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Signatures of Dynamical Star Formation in the Ophiuchus Association of Pre-Main-Sequence Stars
A sample of 58 probable members of the association of pre-main-sequencestars around the filamentary ρ Ophiuchi cloud is investigated. Usingastrometric proper motions from the UCAC-2 catalog and the convergentpoint method, the total heliocentric systemic velocity is estimated at19 km s-1, and the mean distance at 145 pc. A small,statistically insignificant difference between the geometric convergentpoint and the actual direction of velocity defined by the observedradial velocity implies a small, if any, rate of expansion of theassociation. The Ophiuchus association appears to have a considerabledepth, with half of the members lying within 15 pc of the center. Whenthe moving cluster distances are taken into account, the near-infraredMKs versus (J-Ks) H-R diagram reveals an apparentlarge spread of ages between 14 Myr and younger than 1 Myr. Most of theyoungest stars are located along a slightly curved strip just south ofthe densest cloud, extending in the east-west direction roughly alignedwith the central streamer of warm dust. The intersection of this stripwith a thin segment of shocked dust visible in the IRAS 12 μm map at(α,δ)=(16h31m,-24.5deg) ismarked with a small cluster of probably very young stars around ROXs43A. The large extent and depth of the association, the moderate rate ofexpansion, the spread in ages of about 14 Myr, and the alignment of veryyoung stars with the dusty streamer point at a dynamical mode of starformation in this region, scattered far and wide around the main core.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| 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.
| The interstellar reddening in front of globular clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87...65C&db_key=AST
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| Takýmyýldýz: | Akrep |
| Sað Açýklýk: | 16h16m53.38s |
| Yükselim: | -23°06'37.7" |
| Görünürdeki Parlaklýk: | 8.66 |
| Uzaklýk: | 99.404 parsek |
| özdevim Sað Açýklýk: | -5.9 |
| özdevim Yükselim: | -23.5 |
| B-T magnitude: | 9.21 |
| V-T magnitude: | 8.706 |
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