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Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be Stars
Using the three-telescope IOTA interferometer on Mount Hopkins, wereport results from the first near-infrared (λ=1.65 μm)closure-phase survey of young stellar objects (YSOs). These closurephases allow us to unambiguously detect departures from centrosymmetry(i.e., skew) in the emission pattern from YSO disks on the scale of ~4mas, expected from generic ``flared disk'' models. Six of 14 targetsshowed small, yet statistically significant nonzero closure phases, withlargest values from the young binary system MWC 361-A and the(pre-main-sequence?) Be star HD 45677. Our observations are quitesensitive to the vertical structure of the inner disk, and we confrontthe predictions of the ``puffed-up inner wall'' models of Dullemond,Dominik, & Natta (DDN). Our data support disk models with curvedinner rims because the expected emission appears symmetricallydistributed around the star over a wide range of inclination angles. Incontrast, our results are incompatible with the models possessingvertical inner walls because they predict extreme skewness (i.e., largeclosure phases) from the near-IR disk emission that is not seen in ourdata. In addition, we also present the discovery of mysterious H-band``halos'' (~5%-10% of light on scales 0.01"-0.50") around a few objects,a preliminary ``parametric imaging'' study for HD 45677, and the firstastrometric orbit for the young binary MWC 361-A.
| The Multiple System HD 27638
We report spectroscopic observations of HD 27638 B, the secondary in avisual binary in which the physically associated primary (separation~19") is a B9 V star. The secondary shows strong Li λ6708absorption, suggesting youth, and has attracted attention in the past asa candidate post-T Tauri star, although this has subsequently been ruledout. It was previously known to be a double-lined spectroscopic binary(F8+G6) with a period of 17.6 days and to show velocity residualsindicating a more distant massive third companion with a period of atleast 8 yr. Based on our radial velocity measurements covering more thantwo cycles of the outer orbit, along with other measurements, we derivean accurate triple orbital solution giving an outer period of9.447+/-0.017 yr. The third object is more massive than either of theother two components of HD 27638 B but is not apparent in the spectra.We derive absolute visual magnitudes and effective temperatures for thethree visible stars in HD 27638. Isochrone fitting based on thoseproperties gives an age of 200+/-50 Myr for the system. We also infer aninclination angle of ~53.3d for the inner orbit of HD 27638 B. We detecta near-infrared excess in HD 27638 B, which we attribute to the thirdstar being a close binary composed of late-type stars. This explains itslarge mass and lack of a visible signature. Modeling of this excessallows us to infer not only the masses of the components of the unseencompanion but also the inclination angle of the outer orbit (~73°).The HD 27638 system is thus at least quintuple.
| 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
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Rotation periods of Post-T Tauri stars in Lindroos systems
We present a rotational study of Post-T Tauri stars (PTTSs) in Lindroossystems, defined as binaries with early type primaries on themain-sequence (MS) and late-type secondaries on the pre-main-sequence(PMS) phase. The importance of this study in comparison with previousones is that the Lindroos sample is not X-ray selected so we avoid apossible bias towards fast rotators. In this preliminary study we havemonitored eleven stars in the UBVRI bands during two campaigns of tenconsecutive nights each. Eight of the observed PTTSs show periodicmodulations in their lightcurves and the derived periods range from 1.9d to 8.0 d. The comparison of these results with theoretical rotationaltracks based on disk-star locking theory shows that star-disk decouplingtimes of 1-20 Myr could reproduce the rotational properties of thetargets, assuming an initial rotation period of 8 d and a mass of 1Mȯ. We have studied the rotation-activity relations ofLindroos PTTSs and compared them with those found in other groups of PMSand zero-age main-sequence (ZAMS) 1 Mȯ stars. TheLindroos sample displays activity-rotation relations very similar tothose found in TTSs. It contains a mixture of very active stars, withLX/Lbol ratios close to the saturation level of-3, and less active (unsaturated) stars. This could be the result ofdifferent star-disk decoupling times. Future monitoring of a larger andunbiased sample of PTTS will be important to confirm the significance ofthese results.Based on observations collected at Cerro Tololo Inter-AmericanObservatory and the European Southern Observatory, La Silla, underproject 66.C-0119(B).
| Evidence for wind and accretion in the Herbig Be star HD 100546 from FUSE observations
We present the first far-UV spectra of the Herbig Be star HD100546, observed by the Far Ultraviolet Spectroscopic Explorer(FUSE) as part of the Circumstellar Disks team program. We identifiedand analyzed numerous narrow absorption lines of circumstellar origin.Intense, broad and fairly asymmetric emission lines of C II, C III, O VIand S II were also detected, spanning temperatures up to 3×105 K. Comparison of the spectra recorded two years apartreveals strong spectral variations, not only in the emission lines butalso in the circumstellar lines of N I, N II, O I, Ar I and Fe II. Thevarying absorption lines of N I and O I exhibit the largest velocitywidth, from -200 to +320 km s-1, relative to the star'srest-frame. Variations on a timescale of an hour occurred only in the NI resonance triplet and O I (1D) lines. The spectroscopicvariability highlighted by these two observations and the line profileanalysis reveal signatures of both outflow and infall processes, whichappear to be related in this system. We suggest that these spectralsignatures originate in a stellar magnetosphere, which likely interactswith the innermost part of the star's circumstellar disk. Thisinterpretation can account for the main features observed in thespectrum of HD 100546: variable emission and absorption lines as well assuspected continuum variation.
| SCUBA observations of dust around Lindroos stars: evidence for a substantial submillimetre disc population
We have observed 22 young stars from the Lindroos sample at 850 μmwith SCUBA on the James Clerk Maxwell Telescope to search for evidenceof dust discs. Stars in this sample are the less massive companions ofB-type primaries and have well-defined ages that are 10- 170 Myr; i.e.they are about to, or have recently arrived on the main sequence. Dustwas detected around three of these stars (HD 112412, 74067 and 99803B).The emission around HD 74067 is centrally peaked and is approximatelysymmetrically distributed out to ~70 arcsec from the star. This emissionarises from either a two-component disc, one circumstellar and the othercircumbinary with dust masses of 0.3 and <27 M⊕,respectively, or an unrelated background object. The other twodetections we attribute to circumsecondary discs with masses of 0.04 and0.3 M⊕. We were also able to show that a circumprimarydisc is present around HD 112413 with a similar mass to that around thecompanion HD 112412. Cross-correlation of our sample with the IRAScatalogues only showed evidence for dust emission at 25 and 60 μmtoward one star (HD 1438); none of the submillimetre detections wereevident in the far-infrared data implying that these discs are cold(>40 K assuming β= 1). Our submillimetre detections are some ofthe first of dust discs surrounding evolved stars that were not detectedby IRAS or ISO and imply that 9-14 per cent of stars could harbourpreviously undetected dust discs that await discovery in unbiased sub-mmsurveys. If these discs are protoplanetary remnants, rather thansecondary debris discs, dust lifetime arguments show that they must bedevoid of small <0.1 mm grains. Thus it may be possible to determinethe origin of these discs from their spectral energy distributions. Thelow inferred dust masses for this sample support the picture thatprotoplanetary dust discs are depleted to the levels of the brightestdebris discs (~1 M⊕) within 10 Myr, although if theextended emission of HD 74067 is associated with the star, this wouldindicate that >10 M⊕ of circumbinary material canpersist until ~60 Myr and would also support the theory that T Tauridiscs in binary systems are replenished by circumbinary envelopes.
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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.
| Statistics of spectroscopic sub-systems in visual multiple stars
A large sample of visual multiples of spectral types F5-M has beensurveyed for the presence of spectroscopic sub-systems. Some 4200 radialvelocities of 574 components were measured in 1994-2000 with thecorrelation radial velocity meter. A total of 46 new spectroscopicorbits were computed for this sample. Physical relations are establishedfor most of the visual systems and several optical components areidentified as well. The period distribution of sub-systems has a maximumat periods from 2 to 7 days, likely explained by a combination of tidaldissipation with triple-star dynamics. The fraction of spectroscopicsub-systems among the dwarf components of close visual binaries withknown orbits is similar to that of field dwarfs, from 11% to 18% percomponent. Sub-systems are more frequent among the components of widevisual binaries and among wide tertiary components to the known visualor spectroscopic binaries - 20% and 30%, respectively. In triple systemswith both outer (visual) and inner (spectroscopic) orbits known, we findan anti-correlation between the periods of inner sub-systems and theeccentricities of outer orbits which must be related to dynamicalstability constraints. Tables 1, 2, and 6 are only available inelectronic form at the 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/382/118
| The long-period companions of multiple stars tend to have moderate eccentricities
We examined the statistics of an angle gamma between the radius vectorof a visual companion of a multiple star and the vector of its apparentrelative motion in the system. Its distribution f(gamma ) is related tothe orbital eccentricity distribution in the investigated sample. Wefound that for the wide physical subsystems of the 174 objects from theMultiple Star Catalogue f(gamma ) is bell-shaped. The Monte-Carlosimulations have shown that our f(gamma ) corresponds to the populationof the moderate-eccentricity orbits and is not compatible with thelinear distribution f(e)=2e which follows from stellar dynamics andseems to hold for wide binaries. This points to the absence of highlyelongated orbits among the outer subsystems of multiple stars. Theconstraint of dynamical stability of triple systems is not sufficient toexplain the ``rounded-off'' outer orbits; instead, we speculate that itcan result from the angular momentum exchange in multiple systems duringtheir early evolution.
| EXPORT: Optical photometry and polarimetry of Vega-type and pre-main sequence stars
This paper presents optical UBVRI broadband photo-polarimetry of theEXPORT sample obtained at the 2.5 m Nordic Optical Telescope. Thedatabase consists of multi-epoch photo-polarimetry of 68pre-main-sequence and main-sequence stars. An investigation of thepolarization variability indicates that 22 objects are variable at the3sigma level in our data. All these objects are pre-main sequence stars,consisting of both T Tauri and Herbig Ae/Be objects while the mainsequence, Vega type and post-T Tauri type objects are not variable. Thepolarization properties of the variable sources are mostly indicative ofthe UXOR-type behaviour; the objects show highest polarization when thebrightness is at minimum. We add seven new objects to the class of UXORvariables (BH Cep, VX Cas, DK Tau, HK Ori, LkHα 234, KK Oph and RYOri). The main reason for their discovery is the fact that our data-setis the largest in its kind, indicating that many more young UXOR-typepre-main sequence stars remain to be discovered. The set of Vega-likesystems has been investigated for the presence of intrinsicpolarization. As they lack variability, this was done using indirectmethods, and apart from the known case of BD+31o643, thefollowing stars were found to be strong candidates to exhibitpolarization due to the presence of circumstellar disks: 51 Oph,BD+31o643C, HD 58647 and HD 233517. Table A1 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/564
| Optical spectra of five UX Orionis-type stars
We present in this paper several high resolution (R = 27 000) spectra offive UXORs (UX Ori, CQ Tau, BF Ori, RR Tau, WW Vul), which cover theentire visual range, from 3900 to about 8700 Å. There are between4 and 7 spectra per star, obtained over a time interval of two years.Simultaneous or quasi-simultaneous photometric observations were alsoobtained at the Crimean Astrophysical Observatory. The complete, reducedand normalized spectra are available in electronic form. We show foreach star a selection of the most interesting lines, and the fullspectrum of UX Ori computed by averaging the spectra obtained when thestar was at maximum light. For UX Ori we show also the syntheticspectrum and provide an identification of most of the lines. The spectraare too sparse to form true time sequences; however, they provide anextremely useful database for studies of UX Ori-type stars. We discussbriefly the main features of the spectra. We show that they contain manytime-stable photospheric lines that can be described to a goodapproximation by the synthetic spectra of normal A stars with log g =3.5 - 4 and we derive for each star effective temperature, gravity androtational velocity. We examine the time variability of selected linesand study their connection with the photometric activity of the stars.Two different types of spectral variability are identified. One iscommon to all stars with circumstellar (CS) gas and is caused byperturbations of the physical and kinematic conditions of the emittingregion. There is no correlation between this type of activity and thebrightness variations of the star. On the contrary, a second type ofspectral variability correlates well with the brightness variations andis very likely connected with the screening effect of an opaque dustcloud which sporadically intersects the line of sight. This type ofvariability has been observed in its simplest form in one of the RR Tauspectra, where the equivalent width of the forbidden line [O I] 6364Å increased by a factor of about three as the star faded byapproximately the same amount. Based on observations made with theNordic Optical Telescope, operated on the island of La Palma jointly byDenmark, Finland, Iceland, Norway, and Sweden, in the SpanishObservatorio Roque de los Muchachos of the Instituto de Astrofisica deCanarias. Figures 2, 3, 4a-c,e, and 5 are only available in electronicform at http://www.edpsciences.org
| Binary systems with post-T Tauri secondaries
The identification of post-T Tauri (pTT) stars selected throughspectroscopic criteria by Pallavicini et al. (\cite{Pallavicini92}) andby Martín et al. (1992) among the candidates belonging to visualbinary systems is revisited in the present paper by studying theirposition in the HR diagram. These stars belong to the so-called Lindroosbinary sample (Lindroos \cite{Lindroos85}), i.e. to systems withearly-type primaries and late-type companions. If these binaries arephysical and not simply optical pairs, similar ages must be found forthe early-type primary and the late-type component of each system. Theages of these systems have been derived by Lindroos in 1986, by usingcalibrations of the uvbyβ indices. In this paper, we revisit theseages through the position of these stars among new evolutionary tracksin the HR diagram for pre- and post-main sequence stars. We derive newestimations of the ages of each system component, as well as theirmasses, using parallaxes of the early-type component derived fromHipparcos data and by forcing the late-type companion to be at the samedistance. Teff and log g of the early-type components havebeen computed using the calibrations of two independent photometricsystems: the uvbyβ photometry and the Geneva system. TheTeff of the late-type stars have been determined by usingvarious calibrations of several photometric systems: uvbyβ, UBV andVRI, in order to determine the uncertainties and systematic errors onthese parameters and consequently on the ages. Differences in the agesand masses obtained by using various sources of recent evolutionarymodels are considered and discussed. The consistency of the age of thelate type component with that of its early type primary is examined; thevalidity of this criterion for a selection of physical pairs isdiscussed. The accuracy of the observational and theoretical data arenot sufficient to assign stringent values to the age for several of theexamined systems. Nevertheless, in spite of the large error bars, wehave established that we could select a number of systems which,according to their position in the HR diagram, may be physicallyassociated. The selection of possible physically bounded systemsobtained with the present approach and that made by Pallavicini et al.(\cite{Pallavicini92}) or Martín et al. (1992) on the basis ofspectroscopic criteria are not always coincident. Spectroscopiccriteria, for example the presence of a strong Li feature, are morestringent conditions than that of coherent ages of primaries andsecondaries; however the Li I 6708 doublet is expected to fade in thelatest stages of the pre-main sequence life of a star, so that the``oldest" pTTs may not be detected by spectroscopy only. The differentresults so obtained are discussed for each system and we conclude thatthe present approach may be used as a powerful criterion to select newpTT candidates in visual binaries to be observed and analyzed with highresolution spectrographs and to select candidates that have almostreached the main sequence. Partly based on data from the ESA Hipparcosastrometric satellite. Tables 2, 5, 7 and 9 are only available inelectronic form at the 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/379/162
| New spectroscopic components in multiple systems. IV.
New close sub-systems are reported and studied in eight visual multiplesystems. Elements of one double-lined and eight single-linedspectroscopic orbits are given. Magnitudes, colors, spectral types andmasses of individual components are estimated by combining all availabledata. The visual secondary component of the young binary HD 27638 is adouble-lined pair of G-type dwarfs on a 17-day orbit with an unseen butmassive (>1.2 Msun) spectroscopic tertiary on an 8-yearorbit. The invisible secondary of HD 28271A is also massive, but it isnot seen, probably because of a high luminosity of the primary - an F7star with fast axial rotation and an active chromosphere which evolvesoff the Main Sequence. Two additional companions are found in the visualtriple system HD 179484. Table 4 is only 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/374/227
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| EXPORT: Near-IR observations of Vega-type and pre-main sequence stars
We present near-IR JHK photometric data of a sample of 58 main-sequence,mainly Vega-type, and pre-main sequence stars. The data were takenduring four observing runs in the period May 1998 to January 1999 andform part of a coordinated effort with simultaneous optical spectroscopyand photo-polarimetry. The near-IR colors of the MS stars correspond inmost cases to photospheric colors, although noticeable reddening ispresent towards a few objects, and these stars show no brightnessvariability within the observational errors. On the other hand, the PMSstars show near-IR excesses and variability consistent with previousdata. 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-strastg.fr/cgi-bin/qcat?J/A+A/365/110
| X-ray emission from Lindroos binary systems
We present a study of the X-ray emission from binary systems extractedfrom the Lindroos catalogue (Lindroos 1986) based on the ROSAT All-Skysurvey as well as ROSAT PSPC and HRI pointings. The studied sampleconsists of visual binary systems comprised of early-type primaries andlate-type secondaries. The ages of the systems were determined byLindroos (1985) from uvbybeta photometry of the primaries. These agesrange between 33 and 135 Myr, so if the late-type secondaries arephysically bound to the early-type primaries, they could be Post-T Tauristars (PTTS). We have found strong X-ray emission from severalsecondaries. This fact together with their optical and IR data, makethem bona fide PTTS candidates. We have also detected X-ray emissionfrom several early-type primaries and, in particular, from most of thelate-B type stars. Because their HRI hardness ratios are similar tothose from resolved late-type stars, the presence of an unresolvedlate-type companion seems to be the cause of this emission.
| Mapping the contours of the Local bubble: preliminary results
We present preliminary results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,taking advantage of Hipparcos stellar distances. Equivalent widths ofthe NaI D-line doublet at 5890 Å are presented for thelines-of-sight towards some 143 new target stars lying within 300 pc ofthe Sun. Using these data which were obtained at the Observatoire deHaute Provence, together with previously published NaI absorptionmeasurements towards a further 313 nearby targets, we present absorptionmaps of the distribution of neutral gas in the local interstellar mediumas viewed from 3 different galactic projections. In particular, thesemaps reveal the Local Bubble region as a low neutral densityinterstellar cavity in the galactic plane with radii between 65-250 pcthat is surrounded by a (dense) neutral gas boundary (or ``wall''). Wehave compared our iso-column contours with the contours derived bySnowden et al. (\cite{snowden98}) using ROSAT soft X-ray emission data.Consistency in the global dimensions derived for both sets of contoursis found for the case of a million degree hot LB plasma of emissivity0.0023 cm(-6) pc with an electron density of 0.005 cm(-2) . We havedetected only one relatively dense accumulation of cold, neutral gaswithin 60 pc of the Sun that surrounds the star delta Cyg, and note thatthe nearest molecular cloud complex of MBM 12 probably resides at thevery edge of the Local Bubble at a distance of ~ 90 pc. Our observationsmay also explain the very different physical properties of the columnsof interstellar gas in the line-of-sight to the two hot stars epsilonCMa and beta CMa as being due to their locations with respect to theBubble contours. Finally, in the meridian plane the LB cavity is foundto be elongated perpendicularly to the Gould's Belt plane, possiblybeing ``squeezed'' by the expanding shells of the Sco-Cen andPerseus-Taurus OB associations. Tables 1 and 2 are also available inelectronic form at the CDS (Strasbourg) via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Polarizing Power of the Interstellar Medium in Taurus
We present a study of the polarizing power of dust in cold dense regions(dark clouds) compared with that of dust in the general interstellarmedium (ISM). Our study uses new polarimetric, optical, and spectralclassification data for 36 stars to carefully study the relation betweenpolarization percentage (p) and extinction ( AV ) in theTaurus dark cloud complex. We find two trends in our p-AVstudy: (1) stars that are background to the warm ISM show an increase inp with AV , and (2) the percentage of polarization of starsthat are background to cold dark clouds does not increase withextinction. We detect a break in the p-AV relation at anextinction of 1.3+/-0.2 mag, which we expect corresponds to a set ofconditions where the polarizing power of the dust associated with theTaurus dark clouds drops precipitously. This break point placesimportant restrictions on the use of polarimetry in studyinginterstellar magnetic fields.
| MSC - a catalogue of physical multiple stars
The MSC catalogue contains data on 612 physical multiple stars ofmultiplicity 3 to 7 which are hierarchical with few exceptions. Orbitalperiods, angular separations and mass ratios are estimated for eachsub-system. Orbital elements are given when available. The catalogue canbe accessed through CDS (Strasbourg). Half of the systems are within 100pc from the Sun. The comparison of the periods of close and widesub-systems reveals that there is no preferred period ratio and allpossible combinations of periods are found. The distribution of thelogarithms of short periods is bimodal, probably due to observationalselection. In 82\% of triple stars the close sub-system is related tothe primary of a wide pair. However, the analysis of mass ratiodistribution gives some support to the idea that component masses areindependently selected from the Salpeter mass function. Orbits of wideand close sub-systems are not always coplanar, although thecorresponding orbital angular momentum vectors do show a weak tendencyof alignment. Some observational programs based on the MSC aresuggested. Tables 2 and 3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Evidence for dust around POST T Tauri stars
Post T Tauri stars are young stars which, although older than classicalT Tauri stars, have not yet reached the main sequence. We report thedetection of a far-infrared excess in binary systems consisting of apost T-Tauri secondary and a B-type primary. Assuming this excess arisesfrom dust surrounding the secondary, it is not clear whether the primaryor the secondary, i.e., the post T Tauri star, is the dominant heatingsource. We searched for continuum 1.1 mm emission in a small sample ofcandidate (or confirmed) post T Tauri and post Herbig Ae/Be stars withthe caltech Submillimeter Observatory. In no case did we detect anyemission. The inferred upper limits to the amount of dust present istypically one or two orders of magnitude lower than that found aroundclassical T Tauri/Herbig Ae/Be stars suggesting rapid evolution of thedisk before a star reaches the post T Tauri/Herbig Ae/Be phase.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| A new optical extinction law and distance estimate for the Taurus-Auriga molecular cloud
This paper presents optical spectrophotometry of field stars projectedon the Taurus-Auriga molecular cloud. We derive extinction laws forheavily reddened stars in this sample and show that the reddening lawthrough the dark cloud is nearly identical to the standard law forlambda-lambda(3600-6100) and AV approximately less than 3mag. Our spectroscopic parallaxes suggest a distance of 140 +/- 10 pcfor the northern portion of the cloud and show no compelling evidencefor a substantial variation in distance across the leading edge of thecloud.
| Submillimeter constraints on dust near Lindroos' POST T Tauri stars
Young stars from the dynamical sample identified by Lindroos (A&A,156,223 (1986)) have been observed at 800 micrometers wavelength usingthe James Clerk Maxwell Telescope on Mauna Kea. The new data are used toconstrain the mass of circumstellar dust around these stars. TheLindroos sample is dominated by low-mass stars of age (3-150) x106 yr, intermediate in age between the T Tauri andmain-sequence stars. When combined with previous measurements, thepresent observations are compatible with the depletion of circumstellardust on a time scale tau approximately 107.0 yr. If this dustis present in circumstellar disks, then tau represents the lifetime ofthese disks.
| ROSAT detections of X-ray emission from young B-type stars
We present first results of a series of pointings of the Rosat HRI atvisual binaries consisting of a B-star with a later-type companion. Thebinaries selected for this study are very likely physical pairs. Datingof the B-type stars with respect to the zero-age main sequence, as wellas spectroscopic observations of the late-type stars, provides evidencefor the extreme youth of these systems with ages typically near or below10 exp 8 yr. Surprisingly, the late-B component was in many casesdetected as an X-ray source, in contrast to previous findings that X-rayemission among late-B field stars is rather uncommon.
| X-ray emission from age-dated post-T Tauri stars.
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Osservazione e dati astrometrici
| Costellazione: | Toro |
| Ascensione retta: | 04h22m34.90s |
| Declinazione: | +25°37'45.0" |
| Magnitudine apparente: | 5.37 |
| Distanza: | 82.034 parsec |
| Moto proprio RA: | 19.6 |
| Moto proprio Dec: | -17.3 |
| B-T magnitude: | 5.339 |
| V-T magnitude: | 5.372 |
Cataloghi e designazioni:
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