Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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.
| The lithium depletion boundary in NGC 2547 as a test of pre-main-sequence evolutionary models
Intermediate resolution spectroscopy from the European SouthernObservatory Very Large Telescope is analysed for 63 photometricallyselected low-mass (0.08-0.30 Msolar) candidates of the opencluster NGC 2547. We have confirmed membership for most of these starsusing radial velocities, and found that lithium remains undepleted forcluster stars with I > 17.54 +/- 0.14 and Ks > 14.86+/- 0.12. From these results, several pre-main-sequence evolutionarymodels give almost model independent ages of 34-36 Myr, with a precisionof 10 per cent. These ages are only slightly larger than the ages of25-35(+/-5) Myr obtained using the same models to fit isochrones tohigher mass stars descending towards the zero-age main-sequence, both inempirically calibrated and theoretical colour-magnitude diagrams. Thisagreement between age determinations in different mass ranges is anexcellent test of the current generation of low-mass pre-main-sequencestellar models and lends confidence to ages determined with eithermethod between 30 and 120 Myr.
| Spitzer Observations of NGC 2547: The Disk Population at 25 Million Years
We present Spitzer observations of the young cluster NGC 2547, obtainingphotometry at 3.6, 4.5, 5.8, 8.0, and 24 μm, reaching significantlyfainter infrared sensitivities than previous studies. With theseobservations, we investigate the disk frequency in this cluster. A totalof 3770, 2408, 1988, 1238, and 1123 sources were detected in the commonregion of the five respective bands. The detection limits were 14.9,14.0, 13.5, 13.3, and 12.0 mag, respectively. The large majority ofsources are associated with 2MASS objects. From this large ensemble, weutilize the criteria of Naylor et al. to identify 184 likely members ofthe cluster. The analyses in this paper are focused on these likelymembers. Of the 184 candidates, 162 were detected in at least oneInfrared Array Camera (IRAC) band. These objects form a well-definedfamily in the J-K,K-[3.6] color-color diagram. There is no evidence forexcess emission at 3.6 μm for cluster candidates with J-K<0.8,corresponding to spectral types earlier than late K. For later typestars, only 12 have evidence for a 3.6 μm excess. Hence, we derive a3.6 μm emitting disk fraction of less than 7%. The lack of excess forthe more massive stars may indicate a difference in the disk dissipationtimescales for different mass stars. At 24 μm, 32 of the sources aredetected. Most of them have photospheric K-[3.6] and K-[24] colors, butapproximately a quarter show an excess at 24 μm. This observation maybe evidence for cool disks with central holes.
| 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.
| 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.
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| The VELA star cloud. III - The B8 to A0 stars and interstellar reddening
The present discussion of intermediate band and H-beta observations of360 HD stars B8-A0 in Vela, and all of the CPD stars in a small adjacentregion, notes that the interstellar absorption in both cases can beunderstood as a combination of three absorbing clouds of 1 kpc-A(V) =1.5, 0.5, and 0.17. The major difference in the two environments is thepresence of numerous T Tauri stars in Taurus. Several clusters in theVela region are discussed.
| 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.
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| 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
| Uvby-Beta Photometry of Equatorial and Southern Bright Stars - Part Two
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&AS...42..311H&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
| The Scorpio-Centaurus Association, III. Radial velocities of 70 additional stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962MNRAS.124..189B&db_key=AST
| Proper Motions, Radial Velocities and Star Counts in NGC 2547
Not Available
| Photoelectric Magnitudes and Colours in NGC 2547
Not Available
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Vela |
| Ascensió Recta: | 08h10m20.56s |
| Declinació: | -49°14'14.5" |
| Magnitud Aparent: | 6.437 |
| Distancia: | 500 parsecs |
| Moviment propi RA: | -8.6 |
| Moviment propi Dec: | 3.7 |
| B-T magnitude: | 6.263 |
| V-T magnitude: | 6.423 |
Catàlegs i designacions:
|
