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Radial Velocity Studies of Close Binary Stars. XII.
Radial velocity measurements and sine-curve fits to the orbital radialvelocity variations are presented for 10 close binary systems: OO Aql,CC Com, V345 Gem, XY Leo, AM Leo, V1010 Oph, V2612 Oph, XX Sex, W UMa,and XY UMa. Most of these binaries have been observed spectroscopicallybefore, but our data are of higher quality and consistency than in theprevious studies. While most of the studied eclipsing pairs are contactbinaries, V1010 Oph is probably a detached or semidetached double-linedbinary, and XY UMa is a detached, chromospherically active system whosebroadening functions clearly show well-defined and localized dark spotson the primary component. A particularly interesting case is XY Leo,which is a member of visually unresolved quadruple system composed of acontact binary and a detached, noneclipsing, active binary with an 0.805day orbital period. V345 Gem and AM Leo are known members of visualbinaries. We found faint visual companions at about 2"-3" from XX Sexand XY UMa.Based on data obtained at the David Dunlap Observatory, University ofToronto.
| A Photometric and Spectroscopic Search for White Dwarfs in the Open Clusters NGC 6633 and NGC 7063
We present photometric and spectroscopic studies of the white dwarf (WD)populations in the intermediate-age open clusters NGC 6633 and NGC 7063as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-fieldCCD imaging, we locate 41 candidate WDs in the two cluster fields: 32 inNGC 6633, and 9 in NGC 7063. Spectroscopic observations confirm 13 ofthese candidates to be bona fide WDs. We describe in detail ourBalmer-line fitting technique for deriving effective temperatures andsurface gravities from optical DA WD spectra and apply the technique tothe 11 DA WDs in the sample. Of these, only two DA WDs are at thecluster distance moduli, one in each cluster. Two more DAs lie 0.75 magforeground to NGC 6633, raising the possibility that these are doubledegenerate systems in the cluster. If they are nearly equal-massbinaries, both of these systems likely have combined masses above theChandrasekhar limit. One DB WD is found to be consistent with membershipin NGC 6633, which would make this the third confirmed He-atmosphere WDin an open cluster, although further data are needed to confirm clustermembership. The WD consistent with membership in the cluster NGC 7063has a low mass (~0.4 Msolar), suggesting it may be a He-coreWD resulting from close binary evolution. Three of the 11hydrogen-atmosphere WDs in this study are observed to have Ca IIabsorption; the number of DAZs in this study is consistent with previousobservations that ~25% of field WDs are DAZs.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) 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/463/789
| K-band magnitude of the red clump as a distance indicator
We have investigated how the K-band magnitude of the red clump [M_K(RC)]depends on age and metallicity, using 2MASS infrared data for a sampleof 24 open clusters with known distances. We show that a constant valueof M_K(RC)=-1.57 ± 0.05 is a reasonable assumption to use indistance determinations for clusters with metallicity between -0.5 and+0.4 dex and age between 108.5 and 109.9 years.Figures 8 and 9 are available in electronic form at http://www.aanda.org
| Carbon Deficiency in Externally Polluted White Dwarfs: Evidence for Accretion of Asteroids
Existing determinations show that n(C)/n(Fe) is more than a factor of 10below solar in the atmospheres of three white dwarfs that appear to beexternally polluted. These results are not easily explained if the starshave accreted interstellar matter, and we reinterpret these measurementsas evidence that these stars have accreted asteroids with a chondriticcomposition.
| The Chemical Compositions of Stars with Planets: A Review
A number of trends among the properties of exoplanets have becomeevident in the years since the first one was announced in 1995. Oneparticularly interesting trend began to emerge in 1997: the incidence ofgiant planets correlates with the metallicity of the host star. This hassince been established with a high degree of statistical significance byseveral research groups. Other, more subtle trends are beginning toappear as the sample size continues to grow and the statistics improve.I review the state of our knowledge concerning the observedcompositional trends and their possible causes and suggest severalresearch directions.
| New magnetic chemically peculiar stars
Spectropolarimetric observations of 96 chemically peculiar (CP)main-sequence stars have been carried out at the 6-m telescope at theSpecial Astrophysical Observatory of the Russian Academy of Sciences(SAO RAS) with the aim of searching for the presence of stellar magneticfields. The stars selected for investigation were CP stars known to havestrong anomalies in the wavelength region of the continuum fluxdepression around λ 5200Å. This selection was conductedwith the aid of low-resolution spectral observations, made with the SAORAS 1-m telescope, and of published differential photometric data.Magnetic fields have been successfully detected in 72 stars of whichonly three stars were previously known to have magnetic fields. For twostars, the longitudinal component of the magnetic field Beexceeds 5 kG: HD178892 - 7.4 kG, and HD258686 - 6.7 kG. We failed toreliably detect the magnetic field in the other 24 CP stars. These starsare mostly fast rotators, a feature which hampers accurate measurementsof Be. It is demonstrated in this paper that selectingcandidate magnetic stars by considering their photometric indices Z orΔa, or alternatively, by inspecting low-resolution spectra aroundthe λ5200Å flux depression, considerably increases thedetection rate.This paper is based on data obtained at the 6-m telescope of the RussianAcademy of Sciences.E-mail: dkudr@sao.ru
| On the current status of open-cluster parameters
We aim to characterize the current status of knowledge on the accuracyof open-cluster parameters such as the age, reddening and distance.These astrophysical quantities are often used to study the globalcharacteristics of the Milky Way down to the very local stellarphenomena. In general, the errors of these quantities are neglected orset to some kind of heuristic standard value. We attempt to give somerealistic estimates for the accuracy of available cluster parameters byusing the independently derived values published in the literature. Intotal, 6437 individual estimates for 395 open clusters were used in ourstatistical analysis. We discuss the error sources depending ontheoretical as well as observational methods and compare our resultswith those parameters listed in the widely used catalogue by Dias et al.In addition, we establish a list of 72 open clusters with the mostaccurate known parameters which should serve as a standard table in thefuture for testing isochrones and stellar models.
| Survey for Transiting Extrasolar Planets in Stellar Systems. IV. Variables in the Field of NGC 1245
The Survey for Transiting Extrasolar Planets in Stellar Systems (STEPSS)project is a search for planetary transits in open clusters. In thispaper we analyze the STEPSS observations of the open cluster NGC 1245 todetermine the variable-star content of the cluster. Out of 6787 starsobserved with V<22, of which ~870 are cluster members, we find 14stars with clear intrinsic variability that are potential clustermembers and 29 clear variables that are not cluster members. None ofthese variables have been previously identified. We present lightcurves, finder charts, and stellar/photometric data on these variableobjects. Several of the interacting binaries have estimated distancesconsistent with the cluster distance determined from isochrone fits tothe color-magnitude diagram. Four stars at the main-sequence turnoff ofthe cluster have light curves consistent with γ Doradusvariability. If these γ Doradus candidates are confirmed, theyrepresent the oldest and coolest members of this class of variablediscovered to date.
| A new detached K7 dwarf eclipsing binary system
We present an analysis of a new, detached, double-lined eclipsing binarysystem with K7 Ve components, discovered as part of the University ofNew South Wales (UNSW) Extrasolar Planet Search. The object issignificant in that only six other binary systems are known withcomparable or lower mass. Such systems offer important tests ofmass-radius theoretical models. Follow-up photometry and spectroscopywere obtained with the 40-inch and 2.3-m telescopes at Siding SpringObservatory (SSO), respectively. An estimate of the radial velocityamplitude from spectral absorption features, combined with the orbitalinclination (83.5°) estimated from light-curve fitting, yielded atotal mass of Mtotal = 1.041 +/- 0.06Msolar andcomponent masses of MA = 0.529 +/- 0.035Msolar andMB = 0.512 +/- 0.035Msolar. The radial velocityamplitude estimated from absorption features (167 +/- 3kms-1)was found to be less than the estimate from the Hα emission lines(175 +/- 1.5kms-1). The light-curve fit produced radii ofRA = 0.641 +/- 0.05Rsolar and RB =0.608 +/- 0.06Rsolar, and a temperature ratio ofTB/TA = 0.980 +/- 0.015. The apparent magnitude ofthe binary was estimated to be V = 13.9 +/- 0.2. Combined with thespectral type, this gave the distance to the binary as 169 +/- 14pc. Thetiming of the secondary eclipse gave a lower limit on the eccentricityof the binary system of e >= 0.0025 +/- 0.0005. This is the moststatistically significant non-zero eccentricity found for such a system,possibly suggesting the presence of a third companion.
| Caroline Herschel's catalogue of nebulae
Not Available
| Kinematics of the Open Cluster System in the Galaxy
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
| Deep X-ray survey of the young open cluster NGC 2516 with XMM-Newton
Aims.We report a deep X-ray survey of the young (~140 Myr), rich opencluster NGC 2516 obtained with the EPIC camera on board the XMM-Newtonsatellite. Methods: .By combining data from six observations, ahigh sensitivity, greater than a factor of 5 with respect to recentChandra observations, has been achieved. Kaplan-Meier estimators of thecumulative X-ray luminosity distribution are built, statisticallycorrected for non members contaminants and compared to those of thenearly coeval Pleiades. The EPIC spectra of the X-ray brightest starsare fitted using optically thin model plasma with one or two thermalcomponents. Results: .We detected 431 X-ray sources and 234 ofthem have as optical counterparts cluster stars spanning the entire NGC2516 Main Sequence. On the basis of X-ray emission and opticalphotometry, we indicate 20 new candidate members of the cluster; at thesame time we find 49 X-ray sources without known optical or infraredcounterpart. The X-ray luminosities of cluster stars span the range logLX (erg s-1) = 28.4-30.8. The representativetemperatures span the 0.3-0.6 keV (3.5-8 MK) range for the coolcomponent and 1.0-2.0 keV (12-23 MK) for the hot one; similar values arefound in other young open clusters like the Pleiades, IC 2391, andBlanco 1. While no significant differences are found in X-ray spectra,NGC 2516 solar type stars are definitely less luminous in X-rays thanthe nearly coeval Pleiades. The comparison with a previous ROSAT surveyreveals the lack of variability amplitudes larger than a factor of 2 insolar type stars in a 11 yr time scale of the cluster and thusactivity cycles like in the Sun are probably absent or have a differentperiod and amplitude in young stars.
| Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
Context: .About 5% of upper main sequence stars are permeated by astrong magnetic field, the origin of which is still matter of debate. Aims: . With this work we provide observational material to studyhow magnetic fields change with the evolution of stars on the mainsequence, and to constrain theory explaining the presence of magneticfields in A and B-type stars. Methods: . Using FORS1 inspectropolarimetric mode at the ESO VLT, we have carried out a survey ofmagnetic fields in early-type stars belonging to open clusters andassociations of various ages. Results: . We have measured themagnetic field of 235 early-type stars with a typical uncertainty of 100 G. In our sample, 97 stars are Ap or Bp stars. For thesetargets, the median error bar of our field measurements was 80 G.A field has been detected in about 41 of these stars, 37 of which werenot previously known as magnetic stars. For the 138 normal A and B-typestars, the median error bar was 136 G, and no field was detected in anyof them.
| Condensation temperature trends among stars with planets
Results from detailed spectroscopic analyses of stars hosting massiveplanets are employed to search for trends between abundances andcondensation temperatures. The elements C, S, Na, Mg, Al, Ca, Sc, Ti, V,Cr, Mn, Fe, Ni and Zn are included in the analysis of 64 stars withplanets and 33 comparison stars. No significant trends are evident inthe data. This null result suggests that accretion of rocky material onto the photospheres of stars with planets is not the primary explanationfor their high metallicities. However, the differences between the solarphotospheric and meteoritic abundances do display a weak but significanttrend with condensation temperature. This suggests that the metallicityof the Sun's envelope has been enriched relative to its interior byabout 0.07 dex.
| WINGS: a WIde-field Nearby Galaxy-cluster Survey. I. Optical imaging
This is the first paper of a series that will present data andscientific results from the WINGS project, a wide-field, multiwavelengthimaging and spectroscopic survey of galaxies in 77 nearby clusters. Thesample was extracted from the ROSAT catalogs of X-Ray emitting clusters,with constraints on the redshift (0.04< z<0.07) and distance fromthe galactic plane ({\vert}b{\vert}≥ 20 deg). The global goal of theWINGS project is the systematic study of the local cosmic variance ofthe cluster population and of the properties of cluster galaxies as afunction of cluster properties and local environment. This datacollection will allow the definition of a local, "zero-point" referenceagainst which to gauge the cosmic evolution when compared to moredistant clusters. The core of the project consists of wide-field opticalimaging of the selected clusters in the B and V bands. We have alsocompleted a multi-fiber, medium-resolution spectroscopic survey for 51of the clusters in the master sample. The imaging and spectroscopy datawere collected using, respectively, the WFC@INT and WYFFOS@WHT in thenorthern hemisphere, and the WFI@MPG and 2dF@AAT in the southernhemisphere. In addition, a NIR (J, K) survey of 50 clusters and anHα+U survey of some 10 clusters are presently ongoing with theWFCAM@UKIRT and WFC@INT, respectively, while a very-wide-field opticalsurvey has also been programmed with OmegaCam@VST. In this paper webriefly outline the global objectives and the main characteristics ofthe WINGS project. Moreover, the observing strategy and the datareduction of the optical imaging survey (WINGS-OPT) are presented. Wehave achieved a photometric accuracy of 0.025 mag, reachingcompleteness to V 23.5. Field size and resolution (FWHM) span theabsolute intervals (1.6-2.7) Mpc and (0.7-1.7) kpc, respectively,depending on the redshift and on the seeing. This allows the plannedstudies to obtain a valuable description of the local properties ofclusters and galaxies in clusters.
| Caroline Herschel as observer
Not Available
| Time scales of Li evolution: a homogeneous analysis of open clusters from ZAMS to late-MS
We have performed a new and homogeneous analysis of all the Li dataavailable in the literature for main sequence stars (spectral-types fromlate F to K) in open clusters. In the present paper we focus on adetailed investigation of MS Li depletion and its time scales for starsin the 6350-5500 K effective temperature range. For the first time, wewere able to constrain the age at which non-standard mixing processes,driving MS Li depletion, appear. We have also shown that MS Li depletionis not a continuous process and cannot be simply described by at-α law. We confirm that depletion becomes ineffectivebeyond an age of 1-2 Gyr for the majority of the stars, leading to a Liplateau at old ages. We compared the empirical scenario of Li as afunction of age with the predictions of three non-standard models. Wefound that models including only gravity waves as main mixing processare not able to fit the Li vs. age pattern and thus this kind of mixingcan be excluded as the predominant mechanism responsible for Lidepletion. On the other hand, models including slow mixing induced byrotation and angular momentum loss, and in particular those includingalso diffusive processes not related to rotation, can explain to someextent the empirical evidence. However, none of the currently proposedmodels can fit the plateau at old ages.
| Beryllium enhancement as evidence for accretion in a lithium-rich F dwarf
The early F dwarf star `J37' in the open cluster NGC 6633 shows anunusual pattern of photospheric abundances, including anorder-of-magnitude enhancement of lithium and iron-peak elements, but anunder-abundance of carbon. As a consequence of its thin convection zonethese anomalies have been attributed to either radiative diffusion orthe accretion of hydrogen-depleted material. By comparinghigh-resolution Very Large Telescope/UV-Visual Echelle Spectrographspectra of J37 (and other F stars in NGC 6633) with syntheses of theBeII doublet region at 3131 Å, we establish that J37 also has a Beabundance [A(Be) = 3.0 +/- 0.5] that is at least 10 times the cosmicvalue. This contradicts radiative diffusion models that produce a Liover-abundance, as they also predict photospheric Be depletion. Instead,since Be is a highly refractory element, it supports the notion that J37is the first clear example of a star that has accreted volatile-depletedmaterial with a composition similar to chondritic meteorites, althoughsome diffusion may be necessary to explain the low C and O abundances.
| HD 172189: an eclipsing and spectroscopic binary with a δ Sct-type pulsating component in an open cluster
We present a study based on more than 2500 uvby-measurements collectedon HD 172189, a new eclipsing binary system with a δ Sct-typepulsating component that belongs to the open cluster IC 4756. The greatinterest of this object lies in that three important characteristicscoexist: cluster membership, binarity and pulsation. Its binarity andthe δ Sct-type pulsations of one component were detected in thecourse of several Strömgren photometric campaigns. The frequencyanalysis of all the uvby out-of-eclipse data reveals a clear frequencyof 19.5974 cd-1as well as the existence of other high valuesin the range 18-20 cd-1. We have also carried out a firstevaluation of the binary parameters and determined a value of 5.702 dfor the orbital period. An additional potential interest of HD 172189resides in its location in the field of view of the COROT mission and,therefore, this star is an excellent candidate for becoming a target forasteroseismology.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| Outbursts on normal stars. FH Leo misclassified as a novalike variable
We present high resolution spectroscopy of the common proper motionsystem FH Leo (components HD 96273 andBD+07 2411B), which has been classified as a novalike variabledue to an outburst observed by Hipparcos, and we present and review theavailable photometry. We show from our spectra that neither star canpossibly be a cataclysmic variable, instead they are perfectly normallate-F and early-G stars. We measured their radial velocities andderived the atmospheric fundamental parameters, abundances of severalelements including Fe, Ni, Cr, Co, V, Sc, Ti, Ca and Mg, and we derivethe age of the system. From our analysis we conclude that the stars doindeed constitute a physical binary. However, the observed outburstcannot be readily explained. We examine several explanations, includingpollution with scattered light from Jupiter, binarity, microlensing,background supernovae, interaction with unseen companions and planetaryengulfment. While no explanation is fully satisfactory, the scatteredlight and star-planet interaction scenarios emerge as the least unlikelyones, and we give suggestions for further study.
| The University of New South Wales Extrasolar Planet Search: methods and first results from a field centred on NGC 6633
We report on the current status of the University of New South WalesExtrasolar Planet Search project, giving details of the methods we useto obtain millimagnitude precision photometry using the 0.5-m AutomatedPatrol Telescope. We use a novel observing technique to optimallybroaden the point spread function and thus largely eliminate photometricnoise due to intrapixel sensitivity variations on the CCD. We haveobserved eight crowded Galactic fields using this technique during 2003and 2004. Our analysis of the first of these fields (centred on the opencluster NGC 6633) has yielded 49 variable stars and four shallow transitcandidates. Follow-up observations of these candidates have identifiedthem as eclipsing binary systems. We use a detailed simulation of ourobservations to estimate our sensitivity to short-period planets, and toselect a new observing strategy to maximize the number of planetsdetected.
| The Dearth of Massive, Helium-rich White Dwarfs in Young Open Star Clusters
Spectra have been obtained of 21 white dwarfs (WDs) in the direction ofthe young, rich open star cluster NGC 2099. This represents anappreciable fraction (>30%) of the cluster's total WD population. Themean derived mass of the sample is 0.8 Msolar-about 0.2Msolar larger than the mean seen among field WDs. Asurprising result is that all of the NGC 2099 WDs have hydrogen-richatmospheres (DAs); none exhibit helium-rich ones (DBs) or any otherspectral class. The number ratio in the field at the temperatures of theNGC 2099 WDs is DA/DB ~ 3.5. While the probability of seeing no DB WDsin NGC 2099 solely by chance is ~2%, if we include WDs in other openclusters of similar age it then becomes highly unlikely that the dearthof DB WDs in young open clusters is just a statistical fluctuation. Weexplore possible reasons for the lack of DBs in these clusters andconclude that the most promising scenario for the DA/DB number ratiodiscrepancy in young clusters is that hot, high-mass WDs do not developlarge enough helium convection zones to allow helium to be brought tothe surface and turn a hydrogen-rich WD into a helium-rich one.Based on observations with Gemini (run ID GN-2002B-Q-11) and Keck.Gemini is an international partnership managed by the Association ofUniversities for Research in Astronomy, Inc., under a cooperativeagreement with the National Science Foundation. The W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andNASA, was made possible by the generous financial support of the W. M.Keck Foundation.
| Planetary transits and stellar variability. (Thesis abstract)
Not Available
| Deepsky delights.
Not Available
| Photometric Monitoring of Open Clusters. I. The Survey
Open clusters, which have age, abundance, and extinction informationfrom studies of main-sequence turnoff stars, are the ideal location inwhich to determine the mass-luminosity-radius relation for low-massstars. We have undertaken a photometric monitoring survey of openclusters in the Galaxy designed to detect low-mass eclipsing binarysystems through variations in their relative light curves. Our aim is toprovide an improved calibration of the mass-luminosity-radius relationfor low-mass stars and brown dwarfs, to test stellar structure andevolution models, and to help quantify the contribution of low-massstars to the global mass census in the Galaxy. In this paper we presentour survey, describing the data and outlining the analysis techniques.We study six nearby open clusters, with a range of ages from ~0.2 to 4Gyr and metallicities from approximately solar to -0.2 dex. We monitor afield of view of greater than 1 deg2 per target cluster, wellbeyond the characteristic cluster radius, over timescales of hours,days, and months with a sampling rate optimized for the detection ofeclipsing binaries with periods of hours to days. Our survey depth isdesigned to detect eclipse events in a binary with a primary star of<~0.3 Msolar. Our data have a photometric precision of ~3mmag at I~16.
| WIYN/Hydra Detection of Lithium Depletion in F Stars of the Young Open Cluster M35 and Implications for the Development of the Lithium Gap
We report the discovery of significant depletion of Li on the surfacesof F dwarf stars in the 150 Myr old open cluster M35, analagous to afeature in the 700 Myr old Hyades that has been referred to as the ``Ligap.'' We have caught the gap in the act of forming: usinghigh-resolution, high signal-to-noise ratio WIYN/Hydra observations, wedetect Li in all but a few M35 F stars; the maximum depletion lies atleast 0.6-0.8 dex below minimally depleted (or undepleted) stars. TheM35 Li depletion region (1) is quite wide, with clear depletion seenfrom 6000 to 6700 K or hotter, (2) shows a significant dispersion in Liabundance at all Teff, even with stars of the sameTeff, and (3) contains undepleted stars (as well as depletedones) in the (narrow) classical Hyades gap region, which itself shows noundepleted stars. All of these M35 Li depletion properties supportrotationally induced slow mixing as the primary physical mechanism thatforms the gap and argue against other proposed mechanisms, particularlydiffusion and steady main-sequence mass loss. When viewed in the contextof the M35 Li depletion properties, the Hyades Li gap may well be widerthan is usually recognized.This is paper 21 of the WIYN Open Cluster Study (WOCS). The WIYNObservatory is a joint facility of the University of Wisconsin-Madison,Indiana University, Yale University, and the National Optical AstronomyObservatory.
| X-ray astronomy of stellar coronae
X-ray emission from stars in the cool half of the Hertzsprung-Russelldiagram is generally attributed to the presence of a magnetic coronathat contains plasma at temperatures exceeding 1 million K. Coronae areubiquitous among these stars, yet many fundamental mechanisms operatingin their magnetic fields still elude an interpretation through adetailed physical description. Stellar X-ray astronomy is thereforecontributing toward a deeper understanding of the generation of magneticfields in magnetohydrodynamic dynamos, the release of energy in tenuousastrophysical plasmas through various plasma-physical processes, and theinteractions of high-energy radiation with the stellar environment.Stellar X-ray emission also provides important diagnostics to study thestructure and evolution of stellar magnetic fields from the first daysof a protostellar life to the latest stages of stellar evolution amonggiants and supergiants. The discipline of stellar coronal X-rayastronomy has now reached a level of sophistication that makes tests ofadvanced theories in stellar physics possible. This development is basedon the rapidly advancing instrumental possibilities that today allow usto obtain images with sub-arcsecond resolution and spectra withresolving powers exceeding 1000. High-resolution X-ray spectroscopy has,in fact, opened new windows into astrophysical sources, and has played afundamental role in coronal research.
| Practical planet prospecting
A number of space missions dedicated to the search for exoplanets viathe transit method, such as COROT, Eddington and Kepler, are planned forlaunch over the next few years. They will need to address problemsassociated with the automated and efficient detection of planetarytransits in light curves affected by a variety of noise sources,including stellar variability. To maximize the scientific return ofthese missions, it is important to develop and test appropriatealgorithms in advance of their launch dates.Starting from a general-purpose maximum-likelihood approach we discussthe links between a variety of period- and transit-finding methods. Thenatural endpoint of this hierarchy of methods is shown to be a fast,robust and statistically efficient least-squares algorithm based onbox-shaped transits.This approach is predicated on the assumption of periodic transitshidden in random noise, usually assumed to be superposed on a flatcontinuum with regular continuous sampling. We next show how togeneralize the transit-finding method to the more realistic scenariowhere complex stellar (micro) variability, irregular sampling and longgaps in the data are all present.Tests of this methodology on simulated Eddington light curves, includingrealistic stellar microvariability, irregular sampling and gaps in thedata record, are used to quantify the performance. Visually, thesesystematic effects can completely overwhelm the underlying signal ofinterest. However, in the case where transit durations are shortcompared to the dominant time-scales for stellar variability and datarecord segments, it is possible to decouple the transit signal from theremainder.We conclude that even with realistic contamination from stellarvariability, irregular sampling, and gaps in the data record, it isstill possible to detect transiting planets with an efficiency close tothe idealized theoretical bound. In particular, space missions have thepotential to approach the regime of detecting Earth-like planets aroundG2V-type stars.
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