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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 multiplicity survey of the ρ Ophiuchi molecular clouds
We present a volume-limited multiplicity survey with magnitude cutoff({m}K≤ 10.5 mag) of 158 young stellar objects locatedwithin or in the vicinity of the ρ Ophiuchi Dark Cloud. Withexception of eleven already well observed objects, all sources have beenobserved by us in the K-band with 3.5 m telescopes by using speckletechniques. The separation range covered by our survey is0.13''≤θ≤ 6.4'', where the lower limit is given by thediffraction limit of the telescopes and the upper limit by confusionwith background stars. The multiplicity survey is complete for fluxratios ≥ 0.1 (Δ{m}K≤ 2.5) at the diffractionlimit. After taking the background density into account the degree ofmultiplicity is 29.1%± 4.3% and thus only marginally higher thanthe value 23.5%± 4.8 % derived for the given separation range forthe main-sequence solar-like stars in the solar neighbourhood (Duquennoy& Mayor 1991). We discuss the implications of these findings.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| The X-ray emission from Young Stellar Objects in the ρ Ophiuchi cloud core as seen by XMM-Newton.
We observed the main core F of the ρ Ophiuchi cloud, an activestar-forming region located at d 140 pc, using XMM-Newton with anexposure of 33 ks. We detect 87 X-ray sources within the 30 arcmindiameter field-of-view of the EPIC imaging detector array. Wecross-correlate the positions of XMM-Newton X-ray sources with previousX-ray, infrared (IR), and optical catalogs: 25 previously unknown X-raysources are found from our observation; 43 X-ray sources are detected byboth XMM-Newton and Chandra; 68 XMM-Newton X-ray sources have 2MASSnear-IR counterparts. We show that XMM-Newton and Chandra havecomparable sensitivity for point source detection when the exposure timeis set to 30 ks for both. We detect X-ray emission from 7 Class Isources, 26 Class II sources, and 17 Class III sources. The X-raydetection rate of Class I sources is very high (64%), which isconsistent with previous Chandra observations in this area. We proposethat 15 X-ray sources are new class III candidates, which doubles thenumber of known Class III sources, and helps to complete the census ofYSOs in this area. We also detect X-ray emission from two young bonafide brown dwarfs, GY310 and GY141, out of three known in the field ofview. GY141 appears brighter by nearly two orders of magnitude than inthe Chandra observation. We extract X-ray light curves and spectra fromthese YSOs, and find some of them showed weak X-ray flares. We observedan X-ray flare from the bona fide brown dwarf GY310. We find as in theprevious Chandra observation of this region that Class I sources tend tohave higher temperatures and heavier X-ray absorptions than Class II andIII sources.Tables 1 and 2 are 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/429/963Appendices are only available in electronic form athttp://www.edpsciences.org
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are 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/413/1037
| A Multiplicity Survey of the ρ Oph Dark Cloud
Not Available
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| X-rays and regions of star formation: a combined ROSAT-HRI/near-to-mid IR study of the rho Oph dark cloud
We have obtained two deep exposures of the rho Oph cloud core regionwith the ROSAT High Resolution Imager. The improved position accuracy(1arcsec -6arcsec ) with respect to previous recent X-ray observations(ROSAT PSPC, and ASCA ) allows us to remove positional ambiguities forthe detected sources. We also cross-correlate the X-ray positions withIR sources found in the ISOCAM survey of the same region at 6.7 and 14.3mu m, in addition to sources (optical and IR) known from ground-basedobservations, which are young stars (T Tauri stars, with and withoutcircumstellar disks, and protostars). We thus obtain the best-studiedsample of X-ray emitting stars in a star-forming region (63 X-raysources detected, and 55 identified). We find that there is nostatistically significant difference between the X-ray luminosityfunctions of HRI-detected Class II and Class III sources, i.e., T Tauristars with and without disks, confirming that the contribution of thesedisks to X-ray emission (for instance by magnetic reconnection betweenthe star and the disk), or to X-ray absorption, must be small. X-rayvariability of T Tauri stars can be studied by comparing the HRI datawith the previously obtained PSPC data, but also using the fact thatsome HRI observations were done at different epochs. The resultingstatistics show that most of the sources are variable, and that theirvariability is consistent with a solar-like (hence magnetic) flareorigin. We use the information given both by the ISO CAM survey and byour HRI deep exposure to study the T Tauri star population of the rhoOph dense cores. We confirm that essentially all Class II and Class IIIsources (embedded T Tauri stars) are X-ray emitters, and that a strongcorrelation exists between their X-ray luminosity, LX, andtheir stellar luminosity, Lstar, withLX/Lstar ~ 10-4. Most of the new ISOCAM Class II sources are not detected, however, which we explain by thefact that their X-ray luminosities ``predicted'' on the basis of thiscorrelation are too faint to be detected by the HRI. We predict that ~40 unknown faint or embedded Class III sources remain to be discoveredin X-rays in the HRI/ISOCAM overlapping area, down to a limit ofLX ~ 3 x 1028 erg s-1. We show that thebulk of these unknown Class III sources should be made of low- to verylow-mass stars (Mstar <0.1-0.6 Msun). Prospectsfor future detections with XMM-Newton and Chandra are discussed. TableA1, Fig. A1, Table B1 and Fig. B1 are only available in the on-lineedition of the Journal (Table B1 is also available at the CDS).
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Herbig-Haro Objects in the \rho Ophiuchi Cloud
Using deep, narrow-band images of the main $\rho$ Oph dark cloudcentered on the wavelengths of H$\alpha$ and [S~II], we present evidencefor three new Herbig-Haro objects. This increases the total number inthe cloud to five. In addition, positions for 5 candidate Herbig-Haroobjects are given. Relatively high [S~II]/H$\alpha$ ratios indicate lowexcitation conditions for all of these nebulae. We list potentialexciting stars for each Herbig-Haro object and candidate by identifyingnearby young stellar objects with strong infrared excesses and/ormillimeter continuum emission. The location of most of these nebulaenear the cloud edges underscores the important role that extinction bydust plays in the $\rho$ Oph cloud in masking the presence ofHerbig-Haro objects. Among the newly identified Herbig-Haro objects is ajet-like string of emission nebulae emanating from the classical T Tauristar SR~4. [S~II] emission is also found coincident with a knot ofstrong molecular hydrogen emission associated with the highly-collimatedVLA~1623 molecular outflow. Indeed, the low excitation nature of all ofthe objects in our study, coupled with the high extinction of the cloud,suggests that a deep survey for shocked molecular hydrogen at$\lambda$=2.122 $\mu$m would be the best way to search for evidence ofstrong winds from the large population of young stellar objects in thecloud. (SECTION: Interstellar Medium and Nebulae)
| Infrared Point Sources Identified By Lunar Occultation Observations
We present a list of stars unresolved by lunar occultation observationsin the infrared K band. Theses stars may be useful as point spreadfunction calibrators for high angular resolution imaging observations.
| L'emission X des etoiles jeunes de type solaire.
Not Available
| 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.
| Detection of rotation modulation in Rho OPH dark cloud T Tauri stars
Brightness curves for nine T Tauri stars in the Rho Oph dark cloud arestudied by Fourier analysis. A periodic component is found for fivestars: Haro 1-1, Haro 1-8, Haro 1-14, S-R 9 and V2058 Oph show aperiodic variability with periods of 3.35, 14.58, 8.20, 6.54 and 6.90,respectively.
| 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
| The ratio of total to selective absorption in the rho OPH cloud.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974MNRAS.168..371W&db_key=AST
| Possible new members of a subgroup of the Scorpio-Centaurus association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..474G&db_key=AST
| Some Characteristics of the B and A Stars in the Upper Scorpius Complex
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...147.1003G&db_key=AST
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נושא הנחש |
| התרוממות ימנית: | 16h28m25.16s |
| סירוב: | -24°45'01.0" |
| גודל גלוי: | 7.525 |
| מרחק: | 75.019 פארסק |
| תנועה נכונה: | -49.9 |
| תנועה נכונה: | -63.1 |
| B-T magnitude: | 7.979 |
| V-T magnitude: | 7.563 |
קטלוגים וכינוים:
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