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Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
| A Spatially Complete ^13CO J = 1-0 Survey of the Orion A Cloud
We present the results of new ^13CO J = 1-0 observations of the Orion Amolecular cloud made with two 4 m telescopes at Nagoya University. Thearea observed, corresponding to l ~ 208 deg-215 deg and b ~ -20.5d to-18.0d, covers the full extent of this giant molecular cloud at a2.0′ grid spacing with a 2.7′ beam. The presentobservations provide the first complete coverage of the cloud in ^13COwith a reasonably high angular resolution relative to the cloud's size.In addition, the high velocity resolution of 0.1 km s^-1 allowed us toresolve velocity components of the ^13CO emission. The moleculardistribution is highly elongated along the Galactic plane and isfilamentary, as is consistent with previous molecular maps. The totalmolecular mass of the cloud is estimated to be ~5.4 x 10^4 M_ȯ. Byusing the velocity channel maps every 0.5 km s^-1, 39 individualfilamentary components have been identified, and their basic physicalquantities have been estimated. They typically are 4.8 pc in length, 1.4pc in width, and 660 M_ȯ in mass. We also find that thesefilamentary components are nearly in virial equilibrium.
| New massive X-ray binary candidates from the ROSAT Galactic Plane Survey. I. Results from a cross-correlation with OB star catalogues.
We report the discovery of several new OB/X-ray accreting binarycandidates. These massive systems were found by cross-correlating inposition SIMBAD OB star catalogues with the part of the ROSAT all-skysurvey located at low galactic latitudes (|b|<=20°) and selectingthe early type stars which apparently displayed the most significantexcess of X-ray emission over the `normal' stellar level. The presentsearch is restricted to stars earlier than B6 and X-ray luminosities>=10^31^erg/cm^2^/s. Follow-up optical and X-ray observations allowedto remove misidentified OB stars and spurious matches with interloperX-ray emitters (mostly active coronae) leaving five very likely newmassive X-ray binaries: the O7 star LS 5039 and the Be stars BSD 24-491, LS 992, LS 1698 and LS I +61 235. This latter source was alreadymentioned in an earlier paper. LS 1698 is the probable opticalcounterpart of the hard X-ray transient 4U 1036-56. These new candidateshave 0.1-2.4keV un-absorbed luminosities >=2x10^33^erg/cm^2^/sindicating an accreting neutron star or black hole. On the average theirsoft X-ray luminosities are comparable to those observed from hard X-raytransients in quiescence or from persistent low luminosity Be/X-raysources. The four Be stars have Balmer emission slightly less intensethan previously known systems showing strong outbursts. This suggeststhat the relative weakness of the circumstellar envelope may explain thelow luminosities to some extent. Two additional X-ray binary candidates,HD 161103 and SAO 49725 require further confirmation of their X-rayexcess. Their lower soft X-ray luminosities (1-5x10^32^erg/cm^2^/s)could qualify them as Be + accreting white dwarf systems. Four other Bstars in the Orion and Canis Major OB associations, HD 38087, HD 38023,HD 36262 and HD 53339 exhibit X-ray flux excesses in the range2-7x10^31^erg/cm^2^/s whose origin is unclear. Finally very soft X-rayemission was detected from HR 2875 suggesting the presence of anon-accreting white dwarf companion to the B5 star.
| A study of the Orion cometary cloud L1616
With its cometary appearance and a reflection nebula near its edgefacing some bright Orion stars, Lynds' cloud L1616 shows ample evidenceof being affected by one or more of these massive stars. To estimate itsmass and star formation efficiency, as well as to determine if it isgravitationally bound, we mapped this cloud in J=1-->0 transitions of^12CO and ^13CO. It is found that the distribution of the emission inthe line wings shows clear evidence for substantial mass motions. Also,the `virial' mass of the cloud is found to be five times the actualcloud mass determined from the ^13CO column density map. It is arguedthat this cloud has abnormally high star formation efficiency and ispossibly disintegrating. The morphology and the location of the cloudindicate that it is being affected by the star epsilon Orionis, which isalso (possibly) responsible for the cloud's unusual star formationefficiency. Over a range of values of the relevant parameters, the staris found to satisfy quantitatively the requirements of being the causeof the observed characteristics of the cloud.
| Far-Ultraviolet (912--1900 Angstrom ) Energy Distribution in Early-Type Main-Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..280C&db_key=AST
| Diffuse interstellar bands in Orion: The environment dependence of DIB strength
Four Diffuse Intersellar Bands (DIB) have been measured in 22 lines ofsight towards Orion and GMC214-13. The paper reports on the environmentdependence of DIB strength, using reddening, the total extinction in thevisual, and column densities of various forms of hydrogen as indicatorsof line of sight conditions. In lines of sight with small reddening,EB-V less than 0.08 mag, a weakening of lambda(6284) andlambda(5785) is found relative to reddening (= all matter), but noweakening relative to atomic + molecular hydrogen (= all neural matter).This probably implies that the DIB carriers are absent in the ionisedHII medium. At higher reddening, where a significant part of hydrogen isan molecular form, all DIBs in Orion decrease with increasingEB-V in a similar way as is known for the Taurus andOphiuchus dark clouds. In Taurus, where even in low reddened lines ofsight a significant part of hydrogen is in molecular form, lambda(6284)is weakened compared to diffuse medium values at lower reddening thanlambda (6196). In lines of sight towards the Orion Nebula, wheremolecular hydrogen is mostly dissociated, lambda(6284) is some 70%stronger, while lambda(6196) is a factor of 5 weaker than expected fromthe above dependence. The results are discussed in the context that thecarrier of the diffuse bands might be a large molecule in ionised form.The dissociation and ionisation state of hydrogen is used as anindicator of the UV field. The results above indicate that thelambda(6284) carrier is both ionised and destroyed by higher energyphotons than the lambda(6196) carrier, which is consistent with amolecular carrier.
| A Study of the Kinematics of the Local Dark Clouds
Not Available
| Far-ultraviolet stellar photometry: A field in Orion
Far-ultraviolet photometry for 625 objects in Orion is presented. Thesedata were extracted from electrographic camera images obtained duringsounding rocket flights in 1975 and 1982. The 1975 images were centeredclose to the belt of Orion while the 1982 images were centeredapproximately 9 deg further north. One hundred and fifty stars fell inthe overlapping region and were observed with both cameras. Sixty-eightpercent of the objects were tentatively identified with known starsusing the SIMBAD database while another 24% are blends of objects tooclose together to separate with our resolution. As in previous studies,the majority of the identified ultraviolet sources are early-type stars.However, there are a significant number for which no such identificationwas possible, and we suggest that these are interesting objects whichshould be further investigated. Seven stars were found which were brightin the ultraviolet but faint in the visible. We suggest that some ofthese are nearby white dwarfs.
| Infrared luminosity functions for the young stellar population associated with the L1641 molecular cloud
Results are reported of a deep near-IR imaging survey which samples 0.77sq deg of the L1641 star-forming complex and reaches 5 sigma limits at J(1.25 micron,), H (1.65 micron), and K (2.2 microns) of 16.8, 15.8, and14.7 mag, respectively. A population of about 1500 stars spreadthroughout the cloud, seven small aggregates comprised of 10-50 starswhose typical projected surface densities exceed that of the distributedpopulation by factors of 4-10, and a heretofore unknown, partiallyembedded dense cluster comprised of about 150 stars are identified.Analysis of the distribution of (J-H), (H-K), and (R-I) colors for thesegroups suggest that, in all cases, the stellar populations are dominatedby solar-type PMS stars which appear to contain a mix of objectsanalogous to weak-line T Tauri stars. The present observed luminosityfunctions are based on reddening-corrected J-band magnitude.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Polarization of stars in R-associations - Observational data
Polarimetric data are assembled for 95 stars that are illuminatingreflection nebulae. Most of these belong to 18 standard R-associations.The observed dependence of the percentage polarization P on wavelengthand color excess E(B-V) suggest that the unpolarized light ofR-association members may become polarized as it traverses an ensembleof dust grains aligned by a magnetic field which in some cases (Tau R2,Ori R1/R2, Sco R1, Cep R2) is intrinsic to the association. In certainR-associations the grain size is variable and the stochastic magneticfield component fluctuates on a scale of 10-30 pc.
| Molecular clouds associated with reflection nebulae. I - A survey of carbon monoxide emission
The paper presents 2.6 mm wavelength CO and (C-13)O observations of 130molecular clouds associated with reflection nebulae. Enhanced COemission was found in the vicinity of the illuminating star in abouthalf the objects studied. There is a tendency for the CO peak to beslightly displaced from the star. Many examples of peaks that appear toresult from heating of the cloud by the nearby star are found, whileothers appear to be associated with independent concentrations ofmaterial.
| A photometric study of the Orion OB 1 association. III - Subgroup analyses
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...36..497W&db_key=AST
| A photometric study of the Orion OB 1 association. I - Observational data.
A catalog of observational data is presented for stars in the region ofthe young stellar association Orion OB 1. Photoelectric observationsobtained in the uvby-beta and UBV systems are compiled along withprevious photoelectric and spectroscopic data for all these stars aswell as for several bright members of the association with availablephotometric indices. Mean weighted values are computed for thephotometric data and summarized in tables expected to be reasonablycomplete for association members earlier than spectral type A0.Membership criteria are derived, and qualitative membershipprobabilities summarized, for the 526 stars in the final program. Theanalytical procedures are discussed for association stars of B,intermediate, and AF types. Effects of the nebular environment andvarious calibrations of Balmer-line and four-color indices areconsidered for the determination of absolute magnitudes for the B-typestars.
| Interaction between the Barnard Loop Nebula and the interstellar magnetic field
New observations of the linear interstellar polarization of starlightare used to study the geometric structure of the interstellar magneticfield in the vicinity of the Barnard Loop Nebula in Orion. The observedcomplex field structure cannot be explained by a simple radial expansionof a conducting gaseous shell into an initially parallel field. Asatisfactory fit of the observations can be obtained by assuming thatthe interstellar gas in Orion is suspended in an interstellar 'magneticpocket'. It is suggested that the formation of the observed denseinterstellar clouds and very young stars in the Orion aggregate is aresult of the local structure of the interstellar magnetic field.
| Stars in reflection nebulae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..233R&db_key=AST
| A study of reflection nebulae.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..990V&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | אוריון |
| התרוממות ימנית: | 05h42m21.30s |
| סירוב: | -08°08'00.2" |
| גודל גלוי: | 8.878 |
| מרחק: | 346.021 פארסק |
| תנועה נכונה: | 0.9 |
| תנועה נכונה: | -0.4 |
| B-T magnitude: | 9.221 |
| V-T magnitude: | 8.907 |
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