada–Akasofu–Fry version 2.0) predicted a time 0.3 hours after the observed shock arrival time (14:37 UT, 15 July 2000). Of primary interest to this study is the third model, firstly in terms of its capability of propagating shocks through non-uniform solar wind conditions, and secondly, in terms of its ability to integrate multiple solar events and display them graphically along with the background solar wind. This latter capability was brought to bear on ten real-time-reported flares, some with CMEs (coronal mass ejections) that took place as companions to the Bastille flare during the period 7–15 July 2000. Some limited statistics are given regarding the three models' shock arrival prediction capability at Earth, as an extension of our earlier studies with this three model ensemble in the prediction of SAT. HAFv.2, however, was able to describe not only the ten events and their interaction as measured at Earth, but also at the spacecraft NEAR (orbiting the asteroid, Eros, at 1.8 AU), and CASSINI (en route, at 4.0 AU, to Saturn). Several important points are noted: (1) this epoch represents a small statistical sample that should be expanded; and (2) the three models, based on theory, empiricism, and simulations represent the state of the art that should presage a similar community process. This paper was presented earlier as an Invited Talk at the American Geophysical Union Fall Meeting, December 14–19, 2000, in San Francisco, CA, U.S.A.toward space weather objectives in the Sun-Earth domain. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014200719867  相似文献