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Pre-main sequence star Proper Motion Catalogue
We measured the proper motions of 1250 pre-main sequence (PMS) stars andof 104 PMS candidates spread over all-sky major star-forming regions.This work is the continuation of a previous effort where we obtainedproper motions for 213 PMS stars located in the major southernstar-forming regions. These stars are now included in this present workwith refined astrometry. The major upgrade presented here is theextension of proper motion measurements to other northern and southernstar-forming regions including the well-studied Orion and Taurus-Aurigaregions for objects as faint as V≤16.5. We improve the precision ofthe proper motions which benefited from the inclusion of newobservational material. In the PMS proper motion catalogue presentedhere, we provide for each star the mean position and proper motion aswell as important photometric information when available. We providealso the most common identifier. The rms of proper motions vary from 2to 5 mas/yr depending on the available sources of ancient positions anddepending also on the embedding and binarity of the source. With thiswork, we present the first all-sky catalogue of proper motions of PMSstars.
| The Status of ROSAT X-ray Active Young Stars toward Taurus-Auriga
We present an astrometric study of the candidates of T Tauri stars (TTS)and non-TTS X-ray sources around Tau-Aur, based on the HipparcosCatalogue and the ACT Reference Catalogue. The ROSAT selected X-raysources are found to be a mixed population. A few of them areassociated with the Tau-Aur or Orion Star Forming Regions (SFR). Some,with distances similar to that of Tau-Aur but with discrepant propermotions, are probable or sure Pleiades super-cluster members or otherlate type young active stars with unresolved nature, more likely tooriginate in rapidly moving cloudlets, or else having originated fromdifferent sites other than Tau-Aur and moved to the present locations. Agood many of the non-TTS X-ray sources are considered as Hyades clustermembers. Some TTS candidates could be foreground pre-main sequencestars or actually young dwarfs not yet depleted of their Lithium. Underthe hypothesis that the sources we studied are representative of theROSAT selected TTS candidates discovered in the outskirts of the Tau-Aurregion, we conclude that only up to one third of the weak-line TTScandidates could be expected to be physically associated with theTau-Aur association. Along with the parallax and proper motion analysisof the non-TTS X-ray sources around the Tau-Aur SFR, our result suggeststhat the vast majority of the young active X-ray sources within anangular diameter of about 30 ° of the Tau-Aur SFR, belong to fourmain subgroups that are spatially separate.
| A systematic study of X-ray variability in the ROSAT all-sky survey
We present a systematic search for variability among the ROSAT All-SkySurvey (RASS) X-ray sources. We generated lightcurves for about 30 000X-ray point sources detected sufficiently high above background. For ourvariability study different search algorithms were developed in order torecognize flares, periods and trends, respectively. The variable X-raysources were optically identified with counterparts in the SIMBAD, theUSNO-A2.0 and NED data bases, but a significant part of the X-raysources remains without cataloged optical counterparts. Out of the 1207sources classified as variable 767 (63.5%) were identified with stars,118 (9.8%) are of extragalactic origin, 10 (0.8%) are identified withother sources and 312 (25.8%) could not uniquely be identified withentries in optical catalogs. We give a statistical analysis of thevariable X-ray population and present some outstanding examples of X-rayvariability detected in the ROSAT all-sky survey. Most prominent amongthese sources are white dwarfs, apparently single, yet neverthelessshowing periodic variability. Many flares from hitherto unrecognisedflare stars have been detected as well as long term variability in theBL Lac 1E1757.7+7034.The complete version of Table 7 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/403/247
| An IUE Atlas of Pre-Main-Sequence Stars. I. Co-added Final Archive Spectra from the SWP Camera
We have identified 50 T Tauri stars (TTS) and 74 Herbig Ae/Be (HAEBE)stars observed in the IUE short-wavelength bandpass (1150-1980 Å).Each low-resolution (R~6 Å) spectrum was visually inspected forsource contamination and data quality, and then all good spectra werecombined to form a single time-averaged spectrum for each star. Use ofIUE Final Archive spectra processed with NEWSIPS reduces fixed patternnoise in individual spectra, allowing significant signal-to-noise ratiogains in our co-added spectra. For the TTS observed by IUE, we measuredfluxes and uncertainties for 17 spectral features, including twocontinuum windows and four fluoresced H2 complexes. Thirteenof the 32 accreting TTS observed by IUE have detectable H2emission, which until now had been reported only for T Tau. Using anempirical correlation between H2 and C IV line flux, we showthat lack of sensitivity can account for practically all nondetections,suggesting that H2 fluorescence may be intrinsically strongin all accreting TTS systems. Comparison of IUE and GHRS spectra of TTau show extended emission primarily, but not exclusively, in lines ofH2. We also fit reddened main-sequence templates to 72 HAEBEstars, determining extinction and checking spectral types. Several ofthe HAEBE stars could not be fitted well or yielded implausibly lowextinctions, suggesting the presence of a minority emission componenthotter than the stellar photosphere, perhaps caused by white dwarfcompanions or heating in accretion shocks. We identified broadwavelength intervals in the far-UV that contain circumstellar absorptionfeatures ubiquitous in B5-A4 HAEBE stars, declining in prominence forearlier spectral types, perhaps caused by increasing ionization of metalresonance lines. For 61 HAEBE stars, we measured or set upper limits ona depth index that characterizes the strength of circumstellarabsorption and compared this depth index with published IR properties.
| An IUE Atlas of Pre-Main-Sequence Stars. II. Far-Ultraviolet Accretion Diagnostics in T Tauri Stars
We use our ultraviolet (UV) atlas of pre-main-sequence stars constructedfrom all useful, short-wavelength, low-resolution spectra in theInternational Ultraviolet Explorer (IUE) satellite Final Archive toanalyze the short-wavelength UV properties of 49 T Tauri stars (TTSs).We compare the line and continuum fluxes in these TTSs with each otherand with previously published parameters of these systems, includingrotation rate, infrared excess, and mass accretion rate. Theshort-wavelength continuum in the classical TTSs (CTTSs) appears tooriginate in a ~10,000 K optically thick plasma, while in the naked TTSs(NTTSs-stars without dusty disks) the continuum appears to originate inthe stellar atmosphere. We show that all of the TTSs in our sample liein the regime of ``saturated'' magnetic activity due to their smallRossby numbers. However, while some of the TTSs show emission linesurface fluxes consistent with this saturation level, many CTTSs showsignificantly stronger emission than predicted by saturation. In thesestars, the emission line luminosity in the high ionization lines presentin the spectrum between 1200 and 2000 Å correlates well with themass accretion rate. Therefore, we conclude that the bulk of theshort-wavelength emission seen in CTTSs results from accretion relatedprocesses and not from dynamo-driven magnetic activity. Using CTTSs withknown mass accretion rates, we calibrate the relationship between M andLC IV to derive the mass accretion rate for some CTTSs whichfor various reasons have never had their mass accretion rates measured.Finally, several of the CTTSs show strong emission from molecularhydrogen. While emission from H2 cannot form in gas at atemperature of ~105 K, the strength of the molecular hydrogenemission is nevertheless well correlated with all the other emissionsdisplayed in the IUE short-wavelength bandpass. This suggests that theH2 emission is in fact fluorescent emission pumped by theemission (likely Lyα) from hotter gas.
| Photometric observations of weak-line T Tauri stars . II. WTTS in Taurus-Auriga, Orion and Scorpius OB2-2
We present uvby-$beta a photometry of 116 X-ray flux-selected activestars in the directions of the Orion (40), Taurus-Auriga (58) andScorpius OB2-2 (18) star forming regions. Additionally, we give near IRJHK photometry of 20 active stars in the Taurus-Auriga direction. Theprogram stars were selected from the R_\odotsat All Sky Survey andEINSTEIN X-ray surveys and are spectroscopically confirmed weak-line TTauri stars and weak-line T Tauri star candidates. The photometryconfirms the young nature of the program stars and also indicates that asignificant fraction of the sample could be foreground objects. The datagiven here probably represent the largest homogeneous uvby-beta a$photometric sample of new WTTS and WTTS candidates. Many objects in thesample are observed photometrically for the first time. Based onobservations collected at the Observatorio Astronómico Nacionalin Sierra San Pedro Mártir, Baja California, México.Tables 1-4 are also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| High-resolution spectroscopy of ROSAT low-mass pre-main sequence stars in Orion
High-resolution spectroscopic observations of the lithium-rich starsfound on the basis of the ROSAT All-Sky Survey (RASS) in the generaldirection of the Orion star forming region are presented. Differentproperties are derived from the spectra and analyzed: i) the equivalentwidths of the lithium 6708 Ä absorption line have been measured anda revision of spectral types has been performed; ii) radial velocities(RV) and projected rotational velocities, vsin i, have been derived byapplication of cross-correlation techniques. A relatively large numberof spectroscopic binaries and of suspected spectroscopic binary andmultiple systems are found among the stars in the sample. Based on thestrength of the lithium line with respect to young open cluster ZAMSstars of the same spectral type, the pre-main sequence nature isconfirmed for more than 70% of the stars in the sample. Theinterrelation of the derived observational properties, such askinematics, lithium abundance, age and projected rotational velocity ofthe stars in the sample are analyzed also in connection with the spatiallocation of the objects. In particular, the comparison between thekinematics of the stars and that of the gas, provided by the CO and CSmolecular emission observations, reveals different degrees of clusteringof the stars with respect to the cloud material and differentkinematical groups can be distinguished. The sample of RASS lithium-richstars found in the general direction of Orion appears to be a mixture oftrue Orion stars and, possibly, stars belonging to the Gould Belt. Basedon observations carried out at the Calar Alto observatory, the MultipleMirror Telescope (a joint facility of the Smithsonian Institution andthe University of Arizona) and the European Southern Observatory, LaSilla, Chile under proposal number 60.C-0170
| Newly discovered candidate weak-line T Tauri stars in the surrounding area of the Taurus-Auriga region
We present results of an extensive search for weak-line T Tauri stars(WTTS) in the outskirts of the Taurus-Auriga molecular cloud on thebasis of the ROSAT All-Sky Survey Bright Source Catalog. Our surveyedregion extends from 2() h40() m to 5() h40() m in right ascension andfrom 10(deg) to 40(deg) in declination, with the central part ofTaurus-Auriga (4() h
| Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
| Atmospheric Parameters and Iron Abundances of Low-Mass Pre-Main-Sequence Stars in Nearby Star Formation Regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...471..847P&db_key=AST
| New weak-line T Tauri stars in Orion from the ROSAT all-sky survey.
We present results of the spectroscopic and photometric follow-upobservations of the ROSAT all-sky survey in the direction of the Orioncloud complex. The main goal of these observations is the search forX-ray emitting pre-main sequence stars. 820 X-ray sources were detectedwith high confidence in about 450 square degrees. The mean density ofX-ray sources in this region is a factor of about two higher than thatof the whole RASS. 5% of the RASS sources in this region are identifiedwith previously known and likely pre-main sequence stars. We haveinvestigated spectroscopically 181 new RASS sources widely distributedover the entire cloud complex. On the basis of the presence of strong LiI λ6707 absorption, spectral type later than F0 and chromosphericemission, 112 new weak-line T Tauri stars could be found. We presentcoordinates, X-ray count-rates and finding charts of the new PMS.Optical UBV(RI)_KC_, near-infrared JHKLM and uvby-β photometry forthe new WTTS is also provided. In addition 24 dKe-dMe stars were alsofound on the basis of the RASS data.
| Hα emission from pre-main sequence stars.
We present the results of an Hα emission line observational studyof a sample of 75 pre-main sequence stars consisting of 17 HAEBE, 47 CTTand 11 WTT stars. Approximately half of the stars are faint, with abrightness in the V band >13. The spectra have been taken atresolutions =~30km/s and =~80km/s. The data shown provide information onequivalent width, radial velocity, variability and line profile.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| On the Composition and Distribution of Dust in Galactic H II Regions
The dust emission and distribution from two Galactic H II regions, theRosette Nebula and the lambda Orionis H II region, have been modeled andcompared with spatially resolved IRAS observations. The grain modelsused in this study are consistent with observations of isolatedinterstellar clouds and the diffuse interstellar meduim. We exploitedthe wealth of published observations of these two H II regions toconstrain the free parameters of the infrared emission models. Thesemodels represent a comprehensive, multi-wavelength study of each H IIregion. The contribution of nebular lines to the IR emission observed byIRAS was calculated from radio continuum measurements. Emission linesare found to contribute only a few percent of the total IR emission.Despite their regular appearance, both H II regions have significantdeviations from spherical symmetry. In particular, the IR emission forthe lambda Orionis H II region requires a nonspherical distribution ofdust near the central core. I_ν(60)/I_ν(100) is notrepresentative of a single grain temperature within either H II region.Therefore, a grain component separate from the grains emitting at 100microns is required to supply the excess 60 microns emission. Theseemitters could be either small (50 to 200 Angstroms) grains thatexperience strong temperature fluctuations or "astronomical" iron grainsthat attain high equilibrium temperatures. In order to match the IRASobservations, the abundance of the grains that produce the 12 and 25microns emission in the ISM must be reduced inside the ionized regions.This depletion occurs in radiation fields 20 to 36 times the UVcomponent of the diffuse ISRF. The destruction mechanism for the 12 and25 microns carriers is not well modeled by sublimation or moleculardisruption.
| Neutral hydrogen observations of extended galactic structures.
Not Available
| The Einstein Slew Survey
A catalog of 819 sources detected in the Einstein IPC Slew Survey of theX-ray sky is presented; 313 of the sources were not previously known asX-ray sources. Typical count rates are 0.1 IPC count/s, roughlyequivalent to a flux of 3 x 10 exp -12 ergs/sq cm s. The sources havepositional uncertainties of 1.2 arcmin (90 percent confidence) radius,based on a subset of 452 sources identified with previously knownpointlike X-ray sources (i.e., extent less than 3 arcmin).Identifications based on a number of existing catalogs of X-ray andoptical objects are proposed for 637 of the sources, 78 percent of thesurvey (within a 3-arcmin error radius) including 133 identifications ofnew X-ray sources. A public identification data base for the Slew Surveysources will be maintained at CfA, and contributions to this data baseare invited.
| A catalog of co-added IRAS fluxes of Orion population stars
A catalog of co-added IRAS fluxes for the pre-main-sequence objects inthe Herbig-Bell catalog (HBC) is presented. This catalog doubles thenumber of HBC stars with detected IRAS fluxes and provides improved fluxvalues for the previously known sources. Noise level are given for allHBC fields in each band, permitting upper limits to be estimated for allundetected sources.
| A search for evidence of cold dust around naked T Tauri stars
Results of millimeter/ submillimeter photometry of 16 naked T Tauristars, 11 of which lie in the nearby Taurus-Auriga star-forming region,are presented. Evidence of cold circumstellar dust, which could existaround these objects in the form of remnant disks if NTTS evolved fromclassical T Tauri stars, is explored. The only star detected at theprimary observing wavelength of 1100 microns was V836 Tau, which wasalso detected at 800 microns with an upper limit obtained at 450microns. Its spectral energy distribution longward of 10 microns isconsistent with that expected for a flat axisymmetric moderately activedisk with a solar mass of 0.04. Upper limits on the disk masses ofundetected stars in Taurus-Auriga are typically 0.02 solar mass, for anassumed temperature of not less than 6 K at the outer disk radius. It isargued that the high levels of magnetic activity found in NTTS mayproduce detectable gyrosynchroton emission at millimeter wavelengths.
| Catalog of emission line stars of the orion population : 3 : 1988
Not Available
| X-ray observations of the runaway stars HD 206327 and 26 Cephei and of the Lambda-1 Orionis region
Observations made with the IPC on the HEAO 2 satellite (EinsteinObservatory) are reported for the runaway OB-type stars HD 206327 and 26Cephei and also of the Lambda-1 Orionis region. Only upper limits forthe X-ray emissions from the two runaway stars were determined. Assumingboth of these stars to have compact stellar companions, then theselimits, when combined with a suitable model, predict that both systemsshould have orbital periods greater than about 150 days and possiblyranging up into years. Moreover, a single imaging proportional counter(IPC) observation of the region centered on Lambda-1 Orionis has foundfive serendipitous X-ray sources. An astrometric and photometric studyof this region provides evidence that these sources are probable membersof the association. The inferred luminosities range from 5 x 10 to the30th to 5 x 10 to the 31st ergs/s. Two of the sources are identifiedwith normal OB stars, and the others are most likely pre-main-sequencestars that have evolved from T Tauri stars and will be soon burninghydrogen in their cores.
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Observation and Astrometry data
| Constellation: | Ωρίων |
| Right ascension: | 05h34m34.91s |
| Declination: | +10°07'06.3" |
| Apparent magnitude: | 9.968 |
| Proper motion RA: | 11.5 |
| Proper motion Dec: | -35.3 |
| B-T magnitude: | 10.892 |
| V-T magnitude: | 10.045 |
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