Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
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.
| Herbig-Haro Flows in Ophiuchus
We report the results of a new [S II] and nearby off-line, narrowbandcontinuum imaging survey of an approximately 0.5 deg2 area ofthe ρ Ophiuchi cloud core. Higher sensitivity and an improved pixelscale (0.37") over previous surveys has increased the inventory ofHerbig-Haro (HH) flows in the cloud core. We report 11 independentlydiscovered HH objects or newly discovered components of known HHobjects. Three previous candidate HH objects have been confirmed, sevennew highly probable, and an additional five possible HH objectcandidates have been identified. The approximate number of independentlydriven outflows in the ρ Ophiuchi cloud core approaches 50 when thenumber of HH flows detected in the present study is combined with thenumber of known CO outflows. The number of outflows exceeds the numberof known Class I/Class 0 objects in the same area by at least a factorof 2, leading to the conclusion that Class II and Class III objects mustalso be outflow drivers. There is direct evidence in these data forClass II and Class III HH flow drivers, although the lack of detectedemission down to the sources themselves precludes definitiveidentification of the great majority of the driving sources.
| 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
| A Multiplicity Survey of the ρ Oph Dark Cloud
Not Available
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| A Survey of Optical Jets and Herbig-Haro Objects in the rho Ophiuchi Cloud Core
We describe a deep narrowband [S ii] imaging survey of ~0.7 deg^2covering the rho Ophiuchi cloud core (L1688). We detect seven newjet/Herbig-Haro (HH) objects in our survey, of which three are newdetections and four confirm candidates from a recent survey by Wilkinget al. Together with the five previously known objects, this brings thetotal to 12 known jet/HH objects in the cloud. In addition to this, wepropose six new candidate HH objects. The most likely sources to powerthe new jet/HH objects appear to be optically visible stars; however, aconclusive association between the HH objects and pre-main-sequencestars is difficult, as several candidate driving sources lie in closevicinity of the new knots. Practically all of the HH objects are locatedon the perimeter of the cloud. The lack of optical emission toward thecenter of the cloud and the high spatial concentration of the youngestprotostars toward the densest regions strongly suggest that jets insidethe cloud are obscured from our view at optical wavelengths. Anear-infrared H_2 survey is required to penetrate into the cloud and tostudy the outflow activity in this extremely active star-forming region.
| 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)
| BVR Photometry of Six Pre-Main-Sequence Spectroscopic Binaries
Not Available
| UBV(RI)C photometric monitoring of Orion population stars in the Southern Hemisphere
UBV(RI)C photometry on a sample of southern T Tauri stars, selected fromthe Herbig and Bell (1988) catalog, is reported and four new candidates(AS 205, Wa Oph/2, Wa Oph/3, and Wa CrA/2) for rotational modulation aresingled out from the sample. The color trend for the stars showingvariability is considered. Typically, colors become redder when the staris fainter, complying with the general behavior observed in T Tauristars. This can be interpreted as due to the (variable) presence ofsurface inhomogeneities (either dark or bright) or, in some cases, itcould also be consistent with the hypothesis of variable circumstellarextinction. Estimates of gross spot properties (e.g., temperature andfilling factor) are derived for the four stars showing possibleperiodicity, from the amplitudes of the variations observed at differentwavelengths, by use of a simple blackbody model.
| 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.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Ofiuco |
| Ascensione retta: | 16h28m59.00s |
| Declinazione: | -24°32'16.8" |
| Magnitudine apparente: | 7.579 |
| Distanza: | 65.574 parsec |
| Moto proprio RA: | -74.6 |
| Moto proprio Dec: | -196.6 |
| B-T magnitude: | 8.491 |
| V-T magnitude: | 7.655 |
Cataloghi e designazioni:
|
