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The Benchmark Cluster Reddening Project. III. A Comparison of Reddening Values Derived from F and K Stars in NGC 752
A protocol for reddening analysis developed in previous papers in thisseries is reviewed here and applied to NGC 752. The protocol includes(1) detailed scrutiny of the histories of reddening determinations forprogram clusters, (2) adherence to statistical norms, (3) qualitycontrol of all reddening techniques, (4) a primary focus on techniqueswith limited metallicity sensitivity, (5) zero-point control of sourcedata, (6) use of the solar neighborhood to establish a zero point forreddening values, (7) use of a standard permitting meaningful quantitiesto be as small as a few millimagnitudes, and (8) rejection of ad hocdata assessments. After certain published results are set aside, it isfound that a reddening value derived for F stars by using a techniquethat is insensitive to blanketing disagrees by about 0.04 mag with avalue derived for K giants by using DDO photometry. This disagreementdoes not appear to be an artifact of the use of questionable data, andit persists if additional techniques are considered. Partly because twocomparable reddening results for K giants are afterward found todisagree with each other, the problem is attributed to a blanketingeffect (with an unknown source) on the reddening values derived for theK giants. Pending a final resolution of that problem, the adopted valueof E(B-V) for the cluster (44+/-3.4 mmag) is based solely on the initialF-star analysis. A discussion of the potential usefulness of smallstandard errors like the one derived here for E(B-V) is given. In aparallel investigation, it is found that no definitive value of [Fe/H]can be assigned to NGC 752 at present because a statisticallysignificant disagreement between two published high-precisionmetallicities is detected.
| Characterization of open cluster remnants
Context: Despite progress in the theoretical knowledge of open clusterremnants and the growing search for observational identifications inrecent years, open questions still remain. The methods used to analyzeopen cluster remnants and criteria to define them as physical systemsare not homogeneous. In this work we present a systematic method forstudying these objects that provides a view of their properties andallows their characterization. Aims: Eighteen remnant candidates areanalyzed by means of photometric and proper motion data. These dataprovide information on objects and their fields. We establish criteriafor characterizing open cluster remnants, taking observationaluncertainties into account. Methods: 2MASS J and H photometry isemployed (i) to study structural properties of the objects by means ofradial stellar density profiles, (ii) to test for any similarity betweenobjects and fields with a statistical comparison method applied to thedistributions of stars in the CMDs, and (iii) to obtain ages, reddeningvalues, and distances from the CMD, taking an index of isochrone fitinto account. The UCAC2 proper motions allowed an objective comparisonbetween objects and large solid angle offset fields. Results: Theobjective analysis based on the present methods indicates 13open-cluster remnants in the sample. Evidence of the presence of binarystars is found, as expected for dynamically evolved systems. Finally, weinfer possible evolutionary stages among remnants from the structure,proper motion, and CMD distributions. The low stellar statistics forindividual objects is overcome by means of the construction of compositeproper motion and CMD diagrams. The distributions of remnants in thecomposite diagrams resemble the single-star and unresolved binary stardistributions of open clusters.
| 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
| Seven-Color Vilnius Photometry of the Open Cluster NGC 752
New photoelectric seven-color observations in the Vilnius system arepresented for 65 stars in the region of the open cluster NGC 752. Basedon individual stars with accurate photometric classifications, wedetermine the apparent distance modulus (m-M)V = 8.38±0.14 and the mean reddening to the cluster EY-V=0.027± 0.010, or EB-V= 0.034± 0.013 (the errorsgiven are the standard deviations for one star). The mean photometricmetallicity for the main-sequence stars, [Fe/H] = -0.14± 0.03, isfound to be slightly lower than that derived for the red clump giants,[Fe/H] = -0.08± 0.09. This difference suggests that red giants inlater evolutionary phases may not have zero-age surface values of[Fe/H]. We made use of the least-squares minimization techniques to fitthe Padova theoretical isochrones to the CMD, when the binary starpopulation is taken into account. By varying the distance modulus,metallicity and age, the best match has been found between the sevenmagnitudes and colors of the observed stars and those of model binaries,which gives the distance modulus by 0.2 mag smaller than that derivedfrom individual stars, i.e., (m-M)V = 8.18, a closely similarmetallicity ([Fe/H] = -0.12), and age of 1.6 Gyr. With these results,the fraction of photometric binaries among the main-sequence stars is≥40%.
| The changing place of red giant stars in the evolutionary process
Not Available
| Caroline Herschel's catalogue of nebulae
Not Available
| Separation of dwarf and giant stars with ROTSE-IIId
136 stars which were known to be members of the open cluster NGC 752were observed at the R band with the ROTSE-IIId telescope located at theTurkish National Observatory (TUG) site. The data had been evaluatedtogether with BV and 2MASS photometric data. A new practical method forseparating dwarf and giant was described and applied. Evaluating thecolour magnitude-diagrams with Padova isochrones revealed for the opencluster NGC 752 a metallicity similar to the Sun and an age of1.41±0.20 Gyr .
| uvbyCaHβ CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
CCD photometry on the intermediate-band uvbyCaHβ system ispresented for the anticenter, intermediate-age open cluster Melotte 71.Restricting the data to probable single members of the cluster using thecolor-magnitude diagram and the photometric indices alone generates asample of 48 F dwarfs on the unevolved main sequence. The averageE(b-y)=0.148+/-0.003 (standard error of the mean [s.e.m.]) orE(B-V)=0.202+/-0.004 (s.e.m.), where the errors refer to internal errorsalone. With this reddening, [Fe/H] is derived from both m1and hk, using Hβ and b-y as the temperature index, with excellentagreement among the four approaches and a final weighted average of[Fe/H]=-0.17+/-0.02 (s.e.m.) for the cluster, on a scale in which theHyades has [Fe/H]=+0.12. When adjusted for the higher reddeningestimate, the previous metallicity estimates from Washington photometryand from spectroscopy are now in agreement with the intermediate-bandresult. From comparisons to isochrones of appropriate metallicity, thecluster age and distance are determined as 0.9+/-0.1 Gyr and(m-M)=12.2+/-0.1 or (m-M)0=11.6+/-0.1. At this distance fromthe Sun, Mel 71 has a galactocentric distance of 10.0 kpc on a scale inwhich the Sun is 8.5 kpc from the Galactic center. Based on its age,distance, and elemental abundances, Mel 71 appears to be a less populousanalog to NGC 3960.
| 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.
| Element abundances of unevolved stars in the open cluster M 67
Context: .The star-to-star scatter in lithium abundances observed amongotherwise similar stars in the solar-age open cluster M 67 is one of themost puzzling results in the context of the so called "lithium problem".Among other explanations, the hypothesis has been proposed that thedispersion in Li is due to star-to-star differences in Fe or otherelement abundances which are predicted to affect Li depletion. Aims: .The primary goal of this study is the determination of themetallicity ([Fe/H]), α- and Fe-peak abundances in a sample ofLi-poor and Li-rich stars belonging to M 67, in order to test thishypothesis. By comparison with previous studies, the presentinvestigation also allows us to check for intrinsic differences in theabundances of evolved and unevolved cluster stars and to draw moresecure conclusions on the abundance pattern of this cluster.Methods: .We have carried out an analysis of high resolution UVES/VLTspectra of eight unevolved and two slightly evolved cluster membersusing MOOG and measured equivalent widths. For all the stars we havedetermined [Fe/H] and element abundances for O, Na, Mg, Al, Si, Ca, Ti,Cr and Ni. Results: .We find an average metallicity [Fe/H] =0.03±0.01, in very good agreement with previous determinations.All the [ X/Fe] abundance ratios are very close to solar. Thestar-to-star scatter in [Fe/H] and [ X/Fe] ratios for all elements,including oxygen, is lower than 0.05 dex, implying that the largedispersion in lithium among cluster stars is not due to differences inthese element abundances. We also find that, when using a homogeneousscale, the abundance pattern of unevolved stars in our sample is verysimilar to that of evolved stars, suggesting that, at least in thiscluster, RGB and clump stars have not undergone any chemical processing.Finally, our results show that M 67 has a chemical composition that isrepresentative of the solar neighborhood.
| Extended Strömgren Photoelectric Photometry in NGC 752
Photoelectric photometry on the extended Strömgren system (uvbyCa)is presented for 7 giants and 21 main-sequence stars in the old opencluster NGC 752. Analysis of the hk data for the turnoff stars yields anew determination of the cluster mean metallicity. From 10 single-starmembers, [Fe/H]=-0.06+/-0.03, where the error quoted is the standarderror of the mean and the Hyades abundance is set at [Fe/H]=+0.12. Thisresult is unchanged if all 20 stars within the limits of the hkmetallicity calibration are included. The derived [Fe/H] is in excellentagreement with past estimates, using properly zeroed m1 data,transformed moderate-dispersion spectroscopy, and recent high-dispersionspectroscopy.
| Photometric and spectroscopic study of the intermediate-age open cluster NGC 3960
We present charge-coupled device UBVI photometry and high-resolutionspectroscopy of the intermediate-age open cluster NGC 3960. Thecolour-magnitude diagrams (CMDs) derived from the photometric data andinterpreted with the synthetic CMD method allow us to estimate thecluster parameters. We derive the following: age τ= 0.9 or 0.6Gyr(depending on whether or not overshooting from convective regions isincluded in the adopted stellar models); distance (m-M)0=11.6 +/- 0.1; reddening E(B-V) = 0.29 +/- 0.02; differential reddeningΔE(B-V) = 0.05; and approximate metallicity between solar andhalf-solar. We obtained high-resolution spectra of three clump stars,and derived an average [Fe/H]=-0.12 (rms 0.04dex), in very goodagreement with the photometric determination. We also obtained theabundances of α-elements, of Fe-peak elements and of Ba. Thereddenings towards individual stars derived from the spectroscopictemperatures and the calibrations of Alonso et al. give further supportto the existence of significant variations across the cluster.
| vbyCaHβ CCD Photometry of Clusters. VI. The Metal-deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHβ system is presentedfor the metal-deficient open cluster NGC 2420. Restricting the data toprobable single members of the cluster using the CMD and the photometricindices alone generates a sample of 106 stars at the cluster turnoff.The average E(b-y)=0.035+/-0.003 (s.e.m.) or E(B-V)=0.050+/-0.004(s.e.m.), where the errors refer to internal errors alone. With thisreddening, [Fe/H] is derived from both m1 and hk, using b-yand Hβ as the temperature index. The agreement among the fourapproaches is reasonable, leading to a final weighted average of[Fe/H]=-0.37+/-0.05 (s.e.m.) for the cluster, on a scale where theHyades has [Fe/H]=+0.12. When combined with the abundances from DDOphotometry and from recalibrated low-resolution spectroscopy, the meanmetallicity becomes [Fe/H]=-0.32+/-0.03. It is also demonstrated thatthe average cluster abundances based on either DDO data orlow-resolution spectroscopy are consistently reliable to 0.05 dex orbetter, contrary to published attempts to establish an open clustermetallicity scale using simplistic offset corrections among differentsurveys.
| Caroline Herschel as observer
Not Available
| Influence of Gravity Waves on the Internal Rotation and Li Abundance of Solar-Type Stars
The Sun's rotation profile and lithium content have been difficult tounderstand in the context of conventional models of stellar evolution.Classical hydrodynamic models predict that the solar interior mustrotate highly differentially, in disagreement with observations. It hasrecently been shown that internal waves produced by convection insolar-type stars produce an asymmetric, shear layer oscillation, similarto Earth's quasi-biennial oscillation, that leads to efficient angularmomentum redistribution from the core to the envelope. We presentresults of a model that successfully reproduces both the rotationprofile and the surface abundance of lithium in solar-type stars ofvarious ages.
| 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 Dushak-Erekdag Survey of roAp Stars
The search of roAp stars at Mt. Dushak-Erekdag Observatory was startedin 1992 using the 0.8 m Odessa telescope equipped with a two-starhigh-speed photometer. We have observed more than a dozen stars so farand discovered HD 99563 as roAp star while BD +8087 is suspected to haverapid oscillations. Negative results of our observations for the searchof rapid oscillations in four stars in NGC 752 are also discussed.
| Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation
We study the kinematics of 129 W UMa binaries and we discuss itsimplications on the contact binary evolution. The sample is found to beheterogeneous in the velocity space. That is, kinematically younger andolder contact binaries exist in the sample. A kinematically young (0.5Gyr) subsample (moving group) is formed by selecting the systems thatsatisfy the kinematical criteria of moving groups. After removing thepossible moving group members and the systems that are known to bemembers of open clusters, the rest of the sample is called the fieldcontact binary (FCB) group. The FCB group is further divided into fourgroups according to the orbital period ranges. Then, a correlation isfound in the sense that shorter-period less-massive systems have largervelocity dispersions than the longer-period more-massive systems.Dispersions in the velocity space indicate a 5.47-Gyr kinematical agefor the FCB group. Compared with the field chromospherically activebinaries (CABs), presumably detached binary progenitors of the contactsystems, the FCB group appears to be 1.61 Gyr older. Assuming anequilibrium in the formation and destruction of CAB and W UMa systems inthe Galaxy, this age difference is treated as an empirically deducedlifetime of the contact stage. Because the kinematical ages (3.21, 3.51,7.14 and 8.89 Gyr) of the four subgroups of the FCB group are muchlonger than the 1.61-Gyr lifetime of the contact stage, the pre-contactstages of the FCB group must dominantly be producing the largedispersions. The kinematically young (0.5 Gyr) moving group covers thesame total mass, period and spectral ranges as the FCB group. However,the very young age of this group does not leave enough room forpre-contact stages, and thus it is most likely that these systems wereformed in the beginning of the main sequence or during thepre-main-sequence contraction phase, either by a fission process or mostprobably by fast spiralling in of two components in a common envelope.
| Blue Stragglers in Galactic Open Clusters and Integrated Spectral Energy Distributions
Synthetic integrated spectral properties of the old Galactic openclusters are studies in this work, in which 27 Galactic open clusters ofages >=1 Gyr are selected as the working sample. Based on thephotometric observations of these open clusters, a synthetic integratedspectrum has been made for the stellar population of each cluster. Theeffects of blue straggler (BS) stars on the conventional simple stellarpopulation (SSP) model are analyzed on an individual cluster basis. Itis shown that the BSs, whose positions in the color-magnitude diagramscannot be predicted by the current single-star evolution theory, requiresignificant modifications to the integrated properties of theoreticalSSP model. The synthesized integrated spectral energy distributions(ISEDs) of our sample clusters are dramatically different from those ofSSPs based on an isochrone only. The BS-corrected ISEDs of stellarpopulations show systematic enhancements toward shorter wavelengths inthe spectra. When measured with broadband colors in unresolvableconditions, the age of a stellar population can be seriouslyunderestimated by the conventional SSP model. Therefore, considering thecommon existence of BS components in real stellar populations, we shouldexpect considerable alterations of the conventional ISEDs when we applythe technique of evolutionary population synthesis to more complicatedstellar systems.
| uvbyCaHβ CCD Photometry of Clusters. V. The Metal-Deficient Open Cluster NGC 2243
CCD photometry on the intermediate-band uvbyCaHβ systemis presented for the metal-deficient open cluster NGC 2243. Restrictingthe data to probable single members of the cluster using thecolor-magnitude diagram (CMD) and the photometric indices alonegenerates a sample of 100 stars at the cluster turnoff. The averageE(b-y)=0.039+/-0.003 (s.e.m.) or E(B-V)=0.055+/-0.004 (s.e.m.), wherethe errors refer to internal errors alone. With this reddening, [Fe/H]is derived from both m1 and hk, using b-y and Hβ as thetemperature index. The agreement among the four approaches is excellent,leading to a final weighted average of [Fe/H]=-0.57+/-0.03 (s.e.m.) forthe cluster, on a scale where the Hyades has [Fe/H]=+0.12. Using acombination of photometric and spectroscopic data, 27 probable clustermembers are identified and used to delineate the red giant branch and awell-defined clump at V=13.70, while eliminating the so-called secondclump at V=14.1. Interpolation between isochrones of appropriate [Fe/H]leads to an apparent modulus of m-M=13.15+/-0.1 and an age of 3.8+/-0.2Gyr. A differential CMD comparison with Ber 29, a cluster with agalactocentric distance almost twice that of NGC 2243, constrains Ber 29to be at least as young and as metal-rich as NGC 2243.
| Vilnius Photometry of Red Giant Stars in the Open Cluster NGC 7789
Photoelectric Vilnius seven-color photometry is presented and analyzedfor a sample of 24 red giant branch and clump stars in the open clusterNGC 7789. For each star we have determined photometric spectral type,absolute magnitude, interstellar reddening, effective temperature,metallicity, and surface gravity. From averages over the stars in thesample we find the mean reddening to the cluster E Y‑V = 0.21± 0.02 (s.d.), or E B‑V = 0.25,and the apparent distance modulus (m‑M) V =12.21± 0.10 (s.d.), which yield a distance of 1840 pc. The meanoverall metallicity is found to be [Fe/H] = ‑0.18± 0.09(s.d.). The clump stars, on average, appear to be slightly moremetal-rich than the other red giants, which is most probably caused byevolutionary changes of carbon and nitrogen molecular bands falling inthe photometric passbands. A difference in mass between the two groupsof stars has also been detected, which suggests that the clump starsmight have undergone extra mass loss before reaching their coreHe-burning phase of evolution.
| Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas
We present a catalogue (CSOCA ) of stars residing in 520 Galactic opencluster sky areas which is the result of the kinematic (proper motion)and photometric member selection of stars listed in the homogeneousAll-sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5). We describethe structure and contents of the catalogue, the selection procedureapplied, and the proper motion and photometric membership constraintsadopted. In every cluster area the CSOCA contains the complete list ofthe ASCC-2.5 stars regardless of their membership probability. Forevery star the CSOCA includes accurate J2000 equatorial coordinates,proper motions in the Hipparcos system, BV photometric data in theJohnson system, proper motion and photometric membership probabilities,as well as angular distances from the cluster centers for about 166 000ASCC-2.5 stars. If available, trigonometric parallaxes, spectral types,multiplicity and variability flags from the ASCC-2.5, and radialvelocities with their errors from the Catalogue of Radial Velocities ofGalactic Stars with high precision Astrometric Data (CRVAD) are alsogiven.
| Photometry and Spectroscopy of Short-Period Binary Stars in Four Old Open Clusters
We have performed a spectroscopic and photometric study of six contactbinary stars in four old open clusters, M67, Praesepe, NGC 6791 and NGC752, in order to evaluate their suitability for measuring the distanceto their respective clusters. The technique being tested uses the cosineFourier coefficients of the light curves of the binary stars, and themass ratios obtained spectroscopically, to provide distances to thebinaries. The contact binary TX Cnc was used to obtain the distance toPraesepe, which we find to be (V - MV}){o = 6.30± 0.08, which is in good agreement with the values of V -MV = 6.20 - 6.35 found in color-magnitude diagram (CMD)studies. Our spectroscopic study of QX And in NGC 752 provided adistance modulus of (V - MV}){o = 8.30±0.07 for this cluster. This compares to a value of (V -MV}){o = 7.9 ± 0.1 obtained by Milone etal. (1995) using the same star, but is in good agreement with V -MV = 8.25 ± 0.10 obtained by Daniel et al. (1994) fromthe CMD. We obtained a distance modulus of (V -MV}){o = 12.71 ± 0.44 for V7 in NGC 6791,the oldest cluster in our survey. This agrees within ˜ 1σthe values of 13.3 ≤ (V - MV) ≤ 13.42 obtained byisochrone fitting of the cluster CMD. EV Cnc in M67 did not yield adistance to the cluster from our procedure because of faintness of thesystem resulting in poor spectroscopic data.The distances to the clusters as determined from the contact binariesusing our procedure do not seem to give systematically smaller or largerdistances as compared to CMD fitting. However, we have measured thedistances to only three clusters, and only one object per cluster, andso establishing any systematic differences may require a larger survey.R. M. Blake acknowledges the support of the Natural Science andEngineering Research Council of Canada through grants to S. M. Rucinskiand C. T. Bolton.
| Magnetic Feilds of Young Stars in NGC 752
The magnetic fields of stars change in direction and strength not onlyover short time scales, as in the Sun's twenty-two year cycle, but alsoas the star ages. As characteristics of a star like rotational velocityand depth of convection zone change, the magnetic field must alter aswell. To shed light on this ageing process, we studied the magnetic fluxof stars 1.78 gigayears old, an age between that of the Hyades and theSun, both of which have been extensively studied. This study was doneusing data from a deep-field Chandra observation to find the coronalluminosity, a proxy for the magnetic flux, of a total of 130 stars, manyof which are known to be members of NGC 752. Photon count rate wasconverted to luminosity using the Raymond-Smith model. Convective starswere found to have a range of coronal luminosities averaging onlyslightly higher then that of the Sun. Stars with B-V < 0.45, howevershowed a trend towards brighter luminosities. We determined the averagecoronal luminosity of G-type stars to be 2.98 *102{^8}ergs/sec with a range of plus or minus 2.21 *102{^8}ergs/sec, which corresponds to an exponential decline in coronalluminosities from those of the Hyades. This research was funded by theNational Science Foundation's Research Experience for Undergraduatesprogram.
| A new Böhm-Vitense gap in the temperature range 5560 to 5610 K in the main sequence hm-Vitense gap in the main sequence
Highly precise temperatures (σ = 10-15 K) have been determinedfrom line depth ratios for a set of 248 F-K field dwarfs of about solarmetallicity (-0.5 < [Fe/H] < +0.4), based on high resolution (R=42000), high S/N echelle spectra. A new gap has been discovered in thedistribution of stars on the Main Sequence in the temperature range 5560to 5610 K. This gap coincides with a jump in the microturbulent velocityVt and the well-known Li depression near 5600 K in fielddwarfs and open clusters. As the principal cause of the observeddiscontinuities in stellar properties we propose the penetration of theconvective zone into the inner layers of stars slightly less massivethan the Sun and related to it, a change in the temperature gradient.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute-Provence (France).Full Table 1 is only available in electronic form athttp://www.edpsciences.org
| Lithium evolution in intermediate age and old open clusters: NGC 752 revisited
We present new high resolution spectroscopic observations of theintermediate age (2 Gyr) open cluster NGC 752.We investigate the Li vs. Teff distribution and we obtain anew accurate determination of the cluster metallicity. We compare theresults for NGC 752 with other intermediate age and old clustersspanning the age range from the Hyades (0.6 Gyr)to NGC 188 (6-8 Gyr). We find that NGC 752 has asolar iron content ([Fe/H]=+0.01±0.04), at variance with earlyreports of sub-solar metallicity. We find that NGC 752 is only slightlymore Li depleted than the younger Hyades and has a Li pattern almostidentical to that observed in the 2 Gyr old IC4651 and NGC 3680. As for the latterclusters, we find that NGC 752 is characterized by a tight Li vs.Teff distribution for solar-type stars, with no evidence fora Li spread as large as the one observed in the solar age solarmetallicity M 67. We discuss these results in theframework of mixing mechanisms and Li depletion on the main sequence(MS). We conclude that the development of a large scatter in Liabundances in old open clusters might be an exception rather than therule (additional observations of old clusters are required), and thatmetallicity variations of the order of ±0.2 dex do notaffect Li depletion after the age of the Hyades.Based on observations collected at Telescopio Nazionale Galileo, LaPalma, Canary Islands.
| Unsolved problems in observational astronomy. I. Focus on stellar spectroscopy
We present the highlights of current observational programs in stellaroptical spectroscopy carried out with 8-10 m class telescopes as well aswith smaller telescopes. Topics discussed include: 1. light elementsabundances and their cosmological implications; 2. search for PopulationIII stars and spectroscopy of extremely metal deficient stars; 3.abundances of different stellar populations in the Galaxy; 4.spectroscopy of resolved stars in Local Group galaxies; 5. Li and Beabundances and internal mixing in stars; 6. spectroscopy of very-lowmass stars and brown dwarfs; 7. radial velocity search of extrasolarplanets; 8. stellar oscillations and asteroseismology; 9. stellarmagnetic activity and Doppler imaging of stellar surface features. Wealso highlight the role that dedicated 1-2 m automatic telescopes withspectroscopic capabilities can play in several fields of stellar opticalspectroscopy.
| Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
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