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New M Dwarf Debris Disk Candidates in NGC 2547
With only six known examples, M dwarf debris disks are rare, even thoughM dwarfs constitute the majority of stars in the Galaxy. After finding anew M dwarf debris disk in a shallow mid-infrared observation of NGC2547, we present a considerably deeper Spitzer MIPS image of the region,with a maximum exposure time of 15 minutes pixel-1. Amongsources selected from a previously published membership list, weidentify nine new M dwarfs with excess emission at 24 μm tracing warmmaterial close to the snow line of these stars, at orbital radii of lessthan 1 AU. We argue that these are likely debris disks, suggesting thatplanet formation is under way in these systems. Interestingly, theestimated excess fraction of M stars appears to be higher than that of Gand K stars in our sample.
| A revisit to agglomerates of early-type Hipparcos stars
% We study the spatial structure and sub-structure of regions rich in{Hipparcos} stars with blue B_T-V_T colours. These regions, whichcomprise large stellar complexes, OB associations, and young openclusters, are tracers of on-going star formation in the Galaxy. TheDBSCAN (Density-Based Spatial Clustering of Applications with Noise)data clustering algorithm is used to look for spatial overdensities ofearly-type stars. Once an overdensity, ``agglomerate'', is identified,we carry out a data and bibliographic compilation of their star membercandidates. The actual membership in agglomerate of each early-type staris studied based on its heliocentric distance, proper motion, andprevious spectro-photometric information. We identify 35 agglomerates ofearly-type {Hipparcos} stars. Most of them are associated to previouslyknown clusters and OB associations. The previously unknown P Puppisagglomerate is subject of a dedicated study with Virtual Observatorytools. It is actually a new, nearby, young open cluster (d ˜ 470pc, age ˜ 20 Ma) with a clear radial density gradient. We list PPuppis and other six agglomerates (including NGC 2451 A, vdBH 23, andTrumpler 10) as new sites for substellar searches because of theiryouth, closeness, and spatial density. We investigate in detail thesub-structure in the Orion, CMa-Pup and Pup-Vel OB complexes(``super-agglomerates''). We confirm or discover some stellaroverdensities in the Orion complex, like the 25 Ori group, the Horseheadregion (including the σ Orionis cluster), and the η Orionisagglomerate. Finally, we derive accurate parallactic distances to thePleiades, NGC 2451 A, and IC 2391, describe several field early-typestars at d < 200 pc, and discuss the incompleteness of our search.
| Debris Disks in NGC 2547
We have surveyed the 30 Myr old cluster NGC 2547 for planetary debrisdisks using Spitzer. At 4.5-8 μm we are sensitive to the photosphericlevel down to mid-M stars (0.2 Msolar), and at 24 μm toearly G stars (1.2 Msolar). We find only two to four starswith excesses at 8 μm out of ~400-500 cluster members, resulting inan excess fraction <~1% at this wavelength. By contrast, the excessfraction at 24 μm is ~40% (for B-F types). Out of four late-typestars with excesses at 8 μm two marginal ones are consistent withasteroid-like debris disks. Among stars with strong 8 μm excesses oneis possibly from a transitional disk, while another one can be a resultof a catastrophic collision. Our survey demonstrates that the inner0.1-1 AU parts of disks around solar-type stars clear out verythoroughly by 30 Myr of age. Comparing with the much slower decay ofexcesses at 24 and 70 μm, disks clear from the inside out, of order10 Myr for the inner zones probed at 8 μm, compared with 100 or moremegayears for those probed with the two longer wavelengths.This paper includes data gathered with the 6.5 m Magellan telescopeslocated at Las Campanas Observatory, Chile.
| Kinematics of the Scorpius-Centaurus OB association
A fine structure related to the kinematic peculiarities of threecomponents of the Scorpius-Centaurus association (LCC, UCL, and US) hasbeen revealed in the UV-velocity distribution of Gould Belt stars. Wehave been able to identify the most likely members of these groups byapplying the method of analyzing the two-dimensional probability densityfunction of stellar UV velocities that we developed. A kinematicanalysis of the identified structural components has shown that, ingeneral, the center-of-mass motion of the LCC, UCL, and US groupsfollows the motion characteristic of the Gould Belt, notably itsexpansion. The entire Scorpius-Centaurus complex is shown to possess aproper expansion with an angular velocity parameter of 46 ± 8 kms‑1 kpc‑1 for the kinematic centerwith l 0 = ‑40° and R 0 = 110 pc found.Based on this velocity, we have estimated the characteristic expansiontime of the complex to be 21 ± 4 Myr. The proper rotationvelocity of the Scorpius-Centaurus complex is lower in magnitude, isdetermined less reliably, and depends markedly on the data quality.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| A search for hot post-AGB stars in the IRAS Point Source Catalog.
In this paper a first step is made to search for hot post-AGB stars inthe IRAS Point Source Catalog. In order to find objects that evolved offthe AGB a longer time ago than post-AGB objects discussed in theliterature, objects that were not detected at 12 μm by IRAS wereselected, The selection yielded 15 objects, of which 12 have spectraltype B, and would appear to be efficient in finding hot objects.However, this result does not necessarily mean that these are oldevolved objects. Some stars are associated with dense galactic cirrusand are probably normal massive supergiants, and a number of stars aregood post-AGB candidates because of their galactic latitudes and theircool, extended infrared emission. The possibility remains that theseobjects are normal supergiants heating the local interstellar medium.Finally, three remaining objects appear to be genuine post-AGB(candidate) stars, as is attested by their spectral and photometricproperties. The main conclusion derived from modelling their spectralenergy distributions is that the objects evolved off the AGB about 1000years ago, significantly longer than what is found for other post-AGBstars. Emission lines have appeared in the spectrum of one of theseobjects, SAO 243756, over the last 20 years. SAO 243756 bears closeresemblance to other objects that have been proposed to have entered thePlanetary Nebula phase recently. Several aspects of the problem ofselecting post-AGB stars in general are discussed.
| 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.
| 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
| Fundamental data for southern stars (Second List)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959MNRAS.119..638E&db_key=AST
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| קבוצת-כוכבים: | מפרש |
| התרוממות ימנית: | 08h10m16.08s |
| סירוב: | -49°02'05.7" |
| גודל גלוי: | 7.302 |
| מרחק: | 290.698 פארסק |
| תנועה נכונה: | -9.7 |
| תנועה נכונה: | 4.4 |
| B-T magnitude: | 7.129 |
| V-T magnitude: | 7.288 |
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