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Shocked Clouds in the Vela Supernova Remnant
Unusually strong high-excitation C I has been detected in 11 lines ofsight through the Vela supernova remnant (SNR) by means of UV absorptionline studies of IUE data. Most of these lines of sight lie near thewestern edge of the bright X-ray region of the SNR in a spatiallydistinct band approximately 1° by 4° oriented approximatelynorth-south. The high-excitation C I (denoted C I* and C I**) isinterpreted as evidence of a complex of shocked dense clouds interactingwith the SNR, because of the high pressures indicated in this region. Tofurther analyze the properties of this region of enhanced C I* and CI**, we present new HIRES-processed IRAS data of the entire Vela SNR. Atemperature map calculated from the HIRES IRAS data, based on atwo-component dust model, reveals the signature of hot dust at severallocations in the SNR. The hot dust is anticorrelated spatially withX-ray emission, as would be expected for a dusty medium interacting witha shock wave. The regions of hot dust are strongly correlated withoptical filaments, supporting a scenario of dense clouds interior to theSNR that have been shocked and are now cooling behind the supernovablast wave. With few exceptions, the lines of sight to the stronghigh-excitation C I pass through regions of hot dust and opticalfilaments. Possible mechanisms for the production of the unexpectedlylarge columns of high-excitation C I are discussed. Dense clouds on theback western hemisphere of the remnant may explain the relatively lowX-ray emission in the western portion of the Vela SNR due to the slowerforward shock velocity in regions where the shock has encountered thedense clouds. An alternate explanation for the presence of ground-stateand excited-state neutrals, as well as ionized species, along the sameline of sight is a magnetic precursor that heats and compresses the gasahead of the shock.
| FUSE Observations of Highly Ionized Gas in the Vela Supernova Remnant
We present Far Ultraviolet Spectroscopic Explorer (FUSE) data on O VIabsorption lines observed toward nine stars behind the Vela supernovaremnant (SNR). The O VI observations are compared with InternationalUltraviolet Explorer (IUE) observations of C IV absorption toward thesame stars. All of these stars are B stars, which generally have complexcontinua, making the extraction of absorption lines difficult. However,four of the stars, HD 72088, HD 72089, HD 72350, and HD 72537, are rapidrotators (vsini>~150 km s-1), making the derivation ofabsorption column densities much easier. We present O VI and C IV columndensities for the ``main component'' (i.e., the low-velocity component)for these stars. In the FUSE spectra of three of the rapid rotators (HD72088, HD 72089, and HD 72537) we find high-velocity components of O VIat ~150 km s-1 that we attribute to the SNR shock. HD 72350has very strong H2 absorption, which obscures any possiblehigh-velocity O VI absorption. To detect the high-velocity O VIabsorption in HD 72088 requires employing a technique for removing theH2 line at 1032.35 Å (121.6 km s-1 relativeto O VI). The O VI data are consistent with steady radiative shockmodels with vs~150 km s-1, but we do not detect CIV at the same velocities. Instead we find high-velocity C IV at lowervelocities (~100 km s-1). We discuss the implications of ourresults for models of the evolution of the Vela SNR.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| The VELA star cloud. III - The B8 to A0 stars and interstellar reddening
The present discussion of intermediate band and H-beta observations of360 HD stars B8-A0 in Vela, and all of the CPD stars in a small adjacentregion, notes that the interstellar absorption in both cases can beunderstood as a combination of three absorbing clouds of 1 kpc-A(V) =1.5, 0.5, and 0.17. The major difference in the two environments is thepresence of numerous T Tauri stars in Taurus. Several clusters in theVela region are discussed.
| Hyades and Sirius supercluster members brighter than magnitude (V) 7.1. II - Right ascension six to twelve hours
The present star sample is contained in the Bright Star Catalogue andits Supplement, augmented with a further supplement of 788 stars foundduring various observing programs over the past 40 years. Accurate,four-color and H-beta, or (RI), photometry is available for most of thesupercluster members. The criteria for membership are the comparisons ofthe proper motion, radial velocity, and luminosity obtained from thesupercluster parameters with the observed motions and the luminosityderived from the photometric parameters. New proper motions, based onall available catalogs, have been derived for the additional 788 starsdiscussed here, as well as all supercluster members.
| High-resolution IUE observations of interstellar absorption lines in the VELA supernova remnant
Ultraviolet spectra of 45 stars in the vicinity of the Vela supernovaremnant were recorded by the short-wavelength echelle spectrographaboard the International Ultraviolet Explorer (IUE). Over one-third ofthe stars show interstellar absorption lines at large radial velocities(greater than 60 km/s). The mapping of these high-velocity components inthe sky suggests the motions are chaotic, rather than from a coherentexpansion of the remnant material. In accord with earlier conclusionsfrom Copernicus data, the gas at high velocity exhibits higher thannormal ionization and shows substantially less depletion of nonvolatileelements than normal interstellar material at low velocities. Relativelystrong lines from neutral carbon in the two excited fine-structurestates indicate that the neutral clouds within the remnant have hadtheir pressures enhanced by the passage of the blast wave from thesupernova. Also, the remnant seems to show a significant enhancement inthe abundances of low-velocity Si IV, C IV, and N V over those found inthe general interstellar medium.
| The VELA star cloud. II - Early-type stars and long-period Cepheids near the VELA pulsar
Intermediate band, H-beta and RI observations of some 200 stars andthree Cepheids in a small region centered on the Vela pulsar have shownthe presence of additional members of the Vela sheet (450 pc), as wellas two more distant associations, Vel OB1 (800 pc) and Vel OB2 (1800pc). Vel OB2, which may be only some 5-million yr old, probably containsSW (23.4 d), RZ (20.4 d), and SX (19.6 d) Vel. All three Cepheids havean overabundance of metals, relative to the sun, if the photometricindices are abundance dependent only. The luminosities of the threeCepheids, plus AH Vel in the Vela sheet and two other southern Cepheidsdiscussed previously, all based on an independent photometric luminositycalibration, do not indicate a need for a major revision of the zeropoint of the period-luminosity relation.
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