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|Observations and analysis of two type IIP supernovae: the intrinsically faint object SN 2005cs and the ambiguous object SN 2005ay|
Aims. To derive observational properties and physical parameters of theprogenitor stars of type IIP supernovae SN 2005ay and SN 2005cs fromtheir U,B,V,R,I CCD photometry, and to define their velocitybehaviour. Methods: .Light curves are analysed, and the velocitiesand spectral characteristics of SN 2005cs are obtained using syntheticspectra modeling. Results: .Both supernovae are found to befainter than the average SN IIP, with SN 2005cs being more subluminousand showing slight brightening in the second half of plateau stage inthe V,R,I bands and a low expansion velocity. The effects of twodifferent plausible distance moduli on the derived physical parametersof SN 2005ay are considered. Two approaches are used to recover theamounts of the ejected 56Ni, indicating masses of the orderof ~0.02 M_ȯ, although late luminosities might indicate a higheramount for SN 2005ay, especially for the large distance case.Constraints on the progenitor properties are also presented, based onempirical analytical models. Two approaches are used to estimate theexpansion velocities at the middle of the plateau phase. SN 2005csrepresents an example of where all 3 physical parameters, velocity,energy and 56Ni mass are lower than average, a correlationnot always observed in SNe IIP. SN 2005ay may belong to the same classif the shorter distance possibility is adopted. Furthermore, theestimated mass range for SN 2005cs is in agreement with limitsestablished by using pre-supernova imaging.
|Low-mass star formation in Lynds 1333|
Medium-resolution optical spectroscopy of the candidate young stellarobjects associated with the small, nearby molecular cloud Lynds 1333revealed four previously unknown classical T Tauri stars, two of whichare components of a visual double, and a Class I source, IRAS02086+7600. The spectroscopic data, together with newV,RC,IC photometric and 2MASS J, H, andKs data allowed us to estimate the masses and ages of the newT Tauri stars. We touch on the possible scenario of star formation inthe region. L1333 is one of the smallest and nearest known star-formingclouds, therefore it may be a suitable target for studying in detail thesmall-scale structure of a star-forming environment.
|An outbursting protostar of the FU Orionis type in the Cygnus OB7 molecular cloud|
Context: .To follow the early evolution of stars we need to understandhow young stars accrete and eject mass. It is generally assumed that theFU Orionis phenomenon is related to the variations in the diskaccretion, but many questions remain still open, in particular becauseof the rarity of FU Ori type stars. Aims: .We explore here thecharacteristics of the outburst and of the environment of one newobject, discovered recently in the active star formation regioncontaining RNO 127, within the Cygnus OB7 dark cloud complex.Methods: .We present an extensive optical and near-infrared study of anew candidate of FU Orionis object, including its direct imaging,spectroscopy and scanning Fabry-Pérot interferometry.Results: .The source, associated with the variable reflection nebula,underwent prodigious outburst. The "Braid" nebula, which appeared in2000, as is indicated by its name, consists of two intertwined features,illuminated by the outburst. Subsequent NIR observations revealed thebright source, which was not visible on 2MASS images, and its estimatedbrightening was more than 4 mag. Optical and infrared spectral data showfeatures, which are necessary for the system to be referred to as a FUorobject. The bipolar optical flow directed by the axis of nebula also wasfound. Various estimates give the November/December 1999 as the mostprobable date for the eruption.
|The first year of SN 2004dj in NGC 2403|
New BV RI photometry and optical spectroscopy of the Type IIp supernova2004dj in NGC 2403, obtained during the first year since discovery, arepresented. The progenitor cluster, Sandage 96, is also detected onpre-explosion frames. The light curve indicates that the explosionoccurred about 30d before discovery, and the plateau phase lasted about+110 +/- 20 d after that. The plateau-phase spectra have been modelledwith the SYNOW spectral synthesis code using H, NaI, TiII, ScII, FeIIand BaI lines. The SN distance is inferred from the expandingphotosphere method and the standard candle method applicable for SNeIIp.They resulted in distances that are consistent with each other as wellas earlier Cepheid and Tully-Fisher distances. The average distance, D =3.47 +/- 0.29 Mpc is proposed for SN 2004dj and NGC 2403. The nickelmass produced by the explosion is estimated as ~0.02 +/- 0.01Msolar. The spectral energy distribution of the progenitorcluster is reanalysed by fitting population synthesis models to ourobserved BV RI data supplemented by U and JHK magnitudes from theliterature. The χ2 minimization revealed a possible`young' solution with cluster age Tcl = 8 Myr, and an `old'solution with Tcl = 20-30 Myr. The `young' solution wouldimply a progenitor mass M > 20 Msolar, which is higherthan the previously detected progenitor masses for Type II SNe.Based on observations obtained at David Dunlap Observatory (Canada), F.L. Whipple Observatory (USA), Konkoly Observatory and Szeged Observatory(Hungary).E-mail: firstname.lastname@example.org
|Photometric survey of marginally investigated open clusters. I. Basel 11b, King 14, Czernik 43|
Aims.To progress in galactic studies based on open clusters, e.g.cluster formation rate or kinematical properties, one needs to improvethe number of open clusters observed. However, only half of the 1700known galactic open clusters have been properly observed so far, makingany statistical investigation insignificant, especially at largerdistances from the Sun. Methods: .We study marginallyinvestigated or neglected open clusters with Bessell CCD BVR photometry,whose data were used to fit isochrones to the individual color-magnitudediagrams. Results: .We examined the galactic clusters Basel 11b,King 14 and Czernik 43, the last being observed for the first time tothis extent. As well as a careful comparison to available photometry,their parameters such as age, interstellar reddening, distance andapparent diameter were determined. The obtained cluster properties wereverified by near infrared 2MASS data. The three investigatedintermediate age clusters are all located in the galactic disk withdistances between 1.8 and 3.0 kpc from the Sun.
|The association between gas and galaxies - I. CFHT spectroscopy and pair analysis|
We investigate the relative distribution of the gaseous contents of theUniverse (as traced by a sample of Lyα absorbers), and theluminous baryonic matter (as traced by a redshift survey of galaxies inthe same volume searched for Lyα absorbers), along 16 lines ofsight (LOS) between redshifts 0 and 1. Our galaxy redshift survey wasmade with the multi-object spectrograph on the Canada-France-HawaiiTelescope and, when combined with galaxies from the literature in thesame LOS, gives us a galaxy sample of 636 objects. By combining thiswith an absorption-line sample of 406 absorbing systems drawn frompublished works, we are able to study the relationship between gas andgalaxies over the latter half of the age of the Universe. A correlationbetween absorbers and galaxies is detected out to separation of 1.5Mpc.This correlation is weaker than the galaxy-galaxy correlation. There isalso some evidence that the absorbing systems seen in CIV are moreclosely related to galaxies, although this correlation could be withcolumn density rather than metallicity. The above results are allconsistent with the absorbing gas and the galaxies coexisting in darkmatter filaments and knots as predicted by current models where thecolumn density of the absorbing gas is correlated with the underlyingmatter density.
|Photometric observations of Supernovae 2000E, 2001B, 2001V, and 2001X|
CCD BVRI photometry is presented for two type Ia supernovae 2000E and2001V, for SN Ib 2001B and SN II-P 2001X. The parameters of light curvesand absolute magnitudes at maximum light are estimated. It is shown thatall four supernovae are typical for their classes considering the shapeof their light curves and maximum luminosity.
|Multicolor CCD photometry of six lenticular and spiral galaxies. Structure of the galaxies|
The results of multicolor surface photometry of the S0 galaxies NGC 524,NGC 1138, and NGC 7280 and the spiral galaxies NGC 532, NGC 783, and NGC1589 are reported. U BV RI observations were acquired with the 1.5-mtelescope of the Maidanak Observatory (Uzbekistan), while JHK data weretaken from the 2MASS catalog. The overall structure of the galaxies isanalyzed and the galaxy images decomposed into bulge and diskcomponents. The parameters of the galaxy components—rings, bars,spiral arms, and dust lanes—are determined. The bulge/diskdecompositions based on averaged one-dimensional photometric profilesyield incorrect parameters for the bulges of the S0-Sa galaxies withbars and/or rings, whose inner regions are dominated by the radiation ofthe bulge.
|The Bologna Open Cluster Chemical Evolution Project: Midterm Results from the Photometric Sample|
We describe a long-term project aimed at deriving information on thechemical evolution of the Galactic disk from a large sample of openclusters. The main property of this project is that all clusters areanalyzed in a homogeneous way to guarantee the robustness of the rankingin age, distance, and metallicity. Special emphasis is devoted to theevolution of the earliest phases of the Galactic disk evolution, forwhich clusters have superior reliability with respect to other types ofevolution indicators. The project is twofold: on one hand we derive theage, distance, and reddening (and indicative metallicity) byinterpreting deep and accurate photometric data with stellar evolutionmodels, and on the other hand, we derive the chemical abundances fromhigh-resolution spectroscopy. Here we describe our overall goals andapproaches and report on the midterm project status of the photometricpart, with 16 clusters already studied, covering an age interval from0.1 to 6 Gyr and galactocentric distances from 6.6 to 21 kpc. Theimportance of quantifying the theoretical uncertainties by deriving thecluster parameters with various sets of stellar models is emphasized.Stellar evolution models assuming overshooting from convective regionsappear to better reproduce the photometric properties of the clusterstars. The examined clusters show a clear metallicity dependence on thegalactocentric distance and no dependence on age. The tight relationbetween cluster age and magnitude difference between the main-sequenceturnoff and the red clump is confirmed.
|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.
|Search for new T Tauri stars in the Cepheus-Cassiopeia region|
The Cepheus-Cassiopeia star-forming region has beensearched for new T Tauri stars (TTSs) based on the ROSAT all sky survey(RASS). Optical spectroscopic observations were carried out toward 45GSC stellar counterparts of RASS sources looking for the Li absorptionline (6708 Å), a sign of youth. The detection of this lineresulted in finding 11 to 16 new TTSs in this region. Using follow-upoptical photometric observations and evolutionary models these Li-richstars are revealed to be young low-mass stars. The most of the youngstars are separated from the 13CO molecular clouds by ~10 pc,significantly more than in Chamaeleon. A group of thenew TTSs are isolated from the CO clouds and distributed inside thepreviously determined CO void. Possible formation scenarios includingthe interaction with the supernova shock for the isolated TTSs arediscussed.
|Classical Cepheid Pulsation Models. X. The Period-Age Relation|
We present new period-age (PA) and period-age-color (PAC) relations forfundamental and first-overtone classical Cepheids. Current predictionsrely on homogeneous sets of evolutionary and pulsation models covering abroad range of stellar masses and chemical compositions. We found thatPA and PAC relations present a mild dependence on metal content.Moreover, the use of different PA and PAC relations for fundamental andfirst-overtone Cepheids improves the accuracy of age estimates in theshort-period (logP<1) range (old Cepheids), because they presentsmaller intrinsic dispersions. At the same time, the use of the PACrelations improves the accuracy in the long-period (logP>=1) range(young Cepheids), since they account for the position of individualobjects inside the instability strip. We performed a detailed comparisonbetween evolutionary and pulsation ages for a sizable sample of LMC (15)and SMC (12) clusters which host at least two Cepheids. In order toavoid deceptive uncertainties in the photometric absolute zero point, weadopted the homogeneous set of B, V, and I data for clusters andCepheids collected by OGLE. We also adopted the same reddening scale.The different age estimates agree at the level of 20% for LMC clustersand of 10% for SMC clusters. We also performed the same comparison fortwo Galactic clusters (NGC 6067, NGC 7790), and the difference in age issmaller than 20%. These findings support the use of PA and PAC relationsto supply accurate estimates of individual stellar ages in the Galaxyand in external Galaxies. The main advantage of this approach is itsindependence from the distance.
|Search for HH Objects and Emission Stars in Star Formation Regions. III. PMS Stars in NGC 7129|
Slitless spectroscopy is used to discover 22 emission stars in thecentral and northwest regions of the cluster located in the NGC 7129nebula. 16 of them are found for the first time. This sample isessentially complete up to V 20.0. The emission stars are distributednonuniformly over the field of the cluster and are concentrated towardits center. Photometry in the V, R, and I bands is conducted on morethan a hundred stars in the cluster. This yields an average absorptioncoefficient A V=1.7±0.27 for this region. Based on theirpositions in color diagrams for the optical and near IR ranges, most ofthe emission stars can be regarded as T Tau objects.
|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.
|BVR photometry of the resolved dwarf galaxy Ho IX|
We present BVR CCD photometry down to limiting magnitude B=23.5 mag for232 starlike objects and 11 diffuse objects in a 5.4 arcmin × 5.4arcmin field of Ho IX. The galaxy is a gas-rich irregular dwarf galaxypossibly very close to M 81, which makes it especially interesting inthe context of the evolution of satellite galaxies and the accretion ofdwarf galaxies. Investigations of Ho IX were hampered by relativelylarge contradictions in the magnitude scale between earlier studies.With our new photometry we resolved these discrepancies. The colormagnitude diagram (CMD) of Ho IX is fairly typical of a star-formingdwarf irregular, consistent with earlier results. Distance estimatesfrom our new CMD are consistent with Ho IX being very close to M 81 andtherefore being a definite member of the M 81 group, apparently in veryclose physical proximity to M 81.This work is a part of a joint project between the AstronomicalInstitute of the Ruhr-University in Bochum and the Institute ofAstronomy of the Bulgarian Academy of Sciences for the study of nearbydwarf galaxies.
|Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912|
Near-infrared images and K-band spectroscopy of the massive star-formingregion IRAS 23151+5912 are presented. The JHK' images reveal anembedded infrared cluster associated with infrared nebula, and theH2 (2.12μm) narrow-band image provides for the first timeevidence of outflow activity associated with the cluster. That thecluster is young can be shown by the high percentage of infrared excesssources and the outflow activity. We suggest an age of the cluster of 106 yr. Eight young stars are found in the brightnebular core around IRAS 23151+5912. By the color-magnitude diagrams ofthe cluster, we found five high-mass YSOs and four intermediate-massYSOs in the cluster. Eight H2 emission features arediscovered in the region with a scattered and non-axisymmetricdistribution, indicating the existence of multiple outflows driven bythe cluster. Diffuse H2 emission detected to the north and tothe west of the cluster may result from UV leakage of the cluster. Brγ, H2, and CIV emission lines are found in the K-bandspectrum of the brightest source, NIRS 19, indicating the presence ofenvelope, stellar wind, and shock in the circumstellar environment. Wehave estimated an O7--O9 spectral type for the central massive YSO (20 30 Mȯ), with an age of less than 1 ×106 yr
|Eclipsing binaries in open clusters - I. V615 Per and V618 Per in h Persei|
We derive absolute dimensions for two early-type main-sequence detachedeclipsing binaries in the young open cluster h Persei (NGC 869). V615Persei has a spectral type of B7 V and a period of 13.7 d. V618 Perseiis A2 V and has a period of 6.4 d. New ephemerides are calculated forboth systems. The masses of the component stars have been derived usinghigh-resolution spectroscopy and are 4.08 +/- 0.06 and 3.18 +/- 0.05Msolar for V615 Per and 2.33 +/- 0.03 and 1.56 +/- 0.02Msolar for V618 Per. The radii have been measured by fittingthe available light curves using EBOP and are 2.29 +/- 0.14 and 1.90 +/-0.09 Rsolar for V615 Per and 1.64 +/- 0.07 and 1.32 +/- 0.07Rsolar for V618 Per. By comparing the observed spectra ofV615 Per with synthetic spectra from model atmospheres we find that theeffective temperatures of the stars are 15000 +/- 500 K for the primaryand 11000 +/- 500 K for the secondary. The equatorial rotationalvelocities of the primary and secondary components of V615 Per are 28+/- 5 and 8 +/- 5 km s-1, respectively. Both components ofV618 Per rotate at 10 +/- 5 km s-1. The equatorial rotationalvelocities for synchronous rotation are about 10 km s-1 forall four stars. The time-scales for orbital circularization for bothsystems, and the time-scale for rotational synchronization of V615 Per,are much greater than the age of h Per. Their negligible eccentricitiesand equatorial rotational velocities therefore support the hypothesisthat they were formed by delayed break-up. We have compared the radii ofthese stars with models by the Granada and the Padova groups for starsof the same masses but different compositions. We conclude that themetallicity of the stars is Z~ 0.01. This appears to be the firstestimate of the bulk metallicity of h Per. Recent photometric studieshave assumed a solar metallicity so their results should be reviewed.
|Photometric study of the contact binary star V861 Herculis|
First Cousins V(RI)C light curves of the W UMa-type eclipsingvariable star V861 Herculis are presented. The systemwas observed in 2000 and 2003. The light curves obtained at differentepochs showed significant deviation from each other. The O'Connelleffect was about Δ V = 0.05 mag in 2000 but it vanished in 2003(except the night of February 22/23, 2003 when we observed a smallO'Connell effect (Δ V = 0.02)). Further peculiarities of the lightcurves are also discussed. The light curves were solved with theWilson-Devinney code and the spot parameters were determined. The systemseems to be a W-type contact binary system with at least one activecomponent. This is strongly supported by the fact that the system isbrighter by 0.45 mag through an Hα filter than the MS stars withthe same colour index in the open cluster NGC 7790. This deviation canbe explained by chromospheric activity of one of the components.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/417/745
|The Anomalous X-ray Pulsar 4U 0142+61: Variability in the infrared and a spectral break in the optical|
We present new optical and infrared observations of the counterpart tothe Anomalous X-ray Pulsar (AXP) 4U 0142+61 taken with the Keck Itelescope. The counterpart is found to be variable in the infrared. Thiscontrasts with our optical observations, which do not show any evidencefor variability. Apart from the variability the AXP shows a remarkablespectral energy distribution. In particular, we find a sudden drop influx going from V to B, presumably due to a spectral feature. We compareour results to those obtained for the two other securely identified AXPcounterparts, to 1E 2259+586 and 1E 1048.1-5937. 4U 0142+61 is verysimilar to the former source in its X-ray timing and spectralproperties, and we find that this similarity extends to the quiescentinfrared to X-ray flux ratio. For 1E 1048.1-5937, which has differentX-ray properties, the situation is less clear: in one observation, theinfrared to X-ray flux ratio was much larger, but another observationgave an upper limit which is consistent with that observed for 4U0142+61. Assuming the quiescent ratios are all similar, we estimate theoptical and infrared brightnesses for the three AXPs that remain to beidentified as well as for the four Soft Gamma-ray Repeaters. We alsodiscuss briefly how the observed optical and infrared emission mightarise, in particular in the context of the magnetar model.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (188.8.131.52) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/1037
|Observational Data on Galactic Supernova Remnants: II. The Supernova Remnants Within l = 90^o - 270^o|
We have collected all the available data on Galactic supernova remnantsgiven in the literature. The data of Galactic supernova remnants locatedin the Galactic longitude interval l=90^o-270^o in all spectral bandsare represented in this work. We have adopted distance values for theSNRs by examining these data. The data of various types on neutron starsconnected to these supernova remnants are also represented. Remarks ofsome authors and by ourselves regarding the data and some properties ofboth the supernova remnants and the point sources are given.
|Cepheids in LMC Clusters and the Period-Age Relation|
We have made a new comparison of the positions of Cepheids and clustersin the LMC and constructed a new empirical period-age relation takinginto account all available data on Cepheids in the LMC bar provided bythe OGLE project. The most probable relation is logT=8.50-0.65 logP, inreasonably good agreement with theoretical expectations. NumerousCepheids in rich clusters of the LMC provide the best data for comparingtheories of stellar evolution and pulsation and the dynamical evolutionof clusters with observations. These data suggest that stars undergoingtheir first crossing of the instability strip are first-overtonepulsators, though the converse is true of only a small fraction offirst-overtone stars. Several rich clusters with suitable ages have noCepheids—a fact that is not understood and requires verification.Differences in the concentration of Cepheids toward their clustercenters probably reflect the fact that the clusters are at differentstages of their dynamical evolution, with the Cepheids in clustercoronas being ejected from the cluster cores during dynamicalinteractions between stars.
|Metallicity distribution on the galactic disk|
Depending mainly on UBVCCD data, the metallicities of 91 open starclusters nearby the galactic disk have been estimated using Cameron's[A&A 147 (1985b) 39] method. The metallicity radial gradient alongthe galactic plane is found to be -0.09 dex/kpc; which is in a very goodagreement with Panagia and Tosi [A&A 96 (1981) 306] and Carraro etal. [MNRAS 296 (1998) 1045]. Vertically on the galactic disk, withinabout 800 pc, the metallicity gradient is found to be so trivial. Anaverage age-metallicity relation has been examined, which confirms theprevious suggestion that the metallicity of a cluster depending mainlyon its position on the galactic disk more than its age.
|Distances to Cepheid open clusters via optical and K-band imaging|
We investigate the reddening and main-sequence-fitted distances to 11young, Galactic open clusters that contain Cepheids. Each clustercontains or is associated with at least one Cepheid variable star.Reddening to the clusters is estimated using the U-B:B-V colours of theOB stars and the distance modulus to the cluster is estimated via B-V:Vand V-K:V colour-magnitude diagrams. Our main-sequence fitting assumesthat the solar-metallicity zero-age main sequence of Allen appliesuniversally to all the open clusters, although this point iscontroversial at present. In this way we proceed to calibrate theCepheid period-luminosity (PL) relation and find MV=-2.87× logP- 1.243 +/- 0.09, MK=-3.44 × logP- 2.21 +/-0.10 and absolute distance moduli to the Large Magellanic Cloud (LMC) of18.54 +/- 0.10 from the V-band and 18.48 +/- 0.10 from the K-band givingan overall distance modulus to the LMC of μ0= 18.51 +/-0.10. This is in good agreement with the previous Cepheid PL-K result ofLaney & Stobie at μ0= 18.51 +/- 0.09 and with theHipparcos parallax-calibrated Cepheid PL-K estimate of Feast &Catchpole at μ0= 18.66 +/- 0.10 when no account is takenof the LMC metallicity.We also find that the two-colour U-B:B-V diagrams of two importantclusters are not well fitted by the standard main-sequence line. In onecase, NGC 7790, we find that the F stars show a UV excess and in thesecond case, NGC 6664, they are too red in U-B. Previous spectroscopicestimates of the metallicity of the Cepheids in these clusters appear tosuggest that the effects are not due to metallicity variations. Otherpossible explanations for these anomalies are positional variations inthe dust reddening law and contamination by foreground or backgroundstars.
|Photometry of the Supernova SN 2002ap in M 74 during 2002|
UBVR c I c observations of SN 2002ap during February, October, andNovember 2002 at the Crimean Astrophysical Observatory are reported. Anexamination of our photometric data, along with published data, showsthat over a period of about a year from the day the SN 2002ap supernovaburst, the light curve passed through three developmental stages: asharp rise, followed by a stage of rapid exponential decrease, and thena slower fading. Based on the shape of the light curve, this supernovais of type SN I, but according to the variation in its color indices, itmore likely belongs to the SN Ic supernovae. In the premaximum stage,the energy distribution from 3000 to 6000 resembles the emission from astar of spectral class F5V. In the second stage of the light curveevolution, when the brightness falls off rapidly, the changes in thecolor indices are associated with a change in the radiation temperatureindicative of rapid cooling of the ejected material. Taking theeffective radiation temperature in the premaximum stage to be T eff 6500K, we estimate the expansion velocity of the quasiphotosphere to beabout 9700 km/s.
|Homogeneous Photometry. III. A Star Catalog for the Open Cluster NGC 6791|
We present broadband BVI photometry for the open cluster NGC 6791, basedupon analysis of 1764 individual CCD images. We discuss in detail thetransformation of the instrumental magnitudes to the standardphotometric system of Landolt and then discuss methods for selecting asubset of cluster stars whose photometric indices are most likely to beof high reliability. Color-magnitude and color-color diagrams for thecluster are presented and discussed. A detailed comparison of thisphotometry with the results of previous observational studies ispresented. We make preliminary comparisons with theoretical isochronesprovided by D. A. VandenBerg and conclude that an excellent match can beachieved if the metal abundance and age of the cluster are both near theupper end of the range of recent estimates ([Fe/H]~+0.3, age~12 Gyr) andthe reddening and true distance modulus are both near the low end of therange of recent estimates [E(B-V)~0.09 mag and (m-M)0~12.79mag] if the isochrone predictions are reliable. A companion paper willdiscuss candidate variable stars and stars possibly showing planetarytransits. Data tables listing measured magnitudes and standard errors,image-quality indices, a variability index, and equinox J2000.0equatorial coordinates for 14,342 stars to V~24 have been made availableto the public through the services of the Canadian Astronomy DataCentre. Equatorial coordinates only have been provided for a further1916 stars, the photometry for which we were unable to calibrate becauseof lack of color information.Based in part on observations made with the Nordic Optical Telescope,operated on the island of La Palma jointly by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofísica de Canarias.
|On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient|
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
|Carbon Star Survey in the Local Group. V. The Outer Disk of M31|
We employ the CFH12K mosaic to identify carbon stars, using the R, I,CN, and TiO photometric technique, in a 2240 arcmin2 area,ranging from 17 to 30 kpc of the southwest disk of M31, barely reachingthe edge of the observed H I disk. We found 945 C stars with=19.94 and σ=0.47. The surface density of Cstars along the major axis of M31 follows an exponential profile with ascale length of 4.85+/-0.35 kpc, in agreement with adopted values forthe scale length of the disk population. Our survey partially overlapswith the recently discovered G1 density enhancement by Ferguson et al.We confirm that no AGB star excess is detectable in the surveyed part ofthe clump. The C/M ratio, along the major axis, is derived over adistance range of 7 kpc. The strong C/M gradient seen contrasts withresults of previous studies of the C stars in M31.
|Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy|
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
|Morphological analysis of open clusters' propertiesII. Relationships projected onto the galactic plane|
A morphological analysis study of open clusters' properties has beenachieved for a sample of 160 UBVCCD open star clusters of approximately128,000 stars near the galactic plane. The data was obtained and reducedfrom using the same reduction procedures, which makes this catalogue thelargest homogeneous source of open clusters' parameters.
|The Distance Scale for Classical Cepheid Variables|
New radii, derived from a modified version of the Baade-Wesselink (BW)method that is tied to published KHG narrowband spectrophotometry, arepresented for 13 bright Cepheids. The data yield a best-fittingperiod-radius relation given bylog=1.071(+/-0.025)+0.747(+/-0.028)logP0. In combination with other high-quality radiusestimates recently published by Laney & Stobie, the new data yield aperiod-radius relation described bylog=1.064(+/-0.0006)+0.750(+/-0.006)logP0, which simplifies to ~P3/4.The relationship is used to test the scale of Cepheid luminositiesinferred from cluster zero-age main-sequence (ZAMS) fitting, for whichwe present an updated list of calibrating Cepheids located in stellargroups. The cluster ZAMS-fitting distance scale tied to a Pleiadesdistance modulus of 5.56 is found to agree closely with the distancescale defined by Hipparcos parallaxes of cluster Cepheids and alsoyields Cepheid luminosities that are a good match to those inferred fromthe period-radius relation. The mean difference between absolute visualmagnitudes based on cluster ZAMS fitting,C, and those inferred for 23 clusterCepheids from radius and effective temperature estimates,BW, in the sense of C-BW is+0.019+/-0.029 s.e. There is no evidence to indicate the need for amajor revision to the Cepheid cluster distance scale. The absolutemagnitude differences are examined using available [Fe/H] data for thecluster Cepheid sample to test the metallicity dependence of theperiod-luminosity relation. Large scatter and a small range ofmetallicities hinder a reliable estimate of the exact relationship,although the data are fairly consistent with predictions from stellarevolutionary models. The derived dependence isΔMV(C-BW)=+0.06(+/-0.03)-0.43(+/-0.54)[ Fe/H].
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