Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
An X-ray and optical study of the supernova remnant W44
We report the results of a 8000 s observation of the supernova remnantW44 using the ROSAT Position Sensitive Proportional Counter (PSPC). Theimage shows the same centrally peaked morphology observed by theEinstein IPC and contrasts with the shell-like radio morphology. Theeastern limb shows a lack of X-ray emission within the radio shell,probably due to the interaction between the Supernova Remnants (SNR) anda molecular cloud. No counterpart to the pulsar 1853 + 01 in W44 hasbeen detected, with LX less than 1.3 x 1032 ergs/sin the 0.2 to 2.4 keV band. The spectral analysis of the central part ofW44, combining EXOSAT ME and Einstein SSS data, shows that the shockedplasma has not reached ionization equilibrium. The best nonequilibriumfit to PSPC, ME, and SSS spectra gives Eta = 1051 ergscm-6, Ts = 107 K with Te =Ti, suggesting conditions are approaching ionizationequilibrium. There is no evidence of enhanced abundances of Mg, Si, S,or Fe. The variation of temperature and column density was obtainedregion by region using the PSPC and Einstein IPC. The temperature islargely uniform over the remnant, but strong column density variationsare found to be consistent with molecular clouds in the line of sight.An evaporation model with a two-phase interstellar medium structure ofclumps and interclump gas (White & Long 1991) can explain the X-raycentrally peaked morphology of W44. The clumps remaining behind a SNshock provide a reservoir of material, and evaporat e to increase thedensity of X-ray emitting gas in the interior of a SNR. The uniformtemperature distribution of W44 strongly supports the predictions ofthis model. In addition, mosaiced H alpha and (S II) images of W44,taken using the prime focus universal extragalactic instrument (PFUEI)camera on the Palomar 60 sec telescope, reveal the first discovery ofoptical filaments (both H alpha and (S II)) in the northwestern andsoutheastern portion of the remnant, within the X-ray emitting region.The optical filaments and the X-ray image showing locally brighteremission and clumps along the filaments suggest both are produced by theinteraction between the supernova shock front and regions of enhancedambient density.
| Evolved GK stars near the Sun. 2: The young disk population
From a sample of nearly 2000 GK giants a group of young disk stars withwell determined space motions has been selected. The zero point of theluminosity calibrations, both from the ultraviolet flux (modifiedStroemgren system) and that in the region of 4200 to 4900 A (DDOsystem), show a discontinuity of about a half magnitude at the border ofthe young disk and old disk domains. The population separation is basedon the space velocity components, which are also an age discriminant,with the population interface near 2 x 109 yr, based onmodels with convective overshoot at the core. This age corresponds togiant masses near 1.7 solar mass, near the critical mass separating theyoung stars that do not burn helium in degenerate cores from older starsthat do. Ten percent of both populations show CN anomalies in that thederived value of P(Fe/H) from CN (Cm) and fromFe(M1) differ by more than 0.1 dex and the weak and strong CNstars occur equally in the old disk but the weak CN stars predominate inthe young disk. Peculiar stars, where flux distortions affect theluminosity calibrations, are of the CH+(Ba II) and CH-(weak G band)variety and represent less than 1% of the stars in both populations. Theyoung disk giants are restricted to ages greater than about109 yr, because younger stars are bright giants orsupergiants (luminosity class 2 or 1), and younger than about 2 x109 yr, because the old disk-young disk boundary occurs near1.7 solar mass. The distribution of heavy element abundances, P(Fe/H),for young disk giants is both more limited in range (+/- 0.4 dex) and isskewed toward higher abundances, compared with the nearly normaldistribution for old disk giants. The distribution of (U,V) velocityvectors gives (U,V,W) and their dispersions = (+17.6 +/- 18.4, -14.8 +/-8.4, -6.9 +/- 13.0) and (+3.6 +/- 38.4, -20.7 +/- 27.5, -6.7 +/-17.3)km/s for young and old disk giants, respectively.
| Large and kinematically unbiased samples of G- and K-type stars. V - Evolved stars in the selected areas at + 15-deg declination
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990PASP..102..242E&db_key=AST
| Photoelectric radial velocities. IV. 528 7 to 10 mag stars in the +15degree selected areas.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971MNRAS.155....1G&db_key=AST
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Orion |
| Rektaszcenzió: | 05h12m20.79s |
| Deklináció: | +13°55'27.6" |
| Vizuális fényesség: | 8.505 |
| RA sajátmozgás: | -6.8 |
| Dec sajátmozgás: | -34.2 |
| B-T magnitude: | 9.766 |
| V-T magnitude: | 8.61 |
Katalógusok és elnevezések:
|
