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An XMM-Newton observation of the young open cluster NGC 2547: coronal activity at 30 Myr
We report on XMM-Newton observations of the young open cluster NGC 2547which allow us to characterize coronal activity in solar-type stars, andstars of lower mass, at an age of 30Myr. X-ray emission is seen fromstars at all spectral types, peaking among G stars at luminosities(0.3-3keV) of Lx~= 1030.5ergs-1 anddeclining to Lx<= 1029.0ergs-1 amongM stars with masses >=0.2Msolar. Coronal spectra showevidence for multi-temperature differential emission measures and lowcoronal metal abundances of Z~= 0.3. The G- and K-type stars of NGC 2547follow the same relationship between X-ray activity and Rossby numberestablished in older clusters and field stars, although most of thesolar-type stars in NGC 2547 exhibit saturated or even supersaturatedX-ray activity levels. The median levels of Lx andLx/Lbol in the solar-type stars of NGC 2547 arevery similar to those in T-Tauri stars of the Orion Nebula cluster(ONC), but an order of magnitude higher than in the older Pleiades. Thespread in X-ray activity levels among solar-type stars in NGC 2547 ismuch smaller than in older or younger clusters.Coronal temperatures increase with Lx,Lx/Lbol and surface X-ray flux. The most activesolar-type stars in NGC 2547 have coronal temperatures intermediatebetween those in the ONC and the most active older zero-agemain-sequence (ZAMS) stars. We show that simple scaling argumentspredict higher coronal temperature in coronally saturated stars withlower gravities. A number of candidate flares were identified among thelow-mass members and a flaring rate [for total flare energies (0.3-3keV)> 1034erg] of one every350+350-120ks was found for solar-type stars,which is similar to rates found in the ONC and Pleiades. Comparison withROSAT High Resolution Imager (HRI) data taken 7yr earlier reveals thatonly 10-15 per cent of solar-type stars or stars with Lx >3 × 1029ergs-1 exhibit X-ray variability bymore than a factor of 2. This is comparable with clusters of similar agebut less than in both older and younger clusters. The similar medianlevels of X-ray activity and rate of occurrence for large flares in NGC2547 and the ONC demonstrate that the X-ray radiation environment aroundyoung solar-type stars remains relatively constant over their first30Myr.
| Optimal photometry for colour-magnitude diagrams and its application to NGC 2547
We have developed the techniques required to use Naylor's optimalphotometry algorithm of to create colour-magnitude diagrams withwell-defined completeness functions. To achieve this we firstdemonstrate that the optimal extraction is insensitive to uncertaintiesin the measured position of the star. We then show how to correct theoptimally extracted fluxes such that they correspond to those measuredin a large aperture, so aperture photometry of standard stars can beused to place the measurements on a standard system. The techniquesimultaneously removes the effects of a position-dependent point spreadfunction. Finally, we develop a method called `ghosting', whichcalculates the completeness corrections in the absence of an accuratedescription of the point spread function. We apply these techniques tothe young cluster NGC 2547 (=C0809-491), and use an X-ray-selectedsample to find an age of 20-35 Myr and an intrinsic distance modulus of8.00-8.15 mag. We use these isochrones to select members from ourphotometric surveys. Our derived luminosity function shows awell-defined Wielen dip, making NGC 2547 the youngest cluster in whichsuch a feature has been observed. Our derived mass function spans therange 0.1-6 Msolar and is similar to that for the field andthe older, more massive clusters M35 and the Pleiades, supporting theidea of a universal initial mass function.
| 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
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 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
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| X-ray emission and low-mass stars in the young open cluster NGC 2547
We present the results of deep ROSAT High Resolution Imager X-rayobservations and broad-band BVI_C CCD photometry of the young opencluster NGC 2547. We have been able to find cluster counterparts for themajority of the 102 significant X-ray sources detected, confirming thepower of high spatial resolution X-ray observations to find low-mass,magnetically active members of distant open clusters. The age of thecluster has been determined by fitting the main-sequence turn-off andthe positions of low-mass stars on their pre-main-sequence tracks. Thetwo methods yield 55+/-25 and 14+/-4Myr respectively, but we considerthe lower age to be more reliable because of the comparatively largenumber of low-mass stars that constrain the fit. We deduce that any agespread among the low-mass stars is <10Myr and any small spread thatexists could be attributable to binarity and starspots. The distributionof X-ray activity levels in the solar-type stars of NGC 2547 liesconsiderably above our threshold of sensitivity, and it is probable thatour X-ray-selected sample is complete at these masses. For lower massstars our sample is likely to be incomplete. Comparison with initialmass functions indicates there are still of order 100, low-activity Mdwarfs yet to be found. When X-ray activity is gauged in terms of X-rayto bolometric flux ratio, L_x/L_bol, we find that there are G stars inthe older (age 52Myr) alpha Per cluster that are less active than theirleast active counterparts in NGC 2547. This is consistent with thecurrent rotation-activity paradigm if there is modest angular momentumloss between 14 and 52Myr. There are no G or early K stars in NGC 2547that reach the saturated level L_x/L_bol=10^-3, seen in older clusters,whereas saturated late K and M stars are observed. From this, we deducethat there are no fast-rotating G and early K stars in NGC 2547 withequatorial velocities >20 kms^-1. If this is confirmed then, evenwith no angular momentum loss, the fastest rotating NGC 2547 stars couldnot evolve into the fastest rotating stars in the alpha Per cluster.These results cast doubt on the assumption that rotation rates andmagnetic activity seen in one cluster are representative of similarstars at the same age. We hypothesize that the solar-type stars of NGC2547 either still possess, or have recently lost, circumstellaraccretion discs which regulate their angular momentum. This wouldrequire longer disc lifetimes than commonly measured or assumed forother young stars, and we speculate on possible reasons for this.
| 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.
| UBV photometry of HD stars in the fields of selected cataclysmic variables.
Not Available
| Uvby-beta photometry of southern clusters. VII - NGC 2547
Stromgren four-color and beta photometry has been obtained for the 13brightest members of the young galactic cluster NGC 2547. The data aregenerally in good agreement with other photometry for these stars andthe mean distance modulus obtained from several methods, including theBalona and Shobbrook (1984) beta/c0/M(V) calibration for B stars, is8.1.
| The common origin of some open clusters
Eight open clusters have been observed with uvby-beta photometry and forseven of them the metal abundances have been determined. Six of thesehave similar metallicities. They are close in space and are also knownto have similar ages and radial velocities. These clusters are suspectedof having a common origin. Some studies are made of the reliability ofthe photometric system. A large gain in limiting magnitude can beachieved against an unimportant loss of accuracy if interference filtersare removed.
| Membership Basic Parameters and Luminosity Function of the Southern Open Cluster NGC2547
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...47..323C&db_key=AST
| The VELA star cloud. I - NGC 2547, TR 10, the Gamma Velorum system, and bright stars
The first results of an intermediate-band, large-scale photometricsurvey of the Vela star cloud are discussed. Attention is given to theluminosity and reddening, as well as the apparent or proper motions ofall the CPD stars near NGC 2547, the brightest stars in Trumpler 10, arandom selection of stars in the region of Gamma Velorum, and the HRstars. The similarity of the Alpha Persei cluster with the clusters inthe Vela sheet is shown, and it is found that the Vela sheet, at leastover the region surveyed, is nearly perpendicular to the line of sight.The probability is demonstrated that a thin sheet of coeval (2.5 x 10 tothe 7th yr) stars, some 425 pc distant and with a similar metalabundance, lies in front of a dense dark cloud.
| The frequency of peculiar A and metallic-line stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...205..807H&db_key=AST
| Proper Motions, Radial Velocities and Star Counts in NGC 2547
Not Available
| Photoelectric Magnitudes and Colours in NGC 2547
Not Available
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