Contents
Images
Upload your image
DSS Images Other Images
Related articles
Spectroscopy of Globular Clusters out to Large Radius in the Sombrero Galaxy
We present new velocities for 62 globular clusters in M104 (NGC 4594,the Sombrero Galaxy), 56 from 2dF on the AAT and 6 from Hydra on WIYN.Combined with previous data, we have a total sample of 108 M104 globularcluster velocities, extending to 20' radius (~60 kpc), alongwith BVR photometry for each of these. We use this wide-field data setto study the globular cluster kinematics and dark matter content of M104out to 10' radius (30 kpc). We find no rotation in theglobular cluster system. The edge-on nature of M104 makes it unlikelythat there is strong rotation which is face-on and hence unobserved;thus, the absence of rotation over our large radial range appears to bean intrinsic feature of the globular cluster system in M104. We discussways to explain this low rotation, including the possibility thatangular momentum has been transferred to even larger radii throughgalaxy mergers. The cluster velocity dispersion is ~230 kms-1 within several arcminutes of the galaxy center, and dropsto ~150 km s-1 at ~10' radius. We derive the massprofile of M104 using our velocity dispersion profile, together with theJeans equation under the assumptions of spherical symmetry and isotropy,and find excellent agreement with the mass inferred from the stellar andgas rotation curve within 3' radius. The M/LVincreases from ~4 near the galaxy center to ~17 at 7' radius(~20 kpc, or 4 Re), thus giving strong support for thepresence of a dark matter halo in M104. More globular cluster velocitiesat larger radii are needed to further study the low rotation in theglobular cluster system, and to see if the dark matter halo in M104extends beyond a radius of 30 kpc.
| Rotationally Supported Virgo Cluster Dwarf Elliptical Galaxies: Stripped Dwarf Irregular Galaxies?
New observations of 16 dwarf elliptical galaxies (dEs) in the VirgoCluster indicate that at least seven dEs have significant velocitygradients along their optical major axis, with typical rotationamplitudes of 20-30 km s-1. Of the remaining nine galaxies inthis sample, six have velocity gradients of less than 20 kms-1 kpc-1, while the other three observations hadtoo low a signal-to-noise ratio to determine an accurate velocitygradient. Typical velocity dispersions for these galaxies are ~44+/-5 kms-1, indicating that rotation can be a significant componentof the stellar dynamics of Virgo dEs. When corrected for the limitedspatial extent of the spectral data, the rotation amplitudes of therotating dEs are comparable to those of similar-brightness dwarfirregular galaxies (dIs). Evidence of a relationship between therotation amplitude and galaxy luminosity is found and, in fact, agreeswell with the Tully-Fisher relation. The similarity in the scalingrelations of dIs and dEs implies that it is unlikely that dEs evolvefrom significantly more luminous galaxies. These observations reaffirmthe possibility that some cluster dEs may be formed when the neutralgaseous medium is stripped from dIs in the cluster environment. Wehypothesize that several different mechanisms are involved in thecreation of the overall population of dEs and that stripping ofinfalling dIs may be the dominant process in the creation of dEs inclusters like Virgo.
| A Photometric and Spectroscopic Study of Dwarf and Giant Galaxies in the Coma Cluster. II. Spectroscopic Observations
This is the second paper in a series studying the photometric andspectroscopic properties of galaxies of different luminosities in theComa Cluster. We present the sample selection, spectroscopicobservations, and completeness functions. To study the spectralproperties of galaxies as a function of their local environment, twofields were selected for spectroscopic observations to cover both thecore (Coma 1) and outskirts (i.e., southwest of the core and centered onNGC 4839; Coma 3) of the cluster. To maximize the efficiency ofspectroscopic observations, two subsamples were defined, consisting of``bright'' and ``faint'' galaxies, both drawn from magnitude-limitedparent samples. Medium-resolution spectroscopy (6-9 Å) was thencarried out for a total of 490 galaxies in both fields (302 in Coma 1and 188 in Coma 3), using the WYFFOS multifiber spectrograph on theWilliam Herschel Telescope. The galaxies cover a range of 122. The completeness functions for our sampleare calculated. These show that the bright sample is 65% complete atR<17 mag, becoming increasingly incomplete toward fainter magnitudes,while the faint sample follows a monotonically decreasing completenessfunction at R>19 mag. Based on observations made with the WilliamHerschel Telescope, operated on the island of La Palma by the IsaacNewton Group in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| Low-Luminosity Early-Type Galaxies in the Coma Cluster: Variations in Spectral Properties
We present spectra of nine low-luminosity early-type galaxies (M_B >-17.5) in the Coma Cluster. The spectra, which were obtained with theMultiple Mirror Telescope and cover the spectral region 3300-5350Å, exhibit a large variation in Balmer line strengths. In fact,the line-strength variation among the Coma low-luminosity galaxies is aslarge as that found among a sample of low-luminosity elliptical galaxiesin the Virgo Cluster and lower density environments. When compared withdetailed population synthesis models, the variation in Balmer linestrengths among the Coma galaxies indicates a range inluminosity-weighted mean age from ~1 to ~12 Gyr. The two youngestgalaxies are shown to be in a poststarburst state, i.e., they are notsimply former spirals whose star formation was recently terminated.Moreover, the ~1 Gyr ages of these two youngest low-luminosity galaxiesare similar to those of the brighter poststarburst galaxies in the ComaCluster.
| Radial velocities and iron abundances of field RR Lyraes. II.
This is the second of the papers devoted to derive radial velocities andiron abundances of field RR Lyraes observed by HIPPARCOS. Our abundancesshow good agreement with those in the literature obtained both fromphotometric (Delta S index) and spectroscopic methods. Binary candidatesand stars misclassified as RR Lyraes in the original HIPPARCOS list havebeen also identified. Appendix is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u- strasbg.fr/Abstract.html
| The gamma Doradus-type variable 9 Aurigae: results from a multi-site campaign
We present the results of a multi-longitude coordinated photometriccampaign on the gamma Dor variable 9 Aur. Three frequencies can bedetermined from the data (f_1=0.7948, f_3=0.7679, f_5=0.3429 d^-1) twoof them have already been recognized in past seasons while the thirdfrequency is reported for the first time. Analysis shows that the thirdwas `turned off' or present with an amplitude below the limits ofdetection during previous observing seasons. This evidence, togetherwith consistent amplitude changes in the two previously recognizedsignals, suggests that the stellar structure responsible for 9 Aur'svariability is extremely dynamic. Intermediate-resolution spectra andCORAVEL radial velocities collected simultaneously show variability ontime-scales commensurable with the photometry. The only sensibleexplanation appears to be a non-radial pulsation (NRP) model. However,results obtained reveal a number of features that deviate from classicalNRP behaviour. Such features are emphasized in this paper in support ofthe future development of a specific NRP model - a model which has yetto be elucidated for gamma Dor-type variables.
| Spectroscopic orbits of eclipsing binaries - AA UMa
High dispersion and time resolution spectra for the eclipsing binary AAUMa, obtained using an intensified Reticon, were measured bycross-correlation techniques. The spectra of the two components arefound to be very similar, and AA UMa is shown to belong to Subtype W ofW UMa binaries. The orbital elements of the system are determined andcompared with other W UMa binaries. It is found that the orbital periodis 0.48171 days and that the estimated mean mass center velocity for thesystem is -34.8 km/s. The mass ratio between the components isdetermined to be 0.54 and the magnitude difference in the wavelengthobserved is estimated to be 0.36.
| Standard Velocity Stars
Not Available
| Photoelectric radial velocities, paper 6 Heard's IAU standard stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975MNRAS.171..407G&db_key=AST
| The establishment of 21 new ninth magnitude IAU standard radial velocity stars
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Cancer |
| Right ascension: | 08h02m11.09s |
| Declination: | +26°38'16.4" |
| Apparent magnitude: | 7.707 |
| Distance: | 148.81 parsecs |
| Proper motion RA: | -5 |
| Proper motion Dec: | -22.5 |
| B-T magnitude: | 8.897 |
| V-T magnitude: | 7.806 |
Catalogs and designations:
|
