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An updated survey of globular clusters in M 31. I. Classification and radial velocity for 76 candidate clusters
Aims.We present the first results of a large spectroscopic survey ofglobular clusters and candidate globular clusters in the nearby M 31galaxy. The survey is aimed at the classification of known candidate M31 clusters and at the study of their kinematic properties.Methods: .We obtained low-resolution spectroscopy(λ/Δλ ≃ 800-1300) for 133 targets, including76 yet-to-be-confirmed candidate clusters (i.e. with no previousspectroscopic information), 55 already-confirmed genuine M 31 clusters,and 2 uncertain candidates. Our observations allowed a reliable estimateof the target radial velocity, within a typical accuracy of ~± 20km s-1. The observed candidates have been robustly classifiedaccording to their radial velocity and shape parameters that allowed usto confidently discriminate between point sources and extended objectseven from low-spatial-resolution imagery. Results: .In our set of76 candidate clusters we found: 42 newly-confirmed bona-fide M 31clusters, 12 background galaxies, 17 foreground Galactic stars, 2 Hiiregions belonging to M 31 and 3 unclassified (possibly M 31 clusters orforeground stars) objects. The classification of a few other candidatesnot included in our survey has been also reassessed on variousobservational bases. All the sources of radial velocity estimates for M31 known globular clusters available in the literature have beencompared and checked, and a homogeneous general list has been obtainedfor 349 confirmed clusters with radial velocity. Conclusions: .Ourresults suggest that a significant number of genuine clusters(≳100) is still hidden among the plethora of known candidatesproposed by various authors. Hence our knowledge of the globular clustersystem of the M 31 galaxy is still far from complete even in terms ofsimple membership.
| The outermost cluster of M 31
We report on the identification of a new cluster in the far halo of theM 31 galaxy. The cluster, named Bologna 514 (B514) has an integratedmagnitude MV=-8.5 ± 0.6, and a radial velocity, asestimated from two independent low-resolution spectra,Vr=-456 ± 23 km s-1, which fully confirmsits membership to the M 31 system. The observed integrated spectrum isvery similar to those of classical globular clusters. Being located at≃ 4° (≃ 55 kpc in projected distance) from the center ofthe parent galaxy, B514 is by far the most remote M 31 cluster everdiscovered. Its projected position, near the galaxy major axis, and M31-centric velocity, similar to that observed in the outermost regionsof the HI rotation curve, may indicate that it belongs to the subsystemof M 31 clusters that has been recently proposed (Morrison et al. 2004 )to be part of the dynamically-cold thin disc of the galaxy.
| Differential rotation and star-spot evolution on HK Aqr in 2001 and 2002
We present images of the rapidly rotating (Prot= 0.431 d)M1.5Ve dwarf HK Aqr, from data obtained during 2001 and 2002. Star-spotsare found distributed at a range of latitudes during both observingseasons, but unlike other solar-type rapid rotators of higher mass, HKAqr does not show a strong polar cap at either epoch. In addition to thesurface brightness images, we make use of the four-night time-base overwhich the 2002 observations were made, in order to derive an estimate ofthe latitudinal dependent rotation on HK Aqr. We find that theequator-lap-pole time lies in the range -1449 to +448 d. Although verysmall, we are therefore unable to determine whether the degree ofdifferential rotation is in the solar or anti-solar sense.
| High-resolution Doppler images of the spotted contact binary AE Phe
We present Doppler images of the short period (P= 0.362 d) W UMa binaryAE Phe. In order to obtain the necessary S/N ratio and time resolutionrequired to see individual star-spot features in highly rotationallybroadened profiles, we use least-squares deconvolution, which makes useof the information content of the several thousand lines in a typicalechelle spectrum. This yields a single rotation profile (free ofsidelobes due to blending) per spectrum with a typical S/N ratio ofseveral thousand.We use radial velocity curves, generated from standard profile fittingtechniques, to measure velocity amplitudes and the mass ratio. Failureto model star-spots with this method leads to a biased set of values,and we show that an imaging code is essential if accurate systemparameters are to be derived.Images are reconstructed from four nights of data which revealstar-spots at most latitudes on both components of the common envelopesystem. Our model requires that the primary component be several hundredK cooler than the secondary in order to reproduce the profile depthchanges with phase. In a two-temperature imaging model, we interpretthis as being due to 27 per cent greater - but unresolved - spot fillingon the primary relative to the secondary component. The images revealthat dark spots are present on both stars at various latitudes andlongitudes. Star-spots are also found in the neck region of bothcomponents, which appear to be darker on the side of each star leadingin rotation phase - particularly on the secondary component. Weinvestigate the reproducibility of the images from night to night andconclude that the star-spots evolve significantly on very shorttime-scales, of the order of 1 d. This is significantly faster than theweek time-scales found on active single stars and the Sun.
| Gravity Indicators in the Near-Infrared Spectra of Brown Dwarfs
We investigate the sensitivity to temperature and gravity of the strongabsorption features in the J- and K-band spectra of substellar objects.We compare the spectra of giants and young M dwarfs (of low gravity) tofield M and L dwarfs (of high gravity) and to model spectra from theLyon group. We find that low-resolution spectra of M4-M9 stars and youngbrown dwarfs at R~350 and signal-to-noise ratios greater than 70 candetermine the spectral type to a precision of +/-1 subtype using theH2O and CO bands and can measure the surface gravity to+/-0.5 dex using the atomic lines of K I and Na I. This result pointstoward the development of photometric spectral indices to separatelow-mass members from foreground and background objects in youngclusters and associations. We also emphasize the complexity of theinterpretation of the empirical quantities (e.g., spectral types) interms of the physical variables (e.g., temperature, opacities) in thecool atmospheres of young brown dwarfs.Based on observations obtained with the Multiple Mirror TelescopeObservatory, a joint facility of the University of Arizona and theSmithsonian Institution.
| The Kinematics and Metallicity of the M31 Globular Cluster System
With the ultimate aim of distinguishing between various modelsdescribing the formation of galaxy halos (e.g., radial or multiphasecollapse and random mergers), we have completed a spectroscopic study ofthe globular cluster system of M31. We present the results of deepintermediate-resolution fiber-optic spectroscopy of several hundred ofthe M31 globular clusters using the Wide Field Fibre Optic Spectrographat the William Herschel Telescope in La Palma, Canary Islands. Theseobservations have yielded precise radial velocities (+/-12 kms-1) and metallicities (+/-0.26 dex) for over 200 members ofthe M31 globular cluster population out to a radius of 1.5d from thegalaxy center. Many of these clusters have no previous published radialvelocity or [Fe/H] estimates, and the remainder typically representsignificant improvements over earlier determinations. We presentanalyses of the spatial, kinematic, and metal abundance properties ofthe M31 globular clusters. We find that the abundance distribution ofthe cluster system is consistent with a bimodal distribution with peaksat [Fe/H]~-1.4 and -0.5. The metal-rich clusters demonstrate a centrallyconcentrated spatial distribution with a high rotation amplitude,although this population does not appear significantly flattened and isconsistent with a bulge population. The metal-poor clusters tend to beless spatially concentrated and are also found to have a strong rotationsignature.
| The Stellar Kinematic Fields of NGC 3379
We have measured the stellar kinematic profiles of NGC 3379 along fourposition angles, using absorption lines in spectra obtained with theMultiple Mirror Telescope. We derive a far more detailed description ofthe kinematic fields through the main body of the galaxy than could beobtained from previous work. Our data extend 90" from the center, atessentially seeing-limited resolution out to 17". The derived meanvelocities and dispersions have total errors (internal and systematic)better than +/-10 km s^-1, and frequently better than 5 km s^-1, out to55". We find very weak (3 km s^-1) rotation on the minor axis interiorto 12" and no detectable rotation above 6 km s^-1 from 12" to 50" orabove 16 km s^-1 out to 90" (95% confidence limits). However, a Fourierreconstruction of the mean velocity field from all four sampled PAs doesindicate a ~5 deg twist of the kinematic major axis, in the directionopposite to the known isophotal twist. The h_3 and h_4 parameters arefound to be generally small over the entire observed region. Theazimuthally averaged dispersion profile joins smoothly at large radiiwith the velocity dispersions of planetary nebulae. Unexpectedly, wefind sharp bends in the major axis rotation curve, also visible (thoughless pronounced) on the diagonal position angles. The outermost bendclosely coincides in position with other sharp kinematic features: anabrupt flattening of the dispersion profile, and local peaks in h_3 andh_4. All of these features are in a photometrically interesting regionin which the surface brightness profile departs significantly from anr^1/4 law. Features such as these are not generally known in ellipticalgalaxies owing to a lack of data at comparable resolution. Very similarbehavior, however, is seen the kinematics of the edge-on S0 galaxy NGC3115. We discuss the suggestion that NGC 3379 could be a misclassifiedS0 galaxy; preliminary results from dynamical modeling indicate that itmay be a flattened, weakly triaxial system seen in an orientation thatmakes it appear round.
| A truly triple system DI Pegasi
Radial velocity measurements of DI Peg are derived based onspectroscopic observations and existing photometric observations whichhelp confirm the existence of a third body. A total of 30 spectra areobtained at 150 A, 240 A, and 100 A centered at 5050 A, and the phasesare computed from the time of deeper eclipse with the residuals invelocity computed from the adopted sine curves. Data reduction is basedon overclock-mean subtraction, field flattening, cosmic-ray deletion,and the extraction of 1D spectra from 2D components. The spectroscopicelements and mass ratio are given, and the radial velocity of the thirdbody is found to be +40.2 +/- 0.3 km/s suggesting that it is a physicalcompanion to DI Peg. A linear ephemeris is given for the eclipsemoments, and the photometric solutions for the close pair are solved.
| Radial-velocity observations and absolute dimensions of eclipsing binaries - SS Ari
Radial-velocity observations of the binary SS Ari were carried out inthe last quarter of 1990 and on the first clear night of 1991 at theDominion Astrophysical Observatory. A spectroscopic orbit was determinedon the assumption that both components of the binary are undistorted andrevolve in circular orbits. It is shown that SS Ari belongs to the Wsubclass of the W UMa systems and has properties that are typical ofthat subclass.
| Time-resolved spectroscopy of SS Cygni at minimum and maximum light
Double-line spectra were obtained of the dwarf nova SS Cygni in Augustand October 1981 to examine the effects of eruption on the radialvelocity curve of the cataclysmic variable. The data covered the4000-5300 A interval and all phases from maximum to minimum light.Calculations were performed for the absorption line and Balmer emissionline radial velocities. An orbital period close to 0.2751297 d wasfound, along with an effective temperature close to 2,444,842 K and aradial velocity of -16 to -14 km/sec. Since the system, a binaryconsisting of a white dwarf and a late-type star, is not eclipsing nodeterminations of the masses or orbital inclinations of the componentswere possible. It was noted that the velocity of the late-type starapparently increases to 195 km/sec during an outburst.
| Standard Velocity Stars
Not Available
| The establishment of 21 new ninth magnitude IAU standard radial velocity stars
Not Available
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