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Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| ASCA X-Ray Observations of the NGC 2023 and NGC 2024 Regions
This paper presents the properties of X-ray sources in the regions ofNGC 2023 and NGC 2024 observed with ASCA. We found 14 point-like sourcesin the NGC 2023 field. In the NGC 2024 field, on the other hand, wefound extended X-ray emission in the central dust lane of NGC 2024, andresolved 5 point-like sources around the nebula. From the positionalcoincidence and moderate column density of N_H ~ 1.6*E22 Hcm-2, the extended source is mostly attributable to anintegrated emission from X-ray emitting young stellar objects (YSOs)found with ROSAT. However, the plasma temperature of ~ 4 keV is higherthan the ROSAT results as well as those of usual YSOs. Possiblecounterparts have been found for the other resolved sources, except two;one has large absorption at low energies and the other has moderateabsorption. The plasma temperatures and luminosities from the pointsources, except for an O-type star zeta Ori and a star exhibiting X-rayflares, are estimated to be ~ 1-5 keV and1030.6-1031.5 erg s-1 in the 0.5-10.0keV energy band (assuming the distance of 400 pc), respectively. Wefound no X-ray peak at the position of a Class 0 protostar, NGC2023-MM1.
| X-Ray Flares from an Hα Emission-Line Star in the Orion Region, Kiso A0904-105
We analyzed ASCA data, including the reflection nebula NGC 2023, anddiscovered two X-ray flares from an Hα emission-line star, KisoA0904-105, located at ~ 30' to the southwest of NGC 2023. The separationtime between the two flares was ~ 4 hr. The temperatures of the firstand second flares reached (5-7)*E7 K and the luminositiesaround the flare peaks were ~ 1033 erg s-1(0.5-10.0 keV energy band, assuming the distance of 400 pc), which arecomparable to those of the giant X-ray flares from T Tauri stars. Afterthe flare peaks, X-ray intensity exhibited an exponential decay.Comparing the flares with those from T Tauri stars, we found that thephysical parameters in the flaring plasma were within the range of thoseobtained from T Tauri stars.
| X-Ray Observations of the Orion OB1b Association
We report on the broad-band X-ray images and spectra for the Orion OB1bassociation obtained with ASCA. More than forty X-ray sources weredetected in three fields, and about half of them have likely opticalcounterparts in the Guide Star Catalog. Their temperature and X-rayluminosities at the assumed distance of 450 pc are 4 keV and 1 x10^{{30}} --1 x 10^{{31}} erg s^{{-1}} in the total energy band (0.5--10keV), respectively. In one field covering the Horsehead Nebula and NGC2023, several X-ray sources were identified with known candidates forlow-mass pre--main-sequence stars, including V615 Ori. Among them, foursources are emission-line stars with X-ray emission. Some X-ray sourceswere also found in the chain of small reflection nebulositiesilluminated by OB association members near to epsilon Ori. The X-rayemission from sources having optical counterparts is consistent withthin thermal plasma of temperatures of 1--2 keV. X-ray emission frompossible extragalactic sources is also reported.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| The type of variability of Herbig Ae/Be stars
The paper presents a list of 23 Herbig Ae/Be stars and Herbig Ae/Be starcandidates, compiled on the basis of 2 to 8 years of observations in theStromgren photometric system. Results of the study show that spectraltype A0 separates the stars showing large variations in their brightnessfrom stars showing small variations, with the later spectral type starsbeing the more variable. The behavior of the stars in thecolor-magnitude diagram could be divided into three classes: (1) classR, in which there is a monotonic dependence of the color index on visualbrightness, (2) class CR, in which this dependence is not monotonic, and(3) class RB, in which there is no dependence. It was also found thatthe behavior of a star in the color-magnitude diagram is dependent noton the spectral type but on the size of the variation in brightness.
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| 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.
| Spectroscopic studies of stars in ORI OB1 /Belt/
MK spectral classifications are presented for 120 B- and A-type stars inthe Belt subgroup of the Ori OB1 association. Combined with otherpublished spectroscopic data, and the assumed absolute magnitudes givenby Schmidt-Kaler (1965) and Lesh (1979), a mean corrected distancemodulus of 8.56 + or - 0.11 is computed for the eastern region, whilefor the remainder of the Belt a modulus of 8.20 + or - 0.05 is derived.Several B9-A2 subgiants and A7-F0 main-sequence stars were observed inthe western and central regions of the Belt. The ages of these starsimply a spread in formation ages for these subgroups from about 1million yr to at least 10 million yr.
| Photometric studies of stars in ORI OB1 /belt/
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84.1846G&db_key=AST
| 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.
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